Bone Morphogenetic Proteins Stimulate Angiogenesis through Osteoblast-Derived Vascular Endothelial Growth Factor A

Abstract

During bone formation and fracture healing there is a cross-talk between endothelial cells and osteoblasts. We previously showed that vascular endothelial growth factor A (VEGF-A) might be an important factor in this cross-talk, as osteoblast-like cells produce this angiogenic factor in a differentiation-dependent manner. Moreover, exogenously added VEGF-A enhances osteoblast differentiation. In the present study we investigated, given the coupling between angiogenesis and bone formation, whether bone morphogenetic proteins (BMPs) stimulate osteoblastogenesis and angiogenesis through the production of VEGF-A. For this we used the murine preosteoblast-like cell line KS483, which forms mineralized nodules in vitro, and an angiogenesis assay comprising 17-d-old fetal mouse bone explants that have the ability to form tube-like structures in vitro. Treatment of KS483 cells with BMP-2, -4, and -6 enhanced nodule formation, osteocalcin mRNA expression, and subsequent mineralization after 18 d of culture. This was accompanied by a dose-dependent increase in VEGF-A protein levels throughout the culture period. BMP-induced osteoblast differentiation, however, was independent of VEGF-A, as blocking VEGF-A activity by a VEGF-A antibody or a VEGF receptor 2 tyrosine kinase inhibitor did not affect BMP-induced mineralization. To investigate whether BMPs stimulate angiogenesis through VEGF-A, BMPs were assayed for their angiogenic activity. Treatment of bone explants with BMPs enhanced angiogenesis. This was inhibited by soluble BMP receptor 1A or noggin. In the presence of a VEGF-A antibody, both unstimulated and BMP-stimulated angiogenesis were arrested. Conditioned media of KS483 cells treated with BMPs also induced a strong angiogenic response, which was blocked by antimouse VEGF-A but not by noggin. These effects were specific for BMPs, as TGF beta inhibited osteoblast differentiation and angiogenesis while stimulating VEGF-A production. These findings indicate that BMPs stimulate angiogenesis through the production of VEGF-A by osteoblasts. In conclusion, VEGF-A produced by osteoblasts in response to BMPs is not involved in osteoblast differentiation, but couples angiogenesis to bone formation.

Human postnatal dental pulp cells co-differentiate into osteoblasts and endotheliocytes: a pivotal synergy leading to adult bone tissue formation

“…The formation of vessels explains the vitality of bone chips when transplanted in immunosuppressed rats. 5,6 Figure 3 flk-1 þ exerts a pivotal role in coupling osteoblast and endotheliocyte differentiation, as previously hypothesized [21][22][23] and the intimate relationship and interplay between endotheliocytes and osteoblasts is the key to obtain complete differentiation and formation of mature bone.…”

Induced membranes secrete growth factors including vascular and osteoinductive factors and could stimulate bone regeneration

“…The variations of osteoinductive activity of rhBMP-2 observed within the sites could be due to differences in the blood supply [14]. Moreover, VEGF-A produced by osteoblasts in response to BMPs is not involved in osteoblast differentiation, but couples angiogenesis to bone formation [4]. In the model presented here, the membrane seems able to secrete the growth factor, which could act sequentially to provide adequate vascularization and then bone formation.…”

Genes for systemic vascular complications are differentially expressed in the livers of Type 2 diabetic patients

“…One member of the TGF superfamily, TGF-β, plays a critical role in angiogenesis [2], and also mediates expression of angiogenic factors such as VEGF [3], which we also found to be up-regulated in livers of diabetic patients. Another member, BMP-4, was recently found to stimulate VEGF synthesis [17,18]. In development, VEGF acts upstream of the Notch pathway to determine arterial cell fate [19].…”