In a recent study posted to the bioRxiv* preprint server, researchers demonstrated the role of integrin signaling in vascular dysfunction associated with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection.
Following SARS-CoV-2 infection, the vascular barrier is severely damaged. This endothelial malfunctioning by SARS-CoV-2 contributes significantly to life-threatening consequences in coronavirus disease 2019 (COVID-19). The phlogistic phenomena of multiple organ failure, hypoxemia, abnormal coagulation, cytokine storms, and thrombotic complications are linked to endothelial dysfunction caused by SARS-CoV-2 infection.
Angiotensin-converting enzyme 2 (ACE2)-mediated routes have been generally linked to the processes of COVID-19-associated endothelitis. Integrins, on the other hand, have recently surfaced as potential SARS-CoV-2 receptor candidates, and their intricate intracellular signaling processes are critical for preserving endothelial homeostasis.
Of note, the authors of the present study were the first to identify a trend of vascular dysfunction after SARS-CoV-2 infection. They also hypothesized that vascular endothelial cadherin (VE-cadherin), a key endothelial adherens junction protein, was implicated in the SARS-CoV-2-related endothelial dysregulation.
About the study
In the current study, the scientists determined the direct mechanism connecting integrins with vascular dysregulation in SARS-CoV-2 infection. The team also evaluated whether the SARS-CoV-2 spike (S) protein’s arginyl-glycyl-aspartic acid (RGD) motif suppression was enough to alleviate the endothelial dysregulation phenotype in COVID-19.
Primary-derived Human Aortic Endothelial Cells (HAoEC; Promocell C-12271) were used for the investigation. Enzyme-linked immunoassay (ELISA)-based tests were conducted to evaluate contacts between integrins and recombinant SARS-CoV-2 S proteins of wild-type (WT) virus and the Delta and Omicron variants.
These experiments were performed with and without neutralizing antibodies targeting αVβ3 integrin’s active site or its β3 subunit and cyclic RGD peptide molecule, cilengitide. VE-cadherin expression and endothelial barrier damage were quantified using immunofluorescence and transwell permeability tests. Further, Western blot analysis was conducted to detect VE-cadherins.
Results and discussions
The results showed that the SARS-CoV-2 S protein uses its RGD motif to cause the endothelial barrier dysfunction via integrin αVβ3 hijacking. This causes the main junction protein VE-Cadherin to redistribute and internalize, resulting in the barrier disruption phenotype. Similar to the cilengitide, both intracellular and extracellular integrin αVβ3 inhibitors blocked the barrier dysregulation effects induced by SARS-CoV-2.
In detail, the integrin αVβ3 recognizes the SARS-CoV-2 Delta and Omicron variants of concern (VOC)s’ S proteins because they both maintain the RGD site. Both integrin neutralizing antibodies and cilengitide inhibited S binding to integrins in the same way, indicating that this interaction was probably RGD-dependent.
Although integrin antagonists like GLPG-0187 efficiently minimized SARS-CoV-2 infection at high doses, they failed to inhibit S interaction with integrins at comparable concentrations with cilengitide. This might be because of the wide range of GLPG-0187 activity relative to the highly selective binding of cilengitide with αVβ3.
The binding of SARS-CoV-2 S protein with integrin αVβ3 had no discernible influence on VE-cadherin levels. Nonetheless, SARS-CoV-2 infection caused a significant change in VE-cadherin structure by inducing its internalization, which resulted in the malfunctioning endothelial barrier phenotype.
Previous reports, including the current authors’ prior investigations, have demonstrated that the SARS-CoV-2 S protein stimulates Ras homolog family member A (RhoA) in infected venous endothelial cells via Ras-related C3 botulinum toxin substrate 1 (Rac1) downregulation, which enhances endothelial leakage and permeability. After integrin ligation, VE-cadherin collaborates with Rac1 to suppress RhoA and control cell spreading.
Combining the previous and current findings, the authors suggest the prevention of primary interaction between host proteins and SARS-CoV-2 using integrin antagonists might be efficient in precluding vascular damage in COVID-19.
The study findings have revealed the downstream signaling transduction route that connects integrins to vasculopathy observed during COVID-19. The SARS-CoV-2 S protein via its RGD motif interacts with αVβ3 and causes events of vascular leakage. The study suggests integrins as an alternative SARS-CoV-2 receptor, especially because integrin interaction can explain several COVID-19-induced endothelial dysfunction events.
Cilengitide, an αVβ3 integrin inhibitor, has shown potential in preventing the SARS-CoV-2-associated endothelial dysregulation. The present preliminary findings imply that by decreasing the initial signal that activates integrins, the downstream signaling pathways that govern cellular hyperpermeability in COVID-19 can be reduced.
Overall, the study suggests that the endothelial cells are important participants in viral infection, and delineation of the processes governing vascular integrity is necessary for the generation of therapeutics to combat SARS-CoV-2 pathogenesis.
bioRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.