Mitochondrial function in Parkinson's disease cybrids containing an nt2 neuron-like nuclear background

Clinical Significance of NAT2 Genetic Variations in Type II Diabetes Mellitus and Lipid Regulation

Background

N-acetyltransferase 2 (NAT2) enzyme is a Phase II drug-metabolizing enzyme that metabolizes different compounds. Genetic variations in NAT2 can influence the enzyme's activity and potentially lead to the development of certain diseases.

Aim

This study aimed to investigate the association of NAT2 variants with the risk of Type II diabetes mellitus (T2DM) and the lipid profile among Jordanian patients.

Methods

We sequenced the whole protein-coding region in NAT2 using Sanger's method among a sample of 45 Jordanian T2DM patients and 50 control subjects. Moreover, we analyzed the lipid profiles of the patients and examined any potential associations with NAT2 variants.

Results

This study revealed that the heterozygous NAT2*13 C/T genotype is significantly (P = 0.03) more common among T2DM (44%) than non-T2DM subjects (23.5%). Furthermore, the frequency of homozygous NAT2*13 T/T genotype was found to be significantly higher (P = 0.03) among T2DM patients (26.7%) compared to that of non-T2DM subjects (11%). The heterozygous NAT2*7 G/A genotype was exclusively observed in T2DM patients (11.1%) and absent in the control non-T2DM group. Moreover, among T2DM patients, those with a homozygous NAT2*11 T/T genotype exhibited significantly higher levels of triglycerides (381.50 ± 9.19 ng/dL) with a P value of 0.01 compared to those with heterozygous NAT2*11 C/T (136.23 ± 51.12 ng/dL) or wild-type NAT2*11 C/C (193.65 ± 109.89 ng/dL) genotypes. T2DM patients with homozygous NAT2*12 G/G genotype had a significantly (P = 0.04) higher triglyceride levels (275.67 ± 183.42 ng/dL) than the heterozygous NAT2*12 A/G (140.02 ± 49.53 ng/dL) and the wild NAT2*12 A/A (193.65 ± 109.89 ng/dL).

Conclusion

The finding in this study suggests that the NAT2 gene is a potential biomarker for the development of T2DM and changes in triglyceride levels among Jordanians. However, it is important to note that our sample size was limited; therefore, further clinical studies with a larger cohort are necessary to validate these findings.

The Impact of microRNAs on Mitochondrial Function and Immunity: Relevance to Parkinson's Disease

Parkinson's Disease (PD), the second most common neurodegenerative disorder, is characterised by the severe loss of dopaminergic neurons in the Substantia Nigra pars compacta (SNpc) and by the presence of Lewy bodies. PD is diagnosed upon the onset of motor symptoms, such as bradykinesia, resting tremor, rigidity, and postural instability. It is currently accepted that motor symptoms are preceded by non-motor features, such as gastrointestinal dysfunction. In fact, it has been proposed that PD might start in the gut and spread to the central nervous system. Growing evidence reports that the gut microbiota, which has been found to be altered in PD patients, influences the function of the central and enteric nervous systems. Altered expression of microRNAs (miRNAs) in PD patients has also been reported, many of which regulate key pathological mechanisms involved in PD pathogenesis, such as mitochondrial dysfunction and immunity. It remains unknown how gut microbiota regulates brain function; however, miRNAs have been highlighted as important players. Remarkably, numerous studies have depicted the ability of miRNAs to modulate and be regulated by the host's gut microbiota. In this review, we summarize the experimental and clinical studies implicating mitochondrial dysfunction and immunity in PD. Moreover, we gather recent data on miRNA involvement in these two processes. Ultimately, we discuss the reciprocal crosstalk between gut microbiota and miRNAs. Studying the bidirectional interaction of gut microbiome-miRNA might elucidate the aetiology and pathogenesis of gut-first PD, which could lead to the application of miRNAs as potential biomarkers or therapeutical targets for PD.

LPS-induced mitochondrial dysfunction regulates innate immunity activation and α-synuclein oligomerization in Parkinson's disease

Sporadic Parkinson's disease (sPD) is a complex multifactorial disorder which etiology remains elusive. Several mechanisms have been described to contribute to PD development namely mitochondrial dysfunction, activation of inflammatory pathways and the deposition of unfolded proteins such as α-synuclein. Our work shows for the first time that lipopolysaccharide (LPS)-induced activation of innate immunity requires a functional mitochondria and mimics PD pathology in cells. We found in primary mesencephalic neurons that LPS targeted the mitochondria and activated neuronal innate immune responses, which culminated with α-synuclein oligomerization. Moreover, in cybrid cell lines repopulated with mtDNA from sPD subjects with inherent mitochondrial dysfunction and NT2-Rho0 obtained by long-term ethidium bromide exposure, and so without a functional mitochondrial, LPS was not able to further activate innate immunity or increase α-synuclein aggregation. Herein, we showed that mesencephalic neurons are able to activate innate immunity after LPS exposure and this pathway is dependent on mitochondria. Moreover, we disclose that α-synuclein over production is an innate immune response. Our data indicate that mitochondria provide the base for innate immunity activation in idiopathic PD.

Mitochondrial signaling on innate immunity activation in Parkinson disease

Parkinson's disease (PD) is a neurodegenerative disease characterized by the accumulation of alpha-synuclein (aSyn) in the nigrostriatal pathway that is followed by severe neuroinflammatory response. PD etiology is still puzzling; however, the mitocentric view might explain the vast majority of molecular findings not only in the brain, but also at systemic level. While neuronal degeneration is tightly associated with mitochondrial dysfunction, the causal role between aSyn accumulation and mitochondrial dysfunction still requires further investigation. Moreover, mitochondrial dysfunction can elicit an inflammatory response that may be transmitted locally but also in a long range through systemic circulation. Furthermore, mitochondrial-driven innate immune activation may involve the synthesis of antimicrobial peptides, of which aSyn poses as a good candidate. While there is still a need to clarify disease-elicited mechanisms and how aSyn has the ability to modulate mitochondrial and cellular dysfunction, recent studies provide insightful views on mitochondria-inflammation axis in PD etiology.

Emerging Promise of Therapeutic Approaches Targeting Mitochondria in Neurodegenerative Disorders

Mitochondria are critical for homeostasis and metabolism in all cellular eukaryotes. Brain mitochondria are the primary source of fuel that supports many brain functions, including intracellular energy supply, cellular calcium regulation, regulation of limited cellular oxidative capacity, and control of cell death. Much evidence suggests that mitochondria play a central role in neurodegenerative disorders (NDDs) such as Parkinson's disease, Alzheimer's disease, Huntington's disease, and amyotrophic lateral sclerosis. Ongoing studies of NDDs have revealed that mitochondrial pathology is mainly found in inherited or irregular NDDs and is thought to be associated with the pathophysiological cycle of these disorders. Typical mitochondrial disturbances in NDDs include increased free radical production, decreased ATP synthesis, alterations in mitochondrial permeability, and mitochondrial DNA damage. The main objective of this review is to highlight the basic mitochondrial problems that occur in NDDs and discuss the use mitochondrial drugs, especially mitochondrial antioxidants, mitochondrial permeability transition blockade, and mitochondrial gene therapy, for the treatment and control of NDDs.

The Role of Bioenergetics in Neurodegeneration

Bioenergetic and mitochondrial dysfunction are common hallmarks of neurodegenerative diseases. Decades of research describe how genetic and environmental factors initiate changes in mitochondria and bioenergetics across Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS). Mitochondria control many cellular processes, including proteostasis, inflammation, and cell survival/death. These cellular processes and pathologies are common across neurodegenerative diseases. Evidence suggests that mitochondria and bioenergetic disruption may drive pathological changes, placing mitochondria as an upstream causative factor in neurodegenerative disease onset and progression. Here, we discuss evidence of mitochondrial and bioenergetic dysfunction in neurodegenerative diseases and address how mitochondria can drive common pathological features of these diseases.

Modulation of Reactive Oxygen Species Homeostasis as a Pleiotropic Effect of Commonly Used Drugs

Age-associated diseases represent a growing burden for global health systems in our aging society. Consequently, we urgently need innovative strategies to counteract these pathological disturbances. Overwhelming generation of reactive oxygen species (ROS) is associated with age-related damage, leading to cellular dysfunction and, ultimately, diseases. However, low-dose ROS act as crucial signaling molecules and inducers of a vaccination-like response to boost antioxidant defense mechanisms, known as mitohormesis. Consequently, modulation of ROS homeostasis by nutrition, exercise, or pharmacological interventions is critical in aging. Numerous nutrients and approved drugs exhibit pleiotropic effects on ROS homeostasis. In the current review, we provide an overview of drugs affecting ROS generation and ROS detoxification and evaluate the potential of these effects to counteract the development and progression of age-related diseases. In case of inflammation-related dysfunctions, cardiovascular- and neurodegenerative diseases, it might be essential to strengthen antioxidant defense mechanisms in advance by low ROS level rises to boost the individual ROS defense mechanisms. In contrast, induction of overwhelming ROS production might be helpful to fight pathogens and kill cancer cells. While we outline the potential of ROS manipulation to counteract age-related dysfunction and diseases, we also raise the question about the proper intervention time and dosage.

A genome on shaky ground: exploring the impact of mitochondrial DNA integrity on Parkinson's disease by highlighting the use of cybrid models

Mitochondria play important roles in the regulation of key cellular processes, including energy metabolism, oxidative stress response, and signaling towards cell death or survival, and are distinguished by carrying their own genome (mtDNA). Mitochondrial dysfunction has emerged as a prominent cellular mechanism involved in neurodegeneration, including Parkinson’s disease (PD), a neurodegenerative movement disorder, characterized by progressive loss of dopaminergic neurons and the occurrence of proteinaceous Lewy body inclusions. The contribution of mtDNA variants to PD pathogenesis has long been debated and is still not clearly answered. Cytoplasmic hybrid (cybrid) cell models provided evidence for a contribution of mtDNA variants to the PD phenotype. However, conclusive evidence of mtDNA mutations as genetic cause of PD is still lacking. Several models have shown a role of somatic, rather than inherited mtDNA variants in the impairment of mitochondrial function and neurodegeneration. Accordingly, several nuclear genes driving inherited forms of PD are linked to mtDNA quality control mechanisms, and idiopathic as well as familial PD tissues present increased mtDNA damage. In this review, we highlight the use of cybrids in this PD research field and summarize various aspects of how and to what extent mtDNA variants may contribute to the etiology of PD.

No impact of soluble epoxide hydrolase rs4149243, rs2234914 and rs751142 genetic variants on the development of type II diabetes and its hypertensive complication among Jordanian patients

BACKGROUND

Human soluble epoxide hydrolase plays a major role in cardiovascular homoeostasis. Genetic variants in the EPHX2 gene among different ethnic groups are associated with cardiovascular complications, such as hypertension. However, no reports regarding the association of EPHX2 genotype with hypertension among type II diabetic (T2D) patients of Middle Eastern Jordanian origin exist.

OBJECTIVE

The current study aimed to elucidate the association of the EPHX2 allele, genotype and haplotype with T2D, hypertension and parameters of lipid profile parameters among Jordanian T2D patients.

METHODS

Ninety-three genomic DNA samples of non-diabetic controls and 97 samples from T2D patients were genotyped for EPHX2 rs4149243, rs2234914 and rs751142 genetic variants. The DNA samples were amplified using polymerase chain reaction (PCR) and then sequenced using Applied Biosystems Model (ABI3730x1). The functionality of intronic EPHX2 variants was predicted using the in silico Berkely Drosophila Genome Project software.

RESULTS

We found no significant (P >.05) association between the EPHX2 rs4149243, rs2234914 and rs751142 allele, genotype and haplotype and the incidence of T2D and hypertension. Additionally, no association (P >.05) between these EPHX2 genetic variants with the baseline total cholesterol, low- and high-density lipoproteins and triglycerides among both non-diabetic and diabetic volunteers was found. However, we found an inter-ethnic variation (χ² -test, P value ˂ .05) in the allele frequency of the EPHX2 rs4149243 and rs2234914 variants between Jordanians and other ethnic populations. Also, the in silico Berkely Drosophila Genome Project software predicted that the intronic EPHX2 rs4149243 could alter the splicing of intron 7.

CONCLUSIONS

It can be concluded from this study that EPHX2 rs4149243, rs2234914 and rs751142 genetic variants do not play a role in the development of T2D and hypertension among Jordanian T2D patients. Further genetic studies with larger sample sizes are needed to find out the association of other functional EPHX2 variants with cardiovascular diseases among T2D patients in Jordan.

Glycolytic Metabolism, Brain Resilience, and Alzheimer's Disease

Alzheimer's disease (AD) is the most common form of age-related dementia. Despite decades of research, the etiology and pathogenesis of AD are not well understood. Brain glucose hypometabolism has long been recognized as a prominent anomaly that occurs in the preclinical stage of AD. Recent studies suggest that glycolytic metabolism, the cytoplasmic pathway of the breakdown of glucose, may play a critical role in the development of AD. Glycolysis is essential for a variety of neural activities in the brain, including energy production, synaptic transmission, and redox homeostasis. Decreased glycolytic flux has been shown to correlate with the severity of amyloid and tau pathology in both preclinical and clinical AD patients. Moreover, increased glucose accumulation found in the brains of AD patients supports the hypothesis that glycolytic deficit may be a contributor to the development of this phenotype. Brain hyperglycemia also provides a plausible explanation for the well-documented link between AD and diabetes. Humans possess three primary variants of the apolipoprotein E (ApoE) gene - ApoE∗ϵ2, ApoE∗ϵ3, and ApoE∗ϵ4 - that confer differential susceptibility to AD. Recent findings indicate that neuronal glycolysis is significantly affected by human ApoE isoforms and glycolytic robustness may serve as a major mechanism that renders an ApoE2-bearing brain more resistant against the neurodegenerative risks for AD. In addition to AD, glycolytic dysfunction has been observed in other neurodegenerative diseases, including Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis, strengthening the concept of glycolytic dysfunction as a common pathway leading to neurodegeneration. Taken together, these advances highlight a promising translational opportunity that involves targeting glycolysis to bolster brain metabolic resilience and by such to alter the course of brain aging or disease development to prevent or reduce the risks for not only AD but also other neurodegenerative diseases.

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.

The Role of Mitonuclear Incompatibility in Bipolar Disorder Susceptibility and Resilience Against Environmental Stressors

It has been postulated that mitochondrial dysfunction has a significant role in the underlying pathophysiology of bipolar disorder (BD). Mitochondrial functioning plays an important role in regulating synaptic transmission, brain function, and cognition. Neuronal activity is energy dependent and neurons are particularly sensitive to changes in bioenergetic fluctuations, suggesting that mitochondria regulate fundamental aspects of brain function. Vigorous evidence supports the role of mitochondrial dysfunction in the etiology of BD, including dysregulated oxidative phosphorylation, general decrease of energy, altered brain bioenergetics, co-morbidity with mitochondrial disorders, and association with genetic variants in mitochondrial DNA (mtDNA) or nuclear-encoded mitochondrial genes. Despite these advances, the underlying etiology of mitochondrial dysfunction in BD is unclear. A plausible evolutionary explanation is that mitochondrial-nuclear (mitonuclear) incompatibility leads to a desynchronization of machinery required for efficient electron transport and cellular energy production. Approximately 1,200 genes, encoded from both nuclear and mitochondrial genomes, are essential for mitochondrial function. Studies suggest that mitochondrial and nuclear genomes co-evolve, and the coordinated expression of these interacting gene products are essential for optimal organism function. Incompatibilities between mtDNA and nuclear-encoded mitochondrial genes results in inefficiency in electron flow down the respiratory chain, differential oxidative phosphorylation efficiency, increased release of free radicals, altered intracellular Ca²⁺ signaling, and reduction of catalytic sites and ATP production. This review explores the role of mitonuclear incompatibility in BD susceptibility and resilience against environmental stressors.

Mitophagy and the Brain

Stress mechanisms have long been associated with neuronal loss and neurodegenerative diseases. The origin of cell stress and neuronal loss likely stems from multiple pathways. These include (but are not limited to) bioenergetic failure, neuroinflammation, and loss of proteostasis. Cells have adapted compensatory mechanisms to overcome stress and circumvent death. One mechanism is mitophagy. Mitophagy is a form of macroautophagy, were mitochondria and their contents are ubiquitinated, engulfed, and removed through lysosome degradation. Recent studies have implicated mitophagy dysregulation in several neurodegenerative diseases and clinical trials are underway which target mitophagy pathways. Here we review mitophagy pathways, the role of mitophagy in neurodegeneration, potential therapeutics, and the need for further study.

Mitochondrial Dysfunction in Parkinson's Disease: Focus on Mitochondrial DNA

Mitochondria, the energy stations of the cell, are the only extranuclear organelles, containing their own (mitochondrial) DNA (mtDNA) and the protein synthesizing machinery. The location of mtDNA in close proximity to the oxidative phosphorylation system of the inner mitochondrial membrane, the main source of reactive oxygen species (ROS), is an important factor responsible for its much higher mutation rate than nuclear DNA. Being more vulnerable to damage than nuclear DNA, mtDNA accumulates mutations, crucial for the development of mitochondrial dysfunction playing a key role in the pathogenesis of various diseases. Good evidence exists that some mtDNA mutations are associated with increased risk of Parkinson’s disease (PD), the movement disorder resulted from the degenerative loss of dopaminergic neurons of substantia nigra. Although their direct impact on mitochondrial function/dysfunction needs further investigation, results of various studies performed using cells isolated from PD patients or their mitochondria (cybrids) suggest their functional importance. Studies involving mtDNA mutator mice also demonstrated the importance of mtDNA deletions, which could also originate from abnormalities induced by mutations in nuclear encoded proteins needed for mtDNA replication (e.g., polymerase γ). However, proteomic studies revealed only a few mitochondrial proteins encoded by mtDNA which were downregulated in various PD models. This suggests nuclear suppression of the mitochondrial defects, which obviously involve cross-talk between nuclear and mitochondrial genomes for maintenance of mitochondrial functioning.

Antidiabetic drugs for Alzheimer's and Parkinson's diseases: Repurposing insulin, metformin, and thiazolidinediones

Medical and scientific communities have been striving to disentangle the complexity of neurodegenerative diseases, particularly Alzheimer's disease (AD) and Parkinson's disease (PD), in order to develop a cure or effective treatment for these diseases. Along this journey, it has become important to identify the early events occurring in the prodromal phases of these diseases and the disorders that increase the risk of neurodegeneration highlighting common pathological features. This strategy has led to a wealth of evidence identifying diabetes, mainly type 2 diabetes mellitus (T2DM) as a main risk factor for the onset and progression of AD and PD. Impaired glucose metabolism, insulin resistance, and mitochondrial dysfunction are features common to both type 2 diabetes mellitus (T2DM), and AD and PD, and they appear before clinical diagnosis of the two neurodegenerative diseases. These could represent the strategic nodes of therapeutic intervention. Following this line of thought, a conceivable approach is to repurpose antidiabetic drugs as valuable agents that may prevent or reduce the risk of cognitive decline and neurodegeneration. This review summarizes the past and current findings that link AD and PD with T2DM, emphasizing the common pathological mechanisms. The efficacy of antidiabetic drugs, namely intranasal insulin, metformin, and thiazolidinediones, in the prevention and/or treatment of AD and PD is also discussed.

Differential protein expression in diverse brain areas of Parkinson's and Alzheimer's disease patients

Many hypotheses have been postulated to define the etiology of sporadic Parkinson's and Alzheimer's disorders (PD and AD) but there is no consensus on what causes these devastating age-related diseases. Braak staging of both pathologies helped researchers to better understand the progression and to identify their prodromal and symptomatic phases. Indeed, it is well accepted that Lewy body pathology and neurofibrillary tangles appearance correlates with disease progression and severity of symptoms in PD and AD, respectively. Additionally, several studies in PD and AD models try to disclose which cellular mechanisms are defaulted and trigger the neurodegenerative process that culminates with neuronal death causing PD and AD classical symptomatology. Herein, we determined expression levels of proteins involved in microtubule assembly, autophagic-lysosomal pathway and unfolded protein response in the cortex, hippocampus and SNpc of PD and AD patients, vascular dementia patients and aged-match controls. The differential expression allowed us to determine which pathways are determinant to synaptic dysfunction and to establish a time line for disease progression. Our results allow us to challenge the hypothesis that both PD and AD pathologies are caused by α-synuclein or Aβ pathology propagation throughout the brain in a prion-like manner.

Neuroprotective effects of boron nitride nanoparticles in the experimental Parkinson's disease model against MPP+ induced apoptosis

Parkinson's disease (PD) is one of the most aggressive neurodegenerative diseases and characterized by the loss of dopamine-sensitive neurons in the substantia nigra region of the brain. There is no any definitive treatment to completely cure PD and existing treatments can only ease the symptoms of the disease. Boron nitride nanoparticles have been extensively studied in nano-biological studies and researches showed that it can be a promising candidate for PD treatment with its biologically active unique properties. In the present study, it was aimed to investigate ameliorative effects of hexagonal boron nitride nanoparticles (hBNs) against toxicity of 1-methyl-4-phenylpyridinium (MPP⁺) in experimental PD model. Experimental PD model was constituted by application of MPP⁺ to differentiated pluripotent human embryonal carcinoma cell (Ntera-2, NT-2) culture in wide range of concentrations (0.62 to 2 mM). Neuroprotective activity of hBNs against MPP⁺ toxicity was determined by cell viability assays including MTT and LDH release. Oxidative alterations by hBNs application in PD cell culture model were investigated using total antioxidant capacity (TAC) and total oxidant status (TOS) tests. The impacts of hBNs and MPP⁺ on nuclear integrity were analyzed by Hoechst 33258 fluorescent staining method. Acetylcholinesterase (AChE) enzyme activities were determined by a colorimetric assay towards to hBNs treatment. Cell death mechanisms caused by hBNs and MPP+ exposure was investigated by flow cytometry analysis. Experimental results showed that application of hBNs increased cell viability in PD model against MPP⁺ application. TAS and TOS analysis were determined that antioxidant capacity elevated after hBNs applications while oxidant levels were reduced. Furthermore, flow cytometric analysis executed that MPP⁺ induced apoptosis was prevented significantly (p < 0.05) after application with hBNs. In a conclusion, the obtained results indicated that hBNs have a huge potential against MPP⁺ toxicity and can be used in PD treatment as novel neuroprotective agent and drug delivery system.

Biocomplexity and Fractality in the Search of Biomarkers of Aging and Pathology: Mitochondrial DNA Profiling of Parkinson's Disease

Increasing evidence implicates mitochondrial dysfunction in the etiology of Parkinson's disease (PD). Mitochondrial DNA (mtDNA) mutations are considered a possible cause and this mechanism might be shared with the aging process and with other age-related neurodegenerative disorders such as Alzheimer's disease (AD). We have recently proposed a computerized method for mutated mtDNA characterization able to discriminate between AD and aging. The present study deals with mtDNA mutation-based profiling of PD. Peripheral blood mtDNA sequences from late-onset PD patients and age-matched controls were analyzed and compared to the revised Cambridge Reference Sequence (rCRS). The chaos game representation (CGR) method, modified to visualize heteroplasmic mutations, was used to display fractal properties of mtDNA sequences and fractal lacunarity analysis was applied to quantitatively characterize PD based on mtDNA mutations. Parameter β, from the hyperbola model function of our lacunarity method, was statistically different between PD and control groups when comparing mtDNA sequence frames corresponding to GenBank np 5713-9713. Our original method, based on CGR and lacunarity analysis, represents a useful tool to analyze mtDNA mutations. Lacunarity parameter β is able to characterize individual mutation profile of mitochondrial genome and could represent a promising index to discriminate between PD and aging.

Analysis of mitochondrial DNA allelic changes in Parkinson's disease: a preliminary study

BACKGROUND

Mitochondrial DNA (mtDNA) mutations are considered as a possible primary cause of age-associated neurodegenerative disorders like Parkinson's disease (PD).

AIMS

To analyze, along the whole mtDNA sequence of PD patients, the presence of non-reference alleles compared to reference alleles, as defined in the revised Cambridge Reference Sequence (rCRS).

METHODS

mtDNA was extracted from whole blood of PD and control groups, and was sequenced using a chip-based resequencing system.

RESULTS

58 nucleotide positions (np) exhibited a different allelic distribution in the two groups; in 81% of them the non-reference alleles were over-represented in PD patients, similar to findings reported in patients with Alzheimer's disease, albeit in reduced proportion. Closer analysis of the 58 np in PD group showed that they were characterized by low-level heteroplasmy, and that the nucleotide substitutions determined an amino acid change in 84% of cases.

CONCLUSIONS

These results suggest that mtDNA allelic changes are increased in PD and that age-related neurodegenerative diseases could share a common mechanism involving mtDNA.

The unresolved role of mitochondrial DNA in Parkinson's disease: An overview of published studies, their limitations, and future prospects

Parkinson's disease (PD), a progressive neurodegenerative disorder, has long been associated with mitochondrial dysfunction in both sporadic and familial forms of the disease. Mitochondria are crucial for maintaining cellular homeostasis, and their dysfunction is detrimental to dopaminergic neurons. These neurons are highly dependent on mitochondrial adenosine triphosphate (ATP) and degenerate in PD. Mitochondria contain their own genomes (mtDNA). The role of mtDNA has been investigated in PD on the premise that it encodes vital components of the ATP-generating oxidative phosphorylation (OXPHOS) complexes and accumulates somatic variation with age. However, the association between mtDNA variation and PD remains controversial. Herein, we provide an overview of previously published studies on the role of inherited as well as somatic (acquired) mtDNA changes in PD including point mutations, deletions and depletion. We outline limitations of previous investigations and the difficulties associated with studying mtDNA, which have left its role unresolved in the context of PD. Lastly, we highlight the potential for further research in this field and provide suggestions for future studies. Overall, the mitochondrial genome is indispensable for proper cellular function and its contribution to PD requires further, more extensive investigation.

The Nudix Hydrolase 15 (NUDT15) Gene Variants among Jordanian Arab Population

Background: Nudix Hydrolase 15 gene (NUDT15) encodes nucleotide triphosphate diphosphatase which metabolizes the purine analog drugs, such as anticancer thiopurine and anti-gout allopurinol. Genetic variants on Nudix Hydrolase 15 gene (NUDT15) gene effects the drug’s hydrolyses and hence increases the susceptibility to drug-induced toxicity. The NUDT15 gene has been genotyped in various ethnic groups, however, it has not been genotyped among the Middle Eastern Arab Jordanian population. Aim: The current study aimed to identify NUDT15 genetic variants among Jordanian Arab population. Method: The DNA samples were isolated from leukocytes of 85 unrelated Jordanian Arab volunteers. The coding regions of NUDT15 gene; Exon 1,2 and 3, in addition to some regions of intron 1,2 and 3’UTR, were amplified using polymerase chain reaction (PCR). the PCR products were then subjected to purification and sequenced using Applied Biosystems Model (ABI3730x1). Results: Six NUDT15 genetic variants were found among the volunteers.The results were as followed: A novel synonymous variant 36A>G on exon 1 (6%, 95%CI= 3- 9%), the intronic IVS1 +116C>T variant on intron 1 (0.6%, 95%CI= 0-2%), the non-synonymous variant on exon 3; 415C>T (0.6%, 95%CI= 0-2%), A novel non-synonymous variant on exon 3; 404C>A (0.6%, 95%CI= 0-2%) , and two novel variants on 3’UTR ;502G>A (2%, 95%CI= 0.5-4%) and 588T>C (0.6%, 95%CI= 0-2%). NUDT15 36A>G wasfound to be the most common allele among Jordanians was. In silico softwares predicted that the novel NUDT15 404C>A was harmful and affected NUDT15 enzyme’sstability and function. Furthermore, the frequency of NUDT15 IVS1 +116C>T , among Jordanians, showed to be significantly lower from what was reported in other ethnicities with ap value > 0.05 on the other hand, the frequency of 415C>T variant showed to be similar to Europeans in contrast to Asians and Indians that showed to be significantly lower (p value > 0.05). Conclusions: The frequency of NUDT15 genetic variants is low among the Jordanian volunteers and significantly lower than other ethnic groups. The findings of this study may increase our understanding of the inter-individual variation in the response to purine analog drugs. Further clinical studies are needed to investigate the influence of novel NUDT15 404C>A on drug metabolism and response.

The second genome: Effects of the mitochondrial genome on cancer progression

The role of genetics in cancer has been recognized for centuries, but most studies elucidating genetic contributions to cancer have understandably focused on the nuclear genome. Mitochondrial contributions to cancer pathogenesis have been documented for decades, but how mitochondrial DNA (mtDNA) influences cancer progression and metastasis remains poorly understood. This lack of understanding stems from difficulty isolating the nuclear and mitochondrial genomes as experimental variables, which is critical for investigating direct mtDNA contributions to disease given extensive crosstalk exists between both genomes. Several in vitro and in vivo models have isolated mtDNA as an independent variable from the nuclear genome. This review compares and contrasts different models, their advantages and disadvantages for studying mtDNA contributions to cancer, focusing on the mitochondrial-nuclear exchange (MNX) mouse model and findings regarding tumor progression, metastasis, and other complex cancer-related phenotypes.

Acetylation as a major determinant to microtubule-dependent autophagy: Relevance to Alzheimer's and Parkinson disease pathology

Protein post-translational modifications (PTMs) that potentiate protein aggregation have been implicated in several neurological disorders, including Alzheimer's (AD) and Parkinson's disease (PD). In fact, Tau and alpha-synuclein (ASYN) undergo several PTMs potentiating their aggregation and neurotoxicity. Recent data posits a role for acetylation in Tau and ASYN aggregation. Herein we aimed to clarify the role of Sirtuin-2 (SIRT2) and HDAC6 tubulin deacetylases as well as p300 acetyltransferase in AD and PD neurodegeneration. We used transmitochondrial cybrids that recapitulate pathogenic alterations observed in sporadic PD and AD patient brains and ASYN and Tau cellular models. We confirmed that Tau protein and ASYN are microtubules (MTs)-associated proteins (MAPs). Moreover, our results suggest that α-tubulin acetylation induced by SIRT2 inhibition is functionally associated with the improvement of MT dynamic determined by decreased Tau phosphorylation and by increased Tau/tubulin and ASYN/tubulin binding. Our data provide a strong evidence for a functional role of tubulin and MAPs acetylation on autophagic vesicular traffic and cargo clearance. Additionally, we showed that an accumulation of ASYN oligomers imbalance mitochondrial dynamics, which further compromise autophagy. We also demonstrated that an increase in Tau acetylation is associated with Tau phosphorylation. We found that p300, HDAC6 and SIRT2 influences Tau phosphorylation and autophagic flux in AD. In addition, we demonstrated that p300 and HDAC6 modulate Tau and Tubulin acetylation. Overall, our data disclose the role of Tau and ASYN modifications through acetylation in AD and PD pathology, respectively. Moreover, this study indicates that MTs can be a promising therapeutic target in the field of neurodegenerative disorders in which intracellular transport is altered.

Stem Cell Transplantation and Physical Exercise in Parkinson's Disease, a Literature Review of Human and Animal Studies

The absence of effective and satisfactory treatments that contribute to repairing the dopaminergic damage caused by Parkinson's Disease (PD) and the limited recovery capacity of the nervous system are troubling issues and the focus of many research and clinical domains. Recent advances in the treatment of PD through stem cell (SC) therapy have recognized their promising restorative and neuroprotective effects that are implicated in the potentiation of endogenous mechanisms of repair and contribute to functional locomotor improvement. Physical exercise (PE) has been considered an adjuvant intervention that by itself induces beneficial effects in patients and animal models with Parkinsonism. In this sense, the combination of both therapies could provide synergic or superior effects for motor recovery, in contrast with their individual use. This review aims to provide an update on recent progress and the potential effectiveness of SC transplantation and PE for the treatment of locomotor deficits in PD. It has reviewed the neuropathological pathways involved in the classical motor symptoms of this condition and the mechanisms of action described in experimental studies that are associated with locomotor enhancement through exercise, cellular transplantation, and their union in some neurodegenerative conditions.

New Therapeutics to Modulate Mitochondrial Function in Neurodegenerative Disorders

BACKGROUND

Mitochondrial function and energy metabolism are impaired in neurodegenerative diseases. There is evidence for these functional declines both within the brain and systemically in Alzheimer's disease, Parkinson's disease, and Amyotrophic Lateral Sclerosis. Due to these observations, therapeutics targeted to alter mitochondrial function and energy pathways are increasingly studied in pre-clinical and clinical settings.

METHODS

The goal of this article was to review therapies with specific implications on mitochondrial energy metabolism published through May 2016 that have been tested for treatment of neurodegenerative diseases.

RESULTS

We discuss implications for mitochondrial dysfunction in neurodegenerative diseases and how this drives new therapeutic initiatives.

CONCLUSION

Thus far, treatments have achieved varying degrees of success. Further investigation into the mechanisms driving mitochondrial dysfunction and bioenergetic failure in neurodegenerative diseases is warranted.

The Microbiome-Mitochondria Dance in Prodromal Parkinson's Disease

The brain is an immunologically active organ where neurons and glia cells orchestrate complex innate immune responses against infections and injuries. Neuronal responses involve Toll-like or Nod-like receptors and the secretion of antimicrobial peptides and cytokines. The endosymbiotic theory for the evolutionary origin of mitochondria from primitive bacteria, suggests that they may have also retained the capacity to activate neuronal innate immunity. In fact, it was shown that mitochondrial damage-associated molecular patterns could signal and activate innate immunity and inflammation. Moreover, the mitochondrial cascade hypothesis for sporadic Parkinson’s disease (PD) argues that altered mitochondrial metabolism and function can drive neurodegeneration. Additionally, a neuroinflammatory signature with increased levels of pro-inflammatory mediators in PD affected brain areas was recently detected. Herein, we propose that a cascade of events initiating in a dysbiotic gut microbiome drive the production of toxins or antibiotics that target and damage mitochondria. This in turn activates neuronal innate immunity and triggers sterile inflammation phenomena that culminate in the neurodegenerative processes observed in the enteric and in the central nervous systems and that ultimately lead to Parkinson’s disease.

Current perspective of mitochondrial biology in Parkinson's disease

Parkinson's disease (PD) is one of the most common neurodegenerative movement disorder characterized by preferential loss of dopaminergic neurons of the substantia nigra pars compacta and the presence of Lewy bodies containing α-synuclein. Although the cause of PD remains elusive, remarkable advances have been made in understanding the possible causative mechanisms of PD pathogenesis. An explosion of discoveries during the past two decades has led to the identification of several autosomal dominant and recessive genes that cause familial forms of PD. The investigations of these familial PD gene products have shed considerable insights into the molecular pathogenesis of the more common sporadic PD. A growing body of evidence suggests that the etiology of PD is multifactorial and involves a complex interplay between genetic and environmental factors. Substantial evidence from human tissues, genetic and toxin-induced animal and cellular models indicates that mitochondrial dysfunction plays a central role in the pathophysiology of PD. Deficits in mitochondrial functions due to bioenergetics defects, alterations in the mitochondrial DNA, generation of reactive oxygen species, aberrant calcium homeostasis, and anomalies in mitochondrial dynamics and quality control are implicated in the underlying mechanisms of neuronal cell death in PD. In this review, we discuss how familial PD-linked genes and environmental factors interface the pathways regulating mitochondrial functions and thereby potentially converge both familial and sporadic PD at the level of mitochondrial integrity. We also provide an overview of the status of therapeutic strategies targeting mitochondrial dysfunction in PD. Unraveling potential pathways that influence mitochondrial homeostasis in PD may hold the key to therapeutic intervention for this debilitating neurodegenerative movement disorder.

Mitochondria-Derived Damage-Associated Molecular Patterns in Neurodegeneration

Inflammation is increasingly implicated in neurodegenerative disease pathology. As no acquired pathogen appears to drive this inflammation, the question of what does remains. Recent advances indicate damage-associated molecular pattern (DAMP) molecules, which are released by injured and dying cells, can cause specific inflammatory cascades. Inflammation, therefore, can be endogenously induced. Mitochondrial components induce inflammatory responses in several pathological conditions. Due to evidence such as this, a number of mitochondrial components, including mitochondrial DNA, have been labeled as DAMP molecules. In this review, we consider the contributions of mitochondrial-derived DAMPs to inflammation observed in neurodegenerative diseases.

The Universal Non-Neuronal Nature of Parkinson's Disease: A Theory

Parkinson's disease (PD) is one of the most common neurodegenerative disorders, yet the etiology of the majority of its cases remains unknown. In this manuscript, relevant published evidence is interpreted and integrated into a comprehensive hypothesis on the nature, origin, and inter-cellular mode of propagation of sporadic PD. We propose to characterize sporadic PD as a pathological deviation in the global gene expression program of a cell: the PD expression-state, or PD-state for short. A universal cell-generic state, the PD-state deviation would be particularly damaging in a neuronal context, ultimately leading to neuron death and the ensuing observed clinical signs. We review why ageing associated accumulated damage caused by oxidative stress in mitochondria could be the trigger for a primordial cell to shift to the PD-state. We propose that hematopoietic cells could be the first to acquire the PD-state, at hematopoiesis, from the disruption in reactive oxygen species homeostasis that arises with age in the hematopoietic stem-cell niche. We argue that cellular ageing is nevertheless unlikely to explain the shift to the PD-state of all the subsequently affected cells in a patient, thus indicating the existence of a distinct mechanism of cellular propagation of the PD-state. We highlight recently published findings on the inter-cellular exchange of mitochondrial DNA and the ability of mitochondrial DNA to modulate the cellular global gene expression state and propose this could form the basis for the inter-cellular transmission of the PD-state.

Elevated caspase 3 activity and cytosolic cytochrome c in NT2 cybrids containing amyotrophic lateral sclerosis subject mtDNA

Apoptosis of motor neurons is an important feature in amyotrophic lateral sclerosis (ALS). A vital role of mitochondria in apoptosis and cell survival is well documented. Eventually mitochondria have shown to be an early target in the pathogenesis of ALS. On account of these facts, we investigated the involvement of mitochondrial-dependent apoptosis in ALS and control (CTR) cybrids, generated fusing human platelets with mitochondrial DNA-depleted NT2-neuroteratocarcinoma cells. After a 6 week selection process during which transferred subject mtDNA repopulated the NT2 cells and restored mitochondrial oxygen consumption, we assessed cell viability and two programmed cell death parameters, caspase 3 activity and cytosolic cytochrome c levels. Compared to the control cybrid lines (n = 5), the ALS cybrid lines (n = 10) showed 45% less XTT reduction and higher caspase 3 activity ( p < 0.05, two-way Student's t test) exhibiting lesser cell viability and execution of apoptosis. Elevated cytosolic cytochrome c levels in ALS cybrid lines (n = 8) than in CTR (n = 4) ( p < 0.05, two-way Student's t-test) indicating its mitochondrial release and initiation of apoptosis. This indicates apoptosis as one of the possible mechanisms of cell death in ALS. Our findings support the view that in ALS, subject's mitochondria are altered in non-degenerating tissues in such a way that intrinsic apoptotic pathway activity is relatively increased.

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.

Poly(ADP-ribosylation) and neurodegenerative disorders

Impaired mitochondrial structure and function are common features of neurodegenerative disorders, ultimately characterized by the death of neural cells promoted by still unknown signals. Among the possible modulators of neurodegeneration, the activation of poly(ADP-ribosylation), a post-translational modification of proteins, has been considered, being the product of the reaction, poly(ADP-ribose), a signaling molecule for different cell death paradigms. The basic properties of poly(ADP-ribosylation) are here described, focusing on the mitochondrial events; cell death paradigms such as apoptosis, parthanatos, necroptosis and mitophagy are illustrated. Finally, the promising use of poly(ADP-ribosylation) inhibitors to rescue neurodegeneration is addressed.

DRD and GRIN2B polymorphisms and their association with the development of impulse control behaviour among Malaysian Parkinson's disease patients

Background

Impulse control disorder (ICD) and behaviours (ICB) represent a group of behavioural disorders that have become increasingly recognised in Parkinson’s disease (PD) patients who previously used dopaminergic medications, particularly dopamine agonists and levodopa. It has been suggested that these medications can lead to the development of ICB through the abnormal modulation of dopaminergic transmission and signalling in the mesocorticolimbic dopaminergic system. Several studies have reported an association between polymorphisms in the dopamine receptor (DRD) and N-methyl-D-aspartate 2B (GRIN2B) genes with the development of ICB in PD (PD-ICB) patients. Thus, this study aimed to investigate the association of selected polymorphisms within the DRD and GRIN2B genes with the development of ICB among PD patients using high resolution melt (HRM) analysis.

Method

We used high resolution melt (HRM) analysis to genotype 11 polymorphisms in 5 DRD genes [DRD1 (rs4532, rs4867798 and rs265981), DRD2 (ANKK1 rs1800497, rs104894220 and rs144999500), DRD3 (rs3732783 and rs6280), DRD4 (rs1800443), and DRD5 (rs144132215)] and 1 polymorphism in GRIN2B (rs7301328) in PD patients with (cases, n = 52) and without (controls, n = 39) ICB. Cases were obtained from two tertiary movement disorder centres [UKMMC (n = 9) and UMMC (n = 43)]. At both centres, the diagnosis of ICB was made using the QUIP questionnaire. Controls were recruited from PD patients who attended UKMMC and were found to be negative for ICB using the QUIP questionnaire.

Results

The HRM analysis showed that 7 of 11 polymorphisms [DRD1 (rs4532, rs4867798, and rs265981), DRD2 (ANKK1 rs1800497), DRD3 (rs3732783 and rs6280), and GRIN2B (rs7301328)] exhibited a clear distinction between wild-type and variant alleles. Variants of DRD2/ANKK1 rs1800497 (OR = 3.77; 95% CI, 1.38-10.30; p = 0.0044), DRD1 rs4867798 (OR = 24.53; 95% CI, 1.68-357.28; p = 0.0054), DRD1 rs4532 (OR = 21.33; 95% CI, 1.97-230.64; p = 0.0024), and GRIN2B rs7301328 (OR = 25.07; 95% CI, 1.30-483.41; p = 0.0097) were found to be associated with an increased risk of developing ICB among PD patients.

Conclusion

Our findings suggest that polymorphisms in dopamine [DRD1 (rs4532 and rs4867798) and DRD2/ANKK1 rs1800497] and glutamate (GRIN2B rs7301328) receptor genes confer increased risk of ICB development among PD patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s12883-015-0316-2) contains supplementary material, which is available to authorized users.

A cybrid cell model for the assessment of the link between mitochondrial deficits and sporadic Parkinson's disease

Parkinson's disease (PD) is a multifactorial and clinically complex age-related movement disorder. The cause of its most common form (sporadic PD, sPD) is unknown, but one prominent causal factor is mitochondrial dysfunction. Although several genetic- and toxin-based models have been developed along the last decades to mimic the pathological cascade of PD, cellular models that reliably recapitulate the pathological features of the neurons that degenerate in PD are scarce.We describe here the generation of cytoplasmic hybrid cells (or cybrids) as a cellular model of sPD. This approach consists on the fusion of platelets harboring mtDNA from sPD patients with cells in which the endogenous mtDNA has been depleted (Rho0 cells).The sPD cybrid model has been successful in recapitulating most of the hallmarks of sPD, constituting now a validated model for addressing the link between mitochondrial dysfunction and sPD pathology.

Bioenergetic medicine

Here we discuss a specific therapeutic strategy we call 'bioenergetic medicine'. Bioenergetic medicine refers to the manipulation of bioenergetic fluxes to positively affect health. Bioenergetic medicine approaches rely heavily on the law of mass action, and impact systems that monitor and respond to the manipulated flux. Since classically defined energy metabolism pathways intersect and intertwine, targeting one flux also tends to change other fluxes, which complicates treatment design. Such indirect effects, fortunately, are to some extent predictable, and from a therapeutic perspective may also be desirable. Bioenergetic medicine-based interventions already exist for some diseases, and because bioenergetic medicine interventions are presently feasible, new approaches to treat certain conditions, including some neurodegenerative conditions and cancers, are beginning to transition from the laboratory to the clinic.

The Impact of Mitochondrial Fusion and Fission Modulation in Sporadic Parkinson's Disease

Accumulating data suggests that mitochondrial deficits may underline both sporadic and familial Parkinson's disease (PD) neurodegenerative process. Impairment of mitochondrial dynamics results in reactive oxygen species (ROS) production, decreases mitochondrial membrane potential, and could potentiate the accumulation of dysfunctional mitochondria. Excessive mitochondrial fragmentation is associated with the pathology of sporadic PD. Therefore, we modulated mitochondria fusion and fission in different sporadic PD cellular models. We found alterations in two proteins known to regulate mitochondrial fusion and fission events (OPA1 and Drp1, respectively). OPA1 long isoform cleavage seems to be, at least in part, responsible for mitochondrial fragmented pattern observed in sporadic PD cellular models. Moreover, mitochondrial fragmentation can also occur due to an increase in Drp1 that is translocated into the mitochondria by phosphorylation. To disclose the relevance of these alterations to the fragmentation of the mitochondrial network, we overexpressed OPA1 and knock down Drp1. OPA1 overexpression did not rescue MPP(+)-induced increase in ROS. Nevertheless, Drp1 knockdown due to an increase in mitochondrial elongation and interconnectivity rescued mitochondrial membrane potential and decreased ROS production in sporadic PD cells. Overall, our findings suggest that Drp1-dependent mitochondrial fragmentation plays a crucial role in mediating mitochondrial DNA induced mitochondria abnormalities and cellular dysfunction in sporadic PD.

Identification of licopyranocoumarin and glycyrurol from herbal medicines as neuroprotective compounds for Parkinson's disease

In the course of screening for the anti-Parkinsonian drugs from a library of traditional herbal medicines, we found that the extracts of choi-joki-to and daio-kanzo-to protected cells from MPP⁺-induced cell death. Because choi-joki-to and daio-kanzo-to commonly contain the genus Glycyrrhiza, we isolated licopyranocoumarin (LPC) and glycyrurol (GCR) as potent neuroprotective principals from Glycyrrhiza. LPC and GCR markedly blocked MPP⁺-induced neuronal PC12D cell death and disappearance of mitochondrial membrane potential, which were mediated by JNK. LPC and GCR inhibited MPP⁺-induced JNK activation through the suppression of reactive oxygen species (ROS) generation, thereby inhibiting MPP⁺-induced neuronal PC12D cell death. These results indicated that LPC and GCR derived from choi-joki-to and daio-kanzo-to would be promising drug leads for PD treatment in the future.

Cytoplasmic hybrid (cybrid) cell lines as a practical model for mitochondriopathies

Cytoplasmic hybrid (cybrid) cell lines can incorporate human subject mitochondria and perpetuate its mitochondrial DNA (mtDNA)-encoded components. Since the nuclear background of different cybrid lines can be kept constant, this technique allows investigators to study the influence of mtDNA on cell function. Prior use of cybrids has elucidated the contribution of mtDNA to a variety of biochemical parameters, including electron transport chain activities, bioenergetic fluxes, and free radical production. While the interpretation of data generated from cybrid cell lines has technical limitations, cybrids have contributed valuable insight into the relationship between mtDNA and phenotype alterations. This review discusses the creation of the cybrid technique and subsequent data obtained from cybrid applications.

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The cytoplasmic hybrid (cybrid) model can be used to determine mitochondrial DNA (mtDNA) contributions to phenotypic alterations.

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Cybrids are used to study mitochondriopathies such as Parkinson’s disease and Alzheimer’s disease.

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mtDNA heteroplasmy threshold and nuclear DNA-mtDNA compatibility can be determined using cybrid models.

The rescue of microtubule-dependent traffic recovers mitochondrial function in Parkinson's disease

In Parkinson's disease mitochondrial dysfunction can lead to a deficient ATP supply to microtubule protein motors leading to mitochondrial axonal transport disruption. Compromised axonal transport will then lead to a disorganized distribution of mitochondria and other organelles in the cell, as well as, the accumulation of aggregated proteins like alpha-synuclein. Moreover, axonal transport disruption can trigger synaptic accumulation of autophagosomes packed with damaged mitochondria and protein aggregates promoting synaptic failure. We previously observed that neuronal-like cells with an inherent mitochondrial impairment derived from PD patients contain a disorganized microtubule network, as well as, alpha-synuclein oligomer accumulation. In this work we provide new evidence that an agent that promotes microtubule network assembly, NAP (davunetide), improves microtubule-dependent traffic, restores the autophagic flux and potentiates autophagosome-lysosome fusion leading to autophagic vacuole clearance in Parkinson's disease cells. Moreover, NAP is capable of efficiently reducing alpha-synuclein oligomer content and its sequestration by the mitochondria. Most interestingly, NAP decreases mitochondrial ubiquitination levels, as well as, increases mitochondrial membrane potential indicating a rescue in mitochondrial function. Overall, we demonstrate that by improving microtubule-mediated traffic, we can avoid mitochondrial-induced damage and thus recover cell homeostasis. These results prove that NAP may be a promising therapeutic lead candidate for neurodegenerative diseases that involve axonal transport failure and mitochondrial impairment as hallmarks, like Parkinson's disease and related disorders.

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.

Role of platelets in neurodegenerative diseases: a universal pathophysiology

Platelets play an important role in a variety of disorders, namely, cardiovascular, psychosomatic, psychiatric, thrombosis, HIV/AIDS in addition to various neurodegenerative diseases (NDDs). Recent evidence indicates that platelet react to diverse stressors, thereby offering an interesting vantage point for understanding their potential role in contemporary medical research. This review addresses the possible role of platelets as a systemic probe in various NDDs, such as amyotrophic lateral sclerosis, Parkinson's disease, Huntington's disease, Alzheimer's disease, multiple sclerosis, etc. The current review based on published literature, describes a probable link between platelets and pathophysiology of various NDDs. It also discusses how platelets epitomize ultrastructural, morphological, biochemical and molecular changes, highlighting their emerging role as systemic tools in different NDDs.

Mitochondrial quality, dynamics and functional capacity in Parkinson's disease cybrid cell lines selected for Lewy body expression

Background

Lewy bodies (LB) are a neuropathological hallmark of Parkinson’s disease (PD) and other synucleinopathies. The role their formation plays in disease pathogenesis is not well understood, in part because studies of LB have been limited to examination of post-mortem tissue. LB formation may be detrimental to neuronal survival or merely an adaptive response to other ongoing pathological processes. In a human cytoplasmic hybrid (cybrid) neural cell model that expresses mitochondrial DNA from PD patients, we observed spontaneous formation of intracellular protein aggregates (“cybrid LB” or CLB) that replicate morphological and biochemical properties of native, cortical LB. We studied mitochondrial morphology, bioenergetics and biogenesis signaling by creating stable sub-clones of three PD cybrid cell lines derived from cells expressing CLB.

Results

Cloning based on CLB expression had a differential effect on mitochondrial morphology, movement and oxygen utilization in each of three sub-cloned lines, but no long-term change in CLB expression. In one line (PD63_CLB), mitochondrial function declined compared to the original PD cybrid line (PD63_Orig) due to low levels of mtDNA in nucleoids. In another cell line (PD61_Orig), the reverse was true, and cellular and mitochondrial function improved after sub-cloning for CLB expression (PD61_CLB). In the third cell line (PD67_Orig), there was no change in function after selection for CLB expression (PD67_CLB).

Conclusions

Expression of mitochondrial DNA derived from PD patients in cybrid cell lines induced the spontaneous formation of CLB. The creation of three sub-cloned cybrid lines from cells expressing CLB resulted in differential phenotypic changes in mitochondrial and cellular function. These changes were driven by the expression of patient derived mitochondrial DNA in nucleoids, rather than by the presence of CLB. Our studies suggest that mitochondrial DNA plays an important role in cellular and mitochondrial dysfunction in PD. Additional studies will be needed to assess the direct effect of CLB expression on cellular and mitochondrial function.

Distinct effects of rotenone, 1-methyl-4-phenylpyridinium and 6-hydroxydopamine on cellular bioenergetics and cell death

Parkinson's disease is characterized by dopaminergic neurodegeneration and is associated with mitochondrial dysfunction. The bioenergetic susceptibility of dopaminergic neurons to toxins which induce Parkinson's like syndromes in animal models is then of particular interest. For example, rotenone, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and its active metabolite 1-methyl-4-phenylpyridinium (MPP(+)), and 6-hydroxydopamine (6-OHDA), have been shown to induce dopaminergic cell death in vivo and in vitro. Exposure of animals to these compounds induce a range of responses characteristics of Parkinson's disease, including dopaminergic cell death, and Reactive Oxygen Species (ROS) production. Here we test the hypothesis that cellular bioenergetic dysfunction caused by these compounds correlates with induction of cell death in differentiated dopaminergic neuroblastoma SH-SY5Y cells. At increasing doses, rotenone induced significant cell death accompanied with caspase 3 activation. At these concentrations, rotenone had an immediate inhibition of mitochondrial basal oxygen consumption rate (OCR) concomitant with a decrease of ATP-linked OCR and reserve capacity, as well as a stimulation of glycolysis. MPP(+) exhibited a different behavior with less pronounced cell death at doses that nearly eliminated basal and ATP-linked OCR. Interestingly, MPP(+), unlike rotenone, stimulated bioenergetic reserve capacity. The effects of 6-OHDA on bioenergetic function was markedly less than the effects of rotenone or MPP(+) at cytotoxic doses, suggesting a mechanism largely independent of bioenergetic dysfunction. These studies suggest that these dopaminergic neurotoxins induce cell death through distinct mechanisms and differential effects on cellular bioenergetics.

Ubiquitin proteasome system in Parkinson's disease: a keeper or a witness?

OBJECTIVE

The aim of this work was to evaluate the role of ubiquitin-proteasome system (UPS) on mitochondrial-driven alpha-synuclein (aSN) clearance in in vitro, ex vivo and in vivo Parkinson's disease (PD) cellular models.

METHOD

We used SH-SY5Y ndufa2 knock-down (KD) cells, PD cybrids and peripheral blood mononuclear cells (PBMC) from patients meeting the diagnostic criteria for PD. We quantified aSN aggregation, proteasome activity and protein ubiquitination levels. In PBMC of PD patient population we evaluated the aSN levels in the plasma and the influence of several demographic characteristics in the above mentioned determinations.

RESULTS

We found that ubiquitin-independent proteasome activity was up-regulated in SH-SY5Y ndufa2 KD cells while a downregulation was observed in PD cybrids and PBMC. Moreover, we observed an increase in protein ubiquitination that correlates with a decrease in ubiquitin-dependent proteasome activity. Accordingly, proteasome inhibition prevented ubiquitin-dependent aSN clearance. Ubiquitin-independent proteasome activity was positively correlated with ubiquitination in PBMC. We also report a negative correlation of chymotrypsin-like activity with age in control and late-onset PD groups. Total ubiquitin content is positively correlated with aSN oligomer levels, which leads to an age-dependent increase of aSN ubiquitination in LOPD. Moreover, aSN levels are increased in the plasma of PD patients.

INTERPRETATION

aSN oligomers are ubiquitinated and we identified a ubiquitin-dependent clearance insufficiency with the accumulation of both aSN and ubiquitin. However, SH-SY5Y ndufa2 KD cells showed a significant up-regulation of ubiquitin-independent proteasomal enzymatic activity that could mean a cell rescue attempt. Moreover, we identified that UPS function is age-dependent in PBMC.

Mitochondrial metabolism in Parkinson's disease impairs quality control autophagy by hampering microtubule-dependent traffic

Abnormal presence of autophagic vacuoles is evident in brains of patients with Parkinson's disease (PD), in contrast to the rare detection of autophagosomes in a normal brain. However, the actual cause and pathological significance of these observations remain unknown. Here, we demonstrate a role for mitochondrial metabolism in the regulation of the autophagy-lysosomal pathway in ex vivo and in vitro models of PD. We show that transferring mitochondria from PD patients into cells previously depleted of mitochondrial DNA is sufficient to reproduce the alterations in the autophagic system observed in PD patient brains. Although the initial steps of this pathway are not compromised, there is an increased accumulation of autophagosomes associated with a defective autophagic activity. We prove that this functional decline was originated from a deficient mobilization of autophagosomes from their site of formation toward lysosomes due to disruption in microtubule-dependent trafficking. This contributed directly to a decreased proteolytic flux of α-synuclein and other autophagic substrates. Our results lend strong support for a direct impact of mitochondria in autophagy as defective autophagic clearance ability secondary to impaired microtubule trafficking is driven by dysfunctional mitochondria. We uncover mitochondria and mitochondria-dependent intracellular traffic as main players in the regulation of autophagy in PD.