Title

Cytoprotective immune responses to exercise, heat, and dehydration stresses in men

Date of Completion

January 2009

Keywords

Health Sciences, Recreation

Degree

Ph.D.

Abstract

In response to stress, hsp70 (heat shock protein 70) has been observed to increase acutely, and remain elevated with peak expression typically around 24 hours post-stress. Additionally, cells expressing inducible hsp72 are more resilient in the face of in vitro heat shock (42°C, 1+ hr), as measured by early apoptosis marker annexin V. NFAT5 (Nuclear Factor of Activated T cells) has been shown to have a similar protective effect in response to osmolal stimuli. CD40L is, like NFAT5 a less studied protective factor, that has been investigated as a response to exercise stress in the context of cardiovascular risk. This study completed three sets of experiments examining each of these three protective proteins in up to six health, college-aged males ((mean ± SD) age 23 ± 4 years; body mass 82.96 ± kg; height 175.33 ± 9.69; running VO2max 82.96 ± 2.88 mL·min−1·kg−1) who completed five experimental days each. Prior to experimental day, subjects began passive dehydration after noon until the next morning. On experimental day subjects submaximally exercised for two hours in the environmental chamber (35°C, 32% r.h.) to additionally dehydrate to a final value of −4–5% body mass. Subjects rested and rehydrated for 60 minutes and then completed an exercise challenge (25 minutes run at 70% VO2max, 800 m maximal sprint, 5 minutes maximal self-paced box-lifting) in the heat. This study found, according to predefined hypotheses, that intracellular hsp72, extracellular hsp70, and NFAT5 were elevated acutely with stress with acute decrease during rehydration. Values stayed elevated through 24 hours following experimental day. In response to one hour heat shock, PBMCs exhibited less annexin V expression with timepoints where hsp72 levels were concurrently higher when compared among PBMC samples collected at various timepoints. CD40L decreased acutely with stress and increased during recovery, as seen with sCD40L in other studies. ^ Conclusive inferences from this studies are that hsp72 protects cells in response to acute stress and recovery periods, NFAT5 does so in response to hydration status, and surface CD40L appears to decrease with acute stress and increase during recovery to baseline levels. ^