Progressive calcific aortic valve disease (CAVD) is characterized by calcium deposition in the valve cusps as well as frank bone formation. People born with a bicuspid aortic valve (BAV), a common congenital heart defect, can develop significant CAVD during the prime of life. BAV and CAVD are regulated by genetic factors including mutations in the Notch1 gene. We analyzed human genetic datasets to identify gene variants associated with BAV and/or CAVD. Our genetic analysis of the Tufts BAV Genetics Study identified gene variants in the WNT/b-catenin and TGFb signaling pathways, which are known to contribute to aortic valve development as well as valve calcification. Our unpublished genome-wide association analysis of the Framingham Heart Study has further identified gene variants in the cyclin dependent kinase (CDK), the soft tissue calcification and the cell-cell communication pathways associated with CAVD. The association of CDK7 gene SNPs with aortic valve calcification is provocative because we have previously demonstrated that the retinoblastoma protein (pRb) and CDK pathway regulate bone formation through the runx2 transcription factor and by regulating cellular responses to Notch1. Taken together we put forth an over-arching hypothesis that the pRb-CDK pathway regulates CAVD through transcriptional effects on soft tissue calcification and cell-cell communication genes regulated by runx2 and Notch1. We will test this hypothesis in our first specific aim by comparing pRb-deficient and control valve interstitial cell (VIC) growh and expression of bone and calcification gene markers in response to factors that stimulate mineralization. Next, we will compare pRb-deficient and control VIC extracellular matrix stiffness characteristics and calcification. Finally we will determine whether pRb regulates runx2 occupancy of soft tissue calcification gene promoters in VICs. In our second aim we will study mice engineered to have a loss- or a gain-of-function in CDK6 that have significant bone and mineralization phenotypes. Further, we will define the role of cdk6 in regulation of VIC osteogenic responses to Notch, and we will survey pRb-cdk mouse models for aortic valve calcification. In our third aim we will analyze expression and activity of pRb-cdk components in human calcified aortic valve tissue. Finally, to broadly survey expression of the pRb-cdk pathway, as well as genes that regulate soft-tissue calcification and cell-cell communication, we will sequence the CAVD transcriptome (RNA-seq). We have assembled a team of experts with experience in CAVD genetics, the regulation of the osteogenic transcriptional program and calcification by the pRb-CDK pathway, and the heart extracellular matrix. We anticipate that our studies will provide unique insights to the biology of CAVD and that this work will translate meaningfully to the understanding of calcific aortic valve disease as well as help guide potential therapeutic options or raise awareness of potential adverse drug effects on the aortic valve.
Progressive calcium deposition and bone formation in the aortic valve can restrict blood coming out of the heart and thereby create the need for valve replacement surgery. Through analysis of human genes and gene variants we have identified genes and pathways associated with calcific aortic valve disease that may contribute to this disease. Studies proposed here will explore the biological role of the pathways we have identified in order to determine their role in calcific aortic valve disease.
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