Serum leptin level is a regulator of bone mass

Area of Science:

• Endocrinology
• Bone Biology
• Neuroendocrinology

Background:

• Leptin is known to inhibit bone formation (antiosteogenic function) in vivo.
• This function is mediated through leptin receptors on hypothalamic neurons and beta-adrenergic receptors on osteoblasts.
• The precise mechanisms by which leptin regulates antiosteogenic neurons remain unclear.

Purpose of the Study:

• To investigate the mechanisms of leptin's antiosteogenic function.
• To compare leptin's regulation of body weight and bone mass.
• To determine if leptin is synthesized in the central nervous system and its role as an adipocyte product.

Main Methods:

• Compared leptin's effects on body weight and bone mass.
• Utilized knock-in mice (LacZ in leptin locus) to assess central nervous system leptin synthesis.
• Manipulated serum leptin levels by increasing leptin or overexpressing a soluble leptin receptor.
• Studied lipodystrophic mice and patients with altered body fat and leptin levels.

Main Results:

• Leptin's anorexigenic and antiosteogenic functions are sensitive to similar leptin concentrations.
• No leptin synthesis was detected in the central nervous system.
• Elevated serum leptin reduced bone mass; reduced serum-free leptin increased bone mass.
• Restoring leptin levels corrected the high bone mass phenotype in lipodystrophic mice.
• Lipodystrophic patients exhibited advanced bone age, suggesting premature bone formation.

Conclusions:

• Circulating leptin, derived from adipocytes, is a critical determinant of bone formation.
• Leptin's role in regulating bone mass is both necessary and sufficient.
• The antiosteogenic function of leptin is conserved across vertebrate species.