CD36-PPARγ-SPP1 axis mediates hepatocyte-macrophage coordination to drive MASLD-related liver fibrosis

Metabolic dysfunction-associated steatotic liver disease (MASLD) is characterized by profound remodeling of hepatic macrophages, including the emergence of lipid-associated macrophages (LAMs). However, the mechanisms through which LAMs promote fibrosis and their key molecular drivers remain elusive.

Macrophage-specific CD36 knockdown was achieved using AAV8-delivered short hairpin (sh)RNA. A suite of experimental systems, including co-culture models, lipid trafficking assays, chromatin immunoprecipitation sequencing (ChIP)-qPCR, and lipidomics, was used to dissect the cluster of differentiation (CD)36-peroxisome proliferator-activated receptor (PPAR)γ-SPP1 axis. Genetic and pharmacological tools were used for mechanistic and therapeutic studies. Clinical relevance was assessed in well-characterized patient cohorts.

We identified a unique CD36⁺ macrophage subpopulation that aligns with LAMs and expands markedly in human and murine MASLD livers, strongly correlating with fibrosis severity. Macrophage-specific CD36 deletion attenuated steatosis, transaminases (alanine aminotransferase [ALT] and aspartate aminotransferase [AST] reduced by >30%, p <0.01) and fibrosis (reduction in fibrosis area by 30-45%, p <0.01) in two MASH mouse models. Mechanistically, CD36 mediated lipid transfer from steatotic hepatocytes to LAMs. Lipid loading activated PPARγ, triggering its nuclear translocation and direct binding to the SPP1 promoter, stimulating SPP1 secretion. In turn, SPP1 activated hepatic stellate cells. Clinically, the CD36-PPARγ-SPP1 gene signature was independently associated with both fibrosis stage (p = 0.009) and steatosis grade (p = 0.03) in patients (N = 48). Importantly, pharmacological inhibition of CD36 suppressed lipid uptake and SPP1 release, attenuating fibrogenesis, whereas combination therapy with a PPARγ agonist yielded synergistic antisteatotic and antifibrotic effects.

Our study identifies the CD36-PPARγ-SPP1 axis as a core mechanism whereby lipid-loaded macrophages drive liver fibrosis in MASLD. Thus, therapeutic cotargeting of CD36 and PPARγ presents a novel and promising strategy to counteract fibrosis progression in advanced disease.

Our study provides an investigation of the features and signals of lipid-associated macrophages (LAMs) that are present in MASLD liver and express a specific protein called CD36. We found that these cells internalize hepatocyte-derived lipids via CD36 and activate the PPARγ-SPP1 axis, contributing to liver fibrosis. More importantly, targeting CD36 effectively improves serum aminotransferases, liver steatosis, and liver fibrosis. Understanding the novel signal in LAMs and discovering the diverse roles of PPARγ in different cell populations could be therapeutically targeted to treat MASLD-related liver fibrosis.