Loss of the CIC-7 Chloride Channel Leads to Osteopetrosis in Mice and Man

Chloride channels play important roles in the plasma membrane and in intracellular organelles. Mice deficient for the ubiquitously expressed CIC-7 CI super(-) channel show severe osteopetrosis and retinal degeneration. Although osteoclasts are present in normal numbers, they fail to resorb bone because they cannot acidify the extracellular resorption lacuna. CIC-7 resides in late endosomal and lysosomal compartments. In osteoclasts, it is highly expressed in the ruffled membrane, formed by the fusion of H super(+)-ATPase-containing vesicles, that secretes protons into the lacuna. We also identified CLCN7 mutations in a patient with human infantile malignant osteopetrosis. We conclude that CIC-7 provides the chloride conductance required for an efficient proton pumping by the H super(+)-ATPase of the osteoclast ruffled membrane.