AKT activation by N-cadherin regulates beta-catenin signaling and neuronal differentiation during cortical development

Background: During cerebral cortical development, neural precursor-precursor interactions in the ventricular zone neurogenic niche coordinate signaling pathways that regulate proliferation and differentiation. Previous studies with shRNA knockdown approaches indicated that N-cadherin adhesion between cortical precursors regulates β-catenin signaling, but the underlying mechanisms remained poorly understood. Results: Here, with conditional knockout approaches, we find further supporting evidence that N-cadherin maintains β-catenin signaling during cortical development. Using shRNA to N-cadherin and dominant negative N-cadherin overexpression in cell culture, we find that N-cadherin regulates Wnt-stimulated β-catenin signaling in a cell-autonomous fashion. Knockdown or inhibition of N-cadherin with function-blocking antibodies leads to reduced activation of the Wnt co-receptor LRP6. We also find that N-cadherin regulates β-catenin via AKT, as reduction of N-cadherin causes decreased AKT activation and reduced phosphorylation of AKT targets GSK3β and β-catenin. Inhibition of AKT signaling in neural precursors in vivo leads to reduced β-catenin-dependent transcriptional activation, increased migration from the ventricular zone, premature neuronal differentiation, and increased apoptotic cell death. Conclusions: These results show that N-cadherin regulates β-catenin signaling through both Wnt and AKT, and suggest a previously unrecognized role for AKT in neuronal differentiation and cell survival during cortical development

Analysis of α-SMA expression and measurement of apoptosis in fibroblasts induced and non-induced by lung cancer cells.

<p>(A) α-SMA protein assay by immunofluorescence imaging on fibroblasts induced and non-induced by lung cancer cells. (a) Induced. (b) Non-induced. Magnification: ×600. (B) The average expression of α-SMA in per cell was reflected by normalized fluorescent intensity. Data were shown as mean±SD of triplicate determinations. (C) Fluorescent analysis of apoptosis in fibroblasts induced and non-induced by lung cancer cells with PI and Hoechst after treatment with VP-16 (30 µM). Magnification: ×100. (D) The statistic analysis of percentage of apoptotic cells induced and non-induced by the lung cancer cells after treatment with different concentrations of VP-16 (0–60 µM). *p<0.05 compared with the control group. All the experiments were repeated at least three times.</p

Hydrogen Sulfide Prevents Hydrogen Peroxide-Induced Activation of Epithelial Sodium Channel through a PTEN/PI(3,4,5)P₃ Dependent Pathway

<div><p>Sodium reabsorption through the epithelial sodium channel (ENaC) at the distal segment of the kidney plays an important role in salt-sensitive hypertension. We reported previously that hydrogen peroxide (H₂O₂) stimulates ENaC in A6 distal nephron cells via elevation of phosphatidylinositol 3,4,5-trisphosphate (PI(3,4,5)P₃) in the apical membrane. Here we report that H₂S can antagonize H₂O₂-induced activation of ENaC in A6 cells. Our cell-attached patch-clamp data show that ENaC open probability (<i>P_O</i>) was significantly increased by exogenous H₂O₂, which is consistent with our previous finding. The aberrant activation of ENaC induced by exogenous H₂O₂ was completely abolished by H₂S (0.1 mM NaHS). Pre-treatment of A6 cells with H₂S slightly decreased ENaC <i>P_O</i>; however, in these cells H₂O₂ failed to elevate ENaC <i>P_O</i>. Confocal microscopy data show that application of exogenous H₂O₂ to A6 cells significantly increased intracellular reactive oxygen species (ROS) level and induced accumulation of PI(3,4,5)P₃ in the apical compartment of the cell membrane. These effects of exogenous H₂O₂ on intracellular ROS levels and on apical PI(3,4,5)P₃ levels were almost completely abolished by treatment of A6 cells with H₂S. In addition, H₂S significantly inhibited H₂O₂-induced oxidative inactivation of the tumor suppressor phosphatase and tensin homolog (PTEN) which is a negative regulator of PI(3,4,5)P_3. Moreover, BPV_(pic), a specific inhibitor of PTEN, elevated PI(3,4,5)P₃ and ENaC activity in a manner similar to that of H₂O₂ in A6 cells. Our data show, for the first time, that H₂S prevents H₂O₂-induced activation of ENaC through a PTEN-PI(3,4,5)P₃ dependent pathway.</p></div

Analysis of GRP78 expression and effect of EGCG on VP-16 induced apoptosis in myofibroblasts.

<p>(A) GRP78 protein assay by immunofluorescence imaging on (a) myofibroblasts and (b) fibroblasts. Magnification: ×600. (B) The average expression of GRP78 in per cell was reflected by normalized fluorescent intensity. Data were shown as mean±SD of triplicate determinations. (C) Fluorescent analysis of percentage of apoptotic cells for myofibroblasts by EGCG pretreated and non-EGCG pretreated groups after treatment with VP-16 (30 µM). Magnification: ×100. (D) The statistic analysis of percentage of apoptotic cells for myofibroblasts in EGCG pretreated and non-EGCG pretreated groups after treatment with different concentrations of VP-16 (0–60 µM). *p<0.05 compared with the control group. All the experiments were repeated at least three times.</p

Microfluidic co-culture device design.

<p>(A) Image of the microfluidic device mainly composed of a double-layer chip and an injection pump. (B) Schema chart of the double-layer chip: (a)-(b) the layout of each layer. (C) Photograph of medium flow direction in the chip. (a) Injection of red and blue indicators from inlet A and B representing two types of cells, respectively, to demonstrate indirect contact co-culture. (b) Injection of black indicator from medium inlet to demonstrate medium injection. A simple external small clip was served as micro-valves to facilitate the medium flowing downstream. (D) The diffusion of FITC-Dextran in 3D matrix. (a) After 5 min. (b) After 60 min. Magnification: ×100.</p

Illustration of medium flow direction in the microfluidic device.

<p>The blue, red and green indicators represented control group, EGF group, GM6001/EGF group respectively. These three indicators were perfused into microchannels from inlet A, B, C simultaneously and separately, while these indicators could spread out to cell chambers of both sides via oval microchannels uniformly and in parallel without crossing.</p

Actual invadopodia formation of A549 cells in control group (A), EGF group (B), and GM6001/EGF group (C) in 3D extracellular matrix in the microfluidic device with confocal system.

<p>Invadopodia could be obviously induced by EGF in (B), <b>while</b> this induction could be inhibited by GM6001 in (C). White arrowheads represented invadopodia. Magnification: ×1200.</p

Invadopodia formation assay and quantification analysis with confocal system in A549 cells.

<p>The cells in control group (A), EGF group (B), and GM6001/EGF group (C), were cultured on a 3D microfluidic device for 12 h. The cells were stained green represented combined with cortactin, stained red represented combined with F-actin, and arrowheads in merge pictures indicated cells displaying invadopodia. (D) The percent of the cells with invadopodia formation. (E) The average number of invadopodia per cell. Error bars represented the SD of three different determinations. *Statistically significant between control group and EGF group; **statistically significant between EGF group and GM6001/EGF group, p<0.05. Magnification: ×1200.</p

Fluoresent analysis of apoptotic in A549 cells.

<p>Cells were cultured on the 3D microfluidic device for 96 h and then stained by Hoechst and PI. Live cells were stained blue and dead cells were stained red. Magnification: ×200.</p

A microfluidic chip designed for the study of cancer cells invasion in 3D matrix.

<p>(A) Schematic representation of the microfluidic platform. Layout of the integrated microfluidic device is composed of three units sharing a common outlet, each of which contains an inlet, three parallel main channels, three cell culture chambers and an outlet. (B) A magnified illustration of one cell culture chamber. (C) Photograph of the microfluidic system.</p