Ad Libitum Western Diet Feeding Does Not Alter Basal Skeletal Muscle Heat Shock Protein Expression in Sedentary or Aerobically Trained Young Rats

Poor dietary habits can lead to obesity and insulin resistance—both of which can impair basal heat shock protein (HSP) expression and the HSP stress response in skeletal muscle. It remains unclear if impairments in HSP expression occur during the early stages of diet-induced obesity and metabolic dysfunction. We determined if basal HSP expression (HSP70, HSP60, HSP25) was impaired in sedentary or exercised rats following the onset of diet-induced obesity. Male Long-Evans rats (N=6-7/group) were assigned to a Western diet (WD) or purified diet (PD). Animals were divided into sedentary (WD and PD) or exercise-trained (WD+Ex and PD+Ex) groups and fed ad libitum for 12-weeks. WD animals displayed higher body mass, fat mass, blood glucose, and HOMA-IR scores compared to PD (p<0.05). Exercise attenuated elevations in HOMA-IR and body mass for WD+Ex (p>0.05) but did not prevent elevations in fat mass or blood glucose when compared to controls. Basal HSP (HSP70, HSP60, HSP25) expression was not impaired in sedentary WD animals when compared to PD (p>0.05) or when WD+Ex was compared to PD+Ex (p>0.05). Exercise training elevated HSP70 expression in the gastrocnemius muscle (GAST) (p<0.05), but not in the soleus (SOL) (p>0.05) in WD+Ex and PD+Ex animals. HSP60 and pHSP25 were unaffected by exercise training (GAST and SOL, p>0.05). The onset of diet-induced obesity does not impair skeletal muscle HSP expression in sedentary or exercised animals. Thus, obesity and symptomology of metabolic dysfunction may occur before reductions in skeletal muscle HSP expression.