Bicuculline restores frequency-dependent hippocampal I/E ratio and circuit function in PGC-1ɑ null mice.

Altered inhibition/excitation (I/E) balance contributes to various brain disorders. Dysfunctional GABAergic interneurons enhance or reduce inhibition, resulting in I/E imbalances. Differences in short-term plasticity between excitation and inhibition cause frequency-dependence of the I/E ratio, which can be altered by GABAergic dysfunction. However, it is unknown whether I/E imbalances can be rescued pharmacologically using a single dose when the imbalance magnitude is frequency-dependent. Loss of PGC-1α (peroxisome proliferator activated receptor γ coactivator 1α) causes transcriptional dysregulation in hippocampal GABAergic interneurons. PGC-1α-/- slices have enhanced baseline inhibition onto CA1 pyramidal cells, causing increased I/E ratio and impaired circuit function. High frequency stimulation reduces the I/E ratio and recovers circuit function in PGC-1α-/- slices. Here we tested if using a low dose of bicuculline that can restore baseline I/E ratio can also rescue the frequency-dependent I/E imbalances in these mice. Remarkably, bicuculline did not reduce the I/E ratio below that of wild type during high frequency stimulation. Interestingly, bicuculline enhanced the paired-pulse ratio (PPR) of disynaptic inhibition without changing the monosynaptic inhibition PPR, suggesting that bicuculline modifies interneuron recruitment and not GABA release. Bicuculline improved CA1 output in PGC-1α-/- slices, enhancing EPSP-spike coupling to wild type levels at high and low frequencies. Our results show that it is possible to rescue frequency-dependent I/E imbalances in an animal model of transcriptional dysregulation with a single treatment.

PV-specific loss of the transcriptional coactivator PGC-1α slows down the evolution of epileptic activity in an acute ictogenic model.

The transcriptional coactivator, PGC-1α (peroxisome proliferator-activated receptor γ coactivator 1α), plays a key role in coordinating energy requirement within cells. Its importance is reflected in the growing number of psychiatric and neurological conditions that have been associated with reduced PGC-1α levels. In cortical networks, PGC-1α is required for the induction of parvalbumin (PV) expression in interneurons, and PGC-1α deficiency affects synchronous GABAergic release. It is unknown, however, how this affects cortical excitability. We show here that knocking down PGC-1α specifically in the PV-expressing cells (PGC-1αPV-/-) blocks the activity-dependent regulation of the synaptic proteins, SYT2 and CPLX1. More surprisingly, this cell class-specific knockout of PGC-1α appears to have a novel antiepileptic effect, as assayed in brain slices bathed in 0 Mg2+ media. The rate of occurrence of preictal discharges developed approximately equivalently in wild-type and PGC-1αPV-/- brain slices, but the intensity of these discharges was lower in PGC-1αPV-/- slices, as evident from the reduced power in the γ range and reduced firing rates in both PV interneurons and pyramidal cells during these discharges. Reflecting this reduced intensity in the preictal discharges, the PGC-1αPV-/- brain slices experienced many more discharges before transitioning into a seizure-like event. Consequently, there was a large increase in the latency to the first seizure-like event in brain slices lacking PGC-1α in PV interneurons. We conclude that knocking down PGC-1α limits the range of PV interneuron firing and this slows the pathophysiological escalation during ictogenesis.NEW & NOTEWORTHY Parvalbumin expressing interneurons are considered to play an important role in regulating cortical activity. We were surprised, therefore, to find that knocking down the transcriptional coactivator, PGC-1α, specifically in this class of interneurons appears to slow ictogenesis. This anti-ictogenic effect is associated with reduced activity in preictal discharges, but with a far longer period of these discharges before the first seizure-like events finally start. Thus, PGC-1α knockdown may promote schizophrenia while reducing epileptic tendencies.

PGC1α is required for the renoprotective effect of lncRNA Tug1 in vivo and links Tug1 with urea cycle metabolites.

lncRNA taurine-upregulated gene 1 (Tug1) is a promising therapeutic target in the progression of diabetic nephropathy (DN), but the molecular basis of its protection remains poorly understood. Here, we generate a triple-mutant diabetic mouse model coupled with metabolomic profiling data to interrogate whether Tug1 interaction with peroxisome proliferator-activated receptor gamma coactivator 1α (PGC1α) is required for mitochondrial remodeling and progression of DN in vivo. We find that, compared with diabetic conditional deletion of Pgc1α in podocytes alone (db/db; Pgc1αPod-f/f), diabetic Pgc1α knockout combined with podocyte-specific Tug1 overexpression (db/db; TugPodTg; Pgc1αPod-f/f) reverses the protective phenotype of Tug1 overexpression, suggesting that PGC1α is required for the renoprotective effect of Tug1. Using unbiased metabolomic profiling, we find that altered urea cycle metabolites and mitochondrial arginase 2 play an important role in Tug1/PGC1α-induced mitochondrial remodeling. Our work identifies a functional role of the Tug1/PGC1α axis on mitochondrial metabolic homeostasis and urea cycle metabolites in experimental models of diabetes.

PGC-1α regulate critical period plasticity via gene × environment interaction in the developmental trajectory to schizophrenia.

Genes and environmental conditions are thought to interact in the development of postnatal brain in schizophrenia (SZ). Genome wide association studies have identified that PPARGC1A being one of the top candidate genes for SZ. We previously reported GABAergic neuron-specific PGC-1α knockout mice (Dlx5/6-Cre:PGC-1αfl/fl) presented some characteristic features of SZ. However, there is a fundamental gap of the molecular mechanism by which PGC-1α gene involved in the developmental trajectory to SZ. To explore whether PGC-1α regulates environmental factors interacting with genetic susceptibility to trigger symptom onset and disease progression, PGC-1α deficient mice were utilized to model genetic effect and an additional oxidative stress was induced by GBR injection. We confirm that PGC-1α gene deletion prolongs critical period (CP) timing, as revealed by delaying maturation of PV interneurons (PVIs), including their perineuronal nets (PNNs). Further, we confirm that gene × environment (G × E) influences CP plasticity synergistically and the interaction varies as a function of age, with the most sensitive period being at preweaning stage, and the least sensitive one at early adult age in PGC-1α deficient mice. Along this line, we find that the synergic action of G × E is available in ChABC-infusion PGC-1α KO mice, even though during the adulthood, and the neuroplasticity seems to remain open to fluctuate. Altogether, these results refine the observations made in the PGC-1α deficient mice, a potential mouse model of SZ, and illustrate how PGC-1α regulates CP plasticity via G × E interaction in the developmental trajectory to SZ.

PGC-1α isoforms coordinate to balance hepatic metabolism and apoptosis in inflammatory environments.

OBJECTIVE: The liver is regularly exposed to changing metabolic and inflammatory environments. It must sense and adapt to metabolic need while balancing resources required to protect itself from insult. Peroxisome proliferator activated receptor gamma coactivator-1 alpha (PGC-1α) is a transcriptional coactivator expressed as multiple, alternatively spliced variants transcribed from different promoters that coordinate metabolic adaptation and protect against inflammation. It is not known how PGC-1α integrates extracellular signals to balance metabolic and anti-inflammatory outcomes. METHODS: Primary mouse hepatocytes were used to evaluate the role(s) of different PGC-1α proteins in regulating hepatic metabolism and inflammatory signaling downstream of tumor necrosis factor alpha (TNFα). Gene expression and signaling analysis were combined with biochemical measurement of apoptosis using gain- and loss-of-function in vitro and in vivo. RESULTS: Hepatocytes expressed multiple isoforms of PGC-1α, including PGC-1α4, which microarray analysis showed had common and isoform-specific functions linked to metabolism and inflammation compared with canonical PGC-1α1. Whereas PGC-1α1 primarily impacted gene programs of nutrient metabolism and mitochondrial biology, TNFα signaling showed several pathways related to innate immunity and cell death downstream of PGC-1α4. Gain- and loss-of-function models illustrated that PGC-1α4 uniquely enhanced expression of anti-apoptotic gene programs and attenuated hepatocyte apoptosis in response to TNFα or lipopolysaccharide (LPS). This was in contrast to PGC-1α1, which decreased the expression of a wide inflammatory gene network but did not prevent hepatocyte death in response to cytokines. CONCLUSIONS: PGC-1α variants have distinct, yet complementary roles in hepatic responses to metabolism and inflammation, and we identify PGC-1α4 as an important mitigator of apoptosis.

Proliferator-Activated Receptor-Gamma Coactivator-1α Haploinsufficiency Promotes Pain Chronification After Burn Injury.

BACKGROUND: Tissue injuries such as surgery and trauma are usually accompanied by simultaneous development of acute pain, which typically resolves along with tissue healing. However, in many cases, acute pain does not resolve despite proper tissue repair; rather, it transitions to chronic pain. In this study, we examined whether proliferator-activated receptor-gamma coactivator-1α (PGC-1α), a master regulator of mitochondria biogenesis, is implicated in pain chronification after burn injury in mice. METHODS: We used PGC-1α and littermates PGC-1α mice of both sex. Burn injury was induced on these mice. Hindpaw mechanical withdrawal thresholds and thermal withdrawal latency were examined. RESULTS: Hindpaw mechanical withdrawal thresholds and thermal withdrawal latencies were comparable at baseline between PGC-1α and PGC-1α mice. After burn injury, both PGC-1α and PGC-1α mice exhibited an initial dramatic decrease of withdrawal parameters at days 3 and 5 after injury. While PGC-1α mice fully recovered their withdrawal parameters to preinjury levels by days 11-14, PGC-1α mice failed to recover those parameters during the same time frame, regardless of sex. Moreover, we found that PGC-1α mice resolved tissue inflammation in a similar fashion to PGC-1α mice using a chemiluminescence-based reactive oxygen species imaging technique. CONCLUSIONS: Taken together, our data suggest that PGC-1α haploinsufficiency promotes pain chronification after burn injury.

Early induction of senescence and immortalization in PGC-1α-deficient mouse embryonic fibroblasts.

AIMS: Oxidative stress is known to induce early replicative senescence. Senescence has been proposed to work as a barrier to immortalization and tumor development. Here, we aimed to evaluate the impact of the loss of peroxisome proliferator activated receptor γ co-activator 1α (PGC-1α), a master regulator of oxidative metabolism and mitochondrial reactive oxygen species (ROS) generation, on replicative senescence and immortalization in mouse embryonic fibroblasts (MEFs). RESULTS: We found that primary MEFs lacking PGC-1α showed higher levels of ROS than wild-type MEFs at all cell passages tested. The elevated production of ROS was associated with higher levels of oxidative DNA damage and the increased formation of DNA double-strand breaks. Evaluation of the induction of DNA repair systems in response to γ-radiation indicated that the loss of PGC-1α also resulted in a small but significant reduction in their activity. DNA damage induced the early activation of senescence markers, including an increase in the number of ß-galactosidase-positive cells, the induction of p53 phosphorylation, and the increase in p16 and p19 protein. These changes were, however, not sufficient to reduce proliferation rates of PGC-1α-deficient MEFs at any cell passage tested. Moreover, PGC-1α-deficient cells escaped replicative senescence. INNOVATION & CONCLUSION: PGC-1α plays an important role in the control of cellular senescence and immortalization.

PGC-1α deficiency causes spontaneous kidney inflammation and increases the severity of nephrotoxic AKI.

PGC-1α (peroxisome proliferator-activated receptor gamma coactivator-1α, PPARGC1A) regulates the expression of genes involved in energy homeostasis and mitochondrial biogenesis. Here we identify inactivation of the transcriptional regulator PGC-1α as a landmark for experimental nephrotoxic acute kidney injury (AKI) and describe the in vivo consequences of PGC-1α deficiency over inflammation and cell death in kidney injury. Kidney transcriptomic analyses of WT mice with folic acid-induced AKI revealed 1398 up- and 1627 downregulated genes. Upstream transcriptional regulator analyses pointed to PGC-1α as the transcription factor potentially driving the observed expression changes with the highest reduction in activity. Reduced PGC-1α expression was shared by human kidney injury. Ppargc1a-/- mice had spontaneous subclinical kidney injury characterized by tubulointerstitial inflammation and increased Ngal expression. Upon AKI, Ppargc1a-/- mice had lower survival and more severe loss of renal function, tubular injury, and reduction in expression of mitochondrial PGC-1α-dependent genes in the kidney, and an earlier decrease in mitochondrial mass than WT mice. Additionally, surviving Ppargc1a-/- mice showed higher rates of tubular cell death, compensatory proliferation, expression of proinflammatory cytokines, NF-κB activation, and interstitial inflammatory cell infiltration. Specifically, Ppargc1a-/- mice displayed increased M1 and decreased M2 responses and expression of the anti-inflammatory cytokine IL-10. In cultured renal tubular cells, PGC-1α targeting promoted spontaneous cell death and proinflammatory responses. In conclusion, PGC-1α inactivation is a key driver of the gene expression response in nephrotoxic AKI and PGC-1α deficiency promotes a spontaneous inflammatory kidney response that is magnified during AKI. © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Obesity causes PGC-1α deficiency in the pancreas leading to marked IL-6 upregulation via NF-κB in acute pancreatitis.

Obesity is associated with local and systemic complications in acute pancreatitis. PPARγ coactivator 1α (PGC-1α) is a transcriptional coactivator and master regulator of mitochondrial biogenesis that exhibits dysregulation in obese subjects. Our aims were: (1) to study PGC-1α levels in pancreas from lean or obese rats and mice with acute pancreatitis; and (2) to determine the role of PGC-1α in the inflammatory response during acute pancreatitis elucidating the signaling pathways regulated by PGC-1α. Lean and obese Zucker rats and lean and obese C57BL6 mice were used first; subsequently, wild-type and PGC-1α knockout (KO) mice with cerulein-induced pancreatitis were used to assess the inflammatory response and expression of target genes. Ppargc1a mRNA and protein levels were markedly downregulated in pancreas of obese rats and mice versus lean animals. PGC-1α protein levels increased in pancreas of lean mice with acute pancreatitis, but not in obese mice with pancreatitis. Interleukin-6 (Il6) mRNA levels were dramatically upregulated in pancreas of PGC-1α KO mice after cerulein-induced pancreatitis in comparison with wild-type mice with pancreatitis. Edema and the inflammatory infiltrate were more intense in pancreas from PGC-1α KO mice than in wild-type mice. The lack of PGC-1α markedly enhanced nuclear translocation of phospho-p65 and recruitment of p65 to Il6 promoter. PGC-1α bound phospho-p65 in pancreas during pancreatitis in wild-type mice. Glutathione depletion in cerulein-induced pancreatitis was more severe in KO mice than in wild-type mice. PGC-1α KO mice with pancreatitis, but not wild-type mice, exhibited increased myeloperoxidase activity in the lungs, together with alveolar wall thickening and collapse, which were abrogated by blockade of the IL-6 receptor glycoprotein 130 with LMT-28. In conclusion, obese rodents exhibit PGC-1α deficiency in the pancreas. PGC-1α acts as selective repressor of nuclear factor-κB (NF-κB) towards IL-6 in pancreas. PGC-1α deficiency markedly enhanced NF-κB-mediated upregulation of Il6 in pancreas in pancreatitis, leading to a severe inflammatory response. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Loss of NRF-2 and PGC-1α genes leads to retinal pigment epithelium damage resembling dry age-related macular degeneration.

Age-related macular degeneration (AMD) is a multi-factorial disease that is the leading cause of irreversible and severe vision loss in the developed countries. It has been suggested that the pathogenesis of dry AMD involves impaired protein degradation in retinal pigment epithelial cells (RPE). RPE cells are constantly exposed to oxidative stress that may lead to the accumulation of damaged cellular proteins, DNA and lipids and evoke tissue deterioration during the aging process. The ubiquitin-proteasome pathway and the lysosomal/autophagosomal pathway are the two major proteolytic systems in eukaryotic cells. NRF-2 (nuclear factor-erythroid 2-related factor-2) and PGC-1α (peroxisome proliferator-activated receptor gamma coactivator-1 alpha) are master transcription factors in the regulation of cellular detoxification. We investigated the role of NRF-2 and PGC-1α in the regulation of RPE cell structure and function by using global double knockout (dKO) mice. The NRF-2/PGC-1α dKO mice exhibited significant age-dependent RPE degeneration, accumulation of the oxidative stress marker, 4-HNE (4-hydroxynonenal), the endoplasmic reticulum stress markers GRP78 (glucose-regulated protein 78) and ATF4 (activating transcription factor 4), and damaged mitochondria. Moreover, levels of protein ubiquitination and autophagy markers p62/SQSTM1 (sequestosome 1), Beclin-1 and LC3B (microtubule associated protein 1 light chain 3 beta) were significantly increased together with the Iba-1 (ionized calcium binding adaptor molecule 1) mononuclear phagocyte marker and an enlargement of RPE size. These histopathological changes of RPE were accompanied by photoreceptor dysmorphology and vision loss as revealed by electroretinography. Consequently, these novel findings suggest that the NRF-2/PGC-1α dKO mouse is a valuable model for investigating the role of proteasomal and autophagy clearance in the RPE and in the development of dry AMD.

Heart specific PGC-1α deletion identifies metabolome of cardiac restricted metabolic heart failure.

Aims: Heart failure (HF) is associated with drastic changes in metabolism leading to a cardiac energy deficiency well as maladaptive changes in multiple other tissues. It is still unclear which of these changes originates from cardiomyocyte metabolic remodelling or whether they are induced secondarily by systemic factors. Our aim here was to induce cardiac restricted metabolic changes mimicking those seen in HF and to characterize the associated metabolite changes in the heart, circulation, and peripheral tissues. Methods and results: We generated a cardiac specific PGC-1α knockout mice (KO) to specifically induce metabolic dysregulation typically accompanied by HF and performed a non-targeted LC-MS metabolite profiling analysis of heart, plasma, liver, and skeletal muscle to identify metabolites associated with cardiac specific metabolic remodelling. The KO animals developed a progressive cardiomyopathy with cardiac dilatation leading to fatal HF. At 17 weeks of age, when significant remodelling had occurred but before the onset of HF, isolated PGC-1α deficient cardiomyocytes had suppressed glucose and fatty acid oxidation as well as blunted anaerobic metabolism. KO hearts displayed a distinctive metabolite profile with 92 significantly altered molecular features including metabolite changes in energy metabolism, phospholipid metabolism, amino acids, and oxidative stress signalling. Some of the metabolite changes correlated with the specific parameters of cardiac function. We did not observe any significant alterations in the metabolomes of the other measured tissues or in plasma. Conclusions: Heart specific PGC-1α KO induces metabolic, functional, and structural abnormalities leading to dilating cardiomyopathy and HF. The metabolic changes were limited to the cardiac tissue indicating that cardiomyocyte metabolic remodelling is not sufficient to evoke the body wide metabolic alterations usually associated with HF.

Disruption of peroxisome proliferator-activated receptor γ coactivator (PGC)-1α reverts key features of the neoplastic phenotype of glioma cells.

The peroxisome proliferator-activated receptor γ coactivator (PGC)-1α is a master regulator of mitochondrial biogenesis and controls metabolism by coordinating transcriptional events. Here, we interrogated whether PGC-1α is involved in tumor growth and the metabolic flexibility of glioblastoma cells. PGC-1α was expressed in a subset of established glioma cell lines and primary glioblastoma cell cultures. Furthermore, a higher PGC-1α expression was associated with an adverse outcome in the TCGA glioblastoma dataset. Suppression of PGC-1α expression by shRNA in the PGC-1α-positive U343MG glioblastoma line suppressed mitochondrial gene expression, reduced mitochondrial membrane potential, and diminished oxygen as well as glucose consumption, and lactate production. Compatible with the known PGC-1α functions in reactive oxygen species (ROS) metabolism, glioblastoma cells deficient in PGC-1α displayed ROS accumulation, had reduced RNA levels of proteins involved in ROS detoxification, and were more susceptible to death induction by H2O2 compared with control cells. PGC-1αsh cells also had impaired proliferation and migration rates in vitro and displayed less stem cell characteristics. Complementary effects were observed in PGC-1α-low LNT-229 cells engineered to overexpress PGC-1α. In an in vivo xenograft experiment, tumors formed by U343MG PGC-1αsh glioblastoma cells grew much slower than control tumors and were less invasive. Interestingly, the PGC-1α knockdown conferred protection against hypoxia-induced cell death, probably as a result of less active anabolic pathways, and this effect was associated with reduced epidermal growth factor expression and mammalian target of rapamycin signaling. In summary, PGC-1α modifies the neoplastic phenotype of glioblastoma cells toward more aggressive behavior and therefore makes PGC-1α a potential target for anti-glioblastoma therapies.

PGC-1α in hepatic UPR during high-fat high-fructose diet and exercise training in mice.

Diet-induced obesity is associated with hepatic steatosis, which has been linked with activation of the unfolded protein response (UPR). PGC-1α is a transcriptional coactivator involved in exercise training-induced adaptations in muscle and liver. Therefore, the aim of this study was to test the hypothesis that PGC-1α is required for exercise training-mediated prevention of diet-induced steatosis and UPR activation in liver. Male liver-specific PGC-1α knockout (LKO) and littermate floxed (lox/lox) mice were divided into two groups receiving either control diet (CON) or high-fat high-fructose diet (HFF). After 9 weeks, half of the HFF mice were treadmill exercise trained for 4 weeks (HFF+ExT), while the rest were kept sedentary. HFF resulted in increased body and liver weight, adiposity, hepatic steatosis and whole body glucose intolerance as well as decreased hepatic IRE1α phosphorylation. Exercise training prevented the HFF-induced weight gain and partially prevented increased liver weight, adiposity and glucose intolerance, but with no effect on liver triglycerides. In addition, BiP protein and CHOP mRNA content increased with exercise training compared with CON and HFF, respectively. Lack of PGC-1α in the liver only resulted in minor changes in the PERK pathway. In conclusion, this study provides evidence for dissociation between diet-induced hepatic triglyceride accumulation and hepatic UPR activation. In addition, PGC-1α was not required for maintenance of basal UPR in the liver and due to only minor exercise training effects on UPR further studies are needed to conclude on the potential role of PGC-1α in exercise training-induced adaptations in hepatic UPR.

PGC-1α Controls Skeletal Stem Cell Fate and Bone-Fat Balance in Osteoporosis and Skeletal Aging by Inducing TAZ.

Aberrant lineage specification of skeletal stem cells (SSCs) contributes to reduced bone mass and increased marrow adipose tissue (MAT) in osteoporosis and skeletal aging. Although master regulators of osteoblastic and adipogenic lineages have been identified, little is known about factors that are associated with MAT accumulation and osteoporotic bone loss. Here, we identify peroxisome-proliferator-activated receptor γ coactivator 1-α (PGC-1α) as a critical switch of cell fate decisions whose expression decreases with aging in human and mouse SSCs. Loss of PGC-1α promoted adipogenic differentiation of murine SSCs at the expense of osteoblastic differentiation. Deletion of PGC-1α in SSCs impaired bone formation and indirectly promoted bone resorption while enhancing MAT accumulation. Conversely, induction of PGC-1α attenuated osteoporotic bone loss and MAT accumulation. Mechanistically, PGC-1α maintains bone and fat balance by inducing TAZ. Our results suggest that PGC-1α is a potentially important therapeutic target in the treatment of osteoporosis and skeletal aging.

NT-PGC-1α deficiency decreases mitochondrial FA oxidation in brown adipose tissue and alters substrate utilization in vivo.

Transcriptional coactivator PPAR γ coactivator (PGC)-1α and its splice variant N-terminal (NT)-PGC-1α mediate transcriptional regulation of brown adipose tissue (BAT) thermogenesis in response to changes in ambient temperature. PGC-1α is dispensable for cold-induced BAT thermogenesis as long as NT-PGC-1α is present. However, the functional significance of NT-PGC-1α in BAT has not been determined. In the present study, we generated NT-PGC-1α-/- mice to investigate the effect of NT-PGC-1α deficiency on adaptive BAT thermogenesis. At thermoneutrality, NT-PGC-1α-/- mice exhibited abnormal BAT phenotype with increased accumulation of large lipid droplets concomitant with marked downregulation of FA oxidation (FAO)-related genes. Consistent with transcriptional changes, mitochondrial FAO was significantly diminished in NT-PGC-1α-/- BAT. This alteration, in turn, enhanced glucose utilization within the NT-PGC-1α-/- BAT mitochondria. In line with this, NT-PGC-1α-/- mice had higher reliance on carbohydrates. In response to cold or ß3-adrenergic receptor agonist, NT-PGC-1α-/- mice transiently exhibited lower thermogenesis but reached similar thermogenic capacities as their WT littermates. Collectively, these findings demonstrate that NT-PGC-1α is an important contributor to the maintenance of FAO capacity in BAT at thermoneutrality and provide deeper insights into the relative contributions of PGC-1α and NT-PGC-1α to temperature-regulated BAT remodeling.

Ventricular pro-arrhythmic phenotype, arrhythmic substrate, ageing and mitochondrial dysfunction in peroxisome proliferator activated receptor-γ coactivator-1ß deficient (Pgc-1ß-/-) murine hearts.

INTRODUCTION: Ageing and age-related bioenergetic conditions including obesity, diabetes mellitus and heart failure constitute clinical ventricular arrhythmic risk factors. MATERIALS AND METHODS: Pro-arrhythmic properties in electrocardiographic and intracellular recordings were compared in young and aged, peroxisome proliferator-activated receptor-γ coactivator-1ß knockout (Pgc-1ß-/-) and wild type (WT), Langendorff-perfused murine hearts, during regular and programmed stimulation (PES), comparing results by two-way ANOVA. RESULTS AND DISCUSSION: Young and aged Pgc-1ß-/- showed higher frequencies and durations of arrhythmic episodes through wider PES coupling-interval ranges than WT. Both young and old, regularly-paced, Pgc-1ß-/- hearts showed slowed maximum action potential (AP) upstrokes, (dV/dt)max (∼157 vs. 120-130 V s-1), prolonged AP latencies (by ∼20%) and shortened refractory periods (∼58 vs. 51 ms) but similar AP durations (∼50 ms at 90% recovery) compared to WT. However, Pgc-1ß-/- genotype and age each influenced extrasystolic AP latencies during PES. Young and aged WT ventricles displayed distinct, but Pgc-1ß-/- ventricles displayed similar dependences of AP latency upon (dV/dt)max resembling aged WT. They also independently increased myocardial fibrosis. AP wavelengths combining activation and recovery terms paralleled contrasting arrhythmic incidences in Pgc-1ß-/- and WT hearts. Mitochondrial dysfunction thus causes pro-arrhythmic Pgc-1ß-/- phenotypes by altering AP conduction through reducing (dV/dt)max and causing age-dependent fibrotic change.

PGC1ß Organizes the Osteoclast Cytoskeleton by Mitochondrial Biogenesis and Activation.

Osteoclasts are mitochondria-rich cells, but the role of these energy-producing organelles in bone resorption is poorly defined. To this end, we conditionally deleted the mitochondria-inducing co-activator, PGC1ß, in myeloid lineage cells to generate PGC1ßLysM mice. In contrast to previous reports, PGC1ß-deficient macrophages differentiate normally into osteoclasts albeit with impaired resorptive function due to cytoskeletal disorganization. Consequently, bone mass of PGC1ßLysM mice is double that of wild type. Mitochondrial biogenesis and function are diminished in PGC1ßLysM osteoclasts. All abnormalities are normalized by PGC1ß transduction. Furthermore, OXPHOS inhibitors reproduce the phenotype of PGC1ß deletion. PGC1ß's organization of the osteoclast cytoskeleton is mediated by expression of GIT1, which also promotes mitochondrial biogenesis. Thus, osteoclast mitochondria regulate the cell's resorptive activity by promoting cytoskeletal organization. © 2018 American Society for Bone and Mineral Research.

Cardiomyocyte ionic currents in intact young and aged murine Pgc-1ß-/- atrial preparations.

INTRODUCTION: Recent studies reported that energetically deficient murine Pgc-1ß-/- hearts replicate age-dependent atrial arrhythmic phenotypes associated with their corresponding clinical conditions, implicating action potential (AP) conduction slowing consequent upon reduced AP upstroke rates. MATERIALS AND METHODS: We tested a hypothesis implicating Na+ current alterations as a mechanism underlying these electrophysiological phenotypes. We applied loose patch-clamp techniques to intact young and aged, WT and Pgc-1ß-/-, atrial cardiomyocyte preparations preserving their in vivo extracellular and intracellular conditions. RESULTS AND DISCUSSION: Depolarising steps activated typical voltage-dependent activating and inactivating inward (Na+) currents whose amplitude increased or decreased with the amplitudes of the activating, or preceding inactivating, steps. Maximum values of peak Na+ current were independently influenced by genotype but not age or interacting effects of genotype and age on two-way ANOVA. Neither genotype, nor age, whether independently or interactively, influenced voltages at half-maximal current, or steepness factors, for current activation and inactivation, or time constants for recovery from inactivation following repolarisation. In contrast, delayed outward (K+) currents showed similar activation and rectification properties through all experimental groups. These findings directly demonstrate and implicate reduced Na+ in contrast to unchanged K+ current, as a mechanism for slowed conduction causing atrial arrhythmogenicity in Pgc-1ß-/- hearts.

Exercise induces TFEB expression and activity in skeletal muscle in a PGC-1α-dependent manner.

The mitochondrial network in muscle is controlled by the opposing processes of mitochondrial biogenesis and mitophagy. The coactivator peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) regulates biogenesis, while the transcription of mitophagy-related genes is controlled by transcription factor EB (TFEB). PGC-1α activation is induced by exercise; however, the effect of exercise on TFEB is not fully known. We investigated the interplay between PGC-1α and TFEB on mitochondria in response to acute contractile activity in C2C12 myotubes and following exercise in wild-type and PGC-1α knockout mice. TFEB nuclear localization was increased by 1.6-fold following 2 h of acute myotube contractile activity in culture, while TFEB transcription was also simultaneously increased by twofold to threefold. Viral overexpression of TFEB in myotubes increased PGC-1α and cytochrome- c oxidase-IV gene expression. In wild-type mice, TFEB translocation to the nucleus increased 2.4-fold in response to acute exercise, while TFEB transcription, assessed through the electroporation of a TFEB promoter construct, was elevated by fourfold. These exercise effects were dependent on the presence of PGC-1α. Our data indicate that acute exercise provokes TFEB expression and activation in a PGC-1α-dependent manner and suggest that TFEB, along with PGC-1α, is an important regulator of mitochondrial biogenesis in muscle as a result of exercise.

AMPK Maintains Cellular Metabolic Homeostasis through Regulation of Mitochondrial Reactive Oxygen Species.

Reactive oxygen species (ROS) are continuously produced as a by-product of mitochondrial metabolism and eliminated via antioxidant systems. Regulation of mitochondrially produced ROS is required for proper cellular function, adaptation to metabolic stress, and bypassing cellular senescence. Here, we report non-canonical regulation of the cellular energy sensor AMP-activated protein kinase (AMPK) by mitochondrial ROS (mROS) that functions to maintain cellular metabolic homeostasis. We demonstrate that mitochondrial ROS are a physiological activator of AMPK and that AMPK activation triggers a PGC-1α-dependent antioxidant response that limits mitochondrial ROS production. Cells lacking AMPK activity display increased mitochondrial ROS levels and undergo premature senescence. Finally, we show that AMPK-PGC-1α-dependent control of mitochondrial ROS regulates HIF-1α stabilization and that mitochondrial ROS promote the Warburg effect in cells lacking AMPK signaling. These data highlight a key function for AMPK in sensing and resolving mitochondrial ROS for stress resistance and maintaining cellular metabolic balance.