Novel Gene Expression Changes In Bicuspid Aortic Valves

Toronto, Ontario BACKGROUND: The molecular basis of bicuspid aortic valve development and susceptibility to early calcification remain poorly understood. MicroRNAs are essential post-transcriptional modulators of gene expression which coordinate and integrate multiple regulatory pathways involved in normal and abnormal development. We performed microRNA profiling to identify potential novel pathways differentially regulated in bicuspid vs. tricuspid aortic valves. METHODS & RESULTS: Aortic valve leaflets were obtained intraoperatively from patients with stenotic bicuspid (BAV) and tricuspid aortic valves (TAV) at the time of valve replacement (N 10 each). Total RNA extracted from some of the tissue samples was directly labeled with biotin and hybridized to the GenoExplorerTM microRNA (Human) Chip. This microarray contains 1583 human miRNA probes and provides a comprehensive and comparative profile analyses of miRNA expression Fluorescent signals were scanned with the GenePix® 4000B Microarray Scanner. The other tissue samples were either flash frozen for molecular analysis or fixed in formalin and sectioned for histology and histochemical analysis. Microarray analysis revealed 40 differentially expressed miRNA sequences in BAV vs. TAV samples. Nineteen miRNAs including miRNA-152, -373, -30e, and -145 were upregulated and amongst the 21 miRNAs that were down-regulated were miRNA-125b, -1260, -27a, and -141 (Figure). These findings were confirmed by quantitative RT-PCR. Notably, expression of miRNA-141, a known repressor of the master osteogenic transcription factor DLX-5 and a regulator of bone morphogenetic protein (BMP-2), was 14.9-folds lower in BAV vs. TAV. BAV leaflet tissues also demonstrated higher BMP2 expression compared to TAV tissues. CONCLUSION: We identify a novel miRNA profile in calcific BAV vs. TAV leaflet tissues. Specifically, marked downregulation of miRNA-141 in BAV may serve to regulate abnormal cell fate decisions and BMP-2-dependent calcification leading to altered susceptibility towards calcific aortic stenosis. 712 COMPLETE REVASCULARIZATION IS COMPROMISED IN OFFPUMP CORONARY ARTERY BYPASS GRAFTING