Endothelial ZEB1 promotes angiogenesis-dependent bone formation and reverses osteoporosis.

Recent interest in the control of bone metabolism has focused on a specialized subset of CD31^hiendomucin^hi vessels, which are reported to couple angiogenesis with osteogenesis. However, the underlying mechanisms that link these processes together remain largely undefined. Here we show that the zinc-finger transcription factor ZEB1 is predominantly expressed in CD31^hiendomucin^hi endothelium in human and mouse bone. Endothelial cell-specific deletion of ZEB1 in mice impairs CD31^hiendomucin^hi vessel formation in the bone, resulting in reduced osteogenesis. Mechanistically, ZEB1 deletion reduces histone acetylation on Dll4 and Notch1 promoters, thereby epigenetically suppressing Notch signaling, a critical pathway that controls bone angiogenesis and osteogenesis. ZEB1 expression in skeletal endothelium declines in osteoporotic mice and humans. Administration of Zeb1-packaged liposomes in osteoporotic mice restores impaired Notch activity in skeletal endothelium, thereby promoting angiogenesis-dependent osteogenesis and ameliorating bone loss. Pharmacological reversal of the low ZEB1/Notch signaling may exert therapeutic benefit in osteoporotic patients by promoting angiogenesis-dependent bone formation. An endothelial cell subtype, expressing endomucin and CD31, has been reported to couple angiogenesis with osteogenesis. Here, the authors show that loss of ZEB1 in these cells epigenetically suppresses Notch signaling, leading to impaired angiogenesis and osteogenesis, and that Zeb1 delivery via liposomes ameliorates bone loss in osteoporotic mice [ABSTRACT FROM AUTHOR]