Endothelial Notch activity promotes angiogenesis and osteogenesis in bone

Abstract

Blood vessel growth in the skeletal system and osteogenesis appear coupled suggesting the existence of molecular crosstalk between endothelial and osteoblastic cells1,2. Understanding the nature of the mechanisms linking angiogenesis and bone formation should be of great relevance for improved fracture healing or prevention of bone mass loss. Here, we show that vascular growth in bone involves a specialised, tissue-specific form of angiogenesis. Notch signalling promotes endothelial cell proliferation and vessel growth in postnatal long bone, which is the opposite of the well-established function of Notch and its ligand Dll4 in the endothelium of other organs and tumours3,4. Endothelial cell-specific and inducible genetic disruption of Notch signalling in mice not only impaired bone vessel morphology and growth, but also led to reduced osteogenesis, shortening of long bones, chondrocyte defects, loss of trabeculae, and decreased bone mass. Based on a series of genetic experiments, we conclude that skeletal defects in these mutants involved defective angiocrine release of Noggin from endothelial cells, which is positively regulated by Notch. Administration of recombinant Noggin, a secreted antagonist of bone morphogenetic proteins, restored bone growth and mineralisation, chondrocyte maturation, the formation of trabeculae, and osteoprogenitor numbers in endothelial cell-specific Notch pathway mutants. These findings establish a molecular framework coupling angiogenesis, angiocrine signals and osteogenesis, which may prove significant for the development of future therapeutic applications. KeywordsBone formation; endothelial cells; Notch; Dll4; Noggin Dye injection and corrosion cast experiments had indicated that metaphyseal vessels in growing long bone are arranged in parallel, columnar strands with distal anastomotic interconnections5,6. Improved bone processing and immunostaining (see Methods) now

Confocal/two-photon microscopy in studying colonisation of cancer cells in bone using xenograft mouse models

“…We have recently revised and improved the bone processing strategy, which involves short decalcification, and thick bone sectioning combined with high resolution confocal microscopy. [12][13][14] Here, we report this advanced methodology in a stepwise manner that will provide a platform to close several major knowledge gaps and will therefore greatly facilitate future analyses focusing on the bone marrow. In this procedure, freshly isolated bone tissue is fixed immediately using a 4% paraformaldehyde solution for 4 h at room temperature.…”

“…This technical advance led to the identification of a specialised blood vessel subtype (namely type H) in bone, which forms a niche for osteoprogenitors and thereby regulates bone formation. [12][13][14] The principle of the two-photon effect was proposed in 1930s by Maria Gö ppert-Mayer and confirmed in 1961 by Kaiser. 15 During conventional excitation using confocal microscopy, a fluorescent molecule absorbs a single excitation photon with higher energy level and shorter wavelength than emission.…”

PDGFB-based stem cell gene therapy increases bone strength in the mouse

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Local delivery of tetramethylpyrazine eliminates the senescent phenotype of bone marrow mesenchymal stromal cells and creates an anti‐inflammatory and angiogenic environment in aging mice

“…defined the H‐type vessel, which exhibits distinct molecular properties and is strongly positive for the endothelial cell surface markers CD31 and Emcn (CD31 hi Emcn hi ) as assessed by immunofluorescence staining and which is diminished during aging (Kusumbe et al., 2014). Additionally, the H‐type vessel modulates local microenvironments in the skeletal system, plays crucial roles in osteogenesis and provides niches for haematopoietic stem cells (Cui et al., 2016; Ramasamy, Kusumbe, Wang, & Adams, 2014). Interestingly, we sorted CD31 hi Emcn hi endothelial cells in the bone marrow of aging mice via flow cytometry and showed that TMP directly induced H‐type vessel formation in CD31 hi Emcn hi endothelial cells via the AMPK‐mTOR‐Hif1α‐VEGF pathway and promoted anti‐inflammatory factor upregulation in aging bone marrow.…”