Altered surface mGluR5 dynamics provoke synaptic NMDAR dysfunction and cognitive defects in Fmr1 knockout mice

Metabotropic glutamate receptor subtype 5 (mGluR5) is crucially implicated in the pathophysiology of Fragile X Syndrome (FXS); however, its dysfunction at the sub-cellular level, and related synaptic and cognitive phenotypes are unexplored. Here, we probed the consequences of mGluR5/Homer scaffold disruption for mGluR5 cell-surface mobility, synaptic N-methyl-D-Aspartate receptor (NMDAR) function, and behavioral phenotypes in the second-generation Fmr1 knockout (KO) mouse. Using single-molecule tracking, we found that mGluR5 was significantly more mobile at synapses in hippocampal Fmr1 KO neurons, causing an increased synaptic surface co-clustering of mGluR5 and NMDAR. This correlated with a reduced amplitude of synaptic NMDAR currents, a lack of their mGluR5-Activated long-Term depression, and NMDAR/hippocampus dependent cognitive deficits. These synaptic and behavioral phenomena were reversed by knocking down Homer1a in Fmr1 KO mice. Our study provides a mechanistic link between changes of mGluR5 dynamics and pathological phenotypes of FXS, unveiling novel targets for mGluR5-based therapeutics

Dual function of MyD88 in Ras signaling and inflammation, leading to cell transformation

MyD88 est une protéine adaptatrice du système immunitaire inné, impliquée dans la défense de l’organisme contre les agents microbiens. Elle est recrutée aux « Toll-like receptors » (TLRs) suite à la reconnaissance par ces derniers de motifs microbiens conservés, les PAMPs (Pathogens-associated molecular patterns). La voie de signalisation ainsi déclenchée va aboutir à la production de cytokines pro-inflammatoires, de chimiokines et d’espèces actives de l’oxygène. De cette façon, les TLRs, via MyD88, constituent la première ligne de défense contre les pathogènes.De nombreuses études ont permis de démontrer que MyD88 est nécessaire pour la réponse inflammatoire, qui promeut la carcinogenèse. Dans le cadre d’une étude sur les TLRs et le cancer, l’équipe a démontré, grâce à une étude in vivo, que MyD88 participe au processus de tumorigenèse médiée par l’oncogène ras et est nécessaire à l’activation de la voie canonique des MAPKs, ainsi qu’à la transformation cellulaire in vitro. Nous avons ensuite déterminé le mécanisme par lequel MyD88 intervient dans la voie de signalisation Ras/MAPKs, en permettant le maintien de l’activation de cette voie. En effet, MyD88 interagit avec une MAPK clé de cette voie : la kinase ERK, et protège cette dernière de sa déphosphorylation par sa phosphatase spécifique MKP-3, MyD88 et MKP-3 se liant à ERK par le même domaine. Nous avons démontré la pertinence de ce mécanisme, grâce à la mise en évidence d’une surexpression de la protéine MyD88 et de son interaction avec la forme phosphorylée d’ERK dans des coupes de tissus tumoraux humains (estomac, poumon, colon).L’ensemble des résultats obtenus au cours de ma thèse ont permis de montrer qu’en plus de son rôle bien défini en tant qu’adaptateur des récepteurs de l’immunité innée dans les processus inflammatoires, MyD88 joue un rôle direct, qui semble être crucial dans la signalisation Ras, le contrôle du cycle cellulaire et la transformation cellulaireMyD88 is an adaptator protein of the innate immune system, implicated in the défense against microbes. MyD88 is recruited by the Toll-Like Receptors (TLRs) upon there interaction with conserved microbial patterns (PAMPs). Therefore, TLR signaling pathway induces the production of pro-inflammatory cytokines, chemokines and reactive oxygen species. TLRs, via MyD88, form the first line of defense against pathogens. Accumulating evidence points to inflammation as a promoter of carcinogenesis. MyD88 is an adaptor molecule in TLR and IL-1R signaling that was recently implicated in tumorigenesis through proinflammatory mechanisms. Here we have shown that MyD88 is also required in a cell-autonomous fashion for Ras-mediated carcinogenesis in mice in vivo and for MAPK activation and transformation in vitro. Mechanistically, MyD88 bound to the key MAPK, ERK, and prevented its inactivation by its phosphatase, MKP3, thereby amplifying the activation of the canonical Ras pathway. The relevance of this mechanism to human neoplasia was suggested by the finding that MyD88 was overexpressed and interacted with activated ERK in primary human cancer tissues. Collectively, these results show that in addition to its role in inflammation, MyD88 plays what we believe to be a crucial direct role in Ras signaling, cell-cycle control, and cell transformatio

Dual function of MyD88 in RAS signaling and inflammation, leading to mouse and human cell transformation

Accumulating evidence points to inflammation as a promoter of carcinogenesis. MyD88 is an adaptor molecule in TLR and IL-1R signaling that was recently implicated in tumorigenesis through proinflammatory mechanisms. Here we have shown that MyD88 is also required in a cell-autonomous fashion for RAS-mediated carcinogenesis in mice in vivo and for MAPK activation and transformation in vitro. Mechanistically, MyD88 bound to the key MAPK, Erk, and prevented its inactivation by its phosphatase, MKP3, thereby amplifying the activation of the canonical RAS pathway. The relevance of this mechanism to human neoplasia was suggested by the finding that MyD88 was overexpressed and interacted with activated Erk in primary human cancer tissues. Collectively, these results show that in addition to its role in inflammation, MyD88 plays what we believe to be a crucial direct role in RAS signaling, cell-cycle control, and cell transformation

A Gender-Dependent Molecular Switch of Inflammation via MyD88/Estrogen Receptor-Alpha Interaction

International audienceIntroduction: Most Toll-like receptors and IL-1/IL-18 receptors activate a signaling cascade via the adaptor molecule MyD88, resulting in NF-κB activation and inflammatory cytokine and chemokine production. Females are less susceptible than males to inflammatory conditions, presumably due to protection by estrogen. The exact mechanism underlying this protection is unknown.Methods: MCF7 cells expressing wild-type or mutated LXXLL motif were used to determine MyD88/estrogen receptor (ER)-a interaction by immunoprecipitation and cell activation by ELISA and luciferase reporter assay. IL-1b and/or E2 were used to activate MCF7 cells expressing normal or knocked down levels of PRMT1. Finally, in situ proximity ligation assay with anti-MyD88 and anti-methylated ER-a (methER-a) antibodies was used to evaluate MyD88/methylated ER-a interaction in THP1 cells and histological sections.Results: We show that MyD88 interacts with a methylated, cytoplasmic form of estrogen receptor-alpha (methER-α). This interaction is required for NF-κB transcriptional activity and pro-inflammatory cytokine production, and is dissociated by estrogen. Importantly, we show a strong gender segregation in gametogenic reproductive organs, with MyD88/methER-α interactions found in testicular tissues and in ovarian tissues from menopausal women, but not in ovaries from women age 49 and less - suggesting a role for estrogen in disrupting this complex in situ.Discussion: Collectively, our results indicate that the formation of MyD88/methER-α complexes during inflammatory signaling and their disruption by estrogen may represent a mechanism that contributes to gender bias in inflammatory responses

Low glucose microenvironment of normal kidney cells stabilizes a subset of messengers involved in angiogenesis

International audienceAs glucose is a mandatory nutrient for cell proliferation and renewal, it is suspected that glucose microenvironment is sensed by all cell types to regulate angiogenesis. Several glucose-sensing components have been partially described to respond to high glucose levels. However, little is known about the response to low glucose. Here, we used well-differentiated isolated normal rat renal tubules under normal oxygenation conditions to assess the angio-genic response to low glucose. In apparent paradox, but confirming observations made separately in other models, high glucose but also low glucose increased mRNA level of vascular endothelial growth factor A (VEGFA). A subset of mRNAs including hypoxia-inducible factor 1A (HIF1A), angiopoie-tin receptor (TIE-2), and VEGF receptor 2 (FLK1) were similarly glucose-sensitive and responded to low glucose by increased stability independently of HIF1A and HIF2A proteins. These results contribute to gain some insights as to how normal cells response to low glucose may play a role in the tumor microenvironment