Adam J Funk1, Vahram Haroutunian2, James H Meador-Woodruff3, Robert E McCullumsmith4. 1. Department of Psychiatry and Behavioral Neuroscience, University of Cincinnati, CARE 5830, 231 Albert Sabin Way, Cincinnati, OH 45267-0583, USA. 2. Department of Psychiatry, Mount Sinai School of Medicine, One Gustave L. Levy Place, Box 1230, New York, NY 10029, USA. 3. Department of Psychiatry and Behavioral Neurobiology, University of Alabama Birmingham, SC 560, 1530 3rd Avenue South, Birmingham, AL 35294, USA; Evelyn F. McKnight Brain Institute, University of Alabama Birmingham, Shelby 911, 1530 3rd Avenue South, Birmingham, AL 35294, USA. 4. Department of Psychiatry and Behavioral Neuroscience, University of Cincinnati, CARE 5830, 231 Albert Sabin Way, Cincinnati, OH 45267-0583, USA. Electronic address: robert.mccullumsmith@uc.edu.
Abstract
BACKGROUND: Current pharmacological treatments for schizophrenia target G protein-coupled receptors (GPCRs), including dopamine receptors. Ligand-bound GPCRs are regulated by a family of G protein-coupled receptor kinases (GRKs), members of which uncouple the receptor from heterotrimeric G proteins, desensitize the receptor, and induce receptor internalization via the arrestin family of scaffolding and signaling molecules. GRKs initiate the activation of downstream signaling pathways, can regulate receptors and signaling molecules independent of GPCR phosphorylation, and modulate epigenetic regulators like histone deacetylases (HDACs). We hypothesize that the expression of GRK proteins is altered in schizophrenia, consistent with previous findings of alterations upstream and downstream from this family of molecules that facilitate intracellular signaling processes. METHODS: In this study, we measured protein expression via Western blot analysis for GRKs 2, 3, 5, and 6 in the anterior cingulate cortex of patients with schizophrenia (n=36) and a comparison group (n=33). To control for antipsychotic treatment, we measured these same targets in haloperidol-treated vs. untreated rats (n=10 for both). RESULTS: We found increased levels of GRK5 in schizophrenia. No changes were detected in GRK protein expression in rats treated with haloperidol decanoate for 9 months. CONCLUSION: These data suggest that increased GRK5 expression may contribute to the pathophysiology of schizophrenia via abnormal regulation of the cytoskeleton, endocytosis, signaling, GPCRs, and histone modification.
BACKGROUND: Current pharmacological treatments for schizophrenia target G protein-coupled receptors (GPCRs), including dopamine receptors. Ligand-bound GPCRs are regulated by a family of G protein-coupled receptor kinases (GRKs), members of which uncouple the receptor from heterotrimeric G proteins, desensitize the receptor, and induce receptor internalization via the arrestin family of scaffolding and signaling molecules. GRKs initiate the activation of downstream signaling pathways, can regulate receptors and signaling molecules independent of GPCR phosphorylation, and modulate epigenetic regulators like histone deacetylases (HDACs). We hypothesize that the expression of GRK proteins is altered in schizophrenia, consistent with previous findings of alterations upstream and downstream from this family of molecules that facilitate intracellular signaling processes. METHODS: In this study, we measured protein expression via Western blot analysis for GRKs 2, 3, 5, and 6 in the anterior cingulate cortex of patients with schizophrenia (n=36) and a comparison group (n=33). To control for antipsychotic treatment, we measured these same targets in haloperidol-treated vs. untreated rats (n=10 for both). RESULTS: We found increased levels of GRK5 in schizophrenia. No changes were detected in GRK protein expression in rats treated with haloperidol decanoate for 9 months. CONCLUSION: These data suggest that increased GRK5 expression may contribute to the pathophysiology of schizophrenia via abnormal regulation of the cytoskeleton, endocytosis, signaling, GPCRs, and histone modification.
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