Interaction of the catecholamine release-inhibitory peptide catestatin (human chromogranin A(352-372)) with the chromaffin cell surface and Torpedo electroplax: implications for nicotinic cholinergic antagonism

The Role of Catestatin in Preeclampsia

Preeclampsia (PE) is a unique pregnancy disorder affecting women across the world. It is characterized by the new onset of hypertension with coexisting end-organ damage. Although the disease has been known for centuries, its exact pathophysiology and, most importantly, its prevention remain elusive. The basis of its associated molecular changes has been attributed to the placenta and the hormones regulating its function. One such hormone is chromogranin A (CgA). In the placenta, CgA is cleaved to form a variety of biologically active peptides, including catestatin (CST), known inter alia for its vasodilatory effects. Recent studies indicate that the CST protein level is diminished both in patients with hypertension and those with PE. Therefore, the aim of the present paper is to review the most recent and most relevant in vitro, in vivo, and clinical studies to provide an overview of the proposed impact of CST on the molecular processes of PE and to consider the possibilities for future experiments in this area.

Catestatin: Antimicrobial Functions and Potential Therapeutics

The rapid increase in drug-resistant and multidrug-resistant infections poses a serious challenge to antimicrobial therapies, and has created a global health crisis. Since antimicrobial peptides (AMPs) have escaped bacterial resistance throughout evolution, AMPs are a category of potential alternatives for antibiotic-resistant "superbugs". The Chromogranin A (CgA)-derived peptide Catestatin (CST: hCgA352-372; bCgA344-364) was initially identified in 1997 as an acute nicotinic-cholinergic antagonist. Subsequently, CST was established as a pleiotropic hormone. In 2005, it was reported that N-terminal 15 amino acids of bovine CST (bCST1-15 aka cateslytin) exert antibacterial, antifungal, and antiyeast effects without showing any hemolytic effects. In 2017, D-bCST1-15 (where L-amino acids were changed to D-amino acids) was shown to exert very effective antimicrobial effects against various bacterial strains. Beyond antimicrobial effects, D-bCST1-15 potentiated (additive/synergistic) antibacterial effects of cefotaxime, amoxicillin, and methicillin. Furthermore, D-bCST1-15 neither triggered bacterial resistance nor elicited cytokine release. The present review will highlight the antimicrobial effects of CST, bCST1-15 (aka cateslytin), D-bCST1-15, and human variants of CST (Gly364Ser-CST and Pro370Leu-CST); evolutionary conservation of CST in mammals; and their potential as a therapy for antibiotic-resistant "superbugs".

Serum Catestatin Level as a Stratification Assessment Tool in Non-Critical COVID-19 Patients

Introduction: Catestatin (CST) is a peptide with immunomodulatory, anti-inflammatory, and anti-microbial activities. There are only a few studies that have investigated plasma CST levels in COVID-19 patients (mostly in ICU patients). In our work, the aim was to demonstrate serum CST levels and their correlation with clinical outcomes in a group of severe COVID-19 patients admitted to the non-ICU department. Methods: The subjects were 32 patients (25 females, 7 males) admitted to the non-ICU unit for COVID-19 patients. Results: CST levels in our cohort were higher (8.91 ± 7.00) than previously reported CST levels in control subjects. We found a significant positive correlation between serum CST levels and C-reactive protein (r = 0.423, p = 0.008), D-dimers (r = 0.395, p = 0.013), hsTNT (high-sensitivity troponin T) (r = 0.603, p < 0.001), proBNP (N-terminal pro-brain natriuretic peptide) (r = 0.569, p < 0.001), and hospitalization days (r = 0.388, p = 0.014). There was a difference between groups of participants with SOFA <3 (n = 18) and SOFA >=3 (n = 14) in catestatin serum levels (7.25 ± 3.66 vs. 11.05 ± 9.52 ng/mL), but the difference was statistically insignificant (p = 0.065). Conclusion: We considered plasma CST level at hospital admission as a possible tool for early risk assessment in non-critical COVID-19 patients. This study is an attempt to clarify the complex pathophysiological mechanisms present in the development of severe forms of SARS-CoV2 infection.

Catestanin – a promising biological marker for heart failure: A review

The epidemic of heart failure (HF) is one of the problems that the global health system has been facing for decades. HF is a multicomponent clinical syndrome caused by dysfunction of the heart and its pathological remodeling. In addition to the well-known natriuretic peptides, a number of cardiovascular biological markers have now been identified that provide clinicians with additional opportunities in diagnosing, classifying, predicting, and monitoring the effectiveness of treating patients with HF. From the position of establishing the sympathetic load in patients with HF, it seems very promising to assess the concentrations of catestatin. The presented data of our literature review suggest that catestatin is probably a reliable biological marker of the activity of the sympathetic division of the autonomic nervous system, and its elevated concentrations in patients with HF reflect the severity of the pathological process. However, despite the reliable results of studies, the clinical significance of assessing the values of this marker both separately and in the framework of a multimarker model requires further study in larger prospective clinical studies.

Neuropilin-1 and Integrins as Receptors for Chromogranin A-Derived Peptides

Human chromogranin A (CgA), a 439 residue-long member of the "granin" secretory protein family, is the precursor of several peptides and polypeptides involved in the regulation of the innate immunity, cardiovascular system, metabolism, angiogenesis, tissue repair, and tumor growth. Despite the many biological activities observed in experimental and preclinical models for CgA and its most investigated fragments (vasostatin-I and catestatin), limited information is available on the receptor mechanisms underlying these effects. The interaction of vasostatin-1 with membrane phospholipids and the binding of catestatin to nicotinic and b2-adrenergic receptors have been proposed as important mechanisms for some of their effects on the cardiovascular and sympathoadrenal systems. Recent studies have shown that neuropilin-1 and certain integrins may also work as high-affinity receptors for CgA, vasostatin-1 and other fragments. In this case, we review the results of these studies and discuss the structural requirements for the interactions of CgA-related peptides with neuropilin-1 and integrins, their biological effects, their mechanisms, and the potential exploitation of compounds that target these ligand-receptor systems for cancer diagnosis and therapy. The results obtained so far suggest that integrins (particularly the integrin avb6) and neuropilin-1 are important receptors that mediate relevant pathophysiological functions of CgA and CgA fragments in angiogenesis, wound healing, and tumor growth, and that these interactions may represent important targets for cancer imaging and therapy.

Assessment of plasma Catestatin in COVID-19 reveals a hitherto unknown inflammatory activity with impact on morbidity-mortality

Introduction

Neuroendocrine cells release Catestatin (CST) from Chromogranin A (CgA) to regulate stress responses. As regards COVID-19 patients (COVID+) requiring oxygen supply, to date nobody has studied CST as a potential mediator in the regulation of immunity.

Patients & Methods

Admission plasma CST and CgA - its precursor - concentrations were measured (ELISA test) in 73 COVID+ and 27 controls. Relationships with demographics, comorbidities, disease severity and outcomes were analysed (Mann-Whitney, Spearman correlation tests, ROC curves).

Results

Among COVID+, 49 required ICU-admission (COVID+ICU+) and 24 standard hospitalization (COVID+ICU-). Controls were either healthy staff (COVID-ICU-, n=11) or COVID-ICU+ patients (n=16). Median plasma CST were higher in COVID+ than in controls (1.6 [1.02; 3.79] vs 0.87 [0.59; 2.21] ng/mL, p<0.03), with no difference between COVID+ and COVID-ICU+. There was no difference between groups in either CgA or CST/CgA ratios, but these parameters were lower in healthy controls (p<0.01). CST did not correlate with either hypoxia- or usual inflammation-related parameters. In-hospital mortality was similar whether COVID+ or not, but COVID+ had longer oxygen support and more complications (p<0.03). CST concentrations and the CST/CgA ratio were associated with in-hospital mortality (p<0.01) in COVID+, whereas CgA was not. CgA correlated with care-related infections (p<0.001).

Conclusion

Respiratory COVID patients release significant amounts of CST in the plasma making this protein widely available for the neural regulation of immunity. If confirmed prospectively, plasma CST will reliably help in predicting in-hospital mortality, whereas CgA will facilitate the detection of patients prone to care-related infections.

Role of Catestatin in the Cardiovascular System and Metabolic Disorders

Catestatin is a multifunctional peptide that is involved in the regulation of the cardiovascular and immune systems as well as metabolic homeostatis. It mitigates detrimental, excessive activity of the sympathetic nervous system by inhibiting catecholamine secretion. Based on in vitro and in vivo studies, catestatin was shown to reduce adipose tissue, inhibit inflammatory response, prevent macrophage-driven atherosclerosis, and regulate cytokine production and release. Clinical studies indicate that catestatin may influence the processes leading to hypertension, affect the course of coronary artery diseases and heart failure. This review presents up-to-date research on catestatin with a particular emphasis on cardiovascular diseases based on a literature search.

Putative regulation of macrophage-mediated inflammation by catestatin

Catestatin (CST) is a bioactive cleavage product of the neuroendocrine prohormone chromogranin A (CgA). Recent findings show that CST can exert anti-inflammatory and antiadrenergic effects by suppressing the inflammatory actions of mammalian macrophages. However, recent findings also suggest that macrophages themselves are major CST producers. Here, we hypothesize that macrophages produce CST in an inflammation-dependent manner and thereby might self-regulate inflammation in an autocrine fashion. CST is associated with pathological conditions hallmarked by chronic inflammation, including autoimmune, cardiovascular, and metabolic disorders. Since intraperitoneal injection of CST in mouse models of diabetes and inflammatory bowel disease has been reported to be beneficial for mitigating disease, we posit that CST should be further investigated as a candidate target for treating certain inflammatory diseases.

Catestatin as a Biomarker of Cardiovascular Diseases: A Clinical Perspective

Accounting for almost one-third of the global mortality, cardiovascular diseases (CVDs) represent a major global health issue. Emerging data suggest that most of the well-established mechanistic explanations regarding the cardiovascular pathophysiology are flawed, and cannot fully explain the progression and long-term effects of these diseases. On the other hand, dysregulation of the sympathetic nervous system (SNS) has emerged as an important player in the pathophysiology of CVDs. Even though upregulated SNS activity is an essential compensatory response to various stress conditions, in the long term, it becomes a major contributor to both cardiac dysfunction and vascular damage. Despite the fact that the importance of SNS hyperactivity in the setting of CVDs has been well-appreciated, its exact quantification and clinical application in either diagnostics or therapy of CVDs is still out of reach. Nevertheless, in recent years a number of novel laboratory biomarkers implicated in the pathophysiology of SNS activation have been explored. Specifically, in this review, we aimed to discuss the role of catestatin, a potent physiological inhibitor of catecholamine spillover that offers cardioprotective effects. Limited data indicate that catestatin could also be a reliable indirect marker of SNS activity and it is likely that high CST levels reflect advanced CV disease burden. Consequently, large-scale studies are required to validate these observations in the upcoming future.

Cateslytin abrogates lipopolysaccharide-induced cardiomyocyte injury by reducing inflammation and oxidative stress through toll like receptor 4 interaction

Global public health is threatened by new pathogens, antimicrobial resistant microorganisms and a rapid decline of conventional antimicrobials efficacy. Thus, numerous medical procedures become life-threating. Sepsis can lead to tissue damage such as myocardium inflammation, associated with reduction of contractility and diastolic dysfunction, which may cause death. In this perspective, growing interest and attention are paid on host defence peptides considered as new potential antimicrobials. In the present study, we investigated the physiological and biochemical properties of Cateslytin (Ctl), an endogenous antimicrobial chromogranin A-derived peptide, in H9c2 cardiomyocytes exposed to lipopolysaccharide (LPS) infection. We showed that both Ctl (L and D) enantiomers, but not their scrambled counterparts, significantly increased cardiomyocytes viability following LPS, even if L-Ctl was effective at lower concentration (1 nM) compared to D-Ctl (10 nM). L-Ctl mitigated LPS-induced LDH release and oxidative stress, as visible by a reduction of MDA and protein carbonyl groups content, and by an increase of SOD activity. Molecular docking simulations strongly suggested that L-Ctl modulates TLR4 through a direct binding to the partner protein MD-2. Molecular analyses indicated that the protection mediated by L-Ctl against LPS-evoked sepsis targeted the TLR4/ERK/JNK/p38-MAPK pathway, regulating NFkB p65, NFkB p52 and COX2 expression and repressing the mRNA expression levels of the LPS-induced proinflammatory factors IL-1β, IL-6, TNF-α and NOS2. These findings indicate that Ctl could be considered as a possible candidate for the development of new antimicrobials strategies in the treatment of myocarditis. Interestingly, L-enantiomeric Ctl showed remarkable properties in strengthening the anti-inflammatory and anti-oxidant effects on cardiomyocytes.

Catestatin in defense of oxidative-stress-induced apoptosis: A novel mechanism by activating the beta2 adrenergic receptor and PKB/Akt pathway in ischemic-reperfused myocardium

Apoptosis induced by oxidative stress is one of the most important cardiomyocytes losses during ischemia-reperfusion (I/R). Catestatin (CST) has been demonstrated to have the anti-oxidative capacity in vitro. We hypothesized that CST intervention could reduce apoptosis of cardiomyocytes induced by oxidative stress in I/R. In Langendorff-perfused rat heart global I/R model, CST was introduced at the reperfusion stage. In comparison to the control group, CST led to preservation on activities of superoxide dismutase and glutathione peroxidase, improvement of hemodynamics, and reduced infarction area in reperfused myocardium. The protection of CST was also shown by less apoptotic cardiomyocytes in TUNEL staining, less caspase-3 activation, and increased phosphorylation of protein kinase B (PKB/Akt) in Western blot. To further demonstrate the benefits of CST and explore the possible underlying mechanism, H₂O₂-challenged primary-cultured neonatal rat cardiomyocytes were used to simulate the oxidative-stressed scenario. CST incubation with the H₂O₂-challenged cardiomyocytes led to reduction of apoptosis, which was demonstrated by less Hoechst 33342 positive staining of nuclei, less caspase-3 activation, and DNA fragmentation. The effect of CST was abrogated by pretreatment of the cardiomyocytes with the PI3K inhibitor LY294002. Furthermore, Akt activation and the anti-apoptosis effect of CST were abolished by pretreatment of the cardiomyocytes with β2 receptor inhibitor ICI118551. Thus, the salvage of oxidative-stress-induced apoptotic cardiomyocytes in I/R by CST might involve activation β2 receptor and regulation of PI3K/Akt signaling in reperfusion injury salvage kinase (RISK) pathway.

Chromogranin A and its fragments in cardiovascular, immunometabolic, and cancer regulation

Chromogranin A (CgA)-the index member of the chromogranin/secretogranin secretory protein family-is ubiquitously distributed in endocrine, neuroendocrine, and immune cells. Elevated levels of CgA-related polypeptides, consisting of full-length molecules and fragments, are detected in the blood of patients suffering from neuroendocrine tumors, heart failure, renal failure, hypertension, rheumatoid arthritis, and inflammatory bowel disease. Full-length CgA and various CgA-derived peptides, including vasostatin-1, pancreastatin, catestatin, and serpinin, are expressed at different relative levels in normal and pathological conditions and exert diverse, and sometime opposite, biological functions. For example, CgA is overexpressed in genetic hypertension, whereas catestatin is diminished. In rodents, the administration of catestatin decreases hypertension, cardiac contractility, obesity, atherosclerosis, and inflammation, and it improves insulin sensitivity. By contrast, pancreastatin is elevated in diabetic patients, and the administration of this peptide to obese mice decreases insulin sensitivity and increases inflammation. CgA and the N-terminal fragment of vasostatin-1 can enhance the endothelial barrier function, exert antiangiogenic effects, and inhibit tumor growth in animal models, whereas CgA fragments lacking the CgA C-terminal region promote angiogenesis and tumor growth. Overall, the CgA system, consisting of full-length CgA and its fragments, is emerging as an important and complex player in cardiovascular, immunometabolic, and cancer regulation.

Spatiotemporal Regulation of Tumor Angiogenesis by Circulating Chromogranin A Cleavage and Neuropilin-1 Engagement

The unbalanced production of pro- and antiangiogenic factors in tumors can lead to aberrant vasculature morphology, angiogenesis, and disease progression. In this study, we report that disease progression in various murine models of solid tumors is associated with increased cleavage of full-length chromogranin A (CgA), a circulating vasoregulatory neurosecretory protein. Cleavage of CgA led to the exposure of the highly conserved PGPQLR site, which corresponds to residues 368-373 of human CgA_1-373, a fragment that has proangiogenic activity. Antibodies against this site, unable to bind full-length CgA, inhibited angiogenesis and reduced tumor perfusion and growth. The PGPQLR sequence of the fragment, but not of the precursor, bound the VEGF-binding site of neuropilin-1; the C-terminal arginine (R₃₇₃) of the sequence was crucial for binding. The proangiogenic activity of the CgA_1-373 was blocked by anti-neuropilin-1 antibodies as well as by nicotinic acetylcholine receptor antagonists, suggesting that these receptors, in addition to neuropilin-1, play a role in the proangiogenic activity of CgA_1-373. The R₃₇₃ residue was enzymatically removed in plasma, causing loss of neuropilin-1 binding and gain of antiangiogenic activity. These results suggest that cleavage of the R₃₇₃R₃₇₄ site of circulating human CgA in tumors and the subsequent removal of R₃₇₃ in the blood represent an important "on/off" switch for the spatiotemporal regulation of tumor angiogenesis and may serve as a novel therapeutic target. SIGNIFICANCE: This work reveals that the interaction between fragmented chromogranin A and neuropilin-1 is required for tumor growth and represents a novel potential therapeutic target.

Potential applications of catestatin in cardiovascular diseases

Catestatin (CST) was first named in 1997 for its catecholamine-inhibitory activity. It was discovered as a potent inhibitor of catecholamine secretion and as a regulator of histamine release. Accumulating evidence shows that CST is involved with cardiovascular diseases; however, whether CST is a protective factor for these conditions and the mechanisms by which such actions may be mediated are not well understood. In this article, we review recent basic research and clinical trials in the study of CST and summarize the association of CST with cardiovascular diseases. We review data obtained from MedLine via PubMed and from our own investigations.

Decreased plasma Chromogranin A361-372 (Catestatin) but not Chromogranin A17-38 (Vasostatin) in female dogs with bacterial uterine infection (pyometra)

Background

Pyometra often induces systemic inflammatory response syndrome (SIRS) and early diagnosis is crucial for survival. Chromogranin A (CgA) is a neuroendocrine secretory protein that is co-released with catecholamines from the adrenal medulla and sympathetic nerve endings. A prognostic value of CgA has been found in humans that are critically ill or that have SIRS associated with infection. CgA has not yet been studied in dogs with bacterial infection. The aim of the study was to investigate CgA, measured by Chromogranin A361-372 (Catestatin; Cst) and Chromogranin A17-38 (Vasostatin; VS) in healthy dogs and in dogs with pyometra.

Results

Fifty dogs with pyometra, sampled prior to surgery and 64 healthy female dogs were included. In 19 pyometra cases, blood samples were also collected postoperatively. Concentrations of Cst and VS were measured in heparinised plasma and Cst also measured in EDTA plasma, by in-house radioimmunoassays. Student’s t-test and Wilcoxon two-sample test was used to test for differences between dog groups. Pre- and postoperative samples in dogs with pyometra were analysed by paired t-test. Pearson correlation was used to investigate associations of laboratory variables and hospitalization. P < 0.05 was considered significant.

Concentrations of Cst were decreased in pyometra dogs (mean ± SE, 1.01 ± 0.05 nmol/L) compared to healthy dogs (mean ± SE, 1.70 ± 0.03 nmol/L) (p ≤ 0.0001). VS concentrations did not differ significantly between dogs with pyometra (0.40 ± 0.04 nmol/L) and healthy dogs (0.42 ± 0.03 nmol/L). Mean ± SE pre- and postoperative concentration of Cst (1.0 ± 0.04 nmol/L and 0.9 ± 0.2 nmol/L) and VS (0.36 ± 0.04 nmol/L and 0.36 ± 0.04 nmol/L) in dogs with pyometra did not differ significantly. Neither Cst nor VS concentrations were associated with duration of hospitalization and were not significantly different in the four dogs with pyometra that had prolonged (≥3 d) postoperative hospitalization.

Conclusion

Concentrations of Cst, but not VS, were decreased in pyometra. Cst and VS concentrations before and after ovariohysterectomy did not differ significantly and were not associated with duration of hospitalization. Further studies are warranted to evaluate a possible diagnostic or prognostic value for Cst and VS.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-015-0328-6) contains supplementary material, which is available to authorized users.

A molecular dynamics study of catestatin docked on nicotinic acetylcholine receptors to identify amino acids potentially involved in the binding of chromogranin A fragments

Human catestatin, representing potential to regulate nicotinic signal transduction, can bind onto nAChR-β subunits indicating a novel mode of action.

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.

Pleiotropic effects of novel trans-acting loci influencing human sympathochromaffin secretion

Family studies have suggested a genetic contribution to variation in blood pressure, but the genes responsible have thus far eluded identification. The use of intermediate phenotypes associated with hypertension, such as chromogranin plasma concentrations, may assist the discovery of hypertension-predisposing loci. We measured the concentrations of four chromogranin A (CHGA) and B (CHGB) peptides in 742 individuals from 235 nuclear families. The CHGA- and CHGB-derived peptides displayed significant heritability and revealed significant genetic correlations, most strikingly observed between CHGA(361-372) (catestatin) and CHGB(439-451). A 5-cM microsatellite genome scan revealed significant and suggestive evidence for linkage on several chromosomes for three of the peptides. Subsequent bivariate linkage analysis for peptides CHGA(361-372) and CHGB(439-451), which showed evidence for convergent linkage peaks on chromosomes 2, 7, and 13, resulted in increased evidence for linkage to these regions, suggesting pleiotropic effects of these three loci on multiple chromogranin traits. Because CHGA itself is on chromosome 14q32, and CHGB itself is on chromosome 20pter-p12, the pleiotropic regions on chromosomes 2, 7, and 13 must represent trans-acting quantitative trait loci coordinately affecting CHGA/CHGB biosynthesis and/or exocytotic secretion, likely by regulating efferent sympathetic outflow, a conclusion consistent with the in vitro studies presented here of the dual control of both exocytosis and transcription of these peptides by secretory stimuli in chromaffin cells. The results suggest a new approach to heritable autonomic control of circulation and the genetic basis of cardiovascular diseases such as systemic hypertension.

Immunohistochemical assessment of the neurosecretory cells of the chicken thymus using a novel monoclonal antibody against avian chromogranin A

An immunocytochemical approach to the identification of neuroendocrine cells in the thymus of the chicken was taken based on a novel monoclonal antibody against turkey chromogranin A (CgA), a classic marker protein for neuroendocrine cells. CgA-immunoreactive cells were readily observed in the thymus, and were typically confined to the medullary side of the corticomedullary junction of the thymic lobules. Reversed transcription PCR confirmed local production of CgA in the thymus. The majority of CgA+ cells were small and round or oval in shape but some cells were larger and had conspicuous extensions. Immunofluorescent double staining experiments with antibodies against Neuron-specific enolase and with a neural crest marker (HNK-1) indicated no demonstrable overlap between the CgA-positive cells and either of the above cell populations, demonstrating the existence of three distinct neuronal/neuroendocrine cell populations in the avian thymus.

Both rare and common polymorphisms contribute functional variation at CHGA, a regulator of catecholamine physiology

The chromogranin/secretogranin proteins are costored and coreleased with catecholamines from secretory vesicles in chromaffin cells and noradrenergic neurons. Chromogranin A (CHGA) regulates catecholamine storage and release through intracellular (vesiculogenic) and extracellular (catecholamine release-inhibitory) mechanisms. CHGA is a candidate gene for autonomic dysfunction syndromes, including intermediate phenotypes that contribute to human hypertension. Here, we show a surprising pattern of CHGA variants that alter the expression and function of this gene, both in vivo and in vitro. Functional variants include both common alleles that quantitatively alter gene expression and rare alleles that qualitatively change the encoded product to alter the signaling potency of CHGA-derived catecholamine release-inhibitory catestatin peptides.

Distribution of catestatin-like immunoreactivity in the human auditory system

Chromogranin A (CgA) belongs to the family of chromogranin peptides which are contained in large dense-core vesicles. The novel CgA fragment catestatin (bovine CgA(344-364); RSMRLSFRARGYGFRGPGLQL) is a potent inhibitor of catecholamine release by acting as a nicotinic cholinergic antagonist. Catestatin is a recently characterized neuropeptide, consisting of 21 amino acids, which might play an autocrine regulatory role in neuroendocrine secretion through its interaction with different nicotinic acetylcholine receptor subtypes. This study investigates for the first time the distribution of this peptide in the human auditory system using immunohistochemistry. A high density of catestatin-like immunoreactivity (catestatin-LI) is located in the spiral ganglion cells. In the dorsal cochlear nucleus, a high density of catestatin-LI consists of varicose fibers, immunoreactive varicosities and immunoreactive neurons. A moderate density is detected in the ventral cochlear and the medial vestibular nucleus. A low density is found in the inferior colliculus and superior olivary complex. The study indicates that catestatin is distinctly distributed in the auditory system, suggesting a role as a neuromodulatory peptide. Further studies should elucidate a possible interaction with other neurotransmitters in the auditory system.

Catecholamine secretory vesicle stimulus-transcription coupling in vivo. Demonstration by a novel transgenic promoter/photoprotein reporter and inhibition of secretion and transcription by the chromogranin A fragment catestatin

Stimulation of chromaffin cell secretion in vitro triggers not only secretion but also resynthesis of just released catecholamines and chromogranin A, the precursor of the catecholamine release-inhibitory, nicotinic cholinergic antagonist peptide catestatin. Does stimulus-transcription coupling occur in vivo? And does catestatin antagonize secretion and transcription in vivo? To answer these questions, we employed a novel mouse strain harboring a chromogranin A promoter/firefly luciferase reporter transgene. Tissue-specific expression of the reporter was established by both luminescence and reverse transcription-PCR. Secretion and transcription in vivo were triggered by either direct nicotinic stimulation or vesicular transmitter depletion. Nicotinic blockade in vivo was attempted with either the classical antagonist chlorisondamine or the novel antagonist catestatin. Luciferase reporter expression was exquisitely sensitive over a large dynamic range, was specific for the transgenic animals, and paralleled typical neuroendocrine distribution of endogenous chromogranin A. Adrenal ontogeny revealed a rise of embryonic transgene expression until embryonal day 18, with an abrupt postnatal decline. Direct nicotinic stimulation of chromaffin cells caused catecholamine release and transgene transcription, each of which was nearly completely blocked by chlorisondamine. Similar adrenal results were obtained during vesicular catecholamine depletion. Both secretion and transcription were substantially blocked in the adrenal gland by catestatin. In brain and sympathetic nerve, stimulation of transcription was more modest, and reserpine responses were only incompletely blocked by chlorisondamine or catestatin, perhaps because of limited blood-brain barrier penetration by these cationic antagonists. Thus, nicotinic cholinergic stimulus-transcription coupling occurs in vivo and can be provoked either directly or indirectly (by vesicular transmitter depletion). Such coupling triggers the biosynthesis of chromogranin A, the precursor of catestatin. Catestatin itself blocks stimulation of both secretion and transcription in vivo. Thus, chromogranin A and its catestatin fragment may lie at the nexus of nicotinic cholinergic signaling in vivo.

The chromogranins: their roles in secretion from neuroendocrine cells and as markers for neuroendocrine neoplasia

Chromogranins are the major components of the secretory granules of most neuroendocrine cells. Within the secretory pathway, chromogranins are involved in granulogenesis, and in sorting and processing of secretory protein cargo prior to secretion. Once secreted, they have hormonal, autocrine, and paracrine activities. The chromogranin family includes chromogranins A (CgA) and B (CgB) and secretogranin II (SgII, once called chromogranin C). The related "granins" NESP55, 7B2, secretogranin III/1B 1075 (SgIII), and secretogranin IV/HISL-19 antigen (SgIV), are also sometimes included when considering the chromogranins. While it is useful to consider the granin proteins as a family with many common features, it is also necessary to examine the distinct features and properties of individual members of the granin family to understand fully their functions, employ them efficiently as tissue, serum, and urinary markers for neuroendocrine neoplasia, and develop an evolutionary-biologic perspective on their contribution to mammalian physiology. Recent advances in chromogranin research include establishing the role of CgA in granulogenesis and the role of CgB in nuclear transcription; new biologic activities for CgA-, CgB-, and SgII-derived peptides; and new marker functions for granins and their proteolytically processed products in endocrine neoplasias.

Identification of a novel sorting determinant for the regulated pathway in the secretory protein chromogranin A

Chromogranin A (CgA) is the index member of the chromogranin/secretogranin (or 'granin') family of regulated secretory proteins that are ubiquitously distributed in amine- and peptide-containing secretory granules of endocrine, neuroendocrine and neuronal cells. Because of their abundance and such widespread occurrence, granins have often been used as prototype proteins to elucidate mechanisms of protein targeting into dense-core secretory granules. In this study, we used a series of full-length, point mutant or truncated CgA-green fluorescent protein (GFP) chimeras to explore routing of CgA in neuroendocrine PC12 cells. Using sucrose gradient fractionation and 3D deconvolution microscopy to determine the subcellular localization of the GFP chimeras, as well as secretagogue-stimulated release, the present study establishes that a CgA-GFP fusion protein expressed in neuroendocrine PC12 cells is trafficked to the dense core secretory granule and thereby sorted to the regulated pathway for exocytosis. We show that information necessary for such trafficking is contained within the N-terminal but not the C-terminal region of CgA. We find that CgA's conserved N-terminal hydrophobic Cys(17)-Cys(38) loop structure may not be sufficient for sorting of CgA into dense-core secretory granules, nor is its stabilization by a disulfide bond necessary for such sorting. Moreover, our data reveal for the first time that the CgA(77-115) domain of the mature protein may be necessary (though perhaps not sufficient) for trafficking CgA into the regulated pathway of secretion.

Molecular biology of the chromaffin cell

A large number of molecular biology studies have been performed on chromaffin cells, and many genes involved in catecholamine synthesis, storage, and release have been cloned and their function determined. Catecholamine synthesis takes place in different cellular compartments, and enzymes involved in this process are subject to a fine regulation, as demonstrated by recent studies on their gene promoters. Genes coding for such intravesicular proteins as chromogranin A, B, and secretogranin II (chromogranin C) are also regulated in response to a variety of stimuli. Chromogranin gene promoters and transcription factors involved in their regulation have been elucidated. This review serves as an introduction to the studies described in the chapters to follow.