Expression of an N-Methyl-D-Aspartate-Type Receptor by Human and Rat Osteoblasts and Osteoclasts Suggests a Novel Glutamate Signaling Pathway in Bone

Signaling between the various types of cells found in bone is responsible for controlling the activity of osteoblasts and osteoclasts, and therefore the regulation of bone mass. Our identification of a neuronal glutamate transporter in osteoblasts and osteocytes suggests the possibility that bone cells may use the excitatory amino acid glutamate as a signaling molecule. In these studies we report the expression of different subtypes of glutamate receptors in osteoblasts and osteoclasts in vitro and in vivo. We have identified expression in human and rat bone cells of N-methyl-D-aspartate receptor-1 (NMDAR-1) and 2D subunits and PSD-95, the NMDA receptor clustering protein associated with signaling in the central nervous system. In situ hybridization and immunohistochemistry localized NMDAR-1 expression to osteoblasts and osteoclasts in human tissue sections. These findings strengthen the suggestion that glutamate is involved in signaling between bone cells.