Changes in the mitochondrial phosphoproteome during mammalian hibernation

Mammalian hibernation involves periods of substantial suppression of metabolic rate (torpor) allowing energy conservation during winter. In thirteen-lined ground squirrels (Ictidomys tridecemlineatus), suppression of liver mitochondrial respiration during entrance into torpor occurs rapidly (within 2 h) before core body temperature falls below 30°C, whereas reversal of this suppression occurs slowly during arousal from torpor. We hypothesized that this pattern of rapid suppression in entrance and slow reversal during arousal was related to changes in the phosphorylation state of mitochondrial enzymes during torpor catalyzed by temperature-dependent kinases and phosphatases. We compared mitochondrial protein phosphorylation among hibernation metabolic states using immunoblot analyses and assessed how phosphorylation related to mitochondrial respiration rates. No proteins showed torpor-specific changes in phosphorylation, nor did phosphorylation state correlate with mitochondrial respiration. However, sever...