Cathepsin L colocalizes with chromogranin a in chromaffin vesicles to generate active peptides

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.

The immunomodulatory functions of chromogranin A-derived peptide pancreastatin

Chromogranin A (CgA) is a 439 amino acid protein secreted by neuroendocrine cells. Proteolytic processing of CgA results in the production of different bioactive peptides. These peptides have been associated with inflammatory bowel disease, diabetes, and cancer. One of the chromogranin A-derived peptides is ∼52 amino acid long Pancreastatin (PST: human (h)CgA250-301, murine (m)CgA263-314). PST is a glycogenolytic peptide that inhibits glucose-induced insulin secretion from pancreatic islet β-cells. In addition to this metabolic role, evidence is emerging that PST also has inflammatory properties. This review will discuss the immunomodulatory properties of PST and its possible mechanisms of action and regulation. Moreover, this review will discuss the potential translation to humans and how PST may be an interesting therapeutic target for treating inflammatory diseases.

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.

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.

Efficient intracellular delivery of proteins by a multifunctional chimaeric peptide in vitro and in vivo

Protein delivery with cell-penetrating peptide is opening up the possibility of using targets inside cells for therapeutic or biological applications; however, cell-penetrating peptide-mediated protein delivery commonly suffers from ineffective endosomal escape and low tolerance in serum, thereby limiting in vivo efficacy. Here, we present an intracellular protein delivery system consisting of four modules in series: cell-penetrating peptide, pH-dependent membrane active peptide, endosome-specific protease sites and a leucine zipper. This system exhibits enhanced delivery efficiency and serum tolerance, depending on proteolytic cleavage-facilitated endosomal escape and leucine zipper-based dimerisation. Intravenous injection of protein phosphatase 1B fused with this system successfully suppresses the tumour necrosis factor-α-induced systemic inflammatory response and acetaminophen-induced acute liver failure in a mouse model. We believe that the strategy of using multifunctional chimaeric peptides is valuable for the development of cell-penetrating peptide-based protein delivery systems, and facilitate the development of biological macromolecular drugs for use against intracellular targets.

Chromogranin A regulates gut permeability via the antagonistic actions of its proteolytic peptides

AIM

A "leaky" gut barrier has been implicated in the initiation and progression of a multitude of diseases, for example, inflammatory bowel disease (IBD), irritable bowel syndrome and celiac disease. Here we show how pro-hormone Chromogranin A (CgA), produced by the enteroendocrine cells, and Catestatin (CST: hCgA_352-372 ), the most abundant CgA-derived proteolytic peptide, affect the gut barrier.

METHODS

Colon tissues from region-specific CST-knockout (CST-KO) mice, CgA-knockout (CgA-KO) and WT mice were analysed by immunohistochemistry, western blot, ultrastructural and flowcytometry studies. FITC-dextran assays were used to measure intestinal barrier function. Mice were supplemented with CST or CgA fragment pancreastatin (PST: CgA_250-301 ). The microbial composition of cecum was determined. CgA and CST levels were measured in blood of IBD patients.

RESULTS

Plasma levels of CST were elevated in IBD patients. CST-KO mice displayed (a) elongated tight, adherens junctions and desmosomes similar to IBD patients, (b) elevated expression of Claudin 2, and (c) gut inflammation. Plasma FITC-dextran measurements showed increased intestinal paracellular permeability in the CST-KO mice. This correlated with a higher ratio of Firmicutes to Bacteroidetes, a dysbiotic pattern commonly encountered in various diseases. Supplementation of CST-KO mice with recombinant CST restored paracellular permeability and reversed inflammation, whereas CgA-KO mice supplementation with CST and/or PST in CgA-KO mice showed that intestinal paracellular permeability is regulated by the antagonistic roles of these two peptides: CST reduces and PST increases permeability.

CONCLUSION

The pro-hormone CgA regulates the intestinal paracellular permeability. CST is both necessary and sufficient to reduce permeability and primarily acts by antagonizing PST.

Catestatin peptide of chromogranin A as a potential new target for several risk factors management in the course of metabolic syndrome

Obesity, lipodystrophy, diabetes, and hypertension collectively constitute the main features of Metabolic Syndrome (MetS), together with insulin resistance (IR), which is considered as a defining element. MetS generally leads to the development of cardiovascular disease (CVD), which is a determinant cause of mortality and morbidity in humans and animals. Therefore, it is essential to implement and put in place adequate management strategies for the treatment of this disease. Catestatin is a bioactive peptide with 21 amino acids, which is derived through cleaving of the prohormone chromogranin A (CHGA/CgA) that is co-released with catecholamines from secretory vesicles and, which is responsible for hepatic/plasma lipids and insulin levels regulation, improves insulin sensitivity, reduces hypertension and attenuates obesity in murine models. In humans, there were few published studies, which showed that low levels of catestatin are significant risk factors for hypertension in adult patients. These accumulating evidence documents clearly that catestatin peptide (CST) is linked to inflammatory and metabolic syndrome diseases and can be a novel regulator of insulin and lipid levels, blood pressure, and cardiac function. The goal of this review is to provide an overview of the CST effects in metabolic syndrome given its role in metabolic regulation and thus, provide new insights into the use of CST as a diagnostic marker and therapeutic target.

Structure-based Approaches Targeting Parasite Cysteine Proteases

Cysteine proteases are essential hydrolytic enzymes present in the majority of organisms, including viruses and unicellular parasites. Despite the high sequence identity displayed among these proteins, specific structural features across different species grant distinct functions to these biomolecules, frequently related to pathological conditions. Consequently, their relevance as promising targets for potential specific inhibitors has been highlighted and occasionally validated in recent decades. In this review, we discuss the recent outcomes of structure-based campaigns aiming the discovery of new inhibitor prototypes against cruzain and falcipain, as alternative therapeutic tools for Chagas disease and malaria treatments, respectively. Computational and synthetic approaches have been combined on hit optimization strategies and are also discussed herein. These rationales are extended to additional tropical infectious and neglected pathologies, such as schistosomiasis, leishmaniasis and babesiosis, and also to Alzheimer's Disease, a widespread neurodegenerative disease poorly managed by currently available drugs and recently linked to particular physiopathological roles of human cysteine proteases.

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.

Catestatin as a Target for Treatment of Inflammatory Diseases

It is increasingly clear that inflammatory diseases and cancers are influenced by cleavage products of the pro-hormone chromogranin A (CgA), such as the 21-amino acids long catestatin (CST). The goal of this review is to provide an overview of the anti-inflammatory effects of CST and its mechanism of action. We discuss evidence proving that CST and its precursor CgA are crucial for maintaining metabolic and immune homeostasis. CST could reduce inflammation in various mouse models for diabetes, colitis and atherosclerosis. In these mouse models, CST treatment resulted in less infiltration of immune cells in affected tissues, although in vitro monocyte migration was increased by CST. Both in vivo and in vitro, CST can shift macrophage differentiation from a pro- to an anti-inflammatory phenotype. Thus, the concept is emerging that CST plays a role in tissue homeostasis by regulating immune cell infiltration and macrophage differentiation. These findings warrant studying the effects of CST in humans and make it an interesting therapeutic target for treatment and/or diagnosis of various metabolic and immune diseases.

Circulating chromogranin A and its fragments as diagnostic and prognostic disease markers

Chromogranin A (CgA), a secretory protein released in the blood by neuroendocrine cells and neurons, is the precursor of various bioactive fragments involved in the regulation of the cardiovascular system, metabolism, innate immunity, angiogenesis, and tissue repair. After the original demonstration that circulating CgA can serve as a biomarker for a wide range of neuroendocrine tumors, several studies have shown that increased levels of CgA can be present also in the blood of patients with cardiovascular, gastrointestinal, and inflammatory diseases with, in certain cases, important diagnostic and prognostic implications. Considering the high structural and functional heterogeneity of the CgA system, comprising precursor and fragments, it is not surprising that the different immunoassays used in these studies led, in some cases, to discrepant results. Here, we review these notions and we discuss the importance of measuring total-CgA, full-length CgA, specific fragments, and their relative levels for a more thorough assessment of the pathophysiological function and diagnostic/prognostic value of the CgA system.

Identification of novel loci affecting circulating chromogranins and related peptides

Chromogranins are pro-hormone secretory proteins released from neuroendocrine cells, with effects on control of blood pressure. We conducted a genome-wide association study for plasma catestatin, the catecholamine release inhibitory peptide derived from chromogranin A (CHGA), and other CHGA- or chromogranin B (CHGB)-related peptides, in 545 US and 1252 Australian subjects. This identified loci on chromosomes 4q35 and 5q34 affecting catestatin concentration (P = 3.40 × 10-30 for rs4253311 and 1.85 × 10-19 for rs2731672, respectively). Genes in these regions include the proteolytic enzymes kallikrein (KLKB1) and Factor XII (F12). In chromaffin cells, CHGA and KLKB1 proteins co-localized in catecholamine storage granules. In vitro, kallikrein cleaved recombinant human CHGA to catestatin, verified by mass spectrometry. The peptide identified from this digestion (CHGA360-373) selectively inhibited nicotinic cholinergic stimulated catecholamine release from chromaffin cells. A proteolytic cascade involving kallikrein and Factor XII cleaves chromogranins to active compounds both in vivo and in vitro.

Granin-derived peptides

The granin family comprises altogether 7 different proteins originating from the diffuse neuroendocrine system and elements of the central and peripheral nervous systems. The family is dominated by three uniquely acidic members, namely chromogranin A (CgA), chromogranin B (CgB) and secretogranin II (SgII). Since the late 1980s it has become evident that these proteins are proteolytically processed, intragranularly and/or extracellularly into a range of biologically active peptides; a number of them with regulatory properties of physiological and/or pathophysiological significance. The aim of this comprehensive overview is to provide an up-to-date insight into the distribution and properties of the well established granin-derived peptides and their putative roles in homeostatic regulations. Hence, focus is directed to peptides derived from the three main granins, e.g. to the chromogranin A derived vasostatins, betagranins, pancreastatin and catestatins, the chromogranin B-derived secretolytin and the secretogranin II-derived secretoneurin (SN). In addition, the distribution and properties of the chromogranin A-derived peptides prochromacin, chromofungin, WE14, parastatin, GE-25 and serpinins, the CgB-peptide PE-11 and the SgII-peptides EM66 and manserin will also be commented on. Finally, the opposing effects of the CgA-derived vasostatin-I and catestatin and the SgII-derived peptide SN on the integrity of the vasculature, myocardial contractility, angiogenesis in wound healing, inflammatory conditions and tumors will be discussed.

Chromogranin A Regulation of Obesity and Peripheral Insulin Sensitivity

Chromogranin A (CgA) is a prohormone and granulogenic factor in endocrine and neuroendocrine tissues, as well as in neurons, and has a regulated secretory pathway. The intracellular functions of CgA include the initiation and regulation of dense-core granule biogenesis and sequestration of hormones in neuroendocrine cells. This protein is co-stored and co-released with secreted hormones. The extracellular functions of CgA include the generation of bioactive peptides, such as pancreastatin (PST), vasostatin, WE14, catestatin (CST), and serpinin. CgA knockout mice (Chga-KO) display: (i) hypertension with increased plasma catecholamines, (ii) obesity, (iii) improved hepatic insulin sensitivity, and (iv) muscle insulin resistance. These findings suggest that individual CgA-derived peptides may regulate different physiological functions. Indeed, additional studies have revealed that the pro-inflammatory PST influences insulin sensitivity and glucose tolerance, whereas CST alleviates adiposity and hypertension. This review will focus on the different metabolic roles of PST and CST peptides in insulin-sensitive and insulin-resistant models, and their potential use as therapeutic targets.

Polymorphisms at the F12 and KLKB1 loci have significant trait association with activation of the renin-angiotensin system

Background

Plasma coagulation Factor XIIa (Hageman factor; encoded by F12) and kallikrein (KAL or Fletcher factor; encoded by KLKB1) are proteases of the kallikerin-kinin system involved in converting the inactive circulating prorenin to renin. Renin is a key enzyme in the formation of angiotensin II, which regulates blood pressure, fluid and electrolyte balance and is a biomarker for cardiovascular, metabolic and renal function. The renin-angiotensin system is implicated in extinction learning in posttraumatic stress disorder.

Methods & Results

Active plasma renin was measured from two independent cohorts- civilian twins and siblings, as well as U.S. Marines, for a total of 1,180 subjects. Genotyping these subjects revealed that the carriers of the minor alleles at the two loci- F12 and KLKB1 had a significant association with reduced levels of active plasma renin. Meta-analyses confirmed the association across cohorts. In vitro studies verified digestion of human recombinant pro-renin by kallikrein (KAL) to generate active renin. Subsequently, the active renin was able to digest the synthetic substrate angiotensinogen to angiotensin-I. Examination of mouse juxtaglomerular cell line and mouse kidney sections showed co-localization of KAL with renin. Expression of either REN or KLKB1 was regulated in cell line and rodent models of hypertension in response to oxidative stress, interleukin or arterial blood pressure changes.

Conclusions

The functional variants of KLKB1 (rs3733402) and F12 (rs1801020) disrupted the cascade of enzymatic events, resulting in diminished formation of active renin. Using genetic, cellular and molecular approaches we found that conversion of zymogen prorenin to renin was influenced by these polymorphisms. The study suggests that the variant version of protease factor XIIa due to the amino acid substitution had reduced ability to activate prekallikrein to KAL. As a result KAL has reduced efficacy in converting prorenin to renin and this step of the pathway leading to activation of renin affords a potential therapeutic target.

The important role of catestatin in cardiac remodeling

Catestatin (CST) was first discovered as a potent non-competitive and reversible inhibitor of catecholamine secretion. Recent reports on plasma CST level in heart diseases suggested a cardioprotective role for this peptide. Given that cardiac remodeling is the dominant pathologic process in cardiac dysfunction, we propose that CST participates in the regulation of concern pathways and contributes to the inhibition of cardiac remodeling. In this minireview, the potential mechanism of cardiac remodeling involving CST will be discussed from three aspects: hypertrophy, fibrosis, and apoptosis.

Cateslytin, a chromogranin A derived peptide is active against Staphylococcus aureus and resistant to degradation by its proteases

Innate immunity involving antimicrobial peptides represents an integrated and highly effective system of molecular and cellular mechanisms that protects host against infections. One of the most frequent hospital-acquired pathogens, Staphylococcus aureus, capable of producing proteolytic enzymes, which can degrade the host defence agents and tissue components. Numerous antimicrobial peptides derived from chromogranins, are secreted by nervous, endocrine and immune cells during stress conditions. These kill microorganisms by their lytic effect at micromolar range, using a pore-forming mechanism against Gram-positive bacteria, filamentous fungi and yeasts. In this study, we tested antimicrobial activity of chromogranin A-derived peptides (catestatin and cateslytin) against S. aureus and analysed S. aureus-mediated proteolysis of these peptides using HPLC, sequencing and MALDI-TOF mass spectrometry. Interestingly, this study is the first to demonstrate that cateslytin, the active domain of catestatin, is active against S. aureus and is interestingly resistant to degradation by S. aureus proteases.

Genes and environment: novel, functional polymorphism in the human cathepsin L (CTSL1) promoter disrupts a xenobiotic response element (XRE) to alter transcription and blood pressure

BACKGROUND

Cathepsin L (CTSL1) catalyzes the formation of peptides that influence blood pressure (BP). Naturally occurring genetic variation or targeted ablation of the Ctsl1 locus in mice yield cardiovascular pathology. Here, we searched for genetic variation across the human CTSL1 locus and probed its functional effects, especially in the proximal promoter.

METHODS AND RESULTS

Systematic polymorphism discovery by re-sequencing across CTSL1 in 81 patients uncovered 38 genetic variants, five of which were relatively common (MAF >5%), creating a single linkage disequilibrium block in multiple biogeographic ancestries. One of these five common variants lay in a functional domain of the gene: promoter C-171A (rs3118869), which disrupts a predicted xenobiotic response element (XRE; match C>A). In transfected CTSL1 promoter/luciferase reporter plasmids, C-171A allele influenced transcription (C>A, P = 3.36E-6), and transcription was also augmented by co-exposure to the aryl hydrocarbon receptor (AHR) complex (AHR:ARNT) in the presence of their ligand dioxin (P = 6.81E-8); allele (C vs. A) and AHR:ARNT/dioxin stimulus interacted to control gene expression (interaction P = 0.033). Endogenous Ctsl1, Ahr, and Arnt transcripts were present in chromaffin cells. Promoter functional C-171A genotype also predicted hypertension (P = 1.0E-3), SBP (P = 4.0E-4), and DBP (P = 3.0E-3), in an additive pattern for diploid genotypes (A/A > C/A > C/C) in 868 patients, and the results were extended by validation analysis into an independent population sample of 986 patients.

CONCLUSION

We conclude that common genetic variation in the proximal CTSL1 promoter, especially at position C-171A, is functional in cells, and alters transcription so as to explain the association of CTSL1 with BP in vivo. At the XRE, endogenous genetic variation plus exogenous aryl hydrocarbon stimulation interact to control CTSL1 gene expression. These results unveil a novel control point whereby heredity and environment can intersect to control a complex trait, and point to new transcriptional strategies for intervention into transmitter biosynthesis and its cardiovascular consequences.

[Chromogranin A and neuroendocrine tumors]

Chromogranin A (CgA) is the most abundant granin in gastroenteropancreatic neuroendocrine tumors (GEP-NETs). As a tumor marker is moderately sensitive and nonspecific. Despite the limitations of testing methods, which require careful interpretation, especially in the case of gastrinomas, patients treated with somatostatin analogues, and poorly differentiated tumors, it is the best tumor marker in GEP-NETs and may be of value in other tumors with neuroendocrine differentiation. CgA may be used as a marker in blood or tissue samples through immunohistochemical techniques. CgA levels correlate with tumor burden and extension and may be used for diagnosis and monitoring of GEP-NETs, especially midgut carcinoids and endocrine pancreatic tumors. It is also useful as a prognostic marker for detection of recurrence and monitoring of response to different treatments.

Novel peptide isomer strategy for stable inhibition of catecholamine release: application to hypertension

Although hypertension remains the most potent and widespread cardiovascular risk factor, its pharmacological treatment has achieved only limited success. The chromogranin A-derived fragment catestatin inhibits catecholamine release by acting as an endogenous nicotinic cholinergic antagonist and can rescue hypertension in the setting of chromogranin A-targeted ablation. Here, we undertook novel peptide chemistry to synthesize isomers of catestatin: normal/wild-type as well as a retro-inverso (R-I) version, with not only inversion of chirality (L → D amino acids) but also reversal of sequence (carboxyl → amino). The R-I peptide was entirely resistant to proteolytic digestion and displayed enhanced potency as well as preserved specificity of action toward nicotinic cholinergic events: catecholamine secretion, agonist desensitization, secretory protein transcription, and cationic signal transduction. Structural modeling suggested similar side-chain orientations of the wild-type and R-I isomers, whereas circular dichroism spectroscopy documented inversion of chirality. In vivo, the R-I peptide rescued hypertension in 2 mouse models of the human trait: monogenic chromogranin A-targeted ablation, with prolonged efficacy of the R-I version and a polygenic model, with magnified efficacy of the R-I version. These results may have general implications for generation of metabolically stable mimics of biologically active peptides for cardiovascular pathways. The findings also point the way toward a potential new class of drug therapeutics for an important risk trait and, more generally, open the door to broader applications of the R-I strategy in other pathways involved in cardiovascular biology, with the potential for synthesis of diagnostic and therapeutic probes for both physiology and disease.

Chromogranin A binds to αvβ6-integrin and promotes wound healing in mice

Chromogranin A (CgA), a secretory protein expressed by many neuroendocrine cells, neurons, cardiomyocytes, and keratinocytes, is the precursor of various peptides that regulate the carbohydrate/lipid metabolism and the cardiovascular system. We have found that CgA, locally administered to injured mice, can accelerate keratinocyte proliferation and wound healing. This biological activity was abolished by the Asp(45)Glu mutation. CgA and its N-terminal fragments, but not the corresponding Asp(45)Glu mutants, could selectively recognize the αvβ6-integrin on keratinocytes (a cell-adhesion receptor that is up-regulated during wound healing) and regulate keratinocyte adhesion, proliferation, and migration. No binding was observed to other integrins such as αvβ3, αvβ5, αvβ8, α5β1, α1β1, α3β1, α6β4, α6β7 and α9β1. Structure-activity studies showed that the entire CgA(39-63) region is crucial for αvβ6 recognition (K(i) = 7 nM). This region contains an RGD site (residues CgA(43-45)) followed by an amphipathic α-helix (residues CgA(47-63)), both crucial for binding affinity and selectivity. These results suggest that the interaction of the RGD/α-helix motif of CgA with αvβ6 regulates keratinocyte physiology in wound healing.

Human cathepsin V protease participates in production of enkephalin and NPY neuropeptide neurotransmitters

Proteases are required for processing precursors into active neuropeptides that function as neurotransmitters for cell-cell communication. This study demonstrates the novel function of human cathepsin V protease for producing the neuropeptides enkephalin and neuropeptide Y (NPY). Cathepsin V is a human-specific cysteine protease gene. Findings here show that expression of cathepsin V in neuroendocrine PC12 cells and human neuronal SK-N-MC cells results in production of (Met)enkephalin from proenkephalin. Gene silencing of cathepsin V by siRNA in human SK-N-MC cells results in reduction of (Met)enkephalin by more than 80%, illustrating the prominent role of cathepsin V for neuropeptide production. In vitro processing of proenkephalin by cathepsin V occurs at dibasic residue sites to generate enkephalin-containing peptides and an ∼24-kDa intermediate present in human brain. Cathepsin V is present in human brain cortex and hippocampus where enkephalin and NPY are produced and is present in purified human neuropeptide secretory vesicles. Colocalization of cathepsin V with enkephalin and NPY in secretory vesicles of human neuroblastoma cells was illustrated by confocal microscopy. Furthermore, expression of cathepsin V with proNPY results in NPY production. These findings indicate the unique function of human cathepsin V for producing enkephalin and NPY neuropeptides required for neurotransmission in health and neurological diseases.

Molecular interactions of the physiological anti-hypertensive peptide catestatin with the neuronal nicotinic acetylcholine receptor

Catestatin (CST), a chromogranin-A-derived peptide, is a potent endogenous inhibitor of the neuronal nicotinic acetylcholine receptor (nAChR). It exerts an anti-hypertensive effect by acting as a 'physiological brake' on transmitter release into the circulation. However, the mechanism of interaction of CST with nAChR is only partially understood. To unravel molecular interactions of the wild-type human CST (CST-WT) as well as its naturally occurring variants (CST-364S and CST-370L, which have Gly→Ser and Pro→Leu substitutions, respectively) with the human α3β4 nAChR, we generated a homology-modeled human α3β4 nAChR structure and solution structures of CST peptides. Docking and molecular dynamics simulations showed that ~90% of interacting residues were within 15 N-terminal residues of CST peptides. The rank order of binding affinity of these peptides with nAChR was: CST-370L>CST-WT>CST-364S; the extent of occlusion of the receptor pore by these peptides was also in the same order. In corroboration with computational predictions, circular dichroism analysis revealed significant differences in global structures of CST peptides (e.g. the order of α-helical content was: CST-370L>CST-WT>CST-364S). Consistently, CST peptides blocked various stages of nAChR signal transduction, such as nicotine- or acetylcholine-evoked inward current, rise in intracellular Ca(2+) and catecholamine secretion in or from neuron-differentiated PC12 cells, in the same rank order. Taken together, this study shows molecular interactions between human CST peptides and human α3β4 nAChR, and demonstrates that alterations in the CST secondary structure lead to the gain of potency for CST-370L and loss of potency for CST-364S. These findings have implications for understanding the nicotinic cholinergic signaling in humans.

Cysteine Cathepsins in the secretory vesicle produce active peptides: Cathepsin L generates peptide neurotransmitters and cathepsin B produces beta-amyloid of Alzheimer's disease

Recent new findings indicate significant biological roles of cysteine cathepsin proteases in secretory vesicles for production of biologically active peptides. Notably, cathepsin L in secretory vesicles functions as a key protease for proteolytic processing of proneuropeptides (and prohormones) into active neuropeptides that are released to mediate cell-cell communication in the nervous system for neurotransmission. Moreover, cathepsin B in secretory vesicles has been recently identified as a β-secretase for production of neurotoxic β- amyloid (Aβ) peptides that accumulate in Alzheimer's disease (AD), participating as a notable factor in the severe memory loss in AD. These secretory vesicle functions of cathepsins L and B for production of biologically active peptides contrast with the well-known role of cathepsin proteases in lysosomes for the degradation of proteins to result in their inactivation. The unique secretory vesicle proteome indicates proteins of distinct functional categories that provide the intravesicular environment for support of cysteine cathepsin functions. Features of the secretory vesicle protein systems insure optimized intravesicular conditions that support the proteolytic activity of cathepsins. These new findings of recently discovered biological roles of cathepsins L and B indicate their significance in human health and disease. This article is part of a Special Issue entitled: Proteolysis 50 years after the discovery of lysosome.

Regulation of zebrafish hatching by tetraspanin cd63

Tetraspanins cause the clustering of membrane proteins into a level of organisation essential for cellular function. Given the importance and complicated nature of this mechanism, we attempted a novel approach to identify the function of a single component in a biologically relevant context. A morpholino knockdown strategy was used to investigate the role of cd63, a membrane protein associated with intracellular transport and a melanoma marker, in embryonic zebrafish. By using three separate morpholinos targeting cd63, we were able to identify a specific phenotype. Strikingly, morphant fish failed to hatch due to the lack of secreted proteolytic enzymes required for chorion-softening. The morphology of the hatching gland at both the cellular and intracellular levels was disorganised, suggesting a role for cd63 in the functioning of this organ. This work identifies a specific role for cd63 in the zebrafish embryo and provides evidence for the suitability of zebrafish as a model system for the investigation of tetraspanin enriched microdomains.

Dramatic changes in catestatin are associated with hemodynamics in acute myocardial infarction

Acute myocardial infarction (AMI) is characterized by complex neuroendocrine activation. To investigate catestatin profiles, serial catestatin levels were determined by enzyme-linked immunosorbent assay in the first week after AMI in 50 patients. Catestatin levels reduced at admission and negatively correlated with heart rates; it increased significantly on the third day but remained decreased at 1 week and positively with blood pressure. In a subgroup of 20 patients admitted within 4 h after onset, circulating catestatin correlated inversely with norepinephrine. Catestatin might be involved in the course of AMI and act as a tool in monitoring the progression of AMI.

Naturally occurring genetic variants in human chromogranin A (CHGA) associated with hypertension as well as hypertensive renal disease

Chromogranin A (CHGA) plays a fundamental role in the biogenesis of catecholamine secretory granules. Changes in storage and release of CHGA in clinical and experimental hypertension prompted us to study whether genetic variation at the CHGA locus might contribute to alterations in autonomic function, and hence hypertension and its target organ consequences such as hypertensive renal disease (nephrosclerosis). Systematic polymorphism discovery across the human CHGA locus revealed both common and unusual variants in both the open reading frame and such regulatory regions as the proximal promoter and 30-UTR. In chromaffin cell-transfected CHGA 30-UTR and promoter/luciferase reporter plasmids, the functional consequences of the regulatory/non-coding allelic variants were documented. Variants in both the proximal promoter and the 30-UTR displayed statistical associations with hypertension. Genetic variation in the proximal CHGA promoter predicted glomerular filtration rate in healthy twins. However, for hypertensive renal damage, both end-stage renal disease and rate of progression of earlier disease were best predicted by variants in the 30-UTR. Finally, mechanistic studies were undertaken initiated by the clue that CHGA promoter variation predicted circulating endothelin-1. In cultured endothelial cells, CHGA triggered co-release of not only the vasoconstrictor and pro-fibrotic endothelin-1, but also the pro-coagulant von Willebrand Factor and the pro-angiogenic angiopoietin-2. These findings, coupled with stimulation of endothelin-1 release from glomerular capillary endothelial cells by CHGA, suggest a plausible mechanism whereby genetic variation at the CHGA locus eventuates in alterations in human renal function. These results document the consequences of genetic variation at the CHGA locus for cardiorenal disease and suggest mechanisms whereby such variation achieves functional effects.

The novel role of cathepsin L for neuropeptide production illustrated by research strategies in chemical biology with protease gene knockout and expression

Neuropeptides are essential for cell-cell communication in the nervous and endocrine systems. Production of active neuropeptides requires proteolytic processing of proneuropeptide precursors in secretory vesicles that produce, store, and release neuropeptides that regulate physiological functions. This review describes research strategies utilizing chemical biology combined with protease gene knockout and expression to demonstrate the key role of cathepsin L for production of neuropeptides in secretory vesicles. Cathepsin L was discovered using activity-based probes and mass spectrometry to identify proenkephalin cleaving activity as cathepsin L. Significantly, in vivo protease gene knockout and expression approaches illustrate the key role of cathepsin L for neuropeptide production. Notably, cathepsin L is colocalized with neuropeptide secretory vesicles, the major site of proteolytic processing of proneuropeptides to generate active neuropeptides. Cathepsin L participates in producing opioid neuropeptides consisting of enkephalin, β-endorphin, and dynorphin, as well as in generating the POMC-derived peptide hormones ACTH and α-MSH. In addition, NPY, CCK, and catestatin neuropeptides utilize cathepsin L for their biosynthesis. The role of cathepsin L for neuropeptide production indicates its unique biological role in secretory vesicles, which contrasts with its role in lysosomes for protein degradation. Interesting evaluations of protease gene knockout studies in mice that lack cathepsin L compared to the PC1/3 and PC2 (PC, prohormone convertase) indicate the significant role of cathepsin L in neuropeptide production. Thus, dual cathepsin L and prohormone convertase protease pathways participate in neuropeptide production. These recent new findings indicate cathepsin L as a novel 'proprotein convertase' for production of neuropeptides that mediate cell-cell communication in health and disease.

Processing of chromogranins/secretogranin in patients with diabetic retinopathy

AIMS

Inflammation has been linked to the development of diabetic retinopathy (DR). Chromogranins A, B (CgA, CgB) and secretogranin II (SgII), are prohormones overexpressed in inflammatory diseases. The present study was conducted to evaluate the presence and processing of these prohormones in the vitreous of patients with DR (DV), compared with nondiabetic vitreous (NDV).

METHODS

Thirteen DV and 14 NDV samples were collected during vitreoretinal surgery. ELISA, Western blot, RP-HPLC, dot blot, protein sequencing and mass spectrometry were used to study the quantitative expression and the processing of CgA, CgB and SgII.

RESULTS

CgA, CgB and SgII presence was higher in DV than in NDV. Mean concentration of CgA evaluated by ELISA was 90.8 (± 90.1) n L⁻¹ in DV vs. 29.7 (±20.9) in NDV (p=0.039). In NDV, Western blot indicated that only short CgB-derived peptides were identified. In DV, proteomic analyses showed that long CgA-, CgB- and SgII-derived fragments and α1-antitrypsin were overexpressed, suggesting possible inhibition of the proteolytic process.

CONCLUSIONS

This study shows differences in the presence and endogenous processing of CgA, CgB and SgII from DV vs. NDV. In DV, the increase of complete granins and the attenuation of their endogenous proteolytic processing could participate in DR progression by reducing the presence of regulatory peptides, important for the pro-/anti-angiogenic balance in the eye.

Unique biological function of cathepsin L in secretory vesicles for biosynthesis of neuropeptides

Neuropeptides are essential for cell-cell communication in the nervous and neuroendocrine systems. Production of active neuropeptides requires proteolytic processing of proneuropeptide precursors in secretory vesicles that produce, store, and release neuropeptides that regulate physiological functions. This review describes recent findings indicating the prominent role of cathepsin L in secretory vesicles for production of neuropeptides from their protein precursors. The role of cathepsin L in neuropeptide production was discovered using the strategy of activity-based probes for proenkephalin-cleaving activity for identification of the enzyme protein by mass spectrometry. The novel role of cathepsin L in secretory vesicles for neuropeptide production has been demonstrated in vivo by cathepsin L gene knockout studies, cathepsin L gene expression in neuroendocrine cells, and notably, cathepsin L localization in neuropeptide-containing secretory vesicles. Cathepsin L is involved in producing opioid neuropeptides consisting of enkephalin, β-endorphin, and dynorphin, as well as in generating the POMC-derived peptide hormones ACTH and α-MSH. In addition, NPY, CCK, and catestatin neuropeptides utilize cathepsin L for their biosynthesis. The neuropeptide-synthesizing functions of cathepsin L represent its unique activity in secretory vesicles, which contrasts with its role in lysosomes. Interesting evaluations of protease gene knockout studies in mice that lack cathepsin L compared to those lacking PC1/3 and PC2 (PC, prohormone convertase) indicate the key role of cathepsin L in neuropeptide production. Therefore, dual cathepsin L and prohormone convertase protease pathways participate in neuropeptide production. Significantly, the recent new findings indicate cathepsin L as a novel 'proprotein convertase' for production of neuropeptides that mediate cell-cell communication in health and disease.

Reprint of: Catestatin: a multifunctional peptide from chromogranin A

In 1997, we identified a novel peptide, catestatin (CST: bovine chromogranin A [CHGA]₃₄₄₋₃₆₄: RSMRLSFRARGYGFRGPGLQL; human CHGA₃₅₂₋₃₇₂: SSMKLSFRARGYGFRGPGPQL), which is a potent inhibitor of nicotinic-cholinergic-stimulated catecholamine secretion. CST shows characteristic inhibitory effects on nicotinic cationic (Na+, Ca²+) signal transduction, which are specific to the neuronal nicotinic receptor. Utilizing systematic polymorphism discovery at the human CHGA locus we discovered three human variants of CST: G³⁶⁴S, P³⁷⁰L, and R³⁷⁴Q that showed differential potencies towards the inhibition of catecholamine secretion. In humans, CHGA is elevated and its processing to CST is diminished in hypertension. Diminished CST is observed not only in hypertensive individuals but also in the early-normotensive offspring of patients with hypertension, suggesting that an early deficiency of CST might play a pathogenic role in the subsequent development of the disease. Consistent with human findings, prevention of endogenous CST expression by targeted ablation (knockout) of the mouse Chga locus (Chga-KO) resulted in severe hypertension that can be "rescued" specifically by replacement of the CST peptide. CST acts directly on the heart to inhibit the inotropic and lusitropic properties of the rodent heart and also acts as a potent vasodilator in rats and humans. While the G³⁶⁴S CST variant caused profound changes in human autonomic activity and seemed to reduce the risk of developing hypertension, CST replacement rescued Chga-KO mice from dampened baroreflex sensitivity. In addition, CST has been shown to induce chemotaxis and acts as an antimicrobial as well as an antimalarial peptide. The present review summarizes these multiple actions of CST.

Chromogranin/secretogranin proteins in murine heart: myocardial production of chromogranin A fragment catestatin (Chga(364-384))

In the heart, the secretory granules containing the atrial natriuretic peptides (ANP) and B-type myocardial natriuretic peptide (BNP) provide the basis for the endocrine function of this organ. We sought to determine whether atrial and myocardial secretory granules contain chromogranin/secretogranin proteins including chromogranin A (CHGA/Chga), chromogranin B (CHGB/Chgb) and secretogranin II (SCG2/Scg2). Deconvolution microscopy on immunolabeled proteins revealed the presence of Chga, Chgb, and Scg2 in murine cardiac secretory granules. The presence of low plasma catestatin (CST: mChga_364–384) in older mice indicates diminished processing of Chga to CST with advancement of age, which is comparable to that found in humans. We have previously shown that CST (hCHGA_352–372) exerts potent cardio-suppressive effects on frog and rat heart, but the source of CST for such action has remained elusive. In the present study, we found CST-related peptides in cardiomyocytes and in heart, which establishes an autocrine/paracrine function of CST in cardiac tissue. We conclude that cardiac secretory granules contain Chga, Chgb and Scg2 and that Chga is processed to CST in murine heart.

Reprint of: Chromogranin A: a new proposal for trafficking, processing and induction of granule biogenesis

Chromogranin A (CgA), a member of the granin family serves several important cell biological roles in (neuro)endocrine cells which are summarized in this review. CgA is a "prohormone" that is synthesized at the rough endoplasmic reticulum and transported into the cisternae of this organelle via its signal peptide. It is then trafficked to the Golgi complex and then to the trans-Golgi network (TGN) where CgA aggregates at low pH in the presence of calcium. The CgA aggregates provide the physical driving force to induce budding of the TGN membrane resulting in dense core granule (DCG) formation. Within the granule, a small amount of the CgA is processed to bioactive peptides, including a predicted C-terminal peptide, serpinin. Upon stimulation, DCGs undergo exocytosis and CgA and its derived peptides are released. Serpinin, acting extracellularly is able to signal the increase in transcription of a serine protease inhibitor, protease nexin-1 (PN-1) that protects DCG proteins against degradation in the Golgi complex, which then enhances DCG biogenesis to replenish those that were released. Thus CgA and its derived peptide, serpinin, plays a significant role in granule formation and regulation of granule biogenesis, respectively, in (neuro) endocrine cells.

Reprint of: Metabolic effects and mechanism of action of the chromogranin A-derived peptide pancreastatin

Pancreastatin is one of the regulatory peptides derived from intracellular and/or extracellular processing of chromogranin A, the soluble acidic protein present in the secretory granules of the neuroendocrine system. While the intracellular functions of chromogranin A include formation and maturation of the secretory granule, the major extracellular functions are generation of biologically active peptides with demonstrated autocrine, paracrine or endocrine activities. In this review, we will focus on the metabolic function of one of these peptides, pancreastatin, and the mechanisms underlying its effects. Many different reported effects have implicated PST in the modulation of energy metabolism, with a general counterregulatory effect to that of insulin. Pancreastatin induces glycogenolysis in liver and lipolysis in adipocytes. Metabolic effects have been confirmed in humans. Moreover, naturally occurring human variants have been found, one of which (Gly297Ser) occurs in the functionally important carboxy-terminus of the peptide, and substantially increases the peptide's potency to inhibit cellular glucose uptake. Thus, qualitative hereditary alterations in pancreastatin's primary structure may give rise to interindividual differences in glucose and lipid metabolism. Pancreastatin activates a receptor signaling system that belongs to the seven-spanning transmembrane receptor coupled to a Gq-PLCβ-calcium-PKC signaling pathway. Increased pancreastatin plasma levels, correlating with catecholamines levels, have been found in insulin resistance states, such as gestational diabetes or essential hypertension. Pancreastatin plays important physiological role in potentiating the metabolic effects of catecholamines, and may also play a pathophysiological role in insulin resistance states with increased sympathetic activity.

Catestatin in rat RVLM is sympathoexcitatory, increases barosensitivity, and attenuates chemosensitivity and the somatosympathetic reflex

The fundamental role and corollary effects of neuropeptides that govern cardiorespiratory control in the brain stem are poorly understood. One such regulatory peptide, catestatin [Cts, human chromogranin A-(352-372)], noncompetitively inhibits nicotinic-cholinergic-stimulated catecholamine release. Previously, we demonstrated the presence of chromogranin A mRNA in brain stem neurons that are important for the maintenance of arterial pressure. In the present study, using immunofluorescence histochemistry, we show that Cts immunoreactivity is colocalized with tyrosine hydroxylase in C1 neurons of the rostral ventrolateral medulla (RVLM, n = 3). Furthermore, we investigated the effects of Cts on resting blood pressure, splanchnic sympathetic nerve activity, phrenic nerve activity, heart rate, and adaptive reflexes. Cts (1 mM in 50 nl or 100 μM in 50-100 nl) was microinjected into the RVLM in urethane-anesthetized, vagotomized, ventilated Sprague-Dawley rats (n = 19). Cardiovascular responses to stimulation of carotid baroreceptors, peripheral chemoreceptors, and the sciatic nerve (somatosympathetic reflex) were analyzed. Cts (1 mM in 50 nl) increased resting arterial pressure (28 ± 3 mmHg at 2 min postinjection), sympathetic nerve activity (15 ± 3% at 2 min postinjection), and phrenic discharge amplitude (31 ± 4% at 10 min postinjection). Cts increased sympathetic barosensitivity 40% (slope increased from -0.05 ± 0.01 before Cts to -0.07 ± 0.01 after Cts) and attenuated the somatosympathetic reflex [1st peak: 36% (from 132 ± 32.1 to 84.0 ± 17.0 μV); 2nd peak: 44% (from 65.1 ± 21.4 to 36.6 ± 14.1 μV)] and chemoreflex (blood pressure response to anoxia decreased 55%, sympathetic response decreased 46%). The results suggest that Cts activates sympathoexcitatory bulbospinal neurons in the RVLM and plays an important regulatory role in adaptive reflexes.

Human catestatin peptides differentially regulate infarct size in the ischemic-reperfused rat heart

In acute myocardial infarction increased plasma levels of chromogranin A are correlated with decreased survival. At the human chromogranin A gene locus there are two naturally occurring amino acid substitution variants within the catestatin region, i.e. Gly³⁶⁴Ser and Pro³⁷⁰Leu, displaying differential potencies towards inhibition of nicotinic cholinergic agonist-evoked catecholamine secretion from sympathochromaffin cells and different degrees of processing from the prohormone. Here, we examine whether two of the variants and the wild type catestatin may affect the development of infarct size during ischemic reperfusion in the Langendorff rat heart model. The hearts were subjected to regional ischemia followed by reperfusion in the presence or absence of synthetic variants of human catestatin. Compared to the Gly³⁶⁴Ser variant both the wild type and Pro³⁷⁰Leu variants increased infarct size while decreasing the cardiac levels of phosphorylated Akt and two of its downstream targets, FoxO1 and BAD. In conclusion, these findings suggest that, in contrast to the Gly³⁶⁴Ser variant, wild type catestatin and the Pro³⁷⁰Leu variant (allele frequency ~0.3%) increased myocardial infarct size via a mechanism involving dephosphorylation of Akt and the two downstream targets during ischemic reperfusion in the isolated rat heart.

Role of vasostatin-1 C-terminal region in fibroblast cell adhesion

Fibroblast adhesion can be modulated by proteins released by neuroendocrine cells and neurons, such as chromogranin A (CgA) and its N-terminal fragment vasostatin-1 (VS-1, CgA(1-78)). We have investigated the mechanisms of the interaction of VS-1 with fibroblasts and of its pro-adhesive activity and have found that the proadhesive activity of VS-1 relies on its interaction with the fibroblast membrane via a phospholipid-binding amphipathic alpha-helix located within residues 47-66, as well as on the interaction of the adjacent C-terminal region 67-78, which is structurally similar to ezrin-radixin-moesin-binding phosphoprotein 50 (a membrane-cytoskeleton adapter protein), with other cellular components critical for the regulation of cell cytoskeleton.

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.

Metabolic effects and mechanism of action of the chromogranin A-derived peptide pancreastatin

Pancreastatin is one of the regulatory peptides derived from intracellular and/or extracellular processing of chromogranin A, the soluble acidic protein present in the secretory granules of the neuroendocrine system. While the intracellular functions of chromogranin A include formation and maturation of the secretory granule, the major extracellular functions are generation of biologically active peptides with demonstrated autocrine, paracrine or endocrine activities. In this review, we will focus on the metabolic function of one of these peptides, pancreastatin, and the mechanisms underlying its effects. Many different reported effects have implicated PST in the modulation of energy metabolism, with a general counterregulatory effect to that of insulin. Pancreastatin induces glycogenolysis in liver and lipolysis in adipocytes. Metabolic effects have been confirmed in humans. Moreover, naturally occurring human variants have been found, one of which (Gly297Ser) occurs in the functionally important carboxy-terminus of the peptide, and substantially increases the peptide's potency to inhibit cellular glucose uptake. Thus, qualitative hereditary alterations in pancreastatin's primary structure may give rise to interindividual differences in glucose and lipid metabolism. Pancreastatin activates a receptor signaling system that belongs to the seven-spanning transmembrane receptor coupled to a Gq-PLCbeta-calcium-PKC signaling pathway. Increased pancreastatin plasma levels, correlating with catecholamines levels, have been found in insulin resistance states, such as gestational diabetes or essential hypertension. Pancreastatin plays important physiological role in potentiating the metabolic effects of catecholamines, and may also play a pathophysiological role in insulin resistance states with increased sympathetic activity.

Catestatin: a multifunctional peptide from chromogranin A

In 1997, we identified a novel peptide, catestatin (CST: bovine chromogranin A [CHGA](344-364): RSMRLSFRARGYGFRGPGLQL; human CHGA(352-372): SSMKLSFRARGYGFRGPGPQL), which is a potent inhibitor of nicotinic-cholinergic-stimulated catecholamine secretion. CST shows characteristic inhibitory effects on nicotinic cationic (Na(+), Ca(2+)) signal transduction, which are specific to the neuronal nicotinic receptor. Utilizing systematic polymorphism discovery at the human CHGA locus we discovered three human variants of CST: G(364)S, P(370)L, and R(374)Q that showed differential potencies towards the inhibition of catecholamine secretion. In humans, CHGA is elevated and its processing to CST is diminished in hypertension. Diminished CST is observed not only in hypertensive individuals but also in the early-normotensive offspring of patients with hypertension, suggesting that an early deficiency of CST might play a pathogenic role in the subsequent development of the disease. Consistent with human findings, prevention of endogenous CST expression by targeted ablation (knockout) of the mouse Chga locus (Chga-KO) resulted in severe hypertension that can be "rescued" specifically by replacement of the CST peptide. CST acts directly on the heart to inhibit the inotropic and lusitropic properties of the rodent heart and also acts as a potent vasodilator in rats and humans. While the G(364)S CST variant caused profound changes in human autonomic activity and seemed to reduce the risk of developing hypertension, CST replacement rescued Chga-KO mice from dampened baroreflex sensitivity. In addition, CST has been shown to induce chemotaxis and acts as an antimicrobial as well as an antimalarial peptide. The present review summarizes these multiple actions of CST.

Cellular distribution of chromogranin A in excitatory, inhibitory, aminergic and peptidergic neurons of the rodent central nervous system

Immunoreactivity for both processed and unprocessed forms of chromogranin A (CGA) was examined, using an antibody recognizing the WE14 epitope, among terminal fields and cell bodies of anatomically defined GABAergic, glutamatergic, cholinergic, catecholaminergic, and peptidergic cell groups in the rodent central nervous system. CGA is ubiquitous within neuronal cell bodies, with no obvious anatomical or chemically-coded subdivision of the nervous system in which CGA is not expressed in most neurons. CGA expression is essentially absent from catecholaminergic terminal fields in the CNS, suggesting a relative paucity of large dense-core vesicles in CNS compared to peripheral catecholaminergic neurons. Extensive synaptic co-localization with classical transmitter markers is not observed even in areas such as amygdala, where CGA fibers are numerous, suggesting preferential segregation of CGA to peptidergic terminals in CNS. Localization of CGA in dendrites in some areas of CNS may indicate its involvement in regulation of dendritic release mechanisms. Finally, the ubiquitous presence of CGA in neuronal cell somata, especially pronounced in GABAergic neurons, suggests a second non-secretory vesicle-associated function for CGA in CNS. We propose that CGA may function in the CNS as a prohormone and granulogenic factor in some terminal fields, but also possesses as-yet unknown unique cellular functions within neuronal somata and dendrites.

Chromogranin A: a new proposal for trafficking, processing and induction of granule biogenesis

Chromogranin A (CgA), a member of the granin family serves several important cell biological roles in (neuro)endocrine cells which are summarized in this review. CgA is a "prohormone" that is synthesized at the rough endoplasmic reticulum and transported into the cisternae of this organelle via its signal peptide. It is then trafficked to the Golgi complex and then to the trans-Golgi network (TGN) where CgA aggregates at low pH in the presence of calcium. The CgA aggregates provide the physical driving force to induce budding of the TGN membrane resulting in dense core granule (DCG) formation. Within the granule, a small amount of the CgA is processed to bioactive peptides, including a predicted C-terminal peptide, serpinin. Upon stimulation, DCGs undergo exocytosis and CgA and its derived peptides are released. Serpinin, acting extracellularly is able to signal the increase in transcription of a serine protease inhibitor, protease nexin-1 (PN-1) that protects DCG proteins against degradation in the Golgi complex, which then enhances DCG biogenesis to replenish those that were released. Thus CgA and its derived peptide, serpinin, plays a significant role in granule formation and regulation of granule biogenesis, respectively, in (neuro) endocrine cells.