A cross-talk between epithelium and endothelium mediates human alveolar–capillary injury during SARS-CoV-2 infection

Abstract

COVID-19, caused by SARS-CoV-2, is an acute and rapidly developing pandemic, which leads to a global health crisis. SARS-CoV-2 primarily attacks human alveoli and causes severe lung infection and damage. To better understand the molecular basis of this disease, we sought to characterize the responses of alveolar epithelium and its adjacent microvascular endothelium to viral infection under a co-culture system. SARS-CoV-2 infection caused massive virus replication and dramatic organelles remodeling in alveolar epithelial cells, alone. While, viral infection affected endothelial cells in an indirect manner, which was mediated by infected alveolar epithelium. Proteomics analysis and TEM examinations showed viral infection caused global proteomic modulations and marked ultrastructural changes in both epithelial cells and endothelial cells under the co-culture system. In particular, viral infection elicited global protein changes and structural reorganizations across many sub-cellular compartments in epithelial cells. Among the affected organelles, mitochondrion seems to be a primary target organelle. Besides, according to EM and proteomic results, we identified Daurisoline, a potent autophagy inhibitor, could inhibit virus replication effectively in host cells. Collectively, our study revealed an unrecognized cross-talk between epithelium and endothelium, which contributed to alveolar–capillary injury during SARS-CoV-2 infection. These new findings will expand our understanding of COVID-19 and may also be helpful for targeted drug development.

Endothelial cells elicit a pro-inflammatory response to SARS-CoV-2 without productive viral infection

“…Nevertheless, we showed that in vitro, endothelial cells are theoretically susceptible to SARS-CoV-2 infection, as they express ACE2, TMPRSS2 and NRP1, albeit at significantly lower levels than epithelial cells. This is in line with other studies that showed expression of SARS-CoV-2 receptors by the endothelium in human tissue or in cultured cells [14,17,23,28]. However, we did not detect endothelial cell infection following exposure to 6 x 10 4 PFU of SARS-CoV-2, whereas epithelial cells were readily infected at the same viral dose.…”

“…These results support those of Wang et al [28], who showed that epithelial cells are more susceptible to infection than endothelial cells. When exposed to higher viral titres, endothelial cells were positive for viral NP protein, suggesting effective viral entry.…”

“…To create a more physiologically relevant in vitro model of the pulmonary endothelium, we adapted our previously described co-culture model of the lung epithelial-endothelial barrier [42], where epithelial [14,17,23,28]. However, we did not detect endothelial cell infection following exposure to 6 x 10 4 PFU of SARS-CoV-2, whereas epithelial cells were readily infected at the same viral dose.…”

“…Evidence regarding direct infection of the endothelium with SARS-CoV-2 remains equivocal. Autopsy studies on COVID-19 patients have suggested the presence of viral particles in the vascular beds of different organs [3,25,26] and others have shown SARS-CoV-2 infection of cultured endothelial cells [27,28] and human blood vessel organoids [29]. In contrast, several studies have failed to find evidence of endothelial infection in deceased COVID-19 patients [30] and called into question the validity of identifying virally-infected cells based on the presence of the SARS-CoV-2 spike protein [31,32].…”

Pulmonary vascular proliferation in patients with severe COVID-19: an autopsy study

“…In vitro studies have reported that alveolar epithelial cells were more susceptible to SARS-CoV-2 infection than pulmonary microvascular endothelial cells. 10 More probably, endothelial cells can be damaged by excessive exposure to proinflammatory cytokines secreted by epithelial cells, leukocytes and macrophages in the context of DAD. In our series, macrophages were the most frequent inflammatory infiltrate observed, which are well-known producers of proangiogenic factors.…”