Neuroprotection of a Novel Cyclopeptide C*HSDGIC* from the Cyclization of PACAP (1–5) in Cellular and Rodent Models of Retinal Ganglion Cell Apoptosis

Abstract

PurposeTo investigate the protective effects of a novel cyclopeptide C*HSDGIC* (CHC) from the cyclization of Pituitary adenylate cyclase-activating polypeptide (PACAP) (1–5) in cellular and rodent models of retinal ganglion cell apoptosis.Methodology/Principal FindingsDouble-labeling immunohistochemistry was used to detect the expression of Thy-1 and PACAP receptor type 1 in a retinal ganglion cell line RGC-5. The apoptosis of RGC-5 cells was induced by 0.02 J/cm2 Ultraviolet B irradiation. MTT assay, flow cytometry, fluorescence microscopy were used to investigate the viability, the level of reactive oxygen species (ROS) and apoptosis of RGC-5 cells respectively. CHC attenuated apoptotic cell death induced by Ultraviolet B irradiation and inhibited the excessive generation of ROS. Moreover, CHC treatment resulted in decreased expression of Bax and concomitant increase of Bcl-2, as was revealed by western-blot analysis. The in vivo apoptosis of retinal ganglion cells was induced by injecting 50 mM N-methyl-D-aspartate (NMDA) (100 nmol in a 2 µL saline solution) intravitreally, and different dosages of CHC were administered. At day 7, rats in CHC+ NMDA-treated groups showed obvious aversion to light when compared to NMDA rats. Electroretinogram recordings revealed a marked decrease in the amplitudes of a-wave, b-wave, and photopic negative response due to NMDA damage. In retina receiving intravitreal NMDA and CHC co-treatment, these values were significantly increased. CHC treatment also resulted in less NMDA-induced cell loss and a decrease in the proportion of dUTP end-labeling-positive cells in ganglion cell line.ConclusionsC*HSDGIC*, a novel cyclopeptide from PACAP (1–5) attenuates apoptosis in RGC-5 cells and inhibits NMDA-induced retinal neuronal death. The beneficial effects may occur via the mitochondria pathway. PACAP derivatives like CHC may serve as a promising candidate for neuroprotection in glaucoma.

Protective Effects of PACAP in the Retina

“…These alterations were reversed by cyclic PACAP1-5 treatment. This treatment also resulted in decreased ganglion cell loss and apoptosis assessed by TUNEL-staining [ 73 ].…”

“…Furthermore, pretreatment with this short derivative effectively blocked apoptosis, maintained structural integrity, and decreased production of reactive oxygen species (ROS). Both PACAP and cyclic PACAP1-5 counteracted the UV-B-induced decrease in the protective Bcl-2 and the increase in the deleterious Bax protein levels [ 73 ].…”

“…In an in vitro model of UV-B irradiation, PACAP was shown to protect RGC-5 retinal ganglion cells expressing PAC1 receptors [ 73 , 91 ]. This effect was mimicked also by a cyclic PACAP derivative, cyclic PACAP1-5 [ 73 ]. Furthermore, pretreatment with this short derivative effectively blocked apoptosis, maintained structural integrity, and decreased production of reactive oxygen species (ROS).…”

“…A recent study has confi rmed that PACAP-mediated pathways are protective in NMDA-induced retinal lesion. Cheng et al [ 73 ] showed that intravitreal NMDA injection led to a decrease in light aversion, and decreases in the a and b-waves in the electroretinogram accompanied by a photopic negative response. These alterations were reversed by cyclic PACAP1-5 treatment.…”

One Year of Glaucoma Research in Review—2013 to 2014

“…Cheng and colleagues 50 identified a novel cyclopeptide (C*HSDGIC*) that inhibited ultraviolet B irradiation induced apoptotic cell death in a retinal ganglion cell line. Additionally, pretreatment of rats with the novel cyclopeptide resulted in significantly preserved electroretinogram amplitudes of the a-wave, b-wave, and photoptic negative response following induction of in vivo retinal ganglion cell apoptosis compared to untreated rats.…”