3 resultados para Long-Base-Line
em Digital Commons at Florida International University
Resumo:
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. ^
Resumo:
This paper synthesizes research conducted during the first 5–6 years of the Florida Coastal Everglades Long-Term Ecological Research Program (FCE LTER). My objectives are to review our research to date, and to present a new central theme and conceptual approach for future research. Our research has focused on understanding how dissolved organic matter (DOM) from upstream oligotrophic marshes interacted with a marine source of the limiting nutrient, phosphorus (P), to control productivity in the oligohaline estuarine ecotone. We have been working along freshwater to marine transects in two drainage basins located in Everglades National Park (ENP). The Shark River Slough transect (SRS) has a direct connection to the Gulf of Mexico, providing this estuarine ecotone with a source of marine P. The oligohaline ecotone along our southern Everglades transect (TS/Ph), however, is separated from this marine P source by the Florida Bay estuary. We originally hypothesized an ecosystem productivity peak in the SRS ecotone, driven by the interaction of marine P and Everglades DOM, but no such productivity peak in the TS/Ph ecotone because of this lack of marine P. Our research to date has tended to show the opposite pattern, however, with many ecosystem components showing enhanced productivity in the TS/Ph ecotone, but not in the SRS ecotone. Water column P concentrations followed a similar pattern, with unexpectedly high P in the TS/Ph ecotone during the dry season. Our organic geochemical research has shown that Everglades DOM is more refractory than originally hypothesized. We have also begun to understand the importance of detrital organic matter production and transport to ecotone dynamics and as the base of aquatic food webs. Our future research will build on this substantial body of knowledge about these oligotrophic estuaries. We will direct our efforts more strongly on biophysical dynamics in the oligohaline ecotone regions. Specifically, we will be focusing on inputs to these regions from four primary water sources: freshwater Everglades runoff, net precipitation, marine inputs, and groundwater. We are hypothesizing that dry season groundwater inputs of P will be particularly important to TS/Ph ecotone dynamics because of longer water residence times in this area. Our organic geochemical, biogeochemical, and ecosystem energetics work will focus more strongly on the importance of detrital organics and will take advantage of a key Everglades Restoration project, scheduled for 2008 or 2009, that will increase freshwater inputs to our SRS transect only. Finally, we will also begin to investigate the human dimensions of restoration, and of a growing population in south Florida that will become increasingly dependent on the Everglades for critical ecosystem services (including fresh water) even as its growth presents challenges to Everglades sustainability.
Resumo:
This material is based upon work supported by the National Science Foundation through the Florida Coastal Everglades Long-Term Ecological Research program under Cooperative Agreements #DBI-0620409 and #DEB-9910514. This image is made available for non-commercial or educational use only.