ABSTRACT
In pressure overload-induced hypertrophy, the heart increases its reliance on glucose as a fuel while decreasing fatty acid oxidation. A key regulator of this substrate switching in the hypertrophied heart is peroxisome proliferator-activated receptor alpha (PPARalpha). We tested the hypothesis that down-regulation of PPARalpha is an essential component of cardiac hypertrophy at the levels of increased mass, gene expression, and metabolism by pharmacologically reactivating PPARalpha. Pressure overload (induced by constriction of the ascending aorta for 7 days in rats) resulted in cardiac hypertrophy, increased expression of fetal genes (atrial natriuretic factor and skeletal alpha-actin), decreased expression of PPARalpha and PPARalpha-regulated genes (medium chain acyl-CoA dehydrogenase and pyruvate dehydrogenase kinase 4), and caused substrate switching (measured ex vivo in the isolated working heart preparation). Treatment of rats with the specific PPARalpha agonist WY-14,643 (8 days) did not affect the trophic response or atrial natriuretic factor induction to pressure overload. However, PPARalpha activation blocked skeletal alpha-actin induction, reversed the down-regulation of measured PPARalpha-regulated genes in the hypertrophied heart, and prevented substrate switching. This PPARalpha reactivation concomitantly resulted in severe depression of cardiac power and efficiency in the hypertrophied heart (measured ex vivo). Thus, PPARalpha down-regulation is essential for the maintenance of contractile function of the hypertrophied heart.
Subject(s)
Cardiomegaly/metabolism , Myocardium/metabolism , Receptors, Cytoplasmic and Nuclear/metabolism , Transcription Factors/metabolism , Actins/metabolism , Animals , Aorta/metabolism , Atrial Natriuretic Factor/metabolism , Down-Regulation , Glucose/metabolism , Isoenzymes/metabolism , Male , Muscle, Skeletal/metabolism , Oleic Acid/metabolism , Oxygen/metabolism , Oxygen Consumption , Perfusion , Protein Kinases/metabolism , Pyrimidines/pharmacology , Rats , Rats, Sprague-Dawley , Reverse Transcriptase Polymerase Chain Reaction , Time FactorsABSTRACT
Malonyl-CoA decarboxylase (MCD) catalyzes the degradation of malonyl-CoA, an important modulator of fatty acid oxidation. We hypothesized that increased fatty acid availability would increase the expression and activity of heart and skeletal muscle MCD, thereby promoting fatty acid utilization. The results show that high-fat feeding, fasting, and streptozotocin-induced diabetes all significantly increased the plasma concentration of nonesterified fatty acids, with a concomitant increase in both rat heart and skeletal muscle MCD mRNA. Upon refeeding of fasted animals, MCD expression returned to basal levels. Fatty acids are known to activate peroxisome proliferator-activated receptor-alpha (PPARalpha). Specific PPARalpha stimulation, through Wy-14643 treatment, significantly increased the expression of MCD in heart and skeletal muscle. Troglitazone, a specific PPARgamma agonist, decreased MCD expression. The sensitivity of MCD induction by fatty acids and Wy-14643 was soleus > extensor digitorum longus > heart. High plasma fatty acids consistently increased MCD activity only in solei, whereas MCD activity in the heart actually decreased with high-fat feeding. Pressure overload-induced cardiac hypertrophy, in which PPARalpha expression is decreased (and fatty acid oxidation is decreased), resulted in decreased MCD mRNA and activity, an effect that was dependent on fatty acids. The results suggest that fatty acids induce the expression of MCD in rat heart and skeletal muscle. Additional posttranscriptional mechanisms regulating MCD activity appear to exist.