The endogenous opioid dynorphin is required for normal bone homeostasis in mice.
Chronic opiate usage, whether prescribed or illicit, has been associated with changes in bone mass and is a recognized risk factor for the development of osteoporosis; however, the mechanism behind this effect is unknown. Here we show that lack of dynorphin, an endogenous opioid, in mice (Dyn-/-), resulted in a significantly elevated cancellous bone volume associated with greater mineral apposition rate and increased resorption indices. A similar anabolic phenotype was evident in bone of mice lacking dynorphin's cognate receptor, the kappa opioid receptor. Lack of opioid receptor expression in primary osteoblastic cultures and no change in bone cell function after dynorphin agonist treatment in vitro indicates an indirect mode of action. Consistent with a hypothalamic action, central dynorphin signaling induces extracellular signal-regulated kinase (ERK) phosphorylation and c-fos activation of neurons in the arcuate nucleus of the hypothalamus (Arc). Importantly, this signaling also leads to an increase in Arc NPY mRNA expression, a change known to decrease bone formation. Further implicating NPY in the skeletal effects of dynorphin, Dyn-/-/NPY-/- double mutant mice showed comparable increases in bone formation to single mutant mice, suggesting that dynorphin acts upstream of NPY signaling to control bone formation. Thus the dynorphin system, acting via NPY, may represent a pathway by which higher processes including stress, reward/addiction and depression influence skeletal metabolism. Moreover, understanding of these unique interactions may enable modulation of the adverse effects of exogenous opioid treatment without directly affecting analgesic responses.
Neuroscience Research Program, Garvan Institute of Medical Research, 384 Victoria St., Darlinghurst, Sydney, NSW 2010, Australia. p.baldock@garvan.org.au
Paul A
PA
Baldock
Frank
F
Driessler
Shu
S
Lin
Iris P L
IP
Wong
Yanchuan
Y
Shi
Ernie
E
Yulyaningsih
Lesley
L
Castillo
Sonia
S
Janmaat
Ronaldo F
RF
Enriquez
Ayse
A
Zengin
Brigitte L
BL
Kieffer
Christoph
C
Schwarzer
John A
JA
Eisman
Amanda
A
Sainsbury
Herbert
H
Herzog
D000818:Animals; D015153:Blotting, Western; D001823:Body Composition / Q000235:genetics / Q000502:physiology; D001842:Bone and Bones / Q000502:physiology*; D002454:Cell Differentiation / Q000235:genetics / Q000502:physiology; D003598:Cytoskeletal Proteins / Q000378:metabolism; D018076:DNA, Complementary / Q000096:biosynthesis / Q000302:isolation & purification; D004399:Dynorphins / Q000235:genetics / Q000502:physiology*; D005260:Female; D006706:Homeostasis / Q000235:genetics / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008822:Mice, Transgenic; D009419:Nerve Tissue Proteins / Q000378:metabolism; D009474:Neurons / Q000502:physiology; D009478:Neuropeptide Y / Q000502:physiology; D010006:Osteoblasts / Q000502:physiology; D011247:Pregnancy; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D012313:RNA / Q000096:biosynthesis / Q000302:isolation & purification; D060888:Real-Time Polymerase Chain Reaction; D015398:Signal Transduction / Q000502:physiology; D017154:Stromal Cells / Q000502:physiology; D014057:Tomography, X-Ray Computed
D003598:Cytoskeletal Proteins; D018076:DNA, Complementary; D009419:Nerve Tissue Proteins; D009478:Neuropeptide Y; D016760:Proto-Oncogene Proteins c-fos; C092069:activity regulated cytoskeletal-associated protein; D012313:RNA; D004399:Dynorphins