Peroxisomal disorders have been associated with malfunction of peroxisomal metabolic pathways, but the pathogenesis of these disorders is largely unknown. X-linked adrenoleukodystrophy (X-ALD) is associated with elevated levels of very-long-chain fatty acids (VLCFA; C >22:0 ) that have been attributed to reduced peroxisomal VLCFA -oxidation activity. Previously, our laboratory and others have reported elevated VLCFA levels and reduced peroxisomal VLCFA -oxidation in human and mouse X-ALD fibroblasts. In this study, we found normal levels of peroxisomal VLCFA -oxidation in tissues from ALD mice with elevated VLCFA levels. Treatment of ALD mice with pharmacological agents resulted in decreased VLCFA levels without a change in VLCFA -oxidation activity. These data indicate that ALDP does not determine the rate of VLCFA -oxidation and that VLCFA levels are not determined by the rate of VLCFA -oxidation. The rate of peroxisomal VLCFA -oxidation in human and mouse fibroblasts in vitro is affected by the rate of mitochondrial long-chain fatty acid -oxidation. We hypothesize that ALDP facilitates the interaction between peroxisomes and mitochondria, resulting, when ALDP is deficient in X-ALD, in increased VLCFA accumulation despite normal peroxisomal VLCFA -oxidation in ALD mouse tissues. In support of this hypothesis, mitochondrial structural abnormalities were observed in adrenal cortical cells of ALD mice.
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