The effect of high-intensity exercise in temperate and hot ambient conditions on autophagy and the cellular stress response in young and older females

The process of autophagy is vital in maintaining normal cellular function, especially during exposure to elevated states of physiological stress associated with exercise and hot ambient temperatures. Although prior observations are primarily limited to responses in males, the autophagic response to acute physiological stress in females represents a considerable knowledge gap. Therefore, we assessed autophagy and related pathways of cellular stress in peripheral blood mononuclear cells (PBMCs) from 20 healthy young [<i>n</i> = 10, mean (SD): aged 23 yr (3)] and older [<i>n</i> = 10, aged 69 yr (3)] females in response to 30 min of semi-recumbent high-intensity cycling exercise (70% of predetermined maximal oxygen consumption) in temperate (25°C) and hot (40°C) ambient conditions (15% relative humidity). Mean body temperature (rectal and skin) was measured throughout, whereas cellular responses were evaluated before and after exercise, including up to 6 h of seated recovery. Proteins associated with autophagy and related pathways were assessed via Western blot. Mean body temperature was elevated after exercise in both conditions, with significant elevations observed after exercise in the heat (all, <i>P</i> ≤ 0.05). Although young females displayed signs of elevated autophagic activity [elevations in microtubule-associated light chain 3B (LC3)-II and beclin-2] in response to exercise performed in both temperate and hot ambient conditions (all, <i>P</i> ≤ 0.05), responses were attenuated in older females. This was accompanied by elevations in chaperone-mediated autophagy in young but not in older females in response to exercise independent of ambient temperature. Our findings indicate exercise, with and without ambient heat exposure may stimulate the autophagic response in young but not in older females.<b>NEW & NOTEWORTHY</b> We show for the first time that an acute bout (30 min) of high-intensity intensity exercise stimulates autophagy in young females irrespective of ambient heat exposure. However, older females did not display the same increase in autophagy as their younger counterparts when high-intensity exercise was performed in temperate or hot ambient conditions. Consequently, older females may be at an elevated risk of heat-induced cellular damage during exertional heat stress.