Maintenance of mitochondrial DNA copy number and expression are essential for preservation of mitochondrial function and cell growth

Vascular endothelial cells of Mongolian gerbils are resistant to cholesterol-induced mitochondrial dysfunction and oxidative damage

Atherosclerosis is essentially the leading factor behind occurrences of cardiovascular diseases (CVDs)-associated incidents, while mitochondrial dysfunction is also the main cause of atherosclerosis. The present study conducted a comparative analysis of mitochondrial function-related indicators in cholesterol-induced vascular endothelial cells (VECs) from Mongolian gerbils, Sprague-Dawley (SD) rats and humans. It reported that the inhibitory effect of cholesterol treatment on the viability of Mongolian gerbil VECs was markedly lower than the other two types of VECs at the same concentration. Following cholesterol treatment, mitochondrial DNA copy numbers, reactive oxygen species level, calcium concentration and mitochondrial membrane potential of Mongolian gerbil VECs did not change markedly. These results suggested that the function of mitochondria in the VECs of Mongolian gerbil is normal. Additionally, cholesterol treatment also did not alter the levels of superoxide dismutase, glutathione peroxidase, ATP, NADH-CoQ reductase and cytochrome c oxidase in Mongolian gerbil VECs. It was hypothesized that the VECs of Mongolian gerbils have certain resistance to oxidative damage induced by cholesterol. In brief, the present study demonstrated that VECs of Mongolian gerbils are resistant to cholesterol-induced mitochondrial dysfunction and oxidative damage. The aforementioned findings establish a theoretical foundation for the advancement of innovative strategies in the prevention and treatment of atherosclerosis.

Lycopene alleviates Deoxynivalenol-induced toxicity in Porcine intestinal epithelial cells by mediating mitochondrial function

Deoxynivalenol (DON) is widely found in food and feed, posing a threat to human and animal health. Lycopene (Lyc) is a natural plant extracts with significant antioxidant properties. This study was conducted to investigate the protective effects of Lyc on IPEC-J2 cells upon DON exposure. The detection of cell viability and trypan blue staining showed that Lyc alleviated cell damage and decreased cell apoptotic rate induced by DON. The analysis of reactive oxygen species (ROS) level and antioxidant parameter measurements showed that Lyc significantly down-regulated the content of ROS and restored antioxidant enzyme activity. Furthermore, mitochondrial membrane potential (ΔΨm) detection, mitochondrial DNA copy number (mtDNAcn) assay and adenosine triphosphate (ATP) concentration detection showed Lyc improved mitochondrial function after DON exposure. The results of transcriptome analysis, ROS detection and CCK8 assay suggested that Lyc may activated the oxidative phosphorylation (OXPHOS) to improve mitochondrial function. Conclusively, our results suggested that Lyc alleviated DON-induced oxidative stress by improving mitochondrial function through OXPHOS signaling pathway.

An exploration of biomarkers for noise exposure: mitochondrial DNA copy number and micronucleus frequencies in Chinese workers

Few studies have been conducted that use biomarkers as early warning signals for noise-associated health hazards. To explore potentially effective biomarkers for noise-exposed populations, we recruited 218 noise-exposed male workers in China. We calculated cumulative noise exposure (CNE) through noise intensity and noise-exposed duration. When the model was fully adjusted, ln-transformed relative mitochondrial DNA copy number (mtDNAcn) decreased by 0.014 (95% confidence interval (CI): -0.026, -0.003) units with each 1 dB(A)∙year increase in CNE levels. CNE was further included in the model as a grouping variable, and the results showed a negative dose-effect relationship between relative mtDNAcn and CNE (P-trend = 0.045). However, we did not find a correlation between CNE and micronucleus (MN) frequencies. Our findings suggest that CNE in workers was associated with a decrease in relative mtDNAcn which may provide a potential biomarker for noise and for certain health risk but not with MN frequencies.

The Role of Mitochondrial Copy Number in Neurodegenerative Diseases: Present Insights and Future Directions

Neurodegenerative diseases are progressive disorders that affect the central nervous system (CNS) and represent the major cause of premature death in the elderly. One of the possible determinants of neurodegeneration is the change in mitochondrial function and content. Altered levels of mitochondrial DNA copy number (mtDNA-CN) in biological fluids have been reported during both the early stages and progression of the diseases. In patients affected by neurodegenerative diseases, changes in mtDNA-CN levels appear to correlate with mitochondrial dysfunction, cognitive decline, disease progression, and ultimately therapeutic interventions. In this review, we report the main results published up to April 2024, regarding the evaluation of mtDNA-CN levels in blood samples from patients affected by Alzheimer's (AD), Parkinson's (PD), and Huntington's diseases (HD), amyotrophic lateral sclerosis (ALS), and multiple sclerosis (MS). The aim is to show a probable link between mtDNA-CN changes and neurodegenerative disorders. Understanding the causes underlying this association could provide useful information on the molecular mechanisms involved in neurodegeneration and offer the development of new diagnostic approaches and therapeutic interventions.

Long-term demyelination and aging-associated changes in mice corpus callosum; evidence for the role of accelerated aging in remyelination failure in a mouse model of multiple sclerosis

Multiple sclerosis (MS) is a chronic inflammatory and demyelinating disorder affecting the central nervous system. Evidence suggests that age-related neurodegeneration contributes to disability progression during the chronic stages of MS. Aging is characterized by decreased regeneration potential and impaired myelin repair in the brain. It is hypothesized that accelerated cellular aging contributes to the functional decline associated with neurodegenerative diseases. We assessed the impact of aging on myelin content in the corpus callosum (CC) and compared aging with the long-term demyelination (LTD) consequents induced by 12 weeks of feeding with a cuprizone (CPZ) diet. Initially, evaluating myelin content in 2-, 6-, and 18-month-old mice revealed a reduction in myelin content, particularly at 18 months. Myelin thickness was decreased and the g-ratio increased in aged mice. Although a lower myelin content and higher g-ratio were observed in LTD model mice, compared to the normally aged mice, both aging and LTD exhibited relatively similar myelin ultrastructure. Our findings provide evidence that LTD exhibits the hallmarks of aging such as elevated expression of senescence-associated genes, mitochondrial dysfunction, and high level of oxidative stress as observed following normal aging. We also investigated the senescence-associated β-galactosidase activity in O4+ late oligodendrocyte progenitor cells (OPCs). The senescent O4+/β-galactosidase+ cells were elevated in the CPZ diet. Our data showed that the myelin degeneration in CC occurs throughout the lifespan, and LTD induced by CPZ accelerates the aging process which may explain the impairment of myelin repair in patients with progressive MS.

Mitochondrial DNA: Inherent Complexities Relevant to Genetic Analyses

Mitochondrial DNA (mtDNA) exhibits distinct characteristics distinguishing it from the nuclear genome, necessitating specific analytical methods in genetic studies. This comprehensive review explores the complex role of mtDNA in a variety of genetic studies, including genome-wide, epigenome-wide, and phenome-wide association studies, with a focus on its implications for human traits and diseases. Here, we discuss the structure and gene-encoding properties of mtDNA, along with the influence of environmental factors and epigenetic modifications on its function and variability. Particularly significant are the challenges posed by mtDNA's high mutation rate, heteroplasmy, and copy number variations, and their impact on disease susceptibility and population genetic analyses. The review also highlights recent advances in methodological approaches that enhance our understanding of mtDNA associations, advocating for refined genetic research techniques that accommodate its complexities. By providing a comprehensive overview of the intricacies of mtDNA, this paper underscores the need for an integrated approach to genetic studies that considers the unique properties of mitochondrial genetics. Our findings aim to inform future research and encourage the development of innovative methodologies to better interpret the broad implications of mtDNA in human health and disease.

Subtype-Specific Association of Mitochondrial DNA Copy Number With Poststroke/TIA Outcomes in 10 241 Patients in China

BACKGROUND

Mitochondrial DNA copy number (mtDNA-CN) is associated with the severity and mortality in patients with stroke, but the associations in different stroke subtypes remain unexplored.

METHODS

We conducted an observational prospective cohort analysis on patients with ischemic stroke or transient ischemic attack enrolled in the Third China National Stroke Registry. We applied logistic models to assess the association of mtDNA-CN with functional outcome (modified Rankin Scale score, 3-6 versus 0-2) and Cox proportional hazard models to assess the association with stroke recurrence (treating mortality as a competing risk) and mortality during a 12-month follow-up, adjusting for sex, age, physical activity, National Institutes of Health Stroke Scale at admission, history of stroke and peripheral artery disease, small artery occlusion, and interleukin-6. Subgroup analyses stratified by age and stroke subtypes were conducted.

RESULTS

The Third China National Stroke Registry enrolled 15 166 patients, of which 10 241 with whole-genome sequencing data were retained (mean age, 62.2 [SD, 11.2] years; 68.8% men). The associations between mtDNA-CN and poststroke/transient ischemic attack outcomes were specific to patients aged ≤65 years, with lower mtDNA-CN significantly associated with stroke recurrence in 12 months (subdistribution hazard ratio, 1.15 per SD lower mtDNA-CN [95% CI, 1.04-1.27]; P=5.2×10-3) and higher all-cause mortality in 3 months (hazard ratio, 2.19 [95% CI, 1.41-3.39]; P=5.0×10-4). Across subtypes, the associations of mtDNA-CN with stroke recurrence were specific to stroke of undetermined cause (subdistribution hazard ratio, 1.28 [95% CI, 1.11-1.48]; P=6.6×10-4). In particular, lower mtDNA-CN was associated with poorer functional outcomes in stroke of undetermined cause patients diagnosed with embolic stroke of undetermined source (odds ratio, 1.53 [95% CI, 1.20-1.94]; P=5.4×10-4), which remained significant after excluding patients with recurrent stroke (odds ratio, 1.49 [95% CI, 1.14-1.94]; P=3.0×10-3).

CONCLUSIONS

Lower mtDNA-CN is associated with higher stroke recurrence rate and all-cause mortality, as well as poorer functional outcome at follow-up, among stroke of undetermined cause, embolic stroke of undetermined source, and younger patients.

Inverse associations of cord blood mitochondrial DNA copy number with childhood adiposity

OBJECTIVE

The objective of this study was to examine associations between umbilical cord mitochondrial DNA copy number (mtDNAcn) and adiposity across childhood.

METHODS

In a prospective birth cohort of Dominican and African American children from New York City, New York (1998-2006), mtDNAcn was measured in cord blood. Children (N = 336) were evaluated for their height, weight, and bioimpedance at age 5, 7, 9, and 11 years. We used linear mixed-effects models to assess associations of mtDNAcn tertiles in cord blood with child BMI, BMI z scores, fat mass index, and body fat percentage. Latent class growth models and interactions between mtDNAcn and child age or child age2 were used to assess associations between age and adiposity trajectories.

RESULTS

BMI was, on average, 1.5 kg/m2 higher (95% CI: 0.58, 2.5) in individuals with mtDNAcn in the low- compared with the middle-mtDNAcn tertile. Results were similar for BMI z score, fat mass index, and body fat percentage. Moreover, children in the low-mtDNAcn group had increased odds of being in an "increasing" or "high-stable" adiposity class.

CONCLUSIONS

Lower mtDNAcn at birth may predict greater childhood adiposity, highlighting the potential key role of perinatal mitochondrial function in adiposity during development.

Associations between mitochondrial copy number, exercise capacity, physiologic cost of walking, and cardiac strain in young adult survivors of childhood cancer

PURPOSE

Childhood cancer survivors are at risk for cardiac dysfunction and impaired physical performance, though underlying cellular mechanisms are not well studied. In this cross-sectional study, we examined the association between peripheral blood mitochondrial DNA copy number (mtDNA-CN, a proxy for mitochondrial function) and markers of performance impairment and cardiac dysfunction.

METHODS

Whole-genome sequencing, validated by quantitative polymerase chain reaction, was used to estimate mtDNA-CN in 1720 adult survivors of childhood cancer (48.5% female; mean age = 30.7 years, standard deviation (SD) = 9.0). Multivariable logistic regression was performed to evaluate the associations between mtDNA-CN and exercise intolerance, walking inefficiency, and abnormal global longitudinal strain (GLS), adjusting for treatment exposures, age, sex, and race and ethnicity.

RESULTS

The prevalence of exercise intolerance, walking inefficiency, and abnormal GLS among survivors was 25.7%, 10.7%, and 31.7%, respectively. Each SD increase of mtDNA-CN was associated with decreased odds of abnormal GLS (adjusted odds ratio (OR) = 0.88, p = 0.04) but was not associated with exercise intolerance (OR = 1.02, p = 0.76) or walking inefficiency (OR = 1.06, p = 0.46). Alkylating agent exposure was associated with increased odds of exercise intolerance (OR = 2.25, p < 0.0001), walking inefficiency (OR = 2.37, p < 0.0001), and abnormal GLS (OR = 1.78, p = 0.0002).

CONCLUSIONS

Increased mtDNA-CN is associated with decreased odds of abnormal cardiac function in childhood cancer survivors.

IMPLICATIONS FOR CANCER SURVIVORS

These findings demonstrate a potential role for mtDNA-CN as a biomarker of early cardiac dysfunction in this population.

The Association Between Mitochondrial tRNAGlu Variants and Hearing Loss: A Case-Control Study

Purpose

This study aimed to examine the frequencies of mt-tRNAGlu variants in 180 pediatric patients with non-syndromic hearing loss (NSHL) and 100 controls.

Methods

Sanger sequencing was performed to screen for mt-tRNAGlu variants. These mitochondrial DNA (mtDNA) pathogenic mutations were further assessed using phylogenetic conservation and haplogroup analyses. We also traced the origins of the family history of probands carrying potential pathogenic mtDNA mutations. Mitochondrial functions including mtDNA content, ATP and reactive oxygen species (ROS) were examined in cells derived from patients carrying the mt-tRNAGlu A14692G and CO1/tRNASer(UCN) G7444A variants and controls.

Results

We identified four possible pathogenic variants: m.T14709C, m.A14683G, m.A14692G and m.A14693G, which were found in NSHL patients but not in controls. Genetic counseling suggested that one child with the m.A14692G variant had a family history of NSHL. Sequence analysis of mtDNA suggested the presence of the CO1/tRNASer(UCN) G7444A and mt-tRNAGlu A14692G variants. Molecular analysis suggested that, compared with the controls, patients with these variants exhibited much lower mtDNA copy numbers, ATP production, whereas ROS levels increased (p<0.05 for all), suggesting that the m.A14692G and m.G7444A variants led to mitochondrial dysfunction.

Conclusion

mt-tRNAGlu variants are important risk factors for NSHL.

CKLF induces microglial activation via triggering defective mitophagy and mitochondrial dysfunction

Although microglial activation is induced by an increase in chemokines, the role of mitophagy in this process remains unclear. This study aimed to elucidate the role of microglial mitophagy in CKLF/CKLF1 (chemokine-like factor 1)-induced microglial activation and neuroinflammation, as well as the underlying molecular mechanisms following CKLF treatment. This study determined that CKLF, an inducible chemokine in the brain, leads to an increase in mitophagy markers, such as DNM1L, PINK1 (PTEN induced putative kinase 1), PRKN, and OPTN, along with a simultaneous increase in autophagosome formation, as evidenced by elevated levels of BECN1 and MAP1LC3B (microtubule-associated protein 1 light chain 3 beta)-II. However, SQSTM1, a substrate of autophagy, was also accumulated by CKLF treatment, suggesting that mitophagy flux was reduced and mitophagosomes accumulated. These findings were confirmed by transmission electron microscopy and confocal microscopy. The defective mitophagy observed in our study was caused by impaired lysosomal function, including mitophagosome-lysosome fusion, lysosome generation, and acidification, resulting in the accumulation of damaged mitochondria in microglial cells. Further analysis revealed that pharmacological blocking or gene-silencing of mitophagy inhibited CKLF-mediated microglial activation, as evidenced by the expression of the microglial marker AIF1 (allograft inflammatory factor 1) and the mRNA of proinflammatory cytokines (Tnf and Il6). Ultimately, defective mitophagy induced by CKLF results in microglial activation, as observed in the brains of adult mice. In summary, CKLF induces defective mitophagy, microglial activation, and inflammation, providing a potential approach for treating neuroinflammatory diseases.Abbreviation: 3-MA: 3-methyladenine; AIF1: allograft inflammatory factor 1; ANOVA: analysis of variance; BAF: bafilomycin A1; BSA: bovine serum albumin; CCCP: carbonyl cyanide m-chlorophenyl hydrazone; cGAMP: cyclic GMP-AMP; CGAS: cyclic GMP-AMP synthase; CKLF/CKLF1: chemokine-like factor 1; CNS: central nervous system; DMEM: Dulbecco's Modified Eagle Medium; DNM1L: dynamin 1 like; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GFP: green fluorescence protein; IRF3: interferon regulatory factor 3; IgG: immunoglobulin G; LAMP1: lysosomal-associated membrane protein 1; LAPTM4A: lysosomal-associated protein transmembrane 4A; MAP1LC3B: microtubule-associated protein 1 light chain 3 beta; Mdivi-1: mitochondrial division inhibitor 1; mRFP: monomeric red fluorescent protein; mtDNA: mitochondrial DNA; MTORC1: mechanistic target of rapamycin kinase complex 1; OPTN: optineurin; PBS: phosphate-buffered saline; PCR: polymerase chain reaction; PINK1: PTEN induced putative kinase 1; PLL: poly-L-lysine; PRKN: parkin RBR E3 ubiquitin protein ligase; qPCR: quantitative polymerase chain reaction; ROS: reactive oxygen species; SQSTM1: sequestosome 1; TBK1: TANK-binding kinase 1; TFEB: transcription factor EB; VDAC: voltage-dependent anion channel.

Mitochondrial DNA copy number reduction via in vitro TFAM knockout remodels the nuclear epigenome and transcriptome

Mitochondrial DNA copy number (mtDNA-CN) is associated with several age-related chronic diseases and is a predictor of all-cause mortality. Here, we examine site-specific differential nuclear DNA (nDNA) methylation and differential gene expression resulting from in vitro reduction of mtDNA-CN to uncover shared genes and biological pathways mediating the effect of mtDNA-CN on disease. Epigenome and transcriptome profiles were generated for three independent human embryonic kidney (HEK293T) cell lines harbouring a mitochondrial transcription factor A (TFAM) heterozygous knockout generated via CRISPR-Cas9, and matched control lines. We identified 4,242 differentially methylated sites, 228 differentially methylated regions, and 179 differentially expressed genes associated with mtDNA-CN. Integrated analysis uncovered 381 Gene-CpG pairs. GABAA receptor genes and related pathways, the neuroactive ligand receptor interaction pathway, ABCD1/2 gene activity, and cell signalling processes were overrepresented, providing insight into the underlying biological mechanisms facilitating these associations. We also report evidence implicating chromatin state regulatory mechanisms as modulators of mtDNA-CN effect on gene expression. We demonstrate that mitochondrial DNA variation signals to the nuclear DNA epigenome and transcriptome and may lead to nuclear remodelling relevant to development, aging, and complex disease.

Biological aging markers in blood and brain tissue indicate age acceleration in alcohol use disorder

BACKGROUND

Alcohol use disorder (AUD) is associated with increased mortality and morbidity risk. A reason for this could be accelerated biological aging, which is strongly influenced by disease processes such as inflammation. As recent studies of AUD show changes in DNA methylation and gene expression in neuroinflammation-related pathways in the brain, biological aging represents a potentially important construct for understanding the adverse effects of substance use disorders. Epigenetic clocks have shown accelerated aging in blood samples from individuals with AUD. However, no systematic evaluation of biological age measures in AUD across different tissues and brain regions has been undertaken.

METHODS

As markers of biological aging (BioAge markers), we assessed Levine's and Horvath's epigenetic clocks, DNA methylation telomere length (DNAmTL), telomere length (TL), and mitochondrial DNA copy number (mtDNAcn) in postmortem brain samples from Brodmann Area 9 (BA9), caudate nucleus, and ventral striatum (N = 63-94), and in whole blood samples (N = 179) of individuals with and without AUD. To evaluate the association between AUD status and BioAge markers, we performed linear regression analyses while adjusting for covariates.

RESULTS

The majority of BioAge markers were significantly associated with chronological age in all samples. Levine's epigenetic clock and DNAmTL were indicative of accelerated biological aging in AUD in BA9 and whole blood samples, while Horvath's showed the opposite effect in BA9. No significant association of AUD with TL and mtDNAcn was detected. Measured TL and DNAmTL showed only small correlations in blood and none in brain.

CONCLUSIONS

The present study is the first to simultaneously investigate epigenetic clocks, telomere length, and mtDNAcn in postmortem brain and whole blood samples in individuals with AUD. We found evidence for accelerated biological aging in AUD in blood and brain, as measured by Levine's epigenetic clock, and DNAmTL. Additional studies of different tissues from the same individuals are needed to draw valid conclusions about the congruence of biological aging in blood and brain.

Unraveling the intricacies of osteoclast differentiation and maturation: insight into novel therapeutic strategies for bone-destructive diseases

Osteoclasts are the principal cells that efficiently resorb bone. Numerous studies have attempted to reveal the molecular pathways leading to the differentiation and activation of osteoclasts to improve the treatment and prevention of osteoporosis and other bone-destructive diseases. While the cumulative knowledge of osteoclast regulatory molecules, such as receptor activator of nuclear factor-kB ligand (RANKL) and nuclear factor of activated T cells 1 (NFATc1), contributes to the understanding of the developmental progression of osteoclasts, little is known about how the discrete steps of osteoclastogenesis modify osteoclast status but not the absolute number of osteoclasts. The regulatory mechanisms involved in osteoclast maturation but not those involved in differentiation deserve special attention due to their potential use in establishing a more effective treatment strategy: targeting late-phase differentiation while preserving coupled bone formation. Recent studies have shed light on the molecules that govern late-phase osteoclast differentiation and maturation, as well as the metabolic changes needed to adapt to shifting metabolic demands. This review outlines the current understanding of the regulation of osteoclast differentiation, as well as osteoclast metabolic adaptation as a differentiation control mechanism. Additionally, this review introduces molecules that regulate the late-phase osteoclast differentiation and thus minimally impact coupled bone formation.

Mitochondrial DNA Copy Number Variation in Asthma Risk, Severity, and Exacerbations

Rationale

Although airway oxidative stress and inflammation are central to asthma pathogenesis, there is limited knowledge of the relationship of asthma risk, severity, or exacerbations to mitochondrial dysfunction, which is pivotal to oxidant generation and inflammation.

Objectives

We investigated whether mitochondrial DNA copy number (mtDNA-CN) as a measure of mitochondrial function is associated with asthma diagnosis, severity, oxidative stress, and exacerbations.

Methods

We measured mtDNA-CN in blood in two cohorts. In the UK Biobank (UKB), we compared mtDNA-CN in mild and moderate-severe asthmatics to non-asthmatics. In the Severe Asthma Research Program (SARP), we evaluated mtDNA-CN in relation to asthma severity, biomarkers of oxidative stress and inflammation, and exacerbations.

Measures and Main Results

In UK Biobank, asthmatics (n = 29,768) have lower mtDNA-CN compared to non-asthmatics (n = 239,158) (beta, -0.026 [95% CI, -0.038 to -0.014], P = 2.46×10-5). While lower mtDNA-CN is associated with asthma, mtDNA-CN did not differ by asthma severity in either UKB or SARP. Biomarkers of inflammation show that asthmatics have higher white blood cells (WBC), neutrophils, eosinophils, fraction exhaled nitric oxide (FENO), and lower superoxide dismutase (SOD) than non-asthmatics, confirming greater oxidative stress in asthma. In one year follow-up in SARP, higher mtDNA-CN is associated with reduced risk of three or more exacerbations in the subsequent year (OR 0.352 [95% CI, 0.164 to 0.753], P = 0.007).

Conclusions

Asthma is characterized by mitochondrial dysfunction. Higher mtDNA-CN identifies an exacerbation-resistant asthma phenotype, suggesting mitochondrial function is important in exacerbation risk.

Miriplatin-loaded liposome, as a novel mitophagy inducer, suppresses pancreatic cancer proliferation through blocking POLG and TFAM-mediated mtDNA replication

Pancreatic cancer is a more aggressive and refractory malignancy. Resistance and toxicity limit drug efficacy. Herein, we report a lower toxic and higher effective miriplatin (MPt)-loaded liposome, LMPt, exhibiting totally different anti-cancer mechanism from previously reported platinum agents. Both in gemcitabine (GEM)-resistant/sensitive (GEM-R/S) pancreatic cancer cells, LMPt exhibits prominent anti-cancer activity, led by faster cellular entry-induced larger accumulation of MPt. The level of caveolin-1 (Cav-1) determines entry rate and switch of entry pathways of LMPt, indicating a novel role of Cav-1 in nanoparticle entry. After endosome-lysosome processing, in unchanged metabolite, MPt is released and targets mitochondria to enhance binding of mitochondria protease LONP1 with POLG and TFAM, to degrade POLG and TFAM. Then, via PINK1-Parkin axis, mitophagy is induced by POLG and TFAM degradation-initiated mitochondrial DNA (mtDNA) replication blocking. Additionally, POLG and TFAM are identified as novel prognostic markers of pancreatic cancer, and mtDNA replication-induced mitophagy blocking mediates their pro-cancer activity. Our findings reveal that the target of this liposomal platinum agent is mitochondria but not DNA (target of most platinum agents), and totally distinct mechanism of MPt and other formulations of MPt. Self-assembly offers LMPt special efficacy and mechanisms. Prominent action and characteristic mechanism make LMPt a promising cancer candidate.

Effect of acute cold exposure on cardiac mitochondrial function: role of sirtuins

Cardiac function depends mainly on mitochondrial metabolism. Cold conditions increase the risk of cardiovascular diseases by increasing blood pressure. Adaptive thermogenesis leads to increased mitochondrial biogenesis and function in skeletal muscles and adipocytes. Here, we studied the effect of acute cold exposure on cardiac mitochondrial function and its regulation by sirtuins. Significant increase in mitochondrial DNA copy number as measured by the ratio between mitochondrial-coded COX-II and nuclear-coded cyclophilin A gene expression by qRT-PCR and increase in the expression of PGC-1α, a mitochondriogenic factor and its downstream target NRF-1 were observed on cold exposure. This was associated with an increase in the activity of SIRT-1, which is known to activate PGC-1α. Mitochondrial SIRT-3 was also upregulated. Increase in sirtuin activity was reflected in total protein acetylome, which decreased in cold-exposed cardiac tissue. An increase in mitochondrial MnSOD further indicated enhanced mitochondrial function. Further evidence for this was obtained from ex vivo studies of cardiac tissue treated with norepinephrine, which caused a significant increase in mitochondrial MnSOD and SIRT-3. SIRT-3 appears to mediate the regulation of MnSOD, as treatment with AGK-7, a SIRT-3 inhibitor reversed the norepinephrine-induced upregulation of MnSOD. It, therefore, appears that SIRT-3 activation in response to SIRT-1-PGC-1α activation contributes to the regulation of cardiac mitochondrial activity during acute cold exposure.

Mitochondrial Dysfunction Associated with mtDNA in Metabolic Syndrome and Obesity

Metabolic syndrome (MetS) is a precursor to the major health diseases associated with high mortality in industrialized countries: cardiovascular disease and diabetes. An important component of the pathogenesis of the metabolic syndrome is mitochondrial dysfunction, which is associated with tissue hypoxia, disruption of mitochondrial integrity, increased production of reactive oxygen species, and a decrease in ATP, leading to a chronic inflammatory state that affects tissues and organ systems. The mitochondrial AAA + protease Lon (Lonp1) has a broad spectrum of activities. In addition to its classical function (degradation of misfolded or damaged proteins), enzymatic activity (proteolysis, chaperone activity, mitochondrial DNA (mtDNA)binding) has been demonstrated. At the same time, the spectrum of Lonp1 activity extends to the regulation of cellular processes inside mitochondria, as well as outside mitochondria (nuclear localization). This mitochondrial protease with enzymatic activity may be a promising molecular target for the development of targeted therapy for MetS and its components. The aim of this review is to elucidate the role of mtDNA in the pathogenesis of metabolic syndrome and its components as a key component of mitochondrial dysfunction and to describe the promising and little-studied AAA + LonP1 protease as a potential target in metabolic disorders.

Maternal and fetal mitochondrial gene dysregulation in hypertensive disorders of pregnancy

Mitochondrial dysfunction has been implicated in pregnancy-induced hypertension (PIH). The role of mitochondrial gene dysregulation in PIH, and consequences for maternal-fetal interactions, remain elusive. Here, we investigated mitochondrial gene expression and dysregulation in maternal and placental tissues from pregnancies with and without PIH; further, we measured circulating mitochondrial DNA (mtDNA) mutational load, an index of mtDNA integrity. Differential gene expression analysis followed by Time Course Gene Set Analysis (TcGSA) was conducted on publicly available high throughput sequencing transcriptomic data sets. Mutational load analysis was carried out on peripheral mononuclear blood cells from healthy pregnant individuals and individuals with preeclampsia. Thirty mitochondrial differentially expressed genes (mtDEGs) were detected in the maternal cell-free circulating transcriptome, whereas nine were detected in placental transcriptome from pregnancies with PIH. In PIH pregnancies, maternal mitochondrial dysregulation was associated with pathways involved in inflammation, cell death/survival, and placental development, whereas fetal mitochondrial dysregulation was associated with increased production of extracellular vesicles (EVs) at term. Mothers with preeclampsia did not exhibit a significantly different degree of mtDNA mutational load. Our findings support the involvement of maternal mitochondrial dysregulation in the pathophysiology of PIH and suggest that mitochondria may mediate maternal-fetal interactions during healthy pregnancy.NEW & NOTEWORTHY This study identifies aberrant maternal and fetal expression of mitochondrial genes in pregnancies with gestational hypertension and preeclampsia. Mitochondrial gene dysregulation may be a common etiological factor contributing to the development of de novo hypertension in pregnancy-associated hypertensive disorders.

Chronic heat stress induces renal fibrosis and mitochondrial dysfunction in laying hens

BACKGROUND

Heat stress in laying hens negatively affects egg production and shell quality by disrupting the homeostasis of plasma calcium and phosphorus levels. Although the kidney plays an important role in calcium and phosphorus homeostasis, evidence regarding the effect of heat stress on renal injury in laying hens is yet to be elucidated. Therefore, the aim of this study was to evaluate the effects of chronic heat stress on renal damage in hens during laying periods.

METHODS

A total of 16 white-leghorn laying hens (32 weeks old) were randomly assigned to two groups (n = 8). One group was exposed to chronic heat stress (33 °C for 4 weeks), whereas the other group was maintained at 24 °C.

RESULTS

Chronic heat exposure significantly increased plasma creatinine and decreased plasma albumin levels (P < 0.05). Heat exposure also increased renal fibrosis and the transcription levels of fibrosis-related genes (COLA1A1, αSMA, and TGF-β) in the kidney. These results suggest that renal failure and fibrosis were induced by chronic heat exposure in laying hens. In addition, chronic heat exposure decreased ATP levels and mitochondrial DNA copy number (mtDNA-CN) in renal tissue, suggesting that renal mitochondrial dysfunction occurs under conditions of heat stress. Damaged mitochondria leak mtDNAs into the cytosol and mtDNA leakage may activate the cyclic GMP-AMP synthase (cGAS) stimulator of interferon genes (STING) signaling pathway. Our results showed that chronic heat exposure activated the cGAS-STING pathway as indicated by increased expression of MDA5, STING, IRF7, MAVS, and NF-κB levels. Furthermore, the expression of pro-inflammatory cytokines (IL-12) and chemokines (CCL4 and CCL20) was upregulated in heat-stressed hens.

CONCLUSIONS

These results suggest that chronic heat exposure induces renal fibrosis and mitochondrial damage in laying hens. Mitochondrial damage by heat stress may activate the mtDNA-cGAS-STING signaling and cause subsequent inflammation, which contributes to the progression of renal fibrosis and dysfunction.

Influence of a concurrent exercise training program during pregnancy on the placenta mitochondrial DNA integrity and content of minerals with enzymatic relevance. The GESTAFIT project

INTRODUCTION

We aimed i) to investigate the effects of a concurrent (aerobic plus strength) exercise intervention during pregnancy on placental mtDNA copy number, proportion of deleted mtDNA, and on the content of some trace and ultra-trace minerals with coenzymatic relevance; ii) to explore the association of such mitochondrial markers with the concentration of these minerals.

METHODS

For the present study specific aims, 47 placentas were randomly selected from women that participated in the GESTAFIT project into exercise (n = 24) or control (n = 23) groups. The exercise group followed a concurrent aerobic and strength training program, three 60-min sessions/week, from the 17th gestational week until birth. Placenta tissue was collected and processed for minerals determination by the inductively coupled plasma mass spectrometry technique. RT-PCR was used to determine placentas mtDNA copy number and ND1/ND4 deletion.

RESULTS

After adjusting for potential confounders, the mothers who participated in the exercise program had placentas with greater mtDNA copy number (p = 0.04) and lower mtDNA deletion (p = 0.003). Placentas from mothers in the exercise group presented higher manganese content than those from the controls (0.26 ± 0.03 mg/dL vs. 0.13 ± 0.03 mg/dL, p = 0.003). Placenta manganese content was significantly associated with lower mtDNA deletions (r = -0.382) and greater mtDNA copy number (r = 0.513). Iron content was associated with higher mtDNA copy number (r = 0.393). Selenium content was associated with lower mtDNA deletion (r = -0.377) and greater mtDNA copy number (r = 0.442). Finally, zinc and magnesium content were associated with higher mtDNA copy number (r = 0.447 and r = 0.453, respectively).

DISCUSSION

This concurrent exercise training program induced a better placental status, which might be mediated through an improvement of mitochondrial bioenergetics and antioxidative capacity.

Bifenthrin disrupts cytochrome c oxidase activity and reduces mitochondrial DNA copy number through oxidative damage in pool barb (Puntius sophore)

Bifenthrin (BF), a synthetic pyrethroid is used worldwide for both agricultural and non-agricultural purposes due to its high insecticidal activity and low toxicity in mammals. However, its improper usage implies a possible risk to aquatic life. The Study was aimed to correlate the association of BF toxicity with mitochondrial DNA copy number variation in edible fish Punitus sophore. The 96-h LC 50 of BF in P. sophore was 3.4 μg/L, fish was treated with sub-lethal doses (0.34 μg/L,0.68 μg/L) of BF for 15 days. The activity and expression level of cytochrome c oxidase (Mt-COI) were measured to assess mitochondrial dysfunction caused by BF. Results showed BF reduced the level of Mt-COI mRNA in treated groups, hindered complex IV activity and increased ROS generation leading to oxidative damage. mtDNAcn was decreased in the muscle, brain and liver after BF treatment. Furthermore, BF induced neurotoxicity in brain and muscle cells through the inhibition of AchE activity. The treated groups showed elevated level of malondialdehyde (MDA) and an imbalance of antioxidant enzymes activity. Molecular docking and simulation analysis also predicted that BF binds to the active sites of the enzyme and restricts the fluctuation of active sites' residues. Hence, outcome of the study suggests reduction of mtDNAcn could be a potential biomarker to assess Bifenthrin induced toxicity in aquatic ecosystem.

Analysis of Mitochondrial Transfer RNA Mutations in Breast Cancer

Damage of mitochondrial functions caused by mitochondrial DNA (mtDNA) pathogenic mutations had long been proposed to be involved in breast carcinogenesis. However, the detailed pathological mechanism remained deeply undetermined. In this case-control study, we screened the frequencies of mitochondrial tRNA (mt-tRNA) mutations in 80 breast cancer tissues and matched normal adjacent tissues. PCR and Sanger sequence revealed five possible pathogenic mutations: tRNA^Val G1606A, tRNA^Ile A4300G, tRNA^Ser(UCN) T7505C, tRNA^Glu A14693G and tRNA^Thr G15927A. We noticed that these mutations resided at extremely conserved positions of tRNAs and would affect tRNAs transcription or modifications. Furthermore, functional analysis suggested that patients with these mt-tRNA mutations exhibited much lower levels of mtDNA copy number and ATP, as compared with controls (p<0.05). Therefore, it can be speculated that these mutations may impair mitochondrial protein synthesis and oxidative phosphorylation (OXPHOS) complexes, which caused mitochondrial dysfunctions that were involved in the breast carcinogenesis. Taken together, our data indicated that mutations in mt-tRNA were the important contributors to breast cancer, and mutational analyses of mt-tRNA genes were critical for prevention of breast cancer.

Impact of Translocator Protein 18 kDa (TSPO) Deficiency on Mitochondrial Function and the Inflammatory State of Human C20 Microglia Cells

Microglia are the resident immune cells of the central nervous system. Upon stimulus presentation, microglia polarize from a resting to an activated state. Microglial translocator protein 18 kDa (TSPO) is considered a marker of inflammation. Here, we characterized the role of TSPO by investigating the impact of TSPO deficiency on human microglia. We used TSPO knockout (TSPO-/-) variants of the human C20 microglia cell line. We found a significant reduction in the TSPO-associated protein VDAC1 in TSPO-/- cells compared to control cells. Moreover, we assessed the impact of TSPO deficiency on calcium levels and the mitochondrial membrane potential. Cytosolic and mitochondrial calcium concentrations were increased in TSPO-/- cell lines, whereas the mitochondrial membrane potential tended to be lower. Assessment of the mitochondrial DNA copy number via RT-PCR revealed a decreased amount of mtDNA in the TSPO-/- cells when compared to controls. Moreover, the metabolic profiles of C20 cells were strongly dependent on the glycolytic pathway. However, TSPO depletion did not affect the cellular metabolic profile. Measurement of the mRNA expression levels of the pro-inflammatory mediators revealed an attenuated response to pro-inflammatory stimuli in TSPO-depleted cells, implying a role for the TSPO protein in the process of microglial polarization.

Mitochondrial DNA as a marker for treatment-response in post-traumatic stress disorder

Post-traumatic stress disorder (PTSD) is a serious mental health condition thought to be mediated by a dysregulated stress response system. Stress, especially chronic stress, affects mitochondrial activity and their efficiency in duplicating their genomes. Human cells contain numerous mitochondria that harbor multiple copies of their own genome, which consist of a mixture of wild type and variant mtDNA - a condition known as mitochondrial heteroplasmy. Number of mitochondrial genomes in a cell and the degree of heteroplasmy may serve as an indicator of mitochondrial allostatic load. Changes in mtDNA copy number and the proportion of variant mtDNA may be related to mental disorders and symptom severity, suggesting an involvement of mitochondrial dysfunction also in PTSD. Therefore, we examined number and composition of mitochondrial DNA before and after six weeks of inpatient psychotherapy treatment in a cohort of 60 female PTSD patients. We extracted DNA from isolated monocytes before and after inpatient treatment and quantified cellular mtDNA using multiplex qPCR. We hypothesized that treatment would lead to changes in cellular mtDNA levels and that change in mtDNA level would be associated with PTSD symptom severity and treatment response. It could be shown that mtDNA copy number and the ratio of variant mtDNA decreased during therapy, however, this change did not correlate with treatment response. Our results suggest that inpatient treatment can reduce signs of mitochondrial allostatic load, which could have beneficial effects on mental health. The quantification of mtDNA and the determination of cellular heteroplasmy could represent valuable biomarkers for the molecular characterization of mental disorders in the future.

Gene Editing Technologies Targeting TFAM and Its Relation to Mitochondrial Diseases

Mitochondria are organelles present in the cytoplasm of eukaryotic cells; they play a key role in adenosine triphosphate (ATP) synthesis and oxidative phosphorylation. Mitochondria have their own DNA, mitochondrial DNA (mtDNA), keeping the function of the mitochondria. Mitochondrial transcription factor A (TFAM) is a member of the HMGB subfamily that binds to mtDNA promoters is and considered essential in mtDNA replication and transcription. More recently, TFAM has been shown to play a central role in the maintenance and regulation of mitochondrial copy number, inflammatory response, expression regulation, and mitochondrial genome activity. Gene editing tools such as the CRISPR-Cas 9 technique, TALENs, and other gene editing tools have been used to investigate the role of TFAM in mitochondrial mechanics and biogenesis as well as its correlation to mitochondrial disorders. Thus this chapter brings a summary of mitochondria function, dysfunction, the importance of TFAM in the maintenance of mitochondria, and state of the art of gene editing tools involving TFAM and mtDNA.

Prospective association between maternal allostatic load during pregnancy and child mitochondrial content and bioenergetic capacity

BACKGROUND

Mitochondria are multifunctional energy-producing and signaling organelles that support life and contribute to stress adaptation. There is a growing understanding of the dynamic relationship between stress exposure and mitochondrial biology; however, the influence of stress on key domains of mitochondrial biology during early-life, particularly the earliest phases of intra-uterine/prenatal period remains largely unknown. Thus, the goal of this study was to examine the impact of fetal exposure to stress (modeled as the biological construct allostatic load) upon mitochondrial biology in early childhood.

METHODS

In n = 30 children (range: 3.5-6 years, 53% male), we quantified mitochondrial content via citrate synthase (CS) activity and mtDNA copy number (mtDNAcn), and measured mitochondrial bioenergetic capacity via respiratory chain enzyme activities (complexes I (CI), II (CII), and IV (CIV)) in platelet-depleted peripheral blood mononuclear cells (PBMCs). In a cohort of healthy pregnant women, maternal allostatic load was operationalized as a latent variable (sum of z-scores) representing an aggregation of early-, mid- and late-gestation measures of neuroendocrine (cortisol), immune (interleukin-6, C-reactive protein), metabolic (homeostasis model assessment of insulin resistance, free fatty acids), and cardiovascular (aggregate systolic and diastolic blood pressure) systems, as well as an anthropometric indicator (pre-pregnancy body mass index [BMI]).

RESULTS

An interquartile increase in maternal allostatic load during pregnancy was associated with higher mitochondrial content (24% and 15% higher CS and mtDNAcn), and a higher mitochondrial bioenergetic capacity (16%, 23%, and 25% higher CI, CII and CIV enzymatic activities) in child leukocytes. The positive association between maternal allostatic load during pregnancy and child mitochondrial content and bioenergetic capacity remained significant after accounting for the effects of key pre- and post-natal maternal and child covariates (p's < 0.05, except CI p = 0.073).

CONCLUSION

We report evidence that prenatal biological stress exposure, modeled as allostatic load, was associated with elevated child mitochondrial content and bioenergetic capacity in early childhood. This higher mitochondrial content and bioenergetic capacity (per leukocyte) may reflect increased energetic demands at the immune or organism level, and thus contribute to wear-and-tear and pathophysiology, and/or programmed pro-inflammatory phenotypes. These findings provide potential mechanistic insight into the cellular processes underlying developmental programming, and support the potential role that changes in mitochondrial content and bioenergetic functional capacity may play in altering life-long susceptibility for health and disease.

Genetic associations with polycystic ovary syndrome: the role of the mitochondrial genome; a systematic review and meta-analysis

Background

Polycystic ovary syndrome (PCOS) remains the most common female reproductive endocrine disorder. Genetic studies have predominantly focused on the role of the nuclear genome, while the contribution of mitochondrial genetics in PCOS remains largely unknown.

Aim

This study aims to systematically evaluate the literature regarding the associations between the mitochondrial genome and PCOS.

Methods

A literature search focused on PCOS and mitochondrial genetics was conducted on (1) MEDLINE, (2) EMBASE and (3) The Cochrane Library (CENTRAL and Cochrane Reviews). Search results were screened for eligibility, and data involving genetic variants of mitochondrial DNA (mtDNA) were extracted. Quantitative data were presented in forest plots, and where this was not possible, data were analysed in a qualitative manner. Quality of studies was assessed using the Q-Genie tool.

Results

Of the 13 812 identified studies, 15 studies were eligible for inclusion, with 8 studies suitable for meta-analysis. Women with PCOS showed higher frequencies of a 9 bp deletion, and aberrant single nucleotide polymorphisms (SNPs) in the ND5, A6 and 7 transfer RNA-encoding genes. They also showed lower frequencies of two SNPs in the D-loop of the genome. Women with PCOS also exhibited significantly lowered mtDNA copy number.

Conclusion

Women with PCOS harbour genetic variants in coding and non-coding regions of the mitochondrial genome. This may disrupt the electron transport chain and lead to oxidative stress, causing apoptosis of cells and further genetic damage. However, further studies of higher quality are required to confirm these associations.

PROSPERO registration number

CRD42021267991.

Deletion of Tfam in Prx1-Cre expressing limb mesenchyme results in spontaneous bone fractures

INTRODUCTION

Osteoblasts require substantial amounts of energy to synthesize the bone matrix and coordinate skeleton mineralization. This study analyzed the effects of mitochondrial dysfunction on bone formation, nano-organization of collagen and apatite, and the resultant mechanical function in mouse limbs.

MATERIALS AND METHODS

Limb mesenchyme-specific Tfam knockout (Tfam^f/f;Prx1-Cre: Tfam-cKO) mice were analyzed morphologically and histologically, and gene expressions in the limb bones were assessed by in situ hybridization, qPCR, and RNA sequencing (RNA-seq). Moreover, we analyzed the mitochondrial function of osteoblasts in Tfam-cKO mice using mitochondrial membrane potential assay and transmission electron microscopy (TEM). We investigated the pathogenesis of spontaneous bone fractures using immunohistochemical analysis, TEM, birefringence analyzer, microbeam X-ray diffractometer and nanoindentation.

RESULTS

Forelimbs in Tfam-cKO mice were significantly shortened from birth, and spontaneous fractures occurred after birth, resulting in severe limb deformities. Histological and RNA-seq analyses showed that bone hypoplasia with a decrease in matrix mineralization was apparent, and the expression of type I collagen and osteocalcin was decreased in osteoblasts of Tfam-cKO mice, although Runx2 expression was unchanged. Decreased type I collagen deposition and mineralization in the matrix of limb bones in Tfam-cKO mice were associated with marked mitochondrial dysfunction. Tfam-cKO mice bone showed a significantly lower Young's modulus and hardness due to poor apatite orientation which is resulted from decreased osteocalcin expression.

CONCLUSION

Mice with limb mesenchyme-specific Tfam deletions exhibited spontaneous limb bone fractures, resulting in severe limb deformities. Bone fragility was caused by poor apatite orientation owing to impaired osteoblast differentiation and maturation.

Quantitative and structural characteristics of mitochondrial DNA in varicose veins

OBJECTIVE

We examined quantitative (in terms of mtDNA/nuclear DNA) and structural (in terms of common deletions in the MT-ND4 gene region) characteristics of mitochondrial DNA (mtDNA) in varicose veins (VVs) and venous wall layers by comparing mitochondrial genome parameters, as well as mitochondrial function (in terms of mitochondrial membrane potential (MtMP)), in varicose vein (VV) vs. non-varicose vein (NV) tissue samples.

METHODS

We analyzed paired great saphenous vein samples (VV vs. NV segments from each patient left after venous surgery) harvested from patients with VVs. Relative mtDNA level and the proportion of no-deletion mtDNA were determined by a multiplex quantitative PCR (qPCR), confirming the latter with a more sensitive method - droplet digital PCR (ddPCR). Mitochondria's functional state in VVs was assessed using fluorescent (dependent on MtMP) live-staining of mitochondria in venous tissues.

RESULTS

Total mtDNA level was lower in VV than in NV samples (predominantly in the t. media layer). ddPCR analysis showed lower proportion of no-deletion mtDNA in VVs. Because of the decrease in relative MtMP in VVs, our results suggest a possible reduction of mitochondrial function in VVs.

CONCLUSION

Quantitative and structural changes (copy number and integrity) of mtDNA are plausibly involved in VV pathogenesis. Future clinical studies implementing the mitochondrial targeting may be eventually fostered after auxiliary mechanistic studies.

Mitochondrial DNA copy number, metabolic syndrome, and insulin sensitivity: Insights from the Sugar, Hypertension, and Physical Exercise studies

Mitochondrial DNA copy number (mtDNA-CN) measured in blood has been associated with many aging-related diseases, with higher mtDNA-CN typically associated with lower disease risk. Exercise training is an excellent preventative tool against aging-related disorders and has been shown to increase mitochondrial function in muscle. Using the Sugar, Hypertension, and Physical Exercise cohorts (N = 105), we evaluated the effect of 6-months of exercise intervention on mtDNA-CN measured in blood. Although there was no significant relationship between exercise intervention and mtDNA-CN change (P = 0.29), there was a nominally significant association between mtDNA-CN and metabolic syndrome (P = 0.04), which has been seen in previous literature. We also identified a nominally significant association between higher mtDNA-CN and higher insulin sensitivity (P = 0.02).

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 bioinformatics pipeline for estimating mitochondrial DNA copy number and heteroplasmy levels from whole genome sequencing data

Mitochondrial diseases are a heterogeneous group of disorders that can be caused by mutations in the nuclear or mitochondrial genome. Mitochondrial DNA (mtDNA) variants may exist in a state of heteroplasmy, where a percentage of DNA molecules harbor a variant, or homoplasmy, where all DNA molecules have the same variant. The relative quantity of mtDNA in a cell, or copy number (mtDNA-CN), is associated with mitochondrial function, human disease, and mortality. To facilitate accurate identification of heteroplasmy and quantify mtDNA-CN, we built a bioinformatics pipeline that takes whole genome sequencing data and outputs mitochondrial variants, and mtDNA-CN. We incorporate variant annotations to facilitate determination of variant significance. Our pipeline yields uniform coverage by remapping to a circularized chrM and by recovering reads falsely mapped to nuclear-encoded mitochondrial sequences. Notably, we construct a consensus chrM sequence for each sample and recall heteroplasmy against the sample's unique mitochondrial genome. We observe an approximately 3-fold increased association with age for heteroplasmic variants in non-homopolymer regions and, are better able to capture genetic variation in the D-loop of chrM compared to existing software. Our bioinformatics pipeline more accurately captures features of mitochondrial genetics than existing pipelines that are important in understanding how mitochondrial dysfunction contributes to disease.

Mitochondrial health quality control: measurements and interpretation in the framework of predictive, preventive, and personalized medicine

Mitochondria are the “gatekeeper” in a wide range of cellular functions, signaling events, cell homeostasis, proliferation, and apoptosis. Consequently, mitochondrial injury is linked to systemic effects compromising multi-organ functionality. Although mitochondrial stress is common for many pathomechanisms, individual outcomes differ significantly comprising a spectrum of associated pathologies and their severity grade. Consequently, a highly ambitious task in the paradigm shift from reactive to predictive, preventive, and personalized medicine (PPPM/3PM) is to distinguish between individual disease predisposition and progression under circumstances, resulting in compromised mitochondrial health followed by mitigating measures tailored to the individualized patient profile. For the successful implementation of PPPM concepts, robust parameters are essential to quantify mitochondrial health sustainability. The current article analyses added value of Mitochondrial Health Index (MHI) and Bioenergetic Health Index (BHI) as potential systems to quantify mitochondrial health relevant for the disease development and its severity grade. Based on the pathomechanisms related to the compromised mitochondrial health and in the context of primary, secondary, and tertiary care, a broad spectrum of conditions can significantly benefit from robust quantification systems using MHI/BHI as a prototype to be further improved. Following health conditions can benefit from that: planned pregnancies (improved outcomes for mother and offspring health), suboptimal health conditions with reversible health damage, suboptimal life-style patterns and metabolic syndrome(s) predisposition, multi-factorial stress conditions, genotoxic environment, ischemic stroke of unclear aetiology, phenotypic predisposition to aggressive cancer subtypes, pathologies associated with premature aging and neuro/degeneration, acute infectious diseases such as COVID-19 pandemics, among others.

Higher buccal mitochondrial DNA and mitochondrial common deletion number are associated with markers of neurodegeneration and inflammation in cerebrospinal fluid

Human immunodeficiency virus (HIV) infection is potentially associated with premature aging, but demonstrating this is difficult due to a lack of reliable biomarkers. The mitochondrial (mt) DNA "common deletion" mutation (mtCDM) is a 4977-bp deletion associated with aging and neurodegenerative diseases. We examined how mtDNA and mtCDM correlate with markers of neurodegeneration and inflammation in people with and without HIV (PWH and PWOH). Data from 149 adults were combined from two projects involving PWH (n = 124) and PWOH (n = 25). We measured buccal mtDNA and mtCDM by digital droplet PCR and compared them to disease and demographic characteristics and soluble biomarkers in cerebrospinal fluid (CSF) and blood measured by immunoassay. Participants had a median age of 52 years, with 53% white and 81% men. Median mtDNA level was 1,332 copies/cell (IQR 1,201-1,493) and median mtCDM level was 0.36 copies × 102/cell (IQR 0.31-0.42); both were higher in PWH. In the best model adjusting for HIV status and demographics, higher mtDNA levels were associated with higher CSF amyloid-β 1-42 and 8-hydroxy-2'-deoxyguanosine and higher mtCDM levels were associated with higher plasma soluble tumor necrosis factor receptor II. The differences in mtDNA markers between PWH and PWOH support potential premature aging in PWH. Our findings suggest mtDNA changes in oral tissues may reflect CNS processes, allowing the use of inexpensive and easily accessible buccal biospecimens as a screening tool for CSF inflammation and neurodegeneration. Confirmatory and mechanistic studies on mt genome alterations by HIV and ART may identify interventions to prevent or treat neurodegenerative complications.

Association between mitochondrial and nuclear DNA damages and cellular senescence in the patients with biliary atresia undergoing Kasai portoenterostomy and liver transplantation

Biliary atresia (BA) is a cholestatic disease with extrahepatic bile duct obstruction that requires early surgical intervention and occasionally liver transplantation (LT). Accumulation of toxic bile acids induces oxidative stress that results in cell damage, such as cell senescence, mitochondrial dysfunction and others. However, details of their reciprocal association and clinical significance are unexplored. Therefore, we used immuno-localization of markers for cell senescence (p16 and p21), nuclear double-strand DNA damage (γH2AX), autophagy (p62), and mtDNA damage (mtDNA copy number) in patients with BA who underwent Kasai portoenterostomy (KP) and LT. We studied liver biopsy specimens from 54 patients with BA, 14 who underwent LT and 11 from the livers of neonates and infants obtained at autopsy. In hepatocytes, p21 expression was significantly increased in KP. In cholangiocytes, p16 expression was significantly increased in LT, and p21 expression was significantly increased in KP. p62 expression was significantly increased in the KP hepatocytes and LT cholangiocytes. Furthermore, mtDNA copy number significantly decreased in KP and LT compared with the control. Cell senescence and mitochondrial DNA damage progression were dependent on the BA clinical stages and could possibly serve as the markers of indication of LT.

Reduced mitochondrial DNA copy number in occupational workers from brominated flame retardants manufacturing plants

Decabrominated diphenyl ether (BDE-209) and its substitute decabromodiphenyl ethane (DBDPE) are two flame retardants that have similar structure and are widely used in various industrial products. The accumulation and potential toxicity of them to human health have already aroused attention, and some research showed that they may affect mitochondrial function. Therefore, this study focused on the population with high exposure to brominated flame retardants (BFRs) and the related changes in mtDNA copy number (mtDNAcn) in whole blood. 334 blood samples were collected from three groups of people in Shandong Province, including 42 BDE-209 occupational exposure workers from the BDE-209 manufacturing plant, 131 DBDPE occupational exposure workers from the DBDPE manufacturing plant, and 161 non-BFRs occupational exposure residents from the BFRs contaminated area. We measured the levels of BDE-209, DBDPE in serum sample, and the mtDNAcn in whole blood sample and analyzed these data by multiple linear regression. The average concentrations of BDE-209, DBDPE and ∑(BDE-209 + DBDPE) in BDE-209 occupational workers were 3510, 639 and 4600 ng/g lw, respectively; the average concentrations of BDE-209, DBDPE and ∑(BDE-209 + DBDPE) in DBDPE occupational workers were 229, 4040 and 4470 ng/g lw, respectively; the average concentrations of BDE-209, DBDPE and ∑(BDE-209 + DBDPE) in non-BFRs occupational exposure residents were 66.3, 45.7 and 137 ng/g lw, respectively. The relative mtDNAcn was 0.823 in BDE-209 occupational workers, 0.845 in DBDPE occupational workers and 0.989 in non-BFRs occupational exposure residents. A 10-fold increase in BDE-209, DBDPE concentrations was separately associated with a 0.068 and 0.063 decrease in mtDNAcn. Therefore, our study implied that BFRs may affect mitochondrial function. As increasing BFRs exposure has emerged in recent years, the relationship between BFRs exposure and mitochondrial function needs further study.

Genetic Drift and Purifying Selection Shaped Mitochondrial Genome Variation in the High Royal Jelly-Producing Honeybee Strain (Apis mellifera ligustica)

Mitochondrial genomes (mitogenomes) are involved in cellular energy metabolism and have been shown to undergo adaptive evolution in organisms with increased energy-consuming activities. The genetically selected high royal jelly-producing bees (RJBs, Apis mellifera ligustica) in China can produce 10 times more royal jelly, a highly nutritional and functional food, relative to unselected Italian bees (ITBs). To test for potential adaptive evolution of RJB mitochondrial genes, we sequenced mitogenomes from 100 RJBs and 30 ITBs. Haplotype network and phylogenetic analysis indicate that RJBs and ITBs are not reciprocally monophyletic but mainly divided into the RJB- and ITB-dominant sublineages. The RJB-dominant sublineage proportion is 6-fold higher in RJBs (84/100) than in ITBs (4/30), which is mainly attributable to genetic drift rather than positive selection. The RJB-dominant sublineage exhibits a low genetic diversity due to purifying selection. Moreover, mitogenome abundance is not significantly different between RJBs and ITBs, thereby rejecting the association between mitogenome copy number and royal jelly-producing performance. Our findings demonstrate low genetic diversity levels of RJB mitogenomes and reveal genetic drift and purifying selection as potential forces driving RJB mitogenome evolution.

Screening for Mitochondrial tRNA Mutations in 318 Patients with Dilated Cardiomyopathy

OBJECTIVES

Dilated cardiomyopathy (DCM) is a complex cardiovascular disease with unknown etiology. Although nuclear genes play active roles in DCM, mitochondrial dysfunction was believed to be involved in the pathogenesis of DCM. The objective of this study is to analysis the association between mitochondrial tRNA (mt-tRNA) mutations and DCM.

MATERIAL AND METHODS

We performed a mutational analysis of mt-tRNA genes in a cohort of 318 patients with DCM and 200 age- and gender-matched control subjects. To further assess their pathogenicity, phylogenetic analysis and mitochondrial functions including mtDNA copy number, ATP and ROS were analyzed.

RESULTS

7 possible pathogenic mutations: MT-TL1 3302A>G, MT-TI 4295A>G, MT-TM 4435A>G, MT-TA 5655T>C, MT-TH 12201T>C, MT-TE 14692A>G and MT-TT 15927G>A were identified in DCM group but absent in controls. These mutations occurred at extremely conserved nucleotides of corresponding tRNAs, and led to the failure in tRNAs metabolism. Moreover, a significant reduction in ATP and mtDNA copy number, whereas a markedly increased in ROS level were observed in polymononuclear leukocytes (PMNs) derived from the DCM patients carrying these mt-tRNA mutations, suggesting that these mutations may cause mitochondrial dysfunction that was responsible for DCM.

CONCLUSIONS

Our data indicated that mt-tRNA mutations may be the molecular basis for DCM, which shaded novel insight into the pathophysiology of DCM that was manifestated by mitochondrial dysfunction.

Peripheral Blood Mitochondrial DNA Levels Were Modulated by SARS-CoV-2 Infection Severity and Its Lessening Was Associated With Mortality Among Hospitalized Patients With COVID-19

Introduction

During severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, the virus hijacks the mitochondria causing damage of its membrane and release of mt-DNA into the circulation which can trigger innate immunity and generate an inflammatory state. In this study, we explored the importance of peripheral blood mt-DNA as an early predictor of evolution in patients with COVID-19 and to evaluate the association between the concentration of mt-DNA and the severity of the disease and the patient’s outcome.

Methods

A total 102 patients (51 COVID-19 cases and 51 controls) were included in the study. mt-DNA obtained from peripheral blood was quantified by qRT-PCR using the NADH mitochondrial gene.

Results

There were differences in peripheral blood mt-DNA between patients with COVID-19 (4.25 ng/μl ± 0.30) and controls (3.3 ng/μl ± 0.16) (p = 0.007). Lower mt-DNA concentrations were observed in patients with severe COVID-19 when compared with mild (p= 0.005) and moderate (p= 0.011) cases of COVID-19. In comparison with patients with severe COVID-19 who survived (3.74 ± 0.26 ng/μl) decreased levels of mt-DNA in patients with severe COVID-19 who died (2.4 ± 0.65 ng/μl) were also observed (p = 0.037).

Conclusion

High levels of mt-DNA were associated with COVID-19 and its decrease could be used as a potential biomarker to establish a prognosis of severity and mortality of patients with COVID-19.

Mental Disorders Are Associated With Leukocytes Telomere Shortening Among People Who Inject Drugs

Premature biological aging, assessed by shorter telomere length (TL) and mitochondrial DNA (mtDNA) alterations, has been reported among people with major depressive disorders or psychotic disorders. However, these markers have never been assessed together among people who inject drugs (PWIDs), although mental disorders are highly prevalent in this population, which, in addition, is subject to other aggravating exposures. Diagnosis of mental disorders was performed by a psychiatrist using the Mini International Neuropsychiatric Interview test among active PWIDs in Haiphong, Vietnam. mtDNA copy number (MCN), mtDNA deletion, and TL were assessed by quantitative PCR and compared to those without any mental disorder. We next performed a multivariate analysis to identify risk factors associated with being diagnosed with a major depressive episode (MDE) or a psychotic syndrome (PS). In total, 130 and 136 PWIDs with and without psychiatric conditions were analyzed. Among PWIDs with mental disorders, 110 and 74 were diagnosed with MDE and PS, respectively. TL attrition was significantly associated with hepatitis C virus-infected PWIDs with MDE or PS (adjusted odds ratio [OR]: 0.53 [0.36; 0.80] and 0.59 [0.39; 0.88], respectively). TL attrition was even stronger when PWIDs cumulated at least two episodes of major depressive disorders. On the other hand, no difference was observed in mtDNA alterations between groups. The telomeric age difference with drug users without a diagnosis of psychiatric condition was estimated during 4.2-12.8 years according to the number of MDEs, making this group more prone to age-related diseases.

Androgen Excess Induced Mitochondrial Abnormality in Ovarian Granulosa Cells in a Rat Model of Polycystic Ovary Syndrome

BACKGROUND

Androgen excess could profoundly lead to follicular dysplasia or atresia, and finally result in polycystic ovary syndrome (PCOS); however, the exact mechanism remains to be fully elucidated.

METHODS

PCOS model rats were induced by dehydroepiandrosterone, and their fertility was assessed. The ovarian granulosa cells (GCs) from matured follicles of PCOS model rats were collected and identified by immunofluorescence. The mitochondrial ultrastructure was observed by transmission electron microscope and the mitochondrial function was determined by detecting the adenosine triphosphate (ATP) content and mtDNA copy number. Besides, the expressions of respiratory chain complexes and ATP synthases in relation to mitochondrial function were analyzed.

RESULTS

The PCOS model rats were successfully induced, and their reproductive outcomes were obviously adverse. The GCs layer of the ovarian was apparently cut down and the mitochondrial ultrastructure of ovarian GCs was distinctly destroyed. The ATP content and mtDNA copy number of ovarian GCs in PCOS model rats were greatly reduced, and the expressions of NDUFB8 and ATP5j were significantly down-regulated without obvious deletion of mtDNA 4834-bp.

CONCLUSIONS

Androgen excess could damage mitochondrial ultrastructure and function of GCs in rat ovary by down-regulating expression of NDUFB8 and ATP5j in PCOS.

Mitochondrial genomic integrity and the nuclear epigenome in health and disease

Bidirectional crosstalk between the nuclear and mitochondrial genomes is essential for proper cell functioning. Mitochondrial DNA copy number (mtDNA-CN) and heteroplasmy influence mitochondrial function, which can influence the nuclear genome and contribute to health and disease. Evidence shows that mtDNA-CN and heteroplasmic variation are associated with aging, complex disease, and all-cause mortality. Further, the nuclear epigenome may mediate the effects of mtDNA variation on disease. In this way, mitochondria act as an environmental biosensor translating vital information about the state of the cell to the nuclear genome. Cellular communication between mtDNA variation and the nuclear epigenome can be achieved by modification of metabolites and intermediates of the citric acid cycle and oxidative phosphorylation. These essential molecules (e.g. ATP, acetyl-CoA, ɑ-ketoglutarate and S-adenosylmethionine) act as substrates and cofactors for enzymes involved in epigenetic modifications. The role of mitochondria as an environmental biosensor is emerging as a critical modifier of disease states. Uncovering the mechanisms of these dynamics in disease processes is expected to lead to earlier and improved treatment for a variety of diseases. However, the influence of mtDNA-CN and heteroplasmy variation on mitochondrially-derived epigenome-modifying metabolites and intermediates is poorly understood. This perspective will focus on the relationship between mtDNA-CN, heteroplasmy, and epigenome modifying cofactors and substrates, and the influence of their dynamics on the nuclear epigenome in health and disease.

Polycystic ovarian syndrome: signs and feedback effects of hyperandrogenism and insulin resistance

Polycystic ovary syndrome (PCOS) is a disease whose diagnosis is based on the detection of hyperandrogenism (HA) and ovulatory dysfunction. Women with PCOS frequently develop insulin resistance (IR), which generates a metabolic condition that involves a decrease in the action of insulin at the cellular level and is linked to compensatory hyperinsulinemia (HI). In PCOS, the ovary remains sensitive to the action of insulin. Additionally, it has been observed that the main effect of insulin in the ovary is the stimulation of androgen synthesis, resulting in HA, one of the fundamental characteristics of the PCOS. In this sense, the excess of androgens favors the development of IR, thus perpetuating the cycle of IR-HI-HA, and therefore PCOS. Moreover, mitochondrial dysfunction is present in PCOS patients and is a common feature in both IR and HA. This review places electron transfer as a key element in HA and IR development, with emphasis on the relationship between androgen biosynthesis and mitochondrial function. Indeed, metformin has been involved in repair mitochondrial dysfunction, decrease of oxidative stress, reduction of androgens levels and the enhancing of insulin sensitivity. Therefore, we propose that treatment with metformin could decrease HI and consequently HA, restoring, at least in part, the metabolic and hormonal disorders of PCOS.

Reduced leukocyte mitochondrial copy number in metabolic syndrome and metabolically healthy obesity

OBJECTIVE

This study aimed to investigate the associations between peripheral blood leukocyte mitochondrial copy number, metabolic syndrome, and adiposity-related body composition phenotypes in a high prevalence population.

METHODS

A single center cross-sectional study was conducted, consisting of 521 middle-aged subjects of Maltese-Caucasian ethnicity. Participants were stratified according to the presence of metabolic syndrome and different metabolic health definitions based on NCEP-ATP III criteria. Relative leukocyte mitochondrial DNA copy number was determined by quantitative polymerase chain reaction and corrected for leukocyte and platelet count. The associations between mitochondrial copy number and metabolic syndrome components was evaluated and adjusted for age and gender.

RESULTS

Significant negative correlations between mtDNA copy number and BMI, waist circumference, triglyceride levels, fasting plasma glucose, HbA1c, HOMA-IR and hsCRP were observed, along with a positive correlation with HDL-C levels. Mitochondrial copy number was lower in individuals with metabolic syndrome. When compared to metabolically healthy normal weight subjects, a reduction in mtDNA copy number was observed in both the metabolically healthy and unhealthy obese categories.

CONCLUSION

Our data supports the association between reduced leukocyte mtDNA copy number, obesity, and metabolic syndrome. This investigation expands on the spectrum of associations between mtDNA copy number and metabolic phenotypes in different populations and underpins the role of mitochondrial dysfunction in the development and progression of metabolic syndrome and its components.

Molecular markers of DNA repair and brain metabolism correlate with cognition in centenarians

Oxidative stress is an important factor in age-associated neurodegeneration. Accordingly, mitochondrial dysfunction and genomic instability have been considered as key hallmarks of aging and have important roles in age-associated cognitive decline and neurodegenerative disorders. In order to evaluate whether maintenance of cognitive abilities at very old age is associated with key hallmarks of aging, we measured mitochondrial bioenergetics, mitochondrial DNA copy number and DNA repair capacity in peripheral blood mononuclear cells from centenarians in a Danish 1915 birth cohort (n = 120). Also, the circulating levels of brain-derived neurotrophic factor, NAD⁺ /NADH and carbonylated proteins were measured in plasma of the centenarians and correlated to cognitive capacity. Mitochondrial respiration was well preserved in the centenarian cohort when compared to young individuals (21-35 years of age, n = 33). When correlating cognitive performance of the centenarians with mitochondrial function such as basal respiration, ATP production, reserve capacity and maximal respiration, no overall correlations were observed, but when stratifying by sex, inverse associations were observed in the males (p < 0.05). Centenarians with the most severe cognitive impairment displayed the lowest activity of the central DNA repair enzyme, APE1 (p < 0.05). A positive correlation between cognitive capacity and levels of NAD⁺ /NADH was observed (p < 0.05), which may be because NAD⁺ /NADH consuming enzyme activities strive to reduce the oxidative DNA damage load. Also, circulating protein carbonylation was lowest in centenarians with highest cognitive capacity (p < 0.05). An opposite trend was observed for levels of brain-derived neurotrophic factor (p = 0.17). Our results suggest that maintenance of cognitive capacity at very old age may be associated with cellular mechanisms related to oxidative stress and DNA metabolism.

Placental mtDNA copy number and methylation in association with macrosomia in healthy pregnancy

INTRODUCTION

Fetal growth and development depend on metabolic energy from placental mitochondria. However, the impact of placental mitochondria on the occurrence of macrosomia remains unclear. We aimed to explore the association between macrosomia without gestational diabetes mellitus (non-GDM) and changes in placental mitochondrial DNA (mtDNA) copy number and methylation.

METHODS

Fifty-four newborns with macrosomia and 54 normal birthweight controls were enrolled in this study. Placental mtDNA copy number and mRNA expression of nuclear genes related to mitochondrial replication or ATP synthesis-related genes were measured by real-time quantitative polymerase chain reaction (qPCR). Methylation levels of the non-coding regulatory region D-loop and ATP synthesis-related genes were detected by targeted bisulfite sequencing.

RESULTS

Newborns with macrosomia had lower placental mtDNA copy number and higher methylation rates of the CpG15 site in the D-loop region (D-CpG15) and CpG6 site in the cytochrome C oxidase III (COX3) gene (COX3-CpG6) than normal birth weight newborns. After adjusting for potential covariates (gestational age, prepregnancy BMI, and infant sex), decreased placental mtDNA copy number (adjusted odds ratio [aOR] = 2.09, 95% confidence interval [CI] 1.03-4.25), elevated methylation rate of D-CpG15 (aOR = 2.06, 95% CI 1.03-4.09) and COX3-CpG6 (aOR = 2.13, 95% CI 1.08-4.20) remained significantly associated with a higher risk of macrosomia.

DISCUSSION

Reduced mtDNA copy number and increased methylation levels of specific loci at mtDNA would increase the risk of macrosomia. However, the detailed molecular mechanism needs further identification.

Decreased mitochondrial DNA copy number in nerve cells and the hippocampus during nicotine exposure is mediated by autophagy

Cigarette smoke is a harmful air pollutant and nicotine dependence is the essential cause of the tobacco epidemic. Since mitochondrial abnormalities are associated with substance addiction, in this work we used mitochondrial DNA (mtDNA) copy number as an indicator of mitochondrial function to investigate whether nicotine addicts also exhibit mitochondrial abnormalities. We found significantly lower mtDNA copy number in the peripheral blood of healthy nicotine addicts than in non-smokers, indicating that long-term nicotine exposure through smoking has detrimental effects on mitochondria. We also examined the effects of nicotine on mtDNA levels in a rat conditioned place preference (CPP) model of addiction and in cultured neuron cells, which revealed that the mtDNA copy number was significantly reduced in the hippocampus of CPP rats, in human neuroblastoma SH-SY5Y cells, and in rat pheochromocytoma PC12 cells, suggesting that significantly reduced mtDNA copy number is a potential biomarker of nicotine addiction. In SH-SY5Y cells, nicotine treatment induced several mitochondrial defects, such as increased mtDNA damage, increased reactive oxygen species (ROS) levels, decreased mitochondrial membrane potential (△Ψm), and stimulation of autophagic flux via transcriptional up-regulation of several autophagy-related genes and elevated marker protein accumulation, although genes controlling mtDNA replication were unaffected. In addition, pretreatment with the autophagy inhibitor Bafilomycin A1 led to accumulation of microtubule-associated protein 1 light chain 3b-II (LC3B-II) and counteracted the nicotine-induced decrease in mtDNA copy number. These results were recapitulated in PC12 cells, which also showed significant down-regulation of the marker SQSTM1/P62, suggesting that the decrease in mtDNA copy number is mediated by autophagy. This study shows that prolonged nicotine exposure, such as that in nicotine addicts, leads to a decrease of mtDNA copy number in neurons due to enhanced induction of autophagy. CAPSULE: It was found that smoking or nicotine exposure decreased mtDNA copy number based on population, animal, and cell models, and these effects appear to be mediated by autophagy.

Concurrent Measurement of Mitochondrial DNA Copy Number and ATP Concentration in Single Bovine Oocytes

To sustain energy-demanding developmental processes, oocytes must accumulate adequate stores of metabolic substrates and mitochondrial numbers prior to the initiation of maturation. In the past, researchers have utilized pooled samples to study oocyte metabolism, and studies that related multiple metabolic outcomes in single oocytes, such as ATP concentration and mitochondrial DNA copy number, were not possible. Such scenarios decreased sensitivity to intraoocyte metabolic relationships and made it difficult to obtain adequate sample numbers during studies with limited oocyte availability. Therefore, we developed and validated procedures to measure both mitochondrial DNA (mtDNA) copy number and ATP quantity in single oocytes. Validation of our procedures revealed that we could successfully divide oocyte lysates into quarters and measure consistent results from each of the aliquots for both ATP and mtDNA copy number. Coefficient of variation between the values retrieved for mtDNA copy number and ATP quantity quadruplicates were 4.72 ± 0.98 and 1.61 ± 1.19, respectively. We then utilized our methodology to concurrently measure mtDNA copy number and ATP quantity in germinal vesicle (GV) and metaphase two (MII) stage oocytes. Our methods revealed a significant increase in ATP levels (GV = 628.02 ± 199.53 pg, MII = 1326.24 ± 199.86 pg, p < 0.001) and mtDNA copy number (GV = 490,799.4 ± 544,745.9 copies, MII = 1,087,126.9 ± 902,202.8 copies, p = 0.035) in MII compared to GV stage oocytes. This finding is consistent with published literature and provides further validation of the accuracy of our methods. The ability to produce consistent readings and expected results from aliquots of the lysate from a single oocyte reveals the sensitivity and feasibility of using this method.