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

The role of chromogranins in the secretory pathway

Chromogranins (Cgs) are acidic proteins implicated in several physiological processes, including the biogenesis and sorting of secretory vesicles, the generation of bioactive peptides, and the accumulation of soluble species inside large dense core vesicles (LDCV). Indeed, Cgs are the main protein component of the vesicular matrix in LDCV, and they are involved in the concentration of soluble species like neurotransmitters and calcium. Experiments using electrochemical techniques such amperometry, patch amperometry, and intracellular electrochemistry have clarified the functional roles of Cgs in the accumulation and release of catecholamines. We have focused this review at a single event of exocytosis of chromaffin cells from three mouse strains lacking Cgs. Accordingly, in this brief review, we will focus on the role of Cgs in maintaining the intravesicular environment of secretory vesicles and in exocytosis, bringing together the most recent findings from studies on adrenal chromaffin cells.

Pancreastatin is an endogenous peptide that regulates glucose homeostasis

Pancreastatin (PST) is a regulatory peptide containing 49 amino acids, first isolated from porcine pancreas. Intracellular and extracellular processing of the prohormone Chromogranin A (Chga) results various bioactive peptides of which PST has dysglycemic activity. PST regulates glucose, lipid, and protein metabolism in liver and adipose tissues. It also regulates the secretion of leptin and expression of leptin and uncoupling protein 2 in adipose tissue. In Chga knockout mice, PST induces gluconeogenesis in the liver. PST reduces glucose uptake in mice hepatocytes and adipocytes. In rat hepatocytes, PST induces glycogenolysis and glycolysis and inhibits glycogen synthesis. In rat adipocytes, PST inhibits lactate production and lipogenesis. These metabolic effects are confirmed in humans. In the dual signaling mechanism of PST receptor, mostly PST activates Gαq/11 protein leads to the activation of phospholipase C β3-isoform, therefore increasing cytoplasmic free calcium and stimulating protein kinase C. PST inhibits the cell growth in rat HTC hepatoma cells, mediated by nitric oxide and cyclic GMP production. Elevated levels of PST correlating with catecholamines have been found in gestational diabetes and essential hypertension. Rise in the blood PST level in Type 2 diabetes suggests that PST is a negative regulator of insulin sensitivity and glucose homeostasis.

Psychiatric patient stratification using biosignatures based on cerebrospinal fluid protein expression clusters

Psychiatric disorders are caused by perturbed molecular pathways that affect brain circuitries. The identification of specific biosignatures that are the result of altered pathway activities in major depression, bipolar disorder and schizophrenia can contribute to a better understanding of disease etiology and aid in the implementation of diagnostic assays. In the present study we identified disease-specific protein biosignatures in cerebrospinal fluid of depressed (n: 36), bipolar (n: 27) and schizophrenic (n: 35) patients using the Reverse Phase Protein Microarray technology. These biosignatures were able to stratify patient groups in an objective manner according to cerebrospinal fluid protein expression patterns. Correct classification rates were over 90%. At the same time several protein sets that play a role in neuronal growth, proliferation and differentiation (NEGR1, NPDC1), neurotransmission (SEZ6) and protection from oxidative damage (GPX3) were able to distinguish diseased from healthy individuals (n: 35) indicating a molecular signature overlap for the different psychiatric phenotypes. Our study is a first step toward implementing a psychiatric patient stratification system based on molecular biosignatures. Protein signatures may eventually be of use as specific and sensitive biomarkers in clinical trials not only for patient diagnostic and subgroup stratification but also to follow treatment response.

Brain-expressed imprinted genes and adult behaviour: the example of Nesp and Grb10

Imprinted genes are defined by their parent-of-origin-specific monoallelic expression. Although the epigenetic mechanisms regulating imprinted gene expression have been widely studied, their functional importance is still unclear. Imprinted genes are associated with a number of physiologies, including placental function and foetal growth, energy homeostasis, and brain and behaviour. This review focuses on genomic imprinting in the brain and on two imprinted genes in particular, Nesp and paternal Grb10, which, when manipulated in animals, have been shown to influence adult behaviour. These two genes are of particular interest as they are expressed in discrete and overlapping neural regions, recognised as key "imprinting hot spots" in the brain. Furthermore, these two genes do not appear to influence placental function and/or maternal provisioning of offspring. Consequently, by understanding their behavioural function we may begin to shed light on the evolutionary significance of imprinted genes in the adult brain, independent of the recognised role in maternal care. In addition, we discuss the potential future directions of research investigating the function of these two genes and the behavioural role of imprinted genes more generally.

Maternal inheritance of the Gnas cluster mutation Ex1A-T affects size, implicating NESP55 in growth

Genes subjected to genomic imprinting are often associated with prenatal and postnatal growth. Furthermore, it has been observed that maternally silenced/paternally expressed genes tend to favour offspring growth, whilst paternally silenced/maternally expressed genes will restrict growth. One imprinted cluster in which this has been shown to hold true is the Gnas cluster; of the three proteins expressed from this cluster, two, Gsα and XLαs, have been found to affect postnatal growth in a number of different mouse models. The remaining protein in this cluster, NESP55, has not yet been shown to be involved in growth. We previously described a new mutation, Ex1A-T, which upon paternal transmission resulted in postnatal growth retardation due to loss of imprinting of Gsα and loss of expression of the paternally expressed XLαs. Here we describe maternal inheritance of Ex1A-T which gives rise to a small but highly significant overgrowth phenotype which we attribute to reduction of maternally expressed NESP55.

Decreased cerebrospinal fluid secretogranin II concentrations in severe forms of bipolar disorder

BACKGROUND

Bipolar disorder is a common psychiatric mood disorder that is defined by recurrent episodes of abnormally elevated mood and depression. Progressive structural brain changes in individuals with bipolar disorder have been suggested to be associated with defects in the secretion of neurotrophic factors. We sought to assess how the regulated secretory pathway in the brain is affected in patients with bipolar disorder by measuring chromogranin B and secretogranin II, which are 2 cerebrospinal fluid (CSF) biological markers for this process.

METHODS

We measured the concentrations of chromogranin B (peptide 439-451) and secretogranin II (peptide 154-165) in the CSF of patients with well-defined bipolar disorder and healthy controls. The lifetime severity of bipolar disorder was rated using the Clinical Global Impression (CGI) scale.

RESULTS

We included 126 patients with bipolar disorder and 71 healthy controls in our analysis. Concentrations of secretogranin II were significantly lower in patients with bipolar disorder type I than in healthy controls. The reduction was most pronounced in patients with high CGI scores (i.e., severe disease).

LIMITATIONS

The cross-sectional design of the current study limits the ability to pinpoint the causalities behind the observed associations.

CONCLUSION

This study shows that the CSF marker secretogranin II has the potential to act as a biological marker for severe forms of bipolar disorder. Our findings indicate that patients with bipolar disorder possess defects in the regulatory secretory pathway, which may be of relevance to the progressive structural brain changes seen in those with severe forms of the disease.

Peptidomic profiling of secreted products from pancreatic islet culture results in a higher yield of full-length peptide hormones than found using cell lysis procedures

Peptide Hormone Acquisition through Smart Sampling Technique-Mass Spectrometry (PHASST-MS) is a peptidomics platform that employs high resolution liquid chromatography-mass spectrometry (LC-MS) techniques to identify peptide hormones secreted from in vitro or ex vivo cultures enriched in endocrine cells. Application of the methodology to the study of murine pancreatic islets has permitted evaluation of the strengths and weaknesses of the approach, as well as comparison of our results with published islet studies that employed traditional cellular lysis procedures. We found that, while our PHASST-MS approach identified fewer peptides in total, we had greater representation of intact peptide hormones. The technique was further refined to improve coverage of hydrophilic as well as hydrophobic peptides and subsequently applied to human pancreatic islet cultures derived from normal donors or donors with type 2 diabetes. Interestingly, in addition to the expected islet hormones, we identified alpha-cell-derived bioactive GLP-1, consistent with recent reports of paracrine effects of this hormone on beta-cell function. We also identified many novel peptides derived from neurohormonal precursors and proteins related to the cell secretory system. Taken together, these results suggest the PHASST-MS strategy of focusing on cellular secreted products rather than the total tissue peptidome may improve the probability of discovering novel bioactive peptides and also has the potential to offer important new insights into the secretion and function of known hormones.

Continuous stress promotes expression of VGF in melanotroph via suppression of dopamine

Prolonged exposure to stress elicits profound effects on homeostasis that may lead to cryptogenic disorders such as chronic fatigue syndrome. To investigate the pathophysiology associated with the syndrome, we used a rat continuous stress (CS) model where the pituitary represents one of the most affected organs. Here we found that mRNA for VGF (non-acronymic), a member of the granin family, was induced specifically in the intermediate lobe (IL). This was matched by a concomitant increase at the peptide/protein level assessed by C-terminal antibody. Furthermore, the up-regulation of VGF was confirmed by immunohistochemistry in a subset of melanotrophs. VGF expression was altered in the IL of rats receivingthe dopamine D2 receptor agonist bromocriptine or the antagonist sulpiride. In vitro, dopamine dose-dependently decreased the mRNA levels in cultured melanotrophs. These findings suggest that VGF expression under CS is negatively regulated by dopaminergic neurons projecting from the hypothalamus.

Mass spectrometry identification of granins and other proteins secreted by neuroblastoma cells

We used mass spectrometry-based protein identification to determine the presence of granins and other proteins in the mouse neuroblastoma secretome. We detected polypeptides derived from four members of the granin family: chromogranin A, chromogranin B, secretogranin III, and VGF. Many of them are derived from previously described biologically active regions; however, for VGF and CgB, we detected peptides not related to known bioactivities. Along with granins, we identified 115 other proteins secreted by mouse neuroblastoma cells, belonging to different functional categories. Fifty-six out of 119 detected proteins possess the signal fragments required for translocation into endoplasmic reticulum. Sequences of remaining 63 proteins were analyzed using SecretomeP algorithm to determine probability of nonclassical secretion. Identified proteins are involved in the regulation of cell cycle, proliferation, apoptosis, angiogenesis, proteolysis, and cell adhesion.

Large-scale identification of endogenous secretory peptides using electron transfer dissociation mass spectrometry

Mass spectrometry-based unbiased analysis of the full complement of secretory peptides is expected to facilitate the identification of unknown biologically active peptides. However, tandem MS sequencing of endogenous peptides in their native form has proven difficult because they show size heterogeneity and contain multiple internal basic residues, the characteristics not found in peptide fragments produced by in vitro digestion. Endogenous peptides remain largely unexplored by electron transfer dissociation (ETD), despite its widespread use in bottom-up proteomics. We used ETD, in comparison to collision induced dissociation (CID), to identify endogenous peptides derived from secretory granules of a human endocrine cell line. For mass accuracy, both MS and tandem MS were analyzed on an Orbitrap. CID and ETD, performed in different LC-MS runs, resulted in the identification of 795 and 569 unique peptides (ranging from 1000 to 15000 Da), respectively, with an overlap of 397. Peptides larger than 3000 Da accounted for 54% in CID and 46% in ETD identifications. Although numerically outperformed by CID, ETD provided more extensive fragmentation, leading to the identification of peptides that are not reached by CID. This advantage was demonstrated in identifying a new antimicrobial peptide from neurosecretory protein VGF (non-acronymic), VGF[554-577]-NH2, or in differentiating nearly isobaric peptides (mass difference less than 2 ppm) that arise from alternatively spliced exons of the gastrin-releasing peptide gene. CID and ETD complemented each other to add to our knowledge of the proteolytic processing sites of proteins implicated in the regulated secretory pathway. An advantage of the use of both fragmentation methods was also noted in localization of phosphorylation sites. These findings point to the utility of ETD mass spectrometry in the global study of endogenous peptides, or peptidomics.

Serpinins: role in granule biogenesis, inhibition of cell death and cardiac function

Serpinins are a family of peptides derived from proteolytic cleavage of the penultimate and the last pair of basic residues at the C-terminus of Chromogranin A. Three forms of naturally occurring serpinin have been found in AtT-20 pituitary cells and rat heart. They are serpinin, pyrogutaminated (pGlu) -serpinin and a C-terminally extended form, serpinin-RRG. In addition pGlu-serpinin has been found in brain, primarily in neurites and nerve terminals and shown to have protective effects against oxidative stress on neurons and pituitary cells. Serpinin has also been demonstrated to regulate granule biogenesis in endocrine cells by up-regulating the protease inhibitor, protease nexin-1 transcription via a cAMP-PKA-sp1 pathway. This leads to inhibition of granule protein degradation in the Golgi complex which in turn promotes granule formation. More recently, pGlu-serpinin has been demonstrated to enhance both myocardial contractility (inotropy) and relaxation (lusitropy). In the Langendorff perfused rat heart, pGlu-serpinin showed a concentration-dependent positive inotropic effect exerted through a cAMP-PKA dependent pathway. In conclusion, the serpinin peptides have profound effects at many levels that affect the endocrine and nervous systems and cardiac function.

Chronic nicotine treatment impacts the regulation of opioid and non-opioid peptides in the rat dorsal striatum

The chronic use of nicotine, the main psychoactive ingredient of tobacco smoking, alters diverse physiological processes and consequently generates physical dependence. To understand the impact of chronic nicotine on neuropeptides, which are potential molecules associated with dependence, we conducted qualitative and quantitative neuropeptidomics on the rat dorsal striatum, an important brain region implicated in the preoccupation/craving phase of drug dependence. We used extensive LC-FT-MS/MS analyses for neuropeptide identification and LC-FT-MS in conjunction with stable isotope addition for relative quantification. The treatment with chronic nicotine for 3 months led to moderate changes in the levels of endogenous dorsal striatum peptides. Five enkephalin opioid peptides were up-regulated, although no change was observed for dynorphin peptides. Specially, nicotine altered levels of nine non-opioid peptides derived from precursors, including somatostatin and cerebellin, which potentially modulate neurotransmitter release and energy metabolism. This broad but selective impact on the multiple peptidergic systems suggests that apart from the opioid peptides, several other peptidergic systems are involved in the preoccupation/craving phase of drug dependence. Our finding permits future evaluation of the neurochemical circuits modulated by chronic nicotine exposure and provides a number of novel molecules that could serve as potential therapeutic targets for treating drug dependence.

Argonaute2 regulates the pancreatic β-cell secretome

Argonaute2 (Ago2) is an established component of the microRNA-induced silencing complex. Similar to miR-375 loss-of-function studies, inhibition of Ago2 in the pancreatic β-cell resulted in enhanced insulin release underlining the relationship between these two genes. Moreover, as the most abundant microRNA in pancreatic endocrine cells, miR-375 was also observed to be enriched in Ago2-associated complexes. Both Ago2 and miR-375 regulate the pancreatic β-cell secretome, and by using quantitative mass spectrometry, we identified the enhanced release of a set of proteins or secretion "signatures " in response to a glucose stimulus using the murine β-cell line MIN6. In addition, the loss of Ago2 resulted in the increased expression of miR-375 target genes, including gephyrin and ywhaz. These targets positively contribute to exocytosis indicating they may mediate the functional role of both miR-375 and Ago proteins in the pancreatic β-cell by influencing the secretory pathway. This study specifically addresses the role of Ago2 in the systemic release of proteins from β-cells and highlights the contribution of the microRNA pathway to the function of this cell type.

The regulated secretory pathway and human disease: insights from gene variants and single nucleotide polymorphisms

The regulated secretory pathway provides critical control of peptide, growth factor, and hormone release from neuroendocrine and endocrine cells, and neurons, maintaining physiological homeostasis. Propeptides and prohormones are packaged into dense core granules (DCGs), where they frequently undergo tissue-specific processing as the DCG matures. Proteins of the granin family are DCG components, and although their function is not fully understood, data suggest they are involved in DCG formation and regulated protein/peptide secretion, in addition to their role as precursors of bioactive peptides. Association of gene variation, including single nucleotide polymorphisms (SNPs), with neuropsychiatric, endocrine, and metabolic diseases, has implicated specific secreted proteins and peptides in disease pathogenesis. For example, a SNP at position 196 (G/A) of the human brain-derived neurotrophic factor gene dysregulates protein processing and secretion and leads to cognitive impairment. This suggests more generally that variants identified in genes encoding secreted growth factors, peptides, hormones, and proteins involved in DCG biogenesis, protein processing, and the secretory apparatus, could provide insight into the process of regulated secretion as well as disorders that result when it is impaired.

Characterization of the reproductive effects of the Vgf-derived peptide TLQP-21 in female rats: in vivo and in vitro studies

BACKGROUND

VGF (non-acronymic), a protein expressed in the hypothalamus and pituitary, is involved in the control of metabolism and body weight homeostasis. Different active peptide fragments are generated from VGF, including TLQP-21. Previous studies of our group reported that this molecule participates also in the regulation of reproductive function in male rats, with predominant stimulatory effects.

METHODS

We report herein a series of studies on the reproductive effects of TLQP-21 in female rats, as evaluated by a combination of in vivo and in vitro analyses.

RESULTS

TLQP-21 modestly increased serum LH levels after systemic administration and directly stimulated pituitary LH and FSH secretion in prepubertal female rats, while acute central injection of TLQP-21 was unable to modify LH secretion at this age. Repeated central administration of TLQP-21 during the pubertal transition (between PND-28 and -35) to female rats fed ad libitum advanced the timing of vaginal opening and increased the percentage of animals with signs of ovulation. Moreover, an analogous treatment slightly enhanced ovarian maturation in pubertal female rats subjected to chronic undernutrition, but was unable to rescue the delay of vaginal opening induced by food deprivation. In addition, TLQP-21 oppositely modified LH secretion in adult female rats depending on the stage of the ovarian cycle: it stimulated LH secretion when injected in the morning of diestrus and decreased the magnitude of the preovulatory LH (but not FSH) surge when injected in the afternoon of proestrus.

CONCLUSIONS

Our data are the first to document the potential involvement of TLQP-21 in the control of reproductive function in female rats.

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.

Granins and catecholamines: functional interaction in chromaffin cells and adipose tissue

Catecholamines (CAs) and granin peptides are costored in dense-core vesicles within the chromaffin cells of the adrenal medulla and in other endocrine organs and neurons. Granins play a major functional and structural role in chromaffin cells but are ubiquitous proteins, which are present also in secretory cells of the nervous, endocrine, and immune systems, where they regulate a number of cellular functions. Furthermore, recent studies also demonstrate that granin-derived peptides can functionally interact with CA to modulate key physiological functions such as lipolysis and blood pressure. In this chapter, we will provide a brief update on the interaction between CA and granins at the cellular and organ levels. We will first discuss recent data on the regulation of exocytosis of CA and peptides from the chromaffin cells by the sympathetic nervous system with a specific reference to the prominent role played by splanchnic nerve-derived pituitary adenylate cyclase-activating peptide (PACAP). Secondly, we will discuss the role of granins in the storage and regulation of exocytosis in large dense-core vesicles. Finally, we will provide an up-to-date review of the roles played by two granin-derived peptides, the chromogranin A-derived peptide catestatin and the VGF-derived peptide TLQP-21, on lipolysis and obesity. In conclusion, the knowledge gathered from recent findings on the role played by proteins/peptides in the sympathetic/target cell synapses, discussed in this chapter, would contribute to and provide novel mechanistic support for an increased appreciation of the physiological role of CA in human pathophysiology.

Germline ablation of VGF increases lipolysis in white adipose tissue

Targeted deletion of VGF, a neuronal and endocrine secreted protein and neuropeptide precursor, produces a lean, hypermetabolic mouse that is resistant to diet-, lesion-, and genetically induced obesity and diabetes. We hypothesized that increased sympathetic nervous system activity in Vgf-/Vgf- knockout mice is responsible for increased energy expenditure and decreased fat storage and that increased β-adrenergic receptor stimulation induces lipolysis in white adipose tissue (WAT) of Vgf-/Vgf- mice. We found that fat mass was markedly reduced in Vgf-/Vgf- mice. Within knockout WAT, phosphorylation of protein kinase A substrate increased in males and females, phosphorylation of hormone-sensitive lipase (HSL) (ser563) increased in females, and levels of adipose triglyceride lipase, comparative gene identification-58, and phospho-perilipin were higher in male Vgf-/Vgf- WAT compared with wild-type, consistent with increased lipolysis. The phosphorylation of AMP-activated protein kinase (AMPK) (Thr172) and levels of the AMPK kinase, transforming growth factor β-activated kinase 1, were decreased. This was associated with a decrease in HSL ser565 phosphorylation, the site phosphorylated by AMPK, in both male and female Vgf-/Vgf- WAT. No significant differences in phosphorylation of CREB or the p42/44 MAPK were noted. Despite this evidence supporting increased cAMP signaling and lipolysis, lipogenesis as assessed by fatty acid synthase protein expression and phosphorylated acetyl-CoA carboxylase was not decreased. Our data suggest that the VGF precursor or selected VGF-derived peptides dampen sympathetic outflow pathway activity to WAT to regulate fat storage and lipolysis.

Secretory sorting receptors carboxypeptidase E and secretogranin III in amyloid β-associated neural degeneration in Alzheimer's disease

The secretory sorting receptors carboxypeptidase E (CPE) and secretogranin III (SgIII) critically activate peptidic messengers and targeting them at the regulated secretory pathway. In Alzheimer's disease (AD), the wide range of changes includes impaired function of key secretory peptidic cargos such as brain-derived neurotrophic factor (BDNF) and neuropeptides. Here, we analyzed CPE and SgIII in the cerebral cortex of AD patients and transgenic mice. In the normal human cortex, a preferential location in dendrites and perikarya was observed for CPE, whereas SgIII was mainly associated with axons and terminal-like buttons. Interestingly, SgIII and CPE were consistently detected in astroglial cell bodies and thin processes. In AD cortices, a strong wide accumulation of both sorting receptors was detected in dystrophic neurites surrounding amyloid plaques. Occasionally, increased levels of SgIII were also observed in plaque associate-reactive astrocytes. Of note, the main alterations detected for CPE and SgIII in AD patients were faithfully recapitulated by APPswe/PS1dE9 mice. These results implicate for the first time the sorting receptors for regulated secretion in amyloid β-associated neural degeneration. Because CPE and SgIII are essential in the process and targeting of neuropeptides and neurotrophins, their participation in the pathological progression of AD may be suggested.

Neuroendocrine regulatory peptide-2 stimulates glucose-induced insulin secretion in vivo and in vitro

Neuroendocrine regulatory peptide (NERP)-2, recently identified as a bioactive peptide involved in vasopressin secretion and feeding regulation in the central nervous system, is abundantly expressed in endocrine cells in peripheral tissues. To explore the physiological roles of NERP-2 in the pancreas, we examined its effects on insulin secretion. NERP-2 increased glucose-stimulated insulin secretion (GSIS) in a dose-dependent manner, with a lowest effective dose of 10(-7) M, from the pancreatic β-cell line MIN6 and isolated mouse pancreatic islets. NERP-2 did not affect insulin secretion under the low-glucose conditions. Neither NERP-1 nor NERP-2-Gly (nonamidated NERP-2) stimulated insulin secretion. NERP-2 significantly augmented GSIS after intravenous administration to anesthetized rats or intraperitoneal injection to conscious mice. We detected NERP-2 in pancreatic islets, where it co-localized extensively with insulin. Calcium-imaging analysis demonstrated that NERP-2 increased the calcium influx in MIN6 cells. These findings reveal that NERP-2 regulates GSIS by elevating intracellular calcium concentrations.

Functional genetic variants of the catecholamine-release-inhibitory peptide catestatin in an Indian population: allele-specific effects on metabolic traits

Catestatin (CST), a chromogranin A (CHGA)-derived peptide, is a potent inhibitor of catecholamine release from adrenal chromaffin cells and postganglionic sympathetic axons. We re-sequenced the CST region of CHGA in an Indian population (n = 1010) and detected two amino acid substitution variants: G364S and G367V. Synthesized CST variant peptides (viz. CST-Ser-364 and CST-Val-367) were significantly less potent than the wild type peptide (CST-WT) to inhibit nicotine-stimulated catecholamine secretion from PC12 cells. Consistently, the rank-order of blockade of nicotinic acetylcholine receptor (nAChR)-stimulated inward current and intracellular Ca(2+) rise by these peptides in PC12 cells was: CST-WT > CST-Ser-364 > CST-Val-367. Structural analysis by CD spectroscopy coupled with molecular dynamics simulations revealed the following order of α-helical content: CST-WT > CST-Ser-364 > CST-Val-367; docking of CST peptides onto a major human nAChR subtype and molecular dynamics simulations also predicted the above rank order for their binding affinity with nAChR and the extent of occlusion of the receptor pore, providing a mechanistic basis for differential potencies. The G364S polymorphism was in strong linkage disequilibrium with several common CHGA genetic variations. Interestingly, the Ser-364 allele (detected in ∼15% subjects) was strongly associated with profound reduction (up to ∼2.1-fold) in plasma norepinephrine/epinephrine levels consistent with the diminished nAChR desensitization-blocking effect of CST-Ser-364 as compared with CST-WT. Additionally, the Ser-364 allele showed strong associations with elevated levels of plasma triglyceride and glucose levels. In conclusion, a common CHGA variant in an Indian population influences several biochemical parameters relevant to cardiovascular/metabolic disorders.

Distinct Initial SNARE Configurations Underlying the Diversity of Exocytosis

The dynamics of exocytosis are diverse and have been optimized for the functions of synapses and a wide variety of cell types. For example, the kinetics of exocytosis varies by more than five orders of magnitude between ultrafast exocytosis in synaptic vesicles and slow exocytosis in large dense-core vesicles. However, in all cases, exocytosis is mediated by the same fundamental mechanism, i.e., the assembly of soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins. It is often assumed that vesicles need to be docked at the plasma membrane and SNARE proteins must be preassembled before exocytosis is triggered. However, this model cannot account for the dynamics of exocytosis recently reported in synapses and other cells. For example, vesicles undergo exocytosis without prestimulus docking during tonic exocytosis of synaptic vesicles in the active zone. In addition, epithelial and hematopoietic cells utilize cAMP and kinases to trigger slow exocytosis of nondocked vesicles. In this review, we summarize the manner in which the diversity of exocytosis reflects the initial configurations of SNARE assembly, including trans-SNARE, binary-SNARE, unitary-SNARE, and cis-SNARE configurations. The initial SNARE configurations depend on the particular SNARE subtype (syntaxin, SNAP25, or VAMP), priming proteins (Munc18, Munc13, CAPS, complexin, or snapin), triggering proteins (synaptotagmins, Doc2, and various protein kinases), and the submembraneous cytomatrix, and they are the key to determining the kinetics of subsequent exocytosis. These distinct initial configurations will help us clarify the common SNARE assembly processes underlying exocytosis and membrane trafficking in eukaryotic cells.

Peptidome analysis of cerebrospinal fluid by LC-MALDI MS

We report on the analysis of endogenous peptides in cerebrospinal fluid (CSF) by mass spectrometry. A method was developed for preparation of peptide extracts from CSF. Analysis of the extracts by offline LC-MALDI MS resulted in the detection of 3,000–4,000 peptide-like features. Out of these, 730 peptides were identified by MS/MS. The majority of these peptides have not been previously reported in CSF. The identified peptides were found to originate from 104 proteins, of which several have been reported to be involved in different disorders of the central nervous system. These results support the notion that CSF peptidomics may be viable complement to proteomics in the search of biomarkers of CNS disorders.

TLQP-21, a VGF-derived peptide, stimulates exocrine pancreatic secretion in the rat

The aims of this paper were to study: (1) the effects of TLQP-21 (non-acronic name), the C-terminal region of the VGF (non-acronic name), polypeptide (from residue 557 to 576 of VGF), on in vitro amylase release from rat isolated pancreatic lobules and acinar cells; (2) the mechanism through which TLQP-21 regulates exocrine pancreatic secretion, by using the muscarinic receptor antagonist atropine (10(-6)M) and the cyclo-oxygenase inhibitor, indomethacin (10(-6)M). On pancreatic lobules of rats, concentrations of TLQP-21 from 10(-7) to 10(-5)M significantly (p<0.05) induced a 2-3-fold increase of baseline pancreatic amylase release, measured at the end of 60 min incubation period. Co-incubation with atropine 10(-6)M did not antagonise the enzyme outflow induced by the peptide. On the contrary, co-incubation of TLQP-21 (10(-7) and 10(-6)M) with indomethacin, at concentration of 10(-6)M, which alone did not modify enzyme secretion, completely suppressed the increase of amylase evoked by TLQP-21 on pancreatic lobules. On rat pancreatic acinar cells, TLQP-21, at all the concentrations tested, was unable to affect exocrine pancreatic secretion, indicating an indirect mechanism of action on acinar cells. These results put in evidence, for the first time, that TLQP-21, a VGF-derived peptide, modulates exocrine pancreatic secretion in rats through a stimulatory mechanism involving prostaglandin release. In conclusion, TLQP-21 could be included among the neurohumoral signals regulating pancreatic exocrine secretion, and increases the knowledge concerning the systems controlling this function.

Secretogranin II; a protein increased in the myocardium and circulation in heart failure with cardioprotective properties

BACKGROUND

Several beneficial effects have been demonstrated for secretogranin II (SgII) in non-cardiac tissue. As cardiac production of chromogranin A and B, two related proteins, is increased in heart failure (HF), we hypothesized that SgII could play a role in cardiovascular pathophysiology.

METHODOLOGY/PRINCIPAL FINDINGS

SgII production was characterized in a post-myocardial infarction heart failure (HF) mouse model, functional properties explored in experimental models, and circulating levels measured in mice and patients with stable HF of moderate severity. SgII mRNA levels were 10.5 fold upregulated in the left ventricle (LV) of animals with myocardial infarction and HF (p<0.001 vs. sham-operated animals). SgII protein levels were also increased in the LV, but not in other organs investigated. SgII was produced in several cell types in the myocardium and cardiomyocyte synthesis of SgII was potently induced by transforming growth factor-β and norepinephrine stimulation in vitro. Processing of SgII to shorter peptides was enhanced in the failing myocardium due to increased levels of the proteases PC1/3 and PC2 and circulating SgII levels were increased in mice with HF. Examining a pathophysiological role of SgII in the initial phase of post-infarction HF, the SgII fragment secretoneurin reduced myocardial ischemia-reperfusion injury and cardiomyocyte apoptosis by 30% and rapidly increased cardiomyocyte Erk1/2 and Stat3 phosphorylation. SgII levels were also higher in patients with stable, chronic HF compared to age- and gender-matched control subjects: median 0.16 (Q1-3 0.14-0.18) vs. 0.12 (0.10-0.14) nmol/L, p<0.001.

CONCLUSIONS

We demonstrate increased myocardial SgII production and processing in the LV in animals with myocardial infarction and HF, which could be beneficial as the SgII fragment secretoneurin protects from ischemia-reperfusion injury and cardiomyocyte apoptosis. Circulating SgII levels are also increased in patients with chronic, stable HF and may represent a new cardiac biomarker.

Role of neurotrophins in the development and function of neural circuits that regulate energy homeostasis

Members of the neurotrophin family, including nerve growth factor, brain-derived neurotrophic factor, neurotrophin-3, and neurotrophin-4/5, and other neurotrophic growth factors such as ciliary neurotrophic factor and artemin, regulate peripheral and central nervous system development and function. A subset of the neurotrophin-dependent pathways in the hypothalamus, brainstem, and spinal cord, and those that project via the sympathetic nervous system to peripheral metabolic tissues including brown and white adipose tissue, muscle and liver, regulate feeding, energy storage, and energy expenditure. We briefly review the role that neurotrophic growth factors play in energy balance, as regulators of neuronal survival and differentiation, neurogenesis, and circuit formation and function, and as inducers of critical gene products that control energy homeostasis.

Prognostic value of chromogranin A in severe sepsis: data from the FINNSEPSIS study

PURPOSE

To assess the prognostic information of chromogranin A (CgA), a marker associated with adrenergic tone and myocardial function, in patients with severe sepsis.

METHODS

CgA levels were measured at the time of study inclusion and 72 h later in 232 patients with severe sepsis recruited from 24 ICUs in Finland (FINNSEPSIS study).

RESULTS

Sixty-five patients (28%) died during the index hospitalization. CgA levels at inclusion and after 72 h correlated with several established indices of risk in sepsis. Patients who died during the hospitalization had higher baseline CgA levels than hospital survivors: 14.0 (Q1-3, 7.4-27.4) versus 9.1 (5.9-15.8) nmol/l, P = 0.002, and after 72 h: 16.2 (9.0-31.1) versus 9.8 (6.0-18.0) nmol/l, P = 0.001. Prior cardiovascular disease (P = 0.04) and cardiovascular SOFA levels on day 3 (P = 0.03) were associated with higher CgA levels after 72 h by linear regression. CgA levels on study inclusion and after 72 h were independently associated with hospital mortality by logistic regression: OR (logarithmically transformed CgA levels) 1.95 (95% CI 1.01-3.77), P = 0.046 and OR 2.03 (95% CI 1.18-3.49), P = 0.01, respectively. The prognostic accuracy was comparable for CgA measurements and SAPS II score, and the addition of CgA measurements to the SAPS II score improved risk stratification of the patients as assessed by the category-free net reclassification index. A CgA level >6.6 nmol/l on study inclusion was associated with septic shock during the hospitalization.

CONCLUSION

CgA levels measured during hospitalization for severe sepsis are associated with cardiovascular dysfunction and may provide additional prognostic information in patients with severe sepsis.

New roles of carboxypeptidase E in endocrine and neural function and cancer

Carboxypeptidase E (CPE) or carboxypeptidase H was first discovered in 1982 as an enkephalin-convertase that cleaved a C-terminal basic residue from enkephalin precursors to generate enkephalin. Since then, CPE has been shown to be a multifunctional protein that subserves many essential nonenzymatic roles in the endocrine and nervous systems. Here, we review the phylogeny, structure, and function of CPE in hormone and neuropeptide sorting and vesicle transport for secretion, alternative splicing of the CPE transcript, and single nucleotide polymorphisms in humans. With this and the analysis of mutant and knockout mice, the data collectively support important roles for CPE in the modulation of metabolic and glucose homeostasis, bone remodeling, obesity, fertility, neuroprotection, stress, sexual behavior, mood and emotional responses, learning, and memory. Recently, a splice variant form of CPE has been found to be an inducer of tumor growth and metastasis and a prognostic biomarker for metastasis in endocrine and nonendocrine tumors.

Chromogranin A and derived peptides in health and disease

Chromogranin A (CgA) is a member of the granins, a family of acidic proteins found in abundance in (neuro)endocrine cells (e.g., in chromaffin cells) and in some tumors. Like other granins, CgA has a granulogenic role in secretory granule biogenesis and is stored in these organelles. CgA is partially processed differentially in various cell types to yield biologically active peptides, such as vasostatin, pancreastatin, catestatin, and serpinins. In this review, we describe the roles of CgA and several of its derived peptides. CgA, which is elevated in the blood of cancer patients, inhibits angiogenesis and exerts protective effects on the endothelial barrier function in tumors, thus affecting response to chemotherapy. Recent studies indicate that the serpinins promote cell survival and myocardial contractility and relaxation. Other peptides such as pancreastatin were found to have significant effects on inhibition of glucose-stimulated insulin secretion and glucose up-take, induction of glycogenolysis in hepatocytes, and inhibition of lipogenesis. In contrast, catestatin has opposite effects to that of pancreastatin in glucose metabolism and lipogenesis. Catestatin appears to also play a significant role in cardiac function, blood pressure regulation, and mutations in the catestatin domain of the CgA gene are associated with hypertension in humans.

Implication of the VGF-derived peptide TLQP-21 in mouse acute and chronic stress responses

The impact of stress is widely recognized in the etiology of multiple disorders. In particular, psychological stress may increase the risk of cardiovascular, metabolic, immune, and mood disorders. Several genes are considered potential candidates to account for the deleterious consequences of stress and recent data point to role of Vgf. VGF mRNA is abundantly expressed in the hypothalamus, where it has been involved in metabolism and energy homeostasis; more recently a link between VGF-derived peptides and mood disorders has been highlighted. The following experiments were performed to address the contribution of the VGF-system to stress induced changes in mice: the distribution of VGF immuno-reactivity in hypothalamic nuclei and its modulation by social stress; the role of VGF-derived peptide TLQP-21 in plasma catecholamine release induced by acute restraint stress (RS); the efficacy of chronic TLQP-21 in a mouse model of chronic subordination stress (CSS). VGF fibers were found in high density in arcuate, dorsomedial, and suprachiasmatic and, at lower density, in lateral, paraventricular, and ventromedial hypothalamic nuclei. Central administration of either 2 or 4 mM TLQP-21 acutely altered the biphasic serum epinephrine release and decreased norepinephrine serum levels in response to RS. Finally, 28-day of 40 μg/day TLQP-21 treatment increased CSS-induced social avoidance of an unfamiliar conspecific. Overall these data support a role for TLQP-21 in stress responses providing a promising starting point to further elucidate its role as a player in stress-related human pathologies.

Characterization of a novel peripheral pro-lipolytic mechanism in mice: role of VGF-derived peptide TLQP-21

The peptides encoded by the VGF gene are gaining biomedical interest and are increasingly being scrutinized as biomarkers for human disease. An endocrine/neuromodulatory role for VGF peptides has been suggested but never demonstrated. Furthermore, no study has demonstrated so far the existence of a receptor-mediated mechanism for any VGF peptide. In the present study, we provide a comprehensive in vitro, ex vivo and in vivo identification of a novel pro-lipolytic pathway mediated by the TLQP-21 peptide. We show for the first time that VGF-immunoreactivity is present within sympathetic fibres in the WAT (white adipose tissue) but not in the adipocytes. Furthermore, we identified a saturable receptor-binding activity for the TLQP-21 peptide. The maximum binding capacity for TLQP-21 was higher in the WAT as compared with other tissues, and selectively up-regulated in the adipose tissue of obese mice. TLQP-21 increases lipolysis in murine adipocytes via a mechanism encompassing the activation of noradrenaline/β-adrenergic receptors pathways and dose-dependently decreases adipocytes diameters in two models of obesity. In conclusion, we demonstrated a novel and previously uncharacterized peripheral lipolytic pathway encompassing the VGF peptide TLQP-21. Targeting the sympathetic nerve–adipocytes interaction might prove to be a novel approach for the treatment of obesity-associated metabolic complications.