Hepatocyte TGF‐β Signaling Inhibiting WAT Browning to Promote NAFLD and Obesity Is Associated With Let‐7b‐5p

Transforming growth factor beta (TGF‐β) signaling in hepatocytes promotes steatosis and body weight gain. However, processes that TGF‐β signaling in hepatocytes promote pathological body weight gain in nonalcoholic fatty liver disease (NAFLD) are incompletely understood. Obesity and NAFLD were induced by 16 weeks of feeding a high‐fat diet (HFD) in hepatocyte‐specific TGF‐β receptor II–deficient (Tgfbr2(ΔHEP) ) and Tgfbr2(flox/flox) mice. In addition, browning of white adipose tissue (WAT) was induced by administration of CL‐316,243 (a β3‐adrenergic agonist) or cold exposure for 7 days. Compared with Tgfbr2 (flox/flox) mice, Tgfbr2(ΔHEP) mice were resistant to steatosis and obesity. The metabolic changes in Tgfbr2(ΔHEP) mice were due to the increase of mitochondrial oxidative phosphorylation in the liver and white‐to‐beige fat conversion. A further mechanistic study revealed that exosomal let‐7b‐5p derived from hepatocytes was robustly elevated after stimulation with palmitic acid and TGF‐β. Indeed, let‐7b‐5p levels were low in the liver, serum exosomes, inguinal WAT, and epididymal WAT in HFD‐fed Tgfbr2(ΔHEP) mice. Moreover, 3T3‐L1 cells internalized hepatocyte‐derived exosomes. An in vitro experiment demonstrated that let‐7b‐5p overexpression increased hepatocyte fatty acid transport and inhibited adipocyte‐like cell thermogenesis, whereas let‐7b‐5p inhibitor exerted the opposite effects. Conclusion: Hepatocyte TGF‐β‐let‐7b‐5p signaling promotes HFD‐induced steatosis and obesity by reducing mitochondrial oxidative phosphorylation and suppressing white‐to‐beige fat conversion. This effect of hepatocyte TGF‐β signaling in metabolism is partially associated with exosomal let‐7b‐5p.