VEGF signaling has distinct spatiotemporal roles during heart valve development

Abstract

Heart valve malformations are one of the most common types of birth defects, illustrating the complex nature of valve development. Vascular endothelial growth factor (VEGF) signaling is one pathway implicated in valve formation, however its specific spatial and temporal roles remain poorly defined. To decipher these contributions, we use two inducible dominant negative approaches in mice to disrupt VEGF signaling at different stages of embryogenesis. At an early step in valve development, VEGF signals are required for the full transformation of endocardial cells to mesenchymal cells (EMT) at the outflow tract (OFT) but not atrioventricular canal (AVC) endocardial cushions. This role likely involves signaling mediated by VEGF receptor 1 (VEGFR1), which is highly expressed in early cushion endocardium before becoming downregulated after EMT. In contrast, VEGFR2 does not exhibit robust cushion endocardium expression until after EMT is complete. At this point, VEGF signaling acts through VEGFR2 to direct the morphogenesis of the AVC cushions into mature, elongated valve leaflets. This latter role of VEGF requires the VEGF-modulating microRNA, miR-126. Thus, VEGF roles in the developing valves are dynamic, transitioning from a differentiation role directed by VEGFR1 in the OFT to a morphogenetic role through VEGFR2 primarily in the AVC-derived valves.

A Maternally Sequestered, Biopolymer‐Stabilized Vascular Endothelial Growth Factor (VEGF) Chimera for Treatment of Preeclampsia

“…Thus, it is imperative that any potential therapy guarantee that fetal exposure to the drug be minimized and that fetal health is not endangered by maternal therapy. This directive applies especially to VEGF supplementation in the gravid female because of a myriad of adverse fetal effects from VEGF overexposure that have been observed in animal models 81, 82, 83, 84, 85, 86. Previous studies using free VEGF‐A isoforms, including VEGF‐A 165 87, 88, 89 and VEGF‐A 121 ,36, 64, 90, 91 have demonstrated therapeutic efficacy in treating the maternal syndrome of preeclampsia.…”

Valve Interstitial Cells Act in a Pericyte Manner Promoting Angiogensis and Invasion by Valve Endothelial Cells

“…13 NOTCH is the expected ligand for the DLL4 receptor, and there is a reported role for NOTCH signaling in VEC-VEC signaling, VIC-induced calcification, and valvulogenesis. 5,30 However, it is unclear if the same downstream pathways previously related to calcification and NOTCH are at play in this model. Further studies are needed to examine whether sustained angiogenic signaling leads towards valve calcification through angiogenetic-related cell-cell contact NOTCH inhibition.…”

“…Pericytes guide vessel formation through paracrine and direct contact signaling mechanisms, several of which have been investigated in regards to valve cells. 8,9,25,30,37 Despite the evidence for a subpopulation of cells in calcified valves that have pericyte-like characteristics, 35 VIC-endothelial cell studies to date have yet to induce quantifiable pericyte-mimicking behavior.…”

Etiology of Valvular Heart Disease

“…8 The mechanisms of elongation are unclear, but cell proliferation is localized to the distal tips of developing valves, and VEGF has been suggested to play a role. 7,17, 38 As the primordia develop, mesenchymal cells within the developing valves proliferate less and lose expression of mesenchymal markers but maintain smooth muscle α-actin (SMA) expression, suggesting a VIC-like phenotype. These embryonic VICs actively remodel the ECM by expressing matrix degradation enzymes to break down the hyaluronan, and secrete new ECM that that will later form the 3 stratified layers.…”