Methylglyoxal‐mediated anxiolysis involves increased protein modification and elevated expression of glyoxalase 1 in the brain

Abstract

To elucidate physiological mechanisms underlying pathological anxiety, valid animal models are essential (Cryan and Holmes 2005). Previous studies confirmed that the high anxiety-related behavior/low anxiety-related behavior (HAB/ LAB) mouse model for trait anxiety mimics many clinically relevant features typical of psychiatric patients (Krömer et al. 2005;Landgraf et al. 2007). In this model, behavioral phenotyping on the elevated-plus-maze (EPM) test was used as selection criterion for bidirectional intra-strain (CD1) breeding. Consequently, inbreeding for more than 30 generations created hyper-anxious (HAB) and hypo-anxious (LAB) mice. These animals provide robust phenotypes for extremes in anxiety-related behavior, and show high comorbidity with depression-like behavior. Inbreeding with focus on a particular trait included a strong accumulation of specific genetic material. Therefore, HAB/LAB animals serve as a potent model to analyze candidates underlying trait anxiety. One of the first protein markers shown to be differentially regulated in extremes of trait anxiety was glyoxalase1 (GLO1; lactoylglutathione lyase, EC 4.4.1.5).Mouse GLO1 is an enzyme of 21kDa, containing 184 amino acids that is found as a dimer in the cytosol of cells. Its physiological function is the catalytic conversion of Abbreviations used: AGE, advanced glycation end; ARMS, amplification refractory mutation system; CNV, copy number variant; enpp5, ectonucleotide pyrophosphatase/phosphodiesterase 5; EPM, elevatedplus-maze; GC-MS, gas chromatography-mass spectrometry; GLO1, glyoxalase1; HAB, high anxiety-related behavior; i.c.v., intracerebroventricular; LAB, low anxiety-related behavior; LTP, long-term potentiation; MG, methylglyoxal; NAB, normal anxiety-related behavior; TST, tail suspension test; WB, western blotting. AbstractMethylglyoxal (MG) is a highly reactive metabolite that forms adducts with basic amino acid side chains in proteins. MG is degraded by glyoxalase1 (GLO1), an enzyme shown to be differentially expressed in several mouse models of anxietyrelated behavior. As yet, molecular mechanisms by which altered GLO1 expression influences emotionality have not been elucidated. Here we report that both MG concentration and protein modification are altered in brain tissue of a mouse model for trait anxiety, with elevated levels in low anxiety-related behavior relative to high anxiety-related behavior animals. Accordingly, repeated intracerebroventricular injections of MG mediated anxiolysis in inbred high anxiety-related behavior and outbred CD1 mice. We found that anxiolytic-like properties of MG were independent of GLO1 expression. In contrast, antidepressant-like properties of intracerebroventricular MG were suppressed in CD1 mice carrying extra copies of the GLO1 gene. Moreover, MG treatment increased expression of GLO1 only in CD1 mice that did not have extra copies of GLO1. Taken together, these results suggest that the MG levels in brain are negatively correlated with anxiety. Thereby, we identified a novel molecular mec...

Glyoxalase 1 increases anxiety by reducing GABAA receptor agonist methylglyoxal

“…Because supraphysiological levels of MG (100-1,000 μM) induce AGEs, reactive oxygen species, and apoptosis in neurons (21,45,46), these effects have been thought to underlie the role of MG in CNS disorders, including anxiety. For instance, chronic intracerebroventricular administration of MG was reported to reduce anxiety-like behavior, coincident with AGE accumulation (47). In contrast, our data demonstrate that physiological levels of MG have a selective effect on GABA A receptors and elicit behavioral effects within minutes, suggesting a novel role for MG in the CNS that is independent of cytotoxicity.…”

“…This study helps resolve the apparent discrepancy in the literature: it appears that the bidirectionally selected and subsequently inbred lines of Kromer et al (4) differentially fixed the Glo1 CNV. The low anxiety line carried the duplication, while the high anxiety line did not (47). The difference in Glo1 expression is likely offset by numerous other alleles that collectively underlie the response to selection.…”

Intranasally Administered Neuropeptide S (NPS) Exerts Anxiolytic Effects Following Internalization Into NPS Receptor-Expressing Neurons

“…We show here that intranasally applied NPS elicits anxiolytic actions not only in C57BL/6N mice, but also in HAB mice, thus mitigating the phenotypic consequences of the latters' genetic predisposition to high-anxiety-related behavior (Krömer et al, 2005;Hambsch et al, 2010). NPS treatment caused anxiolytic behavior in HAB mice in the dark-light test only, but not in the EPM, like in C57BL/6N mice.…”

“…NPS treatment caused anxiolytic behavior in HAB mice in the dark-light test only, but not in the EPM, like in C57BL/6N mice. These differences possibly result from different neurobiological mechanisms underlying trait vs state anxiety and from the fact that HAB mice are bred for 440 generations for extreme inborn anxiety on the EPM (Krömer et al, 2005;Hambsch et al, 2010), making their behavior particularly resistant against changes in this test.…”

Glycation research in amino acids: a place to call home

“…Involvement in arthritis and cirrhosis (Ahmed et al 2004b(Ahmed et al , 2006, mood affective disordersanxiety and Schizophrenia (Arai et al 2010;Hambsch et al 2010), Parkinson's disease (Kurz et al 2010) and other disease is emerging. In food and nutrition, glycation is increased in culinary processing-particularly during heating and alkaline-treated bakery products (Ahmed et al 2005b;Henle 2001).…”