Expression and purification of asprosin in Pichia pastoris and investigation of its increase glucose uptake activity in skeletal muscle through activation of AMPK

Asprosin is a new hormone released from white adipose tissue (WAT) that not only promotes glucose release in the liver but also activates orexigenic neurons in the hypothalamus to promote appetite and weight gain. Its effect on skeletal muscle glucose uptake is unclear. This research, a stable asprosin expression system was formed by first constructing a eukaryotic expression vector pPIC9K-8His-Asprosin, and then transforming it into the Pichia pastoris strain GS115. Pichia pastoris methanol induction combined with Nickel-NTA magnetic beads purification strategy was used to express and purify asprosin protein. Purified asprosin can promote the phosphorylation of PKA substrate, and intraperitoneal injection of asprosin can increase blood glucose. After proteolysis and detection by mass spectrometry, asprosin was found to have 3 glycosylation sites and multiple glycosyl types. Asprosin up-regulated glucose transporter 4 (GLUT4) expression in myotubes, including mRNA and protein levels. In addition, asprosin enhanced AMP-activated protein kinase (AMPK) phosphorylation, but it had no effect on AKT phosphorylation with or without insulin treatment. Treatment with an AMPK inhibitor (compound C) reduced the asprosin-mediated glucose uptake effect. These results show that purified asprosin activated AMPK signaling in skeletal muscle and further promoted glucose uptake. From the perspective of skeletal muscle uptake of glucose, asprosin may have beneficial effects on type 2 diabetes.