Perspective on the osteoclast: an angiogenic cell?

There have been reports recently that the osteoclast stimulates angiogenesis in vitro. We review the evidence suggesting that the osteoclast directly stimulates angiogenesis, and discuss the feasibility of the hypothesis that the osteoclast can be a proangiogenic cell. Reasons supporting the feasibility of this hypothesis include proangiogenic factors produced by osteoclasts, the angiogenic effects of macrophages, the antiangiogenic effects of nitrogen containing bisphosphonates, and the physical proximity of osteoclasts to endothelial cells.