title: Alterations in mGluR5 expression and signaling in Lewy body disease and in transgenic models of alpha-synucleinopathy--implications for excitotoxicity.
abstract: Dementia with Lewy bodies (DLB) and Parkinson's Disease (PD) are neurodegenerative disorders of the aging population characterized by the abnormal accumulation of alpha-synuclein (alpha-syn). Previous studies have suggested that excitotoxicity may contribute to neurodegeneration in these disorders, however the underlying mechanisms and their relationship to alpha-syn remain unclear. For this study we proposed that accumulation of alpha-syn might result in alterations in metabotropic glutamate receptors (mGluR), particularly mGluR5 which has been linked to deficits in murine models of PD. In this context, levels of mGluR5 were analyzed in the brains of PD and DLB human cases and alpha-syn transgenic (tg) mice and compared to age-matched, unimpaired controls, we report a 40% increase in the levels of mGluR5 and beta-arrestin immunoreactivity in the frontal cortex, hippocampus and putamen in DLB cases and in the putamen in PD cases. In the hippocampus, mGluR5 was more abundant in the CA3 region and co-localized with alpha-syn aggregates. Similarly, in the hippocampus and basal ganglia of alpha-syn tg mice, levels of mGluR5 were increased and mGluR5 and alpha-syn were co-localized and co-immunoprecipitated, suggesting that alpha-syn interferes with mGluR5 trafficking. The increased levels of mGluR5 were accompanied by a concomitant increase in the activation of downstream signaling components including ERK, Elk-1 and CREB. Consistent with the increased accumulation of alpha-syn and alterations in mGluR5 in cognitive- and motor-associated brain regions, these mice displayed impaired performance in the water maze and pole test, these behavioral alterations were reversed with the mGluR5 antagonist, MPEP. Taken together the results from study suggest that mGluR5 may directly interact with alpha-syn resulting in its over activation and that this over activation may contribute to excitotoxic cell death in select neuronal regions. These results highlight the therapeutic importance of mGluR5 antagonists in alpha-synucleinopathies.
authors.affiliation: Department of Neurosciences, University of California San Diego, La Jolla, California, United States of America.
authors.forename: Diana L
authors.initials: DL
authors.lastname: Price
authors.forename: Edward
authors.initials: E
authors.lastname: Rockenstein
authors.forename: Kiren
authors.initials: K
authors.lastname: Ubhi
authors.forename: Van
authors.initials: V
authors.lastname: Phung
authors.forename: Natalie
authors.initials: N
authors.lastname: MacLean-Lewis
authors.forename: David
authors.initials: D
authors.lastname: Askay
authors.forename: Anna
authors.initials: A
authors.lastname: Cartier
authors.forename: Brian
authors.initials: B
authors.lastname: Spencer
authors.forename: Christina
authors.initials: C
authors.lastname: Patrick
authors.forename: Paula
authors.initials: P
authors.lastname: Desplats
authors.forename: Mark H
authors.initials: MH
authors.lastname: Ellisman
authors.forename: Eliezer
authors.initials: E
authors.lastname: Masliah
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D001344:Autopsy; D001921:Brain / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D005260:Female; D006801:Humans; D015151:Immunoblotting; D007150:Immunohistochemistry; D020961:Lewy Body Disease / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D008297:Male; D008569:Memory Disorders / Q000235:genetics / Q000503:physiopathology / Q000517:prevention & control; D051379:Mice; D008822:Mice, Transgenic; D009043:Motor Activity / Q000187:drug effects; D019636:Neurodegenerative Diseases / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D010300:Parkinson Disease / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D011725:Pyridines / Q000494:pharmacology; D064529:Receptor, Metabotropic Glutamate 5; D018094:Receptors, Metabotropic Glutamate / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D051844:alpha-Synuclein / Q000235:genetics / Q000378:metabolism*
chemical_list: D018691:Excitatory Amino Acid Antagonists; C578935:GRM5 protein, human; C578936:Grm5 protein, mouse; D011725:Pyridines; D064529:Receptor, Metabotropic Glutamate 5; D018094:Receptors, Metabotropic Glutamate; D051844:alpha-Synuclein; C121465:6-methyl-2-(phenylethynyl)pyridine