Role of KLF2 in endocardial cushion development in mice

Abstract

Krüppel‐like factor 2 (KLF2) belongs to a family of transcription factors that have 3 C2/H2 zinc finger domains. KLF2 is expressed in endothelial cells and is induced by shear stress. KLF2−/− embryos in FVB/N genetic background die by embryonic day 11.5 (E11.5) (chi‐square p = 0.0044), whereas in mixed genetic background, they die by E14.5. Our studies show that unlike WT hearts, in E9.5 KLF2 KO hearts (n = 3) the cells lining the atrioventricular (AV) cushion, the area that will become the AV valves, form multiple, disorganized layers and the number of cells is 2‐fold higher. Electron microscopy revealed that compared to WT, the E9.5 KLF2−/− AV canal is narrower in some locations but patent and lined by endothelial cells having numerous cytoplasmic processes extending toward the lumen. In E10.5 KLF2−/− embryos (n = 3), the AV and outflow tract cushions are hypoplastic and the cells lining the AV canal form multiple disorganized layers. Alcian blue staining of E10.5 KLF2−/− hearts showed an absence of glycosaminoglycans in the cardiac jelly. These findings suggest that KLF2, directly or indirectly, regulates endothelial to mesenchymal transformation in AV cushion development. The AV phenotype is observed in FVB/N KLF2−/− embryos but not in embryos of mixed background (n = 2). Therefore, KLF2 is required for normal endocardial cushion development in FVB/N genetic background mice. (Supported by NIH R01DK074694)