Osteonectins

Osteonectins are a group of secreted extracellular matrix glycoproteins, with osteonectin (SPARC) as the best-known member. They are produced by osteoblasts and other cells and participate in bone formation and tissue remodeling. As matricellular proteins, they act more in signaling and regulation of cell–matrix interactions than as structural matrix components.

Proteins in the osteonectin family share modular architecture, typically including an acidic N-terminal region, a follistatin-like domain, and a C-terminal calcium-binding domain that can bind calcium and interact with collagen I and hydroxyapatite. This enables regulation of mineralization and matrix organization.

They modulate cell adhesion, migration, proliferation, and differentiation; regulate growth factor activity (for example TGF-β and FGF); influence angiogenesis and wound healing.

Osteonectins are expressed in bone and other tissues such as skin, vasculature, and cartilage, with expression patterns changing during development and in disease.

Altered osteonectin/SPARC expression has been linked to osteoporosis, osteoarthritis, fibrosis, and cancer progression; the proteins are studied as potential biomarkers and therapeutic targets in some contexts.

See also SPARC, SPARC family proteins.