Aberrant Expression of microRNA-9 Contributes to Development of Intracranial Aneurysm by Suppressing Proliferation and Reducing Contractility of Smooth Muscle Cells

BACKGROUND MiR-9 is reportedly involved with many diseases, such as acute myeloid leukemia and liver oncogenesis. In the present study we investigated the molecular mechanism, including the potential regulator and signaling pathways, of MYOCD, which is the gene that in humans encodes the protein myocardin. MATERIAL AND METHODS We searched the online miRNA database (www.mirdb.org) with the "seed sequence" located within the 3'-UTR of the target gene, and then validated MYOCD to be the direct gene via luciferase reporter assay system, and further confirmed it in cultured cells by using Western blot analysis and realtime PCR. RESULTS We established the negative regulatory relationship between miR-9 and MYOCD via studying the relative luciferase activity. We also conducted realtime PCR and Western blot analysis to study the mRNA and protein expression level of MYOCD between different groups (intracranial aneurysm vs. normal control) or cells treated with scramble control, miR-9 mimics, MYOCD siRNA, and miR-9 inhibitors, indicating the negative regulatory relationship between miR-9 and MYOCD. We also investigated the relative viability of smooth muscle cells when transfected with scramble control, miR-9 mimics, MYOCD siRNA, and miR-9 inhibitors to validate that miR-9 t negatively interferes with the viability of smooth muscle cells. We then investigated the relative contractility of smooth muscle cells when transfected with scramble control, miR-9 mimics, MYOCD siRNA, and miR-9 inhibitors, and the results showed that miR-9 weakened contractility. CONCLUSIONS Our findings show that dysregulation of miR-9 is responsible for the development of IA via targeting MYOCD. miR-9 and its direct target, MYOCD, might novel therapeutic targets in the treatment of IA.