The cannabinoid CB1 receptor regulates bone formation by modulating adrenergic signaling.
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 beta-adrenergic receptor agonist isoproterenol. NE from sympathetic terminals is known to tonically inhibit bone formation by activating osteoblastic beta2-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.
Tam
Joseph
J
Bone Laboratory, Hadassah School of Dental Medicine, Hebrew University of Jerusalem, Jerusalem 91120, Israel.
Trembovler
Victoria
V
Di Marzo
Vincenzo
V
Petrosino
Stefania
S
Leo
Gabriella
G
Alexandrovich
Alex
A
Regev
Eran
E
Casap
Nardy
N
Shteyer
Arie
A
Ledent
Catherine
C
Karsak
Meliha
M
Zimmer
Andreas
A
Mechoulam
Raphael
R
Yirmiya
Raz
R
Shohami
Esther
E
Bab
Itai
I
D000818:Animals; D001095:Arachidonic Acids / Q000008:administration & dosage / Q000378:metabolism; D001483:Base Sequence; D001846:Bone Development / Q000502:physiology*; D001842:Bone and Bones / Q000378:metabolism; D017931:DNA Primers; D063388:Endocannabinoids; D005260:Female; D005989:Glycerides / Q000008:administration & dosage / Q000378:metabolism; D007150:Immunohistochemistry; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D043884:Receptor, Cannabinoid, CB1 / Q000235:genetics / Q000502:physiology*; D018343:Receptors, Adrenergic, beta-2 / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*
D001095:Arachidonic Acids; D017931:DNA Primers; D063388:Endocannabinoids; D005989:Glycerides; D043884:Receptor, Cannabinoid, CB1; D018343:Receptors, Adrenergic, beta-2; C094503:glyceryl 2-arachidonate