Abstract 278: Developmental Contractile Function Modulates Notch1b-Mediated Valvular Leaflet Development

Abstract

Cardiac valve formation is a complex process affected by blood flow, but the mechanotransduction mechanisms underlying valvulogenesis remain incompletely understood. Using four-dimensional (4-D) light-sheet imaging, we evaluated the effects of pharmacological and genetic hemodynamic modulation on ventriculobulbar (VB) valve formation in the outflow tracts (OFT) of transgenic Tg(fli1a:GFP) zebrafish embryos. Treatment with isoproterenol increased heart rate and cardiac contractility, increased Notch1b activity in the OFT, and resulted in the development of hyperplastic VB valve leaflets. While metoprolol treatment reduced heart rate without affecting contractility, there were no significant differences in Notch1b expression in the OFT or valve morphology. Meanwhile, BDM treatment significantly reduced heart rate and contractility, reduced Notch1b expression in the OFT, and prevented the formation of normal VB valve leaflets. Similarly, no VB valve leaflets were seen in the cloche mutant or Tnnt2a MO-injected embryos. Additionally, increasing blood viscosity by micro-injection of embryos with EPO mRNA increased Notch1b activity in the OFT and led to hyperplastic VB valve leaflets, but decreasing blood viscosity by gata1a MO micro-injection did not have any significant effect. Further, activation of the Notch signaling pathway with micro-injection of NICD mRNA resulted in hyperplastic VB valve leaflets. By integrating advanced optics with zebrafish genetics at the interface of developmental cardiac mechanics, we provide mechanotransduction insights into cardiac valve development within the OFT.