Osteopontin'Osteopontin' (OPN), also known as bone /sialoprotein I (BSP-1 or BNSP), early T-lymphocyte activation (ETA-1), secreted phosphoprotein 1 (SPP1), 2ar and Rickettsia resistance (Ric), is a protein that in humans is encoded by the SPP1 gene (secreted phosphoprotein 1). The murine ortholog is Spp1. Osteopontin is a SIBLING (glycoprotein) that was first identified in 1986 in osteoblasts. The prefix osteo- indicates that the protein is expressed in bone, although it is also expressed in other tissues.
OsteoclastAn osteoclast () is a type of bone cell that breaks down bone tissue. This function is critical in the maintenance, repair, and remodeling of bones of the vertebral skeleton. The osteoclast disassembles and digests the composite of hydrated protein and mineral at a molecular level by secreting acid and a collagenase, a process known as bone resorption. This process also helps regulate the level of blood calcium. Osteoclasts are found on those surfaces of bone that are undergoing resorption.
