2.1 Macrophage Plasticity and Polarization

Macrophages are a key type of immune cells that fulfill a dual role in the inflammatory response by transitioning between proinflammatory and antiinflammatory subtypes, depending on the prevailing context.

3.1 Classical Polarization Regulatory Pathways

4.1 Phagocytosis

As myeloid-derived immune sentinels, macrophages perform dual immunological roles as professional phagocytes and antigen-presenting cells. These versatile cells orchestrate the elimination of pathogens, initiate inflammatory cascades, and clear cellular debris through their engulfment processes. Recent research underscores their essential contributions to tissue development and metabolic homeostasis, mediated by finely tuned phagocytic activity and cytokine-mediated intercellular communication. Phagocytosis, a specialized mechanism of engulfment, enables both professional phagocytes (e.g., macrophages) and nonspecialized cell types (e.g., epithelial cells) to detect, internalize, and degrade particulate matter larger than 0.5 µm in diameter, serving as a critical defense strategy for maintaining homeostatic equilibrium during pathogenic incursions [84]. The ability of macrophages to recognize foreign pathogens or foreign objects is based on multiple receptors (e.g., FcγR) on their surface. Among them, PRRs play a critical role. These immune surveillance receptors specifically detect PAMPs—evolutionarily conserved structural motifs exclusive to microbial pathogens., such as LPS and peptidoglycan in bacteria, and nucleic acids in viruses. In addition to these mechanisms, macrophages can recognize pathogens labeled by complement proteins via complement receptors (CR). When the complement system is activated, complement components, such as C3b, are deposited on the surface of pathogens, and macrophage CRs (e.g., CR3, CR4) recognize these markers, thereby initiating phagocytosis. A 2007 investigation by Green and colleagues [85] demonstrated the recruitment of autophagy-related (Atg) proteins, including Beclin 1, LC3, Atg5, and Atg7, to maturing phagosomes in macrophages following TLR-mediated signaling. This phenomenon was subsequently characterized as the noncanonical LC3-associated phagocytosis pathway, which is distinct from classical autophagy processes. In addition, recent findings have demonstrated that rhamnose, produced by prokaryotic metabolism, promotes SLC12A4 activation through binding to SLC12A4. This, in turn, induces modulation of Rac1 and CDC42 activity and promotes phagocytosis by macrophages, thereby contributing to the alleviation of sepsis [86] (Figure 3).

The macrophage-expressed inhibitory receptor Siglec-10 engages with tumor-associated CD24 through interactions at its extracellular domain, which triggers intracellular signaling via immunoreceptor tyrosine-based inhibitory motifs (ITIMs) located within its cytoplasmic tail [87]. This molecular recognition event facilitates the recruitment of Src-family tyrosine kinases (SFKs) that phosphorylate the ITIM tyrosine residues, thereby initiating a phosphorylation cascade that mobilizes Src homology 2 (SH2) domain-containing phosphatases, including SHP-1 and SHP-2. The subsequent binding of SHP-1 to the phosphorylated ITIM domains mediates substrate dephosphorylation through its catalytic activity, ultimately leading to actin cytoskeletal reorganization that enables phagocytic clearance. Additionally, SHP-1 negatively regulates intracellular signaling involving cell adhesion molecules, ECM factors, hormones, cytokines, and growth factors [88]. Consequently, the interaction of CD24 with Siglec-10 impedes phagocytosis by macrophages and fosters evasion from tumors. Blocking CD24 or Siglec-10 expression by gene or antibody facilitates macrophage phagocytosis and inhibits tumor growth [89, 90].

SIRPα serves as the endogenous ligand for CD47 [91], a surface-expressed transmembrane glycoprotein predominantly localized on myeloid lineage cells, including macrophages, monocytes, and dendritic cells. The architecture of the SIRPα receptor consists of an extracellular region with three immunoglobulin-like domains, a single transmembrane module, and cytoplasmic tyrosine kinase phosphorylation motifs. Essential to its inhibitory function, the intracellular segment contains ITIMs that mediate the suppression of signal transduction [92, 93]. This counter-regulatory mechanism operates through the competitive antagonism of ITAM-coupled receptor activation. Effective signal inhibition requires the phosphorylation of ITIM tyrosine residues within cytoplasmic sequences, which facilitates the recruitment and enzymatic activation of SH2 domain-containing phosphatases SHP-1 and SHP-2. These effector molecules, equipped with SH2 phosphotyrosine-binding modules, execute downstream dephosphorylation cascades [92, 93]. The enzymatic activation of SHP-1 and SHP-2 phosphatases triggers the phosphorylation of myosin IIA, acting as a molecular switch that antagonizes nonmyosin IIA activity. These nonmuscle myosin isoforms play a critical role in regulating phagocytic machinery by coordinating phagolysosome maturation and orchestrating target engulfment in macrophages. When myosin IIA is dephosphorylated in macrophages, actin depolymerization occurs, resulting in reduced phagocytosis [94, 95]. The CD47–SIRPα interaction between malignant cells and phagocytic effector cells initiates tyrosine phosphorylation of ITIMs within SIRPα’s cytoplasmic domain through SFK-mediated activation. This signaling cascade facilitates recruitment of protein tyrosine phosphatases SHP-1/SHP-2, which contributes to reduced phagocytosis [96].

4.2 Tissue Repair

Tissue regeneration and repair are fundamental biological mechanisms crucial for maintaining organismal homeostasis and ensuring survival [97]. Following tissue damage caused by pathogen invasion or physical trauma, necrotic cells release endogenous damage-associated molecular patterns (DAMPs), while invading microbes secrete PAMPs. Together, these signals activate innate immune signaling cascades that drive inflammatory responses [98]. This molecular alert system mobilizes a complex inflammatory cascade characterized by the sequential recruitment, clonal expansion, and functional maturation of diverse effector populations. These include immune effectors such as neutrophils, macrophages, innate lymphoid cells, NK cells, and adaptive lymphocytes, as well as stromal components like fibroblasts, epithelial and endothelial lineages, and progenitor cells. Collectively, these elements establish an integrated cellular network that promotes regenerative processes [99]. Under physiological conditions, a self-limited inflammatory phase facilitates the precise architectural restoration of native tissue matrices. In contrast, persistent dysregulation of healing mechanisms can lead to maladaptive fibroproliferative responses, which are characterized by excessive ECM deposition that compromises parenchymal functionality and may culminate in terminal organ insufficiency [100]. Therefore, the spatiotemporal regulation of repair pathways is essential. Among the various contributors to tissue restoration, macrophages are identified as pivotal regulators due to their plastic functional adaptability and context-dependent polarization states [101]. They have been shown to play crucial regulatory roles throughout all phases of repair and fibrosis [102]. Recent strides in regenerative medicine and molecular biology have underscored the pivotal role of macrophages in promoting regeneration across diverse tissues, including the heart, liver, kidney, muscle, and nervous system. The capacity of macrophages to transition between distinct phenotypes in response to microenvironmental signals renders them promising therapeutic targets for enhancing tissue repair and regeneration [103].

The modulation of chemokine receptor signaling in mononuclear phagocytes alters their migratory patterns and functional roles in regenerative processes. Experimental evidence demonstrates that M2-polarized macrophages act as crucial regulators of wound resolution and neovascularization [104], thereby highlighting their therapeutic potential in regenerative medicine. In contrast, clinical analyses indicate that the dynamics of TAM infiltration correlate with negative clinical outcomes in cohorts treated with antiangiogenesis therapies [105]. Yang et al. [106] established the proangiogenic functions of M2-like macrophages through a multiplatform analysis that incorporated human pancreatic ductal adenocarcinoma specimens, murine xenograft models, and The Cancer Genome Atlas genomic datasets. In contrast to M0 macrophage-derived exosomes (MDEs), M2 MDEs promote ex vivo and in vivo angiogenesis and tumor progression. Given that conventional anti-VEGF drugs are often ineffective in pancreatic cancer, proangiogenic M2 MDEs associated with TAMs represent emerging therapeutic targets in pancreatic carcinogenesis. Guo et al. [107] demonstrated that Runt-related transcription factor 1 (RUNX1) drives CCL2 expression in colorectal adenocarcinoma through transcriptional upregulation of hematological cell lineage 2 (HCL2), establishing RUNX1 as a critical transcriptional mediator of HCL2-dependent chemokine signaling. In their study of colorectal cancer (CRC), Guo et al. [107] found that RUNX1 recruits macrophages and induces M2-polarized TAM in CRC by promoting the production of CCL2 and the activation of the hedgehog pathway. Emerging evidence reveals macrophages induce endothelial activation through paracrine secretion of angiogenic mediators such as VEGF, driving pathological neointimal hyperplasia. Furthermore, these immune sentinels preserve vascular homeostasis through dual mechanisms: production of immunomodulatory cytokines (e.g., IL-10) and regulation of ECM composition and dynamics, effectively attenuating inflammatory cascades. A recent research by Zenget al. found that macrophages in skin wounds in a diabetic state polarize to M1 type, targeting vascular endothelial cell HELZ2 protein by secreting extracellular vesicles carrying miR-ERIA, thereby inhibiting vascular endothelial cell migration and tube-forming ability and ultimately leading to delayed wound healing [108]. Furthermore, macrophages have been shown to maintain vascular endothelial cell stability by secreting antiinflammatory cytokines (e.g., IL-10) and regulating ECM components to reduce inflammatory responses.

4.3 Immune Regulation

Immunoregulation is defined as the complicated interactions between immune molecules, immune cells, and the immune system with other bodily systems during immune responses. These interactions establish a regulatory network that coordinates and constrains various processes, thereby ensuring that the immune response is appropriately calibrated in terms of strength and quality to maintain the stability of the body's internal environment. Typically, systematic analysis of immunometabolic pathways focuses on macrophages, which are central to both pro- and anti-inflammatory immune responses [109]. It is now widely acknowledged that these cells play a pivotal role in immune regulation, a process that is critical for maintaining health. A mounting body of evidence suggests a critical functional linkage between the bioenergetic reprogramming of polarized macrophages (M1/M2 phenotypes) and their immunomodulatory capacities. Systematic elucidation of the dynamic interactions governing metabolic reprogramming dynamics and PRR cascades within these immune cells may establish a conceptual foundation for designing targeted intervention strategies against chronic inflammatory pathologies [110].

IFN-γ and LPS have been shown to trigger macrophages, leading to the TCA cycle displayed through integrated transcriptional and metabolic pathways. Inhibition of succinate dehydrogenase by the citric acid metabolite succinate in the TCA cycle is a key feature of IFN-γ/LPS-polarized macrophages. Emerging pharmacological studies have demonstrated that succinate, acting as an immune-regulating metabolite, possesses dual therapeutic properties, which include both significant attenuation of inflammatory cascades and effective suppression of pathogenic microorganisms. It is noteworthy that alterations in metabolite concentrations have the capacity to directly modify the function of signaling pathways. HIF-1α stabilization, induced by LPS-induced succinate accumulation in macrophages, has been shown to promote proinflammatory cytokine IL-1β expression [111]. The proteostatic maintenance of HIF-1α drives glycolytic reprogramming in proinflammatory macrophages. This oxygen-sensitive transcription factor orchestrates the transcriptional activation of essential enzymatic components involved in carbohydrate metabolism, such as the lactate export machinery (MCT4/SLC16A3) and hexose uptake systems (GLUT1/SLC2A1). M1 macrophages have also been shown to exhibit an enhanced pentose phosphate pathway, which produces NADPH [112]. It has been established that NADPH plays a crucial role as a cofactor for LPS-induced iNOS, facilitating the catabolism of arginine into NO and l-citrulline. It is noteworthy that NADPH not only generates NO and ROS, but also contributes to the production of the antioxidant glutathione, which is vital for maintaining redox homeostasis and averting cellular damage from ROS [113]. Additionally, NO serves as a central regulatory mediator that governs metabolic reprogramming in classically activated macrophages. Through dual molecular mechanisms involving the nitrosylation of the [4Fe–4S] enzymatic complex and the consequent irreversible disruption of mitochondrial electron transfer, this gaseous signaling molecule fundamentally compromises mitochondrial bioenergetic efficiency. It effectively uncouples the progression of the TCA cycle from ATP synthase activity, while imposing energetic constraints on oxidative metabolism [114].

Distinct bioenergetic configurations characterize macrophage polarization states, with M2 variants exhibiting significant divergence from their proinflammatory M1 counterparts. This dichotomy reflects their specialized roles in immunoregulation and stromal maintenance. Central to this metabolic compartmentalization is the differential engagement of ATP synthesis pathways: M1 polarization preferentially drives flux through the glycolytic pathway, often accompanied by the accumulation of itaconate, whereas M2 activation coordinates mitochondrial oxidative metabolism through the TCA cycle, coupled with mitochondrial OXPHOS, thus optimizing the electron transport chain for energy production. This process is facilitated by the glutamate metabolic pathway, which involves β-fatty acid oxidation and α-ketoglutarate. The IL-4/IL-13 signaling axis orchestrates metabolic reprogramming in macrophages by transcriptionally enhancing fatty acid β-oxidation and mitochondrial biogenesis. This process is mechanistically dependent on the integrated activation of STAT6, members of the PPAR nuclear receptor family, and PGC-1β. M1 and M2 macrophages exhibit opposing arginine metabolism; M1 macrophages upregulate iNOS to metabolize l-arginine into the antimicrobial substances NO and l-citrulline, while M2 macrophages catalyze l-arginine to urea and l-ornithine through the induction of Arg1 [117, 118].

The M1/M2 polarization state of macrophages has been demonstrated to exhibit bidirectional roles in immunomodulation. It has been shown that M1-type macrophages activate antitumor immunity by secreting proinflammatory factors such as TNF-α and IL-12, whereas M2-type macrophages promote immunosuppression and tissue repair through mediators such as IL-10 and TGF-β [119]. Notably, 3,3′,5-triiodothyronine (T3) has been found to have a dual regulatory role, promoting M1 polarization to enhance inflammatory response and inhibiting M2 activity to maintain immune homeostasis, illustrating a dynamic regulatory mechanism with implications for autoimmune disease and tumor therapy [120]. M2-type polarization of TAMs is a fundamental factor in tumor immune escape, which promotes angiogenesis and suppresses T cell function by secreting molecules such as VEGF and PD-L1. Recent studies have developed pH-responsive nanoparticles, which can reprogram TAM to the M1 phenotype by precisely modulating lysosomal function, significantly enhancing antigen presentation efficiency and activating CD8⁺ T cells [121]. In addition, a combination of GM-CSF secretion mediated by engineered bacteria and SIRPα–siRNA delivery has been shown to synergistically block the CD47–SIRPα immune checkpoint pathway, thereby significantly enhancing the antitumor efficacy [122].

4.4 Neuronal Network Protection

The neuronal network is comprised of highly specialized neurons and their synaptic connections, which achieve information integration and regulation through electrochemical signaling. It is a central carrier of nervous system function. Macrophages (e.g., microglia, which are resident macrophages in the central nervous system [CNS]) can regulate the microenvironment of neural stem cells. These cells play a critical role in safeguarding neuronal networks across multiple levels, including the regulation of the inflammatory microenvironment, the maintenance of neurohomeostasis, the execution of phagocytic clearance and damage repair, and the regulation of metabolism and energy homeostasis. M2-type macrophages, in particular, have been shown to inhibit excessive inflammatory responses and reduce neuronal apoptosis by secreting antiinflammatory factors such as IL-10 and TGF-β.

In a spinal cord injury model, TREM2 knockout macrophages significantly improved neuronal survival by decreasing levels of proinflammatory factors TNF-α and IL-1β [123]. Macrophages also promote neuronal survival and axonal regeneration by secreting BDNF) and NT-3 [124]. Following spinal cord injury, an increase in the number of dorsal root ganglion macrophages (DRGMacs) is observed, primarily through self-renewal. A subset of DRGMacs undergoes a transformation into a microglial-like state following nerve injury, with these cells potentially migrating from the spinal cord to DRG and contributing to neuroprotection and repair. A further subset of DRGMacs displays characteristics analogous to satellite glial cells, which have been observed to express macrophage-associated genes post-nerve injury and potentially contribute to immune responses and neuroprotection [125]. Research has demonstrated that fumarate hydratase (FH) modulates the proinflammatory and reparative functions of macrophages by regulating mitochondrial RNA release and interferon-β signaling pathways. Inhibition of FH enhances the antiinflammatory phenotype of macrophages and attenuates neuronal damage in neurodegenerative lesions [126, 127]. Furthermore, the study identified that MDE carry noncoding RNA species, such as miR-155 and miR-21, which traverse the neurovascular unit, achieving cerebral parenchymal infiltration through selective modulation of tight junction complexes and endothelial transcytosis pathways, thereby modulating synaptic plasticity and neuronal electrical activity [128].

Accumulating experimental evidence delineates the pathophysiological contributions of myeloid phagocytes, particularly circulating monocytes, TRMs, and microglial cells, in mediating neuroimmune interactions that drive inflammation-associated axonal degeneration, CNS structural compromise, and resultant neurobehavioral alterations in mammalian models [129, 130]. Notably, cerebral phagocytic populations constitutively express PRRs, including TLR4 and NLRP3 inflammasomes, which mechanistically enable their capacity to mediate structural plasticity through dendritic spine pruning and synaptic remodeling [131, 132]. The functional polarization of these immunoregulatory cells is not merely determined by passive cytokine exposure; rather, it is shaped by the dynamic equilibrium between neurodestructive mediators (e.g., IL-1β/TNF-α) and neurotrophic factors (e.g., glial cell-derived neurotrophic factor [GDNF]/insulin-like growth factor 1), which collectively dictate their dichotomous roles in neural circuit disruption versus restoration. Furthermore, the adrenergic signaling–Arg1–polyamine metabolic axis in muscular macrophages mediates neuroprotective adaptations during infectious challenges, where activation of the β2-adrenergic receptor triggers pharmacological induction of Arg1 enzymatic activity, thereby elevating polyamine biosynthesis to prevent infection-associated neurodegeneration [133].

During the process of tissue healing following acute injury, macrophages are responsible for the removal of cellular debris from the affected area through a process known as thrombospondin-1 (TSP-1)-dependent phagocytosis. In addition to this primary function, these cells also release metabolites, such as adenosine, which play a crucial role in promoting angiogenesis and axon regeneration. The activation of calcitonin gene-related peptide (CGRP) neurons has been observed to enhance the phagocytic activity of macrophages. It has been demonstrated that CGRP neurons are responsible for accelerating the repair of skin and muscle injuries. The neuropeptide CGRP exhibits dual immunomodulatory functions through coordinated molecular mechanisms. It mediates neutrophil efferocytosis via Rho GTPase-dependent cytoskeletal reorganization and drives macrophage phenotypic switching toward an immunoregulatory (M2-like) state through TSP-1-mediated autocrine/paracrine signaling loops [124].

Macrophages, a fundamental component of organismal homeostasis, function as a regulatory axis that orchestrates a multifaceted physiological barrier through phagocytosis. This process encompasses the elimination of metabolic byproducts, the orchestration of tissue repair microenvironments, the maintenance of immune dynamic homeostasis, and the engagement in neural synaptic pruning. However, their high degree of plasticity endows macrophages with the capacity to dynamically transform in pathological microenvironments. In such microenvironments, macrophages can either initiate a protective program by sensing injury signals through PRRs or be driven by abnormal microenvironments to develop proinflammatory or profibrotic phenotypes. These phenotypes ultimately influence the direction of disease progression.

5.1 Autoimmune Diseases

Macrophages play a crucial role in the progression of various autoimmune disorders due to their diverse functional repertoire, which includes immunoregulation, proinflammatory activation, and stromal remodeling. These myeloid sentinels orchestrate complex chemokine networks through the dynamic secretion of soluble mediators that recruit and prime adaptive immune cell populations, thereby establishing self-perpetuating inflammatory circuits via paracrine signaling mechanisms.

SLE is an autoimmune disease characterized by an overactive immune system, the presence of autoantibodies, and multisystem damage, resulting in a wide heterogeneity of clinical manifestations  .The etiology of SLE is complicated and involves both genetic susceptibility and environmental factors [134, 135]. One hypothesis is that residual cellular debris generated by increased cell death initiates immune overactivity and induces immunologic loss [136]. Research efforts have increasingly concentrated on the immunomodulatory effects of regulated cell death modalities, particularly their ability to undermine immunological tolerance and dynamically reconfigure adaptive immune circuits. The study of the role of innate immune cells in the pathogenesis of SLE has also attracted considerable interest, as there is a disruption in the homeostasis between macrophage subtypes in SLE, which is more pronounced in the affected organs. LPS leakage from damaged intestinal barriers was found to induce GSDMD-mediated cellular pyroptosis through the TLR4/caspase 11 pathway in MRL/lpr mice. Moreover, pyroptotic macrophages promoted the differentiation of naive B cells into plasmoblasts and plasma cells, which may exacerbate the pathogenesis of lupus. Additionally, inhibition of caspase 11 and intestinal barrier repair with antibiotics effectively inhibited the caspase 11/GSDMD pathway and attenuated the manifestation of lupus in mice [137] (Figure 4) .

RA, a prevalent immune-mediated disorder, is characterized by a complex disease progression involving inflammatory cascades that target the synovium and lead to destructive polyarticular involvement. This often results in irreversible joint degradation and significant functional impairment [138]. Pathological analyses indicate a marked dysregulation in macrophage polarization dynamics, with a shift in the balance from proinflammatory (M1) to antiinflammatory (M2) phenotypes, favoring dominant M1 activation throughout the pathogenesis of RA [139, 140]. Macrophages are critical in the initiation and maintenance of synovitis in RA, where they can act as antigen-presenting cells leading to T-cell-dependent B-cell activation and production of damaging cytokines, but macrophages are also involved in maintaining tissue homeostasis/repair [141]. Pathological and physiological macrophages differ in phenotype and function (e.g., cytokine secretion) and exhibit polymorphism. Reprogramming M1 macrophages to M2 using targeted IL-10 gene therapy prevents joint inflammation and damage associated with arthritis [142]. Rosmarinic acid, a polyphenolic derivative derived from Prunus serotina, orchestrates immunometabolic reprogramming through the dual-axis suppression of the ERK/hypoxia-inducible factor 1 alpha (HIF-1α)/GLUT1 signaling cascade. This targeted kinase modulation attenuates Warburg-like glycolysis, facilitating a phenotypic transition from classically activated macrophages to alternatively polarized phenotypes. This metabolic switch not only ameliorates synovitis-mediated joint destruction but also enhances chondroprotective repair mechanisms in RA models [143]. Thus, modulation of joint-associated macrophage subtypes has significant therapeutic potential.

Synovial tissue is the primary site of joint inflammation in RA patients. Chronic synovitis results in irreversible damage to cartilage and bone. TAMs are evolutionarily conserved innate immune effectors that originate from fetal liver-derived precursors or bone marrow myeloid progenitors. These sentinel cells perform organ-specific homeostatic functions, ranging from the efferocytic clearance of apoptotic debris to the sequestration of pathogens, as exemplified by the alveolar surveillance mechanisms that maintain sterility during respiratory gas exchange. Crucially, macrophages act as immunoregulatory rheostats, coordinating a biphasic inflammatory cascade that initiates neutrophil recruitment and subsequently resolves sterile injury. During parenchymal damage, local macrophage pools are augmented by circulating monocyte-derived counterparts, establishing heterotypic cellular crosstalk networks that calibrate the intensity of inflammation [144]. The dynamic equilibrium between CD169+ synovial-resident macrophages and CCR2⁺ monocyte-derived infiltrating macrophages dictates the temporal progression of synovitis and the fidelity of articular regeneration processes in rheumatoid joints [145]. Landmark clinical observations, particularly the pathognomonic association of STM (CD68⁺CD163⁻) density gradients with radiographic joint space narrowing [146], coupled with spatial transcriptomic evidence demonstrating the colocalization of macrophage activation markers (CD86/MHC-II) with subchondral bone erosion foci in high-DAS28 joints [147], have provided mechanistic insights into macrophage-mediated synoviocyte hyperplasia and osteoclast activation during the progression of RA.

5.2 Neurodegenerative Diseases

As the predominant neurodegenerative dementia subtype, Alzheimer's disease (AD) clinically manifests as relentless mnestic dysfunction and multidomain cognitive deterioration. Advancing chronological age emerges as the primary nonmodifiable determinant in AD pathogenesis, and both are associated with chronic inflammation (sometimes referred to as “inflammatory aging”) and an impaired immune response. Microglia are the major resident macrophages in the brain, accounting for 10% of all glial cells. In the early stages of AD, they play a protective role by phagocytosing β-amyloid (Aβ) and tau proteins, but as the disease progresses, prolonged activation releases proinflammatory factors (e.g., IL-1β, TNF-α) that exacerbate neuroinflammation [148-150]. In recent years, it has been found that macrophages of peripheral origin can enter the AD brain through the blood–brain barrier and synergize with central microglia to regulate pathological processes. For example, CX3CR1⁺ BAMs are enriched around Aβ plaques, but their clearance is affected by lipid metabolic status [150-152]. Microglia rely on the TREM2 receptor to recognize and phagocytose Aβ, while secreting insulin-degrading enzyme to directly degrade Aβ. Knockdown of the myeloid triggering receptor TREM1 protects glucose metabolism in peripheral macrophages and oxidative phosphorylation in brain neurons. Restoration of immune responses that support healthy brain function [153]. In addition, a study shows that MDM activation is independent of TREM2 and that blocking monocyte migration with anti-Ccr2 antibody completely abolishes the cognitive-improving effects of anti-PD-L1 treatment in Trem2^−/−5XFAD mice [154]. On the other hand, high-fat diet and APOE4 genotype exacerbate lipid droplet deposition in microglia, leading to decreased phagocytosis through inhibition of the PI3K/AKT pathway. Knockdown of Fit2, a key gene for lipid droplet formation, was shown to increase Aβ clearance by 40% [150]. Activated microglia are converted to a glycolytic phenotype, leading to lactate accumulation and disruption of neuronal mitochondrial function [155, 156].

Macrophages play a dynamic, double-edged role in AD and their function is coregulated by genetic, metabolic and microenvironmental factors. Future studies need to combine single-cell multiomics, organoid models, and clinical cohorts to analyze the spatio-temporal specific functions of different subpopulations of macrophages and to develop stage-appropriate therapeutic strategies.

5.3 Cancers

TAMs constitute critical stromal constituents of the neoplastic niche, exerting pleiotropic regulatory effects on malignant proliferation, VEGF-mediated neovascularization, and PD-L1-dependent immune checkpoint activation [157-159]. Ontogenetically stratified, these myeloid populations segregate into embryonically derived tissue-resident and hematopoietic progenitor-derived monocytic lineages. Functionally, these myeloid infiltrates pervasively colonize solid neoplasms, driving oncogenic processes, angiogenic switching, metastatic dissemination, and desmoplastic stromal barrier formation, ultimately facilitating immune-privileged tumor evolution.

Triple-negative breast carcinoma (TNBC), defined by the immunohistochemical absence of estrogen receptor, progesterone receptor, and HER2/neu expression, represents the most therapeutically challenging breast cancer subtype with aggressive metastatic potential. While bidirectional tumor–stroma signaling has been extensively characterized in mammary malignancies [160], the precise molecular circuitry through which TNBC cells reprogram TAMs remains enigmatic. Emerging data delineate a feedforward TNBC–TAM communication IL-6/TGF-β1-mediated paracrine signaling induces constitutive HLF activation in neoplastic cells. Mechanistically, HLF orchestrates ferroptosis resistance via transcriptional upregulation of GGT1, thereby enabling glutathione-mediated redox homeostasis and fueling TNBC malignant progression. These findings unveil the HLF/GGT1 regulatory node as a promising therapeutic vulnerability in TNBC pathobiology [161]. A monocyte-derived subpopulation of STAB1⁺TREM2^high lipid-associated macrophages (LAM) expanded in patients resistant to immune checkpoint blockade (ICB) therapy; this LAM subpopulation is immunosuppressive and acquires tumor-promoting capacity upon recruitment to the tumor site via the cancer-associated fibroblast (CAF)-driven CXCL12–CXCR4 axis, which supports an immunosuppressive microenvironment [162]. IL-1 receptor type 2 (IL1R2) orchestrates breast tumor-initiating cell (BTIC) stemness maintenance and neoplastic expansion in TNBC. Mechanistically, preclinical TNBC models revealed that pharmacological IL1R2 antagonism potently suppressed CCL2-mediated myeloid cell infiltration and M2-like TAM polarization, concomitantly impairing BTIC clonogenicity while mitigating CD8⁺ T-lymphocyte dysfunction. This multimodal immunomodulation consequently attenuated oncogenic progression and conferred significant overall survival extension in murine TNBC systems through STAT3 signaling axis inactivation and glutathione peroxidase 4-mediated ferroptosis sensitization. This suggests that targeting this molecule may improve patient treatment [163]. In addition, TAM secretes IL-1β and TNF-α, which activate the IKK/NF-κB pathway in TNBC cells via IL1R/TNFR, inducing increased autophagy and promoting cell migration and invasion. Animal models showed that targeted inhibition of this pathway significantly reduced lung metastasis [164]. In conclusion, TAM plays a central role in TNBC progression through polarization regulation, metabolic interaction and immune escape mechanisms.

Non-small cell lung cancer (NSCLC) is the most prevalent form of lung cancer, constituting 80–85% of all lung cancers. It encompasses primarily squamous cell carcinoma, adenocarcinoma, and large cell carcinoma. TAMs in the interstitium of NSCLC are predominantly of the M2 phenotype (CD68⁺TGF-β1⁺), which is significantly higher than that in paracancerous tissues, and the M2 phenotype inhibits antitumor immunity by secreting factors such as IL-10 and TGF-β, promoting angiogenesis and stromal remodeling [165]. The infiltration level and spatial distribution of TAMs were found to have a significant impact on the outcome of NSCLC patients treated with ICB [166]. It is also significant that the degree of TAM infiltration in NSCLC was associated with upregulation of CD27, ITGAM, and CCL5 gene expression. The protein products of these genes play a key role in controlling tumor macrophage polarization and may be novel immunotherapeutic targets [165]. An in vitro coculture model study showed that NSCLC cells are capable of inducing macrophages to express an immunosuppressive M2-type phenotype, particularly high expression of Arg1. This model provides an effective tool to study the biological functions of macrophages in NSCLC and to develop therapeutic strategies against macrophages.

Esophageal squamous cell carcinoma (ESCC) is a malignant tumor derived from esophageal squamous epithelial cells and is the major pathological type of esophageal cancer. TAMs potentiate neoplastic invasion through paracrine secretion of protumorigenic factors while simultaneously driving VEGF-A-driven neovascularization. TAM abundance exhibits a linear correlation with CD31⁺ microvessel density indices, suggesting their dual role in stromal remodeling and angiogenic switch regulation during ESCC progression [167]. The M2-polarized phenotype of TAMs is an important feature of the ESCC microenvironment, and M2-type macrophages promote tumor immune escape and angiogenesis by secreting factors such as VEGFA and IL-10 [168]. And, CAFs recruit and induce tumor cell invasion and angiogenesis by secreting PAI-1, CCL2, and other factors to recruit and induce macrophage M2 polarization while enhancing migration and invasion of ESCC cells [169]. Therapeutic strategies that target the Hippo/YAP–CD24/Siglec-15 signaling nexus exhibit bimodal therapeutic efficacy in ESCC by suppressing Hippo/YAP-driven oncogenic signaling cascades and enhancing macrophage-mediated efferocytosis through the blockade of the STAT6-mediated “don't eat me” signal (CD47/SIRPα axis). This mechanism holds significant translational potential in the context of precision oncology for ESCC [170].

5.4 Liver Diseases

5.4.2 Alcohol-Associated Liver Disease

Alcohol-associated liver disease (ALD) represents a preeminent global health burden, accounting for the majority of chronic hepatopathies worldwide [184-187] and constituting the principal indication for hepatic transplantation in Western healthcare systems [188]. Within its clinical spectrum, alcoholic hepatitis emerges as a critical syndrome of acute-on-chronic hepatic decompensation, exhibiting a 28-day mortality risk exceeding 30% and 90-day mortality rates reaching 50% in severe presentations. Orthotopic liver transplantation persists as the sole disease-modifying intervention for eligible candidates meeting stringent abstinence criteria, though its application remains constrained by donor organ scarcity and complex ethical considerations [189-191]. The pathophysiological continuum of ALD is inextricably linked to ethanol-induced enteric dysbiosis, characterized by Bacteroidetes depletion and Proteobacteria expansion [192-194]. These microbial community perturbations potentiate gut barrier dysfunction, driving endotoxin translocation and hepatic inflammasome activation [195-197]. The dysbiosis of intestinal flora, in turn, induces intestinal barrier dysfunction and permits the transfer of live bacteria from the gut to the liver [198, 199]. Alcohol-associated liver injury has been shown to induce changes in the composition and phenotype of hepatic macrophages and a decrease in the number of CRIg⁺ KC. These changes have been demonstrated to impair the clearance of pathogenic bacteria. The detrimental effects of ethanol-induced CRIg suppression in KCs were effectively neutralized through soluble CRIg-Ig supplementation, demonstrating hepatoprotective benefits in murine models of alcohol-related hepatic injury. Alcohol has been shown to reduce CRIg expression in the liver by altering the composition and phenotype of hepatic macrophages, thereby compromising the hepatic firewall [200]. This compromised CRIg expression directly impairs hepatic clearance mechanisms for gut-derived pathogens, establishing a pathophysiological link to aggravated hepatic pathologies ranging from terminal hepatic conditions (such as cirrhotic degeneration) to elevated risks of disseminated infections in alcohol-associated hepatitis. These cascading effects position CRIg modulation as a novel therapeutic frontier in managing ethanol-related hepatic disorders [201, 202] (Figure 5).

5.5 Cardiovascular Disease

Cardiovascular disease (CVD) is a complex group of disorders characterized by atherosclerosis, myocardial infarction (MI), and stroke, with core pathological mechanisms involving vascular endothelial damage, lipid deposition, chronic inflammation, and immune cell infiltration. Macrophages are the major immune cell type within atherosclerotic plaques. They play a dual role in CVD through phenotypic polarization. In particular, macrophages with a TAM-like phenotype (similar to M2 type) may promote tissue repair in atherosclerotic plaques by secreting antiinflammatory factors and stabilize plaques by inhibiting inflammation through phagocytosis of apoptotic cells. In contrast, M1-type macrophages release proinflammatory factors and MMPs, accelerating the risk of plaque rupture. Recent studies have focused on modulating macrophage polarization homeostasis or targeting their metabolic reprogramming (e.g., cholesterol metabolism, glycolysis) to inhibit plaque progression and stabilize the vascular microenvironment, providing new strategies for the treatment of CVD.

Angiopoietin-like proteins 3 (ANGPTL3) demonstrates potent atherogenesis-promoting activity through multitiered mechanisms. Akt pathway activation via phosphorylation mediates ANGPTL3-driven upregulation of TLR4, potentiating robust NF-κB nuclear translocation upon LPS challenge. This signaling cascade culminates in proinflammatory cytokine biosynthesis and M1-skewed polarization in human THP-1 macrophages. In vivo validation using ANGPTL3-overexpressing murine models reveals amplified TLR4-mediated plaque inflammation driving atherosclerotic lesion progression [231].

The mTOR signaling network serves as a multifunctional regulator of cellular homeostasis, coordinating processes including growth regulation, metabolic adaptation, and survival pathways [232]. While mTOR hyperactivation demonstrates pathological correlations with atherogenesis, its cell-specific contributions to plaque evolution and macrophage functionality remain mechanistically elusive. Paradoxically, whereas pharmacological mTORC1 inhibition confers vascular protection [233], genetic ablation of mTORC2 in macrophages precipitates exacerbated atherosclerotic manifestations characterized by complex lesion morphology and elevated apoptotic indices [234]. In vitro mechanistic studies reveal mTORC2-mediated suppression of FoxO1 transcriptional activity, effectively constraining inflammasome assembly and IL-1β production—central mediators of vascular inflammation. Importantly, pharmacological FoxO1 antagonism demonstrates therapeutic efficacy in mitigating inflammation driven by mTORC2 deficiency across experimental models. Notably, the collective deletion of macrophage mTOR disrupts mTORC1- and mTORC2-dependent pathways, resulting in minimal changes in plaque size or complexity, suggesting a balanced yet opposing role of these signaling arms [231].

25-Hydroxycholesterol (25-HC) is an oxidized product of cholesterol, produced by the enzyme cholesterol 25-hydroxylase. Classified within a family of bioactive oxysterols, 25-HC is endogenously synthesized by cells during cholesterol homeostasis dysregulation and immunostimulation [235]. Macrophage-derived 25-HC exacerbates atherosclerotic progression through dual mechanisms: autocrine/paracrine-mediated plaque destabilization and intraplaque smooth muscle cell migration impairment. Mechanistically, 25-HC potentiates proinflammatory activation in lipid-engorged macrophages while restricting vascular smooth muscle cell motility. Experimental investigations further reveal 5-HC modulates membrane cholesterol dynamics, disrupting TLR4 signaling architecture to amplify NF-κB-driven inflammatory transcriptomes and augment apoptotic susceptibility in lesional macrophages [236].

6.1 CCL2, CCR2/5 Antagonist

In MASLD, macrophages are recognized as playing a critical role, with elevated periportal macrophages serving as an early histological indicator. Specifically, periportal CCR2⁺ inflammatory macrophages accumulate in the periportal areas of patients with MASH, which correlates with the severity of the disorder and the presence of fibrosis [237]. Upon activation, macrophages develop secretory competence, enabling the production of a diverse array of immunomodulatory molecules. Notably, these include chemokines such as CCL2 (MCP-1), CCL3 (MIP-1α), and CXCL8 (IL-8), as well as proinflammatory cytokines like IL-1β, IL-6, and TNF-α. This multifaceted repertoire of mediators plays a crucial role in orchestrating the pathological inflammatory cascades that underlie disease pathogenesis.

A notable trend of upregulation in chemokines and their receptors has been identified in patients diagnosed with MASH. This trend encompasses the upregulation of CCL3-5/CCR-5, as well as the chemokine CCL2. Furthermore, hepatic expression of additional cytokines, such as CD44 and CD62E (E-Selectin), has been significantly elevated in MASH patients, indicating their involvement in leukocyte recruitment to inflammatory sites. CD44 interacts with components of the ECM, including osteopontin, to regulate macrophage recruitment to the liver [238]. Additionally, it plays a role in macrophage activation triggered by DAMPs, PAMPs, and saturated fatty acids. Given that the CCL2/CCR2 axis is crucial for recruitment of inflammatory monocytes to the injured liver and for driving the progression of hepatic fibrosis, various studies have explored strategies to mitigate MASH-induced liver injury by blocking this axis. The administration of CCL2 inhibitors in mouse models of steatohepatitis induced by a methionine–choline-deficient diet and chronic liver injury (CCl4-induced) has demonstrated a reduction in monocyte/macrophage infiltration and an improvement in MASH progression [239].

Cenicriviroc (CVC), an orally bioavailable dual chemokine receptor antagonist targeting CCR2/CCR5 with optimal pharmacokinetic properties, was originally developed for HIV management [240] through suppression of Ly6C⁺ monocyte infiltration, CVC depletes hepatic macrophage reservoirs, consequently attenuating fibrotic progression in chronic liver diseases [241]. Clinical validation across randomized placebo-controlled studies and phase IIb trials confirms its therapeutic efficacy in fibrosis, demonstrating acceptable tolerability and sustained hepatic benefits.

Previous studies have investigated the function of CCR2 in concanavalin A-induced immune liver damage with a particular focus on the dual CCR2/CCR5 antagonist, CVC. Demonstrated to be safe in clinical trials and effective in various animal disease models, CVC was evaluated for its effects on liver macrophage populations. Flow cytometry analysis revealed that CVC treatment significantly reduced the overall proportion of liver macrophages in Con A-administered mice, specifically decreasing the levels of MoMFs while leaving KCs unaffected. CVC intervention in Con A-challenged murine models elicited marked depletion of hepatic proinflammatory CX3CR1⁺CCR2⁺Ly6C⁺ macrophage subpopulations. Complementary immunohistochemical quantification revealed attenuated CCR2+ monocyte accumulation in therapeutic cohorts. These congruent findings establish CVC's dual mechanism, suppression of CCR2⁺ monocyte activation, and blockade of hepatic leukocyte trafficking. The therapeutic efficacy of CVC was also assessed through the measurement of serum transaminase levels and the evaluation of liver tissue necrosis, both of which demonstrated a positive response, indicating that CVC significantly mitigates liver injury induced by Con A. Complementary experimental evidence from TUNEL assays and ROS histochemical detection revealed CVC-mediated attenuation of hepatocellular apoptosis and oxidative damage in Con A-challenged murine livers. Extended pharmacological investigations validate CVC's multifunctional hepatoprotective profile, demonstrating antifibrotic efficacy and steatosis suppression across diverse hepatic pathologies [242, 243]. Overall, these findings validate CVC's pharmacological promise in mitigating Con A-triggered immune-mediated hepatic injury.

In murine studies, pharmacological targeting of the CCL2–CCR2 pathway has been shown to reduce monocyte infiltration and the accumulation of MoMF in the injured liver. Consequently, the use of CCL2 inhibitors, in conjunction with CCR2/5 antagonists, has the potential to enhance fibrosis outcomes by diminishing monocyte infiltration and modifying hepatic macrophage subsets. The CCR2/5 pathway has emerged as a prominent goal in the treatment of MASH [244].

6.2 PPAR Agonist

PPARs are ligand-activated core transcription factors that adjust adipocyte disintegration, lipid storage, and insulin sensitivity. This transcription factor facilitates hepatic lipogenesis and steatosis, promotes fatty acid absorption and triglyceride synthesis in hepatocytes, and enhances the secretion of adipokines via SREBP-1c [245]. Conversely, PPAR-γ also protects the liver by inhibiting the proinflammatory polarization of macrophages, thereby reducing oxidative stress and reversing the activation of HSCs [246, 247].

The inactivation of PPAR expression results in the activation of HSCs, an inflammatory response, and increased lipogenesis; conversely, the activation of PPARs can prevent and suppress liver fibrosis. Notably, targeted therapies aimed at activating PPAR expression have demonstrated potential efficacy in the treatment of hepatic diseases associated with liver fibrosis [248].

Multiple synthetic PPAR-α agonists have undergone rigorous clinical assessment. Notably, fenofibrate exhibited therapeutic efficacy in ameliorating histopathological features within experimental murine steatohepatitis models [249]. Concurrently, bezafibrate administration demonstrated dual pharmacodynamic effects—modulating lipometabolic pathways and restoring hepatic architecture in monosodium glutamate-induced rodent models substantiating its therapeutic potential for MASLD management [250].

Certain synthetic PPAR-γ agonists have been shown to mitigate liver inflammation and activate HSCs. Pioglitazone, in particular, has the potential to improve hepatic steatosis, inflammation, and fibrosis in MASLD by downregulating platelet-derived growth factor and TIMP-2 [251]. Pioglitazone demonstrates geroprotective potential with therapeutic implications for senescent hepatic fibrogenesis [251]. Mechanistic parallels emerge for rosiglitazone, which ameliorates acetaminophen-induced acute hepatotoxicity while attenuating diet/age-driven hepatic lipid accumulation and MASH progression [252, 253]. Notably, the PPARβ/δ agonist KD3010 exerts ECM remodeling inhibition in experimental fibrosis models (CCL4 cholestatic), achieved through dual suppression of HSC activation and inflammatory cascade potentiation [254]. L-165041, a synthetic PPAR-β/δ ligand, has also been shown to prevent hepatic steatosis by ameliorating liver inflammation and lipid accumulation in mice subjected to a Western diet [255]. Consequently, there is a pressing need to explore additional PPAR-β/δ agonists for the treatment of liver diseases. Experimental evidence of Wy-14,643-mediated oxidative damage attenuation implicates PPARα-regulated genomic targets that modulate hepatic redox homeostasis and/or sustain mitochondrial β-oxidative flux as critical mediators of APAP hepatoprotection [255]. Further support for the hypothesis that Wy-14,643 mediates protection against ischemia–reperfusion injury (IRI) in fatty livers through the attenuation of the inflammatory response has been provided by studies examining adhesion molecule expression.

Research has revealed a previously unrecognized hepatoprotective mechanism mediated by PPAR-α during acetaminophen-induced liver injury. In this experimental paradigm, prophylactic treatment with the synthetic PPAR-α activator Wy-14,643 effectively prevented all signs of hepatic injury in genetically unmodified mice following administration of a hepatotoxic APAP dosage. The safeguarding effect was confirmed through multiple parameters: preserved macroscopic hepatic appearance, microscopic evaluation of hematoxylin–eosin-stained tissue samples showing absence of notable pathological alterations, and substantially reduced plasma concentrations of hepatocellular enzymes (AST/ALT). Furthermore, in the context of IRI, pretreatment with Wy-14,643 demonstrated protective effects in both MASH and steatosis models, leading to a significant reduction in ALT levels and areas of hepatocellular necrosis [256, 257].

6.3 Glucagon-Like Peptide-1 Receptor Agonists

Gut-derived hormones are currently utilized in the clinical management of metabolic diseases, exemplified by glucagon-like peptide-1 receptor (GLP-1R) agonists such as semaglutide and liraglutide, as well as GLP-1/GIP (glucose-dependent insulinotropic polypeptide) dual agonists like tirzepatide. Additionally, GLP-1/glucagon dual agonists, including cotadutide, are under advanced clinical development [258, 259]. Their influence on liver inflammation and fibrosis is primarily considered to be indirect, potentially through mechanisms such as reduced energy supply and improved hepatocyte metabolism. Sort of evidence proposes that hepatic KCs may possess functional GLP-1 receptors, implying possible susceptibility to pharmacological activation through GLP-1R agonists [260]. Of particular clinical relevance, therapeutic targeting of this pathway has demonstrated efficacy in achieving histological improvement of MASH in phase II clinical trials [261], findings that have stimulated expanded clinical evaluation of this molecular mechanism in subsequent large-scale investigations. Furthermore, tirzepatide exhibits a pronounced dose-dependent effect on body weight reduction, particularly when compared with semaglutide and dulaglutide [262]. Given this body of evidence, certain GLP-1R agonists and tirzepatide are emerging as promising therapeutic options for MASLD and MASH, especially in individuals with concurrent type 2 diabetes mellitus or obesity [263, 264].

The GLP-1R demonstrates extensive expression throughout multiple anatomical systems, spanning pancreatic tissue, central nervous networks, gastrointestinal components, cardiovascular structures, hepatic parenchyma, adipose deposits, and musculoskeletal elements [265]. Binding of GLP-1 to its receptor stimulates insulin secretion while inhibiting glucagon secretion, leading to improved glucose metabolism and lower blood glucose levels. Furthermore, GLP-1R plays a role in regulating gastric emptying, gastric acid secretion, and gastric motility; it also suppresses food and water intake, thereby contributing to weight loss. Recently, GLP-1R agonists and GLP-1R/glucagon receptor (GCGR) dual-target agonists have demonstrated efficacy in the treatment of MASH [266].

Studies have evaluated the potential beneficial effects of GLP-1R and GCGR dual agonists on liver fibrosis in rodent models. These dual-target agonists have been shown to improve liver conditions in rats and mice with CCl4-induced hepatic fibrosis. The underlying mechanism involves the inhibition of TGF-β and the downstream Smad signaling pathways, which ultimately contribute to the reversal of hepatic fibrosis [266]. Furthermore, the histological features of MASH, such as steatosis and ballooning, have also been found to improve with the administration of GLP-1R agonists, including liraglutide and semaglutide [262]. Experimental evidence illustrates liraglutide's capacity to regulate immune cell differentiation patterns. Demonstrated through preclinical models, the GLP-1R agonist lixisenatide ameliorates atherosclerotic pathology in insulin-resistant murine subjects through phenotypic alteration of macrophages [267]. Research by Bruen et al. has documented liraglutide's dual capacity to direct monocyte-derived cell phenotypes while influencing cellular differentiation toward M2-resolution specialized macrophages [268. Complementing these findings, in vitro investigations have revealed liraglutide administration induces antiinflammatory polarization of KCs [269].

There is emerging evidence suggesting that GLP-1RAs may confer benefits in liver fibrosis associated with MASLD. While the precise mechanisms by which GLP-1RAs may reduce liver fibrosis remain unclear, several experimental studies indicate that these agents could modulate ECM homeostasis. This regulatory mechanism appears to be mediated via dual suppression of oxidative stress mediators and downregulation of MAPK cascade activity, thereby impeding the assembly of BATF/JUN transcriptional complexes involving basic leucine zipper ATF-like transcription factors [270]. However, it remains uncertain whether this mechanism is applicable to human livers [271]. A recent systematic review and network meta-analysis highlighted that semaglutide, liraglutide, and the combination of vitamin E with pioglitazone exhibited the highest probability of ranking as the most effective interventions for achieving resolution of MASH [272].

6.4 Thyroid Hormone Receptor-Beta Agonist

As previously mentioned, PPARs, liver X receptors, FXRs, and thyroid hormone receptors (THRs) are recognized as prominent therapeutic target receptors. While FXRs have been extensively studied, this review will primarily focus on THRs, with a particular emphasis on THR-β. THR-β is predominantly expressed in the liver, and THR-β agonists have shown efficacy in reducing LDL levels, TG, and hepatic steatosis in humans. Additionally, THR-β facilitates fatty acid catabolism and stimulates mitochondrial biogenesis, resulting in decreased lipotoxicity and enhanced liver function, which ultimately leads to a reduction in liver fat [273].

Resmetirom (MGL-3196) represents a novel investigational orally bioavailable selective THR-β agonist with pioneering therapeutic potential [274]. Data from mechanistic studies implicate macrophage-mediated processes in its anti-MASH activity [275]. Practically positioned downstream of PI3K/AKT signaling, the NF-κB cascade constitutes a principal regulatory axis for inflammatory mediators, whose aberrant activation is fundamentally linked to MASH pathogenesis. Concurrently, STAT3 stimulation exerts context-dependent immunomodulatory effects, demonstrating dual functionality in both fibrogenic progression and inflammatory modulation during MASH evolution [274]. Through Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analyses conducted in both the resmetirom and control groups, Wang et al. [276] suggest that resmetirom has the potential to ameliorate MASH by restoring the expression of RGS5, which subsequently deactivates the STAT3 and NF-κB signaling pathways.

6.5 Fibroblast Growth Factor 21

Fibroblast growth factor 21 (FGF21) is a member of the FGF superfamily and serves as an endocrine factor closely related to FGF19 and FGF23, which are secreted by the liver to regulate the intake of simple sugars and the preference for sweet foods [277]. This regulatory function is mediated through signaling via FGF21 receptors located in the paraventricular nucleus of the hypothalamus. FGF21 promotes thermogenesis through endocrine signaling to adipose tissue, which helps prevent adipose tissue dysfunction and reduces lipid spillage into the liver [278]. Additionally, it enhances fatty acid oxidation and cholesterol clearance through autocrine signaling to the liver, thereby mitigating hepatic lipotoxicity [279]. Furthermore, FGF21 inhibits the activation of KCs, monocyte recruitment, and the formation of LAMs and SAMs, which may impede collagen accumulation and reduce hepatic fibrosis. Recent studies have demonstrated that FGF21 can diminish alcohol preference and cravings, leading to a reduction in alcoholic liver injury [280]. Consequently, FGF21 represents a promising target for mitigating alcohol-induced hepatic damage.

During the development of MASH, evidence suggests that FGF21 inhibits the activation of KCs and MoMFs. This inhibition prevents the accumulation of CD36^high KCs and CD36^highCD9^high MoMFs under dietary conditions that promote MASH. These findings indicate that FGF21 reduces LAMs and SAMs, thereby inhibiting the synthesis of collagen type I alpha 1 and preventing fibrogenesis [281].

Distinct from canonical fibroblast growth factors, FGF21 exhibits absent heparin affinity, enabling systemic circulation as an endocrine mediator. This pleiotropic hormone exerts profound regulatory effects on whole-body metabolic homeostasis while demonstrating hepatoprotective capacities [282]. Preclinical and clinical investigations collectively validate FGF21's cytoprotective function in hepatic systems [283]. Experimental models employing FGF21-deficient rodents fed lipotoxic diets display aggravated hepatocellular injury, a phenotype rescued through exogenous FGF21 administration [284, 285]. Mechanistic studies further reveal FGF21's capacity to attenuate carbon tetrachloride-induced acute hepatic damage via SIRT1-dependent autophagic induction [285]. Clinical observations demonstrate significantly elevated circulating FGF21 concentrations in ACLF patients, showing positive correlations with hepatic injury biomarkers including CRP and transaminases. Particularly, FGF21 transcription is regulated by CHOP—a terminal effector of endoplasmic reticulum (ER) stress cascades [286]. Paradoxically, increased FGF21 expression reciprocally inhibits the eIF2α–ATF4–CHOP signaling axis, creating negative feedback to mitigate ER stress-mediated hepatocyte injury [281]. Beyond ER stress modulation, oxidative challenges induce dramatic upregulation of both hepatic FGF21 production and systemic secretion. This adaptive response potentially represents the liver's endogenous mechanism to bolster antioxidant defenses and counteract toxic insults [287]. Moreover, clinical evidence indicates diverse changes in serum FGF21 levels among HBV-infected patients under varying clinical conditions. Serum levels of FGF21 were positively correlated with serum aminotransferases, suggesting that FGF21 may serve as an indicator of liver damage associated with HBV infection. CHB patients demonstrate diminished circulating FGF21 concentrations, particularly pronounced in cases of HBV-induced cirrhotic complications, a phenomenon potentially reflecting impaired hepatic biosynthetic capabilities. Conversely, the paradoxical FGF21 surge detected in CHB subjects progressing to HCC suggests diagnostic value for this hepatokine in tracking malignant transformation within this clinical cohort [288].

The intrinsic elevation of FGF21 across multiple pathological states positions this hepatokine as a compelling candidate for emerging as a multipurpose diagnostic and prognostic biomarker. Clinical investigations revealed a 25-fold surge in circulating FGF21 concentrations within 2 h posttransplantation, whereas maximal ALT/AST concentrations emerged at 24-h postprocedural intervals [289]. Temporal trajectory analysis identified concordance between 2-h FGF21 peaks and subsequent 24-h transaminase elevations, establishing its potential as an early-warning indicator with high predictive accuracy for IRI in transplant recipients [290]. While further mechanistic investigations and population-specific validation remain prerequisites for clinical implementation, this emerging pleiotropic hormone exhibits substantial therapeutic potential for both managing and monitoring diverse metabolic pathologies.

The therapeutic potential of natural FGF21 is constrained by its short half-life of approximately 2 h. Consequently, researchers are actively developing a long-acting glycosylated and polyglycolated FGF21 analogue known as pegozafermin, which exhibits an extended in vivo half-life. This analogue demonstrates promise for the treatment of MASH and severe hypertriglyceridemia. In clinical trials, pegozafermin successfully achieved both primary endpoints, indicating potential efficacy in treating MASH. Notably, all three dosage groups (15 mg or 30 mg weekly, or 44 mg biweekly) exhibited one phase of improvement in defibrase, without exacerbation of MASH or worsening of fibrosis, and did so without significant side effects [279, 291].

6.6 Galectin-3 Antagonist

Galectin-3 (Gal - 3), a protein of significant importance, is instrumental in the pathogenesis of MASH and fibrosis, as well as in various fibrotic conditions affecting the lungs, heart, kidneys, liver, and vascular system. It interacts with receptors such as TLR4, TGF - β, dectin-1, and TREM2, leading to a range of intracellular effects. Within cells, Galectin-3 is associated with AKT phosphorylation, transcriptional regulation, Wnt/β-catenin signaling, and the regulation of apoptosis. Extracellularly, it plays a role in inflammation, cell proliferation, differentiation, and migration. Additionally, Galectin-3 promotes morphogenesis in endothelial cells and facilitates tumor angiogenesis [292].

As an upstream factor of TREM2, Gal-3 act a pivotal part in modulating macrophage polarization, specifically reducing M1 polarization while promoting M2 polarization [293]. Additionally, Gal-3 activates NLRP3 inflammatory vesicles by interacting with TLR4 in the liver through its carbohydrate-recognition-binding domains, thereby facilitating the development and expression of inflammatory cells. This research finds a significant association between Gal-3 and progression of chronic MASH in mice subjected to a high-fat diet [294].

Accumulating research identifies Gal-3 as a pathogenic factor in hepatic fibrogenesis, where pharmacological blockade demonstrates therapeutic efficacy against fibrotic resolution [295, 296]. The multifactorial pathogenesis of tissue fibrogenesis involves intricate crosstalk between immunocytes and activated myofibroblasts, with Gal-3 emerging as a pivotal molecular bridge [294]. Functioning as a pleiotropic modulator, Gal-3 orchestrates cellular responses in both stromal (myofibroblasts) and innate immune compartments (macrophages), critically influencing fibrotic progression. Models of carbon tetrachloride-induced hepatic fibrosis reveal that genetic ablation of Gal-3 suppresses stellate cell transdifferentiation and collagen biosynthesis, demonstrating impaired TGF-β responsiveness in Gal-3-deficient cells compared with wild-type counterparts. Mechanistically, Gal-3 deficiency disrupts TGF-β receptor membrane localization while attenuating β-catenin phosphorylation and nuclear trafficking, though Smad2/3 activation remains unaffected. These findings establish Gal-3's indispensable role in TGF-β-driven ECM remodeling through noncanonical signaling pathways. Specifically, Gal-3 mediates IL-4-dependent macrophage polarization toward profibrotic phenotypes [297], with IL-4/IL-13-stimulated macrophages amplifying fibrogenic gene networks that perpetuate collagen deposition and disease advancement. This molecular triad positions Gal-3 as a critical nexus integrating macrophage–fibroblast interactions within the fibrotic microenvironment. A deeper understanding of the mechanisms regulating tissue fibrosis, along with targeted strategies to inhibit Gal-3 in the liver, provides a compelling rationale for developing novel therapeutic approaches for patients suffering from liver fibrosis.

Galectin therapeutics has engineered GR-MD-02, a modified pectic polysaccharide derived from Malus domestica, through synthetic modification processes. This galactoarabino–rhamnogalacturonan polymer contains a heterogeneous sugar composition dominated by galacturonic acid, galactose, arabinose, and rhamnose residues. Preclinical analyses demonstrate its superior binding specificity for Gal-3 over related galectin isoforms. Initial clinical evaluation in a 2015 Phase 1 trial (NCT01899859) involving 31 MASH patients with progressive fibrosis demonstrated acceptable safety profiles and biological activity. Subsequent Phase 2 investigations comprised two parallel cohorts: the MASH FX study (NCT02421094, n = 30) enrolling subjects with significant fibrosis (F3) and the larger MASH CX trial (NCT02462967, n = 162) focusing on cirrhotic patients. Despite these extensive evaluations, GR-MD-02 failed to achieve statistically significant improvements in the primary histological endpoint of fibrosis regression through quantitative MRI-based assessment (LiverMultiSca). Secondary biomarkers including magnetic resonance elastography and vibration-controlled transient elastography (FibroScan) measurements similarly showed no clinically meaningful alterations. The pleiotropic involvement of Gal-3 in chronic inflammatory pathologies has solidified its status as a viable therapeutic target across multiple disease states. This molecular rationale has stimulated substantial commercial investment, with numerous biopharmaceutical entities pursuing diverse targeting approaches including small molecule inhibitors, monoclonal antibodies, and carbohydrate-based antagonists. These strategies include the design and synthesis of powerful small molecule antagonists (such as glycomimetics) and larger biologics derived from natural sources, all aimed at therapeutic intervention for various cancers, fibrosis, and other liver diseases [298]. Gal3-targeting therapies may be utilized either as standalone treatments or in combination with existing medications.

The pivotal involvement of Gal-3 in orchestrating inflammatory cascades and fibrotic remodeling across multiple organ systems has positioned its pharmacological targeting as a priority in novel therapeutic development. Preclinical investigations and emerging clinical evidence collectively substantiate the antifibrotic potential of Gal-3 blockade. In concanavalin A-challenged murine hepatitis models, prophylactic administration of the Gal-3 antagonist TD139 attenuated hepatic inflammatory responses through immunomodulatory mechanisms [299]. DAVANAT—a carbohydrate-based Gal-3 inhibitor demonstrated therapeutic efficacy in experimental cholangitis induced by Novosphingobium aromaticivorans [300] and dextran sulfate sodium-mediated colitis [301] via suppression of NLRP3 inflammasome activation and IL-1β downregulation in macrophage populations. Further supporting this therapeutic paradigm, the orally bioavailable Gal-3 inhibitor GB1211 exhibited dual antifibrotic activity in murine models of hepatotoxic (CCl4-induced) and pulmonary (bleomycin-induced) fibrosis through distinct pathway modulation [302]. Clinically, elevated Gal-3 expression correlates with hepatic decompensation risks, particularly in cirrhotic progression and chronic HBV infections. Patients with HBV-associated ACLF displaying Gal-3 promoter methylation exhibited accelerated disease trajectories characterized by reduced survival durations, elevated 3-month mortality indices, and higher MELD prognostic scores [303]. Moreover, given the involvement of Gal-3 in nearly all inflammatory processes activated during acute intravascular hemolysis, this molecule may represent a viable therapeutic target. Future research is essential to elucidate the precise role of Gal-3 in the development of acute and chronic tissue injuries caused by acute intravascular hemolysis and to further explore its previously demonstrated therapeutic effects in fibrotic diseases, thereby positioning Gal-3 as a potential therapeutic target in hemolysis-induced organ damage.

Furthermore, investigations have revealed temporal elevation of Gal-3 expression during initial hepatic insult phases following α-galactosylceramide administration, detected systemically in circulation and hepatic compartments. Immunohistochemical analyses identified Gal-3-expressing macrophages migrating to inflammatory foci with distinct aggregation patterns. These observations propose macrophage-derived Gal-3 as a promising diagnostic indicator for acute hepatocellular damage in histopathological evaluations [304].

Numerous medications are available for the management of liver inflammation. Inhibitors of apoptosis signal-regulating kinase 1 (ASK1) () have shown efficacy in halting disease progression, which encompasses inflammation, liver fibrosis, insulin resistance, and hepatic lipid accumulation [305, 306]. Additionally, agonists of the A3 adenosine receptor can induce apoptosis in inflammatory cells and inhibit the NF-κB signaling pathway. Below outlines the various drugs, their corresponding targets, and their clinical trial statuses (Table 2).