Electron Microscopy Analysis of Sciatic Nerve Fibers in C57BL/6 Transgenic Mice (original) (raw)
Related papers
Journal of Neuropathology and Experimental Neurology, 2010
X-linked Charcot-Marie-Tooth disease (CMT1X) is an inherited peripheral neuropathy caused by mutations in GJB1, the gene that encodes the gap junction protein connexin32 (Cx32). Cx32 is expressed by myelinating Schwann cells and forms gap junctions in non-compact myelin areas but axonal involvement is more prominent in X-linked compared to other forms of demyelinating Charcot-Marie-Tooth disease. To clarify the cellular and molecular mechanisms of axonal pathology in CMT1X, we studied Gjb1-null mice at early stages (i.e. 2-to 4-month-old) of the neuropathy, when there is minimal or no demyelination. The diameters of large myelinated axons were progressively reduced in Gjb1-null mice compared to those in wild type littermates. Furthermore, neurofilaments were relatively more dephosphorylated and more densely packed starting at 2 months of age. Increased expression of β-amyloid precursor protein, a marker of axonal damage, was also detected in Gjb1-null nerves. Finally, fast axonal transport, assayed by sciatic nerve ligation experiments, was slower in distal axons of Gjb1-null vs. wild type animals with reduced accumulation of synaptic vesicle-associated proteins. These findings demonstrate that axonal abnormalities including impaired cytoskeletal organization and defects in axonal transport precede demyelination in this mouse model of CMT1-X.
Human Molecular Genetics, 2013
Charcot-Marie-Tooth disease type 1C (CMT1C) is a dominantly inherited motor and sensory neuropathy. Despite human genetic evidence linking missense mutations in SIMPLE to CMT1C, the in vivo role of CMT1C-linked SIMPLE mutations remains undetermined. To investigate the molecular mechanism underlying CMT1C pathogenesis, we generated transgenic mice expressing either wild-type or CMT1C-linked W116G human SIMPLE. Mice expressing mutant, but not wild type, SIMPLE develop a late-onset motor and sensory neuropathy that recapitulates key clinical features of CMT1C disease. SIMPLE mutant mice exhibit motor and sensory behavioral impairments accompanied by decreased motor and sensory nerve conduction velocity and reduced compound muscle action potential amplitude. This neuropathy phenotype is associated with focally infolded myelin loops that protrude into the axons at paranodal regions and near Schmidt-Lanterman incisures of peripheral nerves. We find that myelin infolding is often linked to constricted axons with signs of impaired axonal transport and to paranodal defects and abnormal organization of the node of Ranvier. Our findings support that SIMPLE mutation disrupts myelin homeostasis and causes peripheral neuropathy via a combination of toxic gain-of-function and dominant-negative mechanisms. The results from this study suggest that myelin infolding and paranodal damage may represent pathogenic precursors preceding demyelination and axonal degeneration in CMT1C patients.
Shortened internodal length of dermal myelinated nerve fibres in Charcot-Marie-Tooth disease type 1A
Brain, 2009
Charcot-Marie-Tooth disease type 1A is the most common inherited neuropathy and is caused by duplication of chromosome 17p11.2 containing the peripheral myelin protein-22 gene. This disease is characterized by uniform slowing of conduction velocities and secondary axonal loss, which are in contrast with non-uniform slowing of conduction velocities in acquired demyelinating disorders, such as chronic inflammatory demyelinating polyradiculoneuropathy. Mechanisms responsible for the slowed conduction velocities and axonal loss in Charcot-Marie-Tooth disease type 1A are poorly understood, in part because of the difficulty in obtaining nerve samples from patients, due to the invasive nature of nerve biopsies. We have utilized glabrous skin biopsies, a minimally invasive procedure, to evaluate these issues systematically in patients with Charcot-Marie-Tooth disease type 1A (n = 32), chronic inflammatory demyelinating polyradiculoneuropathy (n = 4) and healthy controls (n = 12). Morphology and molecular architecture of dermal myelinated nerve fibres were examined using immunohistochemistry and electron microscopy. Internodal length was uniformly shortened in patients with Charcot-Marie-Tooth disease type 1A, compared with those in normal controls (P50.0001). Segmental demyelination was absent in the Charcot-Marie-Tooth disease type 1A group, but identifiable in all patients with chronic inflammatory demyelinating polyradiculoneuropathy. Axonal loss was measurable using the density of Meissner corpuscles and associated with an accumulation of intra-axonal mitochondria. Our study demonstrates that skin biopsy can reveal pathological and molecular architectural changes that distinguish inherited from acquired demyelinating neuropathies. Uniformly shortened internodal length in Charcot-Marie-Tooth disease type 1A suggests a potential developmental defect of internodal lengthening. Intra-axonal accumulation of mitochondria provides new insights into the pathogenesis of axonal degeneration in Charcot-Marie-Tooth disease type 1A. Abbreviations: Caspr = contactin-associated protein; CIDP = chronic inflammatory demyelinating polyradiculoneuropathy; CMT1A = Charcot-Marie-Tooth disease type 1A; MBP = myelin basic protein; PGP = protein gene product; PMP22 = peripheral myelin protein 22 gene
Peripheral nerve extracellular matrix remodeling in Charcot-Marie-Tooth type I disease
2002
Charcot-Marie-Tooth type 1 disease (CMT1) is a group of inherited demyelinating neuropathies caused by mutations in genes expressed by myelinating Schwann cells. Rather than demyelination per se, alterations of Schwann cell-axon interactions have been suggested as the main cause of motor-sensory impairment in CMT1 patients. In an attempt to identify molecules that may be involved in such altered interactions, the extracellular matrix (ECM) remodeling occurring in CMT1 sural nerves was studied. For comparison, both normal sural nerves and sural nerves affected by neuropathies of different origin were used. The study was performed by immunohistochemical analysis using antibodies against collagen types I, III, IV, V, and VI and the glycoproteins fibronectin, laminin, vitronectin and tenascin. Up-regulation of collagens, fibronectin and laminin was commonly found in nerve biopsy specimens from patients affected by CMT1 and control diseases, but higher levels of overexpression were usually observed in CMT1 cases. On the other hand, vitronectin and tenascin appeared preferentially induced in CMT1 compared to other pathologies investigated here. Vitronectin, whose expression in normal nerves was limited to perineurial layers and to the walls of epineurial and endoneurial vessels, became strongly and diffusely expressed in the endoneurium in most CMT1 biopsy specimens. The expression of tenascin, confined to the peri-neurium, to vessel walls and to the nodes of Ranvier in normal nerves, was displaced and extended along the internodes of several nerve fibers in the majority of CMT1 nerves. Thus, compared with our pathological controls CMT1 seemed to determine the most extensive remodeling of peripheral nerve ECM.
Peripheral nerve extracellular matrix remodeling in Charcot-Marie-Tooth type 1 disease
Acta Neuropathologica, 2002
Charcot-Marie-Tooth type 1 disease (CMT1) is a group of inherited demyelinating neuropathies caused by mutations in genes expressed by myelinating Schwann cells. Rather than demyelination per se, alterations of Schwann cell-axon interactions have been suggested as the main cause of motor-sensory impairment in CMT1 patients. In an attempt to identify molecules that may be involved in such altered interactions, the extracellular matrix (ECM) remodeling occurring in CMT1 sural nerves was studied. For comparison, both normal sural nerves and sural nerves affected by neuropathies of different origin were used. The study was performed by immunohistochemical analysis using antibodies against collagen types I, III, IV, V, and VI and the glycoproteins fibronectin, laminin, vitronectin and tenascin. Up-regulation of collagens, fibronectin and laminin was commonly found in nerve biopsy specimens from patients affected by CMT1 and control diseases, but higher levels of overexpression were usually observed in CMT1 cases. On the other hand, vitronectin and tenascin appeared preferentially induced in CMT1 compared to other pathologies investigated here. Vitronectin, whose expression in normal nerves was limited to perineurial layers and to the walls of epineurial and endoneurial vessels, became strongly and diffusely expressed in the endoneurium in most CMT1 biopsy specimens. The expression of tenascin, confined to the peri-neurium, to vessel walls and to the nodes of Ranvier in normal nerves, was displaced and extended along the internodes of several nerve fibers in the majority of CMT1 nerves. Thus, compared with our pathological controls CMT1 seemed to determine the most extensive remodeling of peripheral nerve ECM.
A Transgenic Rat Model of Charcot-Marie-Tooth Disease
Neuron, 1996
a prevalence of approximately 1 in 2500 (Skre, 1974). and Klaus-Armin Nave* The majority of CMT cases belongs to one subgroup in *Zentrum fü r Molekulare Biologie which the primary genetic defect resides in Schwann University of Heidelberg cells (CMT1). This clinical entity has been further subdi-D-69120 Heidelberg vided by linkage to chromosomes 17 (CMT type 1A), Federal Republic of Germany chromosome 1 (CMT1B), and the X chromosome (CMTX) † Department of Veterinary Clinical Studies (for review, see Patel and Lupski, 1994). About 70%-Glasgow University 80% of all patients are affected by CMT1A, an autoso-Glasgow G61 1QH mal-dominant form, genetically linked to the region United Kingdom 17p11.2 (Wise et al., 1993; Ionasescu, 1995). ‡ Department of Cell Biology Clinically, CMT1A is characterized by slowly progres-Swiss Federal Institute of Technology sive muscle weakness and loss of proprioception, caus-ETH-Hoenggerberg ing gait abnormalities and peroneal muscular atrophy CH-8093 Zü rich in the second to third decade of life (Dyck et al., 1993). Switzerland The severity of the disease is variable, but severely re-§ Department of Neurology duced nerve conduction velocity (NCV) of both motor University of Heidelberg and sensory fibers are a regular finding (Nicholson, D-69120 Heidelberg 1991). Histologically, a progressive demyelination of pe-Federal Republic of Germany ripheral nerves is associated with Schwann cell hypertrophy, leading to the characteristic formation of onion bulb structures and collagen depositions. A major step in unravelling the genetic basis of CMT Summary was the identification of an intrachromosomal duplication on chromosome 17, associated with CMT1A (Lupski Charcot-Marie-Tooth disease (CMT) is the most comet al., 1991; Raeymakers et al., 1991). The duplication mon inherited neuropathy in humans and has been of approximately 1.5 ϫ 10 6 bp DNA in about 90% of associated with a partial duplication of chromosome clinically diagnosed patients (Roa et al., 1993b) sup-17 (CMT type 1A). We have generated a transgenic ported a novel gene-dosage model that assumes that rat model of this disease and provide experimental overexpression of one or more genes contained in the evidence that CMT1A is caused by increased expresduplicated region of 17p11.2 underlies CMT1A. sion of the gene for peripheral myelin protein-22 The gene for peripheral myelin protein 22 (PMP22) has (PMP22, gas-3). PMP22-transgenic rats develop gait emerged as a particularly attractive candidate disease abnormalities caused by a peripheral hypomyelinagene because it is expressed in Schwann cells and maps tion, Schwann cell hypertrophy (onion bulb formation), to chromosome 17p11.2 (Patel et al., 1992; Timmerman and muscle weakness. Reduced nerve conduction veet al., 1992; Matsunami et al., 1992; Valentijn et al., locities closely resemble recordings in human patients 1992a). Moreover, point mutations in PMP22 cause dyswith CMT1A. When bred to homozygosity, transgenic myelination in the Trembler mouse (Suter et al., 1992) animals completely fail to elaborate myelin. We anticiand CMT1A in a small subset of families (Valentijn et pate that the CMT rat model will facilitate the identifial., 1992b; Roa et al., 1993b, 1993c). In accordance with cation of a cellular disease mechanism and serve in a gene dosage model, increased steady-state levels of the evaluation of potential treatment strategies. PMP22 mRNA in some CMT1A nerve biopsies have been reported (Yoshikawa et al., 1994), but the significance of these findings has been questioned by others (Hane
Nerve excitability properties in Charcot-Marie-Tooth disease type 1A
Brain, 2004
ation time constants and the shapes of recovery cycles were normal, although refractoriness and superexcitability were reduced relative to controls. The high thresholds and early fanning out of electrotonus indicated altered cable properties, such that a greater proportion than normal of applied currents reached internodal rather than nodal axolemma. The rapid accommodation to depolarizing currents suggested activation of fast K + channels, which are normally sequestered from the nodal membrane. The excitability abnormalities are therefore consistent with a demyelinating pathology and exposure or spread of K + channels from under the myelin. It remains to be seen whether the TE abnormalities in CMT1A, which resemble previous recordings from normal immature rats, can be distinguished from those in acquired demyelinating neuropathies.
The effect of the mouse mutation claw paw on myelination and nodal frequency in sciatic nerves
The Journal of neuroscience : the official journal of the Society for Neuroscience, 1998
Despite the biophysical and clinical importance of differentiating nodal and internodal axolemma, very little is known about the process. We chose to study myelination and node of Ranvier formation in the hypomyelinating mouse mutant claw paw (clp). The phenotype of clp is delayed myelination in the peripheral nervous system. The specific defect is unknown but is thought to arise from a breakdown in the complex signaling mechanism between axon and Schwann cell. Myelination was assessed in sciatic nerve cross sections from adult and postnatal day 14 (P14) heterozygous and homozygous clp mice. Antibodies to P0, myelin-associated glycoprotein (MAG), and neural cell adhesion molecule were used to assess the stage of myelination. P14 homozygous clp mice showed an atypical staining pattern of immature myelin, which resolved into a relatively normal pattern by adulthood. Sodium channel clustering and node of Ranvier frequency were studied in whole-mount sciatic nerves with sodium channel a...