SPARC interacts with AMPK and regulates GLUT4 expression

AMP-activated protein kinase (AMPK) is a critical regulator of glucose metabolism. To elucidate the biochemical mechanisms by which AMPK regulates glucose and fat metabolism, we conducted a yeast two-hybrid screen to identify its interacting partners. A yeast two-hybrid system was used to screen a mouse embryo cDNA library for proteins able to bind mouse AMPKα1. We also demonstrated an endogenous interaction between AMPKα1 and its interacting partner by co-immunoprecipitation of the endogenous proteins using specific antibodies in HepG2 cells, and in rat kidney, liver, skeletal muscle, and fat tissue. We show that secreted protein acidic and rich in cysteine (SPARC) is an AMPK-interacting protein, and the two proteins enhance each other. AMPK activation increases SPARC expression, and knockdown of AMPK to inhibit endogenous AMPK expression reduces SPARC protein levels. On the other hand, SPARC siRNA reduces AICAR-stimulated AMPK phosphorylation. SPARC affects AMPK-mediated glucose metabolism through regulation of Glut4 expression in L6 myocytes. Our findings suggest that SPARC may be involved in regulating glucose metabolism via AMPK activation. These results provide a starting point for efforts to clarify the relationship between AMPK and SPARC, and deepen our understanding of their roles in fat and glucose metabolism.