Osteocalcin


Osteocalcin, also known as bone gamma-carboxyglutamic acid-containing protein, is a small noncollagenous protein hormone found in bone and dentin, first identified as a calcium-binding protein in chick bone.
Because osteocalcin has gla domains, its synthesis is vitamin K dependent. In humans, osteocalcin is encoded by the BGLAP gene. Its receptors include GPRC6A, GPR158, and possibly a third, yet-to-be-identified receptor.

Function

Osteocalcin is secreted solely by osteoblasts and thought to play a role in the body's metabolic regulation. In its carboxylated form it binds calcium directly and thus concentrates in bone.
In its uncarboxylated form, osteocalcin acts as a hormone in the body, signalling in the pancreas, fat, muscle, testes, and brain.
An acute stress response, colloquially known as the fight-or-flight response, stimulates osteocalcin release from bone within minutes in mice, rats, and humans. Injections of high levels of osteocalcin alone can trigger an ASR in the presence of adrenal insufficiency.

Use as a biochemical marker for bone formation

As osteocalcin is produced by osteoblasts, it is often used as a marker for the bone formation process. It has been observed that higher serum osteocalcin levels are relatively well correlated with increases in bone mineral density during treatment with anabolic bone formation drugs for osteoporosis, such as teriparatide. In many studies, osteocalcin is used as a preliminary biomarker on the effectiveness of a given drug on bone formation. For instance, one study which aimed to study the effectiveness of a glycoprotein called lactoferrin on bone formation used osteocalcin as a measure of osteoblast activity.