Fatty acid oxidation and malonyl-CoA decarboxylase in the vascular remodeling of pulmonary hypertension.

Pulmonary arterial hypertension is caused by excessive growth of vascular cells that eventually obliterate the pulmonary arterial lumen, causing right ventricular failure and premature death. Despite some available treatments, its prognosis remains poor, and the cause of the vascular remodeling remains unknown. The vascular smooth muscle cells that proliferate during pulmonary arterial hypertension are characterized by mitochondrial hyperpolarization, activation of the transcription factor NFAT (nuclear factor of activated T cells), and down-regulation of the voltage-gated potassium channel Kv1.5, all of which suppress apoptosis. We found that mice lacking the gene for the metabolic enzyme malonyl-coenzyme A (CoA) decarboxylase (MCD) do not show pulmonary vasoconstriction during exposure to acute hypoxia and do not develop pulmonary arterial hypertension during chronic hypoxia but have an otherwise normal phenotype. The lack of MCD results in an inhibition of fatty acid oxidation, which in turn promotes glucose oxidation and prevents the shift in metabolism toward glycolysis in the vascular media, which drives the development of pulmonary arterial hypertension in wild-type mice. Clinically used metabolic modulators that mimic the lack of MCD and its metabolic effects normalize the mitochondrial-NFAT-Kv1.5 defects and the resistance to apoptosis in the proliferated smooth muscle cells, reversing the pulmonary hypertension induced by hypoxia or monocrotaline in mice and rats, respectively. This study of fatty acid oxidation and MCD identifies a critical role for metabolism in both the normal pulmonary circulation (hypoxic pulmonary vasoconstriction) and pulmonary hypertension, pointing to several potential therapeutic targets for the treatment of this deadly disease.

Distinct early signaling events resulting from the expression of the PRKAG2 R302Q mutant of AMPK contribute to increased myocardial glycogen.

BACKGROUND: Humans with an R302Q mutation in AMPKgamma(2) (the PRKAG2 gene) develop a glycogen storage cardiomyopathy characterized by a familial form of Wolff-Parkinson-White syndrome and cardiac hypertrophy. This phenotype is recapitulated in transgenic mice with cardiomyocyte-restricted expression of AMPKgamma(2)R302Q. Although considerable information is known regarding the consequences of harboring the gamma(2)R302Q mutation, little is known about the early signaling events that contribute to the development of this cardiomyopathy. METHODS AND RESULTS: To distinguish the direct effects of gamma(2)R302Q expression from later compensatory alterations in signaling, we used transgenic mice expressing either the wild-type AMPKgamma(2) subunit (TGgamma(2)WT) or the mutated form (TGgamma(2)R302Q), in combination with acute expression of these proteins in neonatal rat cardiomyocytes. Although acute expression of gamma(2)R302Q induces AMPK activation and upregulation of glycogen synthase and AS160, with an associated increase in glycogen content, AMPK activity, glycogen synthase activity, and AS160 expression are reduced in hearts from TGgamma(2)R302Q mice, likely in response to the existing 37-fold increase in glycogen. Interestingly, gamma(2)WT expression has similar, yet less marked effects than gamma(2)R302Q expression in both cardiomyocytes and hearts. CONCLUSIONS: Using acute and chronic models of gamma(2)R302Q expression, we have differentiated the direct effects of the gamma(2)R302Q mutation from eventual compensatory modifications. Our data suggest that expression of gamma(2)R302Q induces AMPK activation and the eventual increase in glycogen content, a finding that is masked in hearts from transgenic adult mice. These findings are the first to highlight temporal differences in the effects of the PRKAG2 R302Q mutation on cardiac metabolic signaling events.

The AMPK gamma1 R70Q mutant regulates multiple metabolic and growth pathways in neonatal cardiac myocytes.

Although mutations in the gamma-subunit of AMP-activated protein kinase (AMPK) can result in excessive glycogen accumulation and cardiac hypertrophy, the mechanisms by which this occurs have not been well defined. Because >65% of cardiac AMPK activity is associated with the gamma1-subunit of AMPK, we investigated the effects of expression of an AMPK-activating gamma1-subunit mutant (gamma1 R70Q) on regulatory pathways controlling glycogen accumulation and cardiac hypertrophy in neonatal rat cardiac myocytes. Whereas expression of gamma1 R70Q displayed the expected increase in palmitate oxidation rates, rates of glycolysis were significantly depressed. In addition, glycogen synthase activity was increased in cardiac myocytes expressing gamma1 R70Q, due to both increased expression and decreased phosphorylation of glycogen synthase. The inhibition of glycolysis and increased glycogen synthase activity were correlated with elevated glycogen levels in gamma1 R70Q-expressing myocytes. In association with the reduced phosphorylation of glycogen synthase, glycogen synthase kinase (GSK)-3beta protein and mRNA levels were profoundly decreased in the gamma1 R70Q-expressing myocytes. Consistent with GSK-3beta negatively regulating hypertrophy via inhibition of nuclear factor of activated T cells (NFAT), the dramatic downregulation of GSK-3beta was associated with increased nuclear activity of NFAT. Together, these data provide important new information about the mechanisms by which a mutation in the gamma-subunit of AMPK causes altered AMPK signaling and identify multiple pathways involved in regulating both cardiac myocyte metabolism and growth that may contribute to the development of the gamma mutant-associated cardiomyopathy.