Gliclazide protects pancreatic beta-cells from damage by hydrogen peroxide

Oxidative stress is induced under diabetic conditions and possibly causes various forms of tissue damage in patients with diabetes. Recently, it has become aware that susceptibility of pancreatic beta-cells to oxidative stress contributes to the progressive deterioration of beta-cell function in type 2 diabetes. A hypoglycemic sulfonylurea, gliclazide, is known to be a general free radical scavenger and its beneficial effects on diabetic complications have been documented. In the present study, we investigated whether gliclazide could protect pancreatic beta-cells from oxidative damage. One hundred and fifty microM hydrogen peroxide reduced viability of mouse MIN6 beta-cells to 29.3%. Addition of 2 microM gliclazide protected MIN6 cells from the cell death induced by H(2)O(2) to 55.9%. Glibenclamide, another widely used sulfonylurea, had no significant effects even at 10 microM. Nuclear chromatin staining analysis revealed that the preserved viability by gliclazide was due to inhibition of apoptosis. Hydrogen peroxide-induced expression of an anti-oxidative gene heme oxygenase-1 and stress genes A20 and p21(CIP1/WAF1), whose induction was suppressed by gliclazide. These results suggest that gliclazide reduces oxidative stress of beta-cells by H(2)O(2) probably due to its radical scavenging activity. Gliclazide may be effective in preventing beta-cells from the toxic action of reactive oxygen species in diabetes.     

Epithelia-mesenchyme interaction plays an essential role in transdifferentiation of retinal pigment epithelium of silver mutant quail: localization of FGF and related molecules and aberrant migration pattern of neural crest cells during eye rudiment formation

Homozygotes of the quail silver mutation, which have plumage color changes, also display a unique phenotype in the eye: during early embryonic development, the retinal pigment epithelium (RPE) spontaneously transdifferentiates into neural retinal tissue. Mitf is considered to be the responsible gene and to function similarly to the mouse microphthalmia mutation, and tissue interaction between RPE and surrounding mesenchymal tissue in organ culture has been shown to be essential for the initiation of the transdifferentiation process in which fibroblast growth factor (FGF) signaling is involved. The immunohistochemical results of the present study show that laminin and heparan sulfate proteoglycan, both acting as cofactors for FGF binding, are localized in the area of transdifferentiation of silver embryos much more abundantly than in wild-type embryos. More intense immunohistochemical staining with FGF-1 antibody, but not with FGF-2 antibody, is also found in the neural retina, RPE, and choroidal tissue of silver embryos than in wild-type embryos. HNK-1 immunohistochemistry revealed that clusters of HNK-1-positive cells (presumptive migrating neural crest cells) are frequently located around the developing eyes and in the posterior region of the silver embryonic eye. Finally, chick-quail chimerical eyes were made by grafting silver quail optic vesicles to chicken host embryos: in most cases, no transdifferentiation occurs in the silver RPE, but in a few cases, transdifferentiation occurs where silver quail cells predominate in the choroid tissue. These observations together with our previous in vitro study indicate that the silver mutation affects not only RPE cells but also cephalic neural crest cells, which migrate to the eye rudiment, and that these crest cells play an essential role in the transdifferentiation of RPE, possibly by modifying the FGF signaling pathway. The precise molecular mechanism involved in RPE-neural crest cell interaction is still unknown, and the quail silver mutation is considered to be a good experimental model for studying the role of neural crest cells in vertebrate eye development.     

A Novel Phase-contrast Transmission Electron Microscopy Producing High-contrast Topographic Images of Weak objects

We report a novel class of transmission electron microscope (TEM), the difference-contrast electron microscope (DTEM), which displays nanostructures of thin specimen objects in a topographical manner. Topography obtained by the difference-contrast develops shadowgraphs in pseudo three-dimension, namely volume-like representation of projected objects as if things are illuminated by light from one direction. The specific optical device tomanipulate electron waves for DTEM is the hemicircular phase-plate, which appears to be quite distinguishable from the Zernike phase plate utilized in Zernike phase-contrast TEM, while both have to be placed onto the back-focal plane of the objective lens. The topographic images obtained with DTEM for ultrathin sections of kidney cells were compared with those obtained with conventional TEM. DTEM confirmed the experimental advantage of high contrast topography by visualizing ultrastructural details inside the cells.     

Neurotoxic mechanisms triggered by Alzheimer's disease-linked mutant M146L presenilin 1: involvement of NO synthase via a novel pertussis toxin target

While it has been reported that familial Alzheimer's disease (FAD)-linked mutants of amyloid precursor protein (APP) and presenilin (PS)2 induce neuronal cytotoxicity in a manner sensitive to antioxidant and pertussis toxin (PTX), little of the mechanism for PS1-mediated neuronal cell death has been characterized. We previously found that multiple mechanisms, different in detail, underlie cytotoxicities by two FAD-linked mutants of APP, using neuronal cells with an ecdysone-controlled expression system. Here we report that this system revealed that (i) low expression of FAD-linked M146L-PS1 caused neuronal cell death, whereas that of wild-type (wt)PS1 did not; (ii) mutation-specific cytotoxicity by M146L-PS1 was sensitive to antioxidant glutathione-ethyl-ester and resistant to Ac-DEVD-CHO; (iii) cytotoxicity by higher expression of wtPS1 was resistant to both; and (iv) cytotoxicity by M146L-PS1 was inhibited by PTX. It was also highly likely that the involved superoxide-generating enzyme was nitric oxide synthase (NOS), and that the PTX-sensitive cytotoxic signal by M146L-PS1 was mediated by none of the G(i/o) proteins. We conclude that M146L-PS1 activates a NOS-mediated cytotoxic pathway via a novel PTX target.     

The leucine-rich repeat protein PRELP binds perlecan and collagens and may function as a basement membrane anchor

PRELP (proline arginine-rich end leucine-rich repeat protein) is a heparin-binding leucine-rich repeat protein in connective tissue extracellular matrix. In search of natural ligands and biological functions of this molecule, we found that PRELP binds the basement membrane heparan sulfate proteoglycan perlecan. Also, recombinant perlecan domains I and V carrying heparan sulfate bound PRELP, whereas other domains without glycosaminoglycan substitution did not. Heparin, but not chondroitin sulfate, inhibited the interactions. Glycosaminoglycan-free recombinant perlecan domain V and mutated domain I did not bind PRELP. The dissociation constants of the PRELP-perlecan interactions were in the range of 3-18 nm as determined by surface plasmon resonance. As expected, truncated PRELP, without the heparin-binding domain, did not bind perlecan. Confocal immunohistochemistry showed that PRELP outlines basement membranes with a location adjacent to perlecan. We also found that PRELP binds collagen type I and type II through its leucine-rich repeat domain. Electron microscopy visualized a complex with PRELP binding simultaneously to the triple helical region of procollagen I and the heparan sulfate chains of perlecan. Based on the location of PRELP and its interaction with perlecan heparan sulfate chains and collagen, we propose a function of PRELP as a molecule anchoring basement membranes to the underlying connective tissue.     

P-, E-, and L-selectin mediate migration of activated CD8+ T lymphocytes into inflamed skin

P- and E-selectin mediate CD4+ Th1 cell migration into the inflamed skin in a murine contact hypersensitivity model. In this model, not only CD4+ T cells but also CD8+ T cells infiltrate the inflamed skin, and the role of CD8+ type 1 cytotoxic T (Tc1) cells as effector cells has been demonstrated. Here we show that in mice deficient in both P- and E-selectin, the infiltration of CD8+ T cells in the inflamed skin is reduced, suggesting the role of these selectins in CD8+ T cell migration. We directly studied the role of selectins using in vitro-generated Tc1 cells. These cells are able to migrate into the inflamed skin of wild-type mice. This migration is partially mediated by P- and E-selectin, as shown by the reduced Tc1 cell migration into the inflamed skin of mice deficient in both P- and E-selectin or wild-type mice treated with the combination of anti-P-selectin and anti-E-selectin Abs. During P- and E-selectin-mediated migration of Tc1 cells, P-selectin glycoprotein ligand-1 appears to be the sole ligand for P-selectin and one of the ligands for E-selectin. P- and E-selectin-independent migration of Tc1 cells into the inflamed skin was predominantly mediated by L-selectin. These observations indicate that all three selectins can mediate Tc1 cell migration into the inflamed skin.     

Membrane-rigidifying effects of anti-cancer dietary factors

Since several anti-cancer drugs interact with cell membrane lipids, the effects of anti-cancer dietary factors on liposomal membranes with different lipid composition were comparatively studied by measuring fluorescence polarization. Fluidity was imparted on both hydrophobic and hydrophilic regions of lipid bilayers by decreasing cholesterol and increasing unsaturated phosphatidylcholine in membranes. At 0.625-10 microM, (-)-epigallocatechin gallate, genistein, apigenin, resveratrol and a reference anti-cancer drug, doxorubicin, rigidified the tumor cell model membranes consisting of 20 mol% cholesterol and 80 mol% phosphatidylcholine with the acyl chain 18:1/16:0 ratio of 1.0, but not daidzein. They were more effective on the membrane core than the membrane surface. Quercetin showed a biphasic effect on the hydrophobic regions of membrane lipid bilayers to rigidify above 5 microM and fluidize below 2.5 microM. In contrast, anti-cancer dietary factors and doxorubicin were not or much less effective in rigidifying the normal cell model membranes consisting of 40 mol% cholesterol and 60 mol% phosphatidylcholine with the acyl chain 18:1/16:0 ratio of 0.5. The membrane-rigidifying effects were greater depending on a decrease of the cholesterol/phosphatidylcholine ratio and an increase of the phosphatidylcholine unsaturation degree. Membrane-active dietary factors and doxorubicin inhibited the growth of mouse myeloma cells at 10-100 microM, while the growth inhibition by membrane-inactive daidzein was relatively weak. Anti-cancer dietary factors appear to act on more fluid membranes like tumor cells as well as doxorubicin to induce rigidification, especially in the hydrocarbon core of membrane lipids, which is determined by the composition of cholesterol and unsaturated phospholipids.