PACAP promotes neuron survival in early experimental diabetic retinopathy

Metabolic changes induced by diabetes lead to a multifactorial progressive disease of the retina with an extremely complex pathogenesis. One of the mechanisms of retinal cell death in diabetes is via apoptosis. Our previous results show that pituitary adenylate cyclase activating polypeptide (PACAP) attenuates the morphological and neurochemical changes in a rat model of diabetic retinopathy. The aim of this study was to investigate the mechanisms of this protective effect. Retinas of streptozotocin-induced diabetic rats were analyzed using apoptosis detection combined with immunolabeling. Western blot was used to measure levels of pro- and anti-apoptotic pathways. Intraocular PACAP injection markedly attenuated diabetic retinal injury: increased levels of the anti-apoptotic p-Akt, p-ERK1, p-ERK2, PKC, Bcl-2, while decreased levels of the pro-apoptotic p-p38MAPK and activated caspases (8, 3, 12) were detected. The number of apoptotic cells increased in all nuclear layers of diabetic retinas, but significantly decreased after PACAP treatment. Our results clearly demonstrate that the protective effects of PACAP are mediated, at least partly, by attenuating apoptosis, including also that of the dopaminergic amacrine cells. Inhibition of apoptosis is one of the PACAP-induced pathways with therapeutic potential in early experimental diabetic retinopathy

Urocortin 2 treatment is protective in excitotoxic retinal degeneration

Urocortin 2 (Ucn 2) is a corticotrop releasing factor paralog peptide with many physiological functions and it has widespread distribution. There are some data on the cytoprotective effects of Ucn 2, but less is known about its neuro- and retinoprotective actions. We have previously shown that Ucn 2 is protective in ischemia-induced retinal degeneration. The aim of the present study was to examine the protective potential of Ucn 2 in monosodiumglutamate (MSG)-induced retinal degeneration by routine histology and to investigate cell-type specific effects by immunohistochemistry. Rat pups received MSG applied on postnatal days 1, 5 and 9 and Ucn 2 was injected intravitreally into one eye. Retinas were processed for histology and immunocytochemistry after 3 weeks. Immunolabeling was determined for glial fibrillary acidic protein, vesicular glutamate transporter 1, protein kinase Cα, calbindin, parvalbumin and calretinin. Retinal tissue from animals treated with MSG showed severe degeneration compared to normal retinas, but intravitreal Ucn 2 treatment resulted in a retained retinal structure both at histological and neurochemical levels: distinct inner retinal layers and rescued inner retinal cells (different types of amacrine and rod bipolar cells) could be observed. These findings support the neuroprotective function of Ucn 2 in MSG-induced retinal degeneration

PACAP application improves functional outcome of chronic retinal ischemic injury in rats – evidence from electroretinographic measurements

Retinoprotective effects of pituitary adenylate cyclase activating polypeptide (PACAP) are well-known and have been demonstrated in various pathological conditions, such as diabetic retinopathy, excitotoxic retinal injury, UV light-induced degeneration and ischemic retinal lesion. The neuronal degeneration observed in the different retinal layers under the above pathological conditions can be successfully decreased by PACAP, however, whether this morphological improvement is also reflected in functional amelioration remains unknown. Therefore, our purpose was to investigate the protective effect of PACAP on the rat retina after bilateral common carotid artery occlusion (BCCAO) with electroretinography (ERG) to parallel the functional data with the previous morphological and neurochemical observations. Control eyes received saline treatment while PACAP was injected into the vitreous space of the other eye immediately after the induction of ischemia. Retinal damage and protective effects of PACAP were quantified by the changes in the wave forms and amplitudes. On postoperative days 2 and 14 several parameters were assessed with special attention to the changes of b wave. The results confirm that the previously described morphological protection induced by PACAP treatment is reflected in functional improvement in ischemic retinal lesions

Accelerated retinal aging in PACAP knock-out mice

Pituitary adenylate cyclase activating polypeptide (PACAP) is a neurotrophic and neuroprotective peptide. PACAP and its receptors are widely distributed in the retina. A number of reports provided evidence that PACAP is neuroprotective in retinal degenerations. The current study compared retina cell type-specific differences in young (3-4months) and aged adults (14-16months), of wild-type (WT) mice and knock-out (KO) mice lacking endogenous PACAP production during the course of aging. Histological, immunocytochemical and Western blot examinations were performed. The staining for standard neurochemical markers (tyrosine hydroxylase for dopaminergic cells, calbindin 28 kDa for horizontal cells, protein kinase Calpha for rod bipolar cells) of young adult PACAP KO retinas showed no substantial alterations compared to young adult WT retinas, except for the specific PACAP receptor (PAC1-R) staining. We could not detect PAC1-R immunoreactivity in bipolar and horizontal cells in young adult PACAP KO animals. Some other age-related changes were observed only in the PACAP KO mice only. These alterations included horizontal and rod bipolar cell dendritic sprouting into the photoreceptor layer and decreased ganglion cell number. Also, Muller glial cells showed elevated GFAP expression compared to the aging WT retinas. Furthermore, Western blot analyses revealed significant differences between the phosphorylation state of ERK1/2 and JNK in KO mice, indicating alterations in the MAPK signaling pathway. These results support the conclusion that endogenous PACAP contributes to protection against aging of the nervous system

Novel Neuroprotective Strategies in Ischemic Retinal Lesions

Retinal ischemia can be effectively modeled by permanent bilateral common carotid artery occlusion, which leads to chronic hypoperfusion-induced degeneration in the entire rat retina. The complex pathways leading to retinal cell death offer a complex approach of neuroprotective strategies. In the present review we summarize recent findings with different neuroprotective candidate molecules. We describe the protective effects of intravitreal treatment with: (i) urocortin 2; (ii) a mitochondrial ATP-sensitive K+ channel opener, diazoxide; (iii) a neurotrophic factor, pituitary adenylate cyclase activating polypeptide; and (iv) a novel poly(ADP-ribose) polymerase inhibitor (HO3089). The retinoprotective effects are demonstrated with morphological description and effects on apoptotic pathways using molecular biological techniques

PACAP promotes neuron survival in early experimental diabetic 4 retinopathy

Metabolic changes induced by diabetes lead to a multifactorial progressive disease of the retina with an 33 extremely complex pathogenesis. One of the mechanisms of retinal cell death in diabetes is via apoptosis. 34 Our previous results show that pituitary adenylate cyclase activating polypeptide (PACAP) attenuates the 35 morphological and neurochemical changes in a rat model of diabetic retinopathy. The aim of this study 36 was to investigate the mechanisms of this protective effect. 37 Retinas of streptozotocin-induced diabetic rats were analyzed using apoptosis detection combined 38 with immunolabeling. Western blot was used to measure levels of pro- and anti-apoptotic pathways. 39 Intraocular PACAP injection markedly attenuated diabetic retinal injury: increased levels of the anti- 40 apoptotic p-Akt, p-ERK1, p-ERK2, PKC, Bcl-2, while decreased levels of the pro-apoptotic p-p38MAPK 41 and activated caspases (8, 3, 12) were detected. The number of apoptotic cells increased in all nuclear lay- 42 ers of diabetic retinas, but significantly decreased after PACAP treatment. Our results clearly demonstrate 43 that the protective effects of PACAP are mediated, at least partly, by attenuating apoptosis, including also 44 that of the dopaminergic amacrine cells. Inhibition of apoptosis is one of the PACAP-induced pathways 45 with therapeutic potential in early experimental diabetic retinopathy

www.mdpi.com/journal/ijms Gender-Dependent Effects of Enriched Environment and Social Isolation in Ischemic Retinal Lesion in Adult Rats

Abstract: Exposure to an enriched environment has been shown to have many positive effects on brain structure and function. Numerous studies have proven that enriched environment can reduce the lesion induced by toxic and traumatic injuries. Impoverished environment, on the other hand, can have deleterious effects on the outcome of neuronal injuries. We have previously shown that enriched conditions have protective effects in retinal injury in newborn rats. It is well-known that the efficacy of neuroprotective strategies can depend on age and gender. The aim of the present study, therefore, was to examine the effects of environmental enrichment and social isolation in retinal ischemia. We used bilateral common carotid artery occlusion to induce retinal hypoperfusion in adult Wistar rats of both genders. Groups were housed in standard, enriched or impoverished conditions. Impoverished environment was induced by social isolation. Retinas were processed for histological analysis after two weeks of survival. In the present study, we show that (1) enriched environment has protective effects in adult ischemic retinal lesion, while (2) impoverished environment further increases the degree of ischemic injury, and (3) that these environmental effects are gender-dependent: females are less responsive t