Abstract
X-linked adrenoleukodystrophy (X-ALD) is a neurodegenerative disorder characterized by accumulation of very long-chain fatty acids (VLCFA). This accumulation has been attributed to decreased VLCFA beta-oxidation and peroxisomal very long-chain acyl-CoA synthetase (VLCS) activity. The X-ALD gene, ABCD1, encodes a peroxisomal membrane ATP binding cassette transporter, ALDP, that is hypothesized to affect VLCS activity in peroxisomes by direct interaction with the VLCS enzyme. Recently, a VLCS gene that encodes a protein with significant sequence identity to known rat and human peroxisomal VLCS protein has been identified in mice. We find that the mouse VLCS gene (Vlcs) encodes an enzyme (Vlcs) with VLCS activity that localizes to peroxisomes and is expressed in X-ALD target tissues. We show that the expression of Vlcs in the peroxisomes of X-ALD mouse fibroblasts improves VLCFA beta-oxidation in these cells, implying a role for this enzyme in the biochemical abnormality of X-ALD. X-ALD mice, which accumulate VLCFA in tissues, show no change in the expression of Vlcs, the subcellular localization of Vlcs, or general peroxisomal VLCS activity. These observations imply that ALDP is not necessary for the proper expression or localization of Vlcs protein, and the control of VLCFA levels does not depend on the direct interaction of Vlcs and ALDP.
Highlights
X-linked adrenoleukodystrophy (X-ALD)1 is a progressive neurodegenerative disorder [1] with an incidence of 1 per 17,000 births [2]
Expression of VLCS gene (Vlcs) cDNA in COS-1 Cells Increases Their very long-chain acyl-CoA synthetase (VLCS) Activity—To determine whether Vlcs encodes an enzyme with fatty acid acyl-CoA synthetase activity, Vlcs cDNA was expressed in COS-1 cells, and these cells were assayed for increased acyl-CoA synthetase activity toward a representative very long-chain fatty acid, lignoceric acid (C24:0), and longchain fatty acid, palmitic acid (C16:0) (Fig. 2)
The biochemical phenotype of X-ALD, decreased very long-chain fatty acids (VLCFA) -oxidation, and peroxisomal VLCS activity implies an interaction between ALDP and Vlcs
Summary
X-linked adrenoleukodystrophy (X-ALD) is a progressive neurodegenerative disorder [1] with an incidence of 1 per 17,000 births [2]. Mutations in the X-ALD gene, ABCD1, result in several phenotypic variants that vary in onset age, disease progress rate, and primary affected tissue. All male X-ALD patients and the majority of X-ALD female carriers accumulate straight chain saturated very long-chain fatty acids (VLCFA; 24 or more carbons) in their plasma and tissues This accumulation is associated with decreased VLCFA degradation by peroxisomal -oxidation as observed in patient fibroblasts. VLCS enzyme was initially isolated from rat liver peroxisomes, and a number of VLCS genes have been subsequently cloned from other organisms [17,18,19] All of these enzymes have been localized to both peroxisomes and endoplasmic reticulum, sites of VLCS activity in the cell, and shown to have VLCS activity as well as the ability to activate long chain fatty acids. Vlcs has been identified as a mouse gene with a high degree of identity to these enzymes [20, 21] and, as such, warrants investigation in X-ALD
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