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Endocardial Brg1 disruption illustrates the EMT origins of semilunar valve disease

ABSTRACT: 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.

ORGANISM(S): Mus musculus

PROVIDER: GSE67786 | GEO | 2015/07/16

SECONDARY ACCESSION(S): PRJNA280967

REPOSITORIES: GEO

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Project description:E12.5 AV cushion and E17.5 AV valve from wild-type FVB/N mice and in vitro cultured MC3T3 cells; In the study we demonstrated shared gene expression in embryonic heart valve development and Osteoblast progenitor cells. The atrioventricular (AV) valves of the heart develop from undifferentiated mesenchymal endocardial cushions, that later remodel into stratified valves with diversified extracellular matrix (ECM). Because the mature valves express genes associated with osteogenesis and exhibit disease-associated calcification, we hypothesized the existence of shared regulatory pathways active in the remodeling AV valves and in bone progenitor cells. In order to define gene regulatory programs of valvulogenesis relative to osteoblast progenitors, we undertook Affymetrix gene expression profiling analysis of murine embryonic day (E)12.5 AV cushions compared to E17.5 remodeled AV valves (mitral and tri-cuspid) and to pre-osteoblast MC3T3-E1 (subclone4) cells. Overall MC3T3 cells were significantly more similar to E17.5 valves than to E12.5 cushions, supporting the hypothesis that valve remodeling involves the expression of many genes also expressed in osteoblasts. Several transcription factors characteristic of mesenchymal and osteoblast precursor cells, including Twist1 are predominant in E12.5 cushion. Valve remodeling also includes differential regulation of matrix metalloproteinases and their inhibitors as well as characteristic collagen isoform switching. Among the most highly enriched genes during valvulogenesis were members of the small leucine-rich proteoglycan (SLRP) family including Asporin, a known negative regulator of osteoblast differentiation and mineralization. Together, these data support shared gene expression profiles of the remodeling valves and osteoblast bone precursor cells in normal valve development and homeostasis with potential functions in calcific valve disease. Experiment Overall Design: In the study, we hybridized RNA from E12.5 AV cushion and E17.5 AV valve from wild-type FVB/N mice and in vitro cultured MC3T3 cells to Affymetrix MOE430 2 GeneChipÂ® arrays.

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Endocardial Brg1 disruption illustrates the EMT origins of semilunar valve disease

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