Incomplete Caspase Signaling During Hibernation In The Golden‐Mantled Ground Squirrel, Spermophilus lateralis
Authors: Treat Michael D. , van Breukelen Frank 
Published: June 2021

Hibernating golden‐mantled ground squirrels, Spermophilus lateralis, experience numerous conditions during the winter that are known to be pro‐apoptotic in other mammal systems (e.g. extreme hypothermia, ischemia and reperfusion, acidosis, increased reactive oxygen species, bone and muscle disuse, etc.). However, studies suggest that hibernators may invoke a protective phenotype to limit widespread cell damage and loss during the hibernation season. Could regulating apoptosis provide protection against the harmful conditions experienced during the hibernation season? To address this, we systematically examined the caspase cascade (caspases 1–12) for evidence of apoptotic signaling during hibernation. Caspases comprise a family of cysteine‐aspartate proteases that, upon proteolytic processing and activation, participate in a complex signaling cascade involved in apoptosis and inflammation. Using ground squirrel liver, we determined the availability and activation status of caspases with western blots, performed caspase‐specific proteolysis activity assays, and analyzed multiple caspase‐mediated cellular events for indications of caspase signaling during hibernation. Surprisingly, we found the canonical apoptotic executioner caspases 3 and 6 as well as inflammatory caspases 11 and 12 appeared activated during hibernation. Caspase activation typically has dramatic effects on proteolytic activity. For instance, in other systems, when caspase 3, the “key executioner of apoptosis,” is processed into the active 17 kDa (p17) fragment, caspase 3 proteolytic activity can increase up to ~10,000X vs. the procaspase form. Caspase 3 activation, therefore, is thought to commit a cell to apoptosis. We found caspase 3 p17 increased ~2X during hibernation which may indicate significant apoptotic commitment. Did these “winter‐activated” caspases display increased activity? We found no indications of dramatically increased caspase activity. To better understand the implications of caspase “activation” during hibernation, we used a systems‐level approach to analyze numerous events downstream of caspase activation. We looked for indications of caspase 6 activity (nuclear lamin A cleavage), caspase 3 activity (degradation of the inhibitor of caspase‐activated DNase (ICAD), inactivation of DNA repair enzyme poly (ADP‐ribose) polymerase (PARP), and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) activity), and inflammatory caspase activity (IL‐1b and IL‐18 activation and serum transaminase levels). We found no evidence of downstream caspase activity. Despite the pro‐apoptotic conditions of hibernation and the seeming caspase “activations”, there was no evidence of widespread apoptosis and inflammation during hibernation. Our data demonstrate the importance and utility of the systems‐level approach in studying complex cellular signaling pathways like apoptosis.

This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.