NIPBL haploinsufficient mice recapitulate valve defects observed in Cornelia de Lange syndrome patients

Abstract

Cornelia de Lange (CdL) syndrome, a rare developmental disorder (1/30000 live births), results from mutations in genes encoding the cohesin complex and its partners. The most commonly mutated gene is the cohesin loader, NIPBL . 25–40% of patients display heart malformations, including valve stenosis. We sought to determine whether NIPBL + /− mice recapitulate valve defects observed in patients. To achieve our objectives, we are using a mouse model in which NIPBL exon 2 has been deleted. In order to investigate the effect of NIPBL haploinsufficiency on EMT, embryos were collected at E10.5, outflow tracts (OFT) were dissected and cultured as explants on collagen gels. Explants were treated for 3 weeks with chondrogenic medium to evaluate calcification. Also, valve morphogenesis and function were assessed at 3 and 8 months of age by histology and Doppler echocardiography. NIPBL + / − OFT explants did not reveal any epithelial-to-mesenchymal transition defects. The number of cells expressing osteocalcin after chondrogenic treatment in NIPBL + / − and WT explants did not significantly differ. We found no evidence for differences in calcification of NIPBL + / − cells. At 3 months, an increase in aortic flux was observed in mutants (1/7). Histological analysis revealed a tendency for an enlarged aortic valve in mutants (area of the valve/tibia length: NIPBL + / − = 7692 μm 2 /mm ± 1560, n = 10; WT = 5264 μm 2 /mm ± 1715, n = 10; P -value < 0,05). At 9 months, the aortic valve of NIPBL + / − mice was thicker, as observed in histology, with incomplete penetrance of the phenotype. Aortic valve but not the pulmonary valve is affected in the NIPBL + / − mouse in the, so far, investigated mice. Interestingly, in human patients, the pulmonary valve is more commonly affected.