Specialized post-arterial capillaries facilitate adult bone remodelling.

The vasculature of the skeletal system is crucial for bone formation, homoeostasis and fracture repair, yet the diversity and specialization of bone-associated vessels remain poorly understood. Here we identify a specialized type of post-arterial capillary, termed type R, involved in bone remodelling. Type R capillaries emerge during adolescence around trabecular bone, possess a distinct morphology and molecular profile, and are associated with osteoprogenitors and bone-resorbing osteoclasts.

Angiogenesis is uncoupled from osteogenesis during calvarial bone regeneration.

Bone regeneration requires a well-orchestrated cellular and molecular response including robust vascularization and recruitment of mesenchymal and osteogenic cells. In femoral fractures, angiogenesis and osteogenesis are closely coupled during the complex healing process. Here, we show with advanced longitudinal intravital multiphoton microscopy that early vascular sprouting is not directly coupled to osteoprogenitor invasion during calvarial bone regeneration.

YAP1 and TAZ negatively control bone angiogenesis by limiting hypoxia-inducible factor signaling in endothelial cells.

Blood vessels are integrated into different organ environments with distinct properties and physiology (Augustin and Koh, 2017). A striking example of organ-specific specialization is the bone vasculature where certain molecular signals yield the opposite effect as in other tissues (Glomski et al., 2011; Kusumbe et al.

Parathyroid hormone-induced down-regulation of miR-532-5p for matrix metalloproteinase-13 expression in rat osteoblasts.

Parathyroid hormone (PTH) acts on osteoblasts and functions as an essential regulator of calcium homeostasis and as a mediator of bone remodeling. We previously reported that PTH stimulates the expression of matrix metalloproteinase-13 (MMP-13) in rat osteoblasts and that MMP-13 plays a key role in bone remodeling, endochondral bone formation, and bone repair. Recent evidence indicated that microRNAs (miRNAs) have regulatory functions in bone metabolism.

Regulation of Runx2 by Histone Deacetylases in Bone.

Osteogenesis involves a cascade of processes wherein mesenchymal stem cells differentiate towards osteoblasts, strictly controlled by a number of regulatory factors. Runx2 protein is a key transcription factor which serves as a master regulator for osteogenesis by activating the promoters of various osteoblastic genes. Runx2 is regulated by several cofactors, including the histone deacetylase enzymes known as HDACs.