PACAP activates PKA, PKC and Ca(2+) signaling cascades in rat neuroepithelial cells

Spatial analysis of a complete DIPG-infiltrated brainstem reveals novel ligand-receptor mediators of tumour-to-TME crosstalk

Previous studies have highlighted the capacity of brain cancer cells to functionally interact with the tumour microenvironment (TME). This TME-cancer crosstalk crucially contributes to tumour cell invasion and disease progression. In this study, we performed spatial transcriptomic sequencing analysis of a complete annotated tumour-infiltrated brainstem from a single diffuse intrinsic pontine glioma (DIPG) patient. Gene signatures from ten sequential tumour regions were analysed to assess mechanisms of disease progression and oncogenic interactions with the TME. We identified four distinct tumour subpopulations and assessed respective ligand-receptor pairs that actively promote DIPG tumour progression via crosstalk with endothelial, neuronal and immune cell communities. Our analysis found potential targetable mediators of tumour-to-TME communication, including members of the complement component system and the neuropeptide/GPCR ligand-receptor pair ADCYAP1-ADCYAP1R1. These interactions could influence DIPG tumour progression and represent novel therapeutic targets.

Pituitary adenylate cyclase-activating polypeptide receptor activation in the hypothalamus recruits unique signaling pathways involved in energy homeostasis

Pituitary adenylate cyclase activating polypeptide (PACAP) exerts pleiotropic effects on ventromedial nuclei (VMN) of the hypothalamus and its control of feeding and energy expenditure through the type I PAC1 receptor (PAC1R). However, the endogenous role of PAC1Rs in the VMN and the downstream signaling responsible for PACAP's effects on energy balance are unknown. Numerous studies have revealed that PAC1Rs are coupled to both Gαs/adenylyl cyclase/protein kinase A (Gαs/AC/PKA) and Gαq/phospholipase C/protein kinase C (Gαq/PLC/PKC), while also undergoing trafficking following stimulation. To determine the endogenous role of PAC1Rs and downstream signaling that may explain PACAP's pleiotropic effects, we used RNA interference to knockdown VMN PAC1Rs and pharmacologically inhibited PKA, PKC, and PAC1R trafficking. Knocking down PAC1Rs increased meal sizes, reduced total number of meals, and induced body weight gain. Inhibition of either PKA or PKC alone in awake male Sprague-Dawley rats, attenuated PACAP's hypophagic and anorectic effects during the dark phase. However, PKA or PKC inhibition potentiated PACAP's thermogenic effects during the light phase. Analysis of locomotor activity revealed that PKA inhibition augmented PACAP's locomotor effects, whereas PKC inhibition had no effect. Finally, PACAP administration in the VMN induces surface PAC1R trafficking into the cytosol which was blocked by endocytosis inhibitors. Subsequently, inhibition of PAC1R trafficking into the cytosol attenuated PACAP-induced hypophagia. These results revealed that endogenous PAC1Rs uniquely engage PKA, PKC, and receptor trafficking to mediate PACAP's pleiotropic effects in VMN control of feeding and metabolism.NEW & NOTEWORTHY Endogenous PAC1 receptors, integral to VMN management of feeding behavior and body weight regulation, uniquely engage PKA, PKC, and receptor trafficking to mediate the hypothalamic ventromedial nuclei control of feeding and metabolism. PACAP appears to use different signaling mechanisms to regulate feeding behavior from its effects on metabolism.

Myocyte Enhancer Factor 2A (MEF2A) Defines Oxytocin-Induced Morphological Effects and Regulates Mitochondrial Function in Neurons

The neuropeptide oxytocin (OT) is a well-described modulator of socio-emotional traits, such as anxiety, stress, social behavior, and pair bonding. However, when dysregulated, it is associated with adverse psychiatric traits, such as various aspects of autism spectrum disorder (ASD). In this study, we identify the transcription factor myocyte enhancer factor 2A (MEF2A) as the common link between OT and cellular changes symptomatic for ASD, encompassing neuronal morphology, connectivity, and mitochondrial function. We provide evidence for MEF2A as the decisive factor defining the cellular response to OT: while OT induces neurite retraction in MEF2A expressing neurons, OT causes neurite outgrowth in absence of MEF2A. A CRISPR-Cas-mediated knockout of MEF2A and retransfection of an active version or permanently inactive mutant, respectively, validated our findings. We also identified the phosphatase calcineurin as the main upstream regulator of OT-induced MEF2A signaling. Further, MEF2A signaling dampens mitochondrial functioning in neurons, as MEF2A knockout cells show increased maximal cellular respiration, spare respiratory capacity, and total cellular ATP. In summary, we reveal a central role for OT-induced MEF2A activity as major regulator of cellular morphology as well as neuronal connectivity and mitochondrial functioning, with broad implications for a potential treatment of disorders based on morphological alterations or mitochondrial dysfunction.

Pituitary adenylate cyclase activating polypeptide (PACAP) signalling exerts chondrogenesis promoting and protecting effects: implication of calcineurin as a downstream target

Pituitary adenylate cyclase activating polypeptide (PACAP) is an important neurotrophic factor influencing differentiation of neuronal elements and exerting protecting role during traumatic injuries or inflammatory processes of the central nervous system. Although increasing evidence is available on its presence and protecting function in various peripheral tissues, little is known about the role of PACAP in formation of skeletal components. To this end, we aimed to map elements of PACAP signalling in developing cartilage under physiological conditions and during oxidative stress. mRNAs of PACAP and its receptors (PAC1,VPAC1, VPAC2) were detectable during differentiation of chicken limb bud-derived chondrogenic cells in micromass cell cultures. Expression of PAC1 protein showed a peak on days of final commitment of chondrogenic cells. Administration of either the PAC1 receptor agonist PACAP 1-38, or PACAP 6-38 that is generally used as a PAC1 antagonist, augmented cartilage formation, stimulated cell proliferation and enhanced PAC1 and Sox9 protein expression. Both variants of PACAP elevated the protein expression and activity of the Ca-calmodulin dependent Ser/Thr protein phosphatase calcineurin. Application of PACAPs failed to rescue cartilage formation when the activity of calcineurin was pharmacologically inhibited with cyclosporine A. Moreover, exogenous PACAPs prevented diminishing of cartilage formation and decrease of calcineurin activity during oxidative stress. As an unexpected phenomenon, PACAP 6-38 elicited similar effects to those of PACAP 1-38, although to a different extent. On the basis of the above results, we propose calcineurin as a downstream target of PACAP signalling in differentiating chondrocytes either in normal or pathophysiological conditions. Our observations imply the therapeutical perspective that PACAP can be applied as a natural agent that may have protecting effect during joint inflammation and/or may promote cartilage regeneration during degenerative diseases of articular cartilage.

NMDA and PACAP receptor signaling interact to mediate retinal-induced scn cellular rhythmicity in the absence of light

The "core" region of the suprachiasmatic nucleus (SCN), a central clock responsible for coordinating circadian rhythms, shows a daily rhythm in phosphorylation of extracellular regulated kinase (pERK). This cellular rhythm persists under constant darkness and, despite the absence of light, is dependent upon inputs from the eye. The neural signals driving this rhythmicity remain unknown and here the roles of glutamate and PACAP are examined. First, rhythmic phosphorylation of the NR1 NMDA receptor subunit (pNR1, a marker for receptor activation) was shown to coincide with SCN core pERK, with a peak at circadian time (CT) 16. Enucleation and intraocular TTX administration attenuated the peak in the pERK and pNR1 rhythms, demonstrating that activation of the NMDA receptor and ERK in the SCN core at CT16 are dependent on retinal inputs. In contrast, ERK and NR1 phosphorylation in the SCN shell region were unaffected by these treatments. Intraventricular administration of the NMDA receptor antagonist MK-801 also attenuated the peak in SCN core pERK, indicating that ERK phosphorylation in this region requires NMDA receptor activation. As PACAP is implicated in photic entrainment and is known to modulate glutamate signaling, the effects of a PAC1 receptor antagonist (PACAP 6-38) on SCN core pERK and pNR1 also were examined. PACAP 6-38 administration attenuated SCN core pERK and pNR1, suggesting that PACAP induces pERK directly, and indirectly via a modulation of NMDA receptor signaling. Together, these data indicate that, in the absence of light, retinal-mediated NMDA and PAC1 receptor activation interact to induce cellular rhythms in the SCN core. These results highlight a novel function for glutamate and PACAP release in the hamster SCN apart from their well-known roles in the induction of photic circadian clock resetting.

Stress peptide PACAP engages multiple signaling pathways within the carotid body to initiate excitatory responses in respiratory and sympathetic chemosensory afferents

Consistent with a critical role in respiratory and autonomic stress responses, the carotid bodies are strongly excited by pituitary adenylate cyclase-activating polypeptide (PACAP), a neuropeptide implicated in stress responses throughout the sympathetic nervous system. PACAP excites isolated carotid body glomus cells via activation of PAC1 receptors, with one study suggesting PAC1-induced excitation is due entirely to protein kinase A (PKA)-mediated inhibition of TASK channels. However, in other systems, PAC1 is known to be coupled to multiple intracellular signaling pathways, including PKA, phospholipase C (PLC), phospholipase D (PLD), and protein kinase C (PKC), that trigger multiple downstream effectors including increased Ca²⁺ mobilization, inhibition of various K⁺ channels, and activation of nonselective cation channels. This study tests if non-PKA/TASK channel signaling helps mediate the stimulatory effects of PACAP on the carotid body. Using an ex vivo arterially perfused rat carotid body preparation, we show that PACAP-38 stimulates carotid sinus nerve activity in a biphasic manner (peak response, falling to plateau). PKA blocker H-89 only reduced the plateau response (~41%), whereas the TASK-1-like K⁺ channel blocker/transient receptor potential vanilloid 1 channel agonist anandamide only inhibited the peak response (~48%), suggesting involvement of additional pathways. The PLD blocker CAY10594 significantly inhibited both peak and plateau responses. The PLC blocker U73122 decimated both peak and plateau responses. Brefeldin A, a blocker of Epac (cAMP-activated guanine exchange factor, reported to link Gs-coupled receptors with PLC/PLD), also reduced both phases of the response, as did blocking signaling downstream of PLC/PLD with the PKC inhibitors chelerythrine chloride and GF109203X. Suggesting the involvement of non-TASK ion channels in the effects of PACAP, the A-type K⁺ channel blocker 4-aminopyridine, and the putative transient receptor potential channel (TRPC)/T-type calcium channel blocker SKF96365 each significantly inhibited the peak and steady-state responses. These data suggest the stimulatory effect of PACAP-38 on carotid body sensory activity is mediated through multiple signaling pathways: the PLC-PKC pathways predominates, with TRPC and/or T-type channel activation and Kv channel inactivation; only partial involvement is attributable to PKA and PLD activation.

Pituitary adenylate cyclase-activating polypeptide (PACAP) promotes both survival and neuritogenesis in PC12 cells through activation of nuclear factor κB (NF-κB) pathway: involvement of extracellular signal-regulated kinase (ERK), calcium, and c-REL

The pituitary adenylate cyclase-activating polypeptide (PACAP) is a trophic factor that promotes neuronal survival and neurite outgrowth. However, the signaling pathways and the transcriptional mechanisms involved are not completely elucidated. Our previous studies aimed at characterizing the transcriptome of PACAP-differentiated PC12 cells revealed an increase in the expression of nuclear factor κB2 (NF-κB2) gene coding for p100/p52 subunit of NF-κB transcription factor. Here, we examined the role of the NF-κB pathway in neuronal differentiation promoted by PACAP. We first showed that PACAP-driven survival and neuritic extension in PC12 cells are inhibited following NF-κB pathway blockade. PACAP stimulated both c-Rel and p52 NF-κB subunit gene expression and nuclear translocation, whereas c-Rel down-regulation inhibited cell survival and neuritogenesis elicited by the neuropeptide. PACAP-induced c-Rel nuclear translocation was inhibited by ERK1/2 and Ca(2+) blockers. Furthermore, the neuropeptide stimulated NF-κB p100 subunit processing into p52, indicative of activation of the NF-κB alternative pathway. Taken together, our data show that PACAP promotes both survival and neuritogenesis in PC12 cells by activating NF-κB pathway, most likely via classical and alternative signaling cascades involving ERK1/2 kinases, Ca(2+), and c-Rel/p52 dimers.

Pituitary adenylate cyclase-activating peptide enhances electrical coupling in the mouse adrenal medulla

Neuroendocrine adrenal medullary chromaffin cells receive synaptic excitation through the sympathetic splanchnic nerve to elicit catecholamine release into the circulation. Under basal sympathetic tone, splanchnic-released acetylcholine evokes chromaffin cells to fire action potentials, leading to synchronous phasic catecholamine release. Under elevated splanchnic firing, experienced under the sympathoadrenal stress response, chromaffin cells undergo desensitization to cholinergic excitation. Yet, stress evokes a persistent and elevated adrenal catecholamine release. This sustained stress-evoked release has been shown to depend on splanchnic release of a peptide transmitter, pituitary adenylate cyclase-activating peptide (PACAP). PACAP stimulates catecholamine release through a PKC-dependent pathway that is mechanistically independent of cholinergic excitation. Moreover, it has also been reported that shorter term phospho-regulation of existing gap junction channels acts to increase junctional conductance. In this study, we test if PACAP-mediated excitation upregulates cell-cell electrical coupling to enhance chromaffin cell excitability. We utilize electrophysiological recordings conducted in adrenal tissue slices to measure the effects of PACAP stimulation on cell coupling. We report that PACAP excitation increases electrical coupling and the spread of electrical excitation between adrenal chromaffin cells. Thus PACAP acts not only as a secretagogue but also evokes an electrical remodeling of the medulla, presumably to adapt to the organism's needs during acute sympathetic stress.

The effect of pituitary adenylate cyclase-activating polypeptide on elevated plus maze behavior and hypothermia induced by morphine withdrawal

The aim of the present investigation was to study the effects of pituitary adenylate cyclase-activating polypeptide (PACAP) on morphine withdrawal-induced behavioral changes and hypothermia in male CFLP mice. Elevated plus maze (EPM) and jump tests were used to assess naloxone-precipitated morphine withdrawal-induced behavior responses. Different doses of subcutaneous (s.c.) naloxone, (0.1 and 0.2 mg/kg, respectively) were used to precipitate the emotional and psychical aspects of withdrawal on EPM and 1 mg/kg (s.c.) was used to induce the somatic withdrawal signs such as jumping, and the changes in body temperature. In our EPM studies, naloxone proved to be anxiolytic in mice treated with morphine. Chronic intracerebroventricular (i.c.v.) administration of PACAP alone had no significant effect on withdrawal-induced anxiolysis and total activity at doses of 500 ng and 1 μg. At dose of 500 ng, however, PACAP significantly counteracted the reduced motor activity in the EPM test in mice treated with morphine and diminished the hypothermia and shortened jump latency induced by naloxone in mice treated with morphine. These findings indicate that anxiolytic-like behavior may be mediated via a PACAP-involved pathway and PACAP may play an important role in chronic morphine withdrawal-induced hypothermia as well.

Pituitary adenylate cyclase-activating peptide (PACAP) recruits low voltage-activated T-type calcium influx under acute sympathetic stimulation in mouse adrenal chromaffin cells

Low voltage-activated T-type Ca(v)3.2 calcium channels are expressed in neurosecretory chromaffin cells of the adrenal medulla. Previous studies have shown that naïve adrenal chromaffin cells express a nominal Ca(v)3.2-dependent conductance. However, Ca(v)3.2 conductance is up-regulated following chronic hypoxia or long term exposure to cAMP analogs. Thus, although a link between chronic stressors and up-regulation of Ca(v)3.2 exists, there are no reports testing the specific role of Ca(v)3.2 channels in the acute sympathoadrenal stress response. In this study, we examined the effects of acute sympathetic stress on T-type Ca(v)3.2 calcium influx in mouse chromaffin cells in situ. Pituitary adenylate cyclase-activating peptide (PACAP) is an excitatory neuroactive peptide transmitter released by the splanchnic nerve under elevated sympathetic activity to stimulate the adrenal medulla. PACAP stimulation did not evoke action potential firing in chromaffin cells but did cause a persistent subthreshold membrane depolarization that resulted in an immediate and robust Ca(2+)-dependent catecholamine secretion. Moreover, PACAP-evoked secretion was sensitive to block by nickel chloride and was acutely inhibited by protein kinase C blockers. We utilized perforated patch electrophysiological recordings conducted in adrenal tissue slices to investigate the mechanism of PACAP-evoked calcium entry. We provide evidence that stimulation with exogenous PACAP and native neuronal stress stimulation both lead to a protein kinase C-mediated phosphodependent recruitment of a T-type Ca(v)3.2 Ca(2+) influx. This in turn evokes catecholamine release during the acute sympathetic stress response.

Meta-analysis of microarray-derived data from PACAP-deficient adrenal gland in vivo and PACAP-treated chromaffin cells identifies distinct classes of PACAP-regulated genes

Initial PACAP-regulated transcriptomes of PACAP-treated cultured chromaffin cells, and the adrenal gland of wild-type versus PACAP-deficient mice, have been assembled using microarray analysis. These were compared to previously acquired PACAP-regulated transcriptome sets from PC12 cells and mouse central nervous system, using the same microarray platform. The Ingenuity Pathways Knowledge Base was then employed to group regulated transcripts into common first and second messenger regulatory clusters. The purpose of our meta-analysis was to identify sets of genes regulated distinctly or in common by the neurotransmitter/neurotrophin PACAP in specific physiological contexts. Results suggest that PACAP participates in both the basal differentiated expression, and the induction upon physiological stimulation, of distinct sets of transcripts in neuronal and endocrine cells. PACAP in both developmental and acute regulatory paradigms acts on target genes also regulated by either TNFalpha or TGFbeta, two first messengers acting on transcription mainly through NFkappaB and Smads, respectively.

Chronic gonadotropin-releasing hormone inhibits activin induction of the ovine follicle-stimulating hormone beta-subunit: involvement of 3',5'-cyclic adenosine monophosphate response element binding protein and nitric oxide synthase type I

FSH is induced by activin, and this expression is modulated by GnRH through FSHB expression. This report focuses on the inhibitory effect of GnRH on activin-induced FSHB expression. Activin-treated primary murine pituitary cultures robustly express mutant ovine FSHBLuc-DeltaAP1, a luciferase transgene driven by 4.7 kb of ovine FSHB promoter. This promoter lacks two GnRH-inducible activator protein-1 sites, making it easier to observe GnRH-mediated inhibition. Luciferase expression from this transgene was decreased 94% by 100 nM GnRH with a half-time of approximately 4 h in pituitary cultures, and this inhibition was independent of follistatin. Activators of cAMP and protein kinase C like forskolin and phorbol 12-myristate 3-acetate (PMA), respectively, mimicked GnRH action. Kinetic studies of wild-type ovine FSHBLuc in LbetaT2 cells showed continuous induction by activin (4-fold) over 20 h. Most of this induction (78%) was blocked, beginning at 6 h. cAMP response element binding protein (CREB) was implicated in this inhibition because overexpression of its constitutively active mutant mimicked GnRH, and its inhibitor (inducible cAMP early repressor isoform II) reversed the inhibition caused by GnRH, forskolin, or PMA. In addition, GnRH, forskolin, or PMA increased the expression of a CREB-responsive reporter gene, 6xCRE-37PRL-Luc. Inhibition of nitric oxide type I (NOSI) by 7-nitroindazole also reversed GnRH-mediated inhibition by 60%. It is known that GnRH and CREB induce production of NOSI in gonadotropes and neuronal cells, respectively. These data support the concept that chronic GnRH inhibits activin-induced ovine FSHB expression by sequential activation of CREB and NOSI through the cAMP and/or protein kinase C pathways.

G protein-coupled receptors control NMDARs and metaplasticity in the hippocampus

Long-term potentiation (LTP) and long-term depression (LTD) are the major forms of functional synaptic plasticity observed at CA1 synapses of the hippocampus. The balance between LTP and LTD or "metaplasticity" is controlled by G-protein coupled receptors (GPCRs) whose signal pathways target the N-methyl-D-asparate (NMDA) subtype of excitatory glutamate receptor. We discuss the protein kinase signal cascades stimulated by Galphaq and Galphas coupled GPCRs and describe how control of NMDAR activity shifts the threshold for the induction of LTP.

PACAP/PAC1 autocrine system promotes proliferation and astrogenesis in neural progenitor cells

The Pituitary adenylate cyclase-activating peptide (PACAP) ligand/type 1 receptor (PAC1) system regulates neurogenesis and gliogenesis. It has been well established that the PACAP/PAC1 system induces differentiation of neural progenitor cells (NPCs) through the Gs-mediated cAMP-dependent signaling pathway. However, it is unknown whether this ligand/receptor system has a function in proliferation of NPCs. In this study, we identified that PACAP and PAC1 were highly expressed and co-localized in NPCs of mouse cortex at embryonic day 14.5 (E14.5) and found that the PACAP/PAC1 system potentiated growth factor-induced proliferation of mouse cortical NPCs at E14.5 via Gq-, but not Gs-, mediated PLC/IP3-dependent signaling pathway in an autocrine manner. Moreover, PAC1 activation induced elongation of cellular processes and a stellate morphology in astrocytes that had the bromodeoxyuridine (BrdU)-incorporating ability of NPCs. Consistent with this notion, we determined that the most BrdU positive NPCs differentiated to astrocytes through PAC1 signaling. These results suggest that the PACAP/PAC1 system may play a dual role in neural/glial progenitor cells not only differentiation but also proliferation in the cortical astrocyte lineage via Ca2+-dependent signaling pathways through PAC1.

Signaling involved in pituitary adenylate cyclase-activating polypeptide-stimulated ADNP expression

Activity-dependent neurotrophic protein (ADNP) was discovered as a novel response gene for VIP and has neuroprotective potential. When the VIP paralog, PACAP38 was added to mouse neuron-glia co-cultures, it induced ADNP mRNA expression in a bimodal fashion at subpico- and nanomolar concentrations with greater response at subpicomolar level. The response was attenuated by a PAC1-R antagonist at both concentrations and by a VPAC1-R antagonist at nanomolar concentration only. An IP3/PLC inhibitor attenuated the response at both concentrations of PACAP38, but a MAPK inhibitor had no effect. A PKA inhibitor suppressed the response at nanomolar concentration only. These findings suggest that ADNP expression is mediated through multiple receptors and signaling pathways that are regulated by different concentrations of PACAP.

Modulation of NMDA receptors by pituitary adenylate cyclase activating peptide in CA1 neurons requires G alpha q, protein kinase C, and activation of Src

At CA1 synapses, activation of NMDA receptors (NMDARs) is required for the induction of both long-term potentiation and depression. The basal level of activity of these receptors is controlled by converging cell signals from G-protein-coupled receptors and receptor tyrosine kinases. Pituitary adenylate cyclase activating peptide (PACAP) is implicated in the regulation of synaptic plasticity because it enhances NMDAR responses by stimulating Galphas-coupled receptors and protein kinase A (Yaka et al., 2003). However, the major hippocampal PACAP1 receptor (PAC1R) also signals via Galphaq subunits and protein kinase C (PKC). In CA1 neurons, we showed that PACAP38 (1 nM) enhanced synaptic NMDA, and evoked NMDAR, currents in isolated CA1 neurons via activation of the PAC1R, Galphaq, and PKC. The signaling was blocked by intracellular applications of the Src inhibitory peptide Src(40-58). Immunoblots confirmed that PACAP38 biochemically activates Src. A Galphaq pathway is responsible for this Src-dependent PACAP enhancement because it was attenuated in mice lacking expression of phospholipase C beta1, it was blocked by preventing elevations in intracellular Ca2+, and it was eliminated by inhibiting either PKC or cell adhesion kinase beta [CAKbeta or Pyk2 (proline rich tyrosine kinase 2)]. Peptides that mimic the binding sites for either Fyn or Src on receptor for activated C kinase-1 (RACK1) also enhanced NMDAR in CA1 neurons, but their effects were blocked by Src(40-58), implying that Src is the ultimate regulator of NMDARs. RACK1 serves as a hub for PKC, Fyn, and Src and facilitates the regulation of basal NMDAR activity in CA1 hippocampal neurons.

The neuropeptide PACAP promotes ?‐secretase pathway for processing Alzheimer amyloid precursor protein

The neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) has neurotrophic as well as anti-apoptotic properties and is involved in learning and memory processes. Its specific G protein-coupled receptor PAC1 is expressed in several central nervous system (CNS) regions, including the hippocampal formation. Here we examined the effect of PAC1 receptor activation on alpha-secretase cleavage of the amyloid precursor protein (APP) and the production of secreted APP (APPsalpha). Stimulation of endogenously expressed PAC1 receptors with PACAP in human neuroblastoma cells increased APPsalpha secretion, which was completely inhibited by the PAC1 receptor specific antagonist PACAP-(6-38). In HEK cells stably overexpressing functional PAC1 receptors, PACAP-27 and PACAP-38 strongly stimulated alpha-secretase cleavage of APP. The PACAP-induced APPsalpha production was dose dependent and saturable. This increase of alpha-secretase activity was completely abolished by hydroxamate-based metalloproteinase inhibitors, including a preferential ADAM 10 inhibitor. By using several specific protein kinase inhibitors, we show that the MAP-kinase pathway [including extracellular-regulated kinase (ERK) 1 and ERK2] and phosphatidylinositol 3-kinase mediate the PACAP-induced alpha-secretase activation. Our findings provide evidence for a role of the neuropeptide PACAP in stimulation of the nonamyloidogenic pathway, which might be related to its neuroprotective properties.

Pituitary adenylate cyclase-activating polypeptide promotes differentiation of mouse neural stem cells into astrocytes

We have found that pituitary adenylate cyclase-activating polypeptide (PACAP) employed at the physiological concentrations induces the differentiation of mouse neural stem cells into astrocytes. The differentiation process was not affected by cAMP analogues such as dibutylic cAMP (db-cAMP) or 8Br-cAMP or by the specific competitive inhibitor of protein kinase A, Rp-adenosine-3',5'-cyclic monophosphothioate triethylamine salt (Rp-cAMP). Expression of the PACAP receptor (PAC1) in neural stem cells was detected by both RT-PCR and immunoblot using an affinity-purified antibody. The PACAP selective antagonist, PACAP(6-38), had an inhibitory effect on the PACAP-induced differentiation of neural stem cells into astrocytes. These results indicate that PACAP acts on the PAC1 receptor on the plasma membrane of mouse neural stem cells, with the signal then transmitted intracellularly via a PAC1-coupled G protein, does not involve Gs. This signaling mechanism may thus play a crucial role in the differentiation of neural stem cells into astrocytes.

Effects of peptides, with emphasis on feeding, pain, and behavior A 5-year (1999-2003) review of publications in Peptides

Novel effects of naturally occurring peptides are continuing to be discovered, and their mechanisms of actions as well as interactions with other substances, organs, and systems have been elucidated. Synthetic analogs may have actions similar or antagonistic to the endogenous peptides, and both the native peptides and analogs have potential as drugs or drug targets. The journal Peptides publishes many leading articles on the structure-activity relationship of peptides as well as outstanding reviews on some families of peptides. Complementary to the reviews, here we extract information from the original papers published during the past five years in Peptides (1999-2003) to summarize the effects of different classes of peptides, their modulation by other chemicals and various pathophysiological states, and the mechanisms by which the effects are exerted. Special attention is given to peptides related to feeding, pain, and other behaviors. By presenting in condensed form the effects of peptides which are essential for systems biology, we hope that this summary of existing knowledge will encourage additional novel research to be presented in Peptides.

VPAC Receptor Modulation of Neuroexcitability in Intracardiac Neurons

Pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal polypeptide (VIP) have been found within mammalian intracardiac ganglia, but the cellular effects of these neuropeptides remain poorly understood. Fluorometric calcium imaging and whole cell patch clamp recordings were used to examine the effects of PACAP and VIP on [Ca2+]i and neuroexcitability, respectively, in intracardiac neurons of neonatal rats. PACAP and VIP evoked rapid increases in [Ca2+]i that exhibited both transient and sustained components. Pharmacological experiments using PAC1 and VPAC receptor-selective antagonists demonstrated that the elevations in [Ca2+]i result from the activation of VPAC receptors. The transient increases in [Ca2+]i were shown to be the product of Ca2+ mobilization from caffeine/ryanodine-sensitive intracellular stores and were not due to inositol 1,4,5-trisphosphate-mediated calcium release. In contrast, the sustained [Ca2+]i elevations were dependent on extracellular Ca2+ and were blocked by the transient receptor channel antagonist, 2-aminoethoxydiphenyl borate, which suggests that they are due to Ca2+ entry via store-operated channels. In addition to elevating [Ca2+]i, both PACAP and VIP depolarized intracardiac neurons, and PACAP was further shown to augment action potential firing in these cells. Depolarization of intracardiac neurons by the neuropeptides was dependent on activation of VPAC receptors and the concomitant increases in [Ca2+]i. Although activation of PAC1 receptors alone had no direct effects on neuroexcitability, PAC1 receptor stimulation potentiated the VPAC receptor-induced depolarizations. Furthermore, enhanced action potential firing was only observed upon concurrent stimulation of PAC1 and VPAC receptors, which indicates that these receptors act synergistically to enhance neuroexcitability in intracardiac neurons.

Effects of pituitary adenylate cyclase-activating polypeptide on facial nerve recovery in the Guinea pig

OBJECTIVES/HYPOTHESIS

Pituitary adenylate cyclase-activating polypeptide (PACAP) has neurotrophic effects of neural regeneration and gives protection to the nervous system. We investigated whether PACAP had a neurotrophic effect on peripheral motoneurons and whether PACAP could facilitate glial cell line-derived neurotrophic factor (GDNF), a neurotrophin, in nerve regeneration. The presence and distribution of PACAP receptors following facial nerve transection were also investigated.

STUDY DESIGN

Animal experiment.

METHODS

Unilateral transection of the facial nerve was performed in male Hartley guinea pigs, and PACAP was injected at the site. Saline was substituted as a control. Compound muscle action potentials were recorded to measure the changes of latency. Glial cell line-derived neurotrophic factor (GDNF) content in facial target muscle was measured using enzyme-linked immunosorbent assay. The regenerating site was taken for histological studies.

RESULTS

Pituitary adenylate cyclase-activating polypeptide hastened the appearance of compound muscle action potentials and shortened the latency. Pituitary adenylate cyclase-activating polypeptide increased and prolonged the nerve transection-induced GDNF increase in the facial muscles. The number of myelinated fibers at 1 to 4 weeks after the transection was increased. PAC1 receptor or VPAC1 receptor or both were identified in the injury area at 2 to 4 weeks.

CONCLUSIONS

Pituitary adenylate cyclase-activating polypeptide facilitated the recovery of latency of compound muscle action potentials or the number of myelinated axons, or both. Pituitary adenylate cyclase-activating polypeptide prolonged the GDNF levels in target organs. These data indicated that PACAP promoted regeneration of the facial nerve.

Pituitary adenylate cyclase-activating polypeptide induces a sustained increase in intracellular free Ca(2+) concentration and catechol amine release by activating Ca(2+) influx via receptor-stimulated Ca(2+) entry, independent of store-operated Ca(2+) channels, and voltage-dependent Ca(2+) channels in bovine adrenal medullary chromaffin cells

Characteristics of pituitary adenylate cyclase-activating polypeptide (PACAP)-induced increase of Ca(2+) entry and catecholamine (CA) release were studied in bovine adrenal medullary chromaffin cells. PACAP induced intracellular free Ca(2+) concentration ([Ca(2+)](i)), showing an initial transient [Ca(2+)](i) rise followed by a sustained rise and CA release, which were not blocked by the blocking agents for nicotinic acetylcholine receptor (nAChR) channel, the voltage-dependent Ca(2+) channel (VOC), or the Na(+) channel. The sarcoendoplasmic Ca(2+)-ATPase inhibitors thapsigargin and cyclopiazonic acid did not affect the PACAP-induced sustained rise of [Ca(2+)](i), but did inhibit the initial [Ca(2+)](i) rise. In cells pretreated with cyclopiazonic acid or membrane-permeable, low-affinity Ca(2+) chelator N',N',N',N'-tetrakis(2-pyridylmethyl)ethylenediamine, PACAP further stimulated the entry of Ca(2+) or Mn(2+), whereas these treatments masked [Ca(2+)](i) dynamics induced by bradykinin. PACAP-induced sustained [Ca(2+)](i) rise and Mn(2+) entry were enhanced by acidic extracellular solution and reduced by alkalinization, whereas thapsigargin-induced Mn(2+) entry was regulated by the opposite. PACAP-induced [Ca(2+)](i) rise and Mn(2+) entry were not affected by blockers of cAMP-dependent protein kinase, phospholipase C, or protein kinase C. All store-operated Ca(2+) channel (SOC) blocking agents tested inhibited thapsigargin-induced Mn(2+) entry. 1(beta-[3-(4-Methoxyphenyl)-propoxy]-4-methoxyphenylethyl)-1H-imidazole hydrochloride (SK&F 96365), (R,S)-(3,4-dihydro-6,7-dimethoxy-isoquinoline-1-yl)-2-phenyl-N,N-di-[2-(2,3,4-trimethoxyphenyl)ethyl]-acetamide, and econazole inhibited PACAP-induced Ca(2+) or Mn(2+) entry, whereas GdCl(3), 7,8-benzoflavone, nor-dihydroguaiaretic acid, 5-nitro-2-(3-phenylpropylamino)benzoic acid, fulfenamic acid, and niflumic acid did not. SK&F 96365 and econazole but not GdCl(3) inhibited PACAP-induced CA release. These results suggest that PACAP activates a novel Ca(2+) entry pathway associated with sustained CA release independent of the nAChR channel, VOC and SOC, activated by acid pH, with different sensitivity to blockers of SOC. This pathway may provide a useful model for the study of receptor-operated Ca(2+) entry.