OR04-06 G Protein GSα in Muscle Is Essential for Survival During Cold Adaptation in the Absence of Thermogenesis of Brown Adipose Tissue

Abstract

Adaptive thermogenesis is important for the control of body temperature (Tb) and maintenance of body weight, and it is primarily regulated by sympathetically-driven brown adipose tissue (BAT). Studies indicate that muscle is also involved in thermogenic regulation. Gsα couples to ligands and receptors, including β-adrenergic receptors, to increase intracellular cAMP. Our previous studies have showed that mice with adipose-specific Gsα deficiency had inactive BAT and impaired cold tolerance. To determine whether Gsα/cAMP signaling in skeletal muscle compensates for loss of BAT thermogenesis, we generated mice with Gsα deficiency in adipocyte tissue alone (AdipGsKO), in skeletal muscle alone (SkMGsKO) or in both (AdipSkMGsKO). Compared to control mice, AdipGsKO and SkMGsKO mice had normal body weight, while AdipSkMGsKO showed reduced body weight with normal food intake and energy expenditure. Both AdipGsKO and AdipSkMGsKO mice had elevated fasting glucose levels, but similar glucose tolerance to control or SkMGsKO mice. SkMGsKO mice displayed reduced insulin sensitivity. When acutely exposed to 6oC for 3 hours, AdipGsKO and AdipSkMGsKO mice rapidly decreased their Tb, indicating that they are sensitive to acute cold exposure, consistent with their inactive BAT. To assess adaptation to chronic cold, mice were exposed to gradually declining ambient temperature from 22oC to 6oC with a daily decrease of 2oC and were then kept at 6oC for 5 days. As expected, both AdipGsKO and AdipSkMGsKO mice failed to stimulate BAT UCP1 by cold adaptation. Unexpectedly, AdipGsKO mice maintained normal Tb similar to control and SkMGsKO mice. However, AdipSkMGsKO mice started to rapidly drop their Tb when ambient temperature declined to 14oC and 85% of SkMGsKO mice (11/13) died before the end of experiment. These results suggest that when there is a lack of BAT function, Gsα/cAMP signaling in muscle plays an essential role for mice to survive in response to chronic cold challenge.