Experimental glaucoma and optic nerve transection induce simultaneous upregulation of proapoptotic and prosurvival genes

PURPOSE. To investigate changes in gene expression induced by elevated intraocular pressure (IOP) and complete optic nerve transsection (ONT) over time. METHODS. A gene array of 18 signal transduction pathways was used to examine the changes in RNA profiles of retinas post-ONT in rats. Among the seven genes that were determined to be upregulated, four were confirmed to have higher expression by semiquantitative RT-PCR analysis: Ei24 and Gadd45a (both associated with apoptosis induced via the p53 pathway), IAP-1 (inhibitor of apoptosis protein 1), and Cdk2 (cell cycle regulation and apoptosis). Their mRNA levels were then studied by quantitative RT-PCR in experimental glaucoma and ONT over time. Levels of the corresponding proteins were evaluated by Western blot analysis and immunohistochemistry. RESULTS. Proapoptotic genes from the p-53 pathway (Ei24 and Gadd45a), Cdk2 and the prosurvival gene IAP-1 (a caspase inhibitor) were simultaneously and significantly upregulated early after ONT, returning to baseline at 2 weeks. In experimental glaucoma, Gadd45a was significantly upregulated 1 week after induction of increased IOP and stayed upregulated for 2 months and long after IOP returned to baseline. The prosurvival gene IAP-1 was simultaneously upregulated but returned to baseline earlier than the proapoptotic gene. Ei24 and Cdk2 were only slightly upregulated in glaucoma. Western blot analysis demonstrated upregulation of Gadd45a and IAP-1 proteins. Immunohistochemistry localized these changes to the retinal ganglion cell layer. CONCLUSIONS. Members of the p-53 signal transduction pathway are significantly involved in glaucoma and ONT. The endogenous caspase inhibitor IAP-1 is upregulated simultaneously, possibly as part of an intrinsic neuroprotective mechanism. Changes in glaucoma are gradual and last long after IOP returns to normal.