Pharmacological inhibition of intracellular calcium release blocks acid-induced bone resorption.
In vivo chronic metabolic acidosis induces net Ca2+ efflux from bone, and incubation of neonatal mouse calvariae in medium simulating physiological metabolic acidosis induces bone resorption. It appears that activation of the proton (H+) receptor OGR1 in the osteoblast leads to an increase in intracellular Ca2+, which is associated with an increase in cyclooxygenase 2 (COX2) and PGE2-induced receptor activator of NF-κB ligand (RANKL) and H+-induced osteoclastic bone resorption. To support this hypothesis, we tested whether intracellular Ca2+ signaling was integral to H+-induced bone resorption by determining whether 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate (TMB-8) and 2-aminoethoxydiphenyl borate (2-APB), inhibitors of inositol trisphosphate-mediated Ca2+ signaling, would block H+-induced bone resorption in cultured neonatal calvariae and, if so, would do so by inhibiting H+-induced stimulation of COX2 and RANKL in osteoblastic cells. We found that H+-induced bone resorption is significantly inhibited by TMB-8 and 2-APB. Both compounds also inhibit H+-induced stimulation of COX2 protein in calvariae and COX2 mRNA and protein levels in primary osteoblasts. H+-induced stimulation of RANKL in calvarial cultures, as well as primary cells, is also completely inhibited by TMB-8 and 2-APB. These results support the hypothesis that H+ stimulation of net Ca2+ efflux from bone, mediated by COX2- and subsequent PGE2-induced RANKL production, is initiated in the osteoblast via activation of Ca2+ signaling.
University of Rochester School of Medicine and Dentistry, Division of Nephrology, Department of Medicine, 601 Elmwood Ave., Box 675, Rochester, NY 14642, USA. Nancy_Krieger@urmc.rochester.edu
Nancy S
NS
Krieger
David A
DA
Bushinsky
D000138:Acidosis / Q000503:physiopathology*; D000818:Animals; D001862:Bone Resorption / Q000517:prevention & control*; D001842:Bone and Bones / Q000378:metabolism; D001896:Boron Compounds / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects*; D051546:Cyclooxygenase 2 / Q000378:metabolism; D005707:Gallic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D051379:Mice; D010006:Osteoblasts / Q000378:metabolism; D053245:RANK Ligand / Q000378:metabolism; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism
D001896:Boron Compounds; C525539:GPR68 protein, mouse; D053245:RANK Ligand; D043562:Receptors, G-Protein-Coupled; C505689:Tnfsf11 protein, mouse; C006014:8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate; D005707:Gallic Acid; C109986:2-aminoethoxydiphenyl borate; D051546:Cyclooxygenase 2