Divergent effects of Wnt/β-catenin signaling modifiers on the preservation of human limbal epithelial progenitors according to culture condition

Wnt signaling plays an important role in the regulation of self-renewal in stem cells. Here we investigated the effect of CHIR99021, the primary transducer of the Wnt signaling canonical pathway, and IWP2, a wide action Wnt signal blocker, on the growth and differentiation of the limbal epithelial progenitor cells when these cells are cultured in two different, common culture approaches, outgrowth from limbal biopsy explants and isolated cell seeded in low calcium medium. Consistent with their expected effects, irrespective of the culture system, IWP2 decreased total β-catenin while CHIR99021 increased it in nuclear localization. However, IWP2 increased stem/progenitor cell marker (p63α and ABCG2) content and clonogenic capacity in the explants but had opposite effects on isolated cells. CHIR99021 reduced the growth rate, stem/progenitor cell marker content and clonogenic capacity in the explants but also had the opposite effect on the isolated cells. These results show that the outcome of Wnt/β-catenin signaling modification is dependent on the culture systems. Transplantation of limbal epithelial sheets from explant cultures is one of the standard treatments of limbal stem cell deficiency. Our study shows that Wnt-associated activity has a strong negative impact on stem/progenitor cell preservation in limbal explant cultures.