The cannabinoid CB1 receptor regulates bone formation by modulating adrenergic signaling

Joseph Tam, Victoria Trembovler, Vincenzo Di Marzo, Stefania Petrosino, Gabriella Leo, Alex Alexandrovich, Eran Regev, Nardy Casap, Arie Shteyer, Catherine Ledent, Meliha Karsak, Andreas Zimmer, Raphael Mechoulam, Raz Yirmiya, Esther Shohami, Itai Bab*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

173 Scopus citations

Abstract

We have recently reported that in bone the cannabinoid CB1 receptor is present in sympathetic terminals. Here we show that traumatic brain injury (TBI), which in humans enhances peripheral osteogenesis and fracture healing, acutely stimulates bone formation in a distant skeletal site. At this site we demonstrate i) a high level of the main endocannabinoid, 2-arachidonoylglycerol (2-AG), and expression of diacylglycerol lipases, enzymes essential for 2-AG synthesis; ii) that the TBI-induced increase in bone formation is preceded by elevation of the 2-AG and a decrease in norepinephrine (NE) levels. The TBI stimulation of bone formation was absent in CB1-null mice. In wild-type animals it could be mimicked, including the suppression of NE levels, by 2-AG administration. The TBI- and 2-AG-induced stimulation of osteogenesis was restrained by the β-adrenergic receptor agonist isoproterenol. NE from sympathetic terminals is known to tonically inhibit bone formation by activating osteoblastic β2-adrenergic receptors. The present findings further demonstrate that the sympathetic control of bone formation is regulated through 2-AG activation of prejunctional CB1. Elevation of bone 2-AG apparently suppresses NE release from bone sympathetic terminals, thus alleviating the inhibition of bone formation. The involvement of osteoblastic CB2 signaling in this process is minimal, if any.

Original languageAmerican English
Pages (from-to)285-294
Number of pages10
JournalFASEB Journal
Volume22
Issue number1
DOIs
StatePublished - Jan 2008

Keywords

  • 2-arachidonoylglycerol
  • Norepinephrine
  • Sympathetic nervous system
  • Traumatic brain injury

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