Inactivation of peroxisome proliferator-activated receptor isoforms α, β/δ, and γ mediate distinct facets of hypertrophic transformation of adult cardiac myocytes

Inactivation of peroxisome proliferator-activated receptor (PPARs) isoforms α, β/δ, and γ mediate distinct facets of hypertrophic transformation of adult cardiac myocytes. PPARs are ligand-activated transcription factors that modulate the transcriptional regulation of fatty acid metabolism and the hypertrophic response in neonatal cardiac myocytes. The purpose of this study was to determine the role of PPAR isoforms in the morphologic and metabolic phenotype transformation of adult cardiac myocytes in culture, which, in medium containing 20% fetal calf serum, undergo hypertrophy-like cell growth associated with downregulation of regulatory proteins of fatty acid metabolism. Expression and DNA-binding activity of PPARα, PPARβ/δ, and PPARγ rapidly decreased after cell isolation and remained persistently reduced during the 14-day culture period. Cells progressively increased in size and developed both re-expression of atrial natriuretic factor and downregulation of regulatory proteins of fatty acid metabolism. Supplementation of the medium with fatty acid (oleate 0.25mM/palmitate 0.25mM) prevented inactivation of PPARs and downregulation of metabolic genes. Furthermore, cell size and markers of hypertrophy were markedly reduced. Selective activation of either PPARα or PPARβ/δ completely restored expression of regulatory genes of fatty acid metabolism but did not influence cardiac myocyte size and markers of hypertrophy. Conversely, activation of PPARγ prevented cardiomyocyte hypertrophy but had no effect on fatty acid metabolism. The results indicate that PPAR activity markedly influences hypertrophic transformation of adult rat cardiac myocytes. Inactivation of PPARα and PPARβ/δ accounts for downregulation of the fatty acid oxidation pathway, whereas inactivation of PPARγ enables development of hypertroph

Angiotensin II downregulates the fatty acid oxidation pathway in adult rat cardiomyocytes via release of tumour necrosis factor-α

Aims Advanced heart failure is often associated with reduced myocardial fatty acid oxidation capacity. We have previously observed that failing hearts of mice with overexpression of angiotensinogen in the myocardium exhibit marked reduction of key regulatory proteins of fatty acid oxidation. In the present study, we determined whether exposure of adult rat cardiac (ARC) myocytes to angiotensin II (Ang II) influences expression of fatty acid translocase, muscle-type carnitine palmitoyl transferase-I, and medium-chain acyl-CoA dehydrogenase. Methods and results Ang II reduced mRNA expression of the three regulatory proteins in ARC myocytes during the entire 14-days culture period. However, protein expression and palmitate oxidation rate remained unaltered for 7 days, but subsequently markedly decreased. The decrease of protein expression and of fatty acid oxidation coincided with the onset of increased protein expression of tumour necrosis factor-α (TNF-α). The effect of Ang II was completely abolished by either blocking TNF-α formation through inhibition of reactive oxygen species-mediated activation of nuclear factor-κB or by neutralizing TNF-α with a specific antibody. Activation of peroxisome proliferator-activated receptor-α (PPARα) and PPARβ/δ counteracted Ang II-mediated reduction of the fatty acid oxidation pathway. Conclusion Prolonged exposure of cardiac myocytes to Ang II elicits downregulation of the fatty acid oxidation pathway mediated by enhanced synthesis of TNF-

Effects of insulin-like growth factor-I on the maturation of metabolism in neonatal rat cardiomyocytes

Myocardial metabolism shifts during the perinatal period from predominant utilization of glucose towards oxidation of fatty acids. Expression of enzymes of the fatty acid oxidation (FAO) pathway is under the control of the nuclear receptor/transcription factor peroxisome proliferator-activated receptor α (PPARα). Insulin-like Growth Factor-I (IGF-I) plays an important role in the post-natal growth and differentiation of the heart. We determined the influence of IGF-I on the maturation of myocardial metabolism. In neonatal rat cardiac myocytes, expression of the FAO enzymes MCAD and M-CPT I was induced by treatment with the specific PPARα agonist WY-14643. Concomitant treatment with IGF-I enhanced the expression of both FAO enzymes. By comparison, treatment with FGF-2, which is required for myocyte differentiation of cardiac precursors, did not increase WY-14643-induced expression of FAO enzymes. Despite stimulation of FAO enzyme expression, IGF-I did not further enhance WY-14643-stimulated palmitate oxidation. In contrast, IGF-I relieved WY-14643-mediated inhibition of glucose uptake and promoted storage of fatty acids into cellular neutral lipids. In conclusion, IGF-I promotes a more mature pattern of FAO gene expression but, because of insulin-like metabolic effects, does not concomitantly enhance oxidation of fatty acid

Postinfarction heart failure in rats is associated with upregulation of GLUT-1 and downregulation of genes of fatty acid metabolism

Objectives: Increasing evidence suggests that left ventricular remodeling is associated with a shift from fatty acid to glucose metabolism for energy production. The aim of this study was to determine whether left ventricular remodeling with and without late-onset heart failure after myocardial infarction is associated with regional changes in the expression of regulatory proteins of glucose or fatty acid metabolism. Methods: Myocardial infarction was induced in rats by ligation of the left anterior descending coronary artery (LAD). In infarcted and sham-operated hearts the peri-infarction region (5-mm zone surrounding the region at risk), the interventricular septum and the right ventricular free wall were separated for analysis. Results: At 8 and 20 weeks after LAD ligation, the peri-infarction region and the septum exhibited marked re-expression of atrial natriuretic factor [+252±37 and +1093±279%, respectively, in the septum (P<0.05)] and of α-smooth muscle actin [+34±10 and +43±14%, respectively, in the septum (P<0.05)]. At 8 weeks, when left ventricular hypertrophy was present without signs of heart failure, myocardial mRNA expression of glucose transporters (GLUT-1 and GLUT-4) was not altered, whereas mRNA expression of medium-chain acyl-CoA dehydrogenase (MCAD) was significantly reduced in the peri-infarction region (−25±7%; P<0.05). In hearts exhibiting heart failure 20 weeks after infarct-induction there was a change in all three ventricular regions of both mRNA and protein content of GLUT-1 [+72±28 and +121±15%, respectively, in the peri-infarction region (P<0.05)] and MCAD [−29±9 and −56±4%, respectively, in the peri-infarction region (P<0.05)]. Conclusion: In rats with large myocardial infarction, progression from compensated remodeling to overt heart failure is associated with upregulation of GLUT-1 and downregulation of MCAD in both the peri-infarction region and the septu

Angiotensin II and tumour necrosis factor α as mediators of ATP-dependent potassium channel remodelling in post-infarction heart failure

Aims Angiotensin II (Ang II) and tumour necrosis factor α (TNFα) are involved in the progression from compensated hypertrophy to heart failure. Here, we test their role in the remodelling of ATP-dependent potassium channel (KATP) in heart failure, conferring increased metabolic and diazoxide sensitivity. Methods and results We observed increased expression of both angiotensinogen and TNFα in the failing rat myocardium, with a regional gradient matching that of the KATP subunit Kir6.1 expression. Both angiotensinogen and TNFα expression correlated positively with Kir6.1 and negatively with Kir6.2 expression across the post-infarction myocardium. To further identify a causal relationship, cardiomyocytes isolated from normal rat hearts were exposed in vitro to Ang II or TNFα. We observed increased Kir6.1 and SUR subunit and reduced Kir6.2 subunit mRNA expression in cardiomyocytes cultured with Ang II or TNFα, similar to what was observed in failing hearts. In patch-clamp experiments, cardiomyocytes cultured with Ang II or TNFα exhibited responsiveness to diazoxide, in terms of both KATP current and action potential shortening. This was not observed in untreated cardiomyocytes and resembles the diazoxide sensitivity of failing cardiomyocytes that also overexpress Kir6.1. Ang II exerted its effect through induction of TNFα expression, because TNFα-neutralizing antibody abolished the effect of Ang II, and in failing hearts, regional expression of angiotensinogen matched TNFα expression. Finally, Ang II and TNFα regulated KATP subunit expression, possibly through differential expression of Forkhead box transcription factors. Conclusion This study identifies Ang II and TNFα as mediators of the remodelling of KATP channels in heart failur

Regulation of glucose transporter expression in cardiac myocytes: p38 MAPK is a strong inducer of GLUT4

Objective: In vivo differentiation of cardiac myocytes is associated with downregulation of the glucose transporter isoform GLUT1 and upregulation of the isoform GLUT4. Adult rat cardiomyocytes in primary culture undergo spontaneous dedifferentiation, followed by spreading and partial redifferentiation, which can be influenced by growth factors. We used this model to study the signaling mechanisms modifying the expression of GLUT4 in cardiac myocytes. Results: Adult rat cardiomyocytes in primary culture exhibited spontaneous upregulation of GLUT1 and downregulation of GLUT4, suggesting resumption of a fetal program of GLUT gene expression. Treatment with IGF-1 and, to a minor extent, FGF-2 resulted in restored expression of GLUT4 protein and mRNA. Activation of p38 MAPK mediated the increased expression of GLUT4 in response to IGF-1. Transient transfection experiments in neonatal cardiac myocytes confirmed that p38 MAPK could activate the glut4 promoter. Electrophoretic mobility shift assay in adult rat cardiomyocytes and transient transfection experiments in neonatal cardiac myocytes indicated that MEF2 was the main transcription factor transducing the effect of p38 MAPK activation on the glut4 promoter. Conclusion: Spontaneous dedifferentiation of adult rat cardiomyocytes in vitro is associated with downregulation of GLUT4, which can be reversed by treatment with IGF-1. The effect of IGF-1 is mediated by the p38 MAPK/MEF2 axis, which is a strong inducer of GLUT4 expressio

White Matter Development in Early Puberty: A Longitudinal Volumetric and Diffusion Tensor Imaging Twin Study

White matter microstructure and volume show synchronous developmental patterns in children. White matter volume increases considerably during development. Fractional anisotropy, a measure for white matter microstructural directionality, also increases with age. Development of white matter volume and development of white matter microstructure seem to go hand in hand. The extent to which the same or different genetic and/or environmental factors drive these two aspects of white matter maturation is currently unknown. We mapped changes in white matter volume, surface area and diffusion parameters in mono- and dizygotic twins who were scanned at age 9 (203 individuals) and again at age 12 (126 individuals). Over the three-year interval, white matter volume (+6.0%) and surface area (+1.7%) increased, fiber bundles expanded (most pronounced in the left arcuate fasciculus and splenium), and fractional anisotropy increased (+3.0%). Genes influenced white matter volume (heritability ∼85%), surface area (∼85%), and fractional anisotropy (locally 7% to 50%) at both ages. Finally, volumetric white matter growth was negatively correlated with fractional anisotropy increase (r = –0.62) and this relationship was driven by environmental factors. In children who showed the most pronounced white matter growth, fractional anisotropy increased the least and vice-versa. Thus, white matter development in childhood may reflect a process of both expansion and fiber optimization