Endothelial deletion of murine Jag1 leads to valve calcification and congenital heart defects associated with Alagille syndrome

Abstract

The Notch signaling pathway is an important contributor to the development and homeostasis of the cardiovascular system. Not surprisingly, mutations in Notch receptors and ligands have been linked to a variety of hereditary diseases that impact both the heart and the vasculature. In particular, mutations in the gene encoding the human Notch ligand jagged 1 result in a multisystem autosomal dominant disorder called Alagille syndrome, which includes tetralogy of Fallot among its more severe cardiac pathologies. Jagged 1 is expressed throughout the developing embryo, particularly in endothelial cells. Here, we demonstrate that endothelial-specific deletion of Jag1 leads to cardiovascular defects in both embryonic and adult mice that are reminiscent of those in Alagille syndrome. Mutant mice display right ventricular hypertrophy, overriding aorta, ventricular septal defects, coronary vessel abnormalities and valve defects. Examination of mid-gestational embryos revealed that the loss of Jag1, similar to the loss of Notch1, disrupts endothelial-to-mesenchymal transition during endocardial cushion formation. Furthermore, adult mutant mice exhibit cardiac valve calcifications associated with abnormal matrix remodeling and induction of bone morphogenesis. This work shows that the endothelium is responsible for the wide spectrum of cardiac phenotypes displayed in Alagille Syndrome and it demonstrates a crucial role for Jag1 in valve morphogenesis.

Impairment of endothelial‐mesenchymal transformation during atrioventricular cushion formation in Tmem100 null embryos

“…4C,e-f). While Jag1 null embryos show partial but significant EndMT defect (Hofmann et al, 2012;Wang et al, 2013), Jag1 protein expression (Fig. 4C,g-h) and Jag1 mRNA expression (data not shown) in AVC endocardial cells were below the detection limit.…”

“…While Notch signaling is also required for normal endocardial cushion development (Timmerman et al, 2004;Hofmann et al, 2012;Wang et al, 2013), the expression patterns of Notch1 and NICD, an activated form of Notch receptor, in AVC endocardial cells were comparable between wild-type and Tmem100 null embryos (Fig. 4C,a-d).…”

“…Among those are transforming growth factor beta (TGFb) and bone morphogenetic protein (BMP), which act as myocardium-derived signals to induce EndMT of endocardial cells (Yamagishi et al, 1999;Camenisch et al, 2002;Sugi et al, 2004;Ma et al, 2005). Notch signaling in endocardial cells is also required for cushion development, and the deletion of Notch1, Rbpj, or Jag1 in mice causes EndMT defects and cushion hypoplasia (Timmerman et al, 2004;de la Pompa and Epstein, 2012;Hofmann et al, 2012). In addition, calcineurin signaling and its downstream transcription factors of the NFATc (nuclear factor of activated T cells, cytoplasmic, calcineurin dependent) family are implicated in EndMT during early cushion formation as well as in subsequent valvulogenesis (de la Pompa et al, 1998;Ranger et al, 1998;Crabtree and Olson, 2002;Chang et al, 2004;Combs and Yutzey, 2009b;Wu et al, 2011).…”

Etiology of Valvular Heart Disease

“…Further in vivo evidence of this inhibitory role has been demonstrated in mice heterozygous for Notch1, Rbpj, Jagged1 and Hey2, which develop aortic valve calcification. [67][68][69] Those studies demonstrated that valve development genes may potentially play a role in this adult-onset disease and the mechanisms by which loss of Notch signaling leads to calcification are being investigated. 70 Sox9, which encodes an SRY-related transcription factor found to play a role in acquired VHD.…”

Isolation of Murine Valve Endothelial Cells

“…In diseased valves, the VEC monolayer is disrupted in association with abnormal changes in ECM organization and altered biomechanics 4,5 . In addition, studies in mouse models suggest that VEC dysfunction is the underlying cause of valve disease 1,[6][7][8][9] . As VECs play an important role in valve development, maintenance, and disease, it is important that we fully define their temporal phenotypes in order to advance the field and understand mechanisms of disease.…”