Defective bone remodeling is the physiopathologic basis of most metabolic bone diseases, including postmenopausal and age- dependent osteoporosis. Bone remodeling is the result of a regulated, sequential activation of osteoclasts and osteoblasts within basic multicellular units, and results in a cyclical succession of bone resorptive and formative phases. In turn, bone formation requires the synchronized activity of osteoblasts within each bone remodeling unit Osteoblasts communicate with each other via gap junctions, transcellular channels which allow exchange of ions and small molecules between adjacent cells. Gap junctions in osteoblasts are formed by two different gap junction proteins, called connexins. One of these, connexin43 (Cx43) mediates """"""""chemical"""""""" or """"""""dye"""""""" coupling between osteoblasts. The other, connexin45 (Cx45), forms functional gap functions of different molecular permeabilities than those formed by Cx43. Cx43 and Cx45 interact with each other, so that when Cx45 is expressed in cells that normally express Cx43, chemical communication between cells decreases. Importantly, is change in gap junctional permeability is associated with a decreased expression of osteocalcin and bone sialoprotein, two matrix proteins pivotal for bone formation. We hypothesize that gap junctional communication between osteoblasts is critical to their maturation and function as bone forming cells, and that the relative expression of Cx43 and Cx45 regulates osteoblast function via changes in gap junctional communication. Exploiting the partial """"""""dominant negative"""""""" action of Cx45 on gap junctions formed by Cx43, we propose to determine the regulatory mechanisms of gap junctional communication on osteoblast gene expression, by mapping the regions of the osteocalcin and bone sialoprotein promoters sensitive to gap junctional communication. The consequences of a decreased communication competence induced b overexpressing Cx45 on the capacity of osteoblasts to produce calcified matrix,will be tested in human osteoblastic models. Finally, osteoblasts activity will be characterized in cells derived from Cx43 null (""""""""knockout"""""""") mice, in relation to the type of gap junctional communication existing in these Cx43 null cells. If an adequate degree of gapjunctional communication between osteoblasts is necessary for bone formation, abnormalities of gap junction fi1nction or expression may represent potential novel mechanism at the basis of the osteoblastic """"""""failure"""""""" characteristic of postmenopausal and aging osteoporotic bone. Therefore, the results of this project will define a fundamental mechanism that regulates osteoblast function in health and disease, and lay the basis for novel therapeutic approaches for the management of osteoporotic syndromes.

Agency
National Institute of Health (NIH)
Institute
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Type
Research Project (R01)
Project #
5R01AR041255-09
Application #
6171266
Study Section
Special Emphasis Panel (ZRG4-ORTH (04))
Program Officer
Sharrock, William J
Project Start
1992-01-01
Project End
2002-03-31
Budget Start
2000-07-01
Budget End
2002-03-31
Support Year
9
Fiscal Year
2000
Total Cost
$224,273
Indirect Cost
Name
Barnes-Jewish Hospital
Department
Type
DUNS #
City
Saint Louis
State
MO
Country
United States
Zip Code
63110
Stains, Joseph P; Civitelli, Roberto (2016) A Functional Assay to Assess Connexin 43-Mediated Cell-to-Cell Communication of Second Messengers in Cultured Bone Cells. Methods Mol Biol 1437:193-201
Stains, Joseph P; Civitelli, Roberto (2016) Connexins in the skeleton. Semin Cell Dev Biol 50:31-9
Shen, Hua; Grimston, Susan; Civitelli, Roberto et al. (2015) Deletion of connexin43 in osteoblasts/osteocytes leads to impaired muscle formation in mice. J Bone Miner Res 30:596-605
Chang, Kyung Hee; Sengupta, Amitava; Nayak, Ramesh C et al. (2014) p62 is required for stem cell/progenitor retention through inhibition of IKK/NF-?B/Ccl4 signaling at the bone marrow macrophage-osteoblast niche. Cell Rep 9:2084-97
Stains, Joseph P; Watkins, Marcus P; Grimston, Susan K et al. (2014) Molecular mechanisms of osteoblast/osteocyte regulation by connexin43. Calcif Tissue Int 94:55-67
Grimston, Susan K; Watkins, Marcus P; Stains, Joseph P et al. (2013) Connexin43 modulates post-natal cortical bone modeling and mechano-responsiveness. Bonekey Rep 2:446
Watkins, Marcus P; Norris, Jin Yi; Grimston, Susan K et al. (2012) Bisphosphonates improve trabecular bone mass and normalize cortical thickness in ovariectomized, osteoblast connexin43 deficient mice. Bone 51:787-94
Gonzalez-Nieto, Daniel; Li, Lina; Kohler, Anja et al. (2012) Connexin-43 in the osteogenic BM niche regulates its cellular composition and the bidirectional traffic of hematopoietic stem cells and progenitors. Blood 119:5144-54
Grimston, Susan K; Watkins, Marcus P; Brodt, Michael D et al. (2012) Enhanced periosteal and endocortical responses to axial tibial compression loading in conditional connexin43 deficient mice. PLoS One 7:e44222
Watkins, Marcus; Grimston, Susan K; Norris, Jin Yi et al. (2011) Osteoblast connexin43 modulates skeletal architecture by regulating both arms of bone remodeling. Mol Biol Cell 22:1240-51

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