Flank Sequences of miR‐145/143 and Their Aberrant Expression in Vascular Disease: Mechanism and Therapeutic Application

BACKGROUND Many microRNAs (miRNAs) are downregulated in proliferative vascular disease. Thus, upregulation of these miRNAs has become a major focus of research activity. However, there is a critical barrier in gene therapy to upregulate some miRNAs such as miR-145 and miR-143 because of their significant downregulation by the unclear endogenous mechanisms under disease conditions. The purpose of this study was to determine the molecular mechanisms responsible for their downregulation and to overcome the therapeutic barrier. METHODS AND RESULTS In cultured proliferative rat vascular smooth muscle cells (VSMCs) in vitro and in diseased rat and mouse arteries in vivo, we have identified that the impairment of pri-miR-145 into pre-miR-145 is the critical step related to the downregulation of miR-145, in which the PI3-kinase/Akt/p53 pathway is involved. We further identified that the flank sequences of pri-miR-145 are the critical structural components responsible for the aberrant miR-145 expression. Switching of the flank sequence of downregulated miR-145 and miR-143 to the flank sequence of miR-31 confers resistance to their downregulation. The genetically engineered miR-145 (smart miR-145) restored the downregulated miR-145 in proliferative rat VSMCs and in rat carotid arteries with balloon injury and mouse atherosclerotic aortas and demonstrated much better therapeutic effects on the abnormal growth of VSMCs, expression of its target gene, KLF5 expression, VSMC marker gene expression, and vascular neointimal growth. CONCLUSIONS The flank sequences of miR-145 and miR-143 play a critical role in their aberrant expression in VSMCs and vascular walls. The genetically engineered "smart" miRNAs based on their flank sequences may have broadly therapeutic applications for many vascular diseases.