Abstract

Bone resorption, which is regulated by osteoclasts, is excessively activated in bone destructive diseases such as osteoporosis. Thus, controlling osteoclasts would be an effective strategy to prevent pathological bone loss. Although several transcription factors that regulate osteoclast differentiation and function could serve as molecular targets to inhibit osteoclast formation, those factors have not yet been characterized using a loss of function approach in adults. Here we report such a study showing that inactivation of B-lymphocyte induced maturation protein 1 (Blimp1) in adult mice increases bone mass by suppressing osteoclast formation. Using an ex vivo assay, we show that osteoclast differentiation is significantly inhibited by Blimp1 inactivation at an early stage of osteoclastogenesis. Conditional inactivation of Blimp1 inhibited osteoclast formation and increased bone mass in both male and female adult mice. Bone resorption parameters were significantly reduced by Blimp1 inactivation in vivo. Blimp1 reportedly regulates immune cell differentiation and function, but we detected no immune cell failure following Blimp1 inactivation. These data suggest that Blimp1 is a potential target to promote increased bone mass and prevent osteoclastogenesis.

Highlights

  • B-lymphocyte induced maturation protein 1 (Blimp1) is required for development and maintenance of homeostasis in various tissues

  • IFN was added to the culture 1 day after RANKL stimulation, and osteoclastogenesis was significantly inhibited in Mx1Cre;Blimp1fl/fl cells but not in Blimp1fl/fl cells (Fig. 1, A and B)

  • The number of tartrate-resistant acid phosphatase (TRAP)-positive multinuclear cells formed by RANKL stimulation was significantly reduced in Mx1Cre;Blimp1fl/fl cells compared with Blimp1fl/fl cells, Mx1Cre cells or IFN(Ϫ) controls (Fig. 1C and supplemental Fig. S2)

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Summary

Background

Blimp is required for development and maintenance of homeostasis in various tissues. Several transcription factors that regulate osteoclast differentiation and function could serve as molecular targets to inhibit osteoclast formation, those factors have not yet been characterized using a loss of function approach in adults We report such a study showing that inactivation of B-lymphocyte induced maturation protein 1 (Blimp1) in adult mice increases bone mass by suppressing osteoclast formation. Blimp reportedly regulates immune cell differentiation and function, but we detected no immune cell failure following Blimp inactivation These data suggest that Blimp is a potential target to promote increased bone mass and prevent osteoclastogenesis. We found that osteoclast-specific Blimp1-deficient mice exhibited impaired osteoclast differentiation and increased bone mass due to Bcl accumulation in osteoclast progenitors [7] These findings suggest that Blimp promotes bone resorption by eliminating Bcl, a negative regulator of osteoclastogenesis. Our observations suggest that Blimp could be targeted as a strategy to increase bone mass

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