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Cardiovascular Research Advance Access first published online on April 14, 2008
This version [Accepted Manuscript] published online on April 16, 2008
Cardiovascular Research, doi:10.1093/cvr/cvn095
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Published on behalf of the European Society of Cardiology. All rights reserved. © The Author 2008. For permissions please email: journals.permissions@oxfordjournals.org

Role of iNOS in Induction of RhoA Expression in Hearts from Diabetic Rats

Hesham Soliman, Graham P. Craig, Prabhakara Reddy Nagareddy, Violet G. Yuen, Guorong Lin, Ujendra Kumar, John H. McNeill and Kathleen M. MacLeod*

Division of Pharmacology and Toxicology Faculty of Pharmaceutical Sciences University of British Columbia, Vancouver BC Canada

Corresponding author:K.M. MacLeod Faculty of Pharmaceutical Sciences University of British Columbia 2146 East Mall, Vancouver, BC V6T 1Z3 Canada. e-mail: kmm{at}interchange.ubc.ca Tel: 604-822-0219Fax: 604:822-3035

Aim: Recent studies from our laboratory demonstrated that increased expression of the small GTP-binding protein RhoA and activation of the RhoA/rho kinase (ROCK) pathway plays an important role in the contractile dysfunction associated with diabetic cardiomyopathy in hearts from streptozotocin (STZ)-induced diabetic rats. Nitric oxide (NO) has been reported to be a positive regulator of RhoA expression in vascular smooth muscle, and we have previously found that the expression of inducible nitric oxide synthase (iNOS) is increased in hearts from STZ-diabetic rats. Therefore, in this study we investigated the hypothesis that induction of iNOS positively regulates RhoA expression in diabetic rat hearts.

Methods: To determine whether NO and iNOS could increase RhoA expression in the heart, cardiomyocytes from non-diabetic rats were cultured in the presence of the NO donor sodium nitroprusside (SNP) or lipopolysaccharide (LPS) in the absence and presence of the selective iNOS inhibitor, N6-(1-Iminoethyl)-L-lysine dihydrochloride (L-NIL). In a second study, 1 week after induction of diabetes with STZ, rats were treated with L-NIL (3 mg/kg/day) for 8 more weeks to determine the effect of iNOS inhibition in vivo on RhoA expression and cardiac contractile function.

Results: Expression of iNOS was elevated in cardiomyocytes isolated from diabetic rat hearts. Both SNP and LPS increased RhoA expression in non-diabetic cardiomyocytes. The LPS-induced elevation in RhoA expression was accompanied by an increase in iNOS expression and prevented by L-NIL. Treatment of diabetic rats with L-NIL led to a significant improvement in left ventricular developed pressure and rates of contraction and relaxation concomitant with normalization of total cardiac nitrite levels, RhoA expression and phosphorylation of the ROCK targets LIM (Lin-11, Isl-1, Mec-3) kinase and ezrin/radixin/moesin.

Conclusions: These data suggest that iNOS is involved in the increased expression of RhoA in diabetic hearts and that one of the mechanisms by which iNOS inhibition improves cardiac function is by preventing the upregulation of RhoA and its availability for activation.

Time for primary review: 19


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P. R. Nagareddy, H. Soliman, G. Lin, P. S. Rajput, U. Kumar, J. H. McNeill, and K. M. MacLeod
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