ABSTRACT
Vascular mural cells (vMCs) are essential components of the vertebrate vascular system, controlling blood vessel maturation and homeostasis. Discrete molecular mechanisms have been associated with vMC development and differentiation. The function of hemodynamic forces in controlling vMC recruitment is unclear. Using transgenic lines marking developing vMCs in zebrafish embryos, we find that vMCs are recruited by arterial-fated vessels and that the process is flow dependent. We take advantage of tissue-specific CRISPR gene targeting to demonstrate that hemodynamic-dependent Notch activation and the ensuing arterial genetic program is driven by endothelial primary cilia. We also identify zebrafish foxc1b as a cilia-dependent Notch-specific target that is required within endothelial cells to drive vMC recruitment. In summary, we have identified a hemodynamic-dependent mechanism in the developing vasculature that controls vMC recruitment.
Subject(s)
Cilia/metabolism , Endothelial Cells/metabolism , Forkhead Transcription Factors/metabolism , Zebrafish Proteins/metabolism , Animals , Animals, Genetically Modified/genetics , Animals, Genetically Modified/growth & development , Animals, Genetically Modified/metabolism , Blood Flow Velocity , Clustered Regularly Interspaced Short Palindromic Repeats/genetics , Embryo, Nonmammalian/cytology , Embryo, Nonmammalian/drug effects , Embryo, Nonmammalian/metabolism , Endothelial Cells/cytology , Forkhead Transcription Factors/genetics , Hemodynamics , Morpholinos/genetics , Morpholinos/metabolism , Quinazolinones/pharmacology , RNA Interference , Receptors, Notch/antagonists & inhibitors , Receptors, Notch/genetics , Receptors, Notch/metabolism , Shear Strength , Signal Transduction/drug effects , Troponin T/antagonists & inhibitors , Troponin T/genetics , Troponin T/metabolism , Zebrafish/growth & development , Zebrafish/metabolism , Zebrafish Proteins/antagonists & inhibitors , Zebrafish Proteins/geneticsABSTRACT
While blood vessels play important roles in bone homeostasis and repair, fundamental aspects of vascular function in the skeletal system remain poorly understood. Here we show that the long bone vasculature generates a peculiar flow pattern, which is important for proper angiogenesis. Intravital imaging reveals that vessel growth in murine long bone involves the extension and anastomotic fusion of endothelial buds. Impaired blood flow leads to defective angiogenesis and osteogenesis, and downregulation of Notch signalling in endothelial cells. In aged mice, skeletal blood flow and endothelial Notch activity are also reduced leading to decreased angiogenesis and osteogenesis, which is reverted by genetic reactivation of Notch. Blood flow and angiogenesis in aged mice are also enhanced on administration of bisphosphonate, a class of drugs frequently used for the treatment of osteoporosis. We propose that blood flow and endothelial Notch signalling are key factors controlling ageing processes in the skeletal system.
