Interaction with NEGR1 affects mGlu 5 cell signalling and the neuroprotection induced by the positive allosteric modulator VU0409551

Background and Purpose The metabotropic glutamate receptor mGlu 5 plays an important role in neuronal survival and synaptic plasticity. We and others have shown that mGlu 5 positive allosteric modulators (PAMs) are biased agonists, triggering the activation of neuroprotective pathways and promoting neuronal survival. As mGlu 5 biased pharmacology arises from drug‐induced interactions with different protein partners, in this study, we analysed the mGlu 5 interactome to identify novel binding partners capable of modulating receptor cell signalling. Experimental Approach To identify new mGlu 5 partners, we employed mass spectrometry, followed by co‐immunoprecipitation experiments, which confirmed the interaction between mGlu 5 and the neuronal growth regulator 1 (NEGR1), a cell adhesion molecule. We next evaluated how NEGR1 affects mGlu 5 cell signalling and cellular distribution using lentivirus transduction on primary neuronal cultures to knockdown NEGR1 expression. We also assessed whether NEGR1 plays a role in the neuroprotective effects of the mGlu5 PAM, VU0409551, by evaluating apoptotic cell death and neurite degeneration. Key Results The interaction between NEGR1 and mGlu 5 is important for mGlu 5 synaptic localization and for its coupling with Homer, thereby modulating cell signalling pathways activated by mGlu 5 receptors. For instance, NEGR1 knockdown led to decreased mGlu 5 ‐dependent activation of ERK1/2 and reduced expression of ARC/ARG3.1 and BDNF. Importantly, NEGR1 knockdown affected mGlu 5 pharmacology, as the neuroprotective effect of VU0409551 was not observed in neurons expressing low levels of NEGR1. Conclusions and Implications These results indicate that NEGR1 is essential for mGlu 5 ‐biased activation of neuroprotective cell signalling pathways and for the neuroprotective effects triggered by VU0409551.