endosteumin

Endosteumin is a protein that has been identified in the bone extracellular matrix and is thought to play a role in bone remodeling and mineralization. It is encoded by the ENDOST gene located on chromosome 13 in humans, and the gene produces a 260‑amino‑acid polypeptide that contains a N‑terminal signal peptide for secretion and several glycine‑rich repeats that facilitate interaction with collagen fibers. Endosteumin is predominantly expressed by osteocytes and osteoblasts, with expression levels that increase during periods of active bone formation such as fracture repair and skeletal development.

The protein binds calcium ions and has been shown to associate with type I collagen and osteopontin, suggesting a structural role in the bone matrix. In vitro studies have indicated that endosteumin can enhance mineral deposition by osteoblasts and may act as a signaling molecule that modulates the activity of bone‑resorbing osteoclasts. To date, only a small number of clinical studies have examined serum levels of endosteumin in patients with bone disorders; preliminary data suggest that higher circulating concentrations may be associated with increased bone turnover in osteoporosis, although the causal relationship remains unclear.

Research into endosteumin is ongoing, with particular interest in its potential as a biomarker for bone metabolic activity and as a therapeutic target for enhancing bone healing or counteracting bone loss. Because secretion patterns differ between healthy bone and disease states, future studies aim to clarify the regulatory mechanisms that control ENDOST transcription and to determine whether pharmacological modulation of endosteumin could benefit patients with fractures, osteopenia, or metabolic bone diseases.