Electric Fan Use On Autophagy And Apoptosis In Older Adults During An Extreme Heat Simulation

We recently showed that older adults sustain greater increases in core temperature during daylong exposure to extreme heat (40 °C) compared to their younger counterparts. This was associated with signs of autophagic impairments paralleled with greater apoptotic signaling. Recent guidance has advocated the use of electric fans as a simple and sustainable cooling strategy to safeguard older adults during extreme heat. While we showed that fans have small negligible impacts on core temperature during daylong (8-h) heat exposure (36 °C), their cellular impact remains unknown. PURPOSE: To assess changes in cellular stress responses (autophagy and apoptosis) in older adults exposed to a daylong heatwave simulation with and without the use of a pedestal-mounted electric fan. METHODS: 18 participants (8 females, median age 72 [IQR, 67-76] years) were exposed to 3 heatwave simulations (8-h, 36 °C, 45% RH) with a fan generating air speeds of either 0 (no fan, control), 2, or 4 m/s directed at the front of the body. Participants were seated throughout exposure except for 4 x 10-min periods of simulated activities of daily living (stepping [~2.25 METs]). Core temperature (rectal, Trec) was measured continuously, while proteins associated with autophagy (LC3-II) and apoptosis (caspase-3) were measured before and after each exposure in peripheral blood mononuclear cells via Western blot. Proteins are expressed as relative quantity (RQ [SD]) from baseline and were assessed via one-way ANOVA with Bonferroni correction (α = 0.05). RESULTS: Elevations in Trec were not different between conditions (~1.3 °C, all p ≥ 0.50). Changes in LC3-II were not different with fan use at 2 (1.79 RQ [0.80]) or 4 m/s (1.54 RQ [0.70]) compared to control (1.56 RQ [0.52]; all, p ≥ 0.095). While caspase-3 did not differ between control (1.20 RQ [0.35]) and with a fan at 2 m/s (1.37 RQ [0.45], p > 0.999), fan use at 4 m/s elicited a significant increase in caspase-3 (1.86 RQ [1.15]) when compared to control (p = 0.030). CONCLUSIONS: While fan use did not elicit changes in Trec or autophagy compared to control, fan use at 4 m/s elicited significant elevations in apoptotic signaling. Therefore, fan use at high settings during heatwaves may incur greater cellular stress in older adults. Supported by: Canadian Institutes of Health Research and Health Canada