Chromogranin-B regulation of IAPP and insulin secretion

Combining mass spectrometry and machine learning to discover bioactive peptides

Peptides play important roles in regulating biological processes and form the basis of a multiplicity of therapeutic drugs. To date, only about 300 peptides in human have confirmed bioactivity, although tens of thousands have been reported in the literature. The majority of these are inactive degradation products of endogenous proteins and peptides, presenting a needle-in-a-haystack problem of identifying the most promising candidate peptides from large-scale peptidomics experiments to test for bioactivity. To address this challenge, we conducted a comprehensive analysis of the mammalian peptidome across seven tissues in four different mouse strains and used the data to train a machine learning model that predicts hundreds of peptide candidates based on patterns in the mass spectrometry data. We provide in silico validation examples and experimental confirmation of bioactivity for two peptides, demonstrating the utility of this resource for discovering lead peptides for further characterization and therapeutic development.

Role and function of granin proteins in diabetes mellitus

The granin glycoprotein family consists of nine acidic proteins; chromogranin A (CgA), chromogranin B (CgB), and secretogranin II-VIII. They are produced by a wide range of neuronal, neuroendocrine, and endocrine cells throughout the human body. Their major intracellular function is to sort peptides and proteins into secretory granules, but their cleavage products also take part in the extracellular regulation of diverse biological processes. The contribution of granins to carbohydrate metabolism and diabetes mellitus is a recent research area. CgA is associated with glucose homeostasis and the progression of type 1 diabetes. WE-14, CgA10-19, and CgA43-52 are peptide derivates of CgA, and act as CD4+ or CD8+ autoantigens in type 1 diabetes, whereas pancreastatin (PST) and catestatin have regulatory effects in carbohydrate metabolism. Furthermore, PST is related to gestational and type 2 diabetes. CgB has a crucial role in physiological insulin secretion. Secretogranins II and III have angiogenic activity in diabetic retinopathy (DR), and are novel targets in recent DR studies. Ongoing studies are beginning to investigate the potential use of granin derivatives as drugs to treat diabetes based on the divergent relationships between granins and different types of diabetes.

Characterization of human pineal gland proteome

The pineal gland is a neuroendocrine gland located at the center of the brain. It is known to regulate various physiological functions in the body through secretion of the neurohormone melatonin. Comprehensive characterization of the human pineal gland proteome has not been undertaken to date. We employed a high-resolution mass spectrometry-based approach to characterize the proteome of the human pineal gland. A total of 5874 proteins were identified from the human pineal gland in this study. Of these, 5820 proteins were identified from the human pineal gland for the first time. Interestingly, 1136 proteins from the human pineal gland were found to contain a signal peptide domain, which indicates the secretory nature of these proteins. An unbiased global proteomic profile of this biomedically important organ should benefit molecular research to unravel the role of the pineal gland in neuropsychiatric and neurodegenerative diseases.

Chromogranin B: intra- and extra-cellular mechanisms to regulate catecholamine storage and release, in catecholaminergic cells and organisms

Chromogranin B (CHGB) is the major matrix protein in human catecholamine storage vesicles. CHGB genetic variation alters catecholamine secretion and blood pressure. Here, effective Chgb protein under-expression was achieved by siRNA in PC12 cells, resulting in ~ 48% fewer secretory granules on electron microscopy, diminished capacity for catecholamine uptake (by ~ 79%), and a ~ 73% decline in stores available for nicotinic cholinergic-stimulated secretion. In vivo, loss of Chgb in knockout mice resulted in a ~ 35% decline in chromaffin granule abundance and ~ 44% decline in granule diameter, accompanied by unregulated catecholamine release into plasma. Over-expression of CHGB was achieved by transduction of a CHGB-expressing lentivirus, resulting in ~ 127% elevation in CHGB protein, with ~ 122% greater abundance of secretory granules, but only ~ 14% increased uptake of catecholamines, and no effect on nicotinic-triggered secretion. Human CHGB protein and its proteolytic fragments inhibited nicotinic-stimulated catecholamine release by ~ 72%. One conserved-region CHGB peptide inhibited nicotinic-triggered secretion by up to ~ 41%, with partial blockade of cationic signal transduction. We conclude that bi-directional quantitative derangements in CHGB abundance result in profound changes in vesicular storage and release of catecholamines. When processed and released extra-cellularly, CHGB proteolytic fragments exert a feedback effect to inhibit catecholamine secretion, especially during nicotinic cholinergic stimulation.

Autocrine regulation of insulin secretion

Impaired insulin secretion from pancreatic β-cells is a major factor in the pathogenesis of type 2 diabetes. The main regulator of insulin secretion is the plasma glucose concentration. Insulin secretion is modified by other nutrients, circulating hormones and the autonomic nervous system, as well as local paracrine and autocrine signals. Autocrine signalling involves diffusible molecules that bind to receptors on the same cell from which they have been released. The first transmitter to be implicated in the autocrine regulation of β-cell function was insulin itself. The importance of autocrine insulin signalling is underscored by the finding that mice lacking insulin receptors in β-cells are glucose intolerant. In addition to insulin, β-cells secrete a variety of additional substances, including peptides (e.g. amylin, chromogranin A and B and their cleavage products), neurotransmitters (ATP and γ-aminobutyric acid) and ions (e.g. zinc). Here we review the autocrine effects of substances secreted from β-cells, with a focus on acute effects in stimulus-secretion coupling, present some novel data and discuss the general significance of autocrine signals for the regulation of insulin secretion.

Granins and granin-related peptides in neuroendocrine tumours

This review focus on neuroendocrine tumours (NETs), with special reference to the immunohistochemical analysis of granins and granin-related peptides and their usefulness in identifying and characterizing the great diversity of NET types. Granins, their derived peptides, and complex protein-processing enzyme systems that cleave granins and prohormones, have to some extent cell-specific expression patterns in normal and neoplastic NE cells. The marker most commonly used in routine histopathology to differentiate between non-NETs and NETs is chromogranin (Cg) A, to some extent CgB. Other members of the granin family may also be of diagnostic value by identifying special NET types, e.g. secretogranin (Sg) VI was only found in pancreatic NETs and phaeochromocytomas. SgIII has recently arisen as an important NET marker; it was strongly expressed in NETs, with some exceptions--phaeochromocytomas expressed few cells and parathyroid adenomas none. Some expression patterns of granin-related peptides seem valuable in differentiating between some benign and malignant NETs, some may also provide prognostic information, among which: well-differentiated NET types expressed more CgA epitopes than the poorly differentiated ones, except insulinomas, where the opposite was noted; medullary thyroid carcinomas containing few cells immunoreactive to a CgB antibody were related to a bad prognosis; C-terminal secretoneurin visualized a cell type related to malignancy in phaeochromocytomas. Further research will probably establish new staining patterns with marker functions for granins in NETs which may be of histopathological diagnostic value.

Defective secretion of islet hormones in chromogranin-B deficient mice

Granins are major constituents of dense-core secretory granules in neuroendocrine cells, but their function is still a matter of debate. Work in cell lines has suggested that the most abundant and ubiquitously expressed granins, chromogranin A and B (CgA and CgB), are involved in granulogenesis and protein sorting. Here we report the generation and characterization of mice lacking chromogranin B (CgB-ko), which were viable and fertile. Unlike neuroendocrine tissues, pancreatic islets of these animals lacked compensatory changes in other granins and were therefore analyzed in detail. Stimulated secretion of insulin, glucagon and somatostatin was reduced in CgB-ko islets, in parallel with somewhat impaired glucose clearance and reduced insulin release, but normal insulin sensitivity in vivo. CgB-ko islets lacked specifically the rapid initial phase of stimulated secretion, had elevated basal insulin release, and stored and released twice as much proinsulin as wildtype (wt) islets. Stimulated release of glucagon and somatostatin was reduced as well. Surprisingly, biogenesis, morphology and function of insulin granules were normal, and no differences were found with regard to beta-cell stimulus-secretion coupling. We conclude that CgB is not required for normal insulin granule biogenesis or maintenance in vivo, but is essential for adequate secretion of islet hormones. Consequentially CgB-ko animals display some, but not all, hallmarks of human type-2 diabetes. However, the molecular mechanisms underlying this defect remain to be determined.

New insights into granin-derived peptides: evolution and endocrine roles

The granin protein family is composed of two chromogranin and five secretogranin members that are acidic, heat-stable proteins in secretory granules in cells of the nervous and endocrine systems. We report that there is little evidence for evolutionary relationships among the granins except for the chromogranin group. The main granin members, including chromogranin A and B, and secretogranin II are moderately conserved in the vertebrates. Several small bioactive peptides can be generated by proteolysis from those homologous domains existing within the granin precursors, reflecting the conservation of biological activities in different vertebrates. In this context, we focus on reviewing the distribution and function of the major granin-derived peptides, including vasostatin, bovine CgB(1-41) and secretoneurin in vertebrate endocrine systems, especially those associated with growth, glucose metabolism and reproduction.

Neuroendocrine inhibition of glucose production and resistance to cancer in dwarf mice

Pit1 null (Snell dwarf) and Proph1 null (Ames dwarf) mutant mice lack GH, PRL and TSH. Snell and Ames dwarf mice also exhibit reduced IGF-I, resistance to cancer and a longer lifespan than control mice. Endogenous glucose production during fasting is reduced in Snell dwarf mice compared to fasting control mice. In view of cancer cell dependence on glucose for energy, low endogenous glucose production may provide Snell dwarf mice with resistance to cancer. We investigated whether endogenous glucose production is lower in Snell dwarf mice during feeding. Inhibition of endogenous glucose production by glucose injection was enhanced in 12 to 14 month-old female Snell dwarf mice. Thus, we hypothesize that lower endogenous glucose production during feeding and fasting reduces cancer cell glucose utilization providing Snell dwarf mice with resistance to cancer. The elevation of circulating adiponectin, a hormone produced by adipose tissue, may contribute to the suppression of endogenous glucose production in 12 to 14 month-old Snell dwarf mice. We compared the incidence of cancer at time of death between old Snell dwarf and control mice. Only 18% of old Snell dwarf mice had malignant lesions at the time of death compared to 82% of control mice. The median ages at death for old Snell dwarf and control mice were 33 and 26 months, respectively. By contrast, previous studies showed a high incidence of cancer in old Ames dwarf mice at the time of death. Hence, resistance to cancer in old Snell dwarf mice may be mediated by neuroendocrine factors that reduce glucose utilization besides elevated adiponectin, reduced IGF-I and a lack of GH, PRL and TSH, seen in both Snell and Ames dwarf mice. Proteomics analysis of pituitary secretions from Snell dwarf mice confirmed the absence of GH and PRL, the secretion of ACTH and elevated secretion of Chromogranin B and Secretogranin II. Radioimmune assays confirmed that circulating Chromogranin B and Secretogranin II were elevated in 12 to 14 month-old Snell dwarf mice. In summary, our results in Snell dwarf mice suggest that the pituitary gland and adipose tissue are part of a neuroendocrine loop that lowers the risk of cancer during aging by reducing the availability of glucose.

The importance of chromogranin A in the development and function of endocrine pancreas

BACKGROUND

Chromogranin (Cg) A is expressed in neuroendocrine and neuronal tissues. It is involved in the generation of secretory granules and is cleaved to form biologically active peptides. Targeted ablation of the Chga gene resulted in increased plasma catecholamines, high blood pressure, and decreased size and number of adrenal medullary chromaffin granules. The aim of this study was to determine whether Chga null mice display changes in the morphology and function of the endocrine pancreas.

MATERIALS AND METHODS

Sections of pancreata from Chga-/-, Chga+/- and Chga+/+ mice, were immunostained with antibodies against synaptophysin, CgA, CgB, secretogranin II and the four major pancreatic islet hormones. Plasma was analysed for glucose, insulin, glucagon, somatostatin and pancreatic polypeptide (PP).

RESULTS

CgA epitopes were undetectable in the islets of Chga-/- animals. CgB and secretogranin II epitopes were expressed in the islets of all animal groups albeit with decreased expression in Chga-/- islets. The islet number and size were decreased in the Chga-/- animals compared with Chga+/+. The proportion of insulin cells was decreased but somatostatin and PP cells were increased in Chga-/- mice compared to Chga+/+ mice. The nuclear size was decreased in insulin cells and increased in somatostatin cells in Chga-/- mice. Plasma insulin level was markedly decreased in the Chga-/- mice although fasting plasma glucose and glucagon were normal.

CONCLUSION

Ablation of the Chga gene affected the islet volume, the composition, distribution and nuclear size of islet cell types and plasma insulin concentration. Our data indicate decreased insulin cell function and increased glucagon cell function. Our study shows that CgA exerts a significant influence on the endocrine pancreas with importance in maintaining islet volume, cellular composition and function.

Beta cell chromogranin B is partially segregated in distinct granules and can be released separately from insulin in response to stimulation

AIMS/HYPOTHESIS

We investigated, in three beta cell lines (INS-1E, RIN-5AH, betaTC3) and in human and rodent primary beta cells, the storage and release of chromogranin B, a secretory protein expressed in beta cells and postulated to play an autocrine role. We asked whether chromogranin B is stored together with and discharged in constant ratio to insulin upon various stimuli.

METHODS

The intracellular distribution of insulin and chromogranin B was revealed by immunofluorescence followed by three-dimensional image reconstruction and by immunoelectron microscopy; their stimulated discharge was measured by ELISA and immunoblot analysis of homogenates and incubation media.

RESULTS

Insulin and chromogranin B, co-localised in the Golgi complex/trans-Golgi network, appeared largely segregated from each other in the secretory granule compartment. In INS-1E cells, the percentage of granules positive only for insulin or chromogranin B and of those positive for both was 66, 7 and 27%, respectively. In resting cells, both insulin and chromogranin B were concentrated in the granule cores; upon stimulation, chromogranin B (but not insulin) was largely redistributed to the core periphery and the surrounding halo. Strong stimulation with a secretagogue mixture induced parallel release of insulin and chromogranin B, whereas with 3-isobutyl-1-methylxantine and forskolin +/- high glucose release of chromogranin B predominated. Weak, Ca(2+)-dependent stimulation with ionomycin or carbachol induced exclusive release of chromogranin B, suggesting a higher Ca(2+) sensitivity of the specific granules.

CONCLUSIONS/INTERPRETATION

The unexpected complexity of the beta cell granule population in terms of heterogeneity, molecular plasticity and the differential discharge, could play an important role in physiological control of insulin release and possibly also in beta cell pathology.

Cerebrospinal fluid concentrations of peptides derived from chromogranin B and secretogranin II are decreased in multiple sclerosis

Novel biomarkers for multiple sclerosis (MS) could improve diagnosis and provide clues to pathogenesis. In this study surface-enhanced laser desorption/ionization time-of-flight mass spectrometry was used to analyze protein expression in CSF from 46 MS patients, 46 healthy siblings to the patients, and 50 unrelated healthy controls. Twenty-four proteins in the mass range 2-10 kDa were expressed at significantly different levels (p < 0.01) in a robust manner when comparing the three groups. Identities of three proteins were determined using biochemical purification followed by tandem mass spectrometric analysis. Immunoprecipitation experiments confirmed the identities for two peptides derived from chromogranin B (m/z 6252) and from secretogranin II (m/z 3679). These peptides were all decreased in MS when compared with siblings or controls. Radioimmunoassays specific for each peptide confirmed these differences. The lowered concentrations did not correlate to the axonal damage marker neurofilament light protein and may thus reflect functional changes rather than neurodegeneration. Further studies will investigate the involvement of these peptides in MS pathogenesis.

Functional single-nucleotide polymorphisms in the secretogranin III (SCG3) gene that form secretory granules with appetite-related neuropeptides are associated with obesity

CONTEXT

Genetic factors are important for the development of obesity. However, the genetic background of obesity still remains unclear.

OBJECTIVE

Our objective was to search for obesity-related genes using a large number of gene-based single-nucleotide polymorphisms (SNPs).

DESIGN AND SETTING

We conducted case-control association analyses using 94 obese patients and 658 controls with 62,663 SNPs selected from the SNP database. SNPs that possessed P < or = 0.02 were further analyzed using 796 obese and 711 control subjects. One SNP (rs3764220) in the secretogranin III (SCG3) gene showed the lowest P value (P = 0.0000019). We sequenced an approximately 300-kb genomic region around rs3764220 and discovered SNPs for haplotype analyses. SCG3 was the only gene within a haplotype block that contained rs3764220. The functions of SCG3 were studied.

PATIENTS

Obese subjects (body mass index > or = 30 kg/m(2), n = 890) and control subjects (general population; n = 658, body mass index < or = 25 kg/m(2); n = 711) were recruited for this study.

RESULTS

Twelve SNPs in the SCG3 gene including rs3764220 were in almost complete linkage disequilibrium and significantly associated with an obesity phenotype. Two SNPs (rs16964465, rs16964476) affected the transcriptional activity of SCG3, and subjects with the minor allele seemed to be resistant to obesity (odds ratio, 9.23; 95% confidence interval, 2.77-30.80; chi(2) = 19.2; P = 0.0000067). SCG3 mRNA and immunoreactivity were detected in the paraventricular nucleus, lateral hypothalamic area, and arcuate nucleus, and the protein coexisted with orexin, melanin-concentrating hormone, neuropeptide Y, and proopiomelanocortin. SCG3 formed a granule-like structure together with these neuropeptides.

CONCLUSIONS

Genetic variations in the SCG3 gene may influence the risk of obesity through possible regulation of hypothalamic neuropeptide secretion.

A panel of 13 region-specific radioimmunoassays for measurements of human chromogranin B

INTRODUCTION

The primary structure of human chromogranin B (CgB) contains 15 pairs of basic amino acids, which are potential cleavage sites for specific endogenous proteases, but also other sites in the molecule can be subjected to cleavage. Several CgB-related peptides have been identified in tissue extracts.

MATERIALS AND METHODS

Peptides homologous to defined parts of the human CgB molecule were selected and synthesized. Antibodies were raised and 13 specific radioimmunoassays were developed. Plasma samples from 19 patients with neuroendocrine tumors were collected and measured in all assays.

RESULTS

All region-specific assays measured circulating levels of CgB-related peptides. Only five of the assays measured high concentrations of circulating CgB and two of them correlated with that of intact chromogranin A (CgA).

CONCLUSION

The assays presented allow measurements of defined regions of CgB and will thus become important tools for further studies of the processing of CgB. One of the assays merit further investigations as a new marker for neuroendocrine tumors.

Neuroendocrine cell markers for pancreatic islets and tumors

The authors review the application of a variety of neuroendocrine cell markers to identify pancreatic islet cells and tumors. In the past, several empiric histochemical techniques had been used to demonstrate neuroendocrine cells, particularly the Grimelius argyrophilic stain. The development of immunohistochemistry made it possible to demonstrate specific cell products such as regulatory peptides, thus allowing the classification of pancreatic neuroendocrine tumors with a view to clinical symptoms. However, it is not always possible to visualize regulatory peptides in these tumors. It is therefore important to use broad-spectrum neuroendocrine cell markers to identify the neuroendocrine nature. These markers are proteins localized in the secretory granules (core- or membrane-related), in the cytosol, or in the cellular membrane. The markers most commonly used in routine histopathology are the secretory granule proteins chromogranin A and synaptophysin and the cytosolic enzyme neuronspecific enolase. Other new markers (e.g., synaptic vesicle protein 2) are of general diagnostic value. Region-specific antibodies to chromogranin A can be valuable in differentiating between benign and malignant neuroendocrine tumors. Some markers may be related to the functioning characteristics of pancreatic neuroendocrine tumors, such as prohormone convertases. In addition, markers giving further complementary information have been identified, such as five somatostatin receptor subtypes, the expression of which varies markedly in pancreatic neuroendocrine tumors. Antibodies against all somatostatin receptor subtypes are now commercially available, and immunohistochemical investigation of its expression should be routinely applied when considering treatment with somatostatin analogs.

Presence and release of the chromogranin B-derived secretolytin-like peptide KR-11 from the porcine spleen

Chromogranin B (CgB) is a major matrix protein in secretory granules/large dense-cored vesicles and a precursor for smaller peptides. In an earlier study, we have identified a secretolytin-like peptide (KR-11, pCgB(637-647)) from porcine chromaffin granules. Further evidence is presented here to show the processing of chromogranin B to this peptide during axonal transport in the splenic nerve and its release in the spleen upon various conditions of stimulation. Immunohistochemical staining showed that in the porcine spleen chromogranin B and NPY completely colocalize in nerve fibres and varicosities in blood vessel walls and trabeculae, and along the loose network of smooth muscle cells in the red pulp, as identified by their alpha-smooth muscle cell actin content. No antibacterial activity was found for the porcine secretolytin-like peptide, KR-11. The change of one amino acid residue (Thr-->Asn) in the porcine homologous fragment of secretolytin appears to be responsible for its loss of antibacterial activity.

Cytological and immunocytochemical characterization of the insulin secreting insulinoma cell line RINm5F

The rat insulinoma cell line RINm5F, an insulin secreting pancreatic beta cell line, has been used as an attractive model for basic studies of the mechanisms of insulin secretion and, more recently, as a model for the development of alternative methods for the treatment of diabetes. To elucidate the cytological properties and expression patterns of hormones of the gastro-entero-pancreatic system, suspensions of RINm5F cells were investigated by various methods including immunocytochemistry on serial semithin sections, quantitative immunocytochemistry, routine electron microscopy, immuno-electron microscopy, in situ hybridization, and TUNEL technique. At the ultrastructural level, several phenotypes of RIm5F cells were characterized by differences in the number, shape, size, and density of their secretory granules. The most common type contained a mixture of round granules varying in size and electron density. A second type predominantly contained relatively large, moderately dense granules. Moreover, a minority of cells was characterized by the occurrence of polymorphous electron dense granules or the complete absence of any secretory granules. The immunohistochemical data showed that, among the established islet hormones, insulin was present in more than 50% of cells, whereas glucagon and somatostatin occurred only sporadically. Though cells positive for pancreatic polypeptide (PP) were not found, PP-related peptides (NPY and PYY) however could be detected in a minority of cells. The great majority of RINm5F cells were immunoreactive for chromogranin B (CgB), followed by insulin, chromogranin A (CgA), and serotonin (5-HT). In addition to intercellular differences in the density of immunostaining, numerous colocalizations of immunoreactivities were found, suggesting that RINm5F cells represent a mixture of subtypes concerning the individual pattern of hormone expression. The present results reveal a wide range of heterogeneity with respect to the morphology and especially the hormone content between individual RINm5F cells.

Genome-wide linkage analysis of chromogranin B expression in the CEPH pedigrees: implications for exocytotic sympathochromaffin secretion in humans

Chromogranin B (CgB), a major member of the chromogranin/secretogranin family of catecholamine storage vesicle secretory proteins, plays both intracellular (vesiculogenic) and extracellular (prohormone) roles in the neuroendocrine system, and its biosynthesis and release are under the control of efferent sympathetic nerve traffic ("stimulus-transcription coupling"). To explore the role of heredity in control of CgB, we conducted a genome-wide linkage analysis of CgB release in 12 extended CEPH (Centre d'Etude du Polymorphisme Humain) pedigrees. Region-specific radioimmunoassays were used to measure five CgB fragments in plasma: CgB1-16, CgB312-331, CgB439-451, CgB568-577, and CgB647-657. Substantial heritability, as measured by h2r, was observed for three of the fragment concentrations, CgB312-331, CgB439-451, and CgB568-577, which yielded h2r estimates ranging from 0.378 (P = 0.002) to 0.910 (P < 0.0000001). Variance-component genome-wide linkage analysis with 654 microsatellite markers at 5 cM spacing identified a major quantitative trait locus for CgB312-331 on chromosome 11q24-q25 with a maximum multipoint LOD score of 5.84. Significant allelic associations between markers in the region and CgB levels were also observed. Although the 2-LOD confidence interval for linkage did not include the CgB locus itself, known trans-activators of the CgB gene promoter, or prohormone cleaving proteases, examination of positional candidate loci within this region yielded novel and plausible physiological candidates for further exploration. Allelic variation in this region may thus influence effects of sympathetic outflow on target organs in humans.

Region-specific antibodies to chromogranin B display various immunostaining patterns in human endocrine pancreas

Chromogranin (Cg) B is an acidic glycoprotein present in neuroendocrine tissue. The sequence shows several dibasic amino acid positions susceptible to proteolytic cleavage. The purpose of this study was to elucidate the expression of CgB epitopes in the human endocrine pancreas. Tissue sections of six human pancreata were immunostained with 16 different region-specific antibodies to the CgB molecule, using double immunofluorescence techniques. The CgB epitope pattern varied in the four major islet cell types. B (insulin)-cells expressed immunoreactivity to all region-specific antibodies. The antibodies to the N-terminal and mid-portions of CgB showed moderate immunoreactivity, the C-terminal antibodies weak. A (glucagon)-cells were reactive only to the N-terminal and mid-portion antibodies but, after microwave pretreatment, to all antibodies, whereas D (somatostatin)-cells expressed only the sequence CgB 244-255 and a subpopulation CgB 580-595. PP (pancreatic polypeptide) cells were immunostained with antibodies between CgB 1-417 and a few with CgB 580-593. The fragment CgB 244-255 was expressed in all four cell types. The cause of these differences may be cell-specific cleavage or masking of the molecule, but varying translation of CgB mRNA is also possible. The extent to which these epitopes reflect fragments having biological functions remains to be evaluated.

Presence of chromogranin-derived antimicrobial peptides in plasma during coronary artery bypass surgery and evidence of an immune origin of these peptides

Chromogranin A (CGA) and chromogranin B (CGB) are acidic proteins stored in secretory organelles of endocrine cells and neurons. In addition to their roles as helper proteins in the packaging of peptides, they may serve as prohormones to generate biologically active peptides such as vasostatin-1 and secretolytin. These molecules derived from CGA and CGB, respectively, possess antimicrobial properties. The present study demonstrates that plasmatic levels of both vasostatin-1 and secretolytin increase during surgery in patients undergoing cardiopulmonary bypass (CPB). Vasostatin-1 and secretolytin, initially present in plasma at low levels, are released just after skin incision. Consequently, they can be added to enkelytin, an antibacterial peptide derived from proenkephalin A, for the panoply of components acting as a first protective barrier against hypothetical invasion of pathogens, which may occur during surgery. CGA and CGB, more commonly viewed as markers for endocrine and neuronal cells, were also found to have an immune origin. RNA messengers coding for CGB were amplified by reverse transcription-polymerase chain reaction in human monocytes, and immunocytochemical analysis by confocal microscopy revealed the presence of CGA or CGB or both in monocytes and neutrophils. A combination of techniques including confocal microscopic analysis, mass spectrometry measurement, and antibacterial tests allowed for the identification of the positive role of interleukin 6 (IL-6) in the secretolytin release from monocytes in vitro. Because IL-6 release is known to be strongly enhanced during CPB, we suggest a possible relationship between IL-6 and the increased level of secretolytin in patients undergoing CPB.