SARS-CoV-2 targets mitochondria, exacerbating COVID-19 pneumonia

Mitochondrial damage is a conserved feature of coronavirus infection, occurring with human (SARS-CoV-2, HCoV-OC43) and murine (MHV-1) coronaviruses. Coronaviruses damage mitochondria in airway epithelial cells (AEC), pulmonary artery smooth muscle cells (PASMC), pulmonary artery endothelial cells, immune cells and cardiomyocytes by causing rapid transcriptomic changes in nuclear-encoded genes regulating mitochondria and by viral proteins interacting with host mitochondrial proteins. Coronavirus infection causes mitochondrial depolarization, mitochondrial transition pore (MTP) opening, inhibition of the electron transport chain (ETC) and ATP synthetic apparatus, increased mitochondrial fission, apoptosis, and impaired mitochondrial oxygen sensing. Within hours of infection, SARS-CoV-2 induces transcriptional reprogramming of genes relevant to the mitochondrial matrix in AECs, downregulating mRNA encoding ETC complex I components and the ATP synthesis complex. These bioenergetic consequences of SARS-CoV-2 mitochondriopathy may contribute to long COVID. Infection also upregulates dynamin-related protein 1 (DRP1), activating mitochondrial fission while promoting apoptosis by activating apoptosis inducing factor (AIF) and caspase 7. Even without infection, transfection with specific coronaviral proteins opens the MTP and depolarizes the mitochondria, or activates DRP1 and AIF, promoting AEC damage or apoptosis, thereby contributing to diffuse alveolar damage. In human PASMCs, coronaviral M and Nsp9 proteins suppress hypoxic pulmonary vasoconstriction (HPV), a homeostatic mechanism in PASMCs that uses a mitochondrial oxygen sensor to redistribute blood flow to well-ventilated lung regions during pneumonia. Impairment of HPV, seen as intrapulmonary shunting, contributes to the profound hypoxaemia in COVID-19 pneumonia. Coronavirus-induced mitochondriopathy may have therapeutic relevance as blocking AIF-induced apoptosis or enhancing HPV appears beneficial in a MHV-1 model of COVID-19 pneumonia.