Nerve growth factor‐mediated regulation of pain signalling and proposed new intervention strategies in clinical pain management

Nerve growth factor (NGF) is the founding member of the neurotrophins family of proteins. It was discovered more than half a century ago through its ability to promote sensory and sympathetic neuronal survival and axonal growth during the development of the peripheral nervous system, and is the paradigmatic target‐derived neurotrophic factor on which the neurotrophic hypothesis is based. Since that time, NGF has also been shown to play a key role in the generation of acute and chronic pain and in hyperalgesia in diverse pain states. NGF is expressed at high levels in damaged or inflamed tissues and facilitates pain transmission by nociceptive neurons through a variety of mechanisms. Genetic mutations in NGF or its tyrosine kinase receptor TrkA, lead to a congenital insensitivity or a decreased ability of humans to perceive pain. The hereditary sensory autonomic neuropathies (HSANs) encompass a spectrum of neuropathies that affect one's ability to perceive sensation. HSAN type IV and HSAN type V are caused by mutations in TrkA and NGF respectively. This review will focus firstly on the biology of NGF and its role in pain modulation. We will review neuropathies and clinical presentations that result from the disruption of NGF signalling in HSAN type IV and HSAN type V and review current advances in developing anti‐NGF therapy for the clinical management of pain.     

Fucosyl-GM1 in Human Sensory Nervous Tissue Is a Target Antigen in Patients with Autoimmune Neuropathies

Abstract: Several gangliosides of human nervous tissues have been reported to be potential target antigens in autoimmune neuropathies. To explain the diversity of clinical symptoms in patients with antiganglioside antibodies, we have searched for ganglioside antigens that are specific to individual nervous tissues such as motoneurons, peripheral motor nerves, and sensory nerves. Although the major ganglioside compositions were not different among human peripheral motor and sensory nerves, fucosyl-GM1 was found to be expressed in sensory nervous tissue but not in spinal cord, motor nerve, and sympathetic ganglia. Sera from several patients with sensory nerve involvement also reacted with fucosyl-GM1 as well as GM1. Thus, fucosyl-GM1 may be a responsible target antigen for developing sensory symptoms in some patients with autoimmune neuropathies.     

The Antiepileptic Valproic Acid Ameliorates Charcot-Marie-Tooth 2W (CMT2W) Disease-Associated HARS1 Mutation-Induced Inhibition of Neuronal Cell Morphological Differentiation Through c-Jun N-terminal Kinase

Neurochemical Research - Hereditary peripheral neuropathies called Charcot-Marie-Tooth (CMT) disease affect the sensory nerves as well as motor neurons. CMT diseases are composed of a heterogeneous...     

TRPV4-associated skeletal dysplasias

Dominant mutations in the TRPV4 gene result in a bone dysplasia family and form a continuous phenotypic spectrum that includes, in decreasing severity, lethal, and nonlethal metatropic dysplasia (MD), spondylometaphyseal dysplasia Kozlowski type (SMDK), and autosomal dominant brachyolmia. Several rare variant phenotypes that have some overlap but deviate in some ways from the general pattern have also been described. The known variant phenotypes are spondyloepiphyseal dysplasia Maroteaux type (Pseudo-Morquio type 2), parastremmatic dysplasia, and familial digital arthropathy with brachydactyly. Interestingly, different TRPV4 mutations have been associated with dominantly inherited neurologic disorders such as congenital spinal muscular atrophy and hereditary motor and sensory neuropathy. Finally, a small number of patients have been identified in whom a TRPV4 mutation results in a phenotype combining skeletal dysplasia with peripheral neuropathy. The TRPV4 gene encodes a regulated calcium channel implicated in multiple and diverse cellular processes. Over 50 different TRPV4 mutations have been reported, with two codons appearing to be mutational hot spots: P799 in exon 15, mostly associated with MD, and R594 in exon 11, associated with SMDK. While most pathogenic mutations tested so far result in activation of the calcium channel in vitro, the mechanisms through which TRPV4 activation results in skeletal dysplasia and/or peripheral neuropathy remain unclear and the genotype-phenotype correlations in this group of disorders remains somewhat mysterious. Since the phenotypic expression of most mutations seems to be relatively constant, careful clinical and radiographic assessment is useful in directing molecular analysis.     

Neurotrophic factor therapy for nervous system degenerative diseases

The ability of neurotrophic factors to regulate developmental neuronal survival and adult nervous system planticity suggests the use of these molecuales to treat neurodegeneration associated with human diseases. Solid rationales exist for the use of NGF and neurotrophin-3 in the treatment of neuropathies of the peripheral sensory system, insulin-like growth factor and ciliary neurotrophic factor in motor neuron atrophy, and NGF in Alzheimer's disease. Growth factors have been identified for neurons affected in Parkinson's disease, Huntington's disease, and acute brain and spinal cord injury. Various strategies are actively pursued to deliver neurotrophic factors to the brain, and develop therapeutically useful molecules that mimic neurotrophic factor actions or stimulate their production or receptor mechanisms. 1994 John Wiley & Sons, Inc.     

Molecular genetics and mechanisms of disease in distal hereditary motor neuropathies: insights directing future genetic studies

The distal hereditary motor neuropathies (dHMNs) are a clinically and genetically heterogeneous group of disorders that primarily affect motor neurons, without significant sensory involvement. New dHMN genes continue to be identified. There are now 11 causative genes described for dHMN, and an additional five genetic loci with unidentified genes. This genetic heterogeneity has further delineated the classification of dHMN, which was previously classified according to mode of inheritance, age at onset, and additional complicating features. Some overlap between phenotypically distinct forms of dHMN is also apparent. The mutated genes identified to-date in dHMN include HSPB1, HSPB8, HSPB3, DCTN1, GARS, PLEKHG5, BSCL2, SETX, IGHMBP2, ATP7A and TRPV4. The pathogenesis of mutations remains to be fully elucidated, however common pathogenic mechanisms are emerging. These include disruption of axonal transport, RNA processing defects, protein aggregation and inclusion body formation, disrupted calcium channel activity, and loss of neuroprotective signalling. Some of these dHMN genes are also mutated in Charcot-Marie-Tooth (CMT) disease and spinal muscular atrophy (SMA). This review examines the growing number of identified dHMN genes, discusses recent insights into the functions of these genes and possible pathogenic mechanisms, and looks at the increasing overlap between dHMN and the other neuropathies CMT2 and SMA.     

Thy1.2 YFP-16 Transgenic Mouse Labels a Subset of Large-Diameter Sensory Neurons that Lack TRPV1 Expression

The Thy1.2 YFP-16 mouse expresses yellow fluorescent protein (YFP) in specific subsets of peripheral and central neurons. The original characterization of this model suggested that YFP was expressed in all sensory neurons, and this model has been subsequently used to study sensory nerve structure and function. Here, we have characterized the expression of YFP in the sensory ganglia (DRG, trigeminal and vagal) of the Thy1.2 YFP-16 mouse, using biochemical, functional and anatomical analyses. Despite previous reports, we found that YFP was only expressed in approximately half of DRG and trigeminal neurons and less than 10% of vagal neurons. YFP-expression was only found in medium and large-diameter neurons that expressed neurofilament but not TRPV1. YFP-expressing neurons failed to respond to selective agonists for TRPV1, P2X_2/3 and TRPM8 channels in Ca²⁺ imaging assays. Confocal analysis of glabrous skin, hairy skin of the back and ear and skeletal muscle indicated that YFP was expressed in some peripheral terminals with structures consistent with their presumed non-nociceptive nature. In summary, the Thy1.2 YFP-16 mouse expresses robust YFP expression in only a subset of sensory neurons. But this mouse model is not suitable for the study of nociceptive nerves or the function of such nerves in pain and neuropathies.     

Hereditäre Optikusatrophien

Hereditary optic neuropathies comprise a group of clinically and genetically heterogeneous disorders, which can be divided into 2 subgroups: isolated hereditary optic atrophies and optic neuropathies as part of complex disorders. In the first group of isolated hereditary optic neuropathies, optic nerve dysfunction is typically the only manifestation of the disease. This group comprises autosomal dominant, autosomal recessive and X-linked recessive optic atrophy, and the mitochondrial inherited Leber’s hereditary optic neuropathy (LHON). In the second group of complex disorders, various neurologic and other systemic abnormalities are regularly observed. The most frequent cause in this group are mitochondrial DNA (mtDNA) mutations, inherited peripheral neuropathies, Charcot–Marie–Tooth disorders (CMT2A2, CMTX5), hereditary sensory neuropathy type 3 (HSAN3), Friedreich ataxia, leukodystrophies, sphingolipidoses, ceroid-lipofuscinoses, and neurodegeneration with brain iron accumulation (NBIA). In the present article, the clinical phenotypes and underlying genetic predispositions are described.     

Peripheral Glia Have a Pivotal Role in the Initial Response to Axon Degeneration of Peripheral Sensory Neurons in Zebrafish

Axon degeneration is a feature of many peripheral neuropathies. Understanding the organismal response to this degeneration may aid in identifying new therapeutic targets for treatment. Using a transgenic zebrafish line expressing a bacterial nitroreductase (Ntr)/mCherry fusion protein in the peripheral sensory neurons of the V, VII, IX, and X cranial nerves, we were able to induce and visualize the pathology of axon degeneration in vivo. Exposure of 4 days post fertilization Ntr larvae to the prodrug metronidazole (Met), which Ntr metabolizes into cytotoxic metabolites, resulted in dose-dependent cell death and axon degeneration. This was limited to the Ntr-expressing sensory neurons, as neighboring glia and motor axons were unaffected. Cell death was rapid, becoming apparent 3–4 hours after Met treatment, and was followed by phagocytosis of soma and axon debris by cells within the nerves and ganglia beginning at 4–5 hours of exposure. Although neutrophils appear to be activated in response to the degenerating neurons, they did not accumulate at the sites of degeneration. In contrast, macrophages were found to be attracted to the sites of the degenerating axons, where they phagocytosed debris. We demonstrated that peripheral glia are critical for both the phagocytosis and inflammatory response to degenerating neurons: mutants that lack all peripheral glia (foxD3^−/−; Ntr) exhibit a much reduced reaction to axonal degeneration, resulting in a dramatic decrease in the clearance of debris, and impaired macrophage recruitment. Overall, these results show that this zebrafish model of peripheral sensory axon degeneration exhibits many aspects common to peripheral neuropathies and that peripheral glia play an important role in the initial response to this process.     

Preparation and biological properties of native and recombinant ciliary neurotrophic factor.

CNTF (ciliary neurotrophic factor), purified from rabbit sciatic nerves by a relatively simple procedure, is bioactive in tissue culture at low picomolar concentration and appears as a doublet on polyacrylamide gel electrophoresis (PAGE). In these nerves, CNTF accounts for more than one-half of the survival-promoting activity on ciliary neurons. The concentration of CNTF in rabbit sciatic nerves is estimated to be 5 nmol/kg, more than 1000 times higher than would seem to be required to support neurons if the neurotrophic factor were homogeneously distributed. With recombinant DNA technology, rat CNTF has been synthesized in Escherichia coli, purified without denaturating agents, and found to be bioactive at a slightly lower concentration than CNTF extracted from rabbit sciatic nerves. After radioiodination, CNTF retains biological activity but is not specifically internalized and retrogradely transported in motor and sensory axons. In peripheral nerves, ciliary neurotrophic factor differs biologically from nerve growth factor (NGF) by its much higher tissue concentration and apparent lack of internalization by peripheral nerve axons.     

Retinal ganglion cell neurodegeneration in mitochondrial inherited disorders

Since the early days of mitochondrial medicine, it has been clear that optic atrophy is a very common and sometimes the singular pathological feature in mitochondrial disorders. The first point mutation of mitochondrial DNA (mtDNA) associated with the maternally inherited blinding disorder, Leber's hereditary optic neuropathy (LHON), was recognized in 1988. In 2000, the other blinding disorder, dominant optic atrophy (DOA) Kjer type, was found associated with mutations in the nuclear gene OPA1 that encodes a mitochondrial protein. Besides these two non-syndromic optic neuropathies, optic atrophy is a prominent feature in many other neurodegenerative diseases that are now recognized as due to primary mitochondrial dysfunction.We will consider mtDNA based syndromes such as LHON/dystonia/Mitochondrial Encephalomyopahty Lactic Acidosis Stroke-like (MELAS)/Leigh overlapping syndrome, or nuclear based diseases such as Friedreich ataxia (mutations in FXN gene), deafness-dystonia-optic atrophy (Mohr-Tranebjerg) syndrome (mutations in TIMM8A), complicated hereditary spastic paraplegia (mutations in SPG7), DOA “plus” syndromes (mutations in OPA1), Charcot-Marie-Tooth type 2A (CMT2A) with optic atrophy or hereditary motor and sensory neuropathy type VI (HMSN VI) (mutations in MFN2), and Costeff syndrome and DOA with cataract (mutations in OPA3). Thus, genetic errors in both nuclear and mitochondrial genomes often lead to retinal ganglion cell death, a specific target for mitochondrial mediated neurodegeneration. Many mechanisms have been studied and proposed as the bases for the pathogenesis of mitochondrial optic neuropathies including bioenergetic failure, oxidative stress, glutamate toxicity, abnormal mitochondrial dynamics and axonal transport, and susceptibility to apoptosis.     

Human HSPB1 mutation recapitulates features of distal hereditary motor neuropathy (dHMN) in Drosophila

Distal hereditary motor neuropathies (dHMN) are a group of inherited peripheral nerve disorders characterized by length-dependent motor neuron weakness and subsequent muscle atrophy. Missense mutations in the gene encoding small heat shock protein HSPB1 (HSP27) have been associated with hereditary neuropathies including dHMN. HSPB1 is a member of the small heat shock protein (sHSP) family characterized by a highly conserved α-crystallin domain that is critical to their chaperone activity. In this study, we modeled HSPB1 mutant-induced neuropathies in Drosophila using a human HSPB1^S135F mutant that has a missense mutation in its α-crystallin domain. Overexpression of the HSPB1 mutant produced no significant defect in the Drosophila development, however, a partial reduction in the life span was observed. Further, the HSPB1 mutant gene induced an obvious loss of motor activity when expressed in Drosophila neurons. Moreover, suppression of histone deacetylase 6 (HDAC6) expression, which has critical roles in HSPB1 mutant-induced axonal defects, successfully rescued the motor defects in the HSPB1 mutant Drosophila model.     

Preparation and biological properties of native and recombinant ciliary neurotrophic factor

CNTF (ciliary neurotrophic factor), purified from rabbit sciatic nerves by a relatively simple procedure, is bioactive in tissue culture at low picomolar concentration and appears as a doublet on polyacrylamide gel electrophoresis (PAGE). In these nerves, CNTF accounts for more than one-half of the survival-promoting activity on ciliary neurons. The concentration of CNTF in rabbit sciatic nerves is estimated to be 5 nmol/kg, more than 1000 times higher than would seem to be required to support neurons if the neurotrophic factor were homogeneously distributed. With recombinant DNA technology, rat CNTF has been synthesized in Escherichia coli, purified without denaturating agents, and found to be bioactive at a slightly lower concentration than CNTF extracted from rabbit sciatic nerves. After radioiodination, CNTF retains biological activity but is not specifically internalized and retrogradely transported in motor and sensory axons. In peripheral nerves, ciliary neurotrophic factor differs biologically from nerve growth factor (NGF) by its much higher tissue concentration and apparent lack of internalization by peripheral nerve axons. © 1992 John Wiley & Sons, Inc.     

Transient receptor potential vanilloid 1, calcitonin gene-related peptide, and substance P mediate nociception in acute pancreatitis

The mechanism of pancreatitis-induced pain is unknown. In other tissues, inflammation activates transient receptor potential vanilloid 1 (TRPV1) on sensory nerves to liberate CGRP and substance P (SP) in peripheral tissues and the dorsal horn to cause neurogenic inflammation and pain, respectively. We evaluated the contribution of TRPV1, CGRP, and SP to pancreatic pain in rats. TRPV1, CGRP, and SP were coexpressed in nerve fibers of the pancreas. Injection of the TRPV1 agonist capsaicin into the pancreatic duct induced endocytosis of the neurokinin 1 receptor in spinal neurons in the dorsal horn (T10), indicative of SP release upon stimulation of pancreatic sensory nerves. Induction of necrotizing pancreatitis by treatment with L-arginine caused a 12-fold increase in the number of spinal neurons expressing the proto-oncogene c-fos in laminae I and II of L1, suggesting activation of nociceptive pathways. L-arginine also caused a threefold increase in spontaneous abdominal contractions detected by electromyography, suggestive of referred pain. Systemic administration of the TRPV1 antagonist capsazepine inhibited c-fos expression by 2.5-fold and abdominal contractions by 4-fold. Intrathecal, but not systemic, administration of antagonists of CGRP (CGRP(8-37)) and SP (SR140333) receptors attenuated c-fos expression in spinal neurons by twofold. Thus necrotizing pancreatitis activates TRPV1 on pancreatic sensory nerves to release SP and CGRP in the dorsal horn, resulting in nociception. Antagonism of TRPV1, SP, and CGRP receptors may suppress pancreatitis pain.     

Differential expression of the capsaicin receptor TRPV1 and related novel receptors TRPV3, TRPV4 and TRPM8 in normal human tissues and changes in traumatic and diabetic neuropathy

Background  

Transient receptor potential (TRP) receptors expressed by primary sensory neurons mediate thermosensitivity, and may play a role in sensory pathophysiology. We previously reported that human dorsal root ganglion (DRG) sensory neurons co-expressed TRPV1 and TRPV3, and that these were increased in injured human DRG. Related receptors TRPV4, activated by warmth and eicosanoids, and TRPM8, activated by cool and menthol, have been characterised in pre-clinical models. However, the role of TRPs in common clinical sensory neuropathies needs to be established.     

Therapeutic Potential of CKD-504, a Novel Selective Histone Deacetylase 6 Inhibitor,in a Zebrafish Model of Neuromuscular Junction Disorders

The neuromuscular junction (NMJ), which is a synapse for signal transmission from motor neurons to muscle cells, has emerged as an important region because of its association with several peripheral neuropathies. In particular, mutations in GARS that affect the formation of NMJ result in Charcot-Marie-Tooth disease and distal hereditary motor neuropathy. These disorders are mainly considered to be caused by neuronal axon abnormalities; however, no treatment is currently available. Therefore, in order to determine whether the NMJ could be targeted to treat neurodegenerative disorders, we investigated the NMJ recovery effect of HDAC6 inhibitors, which have been used in the treatment of several peripheral neuropathies. In the present study, we demonstrated that HDAC6 inhibition was sufficient to enhance movement by restoring NMJ impairments observed in a zebrafish disease model. We found that CKD-504, a novel HDAC6 inhibitor, was effective in repairing NMJ defects, suggesting that treatment of neurodegenerative diseases via NMJ targeting is possible.     

Diverse mechanisms for assembly of branchiomeric nerves

The formation of branchiomeric nerves (cranial nerves V, VII, IX and X) from their sensory, motor and glial components is poorly understood. The current model for cranial nerve formation is based on the Vth nerve, in which sensory afferents are formed first and must enter the hindbrain in order for the motor efferents to exit. Using transgenic zebrafish lines to discriminate between motor neurons, sensory neurons and peripheral glia, we show that this model does not apply to the remaining three branchiomeric nerves. For these nerves, the motor efferents form prior to the sensory afferents, and their pathfinding show no dependence on sensory axons, as ablation of cranial sensory neurons by ngn1 knockdown had no effect. In contrast, the sensory limbs of the IXth and Xth nerves (but not the Vth or VIIth) were misrouted in gli1 mutants, which lack hindbrain bmn, suggesting that the motor efferents are crucial for appropriate sensory axon projection in some branchiomeric nerves. For all four nerves, peripheral glia were the intermediate component added and had a critical role in nerve integrity but not in axon guidance, as foxd3 null mutants lacking peripheral glia exhibited defasciculation of gVII, gIX, and gX axons. The bmn efferents were unaffected in these mutants. These data demonstrate that multiple mechanisms underlie formation of the four branchiomeric nerves. For the Vth, sensory axons initiate nerve formation, for the VIIth the sensory and motor limbs are independent, and for the IXth/Xth the motor axons initiate formation. In all cases the glia are patterned by the initiating set of axons and are needed to maintain axon fasciculation. These results reveal that coordinated interactions between the three neural cell types in branchiomeric nerves differ according to their axial position.     

Neurotrophin and GDNF family ligand receptor expression in vagal sensory nerve subtypes innervating the adult guinea pig respiratory tract

We combined retrograde tracing techniques with single-neuron RT-PCR to compare the expression of neurotrophic factor receptors in nodose vs. jugular vagal sensory neurons. The neurons were further categorized based on location of their terminals (tracheal or lungs) and based on expression of the ionotropic capsaicin receptor TRPV1. Consistent with functional studies, nearly all jugular neurons innervating the trachea and lungs expressed TRPV1. With respect to the neurotrophin receptors, the TRPV1-expressing jugular C-fiber neurons innervating both the trachea and lung compartments preferentially expressed tropomyosin-receptor kinase A (TrkA), with only a minority of neurons expressing TrkB or TrkC. The nodose neurons that express TRPV1 (presumed nodose C-fibers) innervate mainly intrapulmonary structures. These neurons preferentially expressed TrkB, with only a minority expressing TrkA or TrkC. The expression pattern in tracheal TRPV1-negative neurons, nodose tracheal presumed Aδ-fiber neurons as well as the intrapulmonary TRPV1-negative presumed Aβ-fiber neurons, was similar to that observed in the nodose C-fiber neurons. We also evaluated the expression of GFRα receptors and RET (receptors for the GDNF family ligands). Virtually all vagal sensory neurons innervating the respiratory tract expressed RET and GFRα1. The jugular neurons also categorically expressed GFRα3, as well as ～50% of the nodose neurons. GFRα2 was expressed in ～50% of the neurons irrespective of subtype. The results reveal that Trk receptor expression in vagal afferent neurons innervating the adult respiratory tract depends more on the location of the cell bodies (jugular vs. nodose ganglion) than either the location of the terminals or the functional phenotype of the nerve. The data also reveal that in addition to neurotrophins, the GDNF family ligands may be important neuromodulators of vagal afferent nerves innervating the adult respiratory tract.     

The GDNF/RET signaling pathway and human diseases

Glial cell line-derived neurotrophic factor (GDNF) and related molecules, neurturin, artemin and persephin, signal through a unique multicomponent receptor system consisting of RET tyrosine kinase and glycosyl-phosphatidylinositol-anchored coreceptor (GFR1–4). These neurotrophic factors promote the survival of various neurons including peripheral autonomic and sensory neurons as well as central motor and dopamine neurons, and have been expected as therapeutic agents for neurodegenerative diseases. In addition, it turned out that the GDNF/RET signaling plays a crucial role in renal development and regulation of spermatogonia differentiation. RET mutations cause several human diseases such as papillary thyroid carcinoma, multiple endocrine neoplasia types 2A and 2B, and Hirschsprung's disease. The mutations resulted in RET activation or inactivation by various mechanisms and the biological properties of mutant proteins appeared to be correlated with disease phenotypes. The signaling pathways activated by GDNF or mutant RET are being extensively investigated to understand the molecular mechanisms of disease development and the physiological roles of the GDNF family ligands.     

Dysfunction of axonal transport in neuropathies and motor neuron diseases

Sensory neurons and motor neurons are particularly vulnerable to axonal transport defects due to the length of their axons. Several mutations have recently been identified in genes coding for cytoskeletal or motor proteins as causative factors in various neurodegenerative diseases. This review synthesizes the main defects found in inherited peripheral neuropathies and in motor neuron diseases as well as in mouse models of these disorders.