title: Activation of GABA-A receptor ameliorates homocysteine-induced MMP-9 activation by ERK pathway.
abstract: Hyperhomocysteinemia (HHcy) is a risk factor for neuroinflammatory and neurodegenerative diseases. Homocysteine (Hcy) induces redox stress, in part, by activating matrix metalloproteinase-9 (MMP-9), which degrades the matrix and leads to blood-brain barrier dysfunction. Hcy competitively binds to gamma-aminbutyric acid (GABA) receptors, which are excitatory neurotransmitter receptors. However, the role of GABA-A receptor in Hcy-induced cerebrovascular remodeling is not clear. We hypothesized that Hcy causes cerebrovascular remodeling by increasing redox stress and MMP-9 activity via the extracellular signal-regulated kinase (ERK) signaling pathway and by inhibition of GABA-A receptors, thus behaving as an inhibitory neurotransmitter. Hcy-induced reactive oxygen species production was detected using the fluorescent probe, 2'-7'-dichlorodihydrofluorescein diacetate. Hcy increased nicotinamide adenine dinucleotide phosphate-oxidase-4 concomitantly suppressing thioredoxin. Hcy caused activation of MMP-9, measured by gelatin zymography. The GABA-A receptor agonist, muscimol ameliorated the Hcy-mediated MMP-9 activation. In parallel, Hcy caused phosphorylation of ERK and selectively decreased levels of tissue inhibitors of metalloproteinase-4 (TIMP-4). Treatment of the endothelial cell with muscimol restored the levels of TIMP-4 to the levels in control group. Hcy induced expression of iNOS and decreased eNOS expression, which lead to a decreased NO bioavailability. Furthermore muscimol attenuated Hcy-induced MMP-9 via ERK signaling pathway. These results suggest that Hcy competes with GABA-A receptors, inducing the oxidative stress transduction pathway and leading to ERK activation.
authors.affiliation: Department of Physiology and Biophysics, School of Medicine, University of Louisville, Louisville, Kentucky 40292, USA.
authors.forename: Neetu
authors.initials: N
authors.lastname: Tyagi
authors.forename: William
authors.initials: W
authors.lastname: Gillespie
authors.forename: Jonathan C
authors.initials: JC
authors.lastname: Vacek
authors.forename: Utpal
authors.initials: U
authors.lastname: Sen
authors.forename: Suresh C
authors.initials: SC
authors.lastname: Tyagi
authors.forename: David
authors.initials: D
authors.lastname: Lominadze
mesh_terms: D000818:Animals; D002460:Cell Line; D024141:Collagen Type IV / Q000378:metabolism; D004549:Elastin / Q000378:metabolism; D042783:Endothelial Cells / Q000187:drug effects* / Q000201:enzymology; D004789:Enzyme Activation; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D018755:GABA Agonists / Q000494:pharmacology*; D058785:GABA-A Receptor Agonists; D006710:Homocysteine / Q000378:metabolism*; D020780:Matrix Metalloproteinase 9 / Q000378:metabolism*; D051379:Mice; D009118:Muscimol / Q000494:pharmacology*; D000074663:NADPH Oxidase 4; D019255:NADPH Oxidases / Q000378:metabolism; D009569:Nitric Oxide / Q000378:metabolism; D052247:Nitric Oxide Synthase Type II / Q000378:metabolism; D052250:Nitric Oxide Synthase Type III / Q000378:metabolism; D018384:Oxidative Stress / Q000187:drug effects; D010766:Phosphorylation; D017382:Reactive Oxygen Species / Q000378:metabolism; D011963:Receptors, GABA-A / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D013879:Thioredoxins / Q000378:metabolism; D019714:Tissue Inhibitor of Metalloproteinases / Q000378:metabolism; D000097792:Tissue Inhibitor of Metalloproteinase-4
chemical_list: D024141:Collagen Type IV; D004549:Elastin; D048049:Extracellular Signal-Regulated MAP Kinases; D018755:GABA Agonists; D058785:GABA-A Receptor Agonists; D006710:Homocysteine; D020780:Matrix Metalloproteinase 9; D009118:Muscimol; D000074663:NADPH Oxidase 4; D019255:NADPH Oxidases; D009569:Nitric Oxide; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III; D017382:Reactive Oxygen Species; D011963:Receptors, GABA-A; D013879:Thioredoxins; D019714:Tissue Inhibitor of Metalloproteinases; D000097792:Tissue Inhibitor of Metalloproteinase-4; C496317:Nos2 protein, mouse; C496315:Nos3 protein, mouse; C422943:Nox4 protein, mouse; C501830:Mmp9 protein, mouse