Skeletal parasympathetic innervation communicates central IL-1 signals regulating bone mass accrual

Alon Bajayo, Arik Bar, Adam Denes, Marilyn Bachar, Vardit Kram, Malka Attar-Namdar, Alberta Zallone, Krisztina J. Kovács, Raz Yirmiya, Itai Bab*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

133 Scopus citations

Abstract

Bone mass accrual is a major determinant of skeletal mass, governed by bone remodeling, which consists of bone resorption by osteoclasts and bone formation by osteoblasts. Bone mass accrual is inhibited by sympathetic signaling centrally regulated through activation of receptors for serotonin, leptin, and ACh. However, skeletal activity of the parasympathetic nervous system (PSNS) has not been reported at the bone level. Here we report skeletal immune-positive fibers for the PSNS marker vesicular ACh transporter (VAChT). Pseudorabies virus inoculated into the distal femoral metaphysis is identifiable in the sacral intermediolateral cell column and central autonomic nucleus, demonstrating PSNS femoral innervation originating in the spinal cord. The PSNS neurotransmitter ACh targets nicotinic (nAChRs), but not muscarinic receptors in bone cells, affecting mainly osteoclasts. nAChR agonists up-regulate osteoclast apoptosis and restrain bone resorption. Mice deficient of the α2nAChR subunit have increased bone resorption and low bone mass. Silencing of the IL-1 receptor signaling in the central nervous system by brain-specific overexpression of the human IL-1 receptor antagonist (hIL1raAst +/+ mice) leads to very low skeletal VAChT expression and ACh levels. These mice also exhibit increased bone resorption and low bone mass. In WT but not in hIL1raAst+/+ mice, the cholinergic ACh esterase inhibitor pyridostigmine increases ACh levels and bone mass apparently by inhibiting bone resorption. Taken together, these results identify a previously unexplored key central IL-1-parasympathetic-bone axis that antagonizes the skeletal sympathetic tone, thus potently favoring bone mass accrual.

Original languageAmerican English
Pages (from-to)15455-15460
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume109
Issue number38
DOIs
StatePublished - 18 Sep 2012

Keywords

  • Autonomic nervous system
  • Postnatal skeletal development

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