Aggressive behavior induces release of nerve growth factor from mouse salivary gland into the bloodstream

Psychosocial vs. "physical" stress situations in rodents and humans: role of neurotrophins

Nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) are well-studied polypeptide growth factors involved in the development and maintenance of specific peripheral and central populations of neuronal cells. In addition to its role as a neurotrophic agent, NGF controls very complex functions in vertebrate physiology. A variety of cells outside the nervous system are in fact able to synthesize NGF including epithelial cells, fibroblasts, lymphocytes, and macrophages. NGF target cells have been identified in the nervous, immune, and endocrine systems, suggesting that NGF may operate through multiple paths to ultimately regulate physiological homeostasis and behavioral coping. We used a mouse model of social stress to demonstrate that NGF levels increase both in plasma and in the hypothalamus following intermale aggressive interactions. The investigation has been extended to other species, including humans, to show that labour, lactation, and the anticipation of the first jump with a parachute also result in increased NGF plasma levels and in changes in the distribution of NGF receptors on lymphocytes. BDNF activation is caused by both physical and social stress events. The aim of this review is to (1) outline the current understanding of the roles of NGF and BDNF in stress-related physiological changes in vertebrates, in particular for physical vs. psychological stressors, which may activate both similar and different neurobiological pathways, and (2) summarize recent efforts to derive pharmacological strategies from the increasing body of BDNF and NGF neurobehavioral data.

Changes in plasma nerve growth factor levels in older adults associated with chronic stress

Evidence indicates that the actions of nerve growth factor (NGF) reach beyond the nervous system and might modulate immune function. Based on reports that blood NGF rises following the acute stress of parachute jumping, we investigated whether exposure to a chronic stressor, caregiving for a cognitively impaired spouse, could alter the levels of blood NGF. High perceived stress and depression in caregivers (vs. well-matched controls) were associated with elevated blood NGF. These data suggest that exposure to this chronic stressor can alter the concentrations of circulating NGF, and that psychological stress can induce changes in NGF concentrations in older adults.

Nerve growth factor and neuroimmune interactions in inflammatory diseases

Discovered almost 50 years ago, nerve growth factor (NGF) has been extensively studied in various biological systems. NGF has recently been suggested to play an important role in mediating and/or regulating immune response, in addition to its trophic and tropic effects on nerve growth and regeneration It is clear that in complex interactions between immune cells and nervous system NGF plays a central role. We have only just begun to identify and understand the direct mechanisms by which NGF activates target cells, the precise identity of the target cells, and the particular factors released from target cells. Nerve growth factor together with possibly other neurotrophins such as BDNF (brain-derived nerve growth factor), GDNF (glial-derived nerve growth factor) or NT3 are important modulators of immunity. More detailed studies are needed at the receptor, mediator and cellular levels to better understand the neuroimmunomodulatory properties of neurothrophins and NGF. The nature of the involvement of NGF in inflammation and inflammatory diseases remains a particularly interesting question. By blocking NGF or mediators released upon NGF activation, we are able to control the progress of inflammation, thereby opening many therapeutic opportunities for the future.

Social disruption, immunity, and susceptibility to viral infection. Role of glucocorticoid insensitivity and NGF

Glucocorticoid (cort) responses have been shown to suppress inflammatory reactions by inhibiting the trafficking of immune cells. Recently, it was demonstrated that restraint stress (RST) and psychosocial stress (social reorganization; SRO) differentially affected the pathophysiology and survival in the mouse influenza viral infection model. While both stressors activated the HPA axis, only SRO affected survival. In RST, elevated cort diminished recruitment of inflammatory cells following intranasal challenge of C57BL/6 mice with A/PR8 virus. However, infected SRO mice developed hypercellularity in the lungs and were more likely to die from lung consolidation than controls. Since elevated cort failed to be anti-inflammatory in SRO mice, the hypothesis that psychosocial stress induced steroid insensitivity was tested. An in vitro cort suppression test was performed by stimulating splenocytes from SRO and control mice with mitogen in the presence or absence of cort. Proliferation of ConA-stimulated cells was inhibited by cort in a dose-dependent fashion in controls, but splenocytes from SRO mice stimulated with ConA were resistant to cort-induced suppression. Thus, psychosocial stress induced a state of steroid insensitivity. SRO also induced the release of nerve growth factor (NGF) from the salivary glands into circulation; plasma NGF correlated with development of steroid insensitivity. NGF has been reported to negatively regulate the expression of type II glucocorticoid receptors, and thus may be a key factor in the induction of steroid insensitivity.

Data and hypotheses on the role of nerve growth factor and other neurotrophins in psychiatric disorders

Nerve growth factor (NGF) was discovered and characterized for its role on the growth, differentiation and maintenance of specific neurons of the peripheral nervous system. Subsequent studies revealed that NGF is synthesized and released within the central nervous system and exerts a trophic and functional role on basal forebrain cholinergic neurons; it is involved in a protective role following brain insults induced by an epileptic status, seizure, as well as surgical and chemical lesions.More recently our collaborative studies provided evidence that NGF is implicated in neurobehavioral response including cerebral alterations associated with psychiatric disorders. In this brief review, ongoing and emerging data are presented and discussed.

Neuropeptide enzyme hydrolysis in human saliva

The possible hydrolysis of neuropeptides by human saliva was studied using leucine enkephalin as a model. The data obtained indicate that in the presence of saliva this substrate is partially hydrolysed, and that its disappearance corresponds to the appearance of peptides whose composition is consistent with that of the substrate hydrolysis by-products. The formation of these peptides indicates the presence of all three classes of enzymes known to hydrolyse enkephalins in other tissues: aminopeptidases, dipeptidylaminopeptidases and dipeptidylcarboxypeptidases. The activity of these enzymes appears to be altered by the presence of low molecular-weight substances, whose inhibitory activity is apparent on all three classes of enkephalin-degrading enzymes. Substrate degradation was higher in male than female saliva; these differences appear to be caused by lower activity of the enzymes, and higher activity of the low molecular-weight inhibitors, measurable in female as compared to male saliva.

Nerve growth factor brain concentration and stress: changes depend on type of stressor and age

In the relationship between the hippocampus and the hypothalamo-pituitary-adrenocortical axis, trophic and tropic actions of nerve growth factor are involved in parallel with those on the cholinergic nuclei of the basal forebrain. Here, we report the changes produced by stress activation of the hypothalamo-pituitary-adrenocortical axis on hippocampal and basal forebrain nerve growth factor concentrations in 3-month-old male Wistar rats. The stressors used were: restraint; cold exposure; foot-shock; and rotatory platform. Restraint stress tended to reduce nerve growth factor in the hippocampus and reduced it significantly in the basal forebrain. Nerve growth factor levels in the hippocampus were not modified by cold exposure. However, a single unrepeated exposure significantly increased nerve growth factor in the basal forebrain. Both acute and chronic foot-shock reduced nerve growth factor in the hippocampus, leaving the levels in the basal forebrain unmodified. Acute but not chronic rotatory platform reduced nerve growth factor in the hippocampus, while showing a tendency, more pronounced after chronic application, toward an increase in the basal forebrain. Since with aging both activity of the hypothalamus-pituitary-adrenal axis and nerve growth factor trophic and tropic functions change, we studied the effect of restraint and cold stress in the 24-month-old male rat. The variations in nerve growth factor concentrations in the basal forebrain following stress activation are no longer present in the aged rat. The picture that emerges is indicative of a complex relationship between stress and nerve growth factor which is influenced by the kind of stressor and by age. Lack of uniformity in the effects produced by different stressors might reside in different qualitative and/or quantitative degree of involvement of neurotransmitters and/or neurohormones for each of them.

Nerve growth factor functions as a chemoattractant for mast cells through both mitogen-activated protein kinase and phosphatidylinositol 3-kinase signaling pathways

Despite being a well-characterized neurotrophic factor, nerve growth factor (NGF) influences survival, differentiation, and functions of mast cells. We investigated whether NGF was able to induce directional migration of rat peritoneal mast cells (PMCs). NGF clearly induced chemotactic movement of PMCs in a dose-dependent manner with the drastic morphological change and distribution of F-actin, which was completely blocked by pretreatment with Clostridium botulinumC2 toxin, an actin-polymerization inhibitor. Because PMCs constitutively express the NGF high-affinity receptor (TrkA) with a tyrosine kinase domain, we focused on downstream effectors in signaling cascades following the TrkA. NGF rapidly activated both mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K), and the addition of inhibitors specific for MAPK kinase and PI3K suppressed cell migration and these signals. In the coculture system with PMCs and fibroblasts, which produce biologically active NGF, directional migration of PMCs to fibroblasts was observed, and the addition of anti-NGF polyclonal antibodies significantly suppressed the migration of PMCs. These findings suggested that NGF initiated chemotactic movement of PMCs through both MAPK and PI3K signaling pathways following TrkA activation. Thus, locally produced NGF may play an important role in mast cell accumulation in allergic and nonallergic inflammatory conditions.

Rodent submandibular gland peptide hormones and other biologically active peptides

The cervical sympathetic trunk-submandibular gland neuroendocrine axis plays an integral role in physiological adaptations and contributes to the maintenance of systemic homeostasis, particularly under the 'stress conditions' seen with tissue damage, inflammation, and aggressive behavior. The variety of polypeptides, whose release from acinar and ductal cells is under sympathetic nervous system control, offers coordinated and progressive levels of endocrine communication. Proteolytic enzymes (e.g. the kallikreins and furin maturases) are involved in the conversion of inactive precursors (e. g. Pro-EGF and SMR1) into biologically active molecules (e.g. EGF, SMR1-pentapeptide), which act on local or distant targets and thereby modulate the homeostatic process.

Enkephalin-degrading enzymes and their inhibitors in human saliva

The possible presence of enzymes able to hydrolyze leucine enkephalin has been investigated in human saliva. The data obtained indicate that, in the presence of saliva, Leu-enkephalin is partially hydrolyzed. The disappearance of the substrate is paired with the formation of hydrolysis byproducts whose composition indicates the presence of all three classes of enzymes known to hydrolyze enkephalins: aminopeptidases, dipeptidylaminopeptidases, and dipeptidylcarboxypeptidases. The presence of low molecular weight substances with inhibitory activity on proteolytic enzymes has also been detected. These substances are active on all three classes of enkephalin-degrading enzymes, although the inhibition is more evident on dipeptidylpeptidases than on aminopeptidases. Substrate degradation was found to be higher in male than in female saliva: this seems to be caused by the activities both of enzymes and low molecular weight inhibitors that are different in the two sexes.

Nerve growth factor: a neurotrophin with activity on cells of the immune system

Numerous studies published in the last two decades provide evidence that nerve growth factor (NGF), a polypeptide originally discovered because of its neurotrophic activity, acts on a variety of cells of the immune system, including mast cells, eosinophils, and B and T lymphocytes. NGF has been shown to increase during inflammatory responses, autoimmune disorders, parasitic infections, and allergic diseases. Moreover, stress, which is characterized also by activation of a variety of immune cells, causes a significant increase in basal plasma NGF levels. Recently published studies reveal that hematopoietic progenitor cells seem to be able to produce and/or respond to NGF. We report these data and discuss the hypothesis of the possible implication of NGF on the functional activities of immune cells.

Acinar cells are target cells for androgens in mouse submandibular glands

The variable coding sequence (VCS) multigene family encodes diverse salivary proteins, such as the SMR1 prohormone and the PR-VB1 proline-rich protein in the rat. In situ hybridization was used to study the cell-specific expression of two new mouse VCS genes, Vcs1 and Vcs2. We show that the Vcs1 transcripts, which code for a proline-rich protein, MSG1, are highly abundant in male and female parotid glands, in which they are specifically detected in acinar cells. No expression was seen in the submandibular or sublingual glands. In contrast, Vcs2 transcripts were found only in the acinar cells of the submandibular glands (SMGs) of male mice, in which they are expressed in response to androgens. Expression was found to be heterogeneous within acinar structures. No Vcs2 transcripts were detected in the SMGs of females or castrated males by Northern blot, RNase protection, or in situ hybridization. Androgen administration to females or castrated males induced expression at a level comparable to that of intact males. The Vcs2 gene is the first example of a mouse androgen-regulated gene that is expressed in SMG acinar cells. This result, in addition to our previous observation on SMR1 expression in rats, demonstrates that both acinar cells and granular convoluted tubule (GCT) cells are target cells for androgen action in rodent SMG.

Nerve growth factor in pituitary development and pituitary tumors

Cells in the anterior pituitary originate from a common pluripotent precursor whose phenotypic development is determined by intrapituitary transcription factors as well as by hypothalamic and peripheral signals. A rapidly growing body of evidence revealed that essential to the differentiation and proliferation of pituitary cells are an array of growth factors that are produced within the pituitary and act mainly through autocrine mechanisms. Growth factors are polypeptides that are released in carefully measured amounts by some cells to regulate cell growth and differentiation by activating specific tyrosine kinase receptors in the plasma membrane of target cells. Both overproduction of mitogenic growth factors and loss of factors inhibiting cell proliferation result in uncontrolled cell growth and tumor development. There is now increasing evidence that disruption of the calibrated signalling network activated by pituitary growth factors plays a central role in pituitary tumorigenesis. This paper is focussed on the role of nerve growth factor (NGF) in pituitary physiology and pathology. In particular, we propose that NGF plays a dual role in the gland: a local one as a stimulator of differentiation and proliferation of lactotrope cells during pituitary development and a systemic one as a neurohormone which is cosecreted with prolactin into the bloodstream. Furthermore, we discuss the evidence that NGF is an autocrine differentiation factor for prolactin-secreting cells. Escape from NGF control appears to be one of the mechanisms involved in the development and progression of prolactinomas. Along the same line, exposure of prolactinomas refractory to dopaminergic therapy to exogenous NGF results in their differentiation into lactotrope-like cells reexpressing the D2 receptor protein. This observation may open the way to a sequential therapy with NGF and bromocriptine for patients refractory to the conventional therapy.

Role of nerve growth factor in cutaneous wound healing: accelerating effects in normal and healing-impaired diabetic mice

Four full-thickness skin wounds made in normal mice led to the significant increase in levels of nerve growth factor (NGF) in sera and in wounded skin tissues. Since sialoadenectomy before the wounds inhibited the rise in serum levels of NGF, the NGF may be released from the salivary gland into the blood stream after the wounds. In contrast, the fact that messenger RNA and protein of NGF were detected in newly formed epithelial cells at the edge of the wound and fibroblasts consistent with the granulation tissue produced in the wound space, suggests that NGF was also produced at the wounded skin site. Topical application of NGF into the wounds accelerated the rate of wound healing in normal mice and in healing-impaired diabetic KK/Ta mice. This clinical effect of NGF was evaluated by histological examination; the increases in the degree of reepithelialization, the thickness of the granulation tissue, and the density of extracellular matrix were observed. NGF also increased the breaking strength of healing linear wounds in normal and diabetic mice. These findings suggested that NGF immediately and constitutively released in response to cutaneous injury may contribute to wound healing through broader biological activities, and NGF improved the diabetic impaired response of wound healing.

The mouse Vcs2 gene is a composite structure which evolved by gene fusion and encodes five distinct salivary mRNA species

Genes of the VCS (variable coding sequence) family are characterized by an extensive evolutionary divergence in the protein-coding sequence. The VCS family has been characterized by cDNA cloning from submandibular glands in the rat, mouse and humans. At the genomic level, the sequences of two members of this family are known in the rat Rattus norvegicus: the VCSA1 gene, encoding the prohormone-like polypeptide SMR1, and the VCSB1 gene, encoding a salivary Pro-rich polypeptide. No genomic data were available for the VCS genes of other species. To understand the evolution of the VCS gene family better, we have now sequenced 23 kilobases (kb) of the mouse Vcs2 gene. The Vcs2 sequence reveals numerous genomic reorganizations such as an inversion, insertions of short elements and an unusually high number of long interspersed repeated elements (LINEs), which make up 42% of this region. Interestingly, Vcs2 is composed of three different VCS-like regions. The first of these regions contains all the exons necessary to encode the previously described mouse submandibular gland polypeptide MSG2alpha. This region aligns with the entire genomic sequences of rat VCSA1 and VCSB1 genes. The two other regions align with fragments of these rat sequences. The three regions are arrayed in tandem and flanked by LINEs. In particular, the third region also contains exons that were found in mRNA species from the submandibular gland. In total, we have characterized five mRNAs from mouse submandibular glands which have in common their first exon, and are produced by alternative splicing. Vcs2 is thus a single gene that arose by the fusion of three genes (or pseudogenes) of the VCS multigene family.

NGF content and expression in the rat pituitary gland and regulation by thyroid hormone

The involvement of nerve growth factor (NGF) in neuroendocrine regulation is supported by several lines of evidence. In this paper, we investigated the NGF content and expression in the pituitary gland and other endocrine organs during dysendocrine states (thyroidectomized, adrenalectomized and gonadectomized male rats). We found an increase of NGF-IR in the pituitary gland and testis of hypothyroid rats whereas no differences were found in the adrenal gland and blood. Also, NGF mRNA expression had increased in the anterior pituitary of hypothyroid rats whereas it had not changed after adrenalectomy and gonadectomy. Moreover, other neurotrophins and neurotrophin high-affinity receptors were unchanged in the anterior pituitary of hypothyroid rats. These data indicate that pituitary NGF is selectively modulated by thyroid status of the animal, further supporting a close link between NGF and thyroid hormone.

Effect of a long-term nerve growth factor treatment on body weight, blood pressure, and serum corticosterone in rats

Nerve growth factor is a well-characterized neurotrophin essential for the development and maintenance of certain central and peripheral neurons. As many neurons affected by aging depend for their survival on a constant supply of neurotrophins, nerve growth factor has been proposed as a possible treatment to prevent aging-associated neurodegeneration. There is evidence that nerve growth factor also plays a role in the immune system and modulates certain aspects of endocrine function. Here we have determined the effects of prolonged peripheral (intraperitoneal) treatment with nerve growth factor on body weight, blood pressure, and serum corticosterone levels in the rat. Our data indicate that intraperitoneally-injected nerve growth factor can affect body weight gain in rats. This effect may not be mediated by nerve growth factor-induced increases in serum corticosterone levels, as exogenous administration of corticosterone did not result in a similar body weight loss. These results show that, as previously reported for intracerebroventricular treatment with nerve growth factor, intraperitoneally-injected nerve growth factor also reduces body weight gain in rats. The data also suggest that exogenous delivery of nerve growth factor as part of therapeutic regimens is likely to have several effects.

Targets for SMR1-pentapeptide suggest a link between the circulating peptide and mineral transport

The submandibular rat 1 protein (SMR1) is selectively processed at pairs of basic amino acid residues in a tissue- and sex-specific manner. We have mapped peripheral targets for the final secretory maturation product of SMR1, the pentapeptide QHNPR, by examining in vivo the tissue distribution of the radiolabeled peptide using beta-radio imager whole body autoradiography. The characteristics of tissue uptake allowed specific binding sites at physiological peptide concentrations to be identified within the renal outer medulla, bone and dental tissue, glandular gastric mucosa, and pancreatic lobules. Direct evidence that pentapeptide binding sites are localized in selective portions of the male rat nephron, within the S3, S2, and S1 segments of the proximal tubules, was obtained. In bone tissue the pentapeptide exclusively accumulates within the trabecular bone remodeling unit, and in dental tissue it concentrates within the tubules of the dentinal rat incisor. In relation to male rat-specific behavioral characteristics, our data suggest that the circulating androgen-regulated SMR1-derived pentapeptide is primarily involved in the modulation of mineral balance between at least four systems: kidney, bone, tooth, and circulation.

The expanding role of nerve growth factor: from neurotrophic activity to immunologic diseases

Numerous studies published in the last 10-15 years have shown that nerve growth factor (NGF), a polypeptide originally discovered in connection with its neurotrophic activity, also acts on cells of the immune system. NGF has been found in various immune organs including the spleen, lymph nodes, and thymus, and cells such as mast cells, eosinophils, and B and T cells. The circulating levels of NGF increase in inflammatory responses, in various autoimmune diseases, in parasitic infections, and in allergic diseases. Stress-related events both in animal models and in man also result in an increase of NGF, suggesting that this molecule is involved in neuroendocrine functions. The rapid release of NGF is part of an alerting signal in response to either psychologically stressful or anxiogenic conditions in response to homeostatic alteration. Thus, the inflammation and stress-induced increase in NGF might alone or in association with other biologic mediators induce the activation of immune cells during immunologic insults. A clearer understanding of the role of NGF in these events may be useful to identify the mechanisms implicated in certain neuroimmune and immune dysfunctions.

Aging in the hippocampus: interrelated actions of neurotrophins and glucocorticoids

Over the past two decades, evidence has been accumulating that diffusible molecules, such as growth factors and steroids hormones, play an important part in neural senescence, particularly in the hippocampus. There is also evidence that these molecules do not act as independent signals, but show interrelated regulation and cooperative control over the aging process. Here, we review some of the changes that occur in the hippocampus with age, and the influence of two classes of signaling substances: glucocorticoids and neurotrophins. We also examine the interactions between these substances and how this could influence the aging process.

Human CD4+ T cell clones produce and release nerve growth factor and express high-affinity nerve growth factor receptors

BACKGROUND

Increasing evidence shows that nerve growth factor (NGF) plays a role in the complex and fascinating linkage between the nervous and the immune systems due to its ability to modulate functions of several inflammatory cells.

OBJECTIVE

To investigate NGF receptor expression and NGF production and release by human CD4+ cells clones, which have primary relevance in modulating inflammatory events through their different subsets of functional phenotypes.

METHODS

The expression of NGF and a transmembrane tyrosine kinase (TrkA) was evaluated by immunohistochemistry and flow cytometry analysis in five T(H0), six T(H1), and five T(H2) cell clones derived from human circulating mononuclear blood cells. Moreover, the amount of NGF protein was assessed by measuring the NGF levels in culture supernatants of the T cell clones before stimulation and 48 hours after phytohemagglutinin (PHA) activation by use of an immunoenzymatic assay.

RESULTS

Our data have shown that in unstimulated conditions, human CD4+ T cell clones express both immunoreactivity for NGF and the TrkA NGF receptor irrespective of their cytokine profile. Moreover, T(H1) and T(H2) clones, but not T(H0) clones, secrete NGF in basal conditions. PHA activation induces NGF secretion in T(H0) clones and a significant increase of NGF levels in T(H2) (p < 0.05), but not in T(H1) culture supernatants.

CONCLUSIONS

Results obtained represent the first evidence of TrkA expression and NGF production and release in human CD4+ cell clones and suggest a possible functional role of NGF in modulating the immune and inflammatory network.

Stress, acute hyperglycemia, and hyperlipidemia role of the autonomic nervous system and cytokines

Stress is accompanied by metabolic alterations that could contribute to the etiology of diabetes mellitus, arteriosclerosis, and cardiovascular diseases; however, the mechanisms by which stress affects glucose and lipid metabolism remain to be resolved. Stress-induced effects on neurotransmission and interleukin-1 (IL-1) signaling rapidly produce hyperglycemia by increasing sympathetic outflow. Activation of the sympathetic nervous system can also rapidly stimulate lipolysis and hepatic triglyceride secretion. Furthermore, stress increases serum interleukin-6 (IL-6) and nerve growth factor (NGF) levels by activating neuroendocrine systems. IL-6 and NGF can rapidly increase lipolysis and hepatic triglyceride secretion without inducing hyperglycemia. The sympathetic nervous system does not mediate cytokine-induced hypertriglyceridemia. Thus, the central nervous system plays an important role in regulation of hepatic glucose and lipid metabolism via the sympathetic nervous system and cytokines. (Trends Endocrinol Metab 1997;8:192-197). (c) 1997, Elsevier Science Inc.

Nerve growth factor induces the expression of certain cytokine genes and bcl-2 in mast cells. Potential role in survival promotion

Nerve growth factor (NGF) promotes mast cell survival in vitro (Horigome, K., Bullock, E. D., and Johnson, E. M., Jr. (1994) J. Biol. Chem. 269, 2695-2702). NGF survival promotion is cell density-dependent, and conditioned medium experiments have shown that NGF increases the production of an autocrine mast cell survival activity. Cytokines are potential candidates for autocrine survival factors. In rat peritoneal mast cells (RPMC), NGF caused an increase in the messenger RNAs for interleukin (IL)-3, IL-4, IL-10, tumor necrosis factor-alpha, and granulocyte-macrophage colony-stimulating factor. This induction was NGF dose-dependent, was blocked by NGF-neutralizing antibodies, and was not observed in the non-mast peritoneal cell population. The immunosuppressive agent, cyclosporin A, blocked both cytokine induction and NGF-activated survival promotion but not survival promotion activated by IL-3 or stem cell factor, suggesting that NGF enhanced RPMC survival by increasing cytokine production. We also examine the effects of NGF on the expression levels of some members of the bcl-2 family and the interleukin-1beta-converting enzyme-like cysteine protease families. NGF markedly increased bcl-2 expression but had little or no effect on the other genes studied. The induction of bcl-2 mRNA by NGF was not blocked by cyclosporin A. These data suggest that induced cytokine gene expression but not increased expression of bcl-2 mediates NGF-survival promotion in RPMC.

Age-dependent changes in insulin-like immunoreactivity in rat submandibular salivary glands

In recent years, a growing interest had arisen in hormonal factors in salivary glands. We have investigated the changes in the content of an insulin-like immunoreactive (ILI) compound in the submandibular salivary glands of Sprague Dawley rats during physiological aging, in the range 15 days-27 months. The amount of ILI in the submandibular glands of young adult rats was found to be doubled in the post-natal period until the age of puberty and was maintained in senescence. No significant correlation was found between age-dependent variations in ILI levels of submandibular salivary glands and circulating insulin concentrations, further supporting previous indications that ILI is being synthesized in situ. It is possible that ILI could exert paracrine effects within the glands, as regards the development of other glandular structures during the first months of life, as well as the preservation of glandular function in senescent animals as well.

Circulating nerve growth factor levels are increased in humans with allergic diseases and asthma

Nerve growth factor (NGF) serum levels were measured in 49 patients with asthma and/or rhinoconjunctivitis and/or urticaria-angioedema. Clinical and biochemical parameters, such as bronchial reactivity, total and specific serum IgE levels, and circulating eosinophil cationic protein levels, were evaluated in relation to NGF values in asthma patients. NGF was significantly increased in the 42 allergic (skin-test- or radioallergosorbent-test-positive) subjects (49.7 +/- 28.8 pg/ml) versus the 18 matched controls (3.8 +/- 1.7 pg/ml; P < 0.001). NGF levels in allergic patients with asthma, rhinoconjunctivitis, and urticaria-angioedema were 132.1 +/- 90.8, 17.6 +/- 6.1, and 7.6 +/- 1.8 pg/ml (P < 0.001, P < 0.002, and P < 0.05 versus controls), respectively. Patients with more than one allergic disease had higher NGF serum values than those with a single disease. When asthma patients were considered as a group, NGF serum values (87.6 +/- 59.8 pg/ml) were still significantly higher than those of control groups (P < 0.001), but allergic asthma patients had elevated NGF serum levels compared with nonallergic asthma patients (132.1 +/- 90.8 versus 4.9 +/- 2.9 pg/ml; P < 0.001). NGF serum levels correlate to total IgE serum values (rho = 0.43; P < 0.02). The highest NGF values were found in patients with severe allergic asthma, a high degree of bronchial hyperreactivity, and high total IgE and eosinophil cationic protein serum levels. This study represents the first observation (that we know of) that NGF is increased in human allergic inflammatory diseases and asthma.

Changes in human plasma nerve growth factor level after chronic alcohol consumption and withdrawal

Numerous studies reported in recent years have shown that withdrawal from chronic consumption of drugs induces high levels of anxiety, both in humans and in animal models. In the present study, we demonstrated that withdrawal from chronic consumption of either ethanol or heroin causes a significant increase in plasma nerve growth factor, suggesting that the resulting anxiety condition triggers the release of this molecule. Although the functional significance of this phenomenon needs to be better defined, it is hypothesized that the increased levels of circulating nerve growth factor might be involved in homeostatic adaptive and/or reparative mechanisms.

Nerve growth factor in the anterior pituitary: localization in mammotroph cells and cosecretion with prolactin by a dopamine-regulated mechanism

Nerve growth factor (NGF) is well characterized for its neurotrophic actions on peripheral sensory and sympathetic neurons and on central cholinergic neurons of the basal forebrain. Recent evidence, however, has shown high levels of NGF to be present in a variety of biological fluids after inflammatory and autoimmune responses, suggesting that NGF is a mediator of immune interactions. Increased NGF serum levels have been reported in both humans and experimental animal models of psychological and physical stress, thus implicating NGF in neuroendocrine interactions as well. The possible source(s) and the regulatory mechanisms involved in the control of serum NGF levels, however, still remain to be elucidated. We now report the presence of both NGF gene transcripts and protein in the anterior pituitary. Immunofluorescence analysis indicated that hypophysial NGF is selectively localized in mammotroph cells and stored in secretory granules. NGF is cosecreted with prolactin from mammotroph cells by a neurotransmitter-dependent mechanism that can be pharmacologically regulated. Activation of the dopamine D2 receptor subtype, which physiologically controls prolactin release, resulted in a complete inhibition of vasoactive intestinal peptide-stimulated NGF secretion in vitro, whereas the specific D2 antagonist (-)-sulpiride stimulated NGF secretion in vivo, suggesting that the anterior pituitary is a possible source of circulating NGF. Given the increased NGF serum levels in stressful conditions and the newly recognized immunoregulatory function of this protein, NGF, together with prolactin, may thus be envisaged as an immunological alerting signal under neuronal control.

Colocalization of NGF and TSH-like immunoreactivity in cultures of adult rat anterior pituitary cells

Nerve growth factor (NGF) has been well-characterized with respect to its role as a trophic agent for various peripheral nervous system (PNS) and central nervous system (CNS) neuronal populations. Recent evidence indicates that NGF may also play a functional role in endocrine systems, although investigations in this field are only beginning to define sites of action and molecular mechanisms involved in NGF-endocrine interactions. A potential site for such an interaction to occur is within the pituitary. Previous investigations have demonstrated the presence of NGF and NGF receptors in the pituitary and our group has recently reported the presence of NGF-like immunoreactivity exclusively within the thyrotrophic cells of the anterior pituitary of the adult rat. Since many questions regarding how NGF interacts in the anterior pituitary will be more efficiently addressed using an in vitro system, it was necessary to first determine if cultured adult anterior pituitary cells retain the NGF-like staining and unique association of NGF with thyroid-stimulating hormone-producing cells seen in vivo. Results of the present investigation confirm that cultured anterior pituitary cells retain the characteristics previously observed in vivo and further demonstrate the stability of these cells and their specific NGF and pituitary hormone contents in culture for as long as 6 days.

Emotional stress induced by parachute jumping enhances blood nerve growth factor levels and the distribution of nerve growth factor receptors in lymphocytes

We examined the plasma nerve growth factor (NGF) level and the distribution of NGF receptors in peripheral lymphocytes of young soldiers (mean age, 20-24 yr) experiencing the thrill of a novice about to make their first parachute jumps. Blood was collected from soldiers who knew they were selected to jump (n = 26), as well as from soldiers who knew they were not selected (n = 17, controls). The former group was sampled the evening before the jump and 20 min after landing. Compared with controls, NGF levels increased 84% in prejump and 107% in postjump sampling. Our studies also showed that the increase of NGF levels preceded the increase of plasma cortisol and adrenocorticotropic hormone. No changes in the baseline levels of circulating interleukin 1 beta or tumor necrosis factor were found, suggesting that the increased levels of NGF were not correlated with change in these cytokines. Moreover, immunofluorescence analysis demonstrated that parachuting stress enhances the distribution of low-affinity p75LNGFR and high-affinity p140trkA NGF receptors in circulating peripheral blood mononuclear cells. These observations suggest that the release of NGF might be involved in the activation of cells of the immune system and is most probably associated with homeostatic adaptive mechanisms, as previously shown for stressed rodents.

Regional CNS uptake of blood-borne nerve growth factor

Nerve growth factor (NGF), in addition to being a neurotrophic substance, has effects on the endocrine and immune systems. For example, intravenous injection of NGF results in a cascade of events leading to an increase in glucocorticoid secretion. While this response appears to be mediated centrally, there has been no evidence that circulating NGF has access to the CNS. Using intravenous injections of 125I-NGF, we find specific uptake at 1 hr but none at 6 hr, into homogenates of the basal forebrain, cerebellum, frontal cortex, hippocampus, and olfactory bulb. By autoradiography, uptake is localized to circumventricular organs, deep layers of the cerebellum, and all layers of the hippocampal region CA1, but not the dentate gyrus. Thus, uptake of blood-borne NGF could affect the hypothalamic-pituitary-adrenal axis via binding to NGF receptors present in the hippocampus. However, the sources of endogenous NGF, the mechanism of access through the blood-brain barrier, the eventual fate of NGF entering from the blood, and the physiological significance of this uptake remain to be elucidated.

Selective processing of submandibular rat 1 protein at dibasic cleavage sites. Salivary and bloodstream secretion products

The amino acid sequence of submandibular rat 1 (SMR1) protein, deduced from its cDNA sequence, led to the prediction that the SMR1 gene encodes a hormone-like precursor [Rosinski-Chupin, I., Tronik, D. & Rougeon, F. (1988) Proc. Natl Acad. Sci. USA 85, 8553-8557]. SMR1 contains an N-terminal putative secretory signal sequence and a tetrapeptide (QHNP), located between dibasic amino acids which constitute the most common signal for prohormone processing. We have isolated and characterized from the male rat submandibular gland and its secretions three structurally related peptides, namely an undecapeptide (VRGPRRQHNPR), a hexapeptide (RQHNPR) and a pentapeptide (QHNPR) generated from SMR1 by selective proteolytic cleavages at pairs of arginine residues. The biosynthesis of these peptides is subjected to distinct regulatory pathways depending on the organ, sex and age of the rat. Furthermore, the peptides are differentially distributed in the submandibular gland and in resting or epinephrine-elicited submandibular salivary secretions, suggesting distinct proteolytic pathways for their maturation. The undecapeptide is generated in the gland of both male and female rats, but under basal conditions it is only released into the saliva in male animals. The hexapeptide is produced in large amounts in the gland of adult male rats and released into the saliva in both resting and stimulated conditions. The pentapeptide appears only in the male saliva and is present mostly under stimulated conditions. In addition, administration of epinephrine induces the release of the hexapeptide from the submandibular gland into the bloodstream. The evidence indicates that the rat submandibular gland can function as a dual exocrine and endocrine organ for the SMR1-derived hexapeptide, as has been reported for nerve growth factor, epidermal growth factor, renin and kallikrein. Although the biological activities of the SMR1-derived peptides are not yet known, their high production and adrenergic-induced release only into the saliva and bloodstream of adult male rats, suggest a physiological involvement in some male-specific processes.

Expression and localization of hepatocyte growth factor in rat submandibular gland

By combination of in situ hybridization and immunohistochemical techniques, the expression of hepatocyte growth factor (HGF) was demonstrated in the submandibular gland of rats. Both the mRNA signal and immunoreactivity for HGF were localized exclusively to the epithelial cells of granular convoluted tubules, whereas they were absent from the other components of the submandibular gland. In the granular convoluted tubule cells, HGF-immunoreactivity was localized to the apical secretory granules, which was further substantiated by immunoelectron microscopy. These results added HGF to the list of many growth factors that are produced in the rat submandibular gland and secreted into the saliva.

Nerve growth factor and autoimmune diseases

The initiation of a humoral immune response to a foreign antigen is a complex biologic process involving the interaction of many cell types and their secreted products. Autoimmune diseases, which are characterized by an abnormal activation of the immune system, probably result from the failure of normal self-tolerance mechanisms. The etiology of such illnesses, however, is far from being understood. While there have been extensive studies on the participation of the immune and endocrine systems in autoimmune diseases, few have dealt with nervous system-mediated immunoregulation in such situations. Evidence continues to grow suggesting that nerve growth factor (NGF), first identified for its activity in promoting the growth and differentiation of sensory and sympathetic neurons, may exert a modulatory role on neuroimmunoendocrine functions of vital importance in the regulation of homeostatic processes. Newly detected NGF-responsive cells belong to the hemopoietic-immune system and to populations in the brain involved in neuroendocrine functions. NGF levels are elevated in a number of autoimmune states, along with increased accumulation of mast cells. NGF and mast cells both appear to be involved in neuroimmune interactions and tissue inflammation. Moreover, mast cells themselves synthesize, store, and release NGF, proposing that alterations in normal mast cell behaviors may provoke maladaptive neuroimmune tissue responses whose consequences could have profound implications in inflammatory disease states, including those of an autoimmune nature. This review focuses on these cellular events and presents a working model which attempts to explain the close interrelationships of the neuroendocrinoimmune triade via a modulatory action of NGF.

The granular convoluted tubule (GCT) cell of rodent submandibular glands

The granular convoluted tubule (GCT) is a segment of the duct system of all rodents, situated between the striated and intercalated ducts. It has the peculiar property of synthesizing a large variety of biologically active polypeptides whose role in saliva remains unknown. The literature on the fine structure of GCT cells is critically reviewed. Some recent developments on endocrine regulation of the structure and contents of rodent GCT cells are summarized, with emphasis on EGF, NGF, renin, and kallikrein proteases. A survey of the distribution of GCT cells in several vertebrate families is presented.

Developmental changes in nerve growth factor level in rat serum

In serum, nerve growth factor (NGF) forms a complex with alpha 2-macroglobulin (alpha 2M), which formation inhibits the immunoreactivity between NGF and its antibodies. For measuring the serum level of NGF, it is thus necessary to liberate NGF from the NGF-alpha 2M complex and prevent reformation of such complex. The pretreatment of rat serum with 1 M guanidine hydrochloride for a few hours and operation of the enzyme immunoassay (EIA) in the presence of guanidine hydrochloride provided a reliable means for determination of the NGF level in serum. By this procedure we followed the serum NGF level in rats developmentally. It increased from prenatal day 2 to postnatal day 5 and decreased slightly at postnatal week 3, thereafter remaining constant throughout adulthood. In pregnant rats, the NGF level in serum increased threefold to fivefold before birth and then decreased rapidly. These data suggest that serum NGF level may reflect the demand for this molecule during establishment of the peripheral nervous system.

Two-site enzyme immunoassay for beta NGF applied to human patient sera

Nerve growth factor (NGF) supports sympathetic and sensory neurons in the peripheral nervous system and serves functions in the development and maintenance of cholinergic neurons in the basal forebrain. NGF distribution can be studied with the use of a sensitive two-site enzyme immunoassay (EIA). The monoclonal antibody 27/21 to mouse NGF was recently shown to effectively block the activity of both recombinant human NGF and native mouse NGF, and a two-site EIA using monoclonal antibody 27/21 was optimized. We have now applied this assay to examine NGF levels in normal human serum and serum from Parkinson, Alzheimer, and Huntington patients. To further test the specificity of conjugate binding, dilutions of the human sera were preincubated with an excess of monoclonal NGF antibody 27/21 in solution. With this strategy it was possible to completely block the signal obtained using the two-site EIA. Furthermore, we show that recombinant BDNF and NT-3 do not cross-react with monoclonal antibody 27/21 under our conditions. We found low levels of specific NGF immunoreactivity in normal human sera (0.4 +/- 0.1 ng/ml). Significantly lower levels of NGF were found in sera from patients with Parkinson's and Huntington's disease whereas sera from Alzheimer patients showed only slight reductions in the NGF level. Two patients who had received intracerebral NGF infusions (one with Parkinson's and other with Alzheimer's disease) showed significantly elevated serum levels of NGF during the period of infusion. Due to an inhibitory activity in human serum, it was impossible to demonstrate the low levels of NGF activity in the human serum samples using explanted embryonic sympathetic ganglia, even after concentration by pressure dialysis. Thus, the serum levels are below the limit to evoke a response in NGF-sensitive neurons and thus to expect any physiological effect. Nevertheless, the levels measured may be used as indicators in clinical conditions such as Parkinson's and Huntington's disease.

Control of growth and differentiation of the mammary gland by growth factors

Mammary gland development is a complex process regulated by various steroid and polypeptide hormones. Although the systemic importance of hormones, such as estrogen, progesterone, prolactin, and growth hormone, in the growth of the mammary gland has been well documented, these hormones are virtually incapable of stimulating mammary cell growth in vitro. Thus, the growth stimuli for mammary cells requires clarification. In recent years, a number of growth factors have been discovered; this has prompted interest in examining possible involvement of these biologically active agents in the process of mammary gland development. Results presented herein indicate that several growth factors including epidermal growth factor, transforming growth factor alpha and beta, basic fibroblast growth factor, insulin-like growth factor-I, and mesenchyme-derived growth factor participate in the regulation of mammary cell growth and differentiation.

Nerve growth factor-like activity detected in equine peripheral blood after running exercise

Addition of sera, collected from Thoroughbred horses after sprint exercise, induced significant neurite outgrowth from chick embryo dorsal root ganglia after a 24-hour culture. The nerve growth factor (NGF)-like activity was detected in sera collected immediately, or 1 hour or more, after the exercise. These findings suggest a possible role of serum NGF-like activity under stress conditions (running exercise) of horses.

Hyperalgesia induced in the rat by the amino-terminal octapeptide of nerve growth factor

Nerve growth factor (NGF) in the mouse submandibular gland undergoes cleavage of its amino-terminal octapeptide when salivation is induced by epinephrine. The significance of this event is uncertain; cleaved NGF demonstrates bioactivity and no function has been attributed to the octapeptide produced (NGF-OP; Ser-Ser-Thr-His-Pro-Val-Phe-His). Enzyme inhibition studies indicating structural relatedness of NGF-OP and bradykinin (BK) prompted us to determine whether NGF-OP would elicit BK-like actions. We found that like BK, NGF-OP induced a decrease in mechanical nociceptive threshold (i.e., produced hyperalgesia) in the hairy skin of the rat. This effect was dose-dependent and sequence-specific; like BK it was attenuated by sympathectomy and indomethacin pretreatment. However, NGF-OP actions appeared to be distinct from those for BK in that tissue injury was required for NGF-OP to induce hyperalgesia. Furthermore, we found no evidence that NGF-OP bound to or activated BK receptors. Our data indicate that NGF-OP is a distinct mediator of hyperalgesia. We suggest that NGF-OP alters pain threshold in the injured target regions of NGF-responsive neurons.

Structure and biosynthesis of nerve growth factor

Most of our knowledge about NGF comes from extensive study of the mouse submaxillary gland protein. NGF from this source is isolated as a high molecular weight complex consisting of beta-NGF and two subunits, alpha and gamma, belonging to the kallikrein family of serine proteases. There are few other tissues where NGF is found in sufficient quantities for protein purification and study, although new molecular biological techniques have accelerated the study of NGFs from a variety of species and tissues. Mouse submaxillary gland NGF is synthesized as a large precursor that is cleaved at both N- and C-terminals to produce mature NGF. This biologically active molecule can be further cleaved by submaxillary gland proteases. The roles of the alpha and gamma subunits in the processing of the beta-NGF precursor, the modulation of the biological activity of beta-NGF, and the protection of mature beta-NGF from degradation have been well studied in the mouse. However, the apparent lack of alpha and gamma subunits in most other tissues and species and the existence of a large family of murine kallikreins, many of which are expressed in the submaxillary gland, challenge the relevance of murine high molecular weight NGF as a proper model for NGF biosynthesis and regulation. It is important therefore to identify and characterize other NGF complexes and to study their subunit interactions, biosynthesis, processing, and regulation. This review points out a number of other species and tissues in which the study of NGF has just begun. At this time, there exist many more questions than answers regarding the presence and the functions of NGF processing and regulatory proteins. By studying NGF in other species and tissues and comparing the processing and regulation of NGF from several sources, we will discover the unifying concepts governing the expression of NGF biological activity.

The gene encoding SMR1, a precursor-like polypeptide of the male rat submaxillary gland, has the same organization as the preprothyrotropin-releasing hormone gene

SMR1 is a precursor-like polypeptide of the submaxillary glands of rats. Sequence analysis predicts that it could be processed by maturation enzymes to release a small peptide resembling the thyrotropin-releasing hormone. The SMR1 gene was isolated from a rat genomic library and sequenced. The SMR1 gene spans 4.7 kb and consists of three exons. The two introns occur a few nucleotides before the initiation codon in the 5' untranslated region, and a few nucleotides before the first predicted processing site, respectively. Such a structure is reminiscent of that of the preprothyrotropin-releasing hormone gene. The site of transcriptional initiation of the SMR1 gene was determined and 1.4 kb of 5'-flanking sequence was sequenced. The sequence analysis revealed the presence of alternating purine-pyrimidine tracts and of purine-rich sequences. In addition, some sequences which could be involved in the regulation of SMR1 gene expression were identified.

Nerve growth factor and neuronal cell death

The regulation of neuronal cell death by the neuronotrophic factor, nerve growth factor (NGF), has been described during neural development and following injury to the nervous system. Also, reduced NGF activity has been reported for the aged NGF-responsive neurons of the sympathetic nervous system and cholinergic regions of the central nervous system (CNS) in aged rodents and man. Although there is some knowledge of the molecular structure of the NGF and its receptor, less is known as to the mechanism of action of NGF. Here, a possible role for NGF in the regulation of oxidant--antioxidant balance is discussed as part of a molecular explanation for the known effects of NGF on neuronal survival during development, after injury, and in the aged CNS.

125I-beta-nerve growth factor binding is reduced in rat brain after stress exposure

In the central nervous system (CNS), the presence of nerve growth factor (NGF) and its receptor, NGFR, in cholinergic neurons has been demonstrated. In this study we report that, after exposure to stress, there was a reduction in total binding of NGF in the hippocampus and basal forebrain of 3.5-month-old rats without significant changes in the frontal cortex or cerebellum. Chronic treatment with acetyl-l-carnitine (ALCAR), that prevents some age-related impairments of CNS, for 1.5 months, decreased NGF binding in hippocampus and basal forebrain but abolished the stress-related reduction of NGF binding observed in the hippocampus of untreated rats.

Social status and nerve growth factor serum levels after agonistic encounters in mice

Ten repeated daily interactions (20 min each) of the same pairs of isolated male mice produced a clear distinction between attacking (dominant) and defeated (subordinate) animals. The fighting level remained fairly constant over the 10 days. One hr after the end of the 10th session, the increase in serum NGF levels described previously (2) was significantly more marked in subordinate than in dominant mice. The mean level of serum NGF was correlated with the number of fighting episodes, particularly in the case of dominant individuals. Moreover, within-pair differences in NGF values were correlated with differences in locomotor activity between dominants and subordinates; this makes it possible that stimuli other than those produced by fighting per se may be responsible for the increase in circulating NGF. As is well known, the adrenal hypertrophy produced by fighting stress is more marked in subordinate than in dominant mice, while previous work has shown that stress of a nonpsychosocial kind does not elevate serum NGF levels. Therefore, the present data support the hypothesis that NGF release contributes to the modulation of adrenal function in a situation-specific fashion.