Oliver R. Gibson & Alex Dennis & Tony Parfitt & Lee Taylor & Peter W. Watt & Neil S. Maxwell
Received: 26 April 2013 /Revised: 20 September 2013 /Accepted: 20 September 2013 Cell Stress Society International 2013
Extracellular heat shock protein 72 (eHsp72) concentration increases during exercise-heat stress when conditions elicit physiological strain. Differences in severity of environmental and exercise stimuli have elicited varied response to stress. The present study aimed to quantify the extent of increased eHsp72 with increased exogenous heat stress, and determine related endogenous markers of strain in an exercise-heat model. Ten males cycled for 90 min at 50 % VO2peak in three conditions (TEMP, 20 °C/63 % RH; HOT, 30.2 °C/51%RH; VHOT, 40.0 °C/37%RH). Plasma was analyzed for eHsp72 pre, immediately post and 24-h post each trial utilizing a commercially available ELISA. Increased eHsp72 concentration was observed post VHOT trial (+172.4 %) (p <0.05), but not TEMP (−1.9 %) or HOT (+25.7 %) conditions. eHsp72 returned to baseline values within 24 h in all conditions. Changes were observed in rectal temperature (Trec), rate of Trec increase, area under the curve for Trec of 38.5 and 39.0 °C, duration Trec≥38.5 and ≥39.0 °C, and change in muscle temperature, between VHOT, and TEMP and HOT, but not between TEMP and HOT. Each condition also elicited significantly increasing physiological strain, described by sweat rate, heart rate, physiological strain index, rating of perceived exertion and thermal sensation. Stepwise multiple regression reported rate of Trec increase and change in Trec to be predictors of increased eHsp72 concentration. Data suggests eHsp72 concentration increases once systemic temperature and sympathetic activity exceeds a minimum endogenous criteria elicited during VHOT conditions and is likely to be modulated by large, rapid changes in core temperature.
The human 72 kDa heat shock protein (Hsp72), HSPA1A (Kampinga et al. 2009) is the highly inducible isoform of a large family of proteins with an important role as a molecular chaperone maintaining cellular homeostasis, particularly in response to thermal stimuli (Mizzen and Welch 1988). Research has identified extracellular changes in Hsp72 concentration within whole blood (Marshall et al. 2006; Yamada et al. 2007; Ogura et al. 2008; Magalhães et al. 2010; Périard et al. 2012), and intracellular changes in total protein expression and/or gene transcription in monocytes and systemic tissue (McClung et al. 2008; Selkirk et al. 2009; Magalhães et al. 2010; Amorim et al. 2011) in response to thermal and exercise stress. Hsp72 binds with high affinity to the plasma membrane (Asea et al. 2000) and up-regulates expression of pro-inflammatory cytokines, tumour necrosis factor-α, interleukin-1β and interleukin-6 in human monocytes. Circulating extracellular heat shock protein 72 (eHsp72) acts as an inflammatory molecule and induces cytokine production in immune cells (Asea 2006). The precise biological role of eHsp72 in response to exercise-heat stress has not been fully elucidated; it is believed to contribute to the exercise-related inflammatory reaction (Asea 2003). Acknowledgements have been made by Ogura et al. (2008) that body temperature elevation, and increased circulating catecholamines by supplementation (Whitham et al. 2006) or exercise response (Whitham et al. 2007), in addition to thermal change increase eHsp72. Acute exercise-heat stress presents both thermal and sympathetic challenge and as such, changes in concentration might be used to describe the magnitude of stress presented to an individual or system exercising in different environments.