miR149-5p: A hepatocyte EXOmotif sequence containing microRNA that attenuates liver fibrosis by specifically targeting PDGFRB in HSCs.

INTRODUCTION: Liver fibrosis is a progressive pathological process driven by liver injury, including viral hepatitis and metabolic dysfunction-associated steatohepatitis (MASH), and can progress to cirrhosis, liver failure, and hepatocellular carcinoma (HCC). Hepatocyte-hepatic stellate cell (HSC) crosstalk plays a central role in disease progression, but its regulatory mechanisms remain incompletely understood. OBJECTIVES: This study aimed to define hepatocyte-HSC crosstalk in liver fibrosis mediated by microRNA-149-5p (miR-149-5p) signaling and to explore its potential as a therapeutic target for intervention. METHODS: Differentially expressed exosomal microRNAs were identified by RNA sequencing of hepatocyte-derived exosomes from fibrotic and control livers. Functional screening using collagen type I alpha 1 chain (COL1A1) reporter assays identified miR-149-5p as an anti-fibrotic candidate. Exosome-mediated intercellular communication was confirmed using co-culture systems and confirmed by tumor susceptibility 101 (TSG101) silencing. Liver fibrosis was induced by bile duct ligation (BDL) and thioacetamide (TAA) in mice. Therapeutic effects were evaluated using AAV-mediated hepatocyte-specific overexpression and miR-149-5p agomir administration. RESULTS: miR-149-5p was selectively enriched in hepatocyte-derived exosomes via a CCUC-based EXOmotif and directly targeted PDGFRB in HSCs, thereby inhibiting HSC activation, proliferation, and collagen deposition without affecting hepatocyte function. During fibrosis progression, PU.1 bound to the miR-149-5p promoter and suppressed its transcription, leading to reduced exosomal miR-149-5p delivery and consequent PDGFRB derepression in HSCs. Both AAV-mediated overexpression and systemic miR-149-5p agomir administration significantly attenuated BDL- and TAA-induced liver fibrosis, as evidenced by reduced collagen deposition, decreased hydroxyproline content, and downregulation of HSC activation markers. CONCLUSION: The PU.1 (hepatocyte)-miR-149-5p (exosome)-PDGFRB (HSC) axis represents a key regulatory pathway in liver fibrosis, wherein PU.1 represses miR-149-5p transcription in hepatocytes, leading to EXOmotif-dependent reduction of exosomal miR-149-5p delivery and consequent derepression of PDGFRB in HSCs, thereby promoting HSC activation and fibrosis progression. Importantly, miR-149-5p agomir administration offers a promising therapeutic strategy for liver fibrosis.