Distribution of mRNAs for Chromogranins A and B and Secretogranin II in Rat Brain

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

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

Catestatin as a Target for Treatment of Inflammatory Diseases

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

Functional Peptidomics: Stimulus- and Time-of-Day-Specific Peptide Release in the Mammalian Circadian Clock

Daily oscillations of brain and body states are under complex temporal modulation by environmental light and the hypothalamic suprachiasmatic nucleus (SCN), the master circadian clock. To better understand mediators of differential temporal modulation, we characterize neuropeptide releasate profiles by nonselective capture of secreted neuropeptides in an optic nerve horizontal SCN brain slice model. Releasates are collected following electrophysiological stimulation of the optic nerve/retinohypothalamic tract under conditions that alter the phase of the SCN activity state. Secreted neuropeptides are identified by intact mass via matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). We found time-of-day-specific suites of peptides released downstream of optic nerve stimulation. Peptide release was modified differentially with respect to time-of-day by stimulus parameters and by inhibitors of glutamatergic or PACAPergic neurotransmission. The results suggest that SCN physiology is modulated by differential peptide release of both known and unexpected peptides that communicate time-of-day-specific photic signals via previously unreported neuropeptide signatures.

Expression variations of chromogranin A and α1,2,4 GABA(A)Rs in discrete limbic and brainstem areas rescue cardiovascular alterations

Recent interferences of hemodynamic functions via modified brain neuronal mechanisms have proven to be major causes of dementia and sleeping disorders. In this work, cerebral expression differences of the neuroactive vesicular chromogranin A (CgA) and distinct α GABA(A)R subunits were detected in the facultative hibernating hamster. In particular, damaged neuronal fields of hypotensive torpor (TORP) state were correlated to elevated CgA and GABA(A)R α1, α4 mRNA levels in the paraventricular hypothalamic nucleus (PVN), central amygdalar nucleus (CeA) plus solitary tractus nucleus (NTS). Conversely, few neurodegeneration signals of hypertensive arousal (AROU) state, accounted for mostly lower CgA levels in the same areas. This state also provided increased α2-containing sites in amygdala, hippocampal and NTS neurons together with elevated α4-containing receptors in the periventricular hypothalamic nucleus (Pe). Interestingly in our hibernating model, CgA appeared to preferentially feature inhibitory neurosignals as indicated by preliminary perfusion of amygdalar sites with its highly specific antihypertensive derived peptide (catestatin) promoting GABA-dependent sIPSCs. Overall, evident neuronal damages plus altered expression capacities of CgA and α1-, α2-, α4-GABA(A)Rs in CeA, Pe, PVN as well as NTS during both hibernating states corroborate for the first time key molecular switching events guaranteeing useful cardiovascular rescuing abilities of neurodegenerative disorders.

Brain-specific rescue of Clock reveals system-driven transcriptional rhythms in peripheral tissue

The circadian regulatory network is organized in a hierarchical fashion, with a central oscillator in the suprachiasmatic nuclei (SCN) orchestrating circadian oscillations in peripheral tissues. The nature of the relationship between central and peripheral oscillators, however, is poorly understood. We used the tetOFF expression system to specifically restore Clock function in the brains of Clock(Δ19) mice, which have compromised circadian clocks. Rescued mice showed normal locomotor rhythms in constant darkness, with activity period lengths approximating wildtype controls. We used microarray analysis to assess whether brain-specific rescue of circadian rhythmicity was sufficient to restore circadian transcriptional output in the liver. Compared to Clock mutants, Clock-rescue mice showed significantly larger numbers of cycling transcripts with appropriate phase and period lengths, including many components of the core circadian oscillator. This indicates that the SCN oscillator overcomes local circadian defects and signals directly to the molecular clock. Interestingly, the vast majority of core clock genes in liver were responsive to Clock expression in the SCN, suggesting that core clock genes in peripheral tissues are intrinsically sensitive to SCN cues. Nevertheless, most circadian output in the liver was absent or severely low-amplitude in Clock-rescue animals, demonstrating that the majority of peripheral transcriptional rhythms depend on a fully functional local circadian oscillator. We identified several new system-driven rhythmic genes in the liver, including Alas1 and Mfsd2. Finally, we show that 12-hour transcriptional rhythms (i.e., circadian "harmonics") are disrupted by Clock loss-of-function. Brain-specific rescue of Clock converted 12-hour rhythms into 24-hour rhythms, suggesting that signaling via the central circadian oscillator is required to generate one of the two daily peaks of expression. Based on these data, we conclude that 12-hour rhythms are driven by interactions between central and peripheral circadian oscillators.

Secretoneurin stimulates the production and release of luteinizing hormone in mouse L{beta}T2 gonadotropin cells

Secretoneurin (SN) is a functional secretogranin II (SgII)-derived peptide that stimulates luteinizing hormone (LH) production and its release in the goldfish. However, the effects of SN on the pituitary of mammalian species and the underlying mechanisms remain poorly understood. To study SN in mammals, we adopted the mouse LβT2 gonadotropin cell line that has characteristics consistent with normal pituitary gonadotrophs. Using radioimmunoassay and real-time RT-PCR, we demonstrated that static treatment with SN induced a significant increment of LH release and production in LβT2 cells in vitro. We found that GnRH increased cellular SgII mRNA level and total SN-immunoreactive protein release into the culture medium. We also report that SN activated the extracellular signal-regulated kinases (ERK) in either 10-min acute stimulation or 3-h chronic treatment. The SN-induced ERK activation was significantly blocked by pharmacological inhibition of MAPK kinase (MEK) with PD-98059 and protein kinase C (PKC) with bisindolylmaleimide. SN also increased the total cyclic adenosine monophosphate (cAMP) levels similarly to GnRH. However, SN did not activate the GnRH receptor. These data indicate that SN activates the protein kinase A (PKA) and cAMP-induced ERK signaling pathways in the LH-secreting mouse LβT2 pituitary cell line.

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

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

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

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

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

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

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.

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.

Inositol 1,4,5 trisphosphate receptor and chromogranin B are concentrated in different regions of the hippocampus

Calcium (Ca(2+)) release from intracellular stores plays a crucial role in many cellular functions in the brain. These intracellular signals have been shown to be transmitted within and between cells. We report a non-uniform distribution of proteins essential for Ca(2+) signaling in acutely prepared brain slice preparations and organotypic slice cultures, both made from rat hippocampus. The Type I inositol-1,4,5 trisphosphate receptor (InsP(3)R1) is the main InsP(3)R subtype in neurons. Immunohistochemistry experiments showed a prominent expression of InsP(3)R1 in the CA1 region of the hippocampus whereas the CA3 region and dentate gyrus (DG) showed only moderate immunoreactivity. In contrast, chromogranin B (CGB), a protein binding to the InsP(3)R1 on the luminal side of the endoplasmic reticular membrane was enriched in the CA3 region whereas DG and the CA1 region showed only faint CGB signals. The neuronal kinases leading to the formation of inositol-1,4,5 trisphosphate (InsP(3)), phosphatidylinositol-4-kinase (PI4K), and phosphatidylinositol-4-phosphate-5-kinase (PIPK), showed strong immunoreactivity throughout all hippocampal cell fields with differences in the subcellular distribution. Moreover, a distinct band of strong CGB and PIPK immunoreactivity was observed in the CA3 region that coincides with the mossy fiber tract (stratum lucidum). These data show differential expression of the components of the signaling toolkit leading to InsP(3)-mediated Ca(2+) release in cells of the hippocampus. The regulation of these differences may play an important role in various neuropathologic conditions such as Alzheimer's disease, epilepsy, or schizophrenia.

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.

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.

Seasonal cyclicity of secretogranin-II expression and its modulation by sex steroids and GnRH in the female goldfish pituitary

The secretory vesicle protein secretogranin-II (SgII), a precursor for the bioactive peptide secretoneurin, is expressed at all levels of the goldfish reproductive axis, including the hypothalamus, pituitary and ovaries. These findings led us to hypothesize that SgII is involved in reproduction and is physiologically regulated. We investigated the effects of different sex steroids on pituitary SgII expression throughout the seasonal reproductive cycle of the female goldfish, as well as the effects of GnRH and testosterone on pituitary LHbeta subunit, GH, and SgII expression in sexually recrudescent female fish using northern blot analysis. We demonstrated that SgII expression levels vary seasonally, with levels being highest in winter and lowest in spring. Sex steroids did not alter SgII expression at any of the time periods studied. In sexually mature goldfish, injection of a GnRH agonist stimulated the expression of LHbeta and SgII specifically in the pars distalis but not the neurointermediate lobe of the pituitary. Although testosterone alone did not alter the expression of either of these genes, it did abolish the stimulatory effects of GnRH on both LHbeta and SgII expression. This represents the first study where testosterone is shown to modulate SgII expression in the pituitary.

The secretory granule-associated protein CAPS2 regulates neurotrophin release and cell survival

Neurotrophins are key modulators of various neuronal functions, including differentiation, survival, and synaptic plasticity, but the molecules that regulate their secretion are poorly understood. We isolated a clone that is predominantly expressed in granule cells of postnatally developing mouse cerebellum, which turned out to be a paralog of CAPS (Ca2+-dependent activator protein for secretion), and named CAPS2. CAPS2 is enriched on vesicular structures of presynaptic parallel fiber terminals of granule cells connecting postsynaptic spines of Purkinje cell dendrites. Vesicle factions affinity-purified by the CAPS2 antibody from mouse cerebella contained significant amounts of neurotrophin-3 (NT-3), brain-derived neurotrophic factor (BDNF), and chromogranin B but not marker proteins for synaptic vesicle synaptophysin and synaptotagmin. In cerebellar primary cultures, punctate CAPS2 immunoreactivities are primarily colocalized with those of NT-3 and BDNF and near those of a postsynaptic marker, postsynaptic density-95, around dendritic arborization of Purkinje cells. Exogenously expressed CAPS2 enhanced release of exogenous NT-3 and BDNF from PC12 cells and endogenous NT-3 from cultured granule cells in a depolarization-dependent manner. Moreover, the overexpression of CAPS2 in granule cells promotes the survival of Purkinje cells in cerebellar cultures. Thus, we suggest that CAPS2 mediates the depolarization-dependent release of NT-3 and BDNF from granule cells, leading to regulation in cell differentiation and survival during cerebellar development.

Differential effects of phencyclidine application on secretogranin II expression in organotypic slices of rat prefrontal cortex

Phencyclidine (PCP) is a non-competitive NMDA glutamate receptor antagonist that induces psychotomimetic effects in humans and experimental animals. Chronic PCP exposure elicits signs of persistently altered frontal brain activity and related behaviors which are also seen in patients with schizophrenia. Secretogranin II (sg II) belongs to the chromogranin family of proteins that exist in large dense core vesicles in nervous tissue. In the brain, 90% of sg II is processed to the small peptide secretoneurin. We previously detected differential effects of single-dose and subchronic PCP administration on sg II expression in the rat prefrontal cortex (PFC). In the present study, we applied PCP to organotypic PFC slices. PCP application for 28 h induced decreased tissue and culture medium secretoneurin content. In contrast, incubation with the adenylate cyclase activator forskolin caused significantly increased secretoneurin levels after 8 h. PCP for 4 h followed by 24 h without PCP resulted in increased culture medium secretoneurin content but no change in tissue levels. sg II mRNA expression was decreased after 28 h PCP application in cortical neurons. Immunohistochemical and TUNEL staining profiles indicated that the alterations were not due to neurodegeneration. PCP for 5 days changed neither the secretoneurin tissue or culture medium levels, nor the sg II mRNA expression. These results demonstrate that PCP modulates sg II expression in PFC tissue in the absence of afferent inputs and that the nature of these changes is dependent upon the duration of exposure to and/or withdrawal from PCP.

Synaptic proteins in Alzheimer's disease

Chromogranin A, chromogranin B, and secretogranin II are acidic proteins which are stored in large dense core vesicles of neurons. An antiserum, raised against a synthetic peptide (PE-11), present in the chromogranin B molecule, and an antiserum raised against secretoneurin contained in the secretogranin II sequence, was used to localize these peptides together with chromogranin A in the human hippocampal formation. The distribution of these peptides was investigated in Alzheimer's disease and compared to control subjects. Chromogranin A, chromogranin B, and secretogranin II are distinctly distributed with an overlap in their distribution patterns. They were only detected in neuronal structures. The highest density of immunoreactivity was found for chromogranin B. A layer specific distribution was especially obvious in the inner molecular layer of the dentate gyrus as secretoneurin-like immunoreactivity was restricted to its innermost part whereas that of chromogranin B was highly concentrated throughout the inner molecular layer. In Alzheimer's disease, about 10 to 20% of the amyloid-immunoreactive plaques contained either chromogranin A, chromogranin B or secretoneurin. The density of secretoneurin-and chromogranin B-like immunoreactivity was significantly reduced in the inner molecular layer of the dentate gyyrs, the CA1 area, the subiculum and in layers I, III and V of the entorhinal cortex. The present study demonstrates that chromogranin peptides are markers for human hippocampal pathways. Thee are particularly suitable to study nerve fibers, terminating at the inner molecular layer of the dentate gyrus. Chromogranin peptides have a potential as neuronal markers for synaptic degeneration in Alzheimer's disease.

Chromogranins in temporal lobe epilepsy

PURPOSE

Chromogranins are neuropeptide precursors stored in large dense core vesicles. Because physiological functions have been postulated for peptides originating from chromogranins, we investigated the distribution of chromogranins A and B and secretoneurin (a peptide derived from secretogranin II) in the control and epileptic hippocampus of humans and rats.

METHODS

Chromogranin immunoreactivity (IR) was investigated in paraformaldehyde-fixed hippocampal specimens from 24 temporal lobe epilepsy patients with intractable seizures, postmortem from 15 patients deceased from nonneurological disorders, in rats 30 days after kainate-induced limbic seizures, and in control rats.

RESULTS

In control rats and in humans, chromogranin A and B IR and secretoneurin IR were present in mossy fibers. In addition, chromogranin B IR was found in granule cells, and chromogranin A IR was found in granule and CA2 pyramidal cells in the human hippocampus. In both species, chromogranin B and secretoneurin were unevenly distributed in the molecular layer of the dentate gyrus. The most intriguing change seen in human temporal lobe epilepsy specimens and in the kainic acid model of the rat was the prominent staining of the inner molecular layer, indicating storage of chromogranins A and B and secretoneurin in terminals of reorganized mossy fibers, from which they may be released upon nerve stimulation.

CONCLUSION

Chromogranins A and B and secretoneurin are valid markers for hippocampal neurons and delineate epilepsy-induced reorganization of mossy fibers.

Co-distribution patterns of chromogranin B-like immunoreactivity with chromogranin A and secretoneurin within the human brainstem

As members of the chromogranin family, chromogranin A, chromogranin B, and secretogranin II are acidic proteins found in large, dense core vesicles. They are endoproteolytically processed to smaller peptides and released after neuronal stimulation. Using immunocytochemistry, this study closely examines chromogranin B-like immunoreactivity within the human brainstem and then takes a comparative view of co-distribution patterns by chromogranin B, chromogranin A, and secretogranin II. We used an antiserum raised against a synthetic peptide (PE-11) present in the chromogranin B molecule. Secretogranin II was localized with an antiserum against secretoneurin, a 33 amino acid peptide, found within the secretogranin II precursor. Like chromogranin A and secretoneurin, chromogranin B is expressed through all levels of the human brainstem. Chromogranin B was exclusively detected in neuronal structures. The medial part of the substantia nigra pars reticulata, the nucleus interpeduncularis, the area of the central gray, and the raphe complex displayed a high density of PE-11-like immunoreactivity. Furthermore, a prominent staining was found in the medial, dorsal and gelatinous subnuclei of the solitary tract and the dorsal motor nucleus of vagus. The substantia gelatinosa of the caudal trigeminal nucleus and spinal cord were also very strongly PE-11-immunopositive. In conclusion, chromogranin B and secretogranin II showed similar distributions while neuronal localization typically differed from chromogranin A aside from a few exceptions. These findings may provide a framework for future research in revealing a functional role of chromogranin peptides in the human brainstem.

Isolation and characterization of the human secretogranin II gene promoter

The goal of this study was to isolate and functionally characterize the human secretogranin II (SgII) gene promoter. SgII is a member of the granin family of proteins which are selectively expressed in neurosecretory cells. The human SgII promoter contains a consensus TATA box and cyclic AMP response element (CRE) 35 and 74 bp upstream of the transcription start site, respectively, elements also found in the mouse and rat SgII gene promoters. Transfection studies showed that 869 bp of the human SgII promoter were sufficient to confer cell type-specific expression of an SgII promoter-luciferase reporter gene in neurosecretory PC-12, GH and BE(2)-M17 cells. The activity of the human SgII promoter was also compared in three N-type, human neuroblastoma cell lines [BE(2)-M17, SMS-KAN and SH-SY5Y], which differ markedly in the level of SgII expression. SgII promoter activities in the neuroblastoma cell lines correlated not only with the levels of SgII but also the levels of the cyclic AMP response element-binding protein CREB which were highest in BE(2)-M17 cells and lowest in SH-SY5Y cells. To establish that the activity of the human SgII promoter in these neuroblastoma cell lines is dependent on the level of CREB, rat CREB was overexpressed in SH-SY5Y cells. SgII promoter activity was up to 8-fold higher in SH-SY5Y cells overexpressing CREB. These results suggest that SgII expression is a marker for neuronal differentiation in human neuroblastoma cell lines and is dependent on the level of CREB expression.

Frog chromogranin A messenger ribonucleic acid encodes three highly conserved peptides. Coordinate regulation of proopiomelanocortin and chromogranin A gene expression in the pars intermedia of the pituitary during background color adaptation

Chromogranin A (CgA) is a neuroendocrine secretory protein that is widely used as a marker for endocrine neoplasms but whose function is not completely understood. In mammals, it is thought that CgA is a precursor for biologically active peptides. Here, we describe the cloning of a complementary DNA encoding CgA from a nonmammalian vertebrate, the frog Rana ridibunda. Sequence analysis revealed that frog CgA exhibits only 40-44% amino acid sequence similarity with its mammalian homologues. The amino acid identity is confined to three regions (70-80% identity) of the protein that are flanked by conserved pairs of basic amino acid residues, suggesting that proteolytic processing at these cleavage sites may give rise to three biologically active peptides whose sequences have been highly preserved during evolution. Tissue distribution analysis by Northern blot and in situ hybridization revealed the widespread expression of frog CgA messenger RNA in the brain and in endocrine tissues, the highest concentration occurring in the distal lobe of the pituitary. Adaptation of frog skin color to a dark background caused a concomitant increase in CgA and POMC messenger RNA levels in the intermediate lobe of the pituitary. Taken together, these data indicate that CgA may function as a precursor to three highly conserved peptides that may exert regulatory functions in the neuroendocrine system.

PE-11, a peptide derived from chromogranin B, in the human brain

This study was performed to investigate the distribution of chromogranin B in the human central nervous system. We used an antiserum raised against a synthetic peptide (PE-11) present in the chromogranin B molecule. PE-11-like immunoreactivity was characterized by molecular size exclusion and reversed-phase high-performance liquid chromatography. Its localization was studied using immunocytochemistry. Only the free peptide and an N-terminally elongated peptide were detected by molecular size exclusion high-performance liquid chromatography, indicating that proteolytic processing of chromogranin B is quite extensive. PE-11-like immunoreactivity was present in differently shaped fibers, varicosities and neurons, but not in glial cells. Its density varied throughout the brain. An especially high density was observed in the bed nucleus of the stria terminalis, the central and cortical nuclei of the amygdala, the hypothalamus, the hippocampus, the raphe complex, the nucleus interpeduncularis, the nucleus of the solitary tract, and laminae I and II of the spinal cord. This study demonstrates a significant processing of chromogranin B and indicates that chromogranin B constitutes a precursor for smaller peptides which are derived by endoproteolytic processing. It provides the neuroanatomical basis to investigate the chromogranin B molecule as a widespread component of large dense-core vesicles in the human central nervous system.

Localization of neuroendocrine secretory protein 55 messenger RNA in the rat brain

Neuroendocrine secretory protein 55 (NESP55) is a recently characterized secretory protein localized to large dense-core vesicles resembling the class of chromogranins. We investigated the distribution of the messenger RNA encoding for NESP55 in the rat brain by in situ hybridization with specific 35S-labelled oligonucleotides. NESP55 messenger RNA was detected only on neuronal but not glial cells. In the brain, expression of NESP55 messenger RNA was most prominent in several areas throughout the midbrain and brainstem, including the locus coeruleus, the raphe complex and the reticular formation. NESP55 messenger RNA-expressing cells were also found in many areas and nuclei throughout the hypothalamus. Neocortical areas, the hippocampus and the cerebellum were devoid of NESP55 messenger RNA-containing neurons. From this distribution pattern, a significant overlap of NESP55 expression with the noradrenergic, adrenergic and serotonergic transmitter systems was evident. The present study defines, for the first time, the cellular localizaton of NESP55 messenger RNA in the rat brain. The present results provide the basis for future studies defining the as yet obscure function of NESP55.

The new chromogranin-like protein NESP55 is preferentially localized in adrenaline-synthesizing cells of the bovine and rat adrenal medulla

The protein NESP55, a new member of the chromogranin family, is present in large dense-core secretory granules of neuroendocrine tissues. We investigated its cellular distribution in adrenal medulla with immunohistochemistry and in situ hybridization. A preferential co-localization of NESP55 with phenylethanolamine-N-methyltransferase in the adrenergic cell population was found by immunolabelling of consecutive sections. Noradrenergic cells also contained small amounts of NESP55, but the levels as measured by radioimmunoassay were five times lower. The distribution of NESP55 mRNA was similar to preproenkephalin mRNA which previously was shown to be confined to adrenaline-producing cells of the adrenal medulla. The present study indicates that stimulation of adrenergic cells will release significantly higher amounts of NESP55. The functional implications of this preferential secretion, however, have yet to be discovered.

Proteolytic processing, axonal transport and differential distribution of chromogranins A and B, and secretogranin II (secretoneurin) in rat sciatic nerve and spinal cord

The chromogranin family comprises chromogranin A and B, and secretogranin II. The present study has focused on the axonal transport of chromogranins/secretogranin II and their detailed distribution in peripheral nerves and the spinal cord. With radioimmunoassay (RIA) and column chromatography, we first studied the processing of chromogranin B and secretogranin II during axonal transport. No larger precursors of these peptides were detected in the sciatic nerves, indicating that they are already processed to a high degree early during axonal transport. We also analysed nerve segments above and below a crush, using RIA, in order to compare these accumulation data with those obtained by the cytofluorimetric-scanning (CFS) technique. For the latter technique, the amounts of accumulation distal to the crush (presumably representing recycling and retrogradely transported peptides) were 30-40% of the amounts in the proximal accumulation for chromogranin A and secretoneurin, in contrast to chromogranin B, which showed 15% recycling. With the RIA, the corresponding values for secretoneurin and PE-11 (antibody against chromogranin B) were 42% and 14%, respectively. Therefore, the data obtained by CFS were in excellent agreement with those obtained by RIA. In crushed sciatic nerves, chromogranin A was present in large axons as well as in small- and medium-sized axons. Chromogranin B was mainly restricted to large axons, while secretoneurin was localized to bundles of small axons. This differential distribution was also found in the spinal roots and in the peripheral terminals. Chromogranin A was present in both ventral and dorsal roots, and chromogranin B was detected in ventral roots and in large sensory axons in the dorsal roots. Secretoneurin was dominant in the dorsal root. Double-labelling studies with antibodies against choline acetyltransferase/vesicular acetylcholine transporter, or against tyrosine hydroxylase, confirmed that chromogranin A was distributed in cholinergic, sensory, as well as adrenergic neurons. Chromogranin B was mainly present in cholinergic motor neurons and large sensory neurons, and secretoneurin was restricted to adrenergic and sensory neurons. The present study demonstrates that chromogranins A and B, and secretoneurin are transported with fast axonal transport in the peripheral nerves, with different amounts of recycling, and that they are differentially distributed in different types of neurons in the peripheral nervous system and the spinal cord, suggesting that each of them may play a special role in subsets of neurons.

Differential increases in chromogranins, but not synapsin I, in cortical neurons following spreading depression: implications for functional roles and transmitter peptide release

Experimental damage of cerebral cortex induces a slow-moving depolarization and subsequent depression of activity called cortical spreading depression (CSD) which is associated with various ionic, metabolic and genomic changes. Chromogranins are a family of water-soluble acidic proteins with a widespread distribution in secretory, large dense-core vesicles of neurons. We have earlier reported that secretogranin II (SgII) mRNA is increased in cerebral cortex hours after a unilateral craniotomy which would have induced CSD. To investigate further the regulation of chromogranin systems and the nature of genomic and biochemical changes produced by CSD, this study examined the temporal changes in chromogranin A (CgA), chromogranin B (CgB) and SgII mRNAs and CgB and SgII immunoreactivity (IR) in cerebral cortex and hippocampus following unilateral KCl-induced CSD. For comparison, the levels of mRNA for synapsin I, a protein present in small synaptic vesicles was also examined. Rats were killed at various times after 10 min or 2 h of CSD and levels of chromogranins mRNAs were determined by semiquantitative in situ hybridization histochemistry, while changes in corresponding peptide products were detected by immunohistochemistry. CSD increased both SgII and CgB mRNA levels in ipsilateral cortex--levels of SgII mRNA were significantly (P < 0.01) increased at 1-6 h after CSD (165-225% of levels in contralateral cortex), but were not significantly above control values at later time points. Increased expression of CgB mRNA was delayed and prolonged compared with SgII and was significantly (P < 0.05) increased between 3 and 24 h (120-145%) after CSD, peaked at 2 days (180%), and was still elevated at 1 week (130%) compared with contralateral cortex. No alteration in CgA mRNA was observed in the ipsilateral cortex of the same animals across the entire time-course except for an increase in piriform cortex at 1-2 days. In contrast, levels of synapsin I mRNA in affected cortex were identical to those in contralateral cortex and cortex in sham-operated rats, at all times after CSD. Levels of chromogranin (SN-IR and PE-11-IR) were also increased in ipsilateral cortex following CSD. A strong increase in SN-IR in neuronal cell bodies and fibres was observed at 12 h and a moderate increase in PE-11-IR was observed 24-72 h after CSD. These results demonstrate that chromogranin transcripts and gene products are differentially regulated by neuronal depolarization/depression occurring during CSD and suggest that these chromogranin proteins may have differing functional roles in peptide transmitter release and distinct effects on neuronal function in rat brain.

Chromogranin A induces a neurotoxic phenotype in brain microglial cells

Chromogranin A (CGA) belongs to a multifunctional protein family widely distributed in secretory vesicles in neurons and neuroendocrine cells. Within the brain, CGA is localized in neurodegenerative areas associated with reactive microglia. By using cultured rodent microglia, we recently described that CGA induces an activated phenotype and the generation of nitric oxide. These findings led us to examine whether CGA might affect neuronal survival, expression of neurofilaments, and high affinity gamma-aminobutyric acid uptake in neurons cultured in the presence or absence of microglial cells. We found that CGA was unable to exert a direct toxic effect on neurons but provoked neuronal injury and degeneration in the presence of microglial cells. These effects were observed with natural and recombinant CGA and with a recombinant N-terminal fragment corresponding to residues 1-78. CGA stimulated microglial cells to secrete heat-stable diffusible neurotoxic agents. CGA also induced a marked accumulation of nitric oxide and tumor necrosis factor-alpha by microglia, but we could not establish a direct correlation between the levels of nitric oxide and tumor necrosis factor-alpha and the neuronal damage. The possibility that CGA represents an endogenous factor that triggers the microglial responses responsible for the pathogenesis of neuronal degeneration is discussed.

Synaptic loss reflected by secretoneurin-like immunoreactivity in the human hippocampus in Alzheimer's disease

Secretoneurin is a recently described peptide derived by endoproteolytic processing from secretogranin II, previously named chromogranin C. In this study, we have investigated the distribution of secretoneurin-like immunoreactivity in the human hippocampus in controls and in Alzheimer's disease patients, and compared the staining pattern to that of calretinin. Secretoneurin-like immunoreactivity is present throughout the hippocampal formation. At the border of the dentate molecular layer and the granule cell layer, a band of dense secretoneurin immunostaining appeared. In this part, as in the area of the CA2 sector, the high density of secretoneurin-immunoreactivity coincided with calretinin-like immunoreactivity. The mossy fibre system displayed a moderate density of secretoneurin-immunoreactivity. In the entorhinal cortex, a particularly high density of secretoneurin-immunoreactivity was observed. The density of secretoneurin-like immunoreactivity was significantly reduced in the innermost part of the molecular layer and in the outer molecular layer of the dentate gyrus in Alzheimer's disease. For calretinin-like immunoreactivity, a less pronounced decrease was found in the innermost part of the molecular layer. About 40-60% of neuritic plaques were secretoneurin-immunopositive. This study shows that secretoneurin is distinctly distributed in the human hippocampus and that significant changes of secretoneurin-like immunoreactivity occur in Alzheimer's disease, reflecting synaptic loss.

Neuronal activation in the forebrain following electrical stimulation of the cuneiform nucleus in the rat: hypothalamic expression of c-fos and NGFI-A messenger RNA

Forebrain neuronal connections associated with the cardiovascular response to unilateral, low-intensity, electrical stimulation of the mesencephalic cuneiform nucleus were examined in the halothane-anesthetized and paralysed rat by in situ hybridization histochemistry using specific 35S-labelled oligonucleotides for detection of c-fos and nerve growth factor inducible-A gene (NGFI-A) messenger RNAs. Stimulation of the cuneiform nucleus led to increases in mean arterial pressure and heart rate, whereas no cardiovascular response was observed in animals stimulated in the inferior colliculus or in sham-operated animals [see concurrent mid- and hindbrain study [Lam W. et al. (1996) Neuroscience 71, 193-211]. Cuneiform nucleus stimulation was associated with increased c-fos and NGFI-A messenger RNA levels bilaterally in the ventromedial, dorsomedial and lateroanterior hypothalamic nuclei, lateral and anterior hypothalamic areas, and ipsilaterally in the medial amygdaloid nucleus, at levels significantly greater than those in inferior colliculus-stimulated, sham-operated and naive, unoperated animals. C-fos, but not NGFI-A, messenger RNA expression was increased bilaterally in the piriform cortex and subparafascicular thalamic nucleus. These results are consistent with the existence of direct and indirect projections between the cuneiform nucleus and the aforementioned activated areas, the functions of which may include the control of reproduction and metabolism, as well as cardiovascular regulation. The ipsilateral nature of responses in certain brain areas may be explained by the absence of decussating pathways and/or the presence of multisynaptic connections which attenuate bilateral signal transmission. The existence of structures that are known to receive afferent projections from the cuneiform nucleus, but that were not activated, may be explained by synaptic depolarization not reaching the threshold for immediate early gene expression or by a net inhibitory effect on innervated neurons. Characterization of these activated forebrain regions using other compatible labelling techniques should further elucidate the mechanisms by which these central nervous system structures are integrated in the response to stimulation of the cuneiform nucleus.

Rat brain: distribution of immunoreactivity of PE-11, a peptide derived from chromogranin B

An antiserum was raised against the peptide PE-11 whose sequence is present in the chromogranin B molecule. The antiserum reacts only with the free C-terminal end of this peptide. PE-11 immunoreactivity in brain was characterized by molecular size exclusion high performance liquid chromatography. Only the free peptide and a N-terminally elongated peptide were detected, indicating that proteolytic processing of chromagranin B in brain is quite extensive. In immunohistochemistry PE-11 immunoreactivity was found in varicosities, fibres and perikarya throughout the brain. Strong staining was detected in the shell sector of the nucleus accumbens, in the lateral septum, in subregions of the extended amygdala, in some areas of the hippocampus and of the hypothalamus, in the locus coeruleus, in the Purkinje cells of the cerebellum and in the dorsal horn of the spinal cord. Our results, which demonstrate significant processing of chromogranin B in brain and its widespread distribution, can be taken as an indication that chromogranin B represents a precursor of peptides with functional relevance for this organ.

Molecular cloning of frog secretogranin II reveals the occurrence of several highly conserved potential regulatory peptides

Secretogranin II (SgII) is an acidic secretory protein present in large dense core vesicles of neuronal and endocrine cells. Based on the sequence of a peptide derived from the processing of SgII in the brain of the frog Rana ridibunda, degenerate oligonucleotides were used to clone the cDNA encoding frog SgII from a pituitary cDNA library. This cDNA encodes a 574 amino acid protein which exhibits 46-48% sequence identity with mammalian SgII and contains 11 pairs of basic amino acids. Four potential processing products delimited by pairs of basic residues exhibited a much higher degree of identity (68-82%) with the corresponding mammalian SgII sequences. The frog SgII mRNA is approximately 4 kb in length and is differentially expressed in the brain and endocrine tissues. The present data reveal that several SgII-derived peptides have been highly conserved during evolution, suggesting that these peptides may play important neuroendocrine regulatory functions.

Localization and axotomy-induced regulation of the peptide secretoneurin in the rat superior cervical ganglion

This study demonstrates the localization and regulation of a novel neuropeptide of 33 amino acids, secretoneurin (SN), in the rat superior cervical ganglion. Gel filtration chromatography of ganglion proteins followed by a specific radioimmunoassay revealed that SN is the predominant cleavage product of secretogranin II, a member of the chromogranin/secretogranin protein family, in adult ganglia. SN was detected within the majority of nerve endings surrounding postganglionic neurons that were identified by the presence of synaptophysin and, in part, colocalized leu-encephalin. Applying immuno-electronmicroscopy, SN was localized to large dense core vesicles of neuronal and small intensely fluorescent (SIF) cells. In situ hybridization revealed the presence of secretogranin II mRNA in postganglionic neurons and, to a lesser extent, in SIF cells. One week after transection of the postganglionic branches SN levels were not significantly altered; however, a decrease of secretogranin II mRNA was observed in postganglionic neurons but not in SIF cells. After decentralization of the ganglion, SN-immunoreactive nerve terminals disappeared and intraganglionic SN levels were reduced by 70%, indicating the preganglionic origin of SN-positive nerve fibres and varicosities. Secretogranin II mRNA was slightly reduced under this condition. Combined axotomy and decentralization further diminished intraganglionic secretogranin II mRNA, although peptide levels increased significantly above control values under these conditions. Double-labelling immunofluorescence with antibodies against the somatodendritic marker microtubule-associated protein 2 (MAP2) revealed that the increase in SN immunoreactivity was due to an accumulation of SN in axonal processes of postganglionic neurons. SN immunoreactivity was also detected in dissociated neonatal superior cervical ganglion cultures and increased significantly upon treatment with nerve growth factor, the survival and differentiation factor of sympathetic neurons during perinatal development. Co-culture with non-neuronal cells or addition of leukaemia inhibitory factor, a cytokine known to stimulate synthesis of various peptides after nerve transection, did not influence SN immunoreactivity. Therefore, since no fixed relationship between SN and any of the known neuropeptides or neurotransmitters expressed in sympathetic neurons was observed, the expression of this novel peptide appears to be independently regulated.

Chromogranin mRNA levels in the brain as a marker for acute and chronic changes in neuronal activity: effect of treatments including seizures, osmotic stimulation and axotomy in the rat

Chromogranin/secretogranins are a family of acidic, soluble proteins with a widespread distribution in secretory vesicles of endocrine and nervous tissues. The effects of experimental stimuli of differing duration and intensity on chromogranin B and secretogranin II mRNA levels in relevant areas of the rat brain were examined by in situ hybridization histochemistry using 35S-labelled oligonucleotides. Effects of two 'chronic stimulation' paradigms were studied - the effect of 4 days of water or food deprivation on mRNA levels in the hypothalamus and the effect of unilateral cervical vagotomy on transcript levels in the dorsal vagal complex 1, 2 and 7 days after surgery. After 4 days of water deprivation secretogranin II mRNA was significantly increased in supraoptic nucleus (366 +/- 21% of control, P < 0.01), the magnocellular paraventricular nucleus (209 +/- 20% of control, P < 0.01) and the parvocellular paraventricular nucleus (147 +/- 6% of control, P < 0. 05) after 4 days of food deprivation. Seven days after unilateral cervical vagotomy, secretogranin II and chromogranin B mRNA levels were markedly decreased in the ipsilateral dorsal motor nucleus of the vagus (25 +/- 4 and 47 +/- 8% of contralateral values respectively, P < 0.01). Rapid changes in chromogranin mRNA were also detected following shorter duration 'acute stimulation' - in the hypothalamus after hypertonic saline injection, in the hippocampus after electrical stimulation-induced kindled seizures, and in the cerebral cortex after unilateral craniotomy. A large increase in secretogranin II mRNA was detected in the supraoptic nucleus (202 +/- 25% of control, P < 0.01) and the magnocellular paraventricular nucleus (168 +/- 29% of control, P < 0.05) 3 h after a single intraperitoneal injection of hypertonic (1.8 M) saline. Markedly increased levels of secretogranin II (125-160% of control) and chromogranin B (140-230% of control) mRNA were observed in granule cells of the dentate gyrus 0.5-2 h after amygdaloid stimulation-induced seizures. A moderate increase in secretogranin II mRNA (144 +/- 11% of contralateral side, P < 0.01) was found in the underlying cerebral cortex 2.5 h after unilateral craniotomy. These results indicate that measurement of changes in chromogranin mRNA, particularly secretogranin II, is a useful means of assessing both rapid and long-lasting increases and decreases in neuronal activity and, in contrast to immediate early gene mRNA levels, may better reflect specific changes in neuronal secretory activity associated with transmitter/peptide release.

Chromogranin A triggers a phenotypic transformation and the generation of nitric oxide in brain microglial cells

Chromogranin A is an ubiquitous 48,000 mol. wt secretory protein stored and released from many neuroendocrine cells and neurons. In human brain, chromogranin A is a common feature of regions that are known to be affected by various neurodegenerative pathologies such as Alzheimer's, Parkinson's and Pick's diseases. Brain degenerative areas are generally infiltrated by activated microglial cells, the resident macrophage cell population within the central nervous system. Here, we report that both recombinant human chromogranin A and chromogranin A purified from bovine chromaffin granules trigger drastic morphological changes in rat microglial cells maintained in culture. Microglial cells exposed to chromogranin A adopted a flattened amoeboid shape and, this change was associated with an accumulation of actin in the subplasmalemmal region, as observed by immunocytochemistry and confocal laser microscopy. In single microglial cells loaded with indo-1, chromogranin A elicited a rapid and transient increase in [Ca2+]i which preceded the reorganization of actin cytoskeleton. The activity of nitric oxide synthase was estimated by measuring the accumulation of nitrite in the culture medium. Both recombinant human chromogranin A and bovine chromogranin A triggered an important accumulation of nitrite comparable to that induced by lipopolysaccharide, a well-known activator of microglia. The effect of chromogranin A was dose dependent, inhibited by N omega-nitro-L-arginine methyl ester, a competitive inhibitor of nitric oxide synthase, and by cycloheximide, an inhibitor of protein synthesis. These findings suggest that chromogranin A induces an activated phenotype of microglia, and thus may have a role in the pathogenesis of neuronal degeneration in the brain.

Presence and distribution of a new neuropeptide, secretoneurin, in human retina

Secretoneurin (SN) is a neuropeptide formed by endoproteolytic processing of secretogranin II (chromogranin C). Chromatographic analysis revealed that the human retina contains significant concentrations (14.2 fmol/mg wet weight) of this peptide. Its cellular localization in the retina was characterized by immunohistochemistry. SN-immunoreactive (IR) fibers showed a distinct distribution in central and peripheral retinal regions. Immunopositive somata were found in the ganglion cell layer and in the inner nuclear layer. The localization was similar to that of substance P. The physiological role of SN in the human retina is at present unknown. However, its presence in ganglion cells and/or amacrine cells suggests that it may play a role in visual processing.

Effects of haloperidol, clozapine and citalopram on messenger RNA levels of chromogranins A and B and secretogranin II in various regions of rat brain

We have measured the messenger RNA levels of chromogranins A and B and secretogranin II in various brain regions of rats subchronically treated with various antipsychotic drugs. Since, as shown previously, the messenger RNA levels of these peptides are increased when neurons are stimulated, we hoped to identify by this approach those nuclei which are subchronically influenced by these drugs. The drugs chosen were the neuroleptic halperidol, a blocker of dopamine receptors, the atypical antipsychotic clozapine, which in addition to blocking dopamine receptors also blocks those for serotonin, and citalopram, a specific serotonin reuptake inhibitor. In agreement with previous data on neuropeptide messenger RNAs, we found in the dorsolateral striatum an increase of the secretogranin II messenger RNA levels after haloperidol and a much smaller one after clozapine. In the nucleus accumbens and in the bed nucleus of the stria terminalis, both compounds had a comparable positive effect. These differential effects can be attributed to a different action of these drugs on dopamine receptor subtypes. In the zona incerta, clozapine decreased the secretogranin II and chromogranin A message, whereas in the dorsal raphe it led to an increase. On the other hand, citalopram induced exactly the opposite effects in these two brain regions. This phenomenon can be explained by the differential interaction of these drugs with serotonergic mechanisms. Additional, relatively small changes of the mRNAs were seen in several other brain regions. These results establish that changes in the mRNA levels of the chromogranins are good indicators for the effect of drugs on certain brain nuclei. The concomitant action of haloperidol and clozapine on the limbic regions, i.e. the nucleus accumbens and the bed nucleus of the stria terminalis, points to these brain regions for the antipsychotic action of these two neuroleptics.

Regulation of secretogranin II mRNA in rat neuronal cultures

The regulation of SgII mRNA expression was investigated in primary cultures of neurons prepared from the hypothalamus and brainstem of 1-day-old rats. The administration of forskolin (FSK) resulted in a time- and dose-dependent increase in SgII mRNA expression, a 9-fold effect within 6 h being achieved with 10 microM FSK, which maximally increased cellular cAMP levels. SgII mRNA levels remained elevated for 24 h. Activation of protein kinase C with 100 nM phorbol 12-myristate 13-acetate (PMA) also increased SgII mRNA expression, although induction with PMA was slower and more moderate (3.8-fold above control after 24 h). Neither 10 microM 1,9-dideoxyforskolin nor 100 nM 4 alpha-phorbol 12,13-didecanoate, inactive analogues of FSK and PMA respectively, had an effect on SgII mRNA. Depolarization of neuronal cultures with 50 mM KCl had a small and variable effect on SgII mRNA levels (1.8-fold above control) in neuronal cultures and did not influence induction with FSK. To investigate whether neuron-like regulation of SgII mRNA expression could be reproduced in PC12 cells, PC12 cells were treated with 100 nM nerve growth factor (NGF) for 7 days prior to challenge with FSK or PMA. Whereas NGF alone modestly increased SgII mRNA expression in PC12 cells (1.8-fold above control), it did not uncover a stimulatory effect of FSK or PMA. These studies indicate that SgII mRNA expression is enhanced by an increase in cellular cAMP and activation of protein kinase C in primary cultures of neurons and emphasize that SgII mRNA is regulated in a cell-specific manner.

Large variations in the proteolytic formation of a chromogranin A-derived peptide (GE-25) in neuroendocrine tissues

We have established a radioimmunoassay for GE-25, a peptide present in the C-terminal end of the primary amino acid sequence of chromogranin A where it is flanked by typical proteolytic cleavage sites. Gel-filtration HPLC was used to characterize the molecular sizes of the immunoreactive molecules. The antiserum recognized not only the free peptide but also larger precursors including the proprotein chromogranin A. The tissues with the highest levels of GE-25 immunoreactivity were in decreasing order: the adrenal medulla, the three lobes of the pituitary gland, intestinal mucosa, pancreas and various brain regions. In adrenal medulla and parathyroid gland most of the immunoreactivity was found to be present as intact chromogranin A and some intermediate-sized peptides, without significant amounts of the free peptide. In anterior pituitary, and even more so in intestine, a shift to smaller peptides was seen. In the posterior and intermediate pituitary and in pancreas the predominant immunoreactive material was apparently represented by the free peptide GE-25. In reverse-phase chromatography this peptide eluted exactly like the synthetic standard, which allows a tentative identification as GE-25. In brain tissue the processing of chromogranin A was intermediate, with significant amounts of immunoreactivity corresponding to GE-25 as well as precursor proteins being present. We suggest that in those organs (endocrine pancreas, intermediate and posterior pituitary) where the major hormones are proteolytically processed there is also a concomitant proteolysis of further susceptible peptides. Since GE-25 is apparently formed in vivo and is well conserved between species it seems a good candidate for having specific physiological functions.

Occurrence of secretogranin II in the prolactin-immunoreactive neurons of the rat lateral hypothalamus: an in situ hybridization and immunocytochemical study

The occurrence of secretogranin II in a neuron population of the rat lateral hypothalamus specifically detected by an anti-serum to ovine prolactin was examined. As this population was previously reported to synthesize dynorphin, the distribution of neurons recognized by ovine prolactin-, dynorphin B- and secretogranin II anti-sera was investigated on adjacent sections of hypothalami. The prolactin immunoreactive neurons were the only cells in the lateral hypothalamus to be stained by secretogranin II anti-serum. Moreover, coupling immunocytochemical detection and in situ hybridization with an oligonucleotide probe complementary to secretogranin II mRNA showed that these neurons expressed the secretogranin II gene. These new findings should help to study the physiological role of the prolactin immunoreactive neurons of the lateral hypothalamus.

Secretoneurin: a new peptide in the human enteric nervous system

Secretoneurin is a functional neuropeptide derived from secretogranin II (chromogranin C). This proprotein is processed to varying degrees in neuroendocrine tissues. In the present study we established by gel filtration high performance liquid chromatography that in human intestinal wall and mucosa an antiserum against secretoneurin detects as the major immunoreactive moiety the free peptide secretoneurin. In the mucosa some larger immunoreactive peptides were also present, however, a significant amount of the intact proprotein secretogranin II could not be detected. By immunohistochemistry we studied the distribution of secretoneurin within the gut. Antibodies to protein gene product 9.5 and chromogranin A were used to identify all neurons and endocrine cells, respectively, whilst those to the peptides substance P, CGRP and somatostatin were used for the further characterization of individual secretoneurin-positive structures. Secretoneurin immunoreactivity was found in nerve fibres in all layers of the gut wall. In both myenteric and submucous plexuses, nerve fibres and the majority of ganglion cells were secretoneurin-immunoreactive. In the mucosa, some secretoneurin-positive nerve processes ran parallel to the basal membrane of epithelial cells, occasionally invading the epithelial layer. Secretoneurin immunoreactivity was found in endocrine cells, mostly D cells, in the following regions in descending order of density: stomach/duodenum; rectum; colon; ileum. Thus, secretoneurin is a new major peptide within the human enteric neuroendocrine system. Its presence in abundant myenteric ganglion cells may imply a role in the modulation of gastrointestinal motility. The chemotactic properties of secretoneurin and its possible localization in sensory fibres suggest that this peptide may be involved in the genesis of intestinal inflammation.

Secretoneurin-immunoreactivity in nerve terminals apposing identified preganglionic sympathetic neurons in the rat: colocalization with substance P and enkephalin

Preganglionic sympathetic neurons projecting to the superior cervical ganglion are innervated by nerve fibers containing classical neurotransmitters as well as neuropeptides. In this study we examined the possible participation of a novel peptide, secretoneurin (a cleavage product of secretogranin II), in regulation of sympathetic outflow to head and neck by using a retrograde labelling-technique combined with immunohistochemistry. In addition, the coexistence of secretoneurin with substance P and leu-enkephalin, peptides known to innervate preganglionic neurons, was investigated. The majority of retrogradely labeled neurons were localized in the nucleus intermediolateralis of spinal cord segments T1-T3 (maximum at T2). Nearly all of Fast Blue positive neuronal perikarya were apposed by nerve fibers and terminals exhibiting immunoreactivity to secretoneurin. The main secretoneurin-immunoreactive form found in the upper thoracic segments corresponded to the free peptide secretoneurin as revealed by chromatography and radioimmunoassay. More than half of labeled neurons were surrounded by nerve endings containing in addition substance P or leu-enkephalin which were also, however, less frequently colocalized. Our results suggest that secretoneurin influences the activity of preganglionic sympathetic neurons projecting to the superior cervical ganglion. Regarding their frequent colocalization with substance P and leu-enkephalin, functional interactions of these peptides on preganglionic sympathetic nerve activity have to be considered.

Secretogranin II: molecular properties, regulation of biosynthesis and processing to the neuropeptide secretoneurin

Secretogranin II is an acidic secretory protein in large dense core vesicles of endocrine, neuroendocrine and neuronal tissues. It comprises, together with chromogranins A and B, the class of proteins collectively called chromogranins. In this review the physico-chemical properties, genomic organization, tissue distribution, synthesis regulation, ontogeny and physiological function of this protein are discussed. Secretogranin II gained interest recently for mainly three reasons: (1) secretogranin II is an excellent marker for the regulated secretory pathway due to its simple and specific metabolic labeling by inorganic sulfate; (2) secretogranin II occurs in a variety of neoplasms arising from endocrine and neuroendocrine cells and was shown to be a useful histological tumor marker for these cells; (3) secretogranin II is the precursor of the recently discovered neuropeptide secretoneurin which induces dopamine release in the striatum of the rat brain.

Measurement of secretogranin II release from individual adenohypophysial gonadotropes

Secretogranin II (SG-II) is an acidic 86-kDa protein found in high abundance in the anterior pituitary gland. In the present studies, we investigated the secretion and the localization of SG-II using pituitary cells from female rats at all stages of the estrous cycle. Double immunofluorescence staining revealed that SG-II immunoreactivity was localized in low abundance in about half of all pituitary cells and in high abundance in all of the luteinizing hormone (LH)-immunoreactive cells (which represent approximately 5% of all pituitary cells). Using a reverse hemolytic plaque assay for measurement of SG-II release from individual pituitary cells in culture, we found that SG-II secretion was strongly stimulated by gonadotropin-releasing hormone in a dose-related fashion, and the amount of SG-II secretion was also related to the stage of the estrous cycle: it was highest at proestrus and lowest at estrus. SG-II plaque assay followed by LH immunofluorescence staining further revealed that all the SG-II-secreting cells contained LH immunoreactivity. At proestrus all the LH-immunoreactive cells secreted SG-II, whereas another days of the estrous cycle only a fraction of them did so. Thus our findings demonstrate a striking resemblance between SG-II and LH with regard to cell localization and secretory regulation.