MUSCARININC RECEPTOR SUBTYPE DETERMINES VULNERABILITY TO AMYLOD BETA TOXICITY IN TRANSFECTED COS-7 CELLS

Authors: Joseph, James; Fisher, Derek

Submitted to: Journal of Alzheimer's Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/5/2003
Publication Date: 6/5/2003
Citation: Joseph, J.A., and Fisher, D.R. Muscarinic receptor subtype determines vulnerability to amyloid beta toxicity in transfected COS 7 cells. J. Alz. Dis. 2003. 5: 197-208.

Interpretive Summary: A great deal of research has indicated that one of the hallmarks of Alzheimer disease is the formation of plaques in various regions of the brain. These plaques are made up of a peptide called amyloid beta, and a large number have studies have shown that this peptide is toxic in cells, and may have similar toxic effects in the brain. In addition studies have shown that this peptide may alter the regulation of calcium in cells such that the cells cannot clear the calcium when it enters the cells during their stimulation. This could lead eventually to loss of function in the cells as has been observed in Alzheimer Disease. We also know that cells lose their ability to clear calcium in senescence. Recently, we showed in cells that different subtypes of a neurotransmitter receptors called muscarinic receptors, which are important in the regulation of calcium, respond differently to agents which produce oxidative stress. In this study we found that cells which contain only M1, M2 or M4 muscarinic receptor subtypes are more sensitive to amyloid beta than those that contain M3 or M5 muscarinic subtypes, in that amyloid beta applied to these cells causes more disruption of calcium clearance from inside the cells. However, it was possible to protect against the deleterious of amyloid beta by using agents which block calcium channels or those which act as antioxidants. These findings indicate that there may be differences in the structures of the various muscarinic receptor subtypes which could provide some protection from or impart vulnerability to amyloid beta toxcity.

Technical 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 (APP 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 (amyloid beta) A 25-35, and A 1-40 showed similar effects on M1 and M3 AChR. No effects were seen with A 35-25 or A 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 A . Results are discussed in terms of differences in MAChR structure that could lead to selective A effects and the possible implications on memory and APP processing.