Summary Activating mutations in BRAF are the most common genetic alterations in melanoma. Inhibition of BRAF by small molecule inhibitors leads to cell cycle arrest and apoptosis. We show here that BRAF inhibition also induces an oxidative phosphorylation gene program, mitochondrial biogenesis, and the increased expression of the mitochondrial master regulator, PGC1α. We further show that a target of BRAF, the melanocyte lineage factor MITF, directly regulates the expression of PGC1α. Melanomas with activation of the BRAF/MAPK pathway have suppressed levels of MITF and PGC1α, and decreased oxidative metabolism. Conversely, treatment of BRAF mutated melanomas with BRAF inhibitors renders them addicted to oxidative phosphorylation. Our data thus identify an adaptive metabolic program that limits the efficacy of BRAF inhibitors.

Sepsis-associated acute kidney injury (AKI) is a common and morbid condition that is distinguishable from typical ischemic renal injury by its paucity of tubular cell death. The mechanisms underlying renal dysfunction in individuals with sepsis-associated AKI are therefore less clear. Here we have shown that endotoxemia reduces oxygen delivery to the kidney, without changing tissue oxygen levels, suggesting reduced oxygen consumption by the kidney cells. Tubular mitochondria were swollen, and their function was impaired. Expression profiling showed that oxidative phosphorylation genes were selectively suppressed during sepsis-associated AKI and reactivated when global function was normalized. PPARγ coactivator-1α (PGC-1α), a major regulator of mitochondrial biogenesis and metabolism, not only followed this pattern but was proportionally suppressed with the degree of renal impairment. Furthermore, tubular cells had reduced PGC-1α expression and oxygen consumption in response to TNF-α; however, excess PGC-1α reversed the latter effect. Both global and tubule-specific PGC-1α-knockout mice had normal basal renal function but suffered persistent injury following endotoxemia. Our results demonstrate what we believe to be a novel mechanism for sepsis-associated AKI and suggest that PGC-1α induction may be necessary for recovery from this disorder, identifying a potential new target for future therapeutic studies.

Peri-partum cardiomyopathy (PPCM) is a frequently fatal disease that affects women near delivery, and occurs more frequently in women with pre-eclampsia and/or multiple gestation. The etiology of PPCM, or why it associates with pre-eclampsia, remains unknown. We show here that PPCM is associated with a systemic angiogenic imbalance, accentuated by pre-eclampsia. Mice that lack cardiac PGC-1α, a powerful regulator of angiogenesis, develop profound PPCM. Importantly, the PPCM is entirely rescued by pro-angiogenic therapies. In humans, the placenta in late gestation secretes VEGF inhibitors like soluble Flt1 (sFlt1), and this is accentuated by multiple gestation and pre-eclampsia. This anti-angiogenic environment is accompanied by sub-clinical cardiac dysfunction, the extent of which correlates with circulating levels of sFlt1. Exogenous sFlt1 alone caused diastolic dysfunction in wildtype mice, and profound systolic dysfunction in mice lacking cardiac PGC-1α. Finally, plasma samples from women with PPCM contained abnormally high levels of sFlt1. These data strongly suggest that PPCM is in large part a vascular disease, caused by excess anti-angiogenic signaling in the peri-partum period. The data also explain how late pregnancy poses a threat to cardiac homeostasis, and why pre-eclampsia and multiple gestation are important risk factors for the development of PPCM.

Epidemiological and experimental data implicate branched chain amino acids (BCAAs) in the development of insulin resistance, but the mechanisms underlying this link remain unclear.1–3 Insulin resistance in skeletal muscle stems from excess accumulation of lipid species4, a process that requires blood-borne lipids to first traverse the blood vessel wall. Little is known, however, of how this trans-endothelial transport occurs or is regulated. Here, we leverage PGC-1α, a transcriptional coactivator that regulates broad programs of FA consumption, to identify 3-hydroxy-isobutyrate (3-HIB), a catabolic intermediate of the BCAA valine, as a novel paracrine regulator of trans-endothelial fatty acids (FA) transport. 3-HIB is secreted from muscle cells, activates endothelial FA transport, stimulates muscle FA uptake in vivo, and promotes muscle lipid accumulation and insulin resistance in animals. Conversely, inhibiting the synthesis of 3-HIB in muscle cells blocks the promotion of endothelial FA uptake. 3-HIB levels are elevated in muscle from db/db mice and from subjects with diabetes. These data thus unveil a novel mechanism that regulates trans-endothelial flux of FAs, revealing 3-HIB as a new bioactive signaling metabolite that links the regulation of FA flux to BCAA catabolism and provides a mechanistic explanation for how increased BCAA catabolic flux can cause diabetes.

Exercise provides numerous salutary effects, but our understanding of how these occur is limited. To gain a clearer picture of exercise-induced metabolic responses, we have developed comprehensive plasma metabolite signatures by using mass spectrometry to measure over 200 metabolites before and after exercise. We identified plasma indicators of glycogenolysis (glucose-6-phosphate), tricarboxylic acid (TCA) cycle span 2 expansion (succinate, malate, and * To whom correspondence should be addressed Corresponding authors Robert E. Gerszten, MD Cardiology Division and Center for Immunology & Inflammatory Diseases Massachusetts General Hospital, Room 8307 149 13th Street Charlestown, MA 02129 rgerszten@partners.org Gregory D. Lewis, MD Cardiology Division Massachusetts General Hospital, GRB 800 55 Fruit Street, Boston, MA 02114 glewis@partners.org. Authors contributions: G.D.L conceived the study, designed the experiments, performed primary data analysis and wrote the manuscript. M.J.W. led the effort to recruit and phenotype marathon subjects, L.F. and M.M. recruited subjects, processed samples, and assisted with experimental design. Z.A. and G.C.R. designed and performed the gene expression profiling experiments, A.S., E.Y., X.S., A.A., S.A.C. and C.B.C. developed the metabolic profiling platform, performed mass spectrometry experiments, and analyzed the data, S.C., E.L.M, T.W., and R.S.V. designed experiments and analyzed data from the Framingham Heart Study cohort, R.D. and F.P.R. assisted with statistical analysis and constructed the metabolite interrelatedness dendrogram, E.P.R. contributed to mass spectrometry data analysis and helped to write the manuscript, D.M.S. and M.J.S. contributed to the cardiopulmonary exercise testing metabolic profiling experiment, M.S.S. helped to conceive and design the exercise treadmill testing studies and assisted in data interpretation and in writing the manuscript, R.E.G. conceived of the study, designed experiments, analyzed data, and wrote the manuscript. Competing interests:The authors declare that they have no competing interests. NIH Public Access Author ManuscriptSci Transl Med. Author manuscript; available in PMC 2010 December 27. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript fumarate), and lipolysis (glycerol), as well as modulators of insulin sensitivity (niacinamide) and fatty acid oxidation (pantothenic acid). Metabolites that were highly correlated with fitness parameters were found in subjects undergoing acute exercise testing, marathon running, and in 302 subjects from a longitudinal cohort study. Exercise-induced increases in glycerol were strongly related to fitness levels in normal individuals and were attenuated in subjects with myocardial ischemia. A combination of metabolites that increased in plasma in response to exercise (glycerol, niacinamide, glucose-6-phosphate, pantothenate, and succinate) upregulated the expression of nur77, a transcriptional regulator of glucose utilization and lipid metabolism genes in skeleta...

Peripheral arterial disease (PAD) affects 5 million people in the US and is the primary cause of limb amputations. Exercise remains the single best intervention for PAD, in part thought to be mediated by increases in capillary density. How exercise triggers angiogenesis is not known. PPAR␥ coactivator (PGC)-1␣ is a potent transcriptional coactivator that regulates oxidative metabolism in a variety of tissues. We show here that PGC-1␣ mediates exercise-induced angiogenesis. Voluntary exercise induced robust angiogenesis in mouse skeletal muscle. Mice lacking PGC-1␣ in skeletal muscle failed to increase capillary density in response to exercise. Exercise strongly induced expression of PGC-1␣ from an alternate promoter. The induction of PGC-1␣ depended on ␤-adrenergic signaling. ␤-adrenergic stimulation also induced a broad program of angiogenic factors, including vascular endothelial growth factor (VEGF). This induction required PGC-1␣. The orphan nuclear receptor ERR␣ mediated the induction of VEGF by PGC-1␣, and mice lacking ERR␣ also failed to increase vascular density after exercise. These data demonstrate that ␤-adrenergic stimulation of a PGC-1␣/ERR␣/VEGF axis mediates exercise-induced angiogenesis in skeletal muscle.VEGF ͉ ERR␣ ͉ ␤-adrenergic

Abstract:The beating heart requires a constant flux of ATP to maintain contractile function, and there is increasing evidence that energetic defects contribute to the development of heart failure. The last 10 years have seen a resurgent interest in cardiac intermediary metabolism and a dramatic increase in our understanding of transcriptional networks that regulate cardiac energetics. The PPAR-␥ coactivator ( Key Words: PGC-1 Ⅲ metabolism Ⅲ heart failure Ⅲ mitochondria T he heart consumes tremendous amounts of energy. ATP consumption, per weight of tissue, is the highest in the body. Energy reserves in the heart are relatively limited, and a heart starved of its fuel and oxygen supply can only beat 20 to 40 times (a few seconds) before succumbing to energy deficiency. Despite this narrow window, the healthy heart will contract billions of times in the average human life. The dynamic range of cardiac activity is large, both acutely (exercise) and chronically (development, especially postnatal). Bioenergetic programs in the heart must therefore be tightly regulated.ATP is the currency of energy in the cell. Oxidative consumption of fuels in mitochondria is by far the most efficient means of generating ATP, yielding Ͼ30 ATP per molecule of glucose, compared to a net 2 ATP via anaerobic glycolysis and lactate production. It is not surprising then that the heart is highly aerobic and sustains Ͼ95% of its ATP output via oxidative breakdown of fuels. Oxidative phosphorylation of ATP occurs strictly in mitochondria, and the heart therefore maintains a high mitochondrial content. The energetic requirements of the heart increase dramatically at birth, and mitochondrial density accordingly increases sharply during the perinatal period. 1-3 Mitochondrial mass makes up fully one-third of the adult heart.The PPAR-␥ coactivator (PGC)-1 transcriptional coactivators have recently emerged as powerful regulators of mitochondrial biology in the heart, by broadly regulating gene expression from both nuclear and mitochondrial genomes. The expression of PGC-1␣ is repressed in numerous models of heart failure, and this has been implicated as an important contributor to the maladaptive energetic profile of failing hearts. This review focuses on the PGC-1s and their role in cardiac biology. PGC-1 CoactivatorsCoactivators are proteins that bind to nuclear receptors or other transcription factors and increase their ability to stimulate transcriptional activity. Most transcription factors likely require coactivators. A subset of coactivators are highly regulated and transduce extra-and intracellular cues to Original

A number of microRNAs (miRNAs, miRs) have been shown to play a role in skeletal muscle atrophy, but their role is not completely understood. Here we show that miR-29b promotes skeletal muscle atrophy in response to different atrophic stimuli in cells and in mouse models. miR-29b promotes atrophy of myotubes differentiated from C2C12 or primary myoblasts, and conversely, its inhibition attenuates atrophy induced by dexamethasone (Dex), TNF-α and H2O2 treatment. Targeting of IGF-1 and PI3K(p85α) by miR-29b is required for induction of muscle atrophy. In vivo, miR-29b overexpression is sufficient to promote muscle atrophy while inhibition of miR-29b attenuates atrophy induced by denervation and immobilization. These data suggest that miR-29b contributes to multiple types of muscle atrophy via targeting of IGF-1 and PI3K(p85α), and that suppression of miR-29b may represent a therapeutic approach for muscle atrophy induced by different stimuli.