Reduced expression of peroxisome-proliferator activated receptor gamma coactivator-1alpha enhances alpha-synuclein oligomerization and down regulates AKT/GSK3beta signaling pathway in human neuronal cells that inducibly express alpha-synuclein

Irisin/PGC-1α/FNDC5 pathway in Parkinson's disease: truth under the throes

Parkinson's disease (PD) is considered one of the most common neurodegenerative brain diseases which involves the deposition of α-synuclein. Irisin hormone, a newly discovered adipokine, has a valuable role in diverse neurodegenerative diseases. Therefore, this review aims to elucidate the possible role of the irisin hormone in PD neuropathology. Irisin hormone has a neuroprotective effect against the development and progression of various neurodegenerative disorders by increasing the expression of brain-derived neurotrophic factor (BDNF). Irisin hormone has anti-inflammatory, anti-apoptotic, and anti-oxidative impacts, thereby reducing the expression of the pro-inflammatory cytokines and the progression of neuroinflammation. Irisin-induced PGC-1α could potentially prevent α-synuclein-induced dopaminergic injury, neuroinflammation, and neurotoxicity in PD. Inhibition of NF-κB by irisin improves PGC-1α and FNDC5 signaling pathway with subsequent attenuation of PD neuropathology. Therefore, the irisin/PGC-1α/FNDC5 pathway could prevent dopaminergic neuronal injury. In conclusion, the irisin hormone has a neuroprotective effect through its anti-inflammatory and antioxidant impacts with the amelioration of brain BDNF levels. Further preclinical and clinical studies are recommended in this regard.

Peroxisome proliferator-activated receptor gamma coactivator-1 (PGC-1) family in physiological and pathophysiological process and diseases

Peroxisome proliferator-activated receptor gamma coactivator-1 (PGC-1) family (PGC-1s), consisting of three members encompassing PGC-1α, PGC-1β, and PGC-1-related coactivator (PRC), was discovered more than a quarter-century ago. PGC-1s are essential coordinators of many vital cellular events, including mitochondrial functions, oxidative stress, endoplasmic reticulum homeostasis, and inflammation. Accumulating evidence has shown that PGC-1s are implicated in many diseases, such as cancers, cardiac diseases and cardiovascular diseases, neurological disorders, kidney diseases, motor system diseases, and metabolic disorders. Examining the upstream modulators and co-activated partners of PGC-1s and identifying critical biological events modulated by downstream effectors of PGC-1s contribute to the presentation of the elaborate network of PGC-1s. Furthermore, discussing the correlation between PGC-1s and diseases as well as summarizing the therapy targeting PGC-1s helps make individualized and precise intervention methods. In this review, we summarize basic knowledge regarding the PGC-1s family as well as the molecular regulatory network, discuss the physio-pathological roles of PGC-1s in human diseases, review the application of PGC-1s, including the diagnostic and prognostic value of PGC-1s and several therapies in pre-clinical studies, and suggest several directions for future investigations. This review presents the immense potential of targeting PGC-1s in the treatment of diseases and hopefully facilitates the promotion of PGC-1s as new therapeutic targets.

Formoterol attenuated mitochondrial dysfunction in rotenone-induced Parkinson's disease in a rat model: Role of PINK-1/PARKIN and PI3K/Akt/CREB/BDNF/TrKB axis

β2-adrenoreceptors (β2AR have been identified recently as regulators of the α-synuclein gene (SNCA), one of the key milieus endorsed in injury of dopamine neurons in Parkinson's disease (PD). Accumulation of α-synuclein leads to mitochondrial dysfunction via downregulation of mitophagy proteins (PINK-1 and PARKIN) and inhibition of mitochondria biogenesis (PGC-1α) along with an increase in the master inflammatory regulator NF-κB p65 production that provokes neurodegeneration and diminishes neuroprotective signaling pathway (PI3k/Akt/CREB/BDNF). Recently, formoterol exhibited a promising neuroprotective effect against neurodegenerative conditions associated with brain inflammation. Therefore, the present investigation aims to unveil the possible neuroprotective activity of formoterol, β2AR agonist, against rotenone-induced PD in rats. Rats received rotenone (1.5 mg/kg; s.c.) every other day for 3 weeks and cured with formoterol (25 μg/kg/day; i.p.) 1 hr. after rotenone administration, starting from day 11. Formoterol treatment succeeded in upregulating β2-adrenoreceptor expression in PD rats and preserving the function and integrity of dopaminergic neurons as witnessed by enhancement of muscular performance in tests, open field, grip strength-meter, and Rotarod, besides the increment in substantia nigra and striatal tyrosine hydroxylase immunoexpression. In parallel, formoterol boosted mitophagy by activation of PINK1 and PARKIN and preserved mitochondrial membrane potential. Additionally, formoterol stimulated the neuro-survival signaling axis via stimulation of PI3k/pS473-Akt/pS133-CREB/BDNF cascade to attenuate neuronal loss. Noteworthy formoterol reduces neuro-inflammatory status by decreasing NFκBp65 immunoexpression and TNF-α content. Finally, formoterol's potential as a stimulant therapy of mitophagy via the PINK1/PARKIN axis and regulation of mitochondrial biogenesis by increasing PGC-1α to maintain mitochondrial homeostasis along with stimulation of PI3k/Akt/CREB/BDNF axis.

The neuroprotective effects of glucagon-like peptide 1 in Alzheimer's and Parkinson's disease: An in-depth review

Currently, there is no disease-modifying treatment available for Alzheimer's and Parkinson's disease (AD and PD) and that includes the highly controversial approval of the Aβ-targeting antibody aducanumab for the treatment of AD. Hence, there is still an unmet need for a neuroprotective drug treatment in both AD and PD. Type 2 diabetes is a risk factor for both AD and PD. Glucagon-like peptide 1 (GLP-1) is a peptide hormone and growth factor that has shown neuroprotective effects in preclinical studies, and the success of GLP-1 mimetics in phase II clinical trials in AD and PD has raised new hope. GLP-1 mimetics are currently on the market as treatments for type 2 diabetes. GLP-1 analogs are safe, well tolerated, resistant to desensitization and well characterized in the clinic. Herein, we review the existing evidence and illustrate the neuroprotective pathways that are induced following GLP-1R activation in neurons, microglia and astrocytes. The latter include synaptic protection, improvements in cognition, learning and motor function, amyloid pathology-ameliorating properties (Aβ, Tau, and α-synuclein), the suppression of Ca2+ deregulation and ER stress, potent anti-inflammatory effects, the blockage of oxidative stress, mitochondrial dysfunction and apoptosis pathways, enhancements in the neuronal insulin sensitivity and energy metabolism, functional improvements in autophagy and mitophagy, elevated BDNF and glial cell line-derived neurotrophic factor (GDNF) synthesis as well as neurogenesis. The many beneficial features of GLP-1R and GLP-1/GIPR dual agonists encourage the development of novel drug treatments for AD and PD.

Elucidating the Neuroprotective Role of PPARs in Parkinson's Disease: A Neoteric and Prospective Target

One of the utmost frequently emerging neurodegenerative diseases, Parkinson's disease (PD) must be comprehended through the forfeit of dopamine (DA)-generating nerve cells in the substantia nigra pars compacta (SN-PC). The etiology and pathogenesis underlying the emergence of PD is still obscure. However, expanding corroboration encourages the involvement of genetic and environmental factors in the etiology of PD. The destruction of numerous cellular components, namely oxidative stress, ubiquitin-proteasome system (UPS) dysfunction, autophagy-lysosome system dysfunction, neuroinflammation and programmed cell death, and mitochondrial dysfunction partake in the pathogenesis of PD. Present-day pharmacotherapy can alleviate the manifestations, but no therapy has been demonstrated to cease disease progression. Peroxisome proliferator-activated receptors (PPARs) are ligand-directed transcription factors pertaining to the class of nuclear hormone receptors (NHR), and are implicated in the modulation of mitochondrial operation, inflammation, wound healing, redox equilibrium, and metabolism of blood sugar and lipids. Numerous PPAR agonists have been recognized to safeguard nerve cells from oxidative destruction, inflammation, and programmed cell death in PD and other neurodegenerative diseases. Additionally, various investigations suggest that regular administration of PPAR-activating non-steroidal anti-inflammatory drugs (NSAIDs) (ibuprofen, indomethacin), and leukotriene receptor antagonists (montelukast) were related to the de-escalated evolution of neurodegenerative diseases. The present review elucidates the emerging evidence enlightening the neuroprotective outcomes of PPAR agonists in in vivo and in vitro models experiencing PD. Existing articles up to the present were procured through PubMed, MEDLINE, etc., utilizing specific keywords spotlighted in this review. Furthermore, the authors aim to provide insight into the neuroprotective actions of PPAR agonists by outlining the pharmacological mechanism. As a conclusion, PPAR agonists exhibit neuroprotection through modulating the expression of a group of genes implicated in cellular survival pathways, and may be a propitious target in the therapy of incapacitating neurodegenerative diseases like PD.

PGC-1s in the Spotlight with Parkinson's Disease

Parkinson's disease is one of the most common neurodegenerative disorders worldwide, characterized by a progressive loss of dopaminergic neurons mainly localized in the substantia nigra pars compacta. In recent years, the detailed analyses of both genetic and idiopathic forms of the disease have led to a better understanding of the molecular and cellular pathways involved in PD, pointing to the centrality of mitochondrial dysfunctions in the pathogenic process. Failure of mitochondrial quality control is now considered a hallmark of the disease. The peroxisome proliferator-activated receptor gamma coactivator 1 (PGC-1) family acts as a master regulator of mitochondrial biogenesis. Therefore, keeping PGC-1 level in a proper range is fundamental to guarantee functional neurons. Here we review the major findings that tightly bond PD and PGC-1s, raising important points that might lead to future investigations.

Dysregulation of PGC-1α-Dependent Transcriptional Programs in Neurological and Developmental Disorders: Therapeutic Challenges and Opportunities

Substantial evidence indicates that mitochondrial impairment contributes to neuronal dysfunction and vulnerability in disease states, leading investigators to propose that the enhancement of mitochondrial function should be considered a strategy for neuroprotection. However, multiple attempts to improve mitochondrial function have failed to impact disease progression, suggesting that the biology underlying the normal regulation of mitochondrial pathways in neurons, and its dysfunction in disease, is more complex than initially thought. Here, we present the proteins and associated pathways involved in the transcriptional regulation of nuclear-encoded genes for mitochondrial function, with a focus on the transcriptional coactivator peroxisome proliferator-activated receptor gamma coactivator-1alpha (PGC-1α). We highlight PGC-1α’s roles in neuronal and non-neuronal cell types and discuss evidence for the dysregulation of PGC-1α-dependent pathways in Huntington’s Disease, Parkinson’s Disease, and developmental disorders, emphasizing the relationship between disease-specific cellular vulnerability and cell-type-specific patterns of PGC-1α expression. Finally, we discuss the challenges inherent to therapeutic targeting of PGC-1α-related transcriptional programs, considering the roles for neuron-enriched transcriptional coactivators in co-regulating mitochondrial and synaptic genes. This information will provide novel insights into the unique aspects of transcriptional regulation of mitochondrial function in neurons and the opportunities for therapeutic targeting of transcriptional pathways for neuroprotection.

Dysregulation of PGC-1α-Dependent Transcriptional Programs in Neurological and Developmental Disorders: Therapeutic Challenges and Opportunities

Substantial evidence indicates that mitochondrial impairment contributes to neuronal dysfunction and vulnerability in disease states, leading investigators to propose that the enhancement of mitochondrial function should be considered a strategy for neuroprotection. However, multiple attempts to improve mitochondrial function have failed to impact disease progression, suggesting that the biology underlying the normal regulation of mitochondrial pathways in neurons, and its dysfunction in disease, is more complex than initially thought. Here, we present the proteins and associated pathways involved in the transcriptional regulation of nuclear-encoded genes for mitochondrial function, with a focus on the transcriptional coactivator peroxisome proliferator-activated receptor gamma coactivator-1alpha (PGC-1α). We highlight PGC-1α's roles in neuronal and non-neuronal cell types and discuss evidence for the dysregulation of PGC-1α-dependent pathways in Huntington's Disease, Parkinson's Disease, and developmental disorders, emphasizing the relationship between disease-specific cellular vulnerability and cell-type-specific patterns of PGC-1α expression. Finally, we discuss the challenges inherent to therapeutic targeting of PGC-1α-related transcriptional programs, considering the roles for neuron-enriched transcriptional coactivators in co-regulating mitochondrial and synaptic genes. This information will provide novel insights into the unique aspects of transcriptional regulation of mitochondrial function in neurons and the opportunities for therapeutic targeting of transcriptional pathways for neuroprotection.

Neuroprotective effects of Shende'an tablet in the Parkinson's disease model

BACKGROUND

Shende'an tablet (SDA) is a newly capsuled Chinese herbal formula derived from the Chinese traditional medicine Zhengan Xifeng Decoction which is approved for the treatment of neurasthenia and insomnia in China. This study aimed to investigate the neuroprotective effects of SDA against Parkinson's disease (PD) in vitro and in vivo.

METHODS

In the present work, the neuroprotective effects and mechanism of SDA were evaluated in the cellular PD model. Male C57BL/6J mice were subject to a partial MPTP lesion alongside treatment with SDA. Behavioural test and tyrosine-hydroxylase immunohistochemistry were used to evaluate nigrostriatal tract integrity. HPLC analysis and Western blotting were used to assess the effect of SDA on dopamine metabolism and the expression of HO-1, PGC-1α and Nrf2, respectively.

RESULTS

Our results demonstrated that SDA had neuroprotective effect in dopaminergic PC12 cells with 6-OHDA lesion. It had also displayed efficient dopaminergic neuronal protection and motor behavior alleviation properties in MPTP-induced PD mice. In the PC12 cells and MPTP-induced Parkinson's disease animal models, SDA was highly efficacious in α-synuclein clearance associated with the activation of PGC-1α/Nrf2 signal pathway.

CONCLUSIONS

SDA demonstrated potential as a future therapeutic modality in PD through protecting dopamine neurons and alleviating the motor symptoms, mediated by the activation of PGC-1α/Nrf2 signal pathway.

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

BACKGROUND

Impairment 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).

PURPOSE

This study investigated whether the neuroprotective mechanism of carnosic acid (CA) from rosemary is mediated via the regulation of PARIS and PGC-1α by parkin.

METHODS

The 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).

RESULTS

SH-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.

CONCLUSION

The 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.

A Role for PGC-1α in Transcription and Excitability of Neocortical and Hippocampal Excitatory Neurons

The transcriptional coactivator peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) is a critical regulator of genes involved in neuronal metabolism, neurotransmission, and morphology. Reduced PGC-1α expression has been implicated in several neurological and psychiatric disorders. An understanding of PGC-1α's roles in different cell types will help determine the functional consequences of PGC-1α dysfunction and/or deficiency in disease. Reports from our laboratory and others suggest a critical role for PGC-1α in inhibitory neurons with high metabolic demand such as fast-spiking interneurons. Here, we document a previously unrecognized role for PGC-1α in maintenance of gene expression programs for synchronous neurotransmitter release, structure, and metabolism in neocortical and hippocampal excitatory neurons. Deletion of PGC-1α from these neurons caused ambulatory hyperactivity in response to a novel environment and enhanced glutamatergic transmission in neocortex and hippocampus, along with reductions in mRNA levels from several PGC-1α neuron-specific target genes. Given the potential role for a reduction in PGC-1α expression or activity in Huntington Disease (HD), we compared reductions in transcripts found in the neocortex and hippocampus of these mice to that of an HD knock-in model; few of these transcripts were reduced in this HD model. These data provide novel insight into the function of PGC-1α in glutamatergic neurons and suggest that it is required for the regulation of structural, neurosecretory, and metabolic genes in both glutamatergic neuron and fast-spiking interneuron populations in a region-specific manner. These findings should be considered when inferring the functional relevance of changes in PGC-1α gene expression in the context of disease.

Role of MicroRNAs in Parkinson's Disease

Parkinson's disease (PD) is a disabling neurodegenerative disease that manifests with resting tremor, bradykinesia, rigidity and postural instability. Since the discovery of microRNAs (miRNAs) in 1993, miRNAs have been shown to be important biological molecules involved in diverse processes to maintain normal cellular functions. Over the past decade, many studies have reported dysregulation of miRNA expressions in PD. Here, we identified 15 miRNAs from 34 reported screening studies that demonstrated dysregulation in the brain and/or neuronal models, cerebrospinal fluid (CSF) and blood. Specific miRNAs-of-interest that have been implicated in PD pathogenesis include miR-30, miR-29, let-7, miR-485 and miR-26. However, there are several challenges and limitations in drawing definitive conclusions due to the small sample size in clinical studies, varied laboratory techniques and methodologies and their incomplete penetrance of the blood-brain barrier. Developing an optimal delivery system and unravelling druggable targets of miRNAs in both experimental and human models and clinical validation of the results may pave way for novel therapeutics in PD.

Delta-9-tetrahydrocannabinol protects against MPP+ toxicity in SH-SY5Y cells by restoring proteins involved in mitochondrial biogenesis

Proliferator-activated receptor γ (PPARγ) activation can result in transcription of proteins involved in oxidative stress defence and mitochondrial biogenesis which could rescue mitochondrial dysfunction in Parkinson's disease (PD).The PPARγ agonist pioglitazone is protective in models of PD; however side effects have limited its clinical use. The cannabinoid Δ9-tetrahydrocannabinol (Δ9-THC) may have PPARγ dependent anti-oxidant properties. Here we investigate the effects of Δ9-THC and pioglitazone on mitochondrial biogenesis and oxidative stress. Differentiated SH-SY5Y neuroblastoma cells were exposed to the PD relevant mitochondrial complex 1 inhibitor 1-methyl-4-phenylpyridinium iodide (MPP+). We found that only Δ9-THC was able to restore mitochondrial content in MPP+ treated SH-SY5Y cells in a PPARγ dependent manner by increasing expression of the PPARγ co-activator 1α (PGC-1α), the mitochondrial transcription factor (TFAM) as well as mitochondrial DNA content. Co-application of Δ9-THC with pioglitazone further increased the neuroprotection against MPP+ toxicity as compared to pioglitazone treatment alone. Furthermore, using lentiviral knock down of the PPARγ receptor we showed that, unlike pioglitazone, Δ9-THC resulted in a PPARγ dependent reduction of MPP+ induced oxidative stress. We therefore suggest that, in contrast to pioglitazone, Δ9-THC mediates neuroprotection via PPARγ-dependent restoration of mitochondrial content which may be beneficial for PD treatment.

Translational approaches to restoring mitochondrial function in Parkinson's disease

There is strong evidence of a key role for mitochondrial dysfunction in both sporadic and all forms of familial Parkinson's disease (PD). However, none of the clinical trials carried out with putative mitochondrial rescue agents have been successful. Firm establishment of a wet biomarker or a reliable readout from imaging studies detecting mitochondrial dysfunction and reflecting disease progression is also awaited. We will provide an overview of our current knowledge about mitochondrial dysfunction in PD and related drug screens. We will also summarise previously undertaken mitochondrial wet biomarker studies and relevant imaging studies with particular focus on 31P-MRI spectroscopy. We will conclude with an overview of clinical trials which tested putative mitochondrial rescue agents in PD patients.

Alpha-synuclein, epigenetics, mitochondria, metabolism, calcium traffic, & circadian dysfunction in Parkinson's disease. An integrated strategy for management

The motor deficits which characterise the sporadic form of Parkinson's disease arise from age-related loss of a subset of dopamine neurons in the substantia nigra. Although motor symptoms respond to dopamine replacement therapies, the underlying disease process remains. This review details some features of the progressive molecular pathology and proposes deployment of a combination of nutrients: R-lipoic acid, acetyl-l-carnitine, ubiquinol, melatonin (or receptor agonists) and vitamin D3, with the collective potential to slow progression of these features. The main nutrient targets include impaired mitochondria and the associated oxidative/nitrosative stress, calcium stress and impaired gene transcription induced by pathogenic forms of alpha- synuclein. Benefits may be achieved via nutrient influence on epigenetic signaling pathways governing transcription factors for mitochondrial biogenesis, antioxidant defences and the autophagy-lysosomal pathway, via regulation of the metabolic energy sensor AMP activated protein kinase (AMPK) and the mammalian target of rapamycin mTOR. Nutrients also benefit expression of the transcription factor for neuronal survival (NR4A2), trophic factors GDNF and BDNF, and age-related calcium signals. In addition a number of non-motor related dysfunctions in circadian control, clock genes and associated metabolic, endocrine and sleep-wake activity are briefly addressed, as are late-stage complications in respect of cognitive decline and osteoporosis. Analysis of the network of nutrient effects reveals how beneficial synergies may counter the accumulation and promote clearance of pathogenic alpha-synuclein.

Insulin resistance and Parkinson's disease: A new target for disease modification?

There is growing evidence that patients with Type 2 diabetes have an increased risk of developing Parkinson's disease and share similar dysregulated pathways suggesting common underlying pathological mechanisms. Historically insulin was thought solely to be a peripherally acting hormone responsible for glucose homeostasis and energy metabolism. However accumulating evidence indicates insulin can cross the blood-brain-barrier and influence a multitude of processes in the brain including regulating neuronal survival and growth, dopaminergic transmission, maintenance of synapses and pathways involved in cognition. In conjunction, there is growing evidence that a process analogous to peripheral insulin resistance occurs in the brains of Parkinson's disease patients, even in those without diabetes. This raises the possibility that defective insulin signalling pathways may contribute to the development of the pathological features of Parkinson's disease, and thereby suggests that the insulin signalling pathway may potentially be a novel target for disease modification. Given these growing links between PD and Type 2 diabetes it is perhaps not unsurprising that drugs used the treatment of T2DM are amongst the most promising treatments currently being prioritised for repositioning as possible novel treatments for PD and several clinical trials are under way. In this review, we will examine the underlying cellular links between insulin resistance and the pathogenesis of PD and then we will assess current and future pharmacological strategies being developed to restore neuronal insulin signalling as a potential strategy for slowing neurodegeneration in Parkinson's disease.

Adult Conditional Knockout of PGC-1α Leads to Loss of Dopamine Neurons

Parkinson’s disease (PD) is a chronic progressive neurodegenerative disorder. Recent studies have implicated a role for peroxisome proliferator-activated receptor γ coactivator protein-1α (PGC-1α) in PD and in animal or cellular models of PD. The role of PGC-1α in the function and survival of substantia nigra pars compacta (SNpc) dopamine neurons is not clear. Here we find that there are four different PGC-1α isoforms expressed in SH-SY5Y cells, and these four isoforms are expressed across subregions of mouse brain. Adult conditional PGC-1α knock-out mice show a significant loss of dopaminergic neurons that is accompanied by a reduction of dopamine in the striatum. In human PD postmortem tissue from the SNpc, there is a reduction of PGC-1α isoforms and mitochondria markers. Our findings suggest that all four isoforms of PGC-1α are required for the proper expression of mitochondrial proteins in SNpc DA neurons and that PGC-1α is essential for SNpc DA neuronal survival, possibly through the maintenance of mitochondrial function.

Sirt1 and the Mitochondria

Sirt1 is the most prominent and extensively studied member of sirtuins, the family of mammalian class III histone deacetylases heavily implicated in health span and longevity. Although primarily a nuclear protein, Sirt1's deacetylation of Peroxisome proliferator-activated receptor Gamma Coactivator-1α (PGC-1α) has been extensively implicated in metabolic control and mitochondrial biogenesis, which was proposed to partially underlie Sirt1's role in caloric restriction and impacts on longevity. The notion of Sirt1's regulation of PGC-1α activity and its role in mitochondrial biogenesis has, however, been controversial. Interestingly, Sirt1 also appears to be important for the turnover of defective mitochondria by mitophagy. I discuss here evidences for Sirt1's regulation of mitochondrial biogenesis and turnover, in relation to PGC-1α deacetylation and various aspects of cellular physiology and disease.

Electron Transport Disturbances and Neurodegeneration: From Albert Szent-Györgyi's Concept (Szeged) till Novel Approaches to Boost Mitochondrial Bioenergetics

Impaired function of certain mitochondrial respiratory complexes has long been linked to the pathogenesis of chronic neurodegenerative disorders such as Parkinson's and Huntington's diseases. Furthermore, genetic alterations of mitochondrial genome or nuclear genes encoding proteins playing essential roles in maintaining proper mitochondrial function can lead to the development of severe systemic diseases associated with neurodegeneration and vacuolar myelinopathy. At present, all of these diseases lack effective disease modifying therapy. Following a brief commemoration of Professor Albert Szent-Györgyi, a Nobel Prize laureate who pioneered in the field of cellular respiration, antioxidant processes, and the roles of free radicals in health and disease, the present paper overviews the current knowledge on the involvement of mitochondrial dysfunction in central nervous system diseases associated with neurodegeneration including Parkinson's and Huntington's disease as well as mitochondrial encephalopathies. The review puts special focus on the involvement and the potential therapeutic relevance of peroxisome proliferator-activated receptor-gamma coactivator 1-alpha (PGC-1α), a nuclear-encoded master regulator of mitochondrial biogenesis and antioxidant responses in these disorders, the transcriptional activation of which may hold novel therapeutic value as a more system-based approach aiming to restore mitochondrial functions in neurodegenerative processes.

PPARγ and PGC-1α as therapeutic targets in Parkinson's

The peroxisome proliferator-activated receptor gamma (PPARγ) is a ligand-activated transcriptional factor that belongs to the nuclear hormone receptor superfamily. PPARγ was initially identified through its role in the regulation of glucose and lipid metabolism and cell differentiation. It also influences the expression or activity of a number of genes in a variety of signalling networks. These include regulation of redox balance, fatty acid oxidation, immune responses and mitochondrial function. Recent studies suggest that the PPARγ agonists may serve as good candidates for the treatment of several neurodegenerative disorders including Parkinson’s disease (PD), Alzheimer’s disease, Huntington’s disease and amyotrophic lateral sclerosis, even though multiple etiological factors contribute to the development of these disorders. Recent reports have also signposted a role for PPARγ coactivator-1α (PGC-1α) in several neurodegenerative disorders including PD. In this review, we explore the current knowledge of mechanisms underlying the beneficial effects of PPARγ agonists and PGC-1α in models of PD.

Neuropathology of partial PGC-1α deficiency recapitulates features of mitochondrial encephalopathies but not of neurodegenerative diseases

BACKGROUND

Deficient peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) function is one component of mitochondrial dysfunction in neurodegenerative diseases. Current molecular classification of such diseases is based on the predominant protein accumulating as intra- or extracellular aggregates. Experimental evidence suggests that mitochondrial dysfunction and impaired protein processing are closely interrelated. In vitro findings further indicate that PGC-1α dysfunction may contribute to protein misfolding in neurodegeneration.

OBJECTIVE

To systematically evaluate the neuropathological alterations of mice lacking the expression of the full-length PGC-1α protein (FL-PGC-1α) but expressing an N-truncated fragment.

METHODS

To assess the pattern of neurodegeneration-related proteins, we performed immunostaining for Tau, pTau, α-synuclein, amyloid-β, amyloid precursor protein, prion protein, FUS, TDP-43 and ubiquitin. Using hematoxylin and eosin, Klüver-Barrera and Bielschowsky silver stainings and anti-GFAP immunohistochemistry, we performed an anatomical mapping to provide a lesion profile.

RESULTS

The immunohistochemical pattern of neurodegeneration-related proteins did not differ between FL-PGC-1α knockout and wild-type animals, and there was a complete lack of protein deposits or ubiquitin-positive inclusions. The analysis of neuropathological alterations revealed widespread vacuolation predominating in the cerebral white matter, caudate-putamen, thalamus and brainstem, and reactive astrogliosis in the brainstem and cerebellar nuclei. This morphological phenotype was thus reminiscent of human mitochondrial encephalopathies, especially the Kearns-Sayre syndrome.

CONCLUSION

We conclude that the lack of FL-PGC-1α per se is insufficient to recapitulate major features of neurodegenerative diseases, but evokes a pathology seen in mitochondrial encephalopathies, which makes PGC-1α-deficient mice a valuable model for this yet incurable group of diseases.

Selective binding of nuclear alpha-synuclein to the PGC1alpha promoter under conditions of oxidative stress may contribute to losses in mitochondrial function: implications for Parkinson's disease

Alpha-synuclein has been reported to be present in the nucleus and levels enhanced by oxidative stress. Herein, we sought to investigate the mechanistic role of nuclear alpha-synuclein. We found that alpha-synuclein nuclear localization coincided with enhanced chromatin binding both in an in vitro and a corresponding in vivo brain oxidative stress model previously characterized by our laboratory as well as in PD brain tissues. Genome-wide chromatin immunoprecipitation (ChIP)-on-chip analysis of alpha-synuclein:promoter binding in response to oxidative stress in vitro revealed that binding occurs at several promoters belonging to a range of functional categories including transcriptional regulation. Interestingly, given the important role of mitochondrial dysfunction in PD, this included binding to the promoter for the master mitochondrial transcription activator, PGC1alpha in vitro, in vivo, and in human brain tissue with age and PD. To test the possible mechanistic impact of alpha-synuclein PGC1alpha promotor binding, we assessed PGC1alpha promoter activity, mRNA, and protein levels and expression of candidate PGC1alpha target genes in our in vitro model. All were found to be reduced in conjunction with increased levels of aberrant mitochondrial morphology and impaired mitochondrial function. Exogenous PGC1alpha expression was found to attenuate alpha-synuclein-mediated mitochondrial dysfunction and subsequent neurotoxicity in vitro. Our data suggest that nuclear alpha-synuclein localization under conditions of oxidative stress may impact on mitochondrial function in part via the protein's capacity to act as a transcriptional modulator of PGC1alpha. This represents a novel role for alpha-synuclein as it relates to mitochondrial dysfunction in PD.

Bioenergetics failure in neurodegenerative diseases: back to the future

Neurodegenerative disease such as Alzheimer's, Parkinson and Huntington's are all characterized by dysfunctional neurons and loss of cognitive/motor functions. Interestingly these three diseases involve overproduction, aggregation or abnormal degradation of a specific aberrant protein, which participates in disease pathogenesis. The aggregated proteins may induce disease causing pathways such as high oxidative stress and reduced neuronal metabolism. Several mechanisms are being considered as disease-causing and there is established and growing evidence that a breakdown in neuronal energy production may be an underlying cause in these diseases. The specific risk factors and molecular drivers for each disease vary, yet there are common defective bioenergetics pathways, which may drive neuronal dysfunction. While it has been appreciated that energy deficits can drive neuronal dysfunction and disease, it has for the most part been overlooked as a target pathway for designing novel disease modifying therapeutics. This editorial reviews selected evidence supporting energy deficits as disease-causing and proposes targets for design of new therapeutics.