Endocardial Brg1 disruption illustrates the EMT origins of semilunar valve disease. Mus musculus

Discreet defects during prenatal semilunar valve (SLV) development frequently progress to pathological states later in life and often require valve replacement surgery. As such, it is challenging to distinguish between the disrupted developmental processes, and their genetic and environmental influences, that trigger valve defects from mechanisms that drive the progression of an anatomically abnormal valve into a disease state. This distinction, which is essential to inform the rationale design of diagnostics and therapeutics, requires carefully characterizing when and where an implicated gene or pathway functions during valve development and/or homeostasis. Disrupted growth, differentiation, and patterning events that trigger SLV disease are coordinated by gene expression changes in endocardial, myocardial, and cushion mesenchymal cells. We explored the roles of chromatin regulation in valve gene regulatory networks via conditional inactivation of the mouse Brg1 associated factor (BAF) chromatin-remodeling complex in the endocardial lineage. Endocardial Brg1-deficient embryos develop thickened and mal-patterned SLV cusps that frequently become bicuspid and myxomatous, including in surviving adults. These SLV disease-like phenotypes originate from deficient endocardial-mesenchymal transformation (EMT) in the proximal outflow tract (pOFT) cushions. Mesenchymal cells of neural crest or other cardiac origins subsequently replace the missing EMT-derived cells but are incompetent to pattern the valve interstitium into regions with distinct extracellular matrix composition. Transcriptomics reveal genes that may promote growth and patterning of SLVs and/or serve as biomarkers of their diseased state. Mechanistic studies of SLV disease genes will distinguish between disease origins and progression; the latter may largely reflect secondary responses to a disrupted developmental system. Overall design: Examination of transcriptional changes (RNAseq) in E14.5 dissected cardiac cushions (two paired samples) of Nfatc1Cre;Brg1F/F mutants and wildtype littermates