Abstract 5316: The Regulating Role of MicroRNAs for Smooth Muscle Cell Function

Abstract

Background: MicroRNAs (miRNAs) comprise key regulators for cellular function. Maturation and expression of miRNAs is tightly controlled by the two processing enzymes Dicer and Drosha. Up to now, the role of miRNAs for vascular smooth muscle cell (VSMC) function and the development of neointimal lesions remains elusive. Methods and Results: Following wire-induced injury of the femoral artery of C57BL/6N mice, Dicer and Drosha mRNA expression was significantly downregulated at day 10 and 21. Microarray analysis of miRNA expression at these time points revealed a significant downregulation of miRNAs implicated to regulate key molecules of the cell cycle maschinery. Indeed, siRNA-mediated knock down of Dicer or Drosha in human coronary SMC significantly augmented the growth factor-induced expression of CDK4, CDK6, SKP2, accelerated cell cycle progression as determined by FACS analysis and increased VSMC proliferation as determined by BrdU incorporation as well as total cell count. Interestingly, knock down of Dicer and Drosha also augmented migration, whereas there was no effect on apoptosis. Since apoptotic (H 2 O 2 ) or inflammatory stimulation had no effect on dicer and Drosha expression, mitogenic stimulation (FCS) resulted in a robust downregulation of Dicer and Drosha expression. In vivo, the knock down of Dicer and Drosha after wire injury led to increased proliferation of neointimal cells, resulting in a significantly enhanced neointima formation. Further in silico analysis revealed similar and phylogenetically well conserved promoter sets in both promoter regions and the FoxO transcription factor FoxO1a was identified as transcriptional regulator of Dicer and Drosha under mitogenic conditions as determined by ChIP-analysis and siRNA-mediated knock down or overexpression of FoxO1a. Conclusion: These data indicate that the key miRNA-processing enzymes Dicer and Drosha are down regulated in neointimal lesions, most likely by mitogenic stimuli via the Foxo transcription factor FoxO1a. Moreover, altered expression of these enzymes and thus of miRNAs seems to regulate VSMC function, especially proliferation and migration, during the development of vascular proliferative diseases.