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The circadian modulation of leptin-controlled bone formation.
Loning Fu1, Millan S Patel, Gerard Karsenty
1Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, USA.
Progress in Brain Research
|August 1, 2006
Summary
Mutations in circadian genes Period and Cryptochrome lead to high bone mass in mice by disrupting leptin-regulated pathways that control osteoblast activity and bone formation. The molecular clock is crucial for regulating bone development.
Area of Science:
- Molecular biology
- Endocrinology
- Bone biology
Background:
- Circadian genes, including Period and Cryptochrome, are known regulators of biological rhythms.
- Leptin signaling influences bone formation through the sympathetic nervous system.
- Disruptions in circadian rhythms can impact metabolic processes and bone health.
Purpose of the Study:
- To investigate the role of the molecular clock in leptin-mediated regulation of bone formation.
- To elucidate the mechanisms by which circadian gene mutations affect bone mass.
- To understand the interplay between leptin signaling, circadian genes, and osteoblast activity.
Main Methods:
- Utilizing mouse models with mutations in Period and Cryptochrome genes.
- Assessing bone mass and osteoblast numbers in mutant mice.
- Investigating the effects of leptin intracerebroventricular infusion.
- Analyzing the expression of AP1, circadian genes, and c-myc in bone and osteoblasts.
Main Results:
- Mice with Period and Cryptochrome mutations exhibit high bone mass and increased osteoblast numbers.
- Leptin intracerebroventricular infusion did not correct the high bone mass phenotype.
- Leptin-dependent sympathetic signaling regulates AP1 and circadian gene expression in bone.
- Mutations in Period 1 and 2 genes lead to uncontrolled c-myc signaling and increased osteoblast proliferation.
Conclusions:
- The molecular clock plays a critical role in leptin-mediated sympathetic regulation of bone formation.
- Leptin-dependent sympathetic signaling modulates bone formation via two antagonistic pathways involving AP1 and circadian genes.
- Disruption of circadian genes results in dysregulated osteoblast proliferation and enhanced bone formation.