ABSTRACT
Purpose : With this research project we wanted to approach the question of whether SARS-CoV 2 can infect the eye. In order to infect ocular tissues, virus-specific receptors;coreceptors or proteases must be present in the eye tissue. SARS-CoV 2 uses the human angiotensin converting enzyme 2 (ACE2) receptor to enter cells. In addition, the mammalian serine protease TMPRSS2, the protease furin and the glycoprotein neuropilin are identified as relevant proteases for the interaction of the virus with ACE2. Last year, we were able to show that ACE2 is significantly more expressed in ocular tissue of covid patients. Here the expression level of the co-receptor and glia markers, as well as the present of virus was confirmed in this study. Methods : Seven eyes from donors without covid disease (COVID-) as well as ten fixed eyes from COVID-19 patients (COVID+) were analysed for their expression profile of ACE2, TMPRSS2, neuropilin and furin in the retina and cornea. The ocular tissues were examined for protein expression by immunohistochemical staining or for RNA expression by quantitative real-time PCR. In addition, viral spike protein was detected histologically in eyes, and expression profiles of GFAP and Iba-1 were assessed. Results : Similar to ACE2 and TMPRSS2, the two proteases neuropilin and furin were detected in the retina and cornea. Interestingly, the expression profile differed in terms of strength and localization, especially in the retina. The presence of the virus in both cornea and retina was also demonstrated by the detection of viral spike protein. In all COVID+ retinas, strong GFAP staining was observed as well as some Iba-1 positive cells, suggesting activation of macro- and microglia. Conclusions : Expression of ACE2, TMPRSS2, furin and neuropilin was demonstrated in COVID+ ocular tissues. In addition to the virus detection in retina and cornea, a glial reaction could also be observed. One can therefore assume an infection of the eye in these cases. However, in summary it can be said that an infection of the eye tissue is possible since all demanded receptors are present.
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.