ABSTRACT
Mounting evidence suggests numerous glutamatergic synapse subtypes exist in the brain, and that these subtypes are likely defined by unique molecular regulatory mechanisms. Recent work has identified substantial divergence of molecular composition between commonly studied Schaffer collateral synapses and perforant path-dentate gyrus (DG) synapses of the hippocampus. However, little is known about the molecular mechanisms that may confer unique properties to perforant path-DG synapses. Here we investigate whether the RhoGEF (Rho guanine-nucleotide exchange factor) protein Tiam1 plays a unique role in the regulation of glutamatergic synapses in dentate granule neurons using a combination of molecular, electrophysiological, and imaging approaches in rat entorhino-hippocampal slices of both sexes. We find that inhibition of Tiam1 function in dentate granule neurons reduces synaptic AMPA receptor function and causes dendritic spines to adopt an elongated filopodia-like morphology. We also find that Tiam1's support of perforant path-DG synapse function is dependent on its GEF domain and identify a potential role for the auto-inhibitory PH domain of Tiam1 in regulating Tiam1 function at these synapses. In marked contrast, reduced Tiam1 expression in CA1 pyramidal neurons produced no effect on glutamatergic synapse development. Together, these data identify a critical role for Tiam1 in the hippocampus and reveal a unique Tiam1-mediated molecular program of glutamatergic synapse regulation in dentate granule neurons.SIGNIFICANCE STATEMENT Several lines of evidence independently point to the molecular diversity of glutamatergic synapses in the brain. Rho guanine-nucleotide exchange factor (RhoGEF) proteins as powerful modulators of glutamatergic synapse function have also become increasingly appreciated in recent years. Here we investigate the synaptic regulatory role of the RhoGEF protein Tiam1, whose expression appears to be remarkably enriched in granule neurons of the dentate gyrus. We find that Tiam1 plays a critical role in the development of glutamatergic perforant path-dentate gyrus synapses, but not in commonly studied in Schaffer collateral-CA1 synapses. Together, these data reveal a unique RhoGEF-mediated molecular program of glutamatergic synapse regulation in dentate granule neurons.
Subject(s)
Glutamic Acid/metabolism , Hippocampus/cytology , Hippocampus/metabolism , Synapses/metabolism , T-Lymphoma Invasion and Metastasis-inducing Protein 1/physiology , Animals , Animals, Newborn , Dentate Gyrus/chemistry , Dentate Gyrus/cytology , Dentate Gyrus/metabolism , Female , Glutamic Acid/analysis , Hippocampus/chemistry , Male , Organ Culture Techniques , Rats , Rats, Sprague-Dawley , Synapses/chemistry , T-Lymphoma Invasion and Metastasis-inducing Protein 1/analysisABSTRACT
Recently, we demonstrated that Rac1 upregulation is involved in augmented bronchial smooth muscle (BSM) contractions of antigen-challenged mice. However, change in G protein-coupled receptor (GPCR)-induced Rac1 activation remains unknown in BSMs of repeatedly antigen-challenged (Chal.) mice. We here examined carbachol (CCh)-induced Rac1 activation in BSMs of Chal. mice. Gene expression levels of both Rac1 and Rac-guanine nucleotide exchange factors (GEFs), such as Tiam1 and Trio, were increased in BSMs of Chal. mice. Furthermore, CCh-induced Rac1 activation was inhibited by pretreatment with Rac1-GEF inhibitor NSC23766 and Rac1 inhibitor EHT1864 in BSMs of sensitized-control (S.C.) and Chal. mice. Compared with S.C. mice, CCh-induced Rac1 activation was increased in BSMs of Chal. mice. In conclusion, we reported that increased CCh-induced Rac1 activation via Tiam1 and Trio upregulation, in addition to upregulate Rac1, may be involved in increased CCh-induced BSM contractions in Chal. mice.
Subject(s)
Bronchi/physiology , Guanine Nucleotide Exchange Factors/physiology , Muscle Contraction/physiology , Muscle, Smooth/physiology , Neuropeptides/physiology , Phosphoproteins/physiology , Protein Serine-Threonine Kinases/physiology , T-Lymphoma Invasion and Metastasis-inducing Protein 1/physiology , rac1 GTP-Binding Protein/physiology , Aminoquinolines/pharmacology , Animals , Antigens , Asthma/genetics , Asthma/physiopathology , Bronchi/drug effects , Carbachol , Guanine Nucleotide Exchange Factors/genetics , Male , Mice, Inbred BALB C , Muscarinic Agonists , Muscle Contraction/drug effects , Muscle, Smooth/drug effects , Neuropeptides/antagonists & inhibitors , Neuropeptides/genetics , Ovalbumin , Phosphoproteins/genetics , Protein Serine-Threonine Kinases/genetics , Pyrimidines/pharmacology , Pyrones/pharmacology , Quinolines/pharmacology , T-Lymphoma Invasion and Metastasis-inducing Protein 1/genetics , Up-Regulation , rac1 GTP-Binding Protein/antagonists & inhibitors , rac1 GTP-Binding Protein/geneticsABSTRACT
Rac-GTPases and their Rac-GEF activators play important roles in the recruitment and host defence functions of neutrophils. These proteins control the activation of adhesion molecules and the cytoskeletal dynamics that enable the adhesion, migration and tissue recruitment of neutrophils. They also regulate the effector functions that allow neutrophils to kill bacterial and fungal pathogens, and to clear debris. This review focuses on the roles of Rac-GTPases and Rac-GEFs in neutrophil adhesion, migration and recruitment.