RESUMO
The coordinated movement of organisms relies on efficient nerve-muscle communication at the neuromuscular junction. After peripheral nerve injury or neurodegeneration, motor neurons and Schwann cells increase the expression of the p75NTR pan-neurotrophin receptor. Even though p75NTR targeting has emerged as a promising therapeutic strategy to delay peripheral neuronal damage progression, the effects of long-term p75NTR inhibition at the mature neuromuscular junction have not been elucidated. We performed quantitative neuroanathomical analyses of the neuromuscular junction in p75NTR null mice by laser confocal and electron microscopy, which were complemented with electromyography, locomotor tests, and pharmacological intervention studies. Mature neuromuscular synapses of p75NTR null mice show impaired postsynaptic organization and ultrastructural complexity, which correlate with altered synaptic function at the levels of nerve activity-induced muscle responses, muscle fiber structure, force production, and locomotor performance. Our results on primary myotubes and denervated muscles indicate that muscle-derived p75NTR does not play a major role on postsynaptic organization. In turn, motor axon terminals of p75NTR null mice display a strong reduction in the number of synaptic vesicles and active zones. According to the observed pre and postsynaptic defects, pharmacological acetylcholinesterase inhibition rescued nerve-dependent muscle response and force production in p75NTR null mice. Our findings revealing that p75NTR is required to organize mature neuromuscular junctions contribute to a comprehensive view of the possible effects caused by therapeutic attempts to target p75NTR.
Assuntos
Neurônios Motores/fisiologia , Junção Neuromuscular/fisiologia , Receptores de Fator de Crescimento Neural/fisiologia , Vesículas Sinápticas/fisiologia , Animais , Camundongos Endogâmicos C57BL , Camundongos Knockout , Atividade Motora , Neurônios Motores/ultraestrutura , Junção Neuromuscular/ultraestrutura , Receptores de Fator de Crescimento Neural/genética , Vesículas Sinápticas/ultraestruturaRESUMO
Schwann cells (SCs) critically maintain the plasticity of the peripheral nervous system. Peripheral nerve injuries and infections stimulate SCs in order to retrieve homeostasis in neural tissues. Previous studies indicate that Mycobacterium leprae (ML) regulates the expression of key factors related to SC identity, suggesting that alterations in cell phenotype may be involved in the pathogenesis of neural damage in leprosy. To better understand whether ML restricts the plasticity of peripheral nerves, the present study sought to determine the expression of Krox20, Sox10, cJun and p75NTR in SC culture and mice sciatic nerves, both infected by ML Thai53 strain. Primary SC cultures were stimulated with two different multiplicities of infection (MOI 100:1; MOI 50:1) and assessed after 7 and 14 days. Sciatic nerves of nude mice (NUFoxn1nu) infected with ML were evaluated after 6 and 9 months. In vitro results demonstrate downregulation of Krox20 and Sox10 along with the increase in p75NTRimmunolabelled cells. Concurrently, sciatic nerves of infected mice showed a significant decrease in Krox20 and increase in p75NTR. Our results corroborate previous findings on the interference of ML in the expression of factors involved in cell maturation, favouring the maintenance of a nonmyelinating phenotype in SCs, with possible implications for the repair of adult peripheral nerves(AU).
Assuntos
Animais , Camundongos , Células de Schwann/microbiologia , Hanseníase/metabolismo , Hanseníase/microbiologia , Mycobacterium leprae/isolamento & purificação , Nervos Periféricos/microbiologia , Células de Schwann/metabolismo , Técnicas In Vitro , Regulação para Baixo , Receptores de Fator de Crescimento Neural/fisiologia , Proteína 2 de Resposta de Crescimento Precoce/biossíntese , Plasticidade Neuronal/fisiologiaRESUMO
It is important to understand the mechanisms that enable peripheral neurons to regenerate after nerve injury in order to identify methods of improving this regeneration. Therefore, we studied nerve regeneration and sensory impairment recovery in the cutaneous lesions of leprosy patients (LPs) before and after treatment with multidrug therapy (MDT). The skin lesion sensory test results were compared to the histopathological and immunohistochemical protein gene product (PGP) 9.5 and the p75 nerve growth factor receptors (NGFr) findings. The cutaneous neural occupation ratio (CNOR) was evaluated for both neural markers. Thermal and pain sensations were the most frequently affected functions at the first visit and the most frequently recovered functions after MDT. The presence of a high cutaneous nerve damage index did not prevent the recovery of any type of sensory function. The CNOR was calculated for each biopsy, according to the presence of PGP and NGFr-immunostained fibres and it was not significantly different before or after the MDT. We observed a variable influence of MDT in the recovery from sensory impairment in the cutaneous lesions of LPs. Nociception and cold thermosensation were the most recovered sensations. The recovery of sensation in the skin lesions appeared to be associated with subsiding inflammation rather than with the regenerative activity of nerve fibres.
Assuntos
Adolescente , Adulto , Idoso , Criança , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Adulto Jovem , Hanseníase/fisiopatologia , Regeneração Nervosa/fisiologia , Doenças do Sistema Nervoso Periférico/fisiopatologia , Receptores de Fator de Crescimento Neural/fisiologia , Imuno-Histoquímica , Hansenostáticos/uso terapêutico , Hanseníase/tratamento farmacológico , Hanseníase/patologia , Doenças do Sistema Nervoso Periférico/patologia , Limiar Sensorial , Sensação TérmicaRESUMO
It is important to understand the mechanisms that enable peripheral neurons to regenerate after nerve injury in order to identify methods of improving this regeneration. Therefore, we studied nerve regeneration and sensory impairment recovery in the cutaneous lesions of leprosy patients (LPs) before and after treatment with multidrug therapy (MDT). The skin lesion sensory test results were compared to the histopathological and immunohistochemical protein gene product (PGP) 9.5 and the p75 nerve growth factor receptors (NGFr) findings. The cutaneous neural occupation ratio (CNOR) was evaluated for both neural markers. Thermal and pain sensations were the most frequently affected functions at the first visit and the most frequently recovered functions after MDT. The presence of a high cutaneous nerve damage index did not prevent the recovery of any type of sensory function. The CNOR was calculated for each biopsy, according to the presence of PGP and NGFr-immunostained fibres and it was not significantly different before or after the MDT. We observed a variable influence of MDT in the recovery from sensory impairment in the cutaneous lesions of LPs. Nociception and cold thermosensation were the most recovered sensations. The recovery of sensation in the skin lesions appeared to be associated with subsiding inflammation rather than with the regenerative activity of nerve fibres.
Assuntos
Hanseníase/fisiopatologia , Regeneração Nervosa/fisiologia , Doenças do Sistema Nervoso Periférico/fisiopatologia , Receptores de Fator de Crescimento Neural/fisiologia , Adolescente , Adulto , Idoso , Criança , Feminino , Humanos , Imuno-Histoquímica , Hansenostáticos/uso terapêutico , Hanseníase/tratamento farmacológico , Hanseníase/patologia , Masculino , Pessoa de Meia-Idade , Doenças do Sistema Nervoso Periférico/patologia , Limiar Sensorial , Sensação Térmica , Adulto JovemRESUMO
Neurotrophins (NTs) are important for the survival, differentiation and function of sympathetic and sensorial neurons of central and peripheral nervous system. However, similar functions have been described of NTs in non-neural organs. Nerve Growth factor (NGF) participates in the foliculogenesis and ovulation in the ovary, as well as in the islet morphogenesis and insulin secretion of the pancreatic beta cell. The NTs act by binding to two distinct classes of transmembranal receptors: p75 and Trks. Both receptor types lead to activation of intracellular signaling cascades that end with cell survival or apoptosis. In this review different actions of the NTs in the ovarian and the pancreas are described.
Assuntos
Fatores de Crescimento Neural/fisiologia , Ovário/fisiologia , Pâncreas/fisiologia , Animais , Apoptose/fisiologia , Feminino , Humanos , Insulina/metabolismo , Secreção de Insulina , Ilhotas Pancreáticas/metabolismo , Masculino , Camundongos , Especificidade de Órgãos , Folículo Ovariano/fisiologia , Ovário/crescimento & desenvolvimento , Ovulação/fisiologia , Pâncreas/crescimento & desenvolvimento , Ratos , Receptores de Fator de Crescimento Neural/fisiologia , Transdução de Sinais/fisiologiaRESUMO
Uterine sympathetic innervation undergoes profound remodelling in response to physiological and experimental changes in the circulating levels of sex hormones. It is not known, however, whether this plasticity results from changes in the innervating neurons, the neuritogenic properties of the target tissue or both. Using densitometric immunohistochemistry, we analysed the effects of prepubertal chronic oestrogen treatment (three subcutaneous injections of 20 microg of beta-oestradiol 17-cypionate on days 25, 27 and 29 after birth), natural peripubertal transition and late pregnancy (19-20 days post coitum) on the levels of TrkA and p75 nerve growth factor receptors in uterine-projecting sympathetic neurons of the thoraco-lumbar paravertebral sympathetic chain (T7-L2) identified using the retrograde tracer Fluorogold. For comparative purposes, levels of TrkA and p75 were assessed in the superior cervical ganglion (SCG) following prepubertal chronic oestrogen treatment. These studies showed that the vast majority of uterine-projecting neurons expressed both TrkA and p75. Both prepubertal chronic oestrogen treatment and the peripubertal transition increased the ratio p75 to TrkA in uterine-projecting neurons, whereas pregnancy elicited the opposite effect. Prepubertal chronic oestrogen treatment had no effects on levels of TrkA or p75 in sympathetic neurons of the SCG. Taken together, our data suggest that neurotrophin receptor-mediated events may contribute to regulate sex hormone-induced plasticity in uterine sympathetic nerves, and are in line with the idea that, in vivo, plasticity in uterine nerves involves changes in both the target and the innervating neurons.
Assuntos
Plasticidade Neuronal/fisiologia , Neurônios/química , Receptor trkA/fisiologia , Receptores de Fator de Crescimento Neural/fisiologia , Sistema Nervoso Simpático/fisiologia , Útero/inervação , Animais , Estradiol/farmacologia , Feminino , Imuno-Histoquímica/métodos , Microscopia de Fluorescência , Gravidez , Ratos , Ratos Wistar , Receptor de Fator de Crescimento Neural , Receptor trkA/análise , Receptores de Fator de Crescimento Neural/análise , Maturidade SexualRESUMO
Peroxisome proliferator-activated receptor gamma (PPARgamma), a member of the nuclear receptor superfamily, is subject to considerable interest because of its role in adipocyte differentiation, metabolic control, and anti-inflammatory action. PPARgamma research in brain cells is presently focused on glial PPARgamma because of its potential as a pharmacological target in the treatment of neurodegenerative diseases with an inflammatory component. In neurons PPARgamma function is far from clear, and PPARgamma agonist-dependent and -independent effects on cell survival or differentiation have been reported. We used PC12 cells, widely used to study neuronal signaling, such as nerve growth factor (NGF)-induced differentiation and survival or epidermal growth factor-dependent cell proliferation to dissect the possible involvement of PPARgamma in these pathways. We show that NGF but not epidermal growth factor increases the transcriptional activity of PPARgamma, and modulates the expression of this transcription factor. Because NGF signals through the tyrosine kinase (TrkA) NGF receptor and/or the p75NTR receptor, we used rescue experiments with a PC12 cell mutant lacking TrkA to show that NGF-induced PPARgamma activation is dependent on TrkA activation. Our results point out PPARgamma as a novel target of the TrkA-mediated neuronal cell survival and differentiating pathway and suggest a potential new inflammatory-independent therapeutic approach for pharmacological intervention in neurological disorders.
Assuntos
Fatores de Crescimento Neural/farmacologia , PPAR gama/fisiologia , Transdução de Sinais/fisiologia , Animais , Sobrevivência Celular/efeitos dos fármacos , Deleção de Genes , Células PC12 , PPAR gama/genética , Feocromocitoma , Ratos , Receptor trkA/deficiência , Receptor trkA/genética , Receptor trkA/fisiologia , Receptores de Fator de Crescimento Neural/fisiologia , Proteínas Recombinantes/metabolismo , Rosiglitazona , Transdução de Sinais/efeitos dos fármacos , Tiazolidinedionas/farmacologia , Transcrição Gênica/efeitos dos fármacos , TransfecçãoRESUMO
Signalling by the p75 neurotrophin receptor has been implicated in diverse neuronal responses, including increased differentiation or survival, inhibition of regeneration, and initiation of apoptotic cell death. These numerous roles are matched by, but are not yet correlated with, a multiplicity of extracellular ligands and intracellular interactors. Membrane proteins such as sortilin, a member of the Vps10p family of sorting receptors, and the glycosylphosphatidylinositol-linked Nogo receptor (NgR) and the associated adaptor lingo 1 have recently been added to the list of p75-interacting modulators. Other studies have described intramembranal cleavage of p75 and the potential nuclear targeting of cleavage fragments or of the complete receptor after it has been internalized into a putative signalling endosome. These findings suggest that some of the diversity in p75 activities might be due to differential subcellular localization and transport of p75 receptor complexes. We therefore argue that cell-biology-driven approaches are now required to make sense of p75 signalling.
Assuntos
Glicoproteínas de Membrana/fisiologia , Proteínas do Tecido Nervoso/fisiologia , Receptores de Fator de Crescimento Neural/fisiologia , Proteínas Adaptadoras de Transporte Vesicular , Ligantes , Neurônios/fisiologia , Receptor de Fator de Crescimento Neural , Transdução de Sinais/fisiologiaRESUMO
INTRODUCTION: The neurotrophins are a family of proteins which are closely related structurally and functionally and include nerve growth factor (NGF), brain derived nerve factor (BDNF) and neurotrophin-3 (NT-3), neurotrophin-4/5 (NT-4/5) and more recently neurotrophin-6 (NT-6). BDNF is one of the most important endogenous proteins for control of survival, growth and differentiation of certain neurone populations both in the peripheral and central nervous systems. DEVELOPMENT: The ARNmt of the BDNF is found in nearly all regions of the brain. The highest levels are those of the hippocampus and cerebral cortex. The large number of effects attributed to BDNF are probably due to the union of this protein to its specific receptor on the cell surface, which leads to the formation of a complex which enables transmission of the signal caused by activation of the specific neurone pathway. Since discovery, BDNF has been detected and/or measured by different methods from biological assay to the application of molecular biology techniques. These methods have permitted analysis of the biochemical characteristics of this factor and its behaviour in different tissues. CONCLUSIONS: In this paper we review the most relevant aspects of distribution, biological actions of BDNF on different neurone populations, its clinical usefulness in neurological disorders, routes of administration and side effects.
Assuntos
Fator Neurotrófico Derivado do Encéfalo , Proteínas do Tecido Nervoso/fisiologia , Esclerose Lateral Amiotrófica/tratamento farmacológico , Animais , Gânglios da Base , Química Encefálica , Transplante de Tecido Encefálico , Transplante de Tecido Fetal , Terapia Genética , Sobrevivência de Enxerto/efeitos dos fármacos , Humanos , Proteínas do Tecido Nervoso/efeitos adversos , Proteínas do Tecido Nervoso/química , Proteínas do Tecido Nervoso/farmacologia , Proteínas do Tecido Nervoso/uso terapêutico , Neurônios/efeitos dos fármacos , Especificidade de Órgãos , Estresse Oxidativo , Doença de Parkinson/terapia , Ratos , Receptores Proteína Tirosina Quinases/efeitos dos fármacos , Receptores Proteína Tirosina Quinases/fisiologia , Receptor do Fator Neutrófico Ciliar , Receptores de Fator de Crescimento Neural/efeitos dos fármacos , Receptores de Fator de Crescimento Neural/fisiologiaRESUMO
INTRODUCTION: The progress made by contemporary neurobiology opens new horizons both for study and for treatment of disorders of the nervous system. At the present time we are in the age of growth factors. These are molecules which affect survival, development and the normal functioning of cell populations. DEVELOPMENT: One of the most widely studied growth factors is nervous growth factor (NGF) which is necessary for normal life of various types of neurones, including sensory nerves and nerves derived from the neural crests. Diabetic neuropathy, worldwide a major neurological disorder, is primarily characterized by involvement of the fine fibres for temperature and pain perception and also by a variety of autonomic disorders. The great dependence of sensory and sympathetic nerves on NGF, the quantity of results which show alterations in the levels of neurotrophic factors in diabetic neuropathy (DN), and the encouraging experimental and clinical results of using NGF as a new alternative to treatment with DN, were the basic reasons which led us to do this study. CONCLUSIONS: We started by considering neurotrophic factors, especially NGF and its connection with DN disorders and its clinical applications, we made a summary of the main findings in this field to date.