Selective activation of the M ₁ muscarinic acetylcholine receptor achieved by allosteric potentiation

Abstract

The forebrain cholinergic system promotes higher brain function in part by signaling through the M1 muscarinic acetylcholine receptor (mAChR). During Alzheimer's disease (AD), these cholinergic neurons degenerate, therefore selectively activating M1 receptors could improve cognitive function in these patients while avoiding unwanted peripheral responses associated with non-selective muscarinic agonists. We describe here benzyl quinolone carboxylic acid (BQCA), a highly selective allosteric potentiator of the M1 mAChR. BQCA reduces the concentration of ACh required to activate M1 up to 129-fold with an inflection point value of 845 nM. No potentiation, agonism, or antagonism activity on other mAChRs is observed up to 100 μM. Furthermore studies in M1−/− mice demonstrates that BQCA requires M1 to promote inositol phosphate turnover in primary neurons and to increase c-fos and arc RNA expression and ERK phosphorylation in the brain. Radioligand-binding assays, molecular modeling, and site-directed mutagenesis experiments indicate that BQCA acts at an allosteric site involving residues Y179 and W400. BQCA reverses scopolamine-induced memory deficits in contextual fear conditioning, increases blood flow to the cerebral cortex, and increases wakefulness while reducing delta sleep. In contrast to M1 allosteric agonists, which do not improve memory in scopolamine-challenged mice in contextual fear conditioning, BQCA induces β-arrestin recruitment to M1, suggesting a role for this signal transduction mechanism in the cholinergic modulation of memory. In summary, BQCA exploits an allosteric potentiation mechanism to provide selectivity for the M1 receptor and represents a promising therapeutic strategy for cognitive disorders.

Antipsychotic Drug-Like Effects of the Selective M4 Muscarinic Acetylcholine Receptor Positive Allosteric Modulator VU0152100

“…Although previous studies indicate that activation of M 1 mAChRs is critical for learning, memory, and executive functions, the role of M 4 mAChRs in modulating cognitive function remains unclear Shirey et al, 2009;Digby et al, 2012;Ma et al, 2009). We found that VU0152100 alone had no effect on PPI or the acquisition of contextual fear conditioning, suggesting that M 4 may not be required for normal hippocampal learning and memory processes in young adult rats.…”

“…However, as the higher doses of amphetamine used in the cognitive studies can induce increases in both dopamine and norepinephrine (McKittrick and Abercrombie 2007), it will be important in future studies to confirm that these effects of VU0152100 are mediated predominately through reversal of dopaminergic signaling. Finally, VU0152100 provides an important M 4 -selective tool compound that used along with recently reported M 1 -selective PAMs (Ma et al, 2009;Shirey et al, 2009) or allosteric agonists (Lebois et al, 2010;Digby et al, 2012) will allow a more complete understanding of the relative roles of these two mAChR subtypes in regulating multiple aspects of cognitive function.…”

A Monod-Wyman-Changeux Mechanism Can Explain G Protein-coupled Receptor (GPCR) Allosteric Modulation

“…As an exemplar system we have utilized the recently described M 1 mAChR allosteric modulator, BQCA ( Fig. 1), which exhibits both in vitro and in vivo efficacy as a potentiator of acetylcholine (ACh) signaling (9,10). We propose that the interaction between BQCA and the M 1 mAChR represents an unprecedented example of GPCR allosteric modulation that is entirely consistent with a strict, two-state MWC mechanism.…”

The M 3 -muscarinic receptor regulates learning and memory in a receptor phosphorylation/arrestin-dependent manner

“…In addition, recent studies using an M 1 -muscarinic receptorpositive allosteric modulator, BQCA, have suggested that M 1 -muscarinic receptors can mediate learning and memory through an indirect mechanism by stimulating the prefrontal cortex (10). There is some controversy, however, because the same compound has been used in studies that suggest that M 1 -muscarinic receptors can directly act on hippocampal-based memory (11).…”