Referenced in: none

Automatically associated channels: ClC4 , ClC7

Title: Characterization of acid flux in osteoclasts from patients harboring a G215R mutation in ClC-7.

Authors: Kim Henriksen, Jeppe Gram, Anita Vibsig Neutzsky-Wulff, Vicki Kaiser Jensen, Morten H Dziegiel, Jens Bollerslev, Morten A Karsdal

Journal, date & volume: Biochem. Biophys. Res. Commun., 2009 Jan 23 , 378, 804-9

PubMed link: http://www.ncbi.nlm.nih.gov/pubmed/19070589

Abstract
The chloride-proton antiporter ClC-7 has been speculated to be involved in acidification of the lysosomes and the resorption lacunae in osteoclasts; however, neither direct measurements of chloride transport nor acidification have been performed. Human osteoclasts harboring a dominant negative mutation in ClC-7 (G215R) were isolated, and used these to investigate bone resorption measured by CTX-I, calcium release and pit scoring. The actin cytoskeleton of the osteoclasts was also investigated. ClC-7 enriched membranes from the osteoclasts were isolated, and used to test acidification rates in the presence of a V-ATPase and a chloride channel inhibitor, using a H(+) and Cl(-) driven approach. Finally, acidification rates in ClC-7 enriched membranes from ADOII osteoclasts and their corresponding controls were compared. Resorption by the G215R osteoclasts was reduced by 60% when measured by both CTX-I, calcium release, and pit area when comparing to age and sex matched controls. In addition, the ADOII osteoclasts showed no differences in actin ring formation. Finally, V-ATPase and chloride channel inhibitors completely abrogated the H(+) and Cl(-) driven acidification. Finally, the acid influx was reduced by maximally 50% in the ClC-7 deficient membrane fractions when comparing to controls. These data demonstrate that ClC-7 is essential for bone resorption, via its role in acidification of the lysosomes and resorption lacunae in osteoclasts.