Adult skeletal muscle peroxisome proliferator-activated receptor γ -related coactivator 1 is involved in maintaining mitochondrial content

The peroxisome proliferator-activated receptor γ coactivator-1 (PGC-1) family of transcriptional coactivators are regulators of mitochondrial oxidative capacity and content in skeletal muscle. Many of these conclusions are based primarily on gain-of-function studies using muscle-specific overexpression of PGC1s. We have previously reported that genetic deletion of both PGC-1α and PGC-1β in adult skeletal muscle resulted in a significant reduction in oxidative capacity with no effect on mitochondrial content. However, the contribution of PGC-1-related coactivator (PRC), the third PGC-1 family member, in regulating skeletal muscle mitochondria is unknown. Therefore, we generated an inducible skeletal muscle-specific PRC knockout mouse (iMS-PRC-KO) to assess the contribution of PRC in skeletal muscle mitochondrial function. We measured mRNA expression of electron transport chain (ETC) subunits as well as markers of mitochondrial content in the iMS-PRC-KO animals and observed an increase in ETC gene expression and mitochondrial content. Furthermore, the increase in ETC gene expression and mitochondrial content was associated with increased expression of PGC-1α and PGC-1β. We therefore generated an adult-inducible PGC-1 knockout mouse in which all PGC-1 family members are deleted (iMS-PGC-1TKO). The iMS-PGC-1TKO animals exhibited a reduction in ETC mRNA expression and mitochondrial content. These data suggest that in the absence of PRC alone, compensation occurs by increasing PGC-1α and PGC-1β to maintain mitochondrial content. Moreover, the removal of all three PGC-1s in skeletal muscle results in a reduction in both ETC mRNA expression and mitochondrial content. Taken together, these results suggest that PRC plays a role in maintaining baseline mitochondrial content in skeletal muscle.

Activation of Autophagic Flux Maintains Mitochondrial Homeostasis during Cardiac Ischemia/Reperfusion Injury

Reperfusion injury after extended ischemia accounts for approximately 50% of myocardial infarct size, and there is no standard therapy. HDAC inhibition reduces infarct size and enhances cardiomyocyte autophagy and PGC1α-mediated mitochondrial biogenesis when administered at the time of reperfusion. Furthermore, a specific autophagy-inducing peptide, Tat-Beclin 1 (TB), reduces infarct size when administered at the time of reperfusion. However, since SAHA affects multiple pathways in addition to inducing autophagy, whether autophagic flux induced by TB maintains mitochondrial homeostasis during ischemia/reperfusion (I/R) injury is unknown. We tested whether the augmentation of autophagic flux by TB has cardioprotection by preserving mitochondrial homeostasis both in vitro and in vivo. Wild-type mice were randomized into two groups: Tat-Scrambled (TS) peptide as the control and TB as the experimental group. Mice were subjected to I/R surgery (45 min coronary ligation, 24 h reperfusion). Autophagic flux, mitochondrial DNA (mtDNA), mitochondrial morphology, and mitochondrial dynamic genes were assayed. Cultured neonatal rat ventricular myocytes (NRVMs) were treated with a simulated I/R injury to verify cardiomyocyte specificity. The essential autophagy gene, ATG7, conditional cardiomyocyte-specific knockout (ATG7 cKO) mice, and isolated adult mouse ventricular myocytes (AMVMs) were used to evaluate the dependency of autophagy in adult cardiomyocytes. In NRVMs subjected to I/R, TB increased autophagic flux, mtDNA content, mitochondrial function, reduced reactive oxygen species (ROS), and mtDNA damage. Similarly, in the infarct border zone of the mouse heart, TB induced autophagy, increased mitochondrial size and mtDNA content, and promoted the expression of PGC1α and mitochondrial dynamic genes. Conversely, loss of ATG7 in AMVMs and in the myocardium of ATG7 cKO mice abolished the beneficial effects of TB on mitochondrial homeostasis. Thus, autophagic flux is a sufficient and essential process to mitigate myocardial reperfusion injury by maintaining mitochondrial homeostasis and partly by inducing PGC1α-mediated mitochondrial biogenesis.

Branched chain amino acids selectively promote cardiac growth at the end of the awake period

Essentially all biological processes fluctuate over the course of the day, manifesting as time-of-day-dependent variations with regards to the way in which organ systems respond to normal behaviors. For example, basic, translational, and epidemiologic studies indicate that temporal partitioning of metabolic processes governs the fate of dietary nutrients, in a manner in which concentrating caloric intake towards the end of the day is detrimental to both cardiometabolic and cardiovascular parameters. Despite appreciation that branched chain amino acids impact risk for obesity, diabetes mellitus, and heart failure, it is currently unknown whether the time-of-day at which dietary BCAAs are consumed influence cardiometabolic/cardiovascular outcomes. Here, we report that feeding mice a BCAA-enriched meal at the end of the active period (i.e., last 4 h of the dark phase) rapidly increases cardiac protein synthesis and mass, as well as cardiomyocyte size; consumption of the same meal at the beginning of the active period (i.e., first 4 h of the dark phase) is without effect. This was associated with a greater BCAA-induced activation of mTOR signaling in the heart at the end of the active period; pharmacological inhibition of mTOR (through rapamycin) blocked BCAA-induced augmentation of cardiac mass and cardiomyocyte size. Moreover, genetic disruption of the cardiomyocyte circadian clock abolished time-of-day-dependent fluctuations in BCAA-responsiveness. Finally, we report that repetitive consumption of BCAA-enriched meals at the end of the active period accelerated adverse cardiac remodeling and contractile dysfunction in mice subjected to transverse aortic constriction. Thus, our data demonstrate that the timing of BCAA consumption has significant implications for cardiac health and disease.

Angiotensin II-induced muscle atrophy via PPARγ suppression is mediated by miR-29b

The activation of the renin-angiotensin system (RAS) induced by increased angiotensin II (AngII) levels has been implicated in muscle atrophy, which is involved in the pathogenesis of congestive heart failure. Although peroxisome proliferator-activated receptor gamma (PPARγ) activation can suppress RAS, the exact role of PPARγ in AngII-induced muscle atrophy is unclear. Here we identified PPARγ as a negative regulator of miR-29b, a microRNA that is able to promote multiple types of muscle atrophy. Suppression of miR-29b could prevent AngII-induced muscle atrophy both in vitro and in vivo. IGF1, PI3K(p85α), and Yin Yang 1 (YY1) were identified as target genes of miR-29b, and overexpression of these targets could rescue AngII-induced muscle atrophy. Importantly, inhibition of PPARγ was sufficient to induce muscle atrophy, while PPARγ overexpression could attenuate that. These data indicate that the PPARγ/miR-29b axis mediates AngII-induced muscle atrophy, and increasing PPARγ or inhibiting miR-29b represents a promising approach to counteract AngII-induced muscle atrophy.

Inhibition of lncRNA MAAT Controls Multiple Types of Muscle Atrophy by cis- and trans-Regulatory Actions

Muscle atrophy is associated with negative outcomes in a variety of diseases. Identification of a common therapeutic target would address a significant unmet clinical need. Here, we identify a long non-coding RNA (lncRNA) (muscle-atrophy-associated transcript, lncMAAT) as a common regulator of skeletal muscle atrophy. lncMAAT is downregulated in multiple types of muscle-atrophy models both in vivo (denervation, Angiotensin II [AngII], fasting, immobilization, and aging-induced muscle atrophy) and in vitro (AngII, H₂O₂, and tumor necrosis factor alpha [TNF-α]-induced muscle atrophy). Gain- and loss-of-function analysis both in vitro and in vivo reveals that downregulation of lncMAAT is sufficient to induce muscle atrophy, while overexpression of lncMAAT can ameliorate multiple types of muscle atrophy. Mechanistically, lncMAAT negatively regulates the transcription of miR-29b through SOX6 by a trans-regulatory module and increases the expression of the neighboring gene Mbnl1 by a cis-regulatory module. Therefore, overexpression of lncMAAT may represent a promising therapy for muscle atrophy induced by different stimuli.

PRDM16 suppresses HIF-targeted gene expression in kidney cancer

Analysis of transcriptomic data demonstrates extensive epigenetic gene silencing of the transcription factor PRDM16 in renal cancer. We show that restoration of PRDM16 in RCC cells suppresses in vivo tumor growth. RNaseq analysis reveals that PRDM16 imparts a predominantly repressive effect on the RCC transcriptome including suppression of the gene encoding semaphorin 5B (SEMA5B). SEMA5B is a HIF target gene highly expressed in RCC that promotes in vivo tumor growth. Functional studies demonstrate that PRDM16's repressive properties, mediated by physical interaction with the transcriptional corepressors C-terminal binding proteins (CtBP1/2), are required for suppression of both SEMA5B expression and in vivo tumor growth. Finally, we show that reconstitution of RCC cells with a PRDM16 mutant unable to bind CtBPs nullifies PRDM16's effects on both SEMA5B repression and tumor growth suppression. Collectively, our data uncover a novel epigenetic basis by which HIF target gene expression is amplified in kidney cancer and a new mechanism by which PRDM16 exerts its tumor suppressive effects.

Genetic Deletion of Syndecan-4 Alters Body Composition, Metabolic Phenotypes, and the Function of Metabolic Tissues in Female Mice Fed A High-Fat Diet

Syndecans are transmembrane proteoglycans that, like integrins, bind to components of the extracellular matrix. Previously, we showed significant associations of genetic variants in the Syndecan-4 (SDC4) gene with intra-abdominal fat, fasting plasma glucose levels, and insulin sensitivity index in children, and with fasting serum triglyceride levels in healthy elderly subjects. An independent study also reported a correlation between SDC4 and the risk of coronary artery disease in middle-aged patients. Here, we investigated whether deletion of Sdc4 promotes metabolic derangements associated with diet-induced obesity by feeding homozygous male and female Sdc4-deficient (Sdc4^-/-) mice and their age-matched wild-type (WT) mice a high-fat diet (HFD). We found that WT and Sdc4^-/- mice gained similar weight. However, while no differences were observed in males, HFD-fed female Sdc4^-/- mice exhibited a higher percentage of body fat mass than controls and displayed increased levels of plasma total cholesterol, triglyceride, and glucose, as well as reduced whole-body insulin sensitivity. Additionally, they had an increased adipocyte size and macrophage infiltration in the visceral adipose tissue, and higher triglyceride and fatty acid synthase levels in the liver. Together with our previous human genetic findings, these results provide evidence of an evolutionarily conserved role of SDC4 in adiposity and its complications.

HDAC inhibition induces autophagy and mitochondrial biogenesis to maintain mitochondrial homeostasis during cardiac ischemia/reperfusion injury

AIMS

The FDA-approved histone deacetylase (HDAC) inhibitor, suberoylanilide hydroxamic acid (SAHA, Vorinostat) has been shown to induce cardiomyocyte autophagy and blunt ischemia/reperfusion (I/R) injury when administered at the time of reperfusion. However, the precise mechanisms underlying the cardioprotective activity of SAHA are unknown. Mitochondrial dysfunction and oxidative damage are major contributors to myocardial apoptosis during I/R injury. We hypothesize that SAHA protects the myocardium by maintaining mitochondrial homeostasis and reducing reactive oxygen species (ROS) production during I/R injury.

METHODS

Mouse and cultured cardiomyocytes (neonatal rat ventricular myocytes and human embryonic stem cell-derived cardiomyocytes) I/R models were used to investigate the effects of SAHA on mitochondria. ATG7 knockout mice, ATG7 knockdown by siRNA and PGC-1α knockdown by adenovirus in cardiomyocytes were used to test the dependency of autophagy and PGC-1α-mediated mitochondrial biogenesis respectively.

RESULTS

Intact and total mitochondrial DNA (mtDNA) content and mitochondrial mass were significantly increased in cardiomyocytes by SAHA pretreatment before simulated I/R. In vivo, I/R induced >50% loss of mtDNA content in the border zones of mouse hearts, but SAHA pretreatment and reperfusion treatment alone reverted mtDNA content and mitochondrial mass to control levels. Moreover, pretreatment of cardiomyocytes with SAHA resulted in a 4-fold decrease in I/R-induced loss of mitochondrial membrane potential and a 25%-40% reduction in cytosolic ROS levels. However, loss-of-function of ATG7 in cardiomyocytes or mouse myocardium abolished the protective effects of SAHA on ROS levels, mitochondrial membrane potential, mtDNA levels, and mitochondrial mass. Lastly, PGC-1α gene expression was induced by SAHA in NRVMs and mouse heart subjected to I/R, and loss of PGC-1α abrogated SAHA's mitochondrial protective effects in cardiomyocytes.

CONCLUSIONS

SAHA prevents I/R induced-mitochondrial dysfunction and loss, and reduces myocardial ROS production when given before or after the ischemia. The protective effects of SAHA on mitochondria are dependent on autophagy and PGC-1α-mediated mitochondrial biogenesis.

Adult skeletal muscle deletion of Mitofusin 1 and 2 impedes exercise performance and training capacity

Endurance exercise has been shown to be a positive regulator of skeletal muscle metabolic function. Changes in mitochondrial dynamics (fusion and fission) have been shown to influence mitochondrial oxidative capacity. We therefore tested whether genetic disruption of mitofusins (Mfns) affected exercise performance in adult skeletal muscle. We generated adult-inducible skeletal muscle-specific Mfn1 (iMS-Mfn1KO), Mfn2 (iMS-Mfn2KO), and Mfn1/2 (iMS-MfnDKO) knockout mice. We assessed exercise capacity by performing a treadmill time to exhaustion stress test before deletion and up to 8 wk after deletion. Analysis of either the iMS-Mfn1KO or the iMS-Mfn2KO did not reveal an effect on exercise capacity. However, analysis of iMS-MfnDKO animals revealed a progressive reduction in exercise performance. We measured individual electron transport chain (ETC) complex activity and observed a reduction in ETC activity in both the subsarcolemmal and intermyofibrillar mitochondrial fractions specifically for NADH dehydrogenase (complex I) and cytochrome- c oxidase (complex IV), which was associated with a decrease in ETC subunit expression for these complexes. We also tested whether voluntary exercise training would prevent the decrease in exercise capacity observed in iMS-MfnDKO animals ( n = 10/group). However, after 8 wk of training we did not observe any improvement in exercise capacity or ETC subunit parameters in iMS-MfnDKO animals. These data suggest that the decrease in exercise capacity observed in the iMS-MfnDKO animals is in part the result of impaired ETC subunit expression and ETC complex activity. Taken together, these results provide strong evidence that mitochondrial fusion in adult skeletal muscle is important for exercise performance. NEW & NOTEWORTHY This study is the first to utilize an adult-inducible skeletal muscle-specific knockout model for Mitofusin (Mfn)1 and Mfn2 to assess exercise capacity. Our findings reveal a progressive decrease in exercise performance with Mfn1 and Mfn2 deletion. The decrease in exercise capacity was accompanied by impaired oxidative phosphorylation specifically for complex I and complex IV. Furthermore, voluntary exercise training was unable to rescue the impairment, suggesting that normal fusion is essential for exercise-induced mitochondrial adaptations.

Abstract 4483: Functional implications of PRDM16 loss in kidney cancer

The most common genetic aberration associated with inherited or sporadic renal cell carcinoma (RCC) is the loss or nonfunctional mutations in the von Hippel-Lindau (VHL) tumor suppressor gene. The mutations lead to the stabilization of hypoxia inducible factor (HIF-1α and 2α), thereby promoting the expression of HIF target genes. HIF target genes are reported to induce tumor phenotypes by altering cellular metabolism and upregulating the expression of protumorigenic/angiogenic factors as well. We report here tissue microarray data and histology-based analyses demonstrating that the gene PRDM16 (PRD1-BF1-RIZ1 homologous domain containing 16) is silenced in many RCC tumors regardless of their VHL status. Bioinformatics analysis demonstrates a role for promoter methylation in silencing PRDM16. We investigated the role of PRDM16 in the context of VHL loss in kidney cancer. PRDM16 is known to regulate brown fat mitochondrial metabolism by inducing expressions of peroxisome proliferator-activated receptor-gamma coactivator-1alpha (PPARGC1A) and estrogen-related receptor-gamma (ESRRG). Altered cellular metabolism, in particular, decreased mitochondrial respiration is a hallmark of RCC, which is in attributed to VHL alterations. Analysis of TCGA data demonstrates that PRDM16 expression strongly correlates with PPARGC1A expression in RCC. Ectopic expression of PRDM16 in RCC cells can induce PPARGC-1α and ESRRG mRNA expression but fails to increase mitochondrial respiration. However, ectopic expression of PRDM16 in RCC cell lines can suppress both in vitro and in vivo tumor phenotypes. These data suggest that the tumor-suppressive activity of PRDM16 may be independent from its effects on mitochondrial metabolism. RNA-seq based analysis of a VHL mutated RCC line re-expressing PRDM16 demonstrates that a transcription suppressive role of PRDM16 predominates in RCC. PRDM16 suppresses genes involved in cell migration and proliferation. In particular, PRDM16 downregulates the expression of semaphorin 5B (SEMA5B). q-PCR analysis validates high-throughput data in a panel of RCC and embryonic kidney cell lines. SEMA5B knock down significantly decreases RCC proliferation supporting the protumorigenic function of SEMA5B in RCC. Given the central role of VHL loss in renal tumor initiation, we demonstrate that the VHL/HIF axis regulates the expression of SEMA5B in RCC. Collectively, these data suggest that transcription suppressive activity of PRDM16 and VHL controls expression of the protumorigenic factor SEMA5B and that epigenetic silencing of PRDM16 thus amplifies this consequence of VHL loss.

Citation Format: Anirban Kundu, Eun-Young Kho, Sandeep B. Shelar, Hyeyoung Nam, Garret Brinkley, Shimoga Darshan, Yawen Tang, Richard Kirkman, David K. Crossman, Sooryanarayana Varambally, Glenn C. Rowe, Shi Wei, Phillip Buckhaults, Sunil Sudarshan. Functional implications of PRDM16 loss in kidney cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4483.

PDK4 Inhibits Cardiac Pyruvate Oxidation in Late Pregnancy

RATIONALE

Pregnancy profoundly alters maternal physiology. The heart hypertrophies during pregnancy, but its metabolic adaptations, are not well understood.

OBJECTIVE

To determine the mechanisms underlying cardiac substrate use during pregnancy.

METHODS AND RESULTS

We use here ¹³C glucose, ¹³C lactate, and ¹³C fatty acid tracing analyses to show that hearts in late pregnant mice increase fatty acid uptake and oxidation into the tricarboxylic acid cycle, while reducing glucose and lactate oxidation. Mitochondrial quantity, morphology, and function do not seem altered. Insulin signaling seems intact, and the abundance and localization of the major fatty acid and glucose transporters, CD36 (cluster of differentiation 36) and GLUT4 (glucose transporter type 4), are also unchanged. Rather, we find that the pregnancy hormone progesterone induces PDK4 (pyruvate dehydrogenase kinase 4) in cardiomyocytes and that elevated PDK4 levels in late pregnancy lead to inhibition of PDH (pyruvate dehydrogenase) and pyruvate flux into the tricarboxylic acid cycle. Blocking PDK4 reverses the metabolic changes seen in hearts in late pregnancy.

CONCLUSIONS

Taken together, these data indicate that the hormonal environment of late pregnancy promotes metabolic remodeling in the heart at the level of PDH, rather than at the level of insulin signaling.

Genetic disruption of the cardiomyocyte circadian clock differentially influences insulin-mediated processes in the heart

Cardiovascular physiology exhibits time-of-day-dependent oscillations, which are mediated by both extrinsic (e.g., environment/behavior) and intrinsic (e.g., circadian clock) factors. Disruption of circadian rhythms negatively affects multiple cardiometabolic parameters. Recent studies suggest that the cardiomyocyte circadian clock directly modulates responsiveness of the heart to metabolic stimuli (e.g., fatty acids) and stresses (e.g., ischemia/reperfusion). The aim of this study was to determine whether genetic disruption of the cardiomyocyte circadian clock impacts insulin-regulated pathways in the heart. Genetic disruption of the circadian clock in cardiomyocyte-specific Bmal1 knockout (CBK) and cardiomyocyte-specific Clock mutant (CCM) mice altered expression (gene and protein) of multiple insulin signaling components in the heart, including p85α and Akt. Both baseline and insulin-mediated Akt activation was augmented in CBK and CCM hearts (relative to littermate controls). However, insulin-mediated glucose utilization (both oxidative and non-oxidative) and AS160 phosphorylation were attenuated in CBK hearts, potentially secondary to decreased Inhibitor-1. Consistent with increased Akt activation in CBK hearts, mTOR signaling was persistently increased, which was associated with attenuation of autophagy, augmented rates of protein synthesis, and hypertrophy. Importantly, pharmacological inhibition of mTOR (rapamycin; 10days) normalized cardiac size in CBK mice. These data suggest that disruption of cardiomyocyte circadian clock differentially influences insulin-regulated processes, and provide new insights into potential pathologic mediators following circadian disruption.

LDB1 Regulates Energy Homeostasis During Diet-Induced Obesity

The broadly expressed transcriptional coregulator LDB1 is essential for β-cell development and glucose homeostasis. However, it is unclear whether LDB1 has metabolic roles beyond the β-cell, especially under metabolic stress. Global Ldb1 deletion results in early embryonic lethality; thus, we used global heterozygous Ldb1+/- and inducible β-cell-specific Ldb1-deficient (Ldb1Δβ-cell) mice. We assessed glucose and insulin tolerance, body composition, feeding, and energy expenditure during high-fat diet exposure. Brown adipose tissue (BAT) biology was evaluated by thermogenic gene expression and LDB1 chromatin immunoprecipitation analysis. We found that partial loss of Ldb1 does not impair the maintenance of glucose homeostasis; rather, we observed improved insulin sensitivity in these mice. Partial loss of Ldb1 also uncovered defects in energy expenditure in lean and diet-induced obese (DIO) mice. This decreased energy expenditure during DIO was associated with significantly altered BAT gene expression, specifically Cidea, Elovl3, Cox7a1, and Dio2. Remarkably, the observed changes in energy balance during DIO were absent in Ldb1Δβ-cell mice, despite a similar reduction in plasma insulin, suggesting a role for LDB1 in BAT. Indeed, LDB1 is expressed in brown adipocytes and occupies a regulatory domain of Elovl3, a gene crucial to normal BAT function. We conclude that LDB1 regulates energy homeostasis, in part through transcriptional modulation of critical regulators in BAT function.

Transcriptome-wide co-expression analysis identifies LRRC2 as a novel mediator of mitochondrial and cardiac function

Mitochondrial dysfunction contributes to myriad monogenic and complex pathologies. To understand the underlying mechanisms, it is essential to define the full complement of proteins that modulate mitochondrial function. To identify such proteins, we performed a meta-analysis of publicly available gene expression data. Gene co-expression analysis of a large and heterogeneous compendium of microarray data nominated a sub-population of transcripts that whilst highly correlated with known mitochondrial protein-encoding transcripts (MPETs), are not themselves recognized as generating proteins either localized to the mitochondrion or pertinent to functions therein. To focus the analysis on a medically-important condition with a strong yet incompletely understood mitochondrial component, candidates were cross-referenced with an MPET-enriched module independently generated via genome-wide co-expression network analysis of a human heart failure gene expression dataset. The strongest uncharacterized candidate in the analysis was Leucine Rich Repeat Containing 2 (LRRC2). LRRC2 was found to be localized to the mitochondria in human cells and transcriptionally-regulated by the mitochondrial master regulator Pgc-1α. We report that Lrrc2 transcript abundance correlates with that of β-MHC, a canonical marker of cardiac hypertrophy in humans and experimentally demonstrated an elevation in Lrrc2 transcript in in vitro and in vivo rodent models of cardiac hypertrophy as well as in patients with dilated cardiomyopathy. RNAi-mediated Lrrc2 knockdown in a rat-derived cardiomyocyte cell line resulted in enhanced expression of canonical hypertrophic biomarkers as well as increased mitochondrial mass in the context of increased Pgc-1α expression. In conclusion, our meta-analysis represents a simple yet powerful springboard for the nomination of putative mitochondrially-pertinent proteins relevant to cardiac function and enabled the identification of LRRC2 as a novel mitochondrially-relevant protein and regulator of the hypertrophic response.

Development of dilated cardiomyopathy and impaired calcium homeostasis with cardiac-specific deletion of ESRRβ

Mechanisms underlying the development of idiopathic dilated cardiomyopathy (DCM) remain poorly understood. Using transcription factor expression profiling, we identified estrogen-related receptor-β (ESRRβ), a member of the nuclear receptor family of transcription factors, as highly expressed in murine hearts and other highly oxidative striated muscle beds. Mice bearing cardiac-specific deletion of ESRRβ (MHC-ERRB KO) develop DCM and sudden death at ~10 mo of age. Isolated adult cardiomyocytes from the MHC-ERRB KO mice showed an increase in calcium sensitivity and impaired cardiomyocyte contractility, which preceded echocardiographic cardiac remodeling and dysfunction by several months. Histological analyses of myocardial biopsies from patients with various cardiomyopathies revealed that ESRRβ protein is absent from the nucleus of cardiomyocytes from patients with DCM but not other forms of cardiomyopathy (ischemic, hypertrophic, and arrhythmogenic right ventricular cardiomyopathy). Taken together these observations suggest that ESRRβ is a critical component in the onset of DCM by affecting contractility and calcium balance.NEW & NOTEWORTHY Estrogen-related receptor-β (ESRRβ) is highly expressed in the heart and cardiac-specific deletion results in the development of a dilated cardiomyopathy (DCM). ESRRβ is mislocalized in human myocardium samples with DCM, suggesting a possible role for ESRRβ in the pathogenesis of DCM in humans.

Adult expression of PGC-1α and -1β in skeletal muscle is not required for endurance exercise-induced enhancement of exercise capacity

Exercise has been shown to be the best intervention in the treatment of many diseases. Many of the benefits of exercise are mediated by adaptions induced in skeletal muscle. The peroxisome proliferator-activated receptor gamma coactivator-1 (PGC-1) family of transcriptional coactivators has emerged as being key mediators of the exercise response and is considered to be essential for many of the adaptions seen in skeletal muscle. However, the contribution of the PGC-1s in skeletal muscle has been evaluated by the use of either whole body or congenital skeletal muscle-specific deletion. In these models, PGC-1s were never present, thereby opening the possibility to developmental compensation. Therefore, we generated an inducible muscle-specific deletion of PGC-1α and -1β (iMyo-PGC-1DKO), in which both PGC-1α and -β can be deleted specifically in adult skeletal muscle. These iMyo-PGC-1DKO animals were used to assess the role of both PGC-1α and -1β in adult skeletal muscle and their contribution to the exercise training response. Untrained iMyo-PGC-1DKO animals exhibited a time-dependent decrease in exercise performance 8 wk postdeletion, similar to what was observed in the congenital muscle-specific PGC-1DKOs. However, after 4 wk of voluntary training, the iMyo-PGC-1DKOs exhibited an increase in exercise performance with a similar adaptive response compared with control animals. This increase was associated with an increase in electron transport complex (ETC) expression and activity in the absence of PGC-1α and -1β expression. Taken together these data suggest that PGC-1α and -1β expression are not required for training-induced exercise performance, highlighting the contribution of PGC-1-independent mechanisms.

Heme oxygenase and carbon monoxide protect from muscle dystrophy

Background

Duchenne muscle dystrophy (DMD) is one of the most common lethal genetic diseases of children worldwide and is 100% fatal. Steroids, the only therapy currently available, are marred by poor efficacy and a high side-effect profile. New therapeutic approaches are urgently needed.

Methods

Here, we leverage PGC-1α, a powerful transcriptional coactivator known to protect against dystrophy in the mdx murine model of DMD, to search for novel mechanisms of protection against dystrophy.

Results

We identify heme oxygenase-1 (HO-1) as a potential novel target for the treatment of DMD. Expression of HO-1 is blunted in the muscles from the mdx murine model of DMD, and further reduction of HO-1 by genetic haploinsufficiency worsens muscle damage in mdx mice. Conversely, induction of HO-1 pharmacologically protects against muscle damage. Mechanistically, HO-1 degrades heme into biliverdin, releasing in the process ferrous iron and carbon monoxide (CO). We show that exposure to a safe low dose of CO protects against muscle damage in mdx mice, as does pharmacological treatment with CO-releasing molecules.

Conclusions

These data identify HO-1 and CO as novel therapeutic agents for the treatment of DMD. Safety profiles and clinical testing of inhaled CO already exist, underscoring the translational potential of these observations.

The tumor suppressor FLCN mediates an alternate mTOR pathway to regulate browning of adipose tissue

Noncanonical mechanistic target of rapamycin (mTOR) pathways remain poorly understood. Mutations in the tumor suppressor folliculin (FLCN) cause Birt-Hogg-Dubé syndrome, a hamartomatous disease marked by mitochondria-rich kidney tumors. FLCN functionally interacts with mTOR and is expressed in most tissues, but its role in fat has not been explored. We show here that FLCN regulates adipose tissue browning via mTOR and the transcription factor TFE3. Adipose-specific deletion of FLCN relieves mTOR-dependent cytoplasmic retention of TFE3, leading to direct induction of the PGC-1 transcriptional coactivators, drivers of mitochondrial biogenesis and the browning program. Cytoplasmic retention of TFE3 by mTOR is sensitive to ambient amino acids, is independent of growth factor and tuberous sclerosis complex (TSC) signaling, is driven by RagC/D, and is separable from canonical mTOR signaling to S6K. Codeletion of TFE3 in adipose-specific FLCN knockout animals rescues adipose tissue browning, as does codeletion of PGC-1β. Conversely, inducible expression of PGC-1β in white adipose tissue is sufficient to induce beige fat gene expression in vivo. These data thus unveil a novel FLCN-mTOR-TFE3-PGC-1β pathway-separate from the canonical TSC-mTOR-S6K pathway-that regulates browning of adipose tissue.

PGC-1α Induces Human RPE Oxidative Metabolism and Antioxidant Capacity

Purpose

Oxidative stress and metabolic dysregulation of the RPE have been implicated in AMD; however, the molecular regulation of RPE metabolism remains unclear. The transcriptional coactivator, peroxisome proliferator-activated receptor-gamma coactivator 1α (PGC-1α) is a powerful mediator of mitochondrial function. This study examines the ability of PGC-1α to regulate RPE metabolic program and oxidative stress response.

Methods

Primary human fetal RPE (hfRPE) and ARPE-19 were matured in vitro using standard culture conditions. Mitochondrial mass of RPE was measured using MitoTracker staining and citrate synthase activity. Expression of PGC-1 isoforms, RPE-specific genes, oxidative metabolism proteins, and antioxidant enzymes was analyzed by quantitative PCR and Western blot. Mitochondrial respiration and fatty-acid oxidation were monitored using the Seahorse extracellular flux analyzer. Expression of PGC-1α was increased using adenoviral delivery. ARPE-19 were exposed to hydrogen peroxide to induce oxidative stress. Reactive oxygen species were measured by CM-H2DCFDA fluorescence. Cell death was analyzed by LDH release.

Results

Maturation of ARPE-19 and hfRPE was associated with significant increase in mitochondrial mass, expression of oxidative phosphorylation (OXPHOS) genes, and PGC-1α gene expression. Overexpression of PGC-1α increased expression of OXPHOS and fatty-acid β-oxidation genes, ultimately leading to the potent induction of mitochondrial respiration and fatty-acid oxidation. PGC-1α gain of function also strongly induced numerous antioxidant genes and, importantly, protected RPE from oxidant-mediated cell death without altering RPE functions.

Conclusions

This study provides important insights into the metabolic changes associated with RPE functional maturation and identifies PGC-1α as a potent driver of RPE mitochondrial function and antioxidant capacity.

Biotinylation: a novel posttranslational modification linking cell autonomous circadian clocks with metabolism

Circadian clocks are critical modulators of metabolism. However, mechanistic links between cell autonomous clocks and metabolic processes remain largely unknown. Here, we report that expression of the biotin transporter slc5a6 gene is decreased in hearts of two distinct genetic mouse models of cardiomyocyte-specific circadian clock disruption [i.e., cardiomyocyte-specific CLOCK mutant (CCM) and cardiomyocyte-specific BMAL1 knockout (CBK) mice]. Biotinylation is an obligate posttranslational modification for five mammalian carboxylases: acetyl-CoA carboxylase α (ACCα), ACCβ, pyruvate carboxylase (PC), methylcrotonyl-CoA carboxylase (MCC), and propionyl-CoA carboxylase (PCC). We therefore hypothesized that the cardiomyocyte circadian clock impacts metabolism through biotinylation. Consistent with decreased slc5a6 expression, biotinylation of all carboxylases is significantly decreased (10-46%) in CCM and CBK hearts. In association with decreased biotinylated ACC, oleate oxidation rates are increased in both CCM and CBK hearts. Consistent with decreased biotinylated MCC, leucine oxidation rates are significantly decreased in both CCM and CBK hearts, whereas rates of protein synthesis are increased. Importantly, feeding CBK mice with a biotin-enriched diet for 6 wk normalized myocardial 1) ACC biotinylation and oleate oxidation rates; 2) PCC/MCC biotinylation (and partially restored leucine oxidation rates); and 3) net protein synthesis rates. Furthermore, data suggest that the RRAGD/mTOR/4E-BP1 signaling axis is chronically activated in CBK and CCM hearts. Finally we report that the hepatocyte circadian clock also regulates both slc5a6 expression and protein biotinylation in the liver. Collectively, these findings suggest that biotinylation is a novel mechanism by which cell autonomous circadian clocks influence metabolic pathways.

Exercise-induced mitochondrial p53 repairs mtDNA mutations in mutator mice

Background

Human genetic disorders and transgenic mouse models have shown that mitochondrial DNA (mtDNA) mutations and telomere dysfunction instigate the aging process. Epidemiologically, exercise is associated with greater life expectancy and reduced risk of chronic diseases. While the beneficial effects of exercise are well established, the molecular mechanisms instigating these observations remain unclear.

Results

Endurance exercise reduces mtDNA mutation burden, alleviates multisystem pathology, and increases lifespan of the mutator mice, with proofreading deficient mitochondrial polymerase gamma (POLG1). We report evidence for a POLG1-independent mtDNA repair pathway mediated by exercise, a surprising notion as POLG1 is canonically considered to be the sole mtDNA repair enzyme. Here, we show that the tumor suppressor protein p53 translocates to mitochondria and facilitates mtDNA mutation repair and mitochondrial biogenesis in response to endurance exercise. Indeed, in mutator mice with muscle-specific deletion of p53, exercise failed to prevent mtDNA mutations, induce mitochondrial biogenesis, preserve mitochondrial morphology, reverse sarcopenia, or mitigate premature mortality.

Conclusions

Our data establish a new role for p53 in exercise-mediated maintenance of the mtDNA genome and present mitochondrially targeted p53 as a novel therapeutic modality for diseases of mitochondrial etiology.

Electronic supplementary material

The online version of this article (doi:10.1186/s13395-016-0075-9) contains supplementary material, which is available to authorized users.

Hypoxic induction of vascular endothelial growth factor (VEGF) and angiogenesis in muscle by N terminus peroxisome proliferator-associated receptor gamma coactivator (NT-PGC)-1α

This article was withdrawn by the authors before final publication on January 15, 2014.

PGC-1α induces SPP1 to activate macrophages and orchestrate functional angiogenesis in skeletal muscle

RATIONALE

Mechanisms of angiogenesis in skeletal muscle remain poorly understood. Efforts to induce physiological angiogenesis hold promise for the treatment of diabetic microvascular disease and peripheral artery disease but are hindered by the complexity of physiological angiogenesis and by the poor angiogenic response of aged and patients with diabetes mellitus. To date, the best therapy for diabetic vascular disease remains exercise, often a challenging option for patients with leg pain. Peroxisome proliferation activator receptor-γ coactivator-1α (PGC-1α), a powerful regulator of metabolism, mediates exercise-induced angiogenesis in skeletal muscle.

OBJECTIVE

To test whether, and how, PGC-1α can induce functional angiogenesis in adult skeletal muscle.

METHODS AND RESULTS

Here, we show that muscle PGC-1α robustly induces functional angiogenesis in adult, aged, and diabetic mice. The process involves the orchestration of numerous cell types and leads to patent, nonleaky, properly organized, and functional nascent vessels. These findings contrast sharply with the disorganized vasculature elicited by induction of vascular endothelial growth factor alone. Bioinformatic analyses revealed that PGC-1α induces the secretion of secreted phosphoprotein 1 and the recruitment of macrophages. Secreted phosphoprotein 1 stimulates macrophages to secrete monocyte chemoattractant protein-1, which then activates adjacent endothelial cells, pericytes, and smooth muscle cells. In contrast, induction of PGC-1α in secreted phosphoprotein 1(-/-) mice leads to immature capillarization and blunted arteriolarization. Finally, adenoviral delivery of PGC-1α into skeletal muscle of either young or old and diabetic mice improved the recovery of blood flow in the murine hindlimb ischemia model of peripheral artery disease.

CONCLUSIONS

PGC-1α drives functional angiogenesis in skeletal muscle and likely recapitulates the complex physiological angiogenesis elicited by exercise.

Genetic models of PGC-1 and glucose metabolism and homeostasis

Type II diabetes and its complications are a tremendous health burden throughout the world. Our understanding of the changes that lead to glucose imbalance and insulin resistance and ultimately diabetes remain incompletely understood. Many signaling and transcriptional pathways have been identified as being important to maintain normal glucose balance, including that of the peroxisome proliferator activated receptor gamma coactivator (PGC-1) family. This family of transcriptional coactivators strongly regulates mitochondrial and metabolic biology in numerous organs. The use of genetic models of PGC-1s, including both tissue-specific overexpression and knock-out models, has helped to reveal the specific roles that these coactivators play in each tissue. This review will thus focus on the PGC-1s and recently developed genetic rodent models that have highlighted the importance of these molecules in maintaining normal glucose homeostasis.

Hypoxic induction of vascular endothelial growth factor (VEGF) and angiogenesis in muscle by truncated peroxisome proliferator-activated receptor γ coactivator (PGC)-1α

The transcriptional coactivator peroxisome proliferator-activator receptor γ coactivator (PGC)-1α is required for full hypoxic induction of vascular endothelial growth factor (VEGF) in skeletal muscle cells. Under normoxic conditions, PGC-1α also strongly induces mitochondrial biogenesis, but PGC-1α does not activate this program under hypoxic conditions. How this specificity is achieved is not known. We show here that hypoxia specifically induces alternatively spliced species encoding for truncated forms of PGC-1α: NT-PGC-1α and PGC-1α4. NT-PGC-1α strongly induces VEGF expression, whereas having little effect on mitochondrial genes. Conditioned medium from cells expressing NT-PGC-1α robustly induces endothelial migration and tube formation, hallmarks of angiogenesis. Transgenic expression of PGC-1α4 in skeletal muscle in mice induces angiogenesis in vivo. Finally, knockdown of these PGC-1α isoforms and hypoxia-inducible factor-1α (HIF-1α) abrogates the induction of VEGF in response to hypoxia. NT-PGC-1α and/or PGC-1α4 thus confer angiogenic specificity to the PGC-1α-mediated hypoxic response in skeletal muscle cells.

Post-natal induction of PGC-1α protects against severe muscle dystrophy independently of utrophin

Background

Duchenne muscle dystrophy (DMD) afflicts 1 million boys in the US and has few effective treatments. Constitutive transgenic expression of the transcriptional coactivator peroxisome proliferator-activated receptor gamma coactivator (PGC)-1α improves skeletal muscle function in the murine “mdx” model of DMD, but how this occurs, or whether it can occur post-natally, is not known. The leading mechanistic hypotheses for the benefits conferred by PGC-1α include the induction of utrophin, a dystrophin homolog, and/or induction and stabilization of the neuromuscular junction.

Methods

The effects of transgenic overexpression of PGC-1β, a homolog of PGC-1α in mdx mice was examined using different assays of skeletal muscle structure and function. To formally test the hypothesis that PGC-1α confers benefit in mdx mice by induction of utrophin and stabilization of neuromuscular junction, PGC-1α transgenic animals were crossed with the dystrophin utrophin double knock out (mdx/utrn^-/-) mice, a more severe dystrophic model. Finally, we also examined the effect of post-natal induction of skeletal muscle-specific PGC-1α overexpression on muscle structure and function in mdx mice.

Results

We show here that PGC-1β does not induce utrophin or other neuromuscular genes when transgenically expressed in mouse skeletal muscle. Surprisingly, however, PGC-1β transgenesis protects as efficaciously as PGC-1α against muscle degeneration in dystrophin-deficient (mdx) mice, suggesting that alternate mechanisms of protection exist. When PGC-1α is overexpressed in mdx/utrn^-/- mice, we find that PGC-1α dramatically ameliorates muscle damage even in the absence of utrophin. Finally, we also used inducible skeletal muscle-specific PGC-1α overexpression to show that PGC-1α can protect against dystrophy even if activated post-natally, a more plausible therapeutic option.

Conclusions

These data demonstrate that PGC-1α can improve muscle dystrophy post-natally, highlighting its therapeutic potential. The data also show that PGC-1α is equally protective in the more severely affected mdx/utrn^-/- mice, which more closely recapitulates the aggressive progression of muscle damage seen in DMD patients. The data also identify PGC-1β as a novel potential target, equally efficacious in protecting against muscle dystrophy. Finally, the data also show that PGC-1α and PGC-1β protect against dystrophy independently of utrophin or of induction of the neuromuscular junction, indicating the existence of other mechanisms.

Disconnecting mitochondrial content from respiratory chain capacity in PGC-1-deficient skeletal muscle

The transcriptional coactivators PGC-1α and PGC-1β are widely thought to be required for mitochondrial biogenesis and fiber typing in skeletal muscle. Here, we show that mice lacking both PGC-1s in myocytes do indeed have profoundly deficient mitochondrial respiration but, surprisingly, have preserved mitochondrial content, isolated muscle contraction capacity, fiber-type composition, in-cage ambulation, and voluntary running capacity. Most of these findings are recapitulated in cell culture and, thus, are cell autonomous. Functional electron microscopy reveals normal cristae density with decreased cytochrome oxidase activity. These data lead to the following surprising conclusions: (1) PGC-1s are in fact dispensable for baseline muscle function, mitochondrial content, and fiber typing, (2) endurance fatigue at low workloads is not limited by muscle mitochondrial capacity, and (3) mitochondrial content and cristae density can be dissociated from respiratory capacity.

Oncogenic BRAF regulates oxidative metabolism via PGC1α and MITF

Activating mutations in BRAF are the most common genetic alterations in melanoma. Inhibition of BRAF by small molecules 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.

PGC-1 coactivators regulate MITF and the tanning response

The production of pigment by melanocytes tans the skin and protects against skin cancers. UV-exposed keratinocytes secrete α-MSH, which then activates melanin formation in melanocytes by inducing the microphthalmia-associated transcription factor (MITF). We show that PPAR-γ coactivator (PGC)-1α and PGC-1β are critical components of this melanogenic system in melanocytes. α-MSH signaling strongly induces PGC-1α expression and stabilizes both PGC-1α and PGC-1β proteins. The PGC-1s in turn activate the MITF promoter, and their expression correlates strongly with that of MITF in human melanoma cell lines and biopsy specimens. Inhibition of PGC-1α and PGC-1β blocks the α-MSH-mediated induction of MITF and melanogenic genes. Conversely, overexpression of PGC-1α induces pigment formation in cell culture and transgenic animals. Finally, polymorphism studies reveal expression quantitative trait loci in the PGC-1β gene that correlate with tanning ability and protection from melanoma in humans. These data identify PGC-1 coactivators as regulators of human tanning.

Energy expenditure and bone formation share a common sensitivity to AP-1 transcription in the hypothalamus

The regulation of bone and fat homeostasis and its relationship to energy expenditure has recently been the focus of increased attention because of its potential relevance to osteoporosis, obesity, and diabetes. Although central effectors within the hypothalamus have been shown to contribute to the regulation of both energy balance and bone homeostasis, little is known of the underlying mechanisms, including the possible involvement of transcriptional factors within the hypothalamus. Transgenic mice overexpressing ΔFosB, a splice variant of the AP-1 transcription factor FosB with mixed agonist-antagonistic properties, have increased energy expenditure and bone mass. Because these mice express ΔFosB in bone, fat, and hypothalamus, we sought to determine 1) whether overexpression of ΔFosB within the hypothalamus was sufficient to regulate energy expenditure and whether it would also regulate bone mass, and 2) whether these effects were the result of antagonism to AP-1. Our results show that stereotactic injection of an adeno-associated virus vector to restrict overexpression of ΔFosB to the ventral hypothalamus of wild-type mice induced a profound increase in both energy expenditure and bone formation and bone mass. This effect was phenocopied, at an even stronger level, by overexpression of a dominant-negative DNJunD, a pure AP-1 antagonist. Taken together, these results suggest that downregulation of AP-1 activity in the hypothalamus profoundly increases energy expenditure and bone formation, leading to both a decrease in adipose mass and an increase in bone mass. These findings may have physiological implications because ΔFosB is expressed and regulated in the hypothalamus.

PGC-1α is dispensable for exercise-induced mitochondrial biogenesis in skeletal muscle

Exercise confers numerous health benefits, many of which are thought to stem from exercise-induced mitochondrial biogenesis (EIMB) in skeletal muscle. The transcriptional coactivator PGC-1α, a potent regulator of metabolism in numerous tissues, is widely believed to be required for EIMB. We show here that this is not the case. Mice engineered to lack PGC-1α specifically in skeletal muscle (Myo-PGC-1αKO mice) retained intact EIMB. The exercise capacity of these mice was comparable to littermate controls. Induction of metabolic genes after 2 weeks of in-cage voluntary wheel running was intact. Electron microscopy revealed no gross abnormalities in mitochondria, and the mitochondrial biogenic response to endurance exercise was as robust in Myo-PGC-1αKO mice as in wildtype mice. The induction of enzymatic activity of the electron transport chain by exercise was likewise unperturbed in Myo-PGC-1αKO mice. These data demonstrate that PGC-1α is dispensable for exercise-induced mitochondrial biogenesis in skeletal muscle, in sharp contrast to the prevalent assumption in the field.

Endonuclease G is a novel determinant of cardiac hypertrophy and mitochondrial function

Left ventricular mass (LVM) is a highly heritable trait and an independent risk factor for all-cause mortality. So far, genome-wide association studies have not identified the genetic factors that underlie LVM variation, and the regulatory mechanisms for blood-pressure-independent cardiac hypertrophy remain poorly understood. Unbiased systems genetics approaches in the rat now provide a powerful complementary tool to genome-wide association studies, and we applied integrative genomics to dissect a highly replicated, blood-pressure-independent LVM locus on rat chromosome 3p. Here we identified endonuclease G (Endog), which previously was implicated in apoptosis but not hypertrophy, as the gene at the locus, and we found a loss-of-function mutation in Endog that is associated with increased LVM and impaired cardiac function. Inhibition of Endog in cultured cardiomyocytes resulted in an increase in cell size and hypertrophic biomarkers in the absence of pro-hypertrophic stimulation. Genome-wide network analysis unexpectedly implicated ENDOG in fundamental mitochondrial processes that are unrelated to apoptosis. We showed direct regulation of ENDOG by ERR-α and PGC1α (which are master regulators of mitochondrial and cardiac function), interaction of ENDOG with the mitochondrial genome and ENDOG-mediated regulation of mitochondrial mass. At baseline, the Endog-deleted mouse heart had depleted mitochondria, mitochondrial dysfunction and elevated levels of reactive oxygen species, which were associated with enlarged and steatotic cardiomyocytes. Our study has further established the link between mitochondrial dysfunction, reactive oxygen species and heart disease and has uncovered a role for Endog in maladaptive cardiac hypertrophy.

PGC-1α promotes recovery after acute kidney injury during systemic inflammation in mice

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.

PGC-1β regulates angiogenesis in skeletal muscle

Aerobic metabolism requires oxygen and carbon sources brought to tissues via the vasculature. Metabolically active tissues such as skeletal muscle can regulate blood vessel density to match metabolic needs; however, the molecular cues that coordinate these processes remain poorly understood. Here we report that the transcriptional coactivator peroxisome proliferator-activated receptor-γ coactivator-1β (PGC-1β), a potent regulator of mitochondrial biology, induces angiogenesis in skeletal muscle. PGC-1β induces the expression of vascular endothelial growth factor (VEGF) in cell culture and in vivo. The induction of VEGF by PGC-1β requires coactivation of the orphan nuclear receptor estrogen-related receptor-α (ERRα) and is independent of the hypoxia-inducible factor (HIF) pathway. In coculture experiments, overexpression of PGC-1β in skeletal myotubes increases the migration of adjacent endothelial cells, and this depends on VEGF signaling. Transgenic expression of PGC-1β in skeletal myocytes dramatically increases muscular vessel density. Taken together, these data indicate that PGC-1β is a potent regulator of angiogenesis, thus providing a novel link between the regulations of oxidative metabolism and vascular density.

PGC-1 coactivators in cardiac development and disease

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-γ coactivator (PGC)-1 family of proteins plays a central role in these pathways. The mechanisms by which PGC-1 proteins regulate transcriptional networks and are regulated by physiological cues, as well as the roles they play in cardiac development and disease, are reviewed here.

Metabolic signatures of exercise in human plasma

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 >200 metabolites before and after exercise. We identified plasma indicators of glycogenolysis (glucose-6-phosphate), tricarboxylic acid cycle span 2 expansion (succinate, malate, and 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 and 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) up-regulated the expression of nur77, a transcriptional regulator of glucose utilization and lipid metabolism genes in skeletal muscle in vitro. Plasma metabolic profiles obtained during exercise provide signatures of exercise performance and cardiovascular disease susceptibility, in addition to highlighting molecular pathways that may modulate the salutary effects of exercise.

Zfp521 antagonizes Runx2, delays osteoblast differentiation in vitro, and promotes bone formation in vivo

Zfp521, a 30 C2H2 Kruppel-like zinc finger protein, is expressed at high levels at the periphery of early mesenchymal condensations prefiguring skeletal elements and in all developing bones in the perichondrium and periosteum, in osteoblast precursors and osteocytes, and in chondroblast precursors and growth plate prehypertrophic chondrocytes. Zfp521 expression in cultured mesenchymal cells is decreased by BMP-2 and increased by PTHrP, which promote and antagonize osteoblast differentiation, respectively. In vitro, Zfp521 overexpression reduces the expression of several downstream osteoblast marker genes and antagonizes osteoblast differentiation. Zfp521 binds Runx2 and represses its transcriptional activity, and Runx2 dose-dependently rescues Zfp521's inhibition of osteoblast differentiation. In contrast, osteocalcin promoter-targeted overexpression of Zfp521 in osteoblasts in vivo results in increased bone formation and bone mass. We propose that Zfp521 regulates the rate of osteoblast differentiation and bone formation during development and in the mature skeleton, in part by antagonizing Runx2.

Increased energy expenditure and insulin sensitivity in the high bone mass DeltaFosB transgenic mice

Obesity and osteoporosis are major health issues affecting millions of individuals. Transgenic mice overexpressing DeltaFosB, an activator protein-1 transcription factor, under the control of the enolase 2 (ENO2) promoter exhibit both an increase in bone density and a decrease in adipose mass. Here we demonstrate that DeltaFosB overexpression increases fatty-acid oxidation and energy expenditure, leading to a decrease in adipocyte size and adipose mass. In addition, the ENO2-DeltaFosB mice exhibit increased insulin sensitivity and glucose tolerance. Targeted overexpression of DeltaFosB in adipocytes using the adipocyte protein 2 promoter failed to induce changes in fat or in bone, showing that the effect on metabolic activity is not due to cell-autonomous effects of DeltaFosB within adipocytes. Detailed analysis of the ENO2-DeltaFosB mice demonstrated that energy expenditure was increased in muscle, independent of locomotor activity. These findings provide evidence that signaling downstream of DeltaFosB is a potential target for not only osteoporosis but also obesity and diabetes.

Doubly truncated FosB isoform (Delta2DeltaFosB) induces osteosclerosis in transgenic mice and modulates expression and phosphorylation of Smads in osteoblasts independent of intrinsic AP-1 activity

INTRODUCTION

Activator protein (AP)-1 family members play important roles in the development and maintenance of the adult skeleton. Transgenic mice that overexpress the naturally occurring DeltaFosB splice variant of FosB develop severe osteosclerosis. Translation of Deltafosb mRNA produces both DeltaFosB and a further truncated isoform (Delta2DeltaFosB) that lacks known transactivation domains but, like DeltaFosB, induces increased expression of osteoblast marker genes.

MATERIALS AND METHODS

To test Delta2DeltaFosB's ability to induce bone formation in vivo, we generated transgenic mice that overexpress only Delta2DeltaFosB using the enolase 2 (ENO2) promoter-driven bitransgenic Tet-Off system.

RESULTS

Despite Delta2DeltaFosB's failure to induce transcription of an AP-1 reporter gene, the transgenic mice exhibited both the bone and the fat phenotypes seen in the ENO2-DeltaFosB mice. Both DeltaFosB and Delta2DeltaFosB activated the BMP-responsive Xvent-luc reporter gene and increased Smad1 expression. Delta2DeltaFosB enhanced BMP-induced Smad1 phosphorylation and the translocation of phospho-Smad1 (pSmad1) to the nucleus more efficiently than DeltaFosB and showed a reduced induction of inhibitory Smad6 expression.

CONCLUSIONS

DeltaFosB's AP-1 transactivating function is not needed to induce increased bone formation, and Delta2DeltaFosB may act, at least in part, by increasing Smad1 expression, phosphorylation, and translocation to the nucleus.

Novel antineoplastic isochalcones inhibit the expression of cyclooxygenase 1,2 and EGF in human prostate cancer cell line LNCaP

Experiments were conducted to determine the effects of novel anti-neoplastic isochalcones (DJ compounds), on cyclooxyegenase 1 and 2 (COX-1 and COX-2) enzyme expression in androgen receptor dependent human prostate cancer cell line LNCaP. Results from Western blot analysis and cell flow cytometry showed that DJ52 and DJ53 decreased the steady state levels of COX-1 and COX-2 protein levels in a dose dependent manner. In addition, DJ52 and DJ53 decreased the levels of epidermal growth factor (EGF) in LNCaP cells. In this study, we report that novel isochalcones decreased COX-1, COX-2 and EGF levels as well as LNCaP cellular growth in a dose responsive manner. Our findings indicate that relative decreases in COX-1, COX-2 and EGF expressions might serve as indicators of tumor growth inhibition in prostate neoplasms.