Search

Alzheimer's disease (AD) is associated with a magnesium ion (Mg2+) deficit in the serum or brain. However, the mechanisms regulating the roles of Mg2+ in the pathologic condition of AD remain unknown. We studied whether brain Mg2+ can decrease β-amyloid (Aβ) deposition and ameliorate the cognitive decline in a model of AD, the APPswe/PS1DE9 transgenic (Tg) mouse. We used a recently developed compound, magnesium-l-threonate (MgT), for a treatment that resulted in enhanced clearance of Aβ in an anterior pharynx-defective (APH)-1α/-1β-dependent manner. To further explore how MgT treatment inhibits cognitive decline in APP/PS1 Tg mice, the critical molecules for amyloid precursor protein (APP) cleavage and signaling pathways were investigated. In neurons, ERK1/2 and PPAR? signaling pathways were activated by MgT treatment, which in turn suppressed (by >80%) the expression of APH-1α/-1β, which is responsible for the deposition of Aβ and potentially contributes to the memory deficit that occurs in AD. More important, Aβ oligomers in the cerebrospinal fluid (CSF) further promoted the expression of APH-1α/-1β (by >2.5-fold), which enhances the ?-cleavage of APP and Aβ deposition during AD progression. These findings provide new insights into the mechanisms of AD progression and are instrumental for developing better strategies to combat the disease. [ABSTRACT FROM AUTHOR]

Renal fibrosis (RF) is thought to be a direct consequence of dedifferentiation of resident epithelial cells via an epithelial-mesenchymal transition (EMT). Increased glomerular flow is a critical initiator of fibrogenesis. Yet, die responses of proximal tubular epithelial cells (PTECs) to fluid flow remain uncharacterized. Here, we investigate die effects of pathological shear stresses on the development of fibrosis in PTECs. Our data reveal that type I collagen accumulation in shear-activated PTECs is accompanied by a ~40-60% decrease in cell motility, thus excluding EMT as a relevant pathological process. In contrast, static incubation of PTECs with TGFβ1 increases cell motility by ~50%, and induces stable expression of key mesenchymal markers, including Snail 1, N-cadherin, and vimentin. Ectopic expression of TGFβ1 in shear-activated PTECs fails to induce EMT-associated changes but abrogates collagen accumulation via SMAD2-depen-dent mechanisms. Shear-mediated inhibition of EMT occurs via cyclic oscillations in both ERK2 activity and downstream expression of EMT genes. A constitutive ERK2 mutant induces stable expression of Snaill, N-cadherin, and vimentin, and increases cell motility in shear-activated PTECs by 250% without concomitant collagen deposition. Collectively, our data reveal that RF not only occurs without EMT but also that these two responses represent mutually exclusive cell fates. [ABSTRACT FROM AUTHOR]

Cell migration on planar surfaces is driven by cycles of actin protrusion, integrin-mediated adhesion, and myosin-mediated contraction; however, this mechanism may not accurately describe movement in 3-dimensional (3D) space. By subjecting cells to restrictive 3D environments, we demonstrate that physical confinement constitutes a biophysical stimulus that alters cell morphology and suppresses mesenchymal motility in human breast carcinoma (MDA-MB-231). Dorsoventral polarity, stress fibers, and focal adhesions are markedly attenuated by confinement. Inhibitors of myosin, Rho/ROCK, or β1-integrins do not impair migration through 3-µm-wide channels (confinement), even though these treatments repress motility in 50-µm-wide channels (unconfined migration) by S50%. Strikingly, confined migration persists even when F-actin is disrupted, but depends largely on microtubule (MT) dynamics. Interfering with MT polymerization/depolymerization causes confined cells to undergo frequent directional changes, thereby reducing the average net displacement by ≥80% relative to vehicle controls. Live-cell EB1-GFP imaging reveals that confinement redirects MT polymerization toward the leading edge, where MTs continuously impact during advancement of the cell front. These results demonstrate that physical confinement can induce cytoskeletal alterations that reduce the dependence of migrating cells on adhesion-contraction force coupling. This mechanism may explain why integrins can exhibit reduced or altered function during migration in 3D environments. [ABSTRACT FROM AUTHOR]

After separating from a primary tumor, metastasizing cells enter the circulatory system and interact with host cells before lodging in secondary organs. Previous studies have implicated the surface glycoproteins CD44 and carcinoembryonic antigen (CEA) in adhesion, migration, and invasion, suggesting that they may influence metastatic progression. To elucidate the role of these multifunctional molecules while avoiding the potential drawbacks of ectopic expression or monoclonal antibody treatments, we silenced the expression of CD44 and/or CEA in LS174T colon carcinoma cells and analyzed their ability to metastasize in 2 independent mouse models. Quantitative PCR revealed that CD44 knockdown increased lung and liver metastasis >10-fold, while metastasis was decreased by >50% following CEA knockdown. These findings were corroborated by in vitro experiments assessing the metastatic potential of LS174T cells. Cell migration was decreased as a result of silencing CEA but was enhanced in CD44-knockdown cells. In addition, CD44 silencing promoted homotypic aggregation of LS147T cells, a phenotype that was reversed by additional CEA knockdown. Finally, CD44-knockdown cells exhibited greater mechanical compliance than control cells, a property that correlates with increased metastatic potential. Collectively, these data indicate that CEA, but not CD44, is a viable target for therapeutics aimed at curbing colon carcinoma metastasis. [ABSTRACT FROM AUTHOR]

Selectins promote metastasis by mediating specific interactions between selectin ligands on tumor cells and selectin-expressing host cells in the microvasculature. Using affinity chromatography in conjunction with tandem mass spectrometry and bioinformatics tools, we identified mucin 16 (MUC16) as a novel selectin ligand expressed by metastatic pancreatic cancer cells. While up-regulated in many pancreatic cancers, the biological function of sialofucosylated MUC16 has yet to be fully elucidated. To address this, we employed blot rolling and cell-free flow-based adhesion assays using MUC16 immunopurified from pancreatic cancer cells and found that it efficiently binds E- and L- but not P-selectin. The selectin-binding determinants are sialofucosylated structures displayed on O- and N-linked glycans. Silencing MUC16 expression by RNAi markedly reduces pancreatic cancer cell binding to E- and L-selectin under flow. These findings provide a novel integrated perspective on the enhanced metastatic potential associated with MUC16 overexpression and the role of selectins in metastasis. [ABSTRACT FROM AUTHOR]

Osteoarthritis (OA) is often a consequence of excessive mechanical loading of cartilage, which produces hydrostatic stress, tensile strain, and fluid flow. Application of high fluid shear to chondrocytes recapitulates the earmarks of OA, as evidenced by the induction of cyclooxygenase-2, prostaglandins (PGs), and interleukin-6 (IL-6). Here, we delineated the signaling pathway by which high fluid shear mediates the temporal regulation of IL-6 synthesis in human chondrocytes. We determined that Toll-like receptor 4 (TLR4) and caveolin-1 are binding partners in chondrocytes. Their expression is temporally regulated by fluid shear via the sequential up-regulation of microsomal PGE synthase-1 (mPGES-1) and L-PGDS. High shear stress rapidly induces an 8-fold up-regulation of TLR4 expression via an mPGES-1-dependent pathway, whereas prolonged shear exposure concurrently down-regulates TLR4 by >4-fold and up-regulates caveolin-1 expression by > 2.5-fold in an L-PGDS-dependent manner. TLR4 and caveolin-1 exert opposing effects on the activation of ERK1/2, PI3-K and PKA signaling pathways, which, in turn, regulate the NF-κB-dependent IL-6 synthesis in a time-dependent fashion. Reconstructing the signaling network regulating shear-induced IL-6 expression in chondrocytes may provide insights for developing therapeutic strategies to combat osteoarthritis. [ABSTRACT FROM AUTHOR]

Presents a study on variant isoforms of CD44 which are P- and L-selectin ligands on a colon carcinoma cells. Comparison of LS174T with HL-60 CD44s in terms of affinity for selectins; Selectin-binding determinants on LS174T CD44 isoforms; Conclusions and significance of the study.