PGC-1? deficiency accelerates the transition to heart failure in pressure overload hypertrophy.
ABSTRACT: Pressure overload cardiac hypertrophy, a risk factor for heart failure, is associated with reduced mitochondrial fatty acid oxidation (FAO) and oxidative phosphorylation (OXPHOS) proteins that correlate in rodents with reduced PGC-1? expression.To determine the role of PGC-1? in maintaining mitochondrial energy metabolism and contractile function in pressure overload hypertrophy.PGC-1? deficient (KO) mice and wildtype (WT) controls were subjected to transverse aortic constriction (TAC). Although LV function was modestly reduced in young KO hearts, there was no further decline with age so that LV function was similar between KO and WT when TAC was performed. WT-TAC mice developed relatively compensated LVH, despite reduced mitochondrial function and repression of OXPHOS and FAO genes. In nonstressed KO hearts, OXPHOS gene expression and palmitoyl-carnitine-supported mitochondrial function were reduced to the same extent as banded WT, but FAO gene expression was normal. Following TAC, KO mice progressed more rapidly to heart failure and developed more severe mitochondrial dysfunction, despite a similar overall pattern of repression of OXPHOS and FAO genes as WT-TAC. However, in relation to WT-TAC, PGC-1? deficient mice exhibited greater degrees of oxidative stress, decreased cardiac efficiency, lower rates of glucose metabolism, and repression of hexokinase II protein.PGC-1? plays an important role in maintaining baseline mitochondrial function and cardiac contractile function following pressure overload hypertrophy by preserving glucose metabolism and preventing oxidative stress.
Project description:During pathological hypertrophy, peroxisome proliferator-activated receptor coactivator 1? (PGC-1?) is repressed in concert with reduced mitochondrial oxidative capacity and fatty acid oxidation (FAO). We therefore sought to determine if maintaining or increasing PGC-1? levels in the context of pressure overload hypertrophy (POH) would preserve mitochondrial function and prevent contractile dysfunction. Pathological cardiac hypertrophy was induced using 4 wk of transverse aortic constriction (TAC) in mice overexpressing the human PGC-1? genomic locus via a bacterial artificial chromosome (TG) and nontransgenic controls (Cont). PGC-1? levels were increased by 40% in TG mice and were sustained following TAC. Although TAC-induced repression of FAO genes and oxidative phosphorylation (oxphos) genes was prevented in TG mice, mitochondrial function and ATP synthesis were equivalently impaired in Cont and TG mice after TAC. Contractile function was also equally impaired in Cont and TG mice following TAC, as demonstrated by decreased +dP/dt and ejection fraction and increased left ventricular developed pressure and end diastolic pressure. Conversely, capillary density was preserved, in concert with increased VEGF expression, while apoptosis and fibrosis were reduced in TG relative to Cont mice after TAC. Hence, sustaining physiological levels of PGC-1? expression following POH, while preserving myocardial vascularity, does not prevent mitochondrial and contractile dysfunction.
Project description:<h4>Objective</h4>To elucidate the molecular basis for mitochondrial dysfunction, which has been implicated in the pathogenesis of diabetes complications.<h4>Research design and methods</h4>Mitochondrial matrix and membrane fractions were generated from liver, brain, heart, and kidney of wild-type and type 1 diabetic Akita mice. Comparative proteomics was performed using label-free proteome expression analysis. Mitochondrial state 3 respirations and ATP synthesis were measured, and mitochondrial morphology was evaluated by electron microscopy. Expression of genes that regulate mitochondrial biogenesis, substrate utilization, and oxidative phosphorylation (OXPHOS) were determined.<h4>Results</h4>In diabetic mice, fatty acid oxidation (FAO) proteins were less abundant in liver mitochondria, whereas FAO protein content was induced in mitochondria from all other tissues. Kidney mitochondria showed coordinate induction of tricarboxylic acid (TCA) cycle enzymes, whereas TCA cycle proteins were repressed in cardiac mitochondria. Levels of OXPHOS subunits were coordinately increased in liver mitochondria, whereas mitochondria of other tissues were unaffected. Mitochondrial respiration, ATP synthesis, and morphology were unaffected in liver and kidney mitochondria. In contrast, state 3 respirations, ATP synthesis, and mitochondrial cristae density were decreased in cardiac mitochondria and were accompanied by coordinate repression of OXPHOS and peroxisome proliferator-activated receptor (PPAR)-gamma coactivator (PGC)-1alpha transcripts.<h4>Conclusions</h4>Type 1 diabetes causes tissue-specific remodeling of the mitochondrial proteome. Preservation of mitochondrial function in kidney, brain, and liver, versus mitochondrial dysfunction in the heart, supports a central role for mitochondrial dysfunction in diabetic cardiomyopathy.
Project description:Heart failure (HF) is characterized by abnormal mitochondrial calcium (Ca<sup>2+</sup>) handling, energy failure and impaired mitophagy resulting in contractile dysfunction and myocyte death. We have previously shown that the 18-kDa mitochondrial translocator protein of the outer mitochondrial membrane (TSPO) can modulate mitochondrial Ca<sup>2+</sup> uptake. Experiments were designed to test the role of the TSPO in a murine pressure-overload model of HF induced by transverse aortic constriction (TAC). Conditional, cardiac-specific TSPO knockout (KO) mice were generated using the Cre-loxP system. TSPO-KO and wild-type (WT) mice underwent TAC for 8 weeks. TAC-induced HF significantly increased TSPO expression in WT mice, associated with a marked reduction in systolic function, mitochondrial Ca<sup>2+</sup> uptake, complex I activity and energetics. In contrast, TSPO-KO mice undergoing TAC had preserved ejection fraction, and exhibited fewer clinical signs of HF and fibrosis. Mitochondrial Ca<sup>2+</sup> uptake and energetics were restored in TSPO KO mice, associated with decreased ROS, improved complex I activity and preserved mitophagy. Thus, HF increases TSPO expression, while preventing this increase limits the progression of HF, preserves ATP production and decreases oxidative stress, thereby preventing metabolic failure. These findings suggest that pharmacological interventions directed at TSPO may provide novel therapeutics to prevent or treat HF.
Project description:<h4>Background</h4>The mechanism of cardiac energy production against sustained pressure overload remains to be elucidated.<h4>Methods and results</h4>We generated cardiac-specific kinase-dead (kd) calcium/calmodulin-dependent protein kinase kinase-? (CaMKK?) transgenic (?-MHC CaMKK?kd TG) mice using ?-myosin heavy chain (?-MHC) promoter. Although CaMKK? activity was significantly reduced, these mice had normal cardiac function and morphology at baseline. Here, we show that transverse aortic binding (TAC) in ?-MHC CaMKK?kd TG mice led to accelerated death and left ventricular (LV) dilatation and dysfunction, which was accompanied by significant clinical signs of heart failure. CaMKK? downstream signaling molecules, including adenosine monophosphate-activated protein kinase (AMPK), were also suppressed in ?-MHC CaMKK?kd TG mice compared with wild-type (WT) mice. The expression levels of peroxisome proliferator-activated receptor-? coactivator (PGC)-1?, which is a downstream target of both of CaMKK? and calcium/calmodulin kinases, were also significantly reduced in ?-MHC CaMKK?kd TG mice compared with WT mice after TAC. In accordance with these findings, mitochondrial morphogenesis was damaged and creatine phosphate/?-ATP ratios assessed by magnetic resonance spectroscopy were suppressed in ?-MHC CaMKK?kd TG mice compared with WT mice after TAC.<h4>Conclusions</h4>These data indicate that CaMKK? exerts protective effects on cardiac adaptive energy pooling against pressure-overload possibly through phosphorylation of AMPK and by upregulation of PGC-1?. Thus, CaMKK? may be a therapeutic target for the treatment of heart failure.
Project description:RATIONALE:Decreased fatty acid oxidation (FAO) with increased reliance on glucose are hallmarks of metabolic remodeling that occurs in pathological cardiac hypertrophy and is associated with decreased myocardial energetics and impaired cardiac function. To date, it has not been tested whether prevention of the metabolic switch that occurs during the development of cardiac hypertrophy has unequivocal benefits on cardiac function and energetics. OBJECTIVE:Because malonyl CoA production via acetyl CoA carboxylase 2 (ACC2) inhibits the entry of long chain fatty acids into the mitochondria, we hypothesized that mice with a cardiac-specific deletion of ACC2 (ACC2H-/-) would maintain cardiac FAO and improve function and energetics during the development of pressure-overload hypertrophy. METHODS AND RESULTS:ACC2 deletion led to a significant reduction in cardiac malonyl CoA levels. In isolated perfused heart experiments, left ventricular function and oxygen consumption were similar in ACC2H-/- mice despite an ?60% increase in FAO compared with controls (CON). After 8 weeks of pressure overload via transverse aortic constriction (TAC), ACC2H-/- mice exhibited a substrate utilization profile similar to sham animals, whereas CON-TAC hearts had decreased FAO with increased glycolysis and anaplerosis. Myocardial energetics, assessed by 31P nuclear magnetic resonance spectroscopy, and cardiac function were maintained in ACC2H-/- after 8 weeks of TAC. Furthermore, ACC2H-/--TAC demonstrated an attenuation of cardiac hypertrophy with a significant reduction in fibrosis relative to CON-TAC. CONCLUSIONS:These data suggest that reversion to the fetal metabolic profile in chronic pathological hypertrophy is associated with impaired myocardial function and energetics and maintenance of the inherent cardiac metabolic profile and mitochondrial oxidative capacity is a viable therapeutic strategy.
Project description:Sestrin2 (Sesn2) is a stress sensor for the mammalian target of rapamycin complex 1 (mTORC1) pathway. Aging impairs cardiac mTORC1 activation, thereby sensitizing the heart to hypertrophy. C57BL/6 J young wild-type (young WT; 4-6 months), aged WT (24-26 months), and young Sestrin2 knockout mice (Y-Sesn2 KO; 4-6 months) underwent transverse aortic constriction (TAC) for pressure overload. Cardiac expression of Sesn2 decreased with age. At 4 weeks after TAC, aged WT and Y-Sesn2 KO exhibited larger hearts and impaired cardiac function, compared with young WT mice. Augmented phosphorylation of mTOR and downstream effectors; damaged mitochondria and elevated redox markers, as well as and impaired glucose and fatty acid oxidation were observed in aged WT and Y-Sesn2 KO hearts. A pressure overload-induced interaction between Sesn2 and GTPase-activating protein activity toward Rags 2 (GATOR2), which positively regulates mTORC1, was impaired in aged WT hearts. Adeno-associated virus 9-Sesn2 treatment rescued Sesn2 expression, attenuated mTORC1 activation, and increased pressure overload tolerance in aged WT and Y-Sesn2 KO hearts. These results indicated that cardiac Sesn2 acts as a pressure overload sensor for mTORC1. Furthermore, Sesn2 deficiency may cause increased sensitivity to hypertrophy in elderly individuals.
Project description:Overexpression of muscle atrophy F-box (MAFbx/atrogin-1), an E3 ubiquitin ligase, induces proteasomal degradation in cardiomyocytes. The role of endogenous MAFbx in regulating cardiac hypertrophy and failure remains unclear.We investigated the role of MAFbx in regulating cardiac hypertrophy and function in response to pressure overload. Transverse aortic constriction (TAC) was applied to MAFbx knockout (KO) and wild-type (WT) mice.Expression of MAFbx in WT mice was significantly increased by TAC. TAC-induced increases in cardiac hypertrophy were significantly smaller in MAFbx KO than in WT mice. There was significantly less lung congestion and interstitial fibrosis in MAFbx KO than in WT mice. MAFbx KO also inhibited ?-adrenergic cardiac hypertrophy. DNA microarray analysis revealed that activation of genes associated with the transcription factor binding site for the nuclear factor-?B family were inhibited in MAFbx KO mice compared with WT mice after TAC. Although the levels of I?B-? were significantly decreased after TAC in WT mice, they were increased in MAFbx KO mice. MAFbx regulates ubiquitination and proteasomal degradation of I?B-? in cardiomyocytes. In primary cultured rat cardiomyocytes, phenylephrine-induced activation of nuclear factor-?B and hypertrophy were significantly suppressed by MAFbx knockdown but were partially rescued by overexpression of nuclear factor-?B p65.MAFbx plays an essential role in mediating cardiac hypertrophy in response to pressure overload. Downregulation of MAFbx inhibits cardiac hypertrophy in part through stabilization of I?B-? and inactivation of nuclear factor-?B. Taken together, inhibition of MAFbx attenuates pathological hypertrophy, thereby protecting the heart from progression into heart failure.
Project description:Aberrant cardiomyocyte microtubule growth is a feature of pressure overload induced cardiac hypertrophy believed to contribute to left ventricular (LV) dysfunction. Microtubule Actin Cross-linking Factor 1 (MACF1/Acf7) is a 600 kd spectraplakin that stabilizes and guides microtubule growth along actin filaments. MACF1 is expressed in the heart, but its impact on cardiac microtubules, and how this influences cardiac structure, function, and adaptation to hemodynamic overload is unknown. Here we used inducible cardiac-specific MACF1 knockout mice (MACF1 KO) to determine the impact of MACF1 on cardiac microtubules and adaptation to pressure overload (transverse aortic constriction (TAC).In adult mouse hearts, MACF1 expression was low under basal conditions, but increased significantly in response to TAC. While MACF1 KO had no observable effect on heart size or function under basal conditions, MACF1 KO exacerbated TAC induced LV hypertrophy, LV dilation and contractile dysfunction. Interestingly, subcellular fractionation of ventricular lysates revealed that MACF1 KO altered microtubule distribution in response to TAC, so that more tubulin was associated with the cell membrane fraction. Moreover, TAC induced microtubule redistribution into this cell membrane fraction in both WT and MACF1 KO mice correlated strikingly with the level of contractile dysfunction (r(2)?=?0.786, p<.001). MACF1 disruption also resulted in reduction of membrane caveolin 3 levels, and increased levels of membrane PKC? and ?1 integrin after TAC, suggesting MACF1 function is important for spatial regulation of several physiologically relevant signaling proteins during hypertrophy. Together, these data identify for the first time, a role for MACF1 in cardiomyocyte microtubule distribution and in adaptation to hemodynamic overload.
Project description:The aim of this study was to determine whether endogenous GLUT1 induction and the increased glucose utilization that accompanies pressure overload hypertrophy (POH) are required to maintain cardiac function during hemodynamic stress, and to test the hypothesis that lack of GLUT1 will accelerate the transition to heart failure. To determine the contribution of endogenous GLUT1 to the cardiac adaptation to POH, male mice with cardiomyocyte-restricted deletion of the GLUT1 gene (G1KO) and their littermate controls (Cont) were subjected to transverse aortic constriction (TAC). GLUT1 deficiency reduced glycolysis and glucose oxidation by 50%, which was associated with a reciprocal increase in fatty acid oxidation (FAO) relative to controls. Four weeks after TAC, glycolysis increased and FAO decreased by 50% in controls, but were unchanged in G1KO hearts relative to shams. G1KO and controls exhibited equivalent degrees of cardiac hypertrophy, fibrosis, and capillary density loss after TAC. Following TAC, in vivo left ventricular developed pressure was decreased in G1KO hearts relative to controls, but+dP/dt was equivalently reduced in Cont and G1KO mice. Mitochondrial function was equivalently impaired following TAC in both Cont and G1KO hearts. GLUT1 deficiency in cardiomyocytes alters myocardial substrate utilization, but does not substantially exacerbate pressure-overload induced contractile dysfunction or accelerate the progression to heart failure.
Project description:Mitochondria play an essential role in the ability of brown fat to generate heat, and the PGC-1 coactivators control several aspects of mitochondrial biogenesis. To investigate their specific roles in brown fat cells, we generated immortal preadipocyte lines from the brown adipose tissue of mice lacking PGC-1±. We could then efficiently knockdown PGC-1Î² expression by shRNA expression. Loss of PGC-1± did not alter brown fat differentiation but severely reduced the induction of thermogenic genes. Cells deficient in either PGC-1Î± or PGC-1Î² coactivators showed a small decrease in the differentiation-dependant program of mitochondrial biogenesis and respiration; however, this increase in mitochondrial number and function was totally abolished during brown fat differentiation when both PGC-1± and PGC-1 were deficient. These data show that PGC-1± is essential for brown fat thermogenesis but not brown fat differentiation, and the PGC-1 coactivators play an absolutely essential but complementary function in differentiation-induced mitochondrial biogenesis. Affymetrix microarray analysis of total RNA from wt, PGC-1± KO and PGC-1± KO; cells expressing an RNAi specific for PGC-1 knockdown was performed. Of the 461; mitochondrial genes analyzed, 181 were found to be at least 20% different between wt; and defective PGC-1± and Î² adipocytes (p < 0.05). More than 85% of these genes were downregulated in cells deficient for PGC-1alpha and PGC-1beta. Experiment Overall Design: Brown preadipocytes that were either WT, KO for PGC-1alpha, or KO for PGC-1alpha and deficient for PGC-1beta (knockdown through siRNA expression) were differentiated for seven days. RNA was made from biological replicates of the three different types of brown adipocytes (WT, KO expressing a control siRNA, KO expressing a siRNA specific for PGC-1beta knockdown).