Neurotrophins and target interactions in the development and regulation of sympathetic neuron electrical and synaptic properties

Reprogramming of the developing heart by Hif1a-deficient sympathetic system and maternal diabetes exposure

Introduction

Maternal diabetes is a recognized risk factor for both short-term and long-term complications in offspring. Beyond the direct teratogenicity of maternal diabetes, the intrauterine environment can influence the offspring's cardiovascular health. Abnormalities in the cardiac sympathetic system are implicated in conditions such as sudden infant death syndrome, cardiac arrhythmic death, heart failure, and certain congenital heart defects in children from diabetic pregnancies. However, the mechanisms by which maternal diabetes affects the development of the cardiac sympathetic system and, consequently, heightens health risks and predisposes to cardiovascular disease remain poorly understood.

Methods and results

In the mouse model, we performed a comprehensive analysis of the combined impact of a Hif1a-deficient sympathetic system and the maternal diabetes environment on both heart development and the formation of the cardiac sympathetic system. The synergic negative effect of exposure to maternal diabetes and Hif1a deficiency resulted in the most pronounced deficit in cardiac sympathetic innervation and the development of the adrenal medulla. Abnormalities in the cardiac sympathetic system were accompanied by a smaller heart, reduced ventricular wall thickness, and dilated subepicardial veins and coronary arteries in the myocardium, along with anomalies in the branching and connections of the main coronary arteries. Transcriptional profiling by RNA sequencing (RNA-seq) revealed significant transcriptome changes in Hif1a-deficient sympathetic neurons, primarily associated with cell cycle regulation, proliferation, and mitosis, explaining the shrinkage of the sympathetic neuron population.

Discussion

Our data demonstrate that a failure to adequately activate the HIF-1α regulatory pathway, particularly in the context of maternal diabetes, may contribute to abnormalities in the cardiac sympathetic system. In conclusion, our findings indicate that the interplay between deficiencies in the cardiac sympathetic system and subtle structural alternations in the vasculature, microvasculature, and myocardium during heart development not only increases the risk of cardiovascular disease but also diminishes the adaptability to the stress associated with the transition to extrauterine life, thus increasing the risk of neonatal death.

Review of Herbal Medicines for the Treatment of Depression

Depression, a mental illness that is receiving increasing attention, is caused by multiple factors and genes and adversely affects social life and health. Several hypotheses have been proposed to clarify the pathogenesis of depression, and various synthetic antidepressants have been introduced to treat patients with depression. However, these drugs are effective only in a proportion of patients and fail to achieve complete remission. Recently, herbal medicines have received much attention as alternative treatments for depression because of their fewer side effects and lower costs. In this review, we have mainly focused on the herbal medicines that have been proven in clinical studies (especially randomized controlled trials and preclinical studies) to have antidepressant effects; we also describe the potential mechanisms of the antidepressant effects of those herbal medicines; the cellular and animal model of depression; and the development of novel drug delivery systems for herbal antidepressants. Finally, we objectively elaborate on the challenges of using herbal medicines as antidepressants and describe the benefits, adverse effects, and toxicity of these medicines.

Increased serum levels of brain-derived neurotrophic factor following wheelchair half marathon race in individuals with spinal cord injury

Objective: Brain-derived neurotrophic factor (BDNF) has beneficial effects on metabolism as well as the peripheral and central nervous systems. The aim of this study was to assess the response of serum BDNF concentration ([BDNF]s) to wheelchair half marathon race in individuals with spinal cord injury (SCI).Design: Prospective observational study.Setting: The 34th Oita International Wheelchair Marathon Race in Japan.Participants: Nine cervical SCIs (CSCI) and 8 thoracic and lumber SCIs (LSCI) male athletes. Interventions: Wheelchair half-Marathon Race.Outcome measures: [BDNF]s, plasma concentrations of adrenaline ([Ad]p), noradrenaline ([Nor]p), and cortisol ([Cor]p), hematocrit, and platelet count were measured the day before, immediately after, and an hour after the race.Results: [BDNF]s increased significantly immediately after the race in both groups (CSCI; P = 0.0055, LSCI; P = 0.0312) but returned to the baseline levels at one hour after the race. However, [BDNF]s immediately and one hour after the race were significantly higher in LSCI than in CSCI (immediately after the race; P = 0.0037, 1 h after the race; P = 0.0206). Hematocrit and platelet count remained unchanged throughout the study. In LSCI, [Ad]p, [Nor]p and [Cor]p increased significantly immediately after and one hour after the race, compared with the baseline values (P < 0.05). On the other hand, these variables remained unchanged throughout the study in the CSCI.Conclusions: [BDNF]_s increased significantly from the baseline in both LCSI and CSCI but was higher in LSCI than in CSCI immediately after and one hour after the race.

A cholinergic neuroskeletal interface promotes bone formation during postnatal growth and exercise

The autonomic nervous system is a master regulator of homeostatic processes and stress responses. Sympathetic noradrenergic nerve fibers decrease bone mass, but the role of cholinergic signaling in bone has remained largely unknown. Here, we describe that early postnatally, a subset of sympathetic nerve fibers undergoes an interleukin-6 (IL-6)-induced cholinergic switch upon contacting the bone. A neurotrophic dependency mediated through GDNF-family receptor-α2 (GFRα2) and its ligand, neurturin (NRTN), is established between sympathetic cholinergic fibers and bone-embedded osteocytes, which require cholinergic innervation for their survival and connectivity. Bone-lining osteoprogenitors amplify and propagate cholinergic signals in the bone marrow (BM). Moderate exercise augments trabecular bone partly through an IL-6-dependent expansion of sympathetic cholinergic nerve fibers. Consequently, loss of cholinergic skeletal innervation reduces osteocyte survival and function, causing osteopenia and impaired skeletal adaptation to moderate exercise. These results uncover a cholinergic neuro-osteocyte interface that regulates skeletogenesis and skeletal turnover through bone-anabolic effects.

The sympathetic nervous system in development and disease

The sympathetic nervous system prepares the body for 'fight or flight' responses and maintains homeostasis during daily activities such as exercise, eating a meal or regulation of body temperature. Sympathetic regulation of bodily functions requires the establishment and refinement of anatomically and functionally precise connections between postganglionic sympathetic neurons and peripheral organs distributed widely throughout the body. Mechanistic studies of key events in the formation of postganglionic sympathetic neurons during embryonic and early postnatal life, including axon growth, target innervation, neuron survival, and dendrite growth and synapse formation, have advanced the understanding of how neuronal development is shaped by interactions with peripheral tissues and organs. Recent progress has also been made in identifying how the cellular and molecular diversity of sympathetic neurons is established to meet the functional demands of peripheral organs. In this Review, we summarize current knowledge of signalling pathways underlying the development of the sympathetic nervous system. These findings have implications for unravelling the contribution of sympathetic dysfunction stemming, in part, from developmental perturbations to the pathophysiology of peripheral neuropathies and cardiovascular and metabolic disorders.

Neurotrophic factors and their receptors in lung development and implications in lung diseases

Although lung innervation has been described by many studies in humans and rodents, the regulation of the respiratory system induced by neurotrophins is not fully understood. Here, we review current knowledge on the role of neurotrophins and the expression and function of their receptors in neurogenesis, vasculogenesis and during the embryonic development of the respiratory tree and highlight key implications relevant to respiratory diseases.

Pleiotropic activity of nerve growth factor in regulating cardiac functions and counteracting pathogenesis

Cardiac innervation density generally reflects the levels of nerve growth factor (NGF) produced by the heart—changes in NGF expression within the heart and vasculature contribute to neuronal remodelling (e.g. sympathetic hyperinnervation or denervation). Its synthesis and release are altered under different pathological conditions. Although NGF is well known for its survival effects on neurons, it is clear that these effects are more wide ranging. Recent studies reported both in vitro and in vivo evidence for beneficial actions of NGF on cardiomyocytes in normal and pathological hearts, including prosurvival and antiapoptotic effects. NGF also plays an important role in the crosstalk between the nervous and cardiovascular systems. It was the first neurotrophin to be implicated in postnatal angiogenesis and vasculogenesis by autocrine and paracrine mechanisms. In connection with these unique cardiovascular properties of NGF, we have provided comprehensive insight into its function and potential effect of NGF underlying heart sustainable/failure conditions. This review aims to summarize the recent data on the effects of NGF on various cardiovascular neuronal and non‐neuronal functions. Understanding these mechanisms with respect to the diversity of NGF functions may be crucial for developing novel therapeutic strategies, including NGF action mechanism‐guided therapies.

Paracervical ganglion in the female pig during prenatal development: Morphology and immunohistochemical characteristics

The present study investigated the development of the paracervical ganglion in 5-, 7- and 10-week-old porcine foetuses using double labelling immunofluorescence method. In 5-week-old foetuses single PGP-positive perikarya were visible only along the mesonephric ducts. They contained DβH or VAChT, and nerve fibres usually were PGP/VAChT-positive. The perikarya were mainly oval. In 7-week-old foetuses, a compact group of PGP-positive neurons (3144±213) was visible on both sides and externally to the uterovaginal canal mesenchyme of paramesonephric ducts. Nerve cell bodies contained only DβH (36.40±1.63%) or VAChT (17.31±1.13%). In the 10-week-old foetuses, the compact group of PGP-positive neurons divided into several large and many small clusters of nerve cells and also became more expanded along the whole uterovaginal canal mesenchyme reaching the initial part of the uterine canal of the paramesonephric duct. The number of neurons located in these neuronal structures increased to 4121±259. Immunohistochemistry revealed that PGP-positive nerve cell bodies contained DβH (40.26±0,73%) and VAChT (30.73±1.34%) and were also immunoreactive for NPY (33.24±1,27%), SOM (23.6±0,44%) or VIP (22.9±1,13%). Other substances studied (GAL, NOS, CGRP, SP) were not determined at this stage of the development. In this study, for the first time, the morphology of PCG formation in the porcine foetus has been described in three stages of development. Dynamic changes in the number of neurons and their sizes were also noted, as well as the changes in immunochistochemical coding of maturing neurons.

Biomarkers of Activation and Inflammation to Track Disparity in Chronological and Physiological Age of People Living With HIV on Combination Antiretroviral Therapy

With advancement, prompt use, and increasing accessibility of antiretroviral therapy, people with HIV are living longer and have comparable lifespans to those negative for HIV. However, people living with HIV experience tradeoffs with quality of life often developing age-associated co-morbid conditions such as cancers, cardiovascular diseases, or neurodegeneration due to chronic immune activation and inflammation. This creates a discrepancy in chronological and physiological age, with HIV-infected individuals appearing older than they are, and in some contexts ART-associated toxicity exacerbates this gap. The complexity of the accelerated aging process in the context of HIV-infection highlights the need for greater understanding of biomarkers involved. In this review, we discuss markers identified in different anatomical sites of the body including periphery, brain, and gut, as well as markers related to DNA that may serve as reliable predictors of accelerated aging in HIV infected individuals as it relates to inflammatory state and immune activation.

TrkB-Induced Inhibition of R-SMAD/SMAD4 Activation is Essential for TGF-β-Mediated Tumor Suppressor Activity

TrkB-mediated activation of the IL6/JAK2/STAT3 signaling pathway is associated with the induction of the epithelial–mesenchymal transition (EMT) program and the acquisition of metastatic potential by tumors. Conversely, the transforming of growth factor-β (TGF-β) is implicated in tumor suppression through the canonical SMAD-dependent signaling pathway. Hence, TrkB could play a role in disrupting the potent TGF-β-mediated growth inhibition, a concept that has not been fully explored. Here, we identified TrkB to be a crucial regulator of the TGF-β signaling pathway as it inhibits the TGF-β-mediated tumor suppression and the activation of TrkB kinase. We further show that the interactions between TrkB and SMADs inhibit TGF-β-mediated R-SMAD/SMAD4 complex formation and suppress TGF-β-induced nuclear translocation and target gene expression. Additionally, the knockdown of TrkB restored the tumor inhibitory activity of TGF-β signaling. These observations suggest that interactions between TrkB and SMADs are critical for the inhibition of TGF-β tumor suppressor activity in cancer cells.

BDNF Actions in the Cardiovascular System: Roles in Development, Adulthood and Response to Injury

The actions of BDNF (Brain-derived Neurotrophic Factor) in regulating neuronal development and modulating synaptic activity have been extensively studied and well established. Equally important roles for this growth factor have been uncovered in the cardiovascular system, through the examination of gene targeted animals to define critical actions in development, and to the unexpected roles of BDNF in modulating the response of the heart and vasculature to injury. Here we review the compartmentally distinct realm of cardiac myocytes, vascular smooth muscle cells, endothelial cells, and hematopoietic cells, focusing upon the actions of BDNF to modulate contractility, migration, neoangiogenesis, apoptosis and survival. These studies indicate that BDNF is an important growth factor which directs the response of the cardiovascular system to acute and chronic injury.

Increased Brain-Derived Neurotrophic Factor in Lumbar Dorsal Root Ganglia Contributes to the Enhanced Exercise Pressor Reflex in Heart Failure

An exaggerated exercise pressor reflex (EPR) is associated with excessive sympatho-excitation and exercise intolerance in the chronic heart failure (CHF) state. We hypothesized that brain-derived neurotrophic factor (BDNF) causes the exaggerated EPR via sensitizing muscle mechanosensitive afferents in CHF. Increased BDNF expression was observed in lumbar dorsal root ganglia (DRGs) from CHF rats compared to sham rats. Immunofluorescence data showed a greater increase in the number of BDNF-positive neurons in medium and large-sized DRG subpopulations from CHF rats. Patch clamp data showed that incubation with BDNF for 4–6 h, significantly decreased the current threshold-inducing action potential (AP), threshold potential and the number of APs during current injection in Dil-labeled isolectin B4 (IB4)-negative medium-sized DRG neurons (mainly mechano-sensitive) from sham rats. Compared to sham rats, CHF rats exhibited an increased number of APs during current injection in the same DRG subpopulation, which was significantly attenuated by 4-h incubation with anti-BDNF. Finally, chronic epidural delivery of anti-BDNF attenuated the exaggerated pressor response to either static contraction or passive stretch in CHF rats whereas this intervention had no effect on the pressor response to hindlimb arterial injection of capsaicin. These data suggest that increased BDNF in lumbar DRGs contributes to the exaggerated EPR in CHF.

BDNF - A key player in cardiovascular system

Neurotrophins (NTs) were first identified as target-derived survival factors for neurons of the central and peripheral nervous system (PNS). They are known to control neural cell fate, development and function. Independently of their neuronal properties, NTs exert unique cardiovascular activity. The heart is innervated by sensory, sympathetic and parasympathetic neurons, which require NTs during early development and in the establishment of mature properties, contributing to the maintenance of cardiovascular homeostasis. The identification of molecular mechanisms regulated by NTs and involved in the crosstalk between cardiac sympathetic nerves, cardiomyocytes, cardiac fibroblasts, and vascular cells, has a fundamental importance in both normal heart function and disease. The article aims to review the recent data on the effects of Brain-Derived Neurotrophic Factor (BDNF) on various cardiovascular neuronal and non-neuronal functions such as the modulation of synaptic properties of autonomic neurons, axonal outgrowth and sprouting, formation of the vascular and neural networks, smooth muscle migration, and control of endothelial cell survival and cardiomyocytes. Understanding these mechanisms may be crucial for developing novel therapeutic strategies, including stem cell-based therapies.

Detection of aberrant methylated SEPT9 and NTRK3 genes in sporadic colorectal cancer patients as a potential diagnostic biomarker

Colorectal cancer (CRC) is one of the most common malignancies, and the third leading cause of cancer mortality worldwide. Timely detection of CRC in patients with earlier stages provides the highest rate of survival. Epigenetic alterations are important in the occurrence and progression of CRC, and represent the primary modifications of cancer cells. Therefore, detection of these alterations in CRC cases are thought to hold great promise as diagnostic biomarkers. It has been shown that the SEPT9 and NTRK3 genes are aberrantly methylated and their detection can be used as biomarkers for early diagnosis of CRC. The present study analyzed promoter methylation status of these genes in CRC patients. Genomic DNA was extracted from 45 CRC and paired adjacent healthy tissues and undergone bisulfite conversion, and the methylation status of NTRK3 and SEPT9 were defined using the MS-HRM assay. Our results showed that there are statistically significant differences in methylation status of NTRK3 and specially SEPT9 between CRC and adjacent normal tissues (P<0.001). High sensitivity and specificity for a specific location in SEPT9 gene promoter as a diagnostic biomarker was observed. SEPT9 promoter hypermethylation may serve as a promising biomarker for the detection of CRC development. However, to validate the biomarker potential of NTRK3 there is a requirement for further investigation.

Studying the pathophysiologic connection between cardiovascular and nervous systems using stem cells

The cardiovascular and nervous systems are deeply connected during development, health, and disease. Both systems affect and regulate the development of each other during embryogenesis and the early postnatal period. Specialized neural crest cells contribute to cardiac structures, and a number of growth factors released from the cardiac tissue (e.g., glial cell line-derived neurotrophic factor, neurturin, nerve growth factor, Neurotrophin-3) ensure proper maturation of the incoming parasympathetic and sympathetic neurons. Physiologically, the cardiovascular and nervous systems operate in harmony to adapt to various physical and emotional conditions to maintain homeostasis through sympathetic and parasympathetic nervous systems. Moreover, neurocardiac regulation involves a neuroaxis consisting of cortex, amygdala, and other subcortical structures, which have the ability to modify lower-level neurons in the hierarchy. Given the interconnectivity of cardiac and neural systems, when one undergoes pathological changes, the other is affected to a certain extent. In addition, there are specific neurocardiac diseases that affect both systems simultaneously, such as Huntington disease, Lewy body diseases, Friedreich ataxia, congenital heart diseases, Danon disease, and Timothy syndrome. Over the last decade, in vitro modeling of neurocardiac diseases using induced pluripotent stem cells (iPSCs) has provided an invaluable opportunity to elevate our knowledge about the brain-heart connection, since previously primary cardiomyocytes and neurons had been extremely difficult to maintain long-term in vitro. Ultimately, the ability of iPSC technology to model abnormal functional phenotypes of human neurocardiac disorders, combined with the ease of therapeutic screening using this approach, will transform patient care through personalized medicine in the future. © 2016 Wiley Periodicals, Inc.

Merkel Cell-Driven BDNF Signaling Specifies SAI Neuron Molecular and Electrophysiological Phenotypes

The extent to which the skin instructs peripheral somatosensory neuron maturation is unknown. We studied this question in Merkel cell-neurite complexes, where slowly adapting type I (SAI) neurons innervate skin-derived Merkel cells. Transgenic mice lacking Merkel cells had normal dorsal root ganglion (DRG) neuron numbers, but fewer DRG neurons expressed the SAI markers TrkB, TrkC, and Ret. Merkel cell ablation also decreased downstream TrkB signaling in DRGs, and altered the expression of genes associated with SAI development and function. Skin- and Merkel cell-specific deletion of Bdnf during embryogenesis, but not postnatal Bdnf deletion or Ntf3 deletion, reproduced these results. Furthermore, prototypical SAI electrophysiological signatures were absent from skin regions where Bdnf was deleted in embryonic Merkel cells. We conclude that BDNF produced by Merkel cells during a precise embryonic period guides SAI neuron development, providing the first direct evidence that the skin instructs sensory neuron molecular and functional maturation.

SIGNIFICANCE STATEMENT

Peripheral sensory neurons show incredible phenotypic and functional diversity that is initiated early by cell-autonomous and local environmental factors found within the DRG. However, the contribution of target tissues to subsequent sensory neuron development remains unknown. We show that Merkel cells are required for the molecular and functional maturation of the SAI neurons that innervate them. We also show that this process is controlled by BDNF signaling. These findings provide new insights into the regulation of somatosensory neuron development and reveal a novel way in which Merkel cells participate in mechanosensation.

Overexpression of NTRK1 Promotes Differentiation of Neural Stem Cells into Cholinergic Neurons

Neurotrophic tyrosine kinase type 1 (NTRK1) plays critical roles in proliferation, differentiation, and survival of cholinergic neurons; however, it remains unknown whether enhanced expression of NTRK1 in neural stem cells (NSCs) can promote their differentiation into mature neurons. In this study, a plasmid encoding the rat NTRK1 gene was constructed and transfected into C17.2 mouse neural stem cells (NSCs). NTRK1 overexpression in C17.2 cells was confirmed by western blot. The NSCs overexpressing NTRK1 and the C17.2 NSCs transfected by an empty plasmid vector were treated with or without 100 ng/mL nerve growth factor (NGF) for 7 days. Expression of the cholinergic cell marker, choline acetyltransferase (ChAT), was detected by florescent immunocytochemistry (ICC). In the presence of NGF induction, the NSCs overexpressing NTRK1 differentiated into ChAT-immunopositive cells at 3-fold higher than the NSCs transfected by the plasmid vector (26% versus 9%, P < 0.05). The data suggest that elevated NTRK1 expression increases differentiation of NSCs into cholinergic neurons under stimulation of NGF. The approach also represents an efficient strategy for generation of cholinergic neurons.

Virtual leak channels modulate firing dynamics and synaptic integration in rat sympathetic neurons: implications for ganglionic transmission in vivo

KEY POINTS

The synaptic organization of paravertebral sympathetic ganglia enables them to relay activity from the spinal cord to the periphery and thereby control autonomic functions, including blood pressure and body temperature. The present experiments were done to reconcile conflicting observations in tissue culture, intact isolated ganglia and living animals. By recording intracellularly from dissociated neurons and intact ganglia, we found that when electrode damage makes cells leaky it could profoundly distort cellular excitability and the integration of synaptic potentials. The experiments relied on the dynamic clamp method, which allows the creation of virtual ion channels by injecting current into a cell based upon a mathematical model and using rapid feedback between the model and cell. The results support the hypothesis that sympathetic ganglia can produce a 2.4-fold amplification of presynaptic activity. This could aid understanding of the neural hyperactivity that is believed to drive high blood pressure in some patients.

ABSTRACT

The excitability of rat sympathetic neurons and integration of nicotinic EPSPs were compared in primary cell culture and in the acutely isolated intact superior cervical ganglion using whole cell patch electrode recordings. When repetitive firing was classified by Hodgkin's criteria in cultured cells, 18% displayed tonic class 1 excitability, 36% displayed adapting class 2 excitability and 46% displayed phasic class 3 excitability. In the intact ganglion, 71% of cells were class 1 and 29% were class 2. This diverges from microelectrode reports that nearly 100% of superior cervical ganglion neurons show phasic class 3 firing. The hypothesis that the disparity between patch and microelectrode data arises from a shunt conductance was tested using the dynamic clamp in cell culture. Non-depolarizing shunts of 3-10 nS converted cells from classes 1 and 2 to class 3 dynamics with current-voltage relations that replicated microelectrode data. Primary and secondary EPSPs recorded from the intact superior cervical ganglion were modelled as virtual synapses in cell culture using the dynamic clamp. Stimulating sympathetic neurons with virtual synaptic activity, designed to replicate in vivo recordings of EPSPs in muscle vasoconstrictor neurons, produced a 2.4-fold amplification of presynaptic activity. This gain in postsynaptic output did not differ between neurons displaying the three classes of excitability. Mimicry of microelectrode damage by virtual leak channels reduced and eventually obliterated synaptic gain by inhibiting summation of subthreshold EPSPs. These results provide a framework for interpreting sympathetic activity recorded from intact animals and support the hypothesis that paravertebral ganglia function as activity-dependent amplifiers of spinal output from preganglionic circuitry.

An NT4/TrkB-dependent increase in innervation links early-life allergen exposure to persistent airway hyperreactivity

Children who are exposed to environmental respiratory insults often develop asthma that persists into adulthood. In this study, we used a neonatal mouse model of ovalbumin (OVA)-induced allergic airway inflammation to understand the long-term effects of early childhood insults on airway structure and function. We showed that OVA sensitization and challenge in early life led to a 2-fold increase in airway smooth muscle (ASM) innervation (P<0.05) and persistent airway hyperreactivity (AHR). In contrast, OVA exposure in adult life elicited short-term AHR without affecting innervation levels. We found that postnatal ASM innervation required neurotrophin (NT)-4 signaling through the TrkB receptor and that early-life OVA exposure significantly elevated NT4 levels and TrkB signaling by 5- and 2-fold, respectively, to increase innervation. Notably, blockade of NT4/TrkB signaling in OVA-exposed pups prevented both acute and persistent AHR without affecting baseline airway function or inflammation. Furthermore, biophysical assays using lung slices and isolated cells demonstrated that NT4 was necessary for hyperreactivity of ASM induced by early-life OVA exposure. Together, our findings show that the NT4/TrkB-dependent increase in innervation plays a critical role in the alteration of the ASM phenotype during postnatal growth, thereby linking early-life allergen exposure to persistent airway dysfunction.

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.

[Autonomic regulation and bradycardia during the neonatal period]

The high frequency of bradycardia observed during the neonatal period requires cardiac monitoring but also understanding its intrinsic mechanisms, including responsiveness of the autonomic nervous system (ANS). Heart rate variability and spontaneous baroreflex analysis can help understand the autonomic dysregulation of cardiorespiratory control, possibly responsible for sudden infant death. In clinical neonatology practice, neonatal bradycardia does not warrant continuation of monitoring if it remains isolated, asymptomatic, and short (<10 s), followed by a rapid cardiac acceleration indicating an adapted sympathetic response. Further evaluation of ANS responsiveness is possible for newborns including analyzing the complexity of the heart rate and respiratory variability. This allows better targeting children with high risk after discharge. The real-time evaluation of autonomic regulation could become a valuable tool in clinical practice.

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.

Metabolic syndrome--from the neurotrophic hypothesis to a theory

Metabolic syndrome (MetS) is a complex and heterogeneous disease characterized by central obesity, impaired glucose metabolism, dyslipidemia, arterial hypertension, insulin resistance and high-sensitivity C-reactive protein. In 2006, a neurotrophic hypothesis of the etiopathogenesis of MetS was launched. This hypothesis considered the neurotrophins a key factor in MetS development. Chronic inflammatory and/or psychoemotional distress provoke a series of neuroimmunoendocrine interactions such as increased tissue and plasma levels of proinflammatory cytokines and neurotrophins, vegetodystonia, disbalance of neurotransmitters, hormones and immunity markers, activation of the hypothalamo-pituitary-adrenal axis, insulin resistance, and atherosclerosis. An early and a late clinical stage in the course of MetS are defined. Meanwhile, evidence of supporting results from the world literature accumulates. This enables the transformation of the definition of the neurotrophic hypothesis into a neurotrophic theory of MetS. The important role of two neurotrophic factors, i.e. the nerve growth factor and brain-derived neurotrophic factor as well as of the proinflammatory cytokines, neurotransmitters, adipokines and, especially, of leptin for the development of MetS, obesity and type 2 diabetes mellitus is illustrated. There are reliable scientific arguments that the metabotrophic deficit due to reduced neurotrophins could be implicated in the pathogenesis of MetS, type 2 diabetes mellitus, and atherosclerosis as well. A special attention is paid to the activity of the hypothalamo-pituitary-adrenal axis after stress. The application of the neurotrophic theory of MetS could contribute to the etiological diagnosis and individualized management of MetS by eliminating the chronic distress, hyponeurotrophinemia and consequent pathology. It helps estimating the risk, defining the prognosis and implementing the effective prevention of this socially significant disease as evidenced by the dramatic recent growth of the world publication output on this interdisciplinary topic.

NTRK3 is a potential tumor suppressor gene commonly inactivated by epigenetic mechanisms in colorectal cancer

NTRK3 is a member of the neurotrophin receptor family and regulates cell survival. It appears to be a dependence receptor, and thus has the potential to act as an oncogene or as a tumor suppressor gene. NTRK3 is a receptor for NT-3 and when bound to NT-3 it induces cell survival, but when NT-3 free, it induces apoptosis. We identified aberrantly methylated NTRK3 in colorectal cancers through a genome-wide screen for hypermethylated genes. This discovery led us to assess whether NTRK3 could be a tumor suppressor gene in the colon. NTRK3 is methylated in 60% of colon adenomas and 67% of colon adenocarcinomas. NTRK3 methylation suppresses NTRK3 expression. Reconstitution of NTRK3 induces apoptosis in colorectal cancers, if NT-3 is absent. Furthermore, the loss of NTRK3 expression associates with neoplastic transformation in vitro and in vivo. We also found that a naturally occurring mutant NTRK3 found in human colorectal cancer inhibits the tumor suppressor activity of NTRK3. In summary, our findings suggest NTRK3 is a conditional tumor suppressor gene that is commonly inactivated in colorectal cancer by both epigenetic and genetic mechanisms whose function in the pathogenesis of colorectal cancer depends on the expression status of its ligand, NT-3.

NTRK3 is a neurotrophin receptor and appears to be a dependence receptor in certain tissues. NTRK3 has been previously shown to be an oncogene in breast cancer and possibly hepatocellular carcinoma. Through a genome-wide methylation screen, we unexpectedly found that NTRK3 is commonly methylated in colorectal cancers but not in normal colon samples, which led us to assess whether NTRK3 could be a tumor suppressor gene in the colon. We now demonstrate that NTRK3 is frequently methylated in colorectal adenomas and cancers. Induced NTRK3 expression in the absence of its ligand, NT-3, causes apoptosis and suppresses in vitro anchorage-independent colony formation and in vivo tumor growth. Reintroduction of NT-3 releases colon cancer cells from NTRK3-mediated apoptosis, which is consistent with NTRK3 being a dependence receptor in the colon. Finally, somatic mutations of NTRK3 have been observed in primary human colorectal cancer. We provide evidence that a subset of these mutations inactivate tumor suppressor activities of NTRK3. These findings suggest that NTRK3 is a conditional tumor suppressor gene in the colon that is inactivated by both genetic and epigenetic mechanisms and whose function in the pathogenesis of colorectal cancer depends on the expression status of its ligand, NT-3.

Brain-derived neurotrophic factor in cigarette smoke-induced airway hyperreactivity

Enhanced airway smooth muscle (ASM) contractility contributes to increased resistance to airflow in diseases such as bronchitis and asthma that occur in passive smokers exposed to secondhand smoke. Little information exists on the cellular mechanisms underlying such airway hyperreactivity. Sputum samples of patients with chronic sinusitis, bronchitis, and asthma show increased concentrations of growth factors called neurotrophins, including brain-derived growth factor (BDNF), but their physiological significance remains unknown. In human ASM, we tested the hypothesis that BDNF contributes to increased contractility with cigarette smoke exposure. The exposure of ASM to 1% or 2% cigarette smoke extract (CSE) for 24 hours increased intracellular calcium ([Ca(2+)](i)) responses to histamine, and further potentiated the enhancing effects of a range of BDNF concentrations on such histamine responses. CSE exposure increased the expression of the both high-affinity and low-affinity neurotrophin receptors tropomyosin-related kinase (Trk)-B and p75 pan-neurotrophin receptor, respectively. Quantitative ELISA showed that CSE increased BDNF secretion by human ASM cells. BDNF small interfering (si)RNA and/or the chelation of extracellular BDNF, using TrkB-fragment crystallizable, blunted the effects of CSE on [Ca(2+)](i) responses as well as the CSE enhancement of cell proliferation, whereas TrkB siRNA blunted the effects of CSE on ASM contractility. These data suggest that cigarette smoke is a potent inducer of BDNF and TrkB expression and signaling in ASM, which then contribute to cigarette smoke-induced airway hyperresponsiveness.

Autonomic cardiac innervation: development and adult plasticity

Autonomic cardiac neurons have a common origin in the neural crest but undergo distinct developmental differentiation as they mature toward their adult phenotype. Progenitor cells respond to repulsive cues during migration, followed by differentiation cues from paracrine sources that promote neurochemistry and differentiation. When autonomic axons start to innervate cardiac tissue, neurotrophic factors from vascular tissue are essential for maintenance of neurons before they reach their targets, upon which target-derived trophic factors take over final maturation, synaptic strength and postnatal survival. Although target-derived neurotrophins have a central role to play in development, alternative sources of neurotrophins may also modulate innervation. Both developing and adult sympathetic neurons express proNGF, and adult parasympathetic cardiac ganglion neurons also synthesize and release NGF. The physiological function of these “non-classical” cardiac sources of neurotrophins remains to be determined, especially in relation to autocrine/paracrine sustenance during development.

 

Cardiac autonomic nerves are closely spatially associated in cardiac plexuses, ganglia and pacemaker regions and so are sensitive to release of neurotransmitter, neuropeptides and trophic factors from adjacent nerves. As such, in many cardiac pathologies, it is an imbalance within the two arms of the autonomic system that is critical for disease progression. Although this crosstalk between sympathetic and parasympathetic nerves has been well established for adult nerves, it is unclear whether a degree of paracrine regulation occurs across the autonomic limbs during development. Aberrant nerve remodeling is a common occurrence in many adult cardiovascular pathologies, and the mechanisms regulating outgrowth or denervation are disparate. However, autonomic neurons display considerable plasticity in this regard with neurotrophins and inflammatory cytokines having a central regulatory function, including in possible neurotransmitter changes. Certainly, neurotrophins and cytokines regulate transcriptional factors in adult autonomic neurons that have vital differentiation roles in development. Particularly for parasympathetic cardiac ganglion neurons, additional examinations of developmental regulatory mechanisms will potentially aid in understanding attenuated parasympathetic function in a number of conditions, including heart failure.

Neurotrophins regulate cholinergic synaptic transmission in cultured rat sympathetic neurons through a p75-dependent mechanism

The sympathetic nervous system regulates many essential physiological systems, and its dysfunction is implicated in cardiovascular diseases. Mechanisms that control the strength of sympathetic output are therefore potential targets for the management of these disorders. Here we show that neurotrophins rapidly potentiate cholinergic transmission between cultured rat sympathetic neurons. We found that brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF), acting at the p75 receptor, increased the amplitude of excitatory postsynaptic currents (EPSCs). We observed increased amplitude but not frequency of miniature synaptic currents after p75 activation, suggesting that p75 acts postsynaptically to modulate transmission at these synapses. This neurotrophic modulation enhances cholinergic EPSCs via sphingolipid signaling. Application of sphingolactone-24, an inhibitor of neutral sphingomyelinase, blocked the effect of BDNF, implicating a sphingolipid pathway. Furthermore, application of the p75-associated sphingolipid second messengers C(2)-ceramide and d-erythro-sphingosine restricted to the postsynaptic cell mimicked BDNF application. Postsynaptic blockade of ceramide production with fumonisin, a ceramide synthase inhibitor, blocked the effects of BDNF and d-erythro-sphingosine, implicating ceramide or ceramide phosphate as the active signal. Together these data suggest that neurotrophin signaling, which occurs in vivo via release from sympathetic neurons and target tissues such as the heart, acutely regulates the strength of the sympathetic postganglionic response to central cholinergic inputs. This pathway provides a potential mechanism for modulating the strength of sympathetic drive to target organs such as the heart and could play a role in the development of cardiovascular diseases.

Brain-derived neurotrophic factor enhances calcium regulatory mechanisms in human airway smooth muscle

Neurotrophins (NTs), which play an integral role in neuronal development and function, have been found in non-neuronal tissue (including lung), but their role is still under investigation. Recent reports show that NTs such as brain-derived neurotrophic factor (BDNF) as well as NT receptors are expressed in human airway smooth muscle (ASM). However, their function is still under investigation. We hypothesized that NTs regulate ASM intracellular Ca²⁺ ([Ca²⁺]_i) by altered expression of Ca²⁺ regulatory proteins. Human ASM cells isolated from lung samples incidental to patient surgery were incubated for 24 h (overnight) in medium (control) or 1 nM BDNF in the presence vs. absence of inhibitors of signaling cascades (MAP kinases; PI3/Akt; NFκB). Measurement of [Ca²⁺]_i responses to acetylcholine (ACh) and histamine using the Ca²⁺ indicator fluo-4 showed significantly greater responses following BDNF exposure: effects that were blunted by pathway inhibitors. Western analysis of whole cell lysates showed significantly higher expression of CD38, Orai1, STIM1, IP₃ and RyR receptors, and SERCA following BDNF exposure, effects inhibited by inhibitors of the above cascades. The functional significance of BDNF effects were verified by siRNA or pharmacological inhibition of proteins that were altered by this NT. Overall, these data demonstrate that NTs activate signaling pathways in human ASM that lead to enhanced [Ca²⁺]_i responses via increased regulatory protein expression, thus enhancing airway contractility.

Motoneuron programmed cell death in response to proBDNF

Motoneurons (MN) as well as most neuronal populations undergo a temporally and spatially specific period of programmed cell death (PCD). Several factors have been considered to regulate the survival of MNs during this period, including availability of muscle-derived trophic support and activity. The possibility that target-derived factors may also negatively regulate MN survival has been considered, but not pursued. Neurotrophin precursors, through their interaction with p75(NTR) and sortilin receptors have been shown to induce cell death during development and following injury in the CNS. In this study, we find that muscle cells produce and secrete proBDNF. ProBDNF through its interaction with p75(NTR) and sortilin, promotes a caspase-dependent death of MNs in culture. We also provide data to suggest that proBDNF regulates MN PCD during development in vivo.

Neurodegeneration and neuroregeneration in Chagas disease

Autonomic dysfunction plays a significant role in the development of chronic Chagas disease (CD). Destruction of cardiac parasympathetic ganglia can underlie arrhythmia and heart failure, while lesions of enteric neurons in the intestinal plexuses are a direct cause of aperistalsis and megasyndromes. Neuropathology is generated by acute infection when the parasite, though not directly damaging to neuronal cells, elicits immune reactions that can become cytotoxic, inducing oxidative stress and neurodegeneration. Anti-neuronal autoimmunity may further contribute to neuropathology. Much less clear is the mechanism of subsequent neuronal regeneration in patients that survive acute infection. Morphological and functional recovery of the peripheral neurons in these patients correlates with the absence of CD clinical symptoms, while persistent neuronal deficiency is observed for the symptomatic group. The discovery that Trypanosoma cruzi trans-sialidase can moonlight as a parasite-derived neurotrophic factor (PDNF) suggests that the parasite might influence the balance between neuronal degeneration and regeneration. PDNF functionally mimics mammalian neurotrophic factors in that it binds and activates neurotrophin Trk tyrosine kinase receptors, a mechanism which prevents neurodegeneration. PDNF binding to Trk receptors triggers PI3K/Akt/GSK-3β and MAPK/Erk/CREB signalling cascades which in neurons translates into resistance to oxidative and nutritional stress, and inhibition of apoptosis, whereas in the cytoplasm of infected cells, PDNF represents a substrate-activator of the host Akt kinase, enhancing host-cell survival until completion of the intracellular cycle of the parasite. Such dual activity of PDNF provides sustained activation of survival mechanisms which, while prolonging parasite persistence in host tissues, can underlie distinct outcomes of CD.

A novel method to quantify gene set functional association based on gene ontology

Numerous gene sets have been used as molecular signatures for exploring the genetic basis of complex disorders. These gene sets are distinct but related to each other in many cases; therefore, efforts have been made to compare gene sets for studies such as those evaluating the reproducibility of different experiments. Comparison in terms of biological function has been demonstrated to be helpful to biologists. We improved the measurement of semantic similarity to quantify the functional association between gene sets in the context of gene ontology and developed a web toolkit named Gene Set Functional Similarity (GSFS; http://bioinfo.hrbmu.edu.cn/GSFS). Validation based on protein complexes for which the functional associations are known demonstrated that the GSFS scores tend to be correlated with sequence similarity scores and that complexes with high GSFS scores tend to be involved in the same functional catalogue. Compared with the pairwise method and the annotation method, the GSFS shows better discrimination and more accurately reflects the known functional catalogues shared between complexes. Case studies comparing differentially expressed genes of prostate tumour samples from different microarray platforms and identifying coronary heart disease susceptibility pathways revealed that the method could contribute to future studies exploring the molecular basis of complex disorders.

Vascular endothelial growth factor protects post-ganglionic sympathetic neurones from the detrimental effects of hydrogen peroxide by increasing catalase

AIM

Vascular production of hydrogen peroxide (H(2)O(2)) is implicated in the development and progression of vascular disease. Hydrogen peroxide also promotes neuronal degeneration, which suggests that vascular H(2)O(2) would promote degeneration of perivascular sympathetic nerves. Vascular cells also produce vascular endothelial growth factor (VEGF), which could protect perivascular nerves from the detrimental effects of H(2)O(2) . The aim of this study was to test these hypotheses.

METHODS

The effects of H(2)O(2) and VEGF on neuronal survival and noradrenaline uptake were studied in cultures of rat post-ganglionic sympathetic neurones. Western analyses of catalase and growth associated protein 43 were performed and reactive oxygen species (ROS) were measured using the fluorescent indicator 5-(and-6)-chloromethyl-2'7'-dichlorodihydrofluorescein diacetate, acetyl ester.

RESULTS

Hydrogen peroxide (30 μm) decreased the survival of post-ganglionic sympathetic neurones (57.8 ± 4.8% of control) and decreased noradrenaline uptake into the neurones (14 ± 6% of control). Hyperglycaemia, which is known to increase H(2)O(2), also decreased survival (31.4 ± 12% of control) and noradrenaline uptake (42 ± 18.4% of control). VEGF reduced the effects of H(2)O(2) (94.3 ± 12% of control) and hyperglycaemia (83.5 ± 23.6% of control) on survival. VEGF increased catalase, a primary determinant of intracellular concentrations of H(2)O(2) , and decreased H(2)O(2) -induced increases in ROS.

CONCLUSION

These results indicate that VEGF protects post-ganglionic sympathetic neurones from the detrimental effects of H(2)O(2). Our data suggest that an increase in catalase is the mechanisms underlying this neuroprotection.

Brain-derived neurotrophic factor mediates non-cell-autonomous regulation of sensory neuron position and identity

During development, neurons migrate considerable distances to reside in locations that enable their individual functional roles. Whereas migration mechanisms have been extensively studied, much less is known about how neurons remain in their ideal locations. We sought to identify factors that maintain the position of postmigratory dorsal root ganglion neurons, neural crest derivatives for which migration and final position play an important developmental role. We found that an early developing population of sensory neurons maintains the position of later born dorsal root ganglia neurons in an activity-dependent manner. Further, inhibiting or increasing the function of brain-derived neurotrophic factor induces or prevents, respectively, migration of dorsal root ganglia neurons out of the ganglion to locations where they acquire a new identity. Overall, the results demonstrate that neurotrophins mediate non-cell-autonomous maintenance of position and thereby the identity of differentiated neurons.

Neurotrophins in lung health and disease

Neurotrophins (NTs) are a family of growth factors that are well-known in the nervous system. There is increasing recognition that NTs (nerve growth factor, brain-derived neurotrophic factor and NT3) and their receptors (high-affinity TrkA, TrkB and TrkC, and low-affinity p75NTR) are expressed in lung components including the nasal and bronchial epithelium, smooth muscle, nerves and immune cells. NT signaling may be important in normal lung development, developmental lung disease, allergy and inflammation (e.g., rhinitis, asthma), lung fibrosis and even lung cancer. In this review, we describe the current status of our understanding of NT signaling in the lung, with hopes of using aspects of the NT signaling pathway in the diagnosis and therapy of lung diseases.

Development of the autonomic nervous system: a comparative view

In this review we summarize current understanding of the development of autonomic neurons in vertebrates. The mechanisms controlling the development of sympathetic and enteric neurons have been studied in considerable detail in laboratory mammals, chick and zebrafish, and there are also limited data about the development of sympathetic and enteric neurons in amphibians. Little is known about the development of parasympathetic neurons apart from the ciliary ganglion in chicks. Although there are considerable gaps in our knowledge, some of the mechanisms controlling sympathetic and enteric neuron development appear to be conserved between mammals, avians and zebrafish. For example, some of the transcriptional regulators involved in the development of sympathetic neurons are conserved between mammals, avians and zebrafish, and the requirement for Ret signalling in the development of enteric neurons is conserved between mammals (including humans), avians and zebrafish. However, there are also differences between species in the migratory pathways followed by sympathetic and enteric neuron precursors and in the requirements for some signalling pathways.

Transgenic BDNF induces nerve fiber regrowth into the auditory epithelium in deaf cochleae

Sensory organs typically use receptor cells and afferent neurons to transduce environmental signals and transmit them to the CNS. When sensory cells are lost, nerves often regress from the sensory area. Therapeutic and regenerative approaches would benefit from the presence of nerve fibers in the tissue. In the hearing system, retraction of afferent innervation may accompany the degeneration of auditory hair cells that is associated with permanent hearing loss. The only therapy currently available for cases with severe or complete loss of hair cells is the cochlear implant auditory prosthesis. To enhance the therapeutic benefits of a cochlear implant, it is necessary to attract nerve fibers back into the cochlear epithelium. Here we show that forced expression of the neurotrophin gene BDNF in epithelial or mesothelial cells that remain in the deaf ear induces robust regrowth of nerve fibers towards the cells that secrete the neurotrophin, and results in re-innervation of the sensory area. The process of neurotrophin-induced neuronal regeneration is accompanied by significant preservation of the spiral ganglion cells. The ability to regrow nerve fibers into the basilar membrane area and protect the auditory nerve will enhance performance of cochlear implants and augment future cell replacement therapies such as stem cell implantation or induced transdifferentiation. This model also provides a general experimental stage for drawing nerve fibers into a tissue devoid of neurons, and studying the interaction between the nerve fibers and the tissue.

Trypanosoma cruzi-Derived Neurotrophic Factor: Role in Neural Repair and Neuroprotection

Some patients infected with the parasite Try-panosoma cruzi develop chronic Chagas' disease, while others remain asymptomatic for life. Although pathological mechanisms that govern disease progression remain unclear, the balance between degeneration and regeneration in the peripheral nervous system seems to contribute to the different clinical outcomes. This review focuses on certain new aspects of host-parasite interactions related to regeneration in the host nervous system induced by the trans-sialidase of T. cruzi, also known as a parasite-derived neurotrophic factor (PDNF). PDNF plays multiple roles in T. cruzi infection, ranging from immunosuppression to functional mimicry of mammalian neurotrophic factors and inhibition of apoptosis. PDNF affinity to neurotrophin Trk receptors provide sustained activation of cellular survival mechanisms resulting in neuroprotection and neuronal repair, resistance to cytotoxic insults and enhancement of neuritogenesis. Such unique PDNF-elicited regenerative responses likely prolong parasite persistence in infected tissues while reducing neuropathology in Chagas' disease.