Protein kinase A-dependent translocation of Hsp90α impairs endothelial nitric-oxide synthase activity in high glucose and diabetes

Diabetes mellitus (DM) and high glucose (HG) are known to reduce the bioavailability of nitric oxide (NO) by modulating endothelial nitric-oxide synthase (eNOS) activity. eNOS is regulated by several mechanisms including its interaction with heat shock protein (Hsp) 90. We previously discovered that DM in vivo and HG in vitro induced the translocation of Hsp90 alpha to the outside of aortic endothelial cells. In this report we tested the hypothesis that translocation of Hsp90a is responsible for the decline in NO production observed in HG-treated cells. We found that HG increased phosphorylation of Hsp90 alpha in a cAMP-dependent protein kinase A-dependent manner, and that this event was required for translocation of Hsp90a in porcine aortic endothelial cells. Furthermore, preventing translocation of Hsp90a protected from the HG-induced decline in eNOS-Hsp90a complex and NO production. Notably, DM increased phosphorylation of Hsp90ce and reduced its association with eNOS in the aortic endothelium of diabetic rats. These studies suggest that translocation of Hsp90a is a novel mechanism by which HG and DM impair eNOS activity and thereby reduce NO production.