Connexin 43 Is Required for the Anti-Apoptotic Effect of Bisphosphonates on Osteocytes and Osteoblasts In Vivo

Authors

  • Lilian I Plotkin,

    Corresponding author
    1. Division of Endocrinology and Metabolism, the Center for Osteoporosis and Metabolic Bone Diseases, the Central Arkansas Veterans Healthcare System, Little Rock, Arkansas, USA
    2. Present address: Department of Anatomy and Cell Biology, Indiana University School of Medicine, Indianapolis, Indiana, USA
    • Address reprint requests to: Lilian I Plotkin, PhD, Department of Anatomy and Cell Biology, Indiana University School of Medicine, 635 Barnhill Drive/MS 5035, Indianapolis, IN 46202-5120, USA
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  • Virginia Lezcano,

    1. Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, Bahía Blanca, Argentina
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  • Jeff Thostenson,

    1. Department of Biostatistics, University of Arkansas for Medical Sciences, Little Rock, Arkansas, USA
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  • Robert S Weinstein,

    1. Division of Endocrinology and Metabolism, the Center for Osteoporosis and Metabolic Bone Diseases, the Central Arkansas Veterans Healthcare System, Little Rock, Arkansas, USA
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  • Stavros C Manolagas,

    1. Division of Endocrinology and Metabolism, the Center for Osteoporosis and Metabolic Bone Diseases, the Central Arkansas Veterans Healthcare System, Little Rock, Arkansas, USA
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  • Teresita Bellido

    1. Division of Endocrinology and Metabolism, the Center for Osteoporosis and Metabolic Bone Diseases, the Central Arkansas Veterans Healthcare System, Little Rock, Arkansas, USA
    2. Present address: Department of Anatomy and Cell Biology, Indiana University School of Medicine, Indianapolis, Indiana, USA
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  • The authors state that they have no conflicts of interest.

Abstract

Connexin (Cx)43 is required for inhibition of osteocyte and osteoblast apoptosis by bisphosphonates in vitro. Herein, we evaluated its requirement for the in vivo actions of bisphosphonates using mice in which Cx43 was deleted specifically from osteocytes and osteoblasts (Cx43ΔOb−Ot/− mice). Effective removal of Cx43 was confirmed by the presence of the deleted form of the gene and by reduced mRNA and protein expression in osteoblastic cells and bones obtained from Cx43ΔOb−Ot/− mice. The amino-bisphosphonate alendronate (2.3 μmol/kg/d) was injected daily into 5-mo-old female mice (n = 6–11) for 31 days, starting 3 days before implantation of pellets releasing the glucocorticoid prednisolone (2.1 mg/kg/d). Cx43ΔOb−Ot/− mice and their littermates (Cx43fl/−, Cx43ΔOb−Ot/+, and Cx43fl/+) gained bone with similar kinetics and exhibited identical bone mass from 2 to 4.5 mo of age, indicating that Cx43 deletion from osteocytes and mature osteoblasts does not impair bone acquisition. In addition, prednisolone induced a similar increase in osteocyte and osteoblast apoptosis in Cx43ΔOb−Ot/− or in control Cx43fl/− littermates. However, whereas alendronate prevented prednisolone-induced apoptosis in control Cx43fl/− mice, it was ineffective in Cx43ΔOb−Ot/− mice. In contrast, alendronate inhibited glucocorticoid-induced bone loss in both type of animals, suggesting that inhibition of resorption is the predominant effect of alendronate against the early phase of glucocorticoid-induced bone loss. Taken together with earlier in vitro evidence, these findings show that Cx43 is required for the anti-apoptotic effect of bisphosphonates on osteocytes and osteoblasts.

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