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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

Increased abundance of NF subunits in the three GAN models. The relative increase of protein content was obtained by comparing the mean abundance in each of the three GAN models (KO1 = our GANex3-5; KO2 = GANYY; KO3 = GANex1) with WT mice (n = 3 mice per genotype, except n = 2 for 48 week-old KO2). (A) Expression levels were quantified in the brain, the lumbar section of spinal cord (Sc-L) and sciatic nerves (SN) by immunoblotting using anti-NFL, NFM and NFH antibodies and normalization with GAPDH antibody. (B) The relative abundance of the gigaxonin's partners MAP1B, MAP1S and TBCB was quantified using the corresponding antibodies, with a similar approach. (Mann-Whitney test, *, p < 0.05; bars represent standard deviation). The immunoblots corresponding to the abundance of the NF subunits and the gigaxonin's partners in brain of 48 week-old GAN models are represented in (C).
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Figure 6: Increased abundance of NF subunits in the three GAN models. The relative increase of protein content was obtained by comparing the mean abundance in each of the three GAN models (KO1 = our GANex3-5; KO2 = GANYY; KO3 = GANex1) with WT mice (n = 3 mice per genotype, except n = 2 for 48 week-old KO2). (A) Expression levels were quantified in the brain, the lumbar section of spinal cord (Sc-L) and sciatic nerves (SN) by immunoblotting using anti-NFL, NFM and NFH antibodies and normalization with GAPDH antibody. (B) The relative abundance of the gigaxonin's partners MAP1B, MAP1S and TBCB was quantified using the corresponding antibodies, with a similar approach. (Mann-Whitney test, *, p < 0.05; bars represent standard deviation). The immunoblots corresponding to the abundance of the NF subunits and the gigaxonin's partners in brain of 48 week-old GAN models are represented in (C).

Mentions: To assess whether the impaired distribution of NFs is associated with an increased abundance of NF proteins, we quantified the expression level of the three subunits NF-L, NF-M and NF-H in mouse brain, spinal cord and sciatic nerves, in the three gigaxonin- mice: (our GANex3-5 mouse, the GANYY and the GANex1 mice). The analysis revealed an increased abundance of all three NF subunits, in all tissues and at all ages (Figure 6A, C). For all three NF subunits the maximum increase, ranging from 2-3 fold, was detected in brain tissues, with 1,5-2,5 fold increases in spinal cord and sciatic nerves. Interestingly, whereas the overabundance of NF-M and NF-H is constant overall from 24 to 48 weeks of age, a spectacular increase of NF-L is observed at 48 weeks of age specifically in the brain (Figure 6A, C). Indeed, the abundance of NF-L is increased 4,3- to 6,7- fold in the brain of the three GAN models.


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

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

Increased abundance of NF subunits in the three GAN models. The relative increase of protein content was obtained by comparing the mean abundance in each of the three GAN models (KO1 = our GANex3-5; KO2 = GANYY; KO3 = GANex1) with WT mice (n = 3 mice per genotype, except n = 2 for 48 week-old KO2). (A) Expression levels were quantified in the brain, the lumbar section of spinal cord (Sc-L) and sciatic nerves (SN) by immunoblotting using anti-NFL, NFM and NFH antibodies and normalization with GAPDH antibody. (B) The relative abundance of the gigaxonin's partners MAP1B, MAP1S and TBCB was quantified using the corresponding antibodies, with a similar approach. (Mann-Whitney test, *, p < 0.05; bars represent standard deviation). The immunoblots corresponding to the abundance of the NF subunits and the gigaxonin's partners in brain of 48 week-old GAN models are represented in (C).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3094382&req=5

Figure 6: Increased abundance of NF subunits in the three GAN models. The relative increase of protein content was obtained by comparing the mean abundance in each of the three GAN models (KO1 = our GANex3-5; KO2 = GANYY; KO3 = GANex1) with WT mice (n = 3 mice per genotype, except n = 2 for 48 week-old KO2). (A) Expression levels were quantified in the brain, the lumbar section of spinal cord (Sc-L) and sciatic nerves (SN) by immunoblotting using anti-NFL, NFM and NFH antibodies and normalization with GAPDH antibody. (B) The relative abundance of the gigaxonin's partners MAP1B, MAP1S and TBCB was quantified using the corresponding antibodies, with a similar approach. (Mann-Whitney test, *, p < 0.05; bars represent standard deviation). The immunoblots corresponding to the abundance of the NF subunits and the gigaxonin's partners in brain of 48 week-old GAN models are represented in (C).
Mentions: To assess whether the impaired distribution of NFs is associated with an increased abundance of NF proteins, we quantified the expression level of the three subunits NF-L, NF-M and NF-H in mouse brain, spinal cord and sciatic nerves, in the three gigaxonin- mice: (our GANex3-5 mouse, the GANYY and the GANex1 mice). The analysis revealed an increased abundance of all three NF subunits, in all tissues and at all ages (Figure 6A, C). For all three NF subunits the maximum increase, ranging from 2-3 fold, was detected in brain tissues, with 1,5-2,5 fold increases in spinal cord and sciatic nerves. Interestingly, whereas the overabundance of NF-M and NF-H is constant overall from 24 to 48 weeks of age, a spectacular increase of NF-L is observed at 48 weeks of age specifically in the brain (Figure 6A, C). Indeed, the abundance of NF-L is increased 4,3- to 6,7- fold in the brain of the three GAN models.

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