Characterizing Autophagic And Apoptotic Responses To Cold Stress In Healthy, Young And Older Men

Cold stress can compromise cellular function by modifying autophagic activity, which disrupts cellular homeostasis and promotes apoptosis (cell death). This response may be exacerbated in older adults due to an age-related reduction in autophagy, leading to greater vulnerability for cold-related injuries, depending on the level of cold stress. PURPOSE: In this study, we evaluated the effect of different levels of cold stress induced by cold water immersion on autophagic activity and apoptosis in young and older men. METHODS: On separate days, young (n = 9, mean [SD]: 23 [4] years) and older (n = 6, 62 [3] years) healthy, habitually active men were immersed in cold water regulated to induce a mild or severe cold stress by a sustained decrease in core (esophageal) temperature (Tco) of 0.5 and 1.0 °C below baseline resting levels for 30 min, respectively. Participants were rewarmed with warm (39 °C) water to baseline Tco and transferred to a thermoneutral room (23 °C) for a 3-h recovery. Blood samples were collected during baseline, end-cold exposure, and end-recovery to isolate peripheral blood mononuclear cells. Proteins associated with autophagy (LC3-II) and apoptosis (cleaved-caspase-3) were assessed via Western blot, normalized to β-actin, and reported as relative quantity (RQ) from baseline. Data were compared using a two-way ANOVA with Fisher’s LSD post-hoc (α = 0.05). RESULTS: Following mild cold exposure and recovery, LC3-II increased in young men (1.51RQ [0.54] and 1.69RQ [0.68], respectively; both p ≤ 0.028), but not in older men (1.07RQ [0.27] and 1.19RQ [0.70], respectively; both p ≥ 0.534). Following the severe cold exposure, however, caspase-3 increased in both the young (1.57RQ [0.45]; p = 0.033) and older (2.52RQ [1.84]; p = 0.025) men, albeit with no change in LC3-II. Further, LC3-II was higher during the mild cold exposure in young compared to older men (p = 0.027) and caspase-3 was greater during the severe cold exposure in older compared to young men (p = 0.044). CONCLUSION: We demonstrated that mild cold stress stimulates autophagic cytoprotection in young, but not older men. Conversely, severe cold exposure blunts autophagic activity, with greater apoptotic signaling in older compared to young men. FUNDING: National Sciences and Engineering Research Council