Alpha-synuclein up-regulation and aggregation during MPP+-induced apoptosis in neuroblastoma cells: intermediacy of transferrin receptor iron and hydrogen peroxide

1-Methyl-4-phenylpyridinium (MPP(+)) is a neurotoxin that causes Parkinson's disease in experimental animals and humans. Despite the fact that intracellular iron was shown to be crucial for MPP(+)-induced apoptotic cell death, the molecular mechanisms for the iron requirement remain unclear. We investigated the role of transferrin receptor (TfR) and iron in modulating the expression of alpha-synuclein (alpha-syn) in MPP(+)-induced oxidative stress and apoptosis. Results show that MPP(+) inhibits mitochondrial complex-1 and aconitase activities leading to enhanced H(2)O(2) generation, TfR expression and alpha-syn expression/aggregation. Pretreatment with cell-permeable iron chelators, TfR antibody (that inhibits TfR-mediated iron uptake), or transfection with glutathione peroxidase (GPx1) enzyme inhibits intracellular oxidant generation, alpha-syn expression/aggregation, and apoptotic signaling as measured by caspase-3 activation. Cells overexpressing alpha-syn exacerbated MPP(+) toxicity, whereas antisense alpha-syn treatment totally abrogated MPP(+)-induced apoptosis in neuroblastoma cells without affecting oxidant generation. The increased cytotoxic effects of alpha-syn in MPP(+)-treated cells were attributed to inhibition of mitogen-activated protein kinase and proteasomal function. We conclude that MPP(+)-induced iron signaling is responsible for intracellular oxidant generation, alpha-syn expression, proteasomal dysfunction, and apoptosis. Relevance to Parkinson's disease is discussed.     

Bayesian semiparametric modeling for matched case-control studies with multiple disease states

We present a Bayesian approach to analyze matched "case-control" data with multiple disease states. The probability of disease development is described by a multinomial logistic regression model. The exposure distribution depends on the disease state and could vary across strata. In such a model, the number of stratum effect parameters grows in direct proportion to the sample size leading to inconsistent MLEs for the parameters of interest even when one uses a retrospective conditional likelihood. We adopt a semiparametric Bayesian framework instead, assuming a Dirichlet process prior with a mixing normal distribution on the distribution of the stratum effects. We also account for possible missingness in the exposure variable in our model. The actual estimation is carried out through a Markov chain Monte Carlo numerical integration scheme. The proposed methodology is illustrated through simulation and an example of a matched study on low birth weight of newborns (Hosmer, D. A. and Lemeshow, S., 2000, Applied Logistic Regression) with two possible disease groups matched with a control group.     

Natural selection for polymorphism in the disease resistance gene Rps2 of Arabidopsis thaliana

Pathogen resistance is an ecologically important phenotype increasingly well understood at the molecular genetic level. In this article, we examine levels of avrRpt2-dependent resistance and Rps2 locus DNA sequence variability in a worldwide sample of 27 accessions of Arabidopsis thaliana. The rooted parsimony tree of Rps2 sequences drawn from a diverse set of ecotypes includes a deep bifurcation separating major resistance and susceptibility clades of alleles. We find evidence for selection maintaining these alleles and identify the N-terminal part of the leucine-rich repeat region as a probable target of selection. Additional protein variants are found within the two major clades and correlate well with measurable differences among ecotypes in resistance to the avirulence gene avrRpt2 of the pathogen Pseudomonas syringae. Long-lived polymorphisms have been observed for other resistance genes of A. thaliana; the Rps2 data suggest that the long-term maintenance of phenotypic variation in resistance genes may be a general phenomenon and are consistent with diversifying selection acting in concert with selection to maintain variation.     

Interactive effects of jasmonic acid, salicylic acid, and gibberellin on induction of trichomes in Arabidopsis

Leaf trichomes protect plants from attack by insect herbivores and are often induced following damage. Hormonal regulation of this plant induction response has not been previously studied. In a series of experiments, we addressed the effects of artificial damage, jasmonic acid, salicylic acid, and gibberellin on induction of trichomes in Arabidopsis. Artificial damage and jasmonic acid caused significant increases in trichome production of leaves. The jar1-1 mutant exhibited normal trichome induction following treatment with jasmonic acid, suggesting that adenylation of jasmonic acid is not necessary. Salicylic acid had a negative effect on trichome production and consistently reduced the effect of jasmonic acid, suggesting negative cross-talk between the jasmonate and salicylate-dependent defense pathways. Interestingly, the effect of salicylic acid persisted in the nim1-1 mutant, suggesting that the Npr1/Nim1 gene is not downstream of salicylic acid in the negative regulation of trichome production. Last, we found that gibberellin and jasmonic acid had a synergistic effect on the induction of trichomes, suggesting important interactions between these two compounds.     

Solubilization of an arabinan arabinosyltransferase activity from mung bean hypocotyls

The biosynthesis of polysaccharides destined for the plant cell wall and the subsequent assembly of the cell wall are poorly understood processes that are currently the focus of much research. Arabinan, a component of the pectic polysaccharide rhamnogalacturonan I, is composed of arabinosyl residues connected via various glycosidic linkages, and therefore, the biosynthesis of arabinan is likely to involve more than one arabinosyltransferase. We have studied the transfer of [(14)C]arabinose (Ara) from UDP-L-arabinopyranose onto polysaccharides using microsomal membranes isolated from mung bean (Vigna radiata) hypocotyls. [(14)C]arabinosyl and [(14)C]xylosyl residues were incorporated into endogenous products due to the presence of UDP-Xyl-4-epimerase activity. Enzymatic digestion of endogenous products with endo-arabinanase released very little radiolabeled sugars, whereas digestion with arabinofuranosidase released some [(14)C]Ara. Microsomal membranes solubilized with the detergent octyl glucoside were able to add a single [(14)C]Ara residue onto (1-->5)-linked alpha-L-arabino-oligosaccharide acceptors. The reaction had a pH optimum of 6.5 and a requirement for manganese ions. However, enzymatic digestion of the radiolabeled oligosaccharides with endo-arabinanase and arabinofuranosidases could not fully release the radiolabeled Ara residue, indicating that the [(14)C]Ara residue was not a (1-->2)-, (1-->3)-, or (1-->5)-linked alpha-L-arabinofuranosyl residue. Rather, mild acid treatment of the product suggested that the radiolabeled Ara residue was in a pyranose conformation, and this result was confirmed by thin-layer chromatography of radiolabeled partially methylated sugars. Using microsomal membranes separated on a discontinuous sucrose gradient, the arabinosyltransferase activity appears to be mainly localized to Golgi membranes.