Regulation of AKT in Richardson’s ground squirrels during hibernation

Abstract

Hibernation is a winter survival strategy for many small mammals metabolic rate falls by >95%, core body temperature can approach 0°C, and all physiological functions are suppressed. Energy savings of ~90% are achieved compared with the costs of remaining euthermic (37°C) over the winter. The protein kinase Akt (or PKB) plays a central role in coordinating growth and survival responses in cells and we hypothesized that regulation of Akt would be critical in hibernation. Kinetic properties of muscle Akt were compared in euthermic vs hibernating states; total and phosphorylated Akt protein was also quantified by Western blotting. Total Akt protein did not change in hibernation but phospho-Akt (the active form) and measured Akt activity decreased significantly by 40% and 60%, respectively, compared with euthermic controls. S0.5 values for Akt peptide fell by 28% during hibernation whereas S0.5 ATP increased by 330%. Low temperature assay (10°C) strongly affected S0.5 ATP of euthermic Akt (a 350% increase). Akt activation energy (Ea) and sensitivity to denaturation by urea did not change between euthermia and hibernation. DEAE Sephadex chromatography showed three peaks (isozymes) of Akt in euthermic muscle but only two peaks during hibernation. The results document differential regulation of Akt during hibernation and suggest a key role for Akt in cell survival during torpor. Funded by NSERC Canada.