Depressing Ubiquitin-Dependent Proteolysis in a Hibernator Whose Body Temperature Is Normally Variable: The Common Tenrec

In a canonical mammalian hibernator like a ground squirrel, the cold body temperatures (T b ) of the torpid squirrel depresses protein degradation at the level of the 26S proteasome. Ubiquitylation per se is less temperature sensitive as ubiquitylation rates of colder temperatures continue at 30% to 60% of the maximal rates of warmer temperatures. This leads to an accumulation of ubiquitin-conjugated proteins of 2-3 fold in torpid squirrels as compared to active squirrels. The common tenrec is a bizarre Afrotherian placental mammal with many plesiomorphic traits such as a cloaca, internal testes, indeterminate growth, and the smallest brain of all extant mammals with very little neocortex. Interestingly, these tenrecs may be fully active with a T b of 12°C or hibernating at a T b of 28°C. Moreover, oxygen consumption rates may vary 25 fold in active tenrecs. We found expected decreases of 26S proteolytic activity at low temperatures. Capacitance for proteolysis varied by state and there was no evidence that torpor per se would arrest protein degradation. Indeed, in sharp contrast to the squirrel, ubiquitylation rates were essentially unaffected by temperature and ranged at colder temperatures from 80% to 90% of the maximal ubiquitylation rates. In other words, the only in vitro evidence for the control of ubiquitin-dependent proteolysis that we found would only be available to very cold tenrecs independent of if they were active or torpid. However, ubiquitin-conjugate concentrations appear low but unaffected by state. All in all, we hypothesize a ‘Life in the Slow Lane’ model for tenrecs wherein an inability to effectively regulate proteolysis led to a modest rate of degradation that is not as affected by changes incurred by torpor state or changes in T b . NSF and Department of Education (GAANN). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.