The Autophagic Response To 7-day Cold-water Acclimation In Young Adults

Cold exposure can elicit profound challenges to both physiological responses (i.e., shivering, hemodynamics) and cellular function. Repeated exposures to the cold via acclimation can enhance thermoregulatory mechanisms. However, the associated impact of acclimation on cellular cold tolerance remains poorly understood. PURPOSE: To evaluate the effect of 7-day cold-water acclimation on the cytoprotective mechanism of autophagy during in vivo cold-water immersion at the beginning and end of acclimation. Further, we assessed the effect of acclimation on cellular cold tolerance employing ex vivo cooling to a range of hypothermic conditions prior to and following the acclimation. METHODS: Ten healthy, habitually active young males (23 ± 3 years) underwent a 7-day cold-water acclimation using 14 °C water for 60 min per day. Peripheral blood mononuclear cells were isolated before and after cold exposure on the first and last day of acclimation. Additional blood samples were collected during baseline of day 1 and 24 h following day 7 of the acclimation for 90 min of ex vivo cold exposure in water baths set to 37, 35, 33, 31, or 4 °C. Proteins associated with autophagy, apoptosis, and the heat shock response were analyzed via Western blot and reported as relative quantity (RQ) to the respective baseline of the day. RESULTS: Autophagic dysfunction was prevalent at the beginning of in vivo cold acclimation as indicated by unchanged LC3-II (mean ± SEM: 0.74 ± 0.13 RQ; p = 0.156), p62 accumulation (2.48 ± 0.51 RQ; p = 0.017), and elevated apoptotic caspase-3 (2.62 ± 0.52 RQ; p = 0.013). Following acclimation, LC3-II increased (1.68 ± 0.21 RQ; p < 0.001) while p62 (0.67 ± 0.10 RQ; p = 0.038) and caspase-3 (1.10 ± 0.18 RQ; p = 0.017) decreased. Further, LC3-II increased (main effect: p = 0.003) and caspase-3 (main effect: p = 0.001) decreased following acclimation during ex vivo hypothermic exposure. While the heat shock response (via HSP70 & HSP90) did not change with in vivo cold exposure (both p ≥ 0.315), HSP90 increased (1.55 ± 0.11 RQ; p = 0.005) following acclimation when exposed to ex vivo temperatures below 33 °C. CONCLUSION: We showed that repeated exposures to cold-water over a 7-day period improves cellular tolerance to the cold in young males by elevating autophagic and heat shock responses while simultaneously reducing apoptotic signaling. National Sciences and Engineering Research Council of Canada and Mitacs