Rapid endothelial infection, endothelialitis and vascular damage characterise SARS-CoV-2 infection in a human lung-on-chip model

Abstract

Background: Severe manifestations of COVID-19 include hypercoagulopathies and systemic endothelialitis. The underlying dynamics of vascular damage, and whether it is a direct consequence of endothelial infection or an indirect consequence of immune cell-mediated cytokine storms is unknown. This is in part because in vitro infection models are typically monocultures of epithelial cells or fail to recapitulate vascular physiology. Methods: We establish a vascularised lung-on-chip infection model consisting of a co-culture of primary human alveolar epithelial (epithelial) cells and human lung microvascular endothelial (endothelial) cells, with the optional addition of CD14+ macrophages to the epithelial side. This model was used to study the dynamics of viral replication and host responses to a low dose infection of SARS-CoV-2 of the epithelial layer. Findings: SARS-CoV-2 inoculation does not lead to a productive amplification of infectious virions. However, both genomic and antisense viral RNA can be found in endothelial cells within 1-day post infection (dpi) and persist upnto 3 dpi. This generates an NF-KB-mediated inflammatory response typified by IL-6 secretion and signalling coupled with a weak antiviral interferon response, even in the absence of immune cells. Endothelial inflammation leads to a progressive loss of barrier integrity, a subset of cells also shows a transient hyperplasic phenotype. Administration of Tocilizumab slows the loss of barrier integrity but does not reduce the occurrence of the latter. Interpretation: Endothelial infection can occur through basolateral transmission from infected epithelial cells at the air-liquid interface. SARS-CoV-2 mediated inflammation occurs despite the lack of rapid viral replication and is transient in epithelial cells but persistent in endothelial cells. Infected endothelial cells might be a key source of circulating IL-6 in COVID-19 patients. Vascular damage occurs independently of immune-cell mediated cytokine storms, whose effect would only exacerbate the damage. Funding: Core support from EPFL.

A human-airway-on-a-chip for the rapid identification of candidate antiviral therapeutics and prophylactics

“…47 ). Subsequent preprints and publications from other laboratories also have described the utility of using Organ Chips to study infection and inflammation responses caused by SARS-CoV-2 infection [48][49][50] . However, all of these reports have used chips lined with human primary alveolar epithelial cells or cell lines rather than airway epithelium, which is the primary target of initial infection in vivo, and none explored drug repurposing.…”

Experimental Models of SARS-CoV-2 Infection: Possible Platforms to Study COVID-19 Pathogenesis and Potential Treatments

“…Recently, a vascularized lungon-a-chip infection model was developed that consists of a coculture of primary human alveolar and human lung microvascular endothelial cells with the optional addition of CD14-positive macrophages. This model was used to study SARS-CoV-2 replication and host response to infection(63). The use of an alveolus chip was reported by Zhang et al(64), who were able to reconstitute the key features of the alveolar-capillary barrier.…”

Human-Based Advanced in vitro Approaches to Investigate Lung Fibrosis and Pulmonary Effects of COVID-19

“…However, based on the analysis of single cell RNA sequencing datasets and in vitro infectivity experiments it has been suggested that ATII cells represent the primary target of SARS-CoV-2 in the alveoli [(82, 83, 92, 95, 100-102); Figure 1E]. Notably, increased susceptibility of an ATII cell subpopulation has been consistently reported by in vitro studies (99,101). Gene expression profiling revealed an apoptotic signature and a strong downregulation of ATII-specific genes including surfactant proteins in heavily infected ATII cell models (101)(102)(103).…”

“…In the alveoli, SARS-CoV-2 can be detected in ATI and ATII cells, endothelial cells and immune cells of deceased COVID-19 patients, which is in line with experimental findings from 3D in vitro models (82, 95, 98-101). Infection of ATI cells, endothelial cells and alveolar immune cells presumably results in a disturbed immune response and persistent inflammation (98)(99)(100). However, based on the analysis of single cell RNA sequencing datasets and in vitro infectivity experiments it has been suggested that ATII cells represent the primary target of SARS-CoV-2 in the alveoli [(82, 83, 92, 95, 100-102); Figure 1E].…”