In conclusion we demonstrated that the atypical high basal a

In conclusion, we demonstrated that the atypical high-basal activity of the mGlu3 KP372-1 results mostly from its activation by low ambient glutamate concentrations. This is due to a unique interaction network located in the extracellular domain of the mGlu3 receptor. This network acts as “Cl− lock” that is strongly stabilizing the glutamate-induced active conformation of the receptors. This strong allosteric control of the mGlu3 receptor by physiological Cl− ions allows it to sense and respond efficiently to low concentrations of glutamate. Thus, the various mGluR subtypes appear as a family of glutamate sensors able to respond to a wide range of conditions, from high nanomolar to millimolar concentrations of glutamate. Among them, mGlu3 receptor is the most sensitive member of this family, able to mediate sustained responses to low tone of glutamate.
Author contribution
Conflict of interest
Acknowledgments The authors thank Ebba L. Lagerqvist for critical reading of the manuscript. This work was supported by grants from the Fondation pour la Recherche Médicale (FRM team DEQ20130326522 and DEQ20170336747) to JPP, the Fundació La Marató de TV3 (Ref 110232), Eranet Neuron, the Agence Nationale de la Recherche (ANR-12-NEUR-0003, ANR-13-BSV1-006 to CG, ANR-09-BIOT-018 to JPP and ANR-13-BSV5-0007 to PR) and “Chercheur d'Avenir” grant from the Region Languedoc Roussillon to EM. Cell-based pharmacological assays were performed on the ARPEGE (Pharmacology Screening-Interactome) platform facility at the IGF. JP Pin's research group belongs to the Labex EpiGenMed (ANR-10-LABX-12-01, « Investissements d'avenir » program). The CBS belongs to the France-BioImaging infrastructure supported by the French National Research Agency (ANR-10-INBS-04, « Investments for the future »), the Labex EpiGenMed and is supported by the GIS "IBiSA: Infrastructures en Biologie Sante et Agronomie". AT and LO were supported by PhD fellowships from the Ministère de l'Education Nationale et de la Recherche. AT was supported by the Fondation pour la Recherche Médicale (FRM FDT20140931071). AMC was supported by a PhD fellowship from Labex EpiGenMed and XR by the Beatriu de Pinos program of Agència de Gestió d’Ajuts Universitaris i de Recerca. AC was supported by ANR-13-BSV1-006 and PS by a PhD fellowship supported by the ANRT and CisBio.
Introduction Intracerebral hemorrhage (ICH) is a serious subtype of stroke characterized by extravasations of blood into brain parenchyma resulting in high mortality and morbidity rates (Qureshi et al., 2009). The hematoma formation produces a transient ischemic effect that ultimately leads to increased levels of extracellular glutamate and further excitotoxicity, oxidative stress and neuronal cell death (Hu et al., 2016; Prabhakaran and Naidech, 2012; Righy et al., 2016; Wagner, 2007; Wu et al., 2013). The extension of hemorrhage and brain edema are key variables responsible for the development of these mechanisms and are the main determinants of neurologic deterioration (Lim-Hing and Rincon, 2017). Glutamate is an excitatory neurotransmitter that plays an important role in the pathogenesis of neuronal injury; it has been implicated in a number of brain disorders such as stroke, traumatic brain injury, amyotrophic lateral sclerosis, Alzheimer's disease, Parkinson disease and Huntington's disease (Amorini et al., 2017; Bi et al., 2017; Lewerenz and Maher, 2015; Qureshi et al., 2003). Glial glutamate transporters 1 (EAAT1) and 2 (EAAT2) are the essential proteins controlling the glutamate reuptake to maintain extracellular glutamate concentrations below neurotoxic levels (López-Bayghen and Ortega, 2011; Martinez-Lozada et al., 2016; Rothstein et al., 1996). Although the changes of glutamate uptake, EAAT1 and EAAT2 have been widely reported in the ischemic condition (Hu et al., 2017; Rao et al., 2001; Yatomi et al., 2013), studies of experimental intracerebral hemorrhage are scarce (Qureshi et al., 2003). Moreover, there are conflicting results of EAAT1 and EAAT2 and of glutamate uptake depending of brain injury and site of lesion (Dumont et al., 2014; Piao et al., 2015). It is now recognized that astrocytic glutamate transporters may have differential expression patterns and act depending of specific transcriptional regulators (Martinez-Lozada et al., 2016). Additionally, the injury effect on Na+/K+-ATPase and glutamine synthetase (GS) activities can also contribute to distinguish patterns of EAAT1/2. Previous studies have demonstrated a direct relationship between both enzyme (Na+/K+-ATPase and GS) activities and the glial glutamate transporters, EAAT1 and EAAT2 (Genda et al., 2011; Lehmann et al., 2009; Zou et al., 2010). Thus, the knowledge of these parameters may help understand the pathogenesis of hemorrhagic stroke.