Alpha-synuclein deficiency leads to increased glyoxalase I expression and glycation stress

Glyoxalase Centennial conference: introduction, history of research on the glyoxalase system and future prospects

On 27–29 November 2013, researchers gathered at the University of Warwick, Coventry, U.K., to celebrate the centennial of the discovery of the glyoxalase pathway. The glyoxalase system was discovered and reported in papers by Carl Neuberg and by Henry Drysdale Dakin and Harold Ward Dudley in 1913. All three were leading extraordinary investigators in the pioneering years of biochemistry. Neuberg proposed glyoxalase as the pathway of mainstream glycolysis and Gustav Embden correctly discounted this, later confirmed by Otto Meyerhof. Albert Szent-Györgyi proposed glyoxalase I as the regulator of cell growth and others discounted this. In the meantime, molecular, structural and mechanistic properties of the enzymatic components of the system, glyoxalase I and glyoxalase II, have been characterized. The physiological function of the glyoxalase pathway of enzymatic defence against dicarbonyl glycation, particularly by endogenous methylglyoxal, now seems secure. We are now in an era of investigation of the regulation of the glyoxalase system where a role in aging and disease, physiological stress and drug resistance and development of healthier foods and new pharmaceuticals is emerging. The history of glyoxalase research illustrates the scientific process of hypothesis proposal, testing and rejection or acceptance with further investigation, standing testament to the need for intuition guided by experience and expertise, as well as indefatigable experimentation.

Assay of methylglyoxal and glyoxal and control of peroxidase interference

Methylglyoxal and glyoxal are endogenous α-oxoaldehyde metabolites and substrates of the glyoxalase system. These and related α-oxoaldehydes are often determined in cell, tissue and body fluid samples by derivatization with 1,2-diaminobenzene and similar compounds. Peroxidase activity in physiological tissues is a potential interference in estimation of methylglyoxal and glyoxal as it catalyses the conversion of 1,2-diaminobenzene into trace amounts of these dicarbonyl metabolites. Residual peroxidase activity in deproteinized extracts is found to cause significant interference in methylglyoxal and glyoxal estimations. This interference is blocked by the addition of sodium azide in the derivatizing buffer. Estimates of methylglyoxal concentration thereby obtained are in keeping with those predicted by systems modelling of methylglyoxal glycation kinetics in situ. Blocking sample peroxidase activity is important to avoid overestimation in the measurement of glyoxal and methylglyoxal. A dicarbonyl assay protocol resistant to interferences is described in the present article.

Aging risk factors and Parkinson's disease: contrasting roles of common dietary constituents

Aging is a Parkinson's disease (PD) risk factor. It is suggested here that certain dietary components may either contribute to or ameliorate PD risk. There is evidence, which indicates that excessive carbohydrate (glucose or fructose) catabolism is a cause of mitochondrial dysfunction in PD, one consequence is increased production of methylglyoxal (MG). However, other dietary components (carnosine and certain plant extracts) not only scavenge MG but can also influence some of the biochemical events (signal transduction, stress protein synthesis, glycation, and toxin generation) associated with PD pathology. As double blind, placebo-controlled carnosine supplementation studies have revealed beneficial outcomes in humans, it is suggested that MG scavengers such as carnosine be further explored for their therapeutic potential toward PD.

The glycolytic metabolite methylglyoxal induces changes in vigilance by generating low-amplitude non-REM sleep

Methylglyoxal (MG), an essential by-product of glycolysis, is a highly reactive endogenous α-oxoaldehyde. Although high levels of MG are cytotoxic, physiological doses of MG were shown to reduce anxiety-related behavior through selective activation of γ-aminobutyric acid type A (GABAA) receptors. Because the latter play a major role in sleep induction, this study examined the potential of MG to regulate sleep. Specifically, we assessed how MG influences sleep-wake behavior in CD1 mice that received intracerebroventricular injections of either vehicle or 0.7 µmol MG at onset of darkness. We used electroencephalogram (EEG) and electromyogram (EMG) recordings to monitor changes in vigilance states, sleep architecture and the EEG spectrum, for 24 h after receipt of injections. Administration of MG rapidly induced non-rapid eye movement sleep (NREMS) and, concomitantly, decreased wakefulness and suppressed EEG delta power during NREMS. In addition, MG robustly enhanced the amount and number of episodes of an unclassified state of vigilance in which EMG, as well as EEG delta and theta power, were very low. MG did not affect overall rapid eye movement sleep (REMS) in a given 24-h period, but significantly reduced the power of theta activity during REMS. Our results provide the first evidence that MG can exert sleep-promoting properties by triggering low-amplitude NREMS.

The glyoxalase pathway: the first hundred years... and beyond

The discovery of the enzymatic formation of lactic acid from methylglyoxal dates back to 1913 and was believed to be associated with one enzyme termed ketonaldehydemutase or glyoxalase, the latter designation prevailed. However, in 1951 it was shown that two enzymes were needed and that glutathione was the required catalytic co-factor. The concept of a metabolic pathway defined by two enzymes emerged at this time. Its association to detoxification and anti-glycation defence are its presently accepted roles, since methylglyoxal exerts irreversible effects on protein structure and function, associated with misfolding. This functional defence role has been the rationale behind the possible use of the glyoxalase pathway as a therapeutic target, since its inhibition might lead to an increased methylglyoxal concentration and cellular damage. However, metabolic pathway analysis showed that glyoxalase effects on methylglyoxal concentration are likely to be negligible and several organisms, from mammals to yeast and protozoan parasites, show no phenotype in the absence of one or both glyoxalase enzymes. The aim of the present review is to show the evolution of thought regarding the glyoxalase pathway since its discovery 100 years ago, the current knowledge on the glyoxalase enzymes and their recognized role in the control of glycation processes.

Behavioral characterization of A53T mice reveals early and late stage deficits related to Parkinson's disease

Parkinson's disease (PD) pathology is characterized by the formation of intra-neuronal inclusions called Lewy bodies, which are comprised of alpha-synuclein (α-syn). Duplication, triplication or genetic mutations in α-syn (A53T, A30P and E46K) are linked to autosomal dominant PD; thus implicating its role in the pathogenesis of PD. In both PD patients and mouse models, there is increasing evidence that neuronal dysfunction occurs before the accumulation of protein aggregates (i.e., α-syn) and neurodegeneration. Characterization of the timing and nature of symptomatic dysfunction is important for understanding the impact of α-syn on disease progression. Furthermore, this knowledge is essential for identifying pathways and molecular targets for therapeutic intervention. To this end, we examined various functional and morphological endpoints in the transgenic mouse model expressing the human A53T α-syn variant directed by the mouse prion promoter at specific ages relating to disease progression (2, 6 and 12 months of age). Our findings indicate A53T mice develop fine, sensorimotor, and synaptic deficits before the onset of age-related gross motor and cognitive dysfunction. Results from open field and rotarod tests show A53T mice develop age-dependent changes in locomotor activity and reduced anxiety-like behavior. Additionally, digigait analysis shows these mice develop an abnormal gait by 12 months of age. A53T mice also exhibit spatial memory deficits at 6 and 12 months, as demonstrated by Y-maze performance. In contrast to gross motor and cognitive changes, A53T mice display significant impairments in fine- and sensorimotor tasks such as grooming, nest building and acoustic startle as early as 1-2 months of age. These mice also show significant abnormalities in basal synaptic transmission, paired-pulse facilitation and long-term depression (LTD). Combined, these data indicate the A53T model exhibits early- and late-onset behavioral and synaptic impairments similar to PD patients and may provide useful endpoints for assessing novel therapeutic interventions for PD.

Transcriptome study of differential expression in schizophrenia

Schizophrenia genome-wide association studies (GWAS) have identified common SNPs, rare copy number variants (CNVs) and a large polygenic contribution to illness risk, but biological mechanisms remain unclear. Bioinformatic analyses of significantly associated genetic variants point to a large role for regulatory variants. To identify gene expression abnormalities in schizophrenia, we generated whole-genome gene expression profiles using microarrays on lymphoblastoid cell lines (LCLs) from 413 cases and 446 controls. Regression analysis identified 95 transcripts differentially expressed by affection status at a genome-wide false discovery rate (FDR) of 0.05, while simultaneously controlling for confounding effects. These transcripts represented 89 genes with functions such as neurotransmission, gene regulation, cell cycle progression, differentiation, apoptosis, microRNA (miRNA) processing and immunity. This functional diversity is consistent with schizophrenia's likely significant pathophysiological heterogeneity. The overall enrichment of immune-related genes among those differentially expressed by affection status is consistent with hypothesized immune contributions to schizophrenia risk. The observed differential expression of extended major histocompatibility complex (xMHC) region histones (HIST1H2BD, HIST1H2BC, HIST1H2BH, HIST1H2BG and HIST1H4K) converges with the genetic evidence from GWAS, which find the xMHC to be the most significant susceptibility locus. Among the differentially expressed immune-related genes, B3GNT2 is implicated in autoimmune disorders previously tied to schizophrenia risk (rheumatoid arthritis and Graves' disease), and DICER1 is pivotal in miRNA processing potentially linking to miRNA alterations in schizophrenia (e.g. MIR137, the second strongest GWAS finding). Our analysis provides novel candidate genes for further study to assess their potential contribution to schizophrenia.

The beneficial role of thiamine in Parkinson disease

Parkinson disease (PD) is the second most common form of neurodegeneration among elderly individuals. PD is clinically characterized by tremors, rigidity, slowness of movement, and postural imbalance. In this paper, we review the evidence for an association between PD and thiamine. Interestingly, a significant association has been demonstrated between PD and low levels of serum thiamine, and thiamine supplements appear to have beneficial clinical effects against PD. Multiple studies have evaluated the connection between thiamine and PD pathology, and candidate pathways involve the transcription factor Sp1, p53, Bcl-2, caspase-3, tyrosine hydroxylase, glycogen synthase kinase-3β, vascular endothelial growth factor, advanced glycation end products, nuclear factor kappa B, mitogen-activated protein kinase, and the reduced form of nicotinamide adenine dinucleotide phosphate. Thus, a review of the literature suggests that thiamine plays a role in PD, although further investigation into the effects of thiamine in PD is needed.

Aging-dependent reduction in glyoxalase 1 delays wound healing

Methylglyoxal (MG), the major dicarbonyl substrate of the enzyme glyoxalase 1 (GLO1), is a reactive metabolite formed via glycolytic flux. Decreased GLO1 activity in situ has been shown to result in an accumulation of MG and increased formation of advanced glycation endproducts, both of which can accumulate during physiological aging and at an accelerated rate in diabetes and other chronic degenerative diseases. To determine the physiological consequences which result from elevated MG levels and the role of MG and GLO1 in aging, wound healing in young (≤12 weeks) and old (≥52 weeks) wild-type mice was studied. Old mice were found to have a significantly slower rate of wound healing compared to young mice (74.9 ± 2.2 vs. 55.4 ± 1.5% wound closure at day 6; 26% decrease; p < 0.0001). This was associated with decreases in GLO1 transcription, expression and activity. The importance of GLO1 was confirmed in mice by inhibition of GLO1. Direct application of MG to the wounds of young mice, decreased wound healing by 24% compared to untreated mice, whereas application of BSA modified minimally by MG had no effect. Treatment of either young or old mice with aminoguanidine, a scavenger of free MG, significantly increased wound closure by 16% (66.8 ± 1.6 vs. 77.2 ± 3.1%; p < 0.05) and 64% (40.4 ± 7.9 vs. 66.4 ± 5.2%; p < 0.05), respectively, by day 6. As a result of the aminoguanidine treatment, the overall rate of wound healing in the old mice was restored to the level observed in the young mice. These findings were confirmed in vitro, as MG reduced migration and proliferation of fibroblasts derived from young and old, wild-type mice. The data demonstrate that the balance between MG and age-dependent GLO1 downregulation contributes to delayed wound healing in old mice.

Hypoxia-inducible factor 1-regulated lysyl oxidase is involved in Staphylococcus aureus abscess formation

Hypoxia-inducible factor 1 (HIF-1) is the key transcription factor involved in the adaptation of mammals to hypoxia and plays a crucial role in cancer angiogenesis. Recent evidence suggests a leading role for HIF-1 in various inflammatory and infectious diseases. Here we describe the role of HIF-1 in Staphylococcus aureus infections by investigating the HIF-1-dependent host cell response. For this purpose, transcriptional profiling of HIF-1α-deficient HepG2 and control cells, both infected with Staphylococcus aureus, was performed. Four hours after infection, the expression of 190 genes, 24 of which were regulated via HIF-1, was influenced. LOX (encoding lysyl oxidase) was one of the upregulated genes with a potential impact on the course of S. aureus infection. LOX is an amine oxidase required for biosynthetic cross-linking of extracellular matrix components. LOX was upregulated in vitro in different cell cultures infected with S. aureus and also in vivo, in kidney abscesses of mice intravenously infected with S. aureus and in clinical skin samples from patients with S. aureus infections. Inhibition of LOX by β-aminopropionitrile (BAPN) did not affect the bacterial load in kidneys or blood but significantly influenced abscess morphology and collagenization. Our data provide evidence for a crucial role of HIF-1-regulated LOX in abscess formation.

Alpha-synuclein elicits glucose uptake and utilization in adipocytes through the Gab1/PI3K/Akt transduction pathway

Insulin is the main glucoregulator that promotes the uptake of glucose by tissues and the subsequent utilization of glucose as an energy source. In this paper, we describe a novel glucoregulator, the alpha-synuclein (SNCA) protein, that has previously been linked to Parkinson's disease. Treatment with recombinant SNCA promotes glucose uptake in vitro in preadipocytes and in vivo in the adipose tissues and skeletal muscles of mice through the LPAR2/Gab1/PI3K/Akt pathway; these effects occur independently of the insulin receptor. This function of SNCA represents a new mechanistic insight that creates novel avenues of research with respect to the process of glucose regulation.

Glycation research in amino acids: a place to call home

This is an introduction to a collection of review articles by leading investigators in the field of protein glycation research, see following articles in this issue. With this we launch a section of this journal now established for presentation of research results, reviews and commentaries on protein glycation and related topics. Glycation is the spontaneous, non-enzymatic reaction of protein with saccharides and saccharide derivatives. Although studied in the modern scientific era for over 100 years, its importance in the biology, medicine, food and nutrition, pharmacology and toxicology, and technological processing remains intriguingly undisclosed. In this section of amino acids, research on glycation is a qualifier for publication. Glycation research now has a place to call home.

Transcriptional control of glyoxalase 1 by Nrf2 provides a stress-responsive defence against dicarbonyl glycation

Abnormal cellular accumulation of the dicarbonyl metabolite MG (methylglyoxal) occurs on exposure to high glucose concentrations, inflammation, cell aging and senescence. It is associated with increased MG-adduct content of protein and DNA linked to increased DNA strand breaks and mutagenesis, mitochondrial dysfunction and ROS (reactive oxygen species) formation and cell detachment from the extracellular matrix. MG-mediated damage is countered by glutathione-dependent metabolism by Glo1 (glyoxalase 1). It is not known, however, whether Glo1 has stress-responsive up-regulation to counter periods of high MG concentration or dicarbonyl stress. We identified a functional ARE (antioxidant-response element) in the 5'-untranslated region of exon 1 of the mammalian Glo1 gene. Transcription factor Nrf2 (nuclear factor-erythroid 2 p45 subunit-related factor 2) binds to this ARE, increasing basal and inducible expression of Glo1. Activators of Nrf2 induced increased Glo1 mRNA, protein and activity. Increased expression of Glo1 decreased cellular and extracellular concentrations of MG, MG-derived protein adducts, mutagenesis and cell detachment. Hepatic, brain, heart, kidney and lung Glo1 mRNA and protein were decreased in Nrf2-/- mice, and urinary excretion of MG protein and nucleotide adducts were increased approximately 2-fold. We conclude that dicarbonyl stress is countered by up-regulation of Glo1 in the Nrf2 stress-responsive system, protecting protein and DNA from increased damage and preserving cell function.

Human DJ-1 and its homologs are novel glyoxalases

Human DJ-1 is a genetic cause of early-onset Parkinson's disease (PD), although its biochemical function is unknown. We report here that human DJ-1 and its homologs of the mouse and Caenorhabditis elegans are novel types of glyoxalase, converting glyoxal or methylglyoxal to glycolic or lactic acid, respectively, in the absence of glutathione. Purified DJ-1 proteins exhibit typical Michaelis-Menten kinetics, which were abolished completely in the mutants of essential catalytic residues, consisting of cysteine and glutamic acid. The presence of DJ-1 protected mouse embryonic fibroblast and dopaminergically derived SH-SY5Y cells from treatments of glyoxals. Likewise, C. elegans lacking cDJR-1.1, a DJ-1 homolog expressed primarily in the intestine, protected worms from glyoxal-induced death. Sub-lethal doses of glyoxals caused significant degeneration of the dopaminergic neurons in C. elegans lacking cDJR-1.2, another DJ-1 homolog expressed primarily in the head region, including neurons. Our findings that DJ-1 serves as scavengers for reactive carbonyl species may provide a new insight into the causation of PD.

Energy metabolism, proteotoxic stress and age-related dysfunction - protection by carnosine

This review will discuss the relationship between energy metabolism, protein dysfunction and the causation and modulation of age-related proteotoxicity and disease. It is proposed that excessive glycolysis, rather than aerobic (mitochondrial) activity, could be causal to proteotoxic stress and age-related pathology, due to the generation of endogenous glycating metabolites: the deleterious role of methylglyoxal (MG) is emphasized. It is suggested that TOR inhibition, exercise, fasting and increased mitochondrial activity suppress formation of MG (and other deleterious low molecular weight carbonyl compounds) which could control onset and progression of proteostatic dysfunction. Possible mechanisms by which the endogenous dipeptide, carnosine, which, by way of its putative aldehyde-scavenging activity, may control age-related proteotoxicity, cellular dysfunction and pathology, including cancer, are also considered. Whether carnosine could be regarded as a rapamycin mimic is briefly discussed.