Hyperlipidemia induced by high cholesterol diet inhibits heat shock response in rat hearts

We examined whether heat shock response is affected by experimental hyperlipidemia in rat hearts. Therefore, isolated hearts of male Wistar rats fed a 2% cholesterol-enriched diet or standard diet for 12 weeks were subjected to either 20 min heat stress at 42 degrees C or global normothermic ischemia followed by 120 min normothermic, normoxic perfusion. Both heat stress and ischemia resulted in a significant increase in cardiac mRNA and protein levels of the inducible member of the 70-kDa heat shock protein family (HSP70) when compared to time-matched controls as assessed by Reverse Transcriptase polymerase chain reaction and Western blotting in hearts of normal rats. However, in hyperlipidemic groups, increase in cardiac HSP70 mRNA and HSP70 protein in response to heat stress and ischemia was markedly attenuated. We further observed that the basal level of HSP70 mRNA was significantly higher in the hyperlipidemic group when compared to normal controls; however, the HSP70 protein level was not different. This is the first demonstration that hyperlipidemia inhibits cardiac heat shock response. We further conclude that basal HSP70 expression might be downregulated at a posttranscriptional level in hyperlipidemia.