Secretoneurin: a functional neuropeptide in health and disease

Intracerebroventricular infusion of secretoneurin inhibits neuronal NLRP3-Apoptosis pathway and preserves learning and memory after cerebral ischemia

Transient global cerebral ischemia (GCI) results in delayed neuronal death, primarily apoptosis, in the hippocampal CA1 subregion, which leads to severe cognitive deficits. While therapeutic hypothermia is an approved treatment for patients following cardiac arrest, it is associated with various adverse effects. Secretoneurin (SN) is an evolutionarily conserved neuropeptide generated in the brain, adrenal medulla and other endocrine tissues. In this study, SN was infused into the rat brain by intracerebroventricular injection 1 day after GCI, and we demonstrated that SN could significantly preserve spatial learning and memory in the Barnes maze tasks examined on days 14-17 after GCI. To further investigate underlying pathways involved, we demonstrated that, on day 5 after GCI, SN could significantly inhibit GCI-induced expression levels of Apoptosis Inducing Factor (AIF) and cleaved-PARP1, as well as neuronal apoptosis and synaptic loss in the hippocampal CA1 region. Additionally, SN could attenuate GCI-induced activation of both caspase-1 and caspase-3, and the levels of pro-inflammatory cytokines IL-1β and IL-18 in the CA1 region. Mechanically, we observed that treatment with SN effectively inhibited NLRP3 protein elevation and the bindings of NLRP3-ASC and ASC-caspase-1 in hippocampal neurons after GCI. In summary, our data indicate that SN could effectively attenuate NLRP3 inflammasome formation, as well as the activation of caspase-1 and -3, the production of pro-inflammatory cytokines, and ultimately the neuronal apoptotic loss induced by GCI. Potential neuronal pyroptosis, or caspase-1-dependent cell death, could also be involved in ischemic neuronal death, which needs further investigation.

Clinical Value of Serum Secretoneurin Levels in Prediction of Delayed Cerebral Ischemia and Prognostic Analysis of Aneurysmal Subarachnoid Hemorrhage: A Prospective Cohort Study

Background

Secretoneurin is a neuropeptide with several neuroprotective properties. Here, we discuss the importance of serum secretoneurin in assessing severity and predicting delayed cerebral ischemia (DCI) and functional outcomes following aneurysmal subarachnoid hemorrhage (aSAH).

Methods

A prospective cohort study of 167 patients with aSAH and 100 controls was performed to determine serum secretoneurin levels. Severity was reflected by the Hunt-Hess and modified Fisher scores. Prognostic parameters included DCI and poor 6-month prognosis (extended Glasgow outcome scale scores of 1-4). Univariate analysis followed by multivariate analysis was performed to determine the correlation between severity and prognosis.

Results

Compared to controls, patients exhibited a marked elevation in serum secretoneurin levels. Serum secretoneurin levels, which were independently correlated with Hunt-Hess scores and modified Fisher scores, independently predicted DCI and bad 6-month prognosis. Serum secretoneurin levels, which were linearly related to the risk of DCI and poor prognosis under a restricted cubic spline, effectively distinguished the risks under the receiver operating characteristic (ROC) curve. Subgroup analysis for prognosis or DCI prediction revealed no substantial interactions between serum secretoneurin levels and other variables, such as age, sex, hypertension, diabetes, alcohol consumption, and cigarette consumption. In addition, the prognosis model, in which serum secretoneurin, Hunt-Hess scale, and modified Fisher scale were merged, was graphically represented by a nomogram and performed well under the calibration, decision, and ROC curves.

Conclusion

Serum secretoneurin levels significantly increased after aSAH, which was intimately correlated with disease severity and independently associated with DCI and worse outcomes, indicating that serum secretoneurin may be a potential prognostic biomarker of aSAH.

Circulating secretoneurin level reflects angiographic coronary collateralization in stable angina patients with chronic total occlusion

OBJECTIVE

To investigate the association between circulating secretoneurin (SN) and angiographic coronary collateralization in stable angina patients with chronic coronary total occlusion (CTO).

METHODS

SN concentrations in serum were measured in 641 stable angina patients with CTO by radioimmunoassay. The status of coronary collaterals from the contra-lateral vessel was visually estimated using the Rentrop grading system, and was categorized into poor (grade 0 or 1) or good (grade 2 or 3) collateralization.

RESULTS

Serum SN levels were significantly higher in patients with good coronary collaterals compared to those with poor collaterals (175.23 ± 52.09 pmol/L vs. 143.29 ± 42.01 pmol/L, P < 0.001). Serum SN increased stepwise across Rentrop score 0 to 3 (P < 0.001), and increasing SN tertiles were associated with higher proportion of good coronary collateralization (OR, 1.907; 95% CI, 1.558 ~ 2.335, P < 0.001). After adjustment for confounding variables, serum SN (per tertile) remained an independent factor for predicting good coronary collaterals (OR, 1.870; 95% CI, 1.515 ~ 2.309; P < 0.001). Moreover, the diagnostic value of serum SN (per tertile) was consistent after stratifying patients based on gender, age, body mass index, hypertension, diabetes, history of smoking, severity of coronary artery disease and kidney function (OR: 1.511 ~ 2.680, P interaction ≥ 0.327).

CONCLUSION

Elevated circulating SN reflects good angiographic coronary collaterals in stable angina patients with CTO. The findings may provide insight into decision-making for these patients.

Evaluation of Serum Secretoneurin Levels in Patients With Ischemic Stroke Who Underwent Mechanical Thrombectomy

Background Ischemic stroke is a focal or global cerebral dysfunction of vascular origin; its treatment aims to provide reperfusion. Secretoneurin is a hypoxia-sensitive biomarker found in high concentrations in brain tissue. We aim to determine secretoneurin levels in patients with ischemic stroke, examine how secretoneurin levels change in the mechanical thrombectomy group, and evaluate the correlation with disease severity and prognosis. Methods Twenty-two patients diagnosed with ischemic stroke in the emergency department underwent mechanical thrombectomy, and twenty healthy volunteers were included in the study. Serum secretoneurin levels were measured by the enzyme-linked immunosorbent assay (ELISA) method. Secretoneurin levels were measured at the 0^th hour, 12^th hour, and 5^th day in patients who underwent mechanical thrombectomy. Results Serum secretoneurin levels were found to be statistically significantly higher in the patient group (7.43 ng/mL) compared to the control group (5.90 ng/mL) (p=0.023). The secretoneurin levels of the patients who underwent mechanical thrombectomy were 7.43 ng/mL, 7.04 ng/mL, and 8.65 ng/mL, measured at the 0^th hour, 12^th hour, and 5^th day, respectively, and no significant difference was detected in all three time periods (p=0.142). Conclusion Secretoneurin appears to be a useful biomarker in the diagnosis of stroke. However, it was found that there was no prognostic value in the mechanical thrombectomy group, and it was not correlated with the severity of the disease.

Neuropeptides and small-molecule amine transmitters: cooperative signaling in the nervous system

Neuropeptides are expressed in cell-specific patterns throughout mammalian brain. Neuropeptide gene expression has been useful for clustering neurons by phenotype, based on single-cell transcriptomics, and for defining specific functional circuits throughout the brain. How neuropeptides function as first messengers in inter-neuronal communication, in cooperation with classical small-molecule amine transmitters (SMATs) is a current topic of systems neurobiology. Questions include how neuropeptides and SMATs cooperate in neurotransmission at the molecular, cellular and circuit levels; whether neuropeptides and SMATs always co-exist in neurons; where neuropeptides and SMATs are stored in the neuron, released from the neuron and acting, and at which receptors, after release; and how neuropeptides affect 'classical' transmitter function, both directly upon co-release, and indirectly, via long-term regulation of gene transcription and neuronal plasticity. Here, we review an extensive body of data about the distribution of neuropeptides and their receptors, their actions after neuronal release, and their function based on pharmacological and genetic loss- and gain-of-function experiments, that addresses these questions, fundamental to understanding brain function, and development of neuropeptide-based, and potentially combinatorial peptide/SMAT-based, neurotherapeutics.

Alterations in Self-Aggregating Neuropeptides in Cerebrospinal Fluid of Patients with Parkinsonian Disorders

Background: Parkinson’s disease (PD), progressive supranuclear palsy (PSP), and multiple system atrophy (MSA) present with similar movement disorder symptoms but distinct protein aggregates upon pathological examination. Objective: Discovery and validation of candidate biomarkers in parkinsonian disorders for differential diagnosis of subgroup molecular etiologies. Methods: Untargeted liquid chromatography (LC)-mass spectrometry (MS) proteomics was used for discovery profiling in cerebral spinal fluid (CSF) followed by LC-MS/MS based multiple reaction monitoring for validation of candidates. We compared clinical variation within the parkinsonian cohort including PD subgroups exhibiting tremor dominance (TD) or postural instability gait disturbance and those with detectable leukocytes in CSF. Results: We have identified candidate peptide biomarkers and validated related proteins with targeted quantitative multiplexed assays. Dopamine-drug naïve patients at first diagnosis exhibit reduced levels of signaling neuropeptides, chaperones, and processing proteases for packaging of self-aggregating peptides into dense core vesicles. Distinct patterns of biomarkers were detected in the parkinsonian disorders but were not robust enough to offer a differential diagnosis. Different biomarker changes were detected in male and female patients with PD. Subgroup specific candidate biomarkers were identified for TD PD and PD patients with leukocytes detected in CSF. Conclusion: PD, MSA, and PSP exhibit overlapping as well as distinct protein biomarkers that suggest specific molecular etiologies. This indicates common sensitivity of certain populations of selectively vulnerable neurons in the brain, and distinct therapeutic targets for PD subgroups. Our report validates a decrease in CSF levels of self-aggregating neuropeptides in parkinsonian disorders and supports the role of native amyloidogenic proteins in etiologies of neurodegenerative diseases.

The lymph node transcriptome of unicentric and idiopathic multicentric Castleman disease

Castleman disease is a polyclonal lymphoproliferative disorder characterized by unicentric or multicentric lymphadenopathy with characteristic histomorphological features, in addition to variable inflammatory symptomatology. The molecular mechanisms and etiologies of unicentric Castleman disease (UCD) and idiopathic multicentric Castleman disease (iMCD) are poorly understood, and identification of targetable disease mediators remains an unmet clinical need. We performed whole exome sequencing on lymph node biopsies from patients with UCD and iMCD and compared the transcriptomic profiles to that of benign control lymph nodes. We identified significantly upregulated genes in UCD (n=443), iMCD (n=316) or both disease subtypes (n=51) and downregulated genes in UCD (n=321), iMCD (n=105) or both (n=10). The transcriptomes of UCD and iMCD showed enrichment and upregulation of elements of the complement cascade. By immunohistochemistry, C4d deposits indicative of complement activation were found to be present in UCD and iMCD, mostly within abnormally regressed germinal centers, but also in association with plasma cell clusters, endothelial cells and stroma cell proliferations. Other enriched gene sets included collagen organization, S1P3 pathway and VEGFR pathway in UCD; and humoral response, oxidative phosphorylation and proteosome in iMCD. Analysis of cytokine transcripts showed upregulation of CXCL13 but not IL6 in UCD and iMCD. Among angiogenic mediators, the VEGFR1 ligand placental growth factor (PGF) was upregulated in both disease subtypes. We hereby report for the first time the whole lymph node transcriptomes of UCD and iMCD, underscoring findings that could aid in the discovery of targetable disease mediators.

Localization of the neuropeptide manserin in rat dorsal root ganglia: Involvement in nociceptive function

Manserin, a neuropeptide discovered in the rat brain, is distributed in the spiral ganglion of the inner ear and carotid body, suggesting it is also localized in another neuron cluster. In this study, we examined manserin's localization in the dorsal root ganglion (DRG) and spinal cord of adult Wistar rats using immunohistochemical analyses. The DRG consists of neurofilament (NF) 200-positive large cells and two types of small cells (calcitonin gene-related peptide (CGRP)-positive peptidergic neurons and isolectin B4 (IB4)-positive non-peptidergic neurons). Manserin was localized in some of the small cells. Fluorescence double immunostaining showed that manserin-positive cells corresponded to some of the CGRP-positive cells. The DRG comprises pseudo-unipolar cells that receive sensory information from the skin and viscera and project to each layer of the dorsal horn of the spinal cord. Manserin was localized in the CGRP-positive layer I and II outer, but not in the IB4-positive layer II inner. These results suggest manserin is localized in CGRP-positive cells in the DRG, projects to the dorsal horn of the spinal cord, and is secreted with other neuropeptides, such as CGRP, to participate in nociceptive function.

Identification of cerebrospinal fluid biomarkers for parkinsonism using a proteomics approach

The aim of our study was to investigate cerebrospinal fluid (CSF) tryptic peptide profiles as potential diagnostic biomarkers for the discrimination of parkinsonian disorders. CSF samples were collected from individuals with parkinsonism, who had an uncertain diagnosis at the time of inclusion and who were followed for up to 12 years in a longitudinal study. We performed shotgun proteomics to identify tryptic peptides in CSF of Parkinson's disease (PD, n = 10), multiple system atrophy patients (MSA, n = 5) and non-neurological controls (n = 10). We validated tryptic peptides with differential levels between PD and MSA using a newly developed selected reaction monitoring (SRM) assay in CSF of PD (n = 46), atypical parkinsonism patients (AP; MSA, n = 17; Progressive supranuclear palsy; n = 8) and non-neurological controls (n = 39). We identified 191 tryptic peptides that differed significantly between PD and MSA, of which 34 met our criteria for SRM development. For 14/34 peptides we confirmed differences between PD and AP. These tryptic peptides discriminated PD from AP with moderate-to-high accuracy. Random forest modelling including tryptic peptides plus either clinical assessments or other CSF parameters (neurofilament light chain, phosphorylated tau protein) and age improved the discrimination of PD vs. AP. Our results show that the discovery of tryptic peptides by untargeted and subsequent validation by targeted proteomics is a suitable strategy to identify potential CSF biomarkers for PD versus AP. Furthermore, the tryptic peptides, and corresponding proteins, that we identified as differential biomarkers may increase our current knowledge about the disease-specific pathophysiological mechanisms of parkinsonism.

Secretoneurin is a secretogranin-2 derived hormonal peptide in vertebrate neuroendocrine systems

Secretogranin-2 (SCG2) is a large precursor protein that is processed into several potentially bioactive peptides, with the 30-43 amino acid central domain called secretoneurin (SN) being clearly evolutionary conserved in vertebrates. Secretoneurin exerts a diverse array of biological functions including regulating nervous, endocrine, and immune systems in part due to its wide tissue distribution. Expressed in some neuroendocrine neurons and pituitary cells, SN is a stimulator of the synthesis and release of luteinizing hormone from both goldfish pituitary cells and the mouse LβT2 cell line. Neuroendocrine, paracrine and autocrine signaling pathways for the stimulation of luteinizing hormone release indicate hormone-like activities to regulate reproduction. Mutation of the scg2a and scg2b genes using TALENs in zebrafish reduces sexual behavior, ovulation, oviposition, and fertility. A single injection of the SNa peptide enhanced reproductive outcomes in scg2a/scg2b double mutant zebrafish. Evidence in goldfish suggests a new role for SN to stimulate food intake by actions on other feeding-related neuropeptides. Expression and regulation of the Scg2a precursor mRNA in goldfish gut also supports a role in feeding. In rodent models, SN has trophic-like properties promoting both neuroprotection and neuronal plasticity and has chemoattractant properties that regulate neuroinflammation. Data obtained from several cellular models suggest that SN binds to and activates a G-protein coupled receptor (GPCR), but a bona fide SN receptor protein needs to be identified. Other signaling pathways for SN have been reported which provides alternatives to the GPCR hypothesis. These include AMP-activated protein kinase (AMPK), extracellular signal-regulated kinases (ERK), mitogen-activated protein kinase (MAPK)and calcium/calmodulin-dependent protein kinase II in cardiomyocytes, phosphatidylinositol 3-kinase (PI3K) and Akt/Protein Kinase B (AKT, and MAPK in endothelial cells and Janus kinase 2/signal transducer and activator of transcription protein (JAK2-STAT) signaling in neurons. Some studies in cardiac cells provide evidence for cellular internalization of SN by an unknown mechanism. Many of the biological functions of SN remain to be fully characterized, which could lead to new and exciting applications.

Characterization of blood-derived exosomal proteins after exercise

Objective

To assess changes in plasma exosome levels and protein content in mice after long-term exercise.

Methods

We subjected 9-month-old adult C57BL/6J mice to daily treadmill running exercise for 4 weeks prior to the isolation of blood-derived exosomes. Exosomal proteins were identified using mass spectrometry.

Results

Extracellular bodies were successfully isolated from mouse blood. Protein levels were altered in blood-derived exosomes after chronic treadmill exercise. Levels of the secretagogue secretogranin 2 were markedly elevated in exercise-induced exosomes.

Conclusion

Our data suggest that levels of secretogranin 2 were increased in mouse exosomes following chronic treadmill exercise. We conclude that exercise increases exocrine secretion of secretogranin 2.

Characterization of the prohormone complement in Amphiprion and related fish species integrating genome and transcriptome assemblies

The Amphiprion (anemonefish or clownfish) family of teleost fish, which is not a common model species, exhibits multiple unique characteristics, including social control of body size and protandrous sex change. The social changes in sex and body size are modulated by neuropeptide signaling pathways. These neuropeptides are formed from complex processing from larger prohormone proteins; understanding the neuropeptide complement requires information on complete prohormones sequences. Genome and transcriptome information within and across 22 teleost fish species, including 11 Amphiprion species, were assembled and integrated to achieve the first comprehensive survey of their prohormone genes. This information enabled the identification of 175 prohormone isoforms from 159 prohormone proteins across all species. This included identification of 9 CART prepropeptide genes and the loss of insulin-like 5B and tachykinin precursor 1B genes in Pomacentridae species. Transcriptome assemblies generally detected most prohormone genes but provided fewer prohormone genes than genome assemblies due to the lack of expression of prohormone genes or specific isoforms and tissue sampled. Comparisons between duplicate genes indicated that subfunctionalization, degradation, and neofunctionalization may be occurring between all copies. Characterization of the prohormone complement lays the foundation for future peptidomic investigation of the molecular basis of social physiology and behavior in the teleost fish.

Cell types and cell circuits in human and non-human primate retina

This review summarizes our current knowledge of primate including human retina focusing on bipolar, amacrine and ganglion cells and their connectivity. We have two main motivations in writing. Firstly, recent progress in non-invasive imaging methods to study retinal diseases mean that better understanding of the primate retina is becoming an important goal both for basic and for clinical sciences. Secondly, genetically modified mice are increasingly used as animal models for human retinal diseases. Thus, it is important to understand to which extent the retinas of primates and rodents are comparable. We first compare cell populations in primate and rodent retinas, with emphasis on how the fovea (despite its small size) dominates the neural landscape of primate retina. We next summarise what is known, and what is not known, about the postreceptoral neurone populations in primate retina. The inventories of bipolar and ganglion cells in primates are now nearing completion, comprising ~12 types of bipolar cell and at least 17 types of ganglion cell. Primate ganglion cells show clear differences in dendritic field size across the retina, and their morphology differs clearly from that of mouse retinal ganglion cells. Compared to bipolar and ganglion cells, amacrine cells show even higher morphological diversity: they could comprise over 40 types. Many amacrine types appear conserved between primates and mice, but functions of only a few types are understood in any primate or non-primate retina. Amacrine cells appear as the final frontier for retinal research in monkeys and mice alike.

Intricacies of the Molecular Machinery of Catecholamine Biosynthesis and Secretion by Chromaffin Cells of the Normal Adrenal Medulla and in Pheochromocytoma and Paraganglioma

The adrenal medulla is composed predominantly of chromaffin cells producing and secreting the catecholamines dopamine, norepinephrine, and epinephrine. Catecholamine biosynthesis and secretion is a complex and tightly controlled physiologic process. The pathways involved have been extensively studied, and various elements of the underlying molecular machinery have been identified. In this review, we provide a detailed description of the route from stimulus to secretion of catecholamines by the normal adrenal chromaffin cell compared to chromaffin tumor cells in pheochromocytomas. Pheochromocytomas are adrenomedullary tumors that are characterized by uncontrolled synthesis and secretion of catecholamines. This uncontrolled secretion can be partly explained by perturbations of the molecular catecholamine secretory machinery in pheochromocytoma cells. Chromaffin cell tumors also include sympathetic paragangliomas originating in sympathetic ganglia. Pheochromocytomas and paragangliomas are usually locally confined tumors, but about 15% do metastasize to distant locations. Histopathological examination currently poorly predicts future biologic behavior, thus long term postoperative follow-up is required. Therefore, there is an unmet need for prognostic biomarkers. Clearer understanding of the cellular mechanisms involved in the secretory characteristics of pheochromocytomas and sympathetic paragangliomas may offer one approach for the discovery of novel prognostic biomarkers for improved therapeutic targeting and monitoring of treatment or disease progression.

Identification and functional characterization of two Secretogranin II genes in orange-spotted grouper (Epinephelus coioides)

Secretoneurin (SN) is an important stimulator of pituitary luteinizing hormone (LH) synthesis and secretion in goldfish. It is unknown whether this neuropeptide performs the same role in other fish species. In this study, the full-length cDNAs encoding Secretogranin IIa (SgIIa) and b (SgIIb) were cloned from the brain of orange-spotted grouper. Sequence analysis showed that a 34-amino acid SN peptide (SNa) is present in SgIIa proprotein, and a 33-amino acid SN peptide (SNb) is present in SgIIb proprotein. The two SN peptides share a low degree of similarity but contain the signature YTPQ-X-LA-X₇-EL sequence. Real-time PCR showed that two SgII genes are mainly expressed in the brain and pituitary. During ovarian development, the expression levels of two SgII genes in the hypothalamus and pituitary were significantly reduced at the stage when the ovary contained full-grown oocytes. The biological functions of the two SN peptides were further investigated in vitro and in vivo. Both SN peptides could significantly elevate the mRNA levels of Gonadotropin-Releasing Hormone 1 (GnRH1) and 3 (GnRH3) in the hypothalamic fragments and upregulated the expression of Follicle-Stimulating Hormone beta (FSHb) and Luteinizing Hormone beta (LHb) in the pituitary cells. The stimulatory effects on the expression of GnRHs and Gonadotropins were also observed after intraperitoneal injection of SN peptides. Our study indicated that the SgII/SN system has stimulatory effects on the reproductive axis of orange-spotted grouper.

Wavy multistratified amacrine cells in the monkey retina contain immunoreactive secretoneurin

The goals of this study were to describe the morphology, neurotransmitter content and synaptic connections of neurons in primate retinas that contain the neuropeptide secretoneurin. Amacrine cells were labeled with antibodies to secretoneurin in macaque and baboon retinas. Their processes formed three distinct plexuses in the inner plexiform layer: one in the outermost stratum, one in the center and one in the innermost stratum. In light microscopic double immunolabeling experiments, GABA was colocalized with secretoneurin in these cells, but glycine transporter 1 and Substance P were not. ON bipolar cell axon terminals labeled with antibody to the cholecystokinin precursor, G6-gly, have ON responses to stimulation of short wavelength sensitive (S) cones. Axons of these bipolar cells made contacts with amacrine cell dendrites containing secretoneurin. Secretoneurin-IR amacrine cells also made contacts with retinal ganglion cell dendrites labeled with antibody to the photopigment melanopsin, which have OFF responses to stimulation of S cones. Using electron microscopic immunolabeling, 436 synapses from macaque retina were analyzed. Axons from bipolar cells were identified by their characteristic synaptic ribbons; their synaptic densities were asymmetric like those of excitatory synapses in the brain. Amacrine cells made and received conventional synapses with symmetric synaptic densities, like those of inhibitory synapses in the brain. Ganglion cell dendrites were identified by their absence of presynaptic specializations; they received inputs from both amacrine cells and bipolar cells. The majority of inputs to the secretoneurin-IR amacrine cells were from other amacrine cells, but they also received 21% of their input from bipolar cells. They directed most of their output, 54%, to amacrine cells, but there were many synapses onto bipolar cell axons and ganglion cell dendrites, as well. The synaptic connections were very similar in the three plexuses with one notable exception; output synapses to bipolar cells were significantly less common in the innermost one, where the S-ON bipolar cells terminate. Taken together, these findings suggest that the secretoneurin-IR amacrine cells in primates receive excitatory input from S-ON bipolar cells and, in turn, inhibit intrinsically photosensitive retinal ganglion cells.

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.

Defining the transcriptomic landscape of the developing enteric nervous system and its cellular environment

BACKGROUND

Motility and the coordination of moving food through the gastrointestinal tract rely on a complex network of neurons known as the enteric nervous system (ENS). Despite its critical function, many of the molecular mechanisms that direct the development of the ENS and the elaboration of neural network connections remain unknown. The goal of this study was to transcriptionally identify molecular pathways and candidate genes that drive specification, differentiation and the neural circuitry of specific neural progenitors, the phox2b expressing ENS cell lineage, during normal enteric nervous system development. Because ENS development is tightly linked to its environment, the transcriptional landscape of the cellular environment of the intestine was also analyzed.

RESULTS

Thousands of zebrafish intestines were manually dissected from a transgenic line expressing green fluorescent protein under the phox2b regulatory elements [Tg(phox2b:EGFP) ^w37 ]. Fluorescence-activated cell sorting was used to separate GFP-positive phox2b expressing ENS progenitor and derivatives from GFP-negative intestinal cells. RNA-seq was performed to obtain accurate, reproducible transcriptional profiles and the unbiased detection of low level transcripts. Analysis revealed genes and pathways that may function in ENS cell determination, genes that may be identifiers of different ENS subtypes, and genes that define the non-neural cellular microenvironment of the ENS. Differential expression analysis between the two cell populations revealed the expected neuronal nature of the phox2b expressing lineage including the enrichment for genes required for neurogenesis and synaptogenesis, and identified many novel genes not previously associated with ENS development. Pathway analysis pointed to a high level of G-protein coupled pathway activation, and identified novel roles for candidate pathways such as the Nogo/Reticulon axon guidance pathway in ENS development.

CONCLUSION

We report the comprehensive gene expression profiles of a lineage-specific population of enteric progenitors, their derivatives, and their microenvironment during normal enteric nervous system development. Our results confirm previously implicated genes and pathways required for ENS development, and also identify scores of novel candidate genes and pathways. Thus, our dataset suggests various potential mechanisms that drive ENS development facilitating characterization and discovery of novel therapeutic strategies to improve gastrointestinal disorders.

Administration of secretoneurin is protective in hypoxic-ischemic neonatal brain injury predominantly in the hypoxic-only hemisphere

Neonatal brain injury is a problem of global importance. To date, no causal therapies are available. A substance with considerable therapeutic potential is the endogenous neuropeptide secretoneurin (SN), which has proven to be beneficial in adult stroke. The aim of this study was to assess its effect in neonatal hypoxic-ischemic brain injury models. In vitro, primary hippocampal neurons were pre-treated with vehicle, 1µg/ml, 10µg/ml, or 50µg/ml SN and subjected to oxygen-glucose deprivation (OGD) for six hours. Cell death was assessed after a 24-h recovery period. In vivo, seven day-old CD-1 mice underwent unilateral common carotid artery ligation and were exposed to 8% oxygen/nitrogen for 20 min. SN plasma concentrations were serially determined by ELISA after insult. One hour after hypoxia, a subgroup of animals was treated with vehicle or SN. SN plasma concentrations significantly decreased 48h after insult. The number of caspase-3-positive cells was significantly lower in the hypoxic-ischemic hemisphere in the thalamus of SN-treated animals. In the hypoxic-only hemisphere administration of SN significantly reduced the number of caspase-3-positive cells (in cortex, white matter, hippocampus, thalamus and striatum) and inhibited microglial cell activation in the thalamus. SN has neuroprotective potential in neonatal brain injury. Its main action seems to be inhibition of apoptosis in the aftermath of the insult, predominantly in the hypoxic-only hemisphere. This might be explained by the less pronounced injury in this hemisphere, where blood flow and thus nutrient supply are maintained.

Comparing label-free quantitative peptidomics approaches to characterize diurnal variation of peptides in the rat suprachiasmatic nucleus

Mammalian circadian rhythm is maintained by the suprachiasmatic nucleus (SCN) via an intricate set of neuropeptides and other signaling molecules. In this work, peptidomic analyses from two times of day were examined to characterize variation in SCN peptides using three different label-free quantitation approaches: spectral count, spectra index and SIEVE. Of the 448 identified peptides, 207 peptides were analyzed by two label-free methods, spectral count and spectral index. There were 24 peptides with significant (adjusted p-value < 0.01) differential peptide abundances between daytime and nighttime, including multiple peptides derived from secretogranin II, cocaine and amphetamine regulated transcript, and proprotein convertase subtilisin/kexin type 1 inhibitor. Interestingly, more peptides were analyzable and had significantly different abundances between the two time points using the spectral count and spectral index methods than with a prior analysis using the SIEVE method with the same data. The results of this study reveal the importance of using the appropriate data analysis approaches for label-free relative quantitation of peptides. The detection of significant changes in so rich a set of neuropeptides reflects the dynamic nature of the SCN and the number of influences such as feeding behavior on circadian rhythm. Using spectral count and spectral index, peptide level changes are correlated to time of day, suggesting their key role in circadian function.

The secretogranin II gene is a signal integrator of glutamate and dopamine inputs

Cooperative gene regulation by different neurotransmitters likely underlies the long-term forms of associative learning and memory, but this mechanism largely remains to be elucidated. Following cDNA microarray analysis for genes regulated by Ca(2+) or cAMP, we found that the secretogranin II gene (Scg2) was cooperatively activated by glutamate and dopamine in primary cultured mouse hippocampal neurons. The Ca(2+) chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid acetoxymethyl ester (BAPTA-AM) and the mitogen-activated protein kinase (MAPK) kinase (MEK) inhibitor PD98059 prevented Scg2 activation by glutamate or dopamine; thus, the Ca(2+) /MEK pathway is predicted to include a convergence point(s) of glutamatergic and dopaminergic signaling. Unexpectedly, the protein kinase A inhibitor KT5720 enhanced Scg2 activation by dopamine. The protein-synthesis inhibitor cycloheximide also enhanced Scg2 activation, and the proteasome inhibitor ZLLLH diminished the KT5720-mediated augmentation of Scg2 activation. These results are concordant with the notion that dopaminergic input leads to accumulation of a KT5720-sensitive transcriptional repressor, which is short-lived because of rapid degradation by proteasomes. This repression pathway may effectively limit the time window permissive to Scg2 activation by in-phase glutamate and dopamine inputs via the Ca(2+) /MEK pathway. We propose that the regulatory system of Scg2 expression is equipped with machinery that is refined for the signal integration of in-phase synaptic inputs. We proposed hypothetical mechanism for the regulation of the secretogranin II gene as a signal integrator of glutamate and dopamine inputs. Glutamate or dopamine activates the Ca(2+) /MEK/ERK pathway, which thus contributes to the signal integration. Concurrently, activation of the PKA inhibitor KT5720-sensitive pathway by dopamine leads to accumulation of the repressor protein X that is otherwise susceptible to proteasome degradation. This repression system may determine the time window permissive to the cooperative activation by in-phase glutamate and dopamine inputs.

[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.

Secretoneurin, substance P and neuropeptide Y in the oxygen-induced retinopathy in C57Bl/6N mice

In this study, we investigated whether the proangiogenic neuropeptides secretoneurin (SN), substance P (SP), and neuropeptide Y (NPY) contribute to the development of abnormal neovascularization in the oxygen-induced retinopathy (OIR) model in mice. By exposing litters of C57Bl/6N mice to 75% oxygen from postnatal day 7 (P7) until postnatal day 11 (P11) and then returning them to normoxic conditions, retinal ischemia and subsequent neovascularization on the retinal surface were induced. Retinae were dissected on P9, P11, P12-P14, P16 and P20, and the concentrations of SN, SP, NPY and VEGF determined by radioimmunoassay or ELISA. The levels of SN and SP increased in controls from P9 until P16 and from P9 until P14, respectively, whereas the levels of NPY were high at P9 and decreased thereafter until P20, suggesting that NPY may participate in the development of the retina. However, dipeptidyl peptidase IV (DPPIV) and the NPY-Y2 receptor were not detectable in the immature retina indicating that NPY is not involved in the physiological vascularization in the retina. Compared to controls, OIR had no effect on the levels of SN, whereas levels of both SP and NPY slightly decreased during hyperoxia. Normalization of the levels of SP, and to a more pronounced extent of NPY, was significantly delayed during relative hypoxia. This clearly indicates that these three neuropeptides are not involved in the pathogenesis of neovascularization in OIR. Moreover, since there were no differences in the expression of two vessel markers in the retina of NPY knockout mice versus controls at P14, NPY is also not involved in the delayed development of the intermediate and deep vascular plexus in the retina in this animal model.

GE-25-like immunoreactivity in the rat eye

This study aimed to investigate the presence and distribution of the chromogranin A-derived peptide GE-25 in the rat eye. The molecular form detected by the GE-25 antiserum was evaluated in the rat trigeminal ganglion, retina and remaining tissues of the rat eye by means of Western blots and the distribution pattern of GE-25-like immunoreactivity was studied in the rat eye and rat trigeminal ganglion by immunofluorescence. One single band of approximately 70kDa was stained in the trigeminal ganglion and retina which represents the uncleaved intact chromogranin A indicating that the proteolytic processing of chromogranin A to GE-25 is limited in these tissues. Sparse GE-25-like immunoreactive nerve fibers were visualized in the corneal stroma, at the limbus around blood vessels, in the sphincter and dilator muscle and stroma of the iris, in the stroma of the ciliary body and ciliary processes and in the stroma and around blood vessels in the choroid. This distribution pattern is characteristic for neuropeptides whereas the presence of immunoreactivity in the corneal endothelium and in Müller glia in the retina is atypical. GE-25-like immunoreactivity was found in small to medium-sized ganglion cells in the rat trigeminal ganglion clearly indicating that the nerve fibers in the rat eye are of sensory origin. The colocalization of GE-25-immunoreactivity with SP-immunoreactivity in the rat ciliary body is in agreement with the presumption of the sensory nature of the innervation of the anterior segment of the eye by GE-25.

Identification of the HSPB4/TLR2/NF-κB axis in macrophage as a therapeutic target for sterile inflammation of the cornea

Sterile inflammation underlies many diseases of the cornea including serious chemical burns and the common dry eye syndrome. In search for therapeutic targets for corneal inflammation, we defined the kinetics of neutrophil infiltration in a model of sterile injury to the cornea and identified molecular and cellular mechanisms triggering inflammatory responses. Neutrophil infiltration occurred in two phases: a small initial phase (Phase I) that began within 15 min after injury, and a larger second phase (Phase II) that peaked at 24–48 h. Temporal analysis suggested that the neuropeptide secretoneurin initiated Phase I without involvement of resident macrophages. Phase II was initiated by the small heat shock protein HSPB4 that was released from injured keratocytes and that activated resident macrophages via the TLR2/NF-κB pathway. The Phase II inflammation was responsible for vision-threatening opacity and was markedly suppressed by different means of inhibition of the HSPB4/TLR2/NF-κB axis: in mice lacking HSPB4 or TLR2, by antibodies to HSPB4 or by TNF-α stimulated gene/protein 6 that CD44-dependently inhibits the TLR2/NF-κB pathway. Therefore, our data identified the HSPB4/TLR2/NF-κB axis in macrophages as an effective target for therapy of corneal inflammation.

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

The chromogranins (chromogranin A and chromogranin B), secretogranins (secretogranin II and secretogranin III), and additional related proteins (7B2, NESP55, proSAAS, and VGF) that together comprise the granin family subserve essential roles in the regulated secretory pathway that is responsible for controlled delivery of peptides, hormones, neurotransmitters, and growth factors. Here we review the structure and function of granins and granin-derived peptides and expansive new genetic evidence, including recent single-nucleotide polymorphism mapping, genomic sequence comparisons, and analysis of transgenic and knockout mice, which together support an important and evolutionarily conserved role for these proteins in large dense-core vesicle biogenesis and regulated secretion. Recent data further indicate that their processed peptides function prominently in metabolic and glucose homeostasis, emotional behavior, pain pathways, and blood pressure modulation, suggesting future utility of granins and granin-derived peptides as novel disease biomarkers.

PE-11, a peptide derived from chromogranin B, in the rat eye

The aim of the study was to investigate the presence and distribution of PE-11, a peptide derived from chromogranin B, in the rat eye. For this purpose, newborn rats were injected with a single dosage of 50mg/kg capsaicin subcutaneously under the neck fold and after three months, particular eye tissues were dissected and the concentration of PE-11-like immunoreactivity was determined by radioimmunoassay. Furthermore, PE-11-like immunoreactivities were characterized in an extract of the rat eye by reversed phase HPLC. Then, the distribution pattern of PE-11 was investigated in the rat eye and rat trigeminal ganglion by immunofluorescence. As a result, PE-11 was present in each tissue of the rat eye and capsaicin pretreatment led to a 88.05% (±7.07) and a 64.26% (±14.17) decrease of the levels of PE-11 in the cornea and choroid/sclera, respectively, and to a complete loss in the iris/ciliary body complex. Approximately 70% of immunoreactivities detected by the PE-11 antiserum have been found to represent authentic PE-11. Sparse nerve fibers were visualized in the corneal and uveal stroma, surrounding blood vessels at the limbus, ciliary body and choroid and in association with the dilator and sphincter muscle. Furthermore, immunoreactivity was present in the corneal endothelium. In the retina and optic nerve, glia was labeled. In the rat trigeminal ganglion, PE-11-immunoreactivity was visualized in small and medium sized ganglion cells with a diameter of up to 30μm. In conclusion, there is unequivocal evidence that PE-11 is a constituent of capsaicin-sensitive sensory neurons innervating the rat eye and the distribution pattern is typically peptidergic in the peripheral innervation but in the retina completely atypical for neuropeptides and unique.

Catecholamine storage vesicles: role of core protein genetic polymorphisms in hypertension

Hypertension is a complex trait with deranged autonomic control of the circulation. The sympathoadrenal system exerts minute-to-minute control over cardiac output and vascular tone. Catecholamine storage vesicles (or chromaffin granules) of the adrenal medulla contain remarkably high concentrations of chromogranins/secretogranins (or "granins"), catecholamines, neuropeptide Y, adenosine triphosphate (ATP), and Ca(2+). Within secretory granules, granins are co-stored with catecholamine neurotransmitters and co-released upon stimulation of the regulated secretory pathway. The principal granin family members, chromogranin A (CHGA), chromogranin B (CHGB), and secretogranin II (SCG2), may have evolved from shared ancestral exons by gene duplication. This article reviews human genetic variation at loci encoding the major granins and probes the effects of such polymorphisms on blood pressure, using twin pairs to probe heritability and individuals with the most extreme blood pressure values in the population to study hypertension.

Cellular expression and subcellular localization of secretogranin II in the mouse hippocampus and cerebellum

Secretogranin II (SgII), or chromogranin C, is thought to participate in the sorting and packaging of peptide hormones and neuropeptides into secretory granules and large dense-core vesicle (LDCVs), and also functions as a precursor of neuropeptide secretoneurin. Although SgII is widely distributed in the brain and is predominantly localized at terminals of mossy fibers in the hippocampus and cerebellum and climbing fibers in the cerebellum, its cellular expression and ultrastructural localization remain largely unknown. In the present study, we addressed this issue in the adult mouse brain by multiple-labeling fluorescence in situ hybridization and immunofluorescence and by preembedding and postembedding immunoelectron microscopies. SgII was expressed in various neurons, distributed as either tiny puncta or coarse aggregates in the neuropil, and intensely accumulated in perikarya of particular neurons, such as parvalbumin-positive interneurons and mossy cells in the hippocampus and Purkinje cells in the cerebellum. Coarse aggregates were typical of terminals of mossy fibers and climbing fibers. In these terminals, numerous immunogold particles were clustered on individual LDCVs, and one or two particles also fell within small synaptic vesicle-accumulating portions. SgII was further detected as tiny puncta in neural elements lacking LDCVs, such as parallel fibers of cerebellar granule cells, somatodendritic elements of various neurons and Bergmann glia. Thus, SgII is present in LDCV and non-LDCV compartments of various neural cells. The wide subcellular localization of SgII may reflect diverse release sites of neuropeptides and secretorneurin, or suggests its role in the sorting and packaging of molecules other than neuropeptides in non-LDCV compartments.

Granins and their derived peptides in normal and tumoral chromaffin tissue: Implications for the diagnosis and prognosis of pheochromocytoma

Pheochromocytomas are rare catecholamine-secreting tumors that arise from chromaffin tissue within the adrenal medulla and extra-adrenal sites. Typical clinical manifestations are sustained or paroxysmal hypertension, severe headaches, palpitations and sweating resulting from hormone excess. However, their presentation is highly variable and can mimic many other diseases. The diagnosis of pheochromocytomas depends mainly upon the demonstration of catecholamine excess by 24-h urinary catecholamines and metanephrines or plasma metanephrines. Occurrence of malignant pheochromocytomas can only be asserted by imaging of metastatic lesions, which are associated with a poor survival rate. The characterization of tissue, circulating or genetic markers is therefore crucial for the management of these tumors. Proteins of the granin family and their derived peptides are present in dense-core secretory vesicles and secreted into the bloodstream, making them useful markers for the identification of neuroendocrine cells and neoplasms. In this context, we will focus here on reviewing the distribution and characterization of granins and their processing products in normal and tumoral chromaffin cells, and their clinical usefulness for the diagnosis and prognosis of pheochromocytomas. It appears that, except SgIII, all members of the granin family i.e. CgA, CgB, SgII, SgIV-SgVII and proSAAS, and most of their derived peptides are present in adrenomedullary chromaffin cells and in pheochromocytes. Moreover, besides the routinely used CgA test assays, other assays have been developed to measure concentrations of tissue and/or circulating granins or their derived peptides in order to detect the occurrence of pheochromocytomas. In most cases, elevated levels of these entities were found, in correlation with tumor occurrence, while rarely discriminating between benign and malignant neoplasms. Nevertheless, measurement of the levels of granins and derived peptides improves the diagnostic sensitivity and may therefore provide a complementary tool for the management of pheochromocytomas. However, the existing data need to be substantiated in larger groups of patients, particularly in the case of malignant disease.

Secretoneurin and the tachykinins substance P and neurokinin-A/B in NMDA-induced excitotoxicity in the rat retina

In a recent investigation using the NMDA-excitotoxicity model in the rat retina, we found that, whereas, following intravitreal injection of NMDA, a time-dependent decrease of the levels of a neuropeptide, namely vasoactive intestinal polypeptide (VIP), was fully counteracted by topical treatment with flunarizine eye drops, the levels of pituitary adenylate-cyclase activating peptide-38 (PACAP-38), another neuropeptide, remained unchanged. The aim of the present study was to find out if NMDA causes reduction in the levels of other neuropeptides such as secretoneurin (SN), neurokinin-A/B (NKA/NKB) and substance P (SP), and if so, whether flunarizine has the ability to counteract this effect or prevent such reduction. The reduction of the levels of SN and NKA/NKB 14 days after intravitreal injection of 2 μl of 100 nmol NMDA into one eye was more pronounced than after 7 days; topical flunarizine had a slight counteracting effect, but could not prevent the decrease in the levels of these peptides. Reduction in SP levels after 28 and 56 days was fully counteracted by flunarizine. By enabling a pronounced influx of Ca²+ ions into peptide-expressing cells, NMDA leads to cell death. Since each of these peptides exerts neuroprotective properties in the central nervous system, the drop in their levels caused by acute insult (e.g. NMDA excitotoxicity) or chronic insult (e.g. glaucoma) may cause a breakdown of endogenous neuroprotection in the retina given that these peptides feature neuroprotective properties in the retina as well.

Chromogranins A and B and secretogranin II as prohormones for regulatory peptides from the diffuse neuroendocrine system

Chromogranin A (CgA), chromogranin B (CgB), and secretogranin II (SgII) belong to a family of uniquely acidic secretory proteins in elements of the diffuse neuroendocrine system. These "granins" are characterized by numerous pairs of basic amino acids as potential sites for intra- and extragranular processing. In response to adequate stimuli, the granins are coreleased with neurotransmitters and hormones and appear in the circulation as potential modulators of homeostatic processes. This review is directed towards functional aspects of the secreted CgA, CgB, and SgII and their biologically active sequences. Widely different effects and targets have been reported for granin-derived peptides. So far, the CgA peptides vasostatin-I, pancreastatin, and catestatin, the CgB peptides CgB(1-41) and secretolytin, and the SgII peptide secretoneurin are the most likely candidates for granin-derived regulatory peptides. Most of their effects fit into patterns of direct or indirect modulations of major functions, in particular associated with inflammatory conditions.

Regulatory peptides from chromogranin A and secretogranin II: putative modulators of cells and tissues involved in inflammatory conditions

Chromogranin A (CgA) and secretogranin II (SgII) of the granin family of uniquely acidic proteins secreted from elements of the diffuse neuroendocrine system are also produced by cells involved in inflammation. CgA and the CgA-derived peptides vasostatin-I and catestatin are products of polymorphonuclear neutrophils accumulating at sites of injury or infections while SgII and the Sg II-derived secretoneurin may contribute to neurogenic inflammation when released from sensory nerve terminals. This review is directed towards vasostatin-I, catestatin and secretoneurin as modulators of cells and tissues associated with inflammatory conditions. The accumulated literature indicates that concerted effects of vasostatin-I and catestatin may be relevant for the first-line host-defence against invading microorganisms, contrasting the apparent lack of antibacterial potencies in secretoneurin. Oppositely directed effects of vasostatin-I and secretoneurin on endothelial permeability and transendothelial extravasation are particularly striking. While vasostatin-I protects the integrity of the endothelial barrier against the disruptive effects of proinflammatory agents, secretoneurin activates transendothelial extravasation, chemotaxis and migration of leukocytes. Oppositely directed effects of vasostatin-I and secretoneurin on formation of blood vessels are also indicated, vasostatin-I inhibiting angiogenetic parameters while secretoneurin activates not only angiogenesis but also vascularization.

Aspects of the neuroendocrine cerebellum: expression of secretogranin II, chromogranin A and chromogranin B in mouse cerebellar unipolar brush cells

Morphologically distinct neuron classes can be subdivided in sublineages by differential chemical phenotypes that correlate with functional diversity. Here we show by immunocytochemistry that chromogranin A (CgA) chromogranin B (CgB) and secretogranin II (SgII), the principal granins situated in neuronal secretory granules and large dense-core vesicles, are widely but differentially expressed in cells of the mouse cerebellum and terminals of cerebellar afferents. While CgA and CgB were nearly panneuronal, SgII was more restricted in distribution. The cells most intensely immunoreactive for SgII were a class of small, excitatory interneurons enriched in the granular layer of the vestibulocerebellum, the unipolar brush cells (UBCs), although larger neurons likely to be a subset of the Golgi-Lugaro-globular cell population were also distinctly immunopositive; by contrast, Purkinje cells and granule cells were, at best, faintly stained and, stellate, basket cells were unstained. SgII was also present in subsets of mossy fibers, climbing fibers and varicose fibers. Neurons in the cerebellar nuclei and inferior olive were distinctly positive for the three granins. Double-labeling with subset-specific cell class markers indicated that, while both CgA and CgB were present in most UBCs, SgII immunoreactivity was present in the calretinin (CR)-expressing subset, but lacked in metabotropic glutamate receptor 1alpha (mGluR1alpha)-expressing UBCs. Thus, we have identified an additional cell class marker, SgII, which serves to study subtype properties in the UBC population. The abundance of SgII in only one of the two known subsets of UBCs is remarkable, as its expression in other neurons of the cortex was moderate or altogether lacking. The data suggest that the CR-positive UBCs represent a unique neuroendocrine component of the mammalian cerebellar cortex, presumably endowed with transynaptically regulated autocrine or paracrine action/s. Because of the well-known organization of the cerebellar system, several of its neuron classes may represent valuable cellular models to analyze granin functions in situ, in acute slices and in dissociated cell and organotypic slice cultures.

The chromaffin vesicle: advances in understanding the composition of a versatile, multifunctional secretory organelle

Chromaffin vesicles (CV) are highly sophisticated secretory organelles synthesized in adrenal medullary chromaffin cells. They contain a complex mixture of structural proteins, catecholamine neurotransmitters, peptide hormones, and the relative processing enzymes, as well as protease inhibitors. In addition, CV store ATP, ascorbic acid, and calcium. During the last decades, extensive studies have contributed to increase our understanding of the molecular composition of CV. Yet, the recent development of biochemical and imaging procedures has greatly increased the list of CV-soluble constituents and opened new horizons as to the complexity of CV involvement in acute stress responses. Thus, a coherent picture of CV molecular composition is still to be drawn. This review article will provide a detailed account of the content of CV soluble molecules as it emerges from the most recent analytical studies. Moreover, this review article will attempt at focussing on the physiological and pathophysiological implications of the products released by CV.

Molecular cloning, mapping, and polymorphism of the porcine SCG2 gene

The secretogranin II (SCG2) gene is associated with the synthesis and secretion of follicle-stimulating hormone and luteinizing hormone. In the present study, we have determined the complete cDNA sequence of pig SCG2, which was submitted to GenBank with accession no. AY870646. Its complete open reading frame of 1,851 nucleotides encodes 616 amino acids. The predicted protein shares 80-87% identity with mouse, human, and bovine SCG2 proteins, and all four species share almost complete identity in the secretoneurin and EM66 domains. Pig SCG2 is a protein of 589 amino acids and 68,132 Da, preceded by a signal peptide of 27 residues. It contains nine pairs of dibasic residues, which are used as potential cleavage sites for generation of physiologically active peptides. Analysis of the SCG2 gene across the INRA-Minnesota porcine radiation hybrid panel indicates close linkage with microsatellite marker SW2608, located on Sus scrofa chromosome 15 (SSC15) q25, which harbors several QTL for ovulation rate and meat quality. Comparative sequencing and EST analysis revealed nine SNPs in porcine SCG2 cDNA, including seven SNPs in the coding region and two SNPs in the 3' UTR. Four nonsynonymous SNPs (G622A, G1671T, C1718T, and A1790C) resulted in amino acid substitutions of Ala-->Thr, Glu-->Asp, Pro-->Leu, and Asn-->Thr, respectively.

Recently identified a novel neuropeptide manserin colocalize with the TUNEL-positive cells in the top villi of the rat duodenum

We recently isolated a novel 40 amino acid neuropeptide designated manserin from the rat brain. Manserin is derived from secretogranin II, a member of granin acidic secretory protein family by proteolytic processing, as previously reported secretoneurin and EM66. Manserin peptide are localized in the endocrine cells of the pituitary. In this study, we further investigated the manserin localization in the digestive system by immunohistochemical analysis using antimanserin antibody. In the duodenum, manserin immunostaining was exclusively observed in the nuclei of top villi instead of cytosol as observed in neurons in our previous study. Interestingly, manserin-positive cells in the duodenum are colocalized with terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) positive cells, the cells whose DNA was damaged. Since the top villi of duodenum epithelial cells are known to undergo spontaneous apoptosis during epithelial cell turn over, and since other peptides such as secretoneurin and EM66 derived from SgII have been reported to be cancer-related, these results indicated that manserin peptide may have a role in apoptosis and/or cancer pathogenesis in the digestive organ.

Secretogranin II: a key AP-1-regulated protein that mediates neuronal differentiation and protection from nitric oxide-induced apoptosis of neuroblastoma cells

Identification of AP-1 target genes in apoptosis and differentiation has proved elusive. Secretogranin II (SgII) is a protein widely distributed in nervous and endocrine tissues, and abundant in neuroendocrine granules. We addressed whether SgII is regulated by AP-1, and if SgII is involved in neuronal differentiation or the cellular response to nitrosative stress. Nitric oxide (NO) upregulated sgII mRNA dependent on a cyclic AMP response element (CRE) in the sgII promoter, and NO stimulated SgII protein secretion in neuroblastoma cells. Upregulation of sgII mRNA, sgII CRE-driven gene expression and SgII protein synthesis/export were attenuated in cells transformed with dominant-negative c-Jun (TAM67), which became sensitized to NO-induced apoptosis and failed to undergo nerve growth factor-dependent neuronal differentiation. Stable transformation of TAM67 cells with sgII restored neuronal differentiation and resistance to NO. RNAi knockdown of sgII in cells expressing functional c-Jun abolished neuronal differentiation and rendered the cells sensitive to NO-induced apoptosis. Therefore, SgII represents a key AP-1-regulated protein that counteracts NO toxicity and mediates neuronal differentiation of neuroblastoma cells.

An ancestral variant of Secretogranin II confers regulation by PHOX2 transcription factors and association with hypertension

Granins regulate secretory vesicle formation in neuroendocrine cells and granin-derived peptides are co-released with neurotransmitters as modulatory signals at sympathetic sites. We report evidence for association between a regulatory polymorphism in Secretogranin II (SCG2) and hypertension in African-American subjects. The minor allele is ancestral in the human lineage and is associated with disease risk in two case-control studies and with elevated blood pressure in a separate familial study. Mechanistically, the ancestral allele acts as a transcriptional enhancer in cells that express endogenous Scg2, whereas the derived allele does not. ARIX (PHOX2A) and PHOX2B are identified as potential transactivating factors by oligonucleotide affinity chromatography and mass spectrometry and confirmed by chromatin immunoprecipitation. Each of these transcription factors preferentially binds the risk allele, both in vitro and in vivo. Population genetic considerations suggest positive selection of the protective allele within the human lineage. These results identify a common regulatory variation in SCG2 and implicate granin gene expression in the control of human blood pressure and susceptibility to hypertension.

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

CONTEXT

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

OBJECTIVE

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

DESIGN AND SETTING

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

PATIENTS

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

RESULTS

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

CONCLUSIONS

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

Inducible and reversible Clock gene expression in brain using the tTA system for the study of circadian behavior

The mechanism of circadian oscillations in mammals is cell autonomous and is generated by a set of genes that form a transcriptional autoregulatory feedback loop. While these “clock genes” are well conserved among animals, their specific functions remain to be fully understood and their roles in central versus peripheral circadian oscillators remain to be defined. We utilized the in vivo inducible tetracycline-controlled transactivator (tTA) system to regulate Clock gene expression conditionally in a tissue-specific and temporally controlled manner. Through the use of Secretogranin II to drive tTA expression, suprachiasmatic nucleus– and brain-directed expression of a tetO::Clock^Δ19 dominant-negative transgene lengthened the period of circadian locomotor rhythms in mice, whereas overexpression of a tetO::Clock^wt wild-type transgene shortened the period. Low doses (10 μg/ml) of doxycycline (Dox) in the drinking water efficiently inactivated the tTA protein to silence the tetO transgenes and caused the circadian periodicity to return to a wild-type state. Importantly, low, but not high, doses of Dox were completely reversible and led to a rapid reactivation of the tetO transgenes. The rapid time course of tTA-regulated transgene expression demonstrates that the CLOCK protein is an excellent indicator for the kinetics of Dox-dependent induction/repression in the brain. Interestingly, the daily readout of circadian period in this system provides a real-time readout of the tTA transactivation state in vivo. In summary, the tTA system can manipulate circadian clock gene expression in a tissue-specific, conditional, and reversible manner in the central nervous system. The specific methods developed here should have general applicability for the study of brain and behavior in the mouse.

Although significant progress has been made in unraveling the molecular mechanism of circadian clocks in mammals, previous work has focused on germline mutations and in vitro methods for analysis. To address the function of clock genes, it is necessary to develop tools to manipulate circadian genes in a conditional and tissue-specific manner in vivo. We report such an approach using the tetracycline transactivator system. Despite the development of the “tet” system in transgenic mice over 10 y ago by Bujard and colleagues, there are still relatively few examples of the successful use of the tet system in the central nervous system. Transgenic expression of the Clock gene in the suprachiasmatic nucleus and brain of mice regulated the period length of circadian locomotor rhythms. These effects could be inhibited by low doses of doxycycline in the drinking water. Importantly, low, but not high, doses of doxycycline were completely reversible and led to a rapid reactivation of the Clock transgenes. In summary, the tetracycline-controlled transactivator system can manipulate circadian clock gene expression in a tissue-specific, conditional, and reversible manner in the central nervous system. The specific methods developed here should have general applicability for the study of brain and behavior in the mouse.

Expression and processing of the neuroendocrine protein secretogranin II in benign and malignant pheochromocytomas

The aim of the present study was to compare the expression levels of secretogranin II (SgII), prohormone convertases (PC)1 and PC2, and the proteolytic processing of SgII in benign versus malignant pheochromocytomas. Quantitative (Q)-PCR experiments indicated that SgII, PC1, and PC2 mRNAs were overexpressed in pheochromocytoma compared to non-tumoral chromaffin cells (P<0.001) and in benign compared to malignant tumors (P<0.01). Western blot analysis using a human SgII antiserum revealed the occurrence of a 97-kDa band corresponding to the expected size of SgII, with significantly higher quantities in benign than in malignant tumors (P<0.05). Using antisera directed against sequential regions of SgII (N-terminal, secretoneurin [SN], EM66, internal, and C-terminal sequences), we observed distinct processing profiles between benign and malignant pheochromocytomas. In contrast, using PC1 and PC2 antisera no differences between the two types of tumors were found. RIA measurement showed that EM66 median values between benign and malignant chromaffin cell tumors were significantly different (128.5 vs. 6.3 ng/mg protein, respectively; P<0.001). Taken together, these results indicate that, in pheochromocytoma, malignancy is associated with reduced PC1, PC2, and SgII mRNA expression and decreased levels of processing products of SgII, in line with the low concentrations of EM66 that occur in malignant tumors. These data support the notion that SgII-processing products, such as EM66, could represent prognostic markers of pheochromocytomas.

Neuronal Control of Skin Function: The Skin as a Neuroimmunoendocrine Organ

This review focuses on the role of the peripheral nervous system in cutaneous biology and disease. During the last few years, a modern concept of an interactive network between cutaneous nerves, the neuroendocrine axis, and the immune system has been established. We learned that neurocutaneous interactions influence a variety of physiological and pathophysiological functions, including cell growth, immunity, inflammation, pruritus, and wound healing. This interaction is mediated by primary afferent as well as autonomic nerves, which release neuromediators and activate specific receptors on many target cells in the skin. A dense network of sensory nerves releases neuropeptides, thereby modulating inflammation, cell growth, and the immune responses in the skin. Neurotrophic factors, in addition to regulating nerve growth, participate in many properties of skin function. The skin expresses a variety of neurohormone receptors coupled to heterotrimeric G proteins that are tightly involved in skin homeostasis and inflammation. This neurohormone-receptor interaction is modulated by endopeptidases, which are able to terminate neuropeptide-induced inflammatory or immune responses. Neuronal proteinase-activated receptors or transient receptor potential ion channels are recently described receptors that may have been important in regulating neurogenic inflammation, pain, and pruritus. Together, a close multidirectional interaction between neuromediators, high-affinity receptors, and regulatory proteases is critically involved to maintain tissue integrity and regulate inflammatory responses in the skin. A deeper understanding of cutaneous neuroimmunoendocrinology may help to develop new strategies for the treatment of several skin diseases.

Secretoneurin increases monolayer permeability in human coronary artery endothelial cells

BACKGROUND

Secretoneurin (SN), a novel neuropeptide, may play a role in inflammation in the vascular system. However, the interaction between SN and endothelial cells is largely unknown. This study's objective is to investigate the effects of SN on endothelial permeability and its associated molecular mechanisms in human coronary artery endothelial cells (HCAECs).

METHODS

HCAECs were treated with SN. Monolayer permeability was assayed with a transwell system and a Texas Red-labeled dextran tracer. The mRNA and protein levels of endothelial junctional molecules were determined by real-time reverse transcriptase polymerase chain reaction (RT-PCR) and Western blot analysis, respectively. Superoxide anion was determined by fluorescent dye dihydroethidium-based flow cytometry detection. Mitogen-activated protein kinase (MAPK) activation was determined by Bio-Plex immunoassay.

RESULTS

HCAECs were treated with SN (15, 30, and 60 ng/ml) for 24 hours and showed a significant increase of monolayer permeability by 12%, 33%, and 47%, respectively, compared with controls (P < 0.05). SN-treated cells showed a significant reduction of zonula occludens-1 (ZO-1) and occludin at both mRNA and protein levels (P < 0.05). In addition, SN significantly increased superoxide anion in HCAECs (P < 0.05). Furthermore, SN activated MAPKs (JNK and ERK1/2) but not p38. Both antioxidant seleno-L-methionine (SeMet) and specific inhibitors of JNK and ERK1/2 effectively blocked SN-induced monolayer permeability increase in HCAECs.

CONCLUSIONS

SN significantly increases monolayer permeability and reduces the expression of ZO-1 and occludin through oxidative stress and the activation of JNK and ERK1/2 in HCAECs. This study provides direct evidence that SN impairs endothelial barrier function.

Secretoneurin stimulates goldfish pituitary luteinizing hormone production

Secretoneurin (SN), a 33-34 amino acid neuropeptide is derived from endoproteolysis of secretogranin II (SgII), a member protein of the chromogranin family. SN is widely distributed in various tissues of vertebrates especially in pituitary and hypothalamus, and is a potential new hormone. In vivo, i.p. injection of SN increased luteinizing hormone (LH) release in goldfish pretreated with the dopamine antagonist domperidone. In 6-h static incubation of goldfish pituitary fragments, 10 and 100 nM but not 1 nM concentrations of goldfish SN had a direct stimulatory effect to increase LH release by 2.3- and 1.5-fold (p<0.05), respectively. In addition, 500 nM SN induced a 2.6-fold increase in LHbeta subunit messenger RNA (mRNA) levels in pituitary fragments, regardless of whether LHbeta mRNA levels were expressed relative to 18S ribosomal RNA or beta-actin mRNA. We suggest that the stimulatory actions of SN on LH release may be a part of a paracrine or autocrine feedback loop in the pituitary.