Abstract 17406: Inhibition of MicroRNA-133a Expression is Associated with Poor Growth Response of Vascular Smooth Muscle Cells to Insulin-Like Growth Factor-1 in Apolipoprotein-E Deficient Mice

Abstract

Background and Objective. Alternations in growth and differentiation of vascular smooth muscle cells (SMC) contribute to the pathogenesis of atherosclerosis. Certain microRNAs (miR) have been shown to regulate cardiovascular cell growth and differentiation. For instance, miR-133a plays a role in cardiac muscle development. However, it is largely unknown if miR-133a affects SMC proliferation in atherosclerosis. This study was designed to analyze miR-133a expression and SMC growth in atherosclerosis and to explore if insulin growth factor (IGF)-1 receptor is involved in the miR-133a effect on SMC growth. Methods and Results. qRT-PCR analysis of total RNA extracted revealed lower levels of miR133a in SMC cultured from apolipoprotein E-null (apoE -/- ) mice than those in wild-type C57BL/6J (WT). Interestingly, IGF-1R mRNA levels were lower in the ApoE -/- cells. Immunofluorescence for IGF-1R was positive in both the sections of WT and ApoE -/- mice aorta but the latter displayed weaker signals. In cultured WT SMCs, IGF-IR protein expression decreased by about 66% after incubation with miR-133a inhibitor. In contrast, IGF-IR levels increased by almost 3-fold when the cells were treated with miR-133a precursor. Growth curves showed that SMC proliferation was attenuated with miR-133a inhibitor(Fig.1). The decreased SMC proliferation was caused by poor response to IGF-1 as addition of IGF-1 did not increase SMC numbers in the cultures. However, incubation with miR-133a precursor increased proliferation of WT SMC by 25% and ApoE -/- SMC by 10%. Conclusions. Down-regulation of miR-133a expression with miR-133a inhibitor decreases IGF-1R expression and inhibits the growth of WT SMCs but to a less degree in Apo -/- SMC. In contrast, overexpression of miR-133a increases IGF-1R expression and promotes the IGF-1 derived the SMC growth. The data suggest that miR-133a may participate in regulation of SMC growth in atherosclerotic vascular tissue.