LAUSR

Background and Aims: Liver fibrosis is a chronic disease characterized by different etiological agents; dysregulated interactions between hepatocytes and HSCs contribute to this disease. β‐arrestin 1 (ARRB1) plays an important role in liver fibrosis; however, the effect of ARRB1 on the crosstalk between hepatocytes and HSCs in liver fibrosis is unknown. The aim of this study is to investigate how ARRB1 modulates hepatocyte and HSC activation during liver fibrosis. Approach and Results: Normal and fibrotic human liver and serum samples were obtained. CCl4‐induced liver fibrosis and methionine‐choline deficiency–induced NASH models were constructed. Primary hepatocytes and HSCs were isolated, and human hepatic LO2 and stellate LX2 cells were used. Small extracellular vesicles (EVs) were purified, and key proteins were identified. ARRB1 was up‐regulated in hepatocytes and associated with autophagic blockage in liver fibrosis. ARRB1 increased the release of hepatocyte‐derived small EVs by inhibiting multivesicular body lysosomal degradation and activating Rab27A, thereby activating HSCs. Proteomic analyses showed that mannan‐binding lectin serine protease 1 (MASP1) was enriched in hepatocyte‐derived small EVs and activated HSCs via p38 mitogen‐activated protein kinase (MAPK)/activating transcription factor 2 (ATF2) signaling. ARRB1 up‐regulated MASP1 expression in hepatocytes. MASP1 promoted liver fibrosis in mice. Clinically, MASP1 expression was increased in the serum and liver tissue of patients with liver fibrosis. Conclusions: ARRB1 up‐regulates the release of hepatocyte‐derived MASP1‐enriched small EVs by regulating the autophagic‐lysosomal/multivesicular body pathway and Rab27A. Hepatocyte‐derived MASP1 activates HSCs to promote liver fibrogenesis through p38 MAPK/ATF2 signaling. Thus, MASP1 is a pivotal therapeutic target in liver fibrosis.