Insulinotropin PACAP potentiates insulin-stimulated glucose uptake in 3T3 L1 cells

Pharmacological modulation of ventral tegmental area neurons elicits changes in trigeminovascular sensory processing and is accompanied by glycemic changes: Implications for migraine

BACKGROUND

Imaging migraine premonitory studies show increased midbrain activation consistent with the ventral tegmental area, an area involved in pain modulation and hedonic feeding. We investigated ventral tegmental area pharmacological modulation effects on trigeminovascular processing and consequent glycemic levels, which could be involved in appetite changes in susceptible migraine patients.

METHODS

Serotonin and pituitary adenylate cyclase-activating polypeptide receptors immunohistochemistry was performed in ventral tegmental area parabrachial pigmented nucleus of male Sprague Dawley rats. In vivo trigeminocervical complex neuronal responses to dura mater nociceptive electrical stimulation, and facial mechanical stimulation of the ophthalmic dermatome were recorded. Changes in trigeminocervical complex responses following ventral tegmental area parabrachial pigmented nucleus microinjection of glutamate, bicuculline, naratriptan, pituitary adenylate cyclase-activating polypeptide-38 and quinpirole were measured, and blood glucose levels assessed pre- and post-microinjection.

RESULTS

Glutamatergic stimulation of ventral tegmental area parabrachial pigmented nucleus neurons reduced nociceptive and spontaneous trigeminocervical complex neuronal firing. Naratriptan, pituitary adenylate cyclase-activating polypeptide-38 and quinpirole inhibited trigeminovascular spontaneous activity, and trigeminocervical complex neuronal responses to dural-evoked electrical and mechanical noxious stimulation. Trigeminovascular sensory processing through modulation of the ventral tegmental area parabrachial pigmented nucleus resulted in reduced circulating glucose levels.

CONCLUSION

Pharmacological modulation of ventral tegmental area parabrachial pigmented nucleus neurons elicits changes in trigeminovascular sensory processing. The interplay between ventral tegmental area parabrachial pigmented nucleus activity and the sensory processing by the trigeminovascular system may be relevant to understand associated sensory and homeostatic symptoms in susceptible migraine patients.

Was it something I ate? Understanding the bidirectional interaction of migraine and appetite neural circuits

Migraine attacks can involve changes of appetite: while fasting or skipping meals are often reported triggers in susceptible individuals, hunger or food craving are reported in the premonitory phase. Over the last decade, there has been a growing interest and recognition of the importance of studying these overlapping fields of neuroscience, which has led to novel findings. The data suggest additional studies are needed to unravel key neurobiological mechanisms underlying the bidirectional interaction between migraine and appetite. Herein, we review information about the metabolic migraine phenotype and explore migraine therapeutic targets that have a strong input on appetite neuronal circuits, including the calcitonin gene-related peptide (CGRP), the pituitary adenylate cyclase-activating polypeptide (PACAP) and the orexins. Furthermore, we focus on potential therapeutic peptide targets that are involved in regulation of feeding and play a role in migraine pathophysiology, such as neuropeptide Y, insulin, glucagon and leptin. We then examine the orexigenic - anorexigenic circuit feedback loop and explore glucose metabolism disturbances. Additionally, it is proposed a different perspective on the most reported feeding-related trigger - skipping meals - as well as a link between contrasting feeding behaviors (skipping meals vs food craving). Our review aims to increase awareness of migraine through the lens of appetite neurobiology in order to improve our understanding of the earlier phase of migraine, encourage better studies and cross-disciplinary collaborations, and provide novel migraine-specific therapeutic opportunities.

Melanotan II, a melanocortin agonist, partially rescues the impaired thermogenic capacity of pituitary adenylate cyclase-activating polypeptide deficient mice

NEW FINDINGS

What is the central question of this study? Can chronic treatment of pituitary adenylate cyclase-activating polypeptide (PACAP) deficient mice with the melanocortin agonist melanotan II during cold acclimation rescue the impaired thermogenic capacity previously observed in PACAP deficient mice? What is the main finding and its importance? Using a genetic model of PACAP deficiency, this study provides evidence that PACAP acts upstream of the melanocortin system in regulating sympathetic nerve activity to brown adipose tissue in mice.

ABSTRACT

Impaired adipose tissue function in obesity, including reduced thermogenic potential, has detrimental consequences for metabolic health. Hormonal regulation of adaptive thermogenesis is being explored as a potential therapeutic target for human obesity. Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide expressed in nuclei of the hypothalamus known to regulate energy expenditure, and functional studies reveal a role for PACAP in the central regulation of thermogenesis, although mechanisms are not well understood. We hypothesized that PACAP acts upstream of the melanocortin system to regulate sympathetic nerve activity to stimulate thermogenesis. To assess this, female PACAP^-/- and PACAP^+/+ mice were given daily peripheral injections of a melanocortin receptor agonist, melanotan II (MTII), for 3 weeks during cold acclimation, and the effect of MTII on thermogenic capacity and adipose tissue remodelling was examined by physiological and histological analyses. MTII partially rescued the impaired thermogenic capacity in PACAP^-/- mice as compared to PACAP^+/+ mice as determined by measuring noradrenaline-induced metabolic rate. In addition, MTII treatment during cold acclimation corrected the previously identified deficit in lipid utilization in response to adrenergic stimulation in PACAP^-/- null mice, suggesting impaired lipid mobilization may contribute to the impaired thermogenic capacity of PACAP^-/- mice. Results presented here provide physiological evidence to suggest that PACAP acts upstream of melanocortin receptors to facilitate sympathetically induced mechanisms of adaptive thermogenesis in response to cold acclimation.

A compendium of G-protein-coupled receptors and cyclic nucleotide regulation of adipose tissue metabolism and energy expenditure

With the ever-increasing burden of obesity and Type 2 diabetes, it is generally acknowledged that there remains a need for developing new therapeutics. One potential mechanism to combat obesity is to raise energy expenditure via increasing the amount of uncoupled respiration from the mitochondria-rich brown and beige adipocytes. With the recent appreciation of thermogenic adipocytes in humans, much effort is being made to elucidate the signaling pathways that regulate the browning of adipose tissue. In this review, we focus on the ligand-receptor signaling pathways that influence the cyclic nucleotides, cAMP and cGMP, in adipocytes. We chose to focus on G-protein-coupled receptor (GPCR), guanylyl cyclase and phosphodiesterase regulation of adipocytes because they are the targets of a large proportion of all currently available therapeutics. Furthermore, there is a large overlap in their signaling pathways, as signaling events that raise cAMP or cGMP generally increase adipocyte lipolysis and cause changes that are commonly referred to as browning: increasing mitochondrial biogenesis, uncoupling protein 1 (UCP1) expression and respiration.

Adipose Tissue Expression of PACAP, VIP, and Their Receptors in Response to Cold Stress

Obesity arises from disrupted energy balance and is caused by chronically higher energy intake compared to expenditure via basal metabolic rate, exercise, and thermogenesis. The brown adipose tissue (BAT), the primary thermogenic organ, has received considerable attention as a potential therapeutic target due to its ability to burn lipids in the production of heat. Pituitary adenylate cyclase-activating polypeptide (PACAP) has been identified as a key regulator of the physiological stress response both centrally and peripherally. While PACAP has been shown to increase thermogenesis by acting at the hypothalamus to increase sympathetic output to BAT, a peripheral role for PACAP-activated thermogenesis has not been studied. We identified PACAP receptor (PAC1, VPAC1/2) expression for the first time in murine BAT and confirmed their expression in white adipose tissues. PAC1 receptor expression was significantly altered in all three adipose tissues studied in response to 3.5-week cold acclimation, with expression patterns differing by depot type. In primary cell culture, VPAC1 was increased in differentiated compared to non-differentiated brown adipocytes, and the same trend was observed for the PACAP-specific receptor PAC1 in gonadal white fat primary cultures. The primary PAC1R mRNA splice variant in interscapular BAT was determined as isoform 2 by RNA-Seq. These results show that PACAP receptors are present in adipose tissues and may have important functional roles in adipocyte differentiation, lipid metabolism, or adipose sensitization to sympathetic signaling in response to thermogenic stimuli.

Emerging roles of endoplasmic reticulum-resident selenoproteins in the regulation of cellular stress responses and the implications for metabolic disease

Chronic metabolic stress leads to cellular dysfunction, characterized by excessive reactive oxygen species, endoplasmic reticulum (ER) stress and inflammation, which has been implicated in the pathogenesis of obesity, type 2 diabetes and cardiovascular disease. The ER is gaining recognition as a key organelle in integrating cellular stress responses. ER homeostasis is tightly regulated by a complex antioxidant system, which includes the seven ER-resident selenoproteins - 15 kDa selenoprotein, type 2 iodothyronine deiodinase and selenoproteins S, N, K, M and T. Here, the findings from biochemical, cell-based and mouse studies investigating the function of ER-resident selenoproteins are reviewed. Human experimental and genetic studies are drawn upon to highlight the relevance of these selenoproteins to the pathogenesis of metabolic disease. ER-resident selenoproteins have discrete roles in the regulation of oxidative, ER and inflammatory stress responses, as well as intracellular calcium homeostasis. To date, only two of these ER-resident selenoproteins, selenoproteins S and N have been implicated in human disease. Nonetheless, the potential of all seven ER-resident selenoproteins to ameliorate metabolic dysfunction warrants further investigation.

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.

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).

Neuropeptide Y impairs insulin-stimulated translocation of glucose transporter 4 in 3T3-L1 adipocytes through the Y1 receptor

Neuropeptide Y (NPY) is expressed in adipose tissue and is involved in adipocyte metabolism. Although NPY impacts on glucose utilization in vivo, the underlying cellular mechanism is yet to be fully elucidated. In this study we investigated the effect of NPY on the insulin-stimulated translocation of glucose transporter 4 (GLUT4) from intracellular stores to the cell surface in vitro. Using cellular fractionation and immunofluorescence we analyzed the cellular localization and content of GLUT4 in 3T3-L1 adipocytes. Additionally we investigated the effect of NPY on insulin action in adipocyte cultures by assessing the phosphorylation of Akt and [(3)H]-deoxyglucose uptake. Our data suggest that in 3T3-L1 adipocytes NPY inhibits insulin-stimulated glucose uptake in a GLUT4-dependent manner. The insulin induced translocation of GLUT4 was attenuated by the Y1 receptor agonist [Phe(7),Pro(34)] pNPY, demonstrating an essential role of the Y1 receptor in GLUT4 translocation. Additionally, we observed an NPY dose-dependent impairment of Akt phosphorylation. This study provides evidence that NPY impairs the insulin sensitivity of adipocytes and suggests that the Y1 receptor could be a potential therapeutic target for type 2 diabetes.

Immunolocalization of neurotransmitter-synthesizing enzymes and neuropeptides with associated receptors in the photophores of the hatchetfish, Argyropelecus hemigymnus Cocco, 1829

Anatomical and functional studies of the autonomic innervation of the photophores of luminescent fishes are scarce. The present immunohistochemical study demonstrated the presence of nerve fibers in the luminous epithelium and lens epithelium of the photophores of the hatchet fish, Argyropelecus hemigymnus and identified the immunoreactive elements of this innervation. Phenylethanolanine N-methyltransferase (PNMT) and catecholamine (CA)-synthesizing enzymes were detected in nerve varicosities inside the two epithelia. Neuropeptides were localized in neuropeptide Y (NPY) and substance P (SP)- and its NK11 receptor-immunopositive nerves in the lens epithelium. Neuropeptides were also localized in non-neural cell types such as the lens cells, which displayed immunoreactivities for pituitary adenylate cyclase activating peptide (PACAP) and their receptors R-12 and 93093-3. This reflects the ability of the neuropeptide-containing nerves and lens cells to turn on and off the expression of selected messengers. It appears that the neuropeptide-containing nerves demonstrated in this study may be sensory. Furthermore, neuronal nitric oxide synthase-immunopositive axons associated with photocytes in the luminous epithelium have previously been described in this species. Whereas it is clear that the photophores receive efferent (motor) fibers of spinal sympathetic origin, the origin of the neuropeptide sensory innervation remains to be determined. The functional roles of the above neuropeptides or their effects on the bioluminescence or the chemical nature of the terminals, either sensory or postganglionic neurons innervating the photophores, are still not known.

Effects of cultural medium and conditions on the proliferation and hypoglycemic activity of Saccharomyces pastorianus no. 54

A yeast strain of Saccharomyces pastorianus no. 54 with hypoglycemic activity was isolated from soils of a winery. The aims of this study were first to investigate the effects of the cultivation conditions on proliferation and hypoglycemic activity of this yeast using the assay model of the differentiated 3T3-L1 adipocytes, and then, to confirm in vivo the hypoglycemic activity of cultured yeast by oral administration in streptozotocin (STZ)-induced diabetic mice. Among 7 diluted fruit juice samples the diluted strawberry juice (1.74 g/L reducing sugar content) was chosen as the basal medium. After investigation of the effects of addition of various substances, including 1% of 5 different sugars and glycerol, 0.1% of 6 nitrogen-containing substances, and 1 ppm of 7 growth factors, the diluted strawberry juice added with 1% glucose, 0.1% yeast extract and 1 ppm aspartic acid was optimized at 20 °C with initial pH value of 6.0 for cultivating S. pastorianus no. 54 in flask. The scale-up system of a 5-L fermentor was further established by using the same medium with initial pH 6.0 and being incubated at 20 °C with an aeration rate of 1.2 vvm for 96 h. The hypoglycemic activity of yeast cells cultivated in fermentor was 3.11 times of that in flask. Oral administration of the cultured yeast at a dosage of 130 mg/kg body weight/day for 6 days could significantly reduce the plasma glucose content in STZ-induced diabetic mice and keep their body weights in the normal range.

Receptors for NPY and PACAP differ in expression and activity during adipogenesis in the murine 3T3-L1 fibroblast cell line

BACKGROUND AND PURPOSE

Neuropeptides are involved in the regulation of food intake in the central nervous system, but they might also act on peripheral fat tissue via neuropeptide receptors.

EXPERIMENTAL APPROACH

We investigated the receptor expression and activity of pituitary adenylate cyclase-activating polypeptide (PACAP) and of neuropeptide Y at the mRNA and protein levels in the 3T3-L1 fibroblast line during differentiation into adipocytes. Intracellular calcium concentration was measured by calcium imaging.

KEY RESULTS

The PACAP receptors PAC(1) and VPAC(2) as well as the neuropeptide Y(1) receptor were expressed at the mRNA level in fibroblasts, pre-adipocytes and adipocytes. The mRNA profile of the PAC(1) receptor isoforms showed the HOP sequence, whereas the HIP-isoform was present in subconfluent 3T3-L1 fibroblasts only. At the protein level, the mature 3T3-L1 adipocytes produced the PAC(1) and Y(1) receptors; only the PAC(1) receptor showed carbohydrate residues. Both neuropeptides induced an increase of intracellular calcium in mature adipocytes, which was absent in the precursor cells. These changes in calcium were mediated by Y(1) and PAC(1) receptors as demonstrated by the effects of specific receptor agonists and antagonists.

CONCLUSIONS AND IMPLICATIONS

As the PAC(1)-HOP receptor variant seems to be responsible for PACAP-mediated calcium influx in many cell types, the HOP sequence might also mediate the increase in intracellular calcium in adipocytes. Because a high intracellular calcium level is associated with lipogenesis, peptidergic innervation of adipose tissue might be involved in stress-induced obesity.

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.

Effects of statins on the adipocyte maturation and expression of glucose transporter 4 (SLC2A4): implications in glycaemic control

AIMS/HYPOTHESIS

Hyperlipidaemia often occurs in patients with type 2 diabetes mellitus. Though HMG-CoA reductase inhibitors (statins) are widely used for controlling hypercholesterolemia, atorvastatin has also been reported to have an adverse effect on glucose metabolism. Based on these findings, the aim of this study was to investigate the effects of statins on adipocytes, which play pivotal roles in glucose metabolism.

METHODS

In 3T3-L1 cells, effects of statins on adipocyte maturation were determined morphologically. Protein and mRNA levels of SLC2A4 and adipocyte marker proteins were determined by immunoblotting and RT-PCR, respectively. Type 2 diabetic NSY mice were treated with atorvastatin for 15 weeks, followed by glucose and insulin tolerance tests and examination of SLC2A4 expression in white adipose tissue (WAT). Seventy-eight Japanese subjects with type 2 diabetes and hypercholesterolaemia were treated with atorvastatin (10 mg/day), and its effects on lipid and glycaemic profiles were measured 12 weeks after treatment initiation.

RESULTS

Treatment with atorvastatin inhibited adipocyte maturation, SLC2A4 and C/EBPalpha expressions and insulin action in 3T3-L1 cells. Atorvastatin also attenuated SLC2A4 and C/EBPalpha expressions in differentiated 3T3-L1 adipocytes. These effects were reversed by L. mevalonate or geranylgeranyl pyrophosphate. In NSY mice, atorvastatin accelerated glucose intolerance as a result of insulin resistance and decreased SLC2A4 expression in WAT. In addition to improving hyperlipidaemia, atorvastatin treatment significantly increased HbA(1c) but not fasting glucose levels in diabetic patients, and this effect was greater in the non-obese subgroup.

CONCLUSIONS/INTERPRETATION

These results demonstrate that atorvastatin attenuates adipocyte maturation and SLC2A4 expression by inhibiting isoprenoid biosynthesis, and impairs glucose tolerance. These actions of atorvastatin could potentially affect the control of type 2 diabetes.

Postulated vasoactive neuropeptide autoimmunity in fatigue-related conditions: a brief review and hypothesis

Disorders such as chronic fatigue syndrome (CFS) and gulf war syndrome (GWS) are characterised by prolonged fatigue and a range of debilitating symptoms of pain, intellectual and emotional impairment, chemical sensitivities and immunological dysfunction. Sudden infant death syndrome (SIDS) surprisingly may have certain features in common with these conditions. Post-infection sequelae may be possible contributing factors although ongoing infection is unproven. Immunological aberration may prove to be associated with certain vasoactive neuropeptides (VN) in the context of molecular mimicry, inappropriate immunological memory and autoimmunity. Adenylate cyclase-activating VNs including pituitary adenylate cyclase-activating polypeptide (PACAP), vasoactive intestinal peptide (VIP) and calcitonin gene-related peptide (CGRP) act as hormones, neurotransmitters, neuroregulators, immune modulators and neurotrophic substances. They and their receptors are potentially immunogenic. VNs are widely distributed in the body particularly in the central and peripheral nervous systems and have been identified in the gut, adrenal gland, blood cells, reproductive system, lung, heart and other tissues. They have a vital role in maintaining cardio-respiratory function, thermoregulation, memory, concentration and executive functions such as emotional responses including social cues and appropriate behaviour. They are co-transmitters for a number of neurotransmitters including acetylcholine and gaseous transmitters, are potent immune regulators with primarily anti-inflammatory activity, and have a significant role in protection of the nervous system against toxic assault as well as being important in the maintenance of homeostasis. This paper describes a biologically plausible mechanism for the development of certain fatigue-related syndromes based on loss of immunological tolerance to these VNs or their receptors following infection, other events or de novo resulting in significant pathophysiology possibly mediated via CpG fragments and heat shock (stress) proteins. These conditions extend the public health context of autoimmunity and VN dysregulation and have implications for military medicine where radiological, biological and chemical agents may have a role in pathogenesis. Possible treatment and prevention options are considered.

Cytosolic Ca2+ responses to sub-picomolar and nanomolar PACAP in pancreatic beta-cells are mediated by VPAC2 and PAC1 receptors

Pituitary adenylate cyclase-activating polypeptide (PACAP) potentiates glucose-induced insulin release and increases cytosolic Ca2+ concentration ([Ca2+]i) in islet beta-cells in a concentration-dependent manner with two peaks at 10(-13) and 10(-9) M. PAC1 receptor (PAC1-R) and VPAC2 receptor (VPAC2-R) are expressed in pancreatic beta-cells and thought to be involved in insulin release. We aimed to determine the receptor types involved in the [Ca2+]i responses to 10(-13) and 10(-9) M PACAP. We measured [Ca2+]i in beta-cells and examined comparative effects of PAC1-R-selective agonist maxadilan, its antagonist M65, VPAC2-R-selective agonist Ro25-1553, and native ligands of PACAP and VIP. In the presence of 8.3 mM glucose, maxadilan, Ro25-1553, PACAP, and VIP at 10(-13) and 10(-9) M all increased [Ca2+]i. PACAP and maxadilan elicited greater effects at 10(-9) M than at 10(-13) M both in the incidence and amplitude of [Ca2+]i responses. For VIP and Ro25-1553, in contrast, the effects at 10(-9) and 10(-13) M were comparable. Furthermore, the amplitude of [Ca2+]i responses to 10(-9) M PACAP, but not 10(-13) M PACAP, was suppressed by M65. The results suggest that VPAC2-R and PAC1-R contribute equally to [Ca2+]i responses to sub-picomolar concentrations of PACAP, while PAC1-R has greater contribution to [Ca2+]i responses to nanomolar concentrations of this peptide.

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.

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.

Overexpression of pituitary adenylate cyclase-activating polypeptide in islets inhibits hyperinsulinemia and islet hyperplasia in agouti yellow mice

Pituitary adenylate cyclase-activating polypeptide (PACAP) is an intraislet neuropeptide and shares insulinotropic and insulin-sensitizing properties with glucagon-like peptide-1 (GLP-1); however, the pathophysiological significance of PACAP in diabetes remains largely unknown. To assess this, we crossed our recently developed transgenic mice overexpressing PACAP in pancreatic beta-cells (Tg/+), with lethal yellow agouti (KKA(y)) mice (A(y)/+), a genetic model for obesity-diabetes, and examined the metabolic and morphological phenotypes of F(1) animals. Tg/+ mice with the A(y) allele (Tg/+:A(y)/+) developed maturity-onset obesity and diabetes associated with hyperglycemia, hyperlipidemia, and hyperphagia, similar to those of A(y)/+ mice, but hyperinsulinemia was significantly ameliorated in Tg/+:A(y)/+ mice. Although A(y)/+ mice exhibited a marked increase in islet mass resulting from hyperplasia and hypertrophy, this increase was significantly attenuated in Tg/+:A(y)/+ mice. Size frequency distribution analysis revealed that the very large islets comprising one-fourth of islets of A(y)/+ mice were selectively reduced in Tg/+:A(y)/+ mice. Because functional defects have been demonstrated in the large islets of obese animal models, together these findings suggest that PACAP regulates hyperinsulinemia and the abnormal increase in islet mass that occurs during the diabetic process.

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.

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.

Intraperitoneal PACAP administration decreases blood glucose in GK rats, and in normal and high fat diet mice

PACAP is an islet peptide that serves as an endogenous amplifier of glucose induced insulin secretion. Furthermore, we has recently found that PACAP also potentiates insulin stimulated glucose uptake in adipocytes. Therefore, an antidiabetic action of PACAP is possible. In the present study, we examined the effect of PACAP treatment of the hyperglycemia in GK rats, an animal model of type 2 diabetes, and in high fat fed C47BL/6J mice, an animal model for glucose intolerance. GK rats housed with normal diet exhibited a normal level of blood glucose until three weeks old but significant hyperglycemia at eight weeks. When GK rats were treated with daily PACAP38 (i.p. injection, 6 pmol/kg) from age three weeks, development of hyperglycemia was prevented. In high fat fed mice, i.p. administration of PACAP27 for five (25 nmol/kg twice daily) reduced plasma glucose levels to 6.9 +/- 0.2 mmol/l compared to 8.1 +/- 0.2 mmol/l in saline injected animals (p < 0.001) without altering baseline insulin levels. We conclude that PACAP reduces circulating glucose in animal models of type 2 diabetes and glucose intolerance. The mechanism of this action needs to be established.

Insulinotropin PACAP potentiates insulin action. Stimulation of glucose uptake in 3T3-LI adipocytes

PAC1 receptor was expressed in the rat fat tissue and 3T3-L1 adipocytes. PACAP-38 (10 nM) significantly enhanced insulin induced 2-deoxyglucose uptake by 3T3-L1 adipocytes. GLP-1 has a similar effect. PACAP-38 further increased insulin stimulated phosphatidylinositol (PI) 3-kinase activity, but has not effect on tyrosine phosphorylation of insulin receptor beta-subunit or IRS-1. These results reveal that PACAP-38 enhances insulin induced glucose uptake, an effect probably mediated by PI 3-kinase. In conclusion, PACAP potentiates not only insulin secretion but also insulin action in adipocytes, thereby exhibiting antidiabetic actions at two important steps of glucose metabolism (Fig. 2).

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.