Secretoneurin promotes pertussis toxin-sensitive neurite outgrowth in cerebellar granule cells

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.

NG2 Glia: Novel Roles beyond Re-/Myelination

Neuron-glia antigen 2-expressing glial cells (NG2 glia) serve as oligodendrocyte progenitors during development and adulthood. However, recent studies have shown that these cells represent not only a transitional stage along the oligodendroglial lineage, but also constitute a specific cell type endowed with typical properties and functions. Namely, NG2 glia (or subsets of NG2 glia) establish physical and functional interactions with neurons and other central nervous system (CNS) cell types, that allow them to constantly monitor the surrounding neuropil. In addition to operating as sensors, NG2 glia have features that are expected for active modulators of neuronal activity, including the expression and release of a battery of neuromodulatory and neuroprotective factors. Consistently, cell ablation strategies targeting NG2 glia demonstrate that, beyond their role in myelination, these cells contribute to CNS homeostasis and development. In this review, we summarize and discuss the advancements achieved over recent years toward the understanding of such functions, and propose novel approaches for further investigations aimed at elucidating the multifaceted roles of NG2 glia.

Secretoneurin-A inhibits aromatase B (cyp19a1b) expression in female goldfish (Carassius auratus) radial glial cells

In the teleost brain, radial glial cells (RGCs) are the main macroglia and are stem-like progenitors that express key steroidogenic enzymes, including the estrogen-synthesizing enzyme, aromatase B (cyp19a1b). As a result, RGCs are integral to neurogenesis and neurosteroidogenesis, however little is known about the regulatory factors and signaling mechanisms that control these functions. A potential new role of the secretogranin II-derived neuropeptide secretoneurin A (SNa) in the control of goldfish (Carassius auratus) RGC function is the subject of this study. Immunohistochemistry revealed a close neuroanatomical relationship between RGCs and soma of SNa-immunoreactive magnocellular and parvocellular neurons in the preoptic nucleus of female goldfish. Five hours following intracerebroventricular injection of 0.2ng/g SNa cyp19a1b mRNA levels were decreased by 86% (P<0.05) in the hypothalamus and by 88% (P<0.05) in the telencephalon. In vitro, 24 h incubation with 500nM SNa decreased cyp19a1b mRNA by 51% (P<0.05) in cultured RGCs. These data provide evidence that SNa can regulate aromatase expression in goldfish RGCs. By regulating neuroestrogen production in RGCs SNa may therefore be implicated in the control of major estrogen-dependent functions of the preoptic region such as reproductive behavior and osmoregulation.

Secretoneurin A Directly Regulates the Proteome of Goldfish Radial Glial Cells In Vitro

Radial glial cells (RGCs) are the main macroglia in the teleost brain and have established roles in neurogenesis and neurosteroidogenesis. They are the only brain cell type expressing aromatase B (cyp19a1b), the enzyme that synthesizes estrogens from androgen precursors. There are few studies on the regulation of RGC functions, but our previous investigations demonstrated that dopamine stimulates cyp19a1b expression in goldfish RGCs, while secretoneurin A (SNa) inhibits the expression of this enzyme. Here, we determine the range of proteins and cellular processes responsive to SNa treatments in these steroidogenic cells. The focus here is on SNa, because this peptide is derived from selective processing of secretogranin II in magnocellular cells embedded within the RGC-rich preoptic nucleus. Primary cultures of RGCs were treated (24 h) with 10, 100, or 1,000 nM SNa. By using isobaric tagging for relative and absolute quantitation and a Hybrid Quadrupole Obritrap Mass Spectrometry system, a total of 1,363 unique proteins were identified in RGCs, and 609 proteins were significantly regulated by SNa at one or more concentrations. Proteins that showed differential expression with all three concentrations of SNa included H1 histone, glutamyl-prolyl-tRNA synthetase, Rho GDP dissociation inhibitor γ, vimentin A2, and small nuclear ribonucleoprotein-associated protein. At 10, 100, and 1,000 nM SNa, there were 5, 195, and 489 proteins that were downregulated, respectively, whereas the number of upregulated proteins were 72, 44, and 51, respectively. Subnetwork enrichment analysis of differentially regulated proteins revealed that processes such as actin organization, cytoskeleton organization and biogenesis, apoptosis, mRNA processing, RNA splicing, translation, cell growth, and proliferation are regulated by SNa based on the proteomic response. Moreover, we observed that, at the low concentration of SNa, there was an increase in the abundance of proteins involved in cell growth, proliferation, and migration, whereas higher concentration of SNa appeared to downregulate proteins involved in these processes, indicating a dose-dependent proteome response. At the highest concentration of SNa, proteins linked to the etiology of diseases of the central nervous system (brain injuries, Alzheimer disease, Parkinson's disease, cerebral infraction, brain ischemia) were also differentially regulated. These data implicate SNa in the control of cell proliferation and neurogenesis.

Secretoneurin A regulates neurogenic and inflammatory transcriptional networks in goldfish (Carassius auratus) radial glia

Radial glial cells (RGCs) are the most abundant macroglia in the teleost brain and have established roles in neurogenesis and neurosteroidogenesis; however, their transcriptome remains uncharacterized, which limits functional understanding of this important cell type. Using cultured goldfish RGCs, RNA sequencing and de novo transcriptome assembly were performed, generating the first reference transcriptome for fish RGCs with 17,620 unique genes identified. These data revealed that RGCs express a diverse repertoire of receptors and signaling molecules, suggesting that RGCs may respond to and synthesize an array of hormones, peptides, cytokines, and growth factors. Building upon neuroanatomical data and studies investigating direct neuronal regulation of RGC physiology, differential gene expression analysis was conducted to identify transcriptional networks that are responsive to the conserved secretogranin II-derived neuropeptide secretoneurin A (SNa). Pathway analysis of the transcriptome indicated that cellular processes related to the central nervous system (e.g., neurogenesis, synaptic plasticity, glial cell development) and immune functions (e.g., immune system activation, leukocyte function, macrophage response) were preferentially modulated by SNa. These data reveal an array of new functions that are proposed to be critical to neuronal-glial interactions through the mediator SNa.

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.

Secretoneurin Serum Levels in Healthy Term Neonates and Neonates with Hypoxic-Ischaemic Encephalopathy

BACKGROUND

Hypoxic-ischaemic encephalopathy is a major cause of neurologic impairment and mortality in neonates. Early knowledge of brain injury is important to guide therapeutic decisions and reliably inform the parents. Increased secretoneurin levels have been detected in adult patients suffering from brain injury and it has also been shown to be a promising early serum biomarker of unfavourable neurological outcome. However, no data are available in neonates.

OBJECTIVE

The aim of this study was to obtain reference values for secretoneurin in healthy term neonates and then to assess the potential of this neuropeptide as a biomarker in the context of hypoxic-ischaemic encephalopathy in asphyxiated term neonates.

METHODS

A total number of 139 term neonates, of which 7 were asphyxiated and 132 were healthy, were prospectively enrolled. Secretoneurin serum concentrations were assessed by radioimmunoassay.

RESULTS

In healthy controls, secretoneurin serum concentrations were influenced by the mode of delivery (highest in infants born per vacuum extraction and lowest in infants born per caesarean section) and abnormal cardiotocography. In asphyxiated term neonates, secretoneurin concentrations were higher in umbilical cord blood and significantly lower 48 h after birth in comparison to healthy controls.

CONCLUSION

Secretoneurin levels are elevated in cord blood in infants suffering from hypoxic-ischaemic encephalopathy following perinatal asphyxia. The potential of secretoneurin as a marker of neonatal hypoxic-ischaemic brain injury should be further evaluated in larger trials.

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.

GPR37 and GPR37L1 are receptors for the neuroprotective and glioprotective factors prosaptide and prosaposin

GPR37 (also known as Pael-R) and GPR37L1 are orphan G protein-coupled receptors that are almost exclusively expressed in the nervous system. We screened these receptors for potential activation by various orphan neuropeptides, and these screens yielded a single positive hit: prosaptide, which promoted the endocytosis of GPR37 and GPR37L1, bound to both receptors and activated signaling in a GPR37- and GPR37L1-dependent manner. Prosaptide stimulation of cells transfected with GPR37 or GPR37L1 induced the phosphorylation of ERK in a pertussis toxin-sensitive manner, stimulated (35)S-GTPγS binding, and promoted the inhibition of forskolin-stimulated cAMP production. Because prosaptide is the active fragment of the secreted neuroprotective and glioprotective factor prosaposin (also known as sulfated glycoprotein-1), we purified full-length prosaposin and found that it also stimulated GPR37 and GPR37L1 signaling. Moreover, both prosaptide and prosaposin were found to protect primary astrocytes against oxidative stress, with these protective effects being attenuated by siRNA-mediated knockdown of endogenous astrocytic GPR37 or GPR37L1. These data reveal that GPR37 and GPR37L1 are receptors for the neuroprotective and glioprotective factors prosaptide and prosaposin.

Is secretoneurin a new hormone?

Numerous small potentially bioactive peptides are derived from the selective processing of the ~600 amino acid secretogranin II (SgII) precursor, but only the 31-42 amino acid segment termed secretoneurin (SN) is well-conserved from sharks to mammals. Both SNa and SNb paralogs have been identified in some teleosts, likely arising as a result of the specific genome duplication event in this lineage. Only one copy of the putative lamprey SgII (188 amino acids) could be identified which gives rise to a divergent agnathan SN that contains the signature YTPQ-X-LA-X(7)-EL sequence typical of the central core of all known SN peptides. In rodent models, SN has regulatory effects on neuroinflammation and neurotransmitter release, and possesses therapeutic potential for the induction of angiogenesis. The wide distribution of SN in neuroendocrine neurons and pituitary cells suggests important endocrine roles. The clearest example of the endocrine action of SN is the stimulatory effects on pituitary luteinizing hormone release from goldfish pituitary and mouse LβT2 gonadotroph cells, indicative of an important role in reproduction. Several lines of evidence suggest that the SN receptor is most likely a G-protein coupled protein. Microarray analysis of SN effects on dispersed goldfish pituitary cells in vitro reveals novel SN actions that include effects on genes involved in notch signaling and the guanylate cyclase pathway. Intracerebroventricular injection of SN increases feeding and locomotory behaviors in goldfish. Given that SgII appeared early in vertebrate evolution, SN is an old peptide with emerging implications as a new multifunctional hormone.

Identification and validation of novel cerebrospinal fluid biomarkers for staging early Alzheimer's disease

BACKGROUND

Ideally, disease modifying therapies for Alzheimer disease (AD) will be applied during the 'preclinical' stage (pathology present with cognition intact) before severe neuronal damage occurs, or upon recognizing very mild cognitive impairment. Developing and judiciously administering such therapies will require biomarker panels to identify early AD pathology, classify disease stage, monitor pathological progression, and predict cognitive decline. To discover such biomarkers, we measured AD-associated changes in the cerebrospinal fluid (CSF) proteome.

METHODS AND FINDINGS

CSF samples from individuals with mild AD (Clinical Dementia Rating [CDR] 1) (n = 24) and cognitively normal controls (CDR 0) (n = 24) were subjected to two-dimensional difference-in-gel electrophoresis. Within 119 differentially-abundant gel features, mass spectrometry (LC-MS/MS) identified 47 proteins. For validation, eleven proteins were re-evaluated by enzyme-linked immunosorbent assays (ELISA). Six of these assays (NrCAM, YKL-40, chromogranin A, carnosinase I, transthyretin, cystatin C) distinguished CDR 1 and CDR 0 groups and were subsequently applied (with tau, p-tau181 and Aβ42 ELISAs) to a larger independent cohort (n = 292) that included individuals with very mild dementia (CDR 0.5). Receiver-operating characteristic curve analyses using stepwise logistic regression yielded optimal biomarker combinations to distinguish CDR 0 from CDR>0 (tau, YKL-40, NrCAM) and CDR 1 from CDR<1 (tau, chromogranin A, carnosinase I) with areas under the curve of 0.90 (0.85-0.94 95% confidence interval [CI]) and 0.88 (0.81-0.94 CI), respectively.

CONCLUSIONS

Four novel CSF biomarkers for AD (NrCAM, YKL-40, chromogranin A, carnosinase I) can improve the diagnostic accuracy of Aβ42 and tau. Together, these six markers describe six clinicopathological stages from cognitive normalcy to mild dementia, including stages defined by increased risk of cognitive decline. Such a panel might improve clinical trial efficiency by guiding subject enrollment and monitoring disease progression. Further studies will be required to validate this panel and evaluate its potential for distinguishing AD from other dementing conditions.

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.

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.

Secretoneurin promotes neuroprotection and neuronal plasticity via the Jak2/Stat3 pathway in murine models of stroke

Secretoneurin (SN), a neuropeptide derived from secretogranin II, promotes neurite outgrowth of immature cerebellar granule cells. SN also aids in the growth and repair of neuronal tissue, although the precise mechanisms underlying the promotion of brain tissue neuroprotection and plasticity by SN are not understood. Here, in a rat model of stroke and in ischemic human brain tissue, SN was markedly upregulated in both neurons and endothelial cells. SN-mediated neuroprotection rescued primary cortical cell cultures from oxygen/glucose deprivation. SN also induced expression of the antiapoptotic proteins Bcl-2 and Bcl-xL through the Jak2/Stat3 pathway and inhibited apoptosis by blocking caspase-3 activation. In addition, rats with occluded right middle cerebral arteries showed less cerebral infarction, improved motor performance, and increased brain metabolic activity following i.v. administration of SN. Furthermore, SN injection enhanced stem cell targeting to the injured brain in mice and promoted the formation of new blood vessels to increase local cortical blood flow in the ischemic hemisphere. Both in vitro and in vivo, SN not only promoted neuroprotection, but also enhanced neurogenesis and angiogenesis. Our results demonstrate that SN acts directly on neurons after hypoxia and ischemic insult to further their survival by activating the Jak2/Stat3 pathway.

Chromogranins A and B and secretogranin II: evolutionary and functional aspects

Chromogranins/secretogranins or granins are a class of acidic, secretory proteins that occur in endocrine, neuroendocrine, and neuronal cells. Granins are the precursors of several bioactive peptides and may be involved in secretory granule formation and neurotransmitter/hormone release. Characterization and analysis of chromogranin A (CgA), chromogranin B (CgB), and secretogranin II (SgII) in distant vertebrate species confirmed that CgA and CgB belong to related monophyletic groups, probably evolving from a common ancestral precursor, while SgII sequences constitute a distinct monophyletic group. In particular, selective sequences within these proteins, bounded by potential processing sites, have been remarkably conserved during evolution. Peptides named vasostatin, secretolytin and secretoneurin, which occur in these regions, have been shown to exert various biological activities. These conserved domains may also be involved in the formation of secretory granules in different vertebrates. Other peptides such as catestatin and pancreastatin may have appeared late during evolution. The function of granins as propeptide precursors and granulogenic factors is discussed in the light of recent data obtained in various model species and using knockout mice strains.

Immunohistochemical distribution of the secretogranin II-derived peptide EM66 in the rat hypothalamus: A comparative study with jerboa

EM66 is a 66-amino acid peptide derived from secretogranin II, a member of granin acidic secretory protein family, by proteolytic processing. EM66 has been previously characterized in the jerboa (Jaculus orientalis) hypothalamus and its potential implication in the neuroendocrine regulation of feeding behaviour has been demonstrated. In the present study, an immunohistochemical analysis of the localization of EM66 within hypothalamic structures of rat was performed and compared to the distribution of EM66 in the jerboa hypothalamus. In the rat hypothalamus, as in the jerboa, EM66 immunostaining was detected in the parvocellular paraventricular, preoptic and arcuate nuclei, as well as the lateral hypothalamus which displayed an important density of EM66-producing neurones. However, unlike jerboa, the suprachiasmatic and supraoptic nuclei of the rat hypothalamus were devoid of cellular EM66-immunolabeling. Thus, the novel peptide EM66 may exert common neuroendocrine activities in rat and jerboa, e.g. control of food intake, and species-specific roles in jerboa such as the regulation of biological rhythms and hydromineral homeostasis. These results suggest the existence of differences between jerboas and rats in neuroendocrine regulatory mechanisms involving EM66.

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.

Quantification of VGF- and pro-SAAS-derived peptides in endocrine tissues and the brain, and their regulation by diet and cold stress

Two novel granin-like polypeptides, VGF and pro-SAAS, which are stored in and released from secretory vesicles and are expressed widely in nervous, endocrine, and neuroendocrine tissues, play roles in the regulation of body weight, feeding, and energy expenditure. Both VGF and pro-SAAS are cleaved into peptide fragments, several of which are biologically active. We utilized a highly sensitive and specific radioimmunoassay (RIA) to immunoreactive, pro-SAAS-derived PEN peptides, developed another against immunoreactive, VGF-derived AQEE30 peptides, and quantified these peptides in various mouse tissues and brain regions. Immunoreactive AQEE30 was most abundant in the pituitary, while brain levels were highest in hypothalamus, striatum, and frontal cortex. Immunoreactive PEN levels were highest in the pancreas and spinal cord, and in brain, PEN was most abundant in striatum, hippocampus, pons and medulla, and cortex. Since both peptides were expressed in hypothalamus, a region of the brain that controls feeding and energy expenditure, double label immunofluorescence studies were employed. These demonstrated that 42% of hypothalamic arcuate neurons coexpress VGF and SAAS peptides, and that the intracellular distributions of these peptides in arcuate neurons differed. By RIA, cold stress increased immunoreactive AQEE30 and PEN peptide levels in female but not male hypothalamus, while a high fat diet increased AQEE30 and PEN peptide levels in female but not male hippocampus. VGF and SAAS-derived peptides are therefore widely expressed in endocrine, neuroendocrine, and neural tissues, can be accurately quantified by RIA, and are differentially regulated in the brain by diet and cold stress.

Proteolytic processing and differential distribution of secretogranin-II in goldfish

Secretoneurin (SN) is a 33-34 amino acid neuropeptide derived by endoproteolysis of secretogranin-II (SgII), a chromogranin. A multi-antigenic strategy was used to generate a rabbit polyclonal goldfish SN antiserum that was characterized for Western blot analysis. In the goldfish pituitary two intermediate proteins containing SN and likely processed from the 69.6-kDa SgII precursor were detected. No immunoreactive proteins were observed in the goldfish interrenal, ovary, cerebellum, and telencephalon whereas SgII mRNA was expressed in all these tissues. Immunoreactive levels of the approximately 57 kDa product were higher in the pars distalis (PD) than in the neurointermediate lobe (NIL). The abundance of the approximately 57 kDa protein indicates that this SgII-product containing the SN sequence is a major stored form in secretory granules of the goldfish pituitary. High expression and processing of SN in the hypothalamus and pituitary suggest important roles for SgII-derived peptides in neuroendocrine tissues.

Biochemical characterisation and immunohistochemical localisation of the secretogranin II-derived peptide EM66 in the hypothalamus of the jerboa (Jaculus orientalis): modulation by food deprivation

The neuroendocrine protein secretogranin II is the precursor of several neuropeptides, including secretoneurin and a novel 66-amino acid peptide, EM66, the sequence of which has been highly conserved across the vertebrae phylum. The presence of EM66 has been detected in the adult and fetal human adrenal gland, as well as the rat pituitary and adrenal glands. The present study aimed to explore a possible neuroendocrine role of EM66 by analysing its occurrence and distribution within the jerboa hypothalamus, and its potential implication in the control of feeding behaviour. High-performance liquid chromatography analysis of jerboa hypothalamic extracts combined with a radioimmunoassay of EM66 revealed a single peak of immunoreactive material exhibiting the same retention time as recombinant EM66. Immunocytochemical labelling showed that EM66-producing neurones are widely distributed in several hypothalamic regions, including the preoptic area, the suprachiasmatic, supraoptic, parvocellular paraventricular and arcuate nuclei, and the lateral hypothalamus. Food deprivation for 5 days induced a significant increase in the number of EM66-containing neurones within the arcuate nucleus (105% increase) and the parvocellular aspect of the paraventricular nucleus (115% increase), suggesting that EM66 could be involved in the control of feeding behaviour and/or the response to stress associated with fasting. Altogether, these data reveal the physiological plasticity of the EM66 system in the hypothalamus and implicate this novel peptide in the regulation of neuroendocrine functions.

The neuropeptide secretoneurin acts as a direct angiogenic cytokine in vitro and in vivo

BACKGROUND

Secretoneurin is an abundant neuropeptide of the central, peripheral, and autonomic nervous systems, located in nerve fibers characterized by a close interaction with blood vessels and known to stimulate endothelial cell migration.

METHODS AND RESULTS

We hypothesized that secretoneurin might act as an angiogenic cytokine and tested for these effects in vivo using a mouse cornea neovascularization model and in vitro by assessing capillary tube formation in a matrigel assay. In vivo, secretoneurin-induced neovasculature is characterized by a distinct pattern of arterial and venous vessels of large diameter and length. Immunohistochemical staining for CD-31 revealed endothelial lining of the inner surface of these vessels, and recruitment of alpha-smooth muscle actin-positive perivascular cells suggests vessel maturation. In vitro, secretoneurin-induced capillary tube formation was dose dependent and specific, confirming that effects of secretoneurin occur directly on endothelial cells. Secretoneurin also stimulated proliferation and exerted antiapoptotic effects on endothelial cells and activated intracellular phosphatidylinositol 3' kinase/Akt and mitogen-activated protein kinase pathways, as demonstrated by increased phosphorylation of Akt and extracellular signal-regulated kinase.

CONCLUSIONS

These data show that secretoneurin represents a novel direct angiogenic cytokine and reiterate the coordinated relationship between nervous and vascular systems.