Differential regulation of neurotrophin expression by mitogens and neurotransmitters in mouse lymphocytes

ProBDNF and its receptors in immune-mediated inflammatory diseases: novel insights into the regulation of metabolism and mitochondria

Immune-mediated inflammatory diseases (IMIDs) consist of a common and clinically diverse group of diseases. Despite remarkable progress in the past two decades, no remission is observed in a large number of patients, and no effective treatments have been developed to prevent organ and tissue damage. Brain-derived neurotrophic factor precursor (proBDNF) and receptors, such as p75 neurotrophin receptor (p75^NTR) and sortilin, have been proposed to mediate intracellular metabolism and mitochondrial function to regulate the progression of several IMIDs. Here, the regulatory role of proBDNF and its receptors in seven typical IMIDs, including multiple sclerosis, rheumatoid arthritis, systemic lupus erythematosus, allergic asthma, type I diabetes, vasculitis, and inflammatory bowel diseases, was investigated.

A Microglial Function for the Nerve Growth Factor: Predictions of the Unpredictable

Microglia are the only immune cell population present in the brain parenchyma. Their vantage position in the central nervous system (CNS) enables these myeloid cells to perform the most disparate of tasks: from the classical immune functions of fighting infections and surveilling the extracellular space for pathogens and damage, to sculpting the neuronal circuitry by pruning unnecessary synapses and assisting neurons in spine formation, aiding in the maintenance of brain homeostasis. The neurotrophin field has always been dominated by the neurocentric view that the primary target of these molecules must be neurons: this holds true even for the Nerve Growth Factor (NGF), which owes its popularity in the neuroscience community to its trophic and tropic activity towards sensory and sympathetic neurons in the peripheral nervous system, and cholinergic neurons in the CNS. The increasing evidence that microglia are an integral part of neuronal computation calls for a closer look as to whether these glial cells are capable of responding directly to NGF. In this review, we will first outline evidence in support of a role for NGF as a molecule mediating neuroimmune communication. Then, we will illustrate some of those non-immune features that have made microglial cells one of the hottest topics of this last decade. In conclusion, we will discuss evidence in support of a microglial function for NGF.

Transcriptional Activity of Neurotrophins Genes and Their Receptors in the Peripheral Blood in Patients with Thyroid Diseases in Bukovinian Population of Ukraine

Objective. Thyroid hormone has an especially strong impact on central nervous system development, and thyroid hormone deficiency has been shown to result in severe mental retardation. It is crucial to identify compensatory mechanisms that can be involved in improving cognitive function and the quality of life of patients with hypothyroidism. Methods: We used the pathway-specific PCR array (Neurotrophins and Receptors RT2 Profiler PCR Array, QIAGEN, Germany) to identify and validate neurotrophins genes and their receptor expression in patients with thyroid pathology and control group. Results: The analysis of gene expression of neurotrophins and their receptors showed that CRHBP, FRS2, FRS3, GFRA1, GFRA2, GMFB, NGF, NRG2, NRG4, NTF4, TRO, and VGF significantly decreased their expression in Group 3, which includes the patients with postoperative hypothyroidism. The patients with primary hypothyroidism stemming from AIT had significantly reduced expression of CRHBP, GFRA1, GFRA2, GMFB, NGF, PTGER2, and VGF, while the expression of NRG4 and TRO increased. In Group 3, which includes the patients with AIT and elevated serum anti-Tg and anti-TPO autoantibodies, the mRNA levels of GFRA2, NGF, NRG2, NTF4, NGF, PTGER were reduced, and the expression of CRHBP, FRS2, FRS3 GFRA1, GMFB, NRG4, TRO, and VGF significantly increased. Conclusion: These results indicate significant variability in the transcriptional activity of the genes of encoding neurotrophins and their receptors in the peripheral blood in people with thyroid diseases.

Exercise-induced BDNF production by mononuclear cells of sedentary and physically active obese men

BACKGROUND

Obesity and low physical activity changes the redox state and neurotrophin secretion by leukocytes. However, the role of exercise on brain derived neurotrophic factor (BDNF) production and oxidative stress markers of peripheral blood mononuclear cells (PBMC) remains unknown. This study aimed to verify the impact of acute maximal exercise on oxidative stress markers and the BDNF production by stimulated PBMC from sedentary and physically active obese men.

METHODS

PBMC from twelve sedentary obese (SED group) and twelve regular exercisers (EXE group) obese men were collected before, immediately and 1-h after maximal exercise. PBMC were stimulated with lipopolysaccharide (LPS) to evaluate the BDNF and nitrite production, lipid peroxidation, and antioxidant enzymes catalase (CAT) and superoxide dismutase (SOD) activities.

RESULTS

PBMC from EXE group presented higher BDNF production (P=0.03) and lower TBARS levels than SED group at baseline. Maximal exercise increased BDNF and nitrite production, and lipid peroxidation immediately and 1-h after the bout in both groups. The EXE group presented higher superoxide dismutase activity immediately after bout and higher catalase activity 1-h after bout in PBMC. On the other hand, PBMC from SED group had lower superoxide dismutase activity immediately after exercise. Furthermore, PBMC from EXE group presented higher BDNF production and SOD activity and lower TBARS concentrations than SED group immediately after maximal exercise.

CONCLUSIONS

Maximal exercise changes the redox state and enhances BDNF production by LPS-stimulated PBMC in obese individuals.

Immune System Activation in Perioperative Thrombectomy Patients: Preliminary Retrospective Study

BACKGROUND

Ischemic stroke is a devastating condition resulting in significant morbidity. Mechanical thrombectomy is now standard for large vessel occlusive stroke. Neuroinflammation is known to play important roles in ischemic stroke. Our aims were to examine our thrombectomy procedures and preliminarily examine systemic immune response in relation to thrombectomy changes.

METHODS

A retrospective review was conducted on mechanical thrombectomy cases from July 2011 through December 2015. Primary outcomes were time to recanalization, final Thrombolysis in Cerebral Infarction score, procedural complications, National Institutes of Health Stroke Scale improvement, and changes in white blood cell (WBC) count.

RESULTS

One-hundred and twenty-nine procedures were performed. We found a significant difference between WBC count on admission and WBC count post thrombectomy day 1 for patients with >90 minutes to recanalization (P = 0.006107). There was a positive association between WBC change and absolute National Institutes of Health Stroke Scale change among females (P = 0.0273) but not among males.

CONCLUSIONS

Overall, we found that systemic immune response has close relationships with speed of recanalization and preliminarily may shift differently on the basis of sex.

Circulating biomarkers in extremely preterm infants associated with ultrasound indicators of brain damage

AIM

To assess to what extent the blood concentrations of proteins with neurotrophic and angiogenic properties measured during the first postnatal month convey information about the risk of sonographically-identified brain damage among very preterm newborns.

METHODS

Study participants were 1219 children who had a cranial ultrasound scan during their stay in the intensive care nursery and blood specimens collected on 2 separate days at least a week apart during the first postnatal month. Concentrations of selected proteins in blood spots were measured with electrochemiluminescence or with a multiplex immunobead assay and the risks of cranial ultrasound images associated with top-quartile concentrations were assessed.

RESULTS

High concentrations of multiple inflammation-related proteins during the first 2 postnatal weeks were associated with increased risk of ventriculomegaly, while high concentrations of just 3 inflammation-related proteins were associated with increased risk of an echolucent/hypoechoic lesion (IL-6, IL-8, ICAM-1), especially on day 7. Concomitant high concentrations of IL6R and bFGF appeared to modulate the increased risks of ventriculomegaly and an echolucent lesion associated with inflammation. More commonly high concentrations of putative protectors/repair-enhancers did not appear to diminish these increased risks.

CONCLUSION

Our findings provide support for the hypothesis that endogenous proteins are capable of either protecting the brain against damage and/or enhancing repair of damage.

Antecedents and correlates of blood concentrations of neurotrophic growth factors in very preterm newborns

AIM

To identify the antecedents and very early correlates of low concentrations of neurotrophic growth factors in the blood of extremely preterm newborns during the first postnatal month.

METHODS

Using an immunobead assay, we measured the concentrations of neurotrophin 4 (NT4), brain-derived neurotrophic factor (BDNF), and basic fibroblast growth factor (bFGF) in blood spots collected on postnatal days 1 (N=1062), 7 (N=1087), 14 (N=989), 21 (N=940) and 28 (N=880) from infants born before the 28th week of gestation. We then sought the correlates of measurements in the top and bottom quartiles for gestational age and day the specimen was collected.

RESULTS

The concentrations of 2 neurotrophic proteins, NT4 and BDNF, were low among children delivered for medical (maternal or fetal) indications, and among those who were growth restricted. Children who had top quartile concentrations of NT4, BDNF, and bFGF tended to have elevated concentrations of inflammation-related proteins that day. This pattern persisted for much of the first postnatal month.

CONCLUSIONS

Delivery for medical indications and fetal growth restriction are associated with a relative paucity of NT4 and BDNF concentrations during the first 24 h after very preterm birth. Elevated blood concentrations of NT4, BDNF, and bFGF tended to co-occur with indicators of systemic inflammation on the same day.

The Role of Neurotrophins in Inflammation and Allergy

Allergic inflammation is the result of a specific pattern of cellular and humoral responses leading to the activation of the innate and adaptive immune system, which, in turn, results in physiological and structural changes affecting target tissues such as the airways and the skin. Eosinophil activation and the production of soluble mediators such as IgE antibodies are pivotal features in the pathophysiology of allergic diseases. In the past few years, however, convincing evidence has shown that neurons and other neurosensory structures are not only a target of the inflammatory process but also participate in the regulation of immune responses by actively releasing soluble mediators. The main products of these activated sensory neurons are a family of protein growth factors called neurotrophins. They were first isolated in the central nervous system and identified as important factors for the survival and differentiation of neurons during fetal and postnatal development as well as neuronal maintenance later in life. Four members of this family have been identified and well defined: nerve growth factor, brain-derived neurotrophic factor, neurotrophin 3, and neurotrophin 4/5. Neurotrophins play a critical role in the bidirectional signaling mechanisms between immune cells and the neurosensory network structures in the airways and the skin. Pruritus and airway hyperresponsiveness, two major features of atopic dermatitis and asthma, respectively, are associated with the disruption of the neurosensory network activities. In this chapter, we provide a comprehensive description of the neuroimmune interactions underlying the pathophysiological mechanisms of allergic and inflammatory diseases.

Neonatal vaccination with bacille Calmette-Guérin promotes the dendritic development of hippocampal neurons

Dendritic structure is sensitive to changes in the environment during brain development. Accumulating evidence has demonstrated that early immune activation can significantly affect neuronal development. Our study concentrated on the morphological study of neural dendrites and spines in the hippocampal CA1 area using Diolistic labeling with Sholl analysis and fractal analysis. The results revealed that Bacille Calmette-Guérin (BCG) vaccination enhanced dendritic complexity, as reflected by the increased number of intersections, number of branch points and fractal dimension, and promoted neurite outgrowth. In addition, BCG increased the density and promoted the maturation of dendritic spines. The alterations in dendritic structure and spine morphology were observed at 2 and 4 w, but the differences were more apparent at 4 w than at 2 w. However, no significant difference was observed at 8 w. Furthermore, we observed that BCG increased the expression of hippocampal brain derived neurotrophic factor (BDNF) and insulin-like growth factor 1 (IGF-1). Hippocampal BDNF/IGF-1 was positively correlated with apical dendritic length, fractal dimension, and spine density. Taken together, we show in this study that neonatal BCG vaccination promotes dendritic development in developing hippocampal CA1 neurons, most likely by increasing the expression of BDNF and IGF-1 in the hippocampus.

Th2 cytokines enhance TrkA expression, upregulate proliferation, and downregulate differentiation of keratinocytes

BACKGROUND

Nerve growth factor (NGF), a neurotrophin that plays a critical role in developmental neurobiology, is released by proliferating keratinocytes and induces proliferation.

OBJECTIVE

The aim of this study was to investigate the role of tyrosine kinase receptor A (TrkA), a high-affinity receptor of NGF, in human keratinocytes.

METHODS

Expression of TrkA and NGF in skin diseases was investigated by immunohistochemistry. Expression of TrkA in cells was examined by Western blotting and RT-PCR. Cell proliferation was assessed by BrdU assay.

RESULTS

We first determined the expression of TrkA and NGF in skin samples from patients with atopic dermatitis, prurigo nodularis, psoriasis vulgaris, and seborrheic keratosis. TrkA was only expressed in proliferating basal cells, and its expression was enhanced in atopic dermatitis samples. NGF expression was enhanced in atopic dermatitis and prurigo nodularis samples and in some samples from seborrheic keratosis patients. Investigation of the role of TrkA in vitro using normal human epidermal keratinocytes (NHEK) revealed that TrkA was significantly enhanced by the T helper type 2 (Th2) cytokines interleukin (IL)-4 and IL-13 but not by other inflammatory cytokines, such as IL-1β, tumor necrosis factor α, interferon γ, or epidermal growth factor. On the other hand, expression of NGF was not altered by Th2 cytokines. Notably, inhibition of TrkA significantly reversed the effects of IL-4 on proliferation and differentiation. Furthermore, overexpression of TrkA enhanced proliferation of NHEK. These results indicate that IL-4-induced TrkA expression in keratinocytes modulates proliferation and differentiation of these cells.

CONCLUSION

Increased TrkA expression in keratinocytes in atopic dermatitis may contribute to the observed epidermal hyperproliferation in these patients.

Epigenetic patterns in successful weight loss maintainers: a pilot study

DNA methylation changes occur in animal models of calorie restriction, simulating human dieting, and in human subjects undergoing behavioral weight loss interventions. This suggests that obese (OB) individuals may possess unique epigenetic patterns that may vary with weight loss. Here, we examine whether methylation patterns in leukocytes differ in individuals who lost sufficient weight to go from OB to normal weight (NW; successful weight loss maintainers; SWLMs) vs currently OB or NW individuals. This study examined peripheral blood mononuclear cell (PBMC) methylation patterns in NW (n=16, current/lifetime BMI 18.5-24.9) and OB individuals (n=16, current body mass index (BMI)⩾30), and SWLM (n=16, current BMI 18.5-24.9, lifetime maximum BMI ⩾30, average weight loss 57.4 lbs) using an Illumina Infinium HumanMethylation450 BeadArray. No leukocyte population-adjusted epigenome-wide analyses were significant; however, potentially differentially methylated loci across the groups were observed in ryanodine receptor-1 (RYR1; P=1.54E-6), myelin protein zero-like 3 (MPZL3; P=4.70E-6) and alpha 3c tubulin (TUBA3C; P=4.78E-6). In 32 obesity-related candidate genes, differential methylation patterns were found in brain-derived neurotrophic factor (BDNF; gene-wide P=0.00018). In RYR1, TUBA3C and BDNF, SWLM differed from OB but not NW. In this preliminary investigation, leukocyte SWLM DNA methylation patterns more closely resembled NW than OB individuals in three gene regions. These results suggest that PBMC methylation is associated with weight status.

The effects of neurotrophins and the neuropeptides VIP and PACAP on HIV-1 infection: histories with opposite ends

The nerve growth factor (NGF) and other neurotrophins, and the neuropeptides vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating peptide (PACAP) are largely present in human tissue and can exert modulatory activities on nervous, endocrine and immune system functions. NGF, VIP and PACAP receptors are expressed systemically in organisms, and thus these mediators exhibit pleiotropic natures. The human immunodeficiency virus type 1 (HIV-1), the causal agent of the acquired immunodeficiency syndrome (AIDS), infects immune cells, and its replication is modulated by a number of endogenous factors that interact with HIV-1-infected cells. NGF, VIP and PACAP can also affect HIV-1 virus particle production upon binding to their receptors on the membranes of infected cells, which triggers cell signaling pathways that modify the HIV-1 replicative cycle. These molecules exert opposite effects on HIV-1 replication, as NGF and other neurotrophins enhance and VIP and PACAP reduce viral production in HIV-1-infected human primary macrophages. The understanding of AIDS pathogenesis should consider the mechanisms by which the replication of HIV-1, a pathogen that causes chronic morbidity, is influenced by neurotrophins, VIP and PACAP, i.e. molecules that exert a broad spectrum of physiological activities on the neuroimmunoendocrine axis. In this review, we will present the main effects of these two groups of mediators on the HIV-1 replicative cycle, as well as the mechanisms that underlie their abilities to modulate HIV-1 production in infected immune cells, and discuss the possible repercussion of the cross talk between NGF and both neuropeptides on the pathogenesis of HIV-1 infection.

Serum and lymphocytic neurotrophins profiles in systemic lupus erythematosus: a case-control study

BACKGROUND

Neurotrophins play a central role in the development and maintenance of the nervous system. However, neurotrophins can also modulate B and T cell proliferation and activation, especially via autocrine loops. We hypothesized that both serum and lymphocytic neurotrophin levels may be deregulated in systemic Lupus erythematosus (SLE) and may reflect clinical symptoms of the disease.

METHODS

Neurotrophins in the serum (ELISA tests) and lymphocytes (flow cytometry) were measured in 26 SLE patients and 26 control subjects. Th1 (interferon-γ) and Th2 (IL-10) profiles and serum concentration of BAFF were assessed by ELISA in the SLE and control subjects.

FINDINGS

We have demonstrated that both NGF and BDNF serum levels are higher in SLE patients than healthy controls (p=0.003 and p<0.001), independently of Th1 or Th2 profiles. Enhanced serum NT-3 levels (p=0.003) were only found in severe lupus flares (i.e. SLEDAI ≥ 10) and significantly correlated with complement activation (decreased CH 50, Γ=-0.28, p=0.03). Furthermore, there was a negative correlation between serum NGF levels and the number of circulating T regulatory cells (Γ=0.48, p=0.01). In circulating B cells, production of both NGF and BDNF was greater in SLE patients than in healthy controls. In particular, the number of NGF-secreting B cells correlated with decreased complement levels (p=0.05). One month after SLE flare treatment, BDNF levels decreased; in contrast, NGF and NT-3 levels remained unchanged.

CONCLUSION

This study demonstrates that serum and B cell levels of both NGF and BDNF are increased in SLE, suggesting that the neurotrophin production pathway is deregulated in this disease. These results must be confirmed in a larger study with naive SLE patients, in order to avoid the potential confounding influence of prior immune-modulating treatments on neurotrophin levels.

Bacillus Calmette-Guerin vaccine-mediated neuroprotection is associated with regulatory T-cell induction in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine mouse model of Parkinson's disease

We previously showed that, in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of Parkinson's disease (PD), vaccination with bacillus Calmette-Guerin (BCG) prior to MPTP exposure limited the loss of striatal dopamine (DA) and dopamine transporter (DAT) and prevented the activation of nigral microglia. Here, we conducted BCG dose studies and investigated the mechanisms underlying BCG vaccination's neuroprotective effects in this model. We found that a dose of 1 × 10(6) cfu BCG led to higher levels of striatal DA and DAT ligand binding (28% and 42%, respectively) in BCG-vaccinated vs. unvaccinated MPTP-treated mice, but without a significant increase in substantia nigra tyrosine hydroxylase-staining neurons. Previous studies showed that BCG can induce regulatory T cells (Tregs) and that Tregs are neuroprotective in models of neurodegenerative diseases. However, MPTP is lymphotoxic, so it was unclear whether Tregs were maintained after MPTP treatment and whether a relationship existed between Tregs and the preservation of striatal DA system integrity. We found that, 21 days post-MPTP treatment, Treg levels in mice that had received BCG prior to MPTP were threefold greater than those in MPTP-only-treated mice and elevated above those in saline-only-treated mice, suggesting that the persistent BCG infection continually promoted Treg responses. Notably, the magnitude of the Treg response correlated positively with both striatal DA levels and DAT ligand binding. Therefore, BCG vaccine-mediated neuroprotection is associated with Treg levels in this mouse model. Our results suggest that BCG-induced Tregs could provide a new adjunctive therapeutic approach to ameliorating pathology associated with PD and other neurodegenerative diseases.

TRPC3 regulates release of brain-derived neurotrophic factor from human airway smooth muscle

Exogenous brain-derived neurotrophic factor (BDNF) enhances Ca(2+) signaling and cell proliferation in human airway smooth muscle (ASM), especially with inflammation. Human ASM also expresses BDNF, raising the potential for autocrine/paracrine effects. The mechanisms by which ASM BDNF secretion occurs are not known. Transient receptor potential channels (TRPCs) regulate a variety of intracellular processes including store-operated Ca(2+) entry (SOCE; including in ASM) and secretion of factors such as cytokines. In human ASM, we tested the hypothesis that TRPC3 regulates BDNF secretion. At baseline, intracellular BDNF was present, and BDNF secretion was detectable by enzyme linked immunosorbent assay (ELISA) of cell supernatants or by real-time fluorescence imaging of cells transfected with GFP-BDNF vector. Exposure to the pro-inflammatory cytokine tumor necrosis factor-alpha (TNFα) (20ng/ml, 48h) or a mixture of allergens (ovalbumin, house dust mite, Alternaria, and Aspergillus extracts) significantly enhanced BDNF secretion and increased TRPC3 expression. TRPC3 knockdown (siRNA or inhibitor Pyr3; 10μM) blunted BDNF secretion, and prevented inflammation effects. Chelation of extracellular Ca(2+) (EGTA; 1mM) or intracellular Ca(2+) (BAPTA; 5μM) significantly reduced secreted BDNF, as did the knockdown of SOCE proteins STIM1 and Orai1 or plasma membrane caveolin-1. Functionally, secreted BDNF had autocrine effects suggested by phosphorylation of high-affinity tropomyosin-related kinase TrkB receptor, prevented by chelating extracellular BDNF with chimeric TrkB-Fc. These data emphasize the role of TRPC3 and Ca(2+) influx in the regulation of BDNF secretion by human ASM and the enhancing effects of inflammation. Given the BDNF effects on Ca(2+) and cell proliferation, BDNF secretion may contribute to altered airway structure and function in diseases such as asthma.

Multilocus analysis of candidate genes involved in neurogenic inflammation in pediatric asthma and related phenotypes: a case-control study

OBJECTIVES

Asthma is a heterogenous complex disorder caused by chronic inflammation of the airways. The key issue in genetic association studies of complex disorders is the identification of multiple low-risk genes that individually have little impact on the phenotype, but in combination account for the clinical manifestation of asthma. Since neurogenic inflammation is emerging as a candidate factor in the pathogenesis of asthma, the aim of the study was to investigate whether genetic variants of neurotrophin genes are associated with asthma disease severity or asthma-related phenotypes in a pediatric population.

METHODS

We genotyped 27 polymorphisms located in neurotrophin genes, using TaqMan SNP genotyping assays or Polymerase Chain Reaction - Restriction Fragments Lengths Polymorphism (PCR-RFLP) in 200 children diagnosed with asthma and 226 controls. Interactions between 27 polymorphic loci and asthma-related phenotypes were determined using the Multifactor Dimensionality Reduction (MDR) method.

RESULTS

In single marker analysis, we observed an association of MAP3K1 gene polymorphisms (rs702689 and rs889312) with asthma. We also observed that four Single Nucleotide Polymorphisms (SNPs) were associated with severe asthma. Analysis stratified by asthma-related phenotype revealed an association between atopy and NGFR (rs3785931), while BDNF (rs7124442), NTRK2 (rs1212171), NGFR (rs2072446), and FYN (rs3730353) variants were associated with increased exhaled nitric oxide (exNO). In addition, gene-gene interaction analysis revealed a significant epistatic interaction between MAPK (rs889312) and NGF (rs11102930) variants in asthma susceptibility.

CONCLUSIONS

Our results suggest that genetic variants of MAP3K1 and NGF genes involved in the regulation of neurogenic inflammation may contribute to asthma, possibly via enhanced NGF expression and MAPK signaling pathway activation.

Immune and nervous systems share molecular and functional similarities: memory storage mechanism

One of the most complex and important features of both the nervous and immune systems is their data storage and retrieval capability. Both systems encounter a common and complex challenge on how to overcome the cumbersome task of data management. Because each neuron makes many synapses with other neurons, they are capable of receiving data from thousands of synaptic connections. The immune system B and T cells have to deal with a similar level of complexity because of their unlimited task of recognizing foreign antigens. As for the complexity of memory storage, it has been proposed that both systems may share a common set of molecular mechanisms. Here, we review the molecular bases of memory storage in neurons and immune cells based on recent studies and findings. The expression of certain molecules and mechanisms shared between the two systems, including cytokine networks, and cell surface receptors, are reviewed. Intracellular signaling similarities and certain mechanisms such as diversity, memory storage, and their related molecular properties are briefly discussed. Moreover, two similar genetic mechanisms used by both systems is discussed, putting forward the idea that DNA recombination may be an underlying mechanism involved in CNS memory storage.

High abundances of neurotrophin 3 in atopic dermatitis mast cell

Background

Neurotrophin 3 (NT-3) is a member of the neurotrophin family, a group of related proteins that are known to regulate neuro-immune interactions in allergic diseases. Their cellular sources and role in the recruitment of mast cell precursors in atopic dermatitis have not been characterized in detail so far.

Objective

Characterize NT-3 on a transcriptional and translational level in individuals with atopic dermatitis with special focus on mast cells.

Methods

To meet this objective NT-3 levels in the serum of AD patients were measured, the effect of NT-3 on keratinocytes was evaluated and the gene expression and regulation assessed using ELISA, immunohistochemistry and RNA quantification.

Results

Systemic levels of NT-3 were found to be higher in individuals with AD as compared to healthy controls. A distinct genetic expression was found in the various cells of the skin. In lesional mast cells of individuals with atopic dermatitis an increased amount of NT-3 was apparent. Functional in vitro experiments demonstrated that NT-3 stimulation led to a suppression of IL-8 secretion by HaCat cells.

Conclusion

These findings could imply a role for NT-3 in the pathogenesis of allergic skin diseases.

Role of endogenous brain-derived neurotrophic factor and sortilin in B cell survival

Brain-derived neurotrophic factor (BDNF), a major neuronal growth factor, is also known to exert an antiapoptotic effect in myeloma cells. Whereas BDNF secretion was described in B lymphocytes, the ability of B cells to produce sortilin, its transport protein, was not previously reported. We studied BDNF production and the expression of its receptors, tyrosine protein kinase receptor B and p75 neurotrophin receptor in the human pre-B, mature, and plasmacytic malignant B cell lines under normal and stress culture conditions (serum deprivation, Fas activation, or their combination). BDNF secretion was enhanced by serum deprivation and exerted an antiapoptotic effect, as demonstrated by neutralization experiments with antagonistic Ab. The precursor form, pro-BDNF, also secreted by B cells, decreases under stress conditions in contrast to BDNF production. Stress conditions induced the membranous expression of p75 neurotrophin receptor and tyrosine protein kinase receptor B, maximal in mature B cells, contrasting with the sequestration of both receptors in normal culture. By blocking Ab and small interfering RNA, we evidenced that BDNF production and its survival function are depending on sortilin, a protein regulating neurotrophin transport in neurons, which was not previously described in B cells. Therefore, in mature B cell lines, an autocrine BDNF production is up-regulated by stress culture conditions and exerts a modulation of apoptosis through the sortilin pathway. This could be of importance to elucidate certain drug resistances of malignant B cells. In addition, primary B lymphocytes contained sortilin and produced BDNF after mitogenic activation, which suggests that sortilin and BDNF might be implicated in the survival and activation of normal B cells also.

TLR4 signaling induces functional nerve growth factor receptor p75NTR on mouse dendritic cells via p38MAPK and NF-kappa B pathways

Many neuropeptides that are produced by immune cells have been shown to be involved in the pathogenesis of immunological disorders. Nerve growth factor (NGF) and its receptors are found to be widely expressed in the immune system and regulate both innate and adaptive immune responses. However, the underlying mechanisms by which NGF contributes to pathogenesis of inflammatory diseases remain to be fully understood. Dendritic cells (DCs) are potent initiator for inflammatory and immune responses upon recognization and activation of Toll-like receptors (TLRs). In this study, we demonstrated that stimulation with TLR ligand lipopolysaccharide (LPS), but not lipoteichoic acid (LTA), Poly (I:C) and CpG oligodeoxynucleotide (ODN), could significantly induce expression of NGF and NGF receptor p75(NTR) on mouse bone marrow-derived DCs (BMDCs) in vitro in dose- and time-dependent manners. The expression of NGF and NGF receptor p75(NTR) also increased on splenic DCs isolated from the mice injected with LPS in vivo. However, there was no such effect on DCs derived from TLR4-deficient mice, indicating the LPS-induced upregulation of NGF and p75(NTR) was TLR4 pathway-dependent. Furthermore, LPS-induced upregulation of NGF and p75(NTR) could be inhibited by p38MAPK inhibitor SB203580 and NF-kappaB inhibitor PDTC, suggesting TLR4-triggered activation of p38MAPK and NF-kappaB pathways are responsible for the process. Interestingly, NGF could markedly promote LPS-pretreated BMDCs to secret IL-12p40 and TNF-alpha, which could be abolished by pretreatment with p75(NTR) antagonist or the specific small interference RNA duplex targeting p75(NTR) (p75-siRNA), suggesting the inducible p75(NTR) is critical for the TLR4-initiated inflammatory effect of NGF on BMDCs. Thus, TLR4 signaling can induce expression of NGF and p75 (NTR) on DCs via activation of p38 MAPK and NF-kappaB pathways, suggesting that NGF may be involved in the pathogenesis of inflammatory diseases.

Neuroimmune crosstalk in asthma: dual role of the neurotrophin receptor p75NTR

BACKGROUND

Neurotrophins have been implicated in the pathogenesis of asthma because of their ability to induce airway inflammation and to promote hyperreactivity of sensory neurons, which reflects an important mechanism in the pathogenesis of airway hyperreactivity. Neurotrophins use a dual-receptor system consisting of Trk-receptor tyrosine kinases and the structurally unrelated p75NTR. Previous studies revealed an important role of p75NTR in the pathogenesis of allergic asthma.

OBJECTIVES

The aim of the study was to investigate the precise mechanisms of neurotrophins in neuroimmune interaction, which can lead to both airway inflammation and sensory nerve hyperreactivity in vivo.

METHODS

Mice selectively expressing p75NTR in immune cells or nerves, respectively, were generated. After sensitization and allergen provocation, hyperreactivity of sensory nerves was tested in response to capsaicin. Airway inflammation was analyzed on the basis of differential cell counts and cytokine levels in bronchoalveolar lavage fluids.

RESULTS

Allergic mice selectively expressing p75NTR in immune cells showed normal inflammation but no sensory nerve hyperreactivity, whereas mice selectively expressing p75NTR in nerve cells had a diminished inflammation and a distinct sensory nerve hyperreactivity.

CONCLUSION

Our data indicate that p75NTR plays a dual role by promoting hyperreactivity of sensory nerves and airway inflammation. Additionally, our study provides experimental evidence that development of sensory nerve hyperreactivity depends on an established airway inflammation in asthma. In contrast, development of airway inflammation seems to be independent from sensory nerve hyperreactivity.

CLINICAL IMPLICATIONS

Because of its dual function, antagonization of p75NTR-mediated signals might be a novel approach in asthma therapy.

Airway hyper-responsiveness in allergic asthma in guinea-pigs is mediated by nerve growth factor via the induction of substance P: a potential role for trkA

BACKGROUND

The neurotrophin nerve growth factor (NGF) has been implicated as a mediator in allergic asthma. Direct evidence that inhibition of NGF-induced activation of neurotrophin receptors leads to improvement of airway symptoms is lacking. We therefore studied the effects of inhibitors of NGF signal transduction on the development of airway hyper-responsiveness (AHR) and pulmonary inflammation in a guinea-pig model for allergic asthma.

METHODS

Airway responsiveness to the contractile agonist histamine was measured in vivo in guinea-pigs that were sensitized and challenged with ovalbumin (OVA). Inflammatory cell influx and NGF levels were determined in bronchoalveolar lavage fluid (BALF). Substance P, a key mediator of inflammation, was measured in lung tissue by radioimmunoassay, while substance P immunoreactive neurons in nodose ganglia were measured by immunohistochemistry.

RESULTS

OVA challenge induced an AHR after 24 h in OVA-sensitized guinea-pigs. This coincided with an increase in the amount of NGF in BALF. Simultaneously, an increase in the percentage of substance P immunoreactive neurons in the nodose ganglia and an increase in the amount of substance P in lung tissue were found. We used tyrosine kinase inhibitors to block the signal transduction of the high-affinity NGF receptor, tyrosine kinase A (trkA). Treatment with the tyrosine kinase inhibitors (K252a or tyrphostin AG879) both inhibited the development of AHR, and prevented the increase in substance P in the nodose ganglia and lung tissue completely whereas both inhibitors had no effect on baseline airway resistance. Neither treatment with K252a or tyrphostin AG879 changed the influx of inflammatory cells in the BALF due to allergen challenge.

CONCLUSIONS

We conclude that substance P plays a role in the induction of AHR in our model for allergic asthma which is most likely mediated by NGF. As both tyrosine kinase inhibitors AG879 and K252a show a similar inhibitory effect on airway function after allergen challenge, although both tyrosine kinase inhibitors exhibit different non-specific inhibitory effects on targets other than trkA tyrosine kinases, it is likely that the induction of substance P derived from sensory nerves is mediated by NGF via its high-affinity receptor trkA.

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

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

Neuro-immune interaction in allergic asthma: role of neurotrophins

The nature of persistent airway hyperreactivity and chronic inflammation in asthma remains unclear. It has been suggested that bi-directional neuro-immune interaction plays an important role in the pathogenesis of this disease, leading to enhanced airway narrowing after contact with unspecific stimuli, as well as infiltration, activation and degranulation of several immune cell subtypes. Important mediators in neuro-immune cross-talk are neurotrophins, which are produced by cells at the site of inflammation. In addition to modulating the function of several leucocyte subsets, they play an important role in the synthesis of neuropeptides by sensory nerve cells. Neuropeptides have been shown to cause smooth-muscle contraction and, in addition, modulate the production of pro-inflammatory molecules by leucocytes. The aim of the present review is to provide an overview of the molecular mechanisms by which neurotrophins and neuropeptides are involved in neuro-immune cross-talk in allergic asthma.

The autotomy relief effect of a silicone tube covering the proximal nerve stump

A technique of covering the proximal nerve stump (PNS) has been reported as a preventative method or treatment for neuroma. However, its detailed pain relief mechanism remains unknown. We created a silicone tube model in which the PNS of the rat sciatic nerve was introduced into the tube, whereas the controls had no tube. The score of autotomy observed in the tube group was lower than that in the control group at 3 days to 2 weeks after surgery, which suggested that the silicone tube had pain-like behavior inhibitory action. To elucidate the mechanism of autotomy inhibition, immunohistochemistry and Toluidine blue staining were performed in the PNS. The increase in S-100-immunoreactivity (IR) including Schwann cells was inhibited at 1 week after surgery in the tube group, and the increase in the number of macrophages shown by ED-1-IR at 1, 2, and 4 weeks after surgery was similarly inhibited. Toluidine blue staining showed that the increase in the number of mast cells was inhibited at 1, 2, and 4 weeks after surgery and in the number of lymphocytes at 1 and 2 weeks after surgery in the tube group. Therefore, blocking of the infiltration of inflammatory cells into the PNS by the silicone tube was thought to be the mechanism of autotomy inhibition. To further explore details of this mechanism, the expression of nerve growth factor (NGF), production of which is induced by inflammatory cells and of the NGF receptor TrkA was examined in the PNS and the dorsal root ganglion using immunohistochemistry and a ribonuclease protection assay. In the PNS, the increase in NGF-IR was inhibited at 1, 2, and 4 weeks after surgery in the tube group, suggesting that this could be one of the pain-like behavior inhibitory effects.

Increased nerve growth factor and its receptors in atopic dermatitis: an immunohistochemical study

Evidence suggests that neurotrophins may regulate certain immune functions and inflammation. In the present study, the localization and distribution of nerve growth factor (NGF) and its receptors were explored using immunohistochemical methods, with the aim of detecting the cause of the neurohyperplasia in early lesions of atopic dermatitis (AD). In AD involved skin, strong NGF-immunoreactive (IR) cells were observed in the epidermis. In some cases, a huge number of infiltrating cells with stronger NGF immunoreactivity was seen mainly in the dermal papillae. Some trkA immunoreactivity was observed in the outer membrane of cells in the basal and spinal layers of the epidermis. In the papillary dermis, a larger number of cells demonstrated strong trkA immunoreactivity. The p75 NGFr-IR nerve fibre profiles were increased (900 per mm(2); p<0.001) compared to normal [the involved skin also differed from the uninvolved skin (p<0.05)] in the dermal papillae. These nerve fibres were larger, coarser and branched, some of them terminated at p75 NGFr-IR basal cells, and also revealed a stronger fluorescence staining than the controls or the uninvolved skin. In normal healthy volunteers and AD uninvolved skin, the NGF immunoreactivity was weak in the basal layer of epidermis. Only a few trkA positive cells were seen in the basal layer of the epidermis and upper dermis. The IR epidermal basal cells revealed a striking patchy arrangement with strong p75 NGFr immunostaining in the peripheral part of the cells, and short and thick NGFr-IR nerve fibre profiles appeared as smooth endings scattered in the dermis including the cutaneous accessory organs. Using NGF and p75 NGFr double staining, both immunoreactivities showed a weak staining in the epidermis and dermis in normal and uninvolved skin. In the involved dermis of AD, the intensity of p75 NGFr-IR nerves was stronger in areas where there were also increased numbers of NGF-IR cells. These findings indicate that NGF and its receptors may contribute to the neurohyperplasia of AD.

Neurotrophins in allergic diseases: From neuronal growth factors to intercellular signaling molecules

Understanding the complex pathophysiology of allergic diseases has been a main challenge of clinical and experimental research for many years. It is well known that the allergic inflammation triggers neuronal dysfunction and structural changes in the diseased tissues such as the airways or the skin. Recent evidence has emerged that the inflammatory response is also controlled by resident tissue cells such as neurons and structural cells. Therefore, signaling molecules that mediate inflammatory interactions among immune, neuronal, and structural cells are becoming a focus of allergy research. Neurotrophins, a family of homologous growth factors initially discovered in the nervous system, display such bidirectional signaling. The expression of neurotrophins, such as nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF), is highly upregulated during allergic inflammation. Neurons, structural cells, and invading immune cells were now identified not only as sources but also as targets of neurotrophins within the inflamed tissue. In this review, we provide an actual overview of the role of neurotrophins in the pathobiology of allergic diseases. We discuss recent findings in human and animal studies such as the regulation of neurotrophin expression during allergic inflammation and the effect of neurotrophins on the development and magnitude of allergic reactions.

Monocytes of allergics and non-allergics produce, store and release the neurotrophins NGF, BDNF and NT-3

INTRODUCTION

Recent studies have shown that neurotrophins (NTs) are involved in inflammatory processes. Elevated plasma levels of NTs were found allergic diseases with the highest levels in allergic asthma. However, the exact cellular sources involved in the regulation and release of neurotrophins in allergic inflammation are still not well defined.

OBJECTIVE

The aim of this study was to assess whether monocytes of allergic and non-allergic subjects produce, store and release the neurotrophins NGF, BDNF and NT-3.

METHODS

Monocytes of allergic and non-allergic donors were purified by immunomagnetic selection. APAAP-staining for the presence of NTs and their receptors was performed. RT-PCR and Western blot evaluated the production and storage of NTs. Monocytes were incubated and supernatants were collected for measurement of neurotrophic factors after stimulation with lipopolysaccharide (LPS) as inflammatory stimulus. The neurotrophin content in lysates and cell culture supernatants was determined by ELISA.

RESULTS

Human monocytes express the neurotrophins NGF, BDNF and NT-3 but also their specific receptors TrkA, TrkB and TrkC. RT-PCR amplification of isolated mRNA demonstrated expression of the examined neurotrophins. Proteins were detectable by Western blot. NTs were found in the monocyte lysates and supernatants at different levels in allergic and non-allergic donors. Cell stimulation with LPS leads to release of NGF and NT3.

CONCLUSIONS

Monocytes, produce, store and release NGF, BDNF and NT-3. They are a possible source of elevated neurotrophin levels found in allergy and asthma.

The release of nerve growth factor from the nasal mucosa following toluene diisocyanate

Toluene diisocyanate (TDI) produces rhinitis, nasal irritation, and increased synthesis and release of substance P (SP) from airway sensory nerves. Nerve growth factor (NGF) secretion in the nasal cavity is believed to mediate the irritant-induced upregulation of SP, but the cellular source of NGF in the nasal mucosa remains unclear. Studies to localize a source of NGF within the nasal mucosa are complicated by inflammatory-cell influx into the nasal mucosa following TDI, which obscures immunocytochemical identification of endogenous NGF sources. The purpose of this study was to determine the cellular source of NGF within the nasal mucosa following irritant exposure using a combined in vivo and ex vivo approach to reduce or eliminate contribution from inflammatory cells. Both nasal cavities of adult, male Sprague-Dawley rats were instilled with 5 microl of 10% TDI or control vehicle. After 15 min, nasal lavages were performed and the nasal mucosa was removed and placed into culture for 3 or 24 h. NGF was measured in the lavage supernatant and the culture media. Fifteen minutes after TDI exposure, NGF was significantly increased in the nasal lavage fluid. NGF levels in the culture medium of nasal mucosa from rats exposed to TDI ex vivo were significantly increased compared to controls following a 3-h culture. NGF levels in media after 24 h in culture was higher than at the 3-h point, but there was no difference between control and TDI groups. Since the nasal mucosa was removed prior to inflammatory cell influx, these findings suggest that cells in the nasal mucosa release NGF following exposure to TDI.

Neurotrophins in clinical diagnostics: pathophysiology and laboratory investigation

There is now growing evidence that a number of multifunctional signaling molecules, originally discovered as signal molecules in specific cells, exert their effects in various other tissue compartments. Neurotrophins, a class of homologues growth factors initially discovered to promote neuronal growth and survival, display such a dual activity and contribute to the development of a variety of non-neuronal tissues. Nowadays, several examples of essential non-neuronal functions played by neurotrophins and of variations of neurotrophin expression that accompany these processes can be presented. As will be shown, neurotrophins are found in many body tissues produced by a variety of non-neuronal cell types such as immune cells, adipocytes, endothelia, epithelia, fibroblasts, keratinocytes and endocrine cells. Assuming a general role as growth and survival factors, changes in neurotrophin expression may reflect physiological or pathological processes, such as activation, proliferation or repair followed by injury in the tissues. Neurotrophins were also present in the systemic blood circulation and variations in blood concentrations indicate vascular as well as peripheral production. In this review, we will discuss changes in local and systemic neurotrophin concentrations as well as their known pathophysiological relationship in various inflammatory and non-inflammatory disorders. Beside the nervous system, these will include diseases of the airways, skin and joints as well as systemic autoimmune diseases. Furthermore, new aspects of neurotrophin actions in maintenance of body energy balance and in reproductive endocrinology will be presented.

Prolonged exposure to NT-3 attenuates cholinergic nerve-mediated contractions in cultured murine airways

Chronic airway inflammation may induce subsequent airway hyper-responsiveness (AHR) including pathological alteration of neural activity. Asthmatic airways contain elevated levels of neurotrophin-3 (NT-3) and brain-derived neurotrophic factor (BDNF) albeit, their effect on neural activity is unclear. This study evaluates the effects of NT-3 and BDNF on nerve mediated airway contractions in vitro. Tracheal segments from BALB/c J mice were cultured for 4 days with NT-3 or BDNF. Responsiveness to electric field stimulation (EFS) was evaluated in organ-bath and innervation patterns were examined by quantitative immunohistochemistry. In cultured segments the EFS-induced contractions were inhibited by tetrodotoxin or atropine. NT-3 reduced the EFS contractions in a concentration-dependent manner whereas BDNF had no effect. The amount of nerve fibers, found in conjunction with the tracheal smooth muscle, was similar in NT-3 treated and control segments. In conclusion, NT-3 attenuates cholinergic nerve-mediated contractions of airway in vitro. Considering the elevated levels of NT-3 found in asthmatic airways, the findings imply a protective role of NT-3 in AHR.

Control of Human Hair Growth by Neurotrophins: Brain-Derived Neurotrophic Factor Inhibits Hair Shaft Elongation, Induces Catagen, and Stimulates Follicular Transforming Growth Factor β2 Expression

Neurotrophins are important modulators of epithelial-mesenchymal interactions. Previously, we had shown that brain-derived neurotrophic factor (BDNF) and its high-affinity receptor tyrosine kinase B (TrkB) are prominently involved in the control of murine hair follicle cycling. We now show that BDNF and TrkB are also expressed in the human hair follicle in a manner that is both hair cycle dependent and suggestive of epithelial-mesenchymal cross-talk between BDNF-secreting dermal papilla fibroblasts of anagen hair follicles and subpopulations of TrkB+ hair follicle keratinocytes. As functional evidence for an involvement of BDNF/TrkB in human hair growth control, we show in organ-cultured human anagen hair follicles that 50 ng per mL BDNF significantly inhibit hair shaft elongation, induce premature catagen development, and inhibit keratinocyte proliferation. Quantitative real-time rtPCR analysis demonstrates upregulation of the potent catagen inducer, transforming growth factor beta2 (TGFbeta2) by BDNF, whereas catagen induction by BDNF was partially reversible through co-administration of TGFbeta-neutralizing antibody. This suggests that TrkB-mediated signaling promotes the switch between anagen and catagen at least in part via upregulation of TGFbeta2. Thus, human scalp hair follicles are both a source and target of bioregulation by BDNF, which invites to target TrkB-mediated signaling for therapeutic hair growth modulation.

Low density of sympathetic nerve fibres and increased density of brain derived neurotrophic factor positive cells in RA synovium

OBJECTIVE

To investigate the correlation between density of nerve fibres and the presence of BDNF(+) cells.

METHODS

Densities of nerve fibres and BDNF(+) cells were detected by quantitative immunohistochemistry in fresh synovial tissue from 52 patients with RA, 59 with OA, and 26 controls (Co). BDNF was also detected by in situ hybridisation.

RESULTS

Sympathetic nerve fibre density was similar in Co and OA but markedly reduced in RA (p = 0.002), whereas density of substance P positive (SP(+)) sensory nerve fibres was lower in OA than in Co and RA (p = 0.002). The ratio of sympathetic/SP(+) sensory nerve fibre density was highest in OA and Co, followed by RA. The correlation between density of sympathetic nerve fibres and SP(+) sensory nerve fibres in OA (R = 0.425, p = 0.001) was strongly positive, had a positive trend in Co (R = 0.243, NS), but was negative in RA (R = -0.292, p = 0.040). In RA and OA tissue the density of BDNF(+) cells was high in sublining areas but markedly lower in Co (p = 0.001). BDNF(+) cell density correlated positively with the ratio of sympathetic/SP(+) sensory nerve fibre density in Co (R = 0.433, p = 0.045) and in OA (R = 0.613, p = 0.015), but not in RA (R = 0.101, NS). Immunohistochemical double staining demonstrated that some macrophages and fibroblasts were positive for BDNF.

CONCLUSIONS

The correlation of density of SP(+) sensory with sympathetic nerve fibres was positive in Co and OA but negative in RA. BDNF may have a stimulatory role on growth of sympathetic in relation to SP(+) sensory nerve fibres in Co and OA, but not in RA.

Human and murine lymphocyte neurotrophin expression is confined to B cells

Recent reports indicate that autoreactive T cells may produce neurotrophic factors capable of mediating repair and regeneration of damaged neurons. By using semiquantitative RT-PCR, we examined gene expression of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and the trkB BDNF receptor in autoreactive T cells from SWXJ mice immunized with the p104-117 encephalitogen of myelin proteolipid protein (PLP 104-117). We observed antigen-inducible expression of NGF and BDNF, but not NT-3 and trkB, in lymph node cells activated with PLP 104-117. To determine which leukocyte subpopulation expressed neurotrophins, CD4(+), CD8(+), B220(+), CD11b(+), and NK1.1(+) cells were purified from activated primary cultures, and their mRNAs were analyzed. Neurotrophin expression was also measured in CD3(+) T cells purified from mouse CNS during acute onset of experimental autoimmune encephalomyelitis as well as in resting and activated human T cells and B cells purified from peripheral blood of normal subjects. In all cases, we found that neurotrophin expression was confined exclusively to B cells (B220(+)) in both mouse and human. CD3(+), CD4(+), and CD8(+) T cells as well as NK1.1(+) cells and CD11b(+) monocytes and macrophages did not express any detectable BDNF, NGF, NT-3, or trkB under any conditions. Our data indicate that B cells rather than T cells are the predominant if not the only source of leukocyte-derived neurotrophins and as such may provide "protective autoimmunity" in repair and regeneration of the injured nervous system.

Interactions between the cells of the immune and nervous system: neurotrophins as neuroprotection mediators in CNS injury

Inflammatory processes in the central nervous system (CNS) are considered neurotoxic, although recent studies suggest that they also can be beneficial and confer neuroprotection (neuroprotective autoimmunity). Cells from the immune system have been detected in CNS injury and found to produce and secrete a variety of neurotrophins such as NGF, BDNF, NT-3 and NT-4/5, and to express (similarly to neuronal cells), members of the tyrosine kinase (Trk) receptor family such as TrkA, TrkB and TrkC. Indeed, autocrine and paracrine interactions are observed at the site of CNS injury, resulting in a variety of homologic-heterologic modulations of immune and neuronal cell function. The end result of the inflammatory process, neurotoxicity and/or neuroprotection, is a function of the fine balance between the two cellular systems, i.e., of the complex signaling relationships between anti-inflammatory neuroprotective factors (neurotrophins and other chemical mediators) and proinflammatory neurotoxic factors (TNF, free radicals, certain cytokines, etc.). Autoimmune neuroprotection is a novel therapeutic approach aimed at shifting the balance between the immune and neuronal cells towards survival pathways in a variety of CNS injuries. This review focuses on data supporting this concept and its future therapeutical implications for optic nerve injury and multiple sclerosis.

Nerve growth factor and substance P regulation in nasal sensory neurons after toluene diisocyanate exposure

Toluene diisocyanate (TDI) exposure produces rhinitis and nasal irritation, and increases the synthesis and release of substance P (SP) from airway sensory nerves. The mechanism leading to enhanced SP production following irritant inhalation remains unclear, but may involve actions of nerve growth factor (NGF). NGF binds trkA receptors located on sensory nerve terminals. Activation of trkA receptors initiates kinase-signaling cascades, which ultimately may increase SP. However, the effects of inhaled irritants on NGF release are not known. In this study, NGF levels in nasal lavages were examined following instillation of 10% TDI into both nasal cavities. NGF was significantly increased 2, 6, 12, and 24 h after TDI exposure compared with controls. The increase in NGF preceded the neuronal and mucosal increases in SP. Pretreatment with K252a, a nonselective tyrosine-kinase inhibitor, prevented the increase in SP-immunoreactivity in TG neurons and epithelial nerve fibers and the inflammatory response to TDI exposure. Because NGF binds to trkA tyrosine-kinase receptors, the NGF released during TDI exposure may mediate SP upregulation in airway sensory neurons, innervating the nasal cavity.

Neurotrophins in inflammatory lung diseases: modulators of cell differentiation and neuroimmune interactions

Chronic inflammatory lung diseases represent a group of severe diseases with increasing prevalence as well as epidemiological importance. Inflammatory lung diseases could result from allergic or infectious genesis. There is growing evidence that the immune and nervous system are closely related not only in physiological but also in pathological reactions in the lung. Extensive communications between neurons and immune cells are responsible for the magnitude of airway inflammation and the development of airway hyperreactivity, a consequence of neuronal dysregulation. Neurotrophins are molecules regulating and controlling this crosstalk between the immune and peripheral nervous system (PNS) during inflammatory lung diseases. They are constitutively expressed by resident lung cells and produced in increasing quantities by immune cells invading the airways under inflammatory conditions. They act as activation, differentiation and survival factors for cells of both the immune and nervous system. This article will review the most recent data of neurotrophin signaling in the normal and inflamed lung and as yet unexplored, roles of neurotrophins in the complex communication within the neuroimmune network.

The neurotrophins nerve growth factor, brain-derived neurotrophic factor, neurotrophin-3, and neurotrophin-4 are survival and activation factors for eosinophils in patients with allergic bronchial asthma

Neurotrophins (nerve growth factor [NGF], brain-derived neurotrophic factor [BDNF], neurotrophin [NT]-3, and NT-4) have been observed in elevated concentrations in allergic diseases. Neurotrophin levels are up-regulated endobronchially after allergen challenge. This coincides with an influx of activated eosinophils into the bronchial lumen. These eosinophils have an increased viability and CD69 expression 18 h after segmental allergen provocation (SAP) which is not present in peripheral blood. To investigate whether these observations are related we studied the influence of neurotrophins on eosinophil function in allergic asthma. Incubation with NGF, BDNF, NT-3, or NT-4 caused a significant increase in the viability and CD69 expression of isolated eosinophils from bronchoalveolar lavage fluid (BALF) but not from peripheral blood, suggesting a unique sensitivity of endobronchial eosinophils to neurotrophins. To elucidate the underlying mechanisms expression of the neurotrophin receptors p75NTR, trkA, trkB, and trkC on eosinophils was analyzed by RT-PCR and immunocytology. After SAP expression of all neurotrophin receptors was markedly elevated on eosinophils from BALF. Our findings suggest that neurotrophin-mediated activation of bronchial eosinophils might play a role in the regulation of eosinophilic inflammation in allergic asthma.

Role of nerve growth factor in modulation of gastric afferent neurons in the rat

Recent studies demonstrated that experimental ulcers are associated with changes in the properties of voltage-sensitive sodium currents in sensory neurons. We hypothesized that nerve growth factor (NGF) contributes to these changes. Gastric ulcers were induced by acetic acid injection into the wall of the rat stomach. NGF expression was determined by ELISA and immunohistochemically. Sensory neurons were labeled by injection of a retrograde tracer into the gastric wall. Sodium currents were recorded in gastric sensory neurons from nodose and dorsal root ganglia cultured for 24 h in the presence of NGF or a neutralizing NGF antibody, respectively. Gastric ulcer formation caused a rise in NGF concentration within the gastric wall and an increase in NGF immunoreactivity. Exposure to NGF caused a significant increase in the TTX-resistant sodium current, whereas the TTX-sensitive sodium current remained unchanged. This was associated with an acceleration of the recovery from inactivation in spinal sensory neurons. Production and release of NGF in the gastric wall may contribute to sensitization of primary afferent neurons during gastric inflammation.

Neurotrophic cross-talk between the nervous and immune systems: implications for neurological diseases

Inflammatory reactions in the central nervous system usually are considered detrimental, but recent evidence suggests that they also can be beneficial and even have neuroprotective effects. Intriguingly, immune cells can produce various neurotrophic factors of various molecular families. The concept of "neuroprotective immunity" will have profound consequences for the pathogenesis and treatment of neuroinflammatory diseases such as multiple sclerosis. It also will prove important for neurodegenerative disorders, in which inflammatory reactions often occur. This review focuses on recent findings that immune cells produce brain-derived neurotrophic factor in multiple sclerosis lesions, whereas neurons and astrocytes express the appropriate tyrosine kinase receptor TrkB. Together with functional evidence for the neuroprotective effects of immune cells, these observations support the concept of "neuroprotective immunity." We next examine current and future therapeutic strategies for multiple sclerosis and experimental autoimmune encephalomyelitis in light of neuroprotective immunity and finally address the broader implications of this new concept for other neuroinflammatory and neurodegenerative diseases.

IL-2 gene knockout affects T lymphocyte trafficking and the microglial response to regenerating facial motor neurons

Following facial nerve axotomy in mice, T cells cross the intact blood-brain barrier (BBB), home to nerve cell bodies in the facial motor nucleus (FMN), and augment neuroregenerative processes. The pivotal T cell immunoregulatory cytokine, IL-2, appears to have bidirectional effects on neuronal and microglial cell function, suggesting rival hypotheses that IL-2 could either enhance or disrupt processes associated with regeneration of axotomized facial motor neurons. We tested these competing hypotheses by comparing the effect of facial nerve axotomy on C57BL/6-IL-2(-/-) knockout and C57BL/6-IL-2(+/+) wild-type littermates. Since IL-2 may also be produced endogenously in the brain, we also sought to determine whether differences between the knockout and wild-type mice were attributable to loss of IL-2 gene expression in the CNS, loss of peripheral sources of IL-2 and the associated effects on T cell function, or a combination of these factors. To address this question, we bred novel congenic mice with the SCID mutation (mice lacking T cell derived IL-2) that were homozygous for either the IL-2 knockout or wild-type gene alleles (C57BL/6scid-IL-2(-/-) and C57BL/6scid-IL-2(+/+) littermates, respectively). Groups were assessed for differences in (1) T lymphocytes entering the axotomized FMN; (2) perineuronal CD11b(+) microglial phagocytic clusters, a measure of motor neuron death; and (3) activated microglial cells as measured by MHC-II positivity. C57BL/6-IL-2(-/-) knockout mice had significantly higher numbers of T cells and lower numbers of activated MHC-II-positive microglial cells in the regenerating FMN than wild-type littermates, although the number of CD11b(+) phagocytic microglia clusters did not differ. Thus, despite the significant impairment of T cell function known to be associated with loss of peripheral IL-2, the increased number of T cells entering the axotomized FMN appears to have sufficient activity to support neuroregenerative processes. Congenic C57BL/6scid-IL-2(-/-) knockout mice had lower numbers of CD11b(+) microglial phagocytic clusters than congenic C57BL/6scid-IL-2(+/+) wild-type littermates, suggesting that loss of the IL-2 gene in the CNS (and possibly the loss of other unknown sources of the gene) enhanced neuronal regeneration. Further study of IL-2's complex actions in neuronal injury may provide greater understanding of key variables that determine whether or not immunological processes in the brain are proregenerative.

Brain-derived neurotrophic factor in patients with multiple sclerosis

The aim of the present research was to verify the production of BDNF by peripheral blood mononuclear cells (PBMCs), unstimulated and stimulated with phytohemagglutinin (PHA), anti-OKT3 Ab and myelin basic protein (MBP), in 35 patients affected by multiple sclerosis (MS), 20 with relapsing-remitting (R-R) MS and 15 with secondary progressive (SP) MS. Seven R-R MS patients were assessed during the attack, in the subsequent recovery phase and also 3 months after relapse. The production of BDNF by PBMCs was also evaluated in 20 age- and sex-matched control subjects. Levels of BDNF were also determined in CSF of both patient groups and 20 control subjects.

RESULTS

Levels of BDNF (pg/ml) in the supernatants of unstimulated and PHA-, anti-OKT3 Ab- and MBP-stimulated PBMCs in patients with R-R MS were significantly higher during relapse and in the recovery phase compared with values detected in the stable phase of the disease. Significantly lower BDNF values were found in unstimulated and stimulated PBMC supernatants of patients with SP MS compared to control subjects. This reduction was greater in patients with a 1-point increase in the EDSS score in the last 6 months compared with that in patients without a progression of the disability score. Reduction in the levels of BDNF was also confirmed in the CSF of SP MS patients compared with R-R MS patients assessed during a stable phase of the disease and control subjects.

DISCUSSION

On the basis of recent experimental findings, a neuroprotective effect of BDNF produced by inflammatory cells can be hypothesized during relapses in MS. This can favor remyelination. The reduced production of BDNF by PBMCs of patients with SP MS can contribute to the progression of demyelinating disease and axonal loss in this form.

Neurotrophin-4 and glial cell line-derived neurotrophic factor in cerebrospinal fluid from meningitis/encephalitis patients

The neurotrophin-4 and glial cell line-derived neurotrophic factor levels were measured in cerebrospinal fluid from 61 patients with bacterial meningitis, viral meningitis, or encephalitis, and other diseases by means of two-site enzyme-linked immunoassay. Elevated cerebrospinal fluid levels of neurotrophin-4 were demonstrated in four of the 11 patients with bacterial meningitis, and seven of the 23 patients with viral meningitis or encephalitis. None of the other patients demonstrated elevation of the neurotrophin-4 level in cerebrospinal fluid. The neurotrophin-4 levels in cerebrospinal fluid were correlated with the numbers of total and mononuclear cells in patients with viral meningitis/encephalitis. In patients with bacterial meningitis, three of the four patients with elevated neurotrophin-4 levels exhibited persistent abnormalities on computed tomography, and one revealed transient subdural effusion. On the other hand, none of the seven patients without neurotrophin-4 elevation had persistent computed tomography abnormalities, and five patients demonstrated transient computed tomography abnormalities. The glial cell line-derived neurotrophic factor levels were below the detection limit, or only slightly higher than the detection limit, in the patients with or without central nervous system infections. Although the precise roles of neurotrophin-4 and glial cell line-derived neurotrophic factor in central nervous system infections remain to be determined, neurotrophin-4 might play a neuroprotective or immunomodulatory role in central nervous system infections.

Autoreactive T cells induce neurotrophin production by immune and neural cells in injured rat optic nerve: implications for protective autoimmunity

Accumulating evidence suggests that activation of the immune system in the central nervous system (CNS) after trauma protects the CNS from damage propagation and facilitates regeneration. Studies by our group have shown that passive transfer of autoimmune T cells specific to myelin basic protein (T(MBP)) can protect injured neurons in the rat CNS from secondary degeneration. In this study, we investigated the effects of T(MBP) treatment on the local immune response (by B cells and macrophages) and on the expression of neurotrophic factors after crush injury of the rat optic nerve. Systemic injection of activated T(MBP) caused an increase in the accumulation of macrophages/microglia and B cells in the injured nerve, which was greater than that seen in the injured optic nerves of untreated animals. This accumulation was accompanied by a transient, but massive, increase in the expression of neurotrophic factors. Immunocytochemical analysis demonstrated differential expression of neurotrophins by resident astrocytes and by infiltrating B cells, T cells, and macrophages. Because postinjury neuronal survival and maintenance are known to be affected by neurotrophins, our findings point to a possible contribution of a neurotrophin-related mechanism to the protective effect conferred by T cell-mediated autoimmunity on injured neurons.

Neurodevelopmental influences on the immune system reflecting brain pathology

A number of studies have shown that early life events can affect the development of the nervous system, contributing to particular individual differences in later vulnerability to different forms of psychosocial stress related to the environment and lifestyle. Neuropeptides, chemokines (CKs), neurotrophins (NTs) belong to the chemical microenvironment of the cells of the central nervous system (CNS). This paper reviews research performed in our and other laboratories indicating that mass spectrometry should play a significant role in future studies of the structures of proteins/peptides in neuroscience. These applications include peptide metabolism associated with normal and impaired neurone/immune function. Detailed information about peptide/protein processing in the CNS may be studied by using the lymphocyte as a model reflecting different chemical modifications of peptides/proteins related to various psychosomatic disturbances reflecting disorders of environment and lifestyle.

Age-related changes in noradrenergic sympathetic innervation of the rat spleen is strain dependent

Previous findings from our laboratory revealed an age-related decline in noradrenergic (NA) sympathetic innervation of the spleen in male Fischer 344 (F344) rats. The purpose of this study was to determine whether other rat strains also progressively lose NA sympathetic nerves in the aging spleen. Sympathetic innervation of spleens from 3- and 21-month-old male F344, Brown Norway (BN), BN X F344 (BNF(1)), and Lewis rats was examined using fluorescence histochemistry to localize catecholamines combined with morphometric analysis and using high-performance liquid chromatography with electrochemical detection for measuring norepinephrine (NE). Neurochemistry revealed a significant age-related decline in NE concentrations in spleens from F344 and Lewis rats. In contrast, there was no effect of age on splenic NE concentrations in BN or BNF(1) rats. Consistent with neurochemical analysis, fluorescence histochemistry revealed a striking decline in NA innervation of spleens from old F344 and Lewis rats not observed in the other two strains. However, in BN and BNF(1) rats, nerve fibers were diminished in distal portions of the spleen but not in the hilar regions. Morphometric analysis confirmed neurochemical and histological findings, revealing approximately 65-70% loss in NA nerve density in spleens from F344 and Lewis rats. These findings indicate that age-related changes in sympathetic innervation of the rat spleen are strain-dependent. Whether the loss of sympathetic nerves in spleens from F344 and Lewis rats is associated with age-related changes in the splenic microenvironment remains to be determined. The functional significance of altered sympathetic innervation of the spleen with advancing age is discussed.

Modulation of neuroendocrine--immune signaling by L-deprenyl and L-desmethyldeprenyl in aging and mammary cancer

The aging process is characterized by a decline in cellular functions of diverse systems of the body, including the neuroendocrine-immune network. One neuroendocrinological theory of aging is based on findings that the loss of hypothalamic neurotransmitter functions and an imbalance in hormonal secretion contribute to the cessation of reproductive cycles and the development of mammary and pituitary tumors. One potential cause of immunosenescence is an age-related decline in the regulatory functions of sympathetic noradrenergic nerve fibers whose neurotransmitters signal lymphoid cells in the bone marrow, thymus, spleen, and lymph nodes. In addition to impairment caused by the generation of free radicals during numerous biochemical processes, there is a shift in the pro-oxidant/anti-oxidant balance resulting in cellular oxidative stress and hastening the aging process. Altered interactions between the neuroendocrine system and the immune system are associated with increased incidence, development, and growth of breast cancer and other neoplastic diseases. We have demonstrated that the disruption in the neuroendocrine-immune interactions in old rats, and in female rats with mammary tumors, can be reversed by deprenyl, a monoamine oxidase inhibitor. Deprenyl treatment leads to enhanced central and peripheral catecholaminergic activity and a readjustment of immunological responses. In this brief review, the nature and changes in the bi-directional communication between the neuroendocrine system and immune system and the possible mechanism(s) of actions of deprenyl in restoring these interactions during aging and mammary cancer are discussed.

Effect of helium/neon laser irradiation on nerve growth factor synthesis and secretion in skeletal muscle cultures

Low energy laser irradiation therapy in medicine is widespread but the mechanisms are not fully understood. The aim of the present study was to elucidate the mechanism by which the light might induce therapeutic effects. Skeletal muscle cultures were chosen as a target for light irradiation and nerve growth factor (NGF) was the biochemical marker for analysis. It was found that there is a transient elevation of intracellular calcium in the myotubes immediately after irradiation (P<0.001). Preincubation of the myotubes with either the photosensitizers 5-amino-levulinic acid (5-ALA), or with hematoporphyrin (Hp) enhanced the elevation of cytosolic calcium (P<0.001) after helium/neon irradiation (633 nm) with an energy of 3 J/cm(2). In addition, helium/neon irradiation augmented the level of NGF mRNA fivefold and increased NGF release to the medium of the myotubes. Thus, it is speculated that transient changes in calcium caused by light can modulate NGF release from the myotubes and also affect the nerves innervating the muscle. The NGF is probably responsible for the beneficial effects of low-level light.