Myeloid TGF-β signaling shapes liver macrophage heterogeneity and metabolic liver disease pathogenesis

Background & Aims: Cellular heterogeneity of innate immune cells, such as macrophages, in the liver is a hallmark of metabolic dysfunction-associated steatohepatitis (MASH) pathogenesis. However, the mechanisms shaping liver macrophage heterogeneity and function during disease progression remain poorly understood. Methods: Control or myeloid-specific Tgfbr1 knockout mice (n = 9-12 per group) were fed a 12-week choline-deficient, amino acid-defined high-fat diet (CDA-HFD) or a 20-week GAN diet (40% fat, 22% fructose, 2% cholesterol). Liver tissue was analyzed using histopathology, quantitative PCR, immunoblotting, flow cytometry, and RNA sequencing (RNA-seq). Bulk RNA-seq (n = 3 per group) and single-nucleus RNA-seq were performed to investigate transcriptional reprogramming. Macrophage population dynamics were evaluated by flow cytometry and immunofluorescence. Results: We identified TGF-β signaling as a crucial regulator of disease-associated expansion of Trem2⁺ and Fcrl5⁺ macrophages in MASH livers. Myeloid-specific inactivation of Tgfbr1 in mice exacerbated diet-induced MASH, with increased hepatocyte injury, inflammation, and liver fibrosis. Mechanistically, loss of TGF-β signaling in myeloid cells altered macrophage composition, marked by a reduction in Trem2⁺ and expansion of Fcrl5⁺ macrophages. Additionally, macrophages lacking Tgfbr1 exhibited gene signatures associated with inflammasome activation, cytokine signaling, cellular senescence, and immunosuppression. These changes in macrophage composition and function promoted effector T cell exhaustion and the development of MASH-associated hepatocellular carcinoma in Tgfbr1-deficient mice. Conclusions: These findings identify myeloid TGF-β signaling as a key driver of liver macrophage heterogeneity and polarization within the microenvironment during the progression of MASH and MASH-associated liver cancer. Impact and implications: Our study reveals that myeloid TGF-β signaling plays a crucial role in shaping liver macrophage heterogeneity, which in turn influences the pathogenesis of metabolic liver disease. These findings are particularly important for researchers studying immune-metabolic interactions and for clinicians seeking new therapeutic strategies for liver disorders. By elucidating how TGF-β signaling regulates macrophage function, our work paves the way for targeted interventions that modulate immune responses to improve liver health. Future research should consider the potential translational applications of these findings while addressing limitations related to model systems and human variability.