Hepatocyte-derived Pumilio1-enriched exosomes inhibit HSC activation by suppressing tropomyosin-4 translation.

BACKGROUND: Metabolic dysfunction-associated steatotic liver disease (MASLD) has become the most common chronic liver disease globally. Abnormal crosstalk between hepatocytes and HSCs leads to liver fibrosis and aggravates MASLD. We explored the role of the RNA-binding protein Pumilio in this process. METHODS: Two isoforms of Pumilio proteins (PUM1, PUM2) expression were analyzed in the livers of MASLD patients and mice. MASLD mice were induced by a western diet combined with intraperitoneal injection of carbon tetrachloride (WD+CCl4), or a choline-deficient, L-amino acid-defined, high-fat diet (CDAHFD). Adeno-associated virus type 8 carrying Pum1-targeting short hairpin RNA or small interfering RNA targeting PUM1 was used to knock down PUM1 in vivo or in vitro. Ultracentrifugation was used to isolate exosomes from cells and serum. RNA sequencing and RNA immunoprecipitation experiments were used to find and identify the target genes of PUM1. RESULTS: The expression of PUM1, not PUM2, was decreased in both MASLD patients and models. PUM1 knockdown aggravated liver injury. PUM1 also decreased in steatotic hepatocytes. Upregulating PUM1 improved lipid deposition and reduced hepatocyte lipotoxic death. Hepatocytes regulate the activation of HSCs by PUM1-enriched exosomes. Tropomyosin 4 (TPM4) was identified as a target of PUM1. PUM1 affected the expression of TPM4 by binding to its mRNA, thereby regulating HSCs activation. CONCLUSIONS: While PUM1 is downregulated during MASLD progression, upregulation of PUM1 improves lipid deposition, reduces hepatocyte lipotoxic death and inhibits TPM4 expression to reduce HSC activation.