Characterization of the Bone Phenotype in ClC-7-Deficient Mice
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- Neutzsky-Wulff, A.V., Karsdal, M.A. & Henriksen, K. Calcif Tissue Int (2008) 83: 425. doi:10.1007/s00223-008-9185-7
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, Ca2+, 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.