High expression of SARS-CoV2 viral entry-related proteins in human limbal stem cells

• Published in: The ocular surface 2022-01, Vol.23, p.197-200
• Main Authors: Sasamoto, Yuzuru, Lee, Catherine A.A., Yoshihara, Masahito, Martin, Gabrielle, Ksander, Bruce R., Frank, Markus H., Frank, Natasha Y.
• Format: Article
• Language: English
• Subjects: ACE2; ATP Binding Cassette Transporter, Subfamily B; COVID-19; COVID-19 Testing; Humans; Limbal stem cells; PAX6; RNA, Viral; SARS-CoV-2; SARS-CoV2; Stem Cells; TMPRSS2; Viral Proteins; Virus Internalization
• ISSN: 1542-0124; 1937-5913; 1937-5913
• DOI: 10.1016/j.jtos.2021.10.002

Coronavirus disease 2019 (COVID-19) is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV2). While the ocular surface is considered one of the major SARS-CoV2 transmission routes, the specific cellular tropism of SARS-CoV2 is not fully understood. In the current study, we evaluated the expression and regulation of two SARS-CoV2 viral entry proteins, TMPRSS2 and ACE2, in human ocular epithelial cells and stem cells. TMPRSS2 and ACE2 expression in ABCB5-positive limbal stem cells (LSCs) were assessed by RNAseq, flow cytometry and immunohistochemistry. PAX6, TMPRSS2, and ACE2 mRNA expression values were obtained from the GSE135455 and DRA002960 RNA-seq datasets. siRNA-mediated PAX6 knockdown (KD) was performed in limbal and conjunctival epithelial cells. TMPRSS2 and ACE2 expression in the PAX6 KD cells was analyzed by qRT-PCR and Western blot. We found that ABCB5-positive LSCs express high levels of TMPRSS2 and ACE2 compared to ABCB5-negative limbal epithelial cells. Mechanistically, gene knockout and overexpression models revealed that the eye transcription factor PAX6 negatively regulates TMPRSS2 expression. Therefore, low levels of PAX6 in ABCB5-positive LSCs promote TMPRSS2 expression, and high levels of TMPRSS2 and ACE2 expression by LSCs indicate enhanced susceptibility to SARS-CoV2 infection in this stem cell population. Our study points to a need for COVID-19 testing of LSCs derived from donor corneas before transplantation to patients with limbal stem cell deficiency. Furthermore, our findings suggest that expandable human ABCB5+ LSC cultures might represent a relevant novel model system for studying cellular SARS-CoV2 viral entry mechanisms and evaluating related targeting strategies. •AABCB5-positive limbal stem cells express high levels of TMPRSS2 and ACE2.•p63 is co-expressed with TMPRSS2 and ACE2 in human limbus.•PAX6 negatively regulates expression of TMPRSS2 in ocular surface epithelial cells.