Downhill running and exercise in hot environments increase leukocyte Hsp72 (HSPA1A) and Hsp90α (HSPC1) gene transcripts

Abstract

Stressors within humans and other species activate Hsp72 and Hsp90α mRNA transcription, although it is unclear which environmental temperature or treadmill gradient induces the largest increase. To determine the optimal stressor for priming the Hsp system, physically active but not heat-acclimated participants (19.8 ± 1.9 and 20.9 ± 3.6 yr) exercised at lactate threshold in either temperate (20°C, 50% relative humidity; RH) or hot (30°C, 50% RH) environmental conditions. Within each condition, participants completed a flat running (temperate flat or hot flat) and a downhill running (temperate downhill or hot downhill) experimental trial in a randomized counterbalanced order separated by at least 7 days. Venous blood samples were taken immediately before (basal), immediately after exercise, and 3 and 24 h postexercise. RNA was extracted from leukocytes and RT-quantitative PCR conducted to determine Hsp72 and Hsp90α mRNA relative expression. Leukocyte Hsp72 mRNA was increased immediately after exercise following downhill running (1.9 ± 0.9-fold) compared with flat running (1.3 ± 0.4-fold; P = 0.001) and in hot (1.9 ± 0.6-fold) compared with temperate conditions (1.1 ± 0.5-fold; P = 0.003). Leukocyte Hsp90α mRNA increased immediately after exercise following downhill running (1.4 ± 0.8-fold) compared with flat running (0.9 ± 0.6-fold; P = 0.002) and in hot (1.6 ± 1.0-fold) compared with temperate conditions (0.9 ± 0.6-fold; P = 0.003). Downhill running and exercise in hot conditions induced the largest stimuli for leukocyte Hsp72 and Hsp90α mRNA increases.

The Hsp72 and Hsp90α mRNA Responses to Hot Downhill Running Are Reduced Following a Prior Bout of Hot Downhill Running, and Occur Concurrently within Leukocytes and the Vastus Lateralis

“…Previous work from our research group has demonstrated that the leukocyte Hsp72 and Hsp90α mRNA responses are larger following exercise in hot compared to temperate environments (Gibson et al, 2015c, 2016), and following downhill compared to flat running (Tuttle et al, 2015). It is known that downhill running is an effective whole body preconditioning strategy (Shima et al, 2008; Touchberry et al, 2012; Isanejad et al, 2015), consequently, an acute preconditioning trial featuring both stressors (hot environmental conditions and downhill running; hot downhill running) was selected in the current experimental design to maximize stimuli to initiate the HSR and subsequent cellular preconditioning.…”

“…It is known that downhill running is an effective whole body preconditioning strategy (Shima et al, 2008; Touchberry et al, 2012; Isanejad et al, 2015), consequently, an acute preconditioning trial featuring both stressors (hot environmental conditions and downhill running; hot downhill running) was selected in the current experimental design to maximize stimuli to initiate the HSR and subsequent cellular preconditioning. This was compared to a temperate flat trial (flat running in a temperate environment) where no change in leukocyte Hsp72 and Hsp90α mRNA has been previously observed (Tuttle et al, 2015) and thus no preconditioning effect was hypothesized to occur. A 7 d period between trials was selected to ensure any spontaneous preconditioning effect from exercise stress on core temperature (Barnett and Maughan, 1993) and leukocyte HSP72 (Fehrenbach et al, 2001; Lee et al, 2014), had returned to baseline following TPC1 TEMPFLAT .…”

“…Fold change in relative mRNA expression was calculated using the 2-ΔΔC T method (Schmittgen and Livak, 2008). β2-Microglobulin was used as a housekeeping gene as it was stable between experimental trials and across time in both the VL and leukocytes, as previously observed following exercise (Mahoney et al, 2004, 2008; Tuttle et al, 2015). The coefficient of variation for β2-M mRNA, Hsp72 mRNA, Hsp90α mRNA and Grp78 mRNA were 0.55, 0.34, and 0.28% respectively.…”

“…Leukocytes are a desirable tissue site for determining thermotolerance given the relative ease by which they can be collected, and because leukocytes, as circulating cells, are exposed to both systemic signals and to signals of the perfused tissues (Sonna et al, 2007). As such Hsp72 mRNA from leukocytes has been utilized as a surrogate to skeletal muscle samples with inferences made from changes in circulating intracellular sites across many exercise, heat, and nutritional experiments whereby the cellular stress response and thermotolerance are augmented (Fehrenbach et al, 2000a,b, 2001; Niess et al, 2002; Connolly et al, 2004; Marshall et al, 2007; Selkirk et al, 2009; Gibson et al, 2015a,c; Tuttle et al, 2015; Mee et al, 2016). Consequently, determining whether the HSR occurs concurrently within both tissues (leukocytes and the vastus lateralis; VL) following an acute stressor (initial experimental trial), and whether this response is attenuated in both tissues following a second trial (i.e., following preconditioning), requires elucidation to assess the viability of the leukocyte HSR to represent the skeletal muscle HSR.…”

“…In addition to Hsp72 mRNA, Hsp90α mRNA is of interest due to its important role within restoration of proteostasis (Kourtis and Tavernarakis, 2011; van Oosten-Hawle et al, 2013), regulation of the transmission of signaling cascades (Taipale et al, 2010), recovery of global protein synthesis (Duncan, 2005) and regulation of cellular repair (Erlejman et al, 2014). Additionally it is unknown if the physiological signals e.g., increases in systemic temperature (Gibson et al, 2016), which elicit increases in leukocyte Hsp72 and Hsp90α mRNA transcription to damaging (Tuttle et al, 2015), and non-damaging exercise-heat stress (Gibson et al, 2015c), are as relevant in skeletal muscle. The current study also sought to investigate the gene transcript response of another HSP, glucose regulated protein 78 mRNA (Grp78 mRNA) given its ability to indicate when the unfolded protein response ends (Ron and Walter, 2007).…”