Inhibition of osteoclast formation and function by bicarbonate: role of soluble adenylyl cyclase.
High [HCO(3)(-)] inhibits and low [HCO(3)(-)] stimulates bone resorption, which mediates part of the effect of chronic acidosis or acid feeding on bone. Soluble adenylyl cyclase (sAC) is a bicarbonate sensor that can potentially mediate the effect of bicarbonate on osteoclasts. Osteoclasts were incubated in 0, 12, and 24 mM HCO(3)(-) at pH 7.4 for 7-8 days and assayed for tartrate-resistant acid phosphatase (TRAP) and vacuolar-ATPase expression, and H+ accumulation. Total number and area of TRAP (+) multinucleated osteoclasts was decreased by HCO(3)(-) in a dose-dependent manner. V-ATPase expression and H+ accumulation normalized to cell cross-sectional area or protein were not significantly changed. The HCO(3)(-) -induced inhibition of osteoclast growth and differentiation was blocked by either 2-hydroxyestradiol, an inhibitor of sAC or sAC knockdown by sAC specific siRNA. The model of HCO(3)(-) inhibiting osteoclast via sAC was further supported by the fact that the HCO(3)(-) dose-response on osteoclasts is flat when cells were saturated with 8-bromo-cAMP, a permeant cAMP analog downstream from sAC thus simulating sAC activation. To confirm our in vitro findings in intact bone, we developed a 1-week mouse calvaria culture system where osteoclasts were shown to be viable. Bone volume density (BV/TV) determined by micro-computed tomography (microCT), was higher in 24 mM HCO(3)(-) compared to 12 mM HCO(3)(-) treated calvaria. This HCO(3)(-) effect on BV/TV was blocked by 2-hydroxyestradiol. In summary, sAC mediates the inhibition of osteoclast function by HCO(3)(-), by acting as a HCO(3)(-) sensor.
Charles and Jane Pak Center for Mineral Metabolism and Clinical Research, University of Texas, Southwestern Medical Center at Dallas, Dallas, TX 75390-8885, USA.
Weidong
W
Geng
Kathy
K
Hill
Joseph E
JE
Zerwekh
Thomas
T
Kohler
Ralph
R
Müller
Orson W
OW
Moe
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000378:metabolism; D000135:Acid Phosphatase / Q000378:metabolism; D000262:Adenylyl Cyclases / Q000494:pharmacology*; D000818:Animals; D001639:Bicarbonates / Q000494:pharmacology*; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology; D002460:Cell Line; D002478:Cells, Cultured; D004958:Estradiol / Q000031:analogs & derivatives / Q000494:pharmacology; D005260:Female; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D010010:Osteoclasts / Q000166:cytology / Q000187:drug effects* / Q000502:physiology*; D011522:Protons; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D012886:Skull / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D000071681:Tartrate-Resistant Acid Phosphatase; D025262:Vacuolar Proton-Translocating ATPases / Q000378:metabolism
D001639:Bicarbonates; D007527:Isoenzymes; D011522:Protons; D034741:RNA, Small Interfering; D015124:8-Bromo Cyclic Adenosine Monophosphate; D004958:Estradiol; C001390:2-hydroxyestradiol; D000135:Acid Phosphatase; C000605511:Acp5 protein, mouse; D000071681:Tartrate-Resistant Acid Phosphatase; D025262:Vacuolar Proton-Translocating ATPases; D000262:Adenylyl Cyclases