RESUMEN
Nonalcoholic fatty liver disease (NAFLD) is a chronic disorder characterized by hepatic fat accumulation and abnormal lipid metabolism. Although miR-21 has been implicated in nonalcoholic fatty liver disease, it is unknown whether miR-21 could function as a therapeutic target. Here, we perform transfection analysis of miR-21 mimic or control mimic to evaluate the effects of miR-21 expression levels on human HepG2 nonalcoholic fatty liver cells. We used siRNA techniques to knock down miR-21 in HepG2 and control 293T cell lines, and then monitored lipid production and the expression levels of genes involved in lipid metabolism. The effects of miR-21 expression levels on LDL receptor-related protein 6 (LRP6) expression were evaluated using qRT-PCR and western blot analyses. Luciferase reporter assays were conducted to confirm the effects of miR-21 expression levels on LRP6. The results indicated that transfection of miR-21 mimic induced changes in the expression levels of lipogenic enzymes, including acetyl-CoA carboxylase 1 (ACC1), stearoyl CoA desaturase (1SCD1), sterol regulatory element-binding protein 1 (SREBP1), and liver X receptor alpha (LXRα). Transfection of miR-21 mimic suppressed the transcription and translation of LRP6 at the mRNA and protein levels, whereas miR-21 knockdown increased the expression levels of LRP6. Transfection of miR-21 mimic in HepG2 cells also induced lipid production and triggered the expression of critical lipid metabolic enzymes. These data suggest that mutation of miR-21 may be a new therapeutic strategy to treat nonalcoholic fatty liver diseases by targeting endogenous LRP6.
RESUMEN
Mutations in the genes low-density lipoprotein (LDL) receptor-related protein-6 (LRP6) and myocyte enhancer factor 2A (MEF2A) were reported in families with coronary artery disease (CAD). We intend to determine the mutational spectrum of these genes among hyperlipidemic and normolipidemic CAD families. Forty probands with early-onset CAD were recruited from 19 hyperlipidemic and 21 normolipidemic Chinese families. We sequenced all exons and intron-exon boundaries of LRP6 and MEF2A, and found a novel heterozygous variant in LRP6 from a proband with normolipidemic CAD. This variant led to a substitution of histidine to tyrosine (Y418H) in an evolutionarily conserved domain YWTD in exon 6 and was not found in 1025 unrelated healthy individuals. Co-segregated with CAD in the affected family, LRP6Y418H significantly debilitated the Wnt3a-associated signaling pathway, suppressed endothelial cell proliferation and migration, and decreased anti-apoptotic ability. However, it exhibited no influences on low-density lipoprotein cholesterol uptake. Thus, mutation Y418H in LRP6 likely contributes to normolipidemic familial CAD via impairing endothelial cell functions and weakening the Wnt3a signaling pathway.