Epicardially derived fibroblasts preferentially contribute to the parietal leaflets of the atrioventricular valves in the murine heart

Abstract

The importance of the epicardium for myocardial and valvuloseptal development has been well established; perturbation of epicardial development results in cardiac abnormalities, including thinning of the ventricular myocardial wall and malformations of the atrioventricular valvuloseptal complex. To determine the spatiotemporal contribution of epicardially derived cells to the developing fibroblast population in the heart we have used a mWt1/IRES/GFP-Cre mouse to trace the fate of EPDCs from embryonic day (ED)10 until birth. EPDCs begin to populate the compact ventricular myocardium around ED12. The migration of epicardially-derived fibroblasts toward the interface between compact and trabecular myocardium is completed around ED14. Remarkably, epicardially-derived fibroblasts do not migrate into the trabecular myocardium until after ED17. Migration of EPDCs into the atrioventricular cushion mesenchyme commences around ED12. As development progresses, the number of EPDCs increases significantly, specifically in the leaflets which derive from the lateral atrioventricular cushions. In these developing leaflets the epicardially-derived fibroblasts eventually largely replace the endocardially-derived cells. Importantly, the contribution of EPDCs to the leaflets derived from the major AV cushions is very limited. The differential contribution of EPDCs to the various leaflets of the atrioventricular valves provides a new paradigm in valve development and could lead to new insights into the pathogenesis of abnormalities that preferentially affect individual components of this region of the heart. The notion that there is a significant difference in the contribution of epicardially and endocardially derived cells to the individual leaflets of the atrioventricular valves has also important pragmatic consequences for the use of endocardial and epicardial cre-mouse models in studies of heart development.

Electrotonic coupling of excitable and nonexcitable cells in the heart revealed by optogenetics

“…Cell typespecific expression of VSFP2.3 (19) was achieved by Cre-lox recombination using FLEX, which allowed for the required levels of cell specificity by preventing offtarget expression, with αMHC for targeting expression to cardiomyocytes (20) or WT1 for targeting expression to nonmyocytes (21). Adult WT1;VSFP2.3 +;+ and WT1;VSFP2.3 +;− mice were subjected to sham operation (n = 4 WT1;VSFP2.3 +;+ mice, n = 2 WT1;VSFP2.3 +;− mice) or standardized LV epicardial cryoinjury (n = 4 WT1;VSFP2.3 +;+ mice, n = 3 WT1;VSFP2.3 +;− mice) to generate a nontransmural…”

Congenital Heart Disease: In Search of Remedial Etiologies

“…5.2), binding to integrin receptors triggers integrin-dependent, downstream signaling kinases/ GTPases (FAK/AKT/PI3k) which activate effector mechanisms of growth, survival, and differentiation into the fibrous structures (valves and septa) that assure coordinated and unidirectional blood flow through the right and left sides of the developing heart. Epicardial-derived mesenchymal cells also express periostin as they invade the ventricular myocardium and, like endothelial-derived mesenchyme, secrete collagen and differentiate into ventricular connective tissue but also contribute to the parietal leaflets of the AV valves [7,8]. Disruption of these signaling pathways by either silencing one or more of the kinases shown in Fig.…”

Casz1 is required for cardiomyocyte G1-to-S phase progression during mammalian cardiac development

“…Wt1/IRES/GFP-Cre mice were previously reported (Wessels et al, 2012). Time-mated females were harvested at E14.5 and processed for immunostaining with anti-GFP as detailed above.…”