Hormonal Regulation of Connexin 43 Expression and Gap Junctional Communication in Human Osteoblastic Cells.

Chiba, Hideki; Sawada, Norimasa; Oyamada, Masahito; Kojima, Takashi; Iba, Kousuke; Ishii, Seiichi; Mori, Makoto

doi:10.1247/csf.19.173

Cited by 43 publications

(32 citation statements)

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“…These conditional Cx43 knockout mice, which use a 2.3-kb collagen I promoter-driven Cre-recombinase to excise a floxed Cx43 allele in cells of the osteoblast lineage, exhibit severe osteopenia as a result of defective osteoblast function. Further, the skeletons of these animals have been shown to be refractory to the anabolic effects of intermittent PTH administration, indicating a critical role of Cx43 in coordinating cell function in response to anabolic cues.Relatively little is known about the precise molecular role of gap junctions in sensing and responding to biological cues during bone formation, though in the past decade critical insights have been gained into the importance of gap junctions in processes such as response to growth factors and hormones (Schiller et al, 1992;Chiba et al, 1994;Van der Molen et al, 1996;Civitelli et al, 1998;Schiller et al, 2001), mechanical load (Jorgensen et al, 1997(Jorgensen et al, , 2000Ziambaras et al, 1998;Romanello and D'Andrea, 2001;Saunders et al, 2001Saunders et al, , 2003Cherian et al, 2003Cherian et al, , 2005Taylor et al, 2007), bisphosphonates (Plotkin et al, 2002(Plotkin et al, , 2005, and interaction with other cells (Villars et al, 2002). Importantly, less still is known regarding the biologically relevant second messengers that osteoblast and osteocyte gap junctions communicate among cells, and many molecular mechanisms have yet to be deduced.…”

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confidence: 99%

Connexin43 Potentiates Osteoblast Responsiveness to Fibroblast Growth Factor 2 via a Protein Kinase C-Delta/Runx2–dependent Mechanism

Lima

Niger

Hebert

et al. 2009

MBoC

100

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In this study, we examine the role of the gap junction protein, connexin43 (Cx43), in the transcriptional response of osteocalcin to fibroblast growth factor 2 (FGF2) in MC3T3 osteoblasts. By luciferase reporter assays, we identify that the osteocalcin transcriptional response to FGF2 is markedly increased by overexpression of Cx43, an effect that is mediated by Runx2 via its OSE2 cognate element, but not by a previously identified connexin-responsive Sp1/Sp3-binding element. Furthermore, disruption of Cx43 function with Cx43 siRNAs or overexpression of connexin45 markedly attenuates the response to FGF2. Inhibition of protein kinase C delta (PKC␦) with rottlerin or siRNA-mediated knockdown abrogates the osteocalcin response to FGF2. Additionally, we show that upon treatment with FGF2, PKC␦ translocates to the nucleus, PKC␦ and Runx2 are phosphorylated and these events are enhanced by Cx43 overexpression, suggesting that the degree of activation is enhanced by increased Cx43 levels. Indeed, chromatin immunoprecipitations of the osteocalcin proximal promoter with antibodies against Runx2 demonstrate that the recruitment of Runx2 to the osteocalcin promoter in response to FGF2 treatment is dramatically enhanced by Cx43 overexpression. Thus, Cx43 plays a critical role in regulating the ability of osteoblasts to respond to FGF2 by impacting PKC␦ and Runx2 function. INTRODUCTIONBone formation and remodeling is a tightly organized and dynamic process that requires the coordinated action of osteoblasts, osteocytes, and osteoclasts to maintain bone homeostasis. It is hypothesized that osteoblasts and osteocytes coordinate their activities, at least in part, through direct cell-to-cell communication through gap junctions. Gap junctions are composed of connexins, a family of transmembrane proteins that constitute the intercellular gap junction channels (Beyer et al., 1990). Six connexins assemble to make up the gap junction hemichannel on the plasma membrane of one cell, which docks with a hemichannel on an adjacent cell to form an aqueous gap junction channel. The resultant gap junctions provide direct conduits for the passage of ions and other low molecular weight molecules, including second messengers, among cells.The gap junction protein connexin43 (Cx43) is abundantly expressed in both osteoblasts and osteocytes, where it has been hypothesized to transmit hormonal signals, mechanical load, and growth factor cues among cells in order to coordinate the synthesis of new bone (reviewed in Stains and Civitelli, 2005a;Jiang et al., 2007). Genetic ablation of gja1, the gene encoding Cx43, in mice leads to a severe delay in the ossification of both intramembranous and endochondral derived skeletal elements during embryonic development (Lecanda et al., 2000). The bones of these animals are remarkably brittle, and the osteoblasts isolated from the Cx43 null animals are dysfunctional, with reduced osteogenic and mineralizing capacity (Lecanda et al., 2000). These Cx43-deficient mice die at birth because of a defect in cardiac f...

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confidence: 99%

Connexin43 Potentiates Osteoblast Responsiveness to Fibroblast Growth Factor 2 via a Protein Kinase C-Delta/Runx2–dependent Mechanism

Lima

Niger

Hebert

et al. 2009

MBoC

100

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“…Connexin43 (Cx43) has been identified as the major component of gap junctions in osteoblastic cells (8 -11) and in bone (12). Cx43 expression and junctional permeability increase during in vitro osteoblastic maturation and are regulated by osteotropic factors (8,13,14). The responsiveness of osteoblastic cells to stimulation by parathyroid hormone is modulated by gap junctional communication (GJC) (15,16).…”

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confidence: 99%

Inhibition of Gap-Junctional Communication Induces the Trans-differentiation of Osteoblasts to an Adipocytic Phenotype in Vitro

Schiller¹,

D’Ippolito²,

Brambilla³

et al. 2001

Journal of Biological Chemistry

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Osteoblasts and adipocytes are thought to differentiate from a common stromal progenitor cell. These two phenotypically mature cell types show a high degree of plasticity, which can be observed when cells are grown under specific culture conditions. Gap junctions are abundant among osteoblastic cells in vivo and in vitro, whereas they are down-regulated during adipogenesis. Gap junctional communication (GJC) modulates the expression of genes associated with the mature osteoblastic phenotype. Inhibition of GJC utilizing 18-␣-glycyrrhetinic acid (AGRA) blocks the maturation of preosteoblastic cells in vitro. Moreover, cytoplasmic lipid droplets are detectable at the end of the culture period, suggesting that GJC inhibition may favor an adipocytic phenotype. We used several human osteoblastic cell lines, as well as bone-derived primary osteoblastic cells, to show that confluent cultures of human osteoblastic cells grown under osteogenic conditions developed an adipocytic phenotype after 3 days of complete inhibition of GJC using AGRA or oleamide, two dissimilar nontoxic reversible inhibitors. Development of an adipogenic phenotype was confirmed by the accumulation of triglyceride droplets and the increase in mRNA expression of the adipocytic markers peroxisome proliferatoractivated receptor ␥2 and lipoprotein lipase. Glycyrrhizic acid, a noninhibitory AGRA analog, or ␣-bromopalmitate, a nondegradable fatty acid, had no effect. Modulation of skeletal GJC may represent a new pharmacological target by which inhibition of marrow adipogenesis can take place with the parallel enhancement of osteoblastogenesis, thus providing a novel therapeutic approach to the treatment of human agerelated osteopenic diseases and postmenopausal osteoporosis.Osteoblasts and adipocytes are phenotypically distinct mature cells thought to differentiate from a common mesenchymal progenitor cell (1-2). The molecular events that determine lineage progression toward a specific phenotype remain to be fully characterized. Either cell type can be cultured in vitro under conditions that foster or maintain their respective phenotypes. Osteogenic conditions include the presence of ascorbic acid, ␤-glycerol phosphate, and dexamethasone or vitamin D 3 , depending on the maturational stage of the osteoblast precursor, in the culture medium. In contrast, adipogenic conditions include the presence of 3-isobutyl-1-methylxanthine (IBMX), 1 insulin, and dexamethasone in the culture medium. Nutall et al. (3) have shown that mature human osteoblastic cells are capable of trans-differentiation to adipocytes when cultured in the presence of dexamethasone and IBMX. On the other hand, Park et al. (4) have shown that cloned single human adipocytes can dedifferentiate into fibroblast-like cells, which subsequently differentiate into osteoblasts or adipocytes under appropriate culture conditions. This plasticity between the differentiation of osteogenic and adipogenic human cells provides further support for a common precursor and has significant physiological impl...

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“…It has been reported that osteoblastic cells have the GJIC function and the function is believed to be critical for the coordinated cell behavior necessary in bone tissue development. [28][29][30] It was reported that enhancing the GJIC function of osteoblasts by connexin gene transfection induced up-regulation of osteocalcin and bone sialoprotein gene transcription. 30) In addition, wear debris particles have been reported to suppress collagen and glycosaminoglycan synthesis from osteoblasts when the particles are included in the osteoblasts.…”

Section: Discussionmentioning

confidence: 99%

Biocompatibility of Various Kinds of Polymer Microspheres Estimated from Their Effect on Gap Junctional Intercellular Communication of Fibroblasts

Nakaoka¹,

Tsuchiya²

2002

Mater. Trans.

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Gap junctional intercellular communication is a function that plays an important role in maintaining cell and tissue homeostasis and in regulating cell growth, development and differentiation. Change in this function when contacting fibroblasts with various polymer microspheres was estimated using the fluorescence recovery after photobleaching (FRAP) assay system. When the cells were in contact on test dishes, the inhibition level increased as the diameters of polystyrene microspheres decreased, except for a microsphere with 0.5 µm diameter. The function was inclined to be recovered with the increase of the incubation time, while it was not recovered when the cells were cultured with pre-coated polystyrene microspheres. As well as inhibitory activities of the function, cytotoxicity potentials of tested microspheres depended on their diameter and their composition. These findings suggest that the size and the physico-chemical character of polymer microspheres, and how cells recognize them plays important roles in causing influences of the microspheres on both gap junctional intercellular communication and their cytotoxicity. Therefore, estimating the inhibitory effect of biomaterials on the gap junctional intercellular communication will provide valuable information about the biocompatibility of materials even in the form of particles.

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Hormonal Regulation of Connexin 43 Expression and Gap Junctional Communication in Human Osteoblastic Cells.

Cited by 43 publications

References 25 publications

Connexin43 Potentiates Osteoblast Responsiveness to Fibroblast Growth Factor 2 via a Protein Kinase C-Delta/Runx2–dependent Mechanism

Connexin43 Potentiates Osteoblast Responsiveness to Fibroblast Growth Factor 2 via a Protein Kinase C-Delta/Runx2–dependent Mechanism

Inhibition of Gap-Junctional Communication Induces the Trans-differentiation of Osteoblasts to an Adipocytic Phenotype in Vitro

Biocompatibility of Various Kinds of Polymer Microspheres Estimated from Their Effect on Gap Junctional Intercellular Communication of Fibroblasts

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