Outflow tract cushions perform a critical valve-like function in the early embryonic heart requiring BMPRIA-mediated signaling in cardiac neural crest

Abstract

. Outflow tract cushions perform a critical valve-like function in the early embryonic heart requiring BMPRIA-mediated signaling in cardiac neural crest. Am J Physiol Heart Circ Physiol 297: H1617-H1628, 2009. First published August 28, 2009 doi:10.1152/ajpheart.00304.2009.-Neural crest-specific ablation of BMP type IA receptor (BMPRIA) causes embryonic lethality by embryonic day (E) 12.5, and this was previously postulated to arise from a myocardial defect related to signaling by a small population of cardiac neural crest cells (cNCC) in the epicardium. However, as BMP signaling via cNCC is also required for proper development of the outflow tract cushions, precursors to the semilunar valves, a plausible alternate or additional hypothesis is that heart failure may result from an outflow tract cushion defect. To investigate whether the outflow tract cushions may serve as dynamic valves in regulating hemodynamic function in the early embryo, in this study we used noninvasive ultrasound biomicroscopy-Doppler imaging to quantitatively assess hemodynamic function in mouse embryos with P0-Cre transgene mediated neural crest ablation of Bmpr1a (P0 mutants). Similar to previous studies, the neural crest-deleted Bmpr1a P0 mutants died at ϳE12.5, exhibiting persistent truncus arteriosus, thinned myocardium, and congestive heart failure. Surprisingly, our ultrasound analyses showed normal contractile indices, heart rate, and atrioventricular conduction in the P0 mutants. However, reversed diastolic arterial blood flow was detected as early as E11.5, with cardiovascular insufficiency and death rapidly ensuing by E12.5. Quantitative computed tomography showed thinning of the outflow cushions, and this was associated with a marked reduction in cell proliferation. These results suggest BMP signaling to cNCC is required for growth of the outflow tract cushions. This study provides definitive evidence that the outflow cushions perform a valve-like function critical for survival of the early mouse embryo. bone morphogenetic proteins; endocardial cushions; heart defects congenital; heart development; ultrasound biomicroscopy BONE MORPHOGENETIC PROTEINS (BMPs), members of the TGF-␤ superfamily, transduce signals by binding to heteromeric type I and type II receptor complexes (23, 28). Among three type I receptors for BMPs, type IA receptor (BMPRIA, also known as ALK3) is highly expressed in the developing heart (7). Bmpr1a knockout mice die by embryonic day (E) 8.5 exhibiting failure in mesoderm formation (30). Mutations in genes encoding their ligands, Bmp2 or Bmp4, also cause early embryonic lethality (52, 55). Myocardial-or endocardial-specific disruptions of Bmpr1a result in defects of the endocardial cushions of the atrioventricular canal (AVC; Refs. 10, 33, 46) or malformation of the atrioventricular valves (11). Conditional disruption of Bmp2 or Bmp4 in the myocardium (19, 26) further suggests a role for BMP2 and BMP4 in regulating endocardial epithelialto-mesenchymal transformation (EMT) in the AVC. BMP signaling also pla...

Cilia and Ciliopathies in Congenital Heart Disease

“…These studies show TGF-b/BMP signaling has multiple roles in cardiovascular development that include the regulation of both endocardial EMT and endocardial cushion development (Potts and Runyan 1989;Camenisch et al 2002). For example, early endocardial cushion development to acquire critical valve-like function requires BMP signaling in cardiac neural crest cells via the BMPRIA receptors (Nomura-Kitabayashi et al 2009). A role for Tgfb2 in OFT and aortic arch remodeling is indicated by the finding that Tgfb2 knockout mice die perinatally with double outlet RV and interrupted aortic arch (Sanford et al 1997).…”

Neural crest–derived SEMA3C activates endothelial NRP1 for cardiac outflow tract septation

“…Furthermore, SMA-positive cells failed to invade the septal bridge; instead, they appeared to stall within the endocardial cushions in the lateral OFT ( Previous observations that SEMA3C binds both NRP1 and NRP2 (27) and that OFT septation occurs normally in Nrp2 -/-mutants or Defects in proliferation may also cause OFT defects. Thus, deletion of the BMP type 1 receptor in NCCs reduces proliferation in the endocardial cushions and correlates with defective OFT remodeling (36). We therefore used the proliferation marker phosphohistone H3 (pHH3) (37,38) to label E11.5 OFT sections of Nrp1-null mutants and their littermates (Supplemental Figure 1C), but found no significant difference (Supplemental Figure 1D; pHH3-positive cells per OFT section: 13.5% ± 3.54% Nrp1 +/+ versus 12.88% ± 1.24% Nrp1 ).…”

Neural crest cell signaling pathways critical to cranial bone development and pathology

“…Neural crest-specific disruption of Acvr1 , one of the type 1 receptors for BMPs, results in multiple craniofacial defects including a hypomorphic mandible and lack of ossification in the squamous parts of frontal bones in addition to cleft palate [74]. Neural crest-specific disruption of another type 1 receptor, Bmpr1a , results in midgestation lethality due to malfunctions of cardiac neural crest [75, 76]. When this failure of cardiac function is compensated for by isoproterenol, a beta-adrenergic agonist, mutant embryos can survive until term, but the rescued embryos develop smaller heads and reduced projection of facial structures [77].…”