Amyloid-β_1-42oligomers enhance mGlu₅R-dependent synaptic weakening via NMDAR activation and complement C3aR/C5aR signaling

AbstractSynaptic dysfunction, weakening, and loss of synapses are well-correlated with the pathology of Alzheimer’s disease (AD). Recent studies have implicated hyper-activation of the complement cascade as the driving force for loss of synapses in AD. However, the synaptic cues to trigger pathological complement activity remain elusive. To address this, we studied the actions of oligomeric, 42 residue length amyloid β (oAβ) on metabotropic glutamate receptor (mGluR) long-term depression (mGluR-LTD) at hippocampal CA1 synapses, a form of synaptic plasticity that is disrupted in rodent models of AD. We found that exogenous application of oAβ to mouse hippocampal slices enhanced the magnitude of mGluR subtype 5 (mGlu5R)-dependent LTD. This enhanced synaptic weakening occurred via both NMDARs and complement C3aR/C5aR signaling, as revealed by pharmacological inhibition experiments. Our findings reveal a novel mechanistic interaction between mGlu5R, NMDARs, and the complement cascade in synaptic weakening induced by oAβ, which could represent an early trigger of synaptic degeneration in AD.