Abstract
Purpose :
The antimicrobial peptide (AMP) expression pattern of the equine ocular surface and amniotic membrane are currently undefined. We hypothesized that putative orthologs of both cathelicidins and defensins, two AMP subfamilies, expressed by the ocular surface of humans would be expressed by the equine cornea, conjunctiva and amniotic membrane. This study characterized AMP expression from healthy equine eyes and amniotic membrane to serve as a reference for future investigations of equine microbial keratitis and for the potential use of amniotic membrane for therapeutic corneal grafts.
Methods :
RNA was extracted from equine corneal epithelium (n=5), conjunctiva (n=4), amniotic membrane (n=6), testis (n=4) and epididymis (n=4). Testis and epididymis were used as positive controls as they have been shown to highly express AMPs in other species. A targeted qPCR approach was used to investigate the equine orthologs of the three most functionally relevant beta-defensins (DEFB1, DEFB4B, and DEFB103A) of the ocular surface and amniotic membrane of humans. RNA from one sample of corneal epithelium, conjunctiva and amniotic membrane were submitted for 3’Tag-sequencing to further investigate their AMP expression.
Results :
Expression of equine orthologs of DEFB1, DEFB4B and DEFB103A were identified in equine corneal epithelium, conjunctiva and amniotic membrane. DEFB103A was expressed at the highest amounts in corneal epithelium, while DEFB4B was most highly expressed in conjunctiva and amniotic membrane. 3’Tag-sequencing confirmed these findings and identified expression of five additional beta-defensins, 11 alpha-defensins and two cathelicidins. The alpha-defensins showed higher normalized read counts than the beta-defensins in these tissues.
Conclusions :
This study characterized the AMP expression profile of the equine cornea, conjunctiva and amniotic membrane. We identified high expression of DEFB103A in the cornea suggesting that it plays a key role in the innate immunity of the equine eye. We also determined that equine amniotic membrane expresses a moderate amount of AMPs suggesting it could provide an antimicrobial effect as a surgical corneal graft in structurally compromised eyes. Finally, we identified high expression of alpha-defensins in ocular tissues and amniotic membrane. Future studies will focus on defining the antimicrobial activity of these AMPs and determining their role in microbial keratitis.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.