ABSTRACT
Muscarinic agonists alter the metabolism of amyloid precursor protein, leading to an increase in alpha-secretase cleavage and a decreased production of amyloidogenic peptides; suggesting that these compounds might modify the Alzheimer's disease process. A second therapeutic target in AD is the accumulation of stably phosphorylated tau into neurofibrillary tangles; an early event correlating with cognitive impairment. Glycogen synthase kinase-3 (GSK-3beta) phosphorylates tau and is inhibited via protein kinase C (PKC). As certain muscarinic receptors are linked to PKC, we examined the effect of a range of agonists on GSK-3beta phosphorylation of tau. In neurons a nonspecific muscarinic agonist, carbachol, reduced tau phosphorylation. In nonneuronal cells expressing the ml receptor a range of ml agonists reduced transiently-expressed tau phosphorylation and altered its microtubulebinding properties. These findings link the two pathological process of AD-APP metabolism and tau phosphorylation - and suggest that muscarinic and other cholinergic compounds might have disease-modifying properties.
Subject(s)
Alzheimer Disease/drug therapy , Calcium-Calmodulin-Dependent Protein Kinases/drug effects , Cells, Cultured/drug effects , Muscarinic Agonists/pharmacology , Neurons/drug effects , Receptors, Muscarinic/drug effects , tau Proteins/drug effects , Acetylcholine/metabolism , Alzheimer Disease/metabolism , Alzheimer Disease/physiopathology , Amyloid beta-Protein Precursor/drug effects , Amyloid beta-Protein Precursor/metabolism , Animals , Binding Sites/drug effects , Binding Sites/physiology , Calcium-Calmodulin-Dependent Protein Kinases/metabolism , Carbachol/pharmacology , Cells, Cultured/cytology , Cells, Cultured/metabolism , Fetus , Glycogen Synthase Kinase 3 , Glycogen Synthase Kinases , Lithium Chloride/pharmacology , Microtubules/drug effects , Microtubules/metabolism , Neurons/cytology , Neurons/metabolism , Phosphorylation/drug effects , Pyridines/pharmacology , Rats , Rats, Sprague-Dawley , Receptors, Muscarinic/metabolism , Tetrazoles/pharmacology , Thiadiazoles/pharmacology , tau Proteins/metabolismABSTRACT
The regulation of the spvR promoter from the Salmonella dublin virulence plasmid was monitored using promoter-reporter gene fusion constructs. Activity was dependent upon the presence of the spv region and was affected by the number of copies of the spv region present within the cell. Activity remained constant throughout exponential growth, and increased rapidly with the onset of stationary phase, under both aerobic and anaerobic conditions. Additionally, the level of spvR expression was controlled by the availability of iron, activity being greatest under low iron conditions in stationary phase. The spvA gene product negatively regulated spvR expression in a dose-dependent manner, indicating that SpvA provides a negative feedback mechanism for this operon.
