Abstract
Purpose :
To infect the eye, SARS-CoV 2 needs virus-specific receptors and coreceptors or proteases in the specific ocular tissue. The human angiotensin-converting enzyme-2 (ACE2) receptor represents the major gateway for SARS-CoV 2 to enter cells. Furthermore, the mammalian serine protease TMPRSS2 and the protease furin have been identified as relevant proteases for the interaction of the virus with ACE2. The expression status of these key receptors in ocular tissues is still not fully elucidated.
Methods :
The expression profile ACE2, TMPRSS2, and furin were analyzed in fresh and fixed eyes from healthy donors, sections from eyes with other ocular diseases, and eyes from patients, who died from COVID-19. Protein expression was examined via immunohistochemical staining, mRNA expression was analyzed via quantitative real-time PCR.
Results :
A relevant difference in the amount of expression of the receptors was observed between fixed and unfixed samples. Interestingly, the eyes from COVID-19 patients expressed a stronger signal than the tissues from non-infected patients. Noteworthy, the results were not consistent with all antibodies used. A pronounced mRNA expression of ACE2 was detected in fresh human cornea, 20 times stronger than in fresh human retina. In contrast, relevant protein expression of ACE2 was not found in fixed corneal samples, while the expression of ACE2 was detected in the retina in the same sections. TMPRSS2 was detected in fresh as well as fixed corneal and retinal samples.
Conclusions :
ACE2 and TMPRSS2 were found in ocular tissue, although to a limited amount. The age of the sample, the method of preservation, the freshness of the tissue, and the selection of antibody/primer have an influence on the detection of the relevant receptor expression. In addition, COVID-19 patients might have a stronger expression of ACE2 in ocular tissue in comparison to non-infected patients. This effect will be investigated in further studies. In conclusion, the infestation of ocular tissue does likely not represent the main route of infection, due to the weak receptor expression.
This is a 2021 ARVO Annual Meeting abstract.