Expression of pluripotency and multipotency factors in human ocular surface tissues

Mechanisms that control ocular surface stem cells (SCs) are unclear. Recent studies have shown that several adult SCs express pluripotency markers. Our objective was to analyze the expression of key molecules of pluripotency in human ocular surface tissues as well as in cultivated limbal epithelium.

Four samples of human corneal, limbal and on amniotic membrane cultivated limbal epithelium (HLEC-AM), as well as bulbar and fornical conjunctiva were analyzed. Human embryonic stem (ES) cells and human umbilical vein endothelial cells served as controls. Expression of corneal epithelial differentiation markers (K3, K12, Cx43), putative limbal SC markers (ABCG2, p63, K15), and molecules associated with pluripotency/multipotency (NANOG, OCT4, SOX2, KLF4, KIT, NESTIN, PAX6, NOTCH1) was examined using real-time polymerase chain reaction (PCR) and immunohistochemical staining.

Limbal epithelium showed a significantly (p < 0.05) higher expression of K15, ABCG2, OCT4, SOX2, NESTIN and NOTCH1, but a lower expression of K3 than corneal epithelium. Besides a higher expression of ABCG2 in fornix, the expression of pluripotency markers was similar in both conjunctival regions, although lower than in limbal epithelium. Expression of pluripotency factors in ES cells was significantly higher than in ocular surface SCs, whereas the expression in limbal epithelium was the closest to ES cells. HLEC-AM in comparison to limbal epithelium showed a lower expression of differentiation markers, a similar expression of ABCG2 but a significantly lower expression of pluripotency factors.

Human ocular surface epithelial cells and especially limbal epithelial cell express genes are important for pluripotency and may have preserved some common mechanisms with pluripotent SCs.