Reduced expression of secretogranin VGF in laryngeal squamous cell carcinoma.

Laryngeal cancer accounts for one-third of all head and neck tumors, with squamous cell carcinoma (SCC) being the most predominant type, followed by neuroendocrine tumors. Chromogranins, are commonly used as biomarkers for neuroendocrine tumors, including laryngeal cancer. It has been reported that secretogranin VGF, a member of the chromogranin family, can be also used as a significant biomarker for neuroendocrine tumors. However, the expression and role of VGF in laryngeal carcinomas have not been previously investigated. Therefore, the present study aimed to determine the expression levels of VGF in laryngeal SCC (LSCC). The present study collected tumor tissues, as well as serum samples, from a cohort of 15 patients with LSCC. The results of reverse transcription-quantitative PCR, western blot analysis and immunofluorescence assays showed that the selective VGF precursor was downregulated in patients with LSCC. Notably, in tumor tissue, the immunoreactivity for VGF was found in vimentin-positive cells, probably corresponding to T lymphocytes. The current preliminary study suggested that the reduced expression levels of VGF observed in tumor tissue and at the systemic level could sustain LSCC phenotype. Overall, VGF could be a potential biomarker for detecting neoplastic lesions with a higher risk of tumor invasiveness, even in non-neuroendocrine tumors.

The VGF-derived peptide TLQP-62 modulates insulin secretion and glucose homeostasis.

Insulin secretion control is critical for glucose homeostasis. Paracrine and autocrine molecules secreted by cells of the islet of Langerhans, as well as by intramural and autonomic neurons, control the release of different hormones that modulate insulin secretion. In pancreatic islets, the abundant presence of the granin protein VGF (nonacronymic; unrelated to VEGF) suggests that some of its proteolytically derived peptides could modulate hormone release. Thus, in the present study, we screened several VGF-derived peptides for their ability to induce insulin secretion, and we identified the VGF C-terminal peptide TLQP-62 as the most effective fragment. TLQP-62 induced a potent increase in basal insulin secretion as well as in glucose-stimulated insulin secretion in several insulinoma cell lines. We found that this peptide stimulated insulin release via increased intracellular calcium mobilization and fast expression of the insulin 1 gene. Moreover, the peripheral injection of TLQP-62 in mice improved glucose tolerance. Together, the present findings suggest that TLQP-62, acting as an endocrine, paracrine, or autocrine factor, can be considered a new, strong insulinotropic peptide that can be targeted for innovative antidiabetic drug discovery programs.

Bindarit, inhibitor of CCL2 synthesis, protects neurons against amyloid-ß-induced toxicity.

One of the hallmarks of Alzheimer's disease (AD), the most common age-related neurodegenerative pathology, is the abnormal extracellular deposition of neurotoxic amyloid-ß (Aß) peptides that accumulate in senile plaques. Aß aggregates are toxic to neurons and are thought to contribute to neuronal loss. Evidence indicates that inflammation is involved in the pathophysiology of AD, and activation of glial cells by a variety of factors, including Aß, appears to be a central event. Among molecules produced during inflammation associated with neuronal death, CCL2, also known as monocyte chemotactic protein-1 (MCP-1), seems to be particularly important. Indeed, CCL2 levels are higher in the cerebrospinal fluid of patients with AD than in controls. In the present study, we demonstrated the protective effect of bindarit (which inhibits CCL2 synthesis) against both Aß25-35 and Aß1-42-induced toxicity in primary mixed neural cultures. Bindarit (30-500 µM) reversed cell death induced by Aß in a dose-dependent manner and reduced the transcription and release of CCL2 by astrocytes after Aß treatment, as revealed by qRT-PCR, ELISA, and immunofluorescence staining. Astroglial activation and CCL2 release was induced by ATP released by damaged neurons through interaction with P2X7 receptors present on astrocyte surface. CCL2, interacting with its cognate receptor CCR2, present on neuron surface, strongly contributes to the toxic activity of Aß. Bindarit was able to disconnect this neuro-glial interaction. Our results demonstrate the ability of bindarit to inhibit Aß-induced neuronal death and suggest the potential role of CCL2 inhibitors in the treatment of neuroinflammatory/neurodegenerative diseases.

Systemic administration of substance P recovers beta amyloid-induced cognitive deficits in rat: involvement of Kv potassium channels.

Reduced levels of Substance P (SP), an endogenous neuropeptide endowed with neuroprotective and anti-apoptotic properties, have been found in brain and spinal fluid of Alzheimer's disease (AD) patients. Potassium (K(+)) channel dysfunction is implicated in AD development and the amyloid-ß (Aß)-induced up-regulation of voltage-gated potassium channel subunits could be considered a significant step in Aß brain toxicity. The aim of this study was to evaluate whether SP could reduce, in vivo, Aß-induced overexpression of Kv subunits. Rats were intracerebroventricularly infused with amyloid-ß 25-35 (Aß25-35, 20 µg) peptide. SP (50 µg/Kg, i.p.) was daily administered, for 7 days starting from the day of the surgery. Here we demonstrate that the Aß infused rats showed impairment in cognitive performances in the Morris water maze task 4 weeks after Aß25-35 infusion and that this impairing effect was prevented by SP administration. Kv1.4, Kv2.1 and Kv4.2 subunit levels were quantified in hippocampus and in cerebral cortex by Western blot analysis and immunofluorescence. Interestingly, SP reduced Kv1.4 levels overexpressed by Aß, both in hippocampus and cerebral cortex. Our findings provide in vivo evidence for a neuroprotective activity of systemic administration of SP in a rat model of AD and suggest a possible mechanism underlying this effect.

Neuropeptide TLQP-21, a VGF internal fragment, modulates hormonal gene expression and secretion in GH3 cell line.

In the present study we demonstrated that TLQP-21, a biologically active peptide derived from the processing of the larger pro-VGF granin, plays a role in mammotrophic cell differentiation. We used an established in vitro model, the GH3 cell line, which upon treatment with epidermal growth factor develops a mammotrophic phenotype consisting of induction of prolactin expression and secretion, and inhibition of growth hormone. Here we determined for the first time that during mammotrophic differentiation, epidermal growth factor also induces Vgf gene expression and increases VGF protein precursor processing and peptide secretion. After this initial observation we set out to determine the specific role of the VGF encoded TLQP-21 peptide on this model. TLQP-21 induced a trophic effect on GH3 cells and increased prolactin expression and its own gene transcription without affecting growth hormone expression. TLQP-21 was also able to induce a significant rise of cytoplasmic calcium, as measured by Fura2AM, due to the release from a thapsigargin-sensitive store. TLQP-21-dependent rise in cytoplasmic calcium was, at least in part, dependent on the activation of phospholipase followed by phosphorylation of PKC and ERK. Taken together, the present results demonstrate that TLQP-21 contributes to differentiation of the GH3 cell line toward a mammotrophic phenotype and suggest that it may exert a neuroendocrine role in vivo on lactotroph cells in the pituitary gland.

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.

VGF metabolic-related gene: distribution of its derived peptides in mammalian pancreatic islets.

The vgf gene has been shown to be involved in several metabolic pathways. Because the pancreas is crucial to metabolism and food intake, we studied the VGF peptides in bovine, rat, and pig Langherans islets using antisera raised against specific sites along the primary sequence of the rat/mouse and human VGF protein precursor. Whereas almost all of the pancreatic endocrine cells expressed vgf mRNA, when using the VGF antisera a different staining pattern became apparent. VGF(556-565) and VGF(282-291) immunoreactivity were exclusively found in delta somatostatin-producing cells, whereas the human C-terminus antiserum selectively immunolabeled alpha glucagon and pancreatic polypeptide cells. The same cells were decorated with the VGF(443-588) antiserum, which also weakly labeled beta insulin-secreting cells. Finally, the VGF(298-306) peptide and the rat C terminus were found in virtually all pancreatic endocrine cells. Using bovine, swine, and rat pancreatic extracts, data from chromatography and ELISA assay showed the presence of a high molecular mass form compatible with the proVGF and lower molecular mass fractions corresponding to short VGF peptides. In conclusion, selective VGF distribution may suggest a multifaceted cell type-specific processing of proVGF, resulting in different peptides probably involved in neuroendocrine regulatory metabolic mechanisms.

Identification of novel peptide hormones in the human proteome by hidden Markov model screening.

Peptide hormones are small, processed, and secreted peptides that signal via membrane receptors and play critical roles in normal and pathological physiology. The search for novel peptide hormones has been hampered by their small size, low or restricted expression, and lack of sequence similarity. To overcome these difficulties, we developed a bioinformatics search tool based on the hidden Markov model formalism that uses several peptide hormone sequence features to estimate the likelihood that a protein contains a processed and secreted peptide of this class. Application of this tool to an alignment of mammalian proteomes ranked 90% of known peptide hormones among the top 300 proteins. An analysis of the top scoring hypothetical and poorly annotated human proteins identified two novel candidate peptide hormones. Biochemical analysis of the two candidates, which we called spexin and augurin, showed that both were localized to secretory granules in a transfected pancreatic cell line and were recovered from the cell supernatant. Spexin was expressed in the submucosal layer of the mouse esophagus and stomach, and a predicted peptide from the spexin precursor induced muscle contraction in a rat stomach explant assay. Augurin was specifically expressed in mouse endocrine tissues, including pituitary and adrenal gland, choroid plexus, and the atrio-ventricular node of the heart. Our findings demonstrate the utility of a bioinformatics approach to identify novel biologically active peptides. Peptide hormones and their receptors are important diagnostic and therapeutic targets, and our results suggest that spexin and augurin are novel peptide hormones likely to be involved in physiological homeostasis.

Median eminence dopaminergic nerve terminals: a novel target in autoimmune polyendocrine syndrome?

CONTEXT: Autoantibodies to adenohypophyseal endocrine cells or to vasopressin neurohypophyseal neurons have long been known. Conversely, autoimmune targeting of further hypothalamic-hypophyseal structures, such as the blood-brain barrier-deprived median eminence, has been little studied. OBJECTIVE AND METHODS: We studied a case of autoimmune polyendocrine syndrome type I with GH secretory deficiency, a distinctly rare event in autoimmune polyendocrine syndrome type I. We used rat and bovine tissue substrates to study autoantibodies against hypothalamic-hypophyseal nerve structures and endocrine cells. RESULTS: In the study case, circulating autoantibodies selectively decorated median eminence dopaminergic nerve terminals, as well as pituitary gonadotropes, but not GHRH nerve terminals or pituitary somatotropes. Such autoantibodies appeared de novo in parallel with the onset of GH secretory deficiency, whereas no median eminence labeling was found in patients suffering of idiopathic GH deficiency (n = 7) or in healthy controls (n = 23). CONCLUSIONS: The pathophysiological significance of our patient's autoantibodies remains to be confirmed. Nonetheless, the heterogeneous neuroendocrine structures of the median eminence are pointed out as potential immune targets, relevant to autoimmune polyendocrinopathy, as well as to a wide range of other conditions.

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.

The neuroendocrine protein VGF is sorted into dense-core granules and is secreted apically by polarized rat thyroid epithelial cells.

We have expressed the neuroendocrine VGF protein in FRT rat thyroid cells to study the molecular mechanisms of its sorting to the regulated and polarized pathways of secretion. By immunoelectron microscopy, we have demonstrated that VGF localizes in dense-core granules. Rapid secretion of VGF is induced by PMA stimulation. Moreover, human chromogranin B, a protein of the regulated pathway, co-localizes in the same granules with VGF. In confluent, FRT monolayers on filters protein secretion occur from the apical cell domain. VGF deletion mutants have been generated. By confocal microscopy, we have found that in transient transfection, all mutant proteins are sorted into granules and co-localize with the full-length VGF. They all retain the apical polarity of secretion. We also found that intracellular VGF and its deletion mutants are largely in an aggregated form. We conclude that FRT thyroid cells correctly decode the sorting information of VGF. The signals present on the protein to enter the granules and to be secreted apically cannot be separated from each other and are not in just one discrete portion of the protein. We propose that selective aggregation might represent the signal for sorting VGF to the regulated, apical route.