Muscarinic receptor subtype determines vulnerability to amyloid β toxicity in transfected cos-7 cells

Abstract

Research has suggested that there are age-related increases in neuronal sensitivity to insult from oxidative stress (OS) and that the CNS alterations seen in Alzheimer disease (AD) and vascular dementia (VaD) are superimposed upon declining nervous and vascular systems. Since muscarinic receptors (mAChR) may be important in regional sensitivity, regulation of micro- circulation, and in various aspects of both neuronal (AβPP processing) and vascular functioning, we postulated that the various mAChR subtypes may show differential sensitivity to OS. Indeed, recent findings indicated that M₁, M₂, or M₄ AChR-transfected COS-7 cells showed greater OS sensitivity [as reflected in Ca²⁺ buffering (i.e., the ability to extrude or sequester Ca²⁺ following oxotremorine-induced depolarization)] than those transfected with M₃ or M₅ AChR when exposed to dopamine. Interestingly, the results from the present study indicate that similar findings were also observed when the cells were exposed to Aβ 25-35 and Aβ 1-40 showed similar effects on₁ and M₃ AChR. No effects were seen with Aβ35-25 or Aβ 40-1. Thus, cells transfected with M₁, M₂ or M₄ AChR showed greater disruptions in calcium regulation (as assessed via fluorescent imaging analysis prior to and following 750 μm oxotremorine) than those transfected with M₃ or M₅ AChR. We also examined the effects of calcium channel antagonists (e.g., Nifedipine) or antioxidants (vitamin E) in protecting against the deleterious effects of Aβ. Results are discussed in terms of differences in MAChR structure that could lead to selective Aβ effects and the possible implications on memory and AβPP processing.