Characterization of the bone phenotype in ClC-7-deficient mice.
Mice deficient in the chloride channel ClC-7, which is likely involved in acidification of the resorption lacuna, display severe osteopetrosis. To fully characterize the osteopetrotic phenotype, the phenotypes of osteoclasts and osteoblasts were evaluated. ClC-7(-/-) mice and their corresponding wild-type littermates were killed at 4-5 weeks of age. Biochemical markers of bone resorption (CTX-I), osteoclast number (TRAP5b), and osteoblast activity (ALP) were evaluated in serum. Splenocytes were differentiated into osteoclasts using M-CSF and RANKL. Mature osteoclasts were seeded on calcified or decalcified bone slices, and CTX-I, Ca(2+), and TRAP were measured. Acidification rates in membrane vesicles from bone cells were measured using acridine orange. Osteoblastogenesis and nodule formation in vitro were investigated using calvarial osteoblasts. ClC-7(-/-) osteoclasts were unable to resorb calcified bone in vitro. However, osteoclasts were able to degrade decalcified bone. Acid influx in bone membrane vesicles was reduced by 70% in ClC-7(-/-) mice. Serum ALP was increased by 30% and TRAP5b was increased by 250% in ClC-7(-/-) mice, whereas the CTX/TRAP5b ratio was reduced to 50% of the wild-type level. Finally, evaluation of calvarial ClC-7(-/-) osteoblasts showed normal osteoblastogenesis. In summary, we present evidence supporting a pivotal role for ClC-7 in acidification of the resorption lacuna and evidence indicating that bone formation and bone resorption are no longer balanced in ClC-7(-/-) mice.
Neutzsky-Wulff
Anita Vibsig
AV
Nordic Bioscience A/S, Herlev Hovedgade 207, 2730, Herlev, Denmark. avn@nordicbioscience.com
Karsdal
Morten A
MA
Henriksen
Kim
K
D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D001862:Bone Resorption; D001842:Bone and Bones / Q000378:metabolism*; D002356:Cartilage / Q000378:metabolism; D018118:Chloride Channels / Q000235:genetics* / Q000502:physiology; D005091:Exons; D051379:Mice; D008822:Mice, Transgenic; D008954:Models, Biological; D010006:Osteoblasts / Q000378:metabolism; D010010:Osteoclasts / Q000378:metabolism; D010022:Osteopetrosis / Q000378:metabolism; D010641:Phenotype; D013154:Spleen / Q000166:cytology / Q000378:metabolism
D018118:Chloride Channels; C490803:Clcn7 protein, mouse; D000469:Alkaline Phosphatase