PACAP Attenuates Optic Nerve Crush-Induced Retinal Ganglion Cell Apoptosis Via Activation of the CREB-Bcl-2 Pathway.

Retinal ganglion cell (RGC) apoptosis is considered an important pathological hallmark of glaucoma. Pituitary adenylate cyclase-activating polypeptide (PACAP) is a pleiotropic peptide with potent neuroprotective properties. In our previous study, we found that the expression of PACAP and its high-affinity receptor PACAP receptor type 1 (PAC1R) increased markedly after optic nerve crush (ONC), and occurred mainly in the ganglion cell layer of the retina. This suggests that the upregulation of PACAP may play a vital role in inhibiting RGC death after ONC. Therefore, in the present study, we investigate the specific effects and underlying mechanism of PACAP in RGC death after ONC. Vehicle (physiological saline) or PACAP (1 nM to 200 nM) solution was injected into the vitreous body. Seven days later, the retinas were harvested, and the surviving RGCs were retrogradely labeled with Fluoro-Gold (FG; Fluorochrome) at different concentrations of PACAP. Immunofluorescence double staining and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay were used to observe the effects of PACAP on RGC apoptosis. Our results showed that PACAP treatment inhibited caspase-3-mediated RGC apoptosis, promoted the phosphorylation of cAMP response element binding protein (CREB), up-regulated the expression of B-cell lymphoma 2 (Bcl-2), and ultimately improved RGC survival. These results suggest that PACAP may prevent RGC apoptosis after ONC via activation of CREB-mediated Bcl-2 transcription. The study thus contributes to a basic understanding of the mechanism by which PACAP decreased RGC apoptosis and provides a theoretical basis for future clinical application of PACAP in the treatment of glaucoma.