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Publication Date

2013-10-01

Availability

UM campus only

Embargo Period

2013-09-30

Degree Name

Master of Science (MS)

Department

Neuroscience (Medicine)

Date of Defense

2013-3

First Committee Member

Richard L. Rotundo

Second Committee Member

Coleen M. Atkins

Third Committee Member

Grace Zhai

Fourth Committee Member

Arun Malhotra

Abstract

Acetylcholinesterase (AChE) is the enzyme that functions in terminating neurotransmission by hydrolyzing acetylcholine (ACh) in the central and peripheral nervous systems. Like all exportable proteins, AChE is synthesized on the rough endoplasmic reticulum (RER), processed in the Golgi apparatus, and externalized at the cell surface following vesicular transport. Interestingly, less than one quarter of the newly synthesized AChE is correctly folded, becomes catalytically active, and transported to the cell surface. The remainder of the molecules are retained in the cell and targeted to the endoplasmic reticulum associated degradation (ERAD) system. How cells distinguish between these two possibilities is unknown. To answer this question, we sought to alter the balance between correctly folded and incorrectly folded AChE molecules. Pharmacological agents such as donepezil, galantamine, and tacrine have been used in many studies demonstrating their ability to inhibit AChE activity. These agents function by binding electrostatically to the active site of AChE preventing the hydrolysis of ACh, therefore modulating synaptic transmission by increasing ACh in the synaptic cleft. Using biochemical and cell biological techniques including enzymatic assays, velocity sedimentation, and Western blot analysis, we demonstrated increased AChE activity in Human Embryonic Kidney 293 cells (HEK293) expressing mouse AChE and in an in vivo mouse model. AChE activity was measured in vitro from newly synthesized AChE molecules generated by the incubation of the cells with these pharmacological agents after total AChE inhibition with an irreversible organophosphate, diisofluropropylphosphate. Differences in AChE activity were measured as an increase over baseline in the mouse model. These results suggest that through the interaction with the catalytic site, Acetylcholinesterase inhibitors (AChEIs) can increase enzyme activity by stabilizing newly synthesized molecules within the endoplasmic reticulum, thus altering the balance between correctly and incorrectly folded enzyme. This provides a mechanism for using small molecules such as AChEIs as a potential pharmacological chaperone, increasing catalytically active AChE through protein stabilization.

Keywords

Acetylcholinesterase; Pharmacological Chaperones; Donepezil; Acetylcholinesterase Inhibitors; Galantamine; Tacrine

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