PACAP modulates expression of Hypoxia Inducible Factors in the early phase of diabetic retinopathy

The pathogenesis of diabetic retinopathy is not been completely elucidated, however retinal hypoxia seems to have a central role. This latter event is mediated by the Hypoxia Inducible Factors (HIFs), including HIF-lα, HIF-2α and HIF-3α. In a previous study, we observed the protective role of pituitary adenylate cyclase-activating peptide (PACAP) in early phase of diabetic retinopathy. In the present work, we investigated whether PACAP effect in hyperglycemic retina is mediated through modulation of HIFs expression. The rats were made diabetic using a single injection of streptozotocin (STZ: 60mg/Kg), whereas vehicle injected animals were used as control. Subsequently, a group of diabetic rats was subjected to either a single intravitreal injection of PACAP peptide (lpM/µl) or saline solution after 1 week from STZ injection. Changes in HIFs expression levels were then evaluated in the retinas after 3 weeks. The expression of HIF-lα and HIF-2α were significantly increased in diabetic rats as compared to controls. Instead, their expression levels were significantly decreased after PACAP intraocular administration, as detected by western blot analysis. Conversely, the expression of HIF-3a was significantly downregulated in retinas of STZ-injected rats as compared to the controls. However, its level was significantly increased in diabetic group after PACAP treatment. These data were supported by the immunohistochemical analysis. HIFs were present either in inner and outer retinal layers. Diabetes interferes with their distribution which is changed following intravitreal injection of PACAP. The present results suggest that the protective effect of this peptide in diabetic retina might also be mediated through modulation in the HIFs expression