Neuroprotective Effects Of Pituitary Adenylate Cyclase-activating Polypeptide Research Articles

The Potential of the Nose-to-Brain Delivery of PACAP for the Treatment of Neuronal Disease.

Research on the neuroprotective effect of pituitary adenylate cyclase-activating polypeptide (PACAP) and its use as a therapeutic agent has grown over the past 30 years. Both in vitro and in vivo experiments have shown that PACAP exerts a strong neuroprotective effect in many central and peripheral neuronal diseases. Various delivery routes have been employed from intravenous (IV) injections to intracerebroventricular (ICV) administration, leading either to systemic or topical delivery of the peptide. Over the last decade, a growing interest in the use of intranasal (IN) administration of PACAP and other therapeutic agents has emerged as an alternative delivery route to target the brain. The aim of this review is to summarize the findings on the neuroprotective effect of PACAP and to discuss how the IN administration of PACAP could contribute to target the effects of this pleiotropic peptide.

Intravitreal Injection of PACAP Attenuates Acute Ocular Hypertension-Induced Retinal Injury Via Anti-Apoptosis and Anti-Inflammation in Mice.

PurposePituitary adenylate cyclase-activating polypeptide (PACAP) has shown potent neuroprotective effects in central nervous system and retina disorders. However, whether PACAP can attenuate retinal neurodegeneration induced by acute ocular hypertension (AOH) and the underlying mechanisms remain unknown. In this study, we aimed to investigate the effects of PACAP on the survival and function of retinal ganglion cells (RGCs), apoptosis, and inflammation in a mouse model of AOH injury.MethodsPACAP was injected into the vitreous body immediately after inducing AOH injury. Hematoxylin and eosin staining and optical coherence tomography were used to evaluate the loss of retina tissue. Pattern electroretinogram was used to evaluate the function of RGCs. TUNEL assay was used to detect apoptosis. Immunofluorescence and western blot were employed to evaluate protein expression levels.ResultsPACAP treatment significantly reduced the losses of whole retina and inner retina thicknesses, Tuj1-positive RGCs, and the amplitudes of pattern electroretinograms induced by AOH injury. Additionally, PACAP treatment remarkably reduced the number of TUNEL-positive cells and inhibited the upregulation of Bim, Bax, and cleaved caspase-3 and downregulation of Bcl-xL after AOH injury. Moreover, PACAP markedly inhibited retinal reactive gliosis and vascular inflammation, as demonstrated by the downregulation of GFAP, Iba1, CD68, and CD45 in PACAP-treated mice. Furthermore, upregulated expression of NF-κB and phosphorylated NF-κB induced by AOH injury was attenuated by PACAP treatment.ConclusionsPACAP could prevent the loss of retinal tissue and improve the survival and function of RGCs. The neuroprotective effect of PACAP is probably associated with its potent anti-apoptotic and anti-inflammatory effects.

Intranasal Administration of PACAP Is an Efficient Delivery Route to Reduce Infarct Volume and Promote Functional Recovery After Transient and Permanent Middle Cerebral Artery Occlusion.

Intranasal (IN) administration appears to be a suitable route for clinical use as it allows direct delivery of bioactive molecules to the central nervous system, reducing systemic exposure and sides effects. Nevertheless, only some molecules can be transported to the brain from the nasal cavity. This led us to compare the efficiency of an IN, intravenous (IV), and intraperitoneal (IP) administration of pituitary adenylate cyclase-activating polypeptide (PACAP) after transient or permanent middle cerebral artery occlusion (MCAO) in C57BL/6 mice. The results show that the neuroprotective effect of PACAP is much more efficient after IN administration than IV injection while IP injection had no effect. IN administration of PACAP reduced the infarct volume when injected within 6 h after the reperfusion and improved functional recovery up to at least 1 week after the ischemia.

Neuroprotective effects of PACAP against paraquat-induced oxidative stress in the Drosophila central nervous system.

Parkinson's disease (PD) is a progressive neurodegenerative movement disorder that can arise after long-term exposure to environmental oxidative stressors, such as the herbicide paraquat (PQ). Here we investigated the potential neuroprotective action of vertebrate pituitary adenylate cyclase-activating polypeptide (PACAP) against PQ in Drosophila. We found that pre-treatment with this neuropeptide applied to the ventral nerve cord (VNC) at low doses markedly extended the survival of wild-type decapitated flies exposed to neurotoxic levels of PQ or dopamine (DA). In contrast and interestingly, application of a PACAP receptor antagonist, PACAP-6-38, had opposite effects, significantly decreasing the resistance of flies to PQ. PACAP also reduced PQ-induced caspase activation and reactive oxygen species (ROS) accumulation in the VNC. We then searched for the endogenous neuropeptide receptor potentially involved in PACAP-mediated neuroprotection in Drosophila. Knocking down the gene encoding the receptor Han/PDFR of the neuropeptide pigment-dispersing factor (PDF) in all neurons conferred to flies higher resistance to PQ, whereas PDFR downregulation restricted to PDF or DA neurons did not increase PQ resistance, but remarkably suppressed the neuroprotective action of PACAP. Further experiments performed with Pdf and Pdfr-deficient mutant strains confirmed that PDF and its receptor are required for PACAP-mediated neuroprotection in flies. We also provide evidence using split-green fluorescent protein (split-GFP) reconstitution that PDF neurons make synaptic contacts onto DA neurons in the abdominal VNC. Our results therefore suggest that the protective action of PACAP against PQ-induced defects in the Drosophila nervous system involves the modulation of PDFR signaling in a small number of interconnected neurons.

Neuroprotective roles of pituitary adenylate cyclase-activating polypeptide in neurodegenerative diseases.

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a pleiotropic bioactive peptide that was first isolated from an ovine hypothalamus in 1989. PACAP belongs to the secretin/glucagon/vasoactive intestinal polypeptide (VIP) superfamily. PACAP is widely distributed in the central and peripheral nervous systems and acts as a neurotransmitter, neuromodulator, and neurotrophic factor via three major receptors (PAC1, VPAC1, and VPAC2). Recent studies have shown a neuroprotective role of PACAP using in vitro and in vivo models. In this review, we briefly summarize the current findings on the neurotrophic and neuroprotective effects of PACAP in different brain injury models, such as cerebral ischemia, Parkinson’s disease (PD), and Alzheimer’s disease (AD). This review will provide information for the future development of therapeutic strategies in treatment of these neurodegenerative diseases. [BMB Reports 2014; 47(7): 369-375]

PACAP stimulates functional recovery after spinal cord injury through axonal regeneration.

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuroprotective peptide expressed in the central nervous system. Although many studies have shown a neuroprotective effect of PACAP, the mechanism of PACAP in the treatment of spinal cord injury (SCI) is yet to be elucidated. The purpose of this study was to examine the efficacy and underlying mechanism of PACAP in a mouse SCI model where PACAP was delivered via a biodegradable hydrogel. When PACAP or saline was delivered immediately after SCI, the functional motor recovery 14days after SCI was significantly improved in the PACAP group compared with that in the saline group. Expression levels of messenger RNA (mRNA) for collapsin response mediator protein 2 (CRMP2), a factor related to axonal regeneration, were increased in the PACAP group 14days after SCI compared with those in the saline group. A significantly increased number of CRMP2-positive cells were observed around the injury lesion in the PACAP group, while CRMP2 co-labeling with neuronal and oligodendrocyte markers was detected in intact spinal cord. Fourteen days after SCI, anterograde tracing revealed that a significantly increased number of neuronal fibers extended caudally from the lesion epicenter in the PACAP group. These results suggest that PACAP stimulates functional motor recovery after SCI through axonal regeneration mediated by CRMP2.

Pituitary adenylate cyclase‐activating polypeptide (PACAP) stimulates the expression and the release of tissue plasminogen activator (tPA) in neuronal cells: involvement of tPA in the neuroprotective effect of PACAP

Pituitary adenylate cyclase-activating polypeptide (PACAP) and tissue plasminogen activator (tPA) play important roles in neuronal migration and survival. However, a direct link between the neurotrophic effects of PACAP and tPA has never been investigated. In this study, we show that, in PC12 cells, PACAP induced a 9.85-fold increase in tPA gene expression through activation of the protein kinase A- and protein kinase C-dependent signaling pathways. In immature cerebellar granule neurons (CGN), PACAP stimulated tPA mRNA expression and release of proteolytically active tPA. Immunocytochemical labeling revealed the presence of tPA in the cytoplasm and processes of cultured CGN. The inhibitory effect of PACAP on CGN motility was not affected by the tPA substrate plasminogen or the tPA inhibitor plasminogen activator inhibitor-1. In contrast, plasminogen activator inhibitor-1 significantly reduced the stimulatory effect of PACAP on CGN survival. Altogether, these data indicate that tPA gene expression is activated by PACAP in both tumoral and normal neuronal cells. The present study also demonstrates that PACAP stimulates the release of tPA which promotes CGN survival by a mechanism dependent of its proteolytic activity.

PACAP and a novel stable analog protect rat brain from ischemia: Insight into the mechanisms of action

Pituitary adenylate cyclase-activating polypeptide (PACAP) shows potent protective effects in numerous models of neurological insults. However, the use of PACAP as a clinically efficient drug is limited by its poor metabolic stability. By combining identification of enzymatic cleavage sites with targeted chemical modifications, a metabolically stable and potent PACAP38 analog was recently developed. The neuroprotective activity of this novel compound was for the first time evaluated and compared to the native peptide using a rat model of middle cerebral artery occlusion (MCAO). Our results show that as low as picomolar doses of PACAP38 and its analog strongly reduce infarct volume and improve neurological impairment induced by stroke. In particular, these peptides inhibit the expression of Bcl-2-associated death promoter, caspase 3, macrophage inflammatory protein-1α, inducible nitric oxide synthase 2, tumor necrosis factor-α mRNAs, and increase extracellular signal-regulated kinase 2, B-cell CLL/lymphoma 2 and interleukin 6 mRNA levels. These results indicate that the neuroprotective effect of PACAP after MCAO is not only due to its ability to inhibit apoptosis but also to modulate the inflammatory response. The present study highlights the potential therapeutic efficacy of very low concentrations of PACAP or its metabolically stable derivative for the treatment of stroke.

Neuroprotective Effect of PACAP Against NMDA-Induced Retinal Damage in the Mouse

Retinal excitotoxicity is one of the major causes of retinal ganglion cell (RGC) death in glaucoma. Pituitary adenylate cyclase-activating polypeptide (PACAP) is a pleiotropic peptide with potent neuroprotective activity; however, whether it exerts such an effect in the retina and the mechanism by which RGCs are protected is still not well understood. In this study, we examined the effect of exogenous and endogenous PACAP on RGC death induced by N-methyl-D: -aspartate acid (NMDA). The vitreous body of anesthetized adult male mice (C57/BL6J) was injected with NMDA (40 nmol in a 2 μL saline solution). The number of RGCs decreased from days 1 to 7 after NMDA injection, and the number of dUTP end-labeling (TUNEL)-positive cells, an indicator of cell death, peaked at day 3. However, when PACAP38 (10(-8), 10(-10), 10(-12), 10(-14), or 10(-16)M) was co-administered with NMDA, the 10(-10)M dose resulted in significantly increased RGC survival at day 7, and a decrease in the number of TUNEL-positive RGCs at day 3. We next investigated the neuroprotective effect of endogenous PACAP using PACAP heterozygote(+/-) mice. Under normal circumstances, there was no significant difference in the number of RGCs in the PACAP(+/-) mice compared with their wild-type counterparts. However, the number of RGCs significantly decreased in the PACAP(+/-) mice 7 days after NMDA injection, relative to their wild-type counterparts. The number of TUNEL-positive RGCs peaked at day 1 in the PACAP(+/-) mice. These effects in the PACAP(+/-) mice were reversed by intravitreous injection of 10(-10)M PACAP38. This suggests that exogenous PACAP is able to counteract NMDA-induced toxicity, and that endogenous PACAP exerts a neuroprotective effect in the retina.

Neuroprotective Effects of PACAP Against Ethanol-Induced Toxicity in the Developing Rat Cerebellum

The developing rat cerebellum is particularly sensitive to alcohol at the end of the first postnatal week, a period of intense neurogenesis. The neuropeptide Pituitary adenylate cyclase-activating polypeptide (PACAP) has previously been shown to prevent the death of cultured neurons in vitro. We have thus investigated the capacity of PACAP to counteract ethanol toxicity in 8-day-old rats. Behavioral studies revealed that PACAP reduces the deleterious action of alcohol in the negative geotaxis test. Administration of ethanol induced a transient increase of the expression of pro-apoptotic genes including c-jun or caspase-3 , which could be partially blocked by PACAP. Alcohol inhibited the expression of the α6 GABA ( A ) subunit while PACAP increased neuroD2 mRNA level, two markers of neuronal differentiation. Although gene regulations occurred rapidly, a third injection of ethanol was required to strongly reduce the number of granule cells in the internal granule cell layer, an effect which was totally blocked by PACAP. The action of PACAP was mimicked by D-JNKi1 and Z-VAD-FMK, indicating the involvement of the jun and caspase-3 pathways in alcohol toxicity. The present data demonstrate that PACAP can counteract in vivo the deleterious effect of ethanol. The beneficial action of PACAP on locomotor activity precedes its activity on cell survival, indicating that PACAP can block the detrimental action of ethanol on cell differentiation.

Mice deficient in pituitary adenylate cyclase activating polypeptide display increased sensitivity to renal oxidative stress in vitro

Pituitary adenylate cyclase activating polypeptide (PACAP) is a multifunctional neuropeptide, showing widespread occurrence in the nervous system and also in peripheral organs. The neuroprotective effects of PACAP are well-established in different neuronal systems against noxious stimuli in vitro and in vivo. Recently, its general cytoprotective actions have been recognized, including renoprotective effects. However, the effect of endogenous PACAP in the kidneys is not known. The main aim of the present study was to investigate whether the lack of this endogenous neuropeptide influences survival of kidney cells against oxidative stress. First, we determined the presence of endogenous PACAP from mouse kidney homogenates by mass spectrometry and PACAP-like immunoreactivity by radioimmunoassay. Second, primary cultures were isolated from wild type and PACAP deficient mice and cell viability was assessed following oxidative stress induced by 0.5, 1.5 and 3mM H2O2. Our mass spectrometry and radioimmunoassay results show that PACAP is endogenously present in the kidney. The main part of our study revealed that the sensitivity of cells from PACAP deficient mice was increased to oxidative stress: both after 2 or 4h of exposure, cell viability was significantly reduced compared to that from control wild type mice. This increased sensitivity of kidneys from PACAP deficient mice could be counteracted by exogenously given PACAP38. These results show, for the first time, that endogenous PACAP protects against oxidative stress in the kidney, and that PACAP may act as a stress sensor in renal cells. These findings further support the general cytoprotective nature of this neuropeptide.

Neuroprotective Effect of PACAP on Translational Control Alteration and Cognitive Decline in MPTP Parkinsonian Mice

Parkinson's disease (PD) is characterized by a triade of motor symptoms due to the degeneration of nigrostriatal pathway. In addition to these motor impairments, cognitive disturbances have been reported to occur in PD patients in the early stage of the disease. The 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is a neurotoxin widely used to produce experimental models of PD. In a previous work, we showed that MPTP altered the expression of proteins involved in mTOR antiapoptotic and PKR apoptotic pathways of translational control (TC) in neuroblastoma cells. In the present study, the results indicated that a subchronic MPTP intoxication in mice decreased the dopaminergic neuron number, produced an activation of PKR way and an inhibition of mTOR way of TC especially in striatum and frontal cortex associated with a great activation of PKR in hippocampus. Moreover, in parallel to biochemical analysis, the mnesic disturbances induced by MPTP were characterized in C57Bl/6 mice, by testing their performance in three versions of the Morris Water Maze task. Behavioral results showed that the MPTP lesion altered mice learning of a spatial working memory, of a cued version and of a spatial reference memory task in the water maze. Furthermore, we previously demonstrated that the neuropeptide pituitary adenylate cyclase activating polypeptide (PACAP) could counteract the MPTP toxicity on TC factors in neuroblastoma cells. Thus, the second objective of our study was to assess the PACAP effect on MPTP-induced TC impairment and cognitive deficit in mice. The pretreatment with PACAP27 by intravenous injections partially protected TH-positive neuron loss induced by MPTP, prevented the MPTP-induced protein synthesis control dysregulation and mnesic impairment of mice. Therefore, our results could indicate that PACAP may be a promising therapeutic agent in Parkinson's disease.

Peroxiredoxin 2 is Involved in the Neuroprotective Effects of PACAP in Cultured Cerebellar Granule Neurons

The neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) is known to counteract in vitro the deleterious effects of toxic agents on cerebellar granule cell survival and differentiation. The potent antiapoptotic action of PACAP is mediated through inhibition of caspase-3 activity; however, additional proteins are likely involved and remain to be identified. Two-dimensional gel electrophoresis analysis coupled with mass spectrometry characterization led to the identification of a protein, peroxiredoxin 2, which was induced after a 6-h treatment with PACAP. Western blot analysis confirmed the regulation of peroxiredoxin 2 by PACAP and revealed that this protein is induced by both cyclic AMP and protein kinase C stimulators. Inhibition of peroxiredoxin 2 expression, using two distinct small-interfering RNAs (siRNAs), reduced the effect of PACAP on caspase-3 activity and cerebellar granule cell survival. Peroxiredoxin 2 expression was also induced in vivo and in vitro by ethanol. Although ethanol and PACAP exert opposite effects on caspase-3 activity, inhibition of peroxiredoxin 2 expression, using siRNAs, only reduced the ability of PACAP to prevent ethanol-induced caspase-3 activity. Taken together, these data indicate that peroxiredoxin 2 is probably involved in the neurotrophic effect of PACAP and suggest that this protein may have a therapeutic potential for the treatment of some neurodegenerative diseases.

Molecular, cellular, and functional characterizations of pituitary adenylate cyclase‐activating polypeptide and its receptors in the cerebellum of New and Old World monkeys

The neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) exerts trophic activities during cerebellar development, and a neuroprotective effect of PACAP has been demonstrated in pathological conditions such as stroke. However, all these data have been obtained in rodents, and neuroprotective effects of PACAP in primates remain unknown. Because of their evolutionary relationships with humans, monkeys represent powerful models for validating the therapeutic interest in PACAP. The objective of the present study was to characterize PACAP and its receptors in the cerebellum of two nonhuman primates. RT-PCR and in situ hybridization experiments revealed that PACAP is expressed in the cerebellum by Purkinje cells. Via immunohistochemistry, PACAP was detected in Purkinje cells and radial glial fibers. With regard to PACAP receptors, PAC1-R and VPAC1-R were detected by RT-PCR. In situ hybridization revealed a strong expression of PAC1-R and VPAC1-R in the granule cell layer (GCL), and VPAC1-R was also expressed in the Purkinje cell layer. A high density of PACAP binding sites was visualized in the GCL and the Purkinje cell layer. Competition studies indicated that, in the GCL, PACAP induced complete displacement of [(125)I]PACAP27 binding, whereas vasoactive intestinal polypeptide (VIP) was a weak competitor. In contrast, in the Purkinje cell layer, both PACAP and VIP displaced [(125)I]PACAP27 binding. Measurement of cAMP levels showed that PACAP is a powerful activator of adenylyl cyclase, whereas VIP is about 100-fold less potent. Altogether, these observations constitute the first demonstration of a functional PACAPergic system in monkey cerebellum. They strongly suggest that neuroprotective effects of PACAP can be transposed to primates, including human.

The neuroprotective effects of PACAP in monosodium glutamate-induced retinal lesion involve inhibition of proapoptotic signaling pathways

Pituitary adenylate cyclase activating polypeptide (PACAP) and its receptors are present in the retina and exert several distinct functions. PACAP has well-known neuroprotective effects in neuronal cultures in vitro and against different insults in vivo. Recently we have shown that PACAP is neuroprotective against monosodium glutamate (MSG)-induced retinal degeneration. In the present study we investigated the possible signal transduction pathways involved in the protective effect of intravitreal PACAP administration against apoptotic retinal degeneration induced by neonatal MSG treatment. MSG induced activation of proapoptotic signaling proteins and reduced the levels of antiapoptotic molecules in neonatal retinas. Co-treatment with PACAP attenuated the MSG-induced activation of caspase-3 and JNK, inhibited the MSG-induced cytosolic translocation of apoptosis inducing factor (AIF) and cytochrome c, and increased the level of phospho-Bad. Furthermore, PACAP treatment alone decreased cytosolic AIF and cytochrome c levels, while PACAP6-38 increased cytochrome c release, caspase-3 and JNK activity and decreased phospho-Bad activity. In summary, our results show that PACAP treatment attenuated the MSG-induced changes in apoptotic signaling molecules in vivo and suggest that also endogenously present PACAP has neuroprotective effects. These results may have further clinical implications in reducing glutamate-induced excitotoxicity in several ophthalmic diseases.

Effect of PACAP in 6-OHDA-induced injury of the substantia nigra in intact young and ovariectomized female rats

Pituitary adenylate cyclase activating polypeptide (PACAP) has neuroprotective effects in various neuronal cultures and in models of brain pathologies in vivo. Among others, it protects dopaminergic neurons in vitro, against 6-OHDA- and rotenone-induced injury. Recently, we have shown that PACAP reduces dopaminergic cell loss and ameliorates behavioral outcome following unilateral 6-OHDA-induced injury of the substantia nigra in male rats. However, after castration, PACAP led only to a slight amelioration of the behavioral symptoms. The aim of the present study was to investigate the degree of neuroprotection exerted by PACAP in female rats, using the same model. It was found that PACAP had no effect on the dopaminergic cell loss in intact female rats, only caused amelioration of certain acute behavioral signs. In contrast, PACAP effectively increased dopaminergic cell survival and decreased behavioral deficits in ovariectomized females. These results indicate that the neuroprotective effect of PACAP in a rat model of Parkinson's disease is gender-specific.

Neuroprotective Effect of PACAP against Kainic Acid‐Induced Neurotoxicity in Rat Retina

Pituitary adenylate cyclase-activating polypeptide (PACAP) is well known to protect delayed neuronal cell death in the brain of rodents. In order to investigate the neuroprotective action of PACAP in the retina, we examined the effects of PACAP on kainic acid (KA)-induced neurotoxicity in the rat retina. Many ganglion cells in the retina died after KA injection in the control group and PACAP treatment significantly promoted cell survival. These findings strongly suggest that PACAP plays very important roles in preventing cell death in the retina.

Neuroprotection against ischemic CA1 neurodegeneration by pituitary adenylate cyclase activating polypeptide via cAMP-response-element-binding protein-mediated enhancement of endogenous DNA repair

Emerging evidence suggests that accumulation of oxidative DNA damage in nuclear genome is an important contributing factor in neuronal cell death after cerebral ischemia. It has been shown in various models of cerebral ischemia/reperfusion that there is accumulation of oxidative DNA base damage and apurinic/apyridinic abasic site (AP site) in injured neurons, which could mediate neuronal degeneration by triggering various pro-apoptotic molecules. In the brain most types of oxidative DNA damage are repaired via the base-excision repair (BER) pathway that is highly inducible in response to various sublethal stimuli. Thus, interventions that enhance the activity of the BER pathway may be a potential therapeutic strategy against ischemic cell death. In the present study, we have examined the neuroprotective effect of the neuropeptide pituitary adenylate cyclase activating polypeptide (PACAP) in the rat model of transient global cerebral ischemia. Further, we have investigated the role of BER regulation as a potential mechanism underlying the effect of PACAP. PACAP, when infused intracerebroventricularly in the rat, potently protected against CA1 neuronal cell death after global cerebral ischemia produced by 12 minutes of 4-vessel occlusion. Associated with this neuroprotection, PACAP treatment reduced the accumulation of oxidative DNA lesions, especially AP site, and subsequently attenuated the activation of pro-apoptotic molecules p53 and PUMA in the CA1 sector, suggesting that the effect of PACAP may involve the acceleration of the repair process of endogenous oxidative DNA damage. To investigate the underlying mechanism, cellular BER activity and the expression of BER enzymes were measured in the hippocampal extracts. The results revealed that PACAP markedly enhanced the hippocampal expression (at both mRNA and protein levels) and activities of the essential BER enzymes AP endonuclase (APE) and DNA polymerase-beta. Furthermore, based on the results of inhibition studies, the inducible effect of PACAP on the BER pathway was found to be dependent on the phosphorylation and nuclear translocation of cAMP-response-element-binding protein (CREB), which mediated the enhanced transcription of both APE and DNA polymerase-beta. Finally, the effect of PACAP on BER and neuroprotection was mimicked by the administration of a cAMP/protein kinase A (PKA) agonist. The results of the present study demonstrate the neuroprotective effect of PACAP in hippocampal CA1 neurons after transient global cerebral ischemia. The effect of PACAP is dependent on the activation and nuclear translocation of CREB, and involves CREB-mediated activation of BER pathway for endogenous DNA repair. The results suggest that enhancement of neuronal DNA repair capacity by PACAP or other means may be a novel potential therapeutic approach to limit ischemic neuronal loss. (This project was supported by NIH grants NS36736, NS38560, NS 43802, and NS45048).

PACAP protects neuronal differentiated PC12 cells against the neurotoxicity induced by a mitochondrial complex I inhibitor, rotenone

In vivo and in vitro studies have suggested a neuroprotective role for Pituitary adenylate cyclase activating polypeptide (PACAP) against neuronal insults. Here, we showed that PACAP27 protects against neurotoxicity induced by rotenone, a mitochondrial complex I inhibitor that has been implicated in the pathogenesis of Parkinson’s disease (PD). The neuroprotective effect of PACAP27 was dose-dependent and blocked by its specific receptor antagonist, PACAP6-27. The effects of PACAP27 on rotenone-induced cell death were mimicked by dibutyryl-cAMP (db-cAMP), forskolin and prevented by the PKA inhibitor H89, the ERK inhibitor PD98059 and the p38 inhibitor SB203580. PACAP27 administration blocked rotenone-induced increases in the level of caspase-3-like activity, whereas could not restore mitochondrial activity damaged by rotenone. Thus, our results demonstrate that PACAP27 has a neuroprotective role against rotenone-induced neurotoxicity in neuronal differentiated PC12 cells and the neuroprotective effects of PACAP are associated with activation of MAP kinase pathways by PKA and with inhibition of caspase-3 activity; the signaling mechanism appears to be mediated through mitochondrial-independent pathways.

Effects of pituitary adenylate cyclase activating polypeptide in retinal degeneration induced by monosodium-glutamate

Pituitary adenylate cyclase activating polypeptide (PACAP) is a pleiotropic neuropeptide with a wide range of effects in the central and peripheral nervous systems. PACAP has well-documented neurotrophic and neuroprotective actions in both in vitro and in vivo models of different neuronal injuries. The aim of the present study was to investigate the possible neuroprotective effect of PACAP in retinal degeneration induced by monosodium-glutamate (MSG) in neonatal rats. Preceding the MSG treatment, PACAP (1 or 100 pmol/5 μl) was injected unilaterally into the vitreous body on postnatal days 1, 5 and 9. Immediately after the PACAP treatment, pups were treated with 2 mg/g body weight MSG subcutaneously. At 3 weeks of age, rats were sacrificed and retinas were removed and processed for histological examination. Our results show that MSG treatment caused severe degeneration, primarily of the inner retinal layers. The thickness of the entire retina was only approximately half of that of the normal retinas, and the inner nuclear layer seemed to be fused with the ganglionic cell layer, with no discernible inner plexiform layer. Retinas of animals treated with 1 pmol PACAP showed a similar degree of degeneration. However, retinas of rats treated with 100 pmol PACAP showed significantly less damage, with clearly distinguishable inner retinal layers. In summary, our present study shows that local PACAP treatment could attenuate the retinal degeneration induced by the excitotoxic effects of glutamate.