Submitted on July 24, 2007
Accepted on October 27, 2007
Exercise-Heat Acclimation in Humans Alters Baseline Levels and Ex Vivo Heat inducibility of HSP72 and HSP90 in Peripheral Blood Mononuclear Cells
James P McClung1, Jeffrey D Hasday2, Ju-ren He3, Scott J. Montain4, Samuel N Cheuvront1, Michael N Sawka1, and Ishwar S Singh2*
1 U.S. Army Research Institute of Environmental Medicine, Natick, Massachusetts, United States
2 Pulmonary and Critical Care Medicine, University of Maryland School of Medicine, Baltimore, Maryland, United States; Research and Medical Services, Veterans Affairs Medical Center, Rm 3C117, Baltimore, Maryland, 21201, United States
3 Pulmonary and Critical Care Medicine, University of Maryland School of Medicine, Baltimore, Maryland, United States
4 Nutrition and Biochemistry Division, US Army Research Inst. Environmental Medicine, Natick, Massachusetts, United States
* To whom correspondence should be addressed. E-mail: isingh{at}umaryland.edu.
The induction of cellular acquired thermal tolerance (ATT) during heat acclimation (HA) in humans is not well described. This study determined whether exercise-HA modifies the human heat shock protein (HSP)-72 and 90 responses and whether changes are correlated with physiologic adaptations to HA. Using a 10-day HA protocol comprised of daily exercise in a hot environment (Ta= 49 °C, 20% RH), we analyzed baseline and ex vivo heat-induced expression of HSP72 and 90 in PBMCs isolated prior to exercise from subjects on day 1 and 10 of the HA protocol. Classical physiologic responses to HA were observed, including reduced heart rate and core body temperature, and increased sweating rate. Baseline levels of HSP72 and HSP90 were significantly increased following acclimation by 17.7% and 21.1%, respectively. Ex vivo induction of HSP72 in PBMCs exposed to heat shock (43 °C) was blunted on day 10 compared to day 1. A correlation was identified (r2 = 0.89) between changes in core temperature elevation and ex vivo HSP90 responses to heat shock between days 1 and 10. In summary, 1) exercise-HA resulted in increased baseline levels of HSP72 and HSP90; 2) ex vivo heat inducibility of HSP72 was blunted after HA; and 3) volunteers demonstrating the greatest physiological HA tended to exhibit the greatest blunting of ex vivo HSP induction in response to heat shock. These data demonstrate that physiologic adaptations in humans undergoing HA are accompanied by both increases in baseline levels and changes in regulation of cytoprotective HSPs.
