Secreted Protein Acidic and Rich in Cysteine Improves Glucose Tolerance via AMP-activated Protein Kinase Activation. Mus musculus

Metabolic dysfunction of skeletal muscle is often prevalent at an early stage in the development of several non-communicable diseases. Here, we investigated the effect of a myokine, secreted protein acidic and rich in cysteine (SPARC), on glucose tolerance in human and mouse skeletal muscles. SPARC knockout mice showed marked decreases in parameters for whole-body glucose metabolism, along with reduced phosphorylation of AMPK and Akt in skeletal muscle tissues compared with wild-type mice. Furthermore, mice injected with SPARC showed improved glucose tolerance concomitant with AMPK activation. Exogenous SPARC treatment accelerated glucose uptake in muscle tissues isolated from wild-type mice but not from AMPKγ3 knockout mice. In muscle cells, SPARC increased glucose uptake concomitant with AMPK activation, mediated by a calcium-dependent signal. Chronic treatment of SPARC restored metabolic functions in diet-induced obese mice. These findings suggest that SPARC improves glucose metabolism via AMPK activation in skeletal muscle, providing mechanistic insights on exercise-induced metabolic benefits and physical inactivity-induced glucose intolerance. Overall design: We performed a microarray analysis to compare the metabolic gene expression profiles in the skeletal muscle from each mouse.