Clcn7, encoding the chloride/proton-exchanger ClC-7, is crucial for multiple biological processes. In osteoclasts, it transports negative charges in parallel with v-ATPase complexes to enable efficient proton transport into the resorption lacuna for bone resorption. In most cell types other than osteoclasts, ClC-7 is located in late endosomes and lysosomes, performing 2Cl⁻/H⁺ exchange across lysosomal membranes to maintain intravesicular ion homeostasis [2,3].

In Fig4 null cell cultures, knockout of Clcn7 corrected lysosomal swelling and partially corrected lysosomal hyperacidification, and in Fig4 null mice, reduction of ClC-7 by expressing the dominant-negative CLCN7 variant p.Gly215Arg improved growth, neurological function, and increased lifespan by 20%, demonstrating its role in the pathogenesis of FIG4 and VAC14 disorders [1]. In Clcn7 knockout mice, the osteopetrosis phenotype suggested ClC-7's responsibility for transporting negative charge in osteoclasts, and different CLCN7 mutations in mice models like Clcn7F318L/+ (a new mouse model of Albers-Schönberg disease) and Clcn7G213R/+ have been used to study autosomal dominant osteopetrosis type 2 [2,4].

In conclusion, Clcn7 is essential for bone resorption and lysosomal ion homeostasis. Gene knockout and related mouse models have revealed its significance in lysosome-related pathologies such as osteopetrosis, and in the pathogenesis of FIG4 and VAC14-associated disorders, providing potential therapeutic targets for diseases lacking specific therapies [1,2].

References:

1. Cao, Xu, Lenk, Guy M, Mikusevic, Vedrana, Mindell, Joseph A, Meisler, Miriam H. 2023. The chloride antiporter CLCN7 is a modifier of lysosome dysfunction in FIG4 and VAC14 mutants. In PLoS genetics, 19, e1010800. doi:10.1371/journal.pgen.1010800. https://pubmed.ncbi.nlm.nih.gov/37363915/

2. Stauber, Tobias, Wartosch, Lena, Vishnolia, Svenja, Schulz, Ansgar, Kornak, Uwe. 2022. CLCN7, a gene shared by autosomal recessive and autosomal dominant osteopetrosis. In Bone, 168, 116639. doi:10.1016/j.bone.2022.116639. https://pubmed.ncbi.nlm.nih.gov/36513280/

3. Polovitskaya, Maya M, Rana, Tanushka, Ullrich, Kurt, Santer, René, Jentsch, Thomas J. 2024. Gain-of-function variants in CLCN7 cause hypopigmentation and lysosomal storage disease. In The Journal of biological chemistry, 300, 107437. doi:10.1016/j.jbc.2024.107437. https://pubmed.ncbi.nlm.nih.gov/38838776/

4. Caetano-Lopes, J, Lessard, S G, Hann, S, Robling, A G, Warman, M L. 2017. Clcn7F318L/+ as a new mouse model of Albers-Schönberg disease. In Bone, 105, 253-261. doi:10.1016/j.bone.2017.09.007. https://pubmed.ncbi.nlm.nih.gov/28942122/