Irisin Regulates Hepatic Glucose Metabolism via AMPK and PI3K/Akt Activation

Irisin plays a crucial role in the glucose metabolism of mammals and fish. However, the mechanism by which irisin regulates hepatic glucose metabolism is not entirely known. To clarify irisin's function and underlying mechanisms in common carp glucose metabolism, the FNDC5 expression patterns were detected after insulin/glucagon injection, long-term high-glucose, and high-fat diet feeding. In vivo, the activity of PFK and the synthesis of liver glycogen were significantly increased, while the enzyme activity of PEPCK was reduced after intraperitoneal injection with irisin. In contrast, irisin siRNA attenuated the brain and liver FNDC5a and FNDC5b expression, and the serum glucose was increased. Glut2, gs, hk, and pfk were considerably downregulated in the brain and liver, while pygl, pepck, and g6pase were remarkably upregulated after siRNA treatment. In vitro, irisin activates the phosphorylation level of AMPK and PI3K/Akt in primary hepatocytes. Compound C and wortmannin inhibit AMPK and PI3K/Akt, reversing irisin-induced expression of g6pase, fbpase, pepck, gk, gs, pfk, hk, and gsk3b. At the same time, compound C attenuated irisin-induced expression of pi3k and akt. Our research reveals the mechanisms of irisinA and irisinB as glucose metabolism regulators in teleost for the first time.