For example, the results shown herein also raise the possibility that derangements in mitochondrial dynamics should be considered in the pathogenesis of child years cardiomyopathies. The lack of an obvious cardiac functional phenotype in adult PGC-1/f/f/MerCremice was amazing. adult heart. Marked mitochondrial structural derangements were observed in hearts of PGC-1/-deficient mice during postnatal growth, including fragmentation and elongation, associated with the development of a lethal cardiomyopathy. The expression of genes involved in mitochondrial fusion [mitofusin 1 (Mfn1), optic atrophy 1 (Opa1)] and fission [dynamin-related protein 1 (Drp1), fission protein 1 (Fis1)] was altered in hearts of PGC-1/-deficient mice. PGC-l was shown to directly regulateMfn1gene transcription by coactivating the estrogen-related receptor (ERR) upon a conserved DNA element. Surprisingly, PGC-1/ deficiency in the adult heart did not result in evidence of abnormal mitochondrial dynamics or NPS-1034 heart failure. However, transcriptional profiling exhibited that this PGC-1 coactivators Rabbit polyclonal to FASTK are required for high level expression of nuclear- and mitochondrial-encoded genes involved in mitochondrial dynamics and energy transduction in adult heart. == Conclusion == These results reveal unique developmental stage-specific programs involved in cardiac mitochondrial dynamics. Keywords:PGC-1 coactivators, mitochondrial fusion, cardiac energy metabolism, cardiomyopathy, mitofusin == INTRODUCTION == The high energy demands of the postnatal heart are largely satisfied by adenosine triphosphate (ATP) generated via mitochondrial oxidative phosphorylation (OXPHOS). Accordingly, cardiac myocytes require a NPS-1034 specialized, high capacity mitochondrial system. The importance of mitochondrial respiration for proper heart function is exhibited by the tight linear relationship between cardiac oxygen consumption and work.1Evidence is emerging that in many forms of heart failure, cardiac mitochondria revert to prenatal levels of function and morphology, leading to energy starvation, contributing to a vicious pathological cycle.2,3 During cardiac development, mitochondria undergo a maturation process. Mitochondrial maturation can be divided into three main developmental stages: prenatal, perinatal, and postnatal. In the prenatal stage, the early embryonic heart relies largely on non-mitochondrial energy sources (i.e. anaerobic glycolysis).4During the transition from late fetal to postnatal periods (perinatal stage), the mitochondrial NPS-1034 functional capacity of the heart raises dramatically, supporting a switch to reliance on fatty acids (FA) as the chief energy substrate.4-6This increase in mitochondrial oxidative capacity is triggered by a burst of mitochondrial biogenesis at birth.7-9The third stage of mitochondrial maturation occurs during the postnatal period when the cardiac myocyte undergoes growth, elongation, and assembly of adult sarcomeres. This final stage entails an increase in mitochondrial size and function, together with redistribution of the organelles throughout the myocyte.6This intracellular redistribution results in the mitochondria being tightly packed between the longitudinally-oriented myofibrils with the development of contacts between mitochondria, myofibrils, and the sarcoplasmic reticulum.6The mitochondrial architectural arrangement of the adult myocyte facilitates efficient high energy phosphate transfer between the mitochondria and key ATPases such as the myosin-ATPase and the sarcoplasmic reticulum ATPase.10Recent evidence suggests that postnatal mitochondrial maturation in the mammalian heart involves coordinated mitochondrial dynamics (fusion and fission).11 The mechanisms regulating mitochondrial maturation are incompletely understood. Peroxisome proliferator-activated receptor gamma coactivator-1 (PGC-1) and PGC-1, are inducible, developmentally-regulated, transcriptional coregulators of cellular energy processes including NPS-1034 OXPHOS and FA oxidation in mitochondrial-rich tissues such as heart, skeletal muscle mass, and brown adipose tissue.12-15Using conditional gene targeting strategies in mice, we have shown that PGC-1 and PGC-1 serve overlapping functions in the surge of mitochondrial biogenesis that occurs in heart immediately following birth.12Combined disruption of the PGC-1 and PGC-1 genes during the embryonic period resulted in a complete arrest of cardiac perinatal mitochondrial biogenesis leading to a lethal cardiomyopathy soon after birth.12Conversely, overexpression of PGC-1 in the immediate postnatal period drives an exuberant mitochondrial biogenic response.16 The PGC-1 loss-of-function studies to date have not defined the role of these transcriptional coactivators during postnatal development or in NPS-1034 the adult heart due to the lethal phenotype of PGC-1/PGC-1-deficient mice shortly after birth. The role of the PGC-1 coactivators after birth is an important question given the potential link of altered PGC-1 signaling to the development of heart failure.17,18To address this question, we took advantage of a conditional gene targeting system in mice that resulted in deletion of the PGC-1 gene in both heart and skeletal muscle mass via the actions of Cre recombinase driven by the muscle mass creatine kinase (MCK) promoter (MCK-Cre) on a generalized PGC-1 null background (PGC-1/f/f/MCK-Cre).19,20MCK-Cre is not fully active in the heart until after the perinatal mitochondrial biogenic surge..