Corneal endothelial cells are protected from apoptosis by gene therapy

Corneal grafting is the most prevalent form of transplantation. Corneal endothelial cells (ECs), which form a monolayer of the cornea with minimal proliferative potential, are pivotal for maintenance of corneal clarity. Loss of EC viability and apoptosis leads to graft failure posttransplantation and reduces the quality of donor corneas in storage, such that up to 30% do not meet selection criteria and must be discarded. The current study investigates antiapoptotic effects of transduced mammalian Bcl-x(L) and baculoviral p35 on human ECs. Multiple apoptotic cell features are observed while inducing apoptosis either via the extrinsic (death receptor) or intrinsic (mitochondrial) apoptotic pathway. Human ECs were studied under three experimental conditions: (1) as an immortalized cell line, (2) as primary cells, and (3) in an intact cornea. Interestingly, in primary EC suspensions, Bcl-x(L) was protective against apoptosis mediated via both pathways. However, p35 was significantly more protective against apoptosis mediated via the intrinsic pathway compared with Bcl-x(L). Our results provide critical insight into the role of apoptotic pathways in the maintenance of EC viability and the efficacy with which these protective proteins exert their effect. These observations could form the basis for future applications of antiapoptotic gene therapy to corneal preservation aiming to reduce both graft failure after transplantation as well as donor corneal damage during storage.