Significance Results from this study represent a breakthrough in our understanding of posttranscriptional control of cholesterol metabolism and how microRNAs (miRNAs) are at the heart of cholesterol regulatory circuitry and homeostasis. Although cells are adept at maintaining proper cholesterol levels, it was unknown how cells posttranscriptionally coordinate cholesterol uptake, efflux, and synthesis. MicroRNA-223 (miR-223) transcription and expression are maintained by cholesterol, and, as a feedback network, miR-223 inhibits cholesterol biosynthesis and uptake and increases cholesterol efflux. This study clearly demonstrates the extensive role that miRNAs play in coordinating metabolic adaptation to disease and general homeostasis. This work highlights a unique regulatory control point for cholesterol homeostasis and illustrates how important the study of miRNAs is to the greater understanding of dyslipidemia and cardiovascular disease.

CB1 receptor blockers increase HDL-C levels. Although genetic variation in the CB1 receptor – encoded by the CNR1 gene – is known to influence HDL-C level as well, human studies conducted to date have been limited to genetic markers such as haplotype tagging SNPs. Here we identify rs806371 in the CNR1 promoter as the causal variant. We resequenced the CNR1 gene and genotype all variants in a DNA biobank linked to comprehensive electronic medical records. By testing each variant for association with HDL-C level in a clinical practice-based setting, we localize a putative functional allele to a 100bp window in the 5′-flanking region. Assessment of variants in this window for functional impact on electrophoretic mobility shift assay identified rs806371 as a novel regulatory binding element. Reporter gene assays confirm that rs806371 reduces HDL-C gene expression, thereby linking CNR1 gene variation to HDL-C level in humans.