Hsp72 and Hsp90α mRNA transcription is characterised by large, sustained changes in core temperature during heat acclimation

Abstract

Increased intracellular heat shock protein-72 (Hsp72) and heat shock protein-90α (Hsp90α) have been implicated as important components of acquired thermotolerance, providing cytoprotection during stress. This experiment determined the physiological responses characterising increases in Hsp72 and Hsp90α mRNA on the first and tenth day of 90-min heat acclimation (in 40.2 °C, 41.0 % relative humidity (RH)) or equivalent normothermic training (in 20 °C, 29 % RH). Pearson's product-moment correlation and stepwise multiple regression were performed to determine relationships between physiological [e.g. (T_rec, sweat rate (SR) and heart rate (HR)] and training variables (exercise duration, exercise intensity, work done), and the leukocyte Hsp72 and Hsp90α mRNA responses via reverse transcription quantitative polymerase chain reaction (RT-QPCR) (n = 15). Significant (p < 0.05) correlations existed between increased Hsp72 and Hsp90α mRNA (r = 0.879). Increased core temperature was the most important criteria for gene transcription with ΔT_rec (r = 0.714), SR (r = 0.709), T_recfinal45 (r = 0.682), area under the curve where T_rec ≥ 38.5 °C (AUC38.5 °C; r = 0.678), peak T_rec (r = 0.661), duration T_rec ≥ 38.5 °C (r = 0.650) and ΔHR (r = 0.511) each demonstrating a significant (p < 0.05) correlation with the increase in Hsp72 mRNA. The T_rec AUC38.5 °C (r = 0.729), ΔT_rec (r = 0.691), peak T_rec (r = 0.680), T_recfinal45 (r = 0.678), SR (r = 0.660), duration T_rec ≥ 38.5 °C (r = 0.629), the rate of change in T_rec (r = 0.600) and ΔHR (r = 0.531) were the strongest correlate with the increase in Hsp90α mRNA. Multiple regression improved the model for Hsp90α mRNA only, when T_rec AUC38.5 °C and SR were combined. Training variables showed insignificant (p > 0.05) weak (r < 0.300) relationships with Hsp72 and Hsp90α mRNA. Hsp72 and Hsp90α mRNA correlates were comparable on the first and tenth day. When transcription of the related Hsp72 and Hsp90α mRNA is important, protocols should rapidly induce large, prolonged changes in core temperature.

Keywords: Core temperature; Heat acclimation; Heat shock proteins; Hyperthermia; Thermotolerance.

Fig. 1

Schematic overview of the study

Fig. 2

Mean ± SD pre- to post-session fold change in Hsp72 mRNA (left) and Hsp90α mRNA (right) for the entire dataset (ALL), and on day1 and day10 of the intervention

Fig. 3

Relationship between the fold change in Hsp72 mRNA and the ΔT_rec (a), SR (b), mean T_recfinal45 (c) and the AUC38.5 °C (d). Figures describe data for the entire dataset (ALL, solid line), and on day1 (open circles, dotted line) and day10 (closed circles, dashed line) of the intervention

Fig. 4

Relationship between the fold change in Hsp90α mRNA and the AUC38.5 °C (a), peak T_rec (b), ΔT_rec (c) and the mean T_recfinal45 (d). Figures describe data for the entire dataset (ALL, solid line), and on day1 (open circles, dotted line) and day10 (closed circles, dashed line) of the intervention

Fig. 5

Mean ± SD relationship between the fold change in Hsp72 mRNA and Hsp90α mRNA entire dataset (ALL, solid line), and on day1 (open circles, dotted line) and day10 (closed circles, dashed line) of the intervention