Autophagy And Apoptosis During Consecutive Moderate-intensity Workdays In The Heat In Young And Older Males

Older males have a reduced capacity to dissipate heat relative to their younger counterparts, which is exacerbated following consecutive days of work. However, we showed this does not translate to altered physiological strain or work tolerance with similar durations of continuous work performed safely (i.e., core temperature ≤ 38 °C). Contrarily, the cellular process of autophagy, which is critical in preventing heat-induced cellular damage, is impaired with aging. Whether age-related autophagic impairments contribute to greater heat-induced cellular vulnerability, that may be exacerbated over consecutive workdays in the heat, remain unknown. PURPOSE: Evaluate the effect of prolonged moderate-intensity work performed in the heat over consecutive days on cellular stress in young and older males. METHODS: Nine young (mean [SD]: 22 [2] years) and 9 older (62 [5] years) males performed 240 min of moderate-intensity treadmill walking (metabolic heat production of ~200 W/m2) in a wet bulb globe temperature of 26 °C. Work was continuous until rectal temperature reached 38 °C, at which point work-rest allocations of 3:1 (15-min rest and 45-min work) were implemented. This work bout was repeated in the afternoon (following a 1 h lunch break) and the next morning. Proteins associated with autophagy (LC3-II) and apoptosis (caspase-3) were assessed via Western blot from peripheral blood mononuclear cells before and after each work bout. Data are reported as relative quantity (RQ) from baseline and analyzed via a two-way ANOVA, with Bonferroni correction (α = 0.05). RESULTS: Autophagic activity (LC3-II) was elevated in young males following day-long work as evidenced by an increase in LC3-II (1.86 RQ [0.79], p < 0.001), which was significantly higher than the first work bout (1.19 RQ [0.55], p = 0.006) and the second-day work bout (1.32 RQ [0.28], p = 0.041). In older males, LC3-II was unchanged (all p ≥ 0.999). However, caspase-3 was significantly higher in response to heated exercise across groups (time main effect, p = 0.002). CONCLUSIONS: We showed elevated autophagy in young males on the initial workday, but not during successive workdays, nor in older males. When combined with excess apoptotic responses, precautions may be necessary when consecutive workdays are performed in hot conditions, particularly in older males. Supported by: Workplace Safety Insurance Board (Ontario)