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Inhibition of osteoclast formation and function by bicarbonate: Role of soluble adenylyl cyclase
Author(s) -
Geng Weidong,
Hill Kathy,
Zerwekh Joseph E.,
Kohler Thomas,
Müller Ralph,
Moe Orson W.
Publication year - 2009
Publication title -
journal of cellular physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.529
H-Index - 174
eISSN - 1097-4652
pISSN - 0021-9541
DOI - 10.1002/jcp.21767
Subject(s) - osteoclast , chemistry , adenylyl cyclase , bicarbonate , bone resorption , calvaria , acid phosphatase , forskolin , resorption , microbiology and biotechnology , endocrinology , medicine , in vitro , biochemistry , enzyme , biology , organic chemistry
Abstract High ${\rm [HCO}_3^ - ]$ inhibits and low ${\rm [HCO}_3^ - ]$ 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 ${\rm HCO}_3^ -$ 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 ${\rm HCO}_3^ -$ in a dose‐dependent manner. V‐ATPase expression and H + accumulation normalized to cell cross‐sectional area or protein were not significantly changed. The ${\rm HCO}_3^ -$ ‐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 ${\rm HCO}_3^ -$ inhibiting osteoclast via sAC was further supported by the fact that the ${\rm HCO}_3^ -$ 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 (µCT), was higher in 24 mM ${\rm HCO}_3^ -$ compared to 12 mM ${\rm HCO}_3^ -$ treated calvaria. This ${\rm HCO}_3^ -$ effect on BV/TV was blocked by 2‐hydroxyestradiol. In summary, sAC mediates the inhibition of osteoclast function by ${\rm HCO}_3^ -$ , by acting as a ${\rm HCO}_3^ -$ sensor. J. Cell. Physiol. 220: 332–340, 2009. © 2009 Wiley‐Liss, Inc.