The α-chemokine CXCL14 is up-regulated in the sciatic nerve of a mouse model of Charcot–Marie–Tooth disease type 1A and alters myelin gene expression in cultured Schwann cells

At present the pathogenesis of CMT1A neuropathy, caused by the overexpression of PMP22, has not yet been entirely understood. The PMP22-overexpressing C61 mutant mouse is a suitable animal model, which mimics the human CMT1A disorder. We observed that myelin gene expression in the sciatic nerve of the C61 mouse was up-regulated at postnatal day 4 to 7 (P4–P7). When investigating the morphology of peripheral nerves in C61 and wildtype mice at early stages of postnatal development, hypermyelination could be detected in the femoral quadriceps and sciatic nerve of transgenic animals at postnatal day 7 (P7). In order to identify genes, other than Pmp22, that are modulated in sciatic nerve of P7 transgenic mice, we applied microarray technology. Amongst the regulated genes, the gene encoding the α-chemokine CXCL14 was most prominently up-regulated. We report that Cxcl14 was expressed exclusively by Schwann cells of the sciatic nerve, as well as by cultured Schwann cells triggered to differentiate. Furthermore, in cultured Schwann cells CXCL14 modulated the expression of myelin genes and altered cell proliferation. Our findings demonstrate that early overexpression of PMP22, in a mouse model of CMT1A, results in a strong up-regulation of CXCL14, which seems to play a novel regulatory role in Schwann cell differentiation.     

Rapid genetic screening of Charcot-Marie-Tooth disease type 1A and hereditary neuropathy with liability to pressure palsies patients

We used the allele-specific PCR-double digestion method on peripheral myelin protein 22 (PMP22) to determine duplication and deletion mutations in the proband and family members of one family with Charcot-Marie-Tooth disease type 1 and one family with hereditary neuropathy with liability to pressure palsies. The proband and one subclinical family member from the Charcot-Marie-Tooth disease type 1 family had a PMP22 gene duplication; one patient from the hereditary neuropathy with liability to pressure palsies family had a PMP22 gene deletion. Electron microscopic analysis of ultrathin sections of the superficial peroneal nerve from the two probands demonstrated demyelination and myelin sheath hyperplasia, as well as an ’onion-like’ structure in the Charcot-Marie-Tooth disease type 1A patient. We observed an irregular thickened myelin sheath and ’mouse-nibbled’-like changes in the patient with hereditary neuropathy with liability to pressure palsies. In the Charcot-Marie-Tooth disease type 1A patient, nerve electrophysiological examination revealed moderate-to-severe reductions in the motor and sensory conduction velocities of the bilateral median nerve, ulnar nerve, tibial nerve, and sural nerve. Moreover, the compound muscle action potential amplitude was decreased. In the patient with hereditary neuropathy with liability to pressure palsies, the nerve conduction velocity of the bilateral tibial nerve and sural nerve was moderately reduced, and the nerve conduction velocity of the median nerve and ulnar nerve of both upper extremities was slightly reduced.     

Central nervous system involvement in hereditary neuropathy with liability to pressure palsies: description of a large family with this association

OBJECTIVE: To describe a large family with hereditary neuropathy with liability to pressure palsies associated with central nervous system demyelination. DESIGN: We examined the 18 members of a pedigree. Genetic analysis was performed on 15 subjects, standard nerve conduction studies on 10 subjects, and brain magnetic resonance imaging studies on 8 subjects. RESULTS: Hereditary neuropathy with liability to pressure palsies was confirmed in 9 patients of the pedigree. Brain magnetic resonance imaging findings showed multiple areas of demyelination in 6 of 6 affected members and were normal in 2 of 2 healthy relatives. Magnetic resonance imaging abnormalities were predominantly located in the subcortical frontal white matter. All patients had acute and recurrent nerve palsies, while clinical features of central nervous system involvement were not a characteristic of this pedigree. CONCLUSIONS: We demonstrate that this association, previously reported in sporadic cases, is not coincidental. Therefore, patients with hereditary neuropathy with liability to pressure palsies can present central nervous system white matter lesions, and the role of the PMP22 (peripheral myelin protein 22) gene deletion in the central nervous system should be further studied.     

Characterisation of autoantibodies to peripheral myelin protein 22 in patients with hereditary and acquired neuropathies

To investigate the possibility that an autoimmune mechanism may play a role in the hereditary neuropathy Charcot-Marie-Tooth type 1A (CMT1A), sera were analysed by Western blot for anti-peripheral myelin protein 22 (PMP22) autoantibodies. These sera were compared with sera from patients with CMT type 2 (CMT2), acquired peripheral neuropathies such as chronic inflammatory demyelinating neuropathy (CIDP), anti-MAG IgM neuropathy, Miller-Fisher syndrome (MFS), diabetic neuropathy and with control blood donors. Anti-PMP22 positive sera were detected in 70% of patients with CMT1 and unexpectedly in 60% of patients with CMT2. Interestingly, 44% of the patients with other peripheral neuropathies and 23% of the apparently healthy controls showed also anti-PMP22 antibody reactivity. Immunohistochemical analysis of the human anti-PMP22 antisera on healthy sural nerve sections and on PMP22-expressing COS cells revealed that these sera did not recognise endogenous PMP22. Our results indicate that anti-PMP22 autoantibodies are found in sera of patients with different types of peripheral neuropathies, but their role in the pathogenesis of these diseases remains to be determined.     

Recurrent familial brachial plexus palsies as the only clinical expression of 'tomaculous' neuropathy

Two familial cases of recurrent brachial plexus are described and similar episodes were noticed in other members of the family. Electrophysiological investigations found impaired motor and sensory nerve conduction velocity in affected and nonaffected members. Tomaculous neuropathy was found at biopsy of peripheral nerve in more than 40% of dissected fibers. In addition, two affected members showed a reduced interpupillary distance, i.e. the most common dysmorphic feature found in the hereditary neuralgic amyotrophy (HNA). A literature review showed only two other instances of recurrent familial brachial plexus palsies as the only manifestation of tomaculous neuropathy (hereditary neuropathy with liability to pressure palsy, HNPP). The dysmorphic feature found in our cases in addition to the clinical, electrophysiological and anatomical data support the hypothesis that these cases of HNPP and the HNA may represent the same disease.     

Mutant HSPB1 overexpression in neurons is sufficient to cause age-related motor neuronopathy in mice

The small heat shock protein HSPB1 is a multifunctional, α-crystallin-based protein that has been shown to be neuroprotective in animal models of motor neuron disease and peripheral nerve injury. Missense mutations in HSPB1 result in axonal Charcot-Marie-Tooth disease with minimal sensory involvement (CMT2F) and distal hereditary motor neuropathy type 2 (dHMN-II). These disorders are characterized by a selective loss of motor axons in peripheral nerve resulting in distal muscle weakness and often severe disability. To investigate the pathogenic mechanisms of HSPB1 mutations in motor neurons in vivo, we have developed and characterized transgenic PrP-HSPB1 and PrP-HSPB1(R136W) mice. These mice express the human HSPB1 protein throughout the nervous system including in axons of peripheral nerve. Although both mouse strains lacked obvious motor deficits, the PrP-HSPB1(R136W) mice developed an age-dependent motor axonopathy. Mutant mice showed axonal pathology in spinal cord and peripheral nerve with evidence of impaired neurofilament cytoskeleton, associated with organelle accumulation. Accompanying these findings, increases in the number of Schmidt-Lanterman incisures, as evidence of impaired axon-Schwann cell interactions, were present. These observations suggest that overexpression of HSPB1(R136W) in neurons is sufficient to cause pathological and electrophysiological changes in mice that are seen in patients with hereditary motor neuropathy.     

Loss-of-function of EBP50 is a new cause of hereditary peripheral neuropathy: EBP50 functions in peripheral nerve system

Finding causative genetic mutations is important in the diagnosis and treatment of hereditary peripheral neuropathies. This study was conducted to find new genes involved in the pathophysiology of hereditary peripheral neuropathy. We identified a new mutation in the EBP50 gene, which is co-segregated with neuropathic phenotypes, including motor and sensory deficit in a family with Charcot–Marie–Tooth disease. EBP50 is known to be important for the formation of microvilli in epithelial cells, and the discovery of this gene mutation allowed us to study the function of EBP50 in the nervous system. EBP50 was strongly expressed in the nodal and paranodal regions of sciatic nerve fibers, where Schwann cell microvilli contact the axolemma, and at the growth tips of primary Schwann cells. In addition, EBP50 expression was decreased in mouse models of peripheral neuropathy. Knockout mice were used to study EBP50 function in the peripheral nervous system. Interestingly motor function deficit and abnormal histology of nerve fibers were observed in EBP50^+/− heterozygous mice at 12 months of age, but not 3 months. in vitro studies using Schwann cells showed that NRG1-induced AKT activation and migration were significantly reduced in cells overexpressing the I325V mutant of EBP50 or cells with knocked-down EBP50 expression. In conclusion, we show for the first time that loss of function due to EBP50 gene deficiency or mutation can cause peripheral neuropathy.     

Nerve biopsy: requirements for diagnosis and clinical value

In many instances, nerve biopsy is not necessary in the diagnostic work-up of a peripheral neuropathy. However, histological examination of a tissue sample is still mandatory to show specific lesions in various conditions involving peripheral nerves. As there are fewer laboratories that examine human nerve samples, practitioners including neurologists and general pathologists may not be completely aware of the technical issues and data that are provided by nerve biopsy. Nerve biopsy is considered an invasive diagnostic method, although, its complications are by far less disabling than most of the disorders that lead to its indications. Nevertheless, the decision to perform a nerve biopsy has to be made on a case-by-case basis, and its results must be discussed between the pathologist and the clinician who is in charge of the patient’s care. In this paper, we review the minimal technical requirements for proper peripheral nerve tissue analysis. Moreover, we provide data on the usefulness of nerve biopsy in various situations including abnormal deposits, cell infiltrates, link between peripheral neuropathy and monoclonal gammopathy, and numerous hereditary disorders.     

PERIPHERAL NEUROPATHY IN MOUSE HEREDITARY DIABETES MELLITUS. II. ULTRASTRUCTURAL CORRELATES OF DEGENERATIVE AND REGENERATIVE CHANGES

Carson K.A., Bossen E.H. & Hanker J.S. (1980) Neuropathology and Applied Neurobiology 6,361–374
Peripheral neuropathy in mouse hereditary diabetes mellitus. II. Ultrastructural correlates of degenerative and regenerative changes
The fine structural changes in some peripheral nerves and sensory ganglia from mice (C57BL/K & J, db/db) with an hereditary diabetic syndrome, similar to human maturity-onset diabetes mellitus, were studied during development of the mild peripheral neuropathy. The abnormalities observed included axonal degeneration, disruption of myelin, accumulation of electron-dense material in axons, satellite cells and Schwann cells, increased frequency of it granules of Reich in Schwann cells, enlarged mitochondria, and proliferated and thickened Schwann cell basal laminae. Distal hind limb nerves were most affected. Sensory ganglion neurons were normal except for occasional chro-matolytic cells, so that nerve cell loss was not present in this peripheral neuropathy. Morphological indications of Schwann cell hyperplasia, hypertrophy, and axonal sprouting supported the contention that a continuous cycle of axonal degeneration and regeneration was occurring. The ultrastructural changes and accumulation of electron-opaque, lipid material suggested that a defect in lipid metabolism, secondary to the diabetic condition, could be an important factor in the peripheral neuropathy in the diabetic mouse.     

Insulin-like growth factor-I prevents development of a vincristine neuropathy in mice

Vincristine is a commonly used antitumor agent whose major dose-limiting side-effect is a mixed sensorimotor neuropathy. To assess whether insulin-like growth factor-I (IGF-I), a neurotrophic agent that supports the survival of motoneurons and enhances regeneration of motor and sensory neurons, could prevent the peripheral neuropathy produced by vincristine, mice were treated with both vincristine (1.7 mg/kg, i.p., 2×/week) and/or IGF-I (0.3 or 1 mg/kg, s.c. daily) for 10 weeks. In mice treated with vincristine alone, there was evidence of a mixed sensorimotor neuropathy as indicated by changes in behavior, nerve conduction and histology. Caudal nerve conduction velocity was significantly slower in mice treated with vincristine alone as compared with vehicle-treated mice. Vincristine treatment alone also significantly increased hot-plate latencies and reduced gait support and stride length, but not toe spread distances. The effects of vincristine were accompanied by degeneration of sciatic nerve fibers and demyelination, indicating a peripheral neuropathy. IGF-I (1 mg/kg, s.c.) administered to vincristine-treated mice prevented the neurotoxic effects of vincristine as measured by nerve conduction, gait, response to noxious stimuli and nerve histology. At a lower dose of 0.3 mg/kg administered s.c., IGF-I partially ameliorated the neuropathy induced by vincristine as this dose only prevented the change in nerve conduction and hot-plate latencies. IGF-I administered alone had no effect on any of these parameters. These results suggest that IGF-I prevents both motor and sensory components of vincristine neuropathy and may be useful clinically in preventing the neuropathy induced by vincristine treatment.     

Charcot–Marie–Tooth disease associated with recurrent optic neuritis

The factors precipitating central nervous system (CNS) demyelination, including optic neuritis, remain largely unknown but are likely to represent a complex interplay between the patient’s environment and their genetic background. We report the development of sequential demyelinating optic neuritis in a patient with genetically confirmed Charcot–Marie–Tooth disease type 1A, a hereditary neuropathy. This neuropathy is characterized by duplication of peripheral myelin protein 22 (PMP22), which results in structurally abnormal peripheral myelin. By characterizing peripheral T-cell responses in this patient to a panel of myelin epitopes expressed in the CNS we describe an immunological process which indicates that overexpression of PMP22 may be causative and account for this association.     

A Transgenic Mouse Model for Human Hereditary Neuropathy with Liability to Pressure Palsies

Mutations in the gene encoding peripheral myelin protein 22 (PMP22) account for several inherited peripheral neuropathies in humans. We now show that transgenic mice expressing antisense PMP22 RNA exhibit modestly reduced levels of PMP22 together with a phenotype that is reminiscent of hereditary neuropathy with liability to pressure palsies (HNPP), a human disease caused by a 1.5-Mb deletion of a chromosome 17 region that contains thePMP22gene. Transgenic antisense homozygotes display a striking movement disorder and a slowing of nerve conduction that worsens with age. Morphological analysis of peripheral nerves demonstrates that a subset of axons have thickened myelin sheaths and tomacula in young adults, with significant myelin degeneration detected in older animals. Together with other recent work, these data suggest that dosage of thePMP22gene alone underlies the pathophysiology observed in HNPP and related disorders.     

Pathologic classification of a late-onset peripheral neuropathy in a spontaneous Labrador retriever dog model

Late-onset peripheral neuropathy (LPN) is a heritable canine neuropathy commonly found in Labrador retrievers and is characterized by laryngeal paralysis and pelvic limb paresis. Our objective was to establish canine LPN as a model for human hereditary peripheral neuropathy by classifying it as either an axonopathy or myelinopathy and evaluating length-dependent degeneration. We conducted a motor nerve conduction study of the sciatic and ulnar nerves, electromyography (EMG) of appendicular and epaxial musculature, and histologic analysis of sciatic and recurrent laryngeal nerves in LPN-affected and control dogs. LPN-affected dogs exhibited significant decreases in compound muscle action potential (CMAP) amplitude, CMAP area, and pelvic limb latencies. However, no differences were found in motor nerve conduction velocity, residual latencies, or CMAP duration. Distal limb musculature showed greater EMG changes in LPN-affected dogs. Histologically, LPN-affected dogs exhibited a reduction in the number of large-diameter axons, especially in distal nerve regions. In conclusion, LPN in Labrador retrievers is a common, spontaneous, length-dependent peripheral axonopathy that is a novel animal model of age-related peripheral neuropathy that could be used for fundamental research and clinical trials.     

Selective calf weakness suggests intraspinal pathology, not peripheral neuropathy

Four patients, referred as having peripheral neuropathy, were noted to be able to walk on their heels but not on their toes. In each, intraspinal disease was found: ependymoma of the filum terminale, spinal muscular atrophy, spinal stenosis, and meningeal carcinomatosis. By comparison, in 86 cases of hereditary motor and sensory neuropathy type 1, ankle plantar flexors were never weaker than ankle dorsiflexors. Patients with greater weakness in plantar flexors than in dorsiflexors should be suspected of having intraspinal disease rather than peripheral neuropathy. Physiologic and biomechanical factors may explain why muscles innervated by the peroneal nerve are weaker, or graded weaker, in peripheral neuropathy.     

An 8.5-kb segment of the PMP22 promoter responds to loss of axon signals during Wallerian degeneration, but does not respond to specific axonal signals during nerve regeneration

Altered expression of the PMP22 gene causes Charcot-Marie-Tooth disease type 1A (CMT1A) and hereditary neuropathy with liability to pressure palsies (HNPP). We have examined the promoter activity of 8.5 kb upstream of the first coding exon of the rat peripheral myelin protein-22 (rPmp22) gene in transgenic mice. We found that the -8.5 kb rPmp22/chloramphenicol acetyl transferase (CAT)/beta-galactosidase (lacZ) construct directs reporter gene expression in a weakly developmental and tissue-specific pattern, consistent with the expression pattern of the endogenous Pmp22 gene. The -8.5 kb rPmp22/CAT/lacZ transgene responds to loss of axonal signals during Wallerian degeneration but unlike the endogenous Pmp22 gene, the transgene fails to respond to axonal signals during nerve regeneration after a sciatic nerve crush injury. In conclusion, the function of the -8.5 kb rPmp22/CAT/lacZ transgene suggests that there are separable regulatory elements in the rPmp22 gene that respond differently to axonal signals received by Schwann cells during nerve development, and during remyelination.     

Expression pattern of the peripheral myelin protein 22kDa (PMP22) in neural and non-neural tissue types of adult wildtype and Trembler mice--a comparative study

The Trembler mouse was the first animal model for Charcot-Marie-Tooth disease type 1 (CMT1), one of the most frequent inherited peripheral neuropathies in man. In Trembler mouse a Gly150Asp amino acid exchange in the peripheral myelin protein 22kDa (PMP22) gene was identified as causative reason for this hypertrophic neuropathy. For most of the CMT patients suffering from the subtype 1A a duplication of the PMP22 gene is found (gene dosage effect); but several PMP22 point mutations, such as that determining the TremblerJ mouse, have also been described. Since PMP22 is expressed in neural, as well as in non-neural tissues, the expression pattern of PMP22 in different tissues seems to be of highest interest for a better understanding of the hypothesized dual function of this protein. We studied different wildtype (wt) and Trembler (Tr) mouse tissues for PMP22 expression by means of radioactive in situ hybridization (RISH) and immunohistochemistry. A PMP22 expression was found in some of the non-neural and in all neural tissue types studied. Our in situ study clearly demonstrated, that PMP22 mRNA expression in non-neural tissues is not due to peripheral innervation. In non-neural tissues no difference in the expression pattern or intensity between wt and Tr mice was detectable, whereas PMP22 expression in the peripheral nervous system (PNS) of the Tr mouse was extremely reduced. Immunohistochemical analysis of sciatic nerve sections revealed the same maldistribution of PMP22 in Tr mice as in sural nerve biopsies of CMT1 patients.     

E-CADHERIN AND β-CATENIN COMPLEX IN ANIMAL MODELS OF HEREDITARY DEMYELINATING PERIPHERAL NEUROPATHY

E‐cadherin, a major adhesive glycoprotein in Schwann cells (Fannon et al., 1995), is localized at the paranode, at Schmidt‐Lanterman incisures in the peripheral nerve along with β‐catenin, and associated with adherens‐type junctions. To investigate the functional role of E‐cadherin/β‐catenin complex in Schwann cells biology, we studied expression and localization of E‐cadherin and β‐catenin complex in sciatic nerve from normal mice and from animal model of hereditary demyelinating peripheral neuropathy. We found that E‐cadherin mRNA and proteins levels are regulated in normal mouse sciatic nerve during development like other myelin proteins. Furthermore, E‐cadherin expression in regenerating nerve is mediated by axonal/SC interaction. On the contrary, β‐catenin mRNA and protein levels did not change during development and following nerve lesion. Moreover, E‐cadherin/β‐catenin complex localization is altered in P0 knockout mice (P0‐/‐). In fact, E‐cadherin was diffusely distributed throughout the fibers in an unusual beaded pattern of staining, and β‐catenin was found in the perinuclear region of P0 ‐/‐ Schwann cells. Furthermore, E‐cadherin/β‐catenin complex localization is altered in peripheral nerve from other model of primary demielination where myelin compaction is lacking, such as Trembler‐J mice, while it is normally localized in Trembler mice, where demyelination is less severe and compaction is preserved. In conclusion, it appears that the process that leads to a restricted localization of E‐cadherin at the paranodal region is highly regulated and is disrupted in the peripheral nerve lacking compaction. Therefore, compaction contributes to the process of reorganization of the Schwann cells membrane during myelination and formation of a mature paranode. Altered E‐cadherin/β‐catenin complex localization, associated with absence of adherens junctions lead to changes in the structure of the paranodal region with important consequences on the molecular architecture of the Node of Ranvier, which lead to an altered transmission of impulses along axons, having important consequences in the pathogenesis of hereditary demyelinating peripheral neuropathy.     

High-resolution sonography of the peripheral nervous system – a review of the literature

High-resolution sonography is capable of depicting peripheral nerves and the brachial plexus. In this study we review the literature on this subject. Normal peripheral nerves have a characteristic echotexture. Most nerves are readily visualized, although this is not always the case with the nerves of the lower extremity. The main pathological changes that can be demonstrated are nerve enlargement and increased hypoechogenicity. In order to demonstrate nerve enlargement, measurements should be performed and compared with a set of reference values. Several neuropathies have been studied by means of ultrasonography. However, many studies concern case reports and show methodological shortcomings. The best studied peripheral neuropathy is the carpal tunnel syndrome in which ultrasonography seems to have an additional value when combined with nerve conduction studies. Nerve enlargement has also been demonstrated in radial neuropathy at the humerus and in ulnar neuropathy at the elbow. The role of sonography in various hereditary and inflammatory neuropathies is uncertain although diffuse nerve thickening could be demonstrated. Further systematic studies are needed to determine the role of sonography in the diagnostic process of the various neuropathies. It would be important to study the subcategories of patients in whom electrodiagnostic studies are normal or show equivocal findings.