Identification and Verification of Differentially Methylated Regions in Cell-Free DNA as a Peripheral Biomarker for Bicuspid Aortic Valve Aortopathy
Date
2020-01-08
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Abstract
Bicuspid aortic valve (BAV) is a common congenital cardiac malformation associated with aortopathy for which the progression of aortic dilation is difficult to predict at present. BAV aortopathy has been linked to genetic factors and abnormal hemodynamic flow with regions of elevated wall shear stress (WSS) on the ascending aorta. The dying vascular smooth muscle cells release fragmented DNA into the circulation and this cell-free DNA (cfDNA) could be leveraged as a biomarker for aortopathy. Identification of tissue-specific differentially methylated regions (DMRs) in DNA provides a potential mechanism to identify cfDNA arising from the ascending aorta. The objective is to identify aorta-specific DMRs in the cfDNA of BAV patients as a biomarker for the severity of the aortopathy. We hypothesize that BAV-associated aortopathy leads to increased cell death and increased release of aorta-specific cfDNA correlating with the severity of aortopathy as defined by aortic cell death, elastin degradation and dysregulation of ECM proteins. BAV patient aortic wall samples corresponding to areas of elevated and normal WSS were collected and stained for cell death. Regions of elevated aortic WSS showed greater cell death when compared to regions of normal aortic WSS (p=0.00006). We established a bioinformatic pipeline for the identification of aorta-specific DMRs and they were verified with BAV patient cfDNA. The levels of aorta specific cfDNA of the DMRs on Chr 11, 18 and 22 of BAV patients had a significant correlation with levels of cell death in elevated aortic WSS regions. However, there was no correlation with elastin thickness, ECM concentrations of matrix metalloproteinases (MMP) types 1, 2 and 3, tissue inhibitor of metalloproteinases-1 and transforming growth factor-β1. Further work needs to be done in order to identify more specific aortic DMRs that have stronger correlation to the severity of BAV aortopathy markers with larger cohorts for biomarker validation. The identification of a peripheral biomarker that correlates with tissue disease will be an important advance in the non-invasive diagnosis of BAV-associated aortopathy and potentially help guide clinical decision-making regarding the need for surgical intervention.
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Keywords
Bicuspid aortic valve, Aortopathy, Biomarker, non-invasive, cell-free DNA, differentially methylated region, methylation, cell death, wall shear stress
Citation
Maredia, A. K. (2020). Identification and Verification of Differentially Methylated Regions in Cell-Free DNA as a Peripheral Biomarker for Bicuspid Aortic Valve Aortopathy (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.