GOUDET, C. | Search bioRxiv

bioRxiv2023

Conformational diversity in class C GPCR positive allosteric modulation

The metabotropic glutamate receptors (mGlus) are class C G protein coupled receptors (GPCR) that form obligate dimers activated by the major excitatory neurotransmitter L-glutamate1,2. The architecture of mGlu receptor comprises an extracellular Venus-Fly Trap domain (VFT) connected to a transmembrane domain (7TM) through a Cysteine-Rich Domain (CRD). The binding of L-glutamate in the VFTs and subsequent conformational change results in the signal being transmitted to the 7TM inducing G-protein binding and activation 3-6. The mGlu receptors signal transduction can be allosterically potentiated by positive allosteric modulators (PAMs) binding to the 7TMs, which are of therapeutic interest in various neurological disorders7-9. Here, we report the cryoEM structures of metabotropic glutamate receptor 5 (mGlu5) purified with three chemically and pharmacologically distinct PAMs. We find that PAMs modulate the receptor equilibrium through their different binding modes, revealing how their interactions in the 7TMs impact the mGlu5 receptor conformational landscape and function. In addition, we identified a PAM-free but agonist-bound intermediate state that is stabilised by interactions mediated by intracellular loop 2. The activation of mGlu5 receptor is a multi-step sequential process in which the binding of the PAMs in the 7TM modulates the equilibrium towards the active state.

biochemistry↗

bioRxiv2022

Differential reduction of neuropathic pain symptoms by mGlu4-mediated neuromodulation of amygdala circuits

Neuropathic pain is a common health problem, resulting in exacerbated response to noxious and non noxious stimuli, as well as impaired emotional and cognitive responses. Unfortunately, neuropathic pain is also one of the most difficult pain syndromes to manage, highlighting the importance of better understanding of the brain regions and neuromodulatory mechanisms involved in its regulation. Among the many interconnected brain areas which process pain, the amygdala is known to play an important role in the integration of sensory and emotional pain signals. Here, we questioned the ability of a recently identified neuromodulatory mechanisms associated to the metabotropic glutamate receptors mGlu4 in the amygdala to modulate neuropathic pain. In a murine model of peripheral mononeuropathy induced by a chronic constriction of the sciatic nerve, we demonstrate that pharmacological activation of amygdala mGlu4 receptors efficiently alleviates sensory and depressive-like symptoms in both male and female mice. Moreover, we reveal a differential modulation of those symptoms, activating mGlu4 receptors in the controlateral amygdala, relatively to the side of the mononeuropathy, is necessary and sufficient to relieve both sensory and depressive-like symptoms while ipsilateral activation solely reduces depressive-like symptoms. Furthermore, using photopharmacology, a recent strategy allowing a precise spatiotemporal photocontrol of deep brain endogenous targets, we further demonstrate the rapid and reversible action of mGlu4-mediated neuromodulation on neuropathic pain symptoms. Finally, coupling photopharmacology and analgesic conditioned place preference, we show an important pain-reducing effect of mGlu4 activation. Taken together, these data highlight the analgesic potential of enhancing amygdala mGlu4 activity to counteract neuropathy in the hope of improving existing treatments.

neuroscience↗