Cholinergic muscarinic mechanisms regulate neuropeptide Y gene expression via protein kinase C in human neuroblastoma cells

Effects of Aging and Nerve Growth Factor on Neuropeptide Expression and Cholinergic Innervation of the Rat Basolateral Amygdala

The basolateral amygdala (BLA) contains interneurons that express neuropeptide Y (NPY) and vasoactive intestinal polypeptide (VIP), both of which are involved in the regulation of functions and behaviors that undergo deterioration with aging. There is considerable evidence that, in some brain areas, the expression of NPY and VIP might be modulated by acetylcholine. Importantly, the BLA is one of the brain regions that has one of the densest cholinergic innervations, which arise mainly from the basal forebrain cholinergic neurons. These cholinergic neurons depend on nerve growth factor (NGF) for their survival, connectivity, and function. Thus, in this study, we sought to determine if aging alters the densities of NPY- and VIP-positive neurons and cholinergic varicosities in the BLA and, in the affirmative, if those changes might rely on insufficient trophic support provided by NGF. The number of NPY-positive neurons was significantly reduced in aged rats, whereas the number of VIP-immunoreactive neurons was unaltered. The decreased NPY expression was fully reversed by the infusion of NGF in the lateral ventricle. The density of cholinergic varicosities was similar in adult and old rats. On the other hand, the density of cholinergic varicosities is significantly higher in old rats treated with NGF than in adult and old rats. Our results indicate a dissimilar resistance of different populations of BLA interneurons to aging. Furthermore, the present data also show that the BLA cholinergic innervation is particularly resistant to aging effects. Finally, our results also show that the reduced NPY expression in the BLA of aged rats can be related to changes in the NGF neurotrophic support.

Neuropeptide Y Peptide Family and Cancer: Antitumor Therapeutic Strategies

Currently available data on the involvement of neuropeptide Y (NPY), peptide YY (PYY), and pancreatic polypeptide (PP) and their receptors (YRs) in cancer are updated. The structure and dynamics of YRs and their intracellular signaling pathways are also studied. The roles played by these peptides in 22 different cancer types are reviewed (e.g., breast cancer, colorectal cancer, Ewing sarcoma, liver cancer, melanoma, neuroblastoma, pancreatic cancer, pheochromocytoma, and prostate cancer). YRs could be used as cancer diagnostic markers and therapeutic targets. A high Y1R expression has been correlated with lymph node metastasis, advanced stages, and perineural invasion; an increased Y5R expression with survival and tumor growth; and a high serum NPY level with relapse, metastasis, and poor survival. YRs mediate tumor cell proliferation, migration, invasion, metastasis, and angiogenesis; YR antagonists block the previous actions and promote the death of cancer cells. NPY favors tumor cell growth, migration, and metastasis and promotes angiogenesis in some tumors (e.g., breast cancer, colorectal cancer, neuroblastoma, pancreatic cancer), whereas in others it exerts an antitumor effect (e.g., cholangiocarcinoma, Ewing sarcoma, liver cancer). PYY or its fragments block tumor cell growth, migration, and invasion in breast, colorectal, esophageal, liver, pancreatic, and prostate cancer. Current data show the peptidergic system's high potential for cancer diagnosis, treatment, and support using Y2R/Y5R antagonists and NPY or PYY agonists as promising antitumor therapeutic strategies. Some important research lines to be developed in the future will also be suggested.

Therapeutic concentrations of valproate but not amitriptyline increase neuropeptide Y (NPY) expression in the human SH-SY5Y neuroblastoma cell line

Neuropeptide Y (NPY) is a peptide found in the brain and autonomic nervous system, which is associated with anxiety, depression, epilepsy, learning and memory, sleep, obesity and circadian rhythms. NPY has recently gained much attention as an endogenous antiepileptic and antidepressant agent, as drugs with antiepileptic and/or mood-stabilizing properties may exert their action by increasing NPY concentrations, which in turn can reduce anxiety and depression levels, dampen seizures or increase seizure threshold. We have used human neuroblastoma SH-SY5Y cells to investigate the effect of valproate (VPA) and amitriptyline (AMI) on NPY expression at therapeutic plasma concentrations of 0.6mM and 630nM, respectively. In addition, 12-O-tetradecanoylphorbol-13-acetate (TPA) known to differentiate SH-SY5Y cells into a neuronal phenotype and to increase NPY expression through activation of protein kinase C (PKC) was applied as a positive control (16nM). Cell viability after drug treatment was tested with a 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. NPY expression was measured using immunofluorescence and quantitative RT-PCR (qRT-PCR). Results from immunocytochemistry have shown NPY levels to be significantly increased following a 72h but not 24h VPA treatment. A further increase in expression was observed with simultaneous VPA and TPA treatment, suggesting that the two agents may increase NPY expression through different mechanisms. The increase in NPY mRNA by VPA and TPA was confirmed with qRT-PCR after 72h. In contrast, AMI had no effect on NPY expression in SH-SY5Y cells. Together, the data point to an elevation of human NPY mRNA and peptide levels by therapeutic concentrations of VPA following chronic treatment. Thus, upregulation of NPY may have an impact in anti-cancer treatment of neuroblastomas with VPA, and antagonizing hypothalamic NPY effects may help to ameliorate VPA-induced weight gain and obesity without interfering with the desired central effects of VPA.

Seizure-induced changes in neuropeptide Y-containing cortical neurons: Potential role for seizure threshold and epileptogenesis

Seizure activity induces transient changes in the levels of neuropeptide Y (NPY) and somatostatin (SS) in various brain regions, but it remains unclear whether this effect can persist for long periods and whether it is relevant to epileptogenesis. We report that brief seizures evoked by electroshock produced an increase in the number of NPY neurons in the dentate hilus and retrosplenial cortex, an effect that lasted 10 weeks. The number of hilar SS neurons remained unchanged. However, the pentylenetetrazole seizure threshold was somewhat decreased in electroshock-treated rats. Despite this, no spontaneous seizures were detected in this group. In contrast, status epilepticus (pilocarpine model) produced loss of the hilar NPY and SS cells. Moreover, all rats with status epilepticus showed spontaneous behavioral seizures and their seizure threshold was markedly decreased. These findings support the notion that sustained NPY overexpression induced by brief seizures can be important in preventing epileptogenesis.

Roles of protein kinase Calpha isozyme in the regulation of oxidative stress and neuropeptide Y gene expression in phenylpropanolamine-mediated appetite suppression

Hypothalamic neuropeptide Y (NPY) is an appetite stimulant in the brain. Although regulation of NPY expression has been reported to contribute to the appetite-suppressing effect of phenylpropanolamine (PPA), it is still unknown if protein kinase C (PKC) is involved in this effect. Rats were daily treated with PPA for 4 days. Changes in food intake, hypothalamic NPY, PKC, and proopiomelanocortin (POMC) mRNA levels were assessed and compared. Results showed that the NPY gene was down-regulated following PPA treatment, which was parallel with the decrease of feeding. Moreover, several isotypes of PKC mRNA level (alpha, betaI, betaII, gamma, delta, eta, lambda, epsilon, and zeta) were changed. Among these, alpha, delta, and lambda PKC were up-regulated along with POMC gene expression which coincided with down-regulation of the NPY gene. To further determine if PKCalpha was involved, infusions of antisense oligonucleotide into the cerebroventricle were performed at 1 h before daily PPA treatment in free-moving rats. Results showed that PKCalpha knock-down could modify both anorexia induced by PPA and the NPY mRNA levels. Moreover, PKCalpha knock-down could also modify superoxide dismutase (SOD) gene expression. It is suggested that PKCalpha participates in the regulation of PPA-mediated appetite suppression via the modulation of NPY and SOD gene expression.

Differential activation of enkephalin, galanin, somatostatin, NPY, and VIP neuropeptide production by stimulators of protein kinases A and C in neuroendocrine chromaffin cells

Neuropeptides function as peptide neurotransmitters and hormones to mediate cell-cell communication. The goal of this study was to understand how different neuropeptides may be similarly or differentially regulated by protein kinase A (PKA) and protein kinase C (PKC) intracellular signaling mechanisms. Therefore, this study compared the differential effects of treating neuroendocrine chromaffin cells with stimulators of PKA and PKC on the production of the neuropeptides (Met)enkephalin, galanin, somatostatin, NPY, and VIP. Significantly, selective increases in production of these neuropeptides were observed by forskolin or phorbol myristate acetate (PMA) which stimulate PKA and PKC mechanisms, respectively. (Met)enkephalin production was stimulated by up to 2-fold by forskolin treatment, but not by PMA. In contrast, PMA treatment (but not forskolin) resulted in a 2-fold increase in production of galanin and somatostatin, and a 3-fold increase in NPY production. Notably, VIP production was highly stimulated by forskolin and PMA, with increases of 3-fold and 10-15-fold, respectively. Differences in elevated neuropeptides occurred in cell extracts compared to secretion media, which consisted of (i) increased NPY primarily in secretion media, (ii) increased (Met)enkephalin and somatostatin in secretion media (not cell extracts), and (iii) increased galanin and VIP in both cell extracts and secretion media. Involvement of PKA or PKC for forskolin or PMA regulation of neuropeptide biosynthesis, respectively, was confirmed with direct inhibitors of PKA and PKC. The selective activation of neuropeptide production by forskolin and PMA demonstrates that PKA and PKC pathways are involved in the differential regulation of neuropeptide production.

Muscarinic receptor activation of AMP-activated protein kinase inhibits orexigenic neuropeptide mRNA expression

AMP-activated protein kinase (AMPK) plays a crucial role in both cellular and whole body energy homeostasis. Here we demonstrate that the muscarinic receptor agonist carbachol activates AMPKalpha1-containing complexes in the human SH-SY5Y cell line via a mechanism specific for the AMPK upstream kinase, Ca(2+)/calmodulin-dependent protein kinase kinase beta. Activation of AMPK inhibits mRNA expression of the orexigenic neuropeptides Agouti-related peptide and melanin-concentrating hormone but surprisingly has no effect on neuropeptide Y mRNA, a neuropeptide previously shown to be regulated by AMPK. Rather than restoring mRNA levels to baseline, pharmacological inhibition of Ca(2+)/calmodulin-dependent protein kinase kinase beta or AMPK greatly increases Agouti-related peptide and melanin-concentrating hormone mRNA expression. These data support a hypothesis that modulating basal AMPK activity in the hypothalamus is essential for maintaining tight regulation of pathways contributing to food intake.

Neuropeptide Y (NPY) in neuroblastoma: effect on growth and vascularization

Neuroblastomas are pediatric tumors of sympathetic origin, expressing neuronal markers, such as NPY and its receptors. Due to this, neuroblastomas are often associated with elevated plasma levels of NPY, which correlates with poor clinical outcome of the disease. This clinical data corroborates the recent discovery of growth-promoting actions of NPY in neuroblastomas. The peptide has been shown to stimulate proliferation of neuroblastoma cells in an autocrine manner and induce tumor vascularization. Since both processes are mediated by the same Y2 and Y5 receptors, targeting this pathway may be a potential bidirectional therapy for these children's tumors.

Role of neuropeptide Y and its receptors in the progression of endocrine-related cancer

The neuropeptide Y (NPY) family of peptides, in addition to its many physiological actions, has also been involved in the modulation of tumor progression, with specific reference to endocrine-related cancers such as neuroendocrine tumors, breast and prostate cancers. These have been found either to express NPY receptors, or to secrete NPY-related peptides, or both. The study of the role of the NPY family of peptides in the biology of endocrine-related tumors, specifically concerning cell proliferation, angiogenesis, invasion and metastatization, may help to clarify some aspects of tumor pathophysiology, as well as to indicate novel diagnostic markers and therapeutical approaches.

Reduced density of neuropeptide Y neurons in the somatosensory cortex of old male and female rats: relation to cholinergic depletion and recovery after nerve growth factor treatment

Synthesis of neuropeptide Y in the neocortex and activity of the basalocortical cholinergic system are both reduced in the aging brain. We hypothesized that, by stimulating the activity of the basal forebrain cholinergic neurons, nerve growth factor might also be capable of restoring the synthesis of neuropeptide Y in cortical neurons. Old male and female rats were intraventricularly infused with nerve growth factor for 14 days and their brains were analyzed in order to quantify the densities of neuropeptide Y-immunoreactive neurons and of fiber varicosities stained for vesicular acetylcholine transporter protein in layers II/III, V and VI of the primary somatosensory barrel-field cortex. The areal densities of neuropeptide Y neurons and of vesicular acetylcholine transporter protein varicosities in all cortical laminae were found to be dramatically decreased in old rats when compared with young rats. However, infusions of nerve growth factor, known to exert a powerful trophic effect upon cortically projecting cholinergic neurons, have led to considerable recovery of vesicular acetylcholine transporter protein-positive terminal fields, which was paralleled by complete restoration of function in neuropeptide Y-producing neurons. With respect to the gender differences, although the density of cortical neuropeptide Y neurons was found to be significantly higher in young females than in young males and the opposite was true for vesicular acetylcholine transporter protein-positive varicosities, the general pattern of age- and treatment-related changes in these neurochemical markers was similar in both sexes. Overall, the age- and treatment-related variations in the density of cortical neuropeptide Y cells were found to correlate with those observed in the density of vesicular acetylcholine transporter protein varicosities. These results lend support to the idea that there is a causal relationship between age-related changes in cortical cholinergic and neuropeptide Y-ergic neurotransmitter systems.

Expression changes of thrombospondin-1 and neuropeptide Y in myocardium of STZ-induced rats

Diabetic cardiomyopathy was the most dangerous diabetic complication facing diabetics, with its exact mechanisms remaining obscure. Our study was conducted to investigate the expression of thrombospondin-1 (TSP-1) and neuropeptide Y (NPY) in myocardium of streptozotocin (STZ)-induced diabetic rats. We employed streptozotocin (STZ)-induced diabetic rats to study the alteration of the TSP-1 and NPY expression in the left ventricle myocardium in diabetic and normal group by immunohistochemistry and immunofluorescence. The data of weight, blood sugar and urine sugar indicated no significant difference between the two groups before the animal model was induced. Four weeks after the induction of diabetes the weight of the diabeteic animals was 189.1+/-18.4 g, plasma glucose was 23.7+/-3.25 mmol/L and urine glucose was (++) to (+++); whereas the weight of the control animals was 260.5+/-32.1 g, plasma glucose was 4.9+/-0.5 mmol/L and urine glucose undetectable (-). The differences between the control and the diabetes group were distinct. A significant increase of the TSP-1 and NPY expression was also observed in the diabetic rat's heart. The number of the NPY positive myocardium and the light density of the positive myocardium in the left ventricle of the diabetic model were 17.3+/-2.1 and 102.5+/-9.3/mm(2), respectively, which were considered as increased when compared with the control that were 10.1+/-2.6 and 61.2+/-6.7, respectively. Our results support the view that high glucose conditions can induce an increased synthesis of TSP-1 through the PKC-TGF-beta-TSP-1 pathway, which in turn facilitate TGF-beta activation. Additionally, the activation of PKC may further lead to the over-expression of NPY. This may be involved in diabetic cardiomyopathy.

Muscarinic acetylcholine receptor stimulation induces expression of the activity-regulated cytoskeleton-associated gene (ARC)

Muscarinic acetylcholine receptors (mAChR) are involved in learning and memory but their molecular function in these processes is not fully understood. In this study, the signal transduction pathway coupling mAChR activation to induction of the activity-regulated cytoskeleton-associated gene (ARC) was examined. ARC was first identified as an effector immediate early gene induced by neuronal activity and ARC protein is thought to play a role in synaptic plasticity. In rats, intraperitoneal injection of pilocarpine, a potent agonist of mAChR, led to increased ARC expression in the brain. In human SH-SY5Y neuroblastoma cells mAChR stimulation with carbachol caused a rapid and robust induction of ARC expression. This effect was inhibited by atropine, a nonselective muscarinic receptor antagonist as well as by M1/M3 subtype-specific antagonists. Analysis of mAChR downstream effectors revealed that protein kinase C (PKC) and tyrosine kinases of the src family are key molecules in the signal cascade leading to ARC expression. Our data suggest, for the first time, that a correlation exists among mAChR-controlled signal cascades, the induction of the effector immediate early gene ARC and synaptic plasticity.

The catalytic domain limits the translocation of protein kinase C alpha in response to increases in Ca2+ and diacylglycerol

Translocation of protein kinase C (PKC) alpha, beta II, delta and epsilon fused to enhanced green fluorescent protein (EGFP) was studied in living neuroblastoma cells by confocal microscopy. Exposure to carbachol elicited transient translocation of PKC alpha-EGFP and beta II-EGFP in most of the cells, PKC delta-EGFP in a few cells and induced sustained translocation of PKC epsilon-EGFP. To monitor levels of Ca(2+) and diacylglycerol and the translocation of PKC in the same cell, the Ca(2+)-sensitive C2 domain, diacylglycerol-sensitive C1 domains and full-length PKC were fused to red, cyan and yellow fluorescent proteins respectively. PKC alpha was translocated a few seconds after the C2 domain, which represents an increase in Ca(2+). This delay was insensitive to removal of the pseudosubstrate in PKC alpha, but the isolated regulatory domain translocated simultaneously with the C2 domain. Translocation of PKC epsilon coincided with the increase in diacylglycerol. Ionomycin induced translocation of PKC alpha and the C2 domain, whereas 1,2-dioctanoylglycerol caused translocation of the C1 domains and PKC epsilon, but not PKC alpha. Experiments with individual C1 domains showed that treatment with carbachol or phorbol 12,13-dibutyrate elicited translocation of PKC alpha C1a, PKC epsilon C1a and PKC epsilon C1b, whereas PKC alpha C1b was largely insensitive to these agents. In contrast with full-length PKC alpha, the regulatory domain of PKC alpha and pseudosubstrate-devoid PKC alpha responded to the carbachol-stimulated increase in diacylglycerol.

Control of the expression of human neuropeptide Y by leptin: in vitro studies

Neuropeptide Y (NPY) participates in the regulation of reproduction and food intake. The adipose-secreted hormone, leptin, has also been involved in these processes, and has been shown to exert its effects in part by controlling NPY synthesis and release at the hypothalamic level. In the present study, we utilized the SH-SY5Y human neuroblastoma cell line, to study the leptin-NPY interrelationships. SH-SY5Y cells were found to express leptin receptors (RT-PCR and Western blot analyses). A 24-h treatment with leptin at different concentrations did not affect NPY gene expression, but resulted in a stimulation of NPY release. This stimulated secretion was blocked by the combined treatment with leptin and the muscarinic agonist carbachol or the phorbol ester TPA. Leptin and carbachol also caused an increased intracellular content of NPY. In conclusion, the SH-SY5Y human neuroblastoma cell line appears to be a suitable in vitro model for studying the pharmacological effects of leptin on the biosynthesis and secretion of NPY.

Leptin: a possible link between food intake, energy expenditure, and reproductive function

Several regulatory substances participate in the regulation of both food intake/energy metabolism and reproduction in mammals. Most of these neuropeptides originate and act in the central nervous system, mainly at specific hypothalamic areas. Leptin represents a signal integrating all these functions, but originating from the periphery (adipose tissue) and carrying information mainly to central structures. Observations in rodent models of leptin deficiency have suggested that leptin participates in the control of reproduction, in conjunction with that of food intake and energy expenditure. Indeed, leptin administration resulted in the restoration of normal body weight, food intake, and fertility in the ob mouse, lacking circulating leptin. Specific targets of leptin in the hypothalamus are neurons expressing neuropeptide Y, proopiomelanocortin and gonadotropin-releasing hormone, but the presence of leptin receptors in peripheral reproductive structures suggests that leptin might also act at these sites. Human obesity is often associated with reproductive disturbances. The situation in humans is more complex than in the animal models of leptin deficit and the presence of leptin resistance in these subjects is suggested. In conclusion, leptin fits many requirements for a molecule linking the regulation of energy balance and the control of reproduction.

Retinoic acid negatively regulates neuropeptide Y expression in human neuroblastoma cells

Retinoids are involved in the regulation of development and differentiation in many tissues, including the nervous system, where they have been associated with some neurotransmitter systems. In the present study, we evaluated the effects of all-trans retinoic acid (RA) on the biosynthesis and secretion of neuropeptide Y (NPY), a widely expressed neuroregulatory peptide. The SH-SY5Y human neuroblastoma cell line has been used as the in vitro model system. Treatment with 10 microM RA induced a marked decrease in NPY gene expression after as little as 3-6 h of incubation and resulted in its almost complete suppression at 12-24 h and after a 6-day differentiating treatment. The NPY content in cell extracts and the NPY secreted and accumulated in the culture medium were also reduced by exposure to 10 microM RA at 12 and 24 h and at 6 days. Moreover, RA treatment for 6 days, but not for 24 h, resulted in a marked stimulation of proNPY processing to mature NPY. The presence of negative retinoic acid-response elements in the human NPY promoter (up to -1078 bp) was excluded by a computer search. When SH-SY5Y cells were treated simultaneously with 20 nM TPA and 10 microM RA for 24 h, the marked stimulatory effect of TPA alone was completely suppressed. These observations suggest that the expression of NPY in SH-SY5Y human neuroblastoma cells is negatively regulated by RA at the level of gene expression, probably by mechanisms involving the interaction of activated RARs with transcription factors (such as AP-1).

Association of neuropeptide Y Y1 receptors with glutamate-positive and NPY-positive neurons in rat hippocampal cultures

The hippocampus is particularly enriched with neuropeptide tyrosine (NPY) and NPY receptors including the Y1, Y2 and Y5 subtypes. We have previously reported on the enrichment of cultured rat hippocampal neurons in specific [125I][Leu31, Pro34]PYY/BIBP3226-sensitive (Y1) binding sites and Y1 receptor mRNAs [St-Pierre et al. (1998) Br. J. Pharmacol., 123, p183]. We have now identified which cell types express the Y1 receptor. The majority of Y1 receptors, visualized using either the radiolabeled probe [125I][Leu31,Pro34]PYY or two antibodies directed against distinct domains of the Y1 receptor, was expressed in neurons as revealed by neuron-specific enolase (NSE) immunostaining. One antibody was directed against the second extracelllular loop of the Y1 receptor (amino acids 185-203) whereas the second was directed against the intracellular C-terminal loop (amino acids 355-382). The labelling was evident over both perikarya and processes. Neurons labelled by the various Y1 receptor probes were mostly glutamate-positive as revealed by double immunostaining. Most interestingly, a number of NPY-positive cultured hippocampal neurons were also enriched with the Y1 receptor, suggesting that this subtype may act as an autoreceptor to regulate NPY release in the hippocampus. These results thus provide an anatomical basis for the modulation of glutamate and NPY release by the Y1 receptor in the hippocampus.