M1 muscarinic allosteric modulators slow prion neurodegeneration and restore memory loss
Sophie J. Bradley, … , Christian C. Felder, Andrew B. Tobin
Sophie J. Bradley, … , Christian C. Felder, Andrew B. Tobin
Published December 19, 2016
Citation Information: J Clin Invest. 2017;127(2):487-499. https://doi.org/10.1172/JCI87526.
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Research Article Neuroscience

M1 muscarinic allosteric modulators slow prion neurodegeneration and restore memory loss

Abstract

The current frontline symptomatic treatment for Alzheimer’s disease (AD) is whole-body upregulation of cholinergic transmission via inhibition of acetylcholinesterase. This approach leads to profound dose-related adverse effects. An alternative strategy is to selectively target muscarinic acetylcholine receptors, particularly the M1 muscarinic acetylcholine receptor (M1 mAChR), which was previously shown to have procognitive activity. However, developing M1 mAChR–selective orthosteric ligands has proven challenging. Here, we have shown that mouse prion disease shows many of the hallmarks of human AD, including progressive terminal neurodegeneration and memory deficits due to a disruption of hippocampal cholinergic innervation. The fact that we also show that muscarinic signaling is maintained in both AD and mouse prion disease points to the latter as an excellent model for testing the efficacy of muscarinic pharmacological entities. The memory deficits we observed in mouse prion disease were completely restored by treatment with benzyl quinolone carboxylic acid (BQCA) and benzoquinazoline-12 (BQZ-12), two highly selective positive allosteric modulators (PAMs) of M1 mAChRs. Furthermore, prolonged exposure to BQCA markedly extended the lifespan of diseased mice. Thus, enhancing hippocampal muscarinic signaling using M1 mAChR PAMs restored memory loss and slowed the progression of mouse prion disease, indicating that this ligand type may have clinical benefit in diseases showing defective cholinergic transmission, such as AD.

Authors

Sophie J. Bradley, Julie-Myrtille Bourgognon, Helen E. Sanger, Nicholas Verity, Adrian J. Mogg, David J. White, Adrian J. Butcher, Julie A. Moreno, Colin Molloy, Timothy Macedo-Hatch, Jennifer M. Edwards, Jurgen Wess, Robert Pawlak, David J. Read, Patrick M. Sexton, Lisa M. Broad, Joern R. Steinert, Giovanna R. Mallucci, Arthur Christopoulos, Christian C. Felder, Andrew B. Tobin

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Figure 3

Prion disease is associated with a disruption in hippocampal cholinergic innervation, a deficit in learning, and memory rescued by donepezil, while maintaining muscarinic receptor expression and signaling.

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Prion disease is associated with a disruption in hippocampal cholinergic...
(A) Cholinergic innervation of the hippocampus was assessed by ChAT (green) immunostaining of the CA1 region of the hippocampus in mice at 9 and 10 w.p.i. Data shown are representative of 3 individual mice per group. Scale bars: 50 μm. (B) Burrowing response of control and prion-infected mice. n = 4–9 mice. *P < 0.05; ***P < 0.001, 1-way ANOVA. (C) Fear-conditioning response of control and prion-infected mice at 9–10 w.p.i. n = 19 mice per group. ***P < 0.001, 2-way ANOVA with Sidak’s multiple comparison test. (D) Pain threshold response of control and prion-infected mice at 9–10 w.p.i. n = 6 mice per group. Unpaired Student’s t test. (E) Anxiety levels of control and prion-infected mice at 9–10 w.p.i. were assessed by elevated plus maze. n = 6 mice per group. Unpaired Student’s t test. (F) Fear-conditioning response of prion-infected mice (9–10 w.p.i.) treated with vehicle or donepezil (0.5 mg/kg) 60 minutes before training. n = 9 (vehicle); n = 15 (donepezil). ***P < 0.001, 2-way ANOVA with Sidak’s multiple comparison test. (G) Determination of the total muscarinic receptor population by [3H]-NMS binding to hippocampal membranes prepared from control or prion-infected mice (10 w.p.i.). Nonspecific binding was determined by the addition of atropine (1 μM). Data are expressed as fmol/mg protein (n = 3). Bmax, maximal binding capacity. (H) Total [3H]-NMS binding to membranes prepared from the frontal cortex of control or AD patients. n = 10. (I) Stimulation of [35S]-GTPγS binding to membranes prepared from control or prion-infected mice (9–10 w.p.i.) in response to oxotremorine-M. Data shown are increases in [35S]-GTPγS binding over basal; mean pEC50 values of 6.45 ± 0.03, 6.63 ± 0.01, and 6.50 ± 0.04, respectively (n = 3). (J) [35S]-GTPγS binding to membranes prepared from the frontal cortex of control or AD patients in response to acetylcholine. Data are the percentage of the maximal [35S]-GTPγS binding stimulated by oxotremorine-M. Mean pEC50 values of 6.00 ± 0.09 and 5.86 ± 0.11, respectively (n = 3).