Preserving mitochondrial function prevents the proteasomal degradation of GTP cyclohydrolase I.

Abstract The development of pulmonary hypertension is a common accompaniment of congenital heart disease (CHD) with increased pulmonary blood flow. Our recent evidence suggests that asymmetric dimethylarginine (ADMA)-induced mitochondrial dysfunction causes endothelial nitric oxide synthase (eNOS) uncoupling secondary to a proteasome-dependent degradation of GTP cyclohydrolase I (GCH1) that results in a decrease in the NOS cofactor tetrahydrobiopterin (BH 4 ). Decreases in NO signaling are thought to be an early hallmark of endothelial dysfunction. As l- carnitine plays an important role in maintaining mitochondrial function, in this study we examined the protective mechanisms and the therapeutic potential of l- carnitine on NO signaling in pulmonary arterial endothelial cells and in a lamb model of CHD and increased pulmonary blood flow (Shunt). Acetyl- l- carnitine attenuated the ADMA-mediated proteasomal degradation of GCH1. This preservation was associated with a decrease in the association of GCH1 with Hsp70 and the C-terminus of Hsp70-interacting protein (CHIP) and a decrease in its ubiquitination. This in turn prevented the decrease in BH 4 levels induced by ADMA and preserved NO signaling. Treatment of Shunt lambs with l- carnitine also reduced GCH1/CHIP interactions, attenuated the ubiquitination and degradation of GCH1, and increased BH 4 levels compared to vehicle-treated Shunt lambs. The increases in BH 4 were associated with decreased NOS uncoupling and enhanced NO generation. Thus, we conclude that L - carnitine may have a therapeutic potential in the treatment of pulmonary hypertension in children with CHD with increased pulmonary blood flow.