Abcd 2 Is a Strong Modifier of the Metabolic Impairments in Peritoneal Macrophages of Abcd 1-Deficient Mice

The inherited peroxisomal disorder X-linked adrenoleukodystrophy (X-ALD), associated with neurodegeneration and inflammatory cerebral demyelination, is caused by mutations in the ABCD1 gene encoding the peroxisomal ATP-binding cassette (ABC) transporter ABCD1 (ALDP). ABCD1 transports CoA-esters of very long-chain fatty acids (VLCFA) into peroxisomes for degradation by b-oxidation; thus, ABCD1 deficiency results in VLCFA accumulation. The closest homologue, ABCD2 (ALDRP), when overexpressed, compensates for ABCD1 deficiency in X-ALD fibroblasts and in Abcd1-deficient mice. Microglia/macrophages have emerged as important players in the progression of neuroinflammation. Human monocytes, lacking significant expression of ABCD2, display severely impaired VLCFA metabolism in X-ALD. Here, we used thioglycollate-elicited primary mouse peritoneal macrophages (MPMW) from Abcd1 and Abcd2 singleand double-deficient mice to establish how these mutations affect VLCFA metabolism. By quantitative RT-PCR, Abcd2 mRNA was about half as abundant as Abcd1 mRNA in wild-type and similarly abundant in Abcd1-deficient MPMW. VLCFA (C26:0) accumulated about twofold in Abcd1-deficient MPMW compared with wild-type controls, as measured by gas chromatography-mass spectrometry. In Abcd2-deficient macrophages VLCFA levels were normal. However, upon Abcd1/Abcd2 double-deficiency, VLCFA accumulation was markedly increased (sixfold) compared with Abcd1-deficient MPMW. Elovl1 mRNA, encoding the rate-limiting enzyme for elongation of VLCFA, was equally abundant across all genotypes. Peroxisomal b-oxidation of C26:0 amounted to 62% of wild-type activity in Abcd1-deficient MPMW and was significantly more impaired (29% residual activity) upon Abcd1/Abcd2 double-deficiency. Single Abcd2 deficiency did not significantly compromise b-oxidation of C26:0. Thus, the striking accumulation of VLCFA in double-deficient MPMW compared with single Abcd1 deficiency was due to the loss of ABCD2-mediated, compensatory transport of VLCFA into peroxisomes. We propose that moderate endogenous expression of Abcd2 in Abcd1-deficient murine macrophages prevents the severe metabolic phenotype observed in human X-ALD monocytes, which lack appreciable expression of ABCD2. This supports upregulation of ABCD2 as a therapeutic concept in X-ALD. Citation: Muneer Z, Wiesinger C, Voigtländer T, Werner HB, Berger J, et al. (2014) Abcd2 Is a Strong Modifier of the Metabolic Impairments in Peritoneal Macrophages of Abcd1-Deficient Mice. PLoS ONE 9(9): e108655. doi:10.1371/journal.pone. 0108655 Editor: Jean-Marc A. Lobaccaro, Clermont Université, France Received May 7, 2014; Accepted August 25, 2014; Published September 25, 2014 Copyright: 2014 Muneer et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability: The authors confirm that all data underlying the findings are fully available without restriction. All relevant data are within the paper and its Supporting Information files. Funding: This work was supported by grants from the European Union (FP7-HEALTH-2009) project No. 241622, ‘‘LEUKOTREAT’’ (URL: http://cordis.europa.eu/ fp7/home_en.html) and from the Austrian Science Fund (FWF) project P26112-B19 (URL: http://www.fwf.ac.at). ZM was supported by a PhD scholarship from the Higher Education Commission of Pakistan (URL: http://www.hec.gov.pk/Pages/HECMain.aspx). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * Email: sonja.forss-petter@meduniwien.ac.at