Putative rabbit conjunctival epithelial stem/progenitor cells preferentially reside in palpebral conjunctiva.

PURPOSE: Conjunctival epithelia play an important role in forming a physical protective barrier of the ocular surface. To protect the integrity of the ocular surface, the conjunctival epithelial cells (CECs) must be self-renewing from local stem cells. In this study, the distribution of conjunctival epithelial stem/progenitor cells was determined. METHODS: In a long-term bromodeoxyuridine (BrdU) label-retaining study, adult New Zealand white rabbits were injected intraperitoneally with BrdU 50 mg/kg/d for 7 days and follow-up for 6 weeks. In the short-term BrdU label-retaining study, rabbits were injected intraperitoneally with BrdU 50 mg/kg once and BrdU-labeled CECs were detected after 1, 3, 5, and 7 days, respectively. In vitro, growth kinetics, proliferating cell nuclear antigen (PCNA) immunocytochemical staining and colony-forming abilities of rabbit palpebral, fornical and bulbar CECs cultured in an identical environment were investigated and compared between different parts. RESULTS: In the long-term BrdU label-retaining study, BrdU-labeled cells concentrated at the mucocutaneous junction. In the short-term BrdU label-retaining study, the peak concentration of BrdU label-retaining conjunctival epithelial cells progressively migrated from the mucocutaneous junction to the fornix in rabbits 1, 3, 5 and 7 days postinjection respectively, but a focus of BrdU-labeled cells remained in the mucocutaneous junction at all postinjection intervals. Rabbit palpebral CECs grew faster and assigned more PCNA-positive cells and higher colony-forming abilities than the other two parts in vitro. CONCLUSIONS: Long-term retention of BrdU-labeled cells at the mucocutaneous junction indicated that slow-cycling stem cells may locate at this position. The epithelial stem/progenitor cells at the mucocutaneous junction may serve as an origination of transient amplifying cells that migrate towards the fornix. Rabbit palpebral CECs (including mucocutaneous junction epithelial cells) possess higher self-renewing ability in vitro. Collectively, conjunctival epithelial stem/progenitor cells in the rabbit may preferentially reside in palpebral conjunctiva, especially the mucocutaneous junction.