Effects of Bone Matrix Components on Osteoclast Differentiation

When implanted subcutaneously in rats, devitalized bone particles (BP) elicit the differentiation of osteoclastic cells. Those cells can be distinguished from foreign body giant cells that form in response to particulate plastics. Osteoclast features include resorption of the bone substrate, ruffled borders, calcitonin receptors, tartrate-resistant acid phosphatase activity, and modulation by bone active agents. To determine whether expression of these features depends on specific components of the matrix, we characterized the multinucleated cells that developed in response to osteocalcin-deficient BPs, particulate microcrystalline hydroxyapatite (HA), and HA containing 0.1% osteocalcin, collagen, or bovine serum albumin. Only those particles that contained mineral and osteocalcin were associated with osteoclastic cells. These studies support the hypothesis that osteocalcin may function as a matrix signal in the differentiation of osteoclasts.