Mitochondria and microbiota dysfunction in COVID-19 pathogenesis.

The COVID-19 pandemic caused by the coronavirus (SARS-CoV-2) has taken the world by surprise into a major crisis of overwhelming morbidity and mortality. This highly infectious disease is associated with respiratory failure unusual in other coronavirus infections. Mounting evidence link the accelerated progression of the disease in COVID-19 patients to the hyper-inflammatory state termed as the "cytokine storm" involving major systemic perturbations. These include iron dysregulation manifested as hyperferritinemia associated with disease severity. Iron dysregulation induces reactive oxygen species (ROS) production and promotes oxidative stress. The mitochondria are the hub of cellular oxidative homeostasis. In addition, the mitochondria may circulate "cell-free" in non-nucleated platelets, in extracellular vesicles and mitochondrial DNA is found in the extracellular space. The heightened inflammatory/oxidative state may lead to mitochondrial dysfunction leading to platelet damage and apoptosis. The interaction of dysfunctional platelets with coagulation cascades aggravates clotting events and thrombus formation. Furthermore, mitochondrial oxidative stress may contribute to microbiota dysbiosis, altering coagulation pathways and fueling the inflammatory/oxidative response leading to the vicious cycle of events. Here, we discuss various cellular and systemic incidents caused by SARS-CoV-2 that may critically impact intra and extracellular mitochondrial function, and contribute to the progression and severity of the disease. It is crucial to understand how these key modulators impact COVID-19 pathogenesis in the quest to identify novel therapeutic targets that may reduce fatal outcomes of the disease.

Murine cytomegalovirus infection exacerbates complex IV deficiency in a model of mitochondrial disease.

The influence of environmental insults on the onset and progression of mitochondrial diseases is unknown. To evaluate the effects of infection on mitochondrial disease we used a mouse model of Leigh Syndrome, where a missense mutation in the Taco1 gene results in the loss of the translation activator of cytochrome c oxidase subunit I (TACO1) protein. The mutation leads to an isolated complex IV deficiency that mimics the disease pathology observed in human patients with TACO1 mutations. We infected Taco1 mutant and wild-type mice with a murine cytomegalovirus and show that a common viral infection exacerbates the complex IV deficiency in a tissue-specific manner. We identified changes in neuromuscular morphology and tissue-specific regulation of the mammalian target of rapamycin pathway in response to viral infection. Taken together, we report for the first time that a common stress condition, such as viral infection, can exacerbate mitochondrial dysfunction in a genetic model of mitochondrial disease.

Targeting mitochondria in the infection strategy of the hepatitis C virus.

Hepatitis C virus (HCV) infection induces a state of oxidative stress more pronounced than that observed in many other inflammatory diseases. Here, we propose a temporal sequence of events in the HCV-infected cell whereby the primary alteration consists of a release of Ca(2+) from the endoplasmic reticulum, followed by uptake into mitochondria. This ensues successive mitochondrial dysfunction leading to the generation of reactive oxygen species and a progressive metabolic adaptive response. Evidence is provided for a positive feed-back mechanism between alterations of calcium and redox homeostasis. This likely involves deregulation of the mitochondrial permeability transition and induces progressive dysfunction of cellular bioenergetics. Pathogenetic implications of the model and new opportunities for therapeutic intervention are discussed. This article is part of a Directed Issue entitled: Bioenergetic dysfunction, adaptation and therapy.

Organelle dysfunction in hepatitis C virus-associated steatosis: anything to learn from nonalcoholic steatohepatitis?

Nonalcoholic fatty liver disease (NAFLD) spans a pathological spectrum from nonalcoholic steatosis to steatohepatitis. The pathophysiology of this disorder is complex, but includes insulin resistance and disrupted lipid and carbohydrate homeostasis, which at a subcellular level results in oxidative stress, free fatty acid-mediated lipotoxicity, defects in mitochondrial function, endoplasmic reticulum stress and cytokine-mediated toxicity. In chronic hepatitis C (CHC), systemic metabolic derangements similar to NAFLD may be operative, but in addition, virus-specific factors contribute to steatosis. The mechanisms for steatosis in CHC appear to share common pathways with those observed in NAFLD. This article outlines our current understanding of the subcellular mechanisms of steatosis in NAFLD and CHC, including their similarities and differences.

Parallel high throughput neuronal toxicity assays demonstrate uncoupling between loss of mitochondrial membrane potential and neuronal damage in a model of HIV-induced neurodegeneration.

Neurocognitive deficits seen in HIV-associated neurocognitive disorders (HANDs) are attributed to the release of soluble factors from CNS-resident, HIV-infected and/or activated macrophages and microglia. To study HIV-associated neurotoxicity, we used our in vitro model in which primary rat neuronal/glial cultures are treated with supernatants from cultured human monocyte-derived macrophages, infected with a CNS-isolated HIV-1 strain (HIV-MDM). We found that neuronal damage, detected as a loss of microtubule-associated protein-2 (MAP2), begins as early as 2h and is preceded by a loss of mitochondrial membrane potential (Δψ(m)). Interestingly, inhibitors of calpains, but not inhibitors of caspases, blocked MAP2 loss, however neither type of inhibitor prevented the loss of Δψ(m). To facilitate throughput for these studies, we refined a MAP2 cell-based-ELISA whose data closely compare with our standardized method of hand counting neurons. In addition, we developed a tetramethyl rhodamine methyl ester (TMRM)-based multi-well fluorescent plate assay for the evaluation of whole culture Δψ(m). Together, these findings indicate that calpain activation and loss of Δψ(m) may be parallel pathways to death in HIV-MDM-treated neurons and also demonstrate the validity of plate assays for assessing multiple experimental parameters as is useful for screening neurotherapeutics for neuronal damage and death.

HIV infection, inflammation, immunosenescence, and aging.

Although antiretroviral therapy for HIV infection prevents AIDS-related complications and prolongs life, it does not fully restore health. Long-term treated patients remain at higher than expected risk for a number of complications typically associated with aging, including cardiovascular disease, cancer, osteoporosis, and other end-organ diseases. The potential effect of HIV on health is perhaps most clearly exhibited by a number of immunologic abnormalities that persist despite effective suppression of HIV replication. These changes are consistent with some of the changes to the adaptive immune system that are seen in the very old ("immunosenescence") and that are likely related in part to persistent inflammation. HIV-associated inflammation and immunosenescence have been implicated as causally related to the premature onset of other end-organ diseases. Novel therapeutic strategies aimed at preventing or reversing these immunologic defects may be necessary if HIV-infected patients are to achieve normal life span.

Hepatitis C virus-induced oxidative stress and mitochondrial dysfunction: a focus on recent advances in proteomics.

The natural history of chronic hepatitis C virus (HCV) infection presents two major aspects. On one side, the illness is by itself benign, whereas, on the other side, epidemiological evidence clearly identifies chronic HCV infection as the principal cause of cirrhosis, hepatocellular carcinoma, and extrahepatic diseases, such as autoimmune type II mixed cryoglobulinemia and some B cell non-Hodgkin's lymphomas. The mechanisms responsible for the progression of liver disease to severe liver injury are still poorly understood. Nonetheless, considerable biological data and studies from animal models suggest that oxidative stress contributes to steatohepatitis and that the increased generation of reactive oxygen and nitrogen species, together with the decreased antioxidant defense, promotes the development of hepatic and extrahepatic complications of HCV infection. The principal mechanisms causing oxidative stress in HCV-positive subjects have only been partially elucidated and have identified chronic inflammation, iron overload, ER stress, and a direct activity of HCV proteins in increasing mitochondrial ROS production, as key events. This review summarizes current knowledge regarding mechanisms of HCV-induced oxidative stress with its long-term effects in the context of HCV-related diseases, and includes a discussion of recent contributions from proteomics studies.

Mitochondrial membrane potential and apoptosis of blood mononuclear cells in untreated HIV-1 infected patients.

OBJECTIVES: Infection with HIV leads to progressive CD4 T-cell loss, resulting in AIDS. Apoptosis is the main mechanism for the loss of infected and bystander cells, but the complex interacting factors inducing and inhibiting apoptosis are not fully understood. Mitochondrial dysfunction is a pivotal step of the apoptotic cascade and can result in reduced mitochondrial membrane potential. METHODS: The mitochondrial membrane potential of peripheral blood mononuclear cells (PBMC) was measured by flow cytometry using the dye JC-1 (Molecular Probes Inc). Apoptotic cells were identified using the Annexin V assay (Becton Dickinson GmbH). RESULTS: The mitochondrial membrane potential of PBMC was significantly decreased and apoptotic cell rate was increased in HIV-infected therapy-naïve patients compared with HIV-negative controls. There was a highly significant correlation between the mitochondrial membrane potential and the rate of apoptosis. CD4 cell count was correlated negatively to the apoptotic rate and positively to the mitochondrial membrane potential. CONCLUSIONS: The JC-1 assay is a sensitive tool to detect changes of mitochondrial membrane potential associated with apoptosis in HIV-infected therapy-naïve patients. We could show in vivo that a reduction of mitochondrial membrane potential is correlated to apoptosis of PBMC, CD4 cell count and HIV viral load during HIV infection.

Longitudinal effects of hepatitis C virus treatment on hepatic mitochondrial dysfunction assessed by C-methionine breath test.

BACKGROUND: Hepatitis C virus (HCV) infection is characterized by remarkable levels of oxidative stress induced by virus interactions with hepatic mitochondria. AIM: To examine hepatic mitochondrial function in HCV-infected patients assessed by a non-invasive (13)C-methionine breath test (MeBT) and to explore longitudinal effects of antiviral treatment. METHODS: Twenty-one patients with chronic hepatitis C undergoing antiviral treatment with pegIFNalpha and ribavirin and 20 healthy controls were studied. MeBT was performed at baseline, week 12, end-of-treatment and after 24 weeks of follow-up in all patients with early virological response (n = 15). RESULTS: Twelve patients achieved sustained virological response (SVR); three patients relapsed for HCV-RNA replication. Cumulative percentage 13C-exhalation (cPDR(1.5h)) was significantly decreased in HCV-infected individuals compared to controls irrespective of genotype and fibrosis stage (P < 0.001). Antiviral treatment induced a further decay in cPDR(1.5h) (P < 0.01). After treatment cessation, 13C-exhalation returned at least to baseline values in all patients. SVR was even associated with a mean cPDR(1.5h) increase of 70% compared to baseline. CONCLUSIONS: Hepatitis C virus infection and antiviral treatment synergistically impair hepatic mitochondrial function, which may return to normal after sustained virus elimination. MeBT may be a valuable diagnostic instrument for monitoring hepatic mitochondrial function in particular in patients with mitochondrial comorbidities.

The influence of HIV infection and antiretroviral therapy on the mitochondrial membrane potential of peripheral mononuclear cells.

OBJECTIVES: Clinical disorders occurring in HIV-infected patients on antiretroviral therapy (ART) have been linked to mitochondrial dysfunction, for example, lactic acidosis and lipodystrophy. Mitochondrial membrane potential (delta psi m) is the most direct measure of the state of energization of the mitochondria. We analysed delta psi m, of peripheral blood mononuclear cells (PBMCs) in HIV-negative, healthy subjects (n=8), HIV-infected, treatment-naive patients (n=30), and HIV-infected patients on ART (n=58). The influence of ART was analysed in six patients who started their first regimen. METHODS: The delta psi m of PBMC was measured by flow cytometry using the dye JC-1. RESULTS: The delta psi m was significantly lower in HIV-infected patients than in HIV-negative controls. This difference was detected in both treated (P = 0.0001) and untreated patients (P = 0.001). The delta psi m of PBMCs was highly correlated with CD4+ T-cell count in therapy-naive patients (P = 0.002, r = 0.546) and in treated patients (P = 0.028, r = 0.288). The delta psi m increased significantly in therapy-naive patients after starting ART (P = 0.001). Patients with lipoatrophy had significantly lower delta psi m than patients without lipodystrophy or with lipohypertrophy (P = 0.023). CONCLUSIONS: In HIV-infected persons delta psi m is significantly reduced. Patients with lipoatrophy have significantly reduced delta psi m. This is the first study showing that the delta psi m of PBMCs is highly correlated with CD4+ T-cell count in HIV infection.

Mitochondrial dysfunction in hepatitis C virus infection.

The mechanisms of liver injury in chronic hepatitis C virus (HCV) infection are poorly understood though HCV induces a state of hepatic oxidative stress that is more pronounced than that present in many other inflammatory diseases. This mini-review will focus on recent findings revealing an unexpected role of mitochondria in providing a central role in the innate immunity and in addition will illustrate the application of stably transfected human-derived cell lines, inducibly expressing the entire HCV open reading frame for in vitro studies on mitochondria. Results obtained by a comparative analysis of the respiratory chain complexes activities along with mitochondrial morpho-functional confocal microscopy imaging show a detrimental effect of HCV proteins on the cell oxidative metabolism with specific inhibition of complex I activity, decrease of mtDeltaPsi, increased production of reactive oxygen species. A possible de-regulation of calcium recycling between the endoplasmic reticulum and the mitochondrial network is discussed to provide new insights in the pathogenesis of hepatitis C.

HIV-associated neuromuscular weakness syndrome.

OBJECTIVE: To investigate progressive, severe neuromuscular weakness associated with lactic acidosis in some HIV-infected patients after exposure to nucleoside reverse transcriptase inhibitors (NRTI). METHODS: HIV-associated neuromuscular weakness syndrome (HANWS) was retrospectively identified and classified based on the level of diagnostic certainty: possible (progressive weakness owing to neuromuscular disease), probable (progressive neuromuscular weakness with documented exclusion of confounding causes), or definite (progressive weakness and electrophysiological or pathological evidence of neuromuscular pathology). RESULTS: Of 69 patients identified with HANWS, 27 had definite HANWS, 19 probable, and 23 possible. In 44 patients with documented follow-up, 16 required intubation and nine died. There was a marginal association between death and hyperlactatemia (P = 0.061). At onset of neurological symptoms, 68 were receiving antiretroviral therapy, including stavudine for 61 (89.7%). Serum lactate level was elevated (> 2.2 mmol/l) in 30/37 (81%), with a trend towards an association between hyperlactatemia and stavudine usage (P = 0.087). In 25, neurological symptoms occurred after antiretroviral therapy discontinuation (median, 14 days). Electrophysiological studies (n = 24) indicated sensorimotor neuropathy in 20 patients and myopathy in three. Nerve biopsy (n = 9) revealed axonal degeneration and inflammation in three, mixed axonal and demyelinating lesions in three, and primary axonal neuropathy in three. Of 15 muscle biopsies, three revealed inflammation and four mitochondrial abnormalities. CONCLUSIONS: A severe neuromuscular weakness syndrome may occur in HIV-infected individuals. The association with hyperlactatemia and NRTI exposure supports mitochondrial toxicity as a pathogenesis. In some, the onset of neurological symptoms lagged significantly after discontinuation of antiretroviral therapy, suggesting that different etiological mechanisms may underlie these cases.