Stable suppression of skeletal muscle fructose-1,6-bisphosphatase during ground squirrel hibernation: Potential implications of reversible acetylation as a regulatory mechanism

Abstract

Mammalian hibernation is a period that involves substantial metabolic change in order to promote survival in harsh conditions, with animals typically relying on non-carbohydrate fuel stores during long bouts of torpor. However, the use and maintenance of carbohydrate fuel stores remains important during periods of arousal from torpor as well as when exiting hibernation. Gluconeogenesis plays a key role in maintaining glucose stores; however, little is known about this process within the muscles of hibernating mammals. Here, we used 13-lined ground squirrels (Ictidomys tridecemlineatus) as our model for mammalian hibernation, and showed that skeletal muscle fructose-1,6-bisphosphatase (FBPase; EC 3.1.3.11), the rate-limiting enzyme for the gluconeogenic pathway, was suppressed during torpor as compared to the euthermic control. A physical assessment of partially purified FBPase via exposure to increasing concentrations of the denaturant urea indicated that FBPase from the two conditions were structurally distinct. Western blot analysis suggests that the kinetic and physical differences between euthermic and torpid FBPase may be derived from differential acetylation, whereby increased acetylation of the torpid enzyme makes FBPase more rigid and less active. This study increases our understanding of skeletal muscle carbohydrate metabolism during mammalian hibernation and sets forth a potentially novel mechanism for the regulation of FBPase during environmental stress.

Keywords: Gluconeogenesis; Glucose metabolism; Mammalian hibernation; Muscle metabolism; Posttranslational acetylation; Torpor.