osteopontine

Osteopontin is a highly conserved, extracellular matrix glycoprotein that plays diverse roles in cellular processes, particularly in bone metabolism, immune responses, and tissue remodeling. Initially identified in bone tissue, it is now recognized as a multifunctional protein expressed in various cell types, including osteoblasts, immune cells, and epithelial cells. The protein consists of approximately 300 amino acids and contains a conserved sequence known as the "acidic calcium-binding domain," which facilitates its binding to hydroxyapatite crystals in bone.

Osteopontin is encoded by the *SPP1* gene in humans and is secreted as a soluble protein or incorporated into the extracellular matrix. Its primary functions include promoting cell adhesion, migration, and survival, as well as modulating inflammatory and immune responses. In bone, osteopontin interacts with integrins and other receptors to regulate osteoblast and osteoclast activity, influencing bone resorption and formation. It also serves as a marker for bone turnover and has been implicated in pathological conditions such as osteoporosis, arthritis, and cancer metastasis.

Beyond skeletal biology, osteopontin is involved in wound healing, fibrosis, and autoimmune diseases. Its expression is upregulated in response to inflammatory signals, where it can modulate cytokine production and immune cell activation. Additionally, osteopontin has been linked to renal stone formation and cardiovascular diseases, highlighting its broad physiological significance. Research continues to explore its potential as a therapeutic target in various disorders, including autoimmune and neoplastic diseases.