An acute bout of high-intensity interval training increases the nuclear abundance of PGC-1α and activates mitochondrial biogenesis in human skeletal muscle

Low-volume, high-intensity interval training (HIT) increases skeletal muscle mitochondrial capacity, yet little is known regarding potential mechanisms promoting this adaptive response. Our purpose was to examine molecular processes involved in mitochondrial biogenesis in human skeletal muscle in response to an acute bout of HIT. Eight healthy men performed 4 × 30-s bursts of all-out maximal intensity cycling interspersed with 4 min of rest. Muscle biopsy samples (vastus lateralis) were obtained immediately before and after exercise, and after 3 and 24 h of recovery. At rest, the majority of peroxisome proliferator-activated receptor γ coactivator (PGC)-1α, a master regulator of mitochondrial biogenesis, was detected in cytosolic fractions. Exercise activated p38 MAPK and AMPK in the cytosol. Nuclear PGC-1α protein increased 3 h into recovery from exercise, a time point that coincided with increased mRNA expression of mitochondrial genes. This was followed by an increase in mitochondrial protein content and enzyme activity after 24 h of recovery. These findings support the hypothesis that an acute bout of low-volume HIT activates mitochondrial biogenesis through a mechanism involving increased nuclear abundance of PGC-1α.     

Promotion of mitochondrial biogenesis via the regulation of PARIS and PGC-1α by parkin as a mechanism of neuroprotection by carnosic acid

BackgroundImpairment of mitochondrial biogenesis is associated with the pathological progression of Parkinson's disease (PD). Parkin-interacting substrate (PARIS) can be ubiquitinated by parkin and prevents the repression of proliferator-activated receptor gamma coactivator-1-alpha (PGC-1α).PurposeThis study investigated whether the neuroprotective mechanism of carnosic acid (CA) from rosemary is mediated via the regulation of PARIS and PGC-1α by parkin.MethodsThe Western blotting and RT-PCR were used to determine protein and mRNA, respectively. To investigate the protein-protein interaction of between PARIS and ubiquitin, the immunoprecipitation assay (IP assay) was utilized. Silencing of endogenous parkin or PGC-1α was performed by using transient transfection of small interfering RNA (siRNA).ResultsSH-SY5Y cells treated with 6-hydroxydopamine (6-OHDA) increased PARIS protein, decreased PGC-1α protein, and reduced protein and mRNA of mitochondrial biogenesis-related genes. CA pretreatment reversed the effects of 6-OHDA. By IP assay, the interaction of PARIS with ubiquitin protein caused by CA was stronger than that caused by 6-OHDA. Moreover, knockdown of parkin attenuated the ability of CA to reverse the 6-OHDA-induced increase in PARIS and decrease in PGC-1α expression. PGC-1α siRNA was used to investigate how CA influenced the effect of 6-OHDA on the modulation of mitochondrial biogenesis and apoptosis. In the presence of PGC-1α siRNA, CA could no longer significantly reverse the reduction of mitochondrial biogenesis or the induction of cleavage of apoptotic-related proteins by 6-OHDA.ConclusionThe cytoprotective of CA is related to the enhancement of mitochondrial biogenesis by inhibiting PARIS and inducing PGC-1α by parkin. The activation of PGC-1α-mediated mitochondrial biogenesis by CA prevents the degeneration of dopaminergic neurons, CA may have therapeutic application in PD.     

The PGC-1α-dependent pathway of mitochondrial biogenesis is upregulated in type I endometrial cancer

PGC-1α-dependent pathway of mitochondrial biogenesis was investigated for the first time in type I endometrial cancer and in normal endometrium. In cancer endometrial tissue the citrate synthase activity, the mitochondrial DNA content and the TFAM level were found doubled compared to control endometrial tissue. Moreover, a 1.6- and 1.8-fold increase, respectively, of NRF-1 and PGG-1α expression was found. This study demonstrates, for the first time, that the increased mitochondrial biogenesis in type I endometrial cancer is associated to the upregulation of PGC-1α signalling pathway.     

The protease Omi regulates mitochondrial biogenesis through the GSK3β/PGC-1α pathway

Loss of the mitochondrial protease activity of Omi causes mitochondrial dysfunction, neurodegeneration with parkinsonian features and premature death in mnd2 (motor neuron degeneration 2) mice. However, the detailed mechanisms underlying this pathology remain largely unknown. Here, we report that Omi participates in the process of mitochondrial biogenesis, which has been linked to several neurodegenerative diseases. The mitochondrial biogenesis is deficit in mnd2 mice, evidenced by severe decreases of mitochondrial components, mitochondrial DNA and mitochondrial density. Omi cleaves glycogen synthase kinase 3β (GSK3β), a kinase promoting PPARγ coactivator-1α (PGC-1α) degradation, to regulate PGC-1α, a factor important for the mitochondrial biogenesis. In mnd2 mice, GSK3β abundance is increased and PGC-1α abundance is decreased significantly. Inhibition of GSK3β by SB216763 or overexpression of PGC-1α can restore mitochondrial biogenesis in mnd2 mice or Omi-knockdown N2a cells. Furthermore, there is a significant improvement of the movement ability of mnd2 mice after SB216763 treatment. Thus, our study identified Omi as a novel regulator of mitochondrial biogenesis, involving in Omi protease-deficient-induced neurodegeneration.Mitochondria have a vital role in neuronal death and survival.¹ As critical cellular organelles, mitochondria have highly dynamic properties, including mitochondrial fission, fusion, transport, biogenesis and degradation. The changes of those properties affect mitochondrial functions, leading to the occurrence of diseases.^{2, 3} Growing lines of evidence suggest that the mitochondrial dysfunction is involved in aging and neurodegenerative diseases, such as Alzheimer''s disease (AD), Huntington''s disease (HD) and Parkinson''s disease (PD).^{4, 5} Similar to other neurodegenerative diseases, PD is a progressive neurological disorder, which is characterized by the development of cytoplasmic aggregates known as Lewy bodies and degeneration of dopaminergic (DA) neurons in the substantia nigra of midbrain and other brain regions.⁶ In PD, dysfunction of mitochondria has been documented to be associated with disease pathogenesis in PD brains and both genetic- and toxin-induced PD animal models. In PD brains, mutations in mitochondrial DNA (mtDNA) occur more frequently than those in age-matched control; and mutations in the nuclear-encoded mtDNA polymerase-γ gene, which impair mtDNA replication and result in multiple mtDNA deletions, cause PD-like symptoms.⁵ Meanwhile, several PD-associated gene products, including α-synuclein, parkin, DJ-1, PINK1 (PTEN-induced putative kinase 1), leucine-rich repeat kinase 2, ubiquitin carboxy-terminal hydrolase L1 and Omi, have been identified to be associated with PD, and lead to mitochondrial dysfunction with changes in mitochondrial morphology, biogenesis and mitophagy in vivo and in vitro.^{5, 7, 8, 9} Besides, mitochondrial toxins, such as MPTP (1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine) and rotenone that inhibit complex I of the mitochondrial respiratory chain, cause clinically parkinsonian phenotype.^{10, 11}The serine protease Omi (also known as HtrA2) belongs to the high-temperature requirement factor A (HtrA) family, and was originally identified as a mammalian homolog of the Escherichia coli heat-shock-induced serine protease HtrA/DegP and DegS.¹² Omi is mainly localized in mitochondria, although a fraction of it is also found in nucleus.¹³ Omi is released from the mitochondria into the cytosol to mediate cell death by caspase-dependent or -independent pathways in response to apoptotic stimuli.^{14, 15} However, the notion that Omi is an apoptosis inducer in the central nervous system was challenged by studies of Omi-overexpressing or -deficient mice. Omi-overexpressing mice show normal development without any sign of apoptotic cell death.¹⁶ On the other hand, mnd2 (motor neuron degeneration 2) mice that harbor protease-deficient Omi S276C mutants, and Omi-knockout mice both suffer from progressive neurodegeneration, especially in striatum, and motor abnormalities similar to PD. Both mice fail to gain weight and die before postnatal day 40 due to neurodegeneration with progressive mitochondrial damage.^{17, 18, 19} Besides, mutations in the Omi gene have also been identified in PD patients.^{20, 21} Previous studies have shown that Omi has a vital role in the mitochondrial integrity, and the loss of protease activity leads to mitochondrial dysfunction, such as abnormal mitochondrial morphology and increased mtDNA mutation and deletions, increased susceptibility of mitochondrial membrane permeabilization, decreased mitochondrial membrane potential, and reduced mitochondrial density in mnd2 mice and Omi-knockout mice.^{17, 18, 22} Omi has been found to act downstream of PINK1, but parallel to parkin, in a mitochondrial stress sensing pathway to sense the different stresses, which may be defective in PD.²³ These findings suggest that the primary function of Omi is involved in neuroprotection, especially in the maintenance of mitochondrial homeostasis.^{23, 24}In this article, we identified that Omi cleaves glycogen synthase kinase 3β (GSK3β) to regulate PPARγ coactivator-1α (PGC-1α) abundance and to ensure mitochondrial biogenesis.     

Dynamic mobilization of PGC-1α mediates mitochondrial biogenesis for the protection of RGC-5 cells by resveratrol during serum deprivation

Mitochondrial dysfunction contributing to the pathogenesis of glaucomatous neurodegeneration has stimulated considerable interest recently. In this study, we explored the role of peroxisome proliferator activated receptor-γ co-activator 1α (PGC-1α) in resveratrol-triggered mitochondrial biogenesis for preventing apoptosis in a retinal ganglion cell line RGC-5. Our results showed that serum deprivation induced cell apoptosis in a time-dependent manner. Applying resveratrol maintained the normal mitochondrial membrane potential, decreased the levels of both total and cleaved caspase-3, and inhibited the release of cytochrome c, which subsequently enhanced cell survival. Moreover, resveratrol stimulated mitochondrial biogenesis by increasing the absolute quantity of mitochondria as well as their DNA copies. Treatment with resveratrol promoted the protein expression of SIRT1, but not PGC-1α; instead, resveratrol facilitated PGC-1α translocation from the cytoplasm to the nucleus and up-regulated NRF1 and TFAM, which were blocked by nicotinamide. Collectively, we demonstrate that the SIRT1-dependent PGC-1α subcellular translocation following resveratrol application potentially attenuates serum deprivation-elicited RGC-5 cell death, thereby raising the possibility of mitigating glaucomatous retinopathy by enhancement of mitochondrial biogenesis.     

Modular Evolution of PGC-1α in Vertebrates

In mammals, the peroxisome proliferator activated receptor (PPAR)γ coactivator-1α (PGC-1α) is a central regulator of mitochondrial gene expression, acting in concert with nuclear respiratory factor-1 (NRF-1) and the PPARs. Its role as a “master regulator” of oxidative capacity is clear in mammals, but its role in other vertebrates is ambiguous. In lower vertebrates, although PGC-1α seems to play a role in coordinating the PPARα axis as in mammals, it does not appear to be involved in NRF-1 regulation of mitochondrial content. To evaluate the evolutionary patterns of this coactivator in fish and mammals, we investigated the evolutionary trajectories of PGC-1α homologs in representative vertebrate lineages. A phylogeny of the PGC-1 paralogs suggested that the family diversified through repeated genome duplication events early in vertebrate evolution. Bayesian and maximum likelihood phylogenetic reconstructions of PGC-1α in representative vertebrate species revealed divergent evolutionary dynamics across the different functional domains of the protein. Specifically, PGC-1α exhibited strong conservation of the activation/PPAR interaction domain across vertebrates, whereas the NRF-1 and MEF2c interaction domains experienced accelerated rates of evolution in actinopterygian (fish lineages) compared to sarcopterygians (tetrapod lineages). Furthermore, analysis of the amino acid sequence of these variable domains revealed successive serine- and glutamine-rich insertions within the teleost lineages, with important ramifications for PGC-1α function in these lineages. Collectively, these results suggest modular evolution of the PGC-1α protein in vertebrates that could allow for lineage-specific divergences in the coactivating capabilities of this regulator.     

Enhanced lipid-but not carbohydrate-supported mitochondrial respiration in skeletal muscle of PGC-1α overexpressing mice

Skeletal muscle mitochondrial dysfunction has been linked to several disease states as well as the process of aging. A possible factor involved is the peroxisome proliferator-activated receptor (PPAR) γ co-activator 1α (PGC-1α), a major player in the regulation of skeletal muscle mitochondrial metabolism. However, it is currently unknown whether PGC-1α, besides stimulating mitochondrial proliferation, also affects the functional capacity per mitochondrion. Therefore, we here tested whether PGC-1α overexpression, besides increasing mitochondrial content, also leads to intrinsic mitochondrial adaptations. Skeletal muscle mitochondria from 10 male, muscle-specific PGC-1α overexpressing mice (PGC-1αTg) and 8 wild-type (WT) mice were isolated. Equal mitochondrial quantities were then analyzed for their oxidative capacity by high-resolution respirometry, fuelled by a carbohydrate-derived (pyruvate) and a lipid (palmitoyl-CoA plus carnitine) substrate. Additionally, mitochondria were tested for reactive oxygen species (superoxide) production and fatty acid (FA)-induced uncoupling. PGC-1αTg mitochondria were characterized by an improved intrinsic mitochondrial fat oxidative capacity as evidenced by pronounced increase in ADP-stimulated respiration (P < 0.001) and maximal uncoupled respiration (P < 0.001) upon palmitoyl-CoA plus carnitine. Interestingly, intrinsic mitochondrial capacity on a carbohydrate-derived substrate tended to be reduced. Furthermore, the sensitivity to FA-induced uncoupling was diminished in PGC-1αTg mitochondria (P = 0.02) and this was accompanied by a blunted reduction in mitochondrial ROS production upon FAs in PGC-1αTg versus WT mitochondria (P = 0.04). Uncoupling protein 3 (UCP3) levels were markedly reduced in PGC-1αTg mitochondria (P < 0.001). Taken together, in addition to stimulating mitochondrial proliferation in skeletal muscle, we show here that overexpression of PGC-1α leads to intrinsic mitochondrial adaptations that seem restricted to fat metabolism.     

The E3 ligase synoviolin controls body weight and mitochondrial biogenesis through negative regulation of PGC-1β

Obesity is a major global public health problem, and understanding its pathogenesis is critical for identifying a cure. In this study, a gene knockout strategy was used in post-neonatal mice to delete synoviolin (Syvn)1/Hrd1/Der3, an ER-resident E3 ubiquitin ligase with known roles in homeostasis maintenance. Syvn1 deficiency resulted in weight loss and lower accumulation of white adipose tissue in otherwise wild-type animals as well as in genetically obese (ob/ob and db/db) and adipose tissue-specific knockout mice as compared to control animals. SYVN1 interacted with and ubiquitinated the thermogenic coactivator peroxisome proliferator-activated receptor coactivator (PGC)-1β, and Syvn1 mutants showed upregulation of PGC-1β target genes and increase in mitochondrion number, respiration, and basal energy expenditure in adipose tissue relative to control animals. Moreover, the selective SYVN1 inhibitor LS-102 abolished the negative regulation of PGC-1β by SYVN1 and prevented weight gain in mice. Thus, SYVN1 is a novel post-translational regulator of PGC-1β and a potential therapeutic target in obesity treatment.     

Lipophilic methylene blue analogues enhance mitochondrial function and increase frataxin levels in a cellular model of Friedreich’s ataxia

Friedreich’s ataxia (FRDA) is an autosomal recessive neurodegenerative disorder resulting from reduced expression of the protein frataxin (FXN). Although its function is not fully understood, frataxin appears to help assemble iron sulfur clusters; these are critical for the function of many proteins, including those needed for mitochondrial energy production. Finding ways to increase FXN levels has been a major therapeutic strategy for this disease. Previously, we described a novel series of methylene violet analogues and their structural optimization as potential therapeutic agents for neurodegenerative and mitochondrial disorders. Presently, a series of methylene blue analogues has been synthesized and characterized for their in vitro biochemical and biological properties in cultured Friedreich’s ataxia lymphocytes. Favorable methylene blue analogues were shown to increase frataxin levels and mitochondrial biogenesis, and to improve aconitase activity. The analogues were found to be good ROS scavengers, and able to protect cultured FRDA lymphocytes from oxidative stress resulting from inhibition of complex I and from glutathione depletion. The analogues also preserved mitochondrial membrane potential and augmented ATP production. Our results suggest that analogue 5, emerging from the initial structure of the parent compound methylene blue (MB), represents a promising lead structure and lacks the cytotoxicity associated with the parent compound MB.     

ATGL-mediated fat catabolism regulates cardiac mitochondrial function via PPAR-α and PGC-1

Peroxisome proliferator-activated receptors (PPARs) are nuclear hormone receptors that regulate genes involved in energy metabolism and inflammation. For biological activity, PPARs require cognate lipid ligands, heterodimerization with retinoic X receptors, and coactivation by PPAR-γ coactivator-1α or PPAR-γ coactivator-1β (PGC-1α or PGC-1β, encoded by Ppargc1a and Ppargc1b, respectively). Here we show that lipolysis of cellular triglycerides by adipose triglyceride lipase (patatin-like phospholipase domain containing protein 2, encoded by Pnpla2; hereafter referred to as Atgl) generates essential mediator(s) involved in the generation of lipid ligands for PPAR activation. Atgl deficiency in mice decreases mRNA levels of PPAR-α and PPAR-δ target genes. In the heart, this leads to decreased PGC-1α and PGC-1β expression and severely disrupted mitochondrial substrate oxidation and respiration; this is followed by excessive lipid accumulation, cardiac insufficiency and lethal cardiomyopathy. Reconstituting normal PPAR target gene expression by pharmacological treatment of Atgl-deficient mice with PPAR-α agonists completely reverses the mitochondrial defects, restores normal heart function and prevents premature death. These findings reveal a potential treatment for the excessive cardiac lipid accumulation and often-lethal cardiomyopathy in people with neutral lipid storage disease, a disease marked by reduced or absent ATGL activity.