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Estrogen augments shear stress-induced signaling and gene expression in osteoblast-like cells via estrogen receptor-mediated expression of beta1-integrin.

ABSTRACT: Estrogen and mechanical forces are positive regulators for osteoblast proliferation and bone formation. We investigated the synergistic effect of estrogen and flow-induced shear stress on signal transduction and gene expression in human osetoblast-like MG63 cells and primary osteoblasts (HOBs) using activations of extracellular signal-regulated kinase (ERK) and p38 mitogen-activated protein kinase (MAPK) and expressions of c-fos and cyclooxygenase-2 (I) as readouts. Estrogen (17beta-estradiol, 10 nM) and shear stress (12 dyn/cm(2)) alone induced transient phosphorylations of ERK and p38 MAPK in MG63 cells. Pretreating MG63 cells with 17beta-estradiol for 6 hours before shearing augmented these shear-induced MAPK phosphorylations. Western blot and flow cytometric analyses showed that treating MG63 cells with 17beta-estradiol for 6 hrs induced their beta(1)-integrin expression. This estrogen-induction of beta(1)-integrin was inhibited by pretreating the cells with a specific antagonist of estrogen receptor ICI 182,780. Both 17beta-estradiol and shear stress alone induced c-fos and Cox-2 gene expressions in MG63 cells. Pretreating MG63 cells with 17beta-estradiol for 6 hrs augmented the shear-induced c-fos and Cox-2 expressions. The augmented effects of 17beta-estradiol on shear-induced MAPK phosphorylations and c-fos and Cox-2 expressions were inhibited by pretreating the cells with ICI 182,780 or transfecting the cells with beta(1)-specific small interfering RNA. Similar results on the augmented effect of estrogen on shear-induced signaling and gene expression were obtained with HOBs. Our findings provide insights into the mechanism by which estrogen augments shear stress responsiveness of signal transduction and gene expression in bone cells via estrogen receptor-mediated increases in beta(1)-integrin expression.

SUBMITTER: Yeh CR

PROVIDER: S-EPMC3153398 | biostudies-literature | 2010 Mar

REPOSITORIES: biostudies-literature

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Estrogen augments shear stress-induced signaling and gene expression in osteoblast-like cells via estrogen receptor-mediated expression of beta1-integrin.

Yeh Chiuan-Ren CR Chiu Jeng-Jiann JJ Lee Chih-I CI Lee Pei-Ling PL Shih Yu-Tsung YT Sun Jui-Sheng JS Chien Shu S Cheng Cheng-Kung CK

Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research 20100301 3

Estrogen and mechanical forces are positive regulators for osteoblast proliferation and bone formation. We investigated the synergistic effect of estrogen and flow-induced shear stress on signal transduction and gene expression in human osetoblast-like MG63 cells and primary osteoblasts (HOBs) using activations of extracellular signal-regulated kinase (ERK) and p38 mitogen-activated protein kinase (MAPK) and expressions of c-fos and cyclooxygenase-2 (I) as readouts. Estrogen (17beta-estradiol, 1 ...[more]

PMID: 19821775

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Project description:BackgroundRecently we reported that fluid shear stress promotes endothelial cell differentiation from a mouse embryo mesenchymal progenitor cell line C3H10T1/2. However, it is not clear whether the transforming growth factor-beta 1 (TGF-beta1) system is associated with shear-induced endothelial differentiation. The purpose of this study was to determine the effect of shear stress on the expression of TGF-beta1 and its signaling molecules in C3H10T1/2 cells.MethodsMurine C3H10T1/2 cells were incubated on collagen Type 1-coated dishes, and subjected to a steady fluid shear stress of 15 dyn/cm(2) for 6, 12, and 24 h. The mRNA levels for TGF-beta1, TGF-beta receptors (TGF-beta R), and Smad molecules were determined with real-time PCR analysis and normalized to glyceraldehyde-3-phosphate dehydrogenase mRNA levels.ResultsTGF-beta1 mRNA expression was down-regulated by 60% and 66% in shear stress-treated cells at 12 and 24 h, respectively, compared with static control group (P < 0.01). In addition, shear stress significantly decreased TGF-beta R1 mRNA levels by 30% and 50% in shear stress-treated cells at 12 and 24 h, respectively (P < 0.01). For TGF-beta R2, shear stress at 6, 12, and 24 h significantly reduced its expression by 93%, 95% and 97%, respectively, compared with static controls (P < 0.01). Furthermore, shear stress significant decreased mRNA levels of positive signaling molecules Smad2, Smad3, and Smad4 in a time-dependent manner (P < 0.01). However, shear stress significantly increased negative signaling molecule Smad7 mRNA levels by 100% at 24 h treatment compared with static control group (P < 0.01).ConclusionsFluid shear stress significantly suppresses TGF-beta1 functions through down-regulation of TGF-beta1, TGF-beta R, positive signaling molecules Smad2, Smad3, Smad4, and up-regulation of negative signaling molecule Smad7 in a mouse embryo mesenchymal progenitor cell line C3H10T1/2. This study suggests that the negative regulation of the TGF-beta1 system may be involved in shear-induced endothelial cell differentiation in C3H10T1/2.

Project description:Vascular endothelial cells (ECs) sense and transduce hemodynamic shear stress into intracellular biochemical signals, and Ca2+ signaling plays a critical role in this mechanotransduction, i.e., ECs release ATP in the caveolae in response to shear stress and, in turn, the released ATP activates P2 purinoceptors, which results in an influx into the cells of extracellular Ca2+. However, the mechanism by which the shear stress evokes ATP release remains unclear. Here, we demonstrated that cellular mitochondria play a critical role in this process. Cultured human pulmonary artery ECs were exposed to controlled levels of shear stress in a flow-loading device, and changes in the mitochondrial ATP levels were examined by real-time imaging using a fluorescence resonance energy transfer-based ATP biosensor. Immediately upon exposure of the cells to flow, mitochondrial ATP levels increased, which was both reversible and dependent on the intensity of shear stress. Inhibitors of the mitochondrial electron transport chain and ATP synthase as well as knockdown of caveolin-1, a major structural protein of the caveolae, abolished the shear stress-induced mitochondrial ATP generation, resulting in the loss of ATP release and influx of Ca2+ into the cells. These results suggest the novel role of mitochondria in transducing shear stress into ATP generation: ATP generation leads to ATP release in the caveolae, triggering purinergic Ca2+ signaling. Thus, exposure of ECs to shear stress seems to activate mitochondrial ATP generation through caveola- or caveolin-1-mediated mechanisms. NEW & NOTEWORTHY The mechanism of how vascular endothelial cells sense shear stress generated by blood flow and transduce it into functional responses remains unclear. Real-time imaging of mitochondrial ATP demonstrated the novel role of endothelial mitochondria as mechanosignaling organelles that are able to transduce shear stress into ATP generation, triggering ATP release and purinoceptor-mediated Ca2+ signaling within the cells.

Dataset Information

Estrogen augments shear stress-induced signaling and gene expression in osteoblast-like cells via estrogen receptor-mediated expression of beta1-integrin.

Publications

Estrogen augments shear stress-induced signaling and gene expression in osteoblast-like cells via estrogen receptor-mediated expression of beta1-integrin.

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