SARS-CoV-2 spike S1-mediated HIF-2α activation in retinal endothelial cells suggests a mechanism contributing to post-COVID endothelial dysfunction.

Background
Post-COVID-19 syndrome (PCS) is characterized by persistent symptoms such as fatigue, cardiovascular abnormalities, and cognitive impairment. Endothelial dysfunction (ED) has been proposed as a contributing factor, but underlying mechanisms remain unclear. We investigated whether SARS-CoV-2 spike protein subunit 1 (S1) is sufficient to induce ED in human retinal endothelial cells (HRECs) in vitro and whether pharmacologic inhibition of HIF-2α signaling modulates endothelial barrier integrity.Methods
In this study, we characterized 41 PCS patients and 24 pre-pandemic healthy controls. The effects of recombinant S1 and plasma from patients with severe PCS on endothelial function were assessed in HRECs. Belzutifan was used as a pharmacologic probe to assess the role of HIF-2α signaling in S1- and plasma-associated endothelial responses.Results
PCS patients exhibited elevated erythropoietin, VEGF, and MCP-1 levels compared with controls. VEGF correlated with anti-S1 IgG and was upregulated at the mRNA level in S1-exposed HRECs. Additionally, in vitro exposure to S1 induced ROS production, transient HIF-1α and sustained HIF-2α activation, VEGFR2 upregulation, and impaired endothelial barrier integrity. Plasma from patients with severe PCS increased ROS production and induced modest alterations in endothelial barrier function in HRECs. In both S1- and PCS-plasma-treated cells, pharmacologic HIF-2α inhibition with belzutifan improved endothelial barrier integrity.Conclusion
These findings identify a spike-responsive, HIF-2α-associated ED pathway in retinal endothelial cells. Modulation of this pathway altered endothelial barrier responses to both recombinant S1 and plasma from patients with PCS, highlighting a candidate mechanism that may contribute to PCS-associated vascular dysfunction.