Cardiac malformations in Pdgfrα mutant embryos are associated with increased expression of WT1 and Nkx2.5 in the second heart field

Abstract

Platelet-derived growth factor receptor alpha (Pdgfra) identifies cardiac progenitor cells in the posterior part of the second heart field. We aim to elucidate the role of Pdgfra in this region. Hearts of Pdgfra-deficient mouse embryos (E9.5-E14.5) showed cardiac malformations consisting of atrial and sinus venosus myocardium hypoplasia, including venous valves and sinoatrial node. In vivo staining for Nkx2.5 showed increased myocardial expression in Pdgfra mutants, confirmed by Western blot analysis. Due to hypoplasia of the primary atrial septum, mesenchymal cap, and dorsal mesenchymal protrusion, the atrioventricular septal complex failed to fuse. Impaired epicardial development and severe blebbing coincided with diminished migration of epicardium-derived cells and myocardial thinning, which could be linked to increased WT1 and altered a4-integrin expression. Our data provide novel insight for a possible role for Pdgfra in transduction pathways that lead to repression of Nkx2.5 and WT1 during development of posterior heart field-derived cardiac structures. Developmental Dynamics 239:2307-2317,

Expression of Id2 in the second heart field and cardiac defects in Id2 knock‐out mice

“…This drainage pattern resembles the pattern observed in platelet-derived growth factor-receptor alpha (Pdgfra) knockout embryos Bax et al, 2010). Interestingly, expression patterns of Id2 resemble Fig.…”

“…Id2 knockout embryos demonstrated hypoplasia of the atrial myocardium and larger interatrial communications than observed in wildtype animals, a phenotype that was also observed in other models with impaired myocardial contributions from the posterior heart field, including the mice lacking podoplanin, Pdgfr-a, and Shox2 (Blaschke et al, 2007;Douglas et al, 2009;Bax et al, 2010). However, in contrast to observations in podoplanin and Pdgfra knockout embryos, atrioventricular septal defects were not observed in Id2 knockouts.…”

“…that of Pdgfr-a, which is expressed both in myocardium of the primary heart tube, as well as in SHF-derived myocardium and mesenchyme (van den Akker et al, 2005;Bax et al, 2009Bax et al, , 2010. Pdgfr-a knockout embryos are further characterized by hypoplasia of the SAN, probably due to an accelerated rate of differentiation.…”

Cilia and coordination of signaling networks during heart development

“…184,185 Furthermore, studies from mice show that mutated or absent PDGFRα, results in prenatal death and heart defects including thinned myocardium, and septa, valve, OFT, and aortic arch malformations. [186][187][188] In conclusion, part of the PDGF signaling system might be specifically coordinated by cardiac primary cilia, potentially in a network with Hh and other signaling pathways to coordinate cardiogenesis.…”

The Lhx9-Integrin pathway is essential for positioning of the proepicardial organ

“…Our data also suggest that integrin activity at focal adhesions is required for the clustering of PE cells. Previous data has implicated Itgα4 as being essential for epicardial development particularly in regulating PE cell clustering, epicardial adhesion and epicardial migration (Sengbusch et al, 2002;Pinco et al, 2001;Yang et al, 1995;Dettman et al, 2003;Dokic and Dettman, 2006;Hirose et al, 2006;Pae et al, 2008;Bax et al, 2010). Integrin heterodimers have been shown to coordinate cytoskeletal interactions and adhesion with the surrounding ECM environment (Gardiner, 2011;Gehler et al, 2013;Huttenlocher and Horwitz, 2011;Manninen, 2015;Wolfenson et al, 2013), which are pertinent processes for epicardial formation and function (Kálmán et al, 1995;Nahirney et al, 2003).…”