Relevance of CD40/CD40L downstream pathways to Alzheimer's disease

The amyloid cascade hypothesis places amyloid-β at the origin of Alzheimer's disease (AD). Amyloid-β (Aβ) is the product of the sequential cleavage of the amyloid precursor protein (APP) by the enzymes β- and γ-secretases. An inflammatory component to AD has been suggested in association with CD40 (a member of the tumor necrosis factor receptor superfamily (TNFRS) and its cognate ligand CD40L. In this study, I hypothesized that the neutralization of pro-inflammatory cytokines produced downstream of CD40/CD40L interaction would reduce APP processing. I also hypothesized that blocking the binding of different adaptor proteins to CD40 by mutating its cytoplasmic tail would result in significant reduction of the APP metabolites: Aβ, sAPPβ, sAPPα, CTFβ and CTFα. ^ Treatment with CD40L of human embryonic kidney cells over-expressing both APP and CD40 (HEK/APPsw/CD40) significantly increased levels of the cytokine granulocyte macrophage colony stimulating factor (GM-CSF). Neutralizing antibodies against GM-CSF mitigated the CD40L-induced production of Aβ in these cells. Treatment of the HEK/APPsw/CD40 cells with recombinant GM-CSF significantly increased Aβ levels. GM-CSF receptor gene silencing with shRNA significantly reduced Aβ levels to below base line in non-stimulated HEK/APPsw/CD40 cells. Silencing of the GM-CSF receptor also decreased APP endocytosis (therefore reducing the availability of APP to be cleaved in the endosomes). ^ Using CD40 mutants, I show that CD40L can increase levels of Aβ(1-40), Aβ(1-42), sAPPβ, sAPPα and CTFβ independently of TRAF signaling. TRAFs had been shown to be necessary for most CD40/CD40L-dependent signaling. An increase in mature/immature APP ratio after CD40L treatment of CD40wt and CD40-mutant cells was observed, reflecting alterations in APP trafficking. CD4OL treatment of a neuroblastoma cell line over-expressing CTFβ suggested that CD40L affected γ-secretase activity. Inhibition of γ-secretase activity significantly reduced sAPPβ levels in the CD40L treated HEK/APPsw CD40wt and the CD40-mutant cells. The latter suggests CD40/CD40L interaction primarily acts on γ-secretase and affects β-secretase via a positive feedback mechanism. ^ Taken together, the results of this dissertation suggest that GM-CSF operates downstream of CD40/CD40L interaction and that GM-CSF modulates Aβ production by influencing APP trafficking. Moreover, the data presented suggest that CD40/CD40L interaction can modulate APP processing via a mechanism independent of TRAF signaling. ^

The effects of content-based ESOL instruction on the overall English proficiency of foreign -born college students

This study investigates the effects of content-based ESOL instruction on the overall English proficiency of foreign-born college students. Based on various psychological and social factors which affect second language acquisition, it is suggested that the techniques of content-based instruction, while focusing on subject matter, allow the learners to overcome the language barrier by neutralizing their subconscious defense mechanism, thus attaining greater proficiency.^ Two groups of Miami-Dade Community College ESOL students were chosen as subjects for this study: a control group composed of students from the North and Wolfson campuses, where the ESOL program is based predominantly on structural or structural-functional approach, and an experimental group of Medical Center campus students, where content-based instruction is incorporated into curriculum. Ethnicity, gender, age, and other differences in the population are discussed in the study.^ The students' English Placement Test (EPT) scores were used as covariate, and the scores on Multiple Assessment Programs and Services (MAPS) test as dependent variables. Multivariate analysis of variance (MANOVA) was applied to test significant difference between the means. The results of the analysis of data indicate that there is a consistent difference in the mean performance of the Medical Center campus ESOL students demonstrated by their scores on MAPS. Although neither ethnicity, nor gender of the subjects has affected the outcome, age had a contributing effect. The implications of these findings suggest that content-based instruction facilitates greater overall English proficiency in foreign-born college students. ^