Abstract
The leukocyte heat shock response (HSR) is used to determine individual's thermotolerance. The HSR and thermotolerance are enhanced following interventions such as preconditioning and/or acclimation/acclimatization. However, it is unclear whether the leukocyte HSR is an appropriate surrogate for the HSR in other tissues implicated within the pathophysiology of exertional heat illnesses (e.g., skeletal muscle), and whether an acute preconditioning strategy (e.g., downhill running) can improve subsequent thermotolerance. Physically active, non-heat acclimated participants were split into two groups to investigate the benefits of hot downhill running as preconditioning strategy. A hot preconditioning group (HPC; n = 6) completed two trials (HPC1HOTDOWN and HPC2HOTDOWN) of 30 min running at lactate threshold (LT) on −10% gradient in 30°C and 50% relative humidity (RH) separated by 7 d. A temperate preconditioning group (TPC; n = 5) completed 30 min running at LT on a −1% gradient in 20°C and 50% (TPC1TEMPFLAT) and 7 d later completed 30 min running at LT on −10% gradient in 30°C and 50% RH (TPC2HOTDOWN). Venous blood samples and muscle biopsies (vastus lateralis; VL) were obtained before, immediately after, 3, 24, and 48 h after each trial. Leukocyte and VL Hsp72, Hsp90α, and Grp78 mRNA relative expression was determined via RT-QPCR. Attenuated leukocyte and VL Hsp72 (2.8 to 1.8 fold and 5.9 to 2.4 fold; p < 0.05) and Hsp90α mRNA (2.9 to 2.4 fold and 5.2 to 2.4 fold; p < 0.05) responses accompanied reductions (p < 0.05) in physiological strain [exercising rectal temperature (−0.3°C) and perceived muscle soreness (~ −14%)] during HPC2HOTDOWN compared to HPC1HOTDOWN (i.e., a preconditioning effect). Both VL and leukocyte Hsp72 and Hsp90α mRNA increased (p < 0.05) simultaneously following downhill runs and demonstrated a strong relationship (p < 0.01) of similar magnitudes with one another. Hot downhill running is an effective preconditioning strategy which ameliorates physiological strain, soreness and Hsp72 and Hsp90α mRNA responses to a subsequent bout. Leukocyte and VL analyses are appropriate tissues to infer the extent to which the HSR has been augmented.
Highlights
Preconditioning of an individual using environmental stressors, with the intent of ameliorating physiological and cellular stress in extreme conditions has applications for athletic, military and occupational populations (Taylor et al, 2012; Lee et al, 2014)
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 Abbreviations: CT, cycling threshold; delayed onset muscle soreness (DOMS), Delayed onset muscle soreness; Grp78, Glucose regulated protein 78; HOT, Hot testing conditions; hot preconditioning group (HPC), Hot preconditioning group; Hsp, Heat shock protein; heat shock factor-1 (HSF-1), Heat Shock factor-1; heat shock response (HSR), Heat shock response; lactate threshold (LT), Lactate threshold; mRNA, Messenger RNA; phosphate-buffered saline (PBS), Phosphate-buffered saline; QT, Quadriceps tenderness; relative humidity (RH), Relative humidity; RNA, Ribonucleic acid; rate of perceived exertion (RPE), Rating of perceived exertion; Reverse Transcription Quantitative Polymerase Chain Reaction (RT-QPCR), Reverse transcription quantitative polymerase chain reaction; TEMP, Temperate testing conditions; temperate preconditioning group (TPC), Temperate preconditioning group; thermal sensation (TS), Thermal sensation; urine osmolality (UOsm), Urine Osmolality; VL, Vastus lateralis; V O2, Oxygen uptake; V O2max, Maximal oxygen uptake
The current study suggests that the leukocyte Hsp72 and Hsp90α mRNA responses could potentially be used as a surrogate measure of the HSR within skeletal muscle, at least within the current experimental model
Summary
Preconditioning of an individual using environmental stressors, with the intent of ameliorating physiological and cellular stress in extreme conditions has applications for athletic, military and occupational populations (Taylor et al, 2012; Lee et al, 2014). The leukocyte HSR, principally heat shock protein 72 (HSP72; protein and mRNA) is used to indicate the extent of cellular heat acclimation (Amorim et al, 2015), and identify individuals at risk of exertional heat illnesses within athletic, military and occupational settings (Moran et al, 2006; Marshall et al, 2007; Ruell et al, 2007) This is primarily due to the role of Hsp mRNA and HSP72 as markers of the cellular stress response and thermotolerance [attenuated cellular stress response suggests a greater likelihood of cellular survival (Kampinga et al, 1995; Theodorakis et al, 1999)] in response to isolated, combined, and cross-environmental stressors (Gibson et al, 2017). As such Hsp mRNA from leukocytes has been utilized as a surrogate to Abbreviations: CT, cycling threshold; DOMS, Delayed onset muscle soreness; Grp, Glucose regulated protein 78; HOT, Hot testing conditions; HPC, Hot preconditioning group; Hsp, Heat shock protein (number indicates molecular weight); HSF-1, Heat Shock factor-1; HSR, Heat shock response; LT, Lactate threshold; mRNA, Messenger RNA; PBS, Phosphate-buffered saline; QT, Quadriceps tenderness; RH, Relative humidity; RNA, Ribonucleic acid; RPE, Rating of perceived exertion; RT-QPCR, Reverse transcription quantitative polymerase chain reaction; TEMP, Temperate testing conditions; TPC, Temperate preconditioning group; TS, Thermal sensation; UOsm, Urine Osmolality; VL, Vastus lateralis; V O2, Oxygen uptake; V O2max, Maximal oxygen uptake
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