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Sensory-motor deficits and neurofilament disorganization in gigaxonin- mice.

Ganay T, Boizot A, Burrer R, Chauvin JP, Bomont P - Mol Neurodegener (2011)

Bottom Line: The identification of gigaxonin, the substrate adaptor of an E3 ubiquitin ligase, as the defective protein in GAN allows us to now investigate the crucial role of the gigaxonin-E3 ligase in sustaining neuronal and intermediate filament integrity.Indeed, neurofilaments were not only more abundant but they also showed the abnormal increase in diameter and misorientation that are characteristics of the human pathology.Our model will allow investigation of the role of the gigaxonin-E3 ligase in organizing neurofilaments and may prove useful in understanding the pathological processes engaged in other neurodegenerative disorders characterized by accumulation of neurofilaments and dysfunction of the Ubiquitin Proteasome System, such as Amyotrophic Lateral Sclerosis, Huntington's, Alzheimer's and Parkinson's diseases.

View Article: PubMed Central - HTML - PubMed

Affiliation: Inserm Unité 901, Marseille, 13009, France. pascale.bomont@inserm.fr.

ABSTRACT

Background: Giant Axonal Neuropathy (GAN) is a fatal neurodegenerative disorder with early onset characterized by a severe deterioration of the peripheral and central nervous system, involving both the motor and the sensory tracts and leading to ataxia, speech defect and intellectual disabilities. The broad deterioration of the nervous system is accompanied by a generalized disorganization of the intermediate filaments, including neurofilaments in neurons, but the implication of this defect in disease onset or progression remains unknown. The identification of gigaxonin, the substrate adaptor of an E3 ubiquitin ligase, as the defective protein in GAN allows us to now investigate the crucial role of the gigaxonin-E3 ligase in sustaining neuronal and intermediate filament integrity. To study the mechanisms controlled by gigaxonin in these processes and to provide a relevant model to test the therapeutic approaches under development for GAN, we generated a Gigaxonin- mouse by gene targeting.

Results: We investigated for the first time in Gigaxonin- mice the deterioration of the motor and sensory functions over time as well as the spatial disorganization of neurofilaments. We showed that gigaxonin depletion in mice induces mild but persistent motor deficits starting at 60 weeks of age in the 129/SvJ-genetic background, while sensory deficits were demonstrated in C57BL/6 animals. In our hands, another gigaxonin- mouse did not display the early and severe motor deficits reported previously. No apparent neurodegeneration was observed in our knock-out mice, but dysregulation of neurofilaments in proximal and distal axons was massive. Indeed, neurofilaments were not only more abundant but they also showed the abnormal increase in diameter and misorientation that are characteristics of the human pathology.

Conclusions: Together, our results show that gigaxonin depletion in mice induces mild motor and sensory deficits but recapitulates the severe neurofilament dysregulation seen in patients. Our model will allow investigation of the role of the gigaxonin-E3 ligase in organizing neurofilaments and may prove useful in understanding the pathological processes engaged in other neurodegenerative disorders characterized by accumulation of neurofilaments and dysfunction of the Ubiquitin Proteasome System, such as Amyotrophic Lateral Sclerosis, Huntington's, Alzheimer's and Parkinson's diseases.

No MeSH data available.


Related in: MedlinePlus

Severe disorganization of cytoskeletal architecture in GAN mice. (A) Electron microscopic examination of the axoplasm of GAN nerves revealed a diminution in microtubule content (arrows), an abnormal orientation and an increase in the diameter of neurofilaments (individual neurofilaments indicated by an arrowhead are magnified in the inserts). (B-D) The quantification of the cytoskeletal alteration in 48 week-old GAN mice was performed in sciatic nerves, L5-ventral and dorsal roots (n = 4 mice per genotype; 4 axons per mouse; 3 random pictures of distinct regions per axon; representing a total of 12 fields per mouse). (B) The mean number of microtubules per field was significantly lower in GAN compared to WT nerves (*, p < 0.05, Mann-Whitney test). (C) The alteration of neurofilament orientation was assessed by the measurement of the circularity of individual neurofilaments (circ = 1 and circ<1 representing a perfect circle and an elongated shape, respectively). The left panel displays average circularity scores, measuring the general orientation of the neurofilaments, for individual mice in the three tissues (the mean score per genotype is represented by a bar). The right panels show the standard deviations of the average circularity scores for the same analysis, a measure that is representative of the variations in the orientation of individual neurofilaments within each tissue section (*, p < 0.05, Mann-Whitney test). (D) Neurofilament diameter is significantly increased in GAN mice (10 individual neurofilaments per field; *, p < 0.05, Mann-Whitney test).
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Figure 5: Severe disorganization of cytoskeletal architecture in GAN mice. (A) Electron microscopic examination of the axoplasm of GAN nerves revealed a diminution in microtubule content (arrows), an abnormal orientation and an increase in the diameter of neurofilaments (individual neurofilaments indicated by an arrowhead are magnified in the inserts). (B-D) The quantification of the cytoskeletal alteration in 48 week-old GAN mice was performed in sciatic nerves, L5-ventral and dorsal roots (n = 4 mice per genotype; 4 axons per mouse; 3 random pictures of distinct regions per axon; representing a total of 12 fields per mouse). (B) The mean number of microtubules per field was significantly lower in GAN compared to WT nerves (*, p < 0.05, Mann-Whitney test). (C) The alteration of neurofilament orientation was assessed by the measurement of the circularity of individual neurofilaments (circ = 1 and circ<1 representing a perfect circle and an elongated shape, respectively). The left panel displays average circularity scores, measuring the general orientation of the neurofilaments, for individual mice in the three tissues (the mean score per genotype is represented by a bar). The right panels show the standard deviations of the average circularity scores for the same analysis, a measure that is representative of the variations in the orientation of individual neurofilaments within each tissue section (*, p < 0.05, Mann-Whitney test). (D) Neurofilament diameter is significantly increased in GAN mice (10 individual neurofilaments per field; *, p < 0.05, Mann-Whitney test).

Mentions: In human, GAN induces a profound alteration of IF architecture. Inside the nervous system, the organization of NFs is severely impaired: they exhibit an abnormal compaction, an alteration in longitudinal orientation and an increase in diameter [4,6]. To evaluate the effect of gigaxonin depletion on cytoskeletal architecture in mice, we conducted an ultrastructural analysis of proximal and distal nerves in our GANex3-5 mouse model. This revealed a profound impairment in cytoskeletal organization in GANex3-5 mice at 48 weeks of age, and in both 129/SvJ and C57BL/6 backgrounds (Figure 5 and Additional file 3).


Sensory-motor deficits and neurofilament disorganization in gigaxonin- mice.

Ganay T, Boizot A, Burrer R, Chauvin JP, Bomont P - Mol Neurodegener (2011)

Severe disorganization of cytoskeletal architecture in GAN mice. (A) Electron microscopic examination of the axoplasm of GAN nerves revealed a diminution in microtubule content (arrows), an abnormal orientation and an increase in the diameter of neurofilaments (individual neurofilaments indicated by an arrowhead are magnified in the inserts). (B-D) The quantification of the cytoskeletal alteration in 48 week-old GAN mice was performed in sciatic nerves, L5-ventral and dorsal roots (n = 4 mice per genotype; 4 axons per mouse; 3 random pictures of distinct regions per axon; representing a total of 12 fields per mouse). (B) The mean number of microtubules per field was significantly lower in GAN compared to WT nerves (*, p < 0.05, Mann-Whitney test). (C) The alteration of neurofilament orientation was assessed by the measurement of the circularity of individual neurofilaments (circ = 1 and circ<1 representing a perfect circle and an elongated shape, respectively). The left panel displays average circularity scores, measuring the general orientation of the neurofilaments, for individual mice in the three tissues (the mean score per genotype is represented by a bar). The right panels show the standard deviations of the average circularity scores for the same analysis, a measure that is representative of the variations in the orientation of individual neurofilaments within each tissue section (*, p < 0.05, Mann-Whitney test). (D) Neurofilament diameter is significantly increased in GAN mice (10 individual neurofilaments per field; *, p < 0.05, Mann-Whitney test).
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Figure 5: Severe disorganization of cytoskeletal architecture in GAN mice. (A) Electron microscopic examination of the axoplasm of GAN nerves revealed a diminution in microtubule content (arrows), an abnormal orientation and an increase in the diameter of neurofilaments (individual neurofilaments indicated by an arrowhead are magnified in the inserts). (B-D) The quantification of the cytoskeletal alteration in 48 week-old GAN mice was performed in sciatic nerves, L5-ventral and dorsal roots (n = 4 mice per genotype; 4 axons per mouse; 3 random pictures of distinct regions per axon; representing a total of 12 fields per mouse). (B) The mean number of microtubules per field was significantly lower in GAN compared to WT nerves (*, p < 0.05, Mann-Whitney test). (C) The alteration of neurofilament orientation was assessed by the measurement of the circularity of individual neurofilaments (circ = 1 and circ<1 representing a perfect circle and an elongated shape, respectively). The left panel displays average circularity scores, measuring the general orientation of the neurofilaments, for individual mice in the three tissues (the mean score per genotype is represented by a bar). The right panels show the standard deviations of the average circularity scores for the same analysis, a measure that is representative of the variations in the orientation of individual neurofilaments within each tissue section (*, p < 0.05, Mann-Whitney test). (D) Neurofilament diameter is significantly increased in GAN mice (10 individual neurofilaments per field; *, p < 0.05, Mann-Whitney test).
Mentions: In human, GAN induces a profound alteration of IF architecture. Inside the nervous system, the organization of NFs is severely impaired: they exhibit an abnormal compaction, an alteration in longitudinal orientation and an increase in diameter [4,6]. To evaluate the effect of gigaxonin depletion on cytoskeletal architecture in mice, we conducted an ultrastructural analysis of proximal and distal nerves in our GANex3-5 mouse model. This revealed a profound impairment in cytoskeletal organization in GANex3-5 mice at 48 weeks of age, and in both 129/SvJ and C57BL/6 backgrounds (Figure 5 and Additional file 3).

Bottom Line: The identification of gigaxonin, the substrate adaptor of an E3 ubiquitin ligase, as the defective protein in GAN allows us to now investigate the crucial role of the gigaxonin-E3 ligase in sustaining neuronal and intermediate filament integrity.Indeed, neurofilaments were not only more abundant but they also showed the abnormal increase in diameter and misorientation that are characteristics of the human pathology.Our model will allow investigation of the role of the gigaxonin-E3 ligase in organizing neurofilaments and may prove useful in understanding the pathological processes engaged in other neurodegenerative disorders characterized by accumulation of neurofilaments and dysfunction of the Ubiquitin Proteasome System, such as Amyotrophic Lateral Sclerosis, Huntington's, Alzheimer's and Parkinson's diseases.

View Article: PubMed Central - HTML - PubMed

Affiliation: Inserm Unité 901, Marseille, 13009, France. pascale.bomont@inserm.fr.

ABSTRACT

Background: Giant Axonal Neuropathy (GAN) is a fatal neurodegenerative disorder with early onset characterized by a severe deterioration of the peripheral and central nervous system, involving both the motor and the sensory tracts and leading to ataxia, speech defect and intellectual disabilities. The broad deterioration of the nervous system is accompanied by a generalized disorganization of the intermediate filaments, including neurofilaments in neurons, but the implication of this defect in disease onset or progression remains unknown. The identification of gigaxonin, the substrate adaptor of an E3 ubiquitin ligase, as the defective protein in GAN allows us to now investigate the crucial role of the gigaxonin-E3 ligase in sustaining neuronal and intermediate filament integrity. To study the mechanisms controlled by gigaxonin in these processes and to provide a relevant model to test the therapeutic approaches under development for GAN, we generated a Gigaxonin- mouse by gene targeting.

Results: We investigated for the first time in Gigaxonin- mice the deterioration of the motor and sensory functions over time as well as the spatial disorganization of neurofilaments. We showed that gigaxonin depletion in mice induces mild but persistent motor deficits starting at 60 weeks of age in the 129/SvJ-genetic background, while sensory deficits were demonstrated in C57BL/6 animals. In our hands, another gigaxonin- mouse did not display the early and severe motor deficits reported previously. No apparent neurodegeneration was observed in our knock-out mice, but dysregulation of neurofilaments in proximal and distal axons was massive. Indeed, neurofilaments were not only more abundant but they also showed the abnormal increase in diameter and misorientation that are characteristics of the human pathology.

Conclusions: Together, our results show that gigaxonin depletion in mice induces mild motor and sensory deficits but recapitulates the severe neurofilament dysregulation seen in patients. Our model will allow investigation of the role of the gigaxonin-E3 ligase in organizing neurofilaments and may prove useful in understanding the pathological processes engaged in other neurodegenerative disorders characterized by accumulation of neurofilaments and dysfunction of the Ubiquitin Proteasome System, such as Amyotrophic Lateral Sclerosis, Huntington's, Alzheimer's and Parkinson's diseases.

No MeSH data available.


Related in: MedlinePlus