PGC-1alpha downstream transcription factors NRF-1 and TFAM are genetic modifiers of Huntington disease

Phoenixin 20 promotes neuronal mitochondrial biogenesis via CREB-PGC-1α pathway

Neurodegenerative disorders are dreadful diseases that affect millions of people worldwide. Mitochondrial dysfunction is closely associated with the development of neurodegenerative disorders. Phoenixin 20 is a newly discovered neuropeptide with a pleiotropic effect. This study showed that the presence of Phoenixin 20 promoted neuronal mitochondrial biogenesis in vitro. In cultured neuronal M17 cells, Phoenixin 20 increased the expression of mitochondrial regulators PGC-1α, NRF-1, and TFAM at both mRNA and protein levels. The treatment of Phoenixin 20 increased the ratio of mitochondrial vs nuclear DNA (mtDNA/nDNA) and the multiple mitochondrial gene expression as revealed by increasing mRNA expression of Tomm22, Timm50, Atp5d, Ndufs3, and protein expression of NDUFB8. At a cellular level, Phoenixin 20 promoted mitochondrial respiratory rate and cellular ATP production. Mechanistically, we found that Phoenixin 20 induced the phosphorylation of CREB, which suggests that Phoenixin 20 promoted the activation of the CREB pathway. The blockage of CREB by its selective inhibitor H89 prevented the effect of Phoenixin 20 on mitochondrial regulators and biogenesis. Moreover, the study showed that Phoenixin 20 induced the expression of its tentative receptor GPR173 at the mRNA and protein level, and the silence of GPR173 in neuronal cells ablated all its effect on mitochondrial regulation. Collectively, we showed that Phoenixin 20 promoted neuronal mitochondrial biogenesis via the regulation of CREB-PGC-1α pathway. This study revealed a new role and underlying mechanism of Phoenixin 20 in neuronal cells, suggesting it influences the therapeutic implication of neurodegenerative diseases.

Red Ginseng Improves Exercise Endurance by Promoting Mitochondrial Biogenesis and Myoblast Differentiation

Red ginseng has been reported to elicit various therapeutic effects relevant to cancer, diabetes, neurodegenerative diseases, and inflammatory diseases. However, the effect of red ginseng on exercise endurance and skeletal muscle function remains unclear. Herein, we sought to investigate whether red ginseng could affect exercise endurance and examined its molecular mechanism. Mice were fed with red ginseng extract (RG) and undertook swimming exercises to determine the time to exhaustion. Animals fed with RG had significantly longer swimming endurance. RG treatment was also observed to enhance ATP production levels in myoblasts. RG increased mRNA expressions of mitochondrial biogenesis regulators, NRF-1, TFAM, and PGC-1α, which was accompanied by an elevation in mitochondrial DNA, suggesting an enhancement in mitochondrial energy-generating capacity. Importantly, RG treatment induced phosphorylation of p38 and AMPK and upregulated PGC1α expression in both myoblasts and in vivo muscle tissue. In addition, RG treatment also stimulated C2C12 myogenic differentiation. Our findings show that red ginseng improves exercise endurance, suggesting that it may have applications in supporting skeletal muscle function and exercise performance.

Knockdown of HMGB1 Suppresses Hypoxia-Induced Mitochondrial Biogenesis in Pancreatic Cancer Cells

Purpose

To explore the regulatory effect of HMGB1 upon hypoxia-induced mitochondrial biogenesis in pancreatic cancer PANC1/CFPAC1 cells.

Methods

After a down-regulation of HMGB1 expression by lentivirus-mediated RNAi, the effect of knocking down HMGB1 on hypoxia-induced mitochondrial biogenesis was examined. NRF-1/TFAM expression, mtDNA copy number, ATP content and mitochondrial number/morphology in hypoxia-treated pancreatic cancer cells were detected by quantitative reverse transcription-polymerase chain reaction (qRT-PCR), Western blot, mtDNA and ATP assay kits and electron microscopy, respectively. Cell proliferation was measured by MTS assay. And protein and acetylation levels of PGC-1α and SIRT1 activity were detected by Western blot, immunoprecipitation (IP) and SIRT1 activity kit.

Results

Hypoxia enhanced the expressions of NRF-1/TFAM, boosted mtDNA copy number and ATP content and increased the number of mitochondria in pancreatic cancer cells while induction was suppressed by a knockdown of HMGB1. Knocking down HMGB1 expression lowered hypoxia-induced PGC-1α/SIRT1 expression and activity, phosphorylation of AMPK. PGC-1α over-expression by a plasmid transfection failed to boost mtDNA copy number or ATP content in HMGB1-knockdown cells. A knockdown of HMGB1 attenuated hypoxia with AICAR (an AMPK activator)-induced expression of NRF-1, TFAM, PGC-1α, SIRT1 and the proteins of complexes Ⅰ& Ⅲ and reduced the acetylation level of PGC-1α/SIRT1 activity. Additionally, SRT1720 (a SIRT1 activator)-induced elevation in SIRT1 activity boosted hypoxia-induced PGC-1α deacetylation, except in HMGB1-knockdown cells.

Conclusion

As a novel regulator of mitochondrial biogenesis via AMPK/SIRT1 pathway under hypoxia, HMGB1 may become a potential drug target for therapeutic interventions in pancreatic cancer.

Innate Immunity: A Common Denominator between Neurodegenerative and Neuropsychiatric Diseases

The intricate relationships between innate immunity and brain diseases raise increased interest across the wide spectrum of neurodegenerative and neuropsychiatric disorders. Barriers, such as the blood–brain barrier, and innate immunity cells such as microglia, astrocytes, macrophages, and mast cells are involved in triggering disease events in these groups, through the action of many different cytokines. Chronic inflammation can lead to dysfunctions in large-scale brain networks. Neurodegenerative diseases, such as Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, amyotrophic lateral sclerosis, and frontotemporal dementia, are associated with a substrate of dysregulated immune responses that impair the central nervous system balance. Recent evidence suggests that similar phenomena are involved in psychiatric diseases, such as depression, schizophrenia, autism spectrum disorders, and post-traumatic stress disorder. The present review summarizes and discusses the main evidence linking the innate immunological response in neurodegenerative and psychiatric diseases, thus providing insights into how the responses of innate immunity represent a common denominator between diseases belonging to the neurological and psychiatric sphere. Improved knowledge of such immunological aspects could provide the framework for the future development of new diagnostic and therapeutic approaches.

Mitochondrial Dysfunction and Changes in High-Energy Compounds in Different Cellular Models Associated to Hypoxia: Implication to Schizophrenia

Schizophrenia (SZ) is a multifactorial mental disorder, which has been associated with a number of environmental factors, such as hypoxia. Considering that numerous neural mechanisms depends on energetic supply (ATP synthesis), the maintenance of mitochondrial metabolism is essential to keep cellular balance and survival. Therefore, in the present work, we evaluated functional parameters related to mitochondrial function, namely calcium levels, mitochondrial membrane potential, redox homeostasis, high-energy compounds levels and oxygen consumption, in astrocytes from control (Wistar) and Spontaneously Hypertensive Rats (SHR) animals exposed both to chemical and gaseous hypoxia. We show that astrocytes after hypoxia presented depolarized mitochondria, disturbances in Ca²⁺ handling, destabilization in redox system and alterations in ATP, ADP, Pyruvate and Lactate levels, in addition to modification in NAD⁺/NADH ratio, and Nfe2l2 and Nrf1 expression. Interestingly, intrauterine hypoxia also induced augmentation in mitochondrial biogenesis and content. Altogether, our data suggest that hypoxia can induce mitochondrial deregulation and a decrease in energy metabolism in the most prevalent cell type in the brain, astrocytes. Since SHR are also considered an animal model of SZ, our results can likewise be related to their phenotypic alterations and, therefore, our work also allow an increase in the knowledge of this burdensome disorder.

Causal roles of mitochondrial dynamics in longevity and healthy aging

Mitochondria are organized in the cell in the form of a dynamic, interconnected network. Mitochondrial dynamics, regulated by mitochondrial fission, fusion, and trafficking, ensure restructuring of this complex reticulum in response to nutrient availability, molecular signals, and cellular stress. Aberrant mitochondrial structures have long been observed in aging and age-related diseases indicating that mitochondrial dynamics are compromised as cells age. However, the specific mechanisms by which aging affects mitochondrial dynamics and whether these changes are causally or casually associated with cellular and organismal aging is not clear. Here, we review recent studies that show specifically how mitochondrial fission, fusion, and trafficking are altered with age. We discuss factors that change with age to directly or indirectly influence mitochondrial dynamics while examining causal roles for altered mitochondrial dynamics in healthy aging and underlying functional outputs that might affect longevity. Lastly, we propose that altered mitochondrial dynamics might not just be a passive consequence of aging but might constitute an adaptive mechanism to mitigate age-dependent cellular impairments and might be targeted to increase longevity and promote healthy aging.

PGC-1α, Sirtuins and PARPs in Huntington's Disease and Other Neurodegenerative Conditions: NAD+ to Rule Them All

In this review, we summarize the available published information on the neuroprotective effects of increasing nicotinamide adenine dinucleotide (NAD+) levels in Huntington's disease models. We discuss the rationale of potential therapeutic benefit of administering nicotinamide riboside (NR), a safe and effective NAD+ precursor. We discuss the agonistic effect on the Sirtuin1-PGC-1α-PPAR pathway as well as Sirtuin 3, which converge in improving mitochondrial function, decreasing ROS production and ameliorating bioenergetics deficits. Also, we discuss the potential synergistic effect of increasing NAD+ combined with PARPs inhibitors, as a clinical therapeutic option not only in HD, but other neurodegenerative conditions.

Overexpression of lncRNA EPB41L4A-AS1 Induces Metabolic Reprogramming in Trophoblast Cells and Placenta Tissue of Miscarriage

Long non-coding RNAs (lncRNAs) have been shown to be crucial regulators in numerous human diseases. However, little is known about their effects on early recurrent miscarriage (RM). Here we aimed to investigate the role of lncRNA EPB41L4A-AS1 on placental trophoblast cell metabolic reprogramming, which might be involved in the pathogenesis of RM. After microarray and GEO database analyses, we found that EPB41L4A-AS1 was significantly increased in early RM placental tissue, and this increase may relate to estradiol-mediated upregulation of PGC-1α. EPB41L4A-AS1 overexpression inhibits glycolysis but increases the dependence on fatty acid oxidation in mitochondrion metabolism and suppresses the Warburg effect, which is necessary for rapid growth of the placental villus, leading to miscarriage. Mechanistic analyses demonstrated that EPB41L4A-AS1 functions as a lncRNA in the regulation of VDAC1 and HIF-1α expression through enhancement of H3K4me3 levels in the promoters of VDAC1 and HIF1A-AS1, a natural antisense transcript (NAT) lncRNA of HIF-1α. Taken together, these findings demonstrate that aberrant expression of EPB41L4A-AS1 is involved in the etiology of early RM, and it may be a candidate diagnostic hallmark and a potential therapeutic target for early RM treatment.

Role of PGC-1α in Mitochondrial Quality Control in Neurodegenerative Diseases

As one of the major cell organelles responsible for ATP production, it is important that neurons maintain mitochondria with structural and functional integrity; this is especially true for neurons with high metabolic requirements. When mitochondrial damage occurs, mitochondria are able to maintain a steady state of functioning through molecular and organellar quality control, thus ensuring neuronal function. And when mitochondrial quality control (MQC) fails, mitochondria mediate apoptosis. An apparently key molecule in MQC is the transcriptional coactivator peroxisome proliferator activated receptor γ coactivator-1α (PGC-1α). Recent findings have demonstrated that upregulation of PGC-1α expression in neurons can modulate MQC to prevent mitochondrial dysfunction in certain in vivo and in vitro aging or neurodegenerative encephalopathy models, such as Huntington's disease, Alzheimer's disease, and Parkinson's disease. Because mitochondrial function and quality control disorders are the basis of pathogenesis in almost all neurodegenerative diseases (NDDs), the role of PGC-1α may make it a viable entry point for the treatment of such diseases. This review focuses on multi-level MQC in neurons, as well as the regulation of MQC by PGC-1α in these major NDDs.

Testosterone Deficiency Caused by Castration Modulates Mitochondrial Biogenesis Through the AR/PGC1α/TFAM Pathway

Mammalian mitochondrial biogenesis is a complex process involving mitochondrial proliferation and differentiation. Mitochondrial DNA transcription factor A (TFAM), which encodes a major component of a protein-mitochondrial DNA (mtDNA) complex, is regulated by peroxisome proliferator-activated receptor γ coactivator 1α (PGC1α). Testosterone is the primary male sex hormone and plays an increasingly important role in mammalian development through its interaction with androgen receptor (AR). However, the function of AR in mitochondrial biogenesis induced by testosterone deficiency has not been investigated. Here, we explored the molecular mechanism underlying the effect of testosterone deficiency on mitochondrial biogenesis using a Yorkshire boar model. Testosterone deficiency caused by castration induced changes in mtDNA copy numbers in various tissues, and AR showed the opposite tendency to that of mtDNA copy number, particularly in adipose tissues and muscle tissues. In addition, castration weakened the correlation of PGC1α and mtDNA copy number, while AR and TFAM showed a relatively high correlation in both control and castrated pigs. Furthermore, luciferase assays revealed that AR binds to potential AR elements in the TFAM promoter to promote TFAM expression. Taken together, testosterone may be involved in the pathway linking PGC1α to mitochondrial biogenesis through the interaction between AR and TFAM.

ATAD3A oligomerization causes neurodegeneration by coupling mitochondrial fragmentation and bioenergetics defects

Mitochondrial fragmentation and bioenergetic failure manifest in Huntington’s disease (HD), a fatal neurodegenerative disease. The factors that couple mitochondrial fusion/fission with bioenergetics and their impacts on neurodegeneration however remain poorly understood. Our proteomic analysis identifies mitochondrial protein ATAD3A as an interactor of mitochondrial fission GTPase, Drp1, in HD. Here we show that, in HD, ATAD3A dimerization due to deacetylation at K135 residue is required for Drp1-mediated mitochondrial fragmentation. Disturbance of ATAD3A steady state impairs mtDNA maintenance by disrupting TFAM/mtDNA binding. Blocking Drp1/ATAD3A interaction with a peptide, DA1, abolishes ATAD3A oligomerization, suppresses mitochondrial fragmentation and mtDNA lesion, and reduces bioenergetic deficits and cell death in HD mouse- and patient-derived cells. DA1 treatment reduces behavioral and neuropathological phenotypes in HD transgenic mice. Our findings demonstrate that ATAD3A plays a key role in neurodegeneration by linking Drp1-induced mitochondrial fragmentation to defective mtDNA maintenance, suggesting that DA1 might be useful for developing HD therapeutics.

Huntington’s disease leads to mitochondrial fragmentation and bioenergetic failure, although how the two events are connected is poorly understood. Here, Zhao et al. identify ATAD3A as a molecular linker and show that a peptide inhibitor of ATAD3A oligomerization suppresses HD phenotypes.

Neuronal Apolipoprotein E4 Expression Results in Proteome-Wide Alterations and Compromises Bioenergetic Capacity by Disrupting Mitochondrial Function

Apolipoprotein (apo) E4, the major genetic risk factor for Alzheimer's disease (AD), alters mitochondrial function and metabolism early in AD pathogenesis. When injured or stressed, neurons increase apoE synthesis. Because of its structural difference from apoE3, apoE4 undergoes neuron-specific proteolysis, generating fragments that enter the cytosol, interact with mitochondria, and cause neurotoxicity. However, apoE4's effect on mitochondrial respiration and metabolism is not understood in detail. Here we used biochemical assays and proteomic profiling to more completely characterize the effects of apoE4 on mitochondrial function and cellular metabolism in Neuro-2a neuronal cells stably expressing apoE4 or apoE3. Under basal conditions, apoE4 impaired respiration and increased glycolysis, but when challenged or stressed, apoE4-expressing neurons had 50% less reserve capacity to generate ATP to meet energy requirements than apoE3-expressing neurons. ApoE4 expression also decreased the NAD+/NADH ratio and increased the levels of reactive oxygen species and mitochondrial calcium. Global proteomic profiling revealed widespread changes in mitochondrial processes in apoE4 cells, including reduced levels of numerous respiratory complex subunits and major disruptions to all detected subunits in complex V (ATP synthase). Also altered in apoE4 cells were levels of proteins related to mitochondrial endoplasmic reticulum-associated membranes, mitochondrial fusion/fission, mitochondrial protein translocation, proteases, and mitochondrial ribosomal proteins. ApoE4-induced bioenergetic deficits led to extensive metabolic rewiring, but despite numerous cellular adaptations, apoE4-expressing neurons remained vulnerable to metabolic stress. Our results provide insights into potential molecular targets of therapies to correct apoE4-associated mitochondrial dysfunction and altered cellular metabolism.

Genetic modifiers of age-at-onset in polyglutamine diseases

Polyglutamine (polyQ) diseases are a group of clinically and genetically heterogeneous neurodegenerative diseases. Expansion size correlates with age-at-onset (AO) and severity, and shows a critical threshold for each polyQ disease. Although an expanded CAG tract is sufficient to trigger disease, not all variation in AO is explained by (CAG)_n length, which suggests the contribution of other modifying factors. Methods used to identify genetic modifiers in polyQ diseases have progressed from candidate genes to unbiased genome-wide searches. Inconsistency of results from candidate-genes studies are partly explained by sample size, study design and variable population frequency of "polymorphisms"; a genome-wide search may help elucidating more precise disease mechanisms underlying specific interaction networks. We review known genetic modifiers for polyQ diseases, and discuss developing strategies to find modulation, from common variants to networks disclosing small cumulative effects of key genes and modifying pathways. This may lead to a better understanding of genotype-phenotype correlation and the proposal of new potential targets for therapeutical interventions.

Mitochondrial dynamics, a key executioner in neurodegenerative diseases

Neurodegenerative diseases (NDs) are the group of disorder that includes brain, peripheral nerves, spinal cord and results in sensory and motor neuron dysfunction. Several studies have shown that mitochondrial dynamics and their axonal transport play a central role in most common NDs such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD) and Amyotrophic Lateral Sclerosis (ALS) etc. In normal physiological condition, there is a balance between mitochondrial fission and fusion process while any alteration to these processes cause defect in ATP (Adenosine Triphosphate) biogenesis that lead to the onset of several NDs. Also, mitochondria mediated ROS may induce lipid and protein peroxidation, energy deficiency environment in the neurons and results in cell death and defective neurotransmission. Though, mitochondria is a well-studied cell organelle regulating the cellular energy demands but still, its detail role or association in NDs is under observation. In this review, we have summarized an updated mitochondria and their possible role in different NDs with the therapeutic strategy to improve the mitochondrial functions.

Essential roles of mitochondrial biogenesis regulator Nrf1 in retinal development and homeostasis

Background

Mitochondrial dysfunction has been implicated in the pathologies of a number of retinal degenerative diseases in both the outer and inner retina. In the outer retina, photoreceptors are particularly vulnerable to mutations affecting mitochondrial function due to their high energy demand and sensitivity to oxidative stress. However, it is unclear how defective mitochondrial biogenesis affects neural development and contributes to neural degeneration. In this report, we investigated the in vivo function of nuclear respiratory factor 1 (Nrf1), a major transcriptional regulator of mitochondrial biogenesis in both proliferating retinal progenitor cells (RPCs) and postmitotic rod photoreceptor cells (PRs).

Methods

We used mouse genetic techniques to generate RPC-specific and rod PR-specific Nrf1 conditional knockout mouse models. We then applied a comprehensive set of tools, including histopathological and molecular analyses, RNA-seq, and electroretinography on these mouse lines to study Nrf1-regulated genes and Nrf1’s roles in both developing retinas and differentiated rod PRs. For all comparisons between genotypes, a two-tailed two-sample student’s t-test was used. Results were considered significant when P < 0.05.

Results

We uncovered essential roles of Nrf1 in cell proliferation in RPCs, cell migration and survival of newly specified retinal ganglion cells (RGCs), neurite outgrowth in retinal explants, reconfiguration of metabolic pathways in RPCs, and mitochondrial morphology, position, and function in rod PRs.

Conclusions

Our findings provide in vivo evidence that Nrf1 and Nrf1-mediated pathways have context-dependent and cell-state-specific functions during neural development, and disruption of Nrf1-mediated mitochondrial biogenesis in rod PRs results in impaired mitochondria and a slow, progressive degeneration of rod PRs. These results offer new insights into the roles of Nrf1 in retinal development and neuronal homeostasis and the differential sensitivities of diverse neuronal tissues and cell types of dysfunctional mitochondria. Moreover, the conditional Nrf1 allele we have generated provides the opportunity to develop novel mouse models to understand how defective mitochondrial biogenesis contributes to the pathologies and disease progression of several neurodegenerative diseases, including glaucoma, age-related macular degeneration, Parkinson’s diseases, and Huntington’s disease.

Increased mitochondrial turnover in the skeletal muscle of fasted, castrated mice is related to the magnitude of autophagy activation and muscle atrophy

Androgen-deficiency promotes muscle atrophy in part by increasing autophagy-mediated muscle protein breakdown during the fasted state, but factors contributing to this remain undefined. To identify novel factors, mice were subjected to sham or castration surgery. Seven-weeks post-surgery, mice were fasted overnight, refed for 30 min, and fasted another 4.5 h before sacrifice. BNIP3-mediated turnover of mitochondria was increased within the atrophied tibialis anterior (TA) of castrated mice and related to the magnitude of muscle atrophy and autophagy activation (i.e. decreased p62 protein content), thus linking turnover of potentially dysfunctional mitochondria with autophagy-mediated atrophy. Autophagy induction was likely facilitated by AMPK activation as a stress survival mechanism since phosphorylation of AMPK (Thr172), as well as the pro survival kinases Akt (Thr308) and (ERK1/2 Thr202/Tyr204), were increased by castration. Together, these data identify a novel relationship between mitochondrial turnover in the fasted state with autophagy activation and muscle atrophy following androgen depletion.

Cocoa beans improve mitochondrial biogenesis via PPARγ/PGC1α dependent signalling pathway in MPP+ intoxicated human neuroblastoma cells (SH-SY5Y)

Polyphenols are shown to protect from or delay the progression of chronic neurodegenerative diseases. Mitochondrial dysfunction plays a key role in the pathogenesis of Parkinson's disease (PD). This study was aims to gain insight into the role of ahydroalcoholic extract of cocoa (standardised for epicatechin content) on mitochondrial biogenesis in MPP⁺ intoxicated human neuroblastoma cells (SHSY5Y). The effects of cocoa on PPARγ, PGC1α, Nrf2 and TFAM protein expression and mitochondrial membrane potential were evaluated. A pre-exposure to cocoa extract decreased reactive oxygen species formation and restored mitochondrial membrane potential. The cocoa extract was found to up-regulate the expression of PPARγ and the downstream signalling proteins PGC1α, Nrf2 and TFAM. It increased the expression of the anti-apoptotic protein BCl2 and increased superoxide dismutase activity. Further, the cocoa extract down-regulated the expression of mitochondria fission 1 (Fis1) and up-regulated the expression of mitochondria fusion 2 (Mfn2) proteins, suggesting an improvement in mitochondrial functions in MPP⁺ intoxicated cells upon treatment with cocoa. Interestingly, cocoa up-regulates the expression of tyrosine hydroxylase, the rate limiting enzyme in dopamine synthesis. No change in the expression of PPARγ on treatment with cocoa extract was observed when the cells were pre-treated with PPARγ antagonist GW9662. This data suggests that cocoa mediates mitochondrial biogenesis via a PPARγ/PGC1α dependent signalling pathway and also has the ability to improve dopaminergic functions by increasing tyrosine hydroxylase expression. Based on our data, we propose that a cocoa bean extract and products thereof could be used as potential nutritional supplements for neuroprotection in PD.

Effects of Rhizome Extract of Dioscorea batatas and Its Active Compound, Allantoin, on the Regulation of Myoblast Differentiation and Mitochondrial Biogenesis in C2C12 Myotubes

With the aging process, a loss of skeletal muscle mass and dysfunction related to metabolic syndrome is observed in older people. Yams are commonly use in functional foods and medications with various effects. The present study was conducted to investigate the effects of rhizome extract of Dioscorea batatas (Dioscoreae Rhizoma, Chinese yam) and its bioactive compound, allantoin, on myoblast differentiation and mitochondrial biogenesis in skeletal muscle cells. Yams were extracted in water and allantoin was analyzed by high performance liquid chromatography (HPLC). The expression of myosin heavy chain (MyHC) and mitochondrial biogenesis-regulating factors, peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), sirtuin-1 (Sirt-1), nuclear respiratory factor-1 (NRF-1) and transcription factor A, mitochondrial (TFAM), and the phosphorylation of AMP-activated protein kinase (AMPK) and acetyl-CoA carboxylase (ACC) were determined in C2C12 myotubes by reverse transcriptase (RT)-polymerase chain reaction (RT-PCR) or western blot. The glucose levels and total ATP contents were measured by glucose consumption, glucose uptake and ATP assays, respectively. Treatment with yam extract (1 mg/mL) and allantoin (0.2 and 0.5 mM) significantly increased MyHC expression compared with non-treated myotubes. Yam extract and allantoin significantly increased the expression of PGC-1α, Sirt-1, NRF-1 and TFAM, as well as the phosphorylation of AMPK and ACC in C2C12 myotubes. Furthermore, yam extract and allantoin significantly increased glucose uptake levels and ATP contents. Finally, HPLC analysis revealed that the yam water extract contained 1.53% of allantoin. Yam extract and allantoin stimulated myoblast differentiation into myotubes and increased energy production through the upregulation of mitochondrial biogenesis regulators. These findings indicate that yam extract and allantoin can help to prevent skeletal muscle dysfunction through the stimulation of the energy metabolism.

Acetylation of Mitochondrial Proteins in the Heart: The Role of SIRT3

A growing number of studies have demonstrated the role of post-translational modifications of proteins, particularly acetylation, in human diseases including neurodegenerative and cardiovascular diseases, diabetes, cancer, and in aging. Acetylation of mitochondrial proteins has been shown to be involved in the pathogenesis of cardiac diseases such as myocardial infarction (ischemia-reperfusion) and heart failure. Indeed, over 60% of mitochondrial proteins contain acetylation sites, and most of these proteins are involved in mitochondrial bioenergetics. Mitochondrial non-enzymatic acetylation is enabled by acetyl-coenzyme A abundance and serves as the primary pathway of acetylation in mitochondria. Hence, regulation of enzymatic deacetylation becomes the most important mechanism to control acetylation/deacetylation of mitochondrial proteins. Acetylation/deacetylation of mitochondrial proteins has been regarded as a key regulator of mitochondrial metabolism and function. Proteins are deacetylated by NAD⁺-dependent deacetylases known as sirtuins (SIRTs). Among seven sirtuin isoforms, only SIRT3, SIRT4, and SIRT5 are localized in the mitochondria. SIRT3 is the main mitochondrial sirtuin which plays a key role in maintaining metabolic and redox balance in the mitochondria under physiological and pathological conditions. SIRT3 regulates the enzymatic activity of proteins involved in fatty acid oxidation, tricarboxylic acid cycle, electron transport chain, and oxidative phosphorylation. Although many enzymes have been identified as targets for SIRT3, cardiac-specific SIRT3 effects and regulations could differ from those in non-cardiac tissues. Therefore, it is important to elucidate the contribution of SIRT3 and mitochondrial protein acetylation/deacetylation in mitochondrial metabolism and cardiac dysfunction. Here, we summarize previous studies and provide a comprehensive analysis of the role of SIRT3 in mitochondria metabolism and bioenergetics under physiological conditions and in cardiac diseases. In addition, the review discusses mitochondrial protein acetylation as a potential target for cardioprotection.

PGC-1α sparks the fire of neuroprotection against neurodegenerative disorders

Recently, growing evidence has demonstrated that peroxisome proliferator activated receptor γ (PPARγ) coactivator-1α (PGC-1α) is a superior transcriptional regulator that acts via controlling the expression of anti-oxidant enzymes and uncoupling proteins and inducing mitochondrial biogenesis, which plays a beneficial part in the central nervous system (CNS). Given the significance of PGC-1α, we summarize the current literature on the molecular mechanisms and roles of PGC-1α in the CNS. Thus, in this review, we first briefly introduce the basic characteristics regarding PGC-1α. We then depict some of its important cerebral functions and discuss upstream modulators, partners, and downstream effectors of the PGC-1α signaling pathway. Finally, we highlight recent progress in research on the involvement of PGC-1α in certain major neurodegenerative disorders (NDDs), including Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis. Collectively, the data presented here may be useful for supporting the future potential of PGC-1α as a therapeutic target.

RNA Aptamers Rescue Mitochondrial Dysfunction in a Yeast Model of Huntington's Disease

Huntington’s disease (HD) is associated with the misfolding and aggregation of mutant huntingtin harboring an elongated polyglutamine stretch at its N terminus. A distinguishing pathological hallmark of HD is mitochondrial dysfunction. Any strategy that can restore the integrity of the mitochondrial environment should have beneficial consequences for the disease. Specific RNA aptamers were selected that were able to inhibit aggregation of elongated polyglutamine stretch containing mutant huntingtin fragment (103Q-htt). They were successful in reducing the calcium overload, which leads to mitochondrial membrane depolarization in case of HD. In one case, the level of Ca²⁺ was restored to the level of cells not expressing 103Q-htt, suggesting complete recovery. The presence of aptamers was able to increase mitochondrial mass in cells expressing 103Q-htt, along with rescuing loss of mitochondrial genome. The oxidative damage to the proteome was prevented, which led to increased viability of cells, as monitored by flow cytometry. Thus, the presence of aptamers was able to inhibit aggregation of mutant huntingtin fragment and restore mitochondrial dysfunction in the HD cell model, confirming the advantage of the strategy in a disease-relevant parameter.

The mitochondrial transcription factor TFAM in neurodegeneration: emerging evidence and mechanisms

The mitochondrial transcription factor A, or TFAM, is a mitochondrial DNA (mtDNA)-binding protein essential for genome maintenance. TFAM functions in determining the abundance of the mitochondrial genome by regulating packaging, stability, and replication. More recently, TFAM has been shown to play a central role in the mtDNA stress-mediated inflammatory response. Emerging evidence indicates that decreased mtDNA copy number is associated with several aging-related pathologies; however, little is known about the association of TFAM abundance and disease. In this Review, we evaluate the potential associations of altered TFAM levels or mtDNA copy number with neurodegeneration. We also describe potential mechanisms by which mtDNA replication, transcription initiation, and TFAM-mediated endogenous danger signals may impact mitochondrial homeostasis in Alzheimer, Huntington, Parkinson, and other neurodegenerative diseases.

Cell-Specific Deletion of PGC-1α from Medium Spiny Neurons Causes Transcriptional Alterations and Age-Related Motor Impairment

Multiple lines of evidence indicate that a reduction in the expression and function of the transcriptional coactivator peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α) is associated with neurodegeneration in diseases such as Huntington's disease (HD). Polymorphisms in the PGC-1α gene modify HD progression and PGC-1α expression is reduced in striatal medium spiny neurons (MSNs) of HD patients and mouse models. However, neither the MSN-specific function of PGC-1α nor the contribution of PGC-1α deficiency to motor dysfunction is known. We identified novel, PGC-1α-dependent transcripts involved in RNA processing, signal transduction, and neuronal morphology and confirmed reductions in these transcripts in male and female mice lacking PGC-1α specifically in MSNs, indicating a cell-autonomous effect in this population. MSN-specific PGC-1α deletion caused reductions in previously identified neuronal and metabolic PGC-1α-dependent genes without causing striatal vacuolizations. Interestingly, these mice exhibited a hypoactivity with age, similar to several HD animal models. However, these newly identified PGC-1α-dependent genes were upregulated with disease severity and age in knock-in HD mouse models independent of changes in PGC-1α transcript, contrary to what would be predicted from a loss-of-function etiological mechanism. These data indicate that PGC-1α is necessary for MSN transcriptional homeostasis and function with age and that, whereas PGC-1α loss in MSNs does not replicate an HD-like phenocopy, its downstream genes are altered in a repeat-length and age-dependent fashion. Understanding the additive effects of PGC-1α gene functional variation and mutant huntingtin on transcription in this cell type may provide insight into the selective vulnerability of MSNs in HD.SIGNIFICANCE STATEMENT Reductions in peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α)-mediated transcription have been implicated in the pathogenesis of Huntington's disease (HD). We show that, although PGC-1α-dependent transcription is necessary to maintain medium spiny neuron (MSN) function with age, its loss is insufficient to cause striatal atrophy in mice. We also highlight a set of genes that can serve as proxies for PGC-1α functional activity in the striatum for target engagement studies. Furthermore, we demonstrate that PGC-1α-dependent genes are upregulated in a dose- and age-dependent fashion in HD mouse models, contrary to what would be predicted from a loss-of-function etiological mechanism. However, given this role for PGC-1α in MSN transcriptional homeostasis, it is important to consider how genetic variation in PGC-1α could contribute to mutant-huntingtin-induced cell death and disease progression.

Mitochondrial Biogenesis in Response to Chromium (VI) Toxicity in Human Liver Cells

Hexavalent chromium (Cr(VI)) is a ubiquitous environmental pollutant, which poses a threat to human public health. Recent studies have shown that mitochondrial biogenesis can be activated by inflammatory and oxidative stress. However, whether mitochondrial biogenesis is involved in Cr(VI)-induced hepatotoxicity is unclear. Here, we demonstrated the induction of inflammatory response and oxidative stress, as indicated by upregulation of inflammatory factors and reactive oxygen species (ROS). Subsequently, we demonstrated that mitochondrial biogenesis, comprising the mitochondrial DNA copy number and mitochondrial mass, was significantly increased in HepG2 cells exposed to low concentrations of Cr(VI). Expression of genes related to mitochondrial function complex I and complex V was upregulated at low concentrations of Cr(VI). mRNA levels of antioxidant enzymes, including superoxide dismutase 1 and 2 (SOD1 and SOD2, respectively), kech like ECH associate protein 1 (KEAP1) and nuclear respiratory factor 2 (NRF-2), were also upregulated. Consistent with the above results, mRNA and protein levels of key transcriptional regulators of mitochondrial biogenesis such as the peroxisome-proliferator-activated receptor γ coactivator-1α (PGC-1α), NRF-1 and mitochondrial transcription factor A (TFAM) were increased by low concentrations of Cr(VI) in HepG2 cells. Moreover, we found that PGC-1α and NRF-1 tended to translocate into the nucleus. The expression of genes potentially involved in mitochondrial biogenesis pathways, including mRNA level of silent information regulator-1 (SIRT1), forkhead box class-O (FOXO1), threonine kinase 1 (AKT1), and cAMP response element-binding protein (CREB1), was also upregulated. In contrast, mitochondrial biogenesis was inhibited and the expression of its regulatory factors and antioxidants was downregulated at high and cytotoxic concentrations of Cr(VI) in HepG2 cells. It is believed that pretreatment with α-tocopherol could be acting against the mitochondrial biogenesis imbalance induced by Cr(VI). In conclusion, our study suggests that the homeostasis of mitochondrial biogenesis may be an important cellular compensatory mechanism against Cr(VI)-induced toxicity and a promising detoxification target.

Laquinimod treatment in the R6/2 mouse model

The transgenic mouse model R6/2 exhibits Huntington's disease (HD)-like deficits and basic pathophysiological similarities. We also used the pheochromocytoma-12 (PC12)-cell-line-model to investigate the effect of laquinimod on metabolic activity. Laquinimod is an orally administered immunomodulatory substance currently under development for the treatment of multiple sclerosis (MS) and HD. As an essential effect, increased levels of BDNF were observed. Therefore, we investigated the therapeutic efficacy of laquinimod in the R6/2 model, focusing on its neuroprotective capacity. Weight course and survival were not influenced by laquinimod. Neither were any metabolic effects seen in an inducible PC12-cell-line model of HD. As a positive effect, motor functions of R6/2 mice at the age of 12 weeks significantly improved. Preservation of morphologically intact neurons was found after treatment in the striatum, as revealed by NeuN, DARPP-32, and ubiquitin. Biochemical analysis showed a significant increase in the brain-derived neurotrophic factor (BDNF) level in striatal but not in cortical neurons. The number of mutant huntingtin (mhtt) and inducible nitric oxide synthase (iNOS) positive cells was reduced in both the striatum and motor cortex following treatment. These findings suggest that laquinimod could provide a mild effect on motor function and striatal histopathology, but not on survival. Besides influences on the immune system, influence on BDNF-dependent pathways in HD are discussed.

Mitochondrial biogenesis and clearance: a balancing act

Mitochondria are semi-autonomous organelles of prokaryotic origin that are postulated to have been acquired by eukaryotic cells through an early endosymbiotic event. Except for their main role in energy production, they are also implicated in fundamental cellular processes, including ion homeostasis, lipid metabolism, and initiation of apoptotic cell death. Perturbed mitochondrial function has been correlated with severe human pathologies such as type-2 diabetes, cardiovascular, and neurodegenerative diseases. Thus, proper mitochondrial physiology is a prerequisite for health and survival. Cells have developed sophisticated and elaborate mechanisms to adapt to stress conditions and alterations in metabolic demands, by regulating mitochondrial number and function. Hence, the generation of new and the removal of damaged or unwanted mitochondria are highly regulated processes that need to be accurately coordinated for the maintenance of mitochondrial and cellular homeostasis. Here, we survey recent research findings that advance our understanding and highlight the importance of the underlying molecular mechanisms.

Mitonuclear linkage disequilibrium in human populations

There is extensive evidence from model systems that disrupting associations between co-adapted mitochondrial and nuclear genotypes can lead to deleterious and even lethal consequences. While it is tempting to extrapolate from these observations and make inferences about the human-health effects of altering mitonuclear associations, the importance of such associations may vary greatly among species, depending on population genetics, demographic history and other factors. Remarkably, despite the extensive study of human population genetics, the statistical associations between nuclear and mitochondrial alleles remain largely uninvestigated. We analysed published population genomic data to test for signatures of historical selection to maintain mitonuclear associations, particularly those involving nuclear genes that encode mitochondrial-localized proteins (N-mt genes). We found that significant mitonuclear linkage disequilibrium (LD) exists throughout the human genome, but these associations were generally weak, which is consistent with the paucity of population genetic structure in humans. Although mitonuclear LD varied among genomic regions (with especially high levels on the X chromosome), N-mt genes were statistically indistinguishable from background levels, suggesting that selection on mitonuclear epistasis has not preferentially maintained associations involving this set of loci at a species-wide level. We discuss these findings in the context of the ongoing debate over mitochondrial replacement therapy.

Complexity of Compensatory Effects in Nrf1 Knockdown: Linking Undeveloped Anxiety-Like Behavior to Prevented Mitochondrial Dysfunction and Oxidative Stress

Anxiety-related disorders are complex illnesses that underlying molecular mechanisms need to be understood. Mitochondria stand as an important link between energy metabolism, oxidative stress, and anxiety. The nuclear factor, erythroid-derived 2,-like 1(Nrf1) is a member of the cap "n" collar subfamily of basic region leucine zipper transcription factors and plays the major role in regulating the adaptive response to oxidants and electrophiles within the cell. Here, we injected small interfering RNA (siRNA) targeting Nrf1 in dorsal third ventricle of adult male albino Wistar rats and subsequently examined the effect of this silencing on anxiety-related behavior. We also evaluated apoptotic markers and mitochondrial biogenesis factors, along with electron transport chain activity in three brain regions: hippocampus, amygdala, and prefrontal cortex. Our data revealed that in the group that received Nrf1-siRNA, anxiety-related behavior did not show any significant changes compared to the control group. Caspase-3 did not increase in Nrf1-siRNA-injected rats even though Bax/Bcl2 ratio markedly elevated in Nrf1-knockdown rats in all three mentioned regions compared to control rats. Also, Nrf1 silencing of complex I and II-III did not alter, generally. In addition, Nrf1-knockdown affected mitochondrial biogenesis markers. The level of peroxisome proliferator-activated receptor gamma coactivator-1α and cytochrome-c increased, which indicates a possible role for mitochondrial biogenesis in anxiety.

Mito-nuclear co-evolution: the positive and negative sides of functional ancient mutations

Most cell functions are carried out by interacting factors, thus underlying the functional importance of genetic interactions between genes, termed epistasis. Epistasis could be under strong selective pressures especially in conditions where the mutation rate of one of the interacting partners notably differs from the other. Accordingly, the order of magnitude higher mitochondrial DNA (mtDNA) mutation rate as compared to the nuclear DNA (nDNA) of all tested animals, should influence systems involving mitochondrial-nuclear (mito-nuclear) interactions. Such is the case of the energy producing oxidative phosphorylation (OXPHOS) and mitochondrial translational machineries which are comprised of factors encoded by both the mtDNA and the nDNA. Additionally, the mitochondrial RNA transcription and mtDNA replication systems are operated by nDNA-encoded proteins that bind mtDNA regulatory elements. As these systems are central to cell life there is strong selection toward mito-nuclear co-evolution to maintain their function. However, it is unclear whether (A) mito-nuclear co-evolution befalls only to retain mitochondrial functions during evolution or, also, (B) serves as an adaptive tool to adjust for the evolving energetic demands as species' complexity increases. As the first step to answer these questions we discuss evidence of both negative and adaptive (positive) selection acting on the mtDNA and nDNA-encoded genes and the effect of both types of selection on mito-nuclear interacting factors. Emphasis is given to the crucial role of recurrent ancient (nodal) mutations in such selective events. We apply this point-of-view to the three available types of mito-nuclear co-evolution: protein-protein (within the OXPHOS system), protein-RNA (mainly within the mitochondrial ribosome), and protein-DNA (at the mitochondrial replication and transcription machineries).

Insulin and IGF-1 improve mitochondrial function in a PI-3K/Akt-dependent manner and reduce mitochondrial generation of reactive oxygen species in Huntington's disease knock-in striatal cells

Oxidative stress and mitochondrial dysfunction have been described in Huntington's disease, a disorder caused by expression of mutant huntingtin (mHtt). IGF-1 was previously shown to protect HD cells, whereas insulin prevented neuronal oxidative stress. In this work we analyzed the role of insulin and IGF-1 in striatal cells derived from HD knock-in mice on mitochondrial production of reactive oxygen species (ROS) and related antioxidant and signaling pathways influencing mitochondrial function. Insulin and IGF-1 decreased mitochondrial ROS induced by mHtt and normalized mitochondrial SOD activity, without affecting intracellular glutathione levels. IGF-1 and insulin promoted Akt phosphorylation without changing the nuclear levels of phosphorylated Nrf2 or Nrf2/ARE activity. Insulin and IGF-1 treatment also decreased mitochondrial Drp1 phosphorylation, suggesting reduced mitochondrial fragmentation, and ameliorated mitochondrial function in HD cells in a PI-3K/Akt-dependent manner. This was accompanied by increased total and phosphorylated Akt, Tfam, and mitochondrial-encoded cytochrome c oxidase II, as well as Tom20 and Tom40 in mitochondria of insulin- and IGF-1-treated mutant striatal cells. Concomitantly, insulin/IGF-1-treated mutant cells showed reduced apoptotic features. Hence, insulin and IGF-1 improve mitochondrial function and reduce mitochondrial ROS caused by mHtt by activating the PI-3K/Akt signaling pathway, in a process independent of Nrf2 transcriptional activity, but involving enhanced mitochondrial levels of Akt and mitochondrial-encoded complex IV subunit.

Reduction in mitochondrial DNA copy number in peripheral leukocytes after onset of Huntington's disease

Huntington's disease (HD) is an inherited neurodegenerative disorder characterised by movement disorder, cognitive symptoms and psychiatric symptoms with predominantly adult-onset. The mutant huntingtin protein leads to mitochondrial dysfunction in blood leukocytes. This discovery led to the investigation of the mitochondrial DNA (mtDNA) copy number relative to nuclear DNA (nDNA) in leukocytes from carriers of the HD mutation compared to healthy individuals. We found significantly reduced mtDNA/nDNA in HD mutation carriers compared to controls. A longitudinal study of archive DNA sample pairs from HD patients revealed a biphasic pattern of increasing mtDNA/nDNA before onset of motor symptoms and decreasing mtDNA/nDNA after.

A single nucleotide polymorphism in the coding region of PGC-1α is a male-specific modifier of Huntington disease age-at-onset in a large European cohort

Background

Genetic modifiers are important clues for the identification of therapeutic targets in neurodegenerative diseases. Huntington disease (HD) is one of the most common autosomal dominant inherited neurodegenerative diseases. The clinical symptoms include motor abnormalities, cognitive decline and behavioral disturbances. Symptom onset is typically between 40 and 50 years of age, but can vary by several decades in extreme cases and this is in part determined by modifying genetic factors. The metabolic master regulator PGC-1α, coded by the PPARGC1A gene, coordinates cellular respiration and was shown to play a role in neurodegenerative diseases, including HD.

Methods

Using a candidate gene approach we analyzed a large European cohort (n = 1706) from the REGISTRY study for associations between PPARGC1A genotype and age at onset (AO) in HD.

Results

We report that a coding variant (rs3736265) in PPARGC1A is associated with an earlier motor AO in men but not women carrying the HD mutation.

Conclusions

These results further strengthen the evidence for a role of PGC-1α in HD and unexpectedly suggest a gender effect.

Mitochondrial diseases of the brain

Neurodegenerative disorders are debilitating diseases of the brain, characterized by behavioral, motor and cognitive impairments. Ample evidence underpins mitochondrial dysfunction as a central causal factor in the pathogenesis of neurodegenerative disorders including Parkinson's disease, Huntington's disease, Alzheimer's disease, Amyotrophic lateral sclerosis, Friedreich's ataxia and Charcot-Marie-Tooth disease. In this review, we discuss the role of mitochondrial dysfunction such as bioenergetics defects, mitochondrial DNA mutations, gene mutations, altered mitochondrial dynamics (mitochondrial fusion/fission, morphology, size, transport/trafficking, and movement), impaired transcription and the association of mutated proteins with mitochondria in these diseases. We highlight the therapeutic role of mitochondrial bioenergetic agents in toxin and in cellular and genetic animal models of neurodegenerative disorders. We also discuss clinical trials of bioenergetics agents in neurodegenerative disorders. Lastly, we shed light on PGC-1α, TORC-1, AMP kinase, Nrf2-ARE, and Sirtuins as novel therapeutic targets for neurodegenerative disorders.

The role of the immune system in Huntington's disease

Huntington's disease (HD) is characterized by a progressive course of disease until death 15-20 years after the first symptoms occur and is caused by a mutation with expanded CAG repeats in the huntingtin (htt) protein. Mutant htt (mhtt) in the striatum is assumed to be the main reason for neurodegeneration. Knowledge about pathophysiology has rapidly improved discussing influences of excitotoxicity, mitochondrial damage, free radicals, and inflammatory mechanisms. Both innate and adaptive immune systems may play an important role in HD. Activation of microglia with expression of proinflammatory cytokines, impaired migration of macrophages, and deposition of complement factors in the striatum indicate an activation of the innate immune system. As part of the adaptive immune system, dendritic cells (DCs) prime T-cell responses secreting inflammatory mediators. In HD, DCs may contain mhtt which brings the adaptive immune system into the focus of interest. These data underline an increasing interest in the peripheral immune system for pathomechanisms of HD. It is still unclear if neuroinflammation is a reactive process or if there is an active influence on disease progression. Further understanding the influence of inflammation in HD using mouse models may open various avenues for promising therapeutic approaches aiming at slowing disease progression or forestalling onset of disease.

Huntington's disease: the past, present, and future search for disease modifiers

Huntington's disease (HD) is an autosomal dominant genetic disorder that specifically causes neurodegeneration of striatal neurons, resulting in a triad of symptoms that includes emotional, cognitive, and motor disturbances. The HD mutation causes a polyglutamine repeat expansion within the N-terminal of the huntingtin (Htt) protein. This expansion causes aggregate formation within the cytosol and nucleus due to the presence of misfolded mutant Htt, as well as altered interactions with Htt's multiple binding partners, and changes in post-translational Htt modifications. The present review charts efforts toward a therapy that delays age of onset or slows symptom progression in patients affected by HD, as there is currently no effective treatment. Although silencing Htt expression appears promising as a disease modifying treatment, it should be attempted with caution in light of Htt's essential roles in neural maintenance and development. Other therapeutic targets include those that boost aggregate dissolution, target excitotoxicity and metabolic issues, and supplement growth factors.

Mitochondrial abnormalities in temporal lobe of autistic brain

Autism spectrum disorder (ASD) consists of a group of complex developmental disabilities characterized by impaired social interactions, deficits in communication and repetitive behavior. Multiple lines of evidence implicate mitochondrial dysfunction in ASD. In postmortem BA21 temporal cortex, a region that exhibits synaptic pathology in ASD, we found that compared to controls, ASD patients exhibited altered protein levels of mitochondria respiratory chain protein complexes, decreased Complex I and IV activities, decreased mitochondrial antioxidant enzyme SOD2, and greater oxidative DNA damage. Mitochondrial membrane mass was higher in ASD brain, as indicated by higher protein levels of mitochondrial membrane proteins Tom20, Tim23 and porin. No differences were observed in either mitochondrial DNA or levels of the mitochondrial gene transcription factor TFAM or cofactor PGC1α, indicating that a mechanism other than alterations in mitochondrial genome or mitochondrial biogenesis underlies these mitochondrial abnormalities. We further identified higher levels of the mitochondrial fission proteins (Fis1 and Drp1) and decreased levels of the fusion proteins (Mfn1, Mfn2 and Opa1) in ASD patients, indicating altered mitochondrial dynamics in ASD brain. Many of these changes were evident in cortical pyramidal neurons, and were observed in ASD children but were less pronounced or absent in adult patients. Together, these findings provide evidence that mitochondrial function and intracellular redox status are compromised in pyramidal neurons in ASD brain and that mitochondrial dysfunction occurs during early childhood when ASD symptoms appear.

Population stratification may bias analysis of PGC-1α as a modifier of age at Huntington disease motor onset

Huntington’s disease (HD) is an inherited neurodegenerative disorder characterized by motor, cognitive and behavioral disturbances, caused by the expansion of a CAG trinucleotide repeat in the HD gene. The CAG allele size is the major determinant of age at onset (AO) of motor symptoms, although the remaining variance in AO is highly heritable. The rs7665116 SNP in PPARGC1A, encoding the mitochondrial regulator PGC-1α, has been reported to be a significant modifier of AO in three European HD cohorts, perhaps due to affected cases from Italy. We attempted to replicate these findings in a large collection of (1,727) HD patient DNA samples of European origin. In the entire cohort, rs7665116 showed a significant effect in the dominant model (p value = 0.008) and the additive model (p value = 0.009). However, when examined by origin, cases of Southern European origin had an increased rs7665116 minor allele frequency (MAF), consistent with this being an ancestry-tagging SNP. The Southern European cases, despite similar mean CAG allele size, had a significantly older mean AO (p < 0.001), suggesting population-dependent phenotype stratification. When the generalized estimating equations models were adjusted for ancestry, the effect of the rs7665116 genotype on AO decreased dramatically. Our results do not support rs7665116 as a modifier of AO of motor symptoms, as we found evidence for a dramatic effect of phenotypic (AO) and genotypic (MAF) stratification among European cohorts that was not considered in previously reported association studies. A significantly older AO in Southern Europe may reflect population differences in genetic or environmental factors that warrant further investigation.

Genetic modifiers of Huntington’s disease: beyond CAG

Huntington’s disease (HD) is caused by the expansion of a CAG repeat within exon 1 of the huntingtin (HTT) gene. Although the variation in age at onset is partly explained by the lengths of the expanded repeat, the unexplained variation is heritable, emphasizing the role of the so-called genetic background on disease expression. Identification of modifier genes can confirm intracellular pathways already suspected to be involved in pathophysiological processes related to HD pathogenesis, but it may also point to completely new pathways and processes that have not yet been considered. Most importantly, confirmed modifier genes provide new targets for the development of therapies. Up to now, a wide range of susceptible HD modifier genes related to different biochemical pathways has been examined. On the basis of the published literature in this field, this review provides an overview of HD modifiers and integrates them into selected pathophysiology aspects.

No evidence of impaired gastric emptying in early Huntington's Disease

Background: Several factors, such as dysphagia, an increased motor activity, increased metabolic rate and a hypermetabolic state have been discussed as contributing to weight loss even at the early stages of Huntington’s Disease (HD). Aim of this pilot study was to investigate gastric emptying as a possible reason for weight loss in HD.

Methods: 11 HD participants at early stages of the disease and matched controls were investigated by using the well-established and non-invasive 13C-octanoate breath test. The “Gastroparesis Cardinal Symptom Index” and the “Short-Form Leeds Dyspepsia Questionnaire” were used for clinical evaluation of gastroparesis or dyspepsia.

Results: When compared to standard values ​​given in literature and controls all HD patients had normal breath test results. There was no evidence of gastroparesis or dyspepsia. There was a correlation of breath test results with the cognitive and functional performance of HD participants.

Conclusion: According to our data, there is no evidence of impaired gastric emptying in early HD. We can not exclude that gastric emptying contributes to weight loss at more advanced stages of the disease.

PGC-1 family coactivators and cell fate: roles in cancer, neurodegeneration, cardiovascular disease and retrograde mitochondria-nucleus signalling

Over the past two decades, a complex nuclear transcriptional machinery controlling mitochondrial biogenesis and function has been described. Central to this network are the PGC-1 family coactivators, characterised as master regulators of mitochondrial biogenesis. Recent literature has identified a broader role for PGC-1 coactivators in both cell death and cellular adaptation under conditions of stress, here reviewed in the context of the pathology associated with cancer, neurodegeneration and cardiovascular disease. Moreover, we propose that these studies also imply a novel conceptual framework on the general role of mitochondrial dysfunction in disease. It is now well established that the complex nuclear transcriptional control of mitochondrial biogenesis allows for adaptation of mitochondrial mass and function to environmental conditions. On the other hand, it has also been suggested that mitochondria alter their function according to prevailing cellular energetic requirements and thus function as sensors that generate signals to adjust fundamental cellular processes through a retrograde mitochondria-nucleus signalling pathway. Therefore, altered mitochondrial function can affect cell fate not only directly by modifying cellular energy levels or redox state, but also indirectly, by altering nuclear transcriptional patterns. The current literature on such retrograde signalling in both yeast and mammalian cells is thus reviewed, with an outlook on its potential contribution to disease through the regulation of PGC-1 family coactivators. We propose that further investigation of these pathways will lead to the identification of novel pharmacological targets and treatment strategies to combat disease.