Restoration of cytoskeleton homeostasis after gigaxonin gene transfer for giant axonal neuropathy.

Giant axonal neuropathy (GAN) is caused by loss of function of the gigaxonin protein. On a cellular level GAN is characterized by intermediate filament (IF) aggregation, leading to a progressive and fatal peripheral neuropathy in humans. This study sought to determine if re-introduction of the GAN gene into GAN-deficient cells and mice would restore proper cytoskeleton IF homeostasis. Treatment of primary skin fibroblast cultures from three different GAN patients with an adeno-associated virus type 2 (AAV2) vector containing a normal human GAN transgene significantly reduced the number of cells displaying vimentin IF aggregates. A proteomic analysis of these treated cells was also performed, wherein the abundance of 32 of 780 identified proteins significantly changed in response to gigaxonin gene transfer. While 29 of these responding proteins have not been directly described in association with gigaxonin, three were previously identified as being disregulated in GAN and were now shifted toward normal levels. To assess the potential application of this approach in vivo and eventually in humans, GAN mice received an intracisternal injection of an AAV9/GAN vector to globally deliver the GAN gene to the brainstem and spinal cord. The treated mice showed a nearly complete clearance of peripherin IF accumulations at 3 weeks post-injection. These studies demonstrate that gigaxonin gene transfer can reverse the cellular IF aggregate pathology associated with GAN.

Proteomic analysis in giant axonal neuropathy: new insights into disease mechanisms.

INTRODUCTION: Giant axonal neuropathy (GAN) is a progressive hereditary disease that affects the peripheral and central nervous systems. It is characterized morphologically by aggregates of intermediate filaments in different tissues. Mutations have been reported in the gene that codes for gigaxonin. Nevertheless, the underlying molecular mechanism remains obscure. METHODS: Cell lines from 4 GAN patients and 4 controls were analyzed by iTRAQ. RESULTS: Among the dysregulated proteins were ribosomal protein L29, ribosomal protein L37, galectin-1, glia-derived nexin, and aminopeptidase N. Also, nuclear proteins linked to formin-binding proteins were found to be dysregulated. Although the major role of gigaxonin is reported to be degradation of cytoskeleton-associated proteins, the amount of 76 structural cytoskeletal proteins was unaltered. CONCLUSIONS: Several of the dysregulated proteins play a role in cytoskeletal reorganization. Based on these findings, we speculate that disturbed cytoskeletal regulation is responsible for formation of aggregates of intermediate filaments.

Giant axonal neuropathy caused by compound heterozygosity for a maternally inherited microdeletion and a paternal mutation within the GAN gene.

Different missense, nonsense and frameshift mutations in the GAN gene encoding gigaxonin have been described to cause giant axonal neuropathy, a severe early-onset progressive neurological disease with autosomal recessive inheritance. By oligonucleotide array CGH analysis, we identified a 57-131 kb microdeletion affecting this gene in a patient with developmental delay, ataxia, areflexia, macrocephaly, and strikingly frizzy hair. The microdeletion was inherited from the mother and mutation analysis revealed a paternally inherited missense mutation c.1456G>A in exon 9 on the other allele. Our findings illustrate the power of higher resolution array CGH studies and highlight the importance of considering copy number variations in autosomal recessive diseases.