miR-146a-5p mediates atherogenic signalling from immune to vascular cells

AIMS: MicroRNAs (miRNAs) regulate gene expression and are involved in various biological processes, including vascular homeostasis. Macrophages (Mϕs) and vascular smooth muscle cells (VSMCs) play key roles in vascular health and disease. However, the communication between Mϕs and VSMCs via miRNAs is not well understood. This study explores the transfer of miR-146a-5p from Mϕs to VSMCs and its role in atherosclerosis. METHODS AND RESULTS: Through unbiased miRNA-sequencing of cellular coculture, miR-146a-5p was identified as a potential messenger between Mϕs and VSMCs. This finding was validated using multiple experimental approaches, including the use of a fluorescent miR-146a-5p mimic and a sensor to document its transfer from Mϕs to VSMCs. Transfer occurred via gap junctions, especially when Mϕs were exposed to a pro-inflammatory stimulus. In VSMCs, miR-146a-5p promoted a contractile, proliferative phenotype and altered their metabolic and transcriptomic profiles, affecting genes involved in differentiation and cholesterol metabolism. Kruppel-like factor 4 (Klf4) was directly targeted by miR-146a-5p to modulate Serum Responsive Factor (SRF) activity and, hence, regulate genes such as Apolipoprotein E, 3-Hydroxy-3-Methylglutaryl-CoA Reductase, Thrombospondin 1, and Galectin 3. Of clinical importance, VSMCs from stenotic human plaque had an elevated miR-146a-5p level. A VSMC-specific sponge system targeting miR-146a-5p and, thus, hindering transfer from Mϕs, reduced plaque formation in a murine model of atherosclerosis. CONCLUSION: MiR-146a-5p is a key mediator of Mϕ-VSMC communication contributing to vascular disease, and is a potential therapeutic target for atherosclerosis.