Increased plasma levels of circulating cell-free mitochondrial DNA in suicide attempters: associations with HPA-axis hyperactivity

Pilot study of circulating cell-free mitochondrial DNA in relation to brain structure in youth bipolar disorder

BACKGROUND

Mitochondrial dysfunction is implicated in the neuropathology of bipolar disorder (BD). Higher circulating cell-free mitochondrial DNA (ccf-mtDNA), generally reflecting poorer mitochondrial health, has been associated with greater symptoms severity in BD. The current study examines the association of serum ccf-mtDNA and brain structure in relation to youth BD. We hypothesized that higher ccf-mtDNA will be associated with measures of lower brain structure, particularly in the BD group.

METHODS

Participants included 40 youth (BD, n = 19; Control group [CG], n = 21; aged 13-20 years). Serum ccf-mtDNA levels were assayed. T1-weighted brain images were acquired using 3T-MRI. Region of interest (ROI) analyses examined prefrontal cortex (PFC) and whole brain gray matter, alongside exploratory vertex-wise analyses. Analyses examined ccf-mtDNA main-effects and ccf-mtDNA-by-diagnosis interaction effects controlling for age, sex, and intracranial volume.

RESULTS

There was no significant difference in ccf-mtDNA levels between BD and CG. In ROI analyses, higher ccf-mtDNA was associated with higher PFC surface area (SA) (β = 0.32 p < 0.001) and PFC volume (β = 0.32 p = 0.002) in the overall sample. In stratified analyses, higher ccf-mtDNA was associated with higher PFC SA within both subgroups (BD: β = 0.39 p = 0.02; CG: β = 0.24 p = 0.045). Higher ccf-mtDNA was associated with higher PFC volume within the BD group (β = 0.39 p = 0.046). In vertex-wise analyses, higher ccf-mtDNA was associated with higher SA and volume in frontal clusters within the overall sample and within the BD group. There were significant ccf-mtDNA-by-diagnosis interactions in three frontal and parietal clusters, whereby higher ccf-mtDNA was associated with higher neurostructural metrics in the BD group but lower neurostructural metrics in CG.

CONCLUSIONS

Contrasting our hypothesis, higher ccf-mtDNA was consistently associated with higher, rather than lower, regional neuralstructural metrics among youth with BD. While this finding may reflect a compensatory mechanism, future repeated-measures prospective studies evaluating the inter-relationship among ccf-mtDNA, mood, and brain structure across developmental epochs and illness stages are warranted.

Cell-free DNA as a potential diagnostic biomarker in academic stress: A case-control study in young adults

Background

Stress is a pervasive issue in modern life, affecting both physical and mental health. Identifying biomarkers like cell-free DNA (cfDNA) could provide insights into stress response and help detect individuals at risk for stress-related disorders.

Objective

The aim of this study is to investigate the potential use of cfDNA as a diagnostic biomarker in individuals experiencing stress.

Methodology

A case-control analysis was conducted using convenient sampling on university participants (N = 285 cases, N = 500 controls) aged 18-24. The study assessed haematological and lipid profile parameters using the Sysmex XP-300TM automated analyzer and an automated biochemistry analyzer, and cfDNA was extracted using a standardized in house developed Phenol-Chloroform protocol and estimated using Agarose Gel Electrophoresis and Nanodrop. Statistical analysis was performed using SPSS ver. 21.0.

Results

The results indicated a significant difference between stressed individuals and healthy controls in demographic, haematological and biochemical parameters. Specifically, stressed cases had significantly higher levels of cholesterol, LDL cholesterol, triglycerides, glucose, VLDL cholesterol, and lower levels of HDL compared to healthy controls. Stressed cases also showed significantly elevated levels of circulating cfDNA relative to healthy controls.

Conclusion

These findings suggest that cfDNA may have potential as a diagnostic biomarker for stress.

A mitochondrial nexus in major depressive disorder: Integration with the psycho-immune-neuroendocrine network

Nervous system processes, including cognition and affective state, fundamentally rely on mitochondria. Impaired mitochondrial function is evident in major depressive disorder (MDD), reflecting cumulative detrimental influences of both extrinsic and intrinsic stressors, genetic predisposition, and mutation. Glucocorticoid 'stress' pathways converge on mitochondria; oxidative and nitrosative stresses in MDD are largely mitochondrial in origin; both initiate cascades promoting mitochondrial DNA (mtDNA) damage with disruptions to mitochondrial biogenesis and tryptophan catabolism. Mitochondrial dysfunction facilitates proinflammatory dysbiosis while directly triggering immuno-inflammatory activation via released mtDNA, mitochondrial lipids and mitochondria associated membranes (MAMs), further disrupting mitochondrial function and mitochondrial quality control, promoting the accumulation of abnormal mitochondria (confirmed in autopsy studies). Established and putative mechanisms highlight a mitochondrial nexus within the psycho-immune neuroendocrine (PINE) network implicated in MDD. Whether lowering neuronal resilience and thresholds for disease, or linking mechanistic nodes within the MDD pathogenic network, impaired mitochondrial function emerges as an important risk, a functional biomarker, providing a therapeutic target in MDD. Several treatment modalities have been demonstrated to reset mitochondrial function, which could benefit those with MDD.

Circulating cell-free mitochondrial DNA levels and glucocorticoid sensitivity in a cohort of male veterans with and without combat-related PTSD

Circulating cell-free mitochondrial DNA (ccf-mtDNA) is a biomarker of cellular injury or cellular stress and is a potential novel biomarker of psychological stress and of various brain, somatic, and psychiatric disorders. No studies have yet analyzed ccf-mtDNA levels in post-traumatic stress disorder (PTSD), despite evidence of mitochondrial dysfunction in this condition. In the current study, we compared plasma ccf-mtDNA levels in combat trauma-exposed male veterans with PTSD (n = 111) with those who did not develop PTSD (n = 121) and also investigated the relationship between ccf mt-DNA levels and glucocorticoid sensitivity. In unadjusted analyses, ccf-mtDNA levels did not differ significantly between the PTSD and non-PTSD groups (t = 1.312, p = 0.191, Cohen's d = 0.172). In a sensitivity analysis excluding participants with diabetes and those using antidepressant medication and controlling for age, the PTSD group had lower ccf-mtDNA levels than did the non-PTSD group (F(1, 179) = 5.971, p = 0.016, partial η2 = 0.033). Across the entire sample, ccf-mtDNA levels were negatively correlated with post-dexamethasone adrenocorticotropic hormone (ACTH) decline (r = -0.171, p = 0.020) and cortisol decline (r = -0.149, p = 0.034) (viz., greater ACTH and cortisol suppression was associated with lower ccf-mtDNA levels) both with and without controlling for age, antidepressant status and diabetes status. Ccf-mtDNA levels were also significantly positively associated with IC50-DEX (the concentration of dexamethasone at which 50% of lysozyme activity is inhibited), a measure of lymphocyte glucocorticoid sensitivity, after controlling for age, antidepressant status, and diabetes status (β = 0.142, p = 0.038), suggesting that increased lymphocyte glucocorticoid sensitivity is associated with lower ccf-mtDNA levels. Although no overall group differences were found in unadjusted analyses, excluding subjects with diabetes and those taking antidepressants, which may affect ccf-mtDNA levels, as well as controlling for age, revealed decreased ccf-mtDNA levels in PTSD. In both adjusted and unadjusted analyses, low ccf-mtDNA levels were associated with relatively increased glucocorticoid sensitivity, often reported in PTSD, suggesting a link between mitochondrial and glucocorticoid-related abnormalities in PTSD.

Circulating Cell-Free Mitochondrial DNA and Depressive Symptoms Among Low-Active Adults Who Smoke

OBJECTIVES

Mitochondrial dysfunction is implicated in the pathophysiology of psychiatric disorders. Levels of circulating cell-free mitochondrial DNA (cf-mtDNA) are observed to be altered in depression. However, the few studies that have measured cf-mtDNA in depression have reported conflicting findings. This study examined cf-mtDNA and depressive symptoms in low-active adults who smoke.

METHODS

Participants were adults 18 to 65 years old ( N = 109; 76% female) with low baseline physical activity and depressive symptoms recruited for a smoking cessation study. Self-report measures assessed depression severity, positive and negative affect, and behavioral activation. Blood was collected and analyzed for cf-mtDNA. Relationships between depressive symptoms and cf-mtDNA were examined with correlations and linear regression.

RESULTS

Levels of cf-mtDNA were associated with categorically defined depression (Center for Epidemiologic Studies Depression Scale score >15), lower positive affect, and decreased behavioral activation ( p < .05). Relationships remained significant after adjustment for age, sex, and nicotine dependence. In a linear regression model including all depressive symptom measures as predictors, Center for Epidemiologic Studies Depression Scale group and lower positive affect remained significant.

CONCLUSIONS

This work suggests that mitochondrial changes are associated with depressive symptoms in low-active adults who smoke. Higher levels of cf-mtDNA in association with depression and with lower positive affect and decreased behavioral activation are consistent with a possible role for mitochondrial function in depressive symptoms.

Mitochondrial DNA oxidation, methylation, and copy number alterations in major and bipolar depression

Background

Mood disorders are common disabling psychiatric disorders caused by both genetic and environmental factors. Mitochondrial DNA (mtDNA) modifications and epigenetics are promising areas of research in depression since mitochondrial dysfunction has been associated with depression. In this study we aimed to investigate the mtDNA changes in depressive disorder (MDD) and bipolar disorder (BD).

Methods

Displacement loop methylation (D-loop-met), relative mtDNA copy number (mtDNA-cn) and mtDNA oxidation (mtDNA-oxi) were investigated in DNA samples of individuals with MDD (n = 34), BD (n = 23), and healthy controls (HC; n = 40) using the Real-Time Polymerase Chain Reaction (RT-PCR). Blood samples were obtained from a subset of individuals with MDD (n = 15) during a depressive episode (baseline) and after remission (8th week).

Results

The study groups exhibited significant differences in D-loop-met (p = 0.020), while relative mtDNA-cn and mtDNA-oxi showed comparable results. During the remission phase (8th week), there were lower levels of relative mtDNA-cn (Z = -2.783, p = 0.005) and D-loop-met (Z = -3.180, p = 0.001) compared to the acute MDD baseline, with no significant change in mtDNA-oxi levels (Z = -1.193, p = 0.233).

Conclusion

Our findings indicate significantly increased D-loop methylation in MDD compared to BD and HCs, suggesting distinct mtDNA modifications in these conditions. Moreover, the observed alterations in relative mtDNA-cn and D-loop-met during remission suggest a potential role of mtDNA alterations in the pathophysiology of MDD. Future studies may provide valuable insights into the dynamics of mtDNA modifications in both disorders and their response to treatment.

Association between mitochondrial DNA levels and depression: a systematic review and meta-analysis

BACKGROUND

Mitochondrial dysfunction leading to disturbances in energy metabolism has emerged as one of the risk factors in the pathogenesis of depression. Numerous studies have identified alterations in the content of mitochondrial DNA (mtDNA) in peripheral blood and cerebrospinal fluid of individuals with depression. Researchers have sought to establish a clear association between mtDNA and depression. Consequently, we conducted a comprehensive meta-analysis to assess the existing evidence regarding the impact of mtDNA on depression.

METHODS

This study conducted a thorough search of the following databases up to March 13, 2023: PubMed, Embase, the Cochrane Library, the Web of Science, Wanfang Database, SINOMED, the China Science and Technology Journal Database, and China National Knowledge Infrastructure. The meta-analysis was carried out using RevMan (version 5.4) and Stata (version 16.0) software. In addition, publication bias was assessed with funnel plots, Begg's test and Egger's test.

RESULTS

Our analysis included data from 10 articles, including 12 studies for further examination. A total of 1400 participants were included in this study, comprising 709 (including 300 males and 409 females) patients with depression and 691 (including 303 males and 388 females) healthy controls. The average age of depressed patients was (42.98 ± 2.55) years, and the average age of healthy people was (41.71 ± 2.6) years. The scales used to assess outcomes are Hamilton-rating scale for Depression(4 articles), Montgomery-Asberg Depression Rating Scale(3 articles), and Mini-Internatioal Neuropsychiatric Interview (1 articles). The meta-analysis revealed significantly higher levels of mtDNA in circulating blood samples and skin fibroblasts of individuals with depression in comparison to healthy controls [standardized mean difference(SMD) = 0.42, 95% confidence intervals(CI): 0.16, 0.67].

CONCLUSIONS

Our study concludes that there is a significant (p < 0.05) increase in mtDNA levels in serum, plasma, and cerebrospinal fluid in individuals with depression. These findings suggest that mtDNA could serve as a potential biomarker for diagnosing depression.

REGISTRATION NUMBER

PROSPERO CRD42023414285.

Single-Nucleotide Polymorphisms in Genes Maintaining the Stability of Mitochondrial DNA Affect the Occurrence, Onset, Severity and Treatment of Major Depressive Disorder

One of the key features of major depressive disorder (MDD, depression) is increased oxidative stress manifested by elevated levels of mtROS, a hallmark of mitochondrial dysfunction, which can arise from mitochondrial DNA (mtDNA) damage. Thus, the current study explores possibility that the single-nucleotide polymorphisms (SNPs) of genes encoding the three enzymes that are thought to be implicated in the replication, repair or degradation of mtDNA, i.e., POLG, ENDOG and EXOG, have an impact on the occurrence, onset, severity and treatment of MDD. Five SNPs were selected: EXOG c.-188T > G (rs9838614), EXOG c.*627G > A (rs1065800), POLG c.-1370T > A (rs1054875), ENDOG c.-394T > C (rs2977998) and ENDOG c.-220C > T (rs2997922), while genotyping was performed on 538 DNA samples (277 cases and 261 controls) using TaqMan probes. All SNPs of EXOG and ENDOG modulated the risk of depression, but the strongest effect was observed for rs1065800, while rs9838614 and rs2977998 indicate that they might influence the severity of symptoms, and, to a lesser extent, treatment effectiveness. Although the SNP located in POLG did not affect occurrence of the disease, the result suggests that it may influence the onset and treatment outcome. These findings further support the hypothesis that mtDNA damage and impairment in its metabolism play a crucial role not only in the development, but also in the treatment of depression.

Activation of cell-free mtDNA-TLR9 signaling mediates chronic stress-induced social behavior deficits

Inflammation and social behavior deficits are associated with a number of neuropsychiatric disorders. Chronic stress, a major risk factor for depression and other mental health conditions is known to increase inflammatory responses and social behavior impairments. Disturbances in mitochondria function have been found in chronic stress conditions, however the mechanisms that link mitochondrial dysfunction to stress-induced social behavior deficits are not well understood. In this study, we found that chronic restraint stress (RS) induces significant increases in serum cell-free mitochondrial DNA (cf-mtDNA) levels in mice, and systemic Deoxyribonuclease I (DNase I) treatment attenuated RS-induced social behavioral deficits. Our findings revealed potential roles of mitophagy and Mitochondrial antiviral-signaling protein (MAVS) in mediating chronic stress-induced changes in cf-mtDNA levels and social behavior. Furthermore, we showed that inhibition of Toll-like receptor 9 (TLR9) attenuates mtDNA-induced social behavior deficits. Together, these findings show that cf-mtDNA-TLR9 signaling is critical in mediating stress-induced social behavior deficits.

MitoQuicLy: A high-throughput method for quantifying cell-free DNA from human plasma, serum, and saliva

Circulating cell-free mitochondrial DNA (cf-mtDNA) is an emerging biomarker of psychobiological stress and disease which predicts mortality and is associated with various disease states. To evaluate the contribution of cf-mtDNA to health and disease states, standardized high-throughput procedures are needed to quantify cf-mtDNA in relevant biofluids. Here, we describe MitoQuicLy: Mitochondrial DNA Quantification in cell-free samples by Lysis. We demonstrate high agreement between MitoQuicLy and the commonly used column-based method, although MitoQuicLy is faster, cheaper, and requires a smaller input sample volume. Using 10 µL of input volume with MitoQuicLy, we quantify cf-mtDNA levels from three commonly used plasma tube types, two serum tube types, and saliva. We detect, as expected, significant inter-individual differences in cf-mtDNA across different biofluids. However, cf-mtDNA levels between concurrently collected plasma, serum, and saliva from the same individual differ on average by up to two orders of magnitude and are poorly correlated with one another, pointing to different cf-mtDNA biology or regulation between commonly used biofluids in clinical and research settings. Moreover, in a small sample of healthy women and men (n = 34), we show that blood and saliva cf-mtDNAs correlate with clinical biomarkers differently depending on the sample used. The biological divergences revealed between biofluids, together with the lysis-based, cost-effective, and scalable MitoQuicLy protocol for biofluid cf-mtDNA quantification, provide a foundation to examine the biological origin and significance of cf-mtDNA to human health.

A systematic literature review and meta-analysis of circulating nucleic acids as biomarkers in psychiatry

Common mental disorders (CMDs) such as depression, anxiety and post-traumatic stress disorders account for 40% of the global burden of disease. In most psychiatric disorders, both diagnosis and monitoring can be challenging, frequently requiring long-term investigation and follow-up. The discovery of better methods to facilitate accurate and fast diagnosis and monitoring of psychiatric disorders is therefore crucial. Circulating nucleic acids (CNAs) are among these new tools. CNAs (DNA or RNA) can be found circulating in body biofluids, and can be isolated from biological samples such as plasma. They can serve as biomarkers for diagnosis and prognoses. They appear to be promising for disorders (such as psychiatric disorders) that involve organs or structures that are difficult to assess. This review presents an accurate assessment of the current literature about the use of plasma and serum cell-free DNA (cfDNA) as biomarkers for several aspects of psychiatric disorders: diagnosis, prognosis, treatment response, and monitor disease progression. For each psychiatric disorder, we examine the effect sizes to give insights on the efficacy of CNAs as biomarkers. The global effect size for plasma nuclear and mitochondrial cfDNA studies was generally moderate for psychiatric disorders. In addition, we discuss future applications of CNAs and particularly cfDNA as non-invasive biomarkers for these diseases.

Whole blood mitochondrial DNA copy number in depression and response to electroconvulsive therapy

Mitochondrial dysfunction may play a role in various psychiatric conditions. Mitochondrial DNA copy number (mtDNAcn), the ratio of mitochondrial DNA to nuclear DNA, represents an attractive marker of mitochondrial health that is easily measured from stored DNA samples, and has been shown to be altered in depression. In this study, we measured mtDNAcn in whole blood samples from medicated patients with depression (n = 100) compared to healthy controls (n = 89) and determined the relationship between mtDNAcn and depression severity and the therapeutic response to electroconvulsive therapy (ECT). We also explored the relationship between mtDNAcn and telomere length and inflammatory markers. Our results show that mtDNAcn was significantly elevated in blood from patients with depression when compared to control samples, and this result survived statistical adjustment for potential confounders (p = 0.002). mtDNAcn was significantly elevated in blood from subgroups of patients with non-psychotic or unipolar depression. There was no difference in mtDNAcn noted in subgroups of ECT remitters/non-remitters or responders/non-responders. Moreover, mtDNAcn was not associated with depression severity, telomere length, or circulating inflammatory marker concentrations. Overall, our results show that mtDNAcn is elevated in blood from patients with depression, though whether this translates to mitochondrial function is unknown. Further work is required to clarify the contribution of mitochondria and mtDNA to the pathophysiology of depression and the therapeutic response to antidepressant treatments.

Breaking the vicious cycle: The interplay between loneliness, metabolic illness, and mental health

Loneliness, or perceived social isolation, is a leading predictor of all-cause mortality and is increasingly considered a public health epidemic afflicting significant portions of the general population. Chronic loneliness is itself associated with two of the most pressing public health epidemics currently facing the globe: the rise of mental illness and metabolic health disorders. Here, we highlight the epidemiological associations between loneliness and mental and metabolic health disorders and argue that loneliness contributes to the etiology of these conditions by acting as a chronic stressor that leads to neuroendocrine dysregulation and downstream immunometabolic consequences that manifest in disease. Specifically, we describe how loneliness can lead to overactivation of the hypothalamic-pituitary-adrenal axis and ultimately cause mitochondrial dysfunction, which is implicated in mental and metabolic disease. These conditions can, in turn, lead to further social isolation and propel a vicious cycle of chronic illness. Finally, we outline interventions and policy recommendations that can reduce loneliness at both the individual and community levels. Given its role in the etiology of the most prevalent chronic diseases of our time, focusing resources on alleviating loneliness is a vitally important and cost-effective public health strategy.

The Interaction between Circulating Cell-Free Mitochondrial DNA and Inflammatory Cytokines in Predicting Human Mental Health Issue Risk in Adolescents: An Explorative Study

Adolescence is often a challenging time in which psychiatric issues have a strong connection to mental health disorders later in life. The early identification of the problems can reduce the burden of disease. To date, the effective identification of adolescents at risk of developing mental health problems remains understudied. Altogether, the interaction between circulating cell-free mtDNA (ccf-mtDNA) and inflammatory cytokines in adolescents is insufficiently understood regarding experienced mental health difficulties. Our study selected the participants based on the Strength and Difficulty Questionnaire (SDQ) score using the cut-off points of 3 and 18 for the low and the high score groups, respectively. The answers of the SDQ at the age of 12.2-15.7 years contributed to the investigation of (i) whether ccf-mtDNA units are associated with cytokines, and (ii) if an interaction model for predicting risk of mental health issues is observed. We discovered a sex-specific correlation between the screened markers associated with mental health problems in the low and high SDQ score groups among the male participants and in the low SDQ score group among the female participants. The mitochondrial MT-ND4 and MT-CO1 genes correlated significantly with interleukin-12p70 (IL-12p70) in males and with monocyte chemoattractant protein-1 (MCP-1) in females. Due to the nature of the explorative study, the studied markers alone did not indicate statistical significance for the prediction of mental health problems. Our analysis provided new insight into potential plasma-based biomarkers to predict mental health issues.

Oxidized Mitochondrial DNA Engages TLR9 to Activate the NLRP3 Inflammasome in Myelodysplastic Syndromes

Myelodysplastic Syndromes (MDSs) are bone marrow (BM) failure malignancies characterized by constitutive innate immune activation, including NLRP3 inflammasome driven pyroptotic cell death. We recently reported that the danger-associated molecular pattern (DAMP) oxidized mitochondrial DNA (ox-mtDNA) is diagnostically increased in MDS plasma although the functional consequences remain poorly defined. We hypothesized that ox-mtDNA is released into the cytosol, upon NLRP3 inflammasome pyroptotic lysis, where it propagates and further enhances the inflammatory cell death feed-forward loop onto healthy tissues. This activation can be mediated via ox-mtDNA engagement of Toll-like receptor 9 (TLR9), an endosomal DNA sensing pattern recognition receptor known to prime and activate the inflammasome propagating the IFN-induced inflammatory response in neighboring healthy hematopoietic stem and progenitor cells (HSPCs), which presents a potentially targetable axis for the reduction in inflammasome activation in MDS. We found that extracellular ox-mtDNA activates the TLR9-MyD88-inflammasome pathway, demonstrated by increased lysosome formation, IRF7 translocation, and interferon-stimulated gene (ISG) production. Extracellular ox-mtDNA also induces TLR9 redistribution in MDS HSPCs to the cell surface. The effects on NLRP3 inflammasome activation were validated by blocking TLR9 activation via chemical inhibition and CRISPR knockout, demonstrating that TLR9 was necessary for ox-mtDNA-mediated inflammasome activation. Conversely, lentiviral overexpression of TLR9 sensitized cells to ox-mtDNA. Lastly, inhibiting TLR9 restored hematopoietic colony formation in MDS BM. We conclude that MDS HSPCs are primed for inflammasome activation via ox-mtDNA released by pyroptotic cells. Blocking the TLR9/ox-mtDNA axis may prove to be a novel therapeutic strategy for MDS.

Circulating Cell-Free DNA Levels in Psychiatric Diseases: A Systematic Review and Meta-Analysis

The cell-free DNA (cfDNA) levels are known to increase in biological fluids in various pathological conditions. However, the data on circulating cfDNA in severe psychiatric disorders, including schizophrenia, bipolar disorder (BD), and depressive disorders (DDs), is contradictory. This meta-analysis aimed to analyze the concentrations of different cfDNA types in schizophrenia, BD, and DDs compared with healthy donors. The mitochondrial (cf-mtDNA), genomic (cf-gDNA), and total cfDNA concentrations were analyzed separately. The effect size was estimated using the standardized mean difference (SMD). Eight reports for schizophrenia, four for BD, and five for DDs were included in the meta-analysis. However, there were only enough data to analyze the total cfDNA and cf-gDNA in schizophrenia and cf-mtDNA in BD and DDs. It has been shown that the levels of total cfDNA and cf-gDNA in patients with schizophrenia are significantly higher than in healthy donors (SMD values of 0.61 and 0.6, respectively; p < 0.00001). Conversely, the levels of cf-mtDNA in BD and DDs do not differ compared with healthy individuals. Nevertheless, further research is needed in the case of BD and DDs due to the small sample sizes in the BD studies and the significant data heterogeneity in the DD studies. Additionally, further studies are needed on cf-mtDNA in schizophrenia or cf-gDNA and total cfDNA in BD and DDs due to insufficient data. In conclusion, this meta-analysis provides the first evidence of increases in total cfDNA and cf-gDNA in schizophrenia but shows no changes in cf-mtDNA in BD and DDs. Increased circulating cfDNA in schizophrenia may be associated with chronic systemic inflammation, as cfDNA has been found to trigger inflammatory responses.

Plasma circulating cell-free mitochondrial DNA in social anxiety disorder

OBJECTIVE

To investigate plasma levels of circulating cell-free mitochondrial DNA (ccf-mtDNA) in patients with social anxiety disorder (SAD) and healthy controls (HC).

METHODS

In this study, 88 participants (46 patients with SAD and 42 HCs) were enrolled and both ccf-mtDNA and peripheral blood mononuclear cells (PBMC) mtDNA copy number (mtDNA-cn) were measured at up to three times per individual (9-11 weeks apart). SAD patients also received cognitive behavioral therapy (CBT) between the second and third time-point.

RESULTS

SAD patients had significantly lower ccf-mtDNA compared to HCs at all time points, but ccf-mtDNA did not change significantly after CBT, and was not associated with severity of anxiety symptoms. Plasma ccf-mtDNA did not significantly correlate with PBMC mtDNA-cn in patients.

CONCLUSION

This is the first report of lower ccf-mtDNA in patients with an anxiety disorder. Our findings could reflect a more chronic illness course in SAD patients with prolonged periods of psychological stress leading to decreased levels of ccf-mtDNA, but future longitudinal studies are needed to confirm or refute this hypothesis.

MitoQuicLy: a high-throughput method for quantifying cell-free DNA from human plasma, serum, and saliva

Circulating cell-free mitochondrial DNA (cf-mtDNA) is an emerging biomarker of psychobiological stress and disease which predicts mortality and is associated with various disease states. To evaluate the contribution of cf-mtDNA to health and disease states, standardized high-throughput procedures are needed to quantify cf-mtDNA in relevant biofluids. Here, we describe MitoQuicLy: Mito chondrial DNA Qu antification in c ell-free samples by Ly sis. We demonstrate high agreement between MitoQuicLy and the commonly used column-based method, although MitoQuicLy is faster, cheaper, and requires a smaller input sample volume. Using 10 µL of input volume with MitoQuicLy, we quantify cf-mtDNA levels from three commonly used plasma tube types, two serum tube types, and saliva. We detect, as expected, significant inter-individual differences in cf-mtDNA across different biofluids. However, cf-mtDNA levels between concurrently collected plasma, serum, and saliva from the same individual differ on average by up to two orders of magnitude and are poorly correlated with one another, pointing to different cf-mtDNA biology or regulation between commonly used biofluids in clinical and research settings. Moreover, in a small sample of healthy women and men (n=34), we show that blood and saliva cf-mtDNAs correlate with clinical biomarkers differently depending on the sample used. The biological divergences revealed between biofluids, together with the lysis-based, cost-effective, and scalable MitoQuicLy protocol for biofluid cf-mtDNA quantification, provide a foundation to examine the biological origin and significance of cf-mtDNA to human health.

Major depression and the biological hallmarks of aging

Major depressive disorder (MDD) is characterized by psychological and physiological manifestations contributing to the disease severity and outcome. In recent years, several lines of evidence have suggested that individuals with MDD have an elevated risk of age-related adverse outcomes across the lifespan. This review provided evidence of a significant overlap between the biological abnormalities in MDD and biological changes commonly observed during the aging process (i.e., hallmarks of biological aging). Based on such evidence, we formulate a mechanistic model showing how abnormalities in the hallmarks of biological aging can be a common denominator and mediate the elevated risk of age-related health outcomes commonly observed in MDD. Finally, we proposed a roadmap for novel studies to investigate the intersection between the biology of aging and MDD, including the use of geroscience-guided interventions, such as senolytics, to delay or improve major depression by targeting biological aging.

Circulating inflammatory markers, cell-free mitochondrial DNA, cortisol, endocannabinoids, and N-acylethanolamines in female depressed outpatients

OBJECTIVES

Major depressive disorder (MDD) involves peripheral low-grade pro-inflammatory activity. This multi-biomarker case-control study characterises the proinflammatory status in MDD beyond C-reactive protein (CRP) and Interleukin (IL)-6 levels through investigating concomitant alterations of immunoregulatory biomolecules.

METHODS

In 20 female MDD patients and 24 non-depressed women, circulating levels of CRP, IL-6, cortisol, selected endocannabinoids (ECs; anandamide [AEA], 2-arachidonylglycerol [2-AG]), and N-acylethanolamines (NAEs), as well as circulating cell-free mitochondrial DNA (ccf-mtDNA) were measured.

RESULTS

We found higher serum CRP and plasma AEA levels in MDD and a positive association of CRP and AEA levels with current depressive symptoms. Blood levels of cortisol, ccf-mtDNA, 2-AG, and NAEs did depend on MDD diagnosis nor correlated with the severity of current depressive symptoms. CRP correlated positively with AEA, and AEA showed positive associations with 2-AG and NAE levels.

CONCLUSIONS

In this study, female MDD outpatients with mild to moderate disorder severity did not substantially differ from non-depressed controls in the resting levels of multiple immunoregulatory markers in peripheral blood. Instead of investigating resting levels, future research on the role of inflammatory activity in MDD should focus on investigating the reactivity of pathways modulating the immune system upon exposure to physical and psychosocial stressors.

Mitochondrial signal transduction

The analogy of mitochondria as powerhouses has expired. Mitochondria are living, dynamic, maternally inherited, energy-transforming, biosynthetic, and signaling organelles that actively transduce biological information. We argue that mitochondria are the processor of the cell, and together with the nucleus and other organelles they constitute the mitochondrial information processing system (MIPS). In a three-step process, mitochondria (1) sense and respond to both endogenous and environmental inputs through morphological and functional remodeling; (2) integrate information through dynamic, network-based physical interactions and diffusion mechanisms; and (3) produce output signals that tune the functions of other organelles and systemically regulate physiology. This input-to-output transformation allows mitochondria to transduce metabolic, biochemical, neuroendocrine, and other local or systemic signals that enhance organismal adaptation. An explicit focus on mitochondrial signal transduction emphasizes the role of communication in mitochondrial biology. This framework also opens new avenues to understand how mitochondria mediate inter-organ processes underlying human health.

New Perspectives on the Importance of Cell-Free DNA Biology

Body fluids are constantly replenished with a population of genetically diverse cell-free DNA (cfDNA) fragments, representing a vast reservoir of information reflecting real-time changes in the host and metagenome. As many body fluids can be collected non-invasively in a one-off and serial fashion, this reservoir can be tapped to develop assays for the diagnosis, prognosis, and monitoring of wide-ranging pathologies, such as solid tumors, fetal genetic abnormalities, rejected organ transplants, infections, and potentially many others. The translation of cfDNA research into useful clinical tests is gaining momentum, with recent progress being driven by rapidly evolving preanalytical and analytical procedures, integrated bioinformatics, and machine learning algorithms. Yet, despite these spectacular advances, cfDNA remains a very challenging analyte due to its immense heterogeneity and fluctuation in vivo. It is increasingly recognized that high-fidelity reconstruction of the information stored in cfDNA, and in turn the development of tests that are fit for clinical roll-out, requires a much deeper understanding of both the physico-chemical features of cfDNA and the biological, physiological, lifestyle, and environmental factors that modulate it. This is a daunting task, but with significant upsides. In this review we showed how expanded knowledge on cfDNA biology and faithful reverse-engineering of cfDNA samples promises to (i) augment the sensitivity and specificity of existing cfDNA assays; (ii) expand the repertoire of disease-specific cfDNA markers, thereby leading to the development of increasingly powerful assays; (iii) reshape personal molecular medicine; and (iv) have an unprecedented impact on genetics research.

Dynamic behavior of cell-free mitochondrial DNA in human saliva

Mitochondria contain their own genome that can be released in multiple biofluids such as blood and cerebrospinal fluid, as cell-free mitochondrial DNA (cf-mtDNA). In clinical studies, blood cf-mtDNA predicts mortality and higher cf-mtDNA levels are associated with mental and physical stress. However, the dynamics of cf-mtDNA has not been defined, and whether it can be measured non-invasively like other neuroendocrine markers in saliva has not been examined. Here we report cf-mtDNA in human saliva and establish its natural within-person dynamic behavior across multiple weeks. In a small proof-of-principle cohort of healthy adults, we first develop an approach to rapidly quantify salivary cf-mtDNA without DNA isolation, and demonstrate the existence of salivary cf-mtDNA. We then deploy this approach to perform an intensive repeated-measures analysis of two healthy men studied at 4 daily timepoints over 53-60 consecutive days (n = 212-220 observations each) with parallel measures of steroid hormones, self-reported daily mood, and health-related behaviors. Salivary cf-mtDNA exhibited a robust awakening response reaching up to two orders of magnitude 30-45 min after awakening, varied from day-to-day, and moderately correlated with the cortisol awakening response. In exploratory analyses, no consistent association with self-reported daily mood/health-related behaviors were found, although this requires further examination in future studies. Dynamic variation in cf-mtDNA was inversely related with salivary interleukin 6 (IL-6), inconsistent with a pro-inflammatory effect of salivary cf-mtDNA. The highly dynamic behavior of salivary cf-mtDNA opens the door to non-invasive studies examining the relevance of mtDNA signaling in relation to human health.

Mitochondrial DNA Together with miR-142-3p in Plasma Can Predict Unfavorable Outcomes in Patients after Acute Myocardial Infarction

Myocardial infarction is one of the leading causes of death worldwide, despite numerous efforts to find efficient prognostic biomarkers and treatment targets. In the present study, we aimed to assess the potential of six microRNAs known to be involved in cardiovascular diseases, cell-free DNA (cfDNA), and mitochondrial DNA (mtDNA) circulating in plasma to be used as prognostic tools for the occurrence of unfavorable outcomes such as major adverse cardiovascular events (MACE) after acute ST-segment elevation myocardial infarction (STEMI). Fifty STEMI patients were enrolled and monitored for 6 months for the occurrence of MACE. Plasma was collected at three time points: upon admission to hospital (T0), at discharge from hospital (T1), and 6 months post-STEMI (T6). Plasma levels of miR-223-3p, miR-142-3p, miR-155-5p, miR-486-5p, miR-125a-5p, and miR-146a-5p, as well as of cfDNA and mtDNA, were measured by RT-qPCR. Results showed that the levels of all measured miRNAs, as well as of cfDNA and mtDNA, were the most increased at T1, compared to the other two time points. In the plasma of STEMI patients with MACE compared to those without MACE, we determined increased levels of miRNAs, cfDNA, and mtDNA at T1. Hence, we used the levels of all measured parameters at T1 for further statistical analysis. Statistical analysis demonstrated that all six miRNAs and cfDNA plus mtDNA levels, respectively, were associated with MACE. The minimal statistical model that could predict MACE in STEMI patients was the combination of mtDNA and miR-142-3p levels, as evidenced by ROC analysis (AUC = 0.97, p < 0.001). In conclusion, the increased plasma levels of mtDNA, along with miR-142-3p, could be used to predict unfavorable outcomes in STEMI patients.

Hair cortisol level might be indicative for a 3PM approach towards suicide risk assessment in depression: comparative analysis of mentally stable and depressed individuals versus individuals after completing suicide

Depression and suicidal behavior are interrelated, stress-associated mental health conditions, each lacking biological verifiability. Concepts of predictive, preventive, and personalized medicine (3PM) are almost completely missing for both conditions but are of utmost importance. Prior research reported altered levels of the stress hormone cortisol in the scalp hair of depressed individuals, however, data on hair cortisol levels (HCL) for suicide completers (SC) are missing. Here, we aimed to identify differences in HCL between subject with depression (n = 20), SC (n = 45) and mentally stable control subjects (n = 12) to establish the usage of HCL as a new target for 3PM. HCL was measured in extracts of pulverized hair (1-cm and 3-cm hair segments) using ELISA. In 3-cm hair segments, an average increase in HCL for depressed patients (1.66 times higher; p = .011) and SC (5.46 times higher; p = 1.65 × 10⁻⁵) compared to that for controls was observed. Furthermore, the average HCL in SC was significantly increased compared to that in the depressed group (3.28 times higher; p = 1.4 × 10⁻⁵). A significant correlation between HCL in the 1-cm and the 3-cm hair segments, as well as a significant association between the severity of depressive symptoms and HCL (3-cm segment) was found. To conclude, findings of increased HCL in subjects with depression compared to that in controls were replicated and an additional increase in HCL was seen in SC in comparison to patients with depression. The usage of HCL for creating effective patient stratification and predictive approach followed by the targeted prevention and personalization of medical services needs to be validated in follow-up studies.

Developmental Timing of Trauma in Women Predicts Unique Extracellular Vesicle Proteome Signatures

BACKGROUND

Exposure to traumatic events is a risk factor for negative physical and mental health outcomes. However, the underlying biological mechanisms that perpetuate these lasting effects are not known.

METHODS

We investigated the impact and timing of sexual trauma, a specific type of interpersonal violence, experienced during key developmental windows of childhood, adolescence, or adulthood on adult health outcomes and associated biomarkers, including circulating cell-free mitochondrial DNA levels and extracellular vesicles (EVs), in a predominantly Black cohort of women (N = 101).

RESULTS

Significant changes in both biomarkers examined, circulating cell-free mitochondrial DNA levels and EV proteome, were specific to developmental timing of sexual trauma. Specifically, we identified a large number of keratin-related proteins from EVs unique to the adolescent sexual trauma group. Remarkably, the majority of these keratin proteins belong to a 17q21 gene cluster, which suggests a potential local epigenetic regulatory mechanism altered by adolescent trauma to impact keratinocyte EV secretion or its protein cargo. These results, along with changes in fear-potentiated startle and skin conductance detected in these women, suggest that sexual violence experienced during the specific developmental window of adolescence may involve unique programming of the skin, the body's largest stress organ.

CONCLUSIONS

Together, these descriptive studies provide novel insight into distinct biological processes altered by trauma experienced during specific developmental windows. Future studies will be required to mechanistically link these biological processes to health outcomes.

Circulating cell-free mitochondrial DNA in brain health and disease: A systematic review and meta-analysis

OBJECTIVES

Circulating cell-free mitochondrial DNA (ccf-mtDNA) are detectable fragments of mtDNA released from the cell as a result of mitochondrial dysfunction or apoptosis. The brain is one of the most energy demanding organs in the human body, and many neuropsychiatric and non-psychiatric neurological diseases have mitochondrial dysfunction associated with disease pathophysiology. Thus, we aimed to assess ccf-mtDNA as a potential biomarker for brain diseases.

METHODS

We conducted a systematic review and meta-analyses of studies that examined peripheral and/or cerebrospinal fluid (CSF) ccf-mtDNA relevant to neuropsychiatric conditions, which we define as disorders of affect, behaviour and mood, and non-psychiatric neurological diseases, which consist of neurological diseases not related to psychiatry including neurodegenerative diseases.

RESULTS

The results of the sensitivity analysis investigating the levels of peripheral ccf-mtDNA in neuropsychiatric studies showed no significant difference between cases and controls (Z = 1.57; p = 0.12), whereas the results of the sensitivity analysis investigating the levels of CSF ccf-mtDNA in non-psychiatric neurological diseases showed a decreasing trend in cases compared with controls (Z = 2.32; p = 0.02). Interestingly, the results indicate an overall mitochondrial stress associated mainly with non-psychiatric neurological diseases.

CONCLUSIONS

Our study supports the involvement of mitochondrial stress, here defined as ccf-mtDNA, in brain diseases and encourage further investigation of ccf-mtDNA among patients with brain diseases.

Plasma Cell-Free DNA Methylomics of Bipolar Disorder With and Without Rapid Cycling

Rapid cycling (RC) burdens bipolar disorder (BD) patients further by causing more severe disability and increased suicidality. Because diagnosing RC can be challenging, RC patients are at risk of rapid decline due to delayed suitable treatment. Here, we aimed to identify the differences in the circulating cell-free DNA (cfDNA) methylome between BD patients with and without RC. The cfDNA methylome could potentially be developed as a diagnostic test for BD RC. We extracted cfDNA from plasma samples of BD1 patients (46 RC and 47 non-RC). cfDNA methylation levels were measured by 850K Infinium MethylationEPIC array. Principal component analysis (PCA) was conducted to assess global differences in methylome. cfDNA methylation levels were compared between RC groups using a linear model adjusted for age and sex. PCA suggested differences in methylation profiles between RC groups (p = 0.039) although no significant differentially methylated probes (DMPs; q > 0.15) were found. The top four CpG sites which differed between groups at p < 1E-05 were located in CGGPB1, PEX10, NR0B2, and TP53I11. Gene set enrichment analysis (GSEA) on top DMPs (p < 0.05) showed significant enrichment of gene sets related to nervous system tissues, such as neurons, synapse, and glutamate neurotransmission. Other top notable gene sets were related to parathyroid regulation and calcium signaling. To conclude, our study demonstrated the feasibility of utilizing a microarray method to identify circulating cfDNA methylation sites associated with BD RC and found the top differentially methylated CpG sites were mostly related to the nervous system and the parathyroid.

Blood-based mitochondrial respiratory chain function in major depression

Mitochondrial dysfunction has been implicated in major depressive disorder (MDD). A measure of mitochondrial respiratory chain (RC) enzymatic activity-the Mitochondrial Health Index (MHI)-has previously been found to correlate with stress and emotional states in caregivers. We here report mitochondrial RC activities, mitochondrial DNA copy number (mtDNAcn), and the composite MHI in unmedicated and somatically healthy subjects with MDD (n = 47) and healthy controls (HC) (n = 11). We also explore, in a subset of the MDD sample (n = 33), whether these markers are associated with response to 8 weeks of SSRI treatment. Mitochondrial RC complexes I, II, IV, citrate synthase (CS), mtDNAcn, and the MHI were assayed in peripheral blood mononuclear cells. Treatment response was defined as >50% decrease on the 25-item Hamilton Depression Rating Scale (HRDS-25). There were no significant differences in MHI or any of the mitochondrial markers between MDD subjects and HCs. Compared to SSRI nonresponders, SSRI responders had significantly higher baseline mitochondrial content markers CS (p = 0.02) and mtDNAcn (p = 0.02), and higher complex I activity (p = 0.01). Complex II activity increased significantly over treatment, irrespective of clinical response (p = 0.03). Complex I activity decreased in responders (n = 9), but increased in nonresponders (n = 18) (group x time interaction, p = 0.02). Absolute treatment-associated change in HDRS-25 scores correlated significantly with change in complex I activity between baseline and week 8 (r = 0.47, p = 0.01). Although mitochondrial markers did not distinguish MDD from controls, they did distinguish SSRI responders from nonresponders. If larger studies validate these mitochondrial differences, they may become useful biomarkers and identify new drug targets.

Plasma circulating cell-free mitochondrial DNA in depressive disorders

Background

Plasma circulating cell-free mitochondrial DNA (ccf-mtDNA) is an immunogenic molecule and a novel biomarker of psychiatric disorders. Some previous studies reported increased levels of ccf-mtDNA in unmedicated depression and recent suicide attempters, while other studies found unchanged or decreased ccf-mtDNA levels in depression. Inconsistent findings across studies may be explained by small sample sizes and between-study variations in somatic and psychiatric co-morbidity or medication status.

Methods

We measured plasma ccf-mtDNA in a cohort of 281 patients with depressive disorders and 49 healthy controls. Ninety-three percent of all patients were treated with one or several psychotropic medications. Thirty-six percent had a personality disorder, 13% bipolar disorder. All analyses involving ccf-mtDNA were a priori adjusted for age and sex.

Results

Mean levels in ccf-mtDNA were significantly different between patients with a current depressive episode (n = 236), remitted depressive episode (n = 45) and healthy controls (n = 49) (f = 8.3, p<0.001). Post-hoc tests revealed that both patients with current (p<0.001) and remitted (p = 0.002) depression had lower ccf-mtDNA compared to controls. Within the depressed group there was a positive correlation between ccf-mtDNA and “inflammatory depression symptoms” (r = 0.15, p = 0.02). We also found that treatment with mood stabilizers lamotrigine, valproic acid or lithium was associated with lower ccf-mtDNA (f = 8.1, p = 0.005).

Discussion

Decreased plasma ccf-mtDNA in difficult-to-treat depression may be partly explained by concurrent psychotropic medications and co-morbidity. Our findings suggest that ccf-mtDNA may be differentially regulated in different subtypes of depression, and this hypothesis should be pursued in future studies.

Mitophagy in depression: Pathophysiology and treatment targets

Mitochondria, the 'powerhouse' of eukaryotic cells, play a key role in cellular homeostasis. However, defective mitochondria increase mitochondrial ROS (mtROS) production and cell-free mitochondrial DNA (mtDNA) release, leading to increased inflammation. Mitophagy is a vital pathway, which selectively removes defective mitochondria through the process of autophagy. Thus, an impairment in the mitophagy pathway might trigger the gradual accumulation of defective mitochondria. Accumulating evidence suggest that inflammation and mitochondrial dysfunction are linked to the pathogenesis of depression. In this article, we have reviewed the role of impaired mitophagy as a contributing factor in depression pathophysiology. Further, we have discussed the potential therapeutic interventions aimed at modulating mitophagy in depression.

Extracellular Mitochondrial Components and Effects on Cardiovascular Disease

Besides being powerhouses of the cell, mitochondria released into extracellular space act as intercellular signaling. Mitochondria and their components mediate cell-to-cell communication in free form or embedded in a carrier. The pathogenesis of cardiovascular disease is complex, which shows close relationship with inflammation and metabolic abnormalities. Since mitochondria sustain optimal function of the heart, extracellular mitochondria are emerging as a key regulator in the development of cardiovascular disease. In this review, we provide recent findings in the presence and forms of mitochondria transfer between cells, as well as the effects of these mitochondria on vascular inflammation and ischemic myocardium. Mitochondrial transplantation is a novel treatment paradigm for patients suffering from acute cardiovascular accident and challenges the traditional methods of mitochondria isolation.

Aging: All roads lead to mitochondria

Mitochondria were described as early as 1890 as ubiquitous intracellular structures by Ernster and Schatz (1981) [1]. Since then, the accretion of knowledge in the past century has revealed much of the molecular details of mitochondria, ranging from mitochondrial origin, structure, metabolism, genetics, and signaling, and their implications in health and disease. We now know that mitochondria are remarkably multifunctional and deeply intertwined with many vital cellular processes. They are quasi-self organelles that still possess remnants of its bacterial ancestry, including an independent genome. The mitochondrial free radical theory of aging (MFRTA), which postulated that aging is a product of oxidative damage to mitochondrial DNA, provided a conceptual framework that put mitochondria on the map of aging research. However, several studies have more recently challenged the general validity of the theory, favoring novel ideas based on emerging evidence to understand how mitochondria contribute to aging and age-related diseases. One prominent topic of investigation lies on the fact that mitochondria are not only production sites for bioenergetics and macromolecules, but also regulatory hubs that communicate and coordinate many vital physiological processes at the cellular and organismal level. The bi-directional communication and coordination between the co-evolved mitochondrial and nuclear genomes is especially interesting in terms of cellular regulation. Mitochondria are dynamic and adaptive, rendering their function sensitive to cellular context. Tissues with high energy demands, such as the brain, seem to be uniquely affected by age-dependent mitochondrial dysfunction, providing a foundation for the development of novel mitochondrial-based therapeutics and diagnostics.

Increased levels of circulating cell-free mtDNA in plasma of late life depression subjects

BACKGROUND

Oxidative stress (OS) has been implicated in the pathophysiology of late-life depression (LLD). Mitochondria are the primary source of oxidative stress and can be significantly damaged with increased OS. Circulating cell-free mtDNA (ccf-mtDNA) is a marker of cellular stress and mitochondria damage triggered by oxidative stress.

METHODS

We evaluated the plasma levels of ccf-mtDNA in between 32 LLD and 21 never-depressed participants. We also investigated the association between ccf-mtDNA and the severity of depressive episodes and cognition performance.

RESULTS

We found a higher ccf-mtDNA level in LLD cases compared with controls (t = -2.91, p = 0.005). Also, ccf-mtDNA was significantly correlated with the severity of depression (r = 0.42, p = 0.001). There was no significant correlation between ccf-mtDNA and measures of cognitive decline.

LIMITATIONS

The small sample size and cross-sectional design were the main limitations of this study.

CONCLUSION

Our results suggest that LLD is associated with elevated mitochondrial damage and cellular stress. If validated, the measurement of ccf-mtDNA in LLD can guide the development of novel treatments focused on cytoprotection and reduction of mitochondrial dysfunction for this condition.

Stress and circulating cell-free mitochondrial DNA: A systematic review of human studies, physiological considerations, and technical recommendations

Cell-free mitochondrial DNA (cf-mtDNA) is a marker of inflammatory disease and a predictor of mortality, but little is known about cf-mtDNA in relation to psychobiology. A systematic review of the literature reveals that blood cf-mtDNA varies in response to common real-world stressors including psychopathology, acute psychological stress, and exercise. Moreover, cf-mtDNA is inducible within minutes and exhibits high intra-individual day-to-day variation, highlighting the dynamic regulation of cf-mtDNA levels. We discuss current knowledge on the mechanisms of cf-mtDNA release, its forms of transport ("cell-free" does not mean "membrane-free"), potential physiological functions, putative cellular and neuroendocrine triggers, and factors that may contribute to cf-mtDNA removal from the circulation. A review of in vitro, pre-clinical, and clinical studies shows conflicting results around the dogma that physiological forms of cf-mtDNA are pro-inflammatory, opening the possibility of other physiological functions, including the cell-to-cell transfer of whole mitochondria. Finally, to enhance the reproducibility and biological interpretation of human cf-mtDNA research, we propose guidelines for blood collection, cf-mtDNA isolation, quantification, and reporting standards, which can promote concerted advances by the community. Defining the mechanistic basis for cf-mtDNA signaling is an opportunity to elucidate the role of mitochondria in brain-body interactions and psychopathology.

Evidence for the Role of Mitochondrial DNA Release in the Inflammatory Response in Neurological Disorders

Mitochondria are regarded as the metabolic centers of cells and are integral in many other cell processes, including the immune response. Each mitochondrion contains numerous copies of mitochondrial DNA (mtDNA), a small, circular, and bacterial-like DNA. In response to cellular damage or stress, mtDNA can be released from the mitochondrion and trigger immune and inflammatory responses. mtDNA release into the cytosol or bloodstream can occur as a response to hypoxia, sepsis, traumatic injury, excitatory cytotoxicity, or drastic mitochondrial membrane potential changes, some of which are hallmarks of neurodegenerative and mood disorders. Released mtDNA can mediate inflammatory responses observed in many neurological and mood disorders by driving the expression of inflammatory cytokines and the interferon response system. The current understanding of the role of mtDNA release in affective mood disorders and neurodegenerative diseases will be discussed.

Mitochondria and early-life adversity

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

Cell-free DNA (cfDNA) and Exosome Profiling from a Year-Long Human Spaceflight Reveals Circulating Biomarkers

Liquid biopsies based on cell-free DNA (cfDNA) or exosomes provide a noninvasive approach to monitor human health and disease but have not been utilized for astronauts. Here, we profile cfDNA characteristics, including fragment size, cellular deconvolution, and nucleosome positioning, in an astronaut during a year-long mission on the International Space Station, compared to his identical twin on Earth and healthy donors. We observed a significant increase in the proportion of cell-free mitochondrial DNA (cf-mtDNA) inflight, and analysis of post-flight exosomes in plasma revealed a 30-fold increase in circulating exosomes and patient-specific protein cargo (including brain-derived peptides) after the year-long mission. This longitudinal analysis of astronaut cfDNA during spaceflight and the exosome profiles highlights their utility for astronaut health monitoring, as well as cf-mtDNA levels as a potential biomarker for physiological stress or immune system responses related to microgravity, radiation exposure, and the other unique environmental conditions of spaceflight.

Severe life stress, mitochondrial dysfunction, and depressive behavior: A pathophysiological and therapeutic perspective

Mitochondria are responsible for providing our cells with energy, as well as regulating oxidative stress and apoptosis, and considerable evidence demonstrates that mitochondria-related alterations are prevalent during chronic stress and depression. Here, we discuss how chronic stress may induce depressive behavior by potentiating mitochondrial allostatic load, which ultimately decreases energy production, elevates the generation of harmful reactive oxygen species, damages mitochondrial DNA and increases membrane permeability and pro-apoptotic factor release. We also discuss how mitochondrial insults can exacerbate the immune response, contributing to depressive symptomology. Furthermore, we illustrate how depression symptoms are associated with specific mitochondrial defects, and how targeting of these defects with pharmacological agents may be a promising avenue for the development of novel, more efficacious antidepressants. In summary, this review supports the notion that severe psychosocial stress induces mitochondrial dysfunction, thereby increasing the vulnerability to developing depressive symptoms.

Animal models built for women's brain health: Progress and potential

Women and men have different levels of risk for a variety of brain disorders. Despite this well-known epidemiological finding, preclinical work utilizing animal models has historically only included male animals. The policies of funders to require consideration of sex as a biological variable has shifted the momentum to include female animals in preclinical neuroscience and to report findings by sex. However, there are many biological questions related to brain health that go beyond sex differences and are indeed specific to women. Here, the focus is on why animal models should be utilized in the pursuit of understanding women's brain health, a brief overview of what they have provided thus far, and why they still hold tremendous promise. This review concludes with a set of suggestions for how to begin to pursue translational animal models in a way that facilitates rapid success and harnesses the most powerful aspects of animal models.

Molecular correlates of mitochondrial dysfunctions in major depression: Evidence from clinical and rodent studies

Major depressive disorder (MDD) is one of the most prevalent stress-related mental disorders worldwide. Several biological mechanisms underlying the pathophysiology of MDD have been proposed, including endocrine disturbances, neurotransmitter deficits, impaired neuronal plasticity, and more recently, mitochondrial dysfunctions. In this review, we provide an overview of relevant molecular correlates of mitochondrial dysfunction in MDD, based on findings from clinical studies and stress-induced rodent models. We also compare differences and similarities between the phenotypes of MDD patients and animal models. Our analysis of the literature reveals that both MDD and stress are associated, in humans and animals, with changes in mitochondrial biogenesis, redox imbalance, increased oxidative damages of cellular macromolecules, and apoptosis. Yet, a considerable amount of conflicting data exist and therefore, the translation of findings from clinical and preclinical research to novel therapies for MDD remains complex. Further studies are needed to advance our understanding of the molecular networks and biological mechanisms involving mitochondria in the pathophysiology of MDD.

An automated, high-throughput methodology optimized for quantitative cell-free mitochondrial and nuclear DNA isolation from plasma

Progress in the study of circulating, cell-free nuclear DNA (ccf-nDNA) in cancer detection has led to the development of noninvasive clinical diagnostic tests and has accelerated the evaluation of ccf-nDNA abundance as a disease biomarker. Likewise, circulating, cell-free mitochondrial DNA (ccf-mtDNA) is under similar investigation. However, optimal ccf-mtDNA isolation parameters have not been established, and inconsistent protocols for ccf-nDNA collection, storage, and analysis have hindered its clinical utility. Until now, no studies have established a method for high-throughput isolation that considers both ccf-nDNA and ccf-mtDNA. We initially optimized human plasma digestion and extraction conditions for maximal recovery of these DNAs using a magnetic bead-based isolation method. However, when we incorporated this method onto a high-throughput platform, initial experiments found that DNA isolated from identical human plasma samples displayed plate edge effects resulting in low ccf-mtDNA reproducibility, whereas ccf-nDNA was less affected. Therefore, we developed a detailed protocol optimized for both ccf-mtDNA and ccf-nDNA recovery that uses a magnetic bead-based isolation process on an automated 96-well platform. Overall, we calculate an improved efficiency of recovery of ∼95-fold for ccf-mtDNA and 20-fold for ccf-nDNA when compared with the initial procedure. Digestion conditions, liquid-handling characteristics, and magnetic particle processor programming all contributed to increased recovery without detectable positional effects. To our knowledge, this is the first high-throughput approach optimized for ccf-mtDNA and ccf-nDNA recovery and serves as an important starting point for clinical studies.

The social nature of mitochondria: Implications for human health

Sociality has profound evolutionary roots and is observed from unicellular organisms to multicellular animals. In line with the view that social principles apply across levels of biological complexity, a growing body of data highlights the remarkable social nature of mitochondria - life-sustaining endosymbiotic organelles with their own genome that populate the cell cytoplasm. Here, we draw from organizing principles of behavior in social organisms to reveal that similar to individuals among social networks, mitochondria communicate with each other and with the cell nucleus, exhibit group formation and interdependence, synchronize their behaviors, and functionally specialize to accomplish specific functions within the organism. Mitochondria are social organelles. The extension of social principles across levels of biological complexity is a theoretical shift that emphasizes the role of communication and interdependence in cell biology, physiology, and neuroscience. With the help of emerging computational methods capable of capturing complex dynamic behavioral patterns, the implementation of social concepts in mitochondrial biology may facilitate cross-talk across disciplines towards increasingly holistic and accurate models of human health.

Mitochondrial respiratory capacity modulates LPS-induced inflammatory signatures in human blood

Mitochondria modulate inflammatory processes in various model organisms, but it is unclear how much mitochondria regulate immune responses in human blood leukocytes. Here, we examine the effect of i) experimental perturbations of mitochondrial respiratory chain function, and ii) baseline inter-individual variation in leukocyte mitochondrial energy production capacity on stimulated cytokine release and glucocorticoid (GC) sensitivity. In a first cohort, whole blood from 20 healthy women and men was stimulated with increasing concentrations of the immune agonist lipopolysaccharide (LPS). Four inhibitors of mitochondrial respiratory chain Complexes I, III, IV, and V were used (LPS + Mito-Inhibitors) to acutely perturb mitochondrial function, GC sensitivity was quantified using the GC-mimetic dexamethasone (DEX) (LPS + DEX), and the resultant cytokine signatures mapped with a 20-cytokine array. Inhibiting mitochondrial respiration caused large inter-individual differences in LPS-stimulated IL-6 reactivity (Cohen's d = 0.72) and TNF-α (d = 1.55) but only minor alteration in EC50-based LPS sensitivity (d = 0.21). Specifically, inhibiting mitochondrial Complex IV potentiated LPS-induced IL-6 levels by 13%, but inhibited TNF-α induction by 72%, indicating mitochondrial regulation of the IL-6/TNF-α ratio. As expected, DEX treatment suppressed multiple LPS-induced pro-inflammatory cytokines (IFN-γ, IL-6, IL-8, IL-1β, .TNF-α) by >85% and increased the anti-inflammatory cytokine IL-10 by 80%. Inhibiting Complex I potentiated DEX suppression of IL-6 by a further 12% (d = 0.73), indicating partial mitochondrial modulation of glucocorticoid sensitivity. Finally, to examine if intrinsic mitochondrial respiratory capacity may explain a portion of immune reactivity differences across individuals, we measured biochemical respiratory chain enzyme activities and mitochondrial DNA copy number in isolated peripheral blood mononuclear cells (PBMCs) from a second cohort of 44 healthy individuals in parallel with LPS-stimulated IL-6 and TNF-α response. Respiratory chain .function, particularly Complex IV activity, was positively correlated with LPS-stimulated IL-6 levels (r = 0.45, p = 0.002). Overall, these data provide preliminary evidence that mitochondrial behavior modulates LPS-induced inflammatory cytokine signatures in human blood.

Peripheral biomarkers of mitochondrial dysfunction in adolescents with bipolar disorder

BACKGROUND

Mitochondrial dysfunction has been implicated in the pathophysiology of bipolar disorder (BD). Impediment of mitochondrial oxidative phosphorylation results in a shift toward anaerobic respiration and lactate production. Elevated CNS lactate levels in adults with BD inform the need to evaluate lactate in peripheral samples and early in the course of BD. Furthermore, there exists a recent surge of investigations looking at circulating cell-free mitochondrial DNA (ccf-mtDNA) as a potential biomarker as they are released from cells under physiological stress, apoptosis, or bioenergetic compromise.

OBJECTIVES

To compare lactate and ccf-mtDNA, two different ways in assessing the mitochondrial health and function, in adolescents with BD versus healthy control adolescents (HC).

METHODS

One-hundred and five adolescents (n = 64 BD, n = 41 HC) were included. Serum lactate level was measured using a commercially available colorimetric kit. Serum ccf-mtDNA concentration was measured using quantitative polymerase chain reaction from ccfDNA purified by commercially available spin columns. Diagnosis and mood symptoms were evaluated using semi-structured interviews.

RESULTS

There is an increase in serum lactate level of adolescents with BD (1.319 ± 0.444 nmol/uL) versus HC (1.168 ± 0.353 nmol/uL; p = 0.043), but not ccf-mtDNA. Among BD adolescents, depression symptoms were negatively correlated with ccf-mtDNA levels (ρ = -0.289; p = 0.038) but loses significance when corrected for multiple comparison. Lactate was positively correlated with ccf-mtDNA in the overall sample (ρ = 0.201; p = 0.043). When examined by diagnosis, this association remained in BD (ρ = 0.273; p = 0.032), but not HC.

CONCLUSION

These preliminary results indicate that elevated lactate is observed even among adolescents early in their course of BD, that the association between lactate and ccf-mtDNA appears to be specific to BD, and that ccf-mtDNA is potentially associated with depression symptoms in adolescent BD. In addition, the effect of psychotropic medications used in the treatment of BD on peripheral lactate and ccf-mtDNA requires further investigation.

Stress and Psychiatric Disorders: The Role of Mitochondria

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

Increased level of circulating cell-free mitochondrial DNA due to a single bout of strenuous physical exercise

Purpose

Physical exercise is reported to affect the immune response in various ways. Thus, the levels of pro-inflammatory cytokines as well as the abundance of circulating leukocytes are changed. In this study, the occurence of circulating cell-free mitochondrial DNA (cfmtDNA) and nuclear DNA (nDNA) was investigated in connection with a single bout of strenuous physical exercise.

Methods

Healthy volunteers performed a controlled ergo-spirometry cycle test and venous blood samples were taken at different time-points to analyze the concentration of blood components before, during and after the test. The number of circulating leukocytes was measured, as well as secretion of the soluble urokinase activator receptor (suPAR).

Results

Cf-mtDNA significantly increased during exercise, compared to baseline values and after 30 and 90 min of rest. Circulating leukocytes increased during exercise, but returned to baseline levels afterwards. Surface expression of the urokinase plasminogen activating receptor (uPAR) on neutrophils decreased significantly during exercise. The concentration of suPAR tended to increase during exercise but only significantly after 90 min of rest.

Conclusion

Increased concentration of cf-mtDNA indicates that cell damage takes place during high intensity training. Hypoxia and tissue damage are likely causes of cf-mtDNA from muscle cells. The levels of cf-mtDNA remain high during the initial rest, due to the decreasing numbers of leukocytes normally clearing the plasma from cf-mtDNA. The increased levels of suPAR further emphasize that strenuous physical exercise causes a reaction similar to inflammation. Further studies are needed to detect the source of increased cf-mtDNA and the corresponding increase of suPAR liberation.

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

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

Biomarkers of suicidal behaviors: A comprehensive critical review

Suicide is a relevant worldwide public health problem. Many studies have shown that different demographic and clinical factors are potentially associated with suicidal behavior. Other studies have reported data about the role of biomarkers in the onset of suicidal behaviors. Specifically, researchers have found that suicidal risk may be increased by abnormalities in serotonergic system, hypothalamic-pituitary-adrenal axis, lipid metabolism, immune system and neuronal plasticity. The identification of specific biological parameters associated with self-harm may be helpful to implement prevention strategies and also to detect new therapeutic strategies. In this review, we summarize and analyze the results of main studies about neurobiological mechanisms related to suicidal behavior, also exploring the possible interconnection between the different biological systems.