Time course of the induction of VGF mRNA in the dorsal vagal complex in rats with cysteamine-induced peptic ulcers

The extended granin family: structure, function, and biomedical implications

The chromogranins (chromogranin A and chromogranin B), secretogranins (secretogranin II and secretogranin III), and additional related proteins (7B2, NESP55, proSAAS, and VGF) that together comprise the granin family subserve essential roles in the regulated secretory pathway that is responsible for controlled delivery of peptides, hormones, neurotransmitters, and growth factors. Here we review the structure and function of granins and granin-derived peptides and expansive new genetic evidence, including recent single-nucleotide polymorphism mapping, genomic sequence comparisons, and analysis of transgenic and knockout mice, which together support an important and evolutionarily conserved role for these proteins in large dense-core vesicle biogenesis and regulated secretion. Recent data further indicate that their processed peptides function prominently in metabolic and glucose homeostasis, emotional behavior, pain pathways, and blood pressure modulation, suggesting future utility of granins and granin-derived peptides as novel disease biomarkers.

Characterization of the mechanisms involved in the gastric antisecretory effect of TLQP-21, a vgf-derived peptide, in rats

TLQP-21, a vgf-derived peptide modulates gastric emptying and prevents ethanol-induced gastric lesions in rats. However, it remains to be studied whether or not TLQP-21 affects gastric acid secretion. In this study, we evaluated the effects of central (0.8-8 nmol/rat) or peripheral (48-240 nmol/kg, intraperitoneally) TLQP-21 administration on gastric acid secretion in pylorus-ligated rats. The mechanisms involved in such activity were also examined. Central TLQP-21 injection significantly reduced gastric acid volume and dose-dependently inhibited total acid output (ED(50) = 2.71 nmol), while peripheral TLQP-21 administration had no effect. The TLQP-21 antisecretory activity was prevented by cysteamine (300 mg/kg, subcutaneously), a depletor of somatostatin, by indomethacin (0.25 mg/rat, intracerebroventricularly), a non-selective cyclooxygenase inhibitor, and by functional ablation of sensory nerves by capsaicin. We conclude that TLQP-21 could be considered a new member of the large group of regulatory peptides affecting gastric acid secretion. The central inhibitory effect of TLQP-21 on gastric acid secretion is mediated by endogenous somatostatin and prostaglandins and requires the integrity of sensory nerve fibres.

In vitro and in vivo pharmacological role of TLQP-21, a VGF-derived peptide, in the regulation of rat gastric motor functions

BACKGROUND AND PURPOSE

Vgf gene expression has been detected in various endocrine and neuronal cells in the gastrointestinal tract. In this study we investigated the pharmacological activity of different VGF-derived peptides. Among these, TLQP-21, corresponding to the 556-576 fragment of the protein was the unique active peptide, and its pharmacological profile was further studied.

EXPERIMENTAL APPROACH

The effects of TLQP-21 were examined in vitro by smooth muscle contraction in isolated preparations from the rat gastrointestinal tract and, in vivo, by assessing gastric emptying in rats. Rat stomach tissues were also processed for immunohistochemical and biochemical characterization.

KEY RESULTS

In rat longitudinal forestomach strips, TLQP-21 (100 nmol x L(-1)-10 micromol x L(-1)) concentration-dependently induced muscle contraction (in female rats, EC(50) = 0.47 micromol.L(-1), E(max): 85.7 +/- 7.9 and in male rats, 0.87 micromol x L(-1), E(max): 33.4 +/- 5.3; n = 8), by release of prostaglandin (PG)E(2) and PGF(2a) from the mucosal layer. This effect was significantly antagonized by indomethacin and selective inhibitors of either cyclooxygenase-1 (S560) or cyclooxygenase-2 (NS398). Immunostaining and biochemical studies confirmed the presence of VGF in the gastric neuronal cells. TLQP-21, injected i.c.v. (2-32 nmol per rat), significantly decreased gastric emptying by about 40%. This effect was significantly (P < 0.05) blocked by i.c.v. injection of indomethacin, suggesting that, also in vivo, this peptide acts in the brain stimulating PG release.

CONCLUSIONS AND IMPLICATIONS

The present results demonstrate that this VGF-derived peptide plays a central and local role in the regulation of rat gastric motor functions.

Growth hormone expression and secretion in pig pituitary and median eminence slices are not influenced by the VGF protein

Body homeostasis is maintained by a complex system that involves the brain and the periphery via many circulating hormones. In recent years the VGF protein has been indicated as an important peptide affecting the regulation of body composition. We examined the effects of VGF on growth hormone (GH) expression and secretion in porcine pituitary slices, incubated alone (group 1) or with stalk median eminence (SME) (group 2). After 2 h (time 0), medium was removed and replaced with a fresh one; tissues were challenged with VGF (10(-6) M, 10(-8) M) alone or with ghrelin (10(-8) M) or growth hormone-releasing hormone (GHRH) (10(-8) M). Medium was replaced again 2 h (+2) and 6 h (+6) later. None of the VGF concentrations influenced GH secretion in either group; the association with GHRH or ghrelin appeared ineffective in influencing GH secretion as compared with the effects of GH mRNA expression and was not influenced by VGF treatments. The presence of SME had an additive effect on GH expression. Collectively, our results confirm previous findings on GH regulation; however, further investigations are needed to establish whether the modulation of GH secretion in the absence of nutrients involves the balance of GHRH/ghrelin receptors at pituitary levels. As for VGF, a crucial aspect to clarify is whether its lack of effects depends on our experimental conditions or, alternatively, it is not effective at all.

Processing, distribution, and function of VGF, a neuronal and endocrine peptide precursor

1. The vgf gene encodes a neuropeptide precursor with a restricted pattern of expression that is limited to a subset of neurons in the central and peripheral nervous systems and to specific populations of endocrine cells in the adenohypophysis, adrenal medulla, gastrointestinal tract, and pancreas. In responsive neurons, vgf transcription is upregulated by neurotrophins. the basis for the original identification of VGF as nerve growth factor- (NGF) inducible in PC12 cells (A. Levi, J. D. Eldridge, and B. M. Paterson, Science 229:393-395, 1985). 2. In this review, we shall summarize data concerning the transcriptional regulation of vgf in vitro, the structural organization of the vgf promoter as well as the transcription factors which regulate its activity. 3. On the basis of in situ hybridization and immunohistochemical studies, the in vivo tissue-specific expression of VGF during differentiation and in the adult will be summarized. 4. Parallel biochemical data will be reviewed, addressing the proteolytical processing of the pro-VGF precursor within the secretory compartment of neuroendocrine cells. 5. Finally, analysis of the phenotype of VGF knockout mice will be discussed, implying a nonredundant role of VGF products in the regulation of energy storage and expenditure.

VGF is required for obesity induced by diet, gold thioglucose treatment, and agouti and is differentially regulated in pro-opiomelanocortin- and neuropeptide Y-containing arcuate neurons in response to fasting

Targeted deletion of the gene encoding the neuronal and neuroendocrine secreted polypeptide VGF (nonacronymic) produces a lean, hypermetabolic mouse. Consistent with this phenotype, VGF mRNA levels are regulated in the hypothalamic arcuate nucleus in response to fasting. To gain insight into the site(s) and mechanism(s) of action of VGF, we further characterized VGF expression in the hypothalamus. Double-label studies indicated that VGF and pro-opiomelanocortin were coexpressed in lateral arcuate neurons in the fed state, and that VGF expression was induced after fasting in medial arcuate neurons that synthesize neuropeptide Y (NPY). Like NPY, VGF mRNA induction in this region of the hypothalamus in fasted mice was inhibited by exogenous leptin. In leptin-deficient ob/ob and receptor-mutant db/db mice, VGF mRNA levels in the medial arcuate were elevated. To identify neural pathways that are functionally compromised by Vgf ablation, VGF mutant mice were crossed with obese A(y)/a (agouti) and ob/ob mice. VGF deficiency completely blocked the development of obesity in A(y)/a mice, whereas deletion of Vgf in ob/ob mice attenuated weight gain but had no impact on adiposity. Hypothalamic levels of NPY and agouti-related polypeptide mRNAs in both double-mutant lines were dramatically elevated 10- to 15-fold above those of wild-type mice. VGF-deficient mice were also found to resist diet- and gold thioglucose-induced obesity. These data and the susceptibility of VGF mutant mice to monosodium glutamate-induced obesity are consistent with a role for VGF in outflow pathways, downstream of hypothalamic and/or brainstem melanocortin 4 receptors, that project via the autonomic nervous system to peripheral metabolic tissues and regulate energy homeostasis.

VGF: a novel role for this neuronal and neuroendocrine polypeptide in the regulation of energy balance

Insight into the mechanisms of action of neurotrophic growth factors has been obtained through the identification and characterization of gene products that are regulated or modified at the transcriptional, translational, and/or posttranslational level in response to neurotrophin treatment. VGF (non-acronymic) was identified approximately 15 years ago as a nerve growth factor (NGF)-regulated transcript in rat PC12 pheochromocytoma cells. Subsequent studies have demonstrated that neurotrophins such as NGF and brain-derived neurotrophic factor induce vgf gene expression relatively rapidly in PC12 cells and cultured cortical neurons, respectively, in comparison to less robust regulation by epidermal growth factor (EGF) and insulin, growth factors which do not trigger the neuronal differentiation of PC12 cells. vgf gene expression is stimulated in vitro by NGF and the ras/map kinase signaling cascade through a CREB-dependent mechanism, while in vivo, VGF mRNA levels are regulated by neuronal activity, including long-term potentiation, seizure, and injury. Both the mRNA and encoded approximately 68-kDa protein (VGF) are selectively synthesized in neuroendocrine and neuronal cells. The predicted VGF sequence is rich in paired basic amino acid residues that are potential sites for proteolytic processing, and VGF undergoes regulated release from dense core secretory vesicles. Although VGF mRNA is synthesized widely, by neurons in the brain, spinal cord, and peripheral nervous system, its expression is particularly abundant in the hypothalamus. In addition, VGF peptides are found in hypophysial, adrenal medullary, gastrointestinal, and pancreatic endocrine cells, suggesting important neuroendocrine functions. Recent analysis of VGF knockout mice indeed demonstrates that VGF plays a critical role in the control of energy homeostasis. VGF knockout mice are thin, small, hypermetabolic, hyperactive, and relatively infertile, with markedly reduced leptin levels and fat stores and altered hypothalamic pro-opiomelanocortin, neuropeptide Y, and agouti-related peptide expression. Coupled with the demonstration that VGF mRNA levels are induced in the normal mouse hypothalamic arcuate nuclei in response to fasting, important central and peripheral roles for VGF in the regulation of metabolism are suggested. Here we review previous studies of VGF in the broader context of its newly recognized role in the control of energy balance and propose several models and experimental approaches that may better define the mechanisms of action of VGF.