Fluid Flow Shear Stress Research Articles

Viscoelastic Fluid Flow Model for Hydrodynamic Behaviour of Magnetorheological Fluid in Valve and Shear Modes for a Damper System

In this present study, the flow behaviour of magnetorheological fluid in valve and shear modes for damping system is modelled and analysed. The fluid is modelled as viscoelastic fluid flowing between two parallel plates in pressure driven flow mode, and also as direct shear mode. In the work, the post-yield shear thinning or thickening behaviour of magnetorheological fluids are accounted for. The velocity and pressure distributions in the unsteady magnetorheological fluid flow between the electrodes of the damper are obtained by solving the momentum equation of the magnetorheological fluid flow using the Laplace transform method. There is an excellent agreement between the results of the present model and the results of the experimental studies. The adopted viscoelastic flow model describes that the rheological behaviour of the fluid is separated into distinct pre-yield and post-yield regimes. The fluid flow velocity, velocity gradient, and shear stresses have all been shown to be enhanced by an increase in the pressure drop. The viscosity of the fluid increases with an increase in the volume fraction of particles in the fluid, which causes the resistance of the fluid to flow to increase and thereby, reduces the fluid flow velocity. Fluid flow velocity is decreased as a result of increasing magnetic field strength. The design of clutches, rotary brakes, dampers, shock absorbers, prosthetic devices, polishing and grinding tools, etc. will all benefit greatly from the adoption of the current model.

Biomechanism of abnormal stress on promoting osteoarthritis of temporomandibular joint through Piezo1 ion channel.

This study aimed to investigate whether flow fluid shear stress (FFSS)-mediated signal transduction affects the function of Piezo1 ion channel in chondrocyte and to further explore the role of mechanical overloading in development of temporomandibular joint osteoarthritis (TMJ OA). Immunohistochemical staining was used to determine the expression of Piezo1 in TMJ OA tissue collected from rat unilateral anterior crossbite (UAC) models. Chondrocytes harvested from normal adult SD rats were treated with FFSS (0, 4, 8, 12 dyn/cm2) invitro. Immunofluorescent staining, real-time polymerase chain reaction, western blotting, flow cytometry and phalloidin assay were performed to detect the changes of cellular morphology as well as the expression of Piezo1 and certain pro-inflammatory and degradative factors in chondrocyte. Immunohistochemical analysis revealed that significantly increased Piezo1 expression was associated with UAC stimulation (p < .05). As applied FFSS escalated (4, 8 and 12 dyn/cm2), the expression levels of Piezo1, ADAMTS-5, MMP-13 and Col-X gradually increased, compared with the non-FFSS group (p < .05). Administering Piezo1 ion channel inhibitor to chondrocytes beforehand, it was observed that expression of ADAMTS-5, MMP-13 and Col-X was substantially decreased following FFSS treatment (p < .05) and the effect of cytoskeletal thinning was counteracted. The activated Piezo1 ion channel enhanced intracellular Ca2+ excess in chondrocytes during abnormal mechanical stimulation and the increased intracellular Ca2+ thinned the cytoskeleton of F-actin. Mechanical overloading activates Piezo1 ion channel to promote pro-inflammation and degradation and to increase Ca2+ concentration in chondrocyte, which may eventually result in TMJ OA.

Switching to external flows: perturbations of developing vasculature within chicken chorioallantoic membrane.

The impact of fluid flow shear stresses, generated by the movement of blood through vasculature, on the organization and maturation of vessels is widely recognized. Nevertheless, it remains uncertain whether external fluid flows outside of the vasculature in the surrounding tissue can similarly play a role in governing these processes. In this research, we introduce an innovative technique called superfusion-induced vascular steering (SIVS). SIVS involves the controlled imposition of external fluid flow patterns onto the vascularized chick chorioallantoic membrane (CAM), allowing us to observe how this impacts the organization of vascular networks. To investigate the concept of SIVS, we conducted superfusion experiments on the intact chick CAM cultured within an engineered eggshell system, using phosphate buffered saline (PBS). To capture and analyze the effects of superfusion, we employed a custom-built microscopy setup, enabling us to image both superfused and non-superfused regions within the developing CAM. This study provides valuable insights into the practical application of fluid superfusion within an in vivo context, shedding light on its significance for understanding tissue development and manipulation in an engineering setting.

Decreased expression of ATP-binding cassette protein G1 promotes abnormal adipogenesis of condylar chondrocytes intemporomandibular joint osteoarthritis.

Abnormal lipid metabolism is involved in the development of osteoarthritis (OA). ATP-binding cassette protein G1 (ABCG1) is crucial in mediating the outflow of cholesterol, phosphatidylcholine and sphingomyelin and reducing intracellular lipid accumulation. This study aimed to evaluate whether ABCG1 participates in the abnormal adipogenesis of chondrocytes in osteoarthritic cartilage of temporomandibular joint. Eight-week-old female rats were subjected to unilateral anterior crossbite (UAC) to induce OA in the temporomandibular joint (TMJ). Histochemical staining, immunohistochemical (IHC) staining, and qRT-PCR were performed. Primary condylar chondrocytes of rats were transfected with ABCG1 shRNA or overexpression lentivirus and then stimulated with fluid flow shear stress (FFSS). Cells were collected for oil red O staining, immunofluorescence staining, and qRT-PCR analysis. Abnormal adipogenesis, characterized by increased expression of Adiponectin, CCAAT/enhancer-binding protein α (Cebpα), fatty acid binding protein 4 (Fabp4) and Perilipin1, was enhanced in the degenerative cartilage of TMJ OA in rats with UAC, accompanied by decreased expression of ABCG1. After FFSS stimulation, we observed lipid droplets in the cytoplasm of cultured cells with increased expression of Adiponectin, Cebpα, Fabp4 and Perilipin1 and decreased expression of ABCG1. Knockdown of Abcg1 induced abnormal adipogenesis and differentiation of condylar chondrocytes. Overexpression of ABCG1 alleviated the abnormal adipogenesis and differentiation of condylar chondrocytes induced by FFSS. Abnormal adipogenesis of chondrocytes and decreased ABCG1 expression were observed in degenerative cartilage of TMJ OA. ABCG1 overexpression effectively inhibits the adipogenesis of chondrocytes and thus alleviates TMJ condylar cartilage degeneration.

Effect of Moderate Exercise on the Superficial Zone of Articular Cartilage in Age-Related Osteoarthritis.

This study aimed to evaluate the effect of exercise on the superficial zone of the osteoarticular cartilage during osteoarthritis progression. Three-month-old, nine-month-old, and eighteen-month-old Sprague Dawley rats were randomly divided into two groups, moderate exercise and no exercise, for 10 weeks. Histological staining, immunostaining, and nanoindentation measurements were conducted to detect changes in the superficial zone. X-ray and micro-CT were quantitated to detect alterations in the microarchitecture of the tibial subchondral bone. Cells were extracted from the superficial zone of the cartilage under fluid-flow shear stress conditions to further verify changes in vitro. The number of cells and proteoglycan content in the superficial zone increased more in the exercise group than in the control group. Exercise can change the content and distribution of collagen types I and III in the superficial layer. In addition, TGFβ/pSmad2/3 and Prg4 expression levels increased under the intervention of exercise on the superficial zone. Exercise can improve the Young's modulus of the cartilage and reduce the abnormal subchondral bone remodeling which occurs after superficial zone changes. Moderate exercise delays the degeneration of the articular cartilage by its effect on the superficial zone, and the TGFβ/pSmad2/3 signaling pathways and Prg4 play an important role.

Fluid flow shear stress and tissue remodeling-an orthodontic perspective: evidence synthesis and differential gene expression network analysis.

Introduction: This study aimed to identify and analyze in vitro studies investigating the biological effect of fluid-flow shear stress (FSS) on cells found in the periodontal ligament and bone tissue. Method: We followed the PRISMA guideline for systematic reviews. A PubMed search strategy was developed, studies were selected according to predefined eligibility criteria, and the risk of bias was assessed. Relevant data related to cell source, applied FSS, and locus-specific expression were extracted. Based on this evidence synthesis and, as an original part of this work, analysis of differential gene expression using over-representation and network-analysis was performed. Five relevant publicly available gene expression datasets were analyzed using gene set enrichment analysis (GSEA). Result: A total of 6,974 articles were identified. Titles and abstracts were screened, and 218 articles were selected for full-text assessment. Finally, 120 articles were included in this study. Sample size determination and statistical analysis related to methodological quality and the ethical statement item in reporting quality were most frequently identified as high risk of bias. The analyzed studies mostly used custom-made fluid-flow apparatuses (61.7%). FSS was most frequently applied for 0.5h, 1h, or 2h, whereas FSS magnitudes ranged from 6 to 20dyn/cm2 depending on cell type and flow profile. Fluid-flow frequencies of 1Hz in human cells and 1 and 5Hz in mouse cells were mostly applied. FSS upregulated genes/metabolites responsible for tissue formation (AKT1, alkaline phosphatase, BGLAP, BMP2, Ca2+, COL1A1, CTNNB1, GJA1, MAPK1/MAPK3, PDPN, RUNX2, SPP1, TNFRSF11B, VEGFA, WNT3A) and inflammation (nitric oxide, PGE-2, PGI-2, PTGS1, PTGS2). Protein-protein interaction networks were constructed and analyzed using over-representation analysis and GSEA to identify shared signaling pathways. Conclusion: To our knowledge, this is the first review giving a comprehensive overview and discussion of methodological technical details regarding fluid flow application in 2D cell culture in vitro experimental conditions. Therefore, it is not only providing valuable information about cellular molecular events and their quantitative and qualitative analysis, but also confirming the reproducibility of previously published results.

Computational modeling based on confocal imaging predicts changes in osteocyte and dendrite shear stress due to canalicular loss with aging.

Exercise and physical activity exert mechanical loading on the bones which induces bone formation. However, the relationship between the osteocyte lacunar-canalicular morphology and mechanical stress experienced locally by osteocytes transducing signals for bone formation is not fully understood. In this study, we used computational modeling to predict the effect of canalicular density, the number of fluid inlets, and load direction on fluid flow shear stress (FFSS) and bone strains and how these might change following the microstructural deterioration of the lacunar-canalicular network that occurs with aging. Four distinct computational models were initially generated of osteocytes with either ten or eighteen dendrites using a fluid-structure interaction method with idealized geometries. Next, a young and a simulated aged osteocyte were developed from confocal images after FITC staining of the femur of a 4-month-old C57BL/6 mouse to estimate FFSS using a computational fluid dynamics approach. The models predicted higher fluid velocities in the canaliculi versus the lacunae. Comparison of idealized models with five versus one fluid inlet indicated that with four more inlets, one-half of the dendrites experienced FFSS greater than 0.8Pa, which has been associated with osteogenic responses. Confocal image-based models of real osteocytes indicated a six times higher ratio of canalicular to lacunar surface area in the young osteocyte model than the simulated aged model and the average FFSS in the young model (FFSS = 0.46Pa) was three times greater than the aged model (FFSS = 0.15Pa). Interestingly, the surface area with FFSS values above 0.8Pa was 23 times greater in the young versus the simulated aged model. These findings may explain the impaired mechano-responsiveness of osteocytes with aging.

CaSR modulates proliferation of the superficial zone cells in temporomandibular joint cartilage via the PTHrP nuclear localization sequence.

The superficial zone cells in mandibular condylar cartilage are proliferative. The present purpose was to delineate the relation of calcium-sensing receptor (CaSR) and parathyroid hormone-related peptide nuclear localization sequence (PTHrP87-139 ), and their role in the proliferation behaviors of the superficial zone cells. A gain- and loss-of-function strategy were used in an in vitro fluid flow shear stress (FFSS) model and an in vivo bilateral elevation bite model which showed mandibular condylar cartilage thickening. CaSR and PTHrP87-139 were modulated through treating the isolated superficial zone cells with activator/SiRNA and via deleting CaSR or parathyroid hormone-related peptide (PTHrP) gene in mice with the promoter gene of proteoglycan 4 (Prg4-CreERT2 ) in the tamoxifen-inducible pattern with or without additional injection of Cinacalcet, the CaSR agonist, or PTHrP87-139 peptide. FFSS stimulated CaSR and PTHrP expression, and accelerated proliferation of the Prg4-expressing superficial zone cells, in which process CaSR acted as an up-streamer of PTHrP. Proteoglycan 4 specific knockout of CaSR or PTHrP reduced the cartilage thickness, suppressed the proliferation and early differentiation of the superficial zone cells, and inhibited cartilage thickening and matrix production promoted by bilateral elevation bite. Injections of CaSR agonist Cinacalcet could not improve the phenotype caused by PTHrP mutation. Injections of PTHrP87-139 peptide rescued the cartilage from knockout of CaSR gene. CaSR modulates proliferation of the superficial zone cells in mandibular condylar cartilage through activation of PTHrP nuclear localization sequence. Our data support the therapeutic target of CaSR in promoting PTHrP production in superficial zone cartilage.

ANGIOTENSIN-(1-7) FORMATION UPON FLUID FLOW SHEAR STRESS IN HUMAN PODOCYTES

Objective: Glomerular hyperfiltration associates with increased fluid flow shear stress (FFSS) on podocytes. This can lead to irreversible podocyte damage, which in turn negatively affects the permeability and integrity of the glomerular filtration barrier. AngiotensinII (AngII) is an important mediator in chronic kidney disease. The negative effects of AngII are at least partially opposed by the alternative signaling pathways within the renin-angiotensin system (RAS) consisting of angiotensin-converting enzyme 2 (ACE2), angiotensin-(1-7) (Ang-[1-7]) and the MAS1 receptor. This counteracting pathway may exert renoprotective effects and support anti-inflammatory processes. As the pathomechanisms and signaling pathways underlying podocyte damage induced by FFSS are not fully understood, our aim is to elucidate the potential renoprotective impact of the alternative RAS axis in human podocytes in the context of glomerular hyperfiltration. Design and method: Conditionally immortalized human podocytes (hPCs) were used for mechanistic studies. Cells seeded on collagen IV coated Culture Slips® were inserted in a Streamer® Shear Stress Device and exposed to FFSS of 1dyne/cm2 for 2h. Control cells were not exposed to FFSS. Afterwards, the formation rate of AngII to Ang-[1-7] was measured in whole cell lysates (1 experiment, n = 6 samples per condition) using spiked AngII as a substrate with and without addition of Z-Pro-Prolinal and MLN-4760. Additionally, gene expression analyses of the enzymes involved in Ang-[1-7] formation were performed. Results: Preliminary data show an increased AngII to Ang-[1-7] formation rate in hPCs following FFSS exposure compared to control. Ang-[1-7] formation under both conditions is reduced by addition of Z-Pro-Prolinal, whereas MLN-4760 has no effect. RNA-expression levels of prolylcarboxypeptidase and prolylendopeptidase are not significantly affected upon FFSS compared to control. In contrast, ACE2 is significantly upregulated by FFSS although expression levels are substantially lower under both conditions compared to prolylcarboxypeptidase and prolylendopeptidase. Conclusions: Our results suggest an elevated AngII to Ang-[1-7] formation rate upon FFSS in hPCs compared to no-flow control. Under both settings, Ang-[1-7] formation in hPCs seems to be mediated by prolylcarboxypeptidase and/or prolylendopeptidase but not ACE2. These results support further studies to confirm the potential role and mechanisms of Ang-[1-7] upregulation in response to glomerular hyperfiltration.

Piezo1 mediates the degradation of cartilage extracellular matrix in malocclusion-induced TMJOA.

To evaluate the role of Piezo1 in the malocclusion-induced osteoarthritic cartilage of the temporomandibular joint. A temporomandibular joint osteoarthritis model was established using a unilateral anterior crossbite in vivo, and cartilage degeneration and Piezo1 expression were observed by histological and immunohistochemical staining. ATDC5 cells were loaded with 24 dyn/cm2 fluid flow shear stress using the Flexcell device in vitro and expression and function of Piezo1 were evaluated. After identifying the function of Piezo1 in YAP translocation under FFSS conditions, the influence of Piezo1 and YAP on metabolism-related enzymes under FFSS was detected through a real-time polymerase chain reaction analysis and western blotting. A UAC-TMJ injection model was established to observe the therapeutic effect of intra-articular injection of a Piezo1 inhibitor on osteoarthritic cartilage matrix loss. Piezo1 was overexpressed in the osteoarthritic cartilage and cultured chondrocytes under shear stress. Piezo1 Silencing inhibited the nuclear translocation of YAP and subsequently downregulated the expression of MMP13 and ADAMTS5. Intra-articular injection of the Piezo1 inhibitor, GsMTx4, could ameliorate proteoglycan degradation in malocclusion-induced TMJOA and suppressed MMP13 and ADAMTS5 expression. Our results revealed that the activation of Piezo1 promotes mechanical-induced cartilage degradation through the YAP-MMP13/ADAMTS5 signaling pathway.

Limited roles of Piezo mechanosensing channels in articular cartilage development and osteoarthritis progression

To investigate the role of Piezo1 and Piezo2 in surgically induced osteoarthritis (OA) in mice. Male conditional knockout (cKO) mice missing Piezo1 and Piezo2 in the joint using Gdf5-Cre transgenic mice were induced with post-traumatic OAby destabilization of the medial meniscus (DMM) of the right knee joint at 12 weeks of age. The severity of OA was histologically assessed at 24 weeks of age. OA-associated pain was evaluated by static weight bearing analysis. Additionally, articular chondrocytes isolated from cKO mice were exposed to fluid flow shear stress (FFSS) to evaluate the expression of OA-associated genes. Mice with conditional deletion of Piezo1 and Piezo2 showed normal joint development with no overt histological changes in the knee joint at 12 weeks and 24 weeks. DMM surgery induced moderate to severe OA in both control and cKO mice (median OARSI score: control, 4.67; cKO, 4.23, P=0.3082), although a few cKO mice showed milder OA. Pain assessment by static weight-bearing analysis suggested Piezo ablation in the joint has no beneficial effects on pain. FFSS increased the expression of OA-related genes both in control and cKO mice to similar extents. Piezo1 and Piezo2 are not essential for normal joint development. Genetic ablation of Piezo channels did not confer evident protective effects on OA progression in mice. In vitro data suggests that different mechanotransducers other than Piezo channels mediate FFSS in mechanical stress-induced gene expression.

Evaluation of hemodynamic significance for paraprosthetic fistula after transcatheter aortic valve implantation

Highlights. Using ECHO and MSCT data, a numerical assessment of hemodynamic effects of paraprosthetic regurgitation following transcatheter aortic valve replacement was performed. A significant increase in the fluid flow, wall and viscous shear stresses in the area of regurgitation is shown. The modeling technique described in the paper can be used prospectively in assessing the optimal treatment modality in terms of predicting the quantitative characteristics of the flow, associated with the risks of destruction of red blood cells and thrombosisAim. To make a numerical assessment of hemodynamic effects of paraprosthetic regurgitation following transcatheter aortic valve replacement based on retrospective clinical data.Methods. The study included echocardiography and multi-slice computed tomography data as input data for modeling one pulsation of a fluid similar in properties to blood. Reconstruction of the paraprosthetic fistula and the ascending aorta was performed in the Mimics medium (Materialise, Belgium). The obtained 3D models were processed in the Salome software (OPEN CASCADE SAS, France), after which they were exported to HELYX-OS (ENGYS, Great Britain) to build a finite element mesh. The flows were modeled using the OpenFOAM software package version 6 (The OpenFOAM Foundation Ltd, UK).Results. The simulation result, expressed quantitatively and qualitatively in the form of diagrams of the measured parameters – fluid flow velocities, wall and viscous shear stresses, shows a significant increase in indicators in the area of paraprosthetic regurgitation. Thus, the velocity in the affected area was 1.9–4.2 m/s, which is 3.8 higher than the average value in the entire computational area. The wall shear stress value was up to 61 Pa in the critical area, which may indicate an increased risk of thrombus formation due to the initiation of the clotting cascade through the von Willebrand factor. The value of viscous shear stress, the main component of the destruction of red blood cells in laminar flow, amounted to 20–26 Pa, which, in general, is not enough for mechanical hemolysis.Conclusion. The modeling technique described in the paper can be used prospectively in assessing the optimal treatment modality in terms of predicting the quantitative characteristics of the flow, associated with the risks of destruction of red blood cells and thrombosis.

THE ROLE OF PPARδ-DRIVEN β-OXIDATION IN BONE HEALTH DURING AGING

Abstract Musculoskeletal disorders are a significant complication of aging, leading to increased morbidity and mortality. However, current understanding of the mechanisms by which aging affects skeletal health is limited. Osteocytes are the most numerous and long-lived bone cells and play key roles in maintaining bone mass by responding to anabolic signals such as mechanical loading. Energy metabolism is dysregulated in many cells with aging, however regulation of energy metabolism in osteocytes and how this is affected during aging and by mechanical loading remains undefined. To investigate this, we first used IDG-SW3 osteocyte cells to determine the effects of mechanical loading on osteocytes in vitro by applying fluid flow shear stress (FFSS). FFSS increased Pparδ and Cpt1 expression, key promoters of fatty acid β-oxidation (FAO). Pharmacological antagonism of PPARδ or CPT1 resulted in dysregulated expression of key bone remodeling genes and impaired ATP release in response to FFSS. In vivo, mechanical loading significantly increased FAO in tibia cortical bone. However, FAO was impaired in the bones from aged mice. To further elucidate the role of osteocyte FAO, we deleted PPARδ specifically in osteocytes (PPARδ cKO), which resulted in decreased FAO and bone volume in female PPARδ cKO mice. Lastly, treatment of aging mice with the PPARδ activator GW0742 resulted in significantly increased bone mineral content, density and trabecular bone volume. These findings suggest important functions of osteocyte energy metabolism during aging and with mechanical loading on bone and identify PPARδ-driven FAO as a novel therapeutic target for improving skeletal health with aging.

Prostanoid receptors in hyperfiltration-mediated glomerular injury: Novel agonists and antagonists reveal opposing roles for EP2 and EP4 receptors.

Increased fluid-flow shear stress (FFSS) contributes to hyperfiltration-induced podocyte and glomerular injury resulting in progression of chronic kidney disease (CKD). We reported that increased FFSS in vitro and in vivo upregulates PGE2 receptor EP2 (but not EP4 expression), COX2-PGE2 -EP2 axis, and EP2-linked Akt-GSK3β-β-catenin signaling pathway in podocytes. To understand and use the disparities between PGE2 receptors, specific agonists, and antagonists of EP2 and EP4 were used to assess phosphorylation of Akt, GSK3β and β-catenin in podocytes using Western blotting, glomerular filtration barrier function using in vitro albumin permeability (Palb ) assay, and mitigation of hyperfiltration-induced injury in unilaterally nephrectomized (UNX) mice at 1 and 6 months. Results show an increase in Palb by PGE2 , EP2 agonist (EP2AGO ) and EP4 antagonist (EP4ANT ), but not by EP2 antagonist (EP2ANT ) or EP4 agonist (EP4AGO ). Pretreatment with EP2ANT blocked the effect of PGE2 or EP2AGO on Palb . Modulation of EP2 and EP4 also induced opposite effects on phosphorylation of Akt and β-Catenin. Individual agonists or antagonists of EP2 or EP4 did not induce significant improvement in albuminuria in UNX mice. However, treatment with a combination EP2ANT + EP4AGO for 1 or 6 months caused a robust decrease in albuminuria. EP2ANT + EP4AGO combination did not impact adaptive hypertrophy or increased serum creatinine. Observed differences between expression of EP2 and EP4 on the glomerular barrier highlight these receptors as potential targets for intervention. Safe and effective mitigating effect of EP2ANT + EP4AGO presents a novel opportunity to delay the progression of hyperfiltration-associated CKD as seen in transplant donors.

Impact of Fluid Flow Shear Stress on Osteoblast Differentiation and Cross-Talk with Articular Chondrocytes.

Bone cells, in particular osteoblasts, are capable of communication with each other during bone growth and homeostasis. More recently it has become clear that they also communicate with other cell-types; including chondrocytes in articular cartilage. One way that this process is facilitated is by interstitial fluid movement within the pericellular and extracellular matrices. This stimulus is also an important mechanical signal in skeletal tissues, and is known to generate shear stresses at the micron-scale (known as fluid flow shear stresses (FFSS)). The primary aim of this study was to develop and characterize an in vitro bone–cartilage crosstalk system, to examine the effect of FFSS on these cell types. Specifically, we evaluated the response of osteoblasts and chondrocytes to FFSS and the effect of FFSS-induced soluble factors from the former, on the latter. This system will ultimately be used to help us understand the role of subchondral bone damage in articular cartilage degeneration. We also carried out a comparison of responses between cell lines and primary murine cells in this work. Our findings demonstrate that primary cells produce a more reliable and reproducible response to FFSS. Furthermore we found that at lower magnitudes , direct FFSS produces anabolic responses in both chondrocytes and osteoblasts, whereas higher levels produce more catabolic responses. Finally we show that exposure to osteoblast-derived factors in conditioned media experiments produced similarly catabolic changes in primary chondrocytes.

GDF11 inhibits abnormal adipogenesis of condylar chondrocytes in temporomandibular joint osteoarthritis.

AimsAbnormal lipid metabolism is involved in the development of osteoarthritis (OA). Growth differentiation factor 11 (GDF11) is crucial in inhibiting the differentiation of bone marrow mesenchymal stem cells into adipocytes. However, whether GDF11 participates in the abnormal adipogenesis of chondrocytes in OA cartilage is still unclear.MethodsSix-week-old female mice were subjected to unilateral anterior crossbite (UAC) to induce OA in the temporomandibular joint (TMJ). Histochemical staining, immunohistochemical staining (IHC), and quantitative real-time polymerase chain reaction (qRT-PCR) were performed. Primary condylar chondrocytes of rats were stimulated with fluid flow shear stress (FFSS) and collected for oil red staining, immunofluorescence staining, qRT-PCR, and immunoprecipitation analysis.ResultsAbnormal adipogenesis, characterized by increased expression of CCAAT/enhancer-binding protein α (CEBPα), fatty acid binding protein 4 (FABP4), Perilipin1, Adiponectin (AdipoQ), and peroxisome proliferator-activated receptor γ (PPARγ), was enhanced in the degenerative cartilage of TMJ OA in UAC mice, accompanied by decreased expression of GDF11. After FFSS stimulation, there were fat droplets in the cytoplasm of cultured cells with increased expression of PPARγ, CEBPα, FABP4, Perilipin1, and AdipoQ and decreased expression of GDF11. Exogenous GDF11 inhibited increased lipid droplets and expression of AdipoQ, CEBPα, and FABP4 induced by FFSS stimulation. GDF11 did not affect the change in PPARγ expression under FFSS, but promoted its post-translational modification by small ubiquitin-related modifier (SUMOylation). Local injection of GDF11 alleviated TMJ OA-related cartilage degeneration and abnormal adipogenesis in UAC mice.ConclusionAbnormal adipogenesis of chondrocytes and decreased GDF11 expression were observed in degenerative cartilage of TMJ OA. GDF11 supplementation effectively inhibits the adipogenesis of chondrocytes and thus alleviates TMJ condylar cartilage degeneration. GDF11 may inhibit the abnormal adipogenesis of chondrocytes by affecting the SUMOylation of PPARγ.Cite this article: Bone Joint Res 2022;11(7):453–464.

GLOMERULAR HYPERFILTRATION MAY CONTRIBUTE TO RENAL TROPISM AND KIDNEY INJURY IN COVID-19 BY UPREGULATING ACE2 IN HUMAN PODOCYTES

Objective: Apart from the respiratory system, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can potentially infect multiple other organs including podocytes in the kidney. The latter play a crucial role in glomerular filtration. Podocytes can be damaged by increased fluid flow shear stress (FFSS) of the ultrafiltrate in Bowman's space in the setting of glomerular hyperfiltration that occurs in disease states such as hypertension, diabetes or in several forms of chronic kidney disease. These conditions are associated with an increased risk of a more severe course of coronavirus disease 2019 (COVID-19) and mortality. Design and method: To assess the susceptibility of human podocytes (hPC) for SARS-CoV-2 infection in the context of hyperfiltration in vitro, we used a recently established model system (Streamer® Shear Stress Device)) to mimic hyperfiltration by exposing hPC to increased FFSS of 1 dyne/cm2 for 2 h. In this setting we nalysed the effects of FFSS on mRNA expression of angiotensin I-converting enzyme 2 (ACE2) as the pivotal entry receptor for SARS-CoV-2 infection in hPC. Moreover, other potential critical host cell factors including transmembrane serine protease 2 (TMPRSS2), furin (FURIN), and neuropilin 1 (NRP1) were also assessed in parallel with changes of the F-actin fiber structure, i.e. an important cytoskeletal marker in hPC. Results: Under control conditions, hPC displayed long, parallel F-actin fibers crossing the entire cell body. After FFSS, an enrichment of cells that express F-actin in a cortically condensed pattern near the cell membrane was observed. FFSS induced a significant upregulation of ACE2 expression (about twofold) and of all other nalysed SARS-CoV-2 entry factors in hPC (p &lt; 0.05, respectively compared to control conditions, Figure 1 with data plotted as log2fold change [FC]). Conclusions: Our data support a potential link between glomerular hyperfiltration, podocyte damage and renal tropism of SARS-CoV-2 that may contribute to kidney damage including albuminuria development in COVID-19 patients.

AUGMENTED PROSTAGLANDIN E2 SIGNALING CAUSES PODOCYTE DAMAGE AND ALBUMINURIA-LIKE PHENOTYPE IN A ZEBRAFISH DISEASE MODEL OF GLOMERULAR HYPERFILTRATION

Objective: Prostaglandins (PGs) are important active lipids synthesized from arachidonic acid with the participation of cyclooxygenases (COXs) and specific prostaglandin synthases. Prostaglandin E2 (PGE2), the most abundant prostaglandin in the kidney, plays a crucial role in renal homeostasis and the pathogenesis of chronic kidney diseases. Augmented PGE2 signaling that may occur in podocytes during increased fluid flow shear stress as observed during glomerular hyperfiltration, results in glomerular filtration barrier (GFB) permeability defects, ultimately leading to albuminuria. The cellular mechanisms that precede podocyte damage are not fully resolved. Here, we deploy a zebrafish model to study the role of PGE2 signaling in glomerulus and its effects on GFB integrity and function. Design and method: To model the outcome of increased PGE2 signaling in podocytes, zebrafish embryos were exposed to 16,16-dimethyl PGE2 (dmPGE2, 125 μM) or DMSO vehicle after the complete formation of GFB, i.e. from 72 hours post fertilization (hpf) to 96 hpf. To probe the PGE2 pathway, embryos were treated with the selective PGE2 receptor (EP) type 2 (EP2) and EP4 antagonists PF04418948 and ONO-AE3-208 or the COX inhibitor indomethacin. Zebrafish embryos of Tg(fabp10a:gc-EGFP) were used to evaluate the functional role of GFB integrity and albuminuria phenotype, while embryos of Tg(wt1b:EGFP) in combination with angiography using BSA-conjugated AlexaFluor555 allowed glomerular morphological analysis. In vivo stereomicroscopy, confocal laser scanning microscopy, and electron microscopy were used to analyze GFB at cellular as well as ultrastructural level. Statistical analysis was performed using GraphPad software. Results: Stimulation with dmPGE2 causes an albuminuria-like phenotype in zebrafish embryos, mimicking the suggested PGE2 effects during glomerular hyperfiltration in rodent models. The albuminuria-like phenotype could be significantly suppressed by the combined and separate inhibition of the EP2 and EP4 receptors as well as by indomethacin treatment. Although the glomerular ultrastructure appeared unaffected, high-resolution confocal imaging showed impaired podocyte intercalation around the glomerular capillaries after dmPGE2 exposure. Importantly, these specific podocyte defects were restored after blockage of EP2 and EP4. Conclusions: Our results support a role of augmented PGE2/EP2/EP4 signaling in the setting of glomerular hyperfiltration and albuminuria.

GLOMERULAR PROSTAGLANDIN E2 IS UPREGULATED DURING ONSET OF ALBUMINURIA THAT IS SUPPRESSED AFTER DUAL BLOCKADE OF ITS EP2 AND EP4 RECEPTORS IN A RAT MODEL OF GLOMERULAR HYPERFILTRA

Objective: Glomerular hyperfiltration (GH) is an important mechanism in the development of albuminuria in hypertension. Recent in vitro data indicated an activation of an autocrine/paracrine cyclooxygenase 2 (COX2)/prostaglandin E2 (PGE2) pathway resulting in podocyte injury in GH by using fluid flow shear stress exposure. This was mediated by concerted ignalling via both prostaglandin E2 receptors (EP), EP2 and EP4. Here, we explored the role to target this pathway in vivo by using a rat model with GH and albuminuria. Design and method: We used the Munich Wistar Frömter (MWF) rat model with an inherited nephron deficit as a model of GH and albuminuria. Because analysis of PGE2 levels in vivo is limited by conventional methods, we developed a modified liquid chromatography tandem mass spectrometry (LC/ESI-MS/MS) protocol to quantify PGE2 levels in glomerular tissue. We then assessed glomerular PGE2 during the onset of albuminuria in young MWF at 4 to 8 weeks of age. Furthermore, the renoprotective effects of either separate or combined pharmacological blockade of EP2 (by PF-04418948) and EP4 (by ONO-AE3-208) in MWF was explored. Treatment started at the onset of albuminuria at 4 weeks and was continued for 8 weeks. Results: During the onset of albuminuria, PGE2 levels were significantly elevated in isolated glomeruli of MWF at both 4 and 8 weeks of age (p &lt; 0.01, respectively) as compared to albuminuria resistant spontaneously hypertensive rats (SHR). At 12 weeks of age, untreated MWF developed pronounced albuminuria, which was significantly, although modestly, reduced by separate EP2 or EP4 blockade. Remarkably, combined EP2 and EP4 blockade resulted in a significant suppression (-71%) of albuminuria in MWF at 12 weeks. Importantly, this pharmacological treatment did not affect systolic blood pressure and creatinine clearance (Figure 1). Conclusions: We demonstrated the activation of glomerular PGE2 in vivo in the setting of hyperfiltration and albuminuria in the MWF rat model. Dual EP2 and EP4 receptor blockade exhibited a marked suppression of albuminuria without affecting systemic blood pressure and glomerular filtration rate. These data support further translational research to explore this therapeutic option for renoprotection.

Effects of Osteocyte Shape on Fluid Flow and Fluid Shear Stress of the Loaded Bone.

This study was conducted to better understand the specific behavior of the intraosseous fluid flow. We calculated the number and distribution of bone canaliculi around the osteocytes based on the varying shapes of osteocytes. We then used these calculated parameters and other bone microstructure data to estimate the anisotropy permeability of the lacunar-canalicular network. Poroelastic finite element models of the osteon were established, and the influence of the osteocyte shape on the fluid flow properties of osteons under an axial displacement load was analyzed. Two types of boundary conditions (BC) that might occur in physiological environments were considered on the cement line of the osteon. BC1 allows free fluid passage from the outer elastic restraint boundary, and BC2 is impermeable and allows no free fluid passage from outer displacement constrained boundary. They both have the same inner boundary conditions that allow fluid to pass through. Changes in the osteocyte shape altered the maximum value of pressure gradient (PG), pore pressure (PP), fluid velocity (FV), and fluid shear stress (FSS) relative to the reference model (spherical osteocytes). The maximum PG, PP, FV, and FSS in BC2 were nearly 100% larger than those in BC1, respectively. It is found that the BC1 was closer to the real physiological environment. The fluid flow along different directions in the elongated osteocyte model was more evident than that in other models, which may have been due to the large difference in permeability along different directions. Changes in osteocyte shape significantly affect the degrees of anisotropy of fluid flow and porous media of the osteon. The model presented in this study can accurately quantify fluid flow in the lacunar-canalicular network.