UC San Diego

In chronic obesity, hepatocytes become insulin resistant and exert important effects on systemic metabolism. Here we show that in early onset obesity (4 weeks high-fat diet), hepatocytes secrete exosomes that enhance insulin sensitivity both in vitro and in vivo. These beneficial effects were due to exosomal microRNA miR-3075, which is enriched in these hepatocyte exosomes. FA2H is a direct target of miR-3075 and small interfering RNA depletion of FA2H in adipocytes, myocytes and primary hepatocytes leads to increased insulin sensitivity. In chronic obesity (16-18 weeks of a high-fat diet), hepatocyte exosomes promote a state of insulin resistance. These chronic obese hepatocyte exosomes do not directly cause impaired insulin signalling in vitro but do promote proinflammatory activation of macrophages. Taken together, these studies show that in early onset obesity, hepatocytes produce exosomes that express high levels of the insulin-sensitizing miR-3075. In chronic obesity, this compensatory effect is lost and hepatocyte-derived exosomes from chronic obese mice promote insulin resistance.