ABSTRACT
The pathology of Alzheimer's disease is closely connected with lipid metabolism. Processing of amyloid precursor protein (APP) is sensitive to membrane alterations in levels of cholesterol and gangliosides. As cholesterol and gangliosides are major components of rafts and BACE I and gamma-secretase are supposed to be localized to rafts there might be a yet unknown biological function underlying this connection. Increasing evidence shows a close connection between cholesterol homeostasis and APP processing and Abeta production respectively. We measured membrane fluidity by anisotropy determination, isolated detergent resistant membrane (DRM) fractions from membrane preparations and determined cholesterol content of these fractions by a coupled enzymatic assay. We found membrane fluidity to be changed in mouse embryonic fibroblasts (MEF) PS1/2 -/- along with altered cholesterol content in DRM fraction of these cells. In addition, total ganglioside levels were enhanced in absence of presenilin (PS).
Subject(s)
Cholesterol/physiology , Fibroblasts/metabolism , Lipid Metabolism/physiology , Membrane Fluidity/physiology , Amyloid beta-Protein Precursor/physiology , Animals , Membrane Proteins/physiology , Mice , Presenilin-1 , Presenilin-2ABSTRACT
The Drosophila model system has been used to study neurodegenerative diseases by expression of human disease genes in transgenic flies. A different approach is to isolate and characterize Drosophila mutants with progressive neurodegeneration to find novel genes required for brain integrity. Mammalian homologues of these genes might be the genetic basis for some of the various progressive neurodegeneration diseases in humans. Here we describe several such mutants. Some of them reveal degeneration in specific parts of the brain while others affect all brain regions. Cell death can occur through apoptosis or necrosis. In one case, mutant flies show abnormal behavior prior to obvious degeneration while most other mutants reveal such defects only in later stages. These mutants offer a new approach to study basic mechanisms of neurodegeneration and for developing fly models for human diseases.
Subject(s)
Heredodegenerative Disorders, Nervous System/physiopathology , Nerve Degeneration , Animals , Apoptosis , Behavior, Animal , Cell Death , Disease Models, Animal , Disease Progression , Drosophila/genetics , Humans , Microscopy, Electron , Mutation , Necrosis , Nerve Degeneration/geneticsABSTRACT
Sulfide oxidation in the phototrophic purple sulfur bacterium Chromatium vinosum D (DSMZ 180(T)) was studied by insertional inactivation of the fccAB genes, which encode flavocytochrome c, a protein that exhibits sulfide dehydrogenase activity in vitro. Flavocytochrome c is located in the periplasmic space as shown by a PhoA fusion to the signal peptide of the hemoprotein subunit. The genotype of the flavocytochrome-c-deficient Chr. vinosum strain FD1 was verified by Southern hybridization and PCR, and the absence of flavocytochrome c in the mutant was proven at the protein level. The oxidation of thiosulfate and intracellular sulfur by the flavocytochrome-c-deficient mutant was comparable to that of the wild-type. Disruption of the fccAB genes did not have any significant effect on the sulfide-oxidizing ability of the cells, showing that flavocytochrome c is not essential for oxidation of sulfide to intracellular sulfur and indicating the presence of a distinct sulfide-oxidizing system. In accordance with these results, Chr. vinosum extracts catalyzed electron transfer from sulfide to externally added duroquinone, indicating the presence of the enzyme sulfide:quinone oxidoreductase (EC 1.8.5.-). Further investigations showed that the sulfide:quinone oxidoreductase activity was sensitive to heat and to quinone analogue inhibitors. The enzyme is strictly membrane-bound and is constitutively expressed. The presence of sulfide:quinone oxidoreductase points to a connection of sulfide oxidation to the membrane electron transport system at the level of the quinone pool in Chr. vinosum.
