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J Immunol. 2018 Jan 15;200(2):749-757. doi: 10.4049/jimmunol.1701170. Epub 2017 Dec 15.

Ca2+-Dependent Regulation of NFATc1 via KCa3.1 in Inflammatory Osteoclastogenesis.

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Division of Rheumatology, Allergy, and Clinical Immunology, Department of Internal Medicine, University of California Davis, Davis, CA 95616.
Center for Musculoskeletal Health, University of California Davis, Sacramento, CA 95817.
Department of Physiology and Membrane Biology, University of California Davis, Davis, CA 95616; and.
Institute for Pediatric Regenerative Medicine, Shriners Hospital for Children - Northern California, Sacramento, CA 95817.
Division of Rheumatology, Allergy, and Clinical Immunology, Department of Internal Medicine, University of California Davis, Davis, CA 95616;


In inflammatory arthritis, the dysregulation of osteoclast activity by proinflammatory cytokines, including TNF, interferes with bone remodeling during inflammation through Ca2+-dependent mechanisms causing pathological bone loss. Ca2+-dependent CREB/c-fos activation via Ca2+-calmodulin kinase IV (CaMKIV) induces transcriptional regulation of osteoclast-specific genes via NFATc1, which facilitate bone resorption. In leukocytes, Ca2+ regulation of NFAT-dependent gene expression oftentimes involves the activity of the Ca2+-activated K+ channel KCa3.1. In this study, we evaluate KCa3.1 as a modulator of Ca2+-induced NFAT-dependent osteoclast differentiation in inflammatory bone loss. Microarray analysis of receptor activator of NF-κB ligand (RANKL)-activated murine bone marrow macrophage (BMM) cultures revealed unique upregulation of KCa3.1 during osteoclastogenesis. The expression of KCa3.1 in vivo was confirmed by immunofluorescence staining on multinucleated cells at the bone surface of inflamed mouse joints. Experiments on in vitro BMM cultures revealed that KCa3.1-/- and TRAM-34 treatment significantly reduced the expression of osteoclast-specific genes (p < 0.05) alongside decreased osteoclast formation (p < 0.0001) in inflammatory (RANKL+TNF) and noninflammatory (RANKL) conditions. In particular, live cell Ca2+ imaging and Western blot analysis showed that TRAM-34 pretreatment decreased transient RANKL-induced Ca2+ amplitudes in BMMs by ∼50% (p < 0.0001) and prevented phosphorylation of CaMKIV. KCa3.1-/- reduced RANKL+/-TNF-stimulated phosphorylation of CREB and expression of c-fos in BMMs (p < 0.01), culminating in decreased NFATc1 protein expression and transcriptional activity (p < 0.01). These data indicate that KCa3.1 regulates Ca2+-dependent NFATc1 expression via CaMKIV/CREB during inflammatory osteoclastogenesis in the presence of TNF, corroborating its role as a target candidate for the treatment of bone erosion in inflammatory arthritis.

[Available on 2019-01-15]
[Indexed for MEDLINE]

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