SARS-CoV-2 SPIKE PROTEIN DESTABILIZES MICROVASCULAR HOMEOSTASIS

ABSTRACT

Background: SARS-CoV-2 infection can compromise respiratory function and cause thrombotic events. SARS-CoV-2 binds to and mediates downregulation of angiotensin converting enzyme 2 (ACE2) on infected cells. Diminished enzymatic activity of ACE2 could result in increased concentrations of the pro-inflammatory molecules angiotensin II and bradykinin, contributing to SARS-CoV-2 pathology. Methods: Immunofluorescence microscopy and digital image data quantification, Computer assisted molecular docking analyses, Western blot. Results: Using immunofluorescence microscopy of lung tissues from uninfected and SARS-CoV-2 infected individuals, we find evidence that ACE2 is highly expressed in the pulmonary alveolar epithelium and is significantly reduced along the alveolar lining of SARS-CoV-2 infected lungs. Ex vivo analyses indicate that ACE2 is readily detected on primary human pulmonary alveolar epithelial and primary human aortic endothelial cells (HAoECs). Exposure of these cells to recombinant SARS-CoV-2 spike protein was sufficient to reduce surface ACE2 expression. Moreover, exposure of HAoECs to spike protein induced endothelial dysfunction (increased expression of von Willebrand Factor and decreased expression of Krüppel-like Factor 2), caspase activation, and apoptosis. Exposure of HAoECs to bradykinin (BK, 10μ M) induced calcium signaling and endothelial dysfunction but did not adversely affect viability. Computer assisted analyses of molecules with potential to bind bradykinin receptor B2 (BKRB2) suggested a potential role for aspirin as a bradykinin antagonist. When tested in our in vitro model, we found that aspirin (1μM) could significantly blunt cell signaling, and endothelial dysfunction caused by bradykinin in these cells. Conclusion: SARS-CoV-2 causes complex effects on microvascular homeostasis that potentially contribute to organ dysfunction and coagulopathies. Reduced ACE2 enzymatic activity could contribute to inflammation and pathology in the lung. Our studies add to this understanding by providing evidence that spike protein alone can mediate adverse effects on vascular cells. Understanding these mechanisms of pathogenesis may provide rationale for interventions, such as interference with the interactions of spike protein or bradykinin with endothelial cells, that could limit microvascular events associated with SARS-CoV-2 infection and stabilize microvascular homeostasis in COVID-19 disease.