John Murphy, M.D., MPH, D.P.H., President The COVID19 Long-haul Foundation<\/p>\n\n\n\n
Abstract<\/strong> The SARS-CoV-2 pandemic has left a substantial subset of survivors with chronic, multisystem symptoms. The term long-COVID<\/em> (or PASC) encompasses a spectrum of manifestations, frequently including profound fatigue, post-exertional malaise, cognitive disturbance (\u201cbrain fog\u201d), orthostatic intolerance, myalgias, and dysautonomia. While pathogenesis is multifactorial \u2014 involving immune dysregulation, viral persistence, endothelial damage, and autoimmunity \u2014 mitochondria have emerged as a plausible unifying locus at which viral insult, inflammation, and metabolic insufficiency converge.[1\u20134] Nature+2PMC+2<\/a><\/p>\n\n\n\n Mitochondria are central to cellular energy generation, redox homeostasis, calcium buffering, innate immune signaling, and apoptosis. Their dysfunction can thus produce systemic symptoms that mirror the multi-organ complaints reported by long-COVID patients. This review focuses on mitochondrial depletion (a sustained or progressive decrease in mtDNA copy number and\/or mass), outlines mechanisms by which SARS-CoV-2 can perturb mitochondrial integrity, and summarizes clinical and laboratory approaches to detect and quantify mitochondrial depletion in long-COVID.<\/p>\n\n\n\n This manuscript focuses on acquired mitochondrial depletion\/dysfunction in the context of SARS-CoV-2 infection and the persistent syndrome that follows.<\/p>\n\n\n\n Population studies and mechanistic cohorts indicate that mitochondrial dysfunction is detectable in a non-trivial fraction of long-COVID patients. Multiple studies show altered mitochondrial parameters in peripheral blood mononuclear cells (PBMCs), platelets, plasma metabolomics, and skeletal muscle biopsies of patients with PASC.[2,9\u201312] PMC+2PMC+2<\/a><\/p>\n\n\n\n While exact prevalence estimates vary (reflecting cohort selection, sampling time since infection, and assay heterogeneity), a consistent picture emerges: a sizable subset of patients with fatigue-predominant PASC exhibit decreased mtDNA copy number, lowered cellular ATP generation, and abnormal mitochondrial morphology on electron microscopy. Population-level mtDNA-copy number studies also link lower leukocyte mtDNA with adverse outcomes in acute COVID-19 and may relate to long-term sequelae.[11,13] Wiley Online Library+1<\/a><\/p>\n\n\n\n Multiple, sometimes overlapping, mechanisms plausibly explain how SARS-CoV-2 causes sustained mitochondrial injury and depletion:<\/p>\n\n\n\n SARS-CoV-2 proteins interact with mitochondrial membranes and regulatory factors, perturbing mitochondrial dynamics, inhibiting mitochondrial antiviral signaling (MAVS), and altering oxidative phosphorylation.[2,14,15] Viral proteins can localize to mitochondria, subvert mitophagy, and dysregulate mitochondrial fission-fusion balance, promoting fragmentation or uncontrolled fusion that impairs function. PMC+2Physiology Journals+2<\/a><\/p>\n\n\n\n Sustained type I and III interferon signaling, persistent immune activation, and cytokine milieu changes can secondarily damage mitochondria through oxidative and nitrosative stress, dysregulate mitochondrial biogenesis, and induce mitochondrial DNA release that perpetuates inflammation.[16\u201318] Persistent IFN-\u03b3 signatures have been associated with long-COVID and may influence mitochondrial physiology. Financial Times+1<\/a><\/p>\n\n\n\n Inflammation and metabolic dysregulation drive excessive ROS formation, damaging mtDNA and mitochondrial membranes. Cumulative mtDNA damage can lower effective mtDNA copy number (via strand breaks and degradation) and impair replication.[12,19] PNAS+1<\/a><\/p>\n\n\n\n Disturbance of PINK1\/Parkin signaling, altered autophagy, and defective mitophagy lead to accumulation of dysfunctional mitochondria and eventual loss of functional mitochondrial mass.[2,20] Electron microscopy studies in some PASC cohorts document abnormal mitochondrial morphology and autophagy marker changes consistent with deranged turnover. SpringerLink+1<\/a><\/p>\n\n\n\n Endotheliitis and microthrombosis noted in COVID-19 produce tissue hypoxia, which alters mitochondrial dynamics and may favor glycolytic shifts while reducing mitochondrial biogenesis, ultimately decreasing functional mitochondrial content in affected tissues (e.g., muscle, brain). Nature<\/a><\/p>\n\n\n\n Variants in nuclear genes that maintain mtDNA (POLG, TK2, RRM2B, DGUOK, etc.) cause classical mtDNA depletion syndromes; subclinical variation in these pathways might predispose some individuals to acquired mitochondrial depletion after viral stress. Emerging genomic studies hint at genetic contributors to PASC susceptibility, including pathways intersecting mitochondrial maintenance.[21,22] Wiley Online Library+1<\/a><\/p>\n\n\n\n In most patients multiple mechanisms overlap; the relative contribution likely determines clinical phenotype (e.g., fatigue-predominant vs. cardiopulmonary vs. cognitive).<\/p>\n\n\n\n Loss of mtDNA copy number and compromised respiratory chain function reduce ATP production. Tissues with high energetic demand (brain, skeletal and cardiac muscle, autonomic ganglia) are especially vulnerable, which aligns with the symptom clusters seen in PASC: cognitive dysfunction, post-exertional malaise, orthostatic intolerance, and myalgias.[4,9,10,23] Nature+2PMC+2<\/a><\/p>\n\n\n\n Excess mitochondrial ROS modifies signaling pathways, causing lipid peroxidation, protein oxidation, and activation of inflammasomes. mtDNA release into circulation functions as a damage-associated molecular pattern (DAMP), stimulating innate immune receptors and sustaining inflammation\u2014thereby creating a feed-forward loop of mitochondrial damage and systemic immune activation.[16,24] PMC+1<\/a><\/p>\n\n\n\n Cells may switch from oxidative phosphorylation toward glycolysis (Warburg-like reprogramming), evident in metabolomic signatures of some PASC cohorts. This switch reduces energy efficiency and can support persistent fatigue, exercise intolerance, and altered immune cell function.[16,25] ScienceDirect+1<\/a><\/p>\n\n\n\n Mitochondrial impairment in neurons and glia can disturb synaptic function, myelination, and neurotransmitter balance. Neuroinflammatory signals and altered cerebrovascular function may exacerbate cognitive symptoms. Recent neuroimaging and immunophenotyping studies in ME\/CFS and PASC point to neuroimmune mechanisms consistent with mitochondrial insufficiency causing cognitive fatigue and effort intolerance.[12,26] PNAS+1<\/a><\/p>\n\n\n\n Multiple study types support mitochondrial involvement:<\/p>\n\n\n\n Collectively, these data support mitochondrial depletion\/dysfunction as a recurring biologic feature in many, though not all, patients with PASC.<\/p>\n\n\n\n A robust clinical-research diagnostic pathway should combine clinical phenotyping with laboratory and functional mitochondrial assessments. Below is a proposed framework for clinical research and specialized clinics.<\/p>\n\n\n\n Given the plausible role of mitochondrial depletion\/dysfunction, therapeutics fall into two broad categories: (1) mitochondrial rescue \/ bioenergetic support<\/em> and (2) upstream modulation of drivers of mitochondrial injury<\/em>.<\/p>\n\n\n\n Mitochondrial depletion and dysfunction provide a biologically plausible and increasingly evidence-supported explanation for many features of long-COVID. The phenomena described span direct viral perturbation of mitochondrial biology, immune-mediated oxidative injury, defective mitophagy, and potential host genetic susceptibility. While heterogeneity and methodological variability complicate interpretation, convergent data from cellular respiration, mtDNA copy number studies, tissue pathology, and metabolomics argue that mitochondria deserve central attention in diagnostic evaluation and therapeutic development for PASC.<\/p>\n\n\n\n Clinical translation requires standardized assays, biomarker-guided trials, and careful patient phenotyping to identify who will benefit from mitochondrial rescue strategies. Given the public-health scale of PASC, coordinated translational programs that test mitochondrial-targeted therapies could have major implications for patient recovery and quality of life.<\/p>\n\n\n\n [Omitted for the draft \u2014 include funding sources, co-authors, and institutional approvals as appropriate.]<\/p>\n\n\n\n Below are peer-reviewed sources and preclinical\/clinical studies cited in this manuscript. Reference numbers correspond to in-text citations. (I\u2019ve included primary articles and reviews from PubMed Central, Nature family journals, Science Advances\/Science reporting, Frontiers, MDPI, and other peer-reviewed journals. The citations below link to the specific sources used during drafting.)<\/p>\n\n\n\n
A growing body of evidence implicates mitochondrial dysfunction \u2014 including depletion of mitochondrial DNA (mtDNA), loss of mitochondrial membrane potential, impaired oxidative phosphorylation, deranged mitochondrial dynamics, and dysfunctional mitophagy \u2014 as central to the clinical syndrome known as long-COVID or post-acute sequelae of SARS-CoV-2 infection (PASC). This review synthesizes mechanistic, cellular, and clinical data relating viral\u2013host interactions to sustained mitochondrial injury, surveys biomarkers and diagnostic strategies that quantify mitochondrial depletion and dysfunction in patients with long-COVID, and outlines implications for therapy and future research. We emphasize heterogeneity in clinical presentation and underlying biology, discuss methodological considerations for mtDNA and bioenergetic assays, and highlight therapeutic avenues aimed at mitochondrial rescue. Finally, we propose a diagnostic algorithm that integrates clinical phenotyping with mitochondrial biomarkers to stratify patients for targeted interventions and clinical trials.<\/p>\n\n\n\n
\n\n\n\nIntroduction<\/h2>\n\n\n\n
\n\n\n\nDefinitions and scope<\/h2>\n\n\n\n
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\n\n\n\nEpidemiology: how common is mitochondrial involvement in long-COVID?<\/h2>\n\n\n\n
\n\n\n\nEtiology: mechanisms linking SARS-CoV-2 infection to mitochondrial depletion<\/h2>\n\n\n\n
1. Direct viral\u2013mitochondrial interactions<\/h3>\n\n\n\n
2. Innate immune activation and persistent inflammation<\/h3>\n\n\n\n
3. Oxidative stress and reactive oxygen species (ROS)\u2013induced mtDNA damage<\/h3>\n\n\n\n
4. Impaired mitophagy and mitochondrial quality control<\/h3>\n\n\n\n
5. Microvascular\/endothelial injury and local hypoxia<\/h3>\n\n\n\n
6. Host genetic predisposition and mtDNA maintenance gene variants<\/h3>\n\n\n\n
\n\n\n\nPathophysiology: from molecular injury to systemic symptoms<\/h2>\n\n\n\n
Energetic failure and tissue vulnerability<\/h3>\n\n\n\n
Redox imbalance and secondary signaling<\/h3>\n\n\n\n
Altered metabolic reprogramming<\/h3>\n\n\n\n
Neuroimmune interface and central symptoms<\/h3>\n\n\n\n
\n\n\n\nEvidence: human studies linking mtDNA, mitochondrial function, and long-COVID<\/h2>\n\n\n\n
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\n\n\n\nDiagnostic parameters and assays: practical approaches<\/h2>\n\n\n\n
1. Clinical phenotyping<\/h3>\n\n\n\n
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2. Blood biomarkers (minimally invasive)<\/h3>\n\n\n\n
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3. Cellular respiration assays<\/h3>\n\n\n\n
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4. Tissue studies (selected patients)<\/h3>\n\n\n\n
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5. Imaging and neurophysiology<\/h3>\n\n\n\n
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6. Genetic testing (selected cases)<\/h3>\n\n\n\n
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\n\n\n\nMethodological considerations and pitfalls<\/h2>\n\n\n\n
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\n\n\n\nTherapeutic implications and potential interventions<\/h2>\n\n\n\n
Mitochondrial rescue \/ metabolic therapies<\/h3>\n\n\n\n
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Upstream immune and viral targets<\/h3>\n\n\n\n
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Clinical trial considerations<\/h3>\n\n\n\n
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\n\n\n\nProposed diagnostic and research algorithm (summary)<\/h2>\n\n\n\n
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\n\n\n\nResearch gaps and priorities<\/h2>\n\n\n\n
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\n\n\n\nConclusion<\/h2>\n\n\n\n
\n\n\n\nAcknowledgments<\/h2>\n\n\n\n
\n\n\n\nReferences<\/h2>\n\n\n\n
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