Ethylene oxide polyneuropathy: clinical follow-up study with morphometric and electron microscopic findings in a sural nerve biopsy

Na V 1.8/Na V 1.9 double deletion mildly affects acute pain responses in mice

ABSTRACT

The 2 tetrodotoxin-resistant (TTXr) voltage-gated sodium channel subtypes Na V 1.8 and Na V 1.9 are important for peripheral pain signaling. As determinants of sensory neuron excitability, they are essential for the initial transduction of sensory stimuli, the electrogenesis of the action potential, and the release of neurotransmitters from sensory neuron terminals. Na V 1.8 and Na V 1.9, which are encoded by SCN10A and SCN11A , respectively, are predominantly expressed in pain-sensitive (nociceptive) neurons localized in the dorsal root ganglia (DRG) along the spinal cord and in the trigeminal ganglia. Mutations in these genes cause various pain disorders in humans. Gain-of-function missense variants in SCN10A result in small fiber neuropathy, while distinct SCN11A mutations cause, i. a., congenital insensitivity to pain, episodic pain, painful neuropathy, and cold-induced pain. To determine the impact of loss-of-function of both channels, we generated Na V 1.8/Na V 1.9 double knockout (DKO) mice using clustered regularly interspaced short palindromic repeats/Cas-mediated gene editing to achieve simultaneous gene disruption. Successful knockout of both channels was verified by whole-cell recordings demonstrating the absence of Na V 1.8- and Na V 1.9-mediated Na + currents in Na V 1.8/Na V 1.9 DKO DRG neurons. Global RNA sequencing identified significant deregulation of C-LTMR marker genes as well as of pain-modulating neuropeptides in Na V 1.8/Na V 1.9 DKO DRG neurons, which fits to the overall only moderately impaired acute pain behavior observed in DKO mice. Besides addressing the function of both sodium channels in pain perception, we further demonstrate that the null-background is a very valuable tool for investigations on the functional properties of individual human disease-causing variants in Na V 1.8 or Na V 1.9 in their native physiological environment.

Novel genetic and neuropathological insights in neurogenic muscle weakness, ataxia, and retinitis pigmentosa (NARP)

INTRODUCTION

Neurogenic muscle weakness, ataxia, and retinitis pigmentosa (NARP) is caused by m.8993T>G/C mutations in the mitochondrial adenosine triphosphate synthase subunit 6 gene (MT-ATP6). Traditionally, heteroplasmy levels between 70% and 90% lead to NARP, and >90% result in Leigh syndrome.

METHODS

In this study we report a 30-year-old man with NARP and m.8993T>G in MT-ATP6.

RESULTS

Although the patient carried the mutation in homoplasmic state in blood with similarly high levels in urine (94%) and buccal swab (92%), he presented with NARP and not the expected, more severe Leigh phenotype. The mutation could not be detected in any of the 3 analyzed tissues of the mother, indicating a large genetic shift between mother and offspring. Nerve biopsy revealed peculiar endoneurial Schwann cell nuclear accumulations, clusters of concentrically arranged Schwann cells devoid of myelinated axons, and degenerated mitochondria.

CONCLUSIONS

We emphasize the phenotypic variability of the m.8993T>G MT-ATP6 mutation and the need for caution in predictive counseling in such patients. Muscle Nerve 54: 328-333, 2016.

Loss of function of the ALS protein SigR1 leads to ER pathology associated with defective autophagy and lipid raft disturbances

Intracellular accumulations of altered, misfolded proteins in neuronal and other cells are pathological hallmarks shared by many neurodegenerative diseases including amyotrophic lateral sclerosis (ALS). Mutations in several genes give rise to familial forms of ALS. Mutations in Sigma receptor 1 have been found to cause a juvenile form of ALS and frontotemporal lobar degeneration (FTLD). We recently described altered localization, abnormal modification and loss of function of SigR1 in sporadic ALS. In order to further elucidate the molecular mechanisms underlying SigR1-mediated alterations in sporadic and familial ALS, we extended our previous studies using neuronal SigR1 knockdown cell lines. We found that loss of SigR1 leads to abnormal ER morphology, mitochondrial abnormalities and impaired autophagic degradation. Consistent with these results, we found that endosomal trafficking of EGFR is impaired upon SigR1 knockdown. Furthermore, in SigR1-deficient cells the transport of vesicular stomatitis virus glycoprotein is inhibited, leading to the accumulation of this cargo protein in the Golgi apparatus. Moreover, depletion of SigR1 destabilized lipid rafts and associated calcium mobilization, confirming the crucial role of SigR1 in lipid raft and intracellular calcium homeostasis. Taken together, our results support the notion that loss of SigR1 function contributes to ALS pathology by causing abnormal ER morphology, lipid raft destabilization and defective endolysosomal pathways.

Diagnostic hallmarks and pitfalls in late-onset progressive transthyretin-related amyloid-neuropathy

Familial amyloid polyneuropathy (FAP) is a progressive systemic autosomal dominant disease caused by pathogenic mutations in the transthyretin (TTR) gene. We studied clinical, electrophysiological, histopathological, and genetic characteristics in 15 (13 late-onset and two early-onset) patients belonging to 14 families with polyneuropathy and mutations in TTR. In comparison, we analysed the features of nine unrelated patients with an idiopathic polyneuropathy, in whom TTR mutations have been excluded. Disease occurrence was familial in 36 % of the patients with TTR-associated polyneuropathy and the late-onset type was observed in 86 % (mean age at onset 65.5 years). Clinically, all late-onset TTR-mutant patients presented with distal weakness, pansensory loss, absence of deep tendon reflexes, and sensorimotor hand involvement. Afferent-ataxic gait was present in 92 % leading to wheelchair dependence in 60 % after a mean duration of 4.6 years. Autonomic involvement was observed in 60 %, and ankle edema in 92 %. The sensorimotor polyneuropathy was from an axonal type in 82 %, demyelinating or mixed type in 9 % each. Compared to the TTR-unmutated idiopathic polyneuropathy patients, we identified rapid progression, early ambulatory loss, and autonomic disturbances, associated with a severe polyneuropathy as red flags for TTR-FAP. In 18 % of the late-onset TTR-FAP patients, no amyloid was found in nerve biopsies. Further diagnostic pitfalls were unspecific electrophysiology, and coincident diabetes mellitus (23 %) or monoclonal gammopathy (7 %). We conclude that a rapid disease course, severely ataxic gait, hand involvement, and autonomic dysfunction are diagnostic hallmarks of late-onset TTR-FAP. Genetic analysis should be performed even when amyloid deposits are lacking or when polyneuropathy-causing comorbidities are concomitant.

Altered localization, abnormal modification and loss of function of Sigma receptor-1 in amyotrophic lateral sclerosis

Intracellular accumulations of mutant, misfolded proteins are major pathological hallmarks of amyotrophic lateral sclerosis (ALS) and related disorders. Recently, mutations in Sigma receptor 1 (SigR1) have been found to cause a form of ALS and frontotemporal lobar degeneration (FTLD). Our goal was to pinpoint alterations and modifications of SigR1 in ALS and to determine how these changes contribute to the pathogenesis of ALS. In the present study, we found that levels of the SigR1 protein were reduced in lumbar ALS patient spinal cord. SigR1 was abnormally accumulated in enlarged C-terminals and endoplasmic reticulum (ER) structures of alpha motor neurons. These accumulations co-localized with the 20s proteasome subunit. SigR1 accumulations were also observed in SOD1 transgenic mice, cultured ALS-8 patient's fibroblasts with the P56S-VAPB mutation and in neuronal cell culture models. Along with the accumulation of SigR1 and several other proteins involved in protein quality control, severe disturbances in the unfolded protein response and impairment of protein degradation pathways were detected in the above-mentioned cell culture systems. Furthermore, shRNA knockdown of SigR1 lead to deranged calcium signaling and caused abnormalities in ER and Golgi structures in cultured NSC-34 cells. Finally, pharmacological activation of SigR1 induced the clearance of mutant protein aggregates in these cells. Our results support the notion that SigR1 is abnormally modified and contributes to the pathogenesis of ALS.

Processing of nerve biopsies: a practical guide for neuropathologists

Nerve biopsy is a valuable tool in the diagnostic work-up of peripheral neuropathies. Currently, major indications include interstitial pathologies such as suspected vasculitis and amyloidosis, atypical cases of inflammatory neuropathy and the differential diagnosis of hereditary neuropathies that cannot be specified otherwise. However, surgical removal of a piece of nerve causes a sensory deficit and – in some cases – chronic pain. Therefore, a nerve biopsy is usually performed only when other clinical, laboratory and electrophysiological methods have failed to clarify the cause of disease. The neuropathological work-up should include at least paraffin and resin semithin histology using a panel of conventional and immunohistochemical stains. Cryostat section staining, teased fiber preparations, electron microscopy and molecular genetic analyses are potentially useful additional methods in a subset of cases. Being performed, processed and read by experienced physicians and technicians nerve biopsies can provide important information relevant for clinical management.

Colony-stimulating factor-1 mediates macrophage-related neural damage in a model for Charcot-Marie-Tooth disease type 1X

Previous studies in our laboratory have shown that in models for three distinct forms of the inherited and incurable nerve disorder, Charcot-Marie-Tooth neuropathy, low-grade inflammation implicating phagocytosing macrophages mediates demyelination and perturbation of axons. In the present study, we focus on colony-stimulating factor-1, a cytokine implicated in macrophage differentiation, activation and proliferation and fostering neural damage in a model for Charcot-Marie-Tooth neuropathy 1B. By crossbreeding a model for the X-linked form of Charcot-Marie-Tooth neuropathy with osteopetrotic mice, a spontaneous null mutant for colony-stimulating factor-1, we demonstrate a robust and persistent amelioration of demyelination and axon perturbation. Furthermore, functionally important domains of the peripheral nervous system, such as juxtaparanodes and presynaptic terminals, were preserved in the absence of colony-stimulating factor-1-dependent macrophage activation. As opposed to other Schwann cell-derived cytokines, colony-stimulating factor-1 is expressed by endoneurial fibroblasts, as revealed by in situ hybridization, immunocytochemistry and detection of β-galactosidase expression driven by the colony-stimulating factor-1 promoter. By both light and electron microscopic studies, we detected extended cell-cell contacts between the colony-stimulating factor-1-expressing fibroblasts and endoneurial macrophages as a putative prerequisite for the effective and constant activation of macrophages by fibroblasts in the chronically diseased nerve. Interestingly, in human biopsies from patients with Charcot-Marie-Tooth type 1, we also found frequent cell-cell contacts between macrophages and endoneurial fibroblasts and identified the latter as main source for colony-stimulating factor-1. Therefore, our study provides strong evidence for a similarly pathogenic role of colony-stimulating factor-1 in genetically mediated demyelination in mice and Charcot-Marie-Tooth type 1 disease in humans. Thus, colony-stimulating factor-1 or its cognate receptor are promising target molecules for treating the detrimental, low-grade inflammation of several inherited neuropathies in humans.

Facioscapulohumeral muscular dystrophy presenting with unusual phenotypes and atypical morphological features of vacuolar myopathy

Facioscapulohumeral muscular dystrophy (FSHD) is the third most common muscular dystrophy and usually follows an autosomal dominant trait. Clinically, FSHD affects facial muscles and proximal upper limb and girdle muscles, but may present with variable clinical phenotypes even within the same family. Most genetically confirmed FSHD patients exhibit unspecific morphological signs of a degenerative myopathy. We report on five unrelated patients who carried the pathogenic FSHD mutation on chromosome 4q35. Muscle biopsies revealed numerous rimmed vacuoles and filamentous cytoplasmic inclusions in all cases. Clinically, the patients suffered from weakness and atrophy predominantly of the lower limb muscles. In conclusion, we suggest considering FSHD in the differential diagnosis of adult-onset distal myopathies with rimmed vacuoles.

[Inflammatory and other myopathies and skeletal muscle vasculitis: the role of muscle and nerve biopsy]

Muscle and nerve biopsies provide valuable information contributing to the diagnosis of diseases of the peripheral nervous system and skeletal muscle. The application of modern histological, immunohistochemical, electron microscopic and molecular methods establishes a definite diagnosis in many cases and narrows the spectrum of possible entities in most of the remaining cases. Inflammatory myopathies and neuropathies are distinguished from non-inflammatory muscular and peripheral nervous conditions. The latter include muscular dystrophies and congenital myopathies, hereditary neuropathies, metabolic diseases affecting skeletal muscle and peripheral nerves as well as degenerative myopathies and neuropathies including sporadic motor neuron diseases.

Congenital type IV glycogenosis: the spectrum of pleomorphic polyglucosan bodies in muscle, nerve, and spinal cord with two novel mutations in the GBE1 gene

A diagnosis of GSD-IV was established in three premature, floppy infants based on characteristic, however unusually pleomorphic polyglucosan bodies at the electron microscopic level, glycogen branching enzyme deficiency in two cases, and the identification of GBE1 mutations in two cases. Pleomorphic polyglucosan bodies in muscle fibers and macrophages, and less severe in Schwann cells and microglial cells were noted. Most of the inclusions were granular and membrane-bound; others had an irregular contour, were more electron dense and were not membrane bound, or homogenous ('hyaline'). A paracrystalline pattern of granules was repeatedly noted showing a periodicity of about 10 nm with an angle of about 60 degrees or 120 degrees at sites of changing linear orientation. Malteser crosses were noted under polarized light in the larger inclusions. Some inclusions were PAS positive and others were not. Severely atrophic muscle fibers without inclusions, but with depletion of myofibrils in the plane of section studied indicated the devastating myopathic nature of the disease. Schwann cells and peripheral axons were less severely affected as was the spinal cord. Two novel protein-truncating mutations (c.1077insT, p.V359fsX16; g.101517_127067del25550insCAGTACTAA, DelExon4-7) were identified in these families. The present findings extend previous studies indicating that truncating GBE1 mutations cause a spectrum of severe diseases ranging from generalized intrauterine hydrops to fatal perinatal hypotonia and fatal cardiomyopathy in the first months of life.

The pathogenesis of neurodegenerative disease: neurotoxic mechanisms of action and genetics

The role of environmental and occupational exposures to neurotoxicants in the pathogenesis of neurodegenerative disease has not been fully elucidated. Recent published research on whether genetic polymorphisms contribute to individual susceptibility to develop neurodegenerative diseases such as Parkinson's disease have been equivocal at best. This review relates putative mechanisms of neurotoxicant-induced cell damage to polymorphisms in the genes that encode for the enzymes involved in the metabolism of neurotoxicants. The effects that genetically induced alterations in enzyme functioning have on neurotoxicant metabolism and how this relates to the risk of neurotoxic effects among exposed individuals are reviewed. A pragmatic approach to future research in the area of neurodegenerative disease is developed on the basis of the interrelationship between known routes of neurotoxicant metabolism and human genetics.

Neurotoxicants and the cytoskeleton

Exposure to occupational and environmental toxicants can result in distal axonopathies through reaction with various components of the axonal cytoskeleton. The solvents n-hexane and methyl n-butyl ketone are metabolized to the beta-diketone, 2,5-hexanedione, which covalently cross-links neurofilaments, resulting in large paranodal axonal swellings filled with neurofilaments. Carbon disulfide exposure leads to an identical axonopathy, achieving neurofilament cross-linking through a parallel series of reactions. Acrylamide and ethylene oxide, on the other hand, adduct proteins but do not lead to cross-linking. These toxicants appear to affect the function of microtubule-associated proteins, such as kinesin, and result in the impaired transport of synaptic vesicles.

Neurophysiological and neuropathological evaluation of primates exposed to ethylene oxide and propylene oxide

Over 500,000 workers in the United States are exposed to ethylene oxide and propylene oxide. These two solvents are used as chemical intermediates, as well as components in the manufacture of fumigants and food preparation. The neurophysiologic and neuropathologic effects of these two organic oxides were investigated in five groups of 12 primates after exposure to 50 or 100 ppm ethylene oxide, 100 or 300 ppm propylene oxide, or no chemical (sham-exposed). Animals were exposed for 7 h/day, 5 days/wk for 24 months. Body weights, electroencephalograms, and motor nerve conduction velocities of the sciatic and ulnar nerves were assessed six times throughout the exposure period. Although the monkeys exposed to 100 ppm ethylene oxide had significantly lower mean weights, nerve conduction velocities did not differ significantly among the groups. Following termination of exposures, ten animals (two from each exposure group) were sacrificed for neuropathological examinations. Multiple axonal bodies were found in the nucleus gracilis in seven of eight oxide-exposed animals, and demyelination was found in two monkeys exposed to ethylene oxide. In contrast, a single axonal body was found in one of the two sham-control monkeys. However, the lack of a dose-response relationship suggests that this effect may not be related to oxide exposure. In a follow-up study, nerve conduction velocity and neuropathology were assessed in the remaining monkeys seven years after exposure terminated, but again, treatment-related effects could not be detected.

HLA-DR expression in peripheral neuropathies: the role of Schwann cells, resident and hematogenous macrophages, and endoneurial fibroblasts

The expression of HLA-DR and the macrophage marker CD 68 was studied in 44 sural nerve biopsies from patients with inflammatory and non-inflammatory neuropathies and controls using immunohistochemistry on non-osmicated semithin sections, a technique that has not been used before in such a biopsy study. Most HLA-DR-immunoreactive (ir) cells were fibroblasts, macrophages or perineural cells, some were perivascular and endothelial cells, and only few were Schwann cells. Counts of immunoreactive cells revealed (a) increased HLA-DR expression in severe as compared to less severe neuropathies and to controls, (b) no correlation between the numbers of HLA-DR-ir cells and CD 68-ir macrophages, and (c) no close correlation between diagnostic groups and the number of HLA-DR-ir cells, but higher numbers in inflammatory neuropathies. We conclude that endoneurial fibroblasts and macrophages as antigen-presenting cells may be mediators in various peripheral nerve diseases, not only in inflammatory disorders.

Rapid axonal transport velocity is reduced in experimental ethylene oxide neuropathy

Chronic exposure of rats to ethylene oxide (EO) causes distal axonal neuropathy of lumbosacral primary sensory neurons. To study the pathogenesis of this neuropathy, we measured rapid axonal transport in peripheral nerves. Rats were exposed for 6 h to 500 ppm EO in a chamber three times a wk for 15 wk. Rapid axonal transport and quantitative histological alterations of peripheral nerves were studied. After [35S]methionine injection into the dorsal root ganglion, the velocity of rapid anterograde axonal transport of radioisotope-labeled protein was measured. The velocity in the rats exposed to EO was 33% less than that in control rats exposed to filtered room air. However, histological differences were slight. Morphometric studies showed that in EO-exposed rats, only the distal portions of the sural nerve had significantly greater incidental degeneration of myelinated fibers than did controls. There were significantly fewer large myelinated fibers only in the distals peroneal nerve. Therefore, a decrease in the velocity of anterograde axonal transport, related to these slight histological abnormalities of the peripheral nerve, may play a causative role in the development of the distal axonal neuropathy owing to chronic EO exposure.

[Polyneuropathy caused by ethylene oxide. Report of a case with clinical, electrophysiological and histopathological studies]

A man who worked as an operator in a factory of sterilization of heat-sensitive materials has been exposed to ethylene oxide for seven years. He developed a mild sensori-motor polyneuropathy. The electromyography and nerve condition studies showed an axonal degenerative type of neuropathy. The sural nerve biopsy revealed mild loss of myelinated fibers, some fibers with axonal degeneration, some clusters of regeneration and few rows of myelin ovoids in the teased nerve fiber preparation. This is the first report of ethylene-oxide polyneuropathy in Brazil.

Residual ethylene oxide in hollow fiber hemodialysis units is neurotoxic in vitro

Ethylene oxide gas is used to sterilize plastic medical equipment including capillary flow dialysis membranes. To test whether ethylene oxide retained in the dialyzers might be neurotoxic, tissue culture medium was incubated in the blood compartment of dialyzers. Embryonic rat dorsal root ganglion neurons were then incubated in this medium for up to 5 days. During the first 24 hours axonal growth was normal. During the next 24-hour period varicosities appeared on axons, and after 4 days neuron cell bodies died. The pattern of degeneration was identical to that observed when cultures were exposed to an atmosphere containing 1 ppm ethylene oxide gas. Culture medium introduced into dialyzers after routine prerinsing still caused degeneration, which was not completely abolished even by a 10-liter rinse. When medium was exposed to identical dialyzers sterilized by gamma irradiation, no changes were seen in culture. Identical morphological changes were produced by using dialysis patient serum in the culture medium in place of the usual calf bovine serum. Such changes were never seen with control human serum. Since ethylene oxide is toxic to the human peripheral nervous system, it is proposed that ethylene oxide in dialyzers may contribute to the progressive neuropathy observed in patients on long-term hemodialysis.

Ethylene oxide neuropathy in rats. Exposure to 250 ppm

In Wistar rats subjected to a 6-h exposure to ethylene oxide at the concentration of 250 parts per million once, 5 times a week for 9 months, histopathologic studies of myelinated fibers of the proximal sural, distal sural and peroneal nerves and of the fasciculus gracilis at the 5th thoracic and 3rd cervical segments of the spinal cord were performed to observe whether ethylene oxide of such a concentration would lead to degeneration of primary sensory neurons. Throughout the study, no definite abnormality of the gait or posture was observed in both control and test rats. Qualitative histologic studies disclosed preferential distal axonal degeneration of myelinated fibers in both sural nerves and gracile fascicles in the test rats, although the extent of the distribution and the severity of the degenerative findings were variable. Such findings are consistent with mild axonal degeneration found among patients suffering from ethylene oxide toxicity. Therefore, in rats, exposure to 250 ppm ethylene oxide produces central-peripheral distal axonal degeneration of primary sensory neurons.