SARS-CoV-2 mitochondriopathy in COVID-19 pneumonia exacerbates hypoxemia.

RATIONALE: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes COVID-19 pneumonia. We hypothesize that SARS-CoV-2 causes alveolar injury and hypoxemia by damaging mitochondria in airway epithelial cells (AEC) and pulmonary artery smooth muscle cells (PASMC), triggering apoptosis and bioenergetic impairment, and impairing hypoxic pulmonary vasoconstriction (HPV), respectively. OBJECTIVES: We examined the effects of: A) human betacoronaviruses, SARS-CoV-2 and HCoV-OC43, and individual SARS-CoV-2 proteins on apoptosis, mitochondrial fission, and bioenergetics in AEC; and B) SARS-CoV-2 proteins and mouse hepatitis virus (MHV-1) infection on HPV. METHODS: We used transcriptomic data to identify temporal changes in mitochondrial-relevant gene ontology (GO) pathways post-SARS-CoV-2 infection. We also transduced AECs with SARS-CoV-2 proteins (M, Nsp7 or Nsp9) and determined effects on mitochondrial permeability transition pore (mPTP) activity, relative membrane potential, apoptosis, mitochondrial fission, and oxygen consumption rates (OCR). In human PASMC, we assessed the effects of SARS-CoV-2 proteins on hypoxic increases in cytosolic calcium, an HPV proxy. In MHV-1 pneumonia, we assessed HPV via cardiac catheterization and apoptosis using the TUNEL assay. RESULTS: SARS-CoV-2 regulated mitochondrial apoptosis, mitochondrial membrane permeabilization and electron transport chain (ETC) GO pathways within 2 hours of infection. SARS-CoV-2 downregulated ETC Complex I and ATP synthase genes, and upregulated apoptosis-inducing genes. SARS-CoV-2 and HCoV-OC43 upregulated and activated dynamin-related protein 1 (Drp1) and increased mitochondrial fission. SARS-CoV-2 and transduced SARS-CoV-2 proteins increased apoptosis inducing factor (AIF) expression and activated caspase 7, resulting in apoptosis. Coronaviruses also reduced OCR, decreased ETC Complex I activity and lowered ATP levels in AEC. M protein transduction also increased mPTP opening. In human PASMC, M and Nsp9 proteins inhibited HPV. In MHV-1 pneumonia, infected AEC displayed apoptosis and HPV was suppressed. BAY K8644, a calcium channel agonist, increased HPV and improved SpO2. CONCLUSIONS: Coronaviruses, including SARS-CoV-2, cause AEC apoptosis, mitochondrial fission, and bioenergetic impairment. SARS-CoV-2 also suppresses HPV by targeting mitochondria. This mitochondriopathy is replicated by transduction with SARS-CoV-2 proteins, indicating a mechanistic role for viral-host mitochondrial protein interactions. Mitochondriopathy is a conserved feature of coronaviral pneumonia that may exacerbate hypoxemia and constitutes a therapeutic target.

Mitochondria in human neutrophils mediate killing of Staphylococcus aureus.

BACKGROUND: Neutrophils play a role in innate immunity and are critical for clearance of Staphylococcus aureus. Current understanding of neutrophil bactericidal effects is that NADPH oxidase produces reactive oxygen species (ROS), mediating bacterial killing. Neutrophils also contain numerous mitochondria; since these organelles lack oxidative metabolism, their function is unclear. We hypothesize that mitochondria in human neutrophils contribute to the bactericidal capacity of S. aureus. METHODS: and Findings: Using human neutrophils isolated from healthy volunteers (n = 13; 7 females, 6 males), we show that mitochondria are critical in the immune response to S. aureus. Using live-cell and fixed confocal, and transmission electron microscopy, we show mitochondrial tagging of bacteria prior to ingestion and surrounding of phagocytosed bacteria immediately upon engulfment. Further, we demonstrate that mitochondria are ejected from intact neutrophils and engage bacteria during vital NETosis. Inhibition of the mitochondrial electron transport chain at Complex III, but not Complex I, attenuates S. aureus killing by 50 ± 7%, comparable to the NADPH oxidase inhibitor apocynin. Similarly, mitochondrial ROS scavenging using MitoTEMPO attenuates bacterial killing 112 ± 60% versus vehicle control. Antimycin A treatment also reduces mitochondrial ROS production by 50 ± 12% and NETosis by 53 ± 5%. CONCLUSIONS: We identify a previously unrecognized role for mitochondria in human neutrophils in the killing of S. aureus. Inhibition of electron transport chain Complex III significantly impairs antimicrobial activity. This is the first demonstration that vital NETosis, an early event in the antimicrobial response, occurring within 5 min of bacterial exposure, depends on the function of mitochondrial Complex III. Mitochondria join NADPH oxidase as bactericidal ROS generators that mediate the bactericidal activities of human neutrophils.

Mitochondrial iron-sulfur clusters: Structure, function, and an emerging role in vascular biology.

Iron-sulfur (Fe-S) clusters are essential cofactors most commonly known for their role mediating electron transfer within the mitochondrial respiratory chain. The Fe-S cluster pathways that function within the respiratory complexes are highly conserved between bacteria and the mitochondria of eukaryotic cells. Within the electron transport chain, Fe-S clusters play a critical role in transporting electrons through Complexes I, II and III to cytochrome c, before subsequent transfer to molecular oxygen. Fe-S clusters are also among the binding sites of classical mitochondrial inhibitors, such as rotenone, and play an important role in the production of mitochondrial reactive oxygen species (ROS). Mitochondrial Fe-S clusters also play a critical role in the pathogenesis of disease. High levels of ROS produced at these sites can cause cell injury or death, however, when produced at low levels can serve as signaling molecules. For example, Ndufs2, a Complex I subunit containing an Fe-S center, N2, has recently been identified as a redox-sensitive oxygen sensor, mediating homeostatic oxygen-sensing in the pulmonary vasculature and carotid body. Fe-S clusters are emerging as transcriptionally-regulated mediators in disease and play a crucial role in normal physiology, offering potential new therapeutic targets for diseases including malaria, diabetes, and cancer.