Mice deficient in pituitary adenylate cyclase activating polypeptide (PACAP) show increased susceptibility to in vivo renal ischemia/reperfusion injury

Effects of PACAP Deficiency on Immune Dysfunction and Peyer's Patch Integrity in Adult Mice

PACAP (pituitary adenylate cyclase activating polypeptide) is a widespread neuropeptide with cytoprotective and anti-inflammatory effects. It plays a role in innate and adaptive immunity, but data are limited about gut-associated lymphoid tissue. We aimed to reveal differences in Peyer's patches between wild-type (WT) and PACAP-deficient (KO) mice. Peyer's patch morphology from young (3-months-old) and aging (12-15-months-old) mice was examined, along with flow cytometry to assess immune cell populations, expression of checkpoint molecules (PD-1, PD-L1, TIM-3, Gal-9) and functional markers (CD69, granzyme B, perforin) in CD3+, CD4+, and CD8+ T cells. We found slight differences between aging, but not in young, WT, and KO mice. In WT mice, aging reduced CD8+ T cell numbers frequency and altered checkpoint molecule expression (higher TIM-3, granzyme B; lower Gal-9, CD69). CD4+ T cell frequency was higher with similar checkpoint alterations, indicating a regulatory shift. In PACAP KO mice, aging did not change cell population frequencies but led to higher TIM-3, granzyme B and lower PD-1, PD-L1, Gal-9, and CD69 expression in CD4+ and CD8+ T cells, with reduced overall T cell activity. Thus, PACAP deficiency impacts immune dysfunction by altering checkpoint molecules and T cell functionality, particularly in CD8+ T cells, suggesting complex immune responses by PACAP, highlighting its role in intestinal homeostasis and potential implications for inflammatory bowel diseases.

Genome-wide association study of SNP- and gene-based approaches to identify susceptibility candidates for lupus nephritis in the Han Chinese population

Background

Lupus nephritis (LN) is one of the most common and serious complications of systemic lupus erythaematosus (SLE). Genetic factors play important roles in the pathogenesis of LN and could be used to predict who might develop LN. The purpose of this study was to screen for susceptible candidates of LN across the whole genome in the Han Chinese population.

Methods

592 LN patients and 453 SLE patients without renal damage were genotyped at 492,970 single nucleotide polymorphisms (SNPs) in the genome-wide association study (GWAS). Fifty-six SNPs were selected for replication in an independent cohort of 188 LN and 171 SLE without LN patients. Further quantitative real-time (qRT) PCR was carried out in 6 LN patients and 6 healthy controls. Gene-based analysis was conducted using the versatile gene-based test for GWAS. Subsequently, enrichment and pathway analyses were performed in the DAVID database.

Results

The GWAS analysis and the following replication research identified 9 SNPs showing suggestive correlation with LN (P<10-4). The most significant SNP was rs12606116 (18p11.32), at P=8.72×10−6. The qRT-PCR results verified the mRNA levels of LINC00470 and ADCYAP1, the closest genes to rs12606116, were significantly lower in LN patients. From the gene-based analysis, 690 genes had suggestive evidence of association (P<0.05), including LINC00470. The enrichment analysis identified the involvement of transforming growth factor beta (TGF-β) signalings in the development of LN. Lower plasma level of TGF-β1 (P<0.05) in LN patients and lower expression of transforming growth factor beta receptor 2 in lupus mice kidney (P<0.05) futher indicate the involvement of TGF-β in LN.

Conclusions

Our analyses identified several promising susceptibility candidates involved in LN, and further verification of these candidates was necessary.

Hearing impairment and associated morphological changes in pituitary adenylate cyclase activating polypeptide (PACAP)-deficient mice

Pituitary adenylate cyclase activating polypeptide (PACAP) is a regulatory and cytoprotective neuropeptide, its deficiency implies accelerated aging in mice. It is present in the auditory system having antiapoptotic effects. Expression of Ca²⁺-binding proteins and its PAC1 receptor differs in the inner ear of PACAP-deficient (KO) and wild-type (WT) mice. Our aim was to elucidate the functional role of PACAP in the auditory system. Auditory brainstem response (ABR) tests found higher hearing thresholds in KO mice at click and low frequency burst stimuli. Hearing impairment at higher frequencies showed as reduced ABR wave amplitudes and latencies in KO animals. Increase in neuronal activity, demonstrated by c-Fos immunolabeling, was lower in KO mice after noise exposure in the ventral and dorsal cochlear nuclei. Noise induced neuronal activation was similar in further relay nuclei of the auditory pathway of WT and KO mice. Based on the similar inflammatory and angiogenic protein profile data from cochlear duct lysates, neither inflammation nor disturbed angiogenesis, as potential pathological components in sensorineural hearing losses, seem to be involved in the pathomechanism of the presented functional and morphological changes in PACAP KO mice. The hearing impairment is probably concomitant with the markedly accelerated aging processes in these animals.

The Neuropeptide Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) is Protective in Inflammation and Oxidative Stress-Induced Damage in the Kidney

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a pleiotropic neuropeptide with a widespread distribution throughout the entire body including the urinary system. PACAP exerts protective actions in different injury models related to several organ systems. Its protective effect is mainly based on its antiapoptotic, anti-inflammatory and antioxidant effects. The present review aims to summarize the effects of PACAP in pathologies associated with inflammation and oxidative stress-induced damage in the kidney. Both in vitro and in vivo data are available proving its protective actions against oxidative stress, hypoxia, renal ischemia/reperfusion, diabetic nephropathy, myeloma kidney injury, amyloidosis and different types of drug-induced nephropathies. Data showing the nephroprotection by PACAP emphasize the potential of PACAP’s therapeutic use in various renal pathologies.

Pituitary Adenylate Cyclase-Activating Polypeptide: 30 Years in Research Spotlight and 600 Million Years in Service

Emerging from the depths of evolution, pituitary adenylate cyclase-activating polypeptide (PACAP) and its receptors (i.e., PAC1, VPAC1, VPAC2) are present in multicellular organisms from Tunicates to humans and govern a remarkable number of physiological processes. Consequently, the clinical relevance of PACAP systems spans a multifaceted palette that includes more than 40 disorders. We aimed to present the versatility of PACAP1-38 actions with a focus on three aspects: (1) when PACAP1-38 could be a cause of a malfunction, (2) when PACAP1-38 could be the cure for a malfunction, and (3) when PACAP1-38 could either improve or impair biology. PACAP1-38 is implicated in the pathophysiology of migraine and post-traumatic stress disorder whereas an outstanding protective potential has been established in ischemia and in Alzheimer’s disease. Lastly, PACAP receptors could mediate opposing effects both in cancers and in inflammation. In the light of the above, the duration and concentrations of PACAP agents must be carefully set at any application to avoid unwanted consequences. An enormous amount of data accumulated since its discovery (1989) and the first clinical trials are dated in 2017. Thus in the field of PACAP research: “this is not the end, not even the beginning of the end, but maybe the end of the beginning.”

PACAP deficiency as a model of aging

Dysregulation of neuropeptides may play an important role in aging-induced impairments. In the long list of neuropeptides, pituitary adenylate cyclase-activating polypeptide (PACAP) represents a highly effective cytoprotective peptide that provides an endogenous control against a variety of tissue-damaging stimuli. PACAP has neuro- and general cytoprotective effects due to anti-apoptotic, anti-inflammatory, and antioxidant actions. As PACAP is also a part of the endogenous protective machinery, it can be hypothesized that the decreased protective effects in lack of endogenous PACAP would accelerate age-related degeneration and PACAP knockout mice would display age-related degenerative signs earlier. Recent results support this hypothesis showing that PACAP deficiency mimics aspects of age-related pathophysiological changes including increased neuronal vulnerability and systemic degeneration accompanied by increased apoptosis, oxidative stress, and inflammation. Decrease in PACAP expression has been shown in different species from invertebrates to humans. PACAP-deficient mice display numerous pathological alterations mimicking early aging, such as retinal changes, corneal keratinization and blurring, and systemic amyloidosis. In the present review, we summarize these findings and propose that PACAP deficiency could be a good model of premature aging.

Immunomodulatory Roles of PACAP and VIP: Lessons from Knockout Mice

A bidirectional cross-talk is established between the nervous and immune systems through common mediators including neuropeptides, neurotransmitters, and cytokines. Among these, PACAP and VIP are two highly related neuropeptides widely distributed in the organism with purported immunomodulatory actions. Due to their well-known anti-inflammatory properties, administration of these peptides has proven to be beneficial in models of acute and chronic inflammatory diseases. Nevertheless, the relevance of the endogenous source of these peptides in the modulation of immune responses remains to be elucidated. The development of transgenic mice with specific deletions in the genes coding for these neuropeptides (Vip and Adcyap1) or for their G-protein-coupled receptors VPAC1, VPAC2, and PAC1 (Vipr1, Vipr2, Adcyap1r1) has allowed to address this question, underscoring the complexity of the immunoregulatory properties of PACAP and VIP. The goal of this review is to integrate the existing information on the immune phenotypes of mice deficient for PACAP, VIP, or their receptors, to provide a global view on the roles of these endogenous neuropeptides during immunological health and disease.

Altered Notch Signaling in Developing Molar Teeth of Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP)-Deficient Mice

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide with neuroprotective and neurotrophic effects. This suggests its influence on the development of teeth, which are, similarly to the nervous system, ectoderm and neural crest derivatives. Our earlier studies have shown morphological differences between wild-type (WT) and PACAP-deficient mice, with upregulated sonic hedgehog (SHH) signaling in the lack of PACAP. Notch signaling is a key element of proper tooth development by regulating apoptosis and cell proliferation. In this study, our main goal was to evaluate the possible effects of PACAP on Notch signaling pathway. Immunohistochemical staining was performed of Notch receptors (Notch1, 2, 3, 4), their ligands [delta-like protein (DLL)1, 3, 4, Jagged1, 2], and intracellular target molecules [CSL (CBF1 humans/Su (H) Drosophila/LAG1 Caenorhabditis elegans transcription factor); TACE (TNF-α converting enzyme), NUMB] in molar teeth of 5-day-old WT, and homozygous and heterozygous PACAP-deficient mice. We measured immunopositivity in the enamel-producing ameloblasts and dentin-producing odontoblasts. Notch2 receptor and DLL1 expression were elevated in ameloblasts of PACAP-deficient mice compared to those in WT ones. The expression of CSL showed similar results both in the ameloblasts and odontoblasts. Jagged1 ligand expression was elevated in the odontoblasts of homozygous PACAP-deficient mice compared to WT mice. Other Notch pathway elements did not show significant differences between the genotype groups. The lack of PACAP leads to upregulation of Notch pathway elements in the odontoblast and ameloblast cells. The underlying molecular mechanisms are yet to be elucidated; however, we propose SHH-dependent and independent processes. We hypothesize that this compensatory upregulation of Notch signaling by the lack of PACAP could represent a salvage pathway in PACAP-deficient animals.

Endogenous factors and mechanisms of renoprotection and renal repair

BACKGROUND

An imbalance between renal damaging molecules and nephroprotective factors contributes to the development and progression of kidney diseases. Molecules with renoprotective properties might serve as biomarkers, drug targets as well as therapeutic options themselves.

MATERIALS AND METHODS

For this review, we generated a set of renoprotective factors based on GeneRIF (Gene Reference Into Function) information available at NCBI's PubMed. The final set of manually curated renoprotective factors was investigated with respect to tissue-specific expression, subcellular location distribution and involvement in biological processes using information from gene ontology as well as information from protein-protein interaction databases. We furthermore investigated the factors in the context of clinical trials of renal disease and diabetes.

RESULTS

One hundred and ninety-three factors could be retrieved from the set of GeneRIFs on nephroprotection and renal repair. A large number of factors were either secretory molecules or plasma membrane receptors. Next to the elevated expression in renal tissue, also higher expression in connective tissue and pancreas was observed. The proteins could be assigned to the broad functional categories of cell proliferation and signalling, inflammatory response, apoptosis, blood pressure regulation as well as cellular response to different kinds of insults such as hypoxia, heat or mechanical stimulus. Eight factors are studied in clinical trials with additional ones being targeted by compounds.

CONCLUSIONS

We have generated a set of renoprotective factors based on the literature information, which was functionally annotated and evaluated with respect to tested compounds in kidney disease and diabetes clinical trials.

Protective effects of PACAP in ischemia

Pituitary adenylate cyclase activating polypeptide (PACAP) is an ubiquitous peptide involved, among others, in neurodevelopment, neuromodulation, neuroprotection, neurogenic inflammation and nociception. Presence of PACAP and its specific receptor, PAC1, in the trigeminocervical complex, changes of PACAP levels in migraine patients and the migraine-inducing effect of PACAP injection strongly support the involvement of PACAP/PAC1 receptor in migraine pathogenesis. While antagonizing PAC1 receptor is a promising therapeutic target in migraine, the diverse array of PACAP's functions, including protection in ischemic events, requires that the cost-benefit of such an intervention is well investigated by taking all the beneficial effects of PACAP into account. In the present review we summarize the protective effects of PACAP in ischemia, especially in neuronal ischemic injuries, and discuss possible points to consider when developing strategies in migraine therapy interfering with the PACAP/PAC1 receptor system.

Effects of pituitary adenylate cyclase activating polypeptide on small intestinal INT 407 cells

Pituitary adenylate cyclase activating polypeptide (PACAP) is an endogenous neuropeptide having a widespread distribution both in the nervous system and peripheral organs including the gastrointestinal tract. It has been shown to exert actions on intestinal functions, mainly affecting glandular secretion and motility. PACAP has several different effects on cell survival depending on the cell type and the applied stimulus. Its influences on small intestinal epithelial cells are not yet elucidated, therefore the aim of the present study was to investigate the effects of PACAP on intestinal epithelial cells having high turnover (INT 407) against different harmful stimuli, such as oxidative stress, in vitro hypoxia and gamma radiation. We tested the effect of PACAP on proliferation and cell survival using MTT assay. Moreover, various cancer-related factors were evaluated by oncology array. PACAP did not influence the proliferation rate of INT 407 cells. Its cell survival-enhancing effect could be detected against oxidative stress, but not against in vitro hypoxia or gamma irradiation. Clonogenic survival assay was performed to analyze the effect of PACAP on clonogenic potential of cells exposed to gamma radiation. Surprisingly, PACAP enhanced the clone-forming ability decrease induced by irradiation. Western blot analysis of ERK1/2 phosphorylation was performed in order to obtain further information on the molecular background. Our data showed phospho-ERK1/2 suppression of PACAP in irradiated cells. Furthermore, the role of endogenous PACAP against oxidative stress was also investigated performing ADCYAP1 small interfering RNA transfection. We found significant difference in the cell vulnerability between cells undergoing silencing and cells without transfection suggesting the protective role of the endogenously present PACAP against oxidative stress in INT 407 cells. In summary, PACAP seems to be able to exert contradictory effects in INT 407 cells depending on the applied stressor, suggesting its regulatory role in the cellular household.

Early Neurobehavioral Development of Mice Lacking Endogenous PACAP

Pituitary adenylate cyclase activating polypeptide (PACAP) is a multifunctional neuropeptide. In addition to its diverse physiological roles, PACAP has important functions in the embryonic development of various tissues, and it is also considered as a trophic factor during development and in the case of neuronal injuries. Data suggest that the development of the nervous system is severely affected by the lack of endogenous PACAP. Short-term neurofunctional outcome correlates with long-term functional deficits; however, the early neurobehavioral development of PACAP-deficient mice has not yet been evaluated. Therefore, the aim of the present study was to describe the postnatal development of physical signs and neurological reflexes in mice partially or completely lacking PACAP. We examined developmental hallmarks during the first 3 weeks of the postnatal period, during which period most neurological reflexes and motor coordination show most intensive development, and we describe the neurobehavioral development using a complex battery of tests. In the present study, we found that PACAP-deficient mice had slower weight gain throughout the observation period. Interestingly, mice partially lacking PACAP weighed significantly less than homozygous mice. There was no difference between male and female mice during the first 3 weeks. Some other signs were also more severely affected in the heterozygous mice than in the homozygous mice, such as air righting, grasp, and gait initiation reflexes. Interestingly, incisor teeth erupted earlier in mice lacking PACAP. Motor coordination, shown by the number of foot-faults on an elevated grid, was also less developed in PACAP-deficient mice. In summary, our results show that mice lacking endogenous PACAP have slower weight gain during the first weeks of development and slower neurobehavioral development regarding a few developmental hallmarks.

The pituitary adenylate cyclase-activating polypeptide (PACAP) protects adrenal function in septic rats administered etomidate

BACKGROUND

Both hyperinflammation during sepsis and etomidate can suppress adrenal function. In this study, we explored whether treatment with pituitary adenylate cyclase-activating polypeptide (PACAP) relieves adrenal suppression in cecal ligation and puncture (CLP)-induced septic rats.

MATERIALS AND METHODS

Female Sprague-Dawley rats were randomly divided into five groups (n=7 per group), including the sham group, sepsis group (CLP group), sepsis and etomidate group (CLP+ETO group), PACAP group, and etomidate alone group (ETO group). Rats were sacrificed on the third day of sepsis, and blood and adrenal gland samples were obtained for further testing.

RESULTS

The PACAP reduced the apoptosis rate of adrenal cells and peripheral lymphocytes, improving adrenal function, inhibiting the secretion of interferon gamma (IFN-γ) from peripheral lymphocytes, and slightly relieving the suppression of the adrenal function induced by the injection of etomidate in sepsis.

CONCLUSION

In septic conditions, the PACAP protects the adrenal gland by regulating peripheral inflammation, which slightly relieves the toxic effects of etomidate on adrenal function.

Ischemia/reperfusion-induced Kidney Injury in Heterozygous PACAP-deficient Mice

Pituitary adenylate cyclase activating polypeptide (PACAP) is a neuropeptide with very diverse distribution and functions. Among others, PACAP is a potent cytoprotective peptide due to its antiapoptotic, anti-inflammatory, and antioxidant actions. This also has been shown in different kidney pathologies, including ischemia/reperfusion-induced kidney injury. Similar protective effects of the endogenous PACAP are confirmed by the increased vulnerability of PACAP-deficient mice to different harmful stimuli. Kidneys of homozygous PACAP-deficient mice have more severe damages in renal ischemia/reperfusion and kidney cell cultures isolated from these mice show increased sensitivity to renal oxidative stress. In our present study we raised the question of whether the partial lack of the PACAP gene is also deleterious, i.e. whether heterozygous PACAP-deficient mice also display more severe damage after renal ischemia/reperfusion. Mice underwent 45 or 60 minutes of ischemia followed by 2 weeks reperfusion. Histological evaluation of the kidneys was performed and individual histopathological parameters were graded. Furthermore, we investigated apoptotic markers, cytokine expression, and the activity of superoxide dismutase (SOD) enzyme 24 hours after 60 minutes of renal ischemia/reperfusion. We found no difference between the intact kidneys of wild-type and heterozygous mice, but marked differences could be observed following ischemia/reperfusion. Heterozygous PACAP-deficient mice had more severe histological alterations, with significantly higher histopathological scores for most of the tested parameters. Higher level of the proapoptotic pp38 MAPK and of some proinflammatory cytokines, as well as lower activity of the antioxidant SOD could be found in these mice. In conclusion, the partial lack of the PACAP gene results in worse outcomes in cases of renal ischemia/reperfusion, confirming that PACAP functions as an endogenous protective factor in the kidney.

Renoprotective approaches and strategies in acute kidney injury

Acute kidney injury (AKI) is a major renal disease associated with high mortality rate and increasing prevalence. Decades of research have suggested numerous chemical and biological agents with beneficial effects in AKI. In addition, cell therapy and molecular targeting have been explored for reducing kidney tissue damage and promoting kidney repair or recovery from AKI. Mechanistically, these approaches may mitigate oxidative stress, inflammation, cell death, and mitochondrial and other organellar damage, or activate cytoprotective mechanisms such as autophagy and pro-survival factors. However, none of these findings has been successfully translated into clinical treatment of AKI. In this review, we analyze these findings and propose experimental strategies for the identification of renoprotective agents or methods with clinical potential. Moreover, we propose the consideration of combination therapy by targeting multiple targets in AKI.

Distribution and Function of PACAP and Its Receptors in the Healthy and Nephrotic Kidney

BACKGROUND/AIMS

Plasma deficiency of pituitary adenylate cyclase-activating polypeptide (PACAP) was recently demonstrated in children with nephrotic syndrome (NS). Previous studies have reported an important protective effect of PACAP on kidney proximal tubules. The aim of this study was to explore the expression of PACAP and its receptors PAC1, VPAC1 and VPAC2 in the healthy and nephrotic kidney and to determine if PACAP has an effect on renal proximal tubular cells exposed to albumin.

METHODS

Expression of PACAP and its receptors was studied using kidney tissue from healthy and nephrotic children, and in 3 human renal cell lines (glomerular microvascular endothelial cells, podocytes and proximal tubular epithelial HK-2 cells). The functionality of the VPAC1 receptor was tested in HK-2 cells, measuring cyclic adenosine monophosphate levels after PACAP exposure. The influence of PACAP on cell viability and transforming growth factor-β1 (TGF-β1) expression was measured in HK-2 cells exposed to albumin, mimicking proteinuria related damage.

RESULTS

VPAC1 expression was detected in the tubular proximal epithelial cells and in the glomerular podocytes of renal tissue from healthy and nephrotic children. Increased staining for PACAP was found in the proximal tubules of renal sections from children with NS compared to healthy renal sections. Expression and functionality of VPAC1 were demonstrated in HK-2 cells. Finally, PACAP did not alter cell viability or TGF-β1 expression of HK-2 cells exposed to albumin.

CONCLUSION

VPAC1 is the predominant receptor in the human kidney. The enhanced presence of PACAP in proximal tubular epithelial cells in nephrotic kidneys points to the reabsorption of filtered PACAP. On short term, PACAP has no in vitro effect on cell viability and TGF-β1 expression of proximal tubular epithelial cells exposed to high concentrations of albumin.

Microglia-Induced Maladaptive Plasticity Can Be Modulated by Neuropeptides In Vivo

Microglia-induced maladaptive plasticity is being recognized as a major cause of deleterious self-sustaining pathological processes that occur in neurodegenerative and neuroinflammatory diseases. Microglia, the primary homeostatic guardian of the central nervous system, exert critical functions both during development, in neural circuit reshaping, and during adult life, in the brain physiological and pathological surveillance. This delicate critical role can be disrupted by neural, but also peripheral, noxious stimuli that can prime microglia to become overreactive to a second noxious stimulus or worsen underlying pathological processes. Among regulators of microglia, neuropeptides can play a major role. Their receptors are widely expressed in microglial cells and neuropeptide challenge can potently influence microglial activity in vitro. More relevantly, this regulator activity has been assessed also in vivo, in experimental models of brain diseases. Neuropeptide action in the central nervous system has been associated with beneficial effects in neurodegenerative and neuroinflammatory pathological experimental models. This review describes some of the mechanisms of the microglia maladaptive plasticity in vivo and how neuropeptide activity can represent a useful therapeutical target in a variety of human brain pathologies.

Pituitary adenylate cyclase-activating polypeptide protects glomerular podocytes from inflammatory injuries

Diabetic nephropathy (DN) is a leading cause of end-stage kidney disease; however, there are few treatment options. Inflammation plays a crucial role in the initiation and/or progression of DN. Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide, which was originally isolated from the ovine hypothalamus and reportedly has diverse biological functions. It has been reported that PACAP has renoprotective effects in different models of kidney pathology. However, the specific cell types within the kidney that are protected by PACAP have not yet been reported. In this study, we localized VPAC1, one of the PACAP receptors, to glomerular podocytes, which also reportedly has crucial roles not only in glomerular physiology but also in pathology. PACAP was effective in the downregulation of proinflammatory cytokines, such as monocyte chemoattractant protein-1 (MCP-1) and interleukin-6, which had been induced by the activation of toll-like receptor (TLR) with lipopolysaccharide. PACAP also had downregulated the expression of MCP-1 through the protein kinase A signaling pathway; this led to the attenuation of the activation of extracellular signal-regulated kinase and nuclear factor-kappa B signaling. Our results suggested that PACAP could be a possible treatment option for DN through the use of anti-inflammation effects on glomerular podocytes.

The effects of pituitary adenylate cyclase activating polypeptide in renal ischemia/reperfusion

Pituitary adenylate cyclase activating polypeptide (PACAP ) is a multifunctional neuropeptide occurring in the nervous system as well as in the peripheral organs. Beneficial action of PACAP has been shown in different pathological processes. The strong protective effects of the peptide are probably due to its complex modulatory actions in antiapoptotic, anti-inflammatory and antioxidant pathways. In the kidney, PACAP is protective in models of diabetic nephropathy, myeloma kidney injury, cisplatin-, gentamycin- and cyclosporin-induced damages. Numerous studies have been published describing the protective effect of this peptide in renal ischemia/reperfusion. The present review focuses on the ischemia/reperfusion-induced kidney injury and gives a brief summary about the results published in this area.

Pituitary adenylate cyclase-activating polypeptide ameliorates experimental acute ileitis and extra-intestinal sequelae

Background

The neuropeptide Pituitary adenylate cyclase-activating polypeptide (PACAP) plays pivotal roles in immunity and inflammation. So far, potential immune-modulatory properties of PACAP have not been investigated in experimental ileitis.

Methodology/Principal Findings

Mice were perorally infected with Toxoplasma (T.) gondii to induce acute ileitis (day 0) and treated daily with synthetic PACAP38 from day 1 to 6 post infection (p.i.; prophylaxis) or from day 4 to 6 p.i. (therapy). Whereas placebo-treated control mice suffered from acute ileitis at day 7 p.i. and succumbed to infection, intestinal immunopathology was ameliorated following PACAP prophylaxis. PACAP-treated mice exhibited increased abundance of small intestinal FOXP3+ cells, but lower numbers of ileal T lymphocytes, neutrophils, monocytes and macrophages, which was accompanied by less ileal expression of pro-inflammatory cytokines such as IL-23p19, IL-22, IFN-γ, and MCP-1. Furthermore, PACAP-treated mice displayed higher anti-inflammatory IL-4 concentrations in mesenteric lymph nodes and liver and higher systemic anti-inflammatory IL-10 levels in spleen and serum as compared to control animals at day 7 p.i. Remarkably, PACAP-mediated anti-inflammatory effects could also be observed in extra-intestinal compartments as indicated by reduced pro-inflammatory mediator levels in spleen (TNF-α, nitric oxide) and liver (TNF-α, IFN-γ, MCP-1, IL-6) and less severe histopathological sequelae in lungs and kidneys following prophylactic PACAP treatment. Strikingly, PACAP prolonged survival of T. gondii infected mice in a time-of-treatment dependent manner.

Conclusion/Significance

Synthetic PACAP ameliorates acute small intestinal inflammation and extra-intestinal sequelae by down-regulating Th1-type immunopathology, reducing oxidative stress and up-regulating anti-inflammatory cytokine responses. These findings provide novel potential treatment options of inflammatory bowel diseases.

Pituitary adenylate cyclase-activating polypeptide protects against β-amyloid toxicity

Pituitary adenylate cyclase activating polypeptide (PACAP) is a neurotrophin. However, its role in human Alzheimer's disease (AD) is largely unknown. We examined PACAP expression in postmortem human AD and triple transgenic mouse (3xTG, Psen1/APPSwe/TauP301L) brains. We established an in vitro model of primary neuronal cell culture to study the protective effects of PACAP against β-amyloid (Aβ) toxicity. We further studied the PACAP-Sirtuin 3 (Sirt3) pathway on mitochondrial function. PACAP expression was reduced in AD and 3xTG mouse brains. This reduction was inversely correlated with Aβ and tau protein levels. Treatment with PACAP effectively protected neurons against Aβ toxicity. PACAP stimulated mitochondrial Sirt3 production. Similar to PACAP, Sirt3 was reduced in AD and 3xTG brains. Knocking down Sirt3 compromised the neuroprotective effects of PACAP, and this was reversed by over-expressing Sirt3. PACAP is reduced in AD and may represent a novel therapeutic strategy.

Examination of calcium-binding protein expression in the inner ear of wild-type, heterozygous and homozygous pituitary adenylate cyclase-activating polypeptide (PACAP)-knockout mice in kanamycin-induced ototoxicity

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide with diverse biological effects. It also occurs and exerts protective effects in sensory organs; however, little is known about its effects in the auditory system. Recently, we have shown that PACAP protects cochlear cells against oxidative-stress-induced apoptosis and homozygous PACAP-deficient animals show stronger expression of Ca(2+)-binding proteins in the hair cells of the inner ear, but there are no data about the consequences of the lack of endogenous PACAP in different ototoxic insults such as aminoglycoside-induced toxicity. In this study, we examined the effect of kanamycin treatment on Ca(2+)-binding protein expression in hair cells of wild-type, heterozygous and homozygous PACAP-deficient mice. We treated 5-day-old mice with kanamycin, and 2 days later, we examined the Ca(2+)-binding protein expression of the hair cells with immunohistochemistry. We found stronger expression of Ca(2+)-binding proteins in the hair cells of control heterozygous and homozygous PACAP-deficient mice compared with wild-type animals. Kanamycin induced a significant increase in Ca(2+)-binding protein expression in wild-type and heterozygous PACAP-deficient mice, but the baseline higher expression in homozygous PACAP-deficient mice did not show further changes after the treatment. Elevated endolymphatic Ca(2+) is deleterious for the cochlear function, against which the high concentration of Ca(2+)-buffers in hair cells may protect. Meanwhile, the increased immunoreactivity of Ca(2+)-binding proteins in the absence of PACAP provide further evidence for the important protective role of PACAP in ototoxicity, but further investigations are necessary to examine the exact role of endogenous PACAP in ototoxic insults.

Neuropeptide PACAP in mouse liver ischemia and reperfusion injury: immunomodulation by the cAMP-PKA pathway

Hepatic ischemia and reperfusion injury (IRI), an exogenous antigen-independent local inflammation response, occurs in multiple clinical settings, including liver transplantation, hepatic resection, trauma, and shock. The immune system and the nervous system maintain extensive communication and mount a variety of integrated responses to danger signals through intricate chemical messengers. This study examined the function and potential therapeutic potential of neuropeptide pituitary adenylate cyclase-activating polypeptides (PACAP) in a murine model of partial liver "warm" ischemia (90 minutes) followed by reperfusion. Liver IRI readily triggered the expression of intrinsic PACAP and its receptors, whereas the hepatocellular damage was exacerbated in PACAP-deficient mice. Conversely, PACAP27, or PACAP38 peptide monotherapy, which elevates intracellular cyclic adenosine monophosphate/protein kinase A (cAMP-PKA) signaling, protected livers from IRI, as evidenced by diminished serum alanine aminotransferase levels and well-preserved tissue architecture. The liver protection rendered by PACAP peptides was accompanied by diminished neutrophil/macrophage infiltration and activation, reduced hepatocyte necrosis/apoptosis, and selectively augmented hepatic interleukin (IL)-10 expression. Strikingly, PKA inhibition readily restored liver damage in otherwise IR-resistant, PACAP-conditioned mice. In vitro, PACAP treatment not only diminished macrophage tumor necrosis factor alpha/IL-6/IL-12 levels in a PKA-dependent manner, but also prevented necrosis and apoptosis in primary mouse hepatocyte cultures.

CONCLUSION

Our novel findings document the importance of PACAP-mediated cAMP-PKA signaling in hepatic homeostasis and cytoprotection in vivo. Because the enhancement of neural modulation differentially regulates local inflammation and prevents hepatocyte death, these results provide the rationale for novel approaches to manage liver inflammation and IRI in transplant patients.

Effects of pituitary adenylate cyclase activating polypeptide in the urinary system, with special emphasis on its protective effects in the kidney

Pituitary adenylate cyclase activating polypeptide (PACAP) is a widespread neuropeptide with diverse effects in the nervous system and peripheral organs. One of the most well-studied effects of PACAP is its cytoprotective action, against different harmful stimuli in a wide variety of cells and tissues. PACAP occurs in the urinary system, from the kidney to the lower urinary tract. The present review focuses on the nephroprotective effects of PACAP and summarizes data obtained regarding the protective effects of PACAP in different models of kidney pathologies. In vitro data show that PACAP protects tubular cells against oxidative stress, myeloma light chain, cisplatin, cyclosporine-A and hypoxia. In vivo data provide evidence for its protective effects in ischemia/reperfusion, cisplatin, cyclosporine-A, myeloma kidney injury, diabetic nephropathy and gentamicin-induced kidney damage. Results accumulated on the renoprotective effects of PACAP suggest that PACAP is an emerging candidate for treatment of human kidney pathologies.

Pituitary adenylate cyclase-activating polypeptide plays an anti-inflammatory role in endotoxin-induced airway inflammation: in vivo study with gene-deleted mice

The presence of pituitary adenylate cyclase-activating polypeptide (PACAP) and its receptors in capsaicin-sensitive peptidergic sensory nerves, inflammatory and immune cells suggest its involvement in inflammation. However, data on its role in different inflammatory processes are contradictory and there is little known about its functions in the airways. Therefore, our aim was to examine intranasal endotoxin-induced subacute airway inflammation in PACAP gene-deficient (PACAP⁻/⁻) and wild-type (PACAP⁺/⁺) mice. Airway responsiveness to inhaled carbachol was determined in unrestrained mice with whole body plethysmography 6 h and 24 h after LPS. Myeloperoxidase (MPO) activity referring to the number of accumulated neutrophils and macrophages was measured with spectrophotometry and interleukin-1β (IL-1β) concentration with ELISA from the lung homogenates. Histological evaluation and semiquantitative scoring were also performed. Bronchial responsiveness, as well as IL-1β concentration and MPO activity markedly increased at both timepoints. Perivascular edema dominated the histological picture at 6 h, while remarkable peribronchial granulocyte accumulation, macrophage infiltration and goblet cell hyperplasia were seen at 24h. In PACAP⁻/⁻ mice, airway hyperreactivity was significantly higher 24 h after LPS and inflammatory histopathological changes were more severe at both timepoints. MPO increase was almost double in PACAP⁻/⁻ mice compared to the wild-types at 6 h. In contrast, there was no difference between the IL-1β concentrations of the PACAP⁺/⁺ and PACAP⁻/⁻ mice. These results provide evidence for a protective role for PACAP in endotoxin-induced airway inflammation and hyperreactivity.

Mice deficient in pituitary adenylate cyclase activating polypeptide (PACAP) are more susceptible to retinal ischemic injury in vivo

Pituitary adenylate cyclase activating polypeptide (PACAP) is a neuroprotective peptide exerting protective effects in neuronal injuries. We have provided evidence that PACAP is neuroprotective in several models of retinal degeneration in vivo. Our previous studies showed that PACAP treatment ameliorated the damaging effects of chronic hypoperfusion modeled by permanent bilateral carotid artery occlusion. We have also demonstrated in earlier studies that treatment with PACAP antagonists further aggravates retinal lesions. It has been shown that PACAP deficient mice have larger infarct size in cerebral ischemia. The aim of this study was to compare the degree of retinal damage in wild type and PACAP deficient mice in ischemic retinal insult. Mice underwent 10 min of bilateral carotid artery occlusion followed by 2-week reperfusion period. Retinas were then processed for histological analysis. It was found that PACAP deficient mice had significantly greater retinal damage, as shown by the thickness of the whole retina, the morphometric analysis of the individual retinal layers, and the cell numbers in the inner nuclear and ganglion cell layers. Exogenous PACAP administration could partially protect against retinal degeneration in PACAP deficient mice. These results clearly show that endogenous PACAP reacts as a stress-response peptide that is necessary for endogenous protection against different retinal insults.