Transcriptional Coactivator PGC-1α Research Articles

Molecular networks in skeletal muscle plasticity.

The skeletal muscle phenotype is subject to considerable malleability depending on use as well as internal and external cues. In humans, low-load endurance-type exercise leads to qualitative changes of muscle tissue characterized by an increase in structures supporting oxygen delivery and consumption, such as capillaries and mitochondria. High-load strength-type exercise leads to growth of muscle fibers dominated by an increase in contractile proteins. In endurance exercise, stress-induced signaling leads to transcriptional upregulation of genes, with Ca(2+) signaling and the energy status of the muscle cells sensed through AMPK being major input determinants. Several interrelated signaling pathways converge on the transcriptional co-activator PGC-1α, perceived to be the coordinator of much of the transcriptional and post-transcriptional processes. Strength training is dominated by a translational upregulation controlled by mTORC1. mTORC1 is mainly regulated by an insulin- and/or growth-factor-dependent signaling cascade as well as mechanical and nutritional cues. Muscle growth is further supported by DNA recruitment through activation and incorporation of satellite cells. In addition, there are several negative regulators of muscle mass. We currently have a good descriptive understanding of the molecular mechanisms controlling the muscle phenotype. The topology of signaling networks seems highly conserved among species, with the signaling outcome being dependent on the particular way individual species make use of the options offered by the multi-nodal networks. As a consequence, muscle structural and functional modifications can be achieved by an almost unlimited combination of inputs and downstream signaling events.

Abstract A52: Overcoming mitochondrial oxidative phosphorylation-mediated resistance to targeted therapies in melanoma

Abstract There is a critical need to understand and overcome resistance to targeted therapy in cancer. While FDA-approved BRAF and MEK inhibitors achieve clinical responses in the majority of metastatic melanoma patients with a BRAFV600 mutation, a significant proportion of patients have minimal responses, and virtually all patients develop acquired resistance in a short period of time. We and others have shown that increased oxidative phosphorylation (OxPhos), which is critically dependent on the transcriptional co-activator PGC1α, can mediate de novo resistance to MAPK pathway inhibitors in melanomas with BRAFV600 mutations. We have also demonstrated that elevated OxPhos (a) mediates de novo resistance to MEK inhibitors in melanoma cell lines without BRAFV600 mutations; (b) characterizes 30-50% of BRAFV600-mutant cell lines and patients with acquired resistance to BRAF +/- MEK inhibitors; and (c) predicts sensitivity to dual inhibition of mTORC1/2 in vitro and in vivo. Inhibition of mTORC1/2 downregulates both PGC1α and OxPhos through a novel mechanism involving the subcellular localization of the transcription factor MITF. To further exploit the therapeutic potential of targeting OxPhos, we have evaluated the molecular and anti-melanoma activities of a novel OxPhos inhibitor, IACS-10759, developed at M.D. Anderson Cancer Center. IACS-10759 potently inhibits the electron transport chain Complex I of mitochondrial OxPhos at low nanomolar concentrations. Additionally, this molecule has favorable safety and pharmacokinetic profile in animal models. Normal melanocytes, skin fibroblasts and most melanoma cell lines were not sensitive to micromolar doses of IACS-10759. However, a subset of de novo and acquired resistant melanomas with high OxPhos were sensitive to low nanomolar concentrations of IACS-10759 and underwent apoptotic cell death with treatment. An additional subset of melanomas were sensitive to the combination of IACS-10759 with MEK or BRAF inhibitors. Early functional studies revealed AMPK-activation associated effects as mediators of sensitivity, in addition to the inability of the cells to use alternate metabolic pathways for energy generation. Our findings demonstrate that a high OxPhos metabolic phenotype is associated with de novo and acquired resistance to MAPK pathway targeted therapies in melanoma, and support that targeting mTORC1/2 and the OxPhos complex 1 are promising strategies for counteracting this resistance. Citation Format: Vashisht Gopal Yennu-Nanda, Zeping Hu, Victoria M. Thiele, Tim Heffernan, Maria DiFrancesco, Joe Marszalek, Ralph Deberadinis, Michael A. Davies. Overcoming mitochondrial oxidative phosphorylation-mediated resistance to targeted therapies in melanoma. [abstract]. In: Proceedings of the AACR Special Conference: Metabolism and Cancer; Jun 7-10, 2015; Bellevue, WA. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(1_Suppl):Abstract nr A52.

SIRT1/PGC1α-Dependent Increase in Oxidative Phosphorylation Supports Chemotherapy Resistance of Colon Cancer.

Chemotherapy treatment of metastatic colon cancer ultimately fails due to development of drug resistance. Identification of chemotherapy-induced changes in tumor biology may provide insight into drug resistance mechanisms. We studied gene expression differences between groups of liver metastases that were exposed to preoperative chemotherapy or not. Multiple patient-derived colonosphere cultures were used to assess how chemotherapy alters energy metabolism by measuring mitochondrial biomass, oxygen consumption, and lactate production. Genetically manipulated colonosphere-initiated tumors were used to assess how altered energy metabolism affects chemotherapy efficacy. Gene ontology and pathway enrichment analysis revealed significant upregulation of genes involved in oxidative phosphorylation (OXPHOS) and mitochondrial biogenesis in metastases that were exposed to chemotherapy. This suggested chemotherapy induces a shift in tumor metabolism from glycolysis towards OXPHOS. Indeed, chemotreatment of patient-derived colonosphere cultures resulted in an increase of mitochondrial biomass, increased expression of respiratory chain enzymes, and higher rates of oxygen consumption. This was mediated by the histone deacetylase sirtuin-1 (SIRT1) and its substrate, the transcriptional coactivator PGC1α. Knockdown of SIRT1 or PGC1α prevented chemotherapy-induced OXPHOS and significantly sensitized patient-derived colonospheres as well as tumor xenografts to chemotherapy. Chemotherapy of colorectal tumors induces a SIRT1/PGC1α-dependent increase in OXPHOS that promotes tumor survival during treatment. This phenomenon is also observed in chemotherapy-exposed resected liver metastases, strongly suggesting that chemotherapy induces long-lasting changes in tumor metabolism that potentially interfere with drug efficacy. In conclusion, we propose a novel mechanism of chemotherapy resistance that may be clinically relevant and therapeutically exploitable.

Acute Exercise‐Induced Mitophagy is Mediated in Part by PGC‐1α

Chronic exercise results in systemic metabolic benefits in the major metabolic centers of the body. Skeletal muscle is a pillar of whole body metabolism and this tissue undergoes metabolic remodelling with repeated bouts of contractile activity. This is accomplished by increased mitochondrial turnover with a concurrent increase in both organelle biogenesis and removal. While biogenesis is largely orchestrated by the transcriptional co-activator PGC-1α, the regulation of mitochondrial degradation (i.e mitophagy) is less well established. Coincidentally, both mitochondrial biogenesis and autophagy are activated by an acute bout of exercise. However, the induction of mitophagy following exercise, and the interplay between autophagy and PGC-1α following acute exercise, have not been thoroughly examined. To address this, we subjected wild type (WT) and PGC-1α knockout animals (KO) to an acute bout of exhaustive exercise. Lack of PGC-1α resulted in a 40% drop in mitochondrial content and a 25% decline in running performance. KO mice also depicted a greater increase and a slower recovery of blood lactate following exercise, indicating metabolic distress. Indeed, exercise-induced activation of AMPK and p38 was greater in KO as compared to WT animals. Exercise also induced a 2-3-fold increase in gene transcripts of various mitochondrial (e.g COXIV, Tfam) and autophagy-related genes (e.g. p62, LC3) in WT animals only. Moreover, both autophagy and mitophagy flux were induced by exercise, but this increase was attenuated in KO animals. These results suggest that an acute bout of exercise is sufficient to induce mitochondrial turnover through increased biogenesis and degradation. Moreover, these two processes appear to be, at least in part, regulated by PGC-1α.

CRTC2 Contributes to PGC‐1α Expression in Skeletal Muscle Cells

Muscle wasting associated with chronic diseases has been linked to decreased expression of the transcriptional coactivator PGC‐1α. Overexpression of PGC‐1α can reduce FoxO‐mediated atrogene expression and counter muscle loss. Previous reports indicate that PGC‐1α transcription is regulated by CREB in a process that requires CREB‐regulated transcription coactivator (CRTC2). We recently found that CRTC2 protein is reduced in skeletal muscle of diabetic rats whereas CREB is highly phosphorylated (i.e., activated). Nuclear translocation of CRTC2 is promoted by dephosphorylation via calcineurin (CnA) while nuclear export occurs by phosphorylation via the salt‐inducible kinases (SIK). Our experiments tested the hypothesis that glucocorticoids decrease PGC‐1α expression, in part, by reducing CRTC2 levels in the nucleus. L6 myotubes were treated ± dexamethasone (Dex, 100nM) for 48hrs. Dex decreased PGC‐1α protein and nuclear level of CRTC2. It also decreased nuclear CnA and increased nuclear SIK, supporting the observed reduction in nuclear CRTC2 levels. Over‐expression of CRTC2 increased PGC‐1α protein and mRNA levels. To assess the role of CRTC2 on PGC‐1α transcription, muscle cells were transfected with a PGC‐1α luciferase reporter plasmid (PGC‐1α‐Luc). Over‐expression of CRTC2 increased PGC‐1α‐Luc activity. Dex decreased PGC‐1α‐Luc activity and deletion of the CRE binding site from PGC‐1α‐Luc (PGC‐1α‐DCRE‐Luc) attenuated the response. These data support the interaction of CRTC2 with phospho‐CREB as a mechanism for increasing PGC‐1α expression. Reduced nuclear CRTC2 may contribute to the loss of muscle mass arising during chronic diseases associated with elevated glucocorticoids.Supported by NIH RO1 DK95610, NIH T32 DK007656 and VA Merit X01BX001456

Fnip1 regulates skeletal muscle fiber type specification, fatigue resistance, and susceptibility to muscular dystrophy

Mammalian skeletal muscle is broadly characterized by the presence of two distinct categories of muscle fibers called type I "red" slow twitch and type II "white" fast twitch, which display marked differences in contraction strength, metabolic strategies, and susceptibility to fatigue. The relative representation of each fiber type can have major influences on susceptibility to obesity, diabetes, and muscular dystrophies. However, the molecular factors controlling fiber type specification remain incompletely defined. In this study, we describe the control of fiber type specification and susceptibility to metabolic disease by folliculin interacting protein-1 (Fnip1). Using Fnip1 null mice, we found that loss of Fnip1 increased the representation of type I fibers characterized by increased myoglobin, slow twitch markers [myosin heavy chain 7 (MyH7), succinate dehydrogenase, troponin I 1, troponin C1, troponin T1], capillary density, and mitochondria number. Cultured Fnip1-null muscle fibers had higher oxidative capacity, and isolated Fnip1-null skeletal muscles were more resistant to postcontraction fatigue relative to WT skeletal muscles. Biochemical analyses revealed increased activation of the metabolic sensor AMP kinase (AMPK), and increased expression of the AMPK-target and transcriptional coactivator PGC1α in Fnip1 null skeletal muscle. Genetic disruption of PGC1α rescued normal levels of type I fiber markers MyH7 and myoglobin in Fnip1-null mice. Remarkably, loss of Fnip1 profoundly mitigated muscle damage in a murine model of Duchenne muscular dystrophy. These results indicate that Fnip1 controls skeletal muscle fiber type specification and warrant further study to determine whether inhibition of Fnip1 has therapeutic potential in muscular dystrophy diseases.

Inhibition of mTORC1/2 Overcomes Resistance to MAPK Pathway Inhibitors Mediated by PGC1α and Oxidative Phosphorylation in Melanoma

Metabolic heterogeneity is a key factor in cancer pathogenesis. We found that a subset of BRAF- and NRAS-mutant human melanomas resistant to the MEK inhibitor selumetinib displayed increased oxidative phosphorylation (OxPhos) mediated by the transcriptional coactivator PGC1α. Notably, all selumetinib-resistant cells with elevated OxPhos could be resensitized by cotreatment with the mTORC1/2 inhibitor AZD8055, whereas this combination was ineffective in resistant cell lines with low OxPhos. In both BRAF- and NRAS-mutant melanoma cells, MEK inhibition increased MITF expression, which in turn elevated levels of PGC1α. In contrast, mTORC1/2 inhibition triggered cytoplasmic localization of MITF, decreasing PGC1α expression and inhibiting OxPhos. Analysis of tumor biopsies from patients with BRAF-mutant melanoma progressing on BRAF inhibitor ± MEK inhibitor revealed that PGC1α levels were elevated in approximately half of the resistant tumors. Overall, our findings highlight the significance of OxPhos in melanoma and suggest that combined targeting of the MAPK and mTORC pathways may offer an effective therapeutic strategy to treat melanomas with this metabolic phenotype.

Regulation of substrate oxidation preferences in muscle by the peptide hormone adropin.

Rigorous control of substrate oxidation by humoral factors is essential for maintaining metabolic homeostasis. During feeding and fasting cycles, carbohydrates and fatty acids are the two primary substrates in oxidative metabolism. Here, we report a novel role for the peptide hormone adropin in regulating substrate oxidation preferences. Plasma levels of adropin increase with feeding and decrease upon fasting. A comparison of whole-body substrate preference and skeletal muscle substrate oxidation in adropin knockout and transgenic mice suggests adropin promotes carbohydrate oxidation over fat oxidation. In muscle, adropin activates pyruvate dehydrogenase (PDH), which is rate limiting for glucose oxidation and suppresses carnitine palmitoyltransferase-1B (CPT-1B), a key enzyme in fatty acid oxidation. Adropin downregulates PDH kinase-4 (PDK4) that inhibits PDH, thereby increasing PDH activity. The molecular mechanisms of adropin’s effects involve acetylation (suggesting inhibition) of the transcriptional coactivator PGC-1α, downregulating expression of Cpt1b and Pdk4. Increased PGC-1α acetylation by adropin may be mediated by inhibiting Sirtuin-1 (SIRT1), a PGC-1α deacetylase. Altered SIRT1 and PGC-1α activity appear to mediate aspects of adropin’s metabolic actions in muscle. Similar outcomes were observed in fasted mice treated with synthetic adropin. Together, these results suggest a role for adropin in regulating muscle substrate preference under various nutritional states.

Cyclin D1 represses gluconeogenesis via inhibition of the transcriptional coactivator PGC1α.

Hepatic gluconeogenesis is crucial to maintain normal blood glucose during periods of nutrient deprivation. Gluconeogenesis is controlled at multiple levels by a variety of signal transduction and transcriptional pathways. However, dysregulation of these pathways leads to hyperglycemia and type 2 diabetes. While the effects of various signaling pathways on gluconeogenesis are well established, the downstream signaling events repressing gluconeogenic gene expression are not as well understood. The cell-cycle regulator cyclin D1 is expressed in the liver, despite the liver being a quiescent tissue. The most well-studied function of cyclin D1 is activation of cyclin-dependent kinase 4 (CDK4), promoting progression of the cell cycle. We show here a novel role for cyclin D1 as a regulator of gluconeogenic and oxidative phosphorylation (OxPhos) gene expression. In mice, fasting decreases liver cyclin D1 expression, while refeeding induces cyclin D1 expression. Inhibition of CDK4 enhances the gluconeogenic gene expression, whereas cyclin D1–mediated activation of CDK4 represses the gluconeogenic gene-expression program in vitro and in vivo. Importantly, we show that cyclin D1 represses gluconeogenesis and OxPhos in part via inhibition of peroxisome proliferator–activated receptor γ coactivator-1α (PGC1α) activity in a CDK4-dependent manner. Indeed, we demonstrate that PGC1α is novel cyclin D1/CDK4 substrate. These studies reveal a novel role for cyclin D1 on metabolism via PGC1α and reveal a potential link between cell-cycle regulation and metabolic control of glucose homeostasis.

Expression of adenine nucleotide translocase (ANT) isoform genes is controlled by PGC-1α through different transcription factors.

Adenine nucleotide translocase (ANT) isoforms are mitochondrial proteins encoded by nuclear DNA that catalyze the exchange of ATP generated in the mitochondria for ADP produced in the cytosol. The aim of this study was to determine the role of the transcriptional coactivator PGC-1α (peroxisome proliferator-activated receptor-γ [PPAR-γ] coactivator 1α), a master regulator of mitochondrial oxidative metabolism, in the regulation of the expression of ANT isoform genes and to identify the transcription factors involved. We found that PGC-1α overexpression induced the expression of all ANT human and mouse isoforms but to different degrees. The transcription factor ERRα was involved in PGC-1α-induced expression of all human ANT isoforms (hANT1-3) in HeLa cells as well as in the regulation of mouse isoforms (mANT1-2) in C2C12 myotubes and 3T3-L1 adipocytes, even though ANT isoforms have important physiological differences and are regulated in a tissue-specific manner. In addition to ERRα, PPARδ and mTOR pathways were involved in the induction of mANT1-2 by PGC-1α in C2C12 myotubes, while PPARγ was involved in PGC-1α-regulation of mANT1-2 in 3T3-L1 adipocytes. Furthermore, the regulation of mANT genes by PGC-1α was also observed in vivo in knockout mouse models lacking PGC-1α. In summary, our results show that the regulation of genes encoding ANT isoforms is controlled by PGC-1α through different transcription factors depending on cell type.

The tumor suppressor folliculin regulates AMPK-dependent metabolic transformation.

The Warburg effect is a tumorigenic metabolic adaptation process characterized by augmented aerobic glycolysis, which enhances cellular bioenergetics. In normal cells, energy homeostasis is controlled by AMPK; however, its role in cancer is not understood, as both AMPK-dependent tumor-promoting and -inhibiting functions were reported. Upon stress, energy levels are maintained by increased mitochondrial biogenesis and glycolysis, controlled by transcriptional coactivator PGC-1α and HIF, respectively. In normoxia, AMPK induces PGC-1α, but how HIF is activated is unclear. Germline mutations in the gene encoding the tumor suppressor folliculin (FLCN) lead to Birt-Hogg-Dubé (BHD) syndrome, which is associated with an increased cancer risk. FLCN was identified as an AMPK binding partner, and we evaluated its role with respect to AMPK-dependent energy functions. We revealed that loss of FLCN constitutively activates AMPK, resulting in PGC-1α-mediated mitochondrial biogenesis and increased ROS production. ROS induced HIF transcriptional activity and drove Warburg metabolic reprogramming, coupling AMPK-dependent mitochondrial biogenesis to HIF-dependent metabolic changes. This reprogramming stimulated cellular bioenergetics and conferred a HIF-dependent tumorigenic advantage in FLCN-negative cancer cells. Moreover, this pathway is conserved in a BHD-derived tumor. These results indicate that FLCN inhibits tumorigenesis by preventing AMPK-dependent HIF activation and the subsequent Warburg metabolic transformation.

Mice lacking the transcriptional coactivator PGC-1α exhibit alterations in inhibitory synaptic transmission in the motor cortex

Peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) is a transcriptional coactivator known to regulate gene programs in a cell-specific manner in energy-demanding tissues, and its dysfunction has been implicated in numerous neurological and psychiatric disorders. Previous work from the Cowell laboratory indicates that PGC-1α is concentrated in inhibitory interneurons and is required for the expression of the calcium buffer parvalbumin (PV) in the cortex; however, the impact of PGC-1α deficiency on inhibitory neurotransmission in the motor cortex is not known. Here, we show that mice lacking PGC-1α exhibit increased amplitudes and decreased frequency of spontaneous inhibitory postsynaptic currents in layer V pyramidal neurons. Upon repetitive train stimulation at the gamma frequency, decreased GABA release is observed. Furthermore, PV-positive interneurons in PGC-1α −/− mice display reductions in intrinsic excitability and excitatory input without changes in gross interneuron morphology. Taken together, these data show that PGC-1α is required for normal inhibitory neurotransmission and cortical PV-positive interneuron function. Given the pronounced motor dysfunction in PGC-1α −/− mice and the essential role of PV-positive interneurons in maintenance of cortical excitatory:inhibitory balance, it is possible that deficiencies in PGC-1α expression could contribute to cortical hyperexcitability and motor abnormalities in multiple neurological disorders.

Phosphodiesterase inhibition increases PGC‐1α in muscle cells (1102.32)

Muscle wasting associated with chronic diseases, such as type I diabetes (DM), can be countered by restoring the reduced expression of the transcriptional coactivator PGC‐1α. Previous reports indicate that PGC‐1α transcription can be regulated by CREB in a process that requires nuclear localization of CRTC (CREB‐regulated transcription coactivator). We recently found that CRTC protein is reduced in skeletal muscle of diabetic rats whereas CREB is highly phosphorylated (i.e., activated). Nuclear translocation of CTRC is promoted by dephosphorylation via calcineurin (CnA) whereas nuclear export occurs by phosphorylation via the salt‐inducible kinases (SIK). Inhibition of phosphodiesterases (PDE), which raise cyclic AMP (cAMP) levels, results in increased PGC‐1α mRNA expression. cAMP also inhibits SIK suggesting this pathway may contribute to CRTC localization and thus PGC‐1α activity. Our experiments tested the hypothesis that inhibition of PDE increases the amount of nuclear CRTC and PGC‐1α transcription. Myotubes were transfected with luciferase reporter plasmids (Luc) and treated with the general PDE inhibitor IBMX (250uM) for 6 hours. IBMX increased PGC‐1α‐Luc promoter activity as well as the transcriptional activity of CREB. Deletion of the CRE site in PGC‐1α‐Luc prevents the increase in luciferase activity suggesting IBMX increases PGC‐1α activity via CREB. In addition, protein analysis indicates IBMX increases the level of nuclear CRTC. Together, these data imply that raising cAMP levels by inhibiting PDEs results in increased PGC‐1α transcriptional activity by a mechanism involving CREB and its coactivator, CRTC.Grant Funding Source: Supported by NIH RO1 DK95610, NIH T32 DK007656 and VA Merit X01BX001456

Why Wounds Won’t Heal for Diabetics

Activation of Notch signaling by the transcriptional coactivator PGC-1α contributes to endothelial cell dysfunction in diabetes.

Endothelial PGC-1α Mediates Vascular Dysfunction in Diabetes

Endothelial dysfunction is a central hallmark of diabetes. The transcriptional coactivator PGC-1α is a powerful regulator of metabolism, but its role in endothelial cells remains poorly understood. We show here that endothelial PGC-1α expression is high in diabetic rodents and humans and that PGC-1α powerfully blocks endothelial migration in cell culture and vasculogenesis invivo. Mechanistically, PGC-1α induces Notch signaling, blunts activation of Rac/Akt/eNOS signaling, and renders endothelial cells unresponsive to established angiogenic factors. Transgenic overexpression of PGC-1α in the endothelium mimics multiple diabetic phenotypes, including aberrant re-endothelialization after carotid injury, blunted wound healing, and reduced blood flow recovery after hindlimb ischemia. Conversely, deletion of endothelial PGC-1α rescues the blunted wound healing and recovery from hindlimb ischemia seen in type 1 and type 2 diabetes. Endothelial PGC-1α thus potently inhibits endothelial function and angiogenesis, and induction of endothelial PGC-1α contributes to multiple aspects of vascular dysfunction in diabetes.

Orphan Nuclear Receptor Errγ Induces C-Reactive Protein Gene Expression through Induction of ER-Bound Bzip Transmembrane Transcription Factor CREBH

The orphan nuclear receptor estrogen-related receptor-γ (ERRγ) is a constitutively active transcription factor regulating genes involved in several important cellular processes, including hepatic glucose metabolism, alcohol metabolism, and the endoplasmic reticulum (ER) stress response. cAMP responsive element-binding protein H (CREBH) is an ER-bound bZIP family transcription factor that is activated upon ER stress and regulates genes encoding acute-phase proteins whose expression is increased in response to inflammation. Here, we report that ERRγ directly regulates CREBH gene expression in response to ER stress. ERRγ bound to the ERRγ response element (ERRE) in the CREBH promoter. Overexpression of ERRγ by adenovirus significantly increased expression of CREBH as well as C-reactive protein (CRP), whereas either knockdown of ERRγ or inhibition of ERRγ by ERRγ specific inverse agonist, GSK5182, substantially inhibited ER stress-mediated induction of CREBH and CRP. The transcriptional coactivator PGC1α was required for ERRγ mediated induction of the CREBH gene as demonstrated by the chromatin immunoprecipitation (ChIP) assay showing binding of both ERRγ and PGC1α on the CREBH promoter. The ChIP assay also revealed that histone H3 and H4 acetylation occurred at the ERRγ and PGC1α binding site. Moreover, chronic alcoholic hepatosteatosis, as well as the diabetic obese condition significantly increased CRP gene expression, and this increase was significantly attenuated by GSK5182 treatment. We suggest that orphan nuclear receptor ERRγ directly regulates the ER-bound transcription factor CREBH in response to ER stress and other metabolic conditions.

Axon degeneration and PGC1α-mediated protection in a vertebrate model of α-synuclein toxicity

α-synuclein (aSyn) expression is implicated in neurodegenerative processes, including Parkinson’s disease (PD) and dementia with Lewy bodies (DLB). In animal models of these diseases, axon pathology often precedes cell death, raising the question of whether aSyn has compartment-specific toxic effects that could require early and/or independent therapeutic intervention. The relevance of axonal pathology to degeneration can only be addressed through longitudinal, in vivo monitoring of different neuronal compartments. With current imaging methods, dopaminergic neurons do not readily lend themselves to such a task in any vertebrate system. We therefore expressed human wild-type aSyn in zebrafish peripheral sensory neurons, which project elaborate superficial axons that can be continuously imaged in vivo. Axonal outgrowth was normal in these neurons but, by 2 days post-fertilization (dpf), many aSyn-expressing axons became dystrophic, with focal varicosities or diffuse beading. Approximately 20% of aSyn-expressing cells died by 3 dpf. Time-lapse imaging revealed that focal axonal swelling, but not overt fragmentation, usually preceded cell death. Co-expressing aSyn with a mitochondrial reporter revealed deficits in mitochondrial transport and morphology even when axons appeared overtly normal. The axon-protective protein Wallerian degeneration slow (WldS) delayed axon degeneration but not cell death caused by aSyn. By contrast, the transcriptional coactivator PGC-1α, which has roles in the regulation of mitochondrial biogenesis and reactive-oxygen-species detoxification, abrogated aSyn toxicity in both the axon and the cell body. The rapid onset of axonal pathology in this system, and the relatively moderate degree of cell death, provide a new model for the study of aSyn toxicity and protection. Moreover, the accessibility of peripheral sensory axons will allow effects of aSyn to be studied in different neuronal compartments and might have utility in screening for novel disease-modifying compounds.

Transcriptional co-activator PGC-1α gene is associated with chicken skeletal muscle fiber types

The peroxisome proliferators-activated receptor-γ coactivator-1α (PGC-1α) is a candidate gene for meat quality traits because of its prominent role in muscle fiber type switching and determination. We investigated the effects of the PGC-1α gene on chicken skeletal muscle fiber type switching and on other meat quality traits. Single nucleotide polymorphisms were detected by PCR-SSCP and DNA sequencing, and then genotyping was performed by PCR-ligation detection reaction methods. Skeletal muscle fiber types, intramuscular fat content, shear forces, and water loss rate of the gastrocnemius lateralis muscle were measured in Qingyuan Partridge chickens and Recessive White chickens. Four SNPs, C171T in exon2, C384T in exon3, G646A in exon5, and A948G in exon8 were detected. Marker-trait association analysis indicated that G646A polymorphism was associated with skeletal myofiber type and that H1 (CCAA) was the most advantageous haplotype for skeletal myofiber type. We concluded that polymorphisms of the PGC-1α gene and their haplotypes are associated with chicken skeletal myofiber type traits.

Upregulation of PGC‐1α expression by Alzheimer's disease‐associated pathway: presenilin 1/amyloid precursor protein (APP)/intracellular domain of APP

Cleavage of amyloid precursor protein (APP) by β- and γ-secretase generates amyloid-β (Aβ) and APP intracellular domain (AICD) peptides. Presenilin (PS) 1 or 2 is the catalytic component of the γ-secretase complex. Mitochondrial dysfunction is an established phenomenon in Alzheimer’s disease (AD), but the causes and role of PS1, APP, and APP’s cleavage products in this process are largely unknown. We studied the effect of these AD-associated molecules on mitochondrial features. Using cells deficient in PSs expression, expressing human wild-type PS1, or PS1 familial AD (FAD) mutants, we found that PS1 affects mitochondrial energy metabolism (ATP levels and oxygen consumption) and expression of mitochondrial proteins. These effects were associated with enhanced expression of the mitochondrial master transcriptional coactivator PGC-1α and its target genes. Importantly, PS1-FAD mutations decreased PS1’s ability to enhance PGC-1α mRNA levels. Analyzing the effect of APP and its γ-secretase-derived cleavage products Aβ and AICD on PGC-1α expression showed that APP and AICD increase PGC-1α expression. Accordingly, PGC-1α mRNA levels in cells deficient in APP/APLP2 or expressing APP lacking its last 15 amino acids were lower than in control cells, and treatment with AICD, but not with Aβ, enhanced PGC-1α mRNA levels in these and PSs-deficient cells. In addition, knockdown of the AICD-binding partner Fe65 reduced PGC-1α mRNA levels. Importantly, APP/AICD increases PGC-1α expression also in the mice brain. Our results therefore suggest that APP processing regulates mitochondrial function and that impairments in the newly discovered PS1/APP/AICD/PGC-1α pathway may lead to mitochondrial dysfunction and neurodegeneration.

PGC-1α supports glutamine metabolism in breast cancer

BackgroundGlutamine metabolism is a central metabolic pathway in cancer. Recently, reductive carboxylation of glutamine for lipogenesis has been shown to constitute a key anabolic route in cancer cells. However, little is known regarding central regulators of the various glutamine metabolic pathways in cancer cells.MethodsThe impact of PGC-1α and ERRα on glutamine enzyme expression was assessed in ERBB2+ breast cancer cell lines with quantitative RT-PCR, chromatin immunoprecipitation, and immunoblotting experiments. Glutamine flux was quantified using 13C-labeled glutamine and GC/MS analyses. Functional assays for lipogenesis were performed using 14C-labeled glutamine. The expression of glutamine metabolism genes in breast cancer patients was determined by bioinformatics analyses using The Cancer Genome Atlas.ResultsWe show that the transcriptional coactivator PGC-1α, along with the transcription factor ERRα, is a positive regulator of the expression of glutamine metabolism genes in ERBB2+ breast cancer. Indeed, ERBB2+ breast cancer cells with increased expression of PGC-1α display elevated expression of glutamine metabolism genes. Furthermore, ERBB2+ breast cancer cells with reduced expression of PGC-1α or when treated with C29, a pharmacological inhibitor of ERRα, exhibit diminished expression of glutamine metabolism genes. The biological relevance of the control of glutamine metabolism genes by the PGC-1α/ERRα axis is demonstrated by consequent regulation of glutamine flux through the citric acid cycle. PGC-1α and ERRα regulate both the canonical citric acid cycle (forward) and the reductive carboxylation (reverse) fluxes; the latter can be used to support de novo lipogenesis reactions, most notably in hypoxic conditions. Importantly, murine and human ERBB2+ cells lines display a significant dependence on glutamine availability for their growth. Finally, we show that PGC-1α expression is positively correlated with that of the glutamine pathway in ERBB2+ breast cancer patients, and high expression of this pathway is associated with reduced patient survival.ConclusionsThese data reveal that the PGC-1α/ERRα axis is a central regulator of glutamine metabolism in ERBB2+ breast cancer. This novel regulatory link, as well as the marked reduction in patient survival time associated with increased glutamine pathway gene expression, suggests that targeting glutamine metabolism may have therapeutic potential in the treatment of ERBB2+ breast cancer.