Neuropeptide Y is expressed in subpopulations of insulin- and non-insulin-producing islet cells in the rat after dexamethasone treatment: a combined immunocytochemical and in situ hybridisation study

Regulation of Pancreatic β-Cell Function by the NPY System

The neuropeptide Y (NPY) system has been recognized as one of the most critical molecules in the regulation of energy homeostasis and glucose metabolism. Abnormal levels of NPY have been shown to contribute to the development of metabolic disorders including obesity, cardiovascular diseases, and diabetes. NPY centrally promotes feeding and reduces energy expenditure, while the other family members, peptide YY (PYY) and pancreatic polypeptide (PP), mediate satiety. New evidence has uncovered additional functions for these peptides that go beyond energy expenditure and appetite regulation, indicating a more extensive function in controlling other physiological functions. In this review, we will discuss the role of the NPY system in the regulation of pancreatic β-cell function and its therapeutic implications for diabetes.

Neuropeptide Y expression marks partially differentiated β cells in mice and humans

β Cells are formed in embryonic life by differentiation of endocrine progenitors and expand by replication during neonatal life, followed by transition into functional maturity. In this study, we addressed the potential contribution of neuropeptide Y (NPY) in pancreatic β cell development and maturation. We show that NPY expression is restricted from the progenitor populations during pancreatic development and marks functionally immature β cells in fetal and neonatal mice and humans. NPY expression is epigenetically downregulated in β cells upon maturation. Neonatal β cells that express NPY are more replicative, and knockdown of NPY expression in neonatal mouse islets reduces replication and enhances insulin secretion in response to high glucose. These data show that NPY expression likely promotes replication and contributes to impaired glucose responsiveness in neonatal β cells. We show that NPY expression reemerges in β cells in mice fed with high-fat diet as well as in diabetes in mice and humans, establishing a potential new mechanism to explain impaired β cell maturity in diabetes. Together, these studies highlight the contribution of NPY in the regulation of β cell differentiation and have potential applications for β cell supplementation for diabetes therapy.

Influence of neuropeptide Y and pancreatic polypeptide on islet function and beta-cell survival

BACKGROUND

In the present study we assessed the impact of neuropeptide Y receptor (NPYR) modulators, neuropeptide Y (NPY) and pancreatic polypeptide (PP), on islet function and beta-cell survival.

METHODS

The effects of NPY and PP on beta-cell function were examined in BRIN BD11 and 1.1B4 beta-cells, as well as isolated mouse islets. Involvement of both peptides in pancreatic islet adaptations to streptozotocin and hydrocortisone, as well as effects on beta-cell proliferation and apoptosis was also evaluated.

RESULTS

Neither NPY nor PP affected in vivo glucose disposal or insulin secretion in mice. However, both peptides inhibited (p<0.05 to p<0.001) glucose stimulated insulin secretion from rat and human beta-cells. NPY exerted similar insulinostatic effects in isolated mouse islets. NPY and PP inhibited alanine-induced changes in BRIN BD11 cell membrane potential and (Ca²⁺)_i. Streptozotocin treatment decreased and hydrocortisone treatment increased beta-cell mass in mice. In addition, streptozotocin, but not hydrocortisone, increased PP cell area. Streptozotocin also shifted the normal co-localisation of NPY with PP, towards more pronounced co-expression with somatostatin in delta-cells. Both streptozotocin and hydrocortisone increased pancreatic exocrine expression of NPY. More detailed in vitro investigations revealed that NPY, but not PP, augmented (p<0.01) BRIN BD11 beta-cell proliferation. In addition, both peptides exerted protective effects against streptozotocin-induced DNA damage in beta-cells.

CONCLUSION

These data emphasise the involvement of PP, and particularly NPY, in the regulation of beta-cell mass and function.

GENERAL SIGNIFICANCE

Modulation of PP and NPY signalling is suitable for further evaluation and possible clinical development for the treatment of diabetes.

CART is overexpressed in human type 2 diabetic islets and inhibits glucagon secretion and increases insulin secretion

AIMS/HYPOTHESIS

Insufficient insulin release and hyperglucagonaemia are culprits in type 2 diabetes. Cocaine- and amphetamine-regulated transcript (CART, encoded by Cartpt) affects islet hormone secretion and beta cell survival in vitro in rats, and Cart (-/-) mice have diminished insulin secretion. We aimed to test if CART is differentially regulated in human type 2 diabetic islets and if CART affects insulin and glucagon secretion in vitro in humans and in vivo in mice.

METHODS

CART expression was assessed in human type 2 diabetic and non-diabetic control pancreases and rodent models of diabetes. Insulin and glucagon secretion was examined in isolated islets and in vivo in mice. Ca(2+) oscillation patterns and exocytosis were studied in mouse islets.

RESULTS

We report an important role of CART in human islet function and glucose homeostasis in mice. CART was found to be expressed in human alpha and beta cells and in a subpopulation of mouse beta cells. Notably, CART expression was several fold higher in islets of type 2 diabetic humans and rodents. CART increased insulin secretion in vivo in mice and in human and mouse islets. Furthermore, CART increased beta cell exocytosis, altered the glucose-induced Ca(2+) signalling pattern in mouse islets from fast to slow oscillations and improved synchronisation of the oscillations between different islet regions. Finally, CART reduced glucagon secretion in human and mouse islets, as well as in vivo in mice via diminished alpha cell exocytosis.

CONCLUSIONS/INTERPRETATION

We conclude that CART is a regulator of glucose homeostasis and could play an important role in the pathophysiology of type 2 diabetes. Based on the ability of CART to increase insulin secretion and reduce glucagon secretion, CART-based agents could be a therapeutic modality in type 2 diabetes.

Neurotransmitters and Neuropeptides: New Players in the Control of Islet of Langerhans' Cell Mass and Function

Islets of Langerhans control whole body glucose homeostasis, as they respond, releasing hormones, to changes in nutrient concentrations in the blood stream. The regulation of hormone secretion has been the focus of attention for a long time because it is related to many metabolic disorders, including diabetes mellitus. Endocrine cells of the islet use a sophisticate system of endocrine, paracrine and autocrine signals to synchronize their activities. These signals provide a fast and accurate control not only for hormone release but also for cell differentiation and survival, key aspects in islet physiology and pathology. Among the different categories of paracrine/autocrine signals, this review highlights the role of neurotransmitters and neuropeptides. In a manner similar to neurons, endocrine cells synthesize, accumulate, release neurotransmitters in the islet milieu, and possess receptors able to decode these signals. In this review, we provide a comprehensive description of neurotransmitter/neuropetide signaling pathways present within the islet. Then, we focus on evidence supporting the concept that neurotransmitters/neuropeptides and their receptors are interesting new targets to preserve β-cell function and mass. A greater understanding of how this network of signals works in physiological and pathological conditions would advance our knowledge of islet biology and physiology and uncover potentially new areas of pharmacological intervention. J. Cell. Physiol. 231: 756-767, 2016. © 2015 Wiley Periodicals, Inc.

Pancreatic islet neuropeptide Y overexpression has minimal effect on islet morphology and β-cell adaptation to high-fat diet

Neuropeptide Y (NPY) is highly expressed in the hypothalamus, where it regulates feeding and energy homeostasis. Interestingly, NPY and its receptors are also expressed in peripheral tissues with roles in metabolism, including pancreatic islets. In islets, NPY is known to suppress insulin secretion acutely. In addition, the role of NPY in β-cell de-differentiation has been postulated recently. Therefore, we studied transgenic mice expressing NPY under rat insulin promoter (TG) to determine the effects of chronic up-regulation of NPY on islet morphology and function. NPY levels were 25 times higher in islets of TG mice compared with wild-type (WT) littermates, whereas no differences in NPY expression were noted in the brains of TG and WT mice. Islet NPY secretion was 2.3-fold higher in TG compared with WT mice. There were no significant changes in body weight, glucose tolerance, or insulin sensitivity in TG mice fed regular rodent diet or high-fat diet (HF). Islet β-cell area was comparable between TG and WT mice both on regular rodent and HF diets, indicating that NPY overexpression is insufficient to alter β-cell maturation or the compensatory increase of β-cell area on HF. One abnormality noted was that the glucose-stimulated insulin secretion in islets isolated from TG was reduced compared with those from WT mice on HF diet. Overall, an increase in islet NPY level has little impact on islet function and is insufficient to affect glucose homeostasis in mice.

Differential expression and localization of neuropeptide Y peptide in pancreatic islet of diabetic and high fat fed rats

Neuropeptide Y (NPY) inhibits insulin secretion. Increased numbers of pancreatic islet cells expressing NPY have been observed in type 1 diabetic rats. To understand the functional significance of NPY expression in islet cells, we investigated the effects of high fat feeding and diabetic conditions on the expression and location of NPY expressing cells in normal and diabetic rats. Twenty rats were maintained on either normal chow (ND) or a high fat dietary regimen (HFD) for 4 weeks. In half of each group, type 1 or type 2 diabetes (groups T1DM and T2DM, respectively) was induced by injection of streptozotocin. At 8 weeks rats were euthanized and the pancreases were processed for immunofluorescence labeling (NPY/insulin, NPY/glucagon, NPY/somatostatin, and NPY/pancreatic polypeptide). Compared with the ND group, HFD rats had significantly fewer alpha cells, but beta cells were similar, while T1DM and T2DM rats showed significant increases in the proportions of alpha, delta, and PP cells. Robust increases in NPY-positive islet cells were found in the HFD, T1DM, and T2DM rats compared with ND controls. In ND rats, 99.7% of the NPY-positive cells were PP cells. However, high fat feeding and diabetes resulted in significant increases in NPY-positive delta cells, with concomitant decreases in NPY-positive PP cells. In summary, high-fat feeding and diabetes resulted in changes in the hormonal composition of pancreatic islet and increased number of NPY-expressing islet cells. Under diabetic conditions NPY expression switched from predominantly a characteristic of PP cells to predominantly that of delta cells. This may be a factor in reduced pancreatic hormone secretion during diabetes.

Neuropeptide Y and somatostatin inhibit insulin secretion through different mechanisms

Pancreatic β-cells regulate glucose homeostasis by secreting insulin in response to glucose elevation and G protein-coupled receptor (GPCR) activation. Neuropeptide Y (NPY) and somatostatin (SST) attenuate insulin secretion through G(i) activation of Y(1) and SSTR(1&5) receptors, respectively. The downstream pathways altered by NPY and SST are poorly understood. Thus, we investigated these underlying mechanisms. NPY and SST increase cellular redox potential, suggesting that their inhibitory effect may not be mediated through metabolic inhibition. NPY does not affect intracellular calcium ([Ca(2+)](i)) activity upon glucose stimulation, whereas SST alters this response. G(βγ)-subunit inhibition by gallein attenuates insulin secretion but does not alter metabolism or [Ca(2+)](i). mSIRK-induced G(βγ) activation does not modulate glucose metabolism but increases [Ca(2+)](i) activity and potentiates insulin release. Cotreatment with gallein and NPY or SST reduces insulin secretion to levels similar to that of gallein alone. mSIRK and NPY cotreatment potentiates insulin secretion similarly to mSIRK alone, whereas mSIRK and SST treatment decreases insulin release. The data support a model where SST attenuates secretion through G(βγ) inhibition of Ca(2+) activity, while NPY activates a Ca(2+)-independent pathway mediated by G(α). GPCR ligands signal through multiple pathways to inhibit insulin secretion, and determining these mechanisms could lead to novel diabetic therapies.

Pancreatic beta cells synthesize neuropeptide Y and can rapidly release peptide co-transmitters

Background

In addition to polypeptide hormones, pancreatic endocrine cells synthesize a variety of bioactive molecules including classical transmitters and neuropeptides. While these co-transmitters are thought to play a role in regulating hormone release little is known about how their secretion is regulated. Here I investigate the synthesis and release of neuropeptide Y from pancreatic beta cells.

Methodology/Principal Findings

NPY appears to be an authentic co-transmitter in neonatal, but not adult, beta cells because (1) early in mouse post-natal development, many beta cells are NPY-immunoreactive whereas no staining is observed in beta cells from NPY knockout mice; (2) GFP-expressing islet cells from an NPY(GFP) transgenic mouse are insulin-ir; (3) single cell RT-PCR experiments confirm that the NPY(GFP) cells contain insulin mRNA, a marker of beta cells. The NPY-immunoreactivity previously reported in alpha and delta cells is therefore likely to be due to the presence of NPY-related peptides. INS-1 cells, a beta cell line, are also NPY-ir and contain NPY mRNA. Using the FMRFamide tagging technique, NPY secretion was monitored from INS-1 beta cells with high temporal resolution. Peptide release was evoked by brief depolarizations and was potentiated by activators of adenylate cyclase and protein kinase A. Following a transient depolarization, NPY-containing dense core granules fused with the cell membrane and discharged their contents within a few milliseconds.

Conclusions

These results indicate that after birth, NPY expression in pancreatic islets is restricted to neonatal beta cells. The presence of NPY suggests that peptide co-transmitters could mediate rapid paracrine or autocrine signaling within the endocrine pancreas. The FMRFamide tagging technique may be useful in studying the release of other putative islet co-transmitters in real time.

Pancreatic beta cells require NeuroD to achieve and maintain functional maturity

NeuroD, a transactivator of the insulin gene, is critical for development of the endocrine pancreas, and NeuroD mutations cause MODY6 in humans. To investigate the role of NeuroD in differentiated beta cells, we generated mice in which neuroD is deleted in insulin-expressing cells. These mice exhibit severe glucose intolerance. Islets lacking NeuroD respond poorly to glucose and display a glucose metabolic profile similar to immature beta cells, featuring increased expression of glycolytic genes and LDHA, elevated basal insulin secretion and O2 consumption, and overexpression of NPY. Moreover, the mutant islets appear to have defective K(ATP) channel-mediated insulin secretion. Unexpectedly, virtually all insulin in the mutant mice is derived from ins2, whereas ins1 expression is almost extinguished. Overall, these results indicate that NeuroD is required for beta cell maturation and demonstrate the importance of NeuroD in the acquisition and maintenance of fully functional glucose-responsive beta cells.

Insulin secretion is increased in pancreatic islets of neuropeptide Y-deficient mice

Neuropeptide Y (NPY), whose role in appetite regulation is well known, is also expressed in pancreatic islets. Although previous studies indicated that application of NPY to pancreatic islets inhibits insulin secretion, its physiological role in the regulation of insulin secretion is not fully understood. We hypothesized that NPY in islets tonically suppresses insulin secretion and the reduction of islet NPY increases insulin secretion. To address the hypothesis, islet function of NPY-deficient mice was analyzed. Although there was little change in glucose homeostasis in vivo, pancreatic islets from NPY-deficient mice had higher basal insulin secretion (1.5 times), glucose-stimulated insulin secretion (1.5 times), and islet mass (1.7 times), compared with wild-type mouse. Next we sought to determine whether the expression of NPY and Y(1) receptor in islets was altered in hyperinsulinemia associated with obesity. Islets from C57BL/6J mice on a high-fat diet had 1.9 times higher basal insulin secretion and 2.4 times higher glucose-stimulated insulin secretion than control mice, indicating islet adaptation to obesity. Expression of NPY and Y(1) receptor mRNA levels was decreased by 70 and 64%, respectively, in high-fat diet islets, compared with controls. NPY and Y(1) receptor in islets were also reduced by 91 and 80%, respectively, in leptin-deficient ob/ob mice that showed marked hyperinsulinemia. Together these results suggest that endogenous NPY tonically inhibits insulin secretion from islets and a reduction of islet NPY may serve as one of the mechanisms to increase insulin secretion when islets compensate for insulin resistance associated with obesity.

A co-localization study on the ovine pancreas innervation

The expression of DbetaH and several neuropeptides was investigated in neuronal elements of the ovine pancreas using double immunocytochemical stainings. Immunoreactivities to DbetaH, NPY, VIP and SP were seen to various extents in nerve terminals associated with the acini, islets, ducts, blood vessels, interlobular connective tissue as well as in the neurons of intrapancreatic ganglia. The expression of CGRP was limited to nerve fibers lying in the connective tissue septa, amongst the acini and in close vicinity to the pancreatic blood vessels. Single GRP-positive nerve endings were located around the acini, ducts and in the interlobular connective tissue. With the exception of the ductal system in a co-localization of NPY with DbetaH was frequently found in all regions of the pancreas. Moderately numerous blood vessel-associated VIP-positive nerve fibers as well as the vast majority of VIP-containing intrapancreatic neurons were found to co-express DbetaH. Single SP-immunoreactive (IR) nerve fibers of the exocrine pancreas and interlobular connective tissue as well as SP-positive intrapancreatic neurons additionally showed the presence of DbetaH. The co-localization of VIP and NPY was found in nerve terminals located around the blood vessels and acini, in the connective tissue septa as well as in numerous pancreatic neuronal perikarya. Rare nerve terminals located between the acini and around small blood vessels as well as several neurons of intrapancreatic ganglia were VIP-IR/ SP-IR. Simultaneous expression of SP and CGRP was found in nerve fibers supplying large pancreatic arteries and veins, interlobular connective tissue and, occasionally, around the acini. Throughout the pancreas the population of CGRP-positive nerve endings showed lack of VIP and NPY. In a moderate number of GRP-containing nerve fibers, a co-expression of NPY was noted. Nerve terminals containing both GRP and VIP were detected sporadically, whereas none of the GRP-positive nerve terminals showed expression of SP. We conclude that the presented noradrenergic as well as peptidergic innervation patterns of the ovine pancreas are species-dependent. On the basis of the occurrence of DbetaH, NPY, VIP and SP (alone or in combination) in pancreatic neuronal elements we can suggest that these substances presumably act as regulators of the endocrine and/or exocrine pancreas. Involvement of CGRP and GRP in the ovine pancreas physiology seems to be of minor importance. The co-localization study indicated that the pancreas of the sheep is innervated from several sources including intrinsic as well as extrinsic ganglia.

CART regulates islet hormone secretion and is expressed in the beta-cells of type 2 diabetic rats

Cocaine- and amphetamine-regulated transcript (CART) is an anorexigenic peptide widely expressed in the central, peripheral, and enteric nervous systems. CART is also expressed in endocrine cells, including beta-cells during rat development and delta-cells of adult rats. We examined the effect of CART 55-102 on islet hormone secretion, using INS-1(832/13) cells and isolated rat islets. In addition, islet CART expression was examined in two rat models of type 2 diabetes: Goto-Kakizaki (GK) rats and dexamethasone (DEX)-treated rats. At high glucose, CART potentiated cAMP-enhanced insulin secretion via the cAMP/protein kinase A-dependent pathway. In the absence of cAMP-elevating agents, CART was without effect on INS-1 cells but modestly inhibited secretion of insulin, glucagon, and somatostatin from isolated islets. CART was markedly upregulated in the beta-cells of both diabetes models. Thus, in DEX-treated rats, islet CART mRNA expression, and the number of CART-immunoreactive beta-cells were 10-fold higher than in control rats. In GK rats, the relative number of CART-expressing beta-cells was 30-fold higher than in control rats. We conclude that CART is a regulator of islet hormone secretion and that CART is upregulated in the beta-cells of type 2 diabetic rats.

Neuropeptide Y and its receptors as potential therapeutic drug targets

Neuropeptide Y (NPY) is a 36-amino-acid peptide that exhibits a large number of physiological activities in the central and peripheral nervous systems. NPY mediates its effects through the activation of six G-protein-coupled receptor subtypes named Y(1), Y(2), Y(3), Y(4), Y(5), and y(6). Evidence suggests that NPY is involved in the pathophysiology of several disorders, such as the control of food intake, metabolic disorders, anxiety, seizures, memory, circadian rhythm, drug addiction, pain, cardiovascular diseases, rhinitis, and endothelial cell dysfunctions. The synthesis of agonists and antagonists for these receptors could be useful to treat several of these diseases.

Beta cell adaptation to dexamethasone-induced insulin resistance in rats involves increased glucose responsiveness but not glucose effectiveness

Islet beta cell adaptation to dexamethasone-induced insulin resistance was characterized with respect to glucose-stimulated insulin secretion and islet innervation. Male Sprague-Dawley rats were injected daily with dexamethasone (2 mg/kg for 12 days), which resulted in hyperinsulinemia and hyperglycemia compared with controls (which were injected with sodium chloride). Insulin secretion was characterized in collagenase-isolated islets. Islet innervation was examined by immunocytochemical analysis of tyrosine hydroxylase, neuropeptide Y (sympathetic nerves), and vasoactive intestinal polypeptide (cholinergic nerves). In islets isolated from the insulin-resistant animals, the insulin response to 3.3 or 8.3 mM glucose was three times greater during perifusion compared with controls (p < 0.001). Incubation of islets at 0 to 20 mM glucose revealed a marked leftward shift of the glucose dose-response relation after dexamethasone treatment (potency ratio, 1.78; p < 0.01), with no difference at 0 or 20 mM glucose. Thus, the potency but not the efficacy of glucose was increased. The number of islet nerves did not differ between dexamethasone-treated rats and controls. Dexamethasone-induced insulin resistance leads to adaptively increased glucose responsiveness of the islet beta cells, with increased potency, but not increased efficacy, of glucose to stimulate insulin secretion without any evidence of altered islet innervation.

Neuropeptide localization in the "migraine generator" region of the human brainstem

Evidence from animals and humans suggests that brainstem nuclei such as the raphe nuclei, the locus coeruleus (LC) and the periaqueductal grey matter (PAG), are involved in the pathophysiology of migraine. In order to understand possible neurotransmitters involved we have, by means of indirect immunocytochemistry, analysed these regions for the occurrence and distribution of calcitonin gene-related peptide (CGRP), substance P (SP), pituitary adenylate-cyclase activating peptide (PACAP) and vasoactive intestinal polypeptide (VIP). CGRP-immunoreactive (-ir) cell bodies, but no fibres, were found to occur in high numbers, constituting 80% of all nerve cell bodies in the LC. A smaller number of these nerve cell bodies (40%) in the LC proved to be PACAP-ir. The LC neurones also stored the vesicular monoamine transporter (VMAT)- and the C-terminal flanking peptide of neuropeptide Y (C-PON)-ir, illustrating their adrenergic nature. Double immunostaining revealed that all VMAT-and C-PON-containing neurones, in addition, stored CGRP. Immunoreactive cell bodies were not seen in the nucleus raphe magnus (NRM) or PAG. Numerous SP-ir nerve fibres were observed in the NRM, the LC and the PAG. Few PACAP-ir nerve fibres were detected in the PAG and few VIP-ir nerve fibres were seen in the NRM and the PAG.

Characterization of neuropeptide Y expression in the brain of a perciform fish, the sea bass (Dicentrarchus labrax)

The distribution of neuropeptide Y (NPY) gene expression was mapped in the brain of the sea bass (Dicentrarchus labrax) by in situ hybridization with 35S-UTP labeled cRNA probes. Gene expression was mainly detected within the forebrain, although NPY mRNA transcripts were also localized in the tectum and tegmentum mesencephali and posterior brain. New NPY-expressing nuclei were found in the dorsal and ventral telencephalon, preoptic area, tuberal hypothalamus, synencephalon, tegmentum mesencephali and posterior brain. The profuse NPY gene expression within the main neuroendocrine areas of the teleost fish further supports a physiological role in the control of the pituitary secretion. In addition, NPY gene was expressed within the primary visual, olfactory and gustatory circuits of teleost which, subsequently, project to hypothalamic feeding center in teleost fish. Our results extend the NPY-expressing areas known in teleost species.

NPY immunoreactivity in endocrine cells of duck pancreas: an ontogenetic study

In the literature, neuropeptide Y (NPY) has been described in the brain and peripheral nerves. More recently, it has also been detected in endocrine cells of hamster, embryonic mouse, and rat pancreas. However, the presence of NPY in avian embryos and the possible colocalization of this peptide with the other pancreatic hormones have not been reported previously. In this study, NPY presence was studied by immunocytochemical methods in the endocrine pancreas of domestic duck during pre- and postnatal development. NPY immunoreactivity (IR) was detected in embryos and adult animals. Around hatching the intensity of IR in endocrine cells decreased. Double immunohistochemical staining revealed that: 1) NPY-IR is extensively colocalized in small and mixed islets with insulin-IR both in embryos and in adults; and 2) in early embryos NPY-IR occasionally colocalized with glucagon and somatostatin. In early embryos, the colocalization of NPY-IR with several pancreatic hormones could be related to the presence of multi-hormonal progenitor cells. The close relation between insulin and NPY, both in embryos and adults, led us to hypothesize a key role for NPY on insulin cells of duck pancreas.

cNeuropeptide Y family of peptides: Structure, anatomical expression, function, and molecular evolution

Evolutionary relationships between neuroendocrine peptides are often difficult to resolve across divergent phyla due to independent duplication events in different lineages. Thanks to peptide purification and molecular cloning in many different species, the situation is beginning to clear for the neuropeptide Y (NPY) family, which also includes peptide YY (PYY), the tetrapod pancreatic polypeptide (PP) and the fish pancreatic peptide Y (PY). It has long been assumed that the first duplication to occur in vertebrate evolution generated NPY and PYY, as both of these are found in all gnathostomes as well as lamprey. Evidence from other gene families show that this duplication was probably a chromosome duplication event. The origin of a second PYY peptide found in lamprey remains to be explained. Our recent cloning of NPY, PYY and PY in the sea bass proves that fish PY is a separate gene product. We favour the hypothesis that PY is a duplicate of the PYY gene and that it may have occurred late in fish evolution, as PY has so far only been found in acanthomorph fishes. Thus, this duplication seems to be independent of the one that generate PP from PYY in tetrapods, although both tetrapod PP and fish PY are expressed in the pancreas. Studies in the sea bass and other fish show that PY, in contrast to PP, is expressed in the nervous system. We review the literature on the distribution and functional aspects of the various NPY-family peptides in vertebrates.

Key words: neuropeptide Y, pancreatic polypeptide, fish pancreatic peptide, gene duplication.

Neuronal messengers and peptide receptors in the human sphenopalatine and otic ganglia

A majority of the parasympathetic nerve fibers to cranial structures derive from the sphenopalatine and otic ganglia. In particular, blood vessels are invested with a rich supply of dilator fibers of parasympathetic origin. In the present study, we have examined the occurrence of noncholinergic neuromessengers and neuropeptide receptors in the human sphenopalatine and otic ganglia. Vasoactive intestinal peptide (VIP)-immunoreactive (ir) nerve cell bodies occurred in high numbers in the sphenopalatine and otic ganglia. Likewise, high numbers of NOS- and PACAP-containing nerve cell bodies were seen in both ganglia. Autofluorescent lipofuscin, characteristic of adult human nervous tissue, was present within many nerve cell bodies in both ganglia. Receptor mRNA was studied with reverse transcriptase-polymerase chain reaction (RT-PCR). Total RNA from the sphenopalatine and otic ganglia was successfully extracted. By using appropriate sense and antisense primers, oligonucleotides were designed from the human sequences derived from GenBank, corresponding to human NPY Y1, CGRP1 and VIP1 receptors. In the sphenopalatine ganglion, we revealed the presence of mRNA for the human NPY Y1 and VIP1 receptors but not the CGRP1 receptor. The otic ganglion was found to react positively only for primers to mRNA for VIP1 but not for CGRP1 or NPY Y1 receptors.

Influence of age, hyperglycemia, leptin, and NPY on islet blood flow in obese-hyperglycemic mice

This study aimed to elucidate possible age-related changes in islet blood perfusion in lean and obese C57BL/6 mice. Obese mice aged 1 mo were hyperglycemic and hyperinsulinemic and had an increased islet blood flow compared with age-matched lean mice. This augmented blood flow could be abolished by pretreatment with leptin. The islet blood perfusion was, in contrast to this, markedly decreased in obese 6- to 7-mo-old animals compared with age-matched lean mice. Reversal of hyperglycemia, but not hyperinsulinemia, in these obese mice with phlorizin normalized the islet blood flow. Spontaneous reversal of hyperglycemia, but not hyperinsulinemia, was seen in the 12-mo-old obese mice. Islet blood perfusion in obese mice at this age did not differ compared with lean mice. It is suggested that the initial increase in islet blood flow in obese mice is due to the leptin deficiency. The subsequent decrease in islet blood perfusion is probably caused by the chronic hyperglycemia. The described islet blood flow changes may be of importance for impairment of islet function in obese-hyperglycemic mice.

Dexamethasone induces neuropeptide Y (NPY) expression and impairs insulin release in the insulin-producing cell line RINm5F. Release of NPY and insulin through different pathways

Neuropeptide Y (NPY) occurs in adrenergic as well as in non-adrenergic nerves innervating the islets of Langerhans and inhibits glucose-stimulated insulin secretion. Recently we demonstrated that NPY is expressed within islet beta cells of the rat pancreas following treatment with dexamethasone in vivo. In this study we examined the cellular expression of NPY following dexamethasone treatment of the insulin-producing cell line RINm5F, which under control conditions does not express or release NPY. The cells were cultured with or without dexamethasone (100 nM) for 5 days. Over the 5-day culture period, dexamethasone time dependently induced an increased release of NPY with a concomitant decrease in the release of insulin. Northern blot and in situ hybridization revealed a corresponding time-dependent increase in the amount of NPY transcripts and in the number of cells labeled for NPY mRNA, whereas immunocytochemistry for NPY revealed only a few immunoreactive cells, indicating a rapid release of the formed peptide. Following 5 days of culture with dexamethasone, acute stimulation with D-glyceraldehyde (10 mM) or KCl (20 mM) Ca2+ dependently stimulated the release of insulin. In contrast neither stimulation with D-glyceraldehyde or KCl nor removal of extracellular Ca2+ affected the release of NPY. Furthermore the D-glyceraldehyde- and KCl-induced increase in cytosolic Ca2+, evident in control RINm5F cells, was impaired after dexamethasone treatment. We conclude that RINm5F cells show steroid-sensitive plasticity and express NPY after dexamethasone treatment concomitantly with a decreased insulin secretion and impaired increase in cytosolic Ca2+ upon depolarization with KCl or stimulation with D-glyceraldehyde. We also conclude that NPY and insulin secretion are regulated differently and suggest that the inability of the removal of extracellular Ca2+ to inhibit NPY secretion and the failure of D-glyceraldehyde and KCl to stimulate NPY secretion reflect a constitutive release of this peptide from the cells in contrast to the regulated release of insulin.

Developmental expression of NPY, PYY and PP in the rat pancreas and their coexistence with islet hormones

It has been suggested that members of the neuropeptide Y (NPY) family of regulatory peptides [NPY, peptide YY (PYY) and pancreatic polypeptide (PP)] play an important role in the development of the endocrine pancreas. The development of rat endocrine pancreas from embryonic (E) day 12 until 30 days postpartum (P) was studied with emphasis on NPY, PYY and PP and their co-existence with insulin, glucagon and somatostatin using single and double immunostaining and in situ hybridization. Already at E12, PYY was detectable in small endocrine cell clusters and found to be co-localised with both insulin and glucagon, which at this stage occurred in the same cells. At E16 most of the insulin-immunoreactive (IR) cells were distinct from the glucagon/PYY-IR cells. Interestingly, at E16 NPY mRNA, and at E17 NPY immunoreactivity appeared in a few, scattered endocrine cells. Virtually all NPY-IR endocrine cells were insulin-producing beta cells. At E18 the endocrine cells started to form typical islets with centrally located insulin/NPY-IR cells surrounded by glucagon/PYY-IR cells. AT E20-E21, the vast majority of insulin-producing cells also expressed NPY. However, at birth (day 0) islet cell NPY mRNA was lacking. Postnatally the number and immunostaining intensity of NPY-IR islet cells rapidly declined, being non-detectable at P5. Cells containing PP immunoreactivity and PP mRNA were first detected at E21. The adult pattern of islet peptide distribution, with NPY confined to neuronal elements. PYY and PP exclusively in endocrine cells, was established at P5. The beta cell expression of NPY during the latter part of embryogenesis coincides with the prepartal glucocorticoid surge and with rapid islet cell replication and differentiation. This is compatible with steroid induction of NPY expression and with a role for NPY in the maturation of beta cells and their hormone release, which occurs in the immediate neonatal period.

Direct glucocorticoid inhibition of insulin secretion. An in vitro study of dexamethasone effects in mouse islets

The direct effects of glucocorticoids on pancreatic beta cell function were studied with normal mouse islets. Dexamethasone inhibited insulin secretion from cultured islets in a concentration-dependent manner: maximum of approximately 75% at 250 nM and IC50 at approximately 20 nM dexamethasone. This inhibition was of slow onset (0, 20, and 40% after 1, 2, and 3 h) and only slowly reversible. It was prevented by a blocker of nuclear glucocorticoid receptors, by pertussis toxin, by a phorbol ester, and by dibutyryl cAMP, but was unaffected by an increase in the fuel content of the culture medium. Dexamethasone treatment did not affect islet cAMP levels but slightly reduced inositol phosphate formation. After 18 h of culture with or without 1 microM dexamethasone, the islets were perifused and stimulated by a rise in the glucose concentration from 3 to 15 mM. Both phases of insulin secretion were similarly decreased in dexamethasone-treated islets as compared with control islets. This inhibition could not be ascribed to a lowering of insulin stores (higher in dexamethasone-treated islets), to an alteration of glucose metabolism (glucose oxidation and NAD(P)H changes were unaffected), or to a lesser rise of cytoplasmic Ca2+ in beta cells (only the frequency of the oscillations was modified). Dexamethasone also inhibited insulin secretion induced by arginine, tolbutamide, or high K+. In this case also the inhibition was observed despite a normal rise of cytoplasmic Ca2+. In conclusion, dexamethasone inhibits insulin secretion through a genomic action in beta cells that leads to a decrease in the efficacy of cytoplasmic Ca2+ on the exocytotic process.

Neuropeptide Y and peptide YY immunoreactivities in the pancreas of various vertebrates

NPY-like immunoreactivity was observed in nerve fibers and endocrine cells in pancreas of all species examined except the eel, which showed no NPY innervation. The density of NPY-positive nerve fibers was higher in mammals than in the lower vertebrates. These nerve fibers were distributed throughout the parenchyma, and were particularly associated with the pancreatic duct and vascular walls. In addition, the density of NPY-positive endocrine cells was found to be higher in lower vertebrates than mammals; in descending order: eel = turtle = chicken > bullfrog > mouse = rat = human > guinea pig = dog. These NPY-positive cells in the cel and certain mammals tended to be localized throughout the islet region, whereas in the turtle and chicken they were mainly scattered in the exocrine region. PYY-immunoreactivity was only present in the pancreatic endocrine cells of all species studied, and localized similarly to NPY. Thus these two peptides may play endocrine or paracrine roles in the regulation of islet hormone secretion in various vertebrate species.