Reduced mitochondrial DNA copy number is a biomarker of Parkinson's disease

Techniques for investigating mitochondrial gene expression

The mitochondrial genome encodes 13 proteins that are components of the oxidative phosphorylation system (OXPHOS), suggesting that precise regulation of these genes is crucial for maintaining OXPHOS functions, including ATP production, calcium buffering, cell signaling, ROS production, and apoptosis. Furthermore, heteroplasmy or mis-regulation of gene expression in mitochondria frequently is associated with human mitochondrial diseases. Thus, various approaches have been developed to investigate the roles of genes encoded by the mitochondrial genome. In this review, we will discuss a wide range of techniques available for investigating the mitochondrial genome, mitochondrial transcription, and mitochondrial translation, which provide a useful guide to understanding mitochondrial gene expression.

Breastfeeding predicts blood mitochondrial DNA content in adolescents

Nutrition during early childhood is linked to metabolic programming. We hypothesized that breastfeeding has long-term consequences on the energy metabolism exemplified by mitochondrial DNA (mtDNA). As part of the third cycle of the Flemish Environment and Health Study (FLEHSIII) cohort, 303 adolescents aged 14–15 years were included. We associated breastfeeding and blood mtDNA content 14–15 years later while adjusting for confounding variables. Compared with non-breastfed adolescents, mtDNA content was 23.1% (95%CI: 4.4–45.2; p = 0.013) higher in breastfed adolescents. Being breastfed for 1–10 weeks, 11–20 weeks, and >20 weeks, was associated with a higher mtDNA content of respectively 16.0% (95%CI: −7.1–44.9; p = 0.191), 23.5% (95%CI: 0.8–51.3; p = 0.042), and 31.5% (95%CI: 4.3–65.7; p = 0.021). Our study showed a positive association between breastfeeding and mtDNA content in adolescents which gradually increased with longer periods of breastfeeding. Higher mtDNA content may be an underlying mechanism of the beneficial effects of breastfeeding on children’s metabolism.

Association Between HIV Infection and Mitochondrial DNA Copy Number in Peripheral Blood: A Population-Based, Prospective Cohort Study

BACKGROUND

Low mitochondrial DNA (mtDNA) copy number (CN) is a predictor of adverse aging outcomes, and its status may be altered in human immunodeficiency virus (HIV)-infected persons. This study evaluated the cross-sectional and longitudinal change of mtDNA CN by HIV markers.

METHODS

mtDNA CN was measured in the ALIVE (AIDS Linked to the Intravenous Experience) cohort of persons with a history of injecting drugs. Multivariable linear regression models controlling for demographic characteristics, behavior, and hepatitis C virus (HCV) seropositivity assessed the relationship of mtDNA CN to HIV markers (CD4+ T-cell counts, viral load, antiretroviral therapy [ART] use). Linear mixed models tested the association between HIV markers and age-related mtDNA CN trajectories.

RESULTS

Among 741 individuals at baseline, 436 (59%) were infected with HIV. HIV-infected individuals who had lower CD4+ T-cell counts (P = .01), had higher viral loads (P < .01), and were not receiving ART (P < .01) had significantly lower mtDNA CNs than uninfected persons; there was no difference between participants who were uninfected and HIV-infected individuals who had well-controlled HIV levels. In longitudinal follow-up of 507 participants, from age 50 years onward, mtDNA CN declined significantly faster among HIV-infected individuals than among HIV-uninfected persons (-0.03 units of change/year vs 0.006 units of change/year; P = .04), even among infected individuals with well-controlled HIV.

CONCLUSION

Before 50 years of age, mtDNA CN is similar between HIV-infected individuals with well-controlled HIV and uninfected persons, but from age 50 onward, mtDNA CN declines significantly faster among all infected individuals than among HIV-uninfected persons.

Mitochondrial DNA Copy Number in Peripheral Blood as a Potential Non-invasive Biomarker for Multiple Sclerosis

The impaired mitochondrial function has been implicated in the pathogenicity of multiple sclerosis (MS), a chronic inflammatory, demyelinating, and neurodegenerative disease of the CNS. Circulating mtDNA copy number in body fluids has been proposed as an indicator for several neurodegenerative diseases, and the altered cerebrospinal fluid mtDNA has been shown as a promising marker for MS. The aim of this study was to determine changes and biomarker potential of circulating mtDNA in peripheral blood in MS. The mtDNA copy number was quantified by real-time PCR in blood samples from 60 patients with relapsing-remitting MS (RRMS) and 64 healthy controls. The RRMS patients had significantly lower circulating mtDNA copy number compared to controls. Subgroup analysis with stratification of RRMS patients based on disease duration under or over 10 years revealed that the mtDNA copy number was significantly lower in the group with longer disease duration. A negative correlation was observed between mtDNA copy number and disease duration. The ROC curve analysis indicated a significant ability of mtDNA copy number to separate RRMS patients from controls with an AUC of 0.859. This is the first study to measure peripheral blood mtDNA copy number in MS patients. Current data suggest that the reduction in peripheral blood mtDNA copy number may be an early event in MS and correlate with the disease progression. The findings of this study indicate that circulating blood-based mtDNA copy number may be a potential non-invasive candidate biomarker for mitochondria-mediated neurodegeneration and MS. This can put forward the clinical applicability over other invasive markers.

Peripheral Blood Mitochondrial DNA Copy Number Obtained From Genome-Wide Genotype Data Is Associated With Neurocognitive Impairment in Persons With Chronic HIV Infection

BACKGROUND

Mitochondrial DNA (mtDNA) copy number varies by cell type and energy demands. Blood mtDNA copy number has been associated with neurocognitive function in persons without HIV. Low mtDNA copy number may indicate disordered mtDNA replication; high copy number may reflect a response to mitochondrial dysfunction. We hypothesized that blood mtDNA copy number estimated from genome-wide genotyping data is related to neurocognitive impairment (NCI) in persons with HIV.

METHODS

In the CNS HIV Antiretroviral Therapy Effects Research (CHARTER) study, peripheral blood mtDNA copy number was obtained from genome-wide genotyping data as a ratio of mtDNA single-nucleotide polymorphism probe intensities relative to nuclear DNA single-nucleotide polymorphisms. In a multivariable regression model, associations between mtDNA copy number and demographics, blood cell counts, and HIV disease and treatment characteristics were tested. Associations of mtDNA copy number with the global deficit score (GDS), GDS-defined NCI (GDS ≥ 0.5), and HIV-associated neurocognitive disorder (HAND) diagnosis were tested by logistic regression, adjusting for potential confounders.

RESULTS

Among 1010 CHARTER participants, lower mtDNA copy number was associated with longer antiretroviral therapy duration (P < 0.001), but not with d-drug exposure (P = 0.85). mtDNA copy number was also associated with GDS (P = 0.007), GDS-defined NCI (P < 0.001), and HAND (P = 0.002). In all analyses, higher mtDNA copy number was associated with poorer cognitive performance.

CONCLUSIONS

Higher mtDNA copy number estimated from peripheral blood genotyping was associated with worse neurocognitive performance in adults with HIV. These results suggest a connection between peripheral blood mtDNA and NCI, and may represent increased mtDNA replication in response to mitochondrial dysfunction.

Cellular alterations identified in pluripotent stem cell-derived midbrain spheroids generated from a female patient with progressive external ophthalmoplegia and parkinsonism who carries a novel variation (p.Q811R) in the POLG1 gene

Variations in the POLG1 gene encoding the catalytic subunit of the mitochondrial DNA polymerase gamma, have recently been associated with Parkinson's disease (PD), especially in patients diagnosed with progressive external ophthalmoplegia (PEO). However, the majority of the studies reporting this association mainly focused on the genetic identification of the variation in POLG1 in PD patient primary cells, and determination of mitochondrial DNA copy number, providing little information about the cellular alterations existing in patient brain cells, in particular dopaminergic neurons. Therefore, through the use of induced pluripotent stem cells (iPSCs), we assessed cellular alterations in novel p.Q811R POLG1 (POLG1^Q811R) variant midbrain dopaminergic neuron-containing spheroids (MDNS) from a female patient who developed early-onset PD, and compared them to cultures derived from a healthy control of the same gender. Both POLG1 variant and control MDNS contained functional midbrain regionalized TH/FOXA2-positive dopaminergic neurons, capable of releasing dopamine. Western blot analysis identified the presence of high molecular weight oligomeric alpha-synuclein in POLG1^Q811R MDNS compared to control cultures. In order to assess POLG1^Q811R-related cellular alterations within the MDNS, we applied mass-spectrometry based quantitative proteomic analysis. In total, 6749 proteins were identified, with 61 significantly differentially expressed between POLG1^Q811R and control samples. Pro- and anti-inflammatory signaling and pathways involved in energy metabolism were altered. Notably, increased glycolysis in POLG1^Q811R MDNS was suggested by the increase in PFKM and LDHA levels and confirmed using functional analysis of glycolytic rate and oxygen consumption levels. Our results validate the use of iPSCs to assess cellular alterations in relation to PD pathogenesis, in a unique PD patient carrying a novel p.Q811R variation in POLG1, and identify several altered pathways that may be relevant to PD pathogenesis.

mtDNA Copy Number Contributes to All-Cause Mortality of Lacunar Infarct in a Chinese Prospective Stroke Population

The study aimed to investigate the relationship between mtDNA copy number and the risk of all-cause mortality in stroke. One thousand four hundred eighty-four stroke patients were documented including 273 deaths (127 thrombosis, 52 lacunar, 94 hemorrhage). Patients in the third quartile had the lowest mortality rates in overall stroke and the three subtypes. The lowest quartile of mtDNA copy number (Q1 < 85.85) indicated an increased risk of all-cause mortality in stroke patients (adjusted HR, 1.52; 95% CI, 1.08-2.14; p = 0.017). In the subtype analysis, the risk of all-cause mortality appeared only in lacunar infarct, and the patients in the Q1 (< 87.76) and Q4 (> 150.61) mtDNA copy number groups showed significantly higher risks of HRs (Q1, adjusted HR, 3.87, 95% CI, 1.52-9.83; Q4, adjusted HR, 3.08, 95% CI, 1.16-8.18). Stroke patients with lacunar infarct in mtDNA copy number < 87.76 or > 150.61 were at a high risk of poor outcomes in all-cause mortality.

Voluntary exercise normalizes the proteomic landscape in muscle and brain and improves the phenotype of progeroid mice

The accumulation of mitochondrial DNA (mtDNA) mutations is a suspected driver of aging and age‐related diseases, but forestalling these changes has been a major challenge. One of the best‐studied models is the prematurely aging mtDNA mutator mouse, which carries a homozygous knock‐in of a proofreading deficient version of the catalytic subunit of mtDNA polymerase‐γ (PolgA). We investigated how voluntary exercise affects the progression of aging phenotypes in this mouse, focusing on mitochondrial and protein homeostasis in both brain and peripheral tissues. Voluntary exercise significantly ameliorated several aspects of the premature aging phenotype, including decreased locomotor activity, alopecia, and kyphosis, but did not have major effects on the decreased lifespan of mtDNA mutator mice. Exercise also decreased the mtDNA mutation load. In‐depth tissue proteomics revealed that exercise normalized the levels of about half the proteins, with the majority involved in mitochondrial function and nuclear–mitochondrial crosstalk. There was also a specific increase in the nuclear‐encoded proteins needed for the tricarboxylic acid cycle and complex II, but not in mitochondrial‐encoded oxidative phosphorylation proteins, as well as normalization of enzymes involved in coenzyme Q biosynthesis. Furthermore, we found tissue‐specific alterations, with brain coping better as compared to muscle and with motor cortex being better protected than striatum, in response to mitochondrial dysfunction. We conclude that voluntary exercise counteracts aging in mtDNA mutator mice by counteracting protein dysregulation in muscle and brain, decreasing the mtDNA mutation burden in muscle, and delaying overt aging phenotypes.

Placental mitochondrial DNA content is associated with childhood intelligence

BACKGROUND

Developmental processes in the placenta and the fetal brain are shaped by the similar biological signals. Evidence accumulates that adaptive responses of the placenta may influence central nervous system development. We hypothesize that placental mtDNA content at birth is associated with intelligence in childhood. In addition, we investigate if intra-pair differences in mtDNA content are associated with intra-pair differences in intelligence.

METHODS

Relative mtDNA content was measured using qPCR in placental tissue of 375 children of the East Flanders Prospective Twin Survey. Intelligence was assessed with the Wechsler Intelligence Scale for Children-Revised (WISC-R) between 8 and 15 years old. We accounted for sex, gestational age, birth weight, birth year, zygosity and chorionicity, cord insertion, age at measurement, indicators of socioeconomic status, smoking during pregnancy, and urban environment.

RESULTS

In multivariable adjusted mixed modelling analysis, each doubling in placental mtDNA content was associated with 2.0 points (95% CI 0.02 to 3.9; p = 0.05) higher total and 2.3 points (95% CI 0.2 to 4.3; p = 0.03) higher performance IQ in childhood. We observed no association between mtDNA content and verbal intelligence. Intra-pair differences in mtDNA content and IQ were significantly (p = 0.01) correlated in monozygotic-monochorionic twin pairs, showing that the twin with the highest mtDNA content was 1.9 times more likely (p = 0.05) to have the highest IQ. This was not observed in dichorionic twin pairs.

CONCLUSIONS

We provide the first evidence that placental mtDNA content is associated with childhood intelligence. This emphasizes the importance of placental mitochondrial function during in utero life on fetal brain development with long-lasting consequences.

Crosstalk between Nrf2 signaling and mitochondrial function in Parkinson's disease

Search for a definitive cure for neurodegenerative disorders like Parkinson's disease (PD) has met with little success. Mitochondrial dysfunction and elevated oxidative stress precede characteristic loss of dopamine-producing neurons from the midbrain in PD. The majority of PD cases are classified as sporadic (sPD) with an unknown etiology, whereas mutations in a handful of genes cause monogenic form called familial (fPD). Both sPD and fPD is characterized by proteinopathy and mitochondrial dysfunction leading to increased oxidative stress. These pathophysiological mechanisms create a vicious cycle feeding into each other, ultimately tipping the neurons to its demise. Effect of iron accumulation and dopamine oxidation adds an additional dimension to mitochondrial oxidative stress and apoptotic pathways affected. Nrf2 is a redox-sensitive transcription factor which regulates basal as well as inducible expression of antioxidant enzymes and proteins involved in xenobiotic detoxification. Recent advances, however, shows a multifaceted role for Nrf2 in the regulation of genes connected with inflammatory response, metabolic pathways, protein homeostasis, iron management, and mitochondrial bioenergetics. Here we review the role of mitochondria and oxidative stress in the PD etiology and the potential crosstalk between Nrf2 signaling and mitochondrial function in PD. We also make a case for the development of therapeutics that safely activates Nrf2 pathway in halting the progression of neurodegeneration in PD patients.

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.

Quantitative mitochondrial DNA copy number determination using droplet digital PCR with single-cell resolution

Mitochondria are involved in a number of diverse cellular functions, including energy production, metabolic regulation, apoptosis, calcium homeostasis, cell proliferation, and motility, as well as free radical generation. Mitochondrial DNA (mtDNA) is present at hundreds to thousands of copies per cell in a tissue-specific manner. mtDNA copy number also varies during aging and disease progression and therefore might be considered as a biomarker that mirrors alterations within the human body. Here, we present a new quantitative, highly sensitive droplet digital PCR (ddPCR) method, droplet digital mitochondrial DNA measurement (ddMDM), to measure mtDNA copy number not only from cell populations but also from single cells. Our developed assay can generate data in as little as 3 h, is optimized for 96-well plates, and also allows the direct use of cell lysates without the need for DNA purification or nuclear reference genes. We show that ddMDM is able to detect differences between samples whose mtDNA copy number was close enough as to be indistinguishable by other commonly used mtDNA quantitation methods. By utilizing ddMDM, we show quantitative changes in mtDNA content per cell across a wide variety of physiological contexts including cancer progression, cell cycle progression, human T cell activation, and human aging.

Mrx6 regulates mitochondrial DNA copy number in Saccharomyces cerevisiae by engaging the evolutionarily conserved Lon protease Pim1

Mitochondrial function depends crucially on the maintenance of multiple mitochondrial DNA (mtDNA) copies. Surprisingly, the cellular mechanisms regulating mtDNA copy number remain poorly understood. Through a systematic high-throughput approach in Saccharomyces cerevisiae, we determined mtDNA–to–nuclear DNA ratios in 5148 strains lacking nonessential genes. The screen revealed MRX6, a largely uncharacterized gene, whose deletion resulted in a marked increase in mtDNA levels, while maintaining wild type–like mitochondrial structure and cell size. Quantitative superresolution imaging revealed that deletion of MRX6 alters both the size and the spatial distribution of mtDNA nucleoids. We demonstrate that Mrx6 partially colocalizes with mtDNA within mitochondria and interacts with the conserved Lon protease Pim1 in a complex that also includes Mam33 and the Mrx6-related protein Pet20. Acute depletion of Pim1 phenocopied the high mtDNA levels observed in Δmrx6 cells. No further increase in mtDNA copy number was observed upon depletion of Pim1 in Δmrx6 cells, revealing an epistatic relationship between Pim1 and Mrx6. Human and bacterial Lon proteases regulate DNA replication by degrading replication initiation factors, suggesting a model in which Pim1 acts similarly with the Mrx6 complex, providing a scaffold linking it to mtDNA.

Serum FGF-21, GDF-15, and blood mtDNA copy number are not biomarkers of Parkinson disease

Background

Strong evidence of mitochondrial dysfunction exists for both familial and sporadic Parkinson disease (PD). A simple test, reliably identifying mitochondrial dysfunction, could be important for future stratified medicine trials in PD. We previously undertook a comparison of serum biomarkers in classic mitochondrial diseases and established that serum growth differentiation factor 15 (GDF-15) outperforms fibroblast growth factor 21 (FGF-21) when distinguishing patients with mitochondrial diseases from healthy controls. This study aimed to systematically assess serum FGF-21 and GDF-15, together with mitochondrial DNA (mtDNA) copy number levels in peripheral blood cells from patients with PD and healthy controls, to determine whether these measures could act as a biomarker of PD.

Methods

One hundred twenty-one patients with PD and 103 age-matched healthy controls were recruited from a single center. Serum FGF-21 and GDF-15, along with blood mtDNA copy number, were quantified using established assays.

Results

There were no meaningful differences identified for any of the measures when comparing patients with PD with healthy controls. This highlights a lack of diagnostic sensitivity that is incompatible with these measures being used as biomarkers for PD.

Conclusion

In this study, serum FGF-21, serum GDF-15, and blood mtDNA levels were similar in patients with PD and healthy controls and therefore unlikely to be satisfactory indicators of mitochondrial dysfunction in patients with PD.

Classification of evidence

This study provides Class III evidence that serum FGF-21, serum GDF-15, and blood mtDNA copy number levels do not distinguish patients with PD from healthy controls. There was no diagnostic uncertainty between patients with PD and healthy controls.

Detection of Cell-Free Mitochondrial DNA in Cerebrospinal Fluid of Creutzfeldt-Jakob Patients

Background: The current diagnosis method for Creutzfeldt-Jakob disease (CJD) is post-mortem examination, so early detection of CJD has been historically problematic. Auxiliary detection of CJD based on changes in levels of components of the cerebrospinal fluid (CSF) has become a focus of research. In other neurodegenerative diseases such as Alzheimer's disease (AD), cell-free mitochondrial DNA (mtDNA) in the CSF of patients may serve as a biomarker that could facilitate early diagnosis and studies of the mechanisms underlying the disease.

Methods: In this study, the cell-free mitochondrial DNA in the CSF of patients with sCJD and control patients was compared by digital droplet PCR.

Results: The cell-free mitochondrial DNA copy number in the CSF of sCJD patients was significantly increased in comparison with that of the control group, and this difference was pathologically related to CJD.

Conclusion: Therefore, we speculate that changes in cerebrospinal fluid mitochondrial DNA copy number play an important role in the study of CJD mechanism and diagnosis.

Low-to-moderate fluoride exposure, relative mitochondrial DNA levels, and dental fluorosis in Chinese children

BACKGROUND

The alteration of mitochondrial DNA (mtDNA) content contributes to many diseases, however, little is known about its effect on the prevalence of dental fluorosis (DF).

OBJECTIVES

We conducted a cross-sectional study to investigate the association of low-to-moderate fluoride exposure with relative mtDNA levels in relation to DF in children.

METHODS

We recruited 616 resident children, aged 7-13 years, randomly from low-to-moderate fluoride areas in Tianjin, China. We measured the fluoride concentrations in drinking water and urine using the national standardized ion selective electrode method, and determined the relative levels of mtDNA using a quantitative real-time polymerase chain reaction assay. The association among fluoride exposure, relative mtDNA levels, and the prevalence of DF were examined using multivariable linear and logistic regression models. We also performed stratified and mediation analyses.

RESULTS

The relative mtDNA levels of participants in the DF group were significantly lower than in the non-DF group (0.95 ± 0.44 vs. 1.12 ± 0.45, P < 0.001). In the adjusted models, we found that a 1 mg/L increment in water fluoride concentration was associated with a 0.10-unit decrease in circulating relative mtDNA levels (95% CI: -0.14, -0.06) and a 2.85-fold increase (95% CI: 2.01, 3.92) in moderate DF prevalence. A 1 mg/L increment in urinary fluoride level was associated with a 0.12-unit decrease in circulating relative mtDNA levels (95% CI: -0.14, -0.09) and a 1.85-fold increase (95% CI: 1.39, 2.39) in moderate DF prevalence. Stratified analysis indicated a weaker positive association of DF prevalence with fluoride exposure, while a stronger inverse relationship with relative mtDNA levels in boys than in girls. Assuming causality, we estimated that circulating mtDNA levels mediated 13.0% (95% CI: 5.2, 28.7%) and 9.6% (95% CI: 4.7, 18.5%) of the estimated effect of a 1 mg/L increment in water fluoride and urinary fluoride on prevalence of moderate DF, respectively.

CONCLUSIONS

Gender potentially modifies the associations of DF prevalence with relative mtDNA levels and low-to-moderate fluoride exposure. The reduced circulating mtDNA levels may partly mediate the elevated prevalence of moderate DF in children under such exposure.

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.

Dopamine receptor activation mitigates mitochondrial dysfunction and oxidative stress to enhance dopaminergic neurogenesis in 6-OHDA lesioned rats: A role of Wnt signalling

Nigral dopaminergic (DAergic) cell degeneration and depletion of dopamine neurotransmitter in the midbrain are cardinal features of Parkinson's disease (PD). Dopamine system regulates different aspects of behavioural phenotypes such as motor control, reward, anxiety and depression via acting on dopamine receptors (D1-D5). Recent studies have shown the potential effects of dopamine on modulation of neurogenesis, a process of newborn neuron formation from neural stem cells (NSCs). Reduced proliferative capacity of NSCs and net neurogenesis has been reported in subventricular zone, olfactory bulb and hippocampus of patients with PD. However, the molecular and cellular mechanism of dopamine mediated modulation of DAergic neurogenesis is not defined. In this study, we attempted to investigate the molecular mechanism of dopamine receptors mediated control of DAergic neurogenesis and whether it affects mitochondrial biogenesis in 6-hydroxydopamine (6-OHDA) induced rat model of PD-like phenotypes. Unilateral administration of 6-OHDA into medial forebrain bundle potentially reduced tyrosine hydroxylase immunoreactivity, dopamine content in substantia nigra pars compacta (SNpc) and striatum region and impaired motor functions in adult rats. We found decreased D1 receptor expression, mitochondrial biogenesis, mitochondrial functions and DAergic differentiation associated with down-regulation of Wnt/β-catenin signalling in SNpc of 6-OHDA lesioned rats. Pharmacological stimulation of D1 receptor enhanced mitochondrial biogenesis, mitochondrial functions and DAergic neurogenesis that lead to improved motor functions in 6-OHDA lesioned rats. D1 agonist induced effects were attenuated following administration of D1 antagonist, whereas shRNA mediated knockdown of Axin-2, a negative regulator of Wnt signalling significantly abolished D1 antagonist induced impairment in mitochondrial biogenesis and DAergic neurogenesis in 6-OHDA lesioned rats. Our results suggest that dopamine receptor regulates DAergic neurogenesis and mitochondrial functions by activation of Wnt/β-catenin signaling in rat model of PD-like phenotypes.

Cell-free mitochondrial DNA in progressive multiple sclerosis

Recent studies have linked cell-free mitochondrial DNA (ccf-mtDNA) to neurodegeneration in both Alzheimer's and Parkinson's disease, raising the possibility that the same phenomenon could be seen in other diseases which manifest a neurodegenerative component. Here, we assessed the role of circulating cell-free mitochondrial DNA (ccf-mtDNA) in end-stage progressive multiple sclerosis (PMS), where neurodegeneration is evident, contrasting both ventricular cerebral spinal fluid ccf-mtDNA abundance and integrity between PMS cases and controls, and correlating ccf-mtDNA levels to known protein markers of neurodegeneration and PMS. Our data indicate that reduced ccf-mtDNA is a component of PMS, concluding that it may indeed be a hallmark of broader neurodegeneration.

Therapeutic approaches to enhance PINK1/Parkin mediated mitophagy for the treatment of Parkinson's disease

The discovery of rare familial monogenic forms of early-onset Parkinson's disease has led to the identification of a mitochondrial quality control process as a key player in this disease. Loss-of-function mutations in the genes encoding PINK1 or Parkin result in insufficient removal of dysfunctional mitochondria through autophagy, a process termed mitophagy. Understanding the mechanism of this process and the function of its two key players, PINK1 and Parkin, has led to the discovery of new therapeutic approaches. Small molecule activators of mitophagy, either activating PINK1 or Parkin directly or inhibiting Parkin's counterplayer, the ubiquitin-specific protease USP30, are in preclinical development. To enable clinical success of future small molecule mitophagy enhancers, biomarkers for mitochondrial integrity and mitophagy are being developed. Only a few years after the discovery of mitophagy deficits in Parkinson's disease, research of the underlying mechanisms, drug discovery of modulators for this mechanism and identification of biomarkers provide new avenues towards the development of disease-modifying therapies.

Pilot study of DNA methylation, molecular aging markers and measures of health and well-being in aging

Relations of DNA methylation markers to other biological aging markers and to psychosocial, behavioral, and health measures remain unclear. The sample included 23 participants (n = 11 cases with psychiatric diagnoses and n = 12 controls without current or lifetime psychiatric disorder), balanced by age and sex. Genomic DNA was extracted from blood samples; the following were performed: genome-wide DNA methylation assay using Illumina 850k methylationEPIC; PCR assays for relative telomere length (RTL) and mitochondrial DNA copy number (mtCN). Exposures were: case status; depression and anxiety symptoms; psychosocial support; subjective and objective cognition. Outcomes were: DNA methylation age (DNAm age); RTL; mtCN; extrinsic and intrinsic epigenetic age acceleration (EEAA and IEAA). Stronger correlation with chronological age was observed for DNAm age (ρ = 0.86; p < 0.0001) compared to RTL (ρ = -0.53; p < 0.01); mtCN was not correlated with age. DNAm age was more strongly correlated with behavioral and health variables than RTL or mtCN; e.g., correlations with DNAm age: body mass index (ρ = 0.36; p = 0.10); smoking pack-years (ρ = 0.37; p = 0.08); physical activity (ρ = -0.56; p = 0.01); alcohol intake (ρ = 0.56; p = 0.01). DNAm age was inversely correlated with psychosocial support (ρ = -0.42; p = 0.048) and Modified Mini-Mental State score (ρ = -0.44; p = 0.01). Anxiety, psychosocial support, and objective cognition were significantly related to accelerated aging; depression and subjective cognition were not. In conclusion, DNAm age correlated more strongly with chronological age and key psychosocial, behavioral, and health variables than RTL or mtCN. Signals for associations with epigenetic aging were observed for psychosocial and neurobehavioral variables.

Circulating mitochondrial DNA: New indices of type 2 diabetes-related cognitive impairment in Mexican Americans

Mitochondrial function has been implicated and studied in numerous complex age-related diseases. Understanding the potential role of mitochondria in disease pathophysiology is of importance due to the rise in prevalence of complex age-related diseases, such as type 2 diabetes (T2D) and Alzheimer's disease (AD). These two diseases specifically share common pathophysiological characteristics which potentially point to a common root cause or factors for disease exacerbation. Studying the shared phenomena in Mexican Americans is of particular importance due to the disproportionate prevalence of both T2D and AD in this population. Here, we assessed the potential role of mitochondria in T2D and cognitive impairment (CI) in a Mexican American cohort by analyzing blood-based indices of mitochondrial DNA copy number (mtDNACN) and cell-free mitochondrial DNA (CFmtDNA). These mitochondrial metrics were also analyzed for correlation with relevant neuropsychological variables and physiological data collected as indicators of disease and/or disease progression. We found mtDNACN to be significantly decreased in individuals with CI, while CFmtDNA was significantly elevated in T2D; further, CFmtDNA elevation was significantly exacerbated in individuals with both diseases. MtDNACN was found to negatively correlate with age and fatty acid binding protein concentration, while positively correlating with CFmtDNA as well as CERAD total recall score. Candidate gene SNP-set analysis was performed on genes previously implicated in maintenance and control of mitochondrial dynamics to determine if nuclear variants may account for variability in mtDNACN. The results point to a single significant locus, in the LRRK2/MUC19 region, encoding leucine rich repeat kinase 2 and mucin 19. This locus has been previously implicated in Parkinson's disease, among others; rs7302859 was the driver SNP. These combined findings further indicate that mitochondrial dysfunction (as assessed by proxy via mtDNACN) is intimately linked to both T2D and CI phenotypes as well as aging.

A genome-wide association study of mitochondrial DNA copy number in two population-based cohorts

BACKGROUND

Mitochondrial DNA copy number (mtDNA CN) exhibits interindividual and intercellular variation, but few genome-wide association studies (GWAS) of directly assayed mtDNA CN exist. We undertook a GWAS of qPCR-assayed mtDNA CN in the Avon Longitudinal Study of Parents and Children (ALSPAC) and the UK Blood Service (UKBS) cohort. After validating and harmonising data, 5461 ALSPAC mothers (16-43 years at mtDNA CN assay) and 1338 UKBS females (17-69 years) were included in a meta-analysis. Sensitivity analyses restricted to females with white cell-extracted DNA and adjusted for estimated or assayed cell proportions. Associations were also explored in ALSPAC children and UKBS males.

RESULTS

A neutrophil-associated locus approached genome-wide significance (rs709591 [MED24], β (change in SD units of mtDNA CN per allele) [SE] - 0.084 [0.016], p = 1.54e-07) in the main meta-analysis of adult females. This association was concordant in magnitude and direction in UKBS males and ALSPAC neonates. SNPs in and around ABHD8 were associated with mtDNA CN in ALSPAC neonates (rs10424198, β [SE] 0.262 [0.034], p = 1.40e-14), but not other study groups. In a meta-analysis of unrelated individuals (N = 11,253), we replicated a published association in TFAM (β [SE] 0.046 [0.017], p = 0.006), with an effect size much smaller than that observed in the replication analysis of a previous in silico GWAS.

CONCLUSIONS

In a hypothesis-generating GWAS, we confirm an association between TFAM and mtDNA CN and present putative loci requiring replication in much larger samples. We discuss the limitations of our work, in terms of measurement error and cellular heterogeneity, and highlight the need for larger studies to better understand nuclear genomic control of mtDNA copy number.

Investigating mitonuclear interactions in human admixed populations

To function properly, mitochondria utilize products of 37 mitochondrial and >1,000 nuclear genes, which should be compatible with each other. Discordance between mitochondrial and nuclear genetic ancestry could contribute to phenotypic variation in admixed populations. Here, we explored potential mitonuclear incompatibility in six admixed human populations from the Americas: African Americans, African Caribbeans, Colombians, Mexicans, Peruvians and Puerto Ricans. By comparing nuclear versus mitochondrial ancestry in these populations, we first show that mitochondrial DNA (mtDNA) copy number decreases with increasing discordance between nuclear and mtDNA ancestry. The direction of this effect is consistent across mtDNA haplogroups of different geographic origins. This observation indicates suboptimal regulation of mtDNA replication when its components are encoded by nuclear and mtDNA genes with different ancestry. Second, while most populations analysed exhibit no such trend, in African Americans and Puerto Ricans, we find a significant enrichment of ancestry at nuclear-encoded mitochondrial genes towards the source populations contributing the most prevalent mtDNA haplogroups (African and Native American, respectively). This possibly reflects compensatory effects of selection in recovering mitonuclear interactions optimized in the source populations. Our results provide evidence of mitonuclear interactions in human admixed populations and we discuss their implications for human health and disease.

Particulate Air Pollution, Blood Mitochondrial DNA Copy Number, and Telomere Length in Mothers in the First Trimester of Pregnancy: Effects on Fetal Growth

Growing evidences have shown that particulate matter (PM) exposures during pregnancy are associated with impaired fetal development and adverse birth outcomes, possibly as a result of an exaggerated systemic oxidative stress and inflammation. Telomere length (TL) is strongly linked to biological age and is impacted by oxidative stress. We hypothesized that PM exposure during different time windows in the first trimester of pregnancy influences both mitochondrial DNA copy number (mtDNAcn), an established biomarker for oxidative stress, and TL. Maternal blood TL and mtDNAcn were analysed in 199 healthy pregnant women recruited at the 11th week of pregnancy by quantitative polymerase chain reaction. We also examined whether maternal mtDNAcn and TL were associated with fetal growth outcomes measured at the end of the first trimester of pregnancy (fetal heart rate, FHR; crown-rump length, CRL; and nuchal translucency, NT) and at delivery (birth weight, length, head circumference). The possible modifying effect of prepregnancy maternal body mass index was evaluated. PM₁₀ exposure during the first pregnancy trimester was associated with an increased maternal mtDNAcn and a reduced TL. As regards ultrasound fetal outcomes, both FHR and CRL were positively associated with PM_2.5, whereas the association with FHR was confirmed only when examining PM₁₀ exposure. PM₁₀ was also associated with a reduced birth weight. While no association was found between mtDNAcn and CRL, we found a negative relationship between mtDNAcn and fetal CRL only in overweight women, whereas normal-weight women exhibited a positive, albeit nonsignificant, association. As abnormalities of growth in utero have been associated with postnatal childhood and adulthood onset diseases and as PM is a widespread pollutant relevant to the large majority of the human population and obesity a rising risk factor, our results, if confirmed in a larger population, might represent an important contribution towards the development of more targeted public health strategies.

Plasmid-normalized quantification of relative mitochondrial DNA copy number

Alterations of mitochondrial DNA (mtDNA) copy number have been associated with a wide variety of phenotypes and diseases. Unfortunately, the literature provides scarce methodical information about duplex targeting of nuclear and mtDNA that meets the quality criteria for qPCR. Therefore, we established a method for mtDNA copy number quantification using a quantitative PCR assay that allows for simultaneous targeting of a single copy nuclear gene (beta-2-microglobulin) and the t-RNA^Leu gene on the mtDNA. We include a plasmid containing both targets in order to normalize against differences in emission intensities of the fluorescent dyes Yakima Yellow and FAM. Applying the plasmid calibrator on an internal control reduced the intra-assay variability from 21% (uncorrected) to 7% (plasmid-corrected). Moreover, we noted that DNA samples isolated with different methods revealed different numbers of mtDNA copies, thus highlighting an important influence of the pre-analytical procedures. In summary, we developed a precise assay for mitochondrial copy number detection relative to nuclear DNA. Our method is applicable to comparative mitochondrial DNA copy number studies since the use of the dual insert plasmid allows correcting for the unequal emission intensities of the different fluorescent labels of the two targets.

Mitochondrial dysfunction in fibroblasts of Multiple System Atrophy

Multiple System Atrophy is a severe neurodegenerative disorder which is characterized by a variable clinical presentation and a broad neuropathological spectrum. The pathogenic mechanisms are almost completely unknown. In the present study, we established a cellular model of MSA by using fibroblasts' primary cultures and performed several experiments to investigate the causative mechanisms of the disease, with a particular focus on mitochondrial functioning. Fibroblasts' analyses (7 MSA-P, 7 MSA-C and 6 healthy controls) displayed several anomalies in patients: an impairment of respiratory chain activity, in particular for succinate Coenzyme Q reductase (p < 0.05), and a reduction of complex II steady-state level (p < 0.01); a reduction of Coenzyme Q10 level (p < 0.001) and an up-regulation of some CoQ10 biosynthesis enzymes, namely COQ5 and COQ7; an impairment of mitophagy, demonstrated by a decreased reduction of mitochondrial markers after mitochondrial inner membrane depolarization (p < 0.05); a reduced basal autophagic activity, shown by a decreased level of LC3 II (p < 0.05); an increased mitochondrial mass in MSA-C, demonstrated by higher TOMM20 levels (p < 0.05) and suggested by a wide analysis of mitochondrial DNA content in blood of large cohorts of patients. The present study contributes to understand the causative mechanisms of Multiple System Atrophy. In particular, the observed impairment of respiratory chain activity, mitophagy and Coenzyme Q10 biosynthesis suggests that mitochondrial dysfunction plays a crucial role in the pathogenesis of the disease. Furthermore, these findings will hopefully contribute to identify novel therapeutic targets for this still incurable disorder.

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

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

Nrf2 activation attenuates the early suppression of mitochondrial respiration due to the α-synuclein overexpression

BACKGROUND

α-synuclein (SNCA) accumulation in the substantia nigra is one of the characteristic pathologies of Parkinson's disease (PD). A53T missense mutations in the SNCA gene has been proved to enhance the expression of SNCA and accelerate the onset of PD. Mitochondrial dysfunction in SNCA aggregation has been under debate for decades but the causal relationship remains uncertain. At a later stage of PD, the cellular dysfunctions are complicated and multiple factors are tangled. Our aim here is to investigate the mitochondrial functional changes and clarify the main causal mechanism at earlier-stage of PD.

METHODS

We used the mutant A53T SNCA-expressed neuro 2a (N2a) cells without detectable cell death to investigate: 1) whether SNCA overexpression impairs the mitochondrial respiration and biogenesis. 2) The role of nuclear factor (erythroid-derived 2)-like 2 (Nrf2) signal in SNCA-induced mitochondria dysfunction.

RESULTS

Accompanying with the increment of SNCA, reactive oxygen species (ROS) accumulation was increased. The maximal respiratory capacity was suppressed. Meanwhile, mitochondrial complex 1 activity and the activity of nicotinamide adenine dinucleotide (NADH) cytochrome C reductase (NCCR) were decreased. Moreover, the mitochondrial DNA (mtDNA) copy number was decreased. On the other hand, the nuclear peroxisome proliferator-activated receptor-gamma coactivator 1α (PGC-1α), Nrf2, and the cytosolic mitochondrial transcription factor A (TFAM) were increased at an early stage and declined thereafter. Above factors triggered by SNCA were reversed by tBHQ, a Nrf2 activator.

CONCLUSION

These results suggested that at an early stage, SNCA-overexpressed increase mtROS accumulation, mitochondrial dysfunction and mtDNA decrement. Nrf2, PGC-1α and TFAM were upregulated to compromise mitochondrial dysfunction. tBHQ effectively reversed the SNCA-induced mitochondrial dysfunction.

nrDNA:mtDNA copy number ratios as a comparative metric for evolutionary and conservation genetics

Identifying genetic cues of functional relevance is key to understanding the drivers of evolution and increasingly important for the conservation of biodiversity. This study introduces nuclear ribosomal DNA (nrDNA) to mitochondrial DNA (mtDNA) copy number ratios as a metric with which to screen for this functional genetic variation prior to more extensive omics analyses. To illustrate the metric, quantitative PCR was used to estimate nrDNA (18S) to mtDNA (16S) copy number ratios in muscle tissue from samples of two zooplankton species: Salpa thompsoni caught near Elephant Island (Southern Ocean) and S. fusiformis sampled off Gough Island (South Atlantic). Average 18S:16S ratios in these samples were 9:1 and 3:1, respectively. nrDNA 45S arrays and mitochondrial genomes were then deep sequenced to uncover the sources of intra-individual genetic variation underlying these 18S:16S copy number differences. The deep sequencing profiles obtained were consistent with genetic changes resulting from adaptive processes, including an expansion of nrDNA and damage to mtDNA in S. thompsoni, potentially in response to the polar environment. Beyond this example from zooplankton, nrDNA:mtDNA copy number ratios offer a promising metric to help identify genetic variation of functional relevance in animals more broadly.

Mitochondrial Dysfunction in Parkinson's Disease: New Mechanistic Insights and Therapeutic Perspectives

Purpose of Review

Parkinson’s disease (PD) is a complex neurodegenerative disorder, the aetiology of which is still largely unknown. Overwhelming evidence indicates that mitochondrial dysfunction is a central factor in PD pathophysiology. Here we review recent developments around mitochondrial dysfunction in familial and sporadic PD, with a brief overview of emerging therapies targeting mitochondrial dysfunction.

Recent Findings

Increasing evidence supports the critical role for mitochondrial dysfunction in the development of sporadic PD, while the involvement of familial PD-related genes in the regulation of mitochondrial biology has been expanded by the discovery of new mitochondria-associated disease loci and the identification of their novel functions.

Summary

Recent research has expanded knowledge on the mechanistic details underlying mitochondrial dysfunction in PD, with the discovery of new therapeutic targets providing invaluable insights into the essential role of mitochondria in PD pathogenesis and unique opportunities for drug development.

β-Guanidinopropionic Acid Stimulates Brain Mitochondria Biogenesis and Alters Cognitive Behavior in Nondiseased Mid-Age Mice

β-guanidinopropionic acid (β-GPA) has been used as a nutritional supplement for increasing physical strength and endurance with positive and predictable results. In muscles, it works as a nonadaptive stimulator of mitochondria biogenesis; it also increases lipid metabolism. There are data indicating that β-GPA can be also neuroprotective, but its mechanisms of action in the brain are less understood. We studied the effects of β-GPA on animal behavior and mitochondrial biogenesis in the cortex and midbrain of mid-age healthy mice. We found that even short-term 3-week-long β-GPA treatment increased the mitochondrial DNA (mtDNA) copy number in the cortex and ventral midbrain, as well as the expression of several key antioxidant and metabolic enzymes—indicators of mitochondria proliferation and the activation of Nrf2/ARE signaling cascade. At the same time, β-GPA downregulated the expression of the β-oxidation genes. Administration of β-GPA in mice for 3 weeks improved the animals’ physical strength and endurance health, ie, increased their physical strength and endurance and alleviated anxiety. Thus, β-GPA might be considered an adaptogene affecting both the muscle and brain metabolism in mammals.

mtDNA copy number associated with age of onset in familial amyloid polyneuropathy

BACKGROUND

Transthyretin-related familial amyloid polyneuropathy (TTR-FAP Val30Met) shows a wide variation in age-at-onset (AO) between generations and genders, as in Portuguese families, where women display a later onset and a larger anticipation (>10 years). Mitochondrial DNA (mtDNA) copy number was assessed to clarify whether it has a modifier effect on AO variability in Portuguese patients.

METHODS

The mtDNA copy number of 262 samples (175 Val30Met TTR carriers and 87 controls (proven Val30Val)) was quantified by quantitative real-time PCR. Statistical analysis was performed using IBM SPSS V.23 software.

RESULTS

This study shows that Val30Met TTR carriers have a significantly higher (p<0.001) mean mtDNA copy number than controls. Furthermore, the highest mtDNA copy number mean was observed in early-onset patients (AO <40 years). Importantly, early-onset offspring showed a significant increase (p=0.002) in the mtDNA copy number, when compared with their late AO parents.

CONCLUSIONS

The present findings suggest, for the first time, that mtDNA copy number may be associated with earlier events and may therefore be further explored as a potential biomarker for follow-up of TTR-FAP Val30Met carriers.

Prenatal particulate matter exposure and mitochondrial dysfunction at the maternal-fetal interface: Effect modification by maternal lifetime trauma and child sex

BACKGROUND

Prenatal ambient fine particulate matter (PM_2.5) and maternal chronic psychosocial stress have independently been linked to changes in mithochondrial DNA copy number (mtDNAcn), a marker of mitochondrial response and dysfunction. Further, overlapping research shows sex-specific effects of PM_2.5 and stress on developmental outcomes. Interactions among PM_2.5, maternal stress, and child sex have not been examined in this context.

METHODS

We examined associations among exposure to prenatal PM_2.5, maternal lifetime traumatic stressors, and mtDNAcn at birth in a sociodemographically diverse pregnancy cohort (N=167). Mothers' daily exposure to PM_2.5 over gestation was estimated using a satellite-based spatio-temporally resolved prediction model. Lifetime exposure to traumatic stressors was ascertained using the Life Stressor Checklist-Revised; exposure was categorized as high vs. low based on a median split. Quantitative real-time polymerase chain reaction (qPCR) was used to determine mtDNAcn in placenta and cord blood leukocytes. Bayesian Distributed Lag Interaction regression models (BDLIMs) were used to statistically model and visualize the PM_2.5 timing-dependent pattern of associations with mtDNAcn and explore effect modification by maternal lifetime trauma and child sex.

RESULTS

Increased PM_2.5 exposure across pregnancy was associated with decreased mtDNAcn in cord blood (cumulative effect estimate=-0.78; 95%CI -1.41, -0.16). Higher maternal lifetime trauma was associated with reduced mtDNAcn in placenta (β=-0.33; 95%CI -0.63, -0.02). Among women reporting low trauma, increased PM_2.5 exposure late in pregnancy (30-38weeks gestation) was significantly associated with decreased mtDNAcn in placenta; no significant association was found in the high trauma group. BDLIMs identified a significant 3-way interaction between PM_2.5, maternal trauma, and child sex. Specifically, PM_2.5 exposure between 25 and 40weeks gestation was significantly associated with increased placental mtDNAcn among boys of mothers reporting high trauma. In contrast, PM_2.5 exposure in this same window was significantly associated with decreased placental mtDNAcn among girls of mothers reporting low trauma. Similar 3-way interactive effects were observed in cord blood.

CONCLUSIONS

These results indicate that joint exposure to PM_2.5 in late pregnancy and maternal lifetime trauma influence mtDNAcn at the maternal-fetal interface in a sex-specific manner. Additional studies will assist in understanding if the sex-specific patterns reflect distinct pathophysiological processes in addition to mitochondrial dysfunction.

Cardiometabolic phenotypes and mitochondrial DNA copy number in two cohorts of UK women

The mitochondrial genome is present at variable copy number between individuals. Mitochondria are vulnerable to oxidative stress, and their dysfunction may be associated with cardiovascular disease. The association of mitochondrial DNA copy number with cardiometabolic risk factors (lipids, glycaemic traits, inflammatory markers, anthropometry and blood pressure) was assessed in two independent cohorts of European origin women, one in whom outcomes were measured at mean (SD) age 30 (4.3) years (N=2278) and the second at 69.4 (5.5) years (N=2872). Mitochondrial DNA copy number was assayed by quantitative polymerase chain reaction. Associations were adjusted for smoking, sociodemographic status, laboratory factors and white cell traits. Out of a total of 12 outcomes assessed in both cohorts, mitochondrial DNA copy number showed little or no association with the majority (point estimates were close to zero and nearly all p-values were >0.01). The strongest evidence was for an inverse association in the older cohort with insulin (standardised beta [95%CI]: -0.06, [-0.098, -0.022], p=0.002), but this association did not replicate in the younger cohort. Our findings do not provide support for variation in mitochondrial DNA copy number having an important impact on cardio-metabolic risk factors in European origin women.

Haplogroup J mitogenomes are the most sensitive to the pesticide rotenone: Relevance for human diseases

There is growing evidence that the sequence variation of mitochondrial DNA (mtDNA), which clusters in population- and/or geographic-specific haplogroups, may result in functional effects that, in turn, become relevant in disease predisposition or protection, interaction with environmental factors and ultimately in modulating longevity. To unravel functional differences between mtDNA haplogroups we here employed transmitochondrial cytoplasmic hybrid cells (cybrids) grown in galactose medium, a culture condition that forces oxidative phosphorylation, and in the presence of rotenone, the classic inhibitor of respiratory Complex I. Under this experimental paradigm we assessed functional parameters such as cell viability and respiration, ATP synthesis, reactive oxygen species production and mtDNA copy number. Our analyses show that haplogroup J1, which is common in western Eurasian populations, is the most sensitive to rotenone, whereas K1 mitogenomes orchestrate the best compensation, possibly because of the haplogroup-specific missense variants impinging on Complex I function. Remarkably, haplogroups J1 and K1 fit the genetic associations previously established with Leber's hereditary optic neuropathy (LHON) for J1, as a penetrance enhancer, and with Parkinson's disease (PD) for K1, as a protective background. Our findings provide functional evidences supporting previous well-established genetic associations of specific haplogroups with two neurodegenerative pathologies, LHON and PD. Our experimental paradigm is instrumental to highlighting the subtle functional differences characterizing mtDNA haplogroups, which will be increasingly needed to dissect the role of mtDNA genetic variation in health, disease and longevity.

Oligomeric amyloid β preferentially targets neuronal and not glial mitochondrial-encoded mRNAs

INTRODUCTION

Our laboratories have demonstrated that accumulation of oligomeric amyloid β (OAβ) in neurons is an essential step leading to OAβ-mediated mitochondrial dysfunction.

METHODS

Alzheimer's disease (AD) and matching control hippocampal neurons, astrocytes, and microglia were isolated by laser-captured microdissection from the same subjects, followed by whole-transcriptome sequencing. Complementary in vitro work was performed in OAβ-treated differentiated SH-SY5Y, followed by the use of a novel CoQ₁₀ analogue for protection. This compound is believed to be effective both in suppressing reactive oxygen species and also functioning in mitochondrial electron transport.

RESULTS

We report decreases in the same mitochondrial-encoded mRNAs in Alzheimer's disease laser-captured CA1 neurons and in OAβ-treated SH-SY5Y cells, but not in laser-captured microglia and astrocytes. Pretreatment with a novel CoQ₁₀ analogue, protects neuronal mitochondria from OAβ-induced mitochondrial changes.

DISCUSSION

Similarity of expression changes in neurons from Alzheimer's disease brain and neuronal cells treated with OAβ, and the effect of a CoQ₁₀ analogue on the latter, suggests a pretreatment option to prevent OAβ toxicity, long before the damage is apparent.

Cell-free DNA as a biomarker in stroke: Current status, problems and perspectives

There is currently no proposed stroke biomarker with consistent application in clinical practice. A number of studies have examined cell-free DNA (cfDNA), which circulates in biological fluids during stroke, as a potential biomarker of this disease. The data available suggest that dynamically-determined levels of blood cfDNA may provide new prognostic information for assessment of stroke severity and outcome. However, such an approach has its own difficulties and limitations. This review covers the potential role of cfDNA as a biomarker in stroke, and includes evidence from both animal models and clinical studies, protocols used to analyze cfDNA, and hypotheses on the origin of cfDNA.

Mitochondrial DNA depletion by ethidium bromide decreases neuronal mitochondrial creatine kinase: Implications for striatal energy metabolism

Mitochondrial DNA (mtDNA), the discrete genome which encodes subunits of the mitochondrial respiratory chain, is present at highly variable copy numbers across cell types. Though severe mtDNA depletion dramatically reduces mitochondrial function, the impact of tissue-specific mtDNA reduction remains debated. Previously, our lab identified reduced mtDNA quantity in the putamen of Parkinson's Disease (PD) patients who had developed L-DOPA Induced Dyskinesia (LID), compared to PD patients who had not developed LID and healthy subjects. Here, we present the consequences of mtDNA depletion by ethidium bromide (EtBr) treatment on the bioenergetic function of primary cultured neurons, astrocytes and neuron-enriched cocultures from rat striatum. We report that EtBr inhibition of mtDNA replication and transcription consistently reduces mitochondrial oxygen consumption, and that neurons are significantly more sensitive to EtBr than astrocytes. EtBr also increases glycolytic activity in astrocytes, whereas in neurons it reduces the expression of mitochondrial creatine kinase mRNA and levels of phosphocreatine. Further, we show that mitochondrial creatine kinase mRNA is similarly downregulated in dyskinetic PD patients, compared to both non-dyskinetic PD patients and healthy subjects. Our data support a hypothesis that reduced striatal mtDNA contributes to energetic dysregulation in the dyskinetic striatum by destabilizing the energy buffering system of the phosphocreatine/creatine shuttle.

Translational approaches to restoring mitochondrial function in Parkinson's disease

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

ALR encoding dCMP deaminase is critical for DNA damage repair, cell cycle progression and plant development in rice

Deoxycytidine monophosphate deaminase (dCMP deaminase, DCD) is crucial to the production of dTTP needed for DNA replication and damage repair. However, the effect of DCD deficiency and its molecular mechanism are poorly understood in plants. Here, we isolated and characterized a rice albinic leaf and growth retardation (alr) mutant that is manifested by albinic leaves, dwarf stature and necrotic lesions. Map-based cloning and complementation revealed that ALR encodes a DCD protein. OsDCD was expressed ubiquitously in all tissues. Enzyme activity assays showed that OsDCD catalyses conversion of dCMP to dUMP, and the ΔDCD protein in the alr mutant is a loss-of-function protein that lacks binding ability. We report that alr plants have typical DCD-mediated imbalanced dNTP pools with decreased dTTP; exogenous dTTP recovers the wild-type phenotype. A comet assay and Trypan Blue staining showed that OsDCD deficiency causes accumulation of DNA damage in the alr mutant, sometimes leading to cell apoptosis. Moreover, OsDCD deficiency triggered cell cycle checkpoints and arrested cell progression at the G1/S-phase. The expression of nuclear and plastid genome replication genes was down-regulated under decreased dTTP, and together with decreased cell proliferation and defective chloroplast development in the alr mutant this demonstrated the molecular and physiological roles of DCD-mediated dNTP pool balance in plant development.

Mitochondrial DNA changes in pedunculopontine cholinergic neurons in Parkinson disease

In Parkinson disease (PD), mitochondrial dysfunction associates with nigral dopaminergic neuronal loss. Cholinergic neuronal loss co-occurs, particularly within a brainstem structure, the pedunculopontine nucleus (PPN). We isolated single cholinergic neurons from postmortem PPNs of aged controls and PD patients. Mitochondrial DNA (mtDNA) copy number and mtDNA deletions were increased significantly in PD patients compared to controls. Furthermore, compared to controls the PD patients had significantly more PPN cholinergic neurons containing mtDNA deletion levels exceeding 60%, a level associated with deleterious effects on oxidative phosphorylation. The current results differ from studies reporting mtDNA depletion in nigral dopaminergic neurons of PD patients. Ann Neurol 2017;82:1016-1021.