title: GRK5 deficiency leads to reduced hippocampal acetylcholine level via impaired presynaptic M2/M4 autoreceptor desensitization.
abstract: G protein-coupled receptor kinase 5 (GRK5) deficiency has been linked recently to early Alzheimer disease (AD), but the mechanism by which GRK5 deficiency may contribute to AD pathogenesis remains elusive. Here we report that overexpression of dominant negative mutant of GRK5 (dnGRK5) in a cholinergic neuronal cell line led to decreased acetylcholine (ACh) release. This reduction was fully corrected by pertussis toxin, atropine (a nonselective muscarinic antagonist), or methoctramine (a selective M2/M4 muscarinic receptor antagonist). Consistent with results in cultured cells, high potassium-evoked ACh release in hippocampal slices from young GRK5 knock-out mice was significantly reduced compared with wild type littermates, and this reduced ACh release was also fully corrected by methoctramine. In addition, following treatment with the nonselective muscarinic agonist oxotremorine-M, M2, and M4 receptors underwent significantly reduced internalization in GRK5KO slices compared with wild type slices, as assessed by plasma membrane retention of receptor immunoreactivity, whereas M1 receptor internalization was not affected by loss of GRK5 expression. Moreover, Western blotting revealed no synaptic or cholinergic degenerative changes in young GRK5 knock-out mice. Altogether, these results suggest that GRK5 deficiency leads to a reduced hippocampal ACh release and cholinergic hypofunction by selective impairment of desensitization of presynaptic M2/M4 autoreceptors. Because this nonstructural cholinergic hypofunction precedes the hippocampal cholinergic hypofunction associated with structural cholinergic degeneration and cognitive decline in aged GRK5 knock-out mice, this nonstructural alteration may be an early event contributing to cholinergic degeneration in AD.
authors.affiliation: Laboratory for Alzheimer's Disease and Aging Research, Kansas City Veterans Affairs Medical Center, Kansas City, Missouri 64128, USA.
authors.forename: Jun
authors.initials: J
authors.lastname: Liu
authors.forename: Imtiaz
authors.initials: I
authors.lastname: Rasul
authors.forename: Yuning
authors.initials: Y
authors.lastname: Sun
authors.forename: Guisheng
authors.initials: G
authors.lastname: Wu
authors.forename: Longxuan
authors.initials: L
authors.lastname: Li
authors.forename: Richard T
authors.initials: RT
authors.lastname: Premont
authors.forename: William Z
authors.initials: WZ
authors.lastname: Suo
mesh_terms: D000109:Acetylcholine / Q000378:metabolism*; D000818:Animals; D017660:Autoreceptors / Q000819:agonists / Q000235:genetics / Q000378:metabolism; D015153:Blotting, Western; D002460:Cell Line; D004705:Endocytosis / Q000187:drug effects; D054774:G-Protein-Coupled Receptor Kinase 5 / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D015870:Gene Expression; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D006624:Hippocampus / Q000166:cytology / Q000378:metabolism; D007150:Immunohistochemistry; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D010095:Oxotremorine / Q000031:analogs & derivatives / Q000494:pharmacology; D037342:Pertussis Toxin / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D043585:Receptor, Muscarinic M2 / Q000819:agonists / Q000235:genetics / Q000378:metabolism*; D043588:Receptor, Muscarinic M4 / Q000819:agonists / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013569:Synapses / Q000378:metabolism; D014162:Transfection
chemical_list: D017660:Autoreceptors; D008565:Membrane Proteins; D043585:Receptor, Muscarinic M2; D043588:Receptor, Muscarinic M4; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D010095:Oxotremorine; C042743:oxotremorine M; D037342:Pertussis Toxin; D054774:G-Protein-Coupled Receptor Kinase 5; C517895:Grk5 protein, mouse; D000109:Acetylcholine; D011188:Potassium