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Am J Physiol Heart Circ Physiol (July 22, 2004). doi:10.1152/ajpheart.00280.2004
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Submitted on March 22, 2004
Accepted on July 15, 2004

Insulin Resistance Does Not Diminish eNOS Expression, Phosphorylation or Binding to hsp90

David Fulton1*, M. Brennan Harris1, Bruce E Kemp2, Richard C Venema1, Mario B Marrero1, and David W Stepp1

1 Vascular Biology Center and Pharmacology and Physiology, Medical College of Georgia, Augusta, Georgia, USA
2 St. Vincent's Institute of Medical Research, Fitzroy, Victoria, Australia

* To whom correspondence should be addressed. E-mail: dfulton{at}mcg.edu.

Previously, using an animal model of Syndrome X, the Obese Zucker Rat (OZR), we have documented impaired endothelium-dependent vasodilation. The aim of this study was to determine whether reduced expression or altered post-translational regulation of eNOS underlies the vascular dysfunction in OZR rats. The relative abundance of eNOS was not significantly different in the hearts, aortae or skeletal muscle of lean zucker rats (LZR) versus OZR regardless of age. eNOS mRNA levels, as determined by real time PCR, were not different between LZR and OZR. The inability of insulin-resistance to modulate eNOS expression was also documented in 2 additional in vivo models, the ob/ob mouse and the fructose fed rat and in vitro via adenoviral expression of PTP-1B in endothelial cells. We next investigated whether changes in the acute, post-translational regulation of eNOS occurs with insulin resistance. The phosphorylation of eNOS at S632 (S633hum) and T494 were not different between LZR and OZR, however the phosphorylation of S1176 was significantly enhanced in the OZR rat. The phosphorylation of S1176 was not different in the ob/ob mouse or in fructose fed rats. The association of hsp90 with eNOS, a key regulatory step controlling both NO and aberrant superoxide production, was not different between OZR versus LZR. Taken together, these results suggest that changes in eNOS expression or post-translation regulation do not underlie the vascular dysfunction seen with insulin resistance and that other mechanisms such as altered localization, reduced availability of cofactors, substrates or the elevated production of superoxide may be responsible.




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