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Nihal Kaplan, Anees Fatima, Hanz Blatt, Robert M. Lavker, Spiro Getsios; Compartmentalized Expression Of Ephrin-A3 In A Subset Of Limbal Epithelial Basal Cells Stimulates Neighboring Cells To Differentiate. Invest. Ophthalmol. Vis. Sci. 2011;52(14):2091.
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© ARVO (1962-2015); The Authors (2016-present)
The limbal basal epithelium is enriched in stem cells (SC) that are interspersed among transit amplifying (TA) cells. These cellular compartments are intimately associated with one another and are essential for homeostasis and repair by giving rise to more differentiated cells of the limbal and corneal epithelia; however, little is known about the signaling pathways that initiate this transition toward a more differentiated phenotype. Ephrin-A3 is a GPI-linked surface protein that mediates cell-cell communication by stimulating EphA2 receptor tyrosine kinase activity on adjacent cells. The restricted expression of ephrin-A3 on limbal basal cells led us to hypothesize that this ligand provides a positional cue for neighboring cells to differentiate.
To determine the role of ephrin-A3 in limbal epithelial cell differentiation, immunofluorescence, immunoblotting and retroviral transduction techniques were employed in primary human limbal epithelial cell (hLEC) cultures, a limbal-derived epithelial cell line (hTCEPi) and organotypic raft cultures of corneal epithelium.
Ephrin-A3 was immunolocalized to a subpopulation of limbal epithelial basal cells that was distinct from keratin(K)17/N-cadherin-positive SCs and K3-positive suprabasal cells, indicating this ligand is expressed on the surface of TA cells at an interface where limbal epithelial cells enter a pathway of differentiation. To determine the role of ephrin-A3 in limbal epithelial cell differentiation, we introduced this ligand into hLEC and hTCEPi cells that express high levels of EphA2 but no detectable ligand. Ectopic ephrin-A3 was capable of triggering receptor tyrosine phoshorylation and subsequent down-regulation of EphA2. Moreover, ephrin-A3-mediated cell-cell communication enhanced limbal epithelial cell differentiation in submerged and raft culture systems as assessed by an increase in the expression of structural proteins found in the suprabasal layers, including K3, MUC1 and PAI-2.
Ephrin-A3 characterizes a discrete population of limbal TA cells that has the potential to stimulate adjacent cells toward a more differentiated phenotype and may be exploited to enhance the regeneration of corneal epithelium during wound healing.
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