Protective Effects of PACAP in the Retina

Pituitary adenylate cyclase activating polypeptide (PACAP) is a widespread neuropeptide that is well known for its general cytoprotective effects in different neuronal injuries, such as traumatic brain and spinal cord injury, models of neurodegenerative diseases, and cerebral ischemia. PACAP and its receptors also occur in the retina. In this review, we summarize the retinoprotective effects of PACAP. In vitro, PACAP is protective against glutamate, thapsigargin, anisomycin, oxidative stress, UV light, high glucose, inflammation, and anoxia. Both the neural retina and the pigment epithelial cells can be protected by PACAP in various experimental paradigms. In vivo, the protective effects of intravitreal PACAP treatment have been shown in the following models in rats and mice: excitotoxic injury induced by glutamate, N-methyl-d-aspartate (NMDA) or kainate, ischemic injury induced by carotid artery ligation and high intraocular pressure, degeneration caused by UV-A light, optic nerve transection, and streptozotocin-induced diabetic retinopathy as well as retinopathy of prematurity. Molecular biological methods have revealed that PACAP activates anti-apoptotic, while inhibits pro-apoptotic signaling pathways, and it also stimulates an anti-inflammatory environment in the retina. Altogether, PACAP is suggested to be a potential therapeutic retinoprotective agent in various retinal diseases.