Maturation of lipid metabolism in the fetal and newborn sheep heart.

At birth, the fetus experiences a dramatic change in environment that is accompanied by a shift in myocardial fuel preference from lactate and glucose in fetal life to fatty acid oxidation after birth. We hypothesized that fatty acid metabolic machinery would mature during fetal life in preparation for this extreme metabolic transformation at birth. We quantified the pre- (94-day and 135-day gestation, term ∼147 days) and postnatal (5 ± 4 days postnatal) gene expression and protein levels for fatty acid transporters and enzymes in hearts from a precocial species, the sheep. Gene expression of fatty acid translocase (), acyl-CoA synthetase long-chain 1 (), carnitine palmitoyltransferase 1 (), hydroxy-acyl dehydrogenase (), acetyl-CoA acetyltransferase (), isocitrate dehydrogenase (), and glycerol phosphate acyltransferase () progressively increased through the perinatal period, whereas several genes [fatty acid transport protein 6 (), acyl-CoA synthetase long chain 3 (), long-chain acyl-CoA dehydrogenase (), very long-chain acyl-CoA dehydrogenase (), pyruvate dehydrogenase kinase (), phosphatidic acid phosphatase (), and diacylglycerol acyltransferase ()] were stable in fetal hearts and had high expression after birth. Protein expression of and progressively increased throughout the perinatal period, whereas protein expression of carnitine palmitoyltransferase 1a (fetal isoform) () decreased and carnitine palmitoyltransferase 1b (adult isoform) () remained constitutively expressed. Using fluorescent-tagged long-chain fatty acids (BODIPY-C), we demonstrated that fetal (125 ± 1 days gestation) cardiomyocytes produce 59% larger lipid droplets ( < 0.05) compared with newborn (8 ± 1 day) cardiomyocytes. These results provide novel insights into the perinatal maturation of cardiac fatty acid metabolism in a precocial species. This study characterized the previously unknown expression patterns of genes that regulate the metabolism of free fatty acids in the perinatal sheep myocardium. This study shows that the prenatal myocardium prepares for the dramatic switch from carbohydrate metabolism to near complete reliance on free fatty acids postnatally. Fetal and neonatal cardiomyocytes also demonstrate differing lipid storage mechanisms where fetal cardiomyocytes form larger lipid droplets compared with newborn cardiomyocytes.