Pigment Epithelium-derived Factor (PEDF) Ameliorates Advanced Glycation End Product (AGE)-induced Hepatic Insulin Resistance In Vitro by Suppressing Rac-1 Activation

Advanced glycation end products (AGEs) could be implicated in insulin resistance. However, the molecular mechanisms underlying this are not fully understood. Since pigment epithelium-derived factor (PEDF) blocks the AGE-signaling pathways, we examined here whether and how PEDF improves insulin resistance in AGE-exposed hepatoma cells, Hep3B cells. Proteins were extracted from Hep3B cells, immunoprecipitated with or without insulin receptor substrate-1 (IRS-1) antibodies, and subjected to Western blot analysis. Glycogen synthesis was measured using [ (14)C]-d-glucose. AGE induced Rac-1 activation and increased phosphorylation of IRS-1 at serine-307 residues, JNK, c-JUN, and IkappaB kinase in association with decreased IkappaB levels in Hep3B cells. PEDF or overexpression of dominant negative Rac-1 blocked these effects of AGE on Hep3B cells. Further, AGEs decreased tyrosine phosphorylation of IRS-1, and subsequently reduced the association of p85 subunit of phosphatidylinositol 3-kinase with IRS-1 and glycogen synthesis in insulin-exposed Hep3B cells, all of which were inhibited by PEDF. Our present study suggests that PEDF could improve the AGE-elicited insulin resistance in Hep3B cells by inhibiting JNK- and IkappaB kinase-dependent serine phosphorylation of IRS-1 via suppression of Rac-1 activation. PEDF may play a protective role against hepatic insulin resistance in diabetes.     

Rho GTPase and cAMP/protein kinase A signaling mediates myocilin-induced alterations in cultured human trabecular meshwork cells

Myocilin is a gene linked to the most common form of glaucoma, a major blinding disease. The trabecular meshwork (TM), a specialized eye tissue, is believed to be involved, at least in part, in the development of glaucoma. The myocilin expression is known to be up-regulated by glucocorticoids in TM cells, and an altered myocilin level may be the culprit in conditions such as corticosteroid glaucoma. Wild type myocilin, when transfected into cultured human TM cells, induced a dramatic loss of actin stress fibers and focal adhesions. Myocilin transfectants displayed a heightened sensitivity to trypsin. Adhesion to fibronectin, collagens, and vitronectin was compromised. The fibronectin deposition and the levels of fibronectin protein and mRNA were also reduced in myocilin transfectants. The fibronectin deposition could be restored by treatment with lysophosphatidic acid, a Rho stimulator. Assays further revealed that upon myocilin overexpression, the activity of RhoA was diminished, whereas the cAMP level and the protein kinase A (PKA) activity were augmented. Myocilin protein did not affect actin polymerization. The collapse of actin stress fibers and increased trypsin sensitivity from myocilin transfection could be reverted by co-expression of constitutively active RhoA or by treatment with PKA inhibitor H-89. The PKA activity, however, was not modified by co-expression of either constitutively active or dominant negative RhoA. These results demonstrate that myocilin has a de-adhesive activity and triggers signaling events. cAMP/PKA activation and the downstream Rho inhibition are possible mechanisms by which myocilin in overabundance may lead to TM cell or tissue damage.     

Regulation of platelet dense granule secretion by the Ral GTPase-exocyst pathway

Non-hydrolyzable GTP analogues, such as guanosine 5'-(beta, gamma-imido)triphosphate (GppNHp), induce granule secretion from permeabilized platelets in the absence of increased intracellular Ca(2+). Here, we show that the GppNHp-induced dense granule secretion from permeabilized platelets occurred concomitantly with the activation of small GTPase Ral. This secretion was inhibited by the addition of GTP-Ral-binding domain (RBD) of Sec5, which is a component of the exocyst complex known to function as a tethering factor at the plasma membrane for vesicles. We generated an antibody against Sec5-RBD, which abolished the interaction between GTP-Ral and the exocyst complex in vitro. The addition of this antibody inhibited the GppNHp-induced secretion. These data indicate that Ral mediates the GppNHp-induced dense granule secretion from permeabilized platelets through interaction with its effector, the exocyst complex. Furthermore, GppNHp enhanced the Ca(2+) sensitivity of dense granule secretion from permeabilized platelets, and this enhancement was inhibited by Sec5-RBD. In intact platelets, the association between Ral and the exocyst complex was induced by thrombin stimulation with a time course similar to that of dense granule secretion and Ral activation. Taken together, our results suggest that the Ral-exocyst pathway participates in the regulation of platelet dense granule secretion by enhancing the Ca(2+) sensitivity of the secretion.     

Development of biodegradable scaffolds based on patient-specific arterial configuration

Biodegradable scaffolds are of great value in tissue engineering. We have developed a method for fabricating patient-specific vascular scaffolds from a biocompatible and biodegradable polymer, poly(L-lactide-co-epsilon-caprolactone). This method's usefulness is due to flexibility in the choice of materials and vascular configurations. Here, we present a way to fabricate scaffolds of human carotid artery by combining processes of rapid prototyping, lost wax, dip coating, selective dissolution, and salt leaching. The result was the successful development of porous biodegradable scaffolds, with mechanical strength covering the range of human blood vessels (1-3 MPa). Human umbilical vein endothelial cells were also cultured on the scaffolds and their biocompatibility was confirmed by cell growth. The Young's modulus of scaffolds could be controlled by changing polymer concentration and porosity. The wall thickness of the tubular scaffold was also controllable by adjusting polymer concentration and pull-up velocity during dip coating. We believe that this fabrication technique can be applied to patient-specific regeneration of blood vessels.     

Over-expression of 70-kDa heat shock protein confers protection against monochloramine-induced gastric mucosal cell injury

The major heat shock protein, HSP70, is known to be involved in cytoprotection against environmental stresses mediated by their function as a "molecular chaperone". Monochloramine (NH(2)Cl) is a potent cytotoxic oxidant generated by neutrophil-derived hypochlorous acid and Helicobacter pylori urease-induced ammonia. In this study, to evaluate the cytoprotective effect of HSP70 against NH(2)Cl-induced gastric mucosal cell injury, rat gastric mucosal cells (RGM-1) were stably transfected with pBK-CMV containing the human HSP70 gene (7018-RGM-1) or pBK-CMV alone (pBK-CMV-12) as control cells. These cells were treated with various concentrations of NH(2)Cl. Cell Viability was determined by MTT assay and the direct plasma membrane damage was analyzed by lactate dehydrogenase (LDH) release assay. Apoptosis was determined by DNA fragmentation analysis. NH(2)Cl caused injury to pBK-CMV-12 cells in a concentration-dependent manner. NH(2)Cl-induced gastric cell injury was significantly diminished in HSP70 over-expressing cell line (7018-RGM-1) both necrosis and apoptosis compared to the control cell line (pBK-CMV-12) transfected with CMV vector alone. These result suggest that overexpression of HSP70 plays an important role in protecting gastric cells against NH(2)Cl-induced injury.     

Cholic acid, a bile acid elicitor of hypersensitive cell death, pathogenesis-related protein synthesis, and phytoalexin accumulation in rice

When plants interact with certain pathogens, they protect themselves by generating various defense responses. These defense responses are induced by molecules called elicitors. Since long ago, composts fermented by animal feces have been used as a fertilizer in plant cultivation, and recently, have been known to provide suppression of plant disease. Therefore, we hypothesized that the compounds from animal feces may function as elicitors of plant defense responses. As a result of examination of our hypothesis, an elicitor of rice defense responses was isolated from human feces, and its structure was identified as cholic acid (CA), a primary bile acid in animals. Treatment of rice (Oryza sativa) leaves with CA induced the accumulation of antimicrobial compounds (phytoalexins), hypersensitive cell death, pathogenesis-related (PR) protein synthesis, and increased resistance to subsequent infection by virulent pathogens. CA induced these defense responses more rapidly than did fungal cerebroside, a sphingolipid elicitor isolated from the rice pathogenic fungus Magnaporthe grisea. Furthermore, fungal cerebroside induced both types of rice phytoalexins, phytocassanes and momilactones, whereas CA mainly induced phytocassanes, but not momilactones. In the structure-activity relationship analysis, the hydroxyl groups at C-7 and C-12, and the carboxyl group at C-24 of CA contributed to the elicitor activity. These results indicate that CA is specifically recognized by rice and is a different type of elicitor from fungal cerebroside. This report demonstrated that bile acid induced defense responses in plants.     

NMDA-induced retinal injury is mediated by an endoplasmic reticulum stress-related protein, CHOP/GADD153

We investigated the role of an endoplasmic reticulum stress-associated protein, CHOP/GADD153, after NMDA-induced mouse retinal damage. After injection of NMDA into the vitreous, TUNEL-positive cells were detected in the retinal ganglion cell layer (GCL) and inner nuclear layer (INL) at 6 h after NMDA injection, and these gradually increased in number up to 24 h. Analysis by real-time RT-PCR revealed that CHOP mRNA was induced by about 3-fold, at 2 h after NMDA injection. Immunoreactivity for the CHOP protein was intense in cells of the GCL following NMDA treatment. Immunoblot analysis showed that NMDA injection increased the expression of CHOP protein in the retina. Compared with wild-type mice, CHOP/ mice were more resistant to NMDA-induced retinal cell death as determined by TUNEL assay. At 7 days after NMDA treatment, the thickness of the inner plexiform layer and INL were larger in CHOP/ mice than in wild-type mice. The number of residual cells in the GCL following NMDA treatment was significantly higher in CHOP/ mice than in wild-type mice. In conclusion, CHOP is induced in mouse retina by NMDA treatment, and CHOP/ mice are more resistant to NMDA-induced retinal damage, suggesting that CHOP plays an important role in NMDA-induced retinal cell death.     

Simulating the contribution of coaggregation to interspecies hydrogen fluxes in syntrophic methanogenic consortia

A simple model (termed the syntrophy model) for simulating the contribution of coaggregation to interspecies hydrogen fluxes between syntrophic bacteria and methanogenic archaea is described. We applied it to analyzing partially aggregated syntrophic cocultures with various substrates, revealing that large fractions of hydrogen molecules were fluxed in aggregates.     

Dynamic transition of a methanogenic population in response to the concentration of volatile fatty acids in a thermophilic anaerobic digester

In this study, the microbial community succession in a thermophilic methanogenic bioreactor under deteriorative and stable conditions that were induced by acidification and neutralization, respectively, was investigated using PCR-mediated single-strand conformation polymorphism (SSCP) based on the 16S rRNA gene, quantitative PCR, and fluorescence in situ hybridization (FISH). The SSCP analysis indicated that the archaeal community structure was closely correlated with the volatile fatty acid (VFA) concentration, while the bacterial population was impacted by pH. The archaeal community consisted mainly of two species of hydrogenotrophic methanogen (i.e., a Methanoculleus sp. and a Methanothermobacter sp.) and one species of aceticlastic methanogen (i.e., a Methanosarcina sp.). The quantitative PCR of the 16S rRNA gene from each methanogen revealed that the Methanoculleus sp. predominated among the methanogens during operation under stable conditions in the absence of VFAs. Accumulation of VFAs induced a dynamic transition of hydrogenotrophic methanogens, and in particular, a drastic change (i.e., an approximately 10,000-fold increase) in the amount of the 16S rRNA gene from the Methanothermobacter sp. The predominance of the one species of hydrogenotrophic methanogen was replaced by that of the other in response to the VFA concentration, suggesting that the dissolved hydrogen concentration played a decisive role in the predominance. The hydrogenotrophic methanogens existed close to bacteria in aggregates, and a transition of the associated bacteria was also observed by FISH analyses. The degradation of acetate accumulated during operation under deteriorative conditions was concomitant with the selective proliferation of the Methanosarcina sp., indicating effective acetate degradation by the aceticlastic methanogen. The simple methanogenic population in the thermophilic anaerobic digester significantly responded to the environmental conditions, especially to the concentration of VFAs.