Hsa-miR-140-5p down-regulates LDL receptor and attenuates LDL-C uptake in human hepatocytes

MicroRNAs (miRs) exert important regulatory effects in cholesterol metabolism. Hepatic low density lipoprotein receptor (LDLR) pathway, as the major mechanism for clearing circulating low density lipoprotein cholesterol (LDL-C) in bloodstream, is a pivotal therapeutic target to treat hypercholesterolemia and atherosclerosis. This study aimed to identify novel miRs that regulate LDLR expression.

Hsa-miR-140-5p was predicted by bioinformatics analyses to interact with human LDLR mRNA. To evaluate its functional effects in regulating LDLR, hsa-miR-140-5p and anti-miR-140-5p were transfected into human and mouse liver cells, followed by qRT-PCR, western blot, immunofluorescence, flow cytometry, and LDL-C uptake assays. It was observed that hsa-miR-140-5p over-expression dramatically down-regulated LDLR expression and reduced LDL-C uptake, whereas inhibition of hsa-miR-140-5p significantly up-regulated LDLR expression and enhanced LDL-C uptake in human HepG2 and LO2 cells, but not in mouse Hepa1-6 cells. Luciferase reporter assay and site-directed mutagenesis identified that hsa-miR-140-5p interacts with the predicted seed sequence "AAACCACU" in the 3'-UTR of human LDLR mRNA. Hsa-miR-140-5p over-expression attenuated LDL-C uptake and decreased intracellular cholesterol levels in the presence of 50 μg/ml ox-LDL in HepG2 cells. Additionally, palmitic acid and simvastatin suppressed, whereas LDL-C up-regulated the expression of miR-140-5p in HepG2 cells.

Hsa-miR-140-5p is a negative regulator of LDLR expression in human hepatocytes, but not in mouse hepatocytes. Simvastatin inhibits hsa-miR-140-5p expression in human hepatocytes, which is likely to be a novel mechanism for treating hypercholesterolemia with statins in clinic. Antagonism of hsa-miR-140-5p could be a new therapeutic strategy for the treatment of hypercholesterolemia and atherosclerosis.