Mitochondrial DNA changes in pedunculopontine cholinergic neurons in Parkinson disease

Identification of Potential Causal Genes for Neurodegenerative Diseases by Mitochondria-Related Genome-Wide Mendelian Randomization

Current research lacks comprehensive investigations into the potential causal link between mitochondrial-related genes and the risk of neurodegenerative diseases (NDDs). We aimed to identify potential causative genes for five NDDs through an examination of mitochondrial-related gene expression levels. Through the integration of summary statistics from expression quantitative trait loci (eQTL) datasets (human blood and brain tissue), mitochondrial DNA copy number (mtDNA-CN), and genome-wide association studies (GWAS) datasets of five NDDs from European ancestry, we conducted a Mendelian randomization (MR) analysis to explore the potential causal relationship between mitochondrial-related genes and Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD), and Lewy body dementia (LBD). Sensitivity analysis and Bayesian colocalization were employed to validate this causal relationship. Through MR analysis, we have identified potential causal relationships between 12 mitochondria-related genes and AD, PD, ALS, and FTD overlapping with motor neuron disease (FTD_MND) in human blood or brain tissue. Bayesian colocalization analysis further confirms 9 causal genes, including NDUFS2, EARS2, and MRPL41 for AD; NDUFAF2, MALSU1, and METTL8 for PD; MYO19 and MRM1 for ALS; and FASTKD1 for FTD_MND. Importantly, in both human blood and brain tissue, NDUFS2 exhibits a significant pathogenic effect on AD, while NDUFAF2 demonstrates a robust protective effect on PD. Additionally, the mtDNA-CN plays a protected role in LBD (OR = 0.62, p = 0.031). This study presents evidence establishing a causal relationship between mitochondrial dysfunction and NDDs. Furthermore, the identified candidate genes may serve as potential targets for drug development aimed at preventing NDDs.

Nanobiopsy investigation of the subcellular mtDNA heteroplasmy in human tissues

Mitochondrial function is critical to continued cellular vitality and is an important contributor to a growing number of human diseases. Mitochondrial dysfunction is typically heterogeneous, mediated through the clonal expansion of mitochondrial DNA (mtDNA) variants in a subset of cells in a given tissue. To date, our understanding of the dynamics of clonal expansion of mtDNA variants has been technically limited to the single cell-level. Here, we report the use of nanobiopsy for subcellular sampling from human tissues, combined with next-generation sequencing to assess subcellular mtDNA mutation load in human tissue from mitochondrial disease patients. The ability to map mitochondrial mutation loads within individual cells of diseased tissue samples will further our understanding of mitochondrial genetic diseases.

Resveratrol Inhibits VDAC1-Mediated Mitochondrial Dysfunction to Mitigate Pathological Progression in Parkinson's Disease Model

An increase in α-synuclein (α-syn) levels and mutations in proteins associated with mitochondria contribute to the development of familial Parkinson's disease (PD); however, the involvement of α-syn and mitochondria in idiopathic PD remains incompletely understood. The voltage-dependent anion channel I (VDAC1) protein, which serves as a crucial regulator of mitochondrial function and a gatekeeper, plays a pivotal role in governing cellular destiny through the control of ion and respiratory metabolite flux. The ability of resveratrol (RES), which is a potent phytoalexin with antioxidant and anti-inflammatory properties, to regulate VDAC1 in PD is unknown. The objective of this study was to evaluate the role of VDAC1 in the pathological process of PD and to explore the mechanism by which resveratrol protects dopaminergic neurons by regulating VDAC1 to maintain the mitochondrial permeability transition pore (mPTP) and calcium ion balance. The effects of RES on the motor and cognitive abilities of A53T mice were evaluated by using small animal behavioral tests. Various techniques, including immunofluorescence staining, transmission electron microscopy, enzyme-linked immunoadsorption, quantitative polymerase chain reaction (PCR), and Western blotting, among others, were employed to assess the therapeutic impact of RES on neuropathy associated with PD and its potential in regulating mitochondrial VDAC1. The findings showed that RES significantly improved motor and cognitive dysfunction and restored mitochondrial function, thus reducing oxidative stress levels in A53T mice. A significant positive correlation was observed between the protein expression level of VDAC1 and mitochondrial α-syn expression, as well as disease progression, whereas no such correlation was found in VDAC2 and VDAC3. Administration of RES resulted in a significant decrease in the protein expression of VDAC1 and in the protein expression of α-syn both in vivo and in vitro. In addition, we found that RES prevents excessive opening of the mPTP in dopaminergic neurons. This may prevent the abnormal aggregation of α-syn in mitochondria and the release of mitochondrial apoptosis signals. Furthermore, the activation of VDAC1 reversed the resveratrol-induced decrease in the accumulation of α-syn in the mitochondria. These findings highlight the potential of VDAC1 as a therapeutic target for PD and identify the mechanism by which resveratrol alleviates PD-related pathology by modulating mitochondrial VDAC1.

Mitochondrial DNA deletions in the cerebrospinal fluid of patients with idiopathic REM sleep behaviour disorder

BACKGROUND

Idiopathic rapid eye movement (REM) sleep behaviour disorder (IRBD) represents the prodromal stage of Lewy body disorders (Parkinson's disease (PD) and dementia with Lewy bodies (DLB)) which are linked to variations in circulating cell-free mitochondrial DNA (cf-mtDNA). Here, we assessed whether altered cf-mtDNA release and integrity are already present in IRBD.

METHODS

We used multiplex digital PCR (dPCR) to quantify cf-mtDNA copies and deletion ratio in cerebrospinal fluid (CSF) and serum in a cohort of 71 participants, including 1) 17 patients with IRBD who remained disease-free (non-converters), 2) 34 patients initially diagnosed with IRBD who later developed either PD or DLB (converters), and 3) 20 age-matched controls without IRBD or Parkinsonism. In addition, we investigated whether CD9-positive extracellular vesicles (CD9-EVs) from CSF and serum samples contained cf-mtDNA.

FINDINGS

Patients with IRBD, both converters and non-converters, exhibited more cf-mtDNA with deletions in the CSF than controls. This finding was confirmed in CD9-EVs. The high levels of deleted cf-mtDNA in CSF corresponded to a significant decrease in cf-mtDNA copies in CD9-EVs in both IRBD non-converters and converters. Conversely, a significant increase in cf-mtDNA copies was found in serum and CD9-EVs from the serum of patients with IRBD who later converted to a Lewy body disorder.

INTERPRETATION

Alterations in cf-mtDNA copy number and deletion ratio known to occur in Lewy body disorders are already present in IRBD and are not a consequence of Lewy body disease conversion. This suggests that mtDNA dysfunction is a primary molecular mechanism of the pathophysiological cascade that precedes the full clinical motor and cognitive manifestation of Lewy body disorders.

FUNDING

Funded by Michael J. Fox Foundation research grant MJFF-001111. Funded by MICIU/AEI/10.13039/501100011033 "ERDF A way of making Europe", grants PID2020-115091RB-I00 (RT) and PID2022-143279OB-I00 (ACo). Funded by Instituto de Salud Carlos III and European Union NextGenerationEU/PRTR, grant PMP22/00100 (RT and ACo). Funded by AGAUR/Generalitat de Catalunya, grant SGR00490 (RT and ACo). MP has an FPI fellowship, PRE2018-083297, funded by MICIU/AEI/10.13039/501100011033 "ESF Investing in your future".

Mitochondrial DNA mutation pathogenicity score and neurocognitive performance in persons with HIV

BACKGROUND

Mitochondrial DNA (mtDNA) genetic variation is associated with neurocognitive (NC) impairment (NCI) in people with HIV (PWH). Other approaches use sequence conservation and protein structure to predict the impact of mtDNA variants on protein function. We examined predicted mtDNA variant pathogenicity in the CHARTER study using MutPred scores, hypothesizing that persons with higher scores (greater predicted pathogenicity) have more NCI.

METHODS

CHARTER included NC testing in PWH from 2003 to 2007. MutPred scores were assigned to CHARTER participants with mtDNA sequence; any score > 0.5 was considered potentially deleterious. Outcomes at cohort entry were NCI, defined by global and seven NC domain deficit scores, and by mean global and domain NC performance T-scores. Univariate and multivariable regression analyses assessed associations between having a deleterious variant and NCI. Additional models included estimated peripheral blood cell mtDNA copy number.

RESULTS

Data were available for 744 PWH (357 African ancestry; 317 European; 70 Hispanic). In the overall cohort, PWH having any potentially deleterious variant were less likely to have motor impairment (16 vs. 25 %, p = 0.001). In multivariable analysis, having a deleterious variant remained associated with lower likelihood of motor impairment (adjusted odds ratio 0.59 [95 % CI 0.41-0.88]; p = 0.009), and better motor performance by T-score (β 1.71 [0.31-3.10], p = 0.02). Associations persisted after adjustment for estimated mtDNA quantity.

CONCLUSIONS

In these PWH, having a potentially deleterious mtDNA variant was associated with less motor impairment. These unexpected findings suggest that potentially deleterious mtDNA variations may confer protection against impaired motor function by as yet unknown mechanisms.

Plausible Role of Mitochondrial DNA Copy Number in Neurodegeneration-a Need for Therapeutic Approach in Parkinson's Disease (PD)

Parkinson's disease (PD) is an advancing age-associated progressive brain disorder which has various diverse factors, among them mitochondrial dysfunction involves in dopaminergic (DA) degeneration. Aging causes a rise in mitochondrial abnormalities which leads to structural and functional modifications in neuronal activity and cell death in PD. This ends in deterioration of mitochondrial function, mitochondrial alterations, mitochondrial DNA copy number (mtDNA CN) and oxidative phosphorylation (OXPHOS) capacity. mtDNA levels or mtDNA CN in PD have reported that mtDNA depletion would be a predisposing factor in PD pathogenesis. To maintain the mtDNA levels, therapeutic approaches have been focused on mitochondrial biogenesis in PD. The depletion of mtDNA levels in PD can be influenced by autophagic dysregulation, apoptosis, neuroinflammation, oxidative stress, sirtuins, and calcium homeostasis. The current review describes the regulation of mtDNA levels and discusses the plausible molecular pathways in mtDNA CN depletion in PD pathogenesis. We conclude by suggesting further research on mtDNA depletion which might show a promising effect in predicting and diagnosing PD.

The Ubiquitin Proteasome System as a Therapeutic Area in Parkinson's Disease

Parkinson's disease (PD) is the most common neurodegenerative movement disorder. There are no available therapeutics that slow or halt the progressive loss of dopamine-producing neurons, which underlies the primary clinical symptoms. Currently approved PD drugs can provide symptomatic relief by increasing brain dopamine content or activity; however, the alleviation is temporary, and the effectiveness diminishes with the inevitable progression of neurodegeneration. Discovery and development of disease-modifying neuroprotective therapies has been hampered by insufficient understanding of the root cause of PD-related neurodegeneration. The etiology of PD involves a combination of genetic and environmental factors. Although a single cause has yet to emerge, genetic, cell biological and neuropathological evidence implicates mitochondrial dysfunction and protein aggregation. Postmortem PD brains show pathognomonic Lewy body intraneuronal inclusions composed of aggregated α-synuclein, indicative of failure to degrade misfolded protein. Mutations in the genes that code for α-synuclein, as well as the E3 ubiquitin ligase Parkin, cause rare inherited forms of PD. While many ubiquitin ligases label proteins with ubiquitin chains to mark proteins for degradation by the proteasome, Parkin has been shown to mark dysfunctional mitochondria for degradation by mitophagy. The ubiquitin proteasome system participates in several aspects of the cell's response to mitochondrial damage, affording numerous therapeutic opportunities to augment mitophagy and potentially stop PD progression. This review examines the role and therapeutic potential of such UPS modulators, exemplified by both ubiquitinating and deubiquitinating enzymes.

mtDNA Maintenance and Alterations in the Pathogenesis of Neurodegenerative Diseases

Considerable evidence indicates that the semiautonomous organelles mitochondria play key roles in the progression of many neurodegenerative disorders. Mitochondrial DNA (mtDNA) encodes components of the OXPHOS complex but mutated mtDNA accumulates in cells with aging, which mirrors the increased prevalence of neurodegenerative diseases. This accumulation stems not only from the misreplication of mtDNA and the highly oxidative environment but also from defective mitophagy after fission. In this review, we focus on several pivotal mitochondrial proteins related to mtDNA maintenance (such as ATAD3A and TFAM), mtDNA alterations including mtDNA mutations, mtDNA elimination, and mtDNA release-activated inflammation to understand the crucial role played by mtDNA in the pathogenesis of neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and Huntington's disease. Our work outlines novel therapeutic strategies for targeting mtDNA.

Skeletal muscle mitochondrial dysfunction in contemporary antiretroviral therapy: a single cell analysis

OBJECTIVE

To quantify mitochondrial function in skeletal muscle of people treated with contemporary antiretroviral therapy.

DESIGN

Cross-sectional observational study.

METHODS

Quantitative multiplex immunofluorescence was performed to determine mitochondrial mass and respiratory chain complex abundance in individual myofibres from tibialis anterior biopsies. Individual myofibres were captured by laser microdissection and mitochondrial DNA (mtDNA) content and large-scale deletions were measured by real-time PCR.

RESULTS

Forty-five antiretroviral therapy (ART)-treated people with HIV (PWH, mean age 58 years, mean duration of ART 125 months) were compared with 15 HIV negative age-matched controls. Mitochondrial complex I (CI) deficiency was observed at higher proportional levels in PWH than negative controls ( P = 0.008). Myofibre mitochondrial mass did not differ by HIV status. No ART class was significantly associated with mitochondrial deficiency, including prior exposure to historical NRTIs (nucleoside analogue reverse transcriptase inhibitors) associated with systemic mitochondrial toxicity. To exclude an effect of untreated HIV, we also studied skeletal muscle from 13 ART-naive PWH (mean age 37). These showed negligible CI defects, as well as comparable myofibre mitochondrial mass to ART-treated PWH. Most CI-deficient myofibres contained mtDNA deletions. No mtDNA depletion was detected.

CONCLUSION

Here, we show that PWH treated with contemporary ART have mitochondrial dysfunction in skeletal muscle, exceeding that expected due to age alone. Surprisingly, this was not mediated by prior exposure to mitochondrially toxic NRTIs, suggesting novel mechanisms of mitochondrial dysfunction in contemporary ART-treated PWH. These findings are relevant for better understanding successful ageing in PWH.

Age-related Mitochondrial Dysfunction in Parkinson's Disease: New Insights Into the Disease Pathology

Aging is a progressive loss of physiological function that increases risk of disease and death. Among the many factors that contribute to human aging, mitochondrial dysfunction has emerged as one of the most prominent features of the aging process. It has been linked to the development of various age-related pathologies, including Parkinson's disease (PD). Mitochondria has a complex quality control system that ensures mitochondrial integrity and function. Perturbations in these mitochondrial mechanisms have long been linked to various age-related neurological disorders. Even though research has shed light on several aspects of the disease pathology, the underlying mechanism of age-related factors responsible for individuals developing this disease is still unknown. This review article aims to discuss the role of mitochondria in the transition from normal brain aging to pathological brain aging, which leads to the progression of PD. We have discussed the emerging evidence on how age-related disruption of mitochondrial quality control mechanisms contributes to the development of PD-related pathophysiology.

Increased blood-derived mitochondrial DNA copy number in African ancestry individuals with Parkinson's disease

INTRODUCTION

Altered levels of mitochondrial DNA copy number (mtDNA-CN) have been proposed as a proxy for mitochondrial dysfunction. Following reports of mtDNA depletion in the blood and substantia nigra of Parkinson's disease (PD) cases, mtDNA-CN was also suggested as a possible biomarker for PD. Therefore, this study aimed to investigate whether blood mtDNA-CN levels of African ancestry PD cases would be altered compared to controls, as previously reported in individuals of Asian and European ancestry.

METHODS

Droplet digital polymerase chain reaction (ddPCR) was performed to quantify blood-derived mtDNA-CN levels as a ratio of a mitochondrial gene (MT-TL1) to a nuclear gene (B2M) in 72 PD cases and 79 controls of African ancestry (i.e. individuals with African mtDNA haplogroups) from South Africa. mtDNA-CN per cell was calculated by the formula 2 × MT-TL1/B2M.

RESULTS

Accepting study limitations, we report significantly higher mtDNA-CN in whole blood of our PD cases compared to controls (median difference = 81 copies/cell), independent of age (95% CI [64, 98]; P < 0.001]). These findings contradict previous reports of mtDNA depletion in PD cases.

CONCLUSIONS

We caution that the observed differences in mtDNA-CN between the present and past studies may be a result of unaccounted-for factors and variability in study designs. Consequently, larger well-designed investigations may help determine whether mtDNA-CN is consistently altered in the blood of PD cases across different ancestries and whether it can serve as a viable biomarker for PD.

A subcellular cookie cutter for spatial genomics in human tissue

Intracellular heterogeneity contributes significantly to cellular physiology and, in a number of debilitating diseases, cellular pathophysiology. This is greatly influenced by distinct organelle populations and to understand the aetiology of disease, it is important to have tools able to isolate and differentially analyse organelles from precise location within tissues. Here, we report the development of a subcellular biopsy technology that facilitates the isolation of organelles, such as mitochondria, from human tissue. We compared the subcellular biopsy technology to laser capture microdissection (LCM) that is the state-of-the-art technique for the isolation of cells from their surrounding tissues. We demonstrate an operational limit of  >20 µm for LCM and then, for the first time in human tissue, show that subcellular biopsy can be used to isolate mitochondria beyond this limit.

Comprehensive summary of mitochondrial DNA alterations in the postmortem human brain: A systematic review

BACKGROUND

Mitochondrial DNA (mtDNA) encodes 37 genes necessary for synthesizing 13 essential subunits of the oxidative phosphorylation system. mtDNA alterations are known to cause mitochondrial disease (MitD), a clinically heterogeneous group of disorders that often present with neuropsychiatric symptoms. Understanding the nature and frequency of mtDNA alterations in health and disease could be a cornerstone in disentangling the relationship between biochemical findings and clinical symptoms of brain disorders. This systematic review aimed to summarize the mtDNA alterations in human brain tissue reported to date that have implications for further research on the pathophysiological significance of mtDNA alterations in brain functioning.

METHODS

We searched the PubMed and Embase databases using distinct terms related to postmortem human brain and mtDNA up to June 10, 2021. Reports were eligible if they were empirical studies analysing mtDNA in postmortem human brains.

FINDINGS

A total of 158 of 637 studies fulfilled the inclusion criteria and were clustered into the following groups: MitD (48 entries), neurological diseases (NeuD, 55 entries), psychiatric diseases (PsyD, 15 entries), a miscellaneous group with controls and other clinical diseases (5 entries), ageing (20 entries), and technical issues (5 entries). Ten entries were ascribed to more than one group. Pathogenic single nucleotide variants (pSNVs), both homo- or heteroplasmic variants, have been widely reported in MitD, with heteroplasmy levels varying among brain regions; however, pSNVs are rarer in NeuD, PsyD and ageing. A lower mtDNA copy number (CN) in disease was described in most, but not all, of the identified studies. mtDNA deletions were identified in individuals in the four clinical categories and ageing. Notably, brain samples showed significantly more mtDNA deletions and at higher heteroplasmy percentages than blood samples, and several of the deletions present in the brain were not detected in the blood. Finally, mtDNA heteroplasmy, mtDNA CN and the deletion levels varied depending on the brain region studied.

INTERPRETATION

mtDNA alterations are well known to affect human tissues, including the brain. In general, we found that studies of MitD, NeuD, PsyD, and ageing were highly variable in terms of the type of disease or ageing process investigated, number of screened individuals, studied brain regions and technology used. In NeuD and PsyD, no particular type of mtDNA alteration could be unequivocally assigned to any specific disease or diagnostic group. However, the presence of mtDNA deletions and mtDNA CN variation imply a role for mtDNA in NeuD and PsyD. Heteroplasmy levels and threshold effects, affected brain regions, and mitotic segregation patterns of mtDNA alterations may be involved in the complex inheritance of NeuD and PsyD and in the ageing process. Therefore, more information is needed regarding the type of mtDNA alteration, the affected brain regions, the heteroplasmy levels, and their relationship with clinical phenotypes and the ageing process.

FUNDING

Hospital Universitari Institut Pere Mata; Institut d'Investigació Sanitària Pere Virgili; Instituto de Salud Carlos III, Ministerio de Ciencia e Innovación (PI18/00514).

Targeted activation of midbrain neurons restores locomotor function in mouse models of parkinsonism

The pedunculopontine nucleus (PPN) is a locomotor command area containing glutamatergic neurons that control locomotor initiation and maintenance. These motor actions are deficient in Parkinson’s disease (PD), where dopaminergic neurodegeneration alters basal ganglia activity. Being downstream of the basal ganglia, the PPN may be a suitable target for ameliorating parkinsonian motor symptoms. Here, we use in vivo cell-type specific PPN activation to restore motor function in two mouse models of parkinsonism made by acute pharmacological blockage of dopamine transmission. With a combination of chemo- and opto-genetics, we show that excitation of caudal glutamatergic PPN neurons can normalize the otherwise severe locomotor deficit in PD, whereas targeting the local GABAergic population only leads to recovery of slow locomotion. The motor rescue driven by glutamatergic PPN activation is independent of activity in nearby locomotor promoting glutamatergic Cuneiform neurons. Our observations point to caudal glutamatergic PPN neurons as a potential target for neuromodulatory restoration of locomotor function in PD.

Here, the authors use cell-type specific stimulation of brainstem neurons within the caudal pedunculopontine nucleus to show that activation of excitatory neurons can normalize severe locomotor deficit in mouse models of parkinsonism. The study defines a potential target for neuromodulatory restoration of locomotor function in Parkinson’s disease.

Gene Therapeutic Approaches for the Treatment of Mitochondrial Dysfunction in Parkinson's Disease

Background: Mitochondrial dysfunction has been identified as a pathophysiological hallmark of disease onset and progression in patients with Parkinsonian disorders. Besides the overall emergence of gene therapies in treating these patients, this highly relevant molecular concept has not yet been defined as a target for gene therapeutic approaches. Methods: This narrative review will discuss the experimental evidence suggesting mitochondrial dysfunction as a viable treatment target in patients with monogenic and idiopathic Parkinson’s disease. In addition, we will focus on general treatment strategies and crucial challenges which need to be overcome. Results: Our current understanding of mitochondrial biology in parkinsonian disorders opens up the avenue for viable treatment strategies in Parkinsonian disorders. Insights can be obtained from primary mitochondrial diseases. However, substantial knowledge gaps and unique challenges of mitochondria-targeted gene therapies need to be addressed to provide innovative treatments in the future. Conclusions: Mitochondria-targeted gene therapies are a potential strategy to improve an important primary disease mechanism in Parkinsonian disorders. However, further studies are needed to address the unique design challenges for mitochondria-targeted gene therapies.

Dopaminergic Axons: Key Recitalists in Parkinson's Disease

Parkinson's disease (PD) is associated with dopamine depletion in the striatum owing to the selective and progressive loss of the nigrostriatal dopaminergic neurons, which results in motor dysfunction and secondary clinical manifestations. The dopamine level in the striatum is preserved because of the innervation of the substantia nigra (SN) dopaminergic neurons into it. Therefore, protection of the SN neurons is crucial for maintaining the dopamine level in the striatum and for ensuring the desired motor coordination. Several strategies have been devised to protect the degenerating dopaminergic neurons or to restore the dopamine levels for treating PD. Most of the methods focus exclusively on preventing cell body death in the neurons. Although advances have been made in understanding the disease, the search for disease-modifying drugs is an ongoing process. The present review describes the evidence from studies involving patients with PD as well as PD models that axon terminals are highly vulnerable to exogenous and endogenous insults and degenerate at the early stage of the disease. Impairment of mitochondrial dynamics, Ca²⁺ homeostasis, axonal transport, and loss of plasticity of axon terminals appear before the neuronal degeneration in PD. Furthermore, distortion of synaptic morphology and reduction of postsynaptic dendritic spines are the neuropathological hallmarks of early-stage disease. Thus, the review proposes a shift in focus from discerning the mechanism of neuronal cell body loss and targeting it to an entirely different approach of preventing axonal degeneration. The review also suggests appropriate strategies to prevent the loss of synaptic terminals, which could induce regrowth of the axon and its auxiliary fibers and might offer relief from the symptomatic features of PD.

Brain-derived neurotrophic factor attenuates cognitive impairment and motor deficits in a mouse model of Parkinson's disease

BACKGROUND

Parkinson's disease (PD) is one of the most common neurodegenerative disorders that seriously impair the life quality and survival of patients. Herein, we aim to investigate the neuroprotective roles of brain-derived neurotrophic factor (BDNF) in PD mice and reveal the underlying mechanisms. BDNF overexpression was achieved via the injection of adeno-associated viruses (AAV) with BDNF gene.

METHODS

PD mouse model was established by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treatment. Tests of rotarod, pole, open field, and novel object recognition were conducted to evaluate the motor and cognitive functions of treated mice.

RESULTS

Mitochondrial impairment, mitochondrial respiratory chain enzymes, and tyrosine hydroxylase (TH)-positive dopaminergic neurons were detected to uncover the molecular mechanism. BDNF overexpression attenuated motor deficits and cognitive impairment in MPTP-induced PD mice. Mechanistically, BDNF mitigated mitochondrial impairment increased the activity of respiratory chain Complex I and Ⅱ+III, and finally alleviated TH-positive dopaminergic neuron loss in MPTP-induced PD mice.

CONCLUSION

This study highlights the potential of BDNF as a therapeutic candidate for the treatment of mitochondrial impairment-associated neurodegenerative diseases.

The Isolation and Deep Sequencing of Mitochondrial DNA

In recent years, next-generation sequencing (NGS) has become a powerful tool for studying both inherited and somatic heteroplasmic mitochondrial DNA (mtDNA) variation. NGS has proved particularly powerful when combined with single-cell isolation techniques, allowing the investigation of low-level heteroplasmic variants both between cells and within tissues. Nevertheless, there remain significant challenges, especially around the selective enrichment of mtDNA from total cellular DNA and the avoidance of nuclear pseudogenes. This chapter summarizes the techniques needed to enrich, amplify, sequence, and analyse mtDNA using NGS .

Contribution of the Nrf2 Pathway on Oxidative Damage and Mitochondrial Failure in Parkinson and Alzheimer's Disease

The increase in human life expectancy has become a challenge to reduce the deleterious consequences of aging. Nowadays, an increasing number of the population suffer from age-associated neurodegenerative diseases including Parkinson's disease (PD) and Alzheimer's disease (AD). These disorders present different signs of neurodegeneration such as mitochondrial dysfunction, inflammation, and oxidative stress. Accumulative evidence suggests that the transcriptional factor nuclear factor (erythroid-derived 2)-like 2 (Nrf2) plays a vital defensive role orchestrating the antioxidant response in the brain. Nrf2 activation promotes the expression of several antioxidant enzymes that exert cytoprotective effects against oxidative damage and mitochondrial impairment. In this context, several studies have proposed a role of Nrf2 in the pathogenesis of PD and AD. Thus, we consider it important to summarize the ongoing literature related to the effects of the Nrf2 pathway in the context of these diseases. Therefore, in this review, we discuss the mechanisms involved in Nrf2 activity and its connection with mitochondria, energy supply, and antioxidant response in the brain. Furthermore, we will lead our discussion to identify the participation of the Nrf2 pathway in mitochondrial impairment and neurodegeneration present in PD and AD. Finally, we will discuss the therapeutic effects that the Nrf2 pathway activation could have on the cognitive impairment, neurodegeneration, and mitochondrial failure present in PD and AD.

Mitochondrial D-Loop Region Methylation and Copy Number in Peripheral Blood DNA of Parkinson's Disease Patients

Altered mitochondrial DNA (mtDNA) methylation has been detected in several human pathologies, although little attention has been given to neurodegenerative diseases. Recently, altered methylation levels of the mitochondrial displacement loop (D-loop) region, which regulates mtDNA replication, were observed in peripheral blood cells of Alzheimer’s disease and amyotrophic lateral sclerosis patients. However, nothing is yet known about D-loop region methylation levels in peripheral blood of Parkinson’s disease (PD) patients. In the current study, we investigated D-loop methylation levels and mtDNA copy number in peripheral blood of 30 PD patients and 30 age- and sex-matched control subjects. DNA methylation analyses have been performed by means of methylation-sensitive high-resolution melting (MS-HRM) and pyrosequencing techniques, while mtDNA copy number was analyzed by quantitative PCR. MS-HRM and pyrosequencing analyses provided very similar D-loop methylation levels in PD patients and control subjects, and no differences between the two groups have been observed. Treatment with L-dopa and duration of the disease had no effect on D-loop methylation levels in PD patients. Additionally, mtDNA copy number did not differ between PD patients and control subjects. Current results suggest that D-loop methylation levels are not altered in peripheral blood of PD patients nor influenced by dopaminergic treatment.

Mitochondria and early-life adversity

Early-life adversity (ELA), which includes maltreatment, neglect, or severe trauma in childhood, increases the life-long risk for negative health outcomes. Mitochondria play a key role in the stress response and may be an important mechanism by which stress is transduced into biological risk for disease. By responding to cues from stress-signaling pathways, mitochondria interact dynamically with physiological stress responses coordinated by the central nervous, endocrine, and immune systems. Preclinical evidence suggests that alterations in mitochondrial function and structure are linked to both early stress and systemic biological dysfunction. Early clinical studies support that increased mitochondrial DNA content and altered cellular energy demands may be present in individuals with a history of ELA. Further research should investigate mitochondria as a potential therapeutic target following ELA.

Neuroinflammation in Parkinson's Disease: Triggers, Mechanisms, and Immunotherapies

Parkinson's disease (PD) is a heterogeneous neurodegenerative disease involving multiple etiologies and pathogenesis, in which neuroinflammation is a common factor. Both preclinical experiments and clinical studies provide evidence for the involvement of neuroinflammation in the pathophysiology of PD, although there are a number of key issues related to neuroinflammatory processes in PD that remain to be addressed. In this review, we highlight the relationship between the common pathological mechanisms of PD and neuroinflammation, including aggregation of α-synuclein, genetic factors, mitochondrial dysfunction, and gut microbiome dysbiosis. We also describe the two positive feedback loops initiated in PD after the immune system is activated, and their role in the pathogenesis of PD. In addition, the interconnections and differences between the central and peripheral immune systems are discussed. Finally, we review the latest progress in immunotherapy research for PD patients, and propose future directions for clinical research.

DREADD Activation of Pedunculopontine Cholinergic Neurons Reverses Motor Deficits and Restores Striatal Dopamine Signaling in Parkinsonian Rats

The brainstem-based pedunculopontine nucleus (PPN) traditionally associates with motor function, but undergoes extensive degeneration during Parkinson's disease (PD), which correlates with axial motor deficits. PPN-deep brain stimulation (DBS) can alleviate certain symptoms, but its mechanism(s) of action remains unknown. We previously characterized rats hemi-intranigrally injected with the proteasomal inhibitor lactacystin, as an accurate preclinical model of PD. Here we used a combination of chemogenetics with positron emission tomography imaging for in vivo interrogation of discrete neural networks in this rat model of PD. Stimulation of excitatory designer receptors exclusively activated by designer drugs expressed within PPN cholinergic neurons activated residual nigrostriatal dopaminergic neurons to produce profound motor recovery, which correlated with striatal dopamine efflux as well as restored dopamine receptor 1- and dopamine receptor 2-based medium spiny neuron activity, as was ascertained with c-Fos-based immunohistochemistry and stereological cell counts. By revealing that the improved axial-related motor functions seen in PD patients receiving PPN-DBS may be due to stimulation of remaining PPN cholinergic neurons interacting with dopaminergic ones in both the substantia nigra pars compacta and the striatum, our data strongly favor the PPN cholinergic-midbrain dopaminergic connectome as mechanism for PPN-DBS's therapeutic effects. These findings have implications for refining PPN-DBS as a promising treatment modality available to PD patients.

Role of mtDNA disturbances in the pathogenesis of Alzheimer's and Parkinson's disease

Neurodegenerative diseases (e.g. Alzheimer's and Parkinson's disease) are becoming increasingly problematic to healthcare systems. Therefore, their underlying mechanisms are trending topics of study in medicinal research. Numerous studies have evidenced a strong association between mitochondrial DNA disturbances (e.g. oxidative damage, mutations, and methylation shifts) and the initiation and progression of neurodegenerative diseases. Therefore, this review discusses the risk and development of neurodegenerative diseases in terms of disturbances in mitochondrial DNA and as a part of a complex ecosystem that includes other important mechanisms (e.g. neuroinflammation and the misfolding and aggregation of amyloid-β peptides, α-synuclein, and tau proteins). In addition, the influence of individual mitochondrial DNA haplogroups on the risk and development of neurodegenerative diseases is also described and discussed.

Damage in Mitochondrial DNA Associated with Parkinson's Disease

Mitochondria are the only organelles that contain their own genetic material (mtDNA). Mitochondria are involved in several key physiological functions, including ATP production, Ca²⁺ homeostasis, and metabolism of neurotransmitters. Since these organelles perform crucial processes to maintain neuronal homeostasis, mitochondrial dysfunctions can lead to various neurodegenerative diseases. Several mitochondrial proteins involved in ATP production are encoded by mtDNA. Thus, any mtDNA alteration can ultimately lead to mitochondrial dysfunction and cell death. Accumulation of mutations, deletions, and rearrangements in mtDNA has been observed in animal models and patients suffering from Parkinson's disease (PD). Also, specific inherited variations associated with mtDNA genetic groups (known as mtDNA haplogroups) are associated with lower or higher risk of developing PD. Consequently, mtDNA alterations should now be considered important hallmarks of this neurodegenerative disease. This review provides an update about the role of mtDNA alterations in the physiopathology of PD.

Stress and Psychiatric Disorders: The Role of Mitochondria

In seeking to understand mental health and disease, it is fundamental to identify the biological substrates that draw together the experiences and physiological processes that underlie observed psychological changes. Mitochondria are subcellular organelles best known for their central role in energetics, producing adenosine triphosphate to power most cellular processes. Converging lines of evidence indicate that mitochondria play a key role in the biological embedding of adversity. Preclinical research documents the effects of stress exposure on mitochondrial structure and function, and recent human research suggests alterations constituting recalibrations, both adaptive and nonadaptive. Current research suggests dynamic relationships among stress exposure, neuroendocrine signaling, inflammation, and mitochondrial function. These complex relationships are implicated in disease risk, and their elucidation may inform prevention and treatment of stress- and trauma-related disorders. We review and evaluate the evidence for mitochondrial dysfunction as a consequence of stress exposure and as a contributing factor to psychiatric disease.

Mitochondrial DNA copy number, damage, repair and degradation in depressive disorder

Objectives: We aimed to explore mitochondrial DNA (mtDNA) copy number, damage, repair and degradation in peripheral blood mononuclear cells (PBMCs) of patients with depression and to compare the results with healthy subjects.Methods: Total genomic DNA was isolated from PBMCs of 25 depressed and 60 healthy subjects before, immediately after, and 3 h after the exposure to H₂O₂. Evaluation of mtDNA copy number was performed using real-time PCR and 2-ΔCt methods. Semi-long run real-time PCR was used to estimate the number of mtDNA lesions.Results: Baseline mtDNA copy number did not differ in cells of healthy and depressed subjects; however, it was negatively correlated with the severity of the episode. After a 10-min challenge with hydrogen peroxide (H₂O₂), depressed patients' PBMCs exhibited slower changes of the copy number, indicating a lower efficiency of mtDNA degradation compared to controls. Moreover, a significantly higher number of mtDNA lesions was found in depressed patients at the baseline as well as at other experimental time points. mtDNA lesions were also elevated in depressed patient cells immediately after H₂O₂ exposure. Induction of oxidative stress had no significant influence on the cells of controls.Conclusions: We are the first to show that impairment in repair and degradation of mtDNA may be involved in the pathophysiology of depression.

Pedunculopontine Nucleus Degeneration Contributes to Both Motor and Non-Motor Symptoms of Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disorder characterized by hypokinetic motor features; however, patients also display non-motor symptoms like sleep disorders. The standard treatment for PD is dopamine replacement with L-DOPA; however, symptoms including gait deficits and sleep disorders are unresponsive to L-DOPA. Notably, these symptoms have been linked to aberrant activity in the pedunculopontine nucleus (PPN). Of late, clinical trials involving PPN deep brain stimulation (DBS) have been employed to alleviate gait deficits. Although preclinical evidence implicating PPN cholinergic neurons in gait dysfunction was initially promising, DBS trials fell short of expected outcomes. One reason for the failure of DBS may be that the PPN is a heterogenous nucleus that consists of GABAergic, cholinergic, and glutamatergic neurons that project to a diverse array of brain structures. Second, DBS trials may have been unsuccessful because PPN neurons are susceptible to mitochondrial dysfunction, Lewy body pathology, and degeneration in PD. Therefore, pharmaceutical or gene-therapy strategies targeting specific PPN neuronal populations or projections could better alleviate intractable PD symptoms. Unfortunately, how PPN neuronal populations and their respective projections influence PD motor and non-motor symptoms remains enigmatic. Herein, we discuss normal cellular and neuroanatomical features of the PPN, the differential susceptibility of PPN neurons to PD-related insults, and we give an overview of literature suggesting a role for PPN neurons in motor and sleep deficits in PD. Finally, we identify future approaches directed towards the PPN for the treatment of PD motor and sleep symptoms.

In Vivo Mitochondrial Function in Idiopathic and Genetic Parkinson's Disease

Parkinson’s disease (PD) is associated with brain mitochondrial dysfunction. High-energy phosphates (HEPs), which rely on mitochondrial functioning, may be considered potential biomarkers for PD. Phosphorus magnetic resonance spectroscopy (³¹P-MRS) is a suitable tool to explore in vivo cerebral energetics. We considered 10 ³¹P-MRS studies in order to highlight the main findings about brain energetic compounds in patients affected by idiopathic PD and genetic PD. The studies investigated several brain areas such as frontal lobes, occipital lobes, temporoparietal cortex, visual cortex, midbrain, and basal ganglia. Resting-state studies reported contrasting results showing decreased as well as normal or increased HEPs levels in PD patients. Functional studies revealed abnormal PCr + βATP levels in PD subjects during the recovery phase and abnormal values at rest, during activation and recovery in one PD subject with PINK1 gene mutation suggesting that mitochondrial machinery is more impaired in PD patients with PINK1 gene mutation. PD is characterized by energetics impairment both in idiopathic PD as well as in genetic PD, suggesting that mitochondrial dysfunction underlies the disease. Studies are still sparse and sometimes contrasting, maybe due to different methodological approaches. Further studies are needed to better assess the role of mitochondria in the PD development.

Altered motor, anxiety-related and attentional task performance at baseline associate with multiple gene copies of the vesicular acetylcholine transporter and related protein overexpression in ChAT::Cre+ rats

Transgenic rodents expressing Cre recombinase cell specifically are used for exploring mechanisms regulating behavior, including those mediated by cholinergic signaling. However, it was recently reported that transgenic mice overexpressing a bacterial artificial chromosome containing choline acetyltransferase (ChAT) gene, for synthesizing the neurotransmitter acetylcholine, present with multiple vesicular acetylcholine transporter (VAChT) gene copies, resulting in altered cholinergic tone and accompanying behavioral abnormalities. Since ChAT::Cre+ rats, used increasingly for understanding the biological basis of CNS disorders, utilize the mouse ChAT promotor to control Cre recombinase expression, we assessed for similar genotypical and phenotypical differences in such rats compared to wild-type siblings. The rats were assessed for mouse VAChT copy number, VAChT protein expression levels and for sustained attention, response control and anxiety. Rats were also subjected to a contextual fear conditioning paradigm using an unconditional fear-inducing stimulus (electrical foot shocks), with blood samples taken at baseline, the fear acquisition phase and retention testing, for measuring blood plasma markers of hypothalamic-pituitary-adrenal gland (HPA)-axis activity. ChAT::Cre+ rats expressed multiple mouse VAChT gene copies, resulting in significantly higher VAChT protein expression, revealed anxiolytic behavior, hyperlocomotion and deficits in tasks requiring sustained attention. The HPA-axis was intact, with unaltered circulatory levels of acute stress-induced corticosterone, leptin and glucose. Our findings, therefore, reveal that in ChAT::Cre+ rats, VAChT overexpression associates with significant alterations of certain cognitive, motor and affective functions. Although highly useful as an experimental tool, it is essential to consider the potential effects of altered cholinergic transmission on baseline behavior in ChAT::Cre rats.

Accumulation of mitochondrial 7S DNA in idiopathic and LRRK2 associated Parkinson's disease

BACKGROUND

Both idiopathic and familial Parkinson's disease are associated with mitochondrial dysfunction. Mitochondria have their own mitochondrial DNA (mtDNA) and previous studies have reported that the release of mtDNA is a biomarker of Parkinson's disease.

METHODS

We have now investigated the relationship between mtDNA replication, transcription and release in fibroblasts from patients with idiopathic (iPD) and Leucine-rich repeat kinase 2^G2019S -associated Parkinson's disease (LRRK2-PD), using Selfie-digital PCR, a method that allows absolute quantification of mtDNA genomes and transcripts.

FINDINGS

In comparison with healthy controls, we found that fibroblasts from patients with iPD or LRRK2-PD had a high amount of mitochondrial 7S DNA along with a low mtDNA replication rate that was associated with a reduction of cf-mtDNA release. Accumulation of 7S DNA in iPD and LRRK2-PD fibroblasts was related with an increase in H-strand mtDNA transcription.

INTERPRETATION

These results show that 7S DNA accumulation, low mtDNA replication, high H-strand transcription, and low mtDNA release compose a pattern of mtDNA dysfunction shared by both iPD and LRRK2-PD fibroblasts. Moreover, these results suggest that the deregulation of the genetic switch formed by 7SDNA that alternates between mtDNA replication and transcription is a fundamental pathophysiological mechanism in both idiopathic and monogenic Parkinson's disease.

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.

Regional mitochondrial DNA and cell-type changes in post-mortem brains of non-diabetic Alzheimer's disease are not present in diabetic Alzheimer's disease

Diabetes increases the risk of Alzheimer's disease (AD), and mitochondrial dysfunction is implicated in both diseases, however the impact of both diabetes and AD on brain mitochondria is not known. We measured mitochondrial DNA (mtDNA), an indicator of mitochondrial function, in frontal, parietal, and cerebellar regions of post-mortem human brains (n = 74) from non-cognitively impaired controls (NCI), mild-cognitively impaired (MCI) and AD cases. In a subset of parietal cortices, we measured mRNAs corresponding to cell types and mitochondrial function and semi-automated stereological assessment was performed on immune-staining of parietal cortex sections. mtDNA showed significant regional variation, highest in parietal cortex, and lowest in cerebellum. Irrespective of cognitive status, all brain regions had significantly higher mtDNA in diabetic cases. In the absence of diabetes, AD parietal cortices had decreased mtDNA, reduced MAP2 (neuronal) and increased GFAP (astrocyte) mRNA, relative to NCI. However, in the presence of diabetes, we did not observe these AD-related changes, suggesting that the pathology observed in diabetic AD may be different to that seen in non-diabetic AD. The lack of clear functional changes in mitochondrial parameters in diabetic AD suggest different cellular mechanisms contributing to cognitive impairment in diabetes which remain to be fully understood.

Mitochondrial Dysfunction in Parkinson's Disease-Cause or Consequence?

James Parkinson first described the motor symptoms of the disease that took his name over 200 years ago. While our knowledge of many of the changes that occur in this condition has increased, it is still unknown what causes this neurodegeneration and why it only affects some individuals with advancing age. Here we review current literature to discuss whether the mitochondrial dysfunction we have detected in Parkinson’s disease is a pathogenic cause of neuronal loss or whether it is itself a consequence of dysfunction in other pathways. We examine research data from cases of idiopathic Parkinson’s with that from model systems and individuals with familial forms of the disease. Furthermore, we include data from healthy aged individuals to highlight that many of the changes described are also present with advancing age, though not normally in the presence of severe neurodegeneration. While a definitive answer to this question may still be just out of reach, it is clear that mitochondrial dysfunction sits prominently at the centre of the disease pathway that leads to catastrophic neuronal loss in those affected by this disease.

MtDNA population variation in Myalgic encephalomyelitis/Chronic fatigue syndrome in two populations: a study of mildly deleterious variants

Myalgic Encephalomyelitis (ME), also known as Chronic Fatigue Syndrome (CFS) is a debilitating condition. There is growing interest in a possible etiologic or pathogenic role of mitochondrial dysfunction and mitochondrial DNA (mtDNA) variation in ME/CFS. Supporting such a link, fatigue is common and often severe in patients with mitochondrial disease. We investigate the role of mtDNA variation in ME/CFS. No proven pathogenic mtDNA mutations were found. We then investigated population variation. Two cohorts were analysed, one from the UK (n = 89 moderately affected; 29 severely affected) and the other from South Africa (n = 143 moderately affected). For both cohorts, ME/CFS patients had an excess of individuals without a mildly deleterious population variant. The differences in population variation might reflect a mechanism important to the pathophysiology of ME/CFS.

Cortisol levels, motor, cognitive and behavioral symptoms in Parkinson's disease: a systematic review

Parkinson's disease (PD) is a progressive and multifactorial neurodegenerative disease. It has been suggested that a dysregulation of the hypothalamic-pituitary-adrenal axis (HPA) occurs in PD. Furthermore, this dysregulation may be involved in triggering, exacerbation or progression of disease. The objective of this study was to systematically review the literature regarding cortisol levels and their relation with motor, cognitive and behavioral symptoms in patients with PD. A systematic search was performed in PubMed and Embase databases, according to PRISMA norms. Twenty-one studies were included, which evaluated baseline levels of cortisol and motor, cognitive, behavioral symptoms, drugs administration or deep brain stimulation to PD treatment. Sample size ranged from 7 to 249 individuals. In 14 studies that assessed cortisol levels in PD patients, seven showed elevation of cortisol levels. In relation to symptomatology, high levels of cortisol were associated with worst functional scores evaluated by UPDRS, depression and behavior in risk preference. Medication interactions showed an influence on the regulation of cortisol release, mainly, conventional drugs used in the PD's treatment, such as levodopa. The results found in this review point to a possible relationship between cortisol levels and symptoms in PD, indicating that an HPA axis dysfunction related to cortisol level occurs in PD.

Acanthopanax senticosus Protects Structure and Function of Mesencephalic Mitochondria in A Mouse Model of Parkinson's Disease

OBJECTIVE

To investigate the neuro-protective effects of Acanthopanax senticosus Harms (EAS) on mesencephalic mitochondria and the mechanism of action, using a mouse model of Parkinson's disease (PD).

METHODS

The chemical fingerprint analysis of the extract of Acanthopanax senticosus Harms (EAS) was performed using the ultra performance liquid chromatograph and time of flight mass spectrometry. Thirty mice were randomly divided into the control group, the MPTP model group, and the EAS treated group with MPTP (MPTP+EAS group, 10 in each group). The MPTP model group and the MPTP+EAS group received MPTP-HCl (30 mg/kg i.p) once a day for 5 days. The control group received an equal volume of saline (20 mL/kg i.p) once a day for 5 days. Induced by 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine hydrochloride daily (MPTP-HCl, 30 mg/kg) for 5 days, the PD mice were treated with EAS at 45.5 mg/kg daily for 20 days. The behavioral testing of mice was carried out using the pole-climbing test. The integrity and functions of neurons were examined in mesencephalic mitochondria in a PD mouse model, including nicotinamide adenine dinucleotide dehydrogenase ubiquinone flavoprotein 2 (NDUFV2), mitochondrially encoded nicotinamide adenine dinucleotide dehydrogenase 1 (MT-ND1), succinate dehydrogenase complex subunit A (SDHA), and succinate dehydrogenase cytochrome b560 subunit (SDHC).

RESULTS

After treatment with EAS, the behavioral changes induced by MPTP were attenuated significantly (P<0.05). EAS protected the mesencephalic mitochondria from swelling and attenuated the decreases in their membrane potential (both P<0.05), which was supported by an ultra-structural level analysis. The changes in reactive oxygen species (ROS), malonic dialdehyde (MDA), oxidative phosphorylation (OXPHOS) system 4 subunits levels and PD-related proteins expressions (parkin, Pink1, DJ-1, α-synuclein, and Lrrk2) reverted to near normal levels (all P<0.05), based on the results of immune-histological and Western blotting observations.

CONCLUSIONS

The neuro-protective effects of EAS are linked to protecting mice against MPTP-induced mitochondrial dysfunction and structural damage. Therefore, EAS is a promising candidate for the prevention or treatment of mitochondrial neurodegenerative disorders, such as PD.

Mitochondrial abnormalities in Parkinson's disease and Alzheimer's disease: can mitochondria be targeted therapeutically?

Mitochondrial abnormalities have been identified as a central mechanism in multiple neurodegenerative diseases and, therefore, the mitochondria have been explored as a therapeutic target. This review will focus on the evidence for mitochondrial abnormalities in the two most common neurodegenerative diseases, Parkinson's disease and Alzheimer's disease. In addition, we discuss the main strategies which have been explored in these diseases to target the mitochondria for therapeutic purposes, focusing on mitochondrially targeted antioxidants, peptides, modulators of mitochondrial dynamics and phenotypic screening outcomes.

What is the therapeutic mechanism of pedunculopontine nucleus stimulation in Parkinson's disease?

Pedunculopontine nucleus (PPN) deep brain stimulation (DBS) is an experimental treatment for Parkinson's disease (PD) which offers a fairly circumscribed benefit for gait freezing and perhaps balance impairment. The benefit on gait freezing is variable and typically incomplete, which may reflect that the clinical application is yet to be optimised or reflect a fundamental limitation of the therapeutic mechanism. Thus, a better understanding of the therapeutic mechanism of PPN DBS may guide the further development of this therapy. The available evidence supports that the PPN is underactive in PD due to a combination of both degeneration and excessive inhibition. Low frequency PPN DBS could enhance PPN network activity, perhaps via disinhibition. A clinical implication is that in some PD patients, the PPN may be too degenerate for PPN DBS to work. Reaction time studies report that PPN DBS mediates a very specific benefit on pre-programmed movement. This seems relevant to the pathophysiology of gait freezing, which can be argued to reflect impaired release of pre-programmed adjustments to locomotion. Thus, the benefit of PPN DBS on gait freezing could be akin to that mediated by external cues. Alpha band activity is a prominent finding in local field potential recordings from PPN electrodes in PD patients. Alpha band activity is implicated in the suppression of task irrelevant processes and thus the effective allocation of attention (processing resources). Attentional deficits are prominent in patients with PD and gait freezing and PPN alpha activity has been observed to drop out prior to gait freezing episodes and to increase with levodopa. This raises the hypothesis that PPN DBS could support or emulate PPN alpha activity and consequently enhance the allocation of attention. Although PPN DBS has not been convincingly shown to increase general alertness or attention, it remains possible that PPN DBS may enhance the allocation of processing resources within the motor system, or "motor attention". For example, this could facilitate the 'switching' of motor state between continuation of pattern generated locomotion towards the intervention of pre-programmed adjustments. However, if the downstream consequence of PPN DBS on movement is limited to a circumscribed unblocking of pre-programmed movement, then this may have a similarly circumscribed degree of benefit for gait. If this is the case, then it may be possible to identify patients who may benefit most from PPN DBS. For example, those in whom pre-programmed deficits are the major contributors to gait freezing.