PACAP stimulates glucose output from the perfused rat liver

Pituitary Adenylate Cyclase-activating Polypeptide (PACAP) -derived Peptide MPAPO Stimulates Adipogenic Differentiation by Regulating the Early Stage of Adipogenesis and ERK Signaling Pathway

Regenerative medicine and tissue engineering have delivered new healing possibilities to the treatment of soft tissue defects, but the selection of seed cells is critical for treatment. Adipose-derived stem cells have perpetually been a preferred candidate for seed cells due to their wealthy sources, simple access, high plasticity, and powerful value-added capabilities. How to improve the efficiency of adipogenic differentiation is the key to the treatment. Pituitary adenylate cyclase-activating peptide, as a biologically active peptide secreted by the pituitary, is widely involved in regulating the body's sugar metabolism and lipid metabolism. However, the effects of MPAPO in ADSCs adipogenic differentiation remain unknown. Our results reveal that MPAPO treatment improves the adipogenic differentiation efficiency of ADSCs, including promoting the accumulation of lipid droplets and triglycerides, and the expression of adipocyte protein biomarkers PPARγ and C/EBPa. Additionally, the mechanism studies showed that the effective window of MPAPO-induced adipogenesis was the first 3 days during ADSCs differentiation. MPAPO selectively binds to the PAC1 receptor and promotes adipogenic differentiation of ADSCs by activating the ERK signaling pathway and elevating cell proliferation during postconfluent mitosis stage. Altogether, we demonstrate that MPAPO plays a crucial role in ADSCs adipogenesis, providing experimental basis and data for exploring therapeutic options in tissue defect repair.

Targeting VIP and PACAP Receptor Signaling: New Insights into Designing Drugs for the PACAP Subfamily of Receptors

Pituitary Adenylate Cyclase-Activating Peptide (PACAP) and Vasoactive Intestinal Peptide (VIP) are neuropeptides involved in a diverse array of physiological and pathological processes through activating the PACAP subfamily of class B1 G protein-coupled receptors (GPCRs): VIP receptor 1 (VPAC1R), VIP receptor 2 (VPAC2R), and PACAP type I receptor (PAC1R). VIP and PACAP share nearly 70% amino acid sequence identity, while their receptors PAC1R, VPAC1R, and VPAC2R share 60% homology in the transmembrane regions of the receptor. PACAP binds with high affinity to all three receptors, while VIP binds with high affinity to VPAC1R and VPAC2R, and has a thousand-fold lower affinity for PAC1R compared to PACAP. Due to the wide distribution of VIP and PACAP receptors in the body, potential therapeutic applications of drugs targeting these receptors, as well as expected undesired side effects, are numerous. Designing selective therapeutics targeting these receptors remains challenging due to their structural similarities. This review discusses recent discoveries on the molecular mechanisms involved in the selectivity and signaling of the PACAP subfamily of receptors, and future considerations for therapeutic targeting.

The PACAP/PAC1 Receptor System and Feeding

Pituitary adenylyl cyclase activating polypeptide (PACAP) belongs to the vasoactive intestinal polypeptide (VIP)/secretin/glucagon superfamily. PACAP is present in two forms (PACAP-38 and PACAP-27) and binds to three guanine-regulatory (G) protein-coupled receptors (PAC1, VPAC1, and VPAC2). PACAP is expressed in the central and peripheral nervous systems, with high PACAP levels found in the hypothalamus, a brain region involved in feeding and energy homeostasis. PAC1 receptors are high-affinity and PACAP-selective receptors, while VPAC1 and VPAC2 receptors show a comparable affinity to PACAP and VIP. PACAP and its receptors are expressed in the central and peripheral nervous systems with moderate to high expression in the hypothalamus, amygdala, and other limbic structures. Consistent with their expression, PACAP is involved in several physiological responses and pathological states. A growing body of literature suggests that PACAP regulates food intake in laboratory animals. However, there is no comprehensive review of the literature on this topic. Thus, the purpose of this article is to review the literature regarding the role of PACAP and its receptors in food intake regulation and to synthesize how PACAP exerts its anorexic effects in different brain regions. To achieve this goal, we searched PubMed and reviewed 68 articles regarding the regulatory action of PACAP on food intake. Here, we present the literature regarding the effect of exogenous PACAP on feeding and the role of endogenous PACAP in this process. We also provide evidence regarding the effect of PACAP on the homeostatic and hedonic aspects of food intake, the neuroanatomical sites where PACAP exerts its regulatory action, which PACAP receptors may be involved, and the role of various signaling pathways and neurotransmitters in hypophagic effects of PACAP.

Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) in Physiological and Pathological Processes within the Gastrointestinal Tract: A Review

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide widely distributed in the central nervous system (CNS) and many peripheral organs, such as the digestive tract, endocrine, reproductive and respiratory systems, where it plays different regulatory functions and exerts a cytoprotective effect. The multifarious physiological effects of PACAP are mediated through binding to different G protein-coupled receptors, including PAC1 (PAC1-R), VPAC1 (VPAC1-R) and VPAC2 (VPAC2-R) receptors. In the gastrointestinal (GI) tract, PACAP plays an important regulatory function. PACAP stimulates the secretion of digestive juices and hormone release, regulates smooth muscle contraction, local blood flow, cell migration and proliferation. Additionally, there are many reports confirming the involvement of PACAP in pathological processes within the GI tract, including inflammatory states, neuronal injury, diabetes, intoxication and neoplastic processes. The purpose of this review is to summarize the distribution and pleiotropic action of PACAP in the control of GI tract function and its cytoprotective effect in the course of GI tract disorders.

Adaptive Changes in the Central Control of Energy Homeostasis Occur in Response to Variations in Energy Status

Energy homeostasis is regulated in coordinate fashion by the brain-gut axis, the homeostatic energy balance circuitry in the hypothalamus and the hedonic energy balance circuitry comprising the mesolimbcortical A10 dopamine pathway. Collectively, these systems convey and integrate information regarding nutrient status and the rewarding properties of ingested food, and formulate it into a behavioral response that attempts to balance fluctuations in consumption and food-seeking behavior. In this review we start with a functional overview of the homeostatic and hedonic energy balance circuitries; identifying the salient neural, hormonal and humoral components involved. We then delve into how the function of these circuits differs in males and females. Finally, we turn our attention to the ever-emerging roles of nociceptin/orphanin FQ (N/OFQ) and pituitary adenylate cyclase-activating polypeptide (PACAP)-two neuropeptides that have garnered increased recognition for their regulatory impact in energy homeostasis-to further probe how the imposed regulation of energy balance circuitry by these peptides is affected by sex and altered under positive (e.g., obesity) and negative (e.g., fasting) energy balance states. It is hoped that this work will impart a newfound appreciation for the intricate regulatory processes that govern energy homeostasis, as well as how recent insights into the N/OFQ and PACAP systems can be leveraged in the treatment of conditions ranging from obesity to anorexia.

Pituitary adenylate cyclase-activating peptide: Potential roles in the pathophysiology and complications of cirrhosis

Pituitary adenylate cyclase-activating peptide (PACAP) is a ubiquitous neuropeptide with diverse functions throughout the organism. Most abundantly investigated for its role in several neurological disorders as well as in circadian rhythms, other fields of medicine, including cardiology, have recently shown interest in the role of PACAP and its potential as a biomarker. Timely diagnosis and treatment of cirrhosis and its complications is a considerable challenge for health services world-wide and development of new areas of research is warranted. Direct and indirect evidence exists of PACAP involvement in the cascade of pathological events and processes ultimately leading to cirrhosis and its complications, but its exact role remains to be determined. Studies have documented PACAP involvement in immune function, metabolism, local vasoconstriction and dilatation and systemic vascular decompensation and there is ongoing research of a possible role in liver reperfusion injury. Considering these reports, PACAP could theoretically exude influence on the disease course of cirrhosis through the hypothalamus-pituitary-adrenal axis, chronic inflammation, fibrogenesis, vasodilation and reduced vascular resistance. The paucity of literature on the specific topic of PACAP and cirrhosis reflects complex mechanisms and difficulty in accurate measurements and sample taking. This does not detract from the need to further characterize and elucidate the role PACAP plays in the underdiagnosed and undertreated condition of cirrhosis.

High-Fat Diet Augments VPAC1 Receptor-Mediated PACAP Action on the Liver, Inducing LAR Expression and Insulin Resistance

Pituitary adenylate cyclase-activating polypeptide (PACAP) acts on multiple processes of glucose and energy metabolism. PACAP potentiates insulin action in adipocytes and insulin release from pancreatic β-cells, thereby enhancing glucose tolerance. Contrary to these effects at organ levels, PACAP null mice exhibit hypersensitivity to insulin. However, this apparent discrepancy remains to be solved. We aimed to clarify the mechanism underlying the antidiabetic phenotype of PACAP null mice. Feeding with high-fat diet (HFD) impaired insulin sensitivity and glucose tolerance in wild type mice, whereas these changes were prevented in PACAP null mice. HFD also impaired insulin-induced Akt phosphorylation in the liver in wild type mice, but not in PACAP null mice. Using GeneFishing method, HFD increased the leukocyte common antigen-related (LAR) protein tyrosine phosphatase in the liver in wild type mice. Silencing of LAR restored the insulin signaling in the liver of HFD mice. Moreover, the increased LAR expression by HFD was prevented in PACAP null mice. HFD increased the expression of VPAC1 receptor (VPAC1-R), one of three PACAP receptors, in the liver of wild type mice. These data indicate that PACAP-VPAC1-R signaling induces LAR expression and insulin resistance in the liver of HFD mice. Antagonism of VPAC1-R may prevent progression of HFD-induced insulin resistance in the liver, providing a novel antidiabetic strategy.

Effects of PACAP on oxidative stress-induced cell death in rat kidney and human hepatocyte cells

Oxidative stress plays an important role in various renal and hepatic pathologies, and reduction of oxidative stress-induced processes is an important protective strategy in tissues of diverse origins against harmful stimuli. Pituitary adenylate cyclase activating polypeptide (PACAP) is a well-known cytotrophic and cytoprotective peptide. PACAP promotes cell survival in numerous cells and tissues exposed to various stimuli. Protective effects of PACAP have been shown in the kidney, but it is not known whether PACAP is protective against oxidative stress in renal cells. Little is known about the effects of PACAP in the liver. The aim of the present study was to investigate whether PACAP is protective against oxidative stress in primary rat kidney cell culture and whether PACAP has any effect on cell survival in human WRL-68 hepatocytes and HEP-G2 hepatocellular carcinoma cells subjected to oxidative stress. Cells were exposed to various concentrations of H(2)O(2) with or without PACAP co-treatment and cell viability was evaluated with the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide test (MTT). We found that oxidative stress induced a significant decrease in cell viability in both cell lines. PACAP could dose-dependently increase the percentage of living cells in kidney cells, but it failed to do so in hepatocytes. Given the survival-promoting effects of PACAP against oxidative stress in rat kidney, we conducted a further experiment to determine whether PACAP influences the markers of oxidative stress in vivo. We have proven earlier that PACAP was effective in kidney ischemia/reperfusion injury in vivo. In the present study, we determined the levels of the oxidative stress marker malondialdehyde and the activity of the scavenger molecules glutathione (GSH) and superoxide dismutase (SOD) following kidney ischemia/reperfusion in rats. We found that PACAP significantly increased the level of GSH and counteracted the marked reduction of SOD activity after ischemia/reperfusion in vivo. In summary, the present study showed that while PACAP was able to significantly increase the cell survival in primary kidney cell cultures exposed to oxidative stress, possibly involving interaction with the endogenous scavenger system, it failed to influence the viability of normal or cancerous hepatocytes.

The role of PACAP in central cardiorespiratory regulation

Pituitary adenylate cyclase activating polypeptide (PACAP) plays a role in almost every biological process from reproduction to hippocampal function. One area where a role for PACAP is not clearly delineated is central cardiorespiratory regulation. PACAP and its receptors (PAC1, VPAC1 and VPAC2) are present in cardiovascular areas of the ventral medulla and spinal cord and in the periphery. Central administration of PACAP generally increases arterial pressure. Knowledge about the role of PACAP in central cardiovascular regulation is growing, but even less is known about PACAP in central respiratory regulation. No specific data is currently available regarding the presence of PACAP or receptors in key respiratory centers, although it is known that neonatal PACAP knock-out mice die suddenly in a manner similar to sudden infant death syndrome (SIDS). Future studies in mature preparations investigating the role of PACAP in the physiology and integration of central cardiorespiratory reflexes are clearly essential for a full understanding of this important neuropeptide in breathing.

Distribution and molecular evolution of the neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) and its receptors in the lizard Podarcis sicula (Squamata, Lacertidae)

The presence of the pituitary adenylate cyclase-activating polypeptide (PACAP) and its receptors PAC(1), VPAC(1), and VPAC(2) was studied in the lizard Podarcis sicula gastrointestinal and respiratory tissues. The expression and distribution of this neuropeptide was investigated using RT-PCR, immunohistochemistry, and in situ hybridization techniques. RT-PCR showed that several tissues of this reptile synthesize an mRNA encoding for PACAP. Performing in situ hybridization and immunohistochemistry, we found a wide distribution of PACAP and its mRNA in intestine, stomach, liver, and lung. PACAP receptors possess a specific distribution in both gastrointestinal and respiratory system. Further, we analyzed the conservation of PACAP amino acid sequence demonstrating that this peptide in the lizard is very similar to that of other vertebrates. Our findings suggest that also in reptiles an effective PACAP system is present and that it could be implicated in some essential physiological functions as a result of its high conservation amongst vertebrates.

Intein-mediated rapid purification of recombinant maxadilan and M65 and their acute effects on plasma glucose

Maxadilan is a potent vasodilatory peptide present in the salivary glands of the sand fly. Maxadilan and M65, a deletion variation of maxadilan, are agonist- and antagonist-specific for the PAC1 receptor. In order to obtain the recombinant maxadilan and M65 efficiently by intein-mediated single column purification, the genes encoding maxadilan and M65 were designed, synthesized and cloned into Escherichia coli expression vector pKYB. The recombinant maxadilan and M65 with homogeneity over 95% were released from the chitin-bound intein tag by beta-mercaptoethanol. Intraperitoneal injection of the recombinant maxadilan caused an acute elevation of plasma glucose, imitating pituitary adenylate cyclase-activating polypeptide (PACAP) 27, in NIH mice, while the VPAC1-agonist and VPAC2-agonist had no significant effects on the levels of plasma glucose. M65 alone had no effect on the plasma glucose, but blocked the glucose excursion caused by maxadilan by 12.7% and blocked the glucose excursion caused by the PACAP 27 by 11.6%. The acute effects of the recombinant maxadilan and M65 on the plasma glucose indicated that they had the characteristics as the agonist and antagonist for PAC1.

Long-term administration of maxadilan improves glucose tolerance and insulin sensitivity in mice

Maxadilan and its truncated variant, M65, are agonist and antagonist specific, respectively, for the PAC1 receptor. PAC1 is the specific receptor for the pituitary adenylate cyclase-activating peptide (PACAP), which is not shared by vasoactive intestinal peptide (VIP). PACAP is a ubiquitous peptide of the glucagon superfamily that is involved in glucose homeostasis and regulation of insulin secretion. This study employed the recombinant maxadilan and M65 to evaluate the PAC1 receptor-mediated effects on energy metabolism using NIH mice. First, the acute effect of maxadilan-induced hyperglycemia was blocked by M65. In long-term studies, NIH mice were given daily intraperitoneal injections with maxadilan, M65, or vehicle for 21 days. Maxadilan suppressed feeding and enhanced water intake significantly for the first several days. After that period, maxadilan treatment continued to promote food and water intake. Long-term administration of maxadilan led to an increase in body weight (P<0.01), decrease in body fat (P<0.01), down-regulation of basal plasma glucose (P<0.01), upregulation of basal plasma insulin (P<0.01) and improved glucose tolerance (P<0.01) and insulin sensitivity (P<0.01). An elevation in plasma LDL (P<0.01) was also observed in the maxadilan group. However, M65 displayed no significant adverse effects on the aforementioned parameters except basal plasma glucose (P<0.05). The significant changes induced by maxadilan indicate that the PAC1 receptor plays multiple key roles in carbohydrate metabolism, lipid metabolism and energy homeostasis in mice.

Role of VIP and PACAP in islet function

Vasoactive intestinal polypeptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) are two closely related neuropeptides that are expressed in islets and in islet parasympathetic nerves. Both peptides bind to their common G-protein-coupled receptors, VPAC1 and VPAC2, and PACAP, in addition to the specific receptor PAC1, all three of which are expressed in islets. VIP and PACAP stimulate insulin secretion in a glucose-dependent manner and they both also stimulate glucagon secretion. This action is achieved through increased formation of cAMP after activation of adenylate cyclase and stimulation of extracellular calcium uptake. Deletion of PAC1 receptors or VPAC2 receptors results in glucose intolerance. These peptides may be of importance in mediating prandial insulin secretion and the glucagon response to hypoglycemia. Animal studies have also suggested that activation of the receptors, in particular VPAC2 receptors, may be used as a therapeutic approach for the treatment of type 2 diabetes. This review summarizes the current knowledge of the potential role of VIP and PACAP in islet function.

A novel recombinant, VPAC2-selective agonist enhancing insulin release and glucose disposal

AIM

To obtain the recombinant, VPAC2-selective ( VPAC2: type 3 receptor of pituitary adenylate cyclase activating polypeptide which shared by vasoactive intestinal peptide) agonist with effects on glucose disposal by intein-mediated, single column purification.

METHODS

A gene encoding 32-amino acid peptide named rMBAY was designed and synthesized and cloned into Escherichia coli expression vector, pKYB (NEB, USA). The recombinant vector was transferred into E coli ER2566 strain and the target protein was overexpressed as a fusion to the N-terminus of a self-cleavable affinity tag. After the fusion protein was purified by chitin-affinity chromatography, the self-cleavage activity of the intein was induced by beta-mercaptoethanol and the target peptide, rMBAY, was released from the chitin-bound intein tag.

RESULTS

Approximately 53 mg rMBAY with the purity over 95% was obtained by single column purification from 1 L induced culture fermented in 5 L fermenter. The results of the competitive binding assay and cAMP accumulation assay indicated that the recombinant rMBAY had special binding selectivity and potency for VPAC2. The recombinant peptide, rMBAY, enhanced insulin release and decreased the plasma glucose level after intraperitoneal injection (50 ng/kg) with a high concentration of glucose (1.8 mmol/kg) in the NIH mice.

CONCLUSION

An efficient production procedure of a recombinant VPAC2-selective agonist with corresponding effects on glucose disposal was established.

Engineering novel VPAC2-selective agonists with improved stability and glucose-lowering activity in vivo

A previously described VPAC2-selective agonist, BAY 55-9837 (peptide HSDAVFTDNYTRLRKQVAAKKYLQSIKNKRY), had several limitations with respect to its potential as an insulin secretagogue for the treatment of type 2 diabetes. These limitations were primarily poor stability in aqueous buffer and short duration of action in vivo. In this report, we describe a series of novel analogs of BAY 55-9837 that were designed around the likely degradation mechanisms and structure-activity relationship of this peptide with a view to overcoming its limitations. These analogs were tested for improved liquid stability and retention of VPAC2-selective binding and activation, as well as prolonged activity in vivo. Although several degradation mechanisms were possible based on the degradation pattern, it was determined that deamidation at the two asparagines (N9 and N28) was the major instability determinant. Changing these two asparagines to glutamines did not negatively affect VPAC2-selective binding and activation. The double glutamine mutein analog, BAY(Q9Q28), retained full VPAC2 activity and selectivity while displaying no significant degradation when stored at 40 degrees C for 4 weeks. This is in contrast to BAY 55-9837, which showed greater than 80% degradation when stored at 40 degrees C for 2 weeks. A cysteine was added to the C terminus of BAY(Q9Q28), followed by site-specific cysteine conjugation with a 22- or 43-kDa polyethylene glycol (PEG) to yield BAY(Q9Q28C32)PEG22 or BAY(Q9Q28C32)PEG43, respectively. These PEGylated peptides retain the ability to selectively bind and activate the VPAC2 receptor and have prolonged glucose-lowering activity in vivo.

Long-term administration of PACAP receptor antagonist, PACAP(6-27), impairs glucose tolerance and insulin sensitivity in obese diabetic ob/ob mice

Pituitary adenylate cyclase-activating peptide (PACAP) is a ubiquitous peptide of the glucagon superfamily that is involved in glucose homeostasis and regulation of insulin secretion. This study employed the PACAP receptor antagonist, PACAP(6-27) to evaluate the role of endogenous PACAP in genetic obesity-related diabetes and related metabolic abnormalities using ob/ob mice. Acute in vivo antagonistic potency of PACAP(6-27) was confirmed in ob/ob mice by blockade of the insulin-releasing action but not hyperglycaemia. In longer-term studies, ob/ob mice were given once daily injections of PACAP(6-27) or vehicle for 14 days. Feeding activity, body weight, basal plasma glucose and plasma insulin concentrations were not significantly affected by chronic PACAP(6-27) treatment. However, PACAP(6-27) treatment impaired glucose tolerance, insulin sensitivity and the glycaemic response to feeding. Plasma glucagon and lipids were unchanged. These observations indicate a role of endogenous PACAP for normal glucose homeostasis, but indicate a minor involvement in the regulation of insulin secretion in ob/ob mice.

Intein-mediated rapid purification and characterization of a novel recombinant agonist for VPAC2

In order to obtain the recombinant VPAC2 agonist efficiently by intein-mediated single column purification, a gene encoding 32-amino acids peptide was designed, synthesized and cloned into Escherichia coli expression vector pKYB. The recombinant vector pKY-ROM was transferred into E. coli ER2566 cells and the target protein was over-expressed as a fusion to the N-terminus of a self-cleavable affinity tag. After the rMROM-intein-CBD fusion protein was purified by chitin-affinity chromatography, the self-cleavage activity of the intein was induced by beta-mercaptoethanol and the rMROM with the homogeneity over 95% was released from the chitin-bound intein tag. The recombinant linear rMROM competitively displaced [125I] PACAP38 on VPAC2 with a half-maximal inhibitory concentration (IC50) of 60 +/- 5 nM, whereas the IC50 of rMROM at human VPAC1 was observed up to 10 microM and no binding was detected at PAC1. rMROM stimulated the cAMP accumulation in Chinese hamster ovary (CHO) cells expressing the human VPAC2 with a half-maximal stimulatory concentration (EC50) of 0.6 nM, which was 500-fold less potent at VPAC1and had no activity on PAC1. An efficient production procedure of a novel recombinant VPAC2-selective agonist was established.

Pituitary adenylate cyclase-activating peptide (PACAP): assessment of dipeptidyl peptidase IV degradation, insulin-releasing activity and antidiabetic potential

Pituitary adenylate cyclase-activating peptide (PACAP) is a member of the glucagon family of peptides. Like other members, most notably glucagon-like peptide-1 (GLP-1), PACAP is rapidly degraded by dipeptidylpeptidase IV (DPP IV). This study investigated how degradation by DPP IV affected the insulinotropic activity of PACAP, and whether PACAP exerted acute antihyperglycemic properties in normal or ob/ob mice. DPP IV degradation of PACAP(1-27) over 18 h led to the formation of PACAP(3-27), PACAP(5-27) and ultimately PACAP(6-27). In contrast to 1.4-1.8-fold concentration-dependent stimulation of insulin secretion by PACAP(1-27), these peptide fragments lacked insulinotropic activity. While PACAP(1-27) and PACAP(1-38) generated significant insulin responses when given alone or together with glucose in ob/ob and normal mice, they also elevated plasma glucose. These actions were eliminated following degradation of the peptide by incubation with DPP IV. The hyperglycemic effects may be explained at least partly by a potent glucagon-releasing action in ob/ob and normal mice. In conclusion, PACAP is inactivated by DPP IV and despite insulin-releasing effects, its actions on glucagon secretion and glucose homeostasis do not make it a good therapeutic tool for the treatment of type 2 diabetes.

PACAP deficient mice display reduced carbohydrate intake and PACAP activates NPY-containing neurons in the rat hypothalamic arcuate nucleus

Pituitary adenylate cyclase-activating polypeptide (PACAP) potentiates both insulin release from islets and insulin action in adipocytes. Therefore, this peptide is considered a regulator of glucose homeostasis. PACAP and its receptors are localized not only in the peripheral tissues but in the central nervous system. The present study examined whether PACAP regulates the feeding behavior and the activity of neurons in the hypothalamic arcuate nucleus (ARC), a feeding center. Food intake was measured in the PACAP knock-out mice. Cytosolic Ca2+ concentration ([Ca2+]i) in single neurons isolated from the ARC of rats was measured by fura-2 microfluorometry, followed by immunocytochemical staining with anti-NPY antiserum. PACAP knock-out mice showed a decrease in the intake of high carbohydrate, but not high fat, food. PACAP increased [Ca2+]i in NPY neurons of the ARC that are implicated in the feeding, particularly the carbohydrate ingestion. Agonists of PACAP receptors, PAC1-R and VPAC2-R, also increased [Ca2+]i. The present study, by demonstrating that PACAP directly reacts with the ARC NPY neurons to increase [Ca2+]i and that ingestion of the carbohydrate-rich food is reduced in PACAP-deficiency, suggests a facilitative role for PACAP in the carbohydrate intake.

[Physiological and therapeutic roles of PACAP in glucose metabolism and diabetes]

Pituitary adenylate cyclase activating polypeptide (PACAP) is a ubiquitous neuropeptide in the central and peripheral nervous systems. Previously we reported that PACAP38 is localized in pancreatic islets and serves as an endogenous amplifier of glucose-induced insulin secretion. PACAP activates Gs-cAMP system, stimulates voltage-dependent Ca(2+) channels, and increases cytosolic Ca(2+) concentration in beta-cells. On the other hand, PAC1 receptor is expressed in adipocytes. PACAP enhances insulin-stimulated glucose uptake in an adipocyte cell-line, 3T3-L1 cells. PACAP does not alter the tyrosine phosphorylation of insulin receptor and IRS-1, but increases the activity of PI-3 kinase, a distal site of insulin signaling. PACAP also promotes differentiation of 3T3-L1 cells from fibroblasts to adipocytes. In GK rats, an animal model of type 2 diabetes, daily i.p. injection of PACAP38 (6 pmol/kg) from the age of 3 weeks prevents development of hyperglycemia between 3 to 8 weeks. These results demonstrate that PACAP enhances glucose-stimulated insulin secretion in islets, enhances insulin action inadipocytes, and prevents hyperglycemia in diabetic animals. This finding presents a possible therapeutic use of PACAP in the treatment of diabetes.

Dual effects of pituitary adenylate cyclase-activating polypeptide and isoproterenol on lipid metabolism and signaling in primary rat adipocytes

Pituitary adenylate cyclase-activating peptide (PACAP) is a neuropeptide that exerts its effects throughout the body by elevating the intracellular amounts of cAMP. In adipocytes, an increased amount of cAMP is associated with increased lipolysis. In this work we evaluated the effects of PACAP38 on triglyceride metabolism in primary rat adipocytes. Stimulation of adipocytes with PACAP (0.1-100 nm) resulted in stimulation of lipolysis to the same extent as isoproterenol. Lipolysis was blocked by 25 microm of the protein kinase A inhibitor H-89 and potentiated in the presence of 10 microm OPC3911, a phosphodiesterase 3 inhibitor. In addition, PACAP38 induced activation of protein kinase A. Insulin efficiently inhibited PACAP38-induced lipolysis in a phosphatidyl inositol 3-kinase and phosphodiesterase 3-dependent manner. Interestingly, we also found that PACAP38, as well as isoproterenol, induced potentiation of lipogenesis in the presence of insulin. These results show that PACAP38 and isoproterenol mediate catabolic as well as anabolic effects in adipocytes, depending on the concentration of insulin present. We speculate that in the early postprandial state and during fasting, when insulin levels are low, PACAP and beta-adrenergic catecholamines induce lipolysis, whereas when higher levels of insulin are present, these agents potentiate the anabolic effect of insulin, i.e. storage of triglycerides.

Overexpression of PACAP in transgenic mouse pancreatic beta-cells enhances insulin secretion and ameliorates streptozotocin-induced diabetes

Pituitary adenylate cyclase-activating polypeptide (PACAP), a member of the vasoactive intestinal peptide/secretin/glucagon family, stimulates insulin secretion from islets in a glucose-dependent manner at femtomolar concentrations. To assess PACAP's pancreatic function in vivo, we generated transgenic mice overexpressing PACAP in the pancreas under the control of human insulin promoter. Northern blot and immunohistochemical analyses showed that PACAP is overexpressed in pancreatic islets, specifically in transgenic mice. Plasma glucose and glucagon levels during a glucose tolerance test were not different between PACAP transgenic mice and nontransgenic littermates. However, plasma insulin levels in transgenic mice were higher after glucose loading. Also, increases of streptozotocin-induced plasma glucose were attenuated in transgenic compared with nontransgenic mice. Notably, an increase in 5-bromo-2-deoxyuridine-positive beta-cells in the streptozotocin-treated transgenic mice was observed but without differences in the staining patterns by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling. Morphometric analysis revealed that total islet mass tends to increase in 12-month-old transgenic mice but showed no difference between 12-week-old transgenic and nontransgenic littermates. This is the first time that PACAP has been observed to play an important role in the proliferation of beta-cells.

Expression and fine mapping of murine vasoactive intestinal peptide receptor 1

Vasoactive intestinal peptide (VIP) plays multiple roles in the nervous, endocrine, and immune systems as a neurotransmitter, a hormone, and a cytokine. VIP is widely distributed in neurons of the central and peripheral nervous systems (CNS/PNS), and recently has been found to be an important neuroprotective agent. VIP actions are mediated through specific G protein-coupled receptors. We have cloned the cDNA of VIP receptor subtype 1 (VIPR1 or VPAC1) and have demonstrated the quantitative expression profile in mice. Fluorometric real-time reverse transcription-polymerase chain reaction (RT-PCR) analysis demonstrated that VPAC1 is expressed in all tissues examined. Expression was highest in the small intestine and colon followed by the liver and brain. The high level of VPAC1 expression in forebrain and cerebellum suggests that VPAC1 may mediate the neuroprotective effect of VIP. We have refined the chromosomal localization of the mouse, rat, and human VPAC1 genes. This fine mapping of the VPAC1 gene extends the respective regions of synteny between the distal region of mouse chromosome 9, rat chromosome 8q32, and human chromosome 3p21.33-p21.31. Thus, VPAC, constitutes a functional-positional candidate for the tumor-suppressor function mapped to human 3p22-p21 where loss-of-heterozygosity is observed in small-cell lung carcinoma (SCLC) cell lines and primary tumors. Availability of the cDNA sequences for mouse VPAC1 will facilitate the generation of VPAC1 null mutant animals. Such studies will ultimately enhance our understanding of the role of VIP in the nervous system.

A potent and highly selective VPAC2 agonist enhances glucose-induced insulin release and glucose disposal: a potential therapy for type 2 diabetes

Pituitary adenylate cyclase-activating peptide (PACAP) and vasoactive intestinal peptide (VIP) activate two shared receptors, VPAC1 and VPAC2. Activation of VPAC1 has been implicated in elevating glucose output, whereas activation of VPAC2 may be involved in insulin secretion. A hypothesis that a VPAC2-selective agonist would enhance glucose disposal by stimulating insulin secretion without causing increased hepatic glucose production was tested using a novel selective agonist of VPAC2. This agonist, BAY 55-9837, was generated through site-directed mutagenesis based on sequence alignments of PACAP, VIP, and related analogs. The peptide bound to VPAC2 with a dissociation constant (K(d)) of 0.65 nmol/l and displayed >100-fold selectivity over VPAC1. BAY 55-9837 stimulated glucose-dependent insulin secretion in isolated rat and human pancreatic islets, increased insulin synthesis in purified rat islets, and caused a dose-dependent increase in plasma insulin levels in fasted rats, with a half-maximal stimulatory concentration of 3 pmol/kg. Continuous intravenous or subcutaneous infusion of the peptide reduced the glucose area under the curve following an intraperitoneal glucose tolerance test. The peptide had effects on intestinal water retention and mean arterial blood pressure in rats, but only at much higher doses. BAY 55-9837 may be a useful therapy for the treatment of type 2 diabetes.

Expression and fine mapping of murine vasoactive intestinal peptide receptor 1

Vasoactive intestinal peptide (VIP) plays multiple roles in the nervous, endocrine, and immune systems as a neurotransmitter, a hormone, and a cytokine. VIP is widely distributed in neurons of the central and peripheral nervous systems (CNS/PNS), and recently has been found to be an important neuroprotective agent. VIP actions are mediated through specific G protein-coupled receptors. We have cloned the cDNA of VIP receptor subtype 1 (VIPR1 or VPAC1) and have demonstrated the quantitative expression profile in mice. Fluorometric real-time reverse transcription-polymerase chain reaction (RT-PCR) analysis demonstrated that VPAC1 is expressed in all tissues examined. Expression was highest in the small intestine and colon followed by the liver and brain. The high level of VPAC1 expression in forebrain and cerebellum suggests that VPAC1 may mediate the neuroprotective effect of VIP. We have refined the chromosomal localization of the mouse, rat, and human VPAC1 genes. This fine mapping of the VPAC1 gene extends the respective regions of synteny between the distal region of mouse chromosome 9, rat chromosome 8q32, and human chromosome 3p21.33-p21.31. Thus, VPAC, constitutes a functional-positional candidate for the tumor-suppressor function mapped to human 3p22-p21 where loss-of-heterozygosity is observed in small-cell lung carcinoma (SCLC) cell lines and primary tumors. Availability of the cDNA sequences for mouse VPAC1 will facilitate the generation of VPAC1 null mutant animals. Such studies will ultimately enhance our understanding of the role of VIP in the nervous system.

The neuropeptide pituitary adenylate cyclase-activating polypeptide and islet function

The neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) is ubiquitously distributed in both the central and peripheral nervous systems and exerts a variety of effects. PACAP is a neuropeptide in pancreatic islets, where it has been suggested as a parasympathetic and sensory neurotransmitter. PACAP stimulates insulin secretion in a glucose-dependent manner, by an effect executed mainly through augmenting the formation of cAMP and stimulating the uptake of calcium. Accumulating evidence in animal studies points to a physiological importance of PACAP in the regulation of the insulin response to feeding. This review summarizes the current knowledge of islet actions and mechanisms and the function of PACAP.

The effects of PACAP on insulin secretion and glucose disposal are altered by adrenalectomy in mice

We previously showed that pituitary adenylate cyclase-activating polypeptide (PACAP) potently stimulates insulin secretion in vivo in mice without altering glucose disposal. Such a combination of results would be explained if epinephrine released by PACAP counteracts the action of insulin and, therefore, that the glucose disposal after PACAP administration is altered by adrenalectomy. In the study reported in this paper, we examined the influence of PACAP27 (1.3 nmol/kg i.v.) on insulin secretion and glucose disposal during an intravenous glucose (1 g/kg) tolerance test in mice subjected to bilateral adrenalectomy 48 h prior to the tolerance test. We found that in control mice, PACAP potentiated glucose-stimulated insulin secretion threefold without affecting glucose disposal. Adrenalectomy potentiated the augmentation by PACAP27 of glucose-stimulated insulin secretion, and in adrenalectomized mice, PACAP27 simultaneously augmented glucose disposal (elimination rate 2.30 +/- 0.07%/min vs. 2.56 +/- 0.05%/min; p = 0.011). Furthermore, PACAP27 augmented glucose elimination stimulated by i.v. insulin administration only in adrenalectomized, but not in control mice. We, therefore, conclude that under in vivo conditions, epinephrine released by PACAP from the adrenals prevents the marked insulinotropic action of the peptide from augmenting glucose disposal.

PAC1 receptor-deficient mice display impaired insulinotropic response to glucose and reduced glucose tolerance

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a ubiquitous neuropeptide of the vasoactive intestinal peptide (VIP) family that potentiates glucose-stimulated insulin secretion. Pancreatic beta cells express two PACAP receptor subtypes, a PACAP-preferring (PAC1) and a VIP-shared (VPAC2) receptor. We have applied a gene targeting approach to create a mouse lacking the PAC1 receptor (PAC1(-/-)). These mice were viable and normoglycemic, but exhibited a slight feeding hyperinsulinemia. In vitro, in the isolated perfused pancreas, the insulin secretory response to PACAP was reduced by 50% in PAC1(-/-) mice, whereas the response to VIP was unaffected. In vivo, the insulinotropic action of PACAP was also acutely reduced, and the peptide induced impairment of glucose tolerance after an intravenous glucose injection. This demonstrates that PAC1 receptor is involved in the insulinotropic action of the peptide. Moreover, PAC1(-/-) mice exhibited reduced glucose-stimulated insulin secretion in vitro and in vivo, showing that the PAC1 receptor is required to maintain normal insulin secretory responsiveness to glucose. The defective insulinotropic action of glucose was associated with marked glucose intolerance after both intravenous and gastric glucose administration. Thus, these results are consistent with a physiological role for the PAC1 receptor in glucose homeostasis, notably during food intake.

Biological relevance of pituitary adenylate cyclase-activating polypeptide (PACAP) in the gastrointestinal tract

Since its initial discovery in 1989, pituitary adenylate cyclase activating peptide (PACAP) has been noted to distribute widely in the brain, the respiratory and the gastrointestinal system. It occurs in two bioactive molecules, PACAP-27 and the C-terminally extended PACAP-38, which evoke activity by binding to three distinct types of high-affinity, G-protein coupled membrane receptors. It is present throughout the entirety of the gut but is rare in certain areas such as the intestinal mucosa and islets of Langerhans. PACAP-induced biological effects are protean and include alterations of motility in the bowel and the gallbladder, stimulation of gastric acid and intestinal secretion, hormone/enzyme release from the exocrine and endocrine pancreas, and the induction as well as inhibition of proliferation in neuroendocrine cells and tumors. Its hepatic activity has to date not been elucidated in detail. One of the interesting features of PACAP is the species and organ dependent variation of its biological effects. Of particular note is its superior potency when compared with other neuropeptides identified in the gut, and the involvement of a number of different second messenger systems upon PACAP receptor activation.

PACAP stimulates insulin secretion but inhibits insulin sensitivity in mice

Although pituitary adenylate cyclase-activating polypeptide (PACAP) stimulates insulin secretion, its net influence on glucose homeostasis in vivo has not been established. We therefore examined the action of PACAP-27 and PACAP-38 on insulin secretion, insulin sensitivity, and glucose disposal as derived from the minimal model of glucose disappearance during an intravenous glucose tolerance test in anesthetized mice. PACAP-27 and PACAP-38 markedly and equipotently potentiated glucose-stimulated insulin secretion, with a half-maximal effect at 33 pmol/kg. After PACAP-27 or PACAP-38 (1.3 nmol/kg), the acute (1-5 min) insulin response was 3.8 +/- 0.4 nmol/l (PACAP-27) and 3.3 +/- 0.3 nmol/l (PACAP-38), respectively, vs. 1.4 +/- 0.1 nmol/l after glucose alone (P < 0.001), and the total area under the curve for insulin (AUCinsulin) was potentiated by 60% (P < 0.001). In contrast, PACAP-27 and PACAP-38 reduced the insulin sensitivity index (SI) [0.23 +/- 0.04 10(-4) min-1/(pmol/l) for PACAP-27 and 0.29 +/- 0.06 10(-4) min-1/(pmol/l) for PACAP-38 vs. 0.46 +/- 0.02 10(-4) min-1/(pmol/l) for controls (P < 0.01)]. Furthermore, PACAP-27 or PACAP-38 did not affect glucose elimination determined as glucose half-time or the glucose elimination rate after glucose injection or the area under the curve for glucose. Moreover, glucose effectiveness and the global disposition index (AUCinsulin times SI) were not affected by PACAP-27 or PACAP-38. Finally, when given together with glucose, PACAP-27 did not alter plasma glucagon or norepinephrine levels but significantly increased plasma epinephrine levels. We conclude that PACAP, besides its marked stimulation of insulin secretion, also inhibits insulin sensitivity in mice, the latter possibly explained by increased epinephrine. This complex action explains why the peptide does not enhance glucose disposal.

PACAP-38 causes phospholipase C-dependent calcium signaling in rat acinar cell line

BACKGROUND

Pituitary adenylate cyclase activating peptide (PACAP-38), a neuropeptide of the vasoactive intestinal peptide/secretin family, localizes to intrapancreatic neurons and stimulates exocrine secretion from the pancreas. PACAP-38 stimulates calcium signaling in the rat pancreatic cell line AR42J. The purpose of this study was to elucidate the mechanisms of PACAP-evoked calcium signaling in these cells.

METHODS

Continuous measurements of intracellular calcium were taken by fluorescent digital microscopy with the dye fura-2. Mechanisms of PACAP-38-evoked calcium signals were determined by a panel of inhibitors. Inositol phosphates production in response to PACAP-38 was measured. The ability of PACAP-38 to stimulate amylase release was used to determine a relevant dose range for these studies.

RESULTS

We have shown that (1) AR42J cells respond to PACAP-38 with biphasic increases in [Ca2+]i in a dose-dependent fashion; (2) PACAP-38 acts through phospholipase C to release inositol triphosphate (IP3)-sensitive Ca2+ stores with (3) a subsequent influx of extracellular Ca2+.

CONCLUSIONS

PACAP-38 activates calcium signaling through phospholipase C at concentrations that stimulate amylase release in AR42J cells.

Genomic organization of the rat pituitary adenylate cyclase-activating polypeptide receptor gene. Alternative splicing within the 5'-untranslated region

Pituitary adenylate cyclase-activating polypeptide (PACAP) elicits its diverse biological actions by interacting with both PACAP-selective type I PACAP receptors (PACAPRs) and type II PACAPRs that do not distinguish between PACAP and vasoactive intestinal polypeptide. Using long distance polymerase chain reaction, we amplified and characterized the entire coding region of the rat type I PACAPR (rPACAPR) gene, which spans 40 kilobases and contains 15 exons. Mapping of the exons and sequencing of all intron-exon boundaries revealed a structural organization of the rPACAPR gene that is very similar to those encoding other members of the calcitonin/secretin/parathyroid hormone receptor family. Southern blot analysis demonstrated a single copy of the rPACAPR gene. A combination of rapid amplification of cDNA ends and reverse transcriptase polymerase chain reaction revealed an unexpected diversity in the rPACAPR mRNA in the 5'-untranslated (5'-UTR) region. Four rPACAPR cDNAs were identified with 5'-UTR sequences that all diverged from the genomic sequence at a site 76 bp upstream of the ATG start codon, where a consensus 3' slice acceptor sequence was located. Sequence analysis of these amplified transcripts demonstrated that they arise by tissue-specific differential usage of four exons in the 5' noncoding region of the rPACAPR gene. This study is the first to elucidate the structural organization of a PACAPR gene and to demonstrate that alternative splicing generates rPACAPR transcripts with unique 5'-UTRs.

Pituitary adenylate cyclase-activating polypeptide induces expression of corticosteroid-binding globulin in cultured fetal hepatocytes: synergy with tri-iodothyronine

The purpose of the present study was to determine whether functional receptors for pituitary adenylate cyclase-activating polypeptide (PACAP) are expressed in cultured rat fetal hepatocytes and eventually play a role in regulating gene expression of corticosteroid-binding globulin (CBG). We found PACAP38 and PACAP27 to elevate cAMP levels in hepatocytes in a dose-dependent manner, with a plateau being achieved at 10 nM and EC50 values of about 0.5-1 nM. PACAP failed to alter the turnover of inositol phosphates, whereas PACAP and VIP stimulated cAMP accumulation in an equipotent manner, suggesting the presence in these cells of type II receptor isoforms. As revealed by measurements of both CBG mRNA levels and concentrations of binding sites, long-term treatment of fetal cells with 10 nM PACAP, although resulting in partial desensitization of peptide-induced cAMP accumulation, caused a significant 3-fold elevation in CBG synthesis. This stimulatory influence of PACAP was mimicked by the cell permeant N6,2'-O-dibutyryladenosine 3',5'-phosphate (dbcAMP). Treatment of hepatocytes with tri-iodothyronine (T3) enhanced CBG expression and, most interestingly, appeared to synergize with PACAP to elicit a 2-3-fold amplification of CBG synthesis. This study thus provides first evidence for the up-regulation by PACAP and cAMP of CBG expression in fetal hepatocytes and for T3's playing a synergistic role in enhancing PACAP-induced synthesis of the binder.