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Published on: May 5, 2023
Endothelial Cell Activation by SARS-CoV-2 Spike S1 Protein: A Crosstalk between Endothelium and Innate Immune Cells
Bianca Maria Rotoli1, Amelia Barilli1, Rossana Visigalli1
1Laboratory of General Pathology, Department of Medicine and Surgery, University of Parma, 43125 Parma, Italy.
Insights
Severe COVID-19 involves a cytokine storm and prothrombotic state. SARS-CoV-2 spike protein activates macrophages, which then amplify endothelial cell activation, contributing to vascular damage and coagulopathy.
Area of Science:
- * Immunology
- * Vascular Biology
- * Virology
Background:
- * Severe COVID-19 is linked to hyperinflammation and a prothrombotic state, with endothelial dysfunction playing a key role.
- * The exact mechanisms of COVID-19-associated coagulopathy and the role of SARS-CoV-2 infection in endothelial cells are debated.
- * This study investigates the impact of the SARS-CoV-2 spike S1 protein on human lung microvascular endothelial cells (HLMVECs) and endothelium-macrophage interactions.
Purpose of the Study:
- * To determine the effect of the SARS-CoV-2 spike S1 protein on HLMVEC activation.
- * To explore the role of macrophage-derived factors in mediating spike protein-induced endothelial cell responses.
- * To elucidate the mechanisms underlying endothelial dysfunction and coagulopathy in severe COVID-19.
Main Methods:
- * HLMVECs were exposed directly to the SARS-CoV-2 spike S1 protein or to conditioned medium from spike S1-activated human monocyte-derived macrophages (MDMs).
- * Expression levels of pro-inflammatory mediators, adhesion molecules, chemokines, and coagulation factors were analyzed.
- * Key markers assessed included ICAM-1, VCAM-1, CXCL8/IL-8, CCL2/MCP1, CXCL10/IP-10, tissue factor (TF), and thrombomodulin (THBD).
Main Results:
- * Both MDMs and HLMVECs showed increased pro-inflammatory mediator expression upon S1 protein exposure.
- * HLMVECs exposed to conditioned medium from activated MDMs exhibited heightened activation, with significant induction of adhesion molecules (ICAM-1, VCAM-1) and chemokines (CXCL8/IL-8, CCL2/MCP1, CXCL10/IP-10).
- * Exposure to conditioned medium from activated MDMs also markedly increased tissue factor (TF) expression and decreased thrombomodulin (THBD) in HLMVECs.
Conclusions:
- * Pro-inflammatory mediators released by macrophages activated by the SARS-CoV-2 spike protein amplify endothelial cell activation.
- * This amplified endothelial activation contributes to impaired vascular integrity and a pro-coagulative endothelium.
- * The findings highlight a critical endothelium-macrophage crosstalk mechanism in COVID-19 pathogenesis, promoting vascular dysfunction and coagulopathy.
Background:
Emerging evidences suggest that in severe COVID-19, multi-organ failure is associated with a hyperinflammatory state (the so-called "cytokine storm") in combination with the development of a prothrombotic state. The central role of endothelial dysfunction in the pathogenesis of the disease is to date accepted, but the precise mechanisms underlying the associated coagulopathy remain unclear. Whether the alterations in vascular homeostasis directly depend upon the SARS-CoV-2 infection of endothelial cells or, rather, occur secondarily to the activation of the inflammatory response is still a matter of debate. Here, we address the effect of the SARS-CoV-2 spike S1 protein on the activation of human lung microvascular endothelial cells (HLMVEC). In particular, the existence of an endothelium-macrophage crosstalk in the response to the spike protein has been explored.
Methods And Results:
The effect of the spike protein is addressed in human lung microvascular endothelial cells (HLMVEC), either directly or after incubation with a conditioned medium (CM) of human monocyte-derived macrophages (MDM) previously activated by the spike S1 protein (CM-MDM). Both MDM and HLMVEC are activated in response to the S1 protein, with an increased expression of pro-inflammatory mediators. However, when HLMVEC are exposed to CM-MDM, an enhanced cell activation occurs in terms of the expression of adhesion molecules, pro-coagulant markers, and chemokines. Under this experimental condition, ICAM-1 and VCAM-1, the chemokines CXCL8/IL-8, CCL2/MCP1, and CXCL10/IP-10 as well as the protein tissue factor (TF) are markedly induced. Instead, a decrease of thrombomodulin (THBD) is observed.
Conclusion:
Our data suggest that pro-inflammatory mediators released by spike-activated macrophages amplify the activation of endothelial cells, likely contributing to the impairment of vascular integrity and to the development of a pro-coagulative endothelium.
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