Mitochondrial DNA damage triggers spread of Parkinson's disease-like pathology

The role of the hippocampus and SLC39A8 in chronic musculoskeletal pain-induced dementia: a Mendelian randomization study

Despite observational studies suggesting a link between chronic musculoskeletal pain (CMP) and increased risk of cognitive decline and dementia, the causal nature of this relationship remains uncertain due to potential confounding factors and reverse causality. We employed two-sample Mendelian Randomization (TSMR), bidirectional MR, mediation MR, drug-target MR, and colocalization analysis, along with gene set enrichment and protein-protein interaction (PPI) analyses. TSMR assessed the causal associations between CMP and the risk of dementia and its subtypes, including Alzheimer's disease (AD), vascular dementia (VaD), Lewy body dementia (LBD), frontotemporal dementia (FTD), and Parkinson's disease (PD). Bidirectional MR evaluated reverse causality, while mediation analyses identified potential mediators, focusing on neuroimaging and cognitive phenotypes. Drug-target MR investigated the role of the SLC39A8 gene, and colocalization analysis determined shared causal genetic variants. Gene set enrichment and PPI analyses elucidated the biological pathways implicated in the CMP-dementia relationship. Robust evidence established a causal relationship between chronic low back pain (LBP) and increased risk of PD, with knee osteoarthritis identified as a partial mediator, suggesting a pathway involving chronic inflammation. Bidirectional MR analysis revealed no evidence of reverse causality, further supporting the unidirectional causal link from LBP to PD. Colocalization analysis confirmed distinct genetic architectures for LBP and PD, while drug-target MR implicated the SLC39A8 gene as a potential mediator. Gene set enrichment and PPI analyses highlighted critical biological pathways, such as purine metabolism and glutamate receptor signaling. Suggestive evidence indicated potential causal links between limb pain and overall dementia, myalgia and VaD, as well as potential protective effects of Polymyalgia Rheumatica (PMR) against AD and rheumatism against PD. This study reveals a complex causal relationship between CMP and neurodegenerative diseases, particularly the robust link between LBP and PD. The findings underscore the need for further research to elucidate the underlying mechanisms and inform targeted prevention and treatment strategies.

Targeting mitochondria-regulated ferroptosis: A new frontier in Parkinson's disease therapy

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized by the progressive loss of dopaminergic neurons in the substantial nigra. Mitochondrial dysfunction and mitochondrial oxidative stress are central to the pathogenesis of PD, with recent evidence highlighting the role of ferroptosis - a type of regulated cell death dependent on iron metabolism and lipid peroxidation. Mitochondria, the central organelles for cellular energy metabolism, play a pivotal role in PD pathogenesis through the production of Reactive oxygen species (ROS) and the disruption of iron homeostasis. This review explores the intricate interplay between mitochondrial dysfunction and ferroptosis in PD, focusing on key processes such as impaired electron transport chain function, tricarboxylic acid (TCA) cycle dysregulation, disruption of iron metabolism, and altered lipid peroxidation. We discuss key pathways, including the role of glutathione (GSH), mitochondrial ferritin, and the regulation of the mitochondrial labile iron pool (mLIP), which collectively influence the susceptibility of neurons to ferroptosis. Furthermore, this review emphasizes the importance of mitochondrial quality control mechanisms, such as mitophagy and mitochondrial biogenesis, in mitigating ferroptosis-induced neuronal death. Understanding these mechanisms linking the interplay between mitochondrial dysfunction and ferroptosis may pave the way for novel therapeutic approaches aimed at preserving mitochondrial integrity and preventing neuronal loss in PD.

Redox modulatory role of DJ-1 in Parkinson's disease

In particular, oxidative stress, generated by excessive reactive oxygen species (ROS), plays a major role in the neurodegenerative component of Parkinson's disease (PD) in aged neurons. DJ-1 (PARK7) is a key factor for maintaining redox homeostasis and modulation of mitochondrial function to preserve the cellular survival pathways. DJ-1 also plays a role in redox signaling independently of its antioxidant capacity by preventing the redox chain disulfide formation and stabilizing the master regulator of cellular antioxidant defense, Nuclear Factor Erythroid 2-Related Factor 2 (Nrf2). In the DJ-1 or Nrf2 axis, expression of key antioxidant enzymes (glutathione peroxidase (GPx), superoxide dismutase (SOD), and heme oxygenase-1 (HO-1) in response to oxidative stress is increased, and decreased neuronal damage resulting from oxidative stress is achieved. It has been demonstrated that DJ-1 functions as an oxidative stress sensor, and mutations like L166P cause loss of antioxidant activity and increased Reactive Oxygen Species (ROS) accumulation with subsequent mitochondrial dysfunction in dopaminergic neurons. The highly conserved cysteine residue at position 106 (Cys106) of DJ-1 becomes stepwise oxidized (Cys-SOH → Cys-SO₂H → Cys-SO3H), functioning as a redox sensor as well as redox modulator of cellular stress responses. Furthermore, by protecting against α-synuclein aggregation, DJ-1 also protects in models lacking DJ-1, whereby DJ-1 deficiency promotes protein misfolding and neurotoxicity. In addition, DJ-1 participates in regulating neuroinflammation since its diminution provokes NF-κB-mediated exacerbation of proinflammatory cytokine production, leading to neuronal death. Oxidized DJ-1 (OxiDJ-1) is generated in aging brains, particularly in the substantia nigra (SN), and is correlated with PD progression both as a biomarker for disease monitoring and diagnosis of PD early in its course. The therapeutic strategies aimed at DJ-1 include small molecular activators, protein supplementation (Tat-DJ-1, ND-13), and gene therapy aiming to restore the neuroprotective function of DJ-1. Since DJ-1 is multitasking to protect neurons from oxidative damage, mitochondrial dysfunction, and even inflammation, it remains a promising therapeutic target. This review highlights the molecular mechanisms through which DJ-1 can protect from PD and aging-related neurodegeneration and has potential utility as a biomarker or therapeutic target.

The neuroimmune nexus: unraveling the role of the mtDNA-cGAS-STING signal pathway in Alzheimer's disease

The relationship between Alzheimer's disease (AD) and neuroimmunity has gradually begun to be unveiled. Emerging evidence indicates that cyclic GMP-AMP synthase (cGAS) acts as a cytosolic DNA sensor, recognizing cytosolic damage-associated molecular patterns (DAMPs), and inducing the innate immune response by activating stimulator of interferon genes (STING). Dysregulation of this pathway culminates in AD-related neuroinflammation and neurodegeneration. A substantial body of evidence indicates that mitochondria are involved in the critical pathogenic mechanisms of AD, whose damage leads to the release of mitochondrial DNA (mtDNA) into the extramitochondrial space. This leaked mtDNA serves as a DAMP, activating various pattern recognition receptors and immune defense networks in the brain, including the cGAS-STING pathway, ultimately leading to an imbalance in immune homeostasis. Therefore, modulation of the mtDNA-cGAS-STING pathway to restore neuroimmune homeostasis may offer promising prospects for improving AD treatment outcomes. In this review, we focus on the mechanisms of mtDNA release during stress and the activation of the cGAS-STING pathway. Additionally, we delve into the research progress on this pathway in AD, and further discuss the primary directions and potential hurdles in developing targeted therapeutic drugs, to gain a deeper understanding of the pathogenesis of AD and provide new approaches for its therapy.

FAM43A coordinates mtDNA replication and mitochondrial biogenesis in response to mtDNA depletion

Mitochondrial retrograde signaling (MRS) pathways relay the functional status of mitochondria to elicit homeostatic or adaptive changes in nuclear gene expression. Budding yeast have "intergenomic signaling" pathways that sense the amount of mitochondrial DNA (mtDNA) independently of oxidative phosphorylation (OXPHOS), the primary function of genes encoded by mtDNA. However, MRS pathways that sense the amount of mtDNA in mammalian cells remain poorly understood. We found that mtDNA-depleted IMR90 cells can sustain OXPHOS for a significant amount of time, providing a robust model system to interrogate human intergenomic signaling. We identified FAM43A, a largely uncharacterized protein, as a CHK2-dependent early responder to mtDNA depletion. Depletion of FAM43A activates a mitochondrial biogenesis program, resulting in an increase in mitochondrial mass and mtDNA copy number via CHK2-mediated upregulation of the p53R2 form of ribonucleotide reductase. We propose that FAM43A performs a checkpoint-like function to limit mitochondrial biogenesis and turnover under conditions of mtDNA depletion or replication stress.

Extracellular vesicles: new horizons in neurodegeneration

Extracellular vesicles (EVs) are lipid-enclosed nanovesicles secreted by diverse cell types that orchestrate intercellular communication through cargo delivery. Their pivotal roles span from supporting the development of normal central nervous system (CNS) to contributing to the pathogenesis of neurological diseases. Particularly noteworthy is their involvement in the propagation of pathogenic proteins, such as those involved in neurodegenerative disorders, and nucleic acids, closely linking them to disease onset and progression. Moreover, EVs have emerged as promising diagnostic biomarkers for neurological disorders and as tools for disease staging, owing to their ability to traverse the blood-brain barrier and their specific, stable, and accessible properties. This review comprehensively explores the realm of CNS-derived EVs found in peripheral blood, encompassing their detection methods, transport mechanisms, and diverse roles in various neurodegenerative diseases. Furthermore, we evaluate the potentials and limitations of EVs in clinical applications and highlight prospective research directions in this rapidly evolving field.

Increased Rate of Unique Mitochondrial DNA Deletion Breakpoints in Young Adults With Early-Life Stress

Background

Mounting evidence suggests that mitochondria respond to psychosocial stress. Recent studies suggest mitochondrial DNA (mtDNA) deletions may be increased in some psychiatric disorders, but no studies have examined early-life stress (ELS) and mtDNA deletions. In this study, we assessed mtDNA deletions in peripheral blood mononuclear cells of medically healthy young adults with and without ELS.

Methods

Participants (n = 181; 69% female), ages 18 to 40 years, were recruited from the community. Participants with ELS (n = 108) had moderate to severe childhood maltreatment; 83 also had parental loss, and 59 had psychiatric disorders. Participants in the control group (n = 73) had no maltreatment, parental loss, or psychiatric disorders. Standardized interviews and self-report measures assessed demographic variables, stress, and mental health. mtDNA from peripheral blood mononuclear cells was amplified via long-range polymerase chain reaction; mtDNA deletions were quantified via Seq-Well, next-generation sequencing, and the Splice-Break pipeline. Linear regression models were used to assess relationships of mtDNA deletion metrics with ELS, adult stressors, psychiatric disorders, and demographics.

Results

Participants with ELS had significantly greater rates of unique mtDNA deletion breakpoints per 10,000 coverage than participants without ELS (p < .001), correcting for age, sex, and sequencing depth. Cumulative mtDNA deletion read percentage was not significantly different between groups. Psychiatric disorders and adult stressors were associated with greater unique mtDNA deletion breakpoints (ps < .05) but did not account for associations of ELS with mtDNA deletions.

Conclusions

The increased number of unique mtDNA deletion breakpoints in participants with ELS suggests that mitochondrial genomes undergo observable alterations in the context of early stress. Future studies will examine mtDNA deletions with metabolic health measures.

"Extracellular Vesicle DNA: Advances and Applications as a Non-Invasive Biomarker in Disease Diagnosis and Treatment"

Extracellular vesicles (EVs) are nanoscale, membrane-enclosed structures released by cells into the extracellular milieu. These vesicles encapsulate a diverse array of molecular constituents, including nucleic acids, proteins, and lipids, which provide insights into the physiological or pathological conditions of their parent cells. Despite their potential, the study of EV-derived DNA (EV-DNA) has gathered relatively limited attention. This review aims to present a thorough examination of the emerging knowledge surrounding the utility of EV-DNA as a non-invasive biomarker across a spectrum of diseases. The review delves into various mechanisms underlying DNA packaging within EVs and the prevalent methodologies employed for extraction of EV-DNA. The relevance of EV-DNA is assessed across numerous health conditions, notably cancer, cardiovascular diseases, neurodegenerative disorders, infectious diseases, and pregnancy-related complications. The use of EV-DNA for cancer mutation detection has demonstrated remarkable sensitivity and specificity, thereby enhancing both diagnostic accuracy and therapeutic monitoring. In the context of cardiovascular diseases, EV-DNA serves as a predictive marker for events such as myocardial infarctions and shows a correlation with the severity of the disease. With respect to neurodegenerative conditions, including Parkinson's and Alzheimer's, EV-DNA contributes to the understanding of disease mechanisms and progression. Additionally, it plays an essential role in modulating immune tolerance and facilitating communication between maternal and fetal systems. Although there is a pressing need for standardized protocols for EV isolation and DNA analysis to facilitate clinical implementation, the prospect of EV-DNA as a non-invasive biomarker for diagnostic and prognostic purposes across diverse pathological conditions is considerable.

Nanotechnology in Parkinson's Disease: overcoming drug delivery challenges and enhancing therapeutic outcomes

The global prevalence of Parkinson's Disease (PD) is on the rise, driven by an ageing population and ongoing environmental conditions. To gain a better understanding of PD pathogenesis, it is essential to consider its relationship with the ageing process, as ageing stands out as the most significant risk factor for this neurodegenerative condition. PD risk factors encompass genetic predisposition, exposure to environmental toxins, and lifestyle influences, collectively increasing the chance of PD development. Moreover, early and precise PD diagnosis remains elusive, relying on clinical assessments, neuroimaging techniques, and emerging biomarkers. Conventional management of PD involves dopaminergic medications and surgical interventions, but these treatments often become less effective over time and do not address disease treatment. Challenges persist due to the blood-brain barrier's (BBB) impermeability, hindering drug delivery. Recent advancements in nanotechnology offer promising novel approaches for PD management. Various drug delivery systems (DDS), including nanosized polymers, lipid-based carriers, and nanoparticles (such as metal/metal oxide, protein, and carbonaceous particles), aim to enhance drug and gene delivery. These modifications seek to improve BBB permeability, ultimately benefiting PD patients. This review underscores the critical role of ageing in PD development and explores how age-related neuronal decline contributes to substantia nigra loss and PD manifestation in susceptible individuals. The review also highlights the advancements and ongoing challenges in nanotechnology-based therapies for PD.

The functional regulation between extracellular vesicles and the DNA damage responses

The DNA damage response (DDR) is a crucial regulatory mechanism for the survival of organisms, and irregularity of DDR may contribute to the development of various diseases, including tumors, making it is a prominent topic in therapeutic research. Extracellular vesicles (EVs), as important mediators of intercellular communication, have been extensively studied in recent years. Notably, an increasing number of studies have revealed a strong connection between DDR and EVs. On one hand, DNA damage affects the release of EVs and their compositional content; on the other hand, EVs can dictate cell survival or death by modulating DDR in both the parental and the recipient cells. This review outlines current progress in the inter-regulatory relationship between EVs and DDR, with special emphasis on the effects of EVs derived from various sources on DDR in recipient cells. In addition, the potential applications of EVs in research and tumor therapy are discussed.

Mitochondrial DNA (mtDNA) as fluid biomarker in neurodegenerative disorders: A systematic review

BACKGROUND

Several studies evaluated peripheral and cerebrospinal fluid (CSF) mtDNA as a putative biomarker in neurodegenerative diseases, often yielding inconsistent findings. We systematically reviewed the current evidence assessing blood and CSF mtDNA levels and variant burden in Parkinson's disease (PD), Alzheimer's disease (AD) and amyotrophic lateral sclerosis (ALS). Multiple sclerosis (MS) was also included as a paradigm of chronic neuroinflammation-driven neurodegeneration.

METHODS

Medline, Embase, Scopus and Web of Science were searched for articles published from inception until October 2023. Studies focused on mtDNA haplogroups or hereditary pathogenic variants were excluded. Critical appraisal was performed using the Quality Assessment for Diagnostic Accuracy Studies criteria.

RESULTS

Fifty-nine original studies met our a priori-defined inclusion criteria. The majority of CSF-focused studies showed (i) decreased mtDNA levels in PD and AD; (ii) increased levels in MS compared to controls. No studies evaluated CSF mtDNA in ALS. Results focused on blood cell-free and intracellular mtDNA were contradictory, even within studies evaluating the same disease. This poor reproducibility is likely due to the lack of consideration of the many factors known to affect mtDNA levels. mtDNA damage and methylation levels were increased and reduced in patients compared to controls, respectively. A few studies investigated the correlation between mtDNA and disease severity, with conflicting results.

CONCLUSIONS

Additional well-designed studies are needed to evaluate CSF and blood mtDNA profiles as putative biomarkers in neurodegenerative diseases. The identification of "mitochondrial subtypes" of disease may enable novel precision medicine strategies to counteract neurodegeneration.

Peripheral immune cell response to stimulation stratifies Parkinson's disease progression from prodromal to clinical stages

The motor stage of idiopathic Parkinson's disease (iPD) can be preceded for years by a prodromal stage characterized by non-motor symptoms like REM sleep behavior disorder (RBD). Here, we show that multiple stages of iPD, including the pre-motor prodromal stage, can be stratified according to the inflammatory and immunometabolic responses to stimulation of peripheral blood mononuclear cells ex vivo. We identified increased stimulation-dependent secretion of TNF, IL-1β, and IL-8 in monocytes from RBD patients and showed diminished proinflammatory cytokine secretion in monocytes and T cells in early and moderate stages of PD. Mechanistically, immune activation revealed deficits in CD8+ T-cell mitochondrial health in moderate PD, and relative mitochondrial health in CD8+ T cells was positively correlated with stimulation-dependent T-cell cytokine secretion across the PD spectrum. Dysregulated immunometabolism may drive peripheral inflammation and PD progression, and ex vivo stimulation-based assays have potential to reveal novel biomarkers for patient stratification and progression with immune endophenotypes.

Roles of chromatin and genome instability in cellular senescence and their relevance to ageing and related diseases

Ageing is a complex biological process in which a gradual decline in physiological fitness increases susceptibility to diseases such as neurodegenerative disorders and cancer. Cellular senescence, a state of irreversible cell-growth arrest accompanied by functional deterioration, has emerged as a pivotal driver of ageing. In this Review, we discuss how heterochromatin loss, telomere attrition and DNA damage contribute to cellular senescence, ageing and age-related diseases by eliciting genome instability, innate immunity and inflammation. We also discuss how emerging therapeutic strategies could restore heterochromatin stability, maintain telomere integrity and boost the DNA repair capacity, and thus counteract cellular senescence and ageing-associated pathologies. Finally, we outline current research challenges and future directions aimed at better comprehending and delaying ageing.

Non-Categorical Analyses Identify Rotenone-Induced 'Parkinsonian' Rats Benefiting from Nano-Emulsified Punicic Acid (Nano-PSO) in a Phenotypically Diverse Population: Implications for Translational Neurodegenerative Therapies

The pursuit of nutraceuticals to improve the quality of life for patients with neurodegenerative conditions is a dynamic field within neuropharmacology. Unfortunately, many nutraceuticals that show promise in preclinical studies fail to demonstrate significant clinical benefits in human trials, leading to their exclusion as therapeutic options. This discrepancy may stem from the categorical interpretation of preclinical and clinical results. Basic researchers often assume that non-human experimental animals exhibit less phenotypic variability than humans. This belief overlooks interindividual phenotype variation, thereby leading to categorical conclusions being drawn from experiments. Consequently, when human clinical trials are conducted, the researchers expect similarly conclusive results. If these results are not achieved, the nutraceutical is deemed ineffective for clinical use, even if numerous individuals might benefit. In our study, we evaluated whether analyzing phenotype variability and similarity through non-categorical methods could help identify rotenone (ROT)-treated rats that might benefit from consuming nano-emulsified punicic acid (Nano-PSO), even if the prevention of "parkinsonism" or the restoration of neurometabolic function is inconsistent across individuals. Our findings supported this hypothesis. The benefits of Nano-PSO were not categorical; however, analyzing phenotype variance allowed us to identify ROT rats with varying degrees of benefit from Nano-PSO consumption. Hence, the translational potential of results from basic science studies testing nutraceuticals as pharmaceutical products against neurodegeneration may improve if researchers also interpret their results using non-categorical methods of data analysis for population screening, even if the overall therapeutic outcomes for the entire population show internal inconsistencies.

The potential role of mitochondria in the microbiota-gut-brain axis: Implications for brain health

Mitochondria are crucial organelles that regulate cellular energy metabolism, calcium homeostasis, and oxidative stress responses, playing pivotal roles in brain development and neurodegeneration. Concurrently, the gut microbiota has emerged as a key modulator of brain physiology and pathology through the microbiota-gut-brain axis. Recent evidence suggests an intricate crosstalk between the gut microbiota and mitochondrial function, mediated by microbial metabolites that can influence mitochondrial activities in the brain. This review aims to provide a comprehensive overview of the emerging role of mitochondria as critical mediators in the microbiota-gut-brain axis, shaping brain health and neurological disease pathogenesis. We discuss how gut microbial metabolites such as short-chain fatty acids, secondary bile acids, tryptophan metabolites, and trimethylamine N-oxide can traverse the blood-brain barrier and modulate mitochondrial processes including energy production, calcium regulation, mitophagy, and oxidative stress in neurons and glial cells. Additionally, we proposed targeting the mitochondria through diet, prebiotics, probiotics, or microbial metabolites as a promising potential therapeutic approach to maintain brain health by optimizing mitochondrial fitness. Overall, further investigations into how the gut microbiota and its metabolites regulate mitochondrial bioenergetics, dynamics, and stress responses will provide valuable insights into the microbiota-gut-brain axis in both health and disease states.

Age-Dependent Pathogenesis of Influenza A Virus H7N9 Mediated Through PB1-F2-Induced Mitochondrial DNA Release and Activation of cGAS-STING-NF-κB Signaling

Exactly why human infection of avian influenza A virus H7N9 causes more severe disease in the elderly remains elusive. In this study, we found that H7N9 PB1-F2 is a pathogenic factor in 15-18-month-old BALB/C mice (aged mice) but not in 6-8-week-old young adult mice (young mice). Recombinant influenza A virus with H7N9 PB1-F2-knockout was less pathogenic in aged mice as indicated with delayed weight loss. In contrast, survival of young mice infected with this virus was diminished. Furthermore, tissue damage, inflammation, proinflammatory cytokine and 2'3'-cGAMP production in the lung were less pronounced in infected aged mice despite no change in viral titer. cGAS is known to produce 2'3'-cGAMP to boost proinflammatory cytokine expression through STING-NF-κB signaling. We found that H7N9 PB1-F2 promoted interferon β (IFNβ) and chemokine gene expression in cultured cells through the mitochondrial DNA-cGAS-STING-NF-κB pathway. H7N9 PB1-F2 formed protein aggregate and caused mitochondrial cristae collapse, complex V-dependent electron transport dysfunction, reverse electron transfer-dependent oxidized mitochondrial DNA release to the cytoplasm and activation of cGAS-STING-NF-κB signaling. PB1-F2 N57 truncation, which is frequently observed in human circulating strains, mitigated H7N9 PB1-F2-mediated mitochondrial dysfunction and cGAS activation. In addition, we found that PB1-F2 of pathogenic avian influenza viruses triggered more robust cGAS activation than their human-adapted descendants. Our findings provide one explanation to age-dependent pathogenesis of H7N9 infection.

Mitochondrial Dysfunction in Parkinson's Disease: A Contribution to Cognitive Impairment?

Among the non-motor symptoms associated with Parkinson's disease (PD), cognitive impairment is one of the most common and disabling. It can occur either early or late during the disease, and it is heterogeneous in terms of its clinical manifestations, such as Subjective Cognitive Dysfunction (SCD), Mild Cognitive Impairment (MCI), and Parkinson's Disease Dementia (PDD). The aim of the present review is to delve deeper into the molecular mechanisms underlying cognitive decline in PD. This is extremely important to delineate the guidelines for the differential diagnosis and prognosis of the dysfunction, to identify the molecular and neuronal mechanisms involved, and to plan therapeutic strategies that can halt cognitive impairment progression. Specifically, the present review will discuss the pathogenetic mechanisms involved in the progression of cognitive impairment in PD, with attention to mitochondria and their contribution to synaptic dysfunction and neuronal deterioration in the brain regions responsible for non-motor manifestations of the disease.

Brain-Region-Specific Differences in Protein Citrullination/Deimination in a Pre-Motor Parkinson's Disease Rat Model

The detection of early molecular mechanisms and potential biomarkers in Parkinson's disease (PD) remains a challenge. Recent research has pointed to novel roles for post-translational citrullination/deimination caused by peptidylarginine deiminases (PADs), a family of calcium-activated enzymes, in the early stages of the disease. The current study assessed brain-region-specific citrullinated protein targets and their associated protein-protein interaction networks alongside PAD isozymes in the 6-hydroxydopamine (6-OHDA) induced rat model of pre-motor PD. Six brain regions (cortex, hippocampus, striatum, midbrain, cerebellum and olfactory bulb) were compared between controls/shams and the pre-motor PD model. For all brain regions, there was a significant difference in citrullinated protein IDs between the PD model and the controls. Citrullinated protein hits were most abundant in cortex and hippocampus, followed by cerebellum, midbrain, olfactory bulb and striatum. Citrullinome-associated pathway enrichment analysis showed correspondingly considerable differences between the six brain regions; some were overlapping for controls and PD, some were identified for the PD model only, and some were identified in control brains only. The KEGG (Kyoto Encyclopedia of Genes and Genomes) pathways identified in PD brains only were associated with neurological, metabolic, immune and hormonal functions and included the following: "Axon guidance"; "Spinocerebellar ataxia"; "Hippo signalling pathway"; "NOD-like receptor signalling pathway"; "Phosphatidylinositol signalling system"; "Rap1 signalling pathway"; "Platelet activation"; "Yersinia infection"; "Fc gamma R-mediated phagocytosis"; "Human cytomegalovirus infection"; "Inositol phosphate metabolism"; "Thyroid hormone signalling pathway"; "Progesterone-mediated oocyte maturation"; "Oocyte meiosis"; and "Choline metabolism in cancer". Some brain-region-specific differences were furthermore observed for the five PAD isozymes (PADs 1, 2, 3, 4 and 6), with most changes in PAD 2, 3 and 4 when comparing control and PD brain regions. Our findings indicate that PAD-mediated protein citrullination plays roles in metabolic, immune, cell signalling and neurodegenerative disease-related pathways across brain regions in early pre-motor stages of PD, highlighting PADs as targets for future therapeutic avenues.

Exosome-associated mitochondrial DNA in late-life depression: Implications for cognitive decline in older adults

BACKGROUND

Disrupted cellular communication, inflammatory responses and mitochondrial dysfunction are consistently observed in late-life depression (LLD). Exosomes (EXs) mediate cellular communication by transporting molecules, including mitochondrial DNA (EX-mtDNA), playing critical role in immunoregulation alongside tumor necrosis factor (TNF). Changes in EX-mtDNA are indicators of impaired mitochondrial function and might increase vulnerability to adverse health outcomes. Our study examined EX-mtDNA levels and integrity, exploring their associations with levels of TNF receptors I and II (TNFRI and TNFRII), and clinical outcomes in LLD.

METHODS

Ninety older adults (50 LLD and 40 controls (HC)) participated in the study. Blood was collected and exosomes were isolated using size-exclusion chromatography. DNA was extracted and EX-mtDNA levels and deletion were assessed using qPCR. Plasma TNFRI and TNFRII levels were quantified by multiplex immunoassay. Correlation analysis explored relationships between EX-mtDNA, clinical outcomes, and inflammatory markers.

RESULTS

Although no differences were observed in EX-mtDNA levels between groups, elevated levels correlated with poorer cognitive performance (r = -0.328, p = 0.002) and increased TNFRII levels (r = 0.367, p = 0.004). LLD exhibited higher deletion rates (F(83,1) = 4.402, p = 0.039), with a trend remaining after adjusting for covariates (p = 0.084). Deletion correlated with poorer cognitive performance (r = -0.335, p = 0.002). No other associations were found.

LIMITATION

Cross-sectional study with a small number of participants from a specialized geriatric psychiatry treatment center.

CONCLUSION

Our findings suggest that EX-mtDNA holds promise as an indicator of cognitive outcomes in LLD. Additional research is needed to further comprehend the role of EX-mtDNA levels/integrity in LLD, paving the way for its clinical application in the future.

Mitochondrial Dysfunction is a Crucial Immune Checkpoint for Neuroinflammation and Neurodegeneration: mtDAMPs in Focus

Neuroinflammation is a pivotal factor in the progression of both age-related and acute neurodegenerative disorders, including Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, multiple sclerosis, and stroke. Mitochondria, essential for neuronal health due to their roles in energy production, calcium buffering, and oxidative stress regulation, become increasingly susceptible to dysfunction under conditions of metabolic stress, aging, or injury. Impaired mitophagy in aged or injured neurons leads to the accumulation of dysfunctional mitochondria, which release mitochondrial-derived damage-associated molecular patterns (mtDAMPs). These mtDAMPs act as immune checkpoints, activating pattern recognition receptors (PRRs) and triggering innate immune signaling pathways. This activation initiates inflammatory responses in neurons and brain-resident immune cells, releasing cytokines and chemokines that damage adjacent healthy neurons and recruit peripheral immune cells, further amplifying neuroinflammation and neurodegeneration. Long-term mitochondrial dysfunction perpetuates a chronic inflammatory state, exacerbating neuronal injury and contributing additional immunogenic components to the extracellular environment. Emerging evidence highlights the critical role of mtDAMPs in initiating and sustaining neuroinflammation, with circulating levels of these molecules potentially serving as biomarkers for disease progression. This review explores the mechanisms of mtDAMP release due to mitochondrial dysfunction, their interaction with PRRs, and the subsequent activation of inflammatory pathways. We also discuss the role of mtDAMP-triggered innate immune responses in exacerbating both acute and chronic neuroinflammation and neurodegeneration. Targeting dysfunctional mitochondria and mtDAMPs with pharmacological agents presents a promising strategy for mitigating the initiation and progression of neuropathological conditions.

The lysosomal β-glucocerebrosidase strikes mitochondria: implications for Parkinson's therapeutics

Parkinson's disease is a neurodegenerative disorder primarily known for typical motor features that arise due to the loss of dopaminergic neurons in the substantia nigra. However, the precise molecular aetiology of the disease is still unclear. Several cellular pathways have been linked to Parkinson's disease, including the autophagy-lysosome pathway, α-synuclein aggregation and mitochondrial function. Interestingly, the mechanistic link between GBA1, the gene that encodes for lysosomal β-glucocerebrosidase (GCase), and Parkinson's disease lies in the interplay between GCase functions in the lysosome and mitochondria. GCase mutations alter mitochondria-lysosome contact sites. In the lysosome, reduced GCase activity leads to glycosphingolipid build-up, disrupting lysosomal function and autophagy, thereby triggering α-synuclein accumulation. Additionally, α-synuclein aggregates reduce GCase activity, creating a self-perpetuating cycle of lysosomal dysfunction and α-synuclein accumulation. GCase can also be imported into the mitochondria, where it promotes the integrity and function of mitochondrial complex I. Thus, GCase mutations that impair its normal function increase oxidative stress in mitochondria, the compartment where dopamine is oxidized. In turn, the accumulation of oxidized dopamine adducts further impairs GCase activity, creating a second cycle of GCase dysfunction. The oxidative state triggered by GCase dysfunction can also induce mitochondrial DNA damage which, in turn, can cause dopaminergic cell death. In this review, we highlight the pivotal role of GCase in Parkinson's disease pathogenesis and discuss promising examples of GCase-based therapeutics, such as gene and enzyme replacement therapies, small molecule chaperones and substrate reduction therapies, among others, as potential therapeutic interventions.

Targeting the NRF2 pathway for disease modification in neurodegenerative diseases: mechanisms and therapeutic implications

Neurodegenerative diseases constitute a global health issue and a major economic burden. They significantly impair both cognitive and motor functions, and their prevalence is expected to rise due to ageing societies and continuous population growth. Conventional therapies provide symptomatic relief, nevertheless, disease-modifying treatments that reduce or halt neuron death and malfunction are still largely unavailable. Amongst the common hallmarks of neurodegenerative diseases are protein aggregation, oxidative stress, neuroinflammation and mitochondrial dysfunction. Transcription factor nuclear factor-erythroid 2-related factor 2 (NRF2) constitutes a central regulator of cellular defense mechanisms, including the regulation of antioxidant, anti-inflammatory and mitochondrial pathways, making it a highly attractive therapeutic target for disease modification in neurodegenerative disorders. Here, we describe the role of NRF2 in the common hallmarks of neurodegeneration, review the current pharmacological interventions and their challenges in activating the NRF2 pathway, and present alternative therapeutic approaches for disease modification.

Intermittent hypoxia exacerbates anxiety in high-fat diet-induced diabetic mice by inhibiting TREM2-regulated IFNAR1 signaling

BACKGROUND

Type 2 diabetes mellitus (T2DM) and obstructive sleep apnea (OSA) are mutual risk factors, with both conditions inducing cognitive impairment and anxiety. However, whether OSA exacerbates cognitive impairment and anxiety in patients with T2DM remains unclear. Moreover, TREM2 upregulation has been suggested to play a protective role in attenuating microglia activation and improving synaptic function in T2DM mice. The aim of this study was to explore the regulatory mechanisms of TREM2 and the cognitive and anxiety-like behavioral changes in mice with OSA combined with T2DM.

METHODS

A T2DM with OSA model was developed by treating mice with a 60% kcal high-fat diet (HFD) combined with intermittent hypoxia (IH). Spatial learning memory capacity and anxiety in mice were investigated. Neuronal damage in the brain was determined by the quantity of synapses density, the number and morphology of brain microglia, and pro-inflammatory factors. For mechanism exploration, an in vitro model of T2DM combined with OSA was generated by co-treating microglia with high glucose (HG) and IH. Regulation of TREM2 on IFNAR1-STAT1 pathway was determined by RNA sequencing and qRT-PCR.

RESULTS

Our results showed that HFD mice exhibited significant cognitive dysfunction and anxiety-like behavior, accompanied by significant synaptic loss. Furthermore, significant activation of brain microglia and enhanced microglial phagocytosis of synapses were observed. Moreover, IH was found to significantly aggravate anxiety in the HFD mice. The mechanism of HG treatment may potentially involve the promotion of TREM2 upregulation, which in turn attenuates the proinflammatory microglia by inhibiting the IFNAR1-STAT1 pathway. Conversely, a significant reduction in TREM2 in IH-co-treated HFD mice and HG-treated microglia resulted in the further activation of the IFNAR1-STAT1 pathway and consequently increased proinflammatory microglial activation.

CONCLUSIONS

HFD upregulated the IFNAR1-STAT1 pathway and induced proinflammatory microglia, leading to synaptic damage and causing anxiety and cognitive deficits. The upregulated TREM2 inT2DM mice brain exerted a negative regulation of the IFNAR1-STAT1 pathway. Mice with T2DM combined with OSA exacerbated anxiety via the downregulation of TREM2, causing heightened IFNAR1-STAT1 pathway activation and consequently increasing proinflammatory microglia.

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

BACKGROUND

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

METHODS

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

FINDINGS

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

INTERPRETATION

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

FUNDING

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

Mitochondria in the Central Nervous System in Health and Disease: The Puzzle of the Therapeutic Potential of Mitochondrial Transplantation

Mitochondria, the energy suppliers of the cells, play a central role in a variety of cellular processes essential for survival or leading to cell death. Consequently, mitochondrial dysfunction is implicated in numerous general and CNS disorders. The clinical manifestations of mitochondrial dysfunction include metabolic disorders, dysfunction of the immune system, tumorigenesis, and neuronal and behavioral abnormalities. In this review, we focus on the mitochondrial role in the CNS, which has unique characteristics and is therefore highly dependent on the mitochondria. First, we review the role of mitochondria in neuronal development, synaptogenesis, plasticity, and behavior as well as their adaptation to the intricate connections between the different cell types in the brain. Then, we review the sparse knowledge of the mechanisms of exogenous mitochondrial uptake and describe attempts to determine their half-life and transplantation long-term effects on neuronal sprouting, cellular proteome, and behavior. We further discuss the potential of mitochondrial transplantation to serve as a tool to study the causal link between mitochondria and neuronal activity and behavior. Next, we describe mitochondrial transplantation's therapeutic potential in various CNS disorders. Finally, we discuss the basic and reverse-translation challenges of this approach that currently hinder the clinical use of mitochondrial transplantation.

Parkinson's Disease and Photobiomodulation: Potential for Treatment

Parkinson's disease is the second most common neurodegenerative disease and is increasing in incidence. The combination of motor and non-motor symptoms makes this a devastating disease for people with Parkinson's disease and their care givers. Parkinson's disease is characterised by mitochondrial dysfunction and neuronal death in the substantia nigra, a reduction in dopamine, accumulation of α-synuclein aggregates and neuroinflammation. The microbiome-gut-brain axis is also important in Parkinson's disease, involved in the spread of inflammation and aggregated α-synuclein. The mainstay of Parkinson's disease treatment is dopamine replacement therapy, which can reduce some of the motor signs. There is a need for additional treatment options to supplement available medications. Photobiomodulation (PBM) is a form of light therapy that has been shown to have multiple clinical benefits due to its enhancement of the mitochondrial electron transport chain and the subsequent increase in mitochondrial membrane potential and ATP production. PBM also modulates cellular signalling and has been shown to reduce inflammation. Clinically, PBM has been used for decades to improve wound healing, treat pain, reduce swelling and heal deep tissues. Pre-clinical experiments have indicated that PBM has the potential to improve the clinical signs of Parkinson's disease and to provide neuroprotection. This effect is seen whether the PBM is directed to the head of the animal or to other parts of the body (remotely). A small number of clinical trials has given weight to the possibility that using PBM can improve both motor and non-motor clinical signs and symptoms of Parkinson's disease and may potentially slow its progression.

Dietary vitamin E intake and risk of Parkinson's disease: a cross-sectional study

Objective

Current evidence on the association between dietary vitamin E intake and the risk of Parkinson's disease (PD) is limited. The aim of the study was to explore the association of dietary vitamin E intake with PD in the United States among adults over 40 years.

Methods

We conducted a cross-sectional study with data collected from National Health and Nutrition Examination Survey (NHANES) from 2009 to 2018. A total of the sample of 13,340 participants were included. To identify the different characteristics of the participants, we utilized propensity score matching (PSM) to reduce the effects of selection bias and confounding variables. Weighted univariate and multivariable logistic regression were used to examine the association between dietary vitamin E intake and PD before and after matching. Then, restricted cubic spline (RCS) was used to visually describe the possible non-linear relationships. Finally, we employed the subgroup analysis to further investigate the relationship between dietary vitamin E intake and PD.

Results

According to the weighted univariate and multivariable logistic regression analysis, vitamin E intake was inversely associated with the risk of PD before and after matching. The results of RCS analysis revealed no non-linear inverse relationship between vitamin E intake and PD before and after matching. The subgroup analysis showed that age may influence the negative association between vitamin E and PD (P < 0.05 for interaction).

Conclusion

Among participants over 40 years of age, vitamin E intake was negatively associated with the risk of PD. Our data may support the supplementation of vitamin E to be used as an intervention strategy for the occurrence of PD.

PRKAG2.2 is essential for FoxA1+ regulatory T cell differentiation and metabolic rewiring distinct from FoxP3+ regulatory T cells

Forkhead box A1 (FoxA1)+ regulatory T cells (Tregs) exhibit distinct characteristics from FoxP3+ Tregs while equally effective in exerting anti-inflammatory properties. The role of FoxP3+ Tregs in vivo has been challenged, motivating a better understanding of other Tregs in modulating hyperactive immune responses. FoxA1+ Tregs are generated on activation of the transcription factor FoxA1 by interferon-β (IFNβ), an anti-inflammatory cytokine. T cell activation, expansion, and function hinge on metabolic adaptability. We demonstrated that IFNβ promotes a metabolic rearrangement of FoxA1+ Tregs by enhancing oxidative phosphorylation and mitochondria clearance by mitophagy. In response to IFNβ, FoxA1 induces a specific transcription variant of adenosine 5'-monophosphate-activated protein kinase (AMPK) γ2 subunit, PRKAG2.2. This leads to the activation of AMPK signaling, thereby enhancing mitochondrial respiration and mitophagy by ULK1-BNIP3. This IFNβ-FoxA1-PRKAG2.2-BNIP3 axis is pivotal for their suppressive function. The involvement of PRKAG2.2 in FoxA1+ Treg, not FoxP3+ Treg differentiation, underscores the metabolic differences between Treg populations and suggests potential therapeutic targets for autoimmune diseases.

Involvement of Mitochondria in Parkinson's Disease

Mitochondrial dysregulation, such as mitochondrial complex I deficiency, increased oxidative stress, perturbation of mitochondrial dynamics and mitophagy, has long been implicated in the pathogenesis of PD. Initiating from the observation that mitochondrial toxins cause PD-like symptoms and mitochondrial DNA mutations are associated with increased risk of PD, many mutated genes linked to familial forms of PD, including PRKN, PINK1, DJ-1 and SNCA, have also been found to affect the mitochondrial features. Recent research has uncovered a much more complex involvement of mitochondria in PD. Disruption of mitochondrial quality control coupled with abnormal secretion of mitochondrial contents to dispose damaged organelles may play a role in the pathogenesis of PD. Furthermore, due to its bacterial ancestry, circulating mitochondrial DNAs can function as damage-associated molecular patterns eliciting inflammatory response. In this review, we summarize and discuss the connection between mitochondrial dysfunction and PD, highlighting the molecular triggers of the disease process, the intra- and extracellular roles of mitochondria in PD as well as the therapeutic potential of mitochondrial transplantation.

Restoring the infected powerhouse: Mitochondrial quality control in sepsis

Sepsis is a dysregulated host response to an infection, characterized by organ failure. The pathophysiology is complex and incompletely understood, but mitochondria appear to play a key role in the cascade of events that culminate in multiple organ failure and potentially death. In shaping immune responses, mitochondria fulfil dual roles: they not only supply energy and metabolic intermediates crucial for immune cell activation and function but also influence inflammatory and cell death pathways. Importantly, mitochondrial dysfunction has a dual impact, compromising both immune system efficiency and the metabolic stability of end organs. Dysfunctional mitochondria contribute to the development of a hyperinflammatory state and loss of cellular homeostasis, resulting in poor clinical outcomes. Already in early sepsis, signs of mitochondrial dysfunction are apparent and consequently, strategies to optimize mitochondrial function in sepsis should not only prevent the occurrence of mitochondrial dysfunction, but also cover the repair of the sustained mitochondrial damage. Here, we discuss mitochondrial quality control (mtQC) in the pathogenesis of sepsis and exemplify how mtQC could serve as therapeutic target to overcome mitochondrial dysfunction. Hence, replacing or repairing dysfunctional mitochondria may contribute to the recovery of organ function in sepsis. Mitochondrial biogenesis is a process that results in the formation of new mitochondria and is critical for maintaining a pool of healthy mitochondria. However, exacerbated biogenesis during early sepsis can result in accumulation of structurally aberrant mitochondria that fail to restore bioenergetics, produce excess reactive oxygen species (ROS) and exacerbate the disease course. Conversely, enhancing mitophagy can protect against organ damage by limiting the release of mitochondrial-derived damage-associated molecules (DAMPs). Furthermore, promoting mitophagy may facilitate the growth of healthy mitochondria by blocking the replication of damaged mitochondria and allow for post sepsis organ recovery through enabling mitophagy-coupled biogenesis. The remaining healthy mitochondria may provide an undamaged scaffold to reproduce functional mitochondria. However, the kinetics of mtQC in sepsis, specifically mitophagy, and the optimal timing for intervention remain poorly understood. This review emphasizes the importance of integrating mitophagy induction with mtQC mechanisms to prevent undesired effects associated with solely the induction of mitochondrial biogenesis.