ORIGINAL ARTICLE Variation in basal heat shock protein 70 is correlated to core temperature in human subjects Marie E. Sandstro ¨m Æ Leigh A. Madden Æ Lee Taylor Æ Jason C. Siegler Æ Ric J. Lovell Æ Adrian Midgley Æ Lars McNaughton Received: 31 May 2008 / Accepted: 30 June 2008 / Published online: 30 July 2008 Ó Springer-Verlag 2008 Abstract Heat shock proteins are highly conserved pro- teins and play an important chaperone role in aiding the folding of nascent proteins within cells. The heat shock protein response to various stressors, both in vitro and in vivo, is well characterised. However, basal levels of heat shock protein 70 (Hsp70) have not previously been inves- tigated. Monocyte-expressed Hsp70 was determined every 4 h, over a 24 h time period, in 17 healthy male subjects (177 ± 6.4 cm, 75.7 ± 10.9 kg, 19.8 ± 4.3 years) within a temperature and activity controlled environment. Core temperature was measured at 5-min intervals during the 24 h period. Hsp70 showed significant diurnal variation (F = 7.4; p \ 0.001), demonstrating peaks at 0900 and 2100 hours, and a nadir at 05.00. Core temperature fol- lowed a similar temporal trend (range = 35.96–38.10°C) and was significantly correlated with Hsp70 expression (r s = 0.44; p \ 0.001). These findings suggest a high responsiveness of Hsp70 expression in monocytes to slight variations in core temperature. Keywords Hsp70 Á Diurnal variation Á Core temperature Introduction During both normal and stress situations (for example exercise), cells are constantly in need of molecular chap- erones for their survival. Heat shock protein 70 (Hsp70) is known to be expressed in response to a wide variety of stressors (for review see (Kregel 2002), particularly heat (Locke and Noble 1995). A variety of cells and organs express Hsp70 upon heat shock (Leger et al. 2000; Lovell et al. 2006; Staib et al. 2007) as well as peripheral blood cells (Oehler et al. 2001). Hsp70 plays a role in preventing and degrading damaged proteins (Bukau and Horwich 1998), and is also important to the immune system where it acts as a danger signal (Horn et al. 2007) and a cytokine (Asea et al. 2000). It is therefore expected that the levels of Hsp70 will vary dependent on the homeostatic environ- ment within the body. Hsp70 also plays an important role in unstressed cells where, for example, it orchestrates de novo protein synthesis (Beckmann et al. 1990) and has the ability to rescue cells from programmed death by inter- rupting the apoptotic cascade (Garrido et al. 2001). This would further indicate that there is a constant basal level of Hsp70, albeit a low level. Several studies have shown the upregulation of Hsp70 in vitro by heat shock (Oehler et al. 2001; Sonna et al. 2002), however these studies exposed cells to relatively high temperatures (39–45°C) and do not, therefore, give an indication to the sensitivity of the up- regulation of Hsp70 induction that may occur under normal physiological conditions. Diurnal variations are well known in terms of whole body homeostasis. Circadian variations in leukocyte activation and endothelial function, for example, have been described (Bridges et al. 1991, 1992). Furthermore, a group of 10 healthy male volunteers were studied for 24 h in respect of soluble levels of adhesion molecules, intracellular adhesion M. E. Sandstro ¨m Á L. A. Madden Á L. Taylor Á J. C. Siegler Á R. J. Lovell Á A. Midgley Á L. McNaughton Department of Sport, Health and Exercise Science, University of Hull, Cottingham Road, Hull HU6 7RX, UK L. A. Madden (&) Post Graduate Medical Institute, University of Hull, Cottingham Road, Hull HU6 7RX, UK e-mail: l.a.madden@hull.ac.uk 123 Amino Acids (2009) 37:279–284 DOI 10.1007/s00726-008-0144-4