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

## TL;DR

This study suggests that the SARS-CoV-2 spike protein may contribute to post-COVID endothelial dysfunction by activating HIF-2α in retinal cells.

## Contribution

The study identifies a novel HIF-2α–mediated pathway linking SARS-CoV-2 spike protein to endothelial dysfunction in retinal cells.

## Key findings

- SARS-CoV-2 spike S1 induces HIF-2α activation and impairs endothelial barrier integrity in retinal endothelial cells.
- Pharmacologic inhibition of HIF-2α with belzutifan improves endothelial barrier function in S1-exposed cells.
- Plasma from severe PCS patients also affects endothelial function, which is partially reversed by HIF-2α inhibition.

## Abstract

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.

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.

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.

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.