Functional interaction between peroxisomes and cholesterol metabolisms in glial cells

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1. Adrenoleukodystrophy (X-ALD) is an inherited disorder characterized by progressive demyelination of the central nervous system. X-ALD is due to the mutations in the ABCD1 gem. It encodes a half-size peroxisomal ABC protein, adrenoleukodystrophy protein (ABCD1), which consists of 745 amino acids. ABCD1 contains a transmembrane and an ATP-binding domain(s), and is supposed to work after dimerization. Among missense mutations in X-ALD patients, more than 70% of the mutant ABCD1s were not detected by immunoblot analysis. We examined intracellular fate of 9 mutant ABCD1s with missense mutation. We have found that not only dysfunction of mutant ABCD1 but also mistargeting as well as degradation of mutant ABCD1s would be associated with X-ALD. Furthermore, we found for the fast time that mutant ABCD1s were degraded rapidly by proteasomes.2. Dysfunction of ABCD1 leads to the accumulation of very long chain fatty acids (VLCFA) in total body fluids, especially in brain. ABCD1 has been thought … More to be a transporter of VLCFA or VLCFA-CoA, but the precise function is still unclear. To investigate the roles of ABCD1 in lipid metabolisms in glial cells, we prepared ABCD1-knockdown glioblastoma cells and ABCD 1-knockout mouse primary astrocytes, and analyzed the VLCFA and cholesterol metabolisms in these cells. This study shows that dysfunction of ABCD1 results in the up-regulation of fatty acid elongases as well as the reduction of peroxisomal VLCFA β-oxidation in glial cells. Disruption of these VLCFA metabolisms might result in the VLCFA accumulation in X-ALD brain. Furthermore, cholesterol level was significantly decreased in ABCD1-knockdown glioblastoma cells.In ABCD1-knockdown THP-1 macrophage, incorporation of cholesterol into macrophage was decreased and ApoAI-dependent cholesterol efflux was increased. In addition, ApoE secretion into medium and cholesterol synthesis was significantly increased. These results suggest that cholesterol efflux was inc eased by the dysfunction of ABCD1 in THP-1 macrophage.Although the functional interaction between ABCD1 and cholesterol metabolisms remains to be determined, ABCD1 might have a role for maintaining the cellular cholesterol homeostasis both in glial cells and macrophage. The disturbed cholesterol as well as VLCFA metabolisms in glial cells might be related to the neurodegeneration in X-ALD. Less