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Fluid Shear Stress (fluid + shear_stress)
Selected AbstractsFluid Flow Induction of Cyclo-Oxygenase 2 Gene Expression in Osteoblasts Is Dependent on an Extracellular Signal-Regulated Kinase Signaling Pathway,,JOURNAL OF BONE AND MINERAL RESEARCH, Issue 2 2002Sunil Wadhwa Abstract Mechanical loading of bone may be transmitted to osteocytes and osteoblasts via shear stresses at cell surfaces generated by the flow of interstitial fluid. The stimulated production of prostaglandins, which mediates some effects of mechanical loading on bone, is dependent on inducible cyclo-oxygenase 2 (COX-2) in bone cells. We examined the fluid shear stress (FSS) induction of COX-2 gene expression in immortalized MC3T3-E1 osteoblastic cells stably transfected with ,371/+70 base pairs (bp) of the COX-2 5,-flanking DNA (Pluc371) and in primary osteoblasts (POBs) from calvaria of mice transgenic for Pluc371. Cells were plated on collagen-coated glass slides and subjected to steady laminar FSS in a parallel plate flow chamber. FSS, from 0.14 to10 dynes/cm2, induced COX-2 messenger RNA (mRNA) and protein. FSS (10 dynes/cm2) induced COX-2 mRNA within 30 minutes, with peak effects at 4 h in MC3T3-E1 cells and at ,8 h in POBs. An inhibitor of new protein synthesis puromycin blocked the peak induction of COX-2 mRNA by FSS. COX-2 promoter activity, measured as luciferase activity, correlated with COX-2 mRNA expression in both MC3T3-E1 and POB cells. FSS induced phosphorylation of extracellular signal-regulated kinase (ERK) in MC3T3-E1 cells, with peak effects at 5 minutes. Inhibiting ERK phosphorylation with the specific inhibitor PD98059 inhibited FSS induction of COX-2 mRNA by 55-70% and FSS stimulation of luciferase activity by ,80% in both MC3T3-E1 and POB cells. We conclude that FSS transcriptionally induces COX-2 gene expression in osteoblasts, that the maximum induction requires new protein synthesis, and that induction occurs largely via an ERK signaling pathway. [source] Nmp4/CIZ contributes to fluid shear stress induced MMP-13 gene induction in osteoblastsJOURNAL OF CELLULAR BIOCHEMISTRY, Issue 5 2007Kanokwan Charoonpatrapong-Panyayong Abstract The expression of matrix metalloproteinase-13 (MMP-13), involved in bone turnover, is elevated in stretched MC3T3-E1 osteoblast-like cells. Strain-mediated forces impact bone remodeling due in large part to the movement of fluid through the canalicular-lacunar network. The resulting fluid shear stress (FSS) over the surface membranes of bone cells initiates bone remodeling. Although the nuclear events mediating putative FSS-induced changes in osteoblast MMP-13 transcription are unknown, previous studies with bone cells suggest an overlap between osteoblast FSS- and PTH-induced signal response pathways. MMP-13 PTH response is regulated by a 110 bp 5, regulatory region, conserved across the mouse, rat, and human genes, that supports the binding of numerous transcription factors including Runx2, c-fos/c-jun, Ets-1, and nuclear matrix protein 4/cas interacting zinc finger protein (Nmp4/CIZ) a nucleocytoplasmic shuttling trans-acting protein that attenuates PTH-driven transcription. Nmp4/CIZ also binds p130cas, an adaptor protein implicated in mechanotransduction. Here we sought to determine whether Nmp4/CIZ contributes to FSS-induced changes in MMP-13 transcription. FSS (12 dynes/cm2, 3,5 h) increased MMP-13 promoter-reporter activity approximately two-fold in MC3T3-E1 osteoblast-like cells attended by a comparable increase in mRNA expression. This was accompanied by a decrease in Nmp4/CIZ binding to its cis-element within the PTH response region, the mutation of which abrogated the MMP-13 response to FSS. Interestingly, FSS enhanced Nmp4/CIZ promoter activity and induced p130cas nuclear translocation. We conclude that the PTH regulatory region of MMP-13 also contributes to FSS response and that Nmp4/CIZ plays similar but distinct roles in mediating hormone- and FSS-driven induction of MMP-13 in bone cells. J. Cell. Biochem. 102: 1202,1213, 2007. © 2007 Wiley-Liss, Inc. [source] Response of periodontal ligament fibroblasts and gingival fibroblasts to pulsating fluid flow: nitric oxide and prostaglandin E2 release and expression of tissue non-specific alkaline phosphatase activityJOURNAL OF PERIODONTAL RESEARCH, Issue 6 2000M. T. M. Van Der Pauw The capacity of the periodontal ligament to alter its structure and mass in response to mechanical loading has long been recognized. However, the mechanism by which periodontal cells can detect physical forces and respond to them is largely unknown. Besides transmission of forces via cell-matrix or cell-cell interactions, the strain-derived flow of interstitial fluid through the periodontal ligament may mechanically activate the periodontal cells, as well as ensure transport of cell signaling molecules, nutrients and waste products. Mechanosensory cells, such as endothelial and bone cells, are reported to respond to a flow of fluid with stimulated prostaglandin E2(PGE2) and nitric oxide production. Therefore, we examined the PGE2 and nitric oxide response of human periodontal ligament and gingival fibroblasts to pulsating fluid flow and assessed the expression of tissue non-specific alkaline phosphatase activity. Periodontal ligament and gingival fibroblasts were subjected to a pulsating fluid flow (0.7±0.02 Pa, 5 Hz) for 60 min. PGE2 and nitric oxide concentrations were determined in the conditioned medium after 5, 10, 30 and 60 min of flowing. After fluid flow the cells were cultured for another 60 min without mechanical stress. Periodontal ligament fibroblasts, but not gingival fibroblasts, responded to fluid flow with significantly elevated release of nitric oxide and decreased expression of tissue non-specific alkaline phosphatase activity. In both periodontal ligament and gingival fibroblasts, PGE2 production was significantly increased after 60 min of flowing. Periodontal ligament fibroblasts, but not gingival fibroblasts, produced significantly higher levels of PGE2 during the postflow culture period. We conclude that human periodontal ligament fibroblasts are more responsive to pulsating fluid flow than gingival fibroblasts. The similarity of the early nitric oxide and PGE2 responses to fluid flow in periodontal fibroblasts with bone cells and endothelial cells suggests that these three cell types possess a similar sensor system for fluid shear stress. [source] Age-Related Changes in Phosphorylation of Endothelial Nitric Oxide Synthase in the Rat PenisTHE JOURNAL OF SEXUAL MEDICINE, Issue 3 2005Biljana Musicki PhD ABSTRACT Aim., Aging is associated with erectile dysfunction (ED) attributed to reduced nitric oxide synthase (NOS) activity and nitric oxide bioavailability. However, the mechanism for this effect has not been fully investigated. We evaluated (i) whether age-related ED involves dysregulation of endothelial NOS (eNOS) phosphorylation; and (ii) whether vascular endothelial growth factor (VEGF) exerts erectile effects and operates via eNOS phosphorylation in aged rats. Methods., Male Fischer 344 "young" (4-month-old) and "aged" (19-month-old) rats were used. Electrical stimulation of the cavernous nerve (CNS) was performed to generate penile erection. Erectile response in the presence of rhVEGF165 was evaluated by intracavernosal pressure monitoring 25 minutes after intracavernosal injection of VEGF. Penes were excised at baseline, with or without rhVEGF treatment, and after CNS for Western immunoblot of phospho-eNOS (Ser-1177 and Thr-495), phospho-Akt, and eNOS. Results., Erectile response was significantly reduced in aged rats compared with young rats. Phospho-eNOS (Ser-1177) and phospho-Akt were significantly reduced, while phospho-eNOS (Thr-495) was significantly increased, in the aged penis at baseline and after CNS. rhVEGF significantly improved erection and reversed downregulated Ser-1177, but not upregulated Thr-495 phosphorylation, on eNOS in aged penes. eNOS protein was significantly increased in aged penes. Conclusions., Age-related ED is associated with eNOS inactivation through a decrease in phosphorylation of its positive regulatory site (Ser-1177) and an increase in phosphorylation of its negative regulatory site (Thr-495) in the penis. Altered phosphorylation/constitutive activation of eNOS by fluid shear stress may be a major determinant of compromised vascular homeostasis of the aged penis. The finding that VEGF rapidly induces erection and partly corrects alterations in eNOS phosphorylation in the aged rat penis suggests impaired eNOS activation by deficient endogenous VEGF and supports the potential for growth factor therapy in the treatment of age-related ED. [source] Regulation of plasminogen activator inhibitor 1 expression in human osteoarthritic chondrocytes by fluid shear stress: Role of protein kinase C,ARTHRITIS & RHEUMATISM, Issue 8 2009Chih-Chang Yeh Objective To test a fluid flow system for the investigation of the influence of shear stress on expression of plasminogen activator inhibitor 1 (PAI-1) in human osteoarthritic (OA) articular chondrocytes (from lesional and nonlesional sites) and human SW-1353 chondrocytes. Methods Human SW-1353 chondrocytes and OA and normal human articular chondrocytes were cultured on type II collagen,coated glass plates under static conditions or placed in a flow chamber to form a closed fluid-circulation system for exposure to different levels of shear stress (2,20 dyn/cm2). Real-time polymerase chain reaction was used to analyze PAI-1 gene expression, and protein kinase C (PKC) inhibitors and small interfering RNA were used to investigate the mechanism of shear stress,induced signal transduction in SW-1353 and OA (lesional and nonlesional) articular chondrocytes. Results There was a significant reduction in PAI-1 expression in OA chondrocytes obtained from lesional sites compared with those obtained from nonlesional sites. In SW-1353 chondrocytes subjected to 2 hours of shear flow, moderate shear stresses (5 and 10 dyn/cm2) generated significant PAI-1 expression, which was regulated through PKC, phosphorylation and Sp-1 activation. These levels of shear stress also increased PAI-1 expression in articular chondrocytes from nonlesional sites and from normal healthy cartilage through the activation of PKC, and Sp-1 signal transduction, but no effect of these levels of fluid shear stress was observed on OA chondrocytes from lesional sites. Conclusion OA chondrocytes from lesional sites and those from nonlesional sites of human cartilage have differential responses to shear stress with regard to PAI-1 gene expression, and therefore diverse functional consequences can be observed. [source] Prediction of Leakage Flow in a Shrouded Centrifugal Blood PumpARTIFICIAL ORGANS, Issue 9 2010Ji-Bin Teo Abstract This article proposes a phenomenological model to predict the leakage flow in the clearance gap of shrouded centrifugal blood pumps. A good washout in the gap clearance between the rotating impeller surfaces and volute casing is essential to avoid thrombosis. However, excessive leakage flow will result in higher fluid shear stress that may lead to hemolysis. Computational fluid dynamics (CFD) analysis was performed to investigate the leakage flow in a miniaturized shrouded centrifugal blood pump operating at a speed of 2000 rpm. Based on an analytical model derived earlier, a phenomenological model is proposed to predict the leakage flow. The leakage flow rate is found to be proportional to h,, where h is the gap size and the exponent , ranges from 2.955 to 3.15 for corresponding gap sizes of 0.2,0.5 mm. In addition, it is observed that , is a linear function of the gap size h. The exponent , compensates for the variation of pressure difference along the circumferential direction as well as inertia effects that are dominant for larger gap clearances. The proposed model displays good agreement with computational results. The CFD analysis also showed that for larger gap sizes, the total leakage flow rate is of the same order of magnitude as the operating flow rate, thus suggesting low volumetric efficiency. [source] | ||||||||||