Stability of the ABCD1 Protein with a Missense Mutation: A Novel Approach to Finding Therapeutic Compounds for X-Linked Adrenoleukodystrophy.

Mutations in the ABCD1 gene that encodes peroxisomal ABCD1 protein cause X-linked adrenoleukodystrophy (X-ALD), a rare neurodegenerative disorder. More than 70% of the patient fibroblasts with this missense mutation display either a lack or reduction of the ABCD1 protein because of posttranslational degradation. In this study, we analyzed the stability of the missense mutant ABCD1 proteins (p.A616T, p.R617H, and p.R660W) in X-ALD fibroblasts and found that the mutant ABCD1 protein p.A616T has the capacity to recover its function by incubating at low temperature. In the case of such a mutation, chemical compounds that stabilize mutant ABCD1 proteins could be therapeutic candidates. Here, we prepared CHO cell lines stably expressing ABCD1 proteins with a missense mutation in fusion with green fluorescent protein (GFP) at the C-terminal. The stability of each mutant ABCD1-GFP in CHO cells was similar to the corresponding mutant ABCD1 protein in X-ALD fibroblasts. Furthermore, it is of interest that the GFP at the C-terminal was degraded together with the mutant ABCD1 protein. These findings prompted us to use CHO cells expressing mutant ABCD1-GFP for a screening of chemical compounds that can stabilize the mutant ABCD1 protein. We established a fluorescence-based assay method for the screening of chemical libraries in an effort to find compounds that stabilize mutant ABCD1 proteins. The work presented here provides a novel approach to finding therapeutic compounds for X-ALD patients with missense mutations.

A Novel Double Mutation in the ABCD1 Gene in a Patient with X-linked Adrenoleukodystrophy: Analysis of the Stability and Function of the Mutant ABCD1 Protein.

We diagnosed an adrenomyeloneuropathy (AMN) patient with a double novel missense mutation, c.284C>A (p.A95D) and c.290A>T (p.H97L) in a single ABCD1 allele. In skin fibroblasts from the patient, no ABCD1 protein was detected by immunoblot analysis, and the C24:0 ß-oxidation activity was decreased to a level at which the ABCD1 protein was absent. To determine the responsible gene mutation in the patient, we constructed three kinds of mutated ABCD1 gene expression vectors (c.284C>A, c.290A>T or c.284C>A/c.290A>T) and transfected them into CHO cells stably expressing GFP-SKL (CHO/GFP-SKL cells) or CADDS fibroblasts lacking the ABCD1 gene. ABCD1 (p.H97L) displayed the correct peroxisomal localization in CHO/GFP-SKL cells, but ABCD1 (p.A95D) and ABCD1 (p.A95D/p.H97L) were diffuse in the cytosol. Furthermore, ABCD1 (p.H97L) was detected by immunoblot analysis and restored the C24:0 ß-oxidation activity in the CADDS fibroblasts, as the wild type ABCD1 did. On the other hand, ABCD1 (p.A95D) and ABCD1 (p.A95D/p.H97L) were not detected and the C24:0 ß-oxidation activity was not restored. These results clearly show that c.284C>A is the responsible gene mutation, whereas c.290A>T is a novel polymorphism.