Distinguishing the proapoptotic and antiresorptive functions of risedronate in murine osteoclasts: Role of the Akt pathway and the ERK/Bim axis

University of Tokyo, Bunkyo-ku, Tokyo, Japan.
Arthritis & Rheumatology (Impact Factor: 7.76). 12/2011; 63(12):3908-17. DOI: 10.1002/art.30646
Source: PubMed


Nitrogen-containing bisphosphonates are one of the most successful therapeutics for osteoporosis. The aim of this study was to elucidate the functional mechanism of one of the typical nitrogen-containing bisphosphonates, risedronate.
Osteoclasts generated from murine bone marrow macrophages were treated with risedronate in vitro, and its effects on apoptosis and bone-resorbing activity were examined. The mechanism of action of risedronate was examined by gene induction of constitutively active Akt-1 and constitutively active MEK-1, and by gene deletion of Bim. Bim(-/-) mice, in which osteoclasts were resistant to apoptosis, were treated with risedronate and analyzed radiographically, biochemically, and histologically.
Risedronate induced osteoclast apoptosis through the mitochondria-dependent pathway with an increased expression of Bim, and the proapoptotic effect of risedronate was suppressed by Bim deletion and constitutively active MEK-1 introduction. In contrast, the risedronate-induced suppression of bone resorption was completely reversed by inducing constitutively active Akt-1, but not by Bim deletion or constitutively active MEK-1 introduction. These results suggested that apoptosis and bone-resorbing activity of osteoclasts were regulated through the ERK/Bim axis and the Akt pathway, respectively, both of which were suppressed by risedronate. Although osteoclast apoptosis in response to risedronate administration was suppressed in the Bim(-/-) mice, risedronate treatment increased bone mineral density in Bim(-/-) mice at a level equivalent to that in wild-type mice.
Our findings indicate that the antiresorptive effect of risedronate in vivo is mainly mediated by the suppression of the bone-resorbing activity of osteoclasts and not by the induction of osteoclast apoptosis.

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