Female reproductive functions of the neuropeptide PACAP

Pituitary adenylate cyclase activating polypeptide (PACAP) is a neuropeptide originally isolated as a hypothalamic peptide. It has a widespread distribution in the body and has a diverse spectrum of actions. Among other processes, PACAP has been shown to be involved in reproduction. In this review we summarize findings related to the entire spectrum of female reproduction. PACAP is a regulatory factor in gonadal hormone production, influences follicular development and plays a role in fertilization and embryonic/placental development. Furthermore, PACAP is involved in hormonal changes during and after birth and affects maternal behavior. Although most data come from cell cultures and animal experiments, increasing number of evidence suggests that similar effects of PACAP can be found in humans. Among other instances, PACAP levels show changes in the serum during pregnancy and birth. PACAP is also present in the human follicular and amniotic fluids and in the milk. Levels of PACAP in follicular fluid correlate with the number of retrieved oocytes in hyperstimulated women. Human milk contains very high levels of PACAP compared to plasma levels, with colostrum showing the highest concentration, remaining steady thereafter for the first 7 months of lactation. All these data imply that PACAP has important functions in reproduction both under physiological and pathological conditions.

PACAP is a pathogen-inducible resident antimicrobial neuropeptide affording rapid and contextual molecular host defense of the brain

Defense of the central nervous system (CNS) against infection must be accomplished without generation of potentially injurious immune cell-mediated or off-target inflammation which could impair key functions. As the CNS is an immune-privileged compartment, inducible innate defense mechanisms endogenous to the CNS likely play an essential role in this regard. Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide known to regulate neurodevelopment, emotion, and certain stress responses. While PACAP is known to interact with the immune system, its significance in direct defense of brain or other tissues is not established. Here, we show that our machine-learning classifier can screen for immune activity in neuropeptides, and correctly identified PACAP as an antimicrobial neuropeptide in agreement with previous experimental work. Furthermore, synchrotron X-ray scattering, antimicrobial assays, and mechanistic fingerprinting provided precise insights into how PACAP exerts antimicrobial activities vs. pathogens via multiple and synergistic mechanisms, including dysregulation of membrane integrity and energetics and activation of cell death pathways. Importantly, resident PACAP is selectively induced up to 50-fold in the brain in mouse models of Staphylococcus aureus or Candida albicans infection in vivo, without inducing immune cell infiltration. We show differential PACAP induction even in various tissues outside the CNS, and how these observed patterns of induction are consistent with the antimicrobial efficacy of PACAP measured in conditions simulating specific physiologic contexts of those tissues. Phylogenetic analysis of PACAP revealed close conservation of predicted antimicrobial properties spanning primitive invertebrates to modern mammals. Together, these findings substantiate our hypothesis that PACAP is an ancient neuro-endocrine-immune effector that defends the CNS against infection while minimizing potentially injurious neuroinflammation.

Pituitary Adenylate Cyclase-Activating Polypeptide Excites Proopiomelanocortin Neurons: Implications for the Regulation of Energy Homeostasis

OBJECTIVE

We examined whether pituitary adenylate cyclase-activating polypeptide (PACAP) excites proopiomelanocortin (POMC) neurons via PAC1 receptor mediation and transient receptor potential cation (TRPC) channel activation.

METHODS

Electrophysiological recordings were done in slices from both intact male and ovariectomized (OVX) female PACAP-Cre mice and eGFP-POMC mice.

RESULTS

In recordings from POMC neurons in eGFP-POMC mice, PACAP induced a robust inward current and increase in conductance in voltage clamp, and a depolarization and increase in firing in current clamp. These postsynaptic actions were abolished by inhibitors of the PAC1 receptor, TRPC channels, phospholipase C, phosphatidylinositol-3-kinase, and protein kinase C. Estradiol augmented the PACAP-induced inward current, depolarization, and increased firing, which was abrogated by estrogen receptor (ER) antagonists. In optogenetic recordings from POMC neurons in PACAP-Cre mice, high-frequency photostimulation induced inward currents, depolarizations, and increased firing that were significantly enhanced by Gq-coupled membrane ER signaling in an ER antagonist-sensitive manner. Importantly, the PACAP-induced excitation of POMC neurons was notably reduced in obese, high-fat (HFD)-fed males. In vivo experiments revealed that intra-arcuate nucleus (ARC) PACAP as well as chemogenetic and optogenetic stimulation of ventromedial nucleus (VMN) PACAP neurons produced a significant decrease in energy intake accompanied by an increase in energy expenditure, effects blunted by HFD in males and partially potentiated by estradiol in OVX females.

CONCLUSIONS

These findings reveal that the PACAP-induced activation of PAC1 receptor and TRPC5 channels at VMN PACAP/ARC POMC synapses is potentiated by estradiol and attenuated under conditions of diet-induced obesity/insulin resistance. As such, they advance our understanding of how PACAP regulates the homeostatic energy balance circuitry under normal and pathophysiological circumstances.

PACAP-PAC1 Signaling Regulates Serotonin 2A Receptor Internalization

Mice lacking pituitary adenylate cyclase-activating polypeptide (PACAP) display psychomotor abnormalities, most of which are ameliorated by atypical antipsychotics with serotonin (5-HT) 2A receptor (5-HT_2A) antagonism. Heterozygous Pacap mutant mice show a significantly higher hallucinogenic response than wild-type mice to a 5-HT_2A agonist. Endogenous PACAP may, therefore, affect 5-HT_2A signaling; however, the underlying neurobiological mechanism for this remains unclear. Here, we examined whether PACAP modulates 5-HT_2A signaling by addressing cellular protein localization. PACAP induced an increase in internalization of 5-HT_2A but not 5-HT_1A, 5-HT_2C, dopamine D₂ receptors or metabotropic glutamate receptor 2 in HEK293T cells. This PACAP action was inhibited by protein kinase C inhibitors, β-arrestin2 silencing, the PACAP receptor PAC1 antagonist PACAP_6-38, and PAC1 silencing. In addition, the levels of endogenous 5-HT_2A were decreased on the cell surface of primary cultured cortical neurons after PACAP stimulation and were increased in frontal cortex cell membranes of Pacap^-/- mice. Finally, intracerebroventricular PACAP administration suppressed 5-HT_2A agonist-induced head twitch responses in mice. These results suggest that PACAP-PAC1 signaling increases 5-HT_2A internalization resulting in attenuation of 5-HT_2A-mediated signaling, although further study is necessary to determine the relationship between behavioral abnormalities in Pacap^-/- mice and PACAP-induced 5-HT_2A internalization.

PACAP: A regulator of mammalian reproductive function

Pituitary adenylate cyclase-activating polypeptide (PACAP) is an ancestral molecule that was isolated from sheep hypothalamic extracts based on its action to stimulate cAMP production by pituitary cell cultures. PACAP is one of a number of ligands that coordinate with GnRH to control reproduction. While initially viewed as a hypothalamic releasing factor, PACAP and its receptors are widely distributed, and there is growing evidence that PACAP functions as a paracrine/autocrine regulator in the CNS, pituitary, gonads and placenta, among other tissues. This review will summarize current knowledge concerning the expression and function of PACAP in the hypothalamic-pituitary-gonadal axis with special emphasis on its role in pituitary function in the fetus and newborn.

Pituitary adenylate cyclase-activating polypeptide: Protective effects in stroke and dementia

Evidence shows that pituitary adenylate cyclase-activating polypeptide (PACAP) improves stroke outcomes and dementia. The blood-brain barrier (BBB) controls the peptide and regulatory protein exchange between the central nervous system and the blood; the transport of these regulatory substances across the BBB has been altered in animal models of stroke and Alzheimer's disease (AD). PACAP is a powerful neurotrophin that can cross the BBB, which may aid in the therapy of neurodegenerative diseases, including stroke and AD. PACAP may function as a potential drug in the treatment, prevention, or management of stroke and AD and other neurodegenerative conditions. Here, we review the effects of PACAP in studies on stroke and dementias.

Protective Effects of PACAP in Peripheral Organs

Pituitary adenylate cyclase activating polypeptide (PACAP) is a neuropeptide widely distributed in the nervous system, where it exerts strong neuroprotective effects. PACAP is also expressed in peripheral organs but its peripheral protective effects have not been summarized so far. Therefore, the aim of the present paper is to review the existing literature regarding the cytoprotective effects of PACAP in non-neuronal cell types, peripheral tissues, and organs. Among others, PACAP has widespread expression in the digestive system, where it shows protective effects in various intestinal pathologies, such as duodenal ulcer, small bowel ischemia, and intestinal inflammation. PACAP is present in both the exocrine and endocrine pancreas as well as liver where it reduces inflammation and steatosis by interfering with hepatic pathology related to obesity. It is found in several exocrine glands and also in urinary organs, where, with its protective effects being mainly published regarding renal pathologies, PACAP is protective in numerous conditions. PACAP displays anti-inflammatory effects in upper and lower airways of the respiratory system. In the skin, it is involved in the development of inflammatory pathology such as psoriasis and also has anti-allergic effects in a model of contact dermatitis. In the non-neuronal part of the visual system, PACAP showed protective effects in pathological conditions of the cornea and retinal pigment epithelial cells. The positive role of PACAP has been demonstrated on the formation and healing processes of cartilage and bone where it also prevents osteoarthritis and rheumatoid arthritis development. The protective role of PACAP was also demonstrated in the cardiovascular system in different pathological processes including hyperglycaemia-induced endothelial dysfunction and age-related vascular changes. In the heart, PACAP protects against ischemia, oxidative stress, and cardiomyopathies. PACAP is also involved in the protection against the development of pre-senile systemic amyloidosis, which is presented in various peripheral organs in PACAP-deficient mice. The studies summarized here provide strong evidence for the cytoprotective effects of the peptide. The survival-promoting effects of PACAP depend on a number of factors which are also shortly discussed in the present review.

Pituitary adenylate cyclase-activating polypeptide (PACAP-38) plays an inhibitory role against inflammation induced by chemical damage to zebrafish hair cells

Pituitary adenylate cyclase-activating polypeptide (PACAP-38) is a common neuropeptide exerting a wide spectrum of functions in many fields, including immunology. In the present study, 5-day post-fertilization (dpf) zebrafish larvae of three diverse genetic lines [transgenic lines Tg(MPX:GFP) with GFP-labelled neutrophils and Tg(pou4f3:GAP-GFP) with GFP-labelled hair cells and the wild-type Tuebingen] were used to investigate an inhibitory role of PACAP-38 in inflammation associated with damaged hair cells of the lateral line. Individuals of each genetic line were assigned to four groups: (1) control, and those consisting of larvae exposed to (2) 10 µM CuSO4, (3) 10 µM CuSO4+100 nM PACAP-38 and (4) 100 nM PACAP-38, respectively. Forty-minute exposure to CuSO4 solution was applied to evoke necrosis of hair cells and consequent inflammation. The inhibitory role of PACAP-38 was investigated in vivo under a confocal microscope by counting neutrophils migrating towards damaged hair cells in Tg(MPX:GFP) larvae. In CuSO4-treated individuals, the number of neutrophils associated with hair cells was dramatically increased, while PACAP-38 co-treatment resulted in its over 2-fold decrease. However, co-treatment with PACAP-38 did not prevent hair cells from extensive necrosis, which was found in Tg(pou4f3:GAP-GFP) individuals. Real-Time PCR analysis performed in wild-type larvae demonstrated differential expression pattern of stress and inflammation inducible markers. The most significant findings showed that CuSO4 exposure up-regulated the expression of IL-8, IL-1β, IL-6 and ATF3, while after PACAP-38 co-treatment expression levels of these genes were significantly decreased. The presence of transcripts for all PACAP receptors in neutrophils was also revealed. Adcyap1r1a and vipr1b appeared to be predominant forms. The present results suggest that PACAP-38 should be considered as a factor playing an important regulatory role in inflammatory response associated with pathological processes affecting zebrafish hair cells and it cannot be excluded that this interesting property has more universal significance.

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.

Stress-related disorders, pituitary adenylate cyclase-activating peptide (PACAP)ergic system, and sex differences

Trauma-related disorders, such as posttraumatic stress disorder (PTSD) are remarkably common and debilitating, and are often characterized by dysregulated threat responses. Across numerous epidemiological studies, females have been found to have an approximately twofold increased risk for PTSD and other stress-related disorders. Understanding the biological mechanisms of this differential risk is of critical importance. Recent data suggest that the pituitary adenylate cyclase-activating polypeptide (PACAP) pathway is a critical regulator of the stress response across species. Moreover, increasing evidence suggests that this pathway is regulated by both stress and estrogen modulation and may provide an important window into understanding mechanisms of sex differences in the stress response. We have recently shown that PACAP and its receptor (PAC1R) are critical mediators of abnormal processes after psychological trauma. Notably, in heavily traumatized human subjects, there appears to be a robust sex-specific association of PACAP blood levels and PAC1R gene variants with fear physiology, PTSD diagnosis, and symptoms, specifically in females. The sex-specific association occurs within a single-nucleotide polymorphism (rs2267735) that resides in a putative estrogen response element involved in PAC1R gene regulation. Complementing these human data, the PAC1R messenger RNA is induced with fear conditioning or estrogen replacement in rodent models. These data suggest that perturbations in the PACAP-PAC1R pathway are regulated by estrogen and are involved in abnormal fear responses underlying PTSD.

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.

C-terminal amidation of PACAP-38 and PACAP-27 is dispensable for biological activity at the PAC1 receptor

PACAP-27 and PACAP-38 are the exclusive physiological ligands for the mammalian PAC1 receptor. The role of C-terminal amidation of these ligands at that receptor was examined in neuroendocrine cells expressing the PAC1 receptor endogenously and in non-neuroendocrine cells in which the human and rat PAC1 receptors were expressed from stable single-copy genes driven by the CMV promoter, providing stoichiometrically appropriate levels of this Gs-coupled GPCR in order to examine the potency and intrinsic activity of PACAP ligands and their des-amidated congeners. We found that replacement of the C-terminal glycine residues of PACAP-27 and -38 with a free acid; or extension of either peptide with the two to three amino acids normally found at these positions in PACAP processing intermediates in vivo following endoproteolytic cleavage and after exoproteolytic trimming and glycine-directed amidated, were equivalent in potency to the fully processed peptides in a variety of cell-based assays. These included real-time monitoring of cyclic AMP generation in both NS-1 neuroendocrine cells and non-neuroendocrine HEK293 cells; PKA-dependent gene activation in HEK293 cells; and neuritogenesis and cell growth arrest in NS-1 cells. The specific implications for the role of amidation in arming of secretin-related neuropeptides for biological function, and the general implications for neuropeptide-based delivery in the context of gene therapy, are discussed.

Altered Circadian Food Anticipatory Activity Rhythms in PACAP Receptor 1 (PAC1) Deficient Mice

Light signals from intrinsically photosensitive retinal ganglion cells (ipRGCs) entrain the circadian clock and regulate negative masking. Two neurotransmitters, glutamate and Pituitary Adenylate Cyclase Activating Polypeptide (PACAP), found in the ipRGCs transmit light signals to the brain via glutamate receptors and the specific PACAP type 1 (PAC1) receptor. Light entrainment occurs during the twilight zones and has little effect on clock phase during daytime. When nocturnal animals have access to food only for a few hours during the resting phase at daytime, they adapt behavior to the restricted feeding (RF) paradigm and show food anticipatory activity (FAA). A recent study in mice and rats demonstrating that light regulates FAA prompted us to investigate the role of PACAP/PAC1 signaling in the light mediated regulation of FAA. PAC1 receptor knock out (PAC1-/-) and wild type (PAC1+/+) mice placed in running wheels were examined in a full photoperiod (FPP) of 12:12 h light/dark (LD) and a skeleton photoperiod (SPP) 1:11:1:11 h L:DD:L:DD at 300 and 10 lux light intensity. Both PAC1-/- mice and PAC1+/+ littermates entrained to FPP and SPP at both light intensities. However, when placed in RF with access to food for 4–5 h during the subjective day, a significant change in behavior was observed in PAC1-/- mice compared to PAC1+/+ mice. While PAC1-/- mice showed similar FAA as PAC1+/+ animals in FPP at 300 lux, PAC1-/- mice demonstrated an advanced onset of FAA with a nearly 3-fold increase in amplitude compared to PAC1+/+ mice when placed in SPP at 300 lux. The same pattern of FAA was observed at 10 lux during both FPP and SPP. The present study indicates a role of PACAP/PAC1 signaling during light regulated FAA. Most likely, PACAP found in ipRGCs mediating non-image forming light information to the brain is involved.

Role of pituitary adenylate cyclase-activating polypeptide in modulating hypothalamus-pituitary neuroendocrine functions in mouse cell models

Pituitary adenylate cyclase-activating polypeptide (PACAP) was originally identified as a hypothalamic activator of cyclic adenosine monophosphate production in pituitary cells. PACAP and its receptor are expressed not only in the central nervous system, but also in peripheral organs, and function to stimulate pituitary hormone synthesis and secretion as both a hypothalamic-pituitary-releasing factor and an autocrine-paracrine factor within the pituitary. PACAP stimulates the expression of the gonadotrophin α, luteinising hormone (LH) β and follicle-stimulating hormone (FSH) β subunits, as well as the gonadotrophin-releasing hormone (GnRH) receptor and its own PACAP type I receptor (PAC1R) in gonadotrophin-secreting pituitary cells. In turn, GnRH, which is known to be a crucial component of gonadotrophin secretion, stimulates the expression of PACAP and PAC1R in gonadotrophs. In addition, PAC1R and PACAP modulate the functions of GnRH-producing neurones in the hypothalamus. This review summarises the current understanding of the possible roles of PACAP and PAC1R in modulating hypothalamus and pituitary neuroendocrine cells in the mouse models.

PACAP is essential for the adaptive thermogenic response of brown adipose tissue to cold exposure

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a widely distributed neuropeptide that acts as a neurotransmitter, neuromodulator, neurotropic factor, neuroprotectant, secretagogue, and neurohormone. Owing to its pleiotropic biological actions, knockout of Pacap (Adcyap1) has been shown to induce several abnormalities in mice such as impaired thermoregulation. However, the underlying physiological and molecular mechanisms remain unclear. A previous report has shown that cold-exposed Pacap null mice cannot supply appropriate levels of norepinephrine (NE) to brown adipocytes. Therefore, we hypothesized that exogenous NE would rescue the impaired thermogenic response of Pacap null mice during cold exposure. We compared the adaptive thermogenic capacity of Pacap(-/-) to Pacap(+/+) mice in response to NE when housed at room temperature (24 °C) and after a 3.5-week cold exposure (4 °C). Biochemical parameters, expression of thermogenic genes, and morphological properties of brown adipose tissue (BAT) and white adipose tissue (WAT) were also characterized. Results showed that there was a significant effect of temperature, but no effect of genotype, on the resting metabolic rate in conscious, unrestrained mice. However, the normal cold-induced increase in the basal metabolic rate and NE-induced increase in thermogenesis were severely blunted in cold-exposed Pacap(-/-) mice. These changes were associated with altered substrate utilization, reduced β3-adrenergic receptor (β3-Ar (Adrb3)) and hormone-sensitive lipase (Hsl (Lipe)) gene expression, and increased fibroblast growth factor 2 (Fgf2) gene expression in BAT. Interestingly, Pacap(-/-) mice had depleted WAT depots, associated with upregulated uncoupling protein 1 expression in inguinal WATs. These results suggest that the impairment of adaptive thermogenesis in Pacap null mice cannot be rescued by exogenous NE perhaps in part due to decreased β3-Ar-mediated BAT activation.

Neuropeptides in learning and memory

Dementia conditions and memory deficits of different origins (vascular, metabolic and primary neurodegenerative such as Alzheimer's and Parkinson's diseases) are getting more common and greater clinical problems recently in the aging population. Since the presently available cognitive enhancers have very limited therapeutical applications, there is an emerging need to elucidate the complex pathophysiological mechanisms, identify key mediators and novel targets for future drug development. Neuropeptides are widely distributed in brain regions responsible for learning and memory processes with special emphasis on the hippocampus, amygdala and the basal forebrain. They form networks with each other, and also have complex interactions with the cholinergic, glutamatergic, dopaminergic and GABA-ergic pathways. This review summarizes the extensive experimental data in the well-established rat and mouse models, as well as the few clinical results regarding the expression and the roles of the tachykinin system, somatostatin and the closely related cortistatin, vasoactive intestinal polypeptide (VIP) and pituitary adenylate-cyclase activating polypeptide (PACAP), calcitonin gene-related peptide (CGRP), neuropeptide Y (NPY), opioid peptides and galanin. Furthermore, the main receptorial targets, mechanisms and interactions are described in order to highlight the possible therapeutical potentials. Agents not only symptomatically improving the functional impairments, but also inhibiting the progression of the neurodegenerative processes would be breakthroughs in this area. The most promising mechanisms determined at the level of exploratory investigations in animal models of cognitive disfunctions are somatostatin sst4, NPY Y2, PACAP-VIP VPAC1, tachykinin NK3 and galanin GALR2 receptor agonisms, as well as delta opioid receptor antagonism. Potent and selective non-peptide ligands with good CNS penetration are needed for further characterization of these molecular pathways to complete the preclinical studies and decide if any of the above described targets could be appropriate for clinical investigations.

CGRP and migraine: could PACAP play a role too?

Migraine is a debilitating neurological disorder that affects about 12% of the population. In the past decade, the role of the neuropeptide calcitonin gene-related peptide (CGRP) in migraine has been firmly established by clinical studies. CGRP administration can trigger migraines, and CGRP receptor antagonists ameliorate migraine. In this review, we will describe multifunctional activities of CGRP that could potentially contribute to migraine. These include roles in light aversion, neurogenic inflammation, peripheral and central sensitization of nociceptive pathways, cortical spreading depression, and regulation of nitric oxide production. Yet clearly there will be many other contributing genes that could act in concert with CGRP. One candidate is pituitary adenylate cyclase-activating peptide (PACAP), which shares some of the same actions as CGRP, including the ability to induce migraine in migraineurs and light aversive behavior in rodents. Interestingly, both CGRP and PACAP act on receptors that share an accessory subunit called receptor activity modifying protein-1 (RAMP1). Thus, comparisons between the actions of these two migraine-inducing neuropeptides, CGRP and PACAP, may provide new insights into migraine pathophysiology.

Pituitary adenylate cyclase activating peptide (PACAP) participates in adipogenesis by activating ERK signaling pathway

Pituitary adenylate cyclase activating peptide (PACAP) belongs to the secretin/glucagon/vasoactive intestinal peptide (VIP) family. Its action can be mediated by three different receptor subtypes: PAC1, which has exclusive affinity for PACAP, and VPAC1 and VPAC2 which have equal affinity for PACAP and VIP. We showed that all three receptors are expressed in 3T3-L1 cells throughout their differentiation into adipocytes. We established the activity of these receptors by cAMP accumulation upon induction by PACAP. Together with insulin and dexamethasone, PACAP induced adipogenesis in 3T3-L1 cell line. PACAP increased cAMP production within 15 min upon stimulation and targeted the expression and phosphorylation of MAPK (ERK1/2), strengthened by the ERK1/2 phosphorylation being partially or completely abolished by different combinations of PACAP receptors antagonists. We therefore speculate that ERK1/2 activation is crucial for the activation of CCAAT/enhancer- binding protein β (C/EBPβ).

Vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase activating polypeptide (PACAP) in humans with multiple sclerosis

Multiple sclerosis (MS) is a chronic neuroinflammatory disease of the central nervous system that leads to demyelination and neurodegeneration. VIP and PACAP are structurally related neuropeptides with neuroprotective and anti-inflammatory activities. To evaluate VIP and PACAP-38 in plasma and CSF in humans in correlation with IL-6, IL-10 and TNFα, we compared 20 MS individuals with 27 healthy controls. In MS, a decrease in PACAP-38 in CSF and a decrease in plasma IL-6 concentration were seen. A positive correlation between plasma VIP and plasma IL-6 was identified. We conclude that VIP and PACAP may influence the course of MS.

Prolonged stimulation with thyrotropin-releasing hormone and pituitary adenylate cyclase-activating polypeptide desensitize their receptor functions in prolactin-producing GH3 cells

We used somatolactotroph GH3 cells to examine changes in response to stimulation with thyrotropin-releasing hormone (TRH) and pituitary adenylate cyclase-activating polypeptide (PACAP) after sustained treatment with these peptides. TRH and PACAP increased prolactin promoter activity in mock- and PACAP type 1 receptor (PAC1R)-transfected cells. When the cells were pretreated with TRH for 48 h, the response of the prolactin promoter to both TRH and PACAP was diminished. Similarly, in PAC1R-transfected GH3 cells pretreated with PACAP, the effects of TRH and PACAP on the prolactin promoter were eliminated. The stimulation of prolactin mRNA expression by TRH and PACAP was eliminated by prolonged pretreatment with these peptides in PAC1R-transfected cells. Both the serum response element (SRE) promoters and cAMP response element (CRE) promoters were activated by TRH and PACAP in either mock- or PAC1R-transfected cells. Pretreatment for 48 h with TRH also eliminated the effects of TRH and PACAP on the SRE and CRE promoters, and pretreatment of PAC1R-transfected cells with PACAP for 48 h reduced the responses of the SRE and CRE promoters to TRH and PACAP. These observations demonstrated that sustained stimulation with TRH and PACAP desensitizes their own and each other's receptors.

Ameliorative effect of PACAP and VIP against increased permeability in a model of outer blood retinal barrier dysfunction

Breakdown of outer blood retinal barrier (BRB) due to the disruption of tight junctions (TJs) is one of the main factors accounting for diabetic macular edema (DME), a major complication of diabetic retinopathy. Previously it has been shown that PACAP and VIP are protective against several types of retinal injuries. However, their involvement in the maintenance of outer BRB function during DME remains uncovered. Here, using an in vitro model of DME, we explored the effects of both PACAP and VIP. Human retinal pigment epithelial cells (ARPE19) were cultured for 26 days either in normal glucose (5.5 mM, NG) or in high glucose (25 mM, HG). In addition, to mimic the inflammatory aspect of the diabetic milieu, cells were also treated with IL-1β (NG+IL-1β and HG+IL-1β). Effects of PACAP or VIP on cells permeability were evaluated by measuring both apical-to-basolateral movements of fluorescein isothyocyanate (FITC) dextran and transepithelial electrical resistance (TEER). Expression of TJ-related proteins was evaluated by immunoblot. Results demonstrated that NG+IL-1β and, to a greater extent, HG+IL-1β significantly increased FITC-dextran diffusion, paralleled by decreased TEER. PACAP or VIP reversed both of these effects. Furthermore, HG+IL-1β-induced reduction of claudin-1 and ZO-1 expression was reversed by PACAP and VIP. Occludin expression was not affected in any of the conditions tested. Altogether, these finding show that both peptides counteract HG+IL-1β-induced damage in ARPE19 cells, suggesting that they might be relevant to the maintenance of outer BRB function in DME.

Pituitary adenylate cyclase-activating polypeptide (PACAP): a master regulator in central and peripheral stress responses

The neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) is a master regulator of central and peripheral stress responses required to restore and maintain homeostasis. PACAP modulates the hypothalamic-pituitary-adrenal (HPA) axis in response to acute psychogenic but not systemic stressors, through activation of corticotropin-releasing hormone (CRH) release to drive adrenal corticosterone (CORT) output. During direct high-frequency stimulation of the splanchnic nerve that is designed to mimic stress, PACAP regulates adrenomedullary catecholamine secretion. In addition to transmission, PACAP simultaneously facilitates the biosynthesis of adrenomedullary catecholamines through stimulus-secretion-synthesis coupling. During periods of chronic psychogenic stress, PACAP-mediated CORT elevation fails to desensitize and contributes to the development of maladaptive behaviors such as anxiety and depression. Based on these findings, PACAP regulates not only adaptive responses to stress but also maladaptive responses to sustained psychological stress. PACAP receptor antagonists could have therapeutic relevance in preventing hyperactivity of the HPA axis and offering protection against chronic stress-associated anxiety and depression.

Induction of RAGE shedding by activation of G protein-coupled receptors

The multiligand Receptor for Advanced Glycation End products (RAGE) is involved in various pathophysiological processes, including diabetic inflammatory conditions and Alzheimes disease. Full-length RAGE, a cell surface-located type I membrane protein, can proteolytically be converted by metalloproteinases ADAM10 and MMP9 into a soluble RAGE form. Moreover, administration of recombinant soluble RAGE suppresses activation of cell surface-located RAGE by trapping RAGE ligands. Therefore stimulation of RAGE shedding might have a therapeutic value regarding inflammatory diseases. We aimed to investigate whether RAGE shedding is inducible via ligand-induced activation of G protein-coupled receptors (GPCRs). We chose three different GPCRs coupled to distinct signaling cascades: the V2 vasopressin receptor (V2R) activating adenylyl cyclase, the oxytocin receptor (OTR) linked to phospholipase Cβ, and the PACAP receptor (subtype PAC1) coupled to adenylyl cyclase, phospholipase Cβ, calcium signaling and MAP kinases. We generated HEK cell lines stably coexpressing an individual GPCR and full-length RAGE and then investigated GPCR ligand-induced activation of RAGE shedding. We found metalloproteinase-mediated RAGE shedding on the cell surface to be inducible via ligand-specific activation of all analyzed GPCRs. By using specific inhibitors we have identified Ca²⁺ signaling, PKCα/PKCβI, CaMKII, PI3 kinases and MAP kinases to be involved in PAC1 receptor-induced RAGE shedding. We detected an induction of calcium signaling in all our cell lines coexpressing RAGE and different GPCRs after agonist treatment. However, we did not disclose a contribution of adenylyl cyclase in RAGE shedding induction. Furthermore, by using a selective metalloproteinase inhibitor and siRNA-mediated knock-down approaches, we show that ADAM10 and/or MMP9 are playing important roles in constitutive and PACAP-induced RAGE shedding. We also found that treatment of mice with PACAP increases the amount of soluble RAGE in the mouse lung. Our findings suggest that pharmacological stimulation of RAGE shedding might open alternative treatment strategies for Alzheimeŕs disease and diabetes-induced inflammation.

Effect of PACAP in central and peripheral nerve injuries

Pituitary adenylate cyclase activating polypeptide (PACAP) is a bioactive peptide with diverse effects in the nervous system. In addition to its more classic role as a neuromodulator, PACAP functions as a neurotrophic factor. Several neurotrophic factors have been shown to play an important role in the endogenous response following both cerebral ischemia and traumatic brain injury and to be effective when given exogenously. A number of studies have shown the neuroprotective effect of PACAP in different models of ischemia, neurodegenerative diseases and retinal degeneration. The aim of this review is to summarize the findings on the neuroprotective potential of PACAP in models of different traumatic nerve injuries. Expression of endogenous PACAP and its specific PAC1 receptor is elevated in different parts of the central and peripheral nervous system after traumatic injuries. Some experiments demonstrate the protective effect of exogenous PACAP treatment in different traumatic brain injury models, in facial nerve and optic nerve trauma. The upregulation of endogenous PACAP and its receptors and the protective effect of exogenous PACAP after different central and peripheral nerve injuries show the important function of PACAP in neuronal regeneration indicating that PACAP may also be a promising therapeutic agent in injuries of the nervous system.

Involvement of PACAP/ADNP signaling in the resistance to cell death in malignant peripheral nerve sheath tumor (MPNST) cells

Malignant peripheral nerve sheath tumors (MPNSTs) are sarcomas able to grow under conditions of metabolic stress caused by insufficient nutrients or oxygen. Both pituitary adenylate cyclase-activating polypeptide (PACAP) and activity-dependent neuroprotective protein (ADNP) have glioprotective potential. However, whether PACAP/ADNP signaling is involved in the resistance to cell death in MPNST cells remains to be clarified. Here, we investigated the involvement of this signaling system in the survival response of MPNST cells against hydrogen peroxide (H(2)O(2))-evoked death both in the presence of normal serum (NS) and in serum-starved (SS) cells. Results showed that ADNP levels increased time-dependently (6-48 h) in SS cells. Treatment with PACAP38 (10(-9) to 10(-5) M) dose-dependently increased ADNP levels in NS but not in SS cells. PAC(1)/VPAC receptor antagonists completely suppressed PACAP-stimulated ADNP increase and partially reduced ADNP expression in SS cells. NS-cultured cells exposed to H(2)O(2) showed significantly reduced cell viability (~50 %), increased p53 and caspase-3, and DNA fragmentation, without affecting ADNP expression. Serum starvation significantly reduced H(2)O(2)-induced detrimental effects in MPNST cells, which were not further ameliorated by PACAP38. Altogether, these finding provide evidence for the involvement of an endogenous PACAP-mediated ADNP signaling system that increases MPNST cell resistance to H(2)O(2)-induced death upon serum starvation.

Pituitary adenylate cyclase-activating polypeptide controls stimulus-transcription coupling in the hypothalamic-pituitary-adrenal axis to mediate sustained hormone secretion during stress

External and internal stimuli that threaten homeostasis trigger coordinated stress responses through activation of specialised neuroendocrine circuits. In mammals, the hypothalamic-pituitary-adrenal (HPA) axis mediates responses to stressors such as restraint, ultimately enhancing adrenocortical hormone secretion. Pituitary adenylate cyclase-activating polypeptide (PACAP) has been implicated in central control of the HPA axis, and we have recently shown PACAP-dependent expression of corticotropin-releasing hormone (CRH) and secretion of corticosterone in response to restraint. We now provide a more detailed analysis of PACAP-dependent HPA axis stimulation in the mouse, indicating that the hypothalamic paraventricular nucleus (PVN) is the primary site of action. We demonstrate by quantitative polymerase chain reaction and in situ hybridisation that up-regulation of mRNAs encoding CRH and inducible transcription factors, from the Nr4a family (Nur77, Nor1) in the PVN is PACAP-dependent. Furthermore, CRH hnRNA is rapidly up-regulated in cultured hypothalamic neurones after treatment with PACAP. Induction of Nr4a factors (Nur77, Nurr1) in response to restraint is attenuated in the pituitary gland of PACAP-deficient mice. In the adrenal glands, restraint elicits a marked PACAP-dependent increase in adrenocortical mRNA levels of all three Nr4a transcription factors, steroidogenic factor 1 (Nr5a1), steroidogenic acute regulatory protein and steroid 21-hydroxylase. Taken together, our results show that PACAP controls HPA responses to restraint primarily at the level of the hypothalamus by up-regulating CRH, possibly involving transcription factors such as Nur77 and Nor1. Subsequent adrenocortical steroidogenesis also appears to involve PACAP-dependent stimulus-transcription coupling, suggesting a mechanism by which PACAP exerts control over HPA axis function during stress.

Discovery of a new reproductive hormone in teleosts: pituitary adenylate cyclase-activating polypeptide-related peptide (PRP)

Pituitary adenylate cyclase-activating polypeptide (PACAP)-related peptide (PRP) is a peptide encoded with PACAP in the same precursor protein. Non-mammalian PRPs were previously termed growth hormone-releasing hormone (GHRH)-like peptide, and was regarded as the mammalian GHRH homologue in non-mammalian vertebrates until the discovery of authentic GHRH genes in teleosts and amphibians. Although a highly specific receptor for PRP, which is lost in mammals, is present in non-mammals, a clear function of PRP in vertebrates remains unknown. Using goldfish as a model, here we show the expression of PRP and its cognate receptor in the brain-pituitary-gonadal (BPG) axis, thus suggesting a function of goldfish (gf) PRP in regulating reproduction. We found that gfPRP controls the expression of reproductive hormones in the brain, pituitary and ovary. Goldfish PRP exerts stimulatory effects on the expression of salmon gonadotropin-releasing hormone (sGnRH) in the brain, follicle-stimulating hormone (FSH) and luteinizing hormone (LH) in pituitary primary culture cells, but inhibits the expression of LH in the ovary. Using the same technique, we showed that gfPRP did not alter the mRNA level of growth hormone in the pituitary primary culture. In summary, we have discovered the first function of vertebrate PRP in regulating reproduction, which provides a new research direction in studying the neuroendocrine control of reproduction not only in teleosts, but also in other non-mammalian vertebrates.

[Research advance of the protective role of PACAP in the nervous system diseases]

In the central nervous system, pituitary adenylate cyclase-activating polypeptide (PACAP) exerts different actions as neurotransmitter, neuromodulator, neurotrophic and neuroprotective factors via multiple signaling pathways. PACAP plays an important protective role in the nervous system diseases, such as focal cerebral ischemia, traumatic brain injury (TBI), schizophrenia, anxiety disorders Parkinson's disease and Alzheimer's disease. Now, we reviewed the research advances about the protective role of PACAP in the nervous system diseases.

PACAP centrally mediates emotional stress-induced corticosterone responses in mice

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a pleiotropic neuropeptide widely distributed in the nervous system. Recently, PACAP was shown to be involved in restraint stress-induced corticosterone release and concomitant expression of the genes involved in hypothalamic-pituitary-adrenal (HPA) axis activation. Therefore, in this study, we have addressed the types of stressors and the levels of the HPA axis in which PACAP signaling is involved using mice lacking PACAP (PACAP⁻/⁻). Among four different types of stressors, open-field exposure, cold exposure, ether inhalation, and restraint, the corticosterone response to open-field exposure and restraint, which are categorized as emotional stressors, but not the other two, was markedly attenuated in PACAP⁻/⁻ mice. Peripheral administration of corticotropin releasing factor (CRF) or adrenocorticotropic hormone induced corticosterone increase similarly in PACAP⁻/⁻ and wild-type mice. In addition, the restraint stress-induced c-Fos expression was significantly decreased in the paraventricular nucleus (PVN) and medial amygdala (MeA), but not the medial prefrontal cortex, in PACAP⁻/⁻ mice. In the PVN of PACAP⁻/⁻ mice, the stress-induced c-Fos expression was blunted in the CRF neurons. These results suggest that PACAP is critically involved in activation of the MeA and PVN CRF neurons to centrally regulate the HPA axis response to emotional stressors.

Signal transduction in the hypothalamic corticotropin-releasing factor system and its clinical implications

Corticotropin-releasing factor (CRF) is a major regulatory peptide in the hypothalamic-pituitary-adrenal (HPA) axis under stress conditions. In response to stress, CRF is produced in the hypothalamic paraventricular nucleus. Forskolin- or pituitary adenylate cyclase-activating polypeptide-stimulated CRF gene transcription is mediated by the cyclic AMP (cAMP) response element on the CRF 5'-promoter region. Estrogens enhance activation of the CRF gene in stress, while inducible cAMP-early repressor suppresses the stress response via inhibition of the cAMP-dependent CRF gene. Glucocorticoid-dependent repression of cAMP-stimulated CRF promoter activity is mediated by both the negative glucocorticoid-response element and the serum-response element, while interleukin-6 (IL-6) stimulates the CRF gene. Suppressor of cytokine signaling-3, stimulated by IL-6 and cAMP, is involved in the negative regulation of CRF gene expression. Such complex mechanisms contribute to stress responses and homeostasis in the hypothalamus. Moreover, disruption of the HPA axis may cause a number of diseases related to stress. For example, CRF-induced p21-activated kinase 3 mRNA expression may be related to the proliferation of corticotrophs in Nelson's syndrome. A higher molecular weight form of immunoreactive β-endorphin, putative proopiomelanocortin (POMC), is increased in CRF-knockout mice, suggesting the important role of CRF in the processing of POMC through changes in prohormone convertase type-1 expression levels.

Stimulatory effect of pituitary adenylate-cyclase activating polypeptide (PACAP) and its PACAP type I receptor (PAC1R) on prolactin synthesis in rat pituitary somatolactotroph GH3 cells

In this present study, we investigated the role of pituitary adenylate cyclase-activating polypeptide (PACAP) and its receptor, PACAP type I receptor (PAC1R) on prolactin synthesis in pituitary somatolactotroph GH3 cells. PACAP increased prolactin promoter activity up to 1.3 ± 0.1-fold. This increase, while significant, was less than the increase resulting from thyrotropin-releasing hormone (TRH) stimulation. By transfection of a PAC1R expression vector to the cells, the response to PACAP on prolactin promoter activity was dramatically potentiated to a degree proportional to the amount of PAC1R transfected. In the PAC1R expressing GH3 cells, TRH and PACAP alone increased prolactin promoter up to 3.3 ± 0.3-fold and 4.9 ± 0.2-fold, respectively, and combined treatment with TRH and PACAP further increased prolactin promoters up to 6.8 ± 0.6-fold. PACAP binds both Gs- and Gq-coupled receptors and stimulates adenylate cyclase/cAMP and protein kinase C/extracellular signal-regulated kinase (ERK) signaling pathways. PACAP increased ERK phosphorylation in PAC1R expressing cells to the same degree as TRH. Combined treatment with TRH and PACAP had a synergistic effect on ERK activation. GH3 cells produce both prolactin and growth hormone. Stimulation of GH3 cells with TRH significantly increased the mRNA level of prolactin and attenuated growth hormone mRNA expression. PACAP increased both prolactin and growth hormone mRNA levels, particularly in PAC1R expressing cells. In addition, increasing amount of PAC1R in GH3 cells potentiated the action of TRH on prolactin promoter activity, as well as on ERK phosphorylation. PAC1R was induced by PACAP itself, but not by TRH. Our current study demonstrates that PACAP and its PAC1R, functions as a stimulator of prolactin alone or with TRH in prolactin producing cells.

VIP and PACAP: recent insights into their functions/roles in physiology and disease from molecular and genetic studies

PURPOSE OF REVIEW

Vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) as well as the three classes of G-protein-coupled receptors mediating their effects, are widely distributed in the central nervous system (CNS) and peripheral tissues. These peptides are reported to have many effects in different tissues, which are physiological or pharmacological, and which receptor mediates which effect, has been difficult to determine, primarily due to lack of potent, stable, selective agonists/antagonists. Recently the use of animals with targeted knockout of the peptide or a specific receptor has provided important insights into their role in normal physiology and disease states.

RECENT FINDINGS

During the review period, considerable progress and insights has occurred in the understanding of the role of VIP/PACAP as well as their receptors in a number of different disorders/areas. Particularly, insights into their roles in energy metabolism, glucose regulation, various gastrointestinal processes including gastrointestinal inflammatory conditions and motility and their role in the CNS as well as CNS diseases has greatly expanded.

SUMMARY

PACAP/VIP as well as their three classes of receptors are important in many physiological/pathophysiological processes, some of which are identified in these studies using knockout animals. These studies may lead to new novel treatment approaches. Particularly important are their roles in glucose metabolism and on islets leading to possible novel approaches in diabetes; their novel anti-inflammatory, cytoprotective effects, their CNS neuroprotective effects, and their possible roles in diseases such as schizophrenia and chronic depression.

Interferon-gamma produced by microglia and the neuropeptide PACAP have opposite effects on the viability of neural progenitor cells

Inflammation is part of many neurological disorders and immune reactions may influence neuronal progenitor cells (NPCs) contributing to the disease process. Our knowledge about the interplay between different cell types in brain inflammation are not fully understood. It is important to know the mechanisms and factors involved in order to enhance regeneration and brain repair. We show here that NPCs express receptors for interferon-gamma (IFNgamma), and IFNgamma activates the signal transducer and activator of transcription (STAT) protein-1. IFNgamma reduced cell proliferation in NPCs by upregulation of the cell cycle protein p21 as well as induced cell death of NPCs by activating caspase-3. Studies of putative factors for rescue showed that the neuropeptide, Pituitary adenylate cyclase-activating polypeptide (PACAP) increased cell viability, the levels of p-Bad and reduced caspase-3 activation in the NPCs. Medium from cultured microglia contained IFNgamma and decreased the viability of NPCs, whilst blocking with anti-IFNgamma antibodies counteracted this effect. The results show that NPCs are negatively influenced by IFNgamma whereas PACAP is able to modulate its action. The interplay between IFNgamma released from immune cells and PACAP is of importance in brain inflammation and may affect the regeneration and recruitment of NPCs in immune diseases. The observed effects of IFNgamma on NPCs deserve to be taken into account in human anti-viral therapies particularly in children with higher rates of brain stem cell proliferation.

Association between pituitary adenylate cyclase-activating polypeptide and reproduction in the blue gourami

In order to gain a better understanding of the roles of pituitary adenylate cyclase-activating polypeptide (PACAP) in reproduction and growth, the expression of the PACAP gene during the reproduction cycle and its potential role in regulating gonadotropin and growth hormone (GH) gene transcription in blue gourami were investigated. The cDNA sequences of the full-length blue gourami brain PACAP and that of its related peptide (PRP) were acquired. PACAP cDNA had two variants, obtainable by alternative splicing: a long form encoding for both PRP and PACAP and a short form encoding only for PACAP. In females, mRNA levels of PACAP were very high only in individuals with oocytes in the maturation stage, as compared to levels in unpaired vitellogenic and non-vitellogenic fish. The PACAP mRNA levels in males were high only in nest builders, as opposed to in non-nest building males and juveniles. In pituitary culture cells from high vitellogenic females, PACAP38 (the 38 amino acid form) only brought about an increase in betaFSH levels, without altering GH and betaLH mRNA levels. On the other hand, in adult non-reproductive male pituitary cells, PACAP38 decreased the GH mRNA level. Based on these results, we propose that in the blue gourami, PACAP is involved in the final oocyte maturation stage in females, whereas in males, it is associated with sexual behavior. In addition, the effect of PACAP38 on pituitary hormone gene expression is different in females and males, indicating that PACAP38 is potentially a hypophysiotropic regulator of reproduction, which mediates pituitary hormone expression.

From patient to mouse to therapy: role of the neuropeptide pacap in platelet function and formation

Megakaryopoiesis and platelet production are very complex processes, orchestrated by different growth factors, cytokines and transcription factors. It's only recently that a role was assigned for the pituitary adenylyl cyclase-activating peptide (PACAP) and the vasoactive intestinal peptide (VIP) via their common Gs-coupled receptor VPAC1 in this process. The basis for this idea originated from studies in two related patients with a partial trisomy 18p11 and therefore carrying 3 copies of the PACAP gene and elevated PACAP concentrations in their plasma which resulted in a bleeding tendency with thrombopathy and a mild thrombocytopenia. This platelet functional and formation defect could be phenocopied in transgenic megakaryocyte specific PACAP-overexpressing mice. The addition of PACAP or VIP to hematopoietic stem cells resulted in an decreased megakaryocyte maturation and DNA polyploidization. In contrast, mice subcutaneously injected with inhibitory anti-PACAP (PP1A4) or anti-VPAC1 (23A11) antibodies presented with increased platelet numbers. This last concept was the basis for the development of these antibodies for the treatment of different types of thrombocytopenia as the therapeutic value for these antibodies was established in mice with a low platelet count due to chemotherapy, anti-platelet antibodies, a congenital factor of after bone marrow transplantation. For all models, the addition of 23A11 or PP1A4 resulted in an increased platelet recovery compared to the control antibody. Further studies are needed to identify the downstream signal transduction components after VPAC1 stimulation in megakaryocytes and platelets.

The effect of PACAP38 on MyD88-mediated signal transduction in ischemia-/hypoxia-induced acute kidney injury

BACKGROUND/AIMS

toll-like receptor 4 (TLR4) and its adaptor protein MyD88 play an important role in ischemia/reperfusion (I/R) injury in the kidney, and pituitary adenylate cyclase-activating polypeptide (PACAP) could ameliorate renal I/R injury.

METHODS

primary cultures of proximal tubule epithelial cells (PTEC) were prepared from wild-type and MyD88(-/-) mice, and subjected to hypoxia in vitro. Acute kidney injury (AKI) was induced by I/R in vivo in wild-type mice only.

RESULTS

hypoxia resulted in significant increases in cytokine production and apoptosis/necrosis in wild-type PTEC, but these responses were markedly blunted in MyD88(-/-) PTEC. Treatment with PACAP38 before or after hypoxia further suppressed the hypoxia-induced cytokine responses and apoptosis in both MyD88(+/+) and MyD88(-/-) PTEC cultures. PACAP38 significantly inhibited TLR4/MyD88/TRAF6 as well as TRIF and IRF3 expression in mouse kidney and PTEC, and inhibited the secretion and mRNA expression of cytokines in kidneys from mice after I/R, paralleling the cytokine responses in vitro. Moreover, treatment with PACAP38 protected mice from renal failure, histological damage, neutrophil influx and tubule cell apoptosis after I/R.

CONCLUSION

our data reveal that the TLR4-mediated cytokine responses to hypoxia are primarily dependent on MyD88 signaling and highlight the pivotal role of MyD88-dependent mechanisms in the coordination of the innate immune responses to ischemic/hypoxic acute renal tubular injury. The renoprotective effect of PACAP in AKI involves both MyD88-dependent and -independent pathways.

Luteinizing hormone-stimulated pituitary adenylate cyclase-activating polypeptide system and its role in progesterone production in human luteinized granulosa cells

The present study examined the gonadotropin regulation of pituitary adenylate cyclase-activating polypeptide (PACAP) and PACAP type I receptor (PAC(1)-R) expression, and its role in progesterone production in the human luteinized granulosa cells. The stimulation of both PACAP and PAC(1)-R mRNA levels by LH was detected using a competitive reverse transcription-polymerase chain reaction (RT-PCR). PACAP transcript was stimulated by LH reaching maximum levels at 12 hours in a dose dependent manner. LH treatment also stimulated PAC(1)-R mRNA levels within 24 hours. Addition of PACAP-38 (10(-7) M) as well as LH significantly stimulated progesterone production during 48 hours culture. Furthermore, co-treatment with PACAP antagonist partially inhibited LH-stimulated progesterone production. Treatment with vasoactive intestinal peptide, however, did not affect progesterone production. Taken together, the present study demonstrates that LH causes a transient stimulation of PACAP and PAC(1)-R expression and that PACAP stimulates progesterone production in the human luteinized granulosa cells, suggesting a possible role of PACAP as a local ovarian regulator in luteinization.

PACAP—A Multifacetted Neuropeptide

Pituitary adenylate cyclase activating polypeptide (PACAP) was originally isolated from ovine hypothalamus based on its ability to stimulate cAMP production in pituitary cell cultures. The peptide exists in two forms, both of which are derived from the same precursor. PACAP38 and the C-terminal truncated PACAP27 can interact with three subtypes of receptors activating adenylate cyclase and/or phospholipase C. Since its discovery, numerous studies have provided evidence that PACAP is a pleiotropic substance having a broad spectrum of biological functions; the peptide can act as a hormone, neurohormone, autocrine/paracrine substance, neurotransmitter, neuromodulator, neurotrophic factor, and immunomodulator. Two examples of the functional role of PACAP on the biological timing system are presented: 1) the transient expression of PACAP during the periovulatory period in ovarian cells, in which PACAP functions as an autocrine/paracrine inducer of progesterone secretion and subsequent luteinization; and 2) the role of PACAP as a neurotransmitter in the retinohypothalamic tract mediating photic regulation of the brain's biological clock.

Calmodulin interacts with PAC1 and VPAC2 receptors and regulates PACAP-induced FOS expression in human neuroblastoma cells

The neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) mediates its physiological functions through activation of PAC1, VPAC1 and VPAC2 receptors, and the ubiquitous Ca(2+)-sensor calmodulin has been implicated in PACAP-induced signaling. The immediate early response gene FOS is a well-known marker of neuronal activation, so we used a human neuroblastoma cell line NB-1 to explore the role of calmodulin in PACAP-induced FOS gene expression. We observed both short-term and prolonged altered PACAP-mediated activation of the FOS gene in the presence of the calmodulin-antagonist W-7. NB-1 cells were shown to express PAC1 and VPAC2 receptors, and immunoprecipitation of both receptors displayed a co-association with calmodulin in the absence of Ca(2+). Our findings indicate a novel mechanism of calmodulin in regulating PACAP signaling by possible interaction with the inactive state of PAC1 and VPAC2 receptors.

Signal transduction in multifactorial neuroendocrine control of gonadotropin secretion and synthesis in teleosts-studies on the goldfish model

In teleosts, gonadotropin (GTH) secretion and synthesis is controlled by multiple neuroendocrine factors from the hypothalamus, pituitary and peripheral sources. Pituitary gonadotropes must be able to differentiate and integrate information from these regulators at the cellular and intracellular level. In this article, the intracellular signal transduction mechanisms mediating the actions of some of these regulators, including GTH-releasing hormones, pituitary adenylate cyclase-activating polypeptide, dopamine, ghrelin, sex steroids, activin, and follistatin from experiments with goldfish are reviewed and discussed in relation with recent findings. Information from other teleost models is briefly compared. Goldfish gonadotropes possess multiple pharmacologically distinct intracellular Ca2+ stores that together with voltage-sensitive Ca2+ channels, Na+/H+ exchangers, protein kinase C, arachidonic acid, NO, protein kinase A, ERK/MAPK, and Smads allows for integrated control by different neuroendocrine factors.

Regulatory mechanisms underlying corticotropin-releasing factor gene expression in the hypothalamus

The hypothalamic-pituitary-adrenal (HPA) axis is activated under various stressors. Corticotropin-releasing factor (CRF) plays a central role in controlling stress response, and regulating the HPA axis. CRF, produced in the hypothalamic paraventricular nucleus (PVN), stimulates adrenocorticotropic hormone (ACTH) production via CRF receptor type 1 (CRF(1) receptor) from the corticotrophs of the anterior pituitary (AP). Cyclic AMP (cAMP)-protein kinase A (PKA) pathway takes a main role in stimulating CRF gene transcription. Forskolin and pituitary adenylate cyclase-activating polypeptide (PACAP) stimulate adenylate cyclase, intracellular cAMP production, and then CRF and arginine vasopressin (AVP) gene expression in hypothalamic 4B cells. Interleukin (IL)-6, produced in the PVN, both directly and indirectly stimulates CRF and AVP gene expression. Estradiol may enhance the activation of CRF gene expression in response to stress. The HPA axis is regulated by a negative feedback mechanism, because glucocorticoids inhibit both CRF production in the hypothalamic PVN and ACTH production in the pituitary. Hypothalamic parvocellular neurons in the PVN are known to express glucocorticoid receptors, and glucocorticoids are able to regulate CRF gene transcription and expression levels directly in the PVN. Glucocorticoids-dependent repression of cAMP-stimulated CRF promoter activity is mainly localized to promoter sequences between -278 and -233 bp. Both negative glucocorticoid regulatory element (nGRE) and serum response element (SRE) are involved in the repression of the CRF gene in the hypothalamic cells.

Characterization, expression, and functional activity of pituitary adenylate cyclase-activating polypeptide and its receptors in human granulosa-luteal cells

CONTEXT

Pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal polypeptide (VIP) are found in the ovary of mammalian species, although nothing is known about the possible role of PACAP and VIP in the human ovary.

OBJECTIVE

We investigated the expression of PACAP and PACAP/VIP receptors in human granulosa-luteal (GL) cells obtained from consenting in vitro fertilization patients attending a private fertility clinic and assessed a possible antiapoptotic effect of these molecules.

MAIN OUTCOME MEASURES

We measured the expression of PACAP and PACAP/VIP receptor mRNAs in GL cells in response to FSH or LH, as well as the effects of PACAP and VIP on apoptosis. We also evaluated the levels of procaspase-3 in GL cells cultured in the absence of serum.

RESULTS

After 7 d in culture, GL cells displayed increased responsiveness to FSH and LH (100 ng/ml). FSH and LH promoted PACAP expression, LH doing so in a time-dependent fashion. VIP receptor (VPAC1-R and VPAC2-R) mRNAs were also induced by gonadotropin stimulation. Although PACAP receptor (PAC1-R) mRNA was barely detectable, Western blot analysis revealed its presence. The apoptotic effect of serum withdrawal from the culture environment was reverted by both PACAP and VIP. Both peptides showed the ability to reverse a decrease in procaspase-3 levels induced by culture in the absence of serum.

CONCLUSIONS

PACAP and VIP appear to play a role in maintenance of follicle viability as a consequence of the antiapoptotic effect. Further studies are warranted to evaluate the respective roles of PACAP and VIP in ovarian physiology and to identify their mechanism of action.

PACAP prevents toxicity induced by cisplatin in rat and primate neurons but not in proliferating ovary cells: involvement of the mitochondrial apoptotic pathway

Cisplatin is a chemotherapeutic agent whose use is limited by side effects including neuropathies. In proliferating cells, toxic action of cisplatin is based on DNA interactions, while, in quiescent cells, it can induce apoptosis by interacting with proteins. In the present study, we compared cytotoxic mechanisms activated by cisplatin in primate and rodent neurons and in ovary cells in order to determine whether the anti-apoptotic peptide PACAP could selectively reduce neurotoxicity. In quiescent neurons, JNK and sphingomyelinase inhibitors blocked cisplatin-induced cell death. Toxicity was associated with DNA laddering, caspase-3 and -9 activations and Bax induction. These effects were prevented by PACAP. In proliferating cells, cisplatin activated caspase-8 but had no effect on caspase-9. PACAP exerted no protective effect. These data indicate that cisplatin activates distinct apoptotic pathways in quiescent neurons and proliferating cells and that PACAP may reduce neurotoxicity of cisplatin without affecting its chemotherapeutic efficacy.

Pituitary adenylate cyclase-activating polypeptide regulates brain-derived neurotrophic factor exon IV expression through the VPAC1 receptor in the amphibian melanotrope cell

In mammals, pituitary adenylate cyclase-activating polypeptide (PACAP) and its receptors PAC1-R, VPAC1-R, and VPAC2-R play a role in various physiological processes, including proopiomelanocortin (POMC) and brain-derived neurotrophic factor (BDNF) gene expression. We have previously found that PACAP stimulates POMC gene expression, POMC biosynthesis, and alpha-MSH secretion in the melanotrope cell of the amphibian Xenopus laevis. This cell hormonally controls the process of skin color adaptation to background illumination. Here, we have tested the hypothesis that PACAP is involved in the regulation of Xenopus melanotrope cell activity during background adaptation and that part of this regulation is through the control of the expression of autocrine acting BDNF. Using quantitative RT-PCR, we have identified the Xenopus PACAP receptor, VPAC1-R, and show that this receptor in the melanotrope cell is under strong control of the background light condition, whereas expression of PAC1-R was absent from these cells. Moreover, we reveal by quantitative immunocytochemistry that the neural pituitary lobe of white-background adapted frogs possesses a much higher PACAP content than the neural lobe of black-background adapted frogs, providing evidence that PACAP produced in the hypothalamic magnocellular nucleus plays an important role in regulating the activity of Xenopus melanotrope cells during background adaptation. Finally, an in vitro study demonstrates that PACAP stimulates the expression of BDNF transcript IV.

Feeding and metabolism in mice lacking pituitary adenylate cyclase-activating polypeptide

Disruption of the pituitary adenylate cyclase-activating polypeptide (PACAP) gene in mice has demonstrated a role for this highly conserved neuropeptide in the regulation of metabolism and temperature control. Localization of PACAP neurons within hypothalamic nuclei that regulate appetite suggest PACAP may affect feeding and thus energy balance. We used PACAP-null mice to address this question, examining both food intake and energy expenditure. PACAP-null mice were leaner than wild-type littermates due to decreased adiposity and displayed increased insulin sensitivity. The lean phenotype in the PACAP-null mice was completely eliminated if animals were fed a high-fat diet or housed near thermoneutrality (28 C). Further metabolic analyses of PACAP-null mice housed at 21 C indicated that the reduced body weight could not be explained by decreased food intake, increased metabolic rate, or increased locomotor activity. The thyroid hormone axis of PACAP-null mice was affected, because mRNA levels of hypothalamic TRH and brown adipose tissue type 2 deiodinase were reduced in PACAP-null mice housed at room temperature, and brain deiodinase activity was lower in PACAP-null mice after an acute cold challenge compared with wild-type controls. These results demonstrate that PACAP is not required for the regulation of food intake yet is necessary to maintain normal energy homeostasis, likely playing a role in central cold-sensing mechanisms.

Role of vasoactive intestinal peptide and pituitary adenylate cyclase activating polypeptide in the vaginal wall of women with stress urinary incontinence and pelvic organ prolapse

Pelvic floor connective tissue degeneration is closely associated with retrogradation of its dominating nerve fibers. We hypothesized that some neuropeptides from pelvic floor tissue might be involved in the pathological progress of stress urinary incontinence (SUI) and pelvic organ prolapse (POP) in women. Thirty premenopausal and 31 postmenopausal patients participated in the study. The morphological appearance in the vaginal tissue was examined. The vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase activating polypeptide-38 (PACAP) immunoreactivities (ir-VIP, ir-PACAP) were tested by immunohistochemistry and radioimmunoassay. We found that the VIP and PACAP immunostainings were weaker and sparser, and ir-VIP and ir-PACAP levels were significantly decreased in the anterior vaginal wall in the premenopausal and postmenopausal SUI or POP patients. Ir-VIP and ir-PACAP levels were reversely correlated with the age and menopausal status in the SUI or POP patients. Our data suggest that VIP and PACAP may participate in the pathophysiological process of SUI and POP.

CGRP, PACAP, and VIP Modulate Langerhans Cell Function by Inhibiting NF-κB Activation

The neuropeptides calcitonin gene-related peptide (CGRP), pituitary adenylate cyclase-activating polypeptide (PACAP), and vasoactive intestinal peptide (VIP) suppress Langerhans cell (LC) antigen presentation and modulate cytokine production. We have tested the hypothesis that these neuropeptides (NP) inhibit LC function by modulating activation of NF-kappaB. Lipopolysaccharide (LPS) activates NF-kappaB in both a LC-like cell line (XS52) and epidermal LC enriched to approximately 95% and this effect is inhibited by each of the NP. Furthermore, CGRP, PACAP, and VIP suppress phosphorylation of IkappaB kinase beta (P-IKKbeta), prevent degradation of the IkappaB alpha, and inhibit activation of NF-kappaB. Thus, these NP modulate LC function by reducing NF-kappaB activation. Bay 11-7085, an inhibitor of IKK, reduced tumor necrosis factor-alpha (TNFalpha) production from LPS-stimulated XS52 cells and inhibited the ability of LC to present antigen to a T-cell clone in vitro. Each NP also inhibited LPS-induced secretion of TNFalpha by XS52 cells and LC enriched to approximately 95% homogeneity. We suggest that the inhibitory activities of CGRP, PACAP, and VIP on LC function are mediated, at least in part, by inhibition of P-IKKbeta, which prevents IkappaB alpha degradation and activation of NF-kappaB. Modulation of this signaling pathway may be useful for therapeutic modulation of immunity in the skin.

Pituitary adenylate cyclase-activating polypeptide (PACAP) as a growth hormone (GH)-releasing factor in grass carp: II. Solution structure of a brain-specific PACAP by nuclear magnetic resonance spectroscopy and functional studies on GH release and gene expression

Pituitary adenylate cyclase-activating polypeptide (PACAP) has been proposed to be the ancestral GHRH. Recently, using grass carp as a model for modern-day bony fish, we demonstrated that PACAP nerve fibers are present in close proximity to carp somatotrophs, and mammalian PACAPs can induce GH secretion in carp pituitary cells. To further examine the role of PACAP as a GH-releasing factor in fish, the structural identity of grass carp PACAP was established by molecular cloning. The newly cloned PACAP was found to be a single-copy gene and expressed in the brain but not other tissues. The mature peptides of PACAP, namely PACAP(27) and PACAP(38), were synthesized. As revealed by nuclear magnetic resonance spectroscopies, carp PACAP(38) is composed of a flexible N terminal from His(1) to Ile(5), an extended central helix from Phe(6) to Val(26), and a short helical tail in the C terminal from Arg(29) to Arg(34). The C-terminal helix is located after a hinge region at Leu(27) to Gly(28) and is absent in the solution structures of PACAP(27). The two forms of PACAPs were effective in elevating GH release and GH transcript expression in grass carp pituitary cells. These stimulatory effects occurred with parallel rises in cAMP and Ca(2+) entry via voltage-sensitive Ca(2+) channels in carp somatotrophs. The present study represents the first report for solution structures of nonmammalian PACAPs and provides evidence that a brain-specific isoform of PACAP in fish can stimulate GH synthesis and release at the pituitary level, presumably by activating the appropriate postreceptor signaling mechanisms.

Pituitary adenylate cyclase-activating polypeptide is up-regulated in cortical pyramidal cells after focal ischemia and protects neurons from mild hypoxic/ischemic damage

The protective effect of pituitary adenylate cyclase-activating polypeptide (PACAP) in stroke models is poorly understood. We studied patterns of PACAP, vasoactive intestinal peptide, and the PACAP-selective receptor PAC1 after middle cerebral artery occlusion and neuroprotection by PACAP in cortical cultures exposed to oxygen/glucose deprivation (OGD). Within hours, focal ischemia caused a massive, NMDA receptor (NMDAR)-dependent up-regulation of PACAP in cortical pyramidal cells. PACAP expression dropped below the control level after 2 days and was normalized after 4 days. Vasoactive intestinal peptide expression was regulated oppositely to that of PACAP. PAC1 mRNA showed ubiquitous expression in neurons and astrocytes with minor changes after ischemia. In cultured cortical neurons PACAP27 strongly activated Erk1/2 at low and p38 MAP kinase at higher nanomolar concentrations via PAC1. In astrocyte cultures, effects of PACAP27 on Erk1/2 and p38 were weak. During OGD, neurons showed severely reduced Erk1/2 activity and dephosphorylation of Erk1/2-regulated Ser112 of pro-apoptotic Bad. PACAP27 stimulation counteracted Erk1/2 inactivation and Bad dephosphorylation during short-term OGD but was ineffective after expanded OGD. Consistently, PACAP27 caused MEK-dependent neuroprotection during mild but not severe hypoxic/ischemic stress. While PACAP27 protected neurons at 1-5 nmol/L, full PAC1 activation by 100 nmol/L PACAP exaggerated hypoxic/ischemic damage. PACAP27 stimulation of astrocytes increased the production of Akt-activating factors and conferred ischemic tolerance to neurons. Thus, ischemia-induced PACAP may act via neuronal and astroglial PAC1. PACAP confers protection to ischemic neurons by maintaining Erk1/2 signaling via neuronal PAC1 and by increasing neuroprotective factor production via astroglial PAC1.