HCEC has been shown to possess proliferative capacity but in vivo conditions seem to contribute to maintenance of a non-replicative monolayer. Several factors are involved in these antiproliferative mechanisms, including TGF beta 2 in aqueous humor and a high contact inhibition present in the corneal endothelial mosaic mediated by the ON-014185 cyclin kinase inhibitor p27Kip1. In absence of these factors, HCEC can be induced to growth in culture. This first result demonstrated that treatment with Y-27632 was not strong enough to induce proliferation and to overcome these antiproliferative mechanisms induced by contact inhibition ex vivo. As ROCK inhibitor has been shown to induce proliferation of rabbit and monkey CEC in vitro, we also evaluated the effect of Y-27632 in human primary cell culture. As per ex vivo evaluation, treatment with ROCK inhibitor did not show any toxicity on HCEC, demonstrating a potential safe use of this compound for cell culture. However, inhibition of Rho-ROCK pathway did not induce proliferation of HCEC as it was the case for rabbit and monkey endothelial cells, but actually reduced cell proliferation capacity of HCEC in vitro. These findings rather confirmed previous studies demonstrating that inhibition of ROCK signaling induced a reduction of proliferation of different cell type, including corneal epithelial cells, vascular smooth muscle cell, cardiomyocytes and myofibroblast. These first results demonstrated that ROCK inhibitor, although non-toxic for the HCEC, will not be the key factor which allows a DprE1-IN-1 greater number of human corneal grafts to become available clinically or which promotes cultivation of HCEC. This unpredicted difference in induction of proliferation could be explained by the effect of donor age on HCEC proliferative capacity. It has been shown that cultivated HCEC from older donors had lower proliferative potential than those derived from younger donors. This lower potential seems to be due to the significant increase with age of two cyclin kinase inhibitors, p21Cip1 and p16INK4, which are important negative regulator of G1-phase of the cell cycle. In our study the mean donors age was 73 years old and could be considered as old donors, whereas animals used for the experiment are generally young and would rather correspond to young donors. Even if younger samples will be difficult to obtain, it would be interesting to evaluate the effect of ROCK inhibitor on HCEC coming from young donors ex vivo and in vitro.
