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A M Clement,
M D Nguyen,
E A Roberts,
M L Garcia,
S Boillée,
M Rule,
A P McMahon,
W Doucette,
D Siwek,
R J Ferrante,
R H Brown, J-P Julien,
L S B Goldstein,
D W Cleveland
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ABSTRACT: The most common inherited [correct] form of amyotrophic lateral sclerosis (ALS), a neurodegenerative disease affecting adult motor neurons, is caused by dominant mutations in the ubiquitously expressed Cu-Zn superoxide dismutase (SOD1). In chimeric mice that are mixtures of normal and SOD1 mutant-expressing cells, toxicity to motor neurons is shown to require damage from mutant SOD1 acting within nonneuronal cells. Normal motor neurons in SOD1 mutant chimeras develop aspects of ALS pathology. Most important, nonneuronal cells that do not express mutant SOD1 delay degeneration and significantly extend survival of mutant-expressing motor neurons.
Science 11/2003; 302(5642):113-7. · 31.20 Impact Factor
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ABSTRACT: Alterations of the axonal transport and microtubule network are potential causes of motor neurodegeneration in mice expressing a mutant form of the superoxide dismutase 1 (SOD1G37R) linked to amyotrophic lateral sclerosis (ALS). In the present study, we investigated the biology of microtubule-associated proteins (MAPs), responsible for the formation and stabilization of microtubules, in SOD1G37R mice. Our results show that the protein levels of MAP2, MAP1A, tau 100 kDa and tau 68 kDa species decrease significantly as early as 5 months before onset of symptoms in the spinal cord of SOD1G37R mice, whereas decrease in levels of tau 52-55 kDa species is most often noted with the manifestation of the clinical symptoms. Interestingly, there was no change in the protein levels of MAPs in the brain of SOD1G37R mice, a CNS organ spared by the mutant SOD1 toxicity. Remarkably, as early as 5 months before disease onset, the binding affinities of MAP1A, MAP2 and tau isoforms to the cytoskeleton decreased in spinal cord of SOD1G37R mice. This change correlated with a hyperphosphorylation of the soluble tau 52-55 kDa species at epitopes recognized by the antibodies AT8 and PHF-1. Finally, a shift in the distribution of MAP2 from the cytosol to the membrane is detected in SOD1G37R mice at the same stage. Thus, alterations in the integrity of microtubules are early events of the neurodegenerative processes in SOD1G37R mice.
Journal of Neurochemistry 02/2003; 84(1):77-86. · 4.06 Impact Factor
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ABSTRACT: The discovery of cell cycle regulators has directed cell research into uncharted territory. In dividing cells, cell cycle-associated protein kinases, which are referred to as cyclin-dependent-kinases (Cdks), regulate proliferation, differentiation, senescence and apoptosis. In contrast, all Cdks in post-mitotic neurons, with the notable exception of Cdk5, are silenced. Surprisingly, misregulation of Cdks occurs in neurons in a wide diversity of neurological disorders, including Alzheimer's disease, Parkinson's disease and amyotrophic lateral sclerosis. Ectopic expression of these proteins in neurons potently induces cell death with hallmarks of apoptosis. Deregulation of the unique, cell cycle-unrelated Cdk5 by its truncated co-activator, p25 and p29, contributes to neurodegeneration by altering the phosphorylation state of non-membrane-associated proteins and possibly through the induction of cell cycle proteins. On the other hand, cycling Cdks such as Cdk2, Cdk4 and Cdk6, initiate death pathways by derepressing E2F-1/Rb-dependent transcription at the neuronal G1/S checkpoint. Thus, Cdk5 and cycling Cdks may have little in common in the healthy CNS, but they likely conspire in leading neurons to their demise.
Cell Death and Differentiation 01/2003; 9(12):1294-306. · 8.85 Impact Factor
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ABSTRACT: Peripherin is a type III intermediate filament (IF) abundantly expressed in developing neurons, but in the adult, it is primarily found in neurons extending to the peripheral nervous system. It has been suggested that peripherin may play a role in axonal elongation and/or cytoskeletal stabilization during development and regeneration. To further clarify the function of peripherin, we generated and characterized mice with a targeted disruption of the peripherin gene. The peripherin null mice were viable, reproduced normally and did not exhibit overt phenotypes. Microscopic analysis revealed no gross morphological defects in the ventral and dorsal roots, spinal cord, retina and gut, but protein analyses showed increased levels of the type IV IF alpha-internexin in ventral roots of peripherin null mice. Whereas the number and caliber of myelinated motor and sensory axons in the L5 roots remained unchanged in peripherin knockout mice, there was a substantial reduction ( approximately 34%) in the number of L5 unmyelinated sensory fibers that correlated with a decreased binding of the lectin IB4. These results demonstrate a requirement of peripherin for the proper development of a subset of sensory neurons.
Journal of Neurochemistry 06/2002; 81(3):525-32. · 4.06 Impact Factor
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ABSTRACT: Recent studies have demonstrated the activation of caspase-1 and caspase-3 in mice expressing mutant superoxide dismutase 1 (SOD1), models of amyotrophic lateral sclerosis. Caspase-1 converts the prointerleukin-1beta into a potent proinflammatory molecule involved in the innate immune response and in neurodegenerative diseases. We report on the chronic expression of interleukin-1beta mRNA in the spinal cord of SOD1G37R mice, together with robust mRNA expression for the nuclear factor-kappaB (NF-kappaB) inhibitor IkappaBalpha, for other proinflammatory cytokines and chemokines (interleukin-6, tumor necrosis factor-alpha, monocyte chemoattractant protein-1) and for the toll-like receptor TLR2 involved in innate immunity. To further assess the interleukin-1beta contribution to neurodegeneration, we generated mice expressing SOD1G37R in a context of interleukin-1beta gene knockout. Surprisingly, the absence of interleukin-1beta had no effect on the life span of SOD1G37R mice, nor on the extent of motor axon degeneration at age 7 and 10 months. Whereas neither compensatory induction of the interleukin-1alpha mRNA nor increases in mRNA levels for IkappaBalpha, tumor necrosis factor-alpha and macrophage chemoattractant protein-1 occurred as a result of interleukin-1beta gene disruption, enhanced levels of TLR2 mRNA were detected in SOD1G37R mice lacking interleukin-1beta. We conclude that interleukin-1beta does not directly contribute to motor neuron degeneration in SOD1G37R mice, but it may act as a modulator of the innate immune response.
Annals of Neurology 12/2001; 50(5):630-9. · 11.09 Impact Factor
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ABSTRACT: Peripherin, a neuronal intermediate filament protein associated with axonal spheroids in amyotrophic lateral sclerosis (ALS), induces the selective degeneration of motor neurons when overexpressed in transgenic mice. To further clarify the selectivity and mechanism of peripherin-induced neuronal death, we analyzed the effects of peripherin overexpression in primary neuronal cultures. Peripherin overexpression led to the formation of cytoplasmic protein aggregates and caused the death not only of motor neurons, but also of dorsal root ganglion (DRG) neurons that were cultured from dissociated spinal cords of peripherin transgenic embryos. Apoptosis of DRG neurons containing peripherin aggregates was dependent on the proinflammatory central nervous system environment of spinal cultures, rich in activated microglia, and required TNF-alpha. This synergistic proapoptotic effect may contribute to neuronal selectivity in ALS.
The Journal of Cell Biology 11/2001; 155(2):217-26. · 10.26 Impact Factor
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ABSTRACT: Recent studies suggest that increased activity of cyclin-dependent kinase 5 (Cdk5) may contribute to neuronal death and cytoskeletal abnormalities in Alzheimer's disease. We report here such deregulation of Cdk5 activity associated with the hyperphosphorylation of tau and neurofilament (NF) proteins in mice expressing a mutant superoxide dismutase (SOD1(G37R)) linked to amyotrophic lateral sclerosis (ALS). A Cdk5 involvement in motor neuron degeneration is supported by our analysis of three SOD1(G37R) mouse lines exhibiting perikaryal inclusions of NF proteins. Our results suggest that perikaryal accumulations of NF proteins in motor neurons may alleviate ALS pathogenesis by acting as a phosphorylation sink for Cdk5 activity, thereby reducing the detrimental hyperphosphorylation of tau and other neuronal substrates.
Neuron 05/2001; 30(1):135-47. · 14.74 Impact Factor
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J P Julien
Cell 03/2001; 104(4):581-91. · 32.40 Impact Factor
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ABSTRACT: Estrogens can influence the survival, plasticity and function of many adult neurons. Many of these effects, such as neurite outgrowth and increased dendritic spine density, are mediated by changes in neuronal cytoskeletal architecture. Since neurofilament proteins play a key role in the maintenance and remodeling of the neuronal cytoskeleton, we postulated that changes in neurofilament light chain mRNA may parallel some of the alterations in neuronal architecture which follow bilateral ovariectomy. We measured neurofilament light chain mRNA levels using a ribonuclease protection assay at two time-points after ovariectomy in mature female rats. One week after ovariectomy, neurofilament light chain mRNA levels (corrected for glucose-6-phosphate dehydrogenase mRNA) did not differ from sham-operated animals in the five brain regions examined (hypothalamus, striatum, hippocampus, frontal cortex and occipital cortex). Four months after ovariectomy, neurofilament light chain mRNA levels were similarly unchanged in the hypothalamus and striatum. In contrast, statistically significant increases in neurofilament light chain mRNA expression were observed in the three regions receiving basal forebrain projections (hippocampus, frontal cortex and occipital cortex). In situ hybridization demonstrated increases in neurofilament light chain mRNA expression involving subpopulations of smaller medial septal neurons. There also appeared to be an increased number of larger septal neurons following long-term ovariectomy. We propose that atrophic changes involving basal forebrain projection fibers are followed by compensatory axonal growth by other 'intact' basal forebrain neurons. Increased neurofilament light chain mRNA expression and somatic hypertrophy in medial septal neurons may both be reflective of the need to sustain an axonal network which is larger and more complex. In contrast, increased neurofilament light chain mRNA expression observed in basal forebrain targets following long-term ovariectomy may be reflective of compensatory changes taking place in local neurons.
Neuroscience 02/2001; 103(3):629-37. · 3.38 Impact Factor
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ABSTRACT: Neurofilament proteins (NFs) are made by co-polymerization of three intermediate filament proteins, NF-L, NF-M and NF-H and constitute the most abundant cytoskeletal element in large myelinated axons. NFs have a well-established role as intrinsic determinants of axon caliber with all the functional implications, but the role of each individual NF subunit is much less clear. The aim of our study was to examine functional properties of large myelinated axons with altered morphology from mice bearing a targeted disruption of each NF genes (NF-L -/-, NF-M-/- and NF-H -/- mice). Membrane properties, action potentials and single axon refractory period were measured in isolated sciatic nerves in vitro, using intra-axonal microelectrode recording in conjunction with current-clamp technique. Some results were obtained from whole nerves by sucrose-gap recording. The NF-knockout mice showed several deficits in physiological properties of low-threshold fibers. In keeping with smaller axon diameter, the conduction velocity was significantly decreased in NF-L -/- and NF-M -/- transgenic animals (control, 39.9+/-1.8 m/s, NF-M -/-; 23.5+/-1. 4 m/s, and NF-L-/-; 12.0+/-0.7 m/s, mean+/-S.E.M.; intra-axonal recording; similar ratios obtained by sucrose-gap recording; 22-26 degrees C). However, in spite of their preserved caliber, large myelinated axons in NF-H -/- mice also showed a significant decrease in conduction velocity (22.8+/-1.0 m/s, mean+/-S.E.M.). Although action potential amplitudes, duration and shape did not differ between control axons and transgenic animals, the refractory period was prolonged in NF-H -/- and NF-M -/- animals. Intracellular injections of 200 ms depolarizing and hyperpolarizing currents revealed outward and inward rectification in all animal groups. In comparison to control animals, NF-H -/- mice expressed a significant decrease in outward rectification. Potassium channel blockers (4AP and TEA) and cesium ions were able to block outward and inward rectification in all myelinated axons in qualitatively the same manner. These results suggest that NF-H may have a specific role in modulating ion channel functions in large myelinated fibers.
Brain Research 01/2001; 885(1):32-44. · 2.73 Impact Factor
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ABSTRACT: Cytoskeletal abnormalities have been reported in cases of amyotrophic lateral sclerosis (ALS) including abnormal inclusions containing neurofilaments (NFs) and/or peripherin, reduced mRNA levels for the NF light (NF-L) protein and mutations in the NF heavy (NF-H) gene. Recently, transgenic mouse approaches have been used to address whether cytoskeletal changes may contribute to motor neuron disease. Mice lacking one of the three NF subunits are viable and do not develop motor neuron disease. Nonetheless, mice with null mutations for NF-L or for both NF-M and NF-H genes developed severe atrophy of ventral and dorsal root axons. The atrophic process is associated with hind limb paralysis during aging in mice deficient for both NF-M and NF-H proteins. The overexpression in mice of transgenes coding for wild-type or mutant NF proteins can provoke abnormal NF accumulations, axonal atrophy and sometimes motor dysfunction. However, the perikaryal NF accumulations are generally well tolerated by motor neurons and, except for expression of a mutant NF-L transgene, they did not provoke massive motor neuron death. Increasing the levels of perikaryal NF proteins may even confer protection in motor neuron disease caused by ALS-linked mutations in the superoxide dismutase (SOD1). In contrast, the overexpression of wild-type peripherin, a type of IF gene upregulated by inflammatory cytokines, provoked the formation of toxic IF inclusions with the high-molecular-weight NF proteins resulting in the death of motor neurons during aging. These results together with the detection of peripherin inclusions at early stage of disease in mice expressing mutant SOD1 suggest that IF inclusions containing peripherin may play a contributory role in ALS pathogenesis.
Journal of the Neurological Sciences 12/2000; 180(1-2):7-14. · 2.35 Impact Factor
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ABSTRACT: It is well established that motor neurons with large axon caliber are selectively affected in amyotrophic lateral sclerosis (ALS). To investigate whether high neurofilament (NF) content and large axonal caliber are factors that predispose motor neurons to selective degeneration in ALS, we generated mice expressing a mutant form of superoxide dismutase 1 (SOD1(G37R)) linked to familial ALS in a context of one allele for each NF gene being disrupted. A approximately 40% decrease of NF protein content detected in triple heterozygous knockout mice shifted the calibers of large axons in L5 ventral root from 5-9 microm to 1-5 microm, altering neither the normal subunit stoichiometry and morphological distribution of NFs nor levels of other cytoskeletal proteins. This considerable reduction in NF burden and caliber of axons did not extend the life span of SOD1(G37R) mice nor did it alleviate the loss of motor axons. Moreover, increasing the density of NFs in axons by overexpressing a NF-L transgene did not accelerate disease in SOD1(G37R) mice. These results do not support the current view that high NF content and large caliber of axons may account for the selective vulnerability of motor neurons in ALS caused by mutant SOD1.
Proceedings of the National Academy of Sciences 11/2000; 97(22):12306-11. · 9.68 Impact Factor
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ABSTRACT: A recent report by T. L. Williamson et al. (1998, Proc. Natl. Acad. Sci. USA 95, 9631-9636) showed that disease caused by expression of mutant Cu,Zn superoxide dismutase (SOD1) in mice was slowed down by disruption of the neurofilament light (NF-L) gene. This led to the conclusion that decreasing the axonal amount of neurofilaments reduces the vulnerability of motor neurons to toxicity mediated by mutant SOD1. We report here that, unexpectedly, overexpression of human NF-L proteins resulting in extra axonal neurofilaments does not shorten the life span of transgenic mice expressing a mutant SOD1 (SOD1(G37R)). Microscopic examination of spinal cord and ventral roots even shows modest protective effects of NF-L overexpression. These results suggest that axonal neurofilaments are not an exacerbating factor in motor neuron disease mediated by mutant SOD1 and that perikaryal neurofilaments may even have beneficial effects.
Neurobiology of Disease 09/2000; 7(4):462-70. · 5.40 Impact Factor
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ABSTRACT: Protein aggregates containing intermediate filaments (IFs) are a hallmark of degenerating spinal motor neurons in amyotrophic lateral sclerosis (ALS). Recently, we reported that a deficiency in neurofilament light subunit (NF-L), a phenomenon associated with ALS, promoted the formation of IF inclusions with ensuing motor neuron death in transgenic mice overproducing peripherin, a type III IF protein detected in axonal inclusions of ALS patients. To further assess the role of NF-L in the formation of abnormal IF inclusions, we generated transgenic mice overexpressing human neurofilament heavy subunits (hNF-H) in a context of targeted disruption of the NF-L gene (hH;L-/- mice). The hH;L-/- mice exhibited motor dysfunction, and they developed nonfilamentous protein aggregates containing NF-H and peripherin proteins in the perikarya of spinal motor neurons. However, the perikaryal protein aggregates in the hH;L-/- mice did not provoke motor neuron death, unlike toxic IF inclusions induced by peripherin overexpression in NF-L null mice (Per;L-/- mice). Our results indicate that different types of IF protein aggregates with distinct properties may occur in a context of NF-L deficiency and that an axonal localization of such aggregates may be an important factor of toxicity.
Journal of Neuroscience 08/2000; 20(14):5321-8. · 7.11 Impact Factor
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ABSTRACT: Neurofilaments (NFs; made by copolymerization of three intermediate filament proteins NF-L, NF-M, and NF-H, for light, medium, and heavy) constitute the most abundant cytoskeletal structure in large myelinated axons. The presence of aberrant NF accumulation has been associated with neurodegenerative diseases (such as ALS). The possible causal role of NF in neurodegeneration has been supported by studies on recently available transgenic mice in which expression of human NF-H (hNF-H +/+) leads to overt neuropathy. We have examined electrophysiological properties of myelinated axons in hNF-H +/+ mice using intraaxonal microelectrode recording from isolated sciatic and tibial nerves. Transgenic mice showed several deficits in physiological properties of low threshold myelinated fibers: conduction velocity and resting membrane potential were significantly decreased (20 +/- 1.6 vs 40 +/- 2 m/s; -71.3 +/- 0.9 vs -75.5 +/- 0.5 m/s; mean +/- SE; n = 25; 22 degrees C). While the amplitude of action potentials was of comparable size (82 +/- 5 vs 86 +/- 3 mV) duration of action potential (at half-amplitude, AP/2) in hNF-H +/+ was significantly prolonged (0.82 +/- 0.02 vs 0.65 +/- 0.02 ms). Voltage-current properties of axonal membrane indicate a significant decrease in inward and outward rectification. Occasionally, impaled axons of hNF-H +/+ showed membrane oscillations and repetitive activity (reminiscent of fasciculations) never observed in normal animals. These results are compatible with an imbalance between ion conductances in axons from transgenic animals (an increase in Na(+) and a decrease in K(+) conductances), in agreement with recent suggestion based on clinical studies on ALS patients (H. Bostock et al., 1995, Brain 118, 217-225). One may hypothesize that these changes could contribute to neurodegenerative processes (i.e., via an increase in [Na(+)](i)), as well as clinical symptoms (fasciculations) observed in patients with degenerative motor neuron diseases.
Experimental Neurology 07/2000; 163(2):414-21. · 4.70 Impact Factor
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ABSTRACT: In transgenic mice expressing ectopic substance P fibres in the spinal white matter, a normally innocuous mechanical stimulus induces hyperalgesia and allodynia which are reversed by substance P and N-methyl-D-aspartate receptor antagonists. This period of enhanced excitation is followed by a rebound overshoot in these animals. As previous evidence indicates opioid mechanisms in a similar rebound in normal animals, the present study was done to determine the effects of systemic administration of morphine and the opiate receptor antagonist, naloxone, on the stimulus-induced responses in the tail withdrawal reflex. Once baseline reaction times had been taken, different combinations of saline, naloxone and morphine were administered intraperitoneally to transgenic and control mice of either sex. A mechanical conditioning stimulus of 450g was then applied to the tip of the tail for 2s. This stimulus was innocuous in control mice given saline or naloxone, but provoked a nociceptive response in transgenic mice given these compounds. In control and transgenic mice, following morphine administration there was an antinociceptive effect. In control mice the subsequent mechanical stimulus had no effect. However, in transgenic mice the mechanical stimulus produced a further antinociception. Naloxone blocked the effect of morphine and the subsequent conditioning stimulus in both control and transgenic mice. The results indicate that while morphine is equally effective on the withdrawal reflex in both types of animal, in the transgenic mice morphine reveals an intrinsic, naloxone-sensitive antinociceptive mechanism. The data are interpreted to suggest that over-expression of substance P or some other factor in the spinal cord of transgenic mice is associated with the up-regulation or facilitation of an opiate-mediated intrinsic antinociceptive mechanism. This is a novel observation because the genetic manipulation in this transgenic mouse results in a transient over-expression of nerve growth factor during development that leads to the formation of ectopic primary afferent fibres in the spinal cord containing substance P. These fibres persist indefinitely after the nerve growth factor levels return to normal. Opioid mechanisms, which are likely of dorsal horn origin, do not fall under the direct influence of nerve growth factor mechanisms and therefore the intriguing possibility is raised that opioid mechanisms in the spinal cord are regulated at least in part by substance P-related mechanisms.
Neuroscience 02/2000; 96(4):785-9. · 3.38 Impact Factor
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ABSTRACT: Peripherin, a type III intermediate filament (IF) protein, upregulated by injury and inflammatory cytokines, is a component of IF inclusion bodies associated with degenerating motor neurons in sporadic amyotrophic lateral sclerosis (ALS). We report here that sustained overexpression of wild-type peripherin in mice provokes massive and selective degeneration of motor axons during aging. Remarkably, the onset of peripherin-mediated disease was precipitated by a deficiency of neurofilament light (NF-L) protein, a phenomenon associated with sporadic ALS. In NF-L null mice, the overexpression of peripherin led to early- onset formation of IF inclusions and to the selective death of spinal motor neurons at 6 mo of age. We also report the formation of similar peripherin inclusions in presymptomatic transgenic mice expressing a mutant form of superoxide dismutase linked to ALS. Taken together, these results suggest that IF inclusions containing peripherin may play a contributory role in motor neuron disease.
The Journal of Cell Biology 12/1999; 147(3):531-44. · 10.26 Impact Factor
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J P Julien
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ABSTRACT: Transgenic approaches have recently been used to investigate the functions of neuronal intermediate filaments. Gene knockout studies have demonstrated that neurofilaments are not required for axogenesis and that individual neurofilament proteins play distinct roles in filament assembly and in the radial growth of axons. The involvement of neurofilaments in disease is supported by the discovery of novel mutations in the neurofilament heavy gene from cases of amyotrophic lateral sclerosis and by reports of neuronal death in mouse models expressing neurofilament and alpha-internexin transgenes. However, mouse studies have shown that axonal neurofilaments are not required for pathogenesis caused by mutations in superoxide dismutase and that increasing perikaryal levels of neurofilament proteins may even confer protection in this disease.
Current Opinion in Neurobiology 11/1999; 9(5):554-60. · 7.44 Impact Factor
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ABSTRACT: Previous studies demonstrated that transgenic mice overexpressing human neurofilament heavy (hNF-H) protein develop a progressive motor neuron disease characterized by the perikaryal accumulations of neurofilaments resembling those found in amyotrophic lateral sclerosis (ALS). To further investigate this neurofilament-induced pathology, we generated transgenic mice expressing, solely or concomitantly, the hNF-H and the human neurofilament light (hNF-L) proteins. We report here that the motor neuron disease caused by excess hNF-H proteins can be rescued by overexpression of hNF-L in a dosage-dependent fashion. In hNF-H transgenic mice, the additional hNF-L led to reduction of perikaryal swellings, relief of axonal transport defect and restoration of axonal radial growth. A gene delivery approach based on recombinant adenoviruses bearing the hNF-L gene also demonstrated the possibility to reduce perikaryal swellings after their formation in adult mice. The finding that extra NF-L can protect against NF-H-mediated pathogenesis is of potential importance for ALS, particularly for cases with NF-H abnormalities.
Journal of Neuropathology and Experimental Neurology 11/1999; 58(10):1099-110. · 4.26 Impact Factor
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ABSTRACT: To clarify the role of the neurofilament (NF) medium (NF-M) and heavy (NF-H) subunits, we generated mice with targeted disruption of both NF-M and NF-H genes. The absence of the NF-M subunit resulted in a two- to threefold reduction in the caliber of large myelinated axons, whereas the lack of NF-H subunits had little effect on the radial growth of motor axons. In NF-M-/- mice, the velocity of axonal transport of NF light (NF-L) and NF-H proteins was increased by about two-fold, whereas the steady-state levels of assembled NF-L were reduced. Although the NF-M or NF-H subunits are each dispensable for the formation of intermediate filaments, the absence of both subunits in double NF-M; NF-H knockout mice led to a scarcity of intermediate filament structures in axons and to a marked approximately twofold increase in the number of microtubules. Protein analysis indicated that the levels of NF-L and alpha-internexin proteins were reduced dramatically throughout the nervous system. Immunohistochemistry of spinal cord from the NF-M-/-;NF-H-/- mice revealed enhanced NF-L staining in the perikaryon of motor neurons but a weak NF-L staining in axons. In addition, axonal transport studies carried out by the injection of [35S]methionine into spinal cord revealed after 30 days very low levels of newly synthesized NF-L proteins in the sciatic nerve of NF-M-/-;NF-H-/- mice. The combined results demonstrate a requirement of the high-molecular-weight subunits for the assembly of type IV intermediate filament proteins and for the efficient translocation of NF-L proteins into the axonal compartment.
Journal of Neurochemistry 10/1999; 73(3):972-84. · 4.06 Impact Factor
