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Calcium/calmodulin‐signaling supports TRPV4 activation in osteoclasts and regulates bone mass
Author(s) -
Masuyama Ritsuko,
Mizuno Atsuko,
Komori Hisato,
Kajiya Hiroshi,
Uekawa Atsushi,
Kitaura Hideki,
Okabe Koji,
Ohyama Kaname,
Komori Toshihisa
Publication year - 2012
Publication title -
journal of bone and mineral research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.882
H-Index - 241
eISSN - 1523-4681
pISSN - 0884-0431
DOI - 10.1002/jbmr.1629
Subject(s) - trpv4 , osteoclast , calmodulin , chemistry , microbiology and biotechnology , transient receptor potential channel , calcium signaling , calcium , signal transduction , calcium in biology , bone resorption , biochemistry , endocrinology , intracellular , biology , receptor , organic chemistry
Osteoclast differentiation is critically dependent on calcium (Ca 2+ ) signaling. Transient receptor potential vanilloid 4 (TRPV4), mediates Ca 2+ influx in the late stage of osteoclast differentiation and thereby regulates Ca 2+ signaling. However, the system‐modifying effect of TRPV4 activity remains to be determined. To elucidate the mechanisms underlying TRPV4 activation based on osteoclast differentiation, TRPV4 gain‐of‐function mutants were generated by the amino acid substitutions R616Q and V620I in TRPV4 and were introduced into osteoclast lineage in Trpv4 null mice to generate Trpv4 R616Q/V620 I transgenic mice. As expected, TRPV4 activation in osteoclasts increased the number of osteoclasts and their resorption activity, thereby resulting in bone loss. During in vitro analysis, Trpv4 R616Q/V620 I osteoclasts showed activated Ca 2+ /calmodulin signaling compared with osteoclasts lacking Trpv4 . In addition, studies of Trpv4 R616Q/V620 I mice that lacked the calmodulin‐binding domain indicated that bone loss due to TRPV4 activation was abrogated by loss of interactions between Ca 2+ /calmodulin signaling and TRPV4. Finally, modulators of TRPV4 interactions with the calmodulin‐binding domain were investigated by proteomic analysis. Interestingly, nonmuscle myosin IIa was identified by liquid chromatography–tandem mass spectroscopy (LC‐MS/MS) analysis, which was confirmed by immunoblotting following coimmunoprecipitation with TRPV4. Furthermore, myosin IIa gene silencing significantly reduced TRPV4 activation concomitant with impaired osteoclast maturation. These results indicate that TRPV4 activation reciprocally regulates Ca 2+ /calmodulin signaling, which involves an association of TRPV4 with myosin IIa, and promotes sufficient osteoclast function. © 2012 American Society for Bone and Mineral Research.