Cold-induced PGC-1α expression modulates muscle glucose uptake through an insulin receptor/Akt-independent, AMPK-dependent pathway

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Abstract
Peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) participates in control of expression of genes involved in adaptive thermogenesis, muscle fiber type differentiation, and fuel homeostasis. The objective of the present study was to evaluate the participation of cold-induced PGC-1α expression in muscle fiber type-specific activity of proteins that belong to the insulin-signaling pathway. Rats were exposed to 4°C for 4 days and acutely treated with insulin in the presence or absence of an antisense oligonucleotide to PGC-1α. Cold exposure promoted a significant increase of PGC-1α and uncoupling protein-3 protein expression in type I and type II fibers of gastrocnemius muscle. In addition, cold exposure led to higher glucose uptake during a hyperinsulinemic clamp, which was accompanied by higher expression and membrane localization of GLUT4 in both muscle fiber types. Cold exposure promoted significantly lower insulin-induced tyrosine phosphorylation of the insulin receptor (IR) and Ser473phosphorylation of acute transforming retrovirus thymoma (Akt) and an insulin-independent increase of Thr172phosphorylation of adenosine 5′-monophosphate-activated protein kinase (AMPK). Inhibition of PGC-1α expression in cold-exposed rats by antisense oligonucleotide treatment diminished glucose clearance rates during a hyperinsulinemic clamp and reduced expression and membrane localization of GLUT4. Reduction of PGC-1α expression resulted in no modification of insulin-induced tyrosine phosphorylation of the IR and Ser473phosphorylation of Akt. Finally, reduction of PGC-1α resulted in lower Thr172phosphorylation of AMPK. Thus cold-induced hyperexpression of PGC-1α participates in control of skeletal muscle glucose uptake through a mechanism that controls GLUT4 expression and subcellular localization independent of the IR and Akt activities but dependent on AMPK.