The gene encoding the transcriptional coactivator peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) was targeted in mice. PGC-1α null (PGC-1α−/−) mice were viable. However, extensive phenotyping revealed multi-system abnormalities indicative of an abnormal energy metabolic phenotype. The postnatal growth of heart and slow-twitch skeletal muscle, organs with high mitochondrial energy demands, is blunted in PGC-1α−/− mice. With age, the PGC-1α−/− mice develop abnormally increased body fat, a phenotype that is more severe in females. Mitochondrial number and respiratory capacity is diminished in slow-twitch skeletal muscle of PGC-1α−/− mice, leading to reduced muscle performance and exercise capacity. PGC-1α−/− mice exhibit a modest diminution in cardiac function related largely to abnormal control of heart rate. The PGC-1α−/− mice were unable to maintain core body temperature following exposure to cold, consistent with an altered thermogenic response. Following short-term starvation, PGC-1α−/− mice develop hepatic steatosis due to a combination of reduced mitochondrial respiratory capacity and an increased expression of lipogenic genes. Surprisingly, PGC-1α−/− mice were less susceptible to diet-induced insulin resistance than wild-type controls. Lastly, vacuolar lesions were detected in the central nervous system of PGC-1α−/− mice. These results demonstrate that PGC-1α is necessary for appropriate adaptation to the metabolic and physiologic stressors of postnatal life.
Eliminating the activity of the gene PGC-1 α in mice reveals its role in post-natal metabolism and provides a link to obesity and some intriguing differences with another report of this knockout
Peroxisome proliferator-activated receptor gamma (PPARγ) coactivator 1α (PGC-1α) and PGC-1β have been shown to be intimately involved in the transcriptional regulation of cellular energy metabolism as well as other biological processes, but both coactivator proteins are expressed in many other tissues and organs in which their function is, in essence, unexplored. Here, we found that both PGC-1 proteins are abundantly expressed in maturing erythroid cells. PGC-1α and PGC-1β compound null mutant (Pgc-1c) animals express less β-like globin mRNAs throughout development; consequently, neonatal Pgc-1c mice exhibit growth retardation and profound anemia. Flow cytometry shows that the number of mature erythrocytes is markedly reduced in neonatal Pgc-1c pups, indicating that erythropoiesis is severely compromised. Furthermore, hematoxylin and eosin staining revealed necrotic cell death and cell loss in Pgc-1c livers and spleen. Chromatin immunoprecipitation studies revealed that both PGC-1α and -1β, as well as two nuclear receptors, TR2 and TR4, coordinately bind to the various globin gene promoters. In addition, PGC-1α and -1β can interact with TR4 to potentiate transcriptional activation. These data provide new insights into our understanding of globin gene regulation and raise the interesting possibility that the PGC-1 coactivators can interact with TR4 to elicit differential stage-specific effects on globin gene transcription.
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.
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.
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.
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.
PGC-1α; PGC-1β; mdx; Duchenne Muscle Dystrophy; Utrophin; Neuromuscular junction
The transcriptional coactivator peroxisome proliferator-activated receptor-gamma coactivator-1β (PGC-1β) has been implicated in important metabolic processes. A mouse lacking PGC-1β (PGC1βKO) was generated and phenotyped using physiological, molecular, and bioinformatic approaches. PGC1βKO mice are generally viable and metabolically healthy. Using systems biology, we identified a general defect in the expression of genes involved in mitochondrial function and, specifically, the electron transport chain. This defect correlated with reduced mitochondrial volume fraction in soleus muscle and heart, but not brown adipose tissue (BAT). Under ambient temperature conditions, PGC-1β ablation was partially compensated by up-regulation of PGC-1α in BAT and white adipose tissue (WAT) that lead to increased thermogenesis, reduced body weight, and reduced fat mass. Despite their decreased fat mass, PGC1βKO mice had hypertrophic adipocytes in WAT. The thermogenic role of PGC-1β was identified in thermoneutral and cold-adapted conditions by inadequate responses to norepinephrine injection. Furthermore, PGC1βKO hearts showed a blunted chronotropic response to dobutamine stimulation, and isolated soleus muscle fibres from PGC1βKO mice have impaired mitochondrial function. Lack of PGC-1β also impaired hepatic lipid metabolism in response to acute high fat dietary loads, resulting in hepatic steatosis and reduced lipoprotein-associated triglyceride and cholesterol content. Altogether, our data suggest that PGC-1β plays a general role in controlling basal mitochondrial function and also participates in tissue-specific adaptive responses during metabolic stress.
The authors conduct an in-depth analysis of a PGC-1β knockout mouse; these animals posses specific defects in basal mitochondrial function and adaptation to metabolic stress.
Hepatitis C virus (HCV) causes not only severe liver problems but also extrahepatic manifestations, such as insulin resistance (IR). Wild-type peroxisome proliferator-activated receptor gamma coactivator 1 alpha (WT-PGC-1α) is essential in hepatic gluconeogenesis and has recently been demonstrated to link HCV infection to hepatic insulin resistance (IR). A recent study has characterized a novel human liver-specific PGC-1α (L-PGC-1α) transcript, which is proposed to reflect human adaption to more complex pathways. However, the effect of HCV infection on L-PGC-1α expression and the mechanism by which HCV modulates WT-PGC-1α/L-PGC-1α remain unclear. In this study, we showed that HCV infection upregulated both WT-PGC-1α and L-PGC-1α, which further promoted HCV production. The upregulation of both PGC-1α isoforms depended on HCV RNA replication. By using promoter-luciferase reporters, kinase inhibitors, and dominant negative mutants, we further observed that the HCV-induced upregulation of WT-PGC-1α was mediated by the phosphorylation of cyclic AMP (cAMP)-responsive element-binding protein (CREB), whereas that of L-PGC-1α was mediated by CREB phosphorylation and forkhead box O1 dephosphorylation. Moreover, HCV infection induced endoplasmic reticulum (ER) stress, and pharmacological induction of ER stress upregulated WT-PGC-1α/L-PGC-1α and phosphorylated CREB. In contrast, pharmacological inhibition of HCV-induced ER stress impaired WT-PGC-1α/L-PGC-1α upregulation along with decreased phosphorylated CREB. The correlation of hepatic mPGC-1α with ER stress was further confirmed in mice. Overall, HCV infection upregulates both WT-PGC-1α and L-PGC-1α through an ER stress-mediated, phosphorylated CREB-dependent pathway, and both PGC-1α isoforms promote HCV production in turn.
IMPORTANCE HCV causes not only severe liver problems but also extrahepatic manifestations, such as insulin resistance (IR). As a key regulator in energy metabolism, wild-type PGC-1α (WT-PGC-1α), has recently been demonstrated to link HCV infection to hepatic IR. A recent study has characterized a novel human liver-specific PGC-1α (L-PGC-1α), which reflects human adaption to more complex pathways. However, the effect of HCV infection on L-PGC-1α expression and the mechanism by which HCV regulates WT-PGC-1α/L-PGC-1α remain unclear. In this study, we showed that HCV infection upregulated both WT-PGC-1α and L-PGC-1α, which further promoted HCV production. WT-PGC-1α upregulation was mediated by CREB phosphorylation, whereas L-PGC-1α upregulation was mediated by CREB phosphorylation and FoxO1 dephosphorylation. HCV-induced ER stress mediated WT-PGC-1α/L-PGC-1α upregulation and CREB phosphorylation. Overall, this study provides new insights into the mechanism by which HCV upregulates WT-PGC-1α/L-PGC-1α and highlights the novel intervention of HCV-ER stress-PGC-1α signaling for HCV therapy and HCV-induced IR therapy.
The transcriptional coactivator peroxisome proliferator activated receptor γ coactivator 1α (PGC-1α) is a master regulator of metabolism in peripheral tissues, and it has been proposed that PGC-1α plays a similar role in the brain. Recent evidence suggests that PGC-1α is concentrated in GABAergic interneurons, so we investigated whether male and female PGC-1α −/− mice exhibit abnormalities in interneuron gene expression and/or function. We found a striking reduction in the expression of the Ca2+ binding protein parvalbumin (PV), but not other GABAergic markers, throughout the cerebrum in PGC-1α +/− and −/− mice. Furthermore, PGC-1α overexpression in cell culture was sufficient to robustly induce PV expression. Consistent with a reduction in PV rather than a loss of PV-expressing interneurons, spontaneous synaptic inhibition was not altered in PGC-1α −/− mice. However, evoked synaptic responses displayed less paired pulse depression and dramatic facilitation in response to repetitive stimulation at the gamma frequency. PV transcript expression was also significantly reduced in retina and heart of PGC-1α −/− animals, suggesting that PGC-1α is required for proper expression of PV in multiple tissues. Together these findings indicate that PGC-1α is a novel regulator of interneuron gene expression and function and a potential therapeutic target for neurological disorders associated with PGC-1α dysregulation.
interneuron; early postnatal development; calcium; γ-aminobutyric acid; PPARGC1A
Atherosclerosis is a chronic inflammatory disease that evolves from the interaction of activated endothelial cells, macrophages, lymphocytes and modified lipoproteins (LDLs). In the last years many molecules with crucial metabolic functions have been shown to prevent important steps in the progression of atherogenesis, including peroxisome proliferator activated receptors (PPARs) and the class III histone deacetylase (HDAC) SIRT1. The PPARγ coactivator 1 alpha (Ppargc1a or PGC-1α) was identified as an important transcriptional cofactor of PPARγ and is activated by SIRT1. The aim of this study was to analyze total PGC-1α deficiency in an atherosclerotic mouse model.
To investigate if total PGC-1α deficiency affects atherosclerosis, we compared ApoE−/− PGC-1α−/− and ApoE−/− PGC-1α+/+ mice kept on a high cholesterol diet. Despite having more macrophages and a higher ICAM-1 expression in plaques, ApoE−/− PGC-1α−/− did not display more or larger atherosclerotic plaques than their ApoE−/− PGC-1α+/+ littermates. In line with the previously published phenotype of PGC-1α−/− mice, ApoE−/− PGC-1α−/− mice had marked reduced body, liver and epididymal white adipose tissue (WAT) weight. VLDL/LDL-cholesterol and triglyceride contents were also reduced. Aortic expression of PPARα and PPARγ, two crucial regulators for adipocyte differentitation and glucose and lipid metabolism, as well as the expression of some PPAR target genes was significantly reduced in ApoE−/− PGC-1α−/− mice. Importantly, the epididymal WAT and aortic expression of IL-18 and IL-18 plasma levels, a pro-atherosclerotic cytokine, was markedly reduced in ApoE−/− PGC-1α−/− mice.
ApoE−/− PGC-1α−/− mice, similar as PGC-1α−/− mice exhibit markedly reduced total body and visceral fat weight. Since inflammation of visceral fat is a crucial trigger of atherogenesis, decreased visceral fat in PGC-1α-deficient mice may explain why these mice do not develop enhanced atherosclerosis.
Sirtuin 3 (SIRT3) is one of the seven mammalian sirtuins, which are homologs of the yeast Sir2 gene. SIRT3 is the only sirtuin with a reported association with the human life span. Peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) plays important roles in adaptive thermogenesis, gluconeogenesis, mitochondrial biogenesis and respiration. PGC-1α induces several key reactive oxygen species (ROS)-detoxifying enzymes, but the molecular mechanism underlying this is not well understood.
Here we show that PGC-1α strongly stimulated mouse Sirt3 gene expression in muscle cells and hepatocytes. Knockdown of PGC-1α led to decreased Sirt3 gene expression. PGC-1α activated the mouse SIRT3 promoter, which was mediated by an estrogen-related receptor (ERR) binding element (ERRE) (−407/−399) mapped to the promoter region. Chromatin immunoprecipitation and electrophoretic mobility shift assays confirmed that ERRα bound to the identified ERRE and PGC-1α co-localized with ERRα in the mSirt3 promoter. Knockdown of ERRα reduced the induction of Sirt3 by PGC-1α in C2C12 myotubes. Furthermore, Sirt3 was essential for PGC-1α-dependent induction of ROS-detoxifying enzymes and several components of the respiratory chain, including glutathione peroxidase-1, superoxide dismutase 2, ATP synthase 5c, and cytochrome c. Overexpression of SIRT3 or PGC-1α in C2C12 myotubes decreased basal ROS level. In contrast, knockdown of mSIRT3 increased basal ROS level and blocked the inhibitory effect of PGC-1α on cellular ROS production. Finally, SIRT3 stimulated mitochondrial biogenesis, and SIRT3 knockdown decreased the stimulatory effect of PGC-1α on mitochondrial biogenesis in C2C12 myotubes.
Our results indicate that Sirt3 functions as a downstream target gene of PGC-1α and mediates the PGC-1α effects on cellular ROS production and mitochondrial biogenesis. Thus, SIRT3 integrates cellular energy metabolism and ROS generation. The elucidation of the molecular mechanisms of SIRT3 regulation and its physiological functions may provide a novel target for treating ROS-related disease.
Despite the role of aerobic glycolysis in cancer, recent studies highlight the importance of the mitochondria and biosynthetic pathways as well. PPARγ coactivator 1α (PGC1α) is a key transcriptional regulator of several metabolic pathways including oxidative metabolism and lipogenesis. Initial studies suggested that PGC1α expression is reduced in tumors compared to adjacent normal tissue. Paradoxically, other studies show that PGC1α is associated with cancer cell proliferation. Therefore the role of PGC1α in cancer and especially carcinogenesis is unclear. Using Pgc1α-/- and Pgc1α+/+ mice we show that loss of PGC1α protects mice from azoxymethane induced colon carcinogenesis. Similarly, diethylnitrosamine induced liver carcinogenesis is reduced in Pgc1α-/- mice compared to Pgc1α+/+ mice. Xenograft studies using gain and loss of PGC1α expression demonstrated that PGC1α also promotes tumor growth. Interestingly, while PGC1α induced oxidative phosphorylation and TCA cycle gene expression, we also observed an increase in the expression of two genes required for de novo fatty acid synthesis, ACC and FASN. In addition, SLC25A1 and ACLY, which are required for the conversion of glucose in to acetyl CoA for fatty acid synthesis, were also increased by PGC1α, thus linking the oxidative and lipogenic functions of PGC1α. Indeed, using 13C stable isotope tracer analysis we show that PGC1α increased de novo lipogenesis. Importantly, inhibition of fatty acid synthesis blunted these progrowth effects of PGC1α. In conclusion, these studies show for the first time that loss of PGC1α protects against carcinogenesis and that PGC1α coordinately regulates mitochondrial and fatty acid metabolism to promote tumor growth.
Cancer metabolism; Warburg Effect; oxidative metabolism; lipogenesis; transcriptional regulation
Reduced peroxisome proliferator-activated receptor-γ coactivator 1α (PGC1α) gene expression has been observed in striatal cell lines, transgenic mouse models of Huntington's disease (HD), and brain tissue from HD patients. As this protein is a key transcription regulator of the expression of many mitochondrial proteins, these observations strongly support the role of aberrant mitochondrial function in the pathogenesis of HD. The PGC1α protein undergoes posttranslational modifications that affect its transcriptional activity. The N-truncated splice variant of PGC1α (NT-PGC1α) is produced in tissues, but the role of truncated splice variants of PGC1α in HD and in the regulation of mitochondrial gene expression has not been elucidated.
To examine the expression and modulation of expression of NT-PGC1α levels in HD.
Methods and Results
We found that the NT-PGC1α protein, a splice variant of ∼38 kDa, but not full-length PGC1α is severely and consistently altered in human HD brain, human HD myoblasts, mouse HD models, and HD striatal cells. NT-PGC1α levels were significantly upregulated in HD cells and mouse brown fat by physiologically relevant stimuli that are known to upregulate PGC1α gene expression. This resulted in an increase in mitochondrial gene expression and cytochrome c content.
Our data suggest that NT-PGC1α is an important component of the PGC1α transcriptional network, which plays a significant role in the pathogenesis of HD.
Copyright © 2011 S. Karger AG, Basel
Neurodegeneration; PGC1α; Mitochondrial gene expression; Alternative splicing; Huntington's disease; Striatal neurons
Cardiac mitochondrial function is altered in a variety of inherited and acquired cardiovascular diseases. Recent studies have identified the transcriptional coactivator peroxisome proliferator–activated receptor γ coactivator-1 (PGC-1) as a regulator of mitochondrial function in tissues specialized for thermogenesis, such as brown adipose. We sought to determine whether PGC-1 controlled mitochondrial biogenesis and energy-producing capacity in the heart, a tissue specialized for high-capacity ATP production. We found that PGC-1 gene expression is induced in the mouse heart after birth and in response to short-term fasting, conditions known to increase cardiac mitochondrial energy production. Forced expression of PGC-1 in cardiac myocytes in culture induced the expression of nuclear and mitochondrial genes involved in multiple mitochondrial energy-transduction/energy-production pathways, increased cellular mitochondrial number, and stimulated coupled respiration. Cardiac-specific overexpression of PGC-1 in transgenic mice resulted in uncontrolled mitochondrial proliferation in cardiac myocytes leading to loss of sarcomeric structure and a dilated cardiomyopathy. These results identify PGC-1 as a critical regulatory molecule in the control of cardiac mitochondrial number and function in response to energy demands.
Peroxisome proliferator-activated receptor-γ coactivators PGC1α and PGC1β modulate mitochondrial biogenesis and energy homeostasis. The function of these transcriptional coactivators is impaired in obesity, insulin resistance, and type 2 diabetes. We searched for transcriptomic, lipidomic, and electrophysiological alterations in PGC1β−/− hearts potentially associated with increased arrhythmic risk in metabolic diseases.
Methods and results
Microarray analysis in mouse PGC1β−/− hearts confirmed down-regulation of genes related to oxidative phosphorylation and the electron transport chain and up-regulation of hypertrophy- and hypoxia-related genes. Lipidomic analysis showed increased levels of the pro-arrhythmic and pro-inflammatory lipid, lysophosphatidylcholine. PGC1β−/− mouse electrocardiograms showed irregular heartbeats and an increased incidence of polymorphic ventricular tachycardia following isoprenaline infusion. Langendorff-perfused PGC1β−/− hearts showed action potential alternans, early after-depolarizations, and ventricular tachycardia. PGC1β−/− ventricular myocytes showed oscillatory resting potentials, action potentials with early and delayed after-depolarizations, and burst firing during sustained current injection. They showed abnormal diastolic Ca2+ transients, whose amplitude and frequency were increased by isoprenaline, and Ca2+ currents with negatively shifted inactivation characteristics, with increased window currents despite unaltered levels of CACNA1C RNA transcripts. Inwardly and outward rectifying K+ currents were all increased. Quantitiative RT-PCR demonstrated increased SCN5A, KCNA5, RYR2, and Ca2+-calmodulin dependent protein kinase II expression.
PGC1β−/− hearts showed a lysophospholipid-induced cardiac lipotoxicity and impaired bioenergetics accompanied by an ion channel remodelling and altered Ca2+ homeostasis, converging to produce a ventricular arrhythmic phenotype particularly during adrenergic stress. This could contribute to the increased cardiac mortality associated with both metabolic and cardiac disease attributable to lysophospholipid accumulation.
Mitochondria; Cardiac arrhythmia; Peroxisome proliferator-activated receptor-γ coactivator 1β; Metabolic disease; Lysophosphatidylcholine
Telomere dysfunction activates p53-mediated cellular growth arrest, senescence and apoptosis to drive progressive atrophy and functional decline in high-turnover tissues. The broader adverse impact of telomere dysfunction across many tissues including more quiescent systems prompted transcriptomic network analyses to identify common mechanisms operative in haematopoietic stem cells, heart and liver. These unbiased studies revealed profound repression of peroxisome proliferator-activated receptor gamma, coactivator 1 alpha and beta (PGC-1α and PGC-1β, also known as Ppargc1a and Ppargc1b, respectively) and the downstream network in mice null for either telomerase reverse transcriptase (Tert) or telomerase RNA component (Terc) genes. Consistent with PGCs as master regulators of mitochondrial physiology and metabolism, telomere dysfunction is associated with impaired mitochondrial biogenesis and function, decreased gluconeogenesis, cardiomyopathy, and increased reactive oxygen species. In the setting of telomere dysfunction, enforced Tert or PGC-1α expression or germline deletion of p53 (also known as Trp53) substantially restores PGC network expression, mitochondrial respiration, cardiac function and gluconeogenesis. We demonstrate that telomere dysfunction activates p53 which in turn binds and represses PGC-1α and PGC-1β promoters, thereby forging a direct link between telomere and mitochondrial biology. We propose that this telomere–p53–PGC axis contributes to organ and metabolic failure and to diminishing organismal fitness in the setting of telomere dysfunction.
Rheumatoid arthritis (RA) is a chronic inflammatory disease leading to joint destruction and disability. Peroxisome proliferator-activated receptor-gamma coactivator-1beta (PGC-1β) is a transcriptional coactivator that plays important roles in regulating multiple aspects of energy metabolism and cytokine signaling pathways. PGC-1β overexpression leads to the attenuation of macrophage-mediated inflammation. In this study, we aimed to determine the expression of PGC-1β in RA synovium and fibroblast-like synoviocytes (FLS), and explore the mechanisms of PGC-1β on both the proinflammatory effects and apoptosis in RA-FLS.
Synovium was obtained from 31 patients with active RA, as well as 13 osteoarthritis (OA) and 10 orthopedic arthropathies (Orth.A) as “less inflamed” disease controls. FLS were then isolated and cultured. Synovial PGC-1β expression was determined by immunohistochemistry staining, while FLS PGC-1β expression was detected by immunofluorescence staining, quantitative real-time PCR (qPCR) assay and western blot. PGC-1β was depleted by lentivirus sh-RNA, and up-regulated by pcDNA3.1- PGC-1β. The expression of proinflammatory cytokines, matrix metalloproteinases and receptor activator of nuclear factor-kappaB ligand was analyzed by qPCR, cytometric bead array and western blot. The expression of mitogen-activated protein kinases and nuclear factor-kappaB (NF-κB) was determined by qPCR and western blot. Besides, cell apoptosis was examined using flow cytometry. The interaction between PGC-1β and NF-κB was performed by dual-luciferase reporter gene assays.
(A) Synovial PGC-1β was over-expressed in RA patients compared with OA or Orth.A patients. (B) PGC-1β expression significantly increased in RA-FLS compared with OA-FLS. (C) PGC-1β mediated the expression of proinflammatory cytokines and apoptosis through extracellular signal-regulated kinase (ERK), p38 and NF-κB in RA-FLS. (D) PGC-1β mediated NF-κB transcription in RA-FLS, but did not affect ERK and p38.
The results indicate that PGC-1β may play important roles in the proinflammatory effects and apoptosis of RA-FLS.
We previously demonstrated a cardiac mitochondrial biogenic response in insulin resistant mice that requires the nuclear receptor transcription factor PPARα. We hypothesized that the PPARα coactivator peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1α) is necessary for mitochondrial biogenesis in insulin resistant hearts and that this response was adaptive. Mitochondrial phenotype was assessed in insulin resistant mouse models in wild-type (WT) versus PGC-1α deficient (PGC-1α−/−) backgrounds. Both high fat-fed (HFD) WT and 6 week-old Ob/Ob animals exhibited a significant increase in myocardial mitochondrial volume density compared to standard chow fed or WT controls. In contrast, HFD PGC-1α−/− and Ob/Ob-PGC-1α−/− hearts lacked a mitochondrial biogenic response. PGC-1α gene expression was increased in 6 week-old Ob/Ob animals, followed by a decline in 8 week-old Ob/Ob animals with more severe glucose intolerance. Mitochondrial respiratory function was increased in 6 week-old Ob/Ob animals, but not in Ob/Ob-PGC-1α−/− mice and not in 8 week-old Ob/Ob animals, suggesting a loss of the early adaptive response, consistent with the loss of PGC-1α upregulation. Animals that were deficient for PGC-1α and heterozygous for the related coactivator PGC-1β (PGC-1α−/−β+/−) were bred to the Ob/Ob mice. Ob/Ob-PGC-1α−/−β+/− hearts exhibited dramatically reduced mitochondrial respiratory capacity. Finally, the mitochondrial biogenic response was triggered in H9C2 myotubes by exposure to oleate, an effect that was blunted with shRNA-mediated PGC-1 “knockdown”. We conclude that PGC-1 signaling is important for the adaptive cardiac mitochondrial biogenic response that occurs during the early stages of insulin resistance. This response occurs in a cell autonomous manner and likely involves exposure to high levels of free fatty acids.
diabetes; insulin resistance; cardiomyopathy; mitochondria; heart failure; metabolism
As a persistent pump, the mammalian heart demands a high-capacity mitochondrial system. Significant progress has been made in delineating the gene regulatory networks that control mitochondrial biogenesis and function in striated muscle. The PPARγ coactivator-1 (PGC-1) coactivators serve as inducible boosters of downstream transcription factors that control the expression of genes involved in mitochondrial energy transduction, ATP synthesis, and biogenesis. PGC-1 gain-of-function and loss-of-function studies targeting two PGC-1 family members, PGC-1α and PGC-1β, have provided solid evidence that these factors are both necessary and sufficient for perinatal mitochondrial biogenesis and maintenance of high-capacity mitochondrial function in postnatal heart. In humans, during the development of heart failure owing to hypertension or obesity-related diabetes, the activity of the PGC-1 coactivators, and several downstream target transcription factors, is altered. Gene targeting studies in mice have demonstrated that loss of PGC-1α and PGC-1β in heart leads to heart failure. Interestingly, the pattern of dysregulation within the PGC-1 transcriptional regulatory circuit distinguishes the heart disease caused by hypertension from that caused by diabetes. This transcriptional regulatory cascade and downstream metabolic pathways should be considered as targets for novel etiology-specific therapeutics aimed at the early stages of heart failure.
Accumulating evidence implicates the transcriptional coactivator peroxisome proliferator activated receptor γ coactivator 1α (PGC-1α) in the pathophysiology of Huntington Disease (HD). Adult PGC-1α −/− mice exhibit striatal neurodegeneration, and reductions in the expression of PGC-1α have been observed in striatum and muscle of HD patients as well as in animal models of the disease. However, it is unknown whether decreased expression of PGC-1α alone is sufficient to lead to the motor phenotype and striatal pathology characteristic of HD. For the first time, we show that young PGC-1α −/− mice exhibit severe rotarod deficits, decreased rearing behavior, and increased occurrence of tremor in addition to the previously described hindlimb clasping. Motor impairment and striatal vacuolation are apparent in PGC-1α −/− mice by four weeks of age and do not improve or decline by twelve weeks of age. The behavioral and pathological phenotype of PGC-1α −/− mice can be completely recapitulated by conditional nervous system deletion of PGC-1α, indicating that peripheral effects are not responsible for the observed abnormalities. Evaluation of the transcriptional profile of PGC-1α −/− striatal neuron populations and comparison to striatal neuron profiles of R6/2 HD mice revealed that PGC-1α deficiency alone is not sufficient to cause the transcriptional changes observed in this HD mouse model. In contrast to R6/2 HD mice, PGC-1α −/− mice show increases in the expression of medium spiny neuron (MSN) markers with age, suggesting that the observed behavioral and structural abnormalities are not primarily due to MSN loss, the defining pathological feature of HD. These results indicate that PGC-1α is required for the proper development of motor circuitry and transcriptional homeostasis in MSNs and that developmental disruption of PGC-1α leads to long-term alterations in motor functioning.
We previously found that estrogen exerts a novel protective effect on mitochondria in brain vasculature. Here we demonstrate in rat cerebral blood vessels that 17β-estradiol (estrogen), both in vivo and ex vivo, affects key transcriptional coactivators responsible for mitochondrial regulation. Treatment of ovariectomized rats with estrogen in vivo lowered mRNA levels of peroxisome proliferator-activated receptor-γ coactivator-1 alpha (PGC-1α) but increased levels of the other PGC-1 isoforms: PGC-1β and PGC-1 related coactivator (PRC). In vessels ex vivo, estrogen decreased protein levels of PGC-1α via activation of phosphatidylinositol 3-kinase (PI3K). Estrogen treatment also increased phosphorylation of forkhead transcription factor, FoxO1, a known pathway for PGC-1α downregulation. In contrast to the decrease in PGC-1α, estrogen increased protein levels of nuclear respiratory factor 1, a known PGC target and mediator of mitochondrial biogenesis. The latter effect of estrogen was independent of PI3K, suggesting a separate mechanism consistent with increased expression of PGC-1β and PRC. We demonstrated increased mitochondrial biogenesis following estrogen treatment in vivo; cerebrovascular levels of mitochondrial transcription factor A and electron transport chain subunits as well as the mitochondrial/ nuclear DNA ratio were increased. We examined a downstream target of PGC-1β, glutamate-cysteine ligase (GCL), the rate-limiting enzyme for glutathione synthesis. In vivo estrogen increased protein levels of both GCL subunits and total glutathione levels. Together these data show estrogen differentially regulates PGC-1 isoforms in brain vasculature, underscoring the importance of these coactivators in adapting mitochondria in specific tissues. By upregulating PGC-1β and/or PRC, estrogen appears to enhance mitochondrial biogenesis, function and reactive oxygen species protection.
Cerebral blood vessels; Estrogen; Glutamate-cysteine ligase; Mitochondria; Peroxisome proliferator-activated; receptor-gamma coactivator-1 (PGC-1); Glutathione
Thiazolidinediones, a family of insulin-sensitizing drugs commonly used to treat type 2 diabetes, are thought to exert their effects in part by promoting mitochondrial biogenesis in white adipose tissue through the transcriptional coactivator PGC-1α (Peroxisome Proliferator-Activated Receptor γ Coactivator-1α).
To assess the role of PGC-1α in the control of rosiglitazone-induced mitochondrial biogenesis, we have generated a mouse model that lacks expression of PGC-1α specifically in adipose tissues (PGC-1α-FAT-KO mice). We found that expression of genes encoding for mitochondrial proteins involved in oxidative phosphorylation, tricarboxylic acid cycle or fatty acid oxidation, was similar in white adipose tissue of wild type and PGC-1α-FAT-KO mice. Furthermore, the absence of PGC-1α did not prevent the positive effect of rosiglitazone on mitochondrial gene expression or biogenesis, but it precluded the induction by rosiglitazone of UCP1 and other brown fat-specific genes in white adipose tissue. Consistent with the in vivo findings, basal and rosiglitazone-induced mitochondrial gene expression in 3T3-L1 adipocytes was unaffected by the knockdown of PGC-1α but it was impaired when PGC-1β expression was knockdown by the use of specific siRNA.
These results indicate that in white adipose tissue PGC-1α is dispensable for basal and rosiglitazone-induced mitochondrial biogenesis but required for the rosiglitazone-induced expression of UCP1 and other brown adipocyte-specific markers. Our study suggests that PGC-1α is important for the appearance of brown adipocytes in white adipose tissue. Our findings also provide evidence that PGC-1β and not PGC-1α regulates basal and rosiglitazone-induced mitochondrial gene expression in white adipocytes.
Alterations in the expression and activity of the transcriptional coactivator peroxisome proliferator-activated receptor γ coactivator-1α (ppargc1a or PGC-1α) have been reported in multiple movement disorders, yet it is unclear how a lack of PGC-1α impacts transcription and function of the cerebellum, a region with high PGC-1α expression. We show here that mice lacking PGC-1α exhibit ataxia in addition to the previously described deficits in motor coordination. Using q-RT-PCR in cerebellar homogenates from PGC-1α−/− mice, we measured expression of 37 microarray-identified transcripts upregulated by PGC-1α in SH-SY5Y neuroblastoma cells with neuroanatomical overlap with PGC-1α or parvalbumin (PV), a calcium buffer highly expressed by Purkinje cells. We found significant reductions in transcripts with synaptic (complexin1, Cplx1; Pacsin2), structural (neurofilament heavy chain, Nefh), and metabolic (isocitrate dehydrogenase 3a, Idh3a; neutral cholesterol ester hydrolase 1, Nceh1; pyruvate dehydrogenase alpha 1, Pdha1; phytanoyl-CoA hydroxylase, Phyh; ubiquinol-cytochrome c reductase, Rieske iron-sulfur polypeptide 1, Uqcrfs1) functions. Using conditional deletion of PGC-1α in PV-positive neurons, we determined that 50% of PGC-1α expression and a reduction in a subset of these transcripts could be explained by its concentration in PV-positive neuronal populations in the cerbellum. To determine whether there were functional consequences associated with these changes, we conducted stereological counts and spike rate analysis in Purkinje cells, a cell type rich in PV, from PGC-1α−/− mice. We observed a significant loss of Purkinje cells by 6 weeks of age, and the remaining Purkinje cells exhibited a 50% reduction in spike rate. Together, these data highlight the complexity of PGC-1α's actions in the central nervous system and suggest that dysfunction in multiple cell types contribute to motor deficits in the context of PGC-1α deficiency.
PPARGC1A; cerebellum; ataxia; Catwalk; stereology; Refsum disease; Friedreich Ataxia
Mitochondria dysfunction contributes to the pathophysiology of obesity, diabetes, neurodegeneration and ageing. The peroxisome proliferator-activated receptor-gamma coactivator-1β (PGC-1β) coordinates mitochondrial biogenesis and function as well as fatty acid metabolism. It has been suggested that endoplasmic reticulum (ER) stress may be one of the mechanisms linking mitochondrial dysfunction and these pathologies. Here we investigate whether PGC-1β ablation affects the ER stress response induced by specific nutritional and pharmacological challenges in the CNS. By using flow cytometry, western blot, real time PCR and several pharmacological and nutritional interventions in PGC-1β knock out and WT mice, we confirmed that PGC-1β coordinates mitochondria function in brain and reported for the first time that a) ablation of PGC-1β is associated with constitutive activation of mTORC1 pathway associated with increased basal GRP78 protein levels in hypothalamus and cortex of animals fed chow diet; and b) in animals fed chronically with high fat diet (HFD) or high protein diet (HPD), we observed a failure to appropriately induce ER stress response in the absence of PGC-1β, associated with an increase in mTOR pathway phosphorylation. This contrasted with the appropriate upregulation of ER stress response observed in wild type littermates. Additionally, inefficient in vitro induction of ER stress by thapsigargin seems result in apoptotic neuronal cell death in PGC-1β KO. Our data indicate that PGC-1β is required for a neuronal ER response to nutritional stress imposed by HFD and HPD diets and that genetic ablation of PGC-1β might increase the susceptibility to neuronal damage and cell death.
► The PGC-1β coordinates mitochondrial function and fatty acid metabolism. ► Ablation of PGC-1β associates with mTORC1 activation and basal increase of GRP78. ► Metabolic stress results in inefficient GRP78 increase in PGC-1β KO mice.
PGC 1 beta; Endoplasmic reticulum stress; Mitochondria; mTOR; Amino acids; Brain
The peroxisome proliferator-activated receptor gamma coactivators (PGC-1) have important roles in mitochondrial biogenesis and metabolic control in a variety of tissues. There are multiple isoforms of PGC-1 including PGC-1α and PGC-1β. Both the PGC-1α and β isoforms promote mitochondrial biogenesis and fatty acid oxidation, but only PGC-1α stimulates gluconeogenesis in the liver. Carnitine palmitoyltransferase I (CPT-I) is a key enzyme regulating mitochondrial fatty acid oxidation. In these studies, we determined that PGC-1β stimulated expression of the “liver” isoform of CPT-I (CPT-Iα) but that PGC-1β did not induce pyruvate dehydrogenase kinase 4 (PDK4) which is a regulator of pyruvate metabolism. The CPT-Iα gene is induced by thyroid hormone. We found that T3 increased the expression of PGC-1β and that PGC-1β enhanced the T3 induction of CPT-Iα. The thyroid hormone receptor interacts with PGC-1β in a ligand dependent manner. Unlike PGC-1α, the interaction of PGC-1β and the T3 receptor does not occur exclusively through the leucine-X-X-leucine-leucine motif in PGC-1β. We have found that PGC-1β is associated with the CPT-Iα gene in vivo. Overall, our results demonstrate that PGC-1β is a coactivator in the T3 induction of CPT-Iα and that PGC-1β has similarities and differences with the PGC-1α isoform.
PGC-1; carnitine palmitoyltransferase (CPT-Iα); fatty acid oxidation; thyroid hormone (T3); CREB binding protein (CBP)
We investigated the role of PPAR γ coactivator 1α (PGC-1α) in muscle dysfunction in Huntington's disease (HD). We observed reduced PGC-1α and target genes expression in muscle of HD transgenic mice. We produced chronic energy deprivation in HD mice by administering the catabolic stressor β-guanidinopropionic acid (GPA), a creatine analogue that reduces ATP levels, activates AMP-activated protein kinase (AMPK), which in turn activates PGC-1α. Treatment with GPA resulted in increased expression of AMPK, PGC-1α target genes, genes for oxidative phosphorylation, electron transport chain and mitochondrial biogenesis, increased oxidative muscle fibers, numbers of mitochondria and motor performance in wild-type, but not in HD mice. In muscle biopsies from HD patients, there was decreased PGC-1α, PGC-1β and oxidative fibers. Oxygen consumption, PGC-1α, NRF1 and response to GPA were significantly reduced in myoblasts from HD patients. Knockdown of mutant huntingtin resulted in increased PGC-1α expression in HD myoblast. Lastly, adenoviral-mediated delivery of PGC-1α resulted increased expression of PGC-1α and markers for oxidative muscle fibers and reversal of blunted response for GPA in HD mice. These findings show that impaired function of PGC-1α plays a critical role in muscle dysfunction in HD, and that treatment with agents to enhance PGC-1α function could exert therapeutic benefits. Furthermore, muscle may provide a readily accessible tissue in which to monitor therapeutic interventions.
Peroxisome proliferator-activated receptor (PPAR) γ coactivator 1α (PGC-1α) is a coactivator of various nuclear receptors and other transcription factors, which is involved in the regulation of energy metabolism, thermogenesis, and other biological processes that control phenotypic characteristics of various organ systems including skeletal muscle. PGC-1α in skeletal muscle is considered to be involved in contractile protein function, mitochondrial function, metabolic regulation, intracellular signaling, and transcriptional responses. Branched-chain amino acid (BCAA) metabolism mainly occurs in skeletal muscle mitochondria, and enzymes related to BCAA metabolism are increased by exercise. Using murine skeletal muscle overexpressing PGC-1α and cultured cells, we investigated whether PGC-1α stimulates BCAA metabolism by increasing the expression of enzymes involved in BCAA metabolism. Transgenic mice overexpressing PGC-1α specifically in the skeletal muscle had increased the expression of branched-chain aminotransferase (BCAT) 2, branched-chain α-keto acid dehydrogenase (BCKDH), which catabolize BCAA. The expression of BCKDH kinase (BCKDK), which phosphorylates BCKDH and suppresses its enzymatic activity, was unchanged. The amount of BCAA in the skeletal muscle was significantly decreased in the transgenic mice compared with that in the wild-type mice. The amount of glutamic acid, a metabolite of BCAA catabolism, was increased in the transgenic mice, suggesting the activation of muscle BCAA metabolism by PGC-1α. In C2C12 cells, the overexpression of PGC-1α significantly increased the expression of BCAT2 and BCKDH but not BCKDK. Thus, PGC-1α in the skeletal muscle is considered to significantly contribute to BCAA metabolism.
Neurons are specialized cells with unique features, including a constant high demand for energy. Mitochondria satisfy this constant demand, and are emerging as a central target for dysfunction in neurodegenerative disorders, such as Huntington’s disease (HD) and Parkinson’s disease. PPARγ co-activator-1α (PGC-1α) is a transcription co-activator for nuclear receptors such as the PPARs, and thereby coordinates a number of gene expression programs to promote mitochondrial biogenesis and oxidative phosphorylation. Studies of PGC-1α knock-out mice have yielded important insights into the role of PGC-1α in normal nervous system function and potentially neurological disease. HD is caused by a polyglutamine repeat expansion in the huntingtin protein, and decades of work have established mitochondrial dysfunction as a key feature of HD pathogenesis. However, after the discovery of the HD gene, numerous reports produced strong evidence for altered transcription in HD. In 2006, a series of studies revealed that PGC-1α transcription interference contributes to HD neurodegeneration, linking the nuclear transcriptionopathy with the mitochondrial dysfunction. Subsequent work has strengthened this view, and further extended the role of PGC-1α within the CNS. Within the last year, studies of Parkinson’s disease, another involuntary movement disorder long associated with mitochondrial dysfunction, have shown that PGC-1α dysregulation is contributing to its pathogenesis. As PGC-1α is likely also important for aging, a process with considerable relevance to neuron function, translational studies aimed at developing therapies based upon the PGC-1α pathway as a high priority target are underway.