Expression of stem cell markers in the bovine corneal endothelium, insert region and trabecular meshwork

Abstract

PURPOSE: Previous studies suggest that adult stem/progenitor cells (SPCs) reside in the human trabecular meshwork insert region (TMI) at the posterior limbus, where the corneal endothelium (CE) joins the trabecular meshwork (TM). They may supply new cells for regenerating the CE and TM. However, the existence of SPCs in these architecturally different regions of non-primate species have not been investigated. In this study, we aimed to examine the localization of the SPCs in the bovine anterior chamber angle, which provides a large tissue model for research. METHODS: Fresh bovine eyes were obtained from the abattoir within 6 hours post mortem. The anterior segment was fixed in 4% formaldehyde, paraffin embedded and cut into serial 5µm-thick sections. The expression of stem cell markers in the CE, TMI and TM was assessed by immunohistochemistry. These markers included ABCG2, Ankyrin G, Nestin, Oct4, Pax6, Sox2, STRO-1 and Telomerase. Parallel immunocytochemical studies on SPCs isolated from the bovine CE and TM using sphere culture were also carried out. RESULTS: Positive immunofluorescence of ABCG2, Nestin, Oct4, Pax6, Sox2, STRO-1 and telomerase were observed in the CE, TM and in isolated cells located within the TMI. These cells were found in deeper layers just beneath the very end of the peripheral CE and they seemed to be continuous with the anterior TM. However, Ankyrin G staining was only restricted to the TMI. SPCs isolated from the CE and TM respectively showed positive immunoreactivity with all the stem cell markers mentioned.CONCLUSIONS: SPCs are present in the bovine anterior chamber angle despite the anatomical structural difference to human. Positive immunostaining observed in the entire CE and TM may be due to the relative young age of the animals. Nevertheless, the exclusive Ankyrin G staining and robust expression of a panel of stem cell markers in the TMI provide strong evidence that the bovine TMI house SPCs which may be comparable to those observed in human.