Neurotrophic factor modulation of corneal endothelium

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Success of corneal transplant is dependent on high corneal endothelial (CE) cell density maintained immediately after surgery and thereafter. CE cells die either by acute necrosis, which initiates detrimental inflammatory responses, or by a slow programmed, apoptotic death, which does not cause inflammation. We found that an aqueous humor neuropeptide, VIP, promotes CE cell survival under acute H2O2-induced oxidative stress and simultaneously stimulates CE cells to release a factor that promotes apoptosis among dying CE cells in corneoscleral explants. The VIP effects are associated with cAMP production, protein tyrosine phosphorylation, and activation of the cAMP- responsive- element binding protein (CREB), a key molecule in cell survival. CE cells express VIP protein and gene, which can be upregulated by the other CE cell autocrine trophic factor, CNTF, which in turn is released by CE cells surviving oxidative stress. Whereas CE cells in human donor corneas stored for transplant continue to express VIP mRNA and receptor for CNTF (CNTFRalpha) and VIP increases the density of CE cells of these corneas in long-term storage, CNTF- and CNTFRalpha-immunoreactivities are present in human aqueous humor. Our goal is to establish VIP and CNTF as CE cell trophic factors capable of: 1) prolonging the duration of preservation of corneas for transplant and 2) maintaining the integrity of transplanted corneas in the recipient eyes. Five aims to test hypotheses that: 1) VIP protection of CE cell against acute oxidative injury is associated with attenuation of lipid peroxidation; 2) VIP-released factor (VRF) switches necrosis to apoptosis in injured CE cells by attenuating H2O2-induced ATP depletion and mitochondrial potential dissipation and by augmentation of poly (ADP-ribose) polymerase cleavage, by using VRF that will be purified by sequential fast performance liquid chromatography from CE cell-conditioned medium and amino acid sequence analyzed; 3) VIP inactivates the pro-apoptotic BAD protein and up-regulates the anti-apoptotic protein Bcl-2 and the cytochrome C; 4) sublethal H2O2-injured CE cells release CNTF to promote own survival and that authentic CNTF and CNTFRalpha are in the aqueous humor of injured (enucleated) eyes; 5) CE cell CNTFRalpha lost during extensive eye bank storage can be restored to function to upregulate VIP mRNA by exogenous CNTFRalpha.