Krüppel-Like Factor 2 Is Required for Normal Mouse Cardiac Development

Abstract

Krüppel-like factor 2 (KLF2) is expressed in endothelial cells in the developing heart, particularly in areas of high shear stress, such as the atrioventricular (AV) canal. KLF2 ablation leads to myocardial thinning, high output cardiac failure and death by mouse embryonic day 14.5 (E14.5) in a mixed genetic background. This work identifies an earlier and more fundamental role for KLF2 in mouse cardiac development in FVB/N mice. FVB/N KLF2−/− embryos die earlier, by E11.5. E9.5 FVB/N KLF2−/− hearts have multiple, disorganized cell layers lining the AV cushions, the primordia of the AV valves, rather than the normal single layer. By E10.5, traditional and endothelial-specific FVB/N KLF2−/− AV cushions are hypocellular, suggesting that the cells accumulating at the AV canal have a defect in endothelial to mesenchymal transformation (EMT). E10.5 FVB/N KLF2−/− hearts have reduced glycosaminoglycans in the cardiac jelly, correlating with the reduced EMT. However, the number of mesenchymal cells migrating from FVB/N KLF2−/− AV explants into a collagen matrix is reduced considerably compared to wild-type, suggesting that the EMT defect is not due solely to abnormal cardiac jelly. Echocardiography of E10.5 FVB/N KLF2−/− embryos indicates that they have abnormal heart function compared to wild-type. E10.5 C57BL/6 KLF2−/− hearts have largely normal AV cushions. However, E10.5 FVB/N and C57BL/6 KLF2−/− embryos have a delay in the formation of the atrial septum that is not observed in a defined mixed background. KLF2 ablation results in reduced Sox9, UDP-glucose dehydrogenase (Ugdh), Gata4 and Tbx5 mRNA in FVB/N AV canals. KLF2 binds to the Gata4, Tbx5 and Ugdh promoters in chromatin immunoprecipitation assays, indicating that KLF2 could directly regulate these genes. In conclusion, KLF2−/− heart phenotypes are genetic background-dependent. KLF2 plays a role in EMT through its regulation of important cardiovascular genes.

The force within: endocardial development, mechanotransduction and signalling during cardiac morphogenesis

“…Within the zebrafish atrioventricular canal, high oscillatory flow increases klf2a expression, which, as indicated by morpholinomediated knockdown studies, is required for zebrafish valve development (Heckel et al, 2015;Vermot et al, 2009). Similarly, in mouse the loss of Klf2 causes defects in the endMT of endocardial cells at the atrioventricular cushions and atrial septation defects (Chiplunkar et al, 2013). On a cautionary note, however, it should be noted that zebrafish klf2a mutants do not exhibit any obvious cardiovascular defects (Novodvorsky et al, 2015).…”

“…The coupling of biochemical and mechanical signalling during cardiac valve morphogenesis is regulated by the mechanosensitive transcription factor Klf2a in zebrafish (Heckel et al, 2015;Vermot et al, 2009) and Klf2 in mouse (Chiplunkar et al, 2013). Zebrafish klf2a morphants exhibit a large reduction in notch1b expression, which marks endocardial cushion differentiation, suggesting that retrograde blood flow acts through klf2a to promote endocardial cushion differentiation.…”

Krüppel-like factors in mammalian stem cells and development

“…Surprisingly, no changes in vasculogenesis and angiogenesis are observed in Klf2 −/− mice; however, these mice do exhibit impaired blood vessel maturation . More recent studies have shown that Klf2 is also expressed at E9.5 in endocardial cells of the atrioventricular canal cushion region and that its deletion results in embryonic heart failure, attributable to a high cardiac output state caused by a profound loss of peripheral vascular resistance (Chiplunkar et al, 2013b;Lee et al, 2006).…”

Kruppel-like transcription factors KLF1 and KLF2 have unique and coordinate roles in regulating embryonic erythroid precursor maturation

“…21 Ablation of KLF2 causes lethality between E11.5 and E14. 5,22,23 which can be due to intra-embryonic hemorrhaging 24 or heart failure. 23,25 KLF1 and KLF2 share functional roles in globin gene regulation.…”

“…5,22,23 which can be due to intra-embryonic hemorrhaging 24 or heart failure. 23,25 KLF1 and KLF2 share functional roles in globin gene regulation. KLF1 and KLF2 can partially compensate for each other, as is evident from the reduced embryonic b-like globin gene expression of KLF1/KLF2 double (KLF1-/-KLF2-/-) compared to single knockout embryos.…”