Isothermic and fixed-intensity heat acclimation methods elicit equal increases in Hsp72 mRNA

Area of Science:

• Exercise Physiology
• Molecular Biology
• Thermoregulation

Background:

• Thermotolerance is crucial for protection against thermal stress, with heat shock protein-72 (Hsp72) playing a key role.
• Heat acclimation (HA) is known to induce thermotolerance, but optimal methods for maximizing the heat shock response (HSR) remain unclear.
• Understanding the HSR is vital for developing effective HA strategies to enhance cellular adaptation.

Purpose of the Study:

• To investigate and compare the effectiveness of different heat acclimation (HA) protocols in eliciting a sustained heat shock response (HSR).
• To determine if fixed-intensity, continuous isothermic, or progressive isothermic HA methods yield superior increases in Hsp72 mRNA expression.
• To identify optimal HA strategies for maximizing cellular adaptation and thermotolerance.

Main Methods:

• Twenty-four males participated in short-term HA (STHA) and long-term HA (LTHA) using three distinct protocols: fixed-intensity (FIXED), continuous isothermic (ISOCONT), and progressive isothermic (ISOPROG).
• Leukocyte Hsp72 mRNA levels were quantified using reverse transcription quantitative polymerase chain reaction (RT-qPCR) before and after specific time points (Day 1, 5, 10) during HA.
• The HSR was assessed by measuring changes in Hsp72 mRNA expression across different HA methods and durations.

Main Results:

• All tested HA methods (FIXED, ISOCONT, ISOPROG) resulted in significant increases in Hsp72 mRNA expression from pre- to post-HA at Day 1, Day 5, and Day 10 (P < 0.05).
• No statistically significant differences in Hsp72 mRNA increases were observed between the different HA protocols (P > 0.05).
• The consistent elevation of Hsp72 mRNA suggests that Hsp72 transcription is triggered upon reaching specific endogenous physiological thresholds during HA.

Conclusions:

• All investigated heat acclimation methods, including fixed-intensity, continuous isothermic, and progressive isothermic protocols, effectively increase Hsp72 mRNA.
• The findings suggest that various HA approaches can elicit cellular adaptations contributing to thermotolerance.
• The study indicates that the attainment of sufficient endogenous physiological criteria, rather than the specific HA protocol, may be the primary driver for Hsp72 mRNA transcription.