Leptin regulation of bone resorption by the sympathetic nervous system and CART.

Elefteriou F, Ahn JD, Takeda S, Starbuck M, Yang X, Liu X, Kondo H, Richards WG, Bannon TW, Noda M, Clement K, Vaisse C, Karsenty G
Nature. 2005 434 (7032): 514-20

PMID: 15724149 · DOI:10.1038/nature03398

Bone remodelling, the mechanism by which vertebrates regulate bone mass, comprises two phases, namely resorption by osteoclasts and formation by osteoblasts; osteoblasts are multifunctional cells also controlling osteoclast differentiation. Sympathetic signalling via beta2-adrenergic receptors (Adrb2) present on osteoblasts controls bone formation downstream of leptin. Here we show, by analysing Adrb2-deficient mice, that the sympathetic nervous system favours bone resorption by increasing expression in osteoblast progenitor cells of the osteoclast differentiation factor Rankl. This sympathetic function requires phosphorylation (by protein kinase A) of ATF4, a cell-specific CREB-related transcription factor essential for osteoblast differentiation and function. That bone resorption cannot increase in gonadectomized Adrb2-deficient mice highlights the biological importance of this regulation, but also contrasts sharply with the increase in bone resorption characterizing another hypogonadic mouse with low sympathetic tone, the ob/ob mouse. This discrepancy is explained, in part, by the fact that CART ('cocaine amphetamine regulated transcript'), a neuropeptide whose expression is controlled by leptin and nearly abolished in ob/ob mice, inhibits bone resorption by modulating Rankl expression. Our study establishes that leptin-regulated neural pathways control both aspects of bone remodelling, and demonstrates that integrity of sympathetic signalling is necessary for the increase in bone resorption caused by gonadal failure.

MeSH Terms (29)

Activating Transcription Factor 4 Amino Acid Sequence Animals Bone Resorption Carrier Proteins Cell Line Child Child, Preschool Cyclic AMP-Dependent Protein Kinases Gene Deletion Humans Leptin Male Membrane Glycoproteins Mice Models, Neurological Neoplasm Proteins Nerve Tissue Proteins Osteoblasts Osteogenesis RANK Ligand Receptor, Melanocortin, Type 4 Receptor Activator of Nuclear Factor-kappa B Receptors, Adrenergic, beta-2 Receptors, Leptin Response Elements Signal Transduction Sympathetic Nervous System Transcription Factors

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