Hepatic insulin resistance promotes fructose-enriched diet-induced fatty liver diseases.

Understanding mechanisms causing MAFLD (Metabolic Associated Fatty Liver Disease) and its progression to MASH (metabolic dysfunction-associated steatohepatitis) is clinically important and scientifically challenging. Hepatic insulin resistance is a common component in the progression of MAFLD in patients and experimental animals; however, hepatic steatosis caused by the HFD45% (high-fat diet) decreases during chronic hepatic IR generated by inactivation of Irs1/2 (LDKO), AKT1/2, or InsR 1-3—which is inconsistent with the expected relationship between IR and MAFLD in humans4. Here we found that complete hepatic insulin resistance promotes the fructose-enriched GAN diet-induced MAFLD, including acute inflammation and MASH in LDKO mice. Unexpectedly, fructose phosphorylation catalyzed by hepatic Khk (ketohexokinase) was not required as acute MAFLD progressed strongly in LDKOŸKhkL/L mice fed the GAN diet. FoxO1 activated during hepatic IR induces Fst (Follistatin) expression and secretion from the liver of LDKO mice. Inactivation of hepatic FoxO1 in LTKO mice (LDKO•FoxO1L/L) or Fst in LDKOFstKO mice prevented acute MAFLD during the GAN diet. Consistently, overexpression of hepatic Fst promoted GAN diet-induced MAFLD/MASH and hepatic carcinoma. Mechanistically, circulating Fst promoted adipose tissue IR and lipolysis, which can deliver FFA (free fatty acid) to the liver for esterification with excess Gro3P (glycerol 3-phosphate) generated by fructose metabolism, although hepatic DNL (de novo lipogenesis) decreased strongly in LDKO mice while. Since circulating FST correlates positively with both T2D and MAFLD in humans, our results suggests that hepatic FST induced by progressive hepatic IR might promote MAFLD/MASH during the consumption of sugar-sweetened food and beverages consumed frequently by people and animals with T2D.