Inactivation of the peroxisomal ABCD2 transporter in the mouse leads to late-onset ataxia involving mitochondria, Golgi and endoplasmic reticulum damage

ATP-binding cassette (ABC) transporters facilitate unidirectional translocation of chemically diverse substances, ranging from peptides to lipids, across cell or organelle membranes. In peroxisomes, a subfamily of four ABC transporters (ABCD1 to ABCD4) has been related to fatty acid transport, because patients with mutations in ABCD1 (ALD gene) suffer from X-linked adrenoleukodystrophy (X-ALD), a disease characterized by an accumulation of very-long-chain fatty acids (VLCFAs). Inactivation in the mouse of the abcd1 gene leads to a late-onset neurodegenerative condition, comparable to the late-onset form of X-ALD [Pujol, A., Hindelang, C., Callizot, N., Bartsch, U., Schachner, M. and Mandel, J.L. (2002) Late onset neurological phenotype of the X-ALD gene inactivation in mice: a mouse model for adrenomyeloneuropathy. Hum. Mol. Genet., 11, 499-505.]. In the present work, we have generated and characterized a mouse deficient for abcd2, the closest paralog to abcd1. The main pathological feature in abcd2−/− mice is a late-onset cerebellar and sensory ataxia, with loss of cerebellar Purkinje cells and dorsal root ganglia cell degeneration, correlating with accumulation of VLCFAs in the latter cellular population. Axonal degeneration was present in dorsal and ventral columns in spinal cord. We have identified mitochondrial, Golgi and endoplasmic reticulum damage as the underlying pathological mechanism, thus providing evidence of a disturbed organelle cross-talk, which may be at the origin of the pathological cascad

ALDP expression in fibroblasts of patients with X-linked adrenoleukodystrophy

The adrenoleukodystrophy gene encodes a peroxisomal integral membrane protein (ALDP) consisting of 745 amino acids with a molecular weight of 75kDa. ALDP expression was studied in fibroblasts from 24 male ALD patients from 17 unrelated ALD kindreds. In four kindreds an identical 2-base-pair deletion was found. We report the absence of ALDP in 12 kindreds carrying nonsense mutations, frame shifts or amino acid substitutions in the carboxy terminus of ALDP, together accounting for 71% of the ALD kindreds. ALDP was present in five kindreds (29%) with amino acid substitutions in the amino terminal half of the protein; in two of these kindreds ALDP was present although at a reduced level. The absence of truncated proteins suggests that the carboxy terminus has a function in the stabilization of ALD

Identification of fatty acid oxidation disorder patients with lowered acyl-CoA thioesterase activity in human skin fibroblasts

BACKGROUND: Acyl-CoA thioesterases are enzymes that hydrolyze acyl-CoAs to the free fatty acid and coenzyme A (CoASH). These enzymes have been identified in several cellular compartments and are thought to regulate intracellular levels of acyl-CoAs, free fatty acids and CoASH. However, to date no patients deficient in acyl-CoA thioesterases have been identified. DESIGN: Acyl-CoA thioesterase activity was measured in human skin fibroblasts. Western-blot analysis was used to determine Type-II acyl-CoA thioesterase protein levels in patients. RESULTS: Acyl-CoA thioesterase activity was found in human fibroblasts with all saturated acyl-CoAs from C4-CoA to C18-CoA, with highest activity detected with lauroyl-CoA and myristoyl-CoA (C12-CoA and C14-CoA). An antibody that recognizes the major isoforms of Type-II acyl-CoA thioesterases precipitated the majority of acyl-CoA thioesterase activity in fibroblasts, showing that the main thioesterase activity detected in fibroblasts is catalyzed by Type-II thioesterases. Measurement of acyl-CoA thioesterase activity from fibroblasts of 34 patients with putative fatty acid oxidation disorders resulted in the identification of three patients with lowered Type-II acyl-CoA thioesterase activity in fibroblasts. These patients also had lowered expression of Type-II acyl-CoA thioesterase protein in fibroblasts as judged by Western-blot analysis. However, mutation analysis failed to identify any mutation in the coding sequences for the mitochondrial acyl-CoA thioesterase II (MTE-II) or the cytosolic acyl-CoA thioesterase II (CTE-II). CONCLUSIONS: We have described three patients with lowered Type-II acyl-CoA thioesterase protein and activity in human skin fibroblasts, which is the first description of patients with a putative defect in acyl-CoA thioesterase

Autosomal recessive HEM/greenberg skeletal dysplasia is caused by 3 beta-hydroxysterol Delta(14)-reductase deficiency due to mutations in the lamin B receptor gene

Hydrops-ectopic calcification-"moth-eaten" (HEM) or Greenberg skeletal dysplasia is an autosomal recessive chondrodystrophy with a lethal course, characterized by fetal hydrops, short limbs, and abnormal chondro-osseous calcification. We found elevated levels of cholesta-8,14-dien-3beta-ol in cultured skin fibroblasts of an 18-wk-old fetus with HEM, compatible with a deficiency of the cholesterol biosynthetic enzyme 3beta-hydroxysterol delta(14)-reductase. Sequence analysis of two candidate genes encoding putative human sterol delta(14)-reductases (TM7SF2 and LBR) identified a homozygous 1599-1605TCTTCTA-->CTAGAAG substitution in exon 13 of the LBR gene encoding the lamin B receptor, which results in a truncated protein. Functional complementation of the HEM cells by transfection with control LBR cDNA confirmed that LBR encoded the defective sterol delta(14)-reductase. Mutations in LBR recently have been reported also to cause Pelger-Huët anomaly, an autosomal dominant trait characterized by hypolobulated nuclei and abnormal chromatin structure in granulocytes. The fact that the healthy mother of the fetus showed hypolobulated nuclei in 60% of her granulocytes confirms that classic Pelger-Huët anomaly represents the heterozygous state of 3beta-hydroxysterol delta(14)-reductase deficiency

Impaired neuronal migration and endochondral ossification in Pex7 knockout mice: a model for rhizomelic chondrodysplasia punctata

Rhizomelic chondrodysplasia punctata is a human autosomal recessive disorder characterized by skeletal, eye and brain abnormalities. The disorder is caused by mutations in the PEX7 gene, which encodes the receptor for a class of peroxisomal matrix enzymes. We describe the generation and characterization of a Pex7 mouse knockout (Pex7(-/-)). Pex7(-/-) mice are born severely hypotonic and have a growth impairment. Mortality in Pex7(-/-) mice is highest in the perinatal period although some Pex7(-/-) mice survived beyond 18 months. Biochemically Pex7(-/-) mice display the abnormalities related to a Pex7 deficiency, i.e. a severe depletion of plasmalogens, impaired alpha-oxidation of phytanic acid and impaired beta-oxidation of very-long-chain fatty acids. In the intermediate zone of the developing cerebral cortex Pex7(-/-) mice have an increase in neuronal density. In vivo neuronal birthdating revealed that Pex7(-/-) mice have a delay in neuronal migration. Analysis of bone ossification in newborn Pex7(-/-) mice revealed a defect in ossification of distal bone elements of the limbs as well as parts of the skull and vertebrae. These findings demonstrate that Pex7 knockout mice provide an important model to study the role of peroxisomal functioning in the pathogenesis of the human disorde