Abstract 1316: Deficiency of the WW Domain-Containing Oxidoreductase (WWOX) Impairs the HDL Biogenesis Pathway
Low plasma HDL cholesterol (HDL-C) is a well-established risk factor for coronary artery disease (CAD). We have recently identified a close association of region-wide significance between the WWOX gene and low plasma HDL-C in dyslipidemic families of Mexican and European descent and in low HDL-C cases and controls subjects (rs2548861, p=6.9 × 10−7). WWOX encodes a 46-kDa tumor suppressor, the expression of which is altered in several types of human malignancies. However, its role in HDL metabolism is unknown. Here, through in vitro and in vivo studies, we investigated the potential role of WWOX in HDL biogenesis. Using siRNA directed against WWOX in cultured human HepG2 cells, we observed a significant reduction in ABCA1 and ApoA-I mRNA and protein levels. To support these observations, we examined whether in vivo inactivation of the WWOX gene leads to HDL-C deficiency. Analyses of lipoprotein profiles in Wwox-deficient (Wwox−/−) mice by fast protein liquid chromatography (FPLC) and two-dimensional polyacrylamide nondenaturing gradient gel electrophoresis (2D-PAGGE) showed a drastic reduction in the levels of both HDL-C and larger ApoA-I-containing particles. Affymetrix microarray analysis of gene expression revealed that several genes involved in cholesterol biosynthesis, transport and efflux are significantly downregulated in Wwox−/− mice compared to wild-type (WT) mice. In particular, SREBP-dependent genes and ABC transporters displayed a two- to seven-fold difference when compared between the two groups. Additionally, hepatic tissues from Wwox−/− mice showed a decrease in ABCA1 and ApoA-I protein levels, as compared to WT mice. In parallel, we also observed that ABCA1 mutations causing Tangier disease intriguingly reduced levels of WWOX protein in human fibroblasts, the decrease of which was not corrected by treatment with 22(R)-hydroxycholesterol/9-cis-retinoic acid LXR agonists. Altogether, our findings suggest a novel role for the WWOX gene in HDL biogenesis, likely through an ABCA1-mediated pathway, raising the possibility that WWOX may be involved in the complex network of cellular cholesterol homeostasis.