Irisin promotes lipid clearance through the CD81-integrin-FAK axis in steatotic hepatocytes.

Irisin, an exercise-induced myokine, regulates metabolic homeostasis, but its receptor mechanisms in metabolic dysfunction-associated steatotic liver disease (MASLD) remain unclear. This study investigates the role of the co-receptor CD81 in modulating irisin signaling and intrahepatic lipid homeostasis. Clinical correlations were analyzed in 88 bariatric surgery patients and liver biopsy cohorts (n = 62). In vitro steatosis models included Clone-9 rat hepatocytes, primary mouse hepatocytes, and human HepG2 and Huh-7 cells treated with fatty acids and recombinant irisin. Receptor interactions and downstream signaling were evaluated using co-immunoprecipitation, RT-qPCR, Western blotting, subcellular fractionation, and lipid staining. Serum irisin positively correlated with BMI and steatosis grade, but inversely associated with triglycerides, fasting glucose, and HbA1c. Intrahepatic FNDC5/irisin and integrin β5 correlated with serum triglycerides, whereas membranous CD81 expression declined with advancing steatosis. Free fatty acids induced FNDC5/irisin and perilipins (Plin2/Plin5) while downregulating CD81. Co-immunoprecipitation confirmed physical interaction between CD81 and integrins αV/β5 subunits. CD81 overexpression enhanced irisin-induced focal adhesion kinase (FAK) phosphorylation, restricted PPARγ nuclear translocation, suppressed Plin2/Plin5 expression, and attenuated lipid accumulation. Conversely, FAK inhibition using BI 853520 or CD81 knockdown abrogated these protective anti-steatotic effects. In conclusion, CD81 serves as a functional co-receptor that physically associates with the integrin αV/β5 complex to amplify irisin-FAK signaling, restrict PPARγ nuclear transactivation, and suppress lipid droplet accumulation in cultured hepatocytes in vitro. These findings highlight the CD81-integrin-FAK axis as a potential candidate for further translational exploration in MASLD.