YAP and TAZ couple osteoblast precursor mobilization to angiogenesis and mechanoregulated bone development

Abstract

Endochondral ossification requires coordinated mobilization of osteoblast precursors with blood vessels. During adult bone homeostasis, vessel adjacent osteoblast precursors respond to and are maintained by mechanical stimuli; however, the mechanisms by which these cells mobilize and respond to mechanical cues during embryonic development are unknown. Previously, we found that deletion of the mechanoresponsive transcriptional regulators, YAP and TAZ, from Osterix-expressing osteoblast precursors and their progeny caused perinatal lethality. Here, we show that embryonic YAP/TAZ signaling couples vessel-associated osteoblast precursor mobilization to angiogenesis in developing long bones. Osterix-conditional YAP/TAZ deletion impaired endochondral ossification in the primary ossification center but not intramembranous osteogenesis in the bone collar. Single-cell RNA sequencing revealed YAP/TAZ regulation of the angiogenic chemokine, Cxcl12, which was expressed uniquely in vessel-associated osteoblast precursors. YAP/TAZ signaling spatially coupled osteoblast precursors to blood vessels and regulated vascular morphogenesis and vessel barrier function. Further, YAP/TAZ signaling regulated vascular loop morphogenesis at the chondro-osseous junction to control hypertrophic growth plate remodeling. In human cells, mesenchymal stromal cell co-culture promoted 3D vascular network formation, which was impaired by stromal cell YAP/TAZ depletion, but rescued by recombinant CXCL12 treatment. Lastly, YAP and TAZ mediated mechanotransduction for load-induced osteogenesis in embryonic bone.

Cyr61 delivery promotes angiogenesis during bone fracture repair

“…Previously, we and others have established the mechanoresponsive transcriptional regulators, YAP and TAZ, as critical mediators of mechanobiology (19) of both neovascularization (40)(41)(42) and endochondral ossification (43) during bone development (14,15,18) and fracture repair (11,13). For example, conditional deletion of YAP and TAZ from Osx-expressing osteoblast-lineage cells impaired the comobilization of osteoprogenitors and blood vessels into the limb primary ossification center, disrupting vessel morphogenesis and vessel-mediated cartilage anlage remodeling (14).…”

“…Previously, we and others have established the mechanoresponsive transcriptional regulators, YAP and TAZ, as critical mediators of mechanobiology (19) of both neovascularization (40)(41)(42) and endochondral ossification (43) during bone development (14,15,18) and fracture repair (11,13). For example, conditional deletion of YAP and TAZ from Osx-expressing osteoblast-lineage cells impaired the comobilization of osteoprogenitors and blood vessels into the limb primary ossification center, disrupting vessel morphogenesis and vessel-mediated cartilage anlage remodeling (14). Further, using a fracture healing model (intramedullary pin fixation) that allows large interfragmentary strains and heals via endochondral ossification, we found that Osx-conditional YAP/TAZ deletion impaired vascularized fracture healing by regulating periosteal progenitor cell proliferation, osteoblastic differentiation, and osteogenic-angiogenic coupling, coincident with reduced Cyr61 expression (13).…”

“…HUVECs were starved with EGM with 0.1% v/v FBS 12h prior to the begin of the experiment. For 3D construct formation, HUVECs and hMSCs were detached from the culture flasks independently washed with PBS and mixed at a concentration of 4:1 in the liquid GelMA/fibrin hydrogel already containing thrombin (14,56). The hydrogel/cell mixture was immediately transferred into a disc sized, silicone mold with a diameter of 6 mm and a thickness of 2 mm (capacity for 50 microL).…”

“…Further, we found that these mechanical cues directly regulate neovascularization during bone regeneration (10)(11)(12). Mechanistically, we identified the transcriptional regulator Yes-associated protein (YAP) and transcriptional co-activator with PDZ-binding motif (TAZ) as key mechano-transducers during fracture repair (13), bone development (14,15) and angiogenesis (12,16). However, YAP and TAZ are oncogenes (17), suggesting that targeted activation of YAP/TAZ themselves would not be a feasible therapeutic for bone repair.…”

Endothelial SMAD1/5 signaling couples angiogenesis to osteogenesis in juvenile bone

“…The development of the skeleton depends on spatiotemporally coordinated blood vessel morphogenesis and bone formation [1][2][3] . In development, multicellular patterning is coordinated by morphogens 4 .…”