The Impact of COVID-19 Spike Protein on Retinal Microvascular Environment

ABSTRACT

Purpose: Background: Despite being primarily a respiratory disease, COVID-19 can lead to non-respiratory complications, including myocardial infarction and acute ischemic stroke. Moreover, COVID-19 spike protein (SP) was reported in the retina of deceased patients with COVID-19. Retinal microvascular abnormalities as loss of microvasculature and distinct thinning of the microcapillaries were reported in patients who recovered from COVID-19. We are still in the midst of the COVID-19 pandemic, with more deaths and cases every day. Therefore investigating the impact of COVID-19 on the retinal neurovascular environment and the long-term effect of this virus on vision is of great interest. Purpose: To study the contribution of COVID-19 SP to retinal inflammation and vascular death. Methods: Methods: COVID-19 SP, a highly glycosylated protein that allows the virus to penetrate the cell and cause infection, was injected intravitreally in 6-8 weeks global h-ACE2 knock-in mice and wild-type mice. Mice were sacrificed after 14 days, then vascular cell death and inflammation were evaluated by the presence of acellular capillaries and the expression of inflammatory and apoptotic markers. To complement our in-vivo studies, Human Microvascular Endothelial Cells (HMEC) were treated with 100 nM COVID-19 SP for 48 hours. The expression of inflammatory and apoptotic markers was assessed by PCR western blot. Results: Results: Our results showed that HMEC exposed to COVID-19 SP for 48 hours displayed an increase in inflammatory and apoptotic markers expression including TNF-α, IL-1β, IL-6, and cleaved caspase-3 compared to control conditions. Additionally, COVID-19 SP enhanced the oxidative stress in HMEC, evident by the increase in nitro-tyrosine formation, superoxide dismutase, and NADPH oxidase complex 1 (NOX1 and NOX5) expression. The in-vivo findings came in agreement with our in-vitro studies. We found that intravitreal injection of the COVID-19 SP-induced 1) strong activation of the retinal glial cells, assessed by GFAP radial staining, and 2) increased vascular death, assessed by acellular capillaries formation 14 days after the injection. Conclusions: Conclusions: Our findings highlight the possible role of COVID-19 SP in inducing retinal inflammation and vascular death. Further studies are required to reveal the impact of COVID-19 SP on visual acuity and the possibility of causing visual impairment using various animal models.