title: Bisphosphonates improve trabecular bone mass and normalize cortical thickness in ovariectomized, osteoblast connexin43 deficient mice.
abstract: The gap junction protein, connexin43 (Cx43) controls both bone formation and osteoclastogenesis via osteoblasts and/or osteocytes. Cx43 has also been proposed to mediate an anti-apoptotic effect of bisphosphonates, potent inhibitors of bone resorption. We studied whether bisphosphonates are effective in protecting mice with a conditional Cx43 gene deletion in osteoblasts and osteocytes (cKO) from the consequences of ovariectomy on bone mass and strength. Ovariectomy resulted in rapid loss of trabecular bone followed by a slight recovery in wild type (WT) mice, and a similar degree of trabecular bone loss, albeit slightly delayed, occurred in cKO mice. Treatment with either risedronate (20 μg/kg) or alendronate (40 μg/kg) prevented ovariectomy-induced bone loss in both genotypes. In basal conditions, bones of cKO mice have larger marrow area, higher endocortical osteoclast number, and lower cortical thickness and strength relative to WT. Ovariectomy increased endocortical osteoclast number in WT but not in cKO mice. Both bisphosphonates prevented these increases in WT mice, and normalized endocortical osteoclast number, cortical thickness and bone strength in cKO mice. Thus, lack of osteoblast/osteocyte Cx43 does not alter bisphosphonate action on bone mass and strength in estrogen deficiency. These results support the notion that one of the main functions of Cx43 in cortical bone is to restrain osteoblast and/or osteocytes from inducing osteoclastogenesis at the endocortical surface.
authors: Division of Bone and Mineral Diseases, Departments of Internal Medicine and Cell Biology and Physiology, Washington University School of Medicine, St. Louis, MO, USA.
authors: Marcus P
authors: MP
authors: Watkins
authors: Jin Yi
authors: JY
authors: Norris
authors: Susan K
authors: SK
authors: Grimston
authors: Xiaowen
authors: X
authors: Zhang
authors: Roger J
authors: RJ
authors: Phipps
authors: Frank H
authors: FH
authors: Ebetino
authors: Roberto
authors: R
authors: Civitelli
mesh_terms: D015502:Absorptiometry, Photon; D000818:Animals; D001696:Biomechanical Phenomena; D015519:Bone Density; D001842:Bone and Bones / Q000187:drug effects*; D018031:Connexin 43 / Q000235:genetics*; D004164:Diphosphonates / Q000494:pharmacology*; D005260:Female; D051379:Mice; D008822:Mice, Transgenic; D009929:Organ Size / Q000187:drug effects*; D010006:Osteoblasts / Q000378:metabolism*; D010052:Ovariectomy
chemical_list: D018031:Connexin 43; D004164:Diphosphonates; C543076:GJA1 protein, mouse