Exercise Induces Skeletal Muscle Heat Shock Protein Expression Independent of Dietary Macronutrient Content

Abstract

Diet‐induced obesity is directly associated with the development of hyperglycemia and stress kinase activation in target tissues, leading to impaired glucose tolerance and insulin resistance (IR) in skeletal muscle. Heat shock protein (HSP) induction is shown to attenuate the development of hyperglycemia and IR by precluding the activation of stress kinases. While HSP‐mediated improvements in metabolic function are observed with acute heat treatment, little is known about the effects of other known inducers of HSPs in skeletal muscle such as exercise and dietary modification. Therefore, the objective of this study was to compare the effects of dietary modification and chronic exercise on skeletal muscle HSP expression and fasting blood glucose levels (GLUC) in rats. Male Long‐Evans rats (N=27), were randomly assigned into Western diet (WD, 40% FAT/43% CHO/17% PRO) or vegan style Daniel Fast diet (DF, 25% FAT/60% CHO/15% PRO) groups. Rats were further divided into exercise (+EX) (25m·min−1 for 35 min·day−1, 3X/week) and sedentary groups. All rats were fed ad libitum for a 12 week intervention period. Soleus and gastrocnemius tissues were harvested and analyzed via western immunoblotting and densitometry for HSP70, pHSP27, HSP27, and HSP60 content. GLUC was measured using a standard enzymatic colorimetric assay. A two‐way ANOVA, with Tukey's post hoc test, was used to examine the differences in HSP expression between the diet and exercise groups for each tissue. A Pearson product‐moment correlation was used to determine if there was an association between HSP expression and GLUC. After 12 weeks of chronic exercise and dietary modification, gastrocnemius samples from the WD+EX and DF+EX groups had significant (P < 0.05) increases in HSP70 expression (+194% and +196% respectively) in comparison to sedentary controls. Non‐significant changes in HSP70 expression were also seen in the soleus of WD+EX (+140%) and DF+EX (+185%) groups. There was no change in pHSP27, HSP27, and HSP60 due to exercise for both gastrocnemius and soleus tissues. Additionally, no change in HSP expression (HSP70, pHSP27, HSP27, and HSP60) was observed when comparing diets (WD:DF, WD+EX:DF+EX) for either tissue. GLUC values in the WD (183.47 mg/dL ± 18.27), WD+EX (158.34 mg/dL ± 24.39), and DF (129.34 mg/dL ± 22.86) groups were indicative of rats being hyperglycemic, while values in the DF+EX (112.95 mg/dL ± 7.19) group were within the normal physiologic range. Unlike previous reports, no correlation was observed between HSP expression and the degree of hyperglycemia (HSP70:GLUC, r = −.139). In conclusion, our data suggests that chronic exercise induces a uniform increase in HSP70 expression in rats fed either a Western diet or vegan style Daniel Fast diet. As such, exercise may be an effective means to obtain the therapeutic effects of HSP expression in hyperglycemic rats regardless of dietary macronutrient content.