Ophiopogonin D promotes bone regeneration by stimulating CD31^hi EMCN^hi vessel formation

CD31^hi EMCN^hi vessels (CD31, also known as PECAM1 [platelet and endothelial cell adhesion molecule 1]; EMCN, endomucin), which are strongly positive for CD31 and endomucin, couple angiogenesis and osteogenesis. However, the role of CD31^hi EMCN^hi vessels in bone regeneration remains unknown. In the present study, we investigated the role of CD31^hi EMCN^hi vessels in the process of bone regeneration.

We used endothelial-specific Krüppel like factor 3 (Klf3) knockout mice and ophiopogonin D treatment to interfere with CD31^hi EMCN^hi vessel formation. We constructed a bone regeneration model by surgical ablation of the trabecular bone. Immunofluorescence and micro-computed tomography (CT) were used to detect CD31^hi EMCN^hi vessels and bone formation.

CD31^hi EMCN^hi vessels participate in the process of bone regeneration, such that endothelial-specific Klf3 knockout mice showed increased CD31^hi EMCN^hi vessels and osteoprogenitors in the bone regeneration area, and further accelerated bone formation. We also demonstrated that the natural compound, ophiopogonin D, acts as a KLF3 inhibitor to promote vessels formation both in vitro and in vivo. Administration of ophiopogonin D increased the abundance of CD31^hi Emcn^hi vessels and accelerated bone healing.

Our findings confirmed the important role of CD31^hi Emcn^hi vessels in bone regeneration and provided a new target to treat bone fracture or promote bone regeneration.