Search for macrophage-derved factors related to angiogenesis and wound healing

Macrophages are progenitors of osteoclasts, but macrophages themselves also regulates bone metabolism. Macrophages mediate not only bone formation by osteoblasts in physiological conditions, but also regeneration after fracture. However, the mechanisms how macrophages control bone formation and regeneration remain unclear. Here we demonstrate that liposome-encapsulated Clodronate (Clod-lip) model with targeted depletion of phagocytic macrophages exhibits impaired angiogenesis of type H vessels, which couple angiogenesis and osteogenesis, in mouse cortical bone defect model by drill-hole injury. Additionaly, we identify Tgfbi (encoding TGF, beta-induced protein), Plau (encoding uPA), and Tgfb1 (encoding TGF-ß1) as genes of macrophage-secreted factors mediating angiogenesis and wound healing by RNA-seq analysis. These mRNAs were highly expressed in bone marrow-derived macrophages among bone cells by qRT-PCR. Finally, we show that treatment with uPA inhibitor or TGF-ß Receptor I, Receptor II inhibitor impaired bone regeneration after injury, confirming importance of uPA and TGF-ß1 for bone repair. Therefore, we proposed that these factors may be potential for therapeutic targets for delayed union, or non-union patients. Our findings reveal a novel mechanism of bone regeneration mediated by macrophages. Overall design: Repair tissue mRNA profiles of Empty-lip or Clod-lip injected mice