Receptors for nerve growth factor on rat spleen mononuclear cells

Whole transcriptome analysis of multiple Sclerosis patients reveals active inflammatory profile in relapsing patients and downregulation of neurological repair pathways in secondary progressive cases

BACKGROUND

Multiple sclerosis (MS) is an inflammatory autoimmune neurologic disease that causes progressive destruction of myelin sheath and axons. Affecting more than 2 million people worldwide, MS may presents distinct clinical courses. However, information regarding key gene expression and genic pathways related to each clinical form is still limited.

OBJECTIVE

To assess the whole transcriptome of blood leukocytes from patients with remittent-recurrent (RRMS) and secondary-progressive (SPMS) forms to explore the gene expression profile of each form.

METHODS

Total RNA was obtained and sequenced in Illumina HiSeq platform. Reads were aligned to human genome (GRCh38/hg38), BAM files were mapped and differential expression was obtained with DeSeq2. Up or downregulated pathways were obtained through Ingenuity IPA. Pro-inflammatory cytokines levels were also assessed.

RESULTS

The transcriptome was generated for nine patients (6 SPMS and 3 RRMS) and 5 healthy controls. A total of 731 and 435 differentially expressed genes were identified in SPMS and RRMS, respectively. RERE, IRS2, SIPA1L1, TANC2 and PLAGL1 were upregulated in both forms, whereas PAD2 and PAD4 were upregulated in RRMS and downregulated in SPMS. Inflammatory and neuronal repair pathways were upregulated in RRMS, which was also observed in cytokine analysis. Conversely, SPMS patients presented IL-8, IL-1, Neurothrophin and Neuregulin pathways down regulated.

CONCLUSIONS

Overall, the transcriptome of RRMS and SPMS clearly indicated distinct inflammatory profiles, where RRMS presented marked pro-inflammatory profile but SPMS did not. SPMS individuals also presented a decrease on expression of neuronal repair pathways.

Sympathetic innervation regulates macrophage activity in rats with polycystic ovary

Polycystic ovarian syndrome (PCOS) is a low-grade inflammatory disease characterized by hyperandrogenism and ovarian hyperinnervation. The aim of this work is to investigate whether in vivo bilateral superior ovarian nerve (SON) section in adult rats with estradiol valerate-induced PCOS (PCO rats) affects macrophage spleen cells (MФ) and modifies the steroidogenic ability of their secretions. Culture media of MФ from PCO rats and PCO rats with SON section (PCO-SON rats) were used to stimulate in vitro intact ovaries. Compared with macrophages PCO, macrophages from PCO-SON rats released less tumor necrosis factor-α and nitric oxide, expressed lower Bax and Nfkb mRNA and showed reduced TUNEL staining. Also, in PCO rats, the SON section decreased kisspeptin and nerve growth factor mRNA expressions, without changes in Trka receptor mRNA levels. Macrophage secretions from PCO-SON rats decreased androstenedione and stimulated progesterone release in PCO ovaries, compared to macrophage secretions from PCO rats. No changes were observed in ovarian estradiol response. These findings emphasize the importance of the SON in spleen MΦ, since its manipulation leads to secondary modifications of immunological and neural mediators, which might influence ovarian steroidogenesis. In PCO ovaries, the reduction of androstenedione and the improvement of progesterone release induced by PCO-SON MΦ secretion, might be beneficial considering the hormonal anomalies characteristic of PCOS. We present functional evidence that modulation of the immune-endocrine function by peripheral sympathetic nervous system might have implications for understanding the pathophysiology of PCOS.

NGF and Its Receptors in the Regulation of Inflammatory Response

There is growing interest in the complex relationship between the nervous and immune systems and how its alteration can affect homeostasis and result in the development of inflammatory diseases. A key mediator in cross-talk between the two systems is nerve growth factor (NGF), which can influence both neuronal cell function and immune cell activity. The up-regulation of NGF described in inflamed tissues of many diseases can regulate innervation and neuronal activity of peripheral neurons, inducing the release of immune-active neuropeptides and neurotransmitters, but can also directly influence innate and adaptive immune responses. Expression of the NGF receptors tropomyosin receptor kinase A (TrkA) and p75 neurotrophin receptor (p75NTR) is dynamically regulated in immune cells, suggesting a varying requirement for NGF depending on their state of differentiation and functional activity. NGF has a variety of effects that can be either pro-inflammatory or anti-inflammatory. This apparent contradiction can be explained by considering NGF as part of an endogenous mechanism that, while activating immune responses, also activates pathways necessary to dampen the inflammatory response and limit tissue damage. Decreases in TrkA expression, such as that recently demonstrated in immune cells of arthritis patients, might prevent the activation by NGF of regulatory feed-back mechanisms, thus contributing to the development and maintenance of chronic inflammation.

Noni (Morinda citrifolia L.) fruit juice reverses age-related decline in neural-immune interactions in the spleens of old F344 rats

ETHNOPHARMACOLOGICAL RELEVANCE

Various parts of the tropical plant, Morinda citrifolia L. (Noni), have been widely used in traditional medicine in South and Southeast Asia for several centuries. The therapeutic effects of the noni are believed to be mediated through several phytochemicals such as anthraquinones, iridoid, fatty acid glycosides, alcohols, etc.

AIM OF THE STUDY

The aim of the study is to investigate the effects of Morinda citrifolia fruit juice (noni fruit juice; NFJ) on neural-immune interactions through the involvement of intracellular signaling pathways both in vitro and in vivo in the splenic lymphocytes of young and old male F344 rats.

MATERIAL AND METHODS

In the in vitro study, splenocytes from young and old F344 rats were isolated and treated with 0.0001-1% concentrations of NFJ for a period of 24h, while in the in vivo study, old F344 rats were orally administered (5ml/kg body weight) with NFJ (5%, 10% and 20%) twice daily for 60 days. After the treatment period, concanavalin A (Con A)-induced lymphocyte proliferation, cytokines (IL-2, IFN-γ, IL-6, and TNF-α) production, expression of tyrosine hydroxylase (p-TH), nerve growth factor (NGF), m-TOR, IκB-α, p-NF-κB (p50 and p65), p-ERK, p-Akt, p-CREB and lipid peroxidation, protein carbonyl formation, nitric oxide (NO) production were examined in the splenocytes.

RESULTS

In vitro NFJ incubation of splenic lymphocytes increased Con A-induced lymphocyte proliferation, IL-2 and IFN-γ production, and expression of p-ERK, p-Akt, and p-CREB in young and old rats. In vivo treatment of old rats with NFJ increased lymphoproliferation, IL-2 and IFN-γ production, the expression of p-TH, NGF, and NO production, and suppressed IL-6 production, lipid peroxidation, protein carbonyl formation, and the expression of IκB-α and p-NF-κB (p50) in the splenocytes.

CONCLUSION

Taken together, these results suggest that Morinda citrifolia fruit juice enhanced neural-immune interactions and cell survival pathways while inhibiting inflammatory processes that may be useful in the treatment of age-associated diseases.

Nerve growth factor: from the early discoveries to the potential clinical use

The physiological role of the neurotrophin nerve growth factor (NGF) has been characterized, since its discovery in the 1950s, first in the sensory and autonomic nervous system, then in central nervous, endocrine and immune systems. NGF plays its trophic role both during development and in adulthood, ensuring the maintenance of phenotypic and functional characteristic of several populations of neurons as well as immune cells. From a translational standpoint, the action of NGF on cholinergic neurons of the basal forebrain and on sensory neurons in dorsal root ganglia first gained researcher's attention, in view of possible clinical use in Alzheimer's disease patients and in peripheral neuropathies respectively. The translational and clinical research on NGF have, since then, enlarged the spectrum of diseases that could benefit from NGF treatment, at the same time highlighting possible limitations in the use of the neurotrophin as a drug. In this review we give a comprehensive account for almost all of the clinical trials attempted until now by using NGF. A perspective on future development for translational research on NGF is also discussed, in view of recent proposals for innovative delivery strategies and/or for additional pathologies to be treated, such as ocular and skin diseases, gliomas, traumatic brain injuries, vascular and immune diseases.

The nerve growth factor reduces APOBEC3G synthesis and enhances HIV-1 transcription and replication in human primary macrophages

Macrophages infected with HIV-1 sustain viral replication for long periods of time, functioning as viral reservoirs. Therefore, recognition of factors that maintain macrophage survival and influence HIV-1 replication is critical to understanding the mechanisms that regulate the HIV-1-replicative cycle. Because HIV-1-infected macrophages release the nerve growth factor (NGF), and NGF neutralization reduces viral production, we further analyzed how this molecule affects HIV-1 replication. In the present study, we show that NGF stimulates HIV-1 replication in primary macrophages by signaling through its high-affinity receptor Tropomyosin-related Kinase A (TrKA), and with the involvement of reticular calcium, protein kinase C, extracellular signal-regulated kinase, p38 kinase, and nuclear factor-κB. NGF-induced enhancement of HIV-1 replication occurred during the late events of the HIV-1-replicative cycle, with a concomitant increase in viral transcription and production. In addition, NGF reduced the synthesis of the cellular HIV-1 restriction factor APOBEC3G and also overrode its interferon-γ-induced up-regulation, allowing the production of a well-fitted virus. Because NGF-TrKA signaling is a crucial event for macrophage survival, it is possible that NGF-induced HIV-1 replication plays a role in the maintenance of HIV-1 reservoirs. Our study may contribute to the understanding of the immunopathogenesis of HIV-1 infection and provide insights about approaches aimed at limiting viral replication in HIV-1 reservoirs.

Stress and reactivation of latent herpes simplex virus: a fusion of behavioral medicine and molecular biology

Since 1978, the study of health and behavior has become a major focus of scientists in psychology, psychiatry, nursing, neuroscience, and in traditional medical science disciplines. Investigation of psychological or behavioral influences on biological systems has established that biobehavioral processes such as stress play an important role in disease processes. An excellent example of the interactions between stress and health outcomes is the reactivation of latent herpes simplex virus (HSV) leading to recurrent lesions. This article describes what is currently known about HSV latency and reactivation and considers some mechanisms by which stress-induced changes in the host's immune and nervous systems might allow for either the establishment or reactivation of latent viral infections.

Involvement of growth factors in thymic involution

The thymus undergoes an age-dependent degenerative process which is mainly characterized by a progressive loss of lymphoid tissue. Thymic involution is particularly important in relation to immunosenescence and its various associated diseases; this fact has prompted many studies aimed at understanding the causes and mechanisms of thymic degeneration which may, ultimately, lead to the possibility of manipulating it. In this sense, one of the aspects which has deserved most attention is the thymic microenvironment, and more precisely, the many growth factors to which the cells present in the organ are exposed. Thus, the levels of several of such factors have been reported to undergo age-dependent changes in the thymus, which may point at an influence on the regression of the organ. In this article we consider which growth factors and growth factor receptors occur in the vertebrate thymus. Then, focusing on those whose influences are better documented, i.e., neurotrophins, cytokines and IGFs, we discuss their potential role in the organ and the possibility of their being involved in thymic involution.

Schwann cell apoptosis in the postnatal axotomized sciatic nerve is mediated via NGF through the low-affinity neurotrophin receptor

Schwann cell death is a developmentally regulated phenomenon and is also induced after peripheral nerve axotomy in neonatal rodents. In this study, we explored whether ligand-induced activation of the low-affinity neurotrophin receptor (p75(NTR)) is responsible for inducing Schwann cell death in vivo. Administration of exogenous nerve growth factor (NGF) to the axotomized nerve site in wild-type animals resulted in a 2.6-fold increase in Schwann cell apoptosis in the distal nerve stumps compared to axotomy alone. No increase in apoptosis, above baseline levels, was seen in p75(NTR)-mutant mice either with or without NGF When anti-NGF antibodies were administered to the site of the peripheral nerve lesion in wild-type mice there was a reduction in the percentage of Schwann cell apoptosis to levels seen in both the quiescent state and in the axotomized nerves of the p75(NTR)-mutant mice. These results demonstrate that apoptosis of Schwann cells in axotomized peripheral nerve is mediated predominantly through p75(NTR) signaling and initiated via endogenously produced NGF.

CD34-positive cells in human umbilical cord blood express nerve growth factor and its specific receptor TrkA

In this study, we investigated whether hematopoietic stem cells (HSC) and progenitors present in human cord blood can express nerve growth factor (NGF)-specific receptors, TrkA and p75. Our results showed a marked expression of TrkA and NGF in cord blood CD34(+) cells. A gradient of TrkA and NGF expression exists and is highest in cord blood CD34(+) cells, reduced in cord blood mononuclear cells (MNC) and minimal in mononuclear cells isolated from adult peripheral blood. Our findings suggest that NGF may play a role in the differentiation of hematopoietic progenitors and indicate a different requirement for NGF by immune cells, depending on their state of maturity.

Upregulation of TrkA neurotrophin receptor expression in the thymic subcapsular, paraseptal, perivascular, and cortical epithelial cells during thymus regeneration

Neuroimmune networks in the thymic microenvironment are thought to be involved in the regulation of T cell development. Here, we report upon an examination of the expression of the TrkA neurotrophin receptor, the high affinity receptor for nerve growth factor, during regeneration following acute involution induced by cyclophosphamide in the rat thymus. Light and electron microscopic immunocytochemistry demonstrated enhanced expression of the TrkA receptor in the subcapsular, paraseptal, perivascular, and cortical epithelial cells during thymus regeneration. In addition, various morphological alterations, suggestive of a hyperfunctional and dynamic state, of the subcapsular, paraseptal, and perivascular epithelial cells were also observed. The presence of TrkA protein in extracts from the control and regenerating rat thymus was confirmed by western blot. Furthermore, RT-PCR analysis supported these results by demonstrating that thymic extracts contain TrkA mRNA at higher levels during thymus regeneration. Thus, our results suggest that the TrkA receptor located on the thymic subcapsular, paraseptal, perivascular, and cortical epithelial cells could play a role in the development of new T cells to replace T cells damaged during thymus regeneration.

NGF modulates CGRP synthesis in human B-lymphocytes: a possible anti-inflammatory action of NGF?

We investigated whether the sensory neuropeptide, calcitonin gene-related peptide (CGRP), could be synthesised by human lymphocytes. Our results indicate that in activated B-cells, there is a strong expression of CGRP gene transcripts, which is almost absent in resting cells. Since B-cells autocrinally produce NGF, the neutralisation of endogenous NGF by anti-NGF antibodies resulted in a marked reduction in CGRP expression in both resting and activated B-cells. Thus, NGF appears to directly affect the synthesis of CGRP in B-cells as in sensory neurons. By regulating CGRP synthesis in lymphocytes and neuronal cells, NGF can influence the intensity and duration of the immune response.

Treatment of experimental autoimmune encephalomyelitis with antisense oligonucleotides against the low affinity neurotrophin receptor

Upregulated expression of the low-affinity neurotrophin receptor (p75) in the central nervous system (CNS) during experimental autoimmune encephalomyelitis (EAE) has recently been demonstrated. To investigate whether p75 plays a role in disease pathogenesis, we adopted a gene therapy approach, utilizing antisense oligonucleotides to downregulate p75 expression during EAE. Phosphorothioate antisense oligonucleotides (AS), nonsense oligonucleotides (NS) or phosphate buffered saline (PBS) were injected daily for 18 days after immunization of SJL/J (H-2s)-mice with myelin proteolipid protein (PLP) peptide 139-151. In the AS group, there was a statistically significant reduction in both the mean maximal disease score (1.85 in the AS, 2.94 in the NS and 2.75 in the PBS-groups, respectively, P < 0.025) and in the cumulative disease incidence ( approximately 60% in the AS group and approximately 90% in the control groups). Histological and immunohistochemical analysis showed reduced inflammation and demyelination, as well as reduced p75 expression at the blood-brain barrier (BBB) in the AS-treated mice in comparison with both control groups. There was no difference, however, in p75 expression on neural cells within the CNS between the three groups of mice. We conclude that p75 could play a proactive role in the pathogenesis of EAE and may exert its effect at the level of the BBB.

Effects of L-deprenyl treatment on noradrenergic innervation and immune reactivity in lymphoid organs of young F344 rats

Sympathetic noradrenergic (NA) neuronal activities in the thymus, spleen and mesenteric lymph nodes (MLN) and immune responses in the spleen were examined in young male F344 rats treated daily with 0, 0.25 mg, or 2.5 mg/kg body weight of L-deprenyl, an irreversible monoamine oxidase-B (MAO-B) inhibitor. Rats were treated daily for 1, 15, or 30 days, and sacrificed 7 days after the last deprenyl treatment. Deprenyl treatment increased norepinephrine (NE) content in the spleen without modifying the pattern and density of NA innervation in the splenic white pulp. The concentration of NE was unaltered in the thymus, but it was increased in the MLN of deprenyl-treated rats. One day of treatment with deprenyl decreased splenic NK cell activity while 15 days of deprenyl treatment enhanced splenic NK cell activity. Deprenyl elevated Con A-induced T lymphocyte proliferation following 30 days of treatment, but did not alter spleen cell Con A-induced IL-2 production or the percentage of CD5 + T cells in the spleen. A moderate decrease in the percentage of sIgM + B cells was observed in the spleens of 15- and 30-day deprenyl-treated rats. These results suggest that deprenyl has sympathomimetic action on sympathetic NA nerve fibers in the spleen; the enhancement of NA neuronal activity may contribute to the modulation of immune responses in the spleen.

L-deprenyl-induced increase in IL-2 and NK cell activity accompanies restoration of noradrenergic nerve fibers in the spleens of old F344 rats

Previously, we have hypothesized a causal relationship between some measures of immunosenescence and the age-related decline in sympathetic noradrenergic (NA) nerve fibers in spleen and lymph nodes of F344 rats. In the present study, we investigated this interrelationship further by measuring NK cell activity, Con A-induced IL-2 production, norepinephrine (NE) concentration, and morphological localization of NA and neuropeptide-Y (NPY) nerve fibers in the spleens of old (21 months old) male F344 rats after 10 weeks of daily treatment with low doses of L-deprenyl, an irreversible monoamine oxidase-B inhibitor, followed by a 9-day wash-out period. NK cell activity and Con A-induced IL-2 production were increased in deprenyl-treated old rats in comparison to untreated and saline-treated old rats. Deprenyl treatment did not alter the percentage of CD5+ T-cells, but moderately increased the percentage of sIgM+ B-cells in the spleens of old rats. In addition to changes in immune responses, NE content and the volume density of NA and NPY nerve fibers were partially augmented in the spleens of deprenyl-treated old rats. In a separate study, various concentrations of deprenyl were added in vitro to spleen cells from young and old F344 rats to examine the direct effects of the drug on Con A-induced IL-2 production. In contrast to in vivo treatment, in vitro addition of deprenyl did not alter the Con A-induced IL-2 production by splenocytes from old rats. Together, these results suggest that the ability of deprenyl to enhance certain immune responses are interlinked to the restoration of sympathetic NA and NPY nerve fibers in the spleens of old rats.

Overstimulation of nerve growth factors in postinfectious and autoimmune diseases

Nerve growth factor (NGF) in cerebrospinal fluid was measured by ELISA in ten children with postinfectious diseases and in five children with diseases suggested to be of autoimmune etiology. Three groups of patients were studied: (1) those with moderately elevated concentrations (50.67 +/- 17.02 pg/mL, mean and SEM), (2) those with high concentrations (mean 424.25 +/- 125.41 pg/mL, mean and SEM), and (3) those with enormously high concentrations (mean 2,745 +/- 1,819.46 pg/mL, mean and SEM). We suggest that CSF-NGF could be used as an immunologic marker of an ongoing CNS process. Uncontrolled signaling of NGF receptors may lead to long-term inflammatory and autoimmune responses, which in turn can lead to disease.

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.

Nerve growth factor enhances antigen-specific antibody production in ascorbate-stimulated murine splenocytes

In murine splenocytes, a primary antigen-specific antibody response is stimulated by 2-O-alpha-D-glucopyranosyl-L-ascorbic acid (AA-2G), a stable form of ascorbate, as described in our previous paper. We examined here the effect of nerve growth factor (NGF) on the antigen-specific antibody production in vitro augmented by AA-2G. NGF (> or = 10 ng/ml), which alone had no effect, enhanced the anti-sheep-red-blood-cell (SRBC) antibody response stimulated by AA-2G. The effect of NGF plus AA-2G or AA-2G alone was abrogated by the presence of castanospermine, an alpha-glucosidase inhibitor, suggesting that the active form of AA-2G is ascorbate. The repeated additions; but not one addition, of ascorbate also resulted in a synergism with NGF on the antibody production. These results suggest that NGF might be a cytokine which functions as a regulatory factor for ascorbate-dependent immune responses.

Effects of nerve growth factor on splenic norepinephrine and pineal N-acetyl-transferase in neonate rats exposed to alcohol in utero: neuroimmune correlates

Prenatal alcohol exposure (FAE) has been associated with multiple anomalies, including a selective developmental delay of sympathetic innervation in lymphoid organs. Sympathetic neurons require nerve growth factor (NGF) for their development and maintenance, and recent evidence has suggested that alcohol impairs the synthesis and/or biological activity of NGF in selected central and peripheral neurons. Thus, the present study examined the hypothesis that NGF administration to FAE rats during early postnatal development would reverse some of the peripheral sympathetic deficits. Neonate rats, FAE and the corresponding control cohorts, received daily treatments of NGF or cytochrome C (0.3 mg/kg; s.c.) for various time intervals, and were killed 24 hr or 10 days after the last treatment. The measured parameters included norepinephrine (NE) concentrations in the spleen and heart, which receive nor-adrenergic innervation from the coeliac ganglion and the superior cervical ganglion (SCG), respectively. In addition, we measured the activity of pineal N-acetyltransferase (NAT), the rate-limiting enzyme of melatonin biosynthesis, which depends on sympathetic innervation from the SCG. The data show that chronic, but not acute, NGF treatments reversed the FAE-related deficits in splenic NE concentrations as well as in pineal NAT activity in a time- and age-dependent manner. Sympathetic neurons play an important role in immune modulation. Thus, the altered splenic NE levels and pineal NAT activity may play a role in immune deficits associated with exposure to alcohol in utero.

Nerve growth factors from snake venoms: chemical properties, mode of action and biological significance

An overview of nerve growth factors (NGF) and their receptor system is presented. This general introduction deals with mouse and human NGF, since most of the fundamental knowledge is based on these mammalian proteins. Great emphasis is laid on the nonneuronal NGF effects which are well discussed for their possible toxinological function. The snake venom NGFs were reviewed with respect to their purification, classification and properties. From the date of their discovery about 40 years ago, researchers have been interested in the possible function of mouse salivary and snake venom NGFs. The physiological relevance of snake venom NGF is therefore widely discussed on the base of experimental facts and hypothetical considerations.

Nerve growth factor from the venom of the Chinese cobra Naja naja atra: purification and description of non-neuronal activities

Nerve growth factor (NGF) was separated from crude Naja naja atra venom by using weak cation-exchange chromatography, followed by reversed-phase liquid chromatography. The yield of the purification was 0.2-0.5% (w/w). The mol. wt was determined to be 13,600 and the protein still induced the typical fibre outgrowth of cultured PC-12 cells in a concentration range of 5-10 ng/ml. Beside this neuronal effect we demonstrated non-neuronal effects of cobra venom NGF, such as induction of plasma extravasation and histamine release from whole blood cells. With human leucocyte preparations, including enriched basophils, there was an increase in C5a-induced histamine release, whereas NGF alone was inactive. Cobra NGF was one-tenth as potent as human recombinant NGF, with a half-maximal stimulation occurring at 10 ng/ml. Cobra NGF and human recombinant NGF showed a modulatory effect on histamine release comparable to the haematopoietic growth factor IL-3. Thus, the non-neuronal effects of cobra NGF may account for immunomodulatory activities during inflammatory events.

Expression of mRNA encoding neurotrophins and neurotrophin receptors in rat thymus, spleen tissue and immunocompetent cells. Regulation of neurotrophin-4 mRNA expression by mitogens and leukotriene B4

The expression of neurotrophin and neurotrophin receptor mRNAs was examined using RNase protection assays and Northern-blot analysis in rat thymus, spleen tissue and immunocompetent mononuclear cells purified from these two organs. Nerve growth factor, brain-derived neurotrophic factor, neurotrophin-3 and neurotrophin-4 mRNAs were all expressed in thymus and spleen tissue although at different levels, while immunocompetent cells expressed neurotrophin-3 and neurotrophin-4 mRNAs. Thymus and spleen tissue expressed mRNAs encoding the low-affinity nerve-growth-factor receptor, the non-neuronal TrkA I receptor, the truncated (kinase deficient) and full-length TrkB, and the TrkC receptor. Low-affinity nerve-growth-factor receptor and non-neuronal TrkA I mRNAs were detected in both thymus and spleen immunocompetent cells. In addition, thymus cells expressed neuronal TrkA II mRNA and spleen cells expressed truncated TrkB mRNA. The expression of TrkA I and TrkA II mRNAs was enhanced in both thymus and spleen cells after cell culture. Enhanced levels of neurotrophin-4 mRNA were observed in spleen immunocompetent cells after adrenalectomy. Moreover, the expression of neurotrophin-4 mRNA was up-regulated after stimulation of immune cells with the mitogens concanavalin A or lipopolysaccharide or with the inflammatory mediator leukotriene B4. This suggests that neurotrophin-4 could be secreted by immunocompetent cells and may be involved in inflammatory processes.

Immunology of the testicular excurrent ducts

The sperm autoantigen concentration in the epididymis equals or exceeds that in the testis. This makes the epididymis a probable site of initiation of an antisperm autoimmune response. The mechanisms regulating antisperm antibody formation in the testicular excurrent ducts and some related aspects with clinical interest are reviewed.

NGF retards apoptosis in chick embryo bursal cell in vitro

Recent studies have demonstrated that the action of nerve growth factor (NGF) is not restricted to neuronal cells but also affects cells of the immune system. In a previous work on the effect of NGF on the chick embryo bursa of Fabricius both in vivo and in vitro, we observed that NGF prolongs bursal cell survival in vitro. In the present study we report that the increase of viable cells in NGF-treated cultures is not due to a proliferative effect of NGF on bursal cells but to a reduction of cell mortality. The morphological analysis revealed that bursal cells in cultures die by apoptosis, which was also shown by the typical pattern of DNA fragmentation, a hallmark of this cell death process. It is concluded that NGF, with an action similar to that described in sympathetic neurons and PC12, could retard bursal cell death by influencing apoptosis.

Neuroimmune modulation: signal transduction and catecholamines

In recent years, much interest has centered on the commonalities and bi-directional interactions between the nervous system and the immune system. This review focuses on mechanisms through which, catecholamines, a class of neuro-endocrine molecules, modulate immune functions. Catecholamines can be immune suppressive and inhibit lymphocyte activation of both T and B cells as well as the generation of immune-mediated anti-tumor responses. Some of these catecholamine-regulated activities appear to be modulated through the second messenger, cyclic AMP, whereas others appear to be catecholamine-dependent but cyclic AMP independent. Further delineation of the interacting ligand-receptor complexes, populations of responding cells and signal transduction mechanisms leading to the activation of specifically involved genes and gene products, will lead to enhanced understanding of the integratory functions of the nervous system in immune responses, the biology of stress, the role of stress-associated molecular mechanisms in perturbations of physiological homeostasis and the development of a new biological psychiatry with accompanying rational therapeutic modalities.

Studies on carrageenan-induced arthritis in adult rats: presence of nerve growth factor and role of sympathetic innervation

Recent studies effected by our Institute indicate that various forms of human arthritis express both immunohistochemically and biologically active nerve growth factor (NGF) in the synovium. In the present study, we used a model of carrageenan-induced arthritis to further evaluate the effects of joint inflammation on NGF level. These studies showed that experimentally-induced arthritis in rats caused a significant increase in NGF in the perivascular area of the synovium. We also showed that injection into the synovium of purified NGF did not cause inflammation per se and that the destruction of peripheral sympathetic innervation significantly reduced both the inflammation and the level of NGF following carrageenan injection.

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.

Nerve growth factor receptor gene expression in human peripheral blood lymphocytes in aging

Nerve growth factor (NGF) has a modulating effect on immune function, which may occur as a consequence of binding to the NGF receptor (NGF-R). To determine if mRNA for the gene coding for p75NGFR (low affinity NGF-R) is present in lymphocytes, Northern blot analysis of mRNA from human peripheral blood lymphocytes (PBL) and purified T lymphocytes was initiated using cDNA probe for human p75NGFR. p75NGFR mRNA was present in PBL and T lymphocytes, and the mRNA in response to phytohemagglutinin stimulation showed maximum levels at 14 hr of stimulation. p75NGFR mRNA content when analyzed in PBL and T cells from volunteers of various ages showed that p75NGFR mRNA expression does not change with the age of the cell donor.

Naturally occurring antibodies against nerve growth factor in human and rabbit sera: comparison between control and herpes simplex virus-infected patients

Antibodies against nerve growth factor (NGF) in sera were detected by enzyme-linked immunosorbent assays (ELISA), by their isolation after passage of sera through NGF immunoadsorbent columns and by their specificity to bind and immunoprecipitate mouse NGF as well as to stain by immunohistochemical methods cellular sites of NGF synthesis. Increased levels of anti-NGF antibodies were found in sera of herpes simplex virus (HSV)-infected patients but not in HSV-inoculated rabbits. As HSV latency is known to be promoted by NGF in vitro, these results may suggest that anti-NGF antibodies modulate the cytokine function of NGF and thus might play a role in HSV infection. The biological function of circulating antibodies against NGF, in general, is now open to future investigation.

In vivo and in vitro effect of NGF on bursa of Fabricius cells during chick embryo development

NGF exerts a broader biological action than previously believed. The growing-evidence of NGF's effect on lymphocytes and the presence of high levels of mRNA for NGF receptors in the embryonic bursa of Fabricius led us to study the action of NGF on bursal cells during chick embryo development. Our in vivo experiments indicate that NGF administration in ovo caused a significant increase in size of the lymphoid follicles in the embryonic bursa at E15. The in vitro experiments demonstrated that NGF exhibits different effects on bursal cells depending on the stage of development. At E9 bursal cells survive for longer periods when NGF is added to the medium. At E15 NGF act as a colony-stimulating factor by significantly increasing the number of colonies in soft agar cultures.

The effect of nerve growth factor on DNA synthesis, cyclic AMP and cyclic GMP accumulation by mouse spleen lymphocytes

Nerve growth factor (NGF), a trophic neuropeptide, is known to stimulate development, and to be important in the maintenance and survival of sympathetic and sensory neurons. Considering the presence of specific receptors on the surface of spleen cells, the effect of 2.5s nerve growth factor on 3H-thymidine uptake, cAMP and cGMP accumulation in mouse spleen lymphocytes has been studied. It was found that NGF added in vitro at the concentrations between 4 x 10(-7) and 4 x 10(-8) M significantly inhibited the incorporation of 3H-thymidine into lymphocytes DNA and increased cAMP levels in a dose-dependent manner but had no effect on cGMP levels. The maximal stimulation of cAMP synthesis occurred between 5 and 30 min after the NGF addition to the culture medium. When NGF was administered in vivo a significant dose-dependent inhibition of the lymphocytes proliferation was observed. These results indicate that an early increase of cAMP concentration is responsible for the antiproliferative action of NGF on mouse spleen lymphocytes and suggest that NGF could play an important role in the regulation of immune system function.

Testicular immunoregulatory factors

The present data indicate that immune cells are regulated locally in the testis by Leydig cells, Sertoli cells and resident testicular macrophages. The effects of these cells are mediated by several peptide factors, including protectin, a group of high molecular weight testicular immunosuppressive factors, and testicular interleukin-1 alpha-like factor. The testicular interleukin-1 alpha-like factor is produced by Sertoli cells and is under hypophyseal control. Its synthesis starts at puberty concomitantly with the onset of spermatogenesis and it may act as a spermatogonial growth factor. Protectin, which is under hypophyseal control, may be involved in the mechanism of prolonged transplant survival in the testicular interstitial tissue. Its levels increase at puberty. Both the testicular interleukin-1 alpha-like activity and protectin may be important in testicular pathophysiology.

Prenatal alcohol exposure alters the development of sympathetic synaptic components and of nerve growth factor receptor expression selectivity in lymphoid organs

Exposure to alcohol in utero has been associated with long-term immune deficits. In addition, adult mice exposed to alcohol prenatally display altered noradrenergic synaptic transmission selectively in lymphoid organs. This is consistent with the hypothesis that sympathetic neurons play an important role in immunomodulation. The development and maintenance of sympathetic neurons are critically dependent on nerve growth factor (NGF). Furthermore, NGF has been shown to modulate immune responses and NGF receptor expression has been localized to lymphoid organs. The present work examined the effects of prenatal alcohol exposure on the development and maturation of pre- and postsynaptic sympathetic components, including norepinephrine and beta-adrenoceptors, respectively, as well as the early expression of NGF receptors in lymphoid and other organs of the C57BL/6 mouse. Infant mice that were exposed to alcohol in utero displayed reduced levels of norepinephrine and beta-adrenoceptor density, as well as increased NGF receptor expression in the thymus and spleen, but not the heart. These selective changes may account, in part, for the persistent immune incompetence characteristic of fetal alcohol syndrome.

Conditioned medium from activated splenocytes increases substance P in sympathetic ganglia

Following removal of the presynaptic input to the superior cervical ganglion (SCG) of the neonatal rat, there is an increase in substance P (Kessler et al.: Science 214:335-336, 1981; Kessler and Black: Brain Res 234:182-187, 1982) and the mRNA coding for its prohormone precursor (Roach et al.: Proc Natl Acad Sci USA 84:5078-5081, 1987). However, the functional significance of this increase has been unclear. We report here that SP increases dramatically in cultures of SCG grown in the presence of conditioned medium from con-A-stimulated splenocytes. The effect is mimicked by growing SCG explants in the presence of human recombinant interleukin-1 (hrIL-1) but not hrIL-2. Nerve growth factor (NGF) is not involved in mediating this effect since antibodies to NGF included in the culture fail to alter the lymphokine-induced increase in SP. Moreover, the effect is somewhat specific for SP since the activities of tyrosine hydroxylase, tryptophan hydroxylase, and choline acetyltransferase (enzymes in the biosynthetic pathways for norepinephrine, serotonin, and acetylcholine) are not similarly elevated. Dorsal root ganglia respond with only modest increases in SP. The action of lymphokines in stimulating SP may, therefore, be a ganglion-specific action in promoting recovery following injury.

Role of nerve growth factor in oxidant-antioxidant balance and neuronal injury. I. Stimulation of hydrogen peroxide resistance

The nerve growth factor protein (NGF) regulates neuronal cell death during the development of embryonic sensory and sympathetic neurons in the peripheral nervous system (PNS). NGF protects the rat pheochromocytoma line PC12, a useful model of NGF responsive peripheral neurons, from hydrogen peroxide, which interacts with ferrous iron to generate hydroxyl radicals. Exogenous catalase provides protection, whereas superoxide dismutase (SOD) has no effect on neuronal survival when PC12 cells are challenged with hydrogen peroxide. NGF treatment of PC12 cells increases the activity of catalase. NGF protection from hydrogen peroxide is partially abolished by aminotriazole (Az), a low molecular weight catalase inhibitor. Taken together, these data are consistent with the hypothesis that NGF protects from peroxidative events and consequent cell death via an induction of free radical detoxifying mechanisms, such as catalase activity.

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.

Nerve growth factor induces growth and differentiation of human B lymphocytes

Nerve growth factor (NGF) is known to affect peripheral sympathetic and sensory neurons as well as defined populations of neurons in the central nervous system. This paper presents evidence that NGF is also active in modulation of B-cell-mediated immune responses. NGF receptors were immunoprecipitated from highly purified human B-cell populations, and to a lesser extent, from T-cell populations, by using a monoclonal antibody recognizing NGF receptors present on neural cells. NGF receptors were also detected in significant amounts in human spleen and lymph node tissue. In addition, NGF induced a dose-dependent increase in B-cell DNA synthesis as determined by incorporation of [3H]thymidine. This B-cell growth-promoting activity was inhibited by a neutralizing anti-NGF monoclonal antibody. Immunoglobulin secretion, principally affecting IgM synthesis, was also modulated by NGF. The concentrations that affected B-cell proliferation are consistent with the presence of functional high-affinity NGF receptors. The results suggest that NGF, in addition to its neurotrophic function, also acts as an immunoregulatory cytokine.

Functional receptors for nerve growth factor on Ewing's sarcoma and Wilm's tumor cells

Quantification of changes in levels of c-fos RNA was used as an indicator of the presence of functional responses to nerve growth factor in several human non-neuronal cell lines which have previously been shown to express high levels of NGF receptors. Four Ewing's sarcomas, one Wilm's tumor, and one melanoma were examined. Of these cell lines, the Ewing's sarcoma IARC-EW1 showed greatly increased levels (10-20-fold) of c-fos RNA after 1 hour of exposure to NGF. Except for the melanoma line, the other tumor lines exhibited small, but reproducible, elevation of c-fos RNA expression. In IARC-EW1 cells, this induction was analyzed for kinetics, dose-response, and suppression by selective inhibitors of NGF action. The results indicate that these cells bear high-affinity receptors for NGF, which utilize signal pathways similar to NGF receptors on PC12 cells. Thus, we report new types of cells with functional responses to NGF and indicate that these may constitute a new model which will usefully complement those presently used for studying the mechanism of action of NGF.

Function of neurotrophic factors in the adult and aging brain and their possible use in the treatment of neurodegenerative diseases

This review summarizes the current knowledge of characterized neurotrophic factors, including nerve growth factor (NGF) which serves as paradigmatic example when studying novel molecules. Special consideration is given to the function of neurotrophic factors in the adult and aging brain. Strategies are discussed for the eventual development of pharmacological applications of these molecules in the treatment of neurodegenerative diseases.