Submitted on June 28, 2007
Accepted on November 13, 2007
Altered Carnitine Homeostasis is Associated with Decreased Mitochondrial Function and Altered Nitric Oxide Signaling in Lambs with Pulmonary Hypertension
Shruti Sharma1, Neetu Sud1, Dean A Wiseman1, A Lee Carter2, Sanjiv Kumar1, Yali Hou3, Thomas Rau4, Jason Wilham4, Cynthia Harmon5, Peter E Oishi6, Jeffrey R. Fineman5, and Stephen M Black7*
1 Vascular Biology Center, Medical College of Georgia, Augusta, Georgia, United States
2 Biochemistry and Molecular Biology, Medical College of Georgia, Augusta, Georgia, United States
3 Vascualr Biology Center, Medical College of Georgia, Augusta, Georgia, United States
4 Biomedical & Pharmaceutical Sciences, The University of Montana, Missoula, Montana, United States
5 Pediatrics, University of California, San Francisco, San Francisco, California, United States
6 Pediatrics, University of California San Francisco, San Francisco, California, United States
7 Vascular Biology Center, Medical College of Georgia, Augusta, Georgia, United States; Biomedical & Pharmaceutical Sciences, The University of Montana, Missoula, Montana, United States
* To whom correspondence should be addressed. E-mail: Sblack{at}mail.mcg.edu.
Utilizing aortopulmonary shunt placement in the fetal lamb, we have developed a model (shunt) of pulmonary hypertension that mimics congenital heart disease with increased pulmonary blood flow. Our previous studies have identified a progressive development of endothelial dysfunction in shunt lambs that is dependent, at least in part, on decreased NO signaling. The purpose of this study was to evaluate the possible role of a disruption in carnitine metabolism in shunt lambs, and to determine the efefct on NO signaling. Our data indicate that at 2-weeks of age shunt lambs have significantly reduced expression (P<0.05) of the key enzymes in carnitine metabolism: carnitine palmitoyltransferases 1 and 2 as well as carnitine acetyl transferase (CrAT). In addition, we found that CrAT activity was inhibited due to increased nitration. Further, free carnitine levels were significantly decreased while acylcarnitine levels were significantly higher in shunt lambs (P<0.05). We also found that alterations in carnitine metabolism resulted in mitochondrial dysfunction as shunt lambs had significantly decreased pyruvate, increased lactate, and a reduced pyruvate:lactate ratio. In pulmonary arterial endothelial cells cultured from juvenile lambs we found that mild uncoupling of the mitochondria led to a decrease in cellular ATP levels and a reduction in both eNOS/Hsp90 interactions and NO signaling. Similarly, in shunt lambs we found a loss of eNOS/Hsp90 interactions that correlated with a progressive decrease in NO signaling. Our data suggest that mitochondrial dysfunction may play a role in the development of endothelial dysfunction and pulmonary hypertension and increased pulmonary blood flow.
