Diabetic liver injury from streptozotocin is regulated through the caspase-8 homolog cFLIP involving activation of JNK2 and intrahepatic immunocompetent cells

The endemic occurrence of obesity and the associated risk factors that constitute the metabolic syndrome have been predicted to lead to a dramatic increase in chronic liver disease. Non-alcoholic steatohepatitis (NASH) has become the most frequent liver disease in countries with a high prevalence of obesity. In addition, hepatic steatosis and insulin resistance have been implicated in disease progression of other liver diseases, including chronic viral hepatitis and hepatocellular carcinoma. The molecular mechanisms underlying the link between insulin signaling and hepatocellular injury are only partly understood. We have explored the role of the antiapoptotic caspase-8 homolog cellular FLICE-inhibitory protein (cFLIP) on liver cell survival in a diabetic model with hypoinsulinemic diabetes in order to delineate the role of insulin signaling on hepatocellular survival. cFLIP regulates cellular injury from apoptosis signaling pathways, and loss of cFLIP was previously shown to promote injury from activated TNF and CD95/Apo-1 receptors. In mice lacking cFLIP in hepatocytes (flip^−/−), loss of insulin following streptozotocin treatment resulted in caspase- and c-Jun N-terminal kinase (JNK)-dependent liver injury after 21 days. Substitution of insulin, inhibition of JNK using the SP600125 compound in vivo or genetic deletion of the mitogen-activated protein kinase (MAPK)9 (JNK2) in all tissues abolished the injurious effect. Strikingly, the difference in injury between wild-type and cFLIP-deficient mice occurred only in vivo and was accompanied by liver-infiltrating inflammatory cells with a trend toward increased amounts of NK1.1-positive cells and secretion of proinflammatory cytokines. Transfer of bone marrow from rag-1-deficient mice that are depleted from B and T lymphocytes prevented liver injury in flip^−/− mice. These findings support a direct role of insulin on cellular survival by alternating the activation of injurious MAPK, caspases and the recruitment of inflammatory cells to the liver. Thus, increasing resistance to insulin signaling pathways in hepatocytes appears to be an important factor in the initiation and progression of chronic liver disease.     

Identification of a Bifunctional UDP-4-keto-pentose/UDP-xylose Synthase in the Plant Pathogenic Bacterium Ralstonia solanacearum Strain GMI1000, a Distinct Member of the 4,6-Dehydratase and Decarboxylase Family

The UDP-sugar interconverting enzymes involved in UDP-GlcA metabolism are well described in eukaryotes but less is known in prokaryotes. Here we identify and characterize a gene (RsU4kpxs) from Ralstonia solanacearum str. GMI1000, which encodes a dual function enzyme not previously described. One activity is to decarboxylate UDP-glucuronic acid to UDP-β-l-threo-pentopyranosyl-4″-ulose in the presence of NAD⁺. The second activity converts UDP-β-l-threo-pentopyranosyl-4″-ulose and NADH to UDP-xylose and NAD⁺, albeit at a lower rate. Our data also suggest that following decarboxylation, there is stereospecific protonation at the C5 pro-R position. The identification of the R. solanacearum enzyme enables us to propose that the ancestral enzyme of UDP-xylose synthase and UDP-apiose/UDP-xylose synthase was diverged to two distinct enzymatic activities in early bacteria. This separation gave rise to the current UDP-xylose synthase in animal, fungus, and plant as well as to the plant Uaxs and bacterial ArnA and U4kpxs homologs.     

Cloning of a Novel Omega-6 Desaturase from Flax (<Emphasis Type="Italic">Linum usitatissimum</Emphasis> L.) and Its Functional Analysis in <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis>

The Δ12 desaturase represents a diverse gene family in plants and is responsible for conversion of oleic acid (18:1) to linoleic acid (18:2). Several members of this family are known from plants like Arabidopsis and Soybean. Using primers from conserved C- and N-terminal regions, we have cloned a novel Δ12 desaturase gene amplified from flax genomic DNA, denoted as LuFAD2-2. This intron-less gene is 1,149-base pair long encoding 382 amino acids—putative membrane-bound Δ12 desaturase protein. Sequence comparisons show that the novel sequence has 85% similarity with previously reported flax Δ12 desaturase at amino acid level and shows typical features of membrane-bound desaturase such as three conserved histidine boxes along with four membrane-spanning regions that are universally present among plant desaturases. The signature amino acid sequence ‘YNNKL’ was also found to be present at the N terminus of the protein, which is necessary and sufficient for ER localization of enzyme. Neighbor-Joining tree generated from the sequence alignment grouped LuFAD2-2 among the other FAD2 sequences from Ricinus, Hevea, Jatropha, and Vernicia. When LuFAD2-2 and LuFAD2 were expressed in Saccharomyces cerevisiae, they could convert the oleic acid to linoleic acid, with an average conversion rate of 5.25 and 8.85%, respectively. However, exogenously supplied linoleic acid was feebly converted to linolenic acid suggesting that LuFAD2-2 encodes a functional FAD2 enzyme and has substrate specificity similar to LuFAD2.     

Characterization of cryobiological responses in TF-1 cells using interrupted freezing procedures

Cryopreservation currently is the only method for long-term preservation of cellular viability and function for uses in cellular therapies. Characterizing the cryobiological response of a cell type is essential in the approach to designing and optimizing cryopreservation protocols. For cells used in therapies, there is significant interest in designing cryopreservation protocols that do not rely on dimethyl sulfoxide (Me₂SO) as a cryoprotectant, since this cryoprotectant has been shown to have adverse effects on hematopoietic stem cell (HSC) transplant patients. This study characterized the cryobiological responses of the human erythroleukemic stem cell line TF-1, as a model for HSC. We measured the osmotic parameters of TF-1 cells, including the osmotically-inactive fraction, temperature-dependent membrane hydraulic conductivity and the membrane permeability to 1 M Me₂SO. A two-step freezing procedure (interrupted rapid cooling with hold time) and a graded freezing procedure (interrupted slow cooling without hold time) were used to characterize TF-1 cell recovery during various phases of the cooling process. One outcome of these experiments was high recovery of TF-1 cells cryopreserved in the absence of traditional cryoprotectants. The results of this study of the cryobiology of TF-1 cells will be critical for future understanding of the cryobiology of HSC, and to the design of cryopreservation protocols with specific design criteria for applications in cellular therapies.     

Mitogen-activated protein kinase signaling is involved in suramin-induced neurite outgrowth in a neuronal cell line

Suramin is a well-known antitrypanosomal drug and a novel experimental agent for the treatment of several cancers. Previous study showed that suramin is an activator of extracellular signal-regulated kinase (ERK1/2) signaling in several cell lines including Chinese hamster ovary cells, although the physiological relevance of this activation remains uncertain. Here, it was shown that suramin enhances neurite outgrowth concomitant with activation of ERK1/2 in Neuro-2a cells, a neuronal cell line. These neurite outgrowth and ERK1/2 activation were significantly inhibited by PD98059, an inhibitor of mitogen-activated protein kinase kinase, as well as by activation of endogenous adenosine A2A receptors. The suramin-induced phosphorylation of ERK1/2 was also inhibited by inhibitors of Src family kinases. This attenuation of ERK1/2 activity was accompanied by a significant decrease in suramin-induced neurite outgrowth. These results suggest that suramin activates the Src/ERK1/2 signaling pathway that induces neurite outgrowth, both of which are negatively regulated by cAMP produced in response to activation of endogenous adenosine A2A receptors.     

Suppression of polydactyly of the Gli3 mutant (extra toes) by deltaEF1 homozygous mutation

Digit patterning is established through multiple genetic interactions. Delta-crystallin enhancer/E2-box factor (deltaEF1) is a zinc finger and homeodomain containing repressor protein, and is expressed in the posterior half of the forelimb bud and in the entire hindlimb bud during the early stage of limb development. The 6EF1-deficient mutant mice display various skeletal abnormalities, among which inferior ossification and abnormal patterning of autopodial bones are similar to those observed in Hox and Gli gene mutants. Gli3 mutant mice, extra toes (Xt), exhibit pre-axial polydactyly losing the identity of digit I. It is demonstrated here that deltaEF1null(lacZ) homozygosity suppressed formation of the extra digit, uniquely of the hindlimb, in both Gli3XtJ heterozygous and homozygous mutants, but with no restoration of digit I identity. In Gli3XtJ mutants, the Hoxd13 expression domain was expanded more dramatically in homozygotes. In Gli3XtJ;deltaEF1null(lacZ) double homozygous mutants, Hoxd13 expression once expanded in Gli3XtJ homozygous mutant was reduced, more conspicuously in the hindlimbs, which may account for hindlimb-restricted suppression of formation of the extra digit. The data suggest the possibility that the extent of Hoxd13 expression along the distal margin of the limb bud is determinative in defining the digit number.