ABSTRACT
Multiple lines of evidence point to glutamatergic signaling in the postsynaptic density (PSD) as a pathophysiologic mechanism in schizophrenia. Integral to PSD glutamatergic signaling is reciprocal interplay between GluN and mGluR5 signaling. We examined agonist-induced mGluR5 signaling in the postmortem dorsolateral prefrontal cortex (DLPFC) derived from 17 patients and age-matched and sex-matched controls. The patient group showed a striking reduction in mGluR5 signaling, manifested by decreases in Gq/11 coupling and association with PI3K and Homer compared to controls (p < 0.01 for all). This was accompanied by increases in serine and tyrosine phosphorylation of mGluR5, which can decrease mGluR5 activity via desensitization (p < 0.01). In addition, we find altered protein-protein interaction (PPI) of mGluR5 with RGS4, norbin, Preso 1 and tamalin, which can also attenuate mGluR5 activity. We previously reported molecular underpinnings of GluN hypofunction (decreased GluN2 phosphorylation) and here we show those of reduced mGluR5 signaling in schizophrenia. We find that reduced GluN2 phosphorylation can be precipitated by attenuated mGluR5 activity and that increased mGluR5 phosphorylation can result from decreased GluN function, suggesting a reciprocal interplay between the two pathways in schizophrenia. Interestingly, the patient group showed decreased mGluR5-GluN association (p < 0.01), a mechanistic basis for the reciprocal facilitation. In sum, we present the first direct evidence for mGluR5 hypoactivity, propose a reciprocal interplay between GluN and mGluR5 pathways as integral to glutamatergic dysregulation and suggest protein-protein interactions in mGluR5-GluN complexes as potential targets for intervention in schizophrenia.
Subject(s)
Receptor, Metabotropic Glutamate 5/metabolism , Receptors, N-Methyl-D-Aspartate/metabolism , Schizophrenia/metabolism , Aged , Aged, 80 and over , Antipsychotic Agents/therapeutic use , Brain/metabolism , Excitatory Amino Acid Agents/metabolism , Female , Humans , Male , Membrane Proteins/metabolism , Phosphorylation , Post-Synaptic Density/metabolism , Prefrontal Cortex/metabolism , Receptor, Metabotropic Glutamate 5/physiology , Signal Transduction/drug effectsABSTRACT
Recently identified candidate susceptibility genes for schizophrenia are likely to play, important roles in the pathophysiology of the illness. It is also clear, however, that the etiologic, contribution of these genes is not only via their own functions but also through interactions with other, genes and environmental factors. Genetic, transgenic and postmortem brain studies support a, potential role for NRG1-erbB4 signaling in schizophrenia. Embedded in the results of these studies, however, are clues to the notion that NRG1-erbB4 signaling does not act alone but in conjunction with, other pathways. This article aims to re-evaluate the evidence for the role of neuregulin 1 (NRG1)-erbB4 signaling in schizophrenia by focusing on its interactions with other candidate susceptibility, pathways. In addition, we consider molecular substrates upon which the NRG1-erbB4 and other, candidate pathways converge contributing to susceptibility for the illness (schizophrenia interactome). Glutamatergic signaling can be an interesting candidate for schizophrenia interactome. Schizophrenia is associated with NMDA receptor hypofunction and moreover, several susceptibility genes for, schizophrenia converge on NMDA receptor signaling. These candidate genes influence NMDA receptor, signaling via diverse mechanisms, yet all eventually impact on protein composition of NMDA receptor, complexes. Likewise, the protein associations in the receptor complexes can themselves modulate, signaling molecules of candidate genes and their pathways. Therefore, protein-protein interactions in the NMDA receptor complexes can mediate reciprocal interactions between NMDA receptor function, and susceptibility candidate pathways including NRG1-erbB4 signaling and thus can be a, schizophrenia interactome.
Subject(s)
ErbB Receptors/genetics , Neuregulin-1/genetics , Schizophrenia/genetics , Schizophrenia/pathology , Signal Transduction/physiology , Animals , Humans , Receptor, ErbB-4 , Receptors, N-Methyl-D-Aspartate/physiologyABSTRACT
Vascular cell adhesion molecule-1 (VCAM-1) mediates recruitment of leukocytes to endothelial cells and is implicated in many inflammatory conditions. Since part of the signal transduction pathway that regulates the activation of VCAM-1 expression is redox-sensitive, compounds with antioxidant properties may have inhibitory effects on VCAM-1 expression. Novel phenolic compounds have been designed and synthesized starting from probucol (1). Many of these compounds demonstrated potent inhibitory effects on cytokine-induced VCAM-1 expression and displayed potent antioxidant effects in vitro. Some of these derivatives (4o, 4p, 4w, and 4x) inhibited lipopolysaccharide (LPS)-induced secretion of pro-inflammatory cytokines such as tumor necrosis factor-alpha (TNF-alpha), interleukin-1 beta (IL-1 beta), and IL-6 from human peripheral blood mononuclear cells (hPBMCs) in a concentration-dependent manner in vitro and showed antiinflammatory effects in an animal model. Compounds 4ad and 4ae are currently in clinical trials for the treatment of rheumatoid arthritis (RA) and prevention of chronic organ transplant rejection, respectively.
