Activation of M1 Muscarinic Receptors by AF267B Protects Hippocampal Neurons from Amyloid β Peptide Toxicity by Acting on the WNT Signalling

Abstract

A loss of pre-synaptic cholinergic neurons, as observed in Alzheimer’s disease (AD), may lead to a decrease in M1 muscarinic receptor-mediated signaling. This, in turn, may affect an amyloid precursor protein processing and tau phosphorylation, two major features of AD. Defects in Wnt signaling have been postulated to contribute to the pathogenesis of the disease. How Wnt signaling may play a role in AD pathology remains to be elucidated. We report here that the activation of M1 receptor, by the M1 agonist AF267B, protects hippocampal neurons from amyloid-â-peptide and this effect involves the Wnt signaling pathway. The studies were carried out in primary cultures of rat hippocampal neurons, in the presence and absence of amyloid-â-peptide; plus and minus AF267B with and without pirenzepine, a selective M1 antagonist. Results indicate that AF267B protects neuronal cells as evaluated by the MTT reduction, immunofluorescence of neurofilaments and apoptotic analysis. To evaluate the role of the Wnt pathway on neuroprotection, we studied the stabilization of cytoplasmic and nuclear â-catenin, glycogen synthase kinase3-â activity as well as the expression of Wnt target genes. Results show that the neuroprotection induced by AF267B but not by the antagonist pirenzepine on the M1 mAChR is accomplished by the activation of the Wnt signaling pathway. We conclude that the cross talk between the M1 receptor signaling and the Wnt components underlie the neuroprotective effect of the M1 muscarinic agonist AF267B on rat hippocampal neurons. This may be highly relevant in the treatment of AD with M1 agonists. Supported by FONDAP-Biomedicine (No. 13980001) and Millennium Institute (MIFAB).