Eye and Covid-19 Host -pathogens interaction at the ocular surface in the SARS-CoV-2 era: viral receptors and RNA editing enzymes
At the end of December 2019, Dr Li Wenliang, a 34 year-old ophthalmologist from Wuhan, sent a message to fellow doctors warning them after visiting several patients with conjunctivitis and respiratory symptoms that he thought looked like SARS. In February 2020 he also died of Covid-19.
Although the ocular involvement is not within the main manifestation of the disease, the virus has been detected in the conjunctiva and tear secretions suggesting that tears may be a source of transmission of the virus. Conjunctivitis can a concomitant manifestation or even an anticipatory sign of the disease, prior to the onset of respiratory symptoms. Our experience confirms a minimal ocular involvement, even though probably underestimated. Therefore, conjunctivitis may anticipate the disease and the conjunctiva may be a first gate for the virus to enter the body.
The entry of the virus into host cells is mediated by the spike protein of SARS-CoV-2 in interaction with the host receptor angiotensin-converting enzyme 2 (ACE2).
We recently described the expression of ACE2 in conjunctival and corneal tissues from healthy donors (Leonardi et al. OII, 2020). In addition, in collaboration with the Microbiology Department of University of Padova and the Veneto Eye Bank Foundation, SARS-CoV-2 mRNA has been detected in the cornea and in the cornea storage medium from donors who resulted SARS-CoV-2 positive at the post-mortem nasopharyngeal SARS-CoV-2 RT-PCR testing, suggesting that the virus may remain resident for a long time in non-vascularized tissues such as the cornea. Further research to better understand if corneal/organ transplantation may play a role in viral transmission are needed.
We previously reported that two RNA editing enzymes involved in antiviral responses, APOBEC3A and ADAR-1, are highly expressed in conjunctival and corneal tissues possible interacting with the virus RNA, suggesting that the low involvement of ocular tissues in covid-19 active disease may be associated to this innate antiviral activity of the ocular surface. We suggest the ocular surface as a model to study the SARS-CoV-2 interactions with the host.