Blocking Connexin-43 mediated hemichannel activity protects against early tubular injury in experimental chronic kidney disease

Background: Tubulointerstitial fibrosis represents the key underlying pathology of Chronic Kidney Disease (CKD), yet treatment options remain limited. In this study, we investigated the role of connexin43 (Cx43) hemichannel-mediated adenosine triphosphate (ATP) release in purinergic-mediated disassembly of adherens and tight junction complexes in early tubular injury. Methods: Human primary proximal tubule epithelial cells (hPTECs) and clonal tubular epithelial cells (HK2) were treated with Transforming Growth Factor Beta1 (TGFβ1) ± apyrase, or ATPγS for 48h. For inhibitor studies, cells were co-incubated with Cx43 mimetic Peptide 5, or purinergic receptor antagonists Suramin, A438079 or A804598. Immunoblotting, single-cell force spectroscopy and trans-epithelial electrical resistance assessed protein expression, cell-cell adhesion and paracellular permeability. Carboxyfluorescein uptake and biosensing measured hemichannel activity and real-time ATP release, whilst a heterozygous Cx43+/- mouse model with unilateral ureteral obstruction (UUO) assessed the role of Cx43 in vivo. Results: Immunohistochemistry of biopsy material from patients with diabetic nephropathy confirmed increased expression of purinergic receptor P2X7. TGFβ1 increased Cx43 mediated hemichannel activity and ATP release in hPTECs and HK2 cells. The cytokine reduced maximum unbinding forces and reduced cell-cell adhesion, which translated to increased paracellular permeability. Changes were reversed when cells were co-incubated with either Peptide 5 or P2-purinoceptor inhibitors. Cx43+/- mice did not exhibit protein changes associated with early tubular injury in a UUO model of fibrosis. Conclusion: Data suggest that Cx43 mediated ATP release represents an initial trigger in early tubular injury via its actions on the adherens and tight junction complex. Since Cx43 is highly expressed in nephropathy, it represents a novel target for intervention of tubulointerstitial fibrosis in CKD

Tunnelling with Full-Face Shielded Machines: A 3D Numerical Analysis of an Earth Pressure Balance (EPB) Excavation Sequence Using the Finite Element Method (FEM)

Urban tunnelling can be highly challenging, especially in areas where limited ground settlements and environmental disturbance is required. Mechanised tunnelling is usually preferred in such ground environments, specifically Slurry or EPBM (Earth Pressure Balance Machine), depending on the ground properties. Being able to predict the anticipated tunnel behaviour at the preliminary stages of the project can be very beneficial in optimising not only the design, but also control the construction activities and completion times. In practice, the short-term excavation response and support performance focus primarily on design, since most site characterisation inputs are focused on material properties gained from short-term testing. Although the analysis of tunnelling is a three-dimensional (3D) problem, conventional approaches and design methods employed during the design and construction of underground openings are often based on the ground’s static response in two dimensions (2D). In this paper, an initial 2D model is generated in PLAXIS2D and RS2 (Rocscience) to test advanced constitutive models and compare transverse settlement profiles; subsequently, a complete 3D FEM numerical model in RS3 (Rocscience) was used to simulate an Earth Pressure Balance (EPB) excavation sequence. The 3D numerical model simulates the relevant EPB components such as face pressure, TBM shield, backfilling of the tail void (time-dependent hardening of the grout) and gradual segmental lining erections in the longitudinal direction. The presented numerical approach can be used by tunnel designers and engineers to predict the soil response in EPBM tunnelling

Fully coupled dynamic analysis of an Earth dam

The paper studies the seismic behaviour of an existing homogeneous earth dam using a fully coupled finite-element effective stress approach in conjunction with a recently developed multi-surface, elasto-plastic constitutive model for structured soils. The model is calibrated using laboratory test results for the embankment material and the foundation soils. The initial state variables (stress, hardening parameters) are determined by simulating a simplified geological history of the foundation soil, dam construction stages and reservoir impounding, prior to the application of the earthquake shaking at the bedrock level. The paper critically reviews the role of the constitutive model parameters, the hysteretic damping introduced by the model and the additional viscous damping parameters in the accumulation of permanent displacements and in the development and subsequent dissipation of excess pore water pressures due to the seismic loading. The analyses, carried out with reference to a set of earthquake records related to different return periods, show that the overall behaviour of the system in terms of displacements is characterised by a more enhanced deformation pattern of the downstream slope as compared with the upstream one. The large plastic strains accumulation induced throughout the shaking is followed by the development of excess pore water pressures inside the dam and the foundation deposit. Nonetheless, the results are indicative of a satisfactory dynamic performance of the dam, even when subjected to severe seismic loading conditions

Finite element analysis of the non-uniform behavior of structured clay under shear

Conventional triaxial tests are widely used to interpret the stress-strain behavior of soils. The non-uniformity of their stress-strain relationship and the localization of deformation normally occur during shear test and affect the observed test results. This article investigates the non-uniform behavior of artificially structured (i.e., cemented) specimens experiencing shear due to an end restraint under various testing conditions. The conditions investigated include the stress state, the drainage conditions, and the strength improvement associated with the cementation effect. A finite element analysis has been performed using the Modified Structured Cam Clay (MSCC) model, which was developed as a generalized constitutive model for destructured, naturally structured, and artificially structured clays. The shear behavior of artificially structured cylindrical specimens was simulated under both drained and undrained shearing by a coupled hydro-mechanical finite element analysis. The stress-strain distributions and the local stress-strain relations of the artificially structured specimens are compared with those of the destructured specimens. It is evident that the end restraint significantly influences the shear response in drained conditions, particularly for the tests with a high yield stress ratio (YSRiso, which is the ratio of the yield stress to the current stress) and a highly cemented structure. The non-uniform stress-strain behavior is attributed to the non-uniform lateral deformation, which results in a variation in stress paths for different points within the specimen. The different effective stress paths for different points within the specimen affect the overall performance of the specimen, including the yield stresses, the yield strengths and the destructuring processes for a structured specimen. The specimens experiencing shear with high confinement in a Normally Consolidated (NC) state deform relatively uniformly, while those with low confinement in an Over-Consolidated (OC) state display a non-uniform lateral deformation. Hence, the destructured and structured NC specimens exhibit more uniform stress-strain behavior than the OC specimens. The highly structured specimens show more nonuniform stress-strain behavior than the destructured specimens. In conclusion, the end restraint plays significant role in the specimen deformation for both destructured and structured specimens. Special care should be taken for destructured specimens in an overconsolidated state, and for structured specimens in both normally and over-consolidated states