A four-season molecule: osteocalcin. Updates in its physiological roles

Area of Science:

• Biochemistry
• Endocrinology
• Bone Biology

Background:

• Osteocalcin (OC) is a key non-collagenous protein synthesized by bone cells.
• It plays a crucial role in bone mineralization and serves as a marker for bone cell metabolism.
• Emerging evidence highlights significant extra-skeletal functions, positioning OC as a potential hormone.

Purpose of the Study:

• To provide a comprehensive overview of osteocalcin's physiological roles.
• To synthesize recent experimental findings on osteocalcin's functions.
• To explore osteocalcin's hormonal characteristics and regulatory mechanisms.

Main Methods:

• Literature review of recent experimental findings on osteocalcin.
• Analysis of osteocalcin's structure-function relationship, particularly carboxylation.
• Examination of osteocalcin's involvement in endocrine and physiological processes.

Main Results:

• Osteocalcin exhibits hormonal features like tissue-specific expression and circadian rhythm.
• The degree of glutamic acid carboxylation in OC modulates its affinity for calcium ions.
• Carboxylation potentially controls circulating OC levels and its hormonal function.
• Evidence links OC to glucose metabolism, energy balance, fertility, muscle activity, and ectopic calcification.

Conclusions:

• Osteocalcin is a unique molecule with both skeletal and endocrine functions.
• Its carboxylation status is a critical determinant of its biological activity.
• Further research into osteocalcin's hormonal roles is warranted to understand its full physiological and pathological implications.