A 7-day cold water acclimation protocol may significantly improve cellular cold tolerance in young males through enhanced autophagic responses and reduced apoptotic signaling.
Researchers from the University of Ottawa found that daily exposure to cold water (14°C) for 60 minutes over a week-long period transitions cellular response from initial autophagic dysfunction and elevated apoptotic signaling to improved cytoprotective mechanisms.
"This work shows that 7-day cold acclimation elicits improvements in cellular cold tolerance in young males through enhanced autophagic responses concomitant with reductions in apoptotic signaling," noted researchers in their published study in Advanced Biology.
Ten men (23 ± 3 years) underwent daily 60-minute immersions in 14°C water for 7 consecutive days. The researchers isolated peripheral blood mononuclear cells (PBMCs) before and after cold exposures on days 1, 4, and 7 to analyze protein expression related to cellular protective mechanisms.
At the beginning of the acclimation (day 1), the men showed signs of autophagic dysfunction characterized by accumulation of p62 protein (2.48 ± 0.51 relative quantity). There was no significant change in LC3-II; elevated apoptotic markers (cleaved-caspase-3 at 2.62 ± 0.52 relative quantity); or increased inflammatory signaling (TNF-α at 1.47 ± 0.15 relative quantity).
By day 7, subjects demonstrated a marked shift in cellular responses. There was a significant increase in LC3-II (1.68 ± 0.21 relative quantity); decreased p62 (0.67 ± 0.10 relative quantity); normalized apoptotic signaling (cleaved-caspase-3 at 1.10 ± 0.18 relative quantity); and reduced inflammatory response (TNF-α at 0.97 ± 0.09 relative quantity).
The researchers also conducted ex vivo experiments exposing blood samples to various hypothermic temperatures (37, 35, 33, 31, and 4°C) before and after the 7-day acclimation, finding improved cold tolerance at the cellular level post-acclimation.
"Following acclimation, LC3-II increased during exposure to ex vivo temperatures at 35°C and below despite no main effect of temperature in LC3-II/LC3-I," the authors reported. "Further, p62 increased in response to ex vivo cooling prior to acclimation with no change in p62 post-acclimation."
While core temperature measurements didn't show significant differences between days 1 and 7, the researchers noted that the time it took for participants to reach a cutoff temperature (35.5°C) extended from 40 minutes on day 1 to 55 minutes by day 7.
This finding, paired with a smaller change in blood lactate following day 7 compared to day 1 (indicating a reduction in shivering thermogenesis), suggests the cold-water immersions produced an insulative pattern of cold acclimation.
"Although the present investigation demonstrates that a 7-day cold acclimation may enhance cold-induced autophagic cytoprotection, the exhibited enhancements in autophagic activity via acclimation suggest that cold exposure may be a viable approach to improve autophagic function utilizing non-pharmacological interventions, thereby leading to potential improvements in human health," the researchers concluded.
They declared having no competing interests.