Activity, regulation, copy number and function in the glyoxalase system

Expression analysis of glyoxalase I gene among patients of diabetic retinopathy

Objectives:

To study expression of glyoxalase I in patients of diabetic retinopathy.

Methods:

This cross-sectional comparative study was conducted at Centre for Research in Experimental and Applied Medicine (CREAM), Department of Biochemistry and Molecular Biology, Army Medical College, Rawalpindi in collaboration with Armed Forces Institute of Ophthalmology (AFIO) from January 2015 to November 2015. Sampling technique was non- probability purposive sampling. Total 60 subjects were enrolled in two groups. Group-I comprised 30 patients of diabetic retinopathy and Group-II of 30 normal healthy controls. Clinical and demographic data was collected and fasting venous blood samples (2 ml) were drawn. RNA was extracted and subjected to cDNA synthesis. Expression analysis for glyoxalase I was carried out and relative quantification done by double delta Ct method.

Results:

Mean age of the patients was 61.30 ±7.06 years and mean age of controls was 59.60 ± 6.43 years. There were 17 (56.7%) males and 13 (43.3%) females in Group-I while Group-II comprised 14 (46.7%) males and 16 (53.3%) females. There was down regulation of glyoxalase I among patients of diabetic retinopathy in comparison with controls when relative gene expression was calculated.

Conclusion:

Down regulation of glyoxalase I in patients of diabetic retinopathy suggests it to be a contributory factor in the development of disease.

Concomitant Loss of the Glyoxalase System and Glycolysis Makes the Uncultured Pathogen "Candidatus Liberibacter asiaticus" an Energy Scavenger

Methylglyoxal (MG) is a cytotoxic, nonenzymatic by-product of glycolysis that readily glycates proteins and DNA, resulting in carbonyl stress. Glyoxalase I and II (GloA and GloB) sequentially convert MG into d-lactic acid using glutathione (GSH) as a cofactor. The glyoxalase system is essential for the mitigation of MG-induced carbonyl stress, preventing subsequent cell death, and recycling GSH for maintenance of cellular redox poise. All pathogenic liberibacters identified to date are uncultured, including "Candidatus Liberibacter asiaticus," a psyllid endosymbiont and causal agent of the severely damaging citrus disease "huanglongbing." In silico analysis revealed the absence of gloA in "Ca Liberibacter asiaticus" and all other pathogenic liberibacters. Both gloA and gloB are present in Liberibacter crescens, the only liberibacter that has been cultured. L. crescens GloA was functional in a heterologous host. Marker interruption of gloA in L. crescens appeared to be lethal. Key glycolytic enzymes were either missing or significantly downregulated in "Ca Liberibacter asiaticus" compared to (cultured) L. crescens Marker interruption of sut, a sucrose transporter gene in L. crescens, decreased its ability to take up exogenously supplied sucrose in culture. "Ca Liberibacter asiaticus" lacks a homologous sugar transporter but has a functional ATP/ADP translocase, enabling it to thrive both in psyllids and in the sugar-rich citrus phloem by (i) avoiding sucrose uptake, (ii) avoiding MG generation via glycolysis, and (iii) directly importing ATP from the host cell. MG detoxification enzymes appear to be predictive of "Candidatus" status for many uncultured pathogenic and environmental bacteria.IMPORTANCE Discovered more than 100 years ago, the glyoxalase system is thought to be present across all domains of life and fundamental to cellular growth and viability. The glyoxalase system protects against carbonyl stress caused by methylglyoxal (MG), a highly reactive, mutagenic and cytotoxic compound that is nonenzymatically formed as a by-product of glycolysis. The uncultured alphaproteobacterium "Ca Liberibacter asiaticus" is a well-adapted endosymbiont of the Asian citrus psyllid, which transmits the severely damaging citrus disease "huanglongbing." "Ca Liberibacter asiaticus" lacks a functional glyoxalase pathway. We report here that the bacterium is able to thrive both in psyllids and in the sugar-rich citrus phloem by (i) avoiding sucrose uptake, (ii) avoiding (significant) MG generation via glycolysis, and (iii) directly importing ATP from the host cell. We hypothesize that failure to culture "Ca Liberibacter asiaticus" is at least partly due to its dependence on host cells for both ATP and MG detoxification.

Probing Protein Glycation by Chromatography and Mass Spectrometry: Analysis of Glycation Adducts

Glycation is a non-enzymatic post-translational modification of proteins, formed by the reaction of reducing sugars and α-dicarbonyl products of their degradation with amino and guanidino groups of proteins. Resulted early glycation products are readily involved in further transformation, yielding a heterogeneous group of advanced glycation end products (AGEs). Their formation is associated with ageing, metabolic diseases, and thermal processing of foods. Therefore, individual glycation adducts are often considered as the markers of related pathologies and food quality. In this context, their quantification in biological and food matrices is required for diagnostics and establishment of food preparation technologies. For this, exhaustive protein hydrolysis with subsequent amino acid analysis is the strategy of choice. Thereby, multi-step enzymatic digestion procedures ensure good recoveries for the most of AGEs, whereas tandem mass spectrometry (MS/MS) in the multiple reaction monitoring (MRM) mode with stable isotope dilution or standard addition represents “a gold standard” for their quantification. Although the spectrum of quantitatively assessed AGE structures is continuously increases, application of untargeted profiling techniques for identification of new products is desired, especially for in vivo characterization of anti-glycative systems. Thereby, due to a high glycative potential of plant metabolites, more attention needs to be paid on plant-derived AGEs.

Non-enzymatic N-acetylation of Lysine Residues by AcetylCoA Often Occurs via a Proximal S-acetylated Thiol Intermediate Sensitive to Glyoxalase II

Acetyl coenzyme A (AcCoA), a key intermediate in mitochondrial metabolism, N-acetylates lysine residues, disrupting and, in some cases, regulating protein function. The mitochondrial lysine deacetylase Sirtuin 3 (Sirt3) reverses this modification with benefits reported in diabetes, obesity, and aging. We show that non-enzymatic lysine N-acetylation by AcCoA is greatly enhanced by initial acetylation of a cysteine residue, followed by SN-transfer of the acetyl moiety to a nearby lysine on mitochondrial proteins and synthetic peptides. The frequent occurrence of an S-acetyl intermediate before lysine N-acetylation suggests that proximity to a thioester is a key determinant of lysine susceptibility to acetylation. The thioesterase glyoxalase II (Glo2) can limit protein S-acetylation, thereby preventing subsequent lysine N-acetylation. This suggests that the hitherto obscure role of Glo2 in mitochondria is to act upstream of Sirt3 in minimizing protein N-acetylation, thus limiting protein dysfunction when AcCoA accumulates.

•

AcCoA and acetylglutathione reversibly acetylate protein cysteine residues

•

Non-enzymatic lysine acetylation proceeds via a proximal S-acetylated thiol intermediate

•

Glyoxalase II and glutathione limit lysine N-acetylation and N-succinylation

•

These findings have implications for N-acetylation of lysines in regulation and pathology

Structural insights into GDP-mediated regulation of a bacterial acyl-CoA thioesterase

Thioesterases catalyze the cleavage of thioester bonds within many activated fatty acids and acyl-CoA substrates. They are expressed ubiquitously in both prokaryotes and eukaryotes and are subdivided into 25 thioesterase families according to their catalytic active site, protein oligomerization, and substrate specificity. Although many of these enzyme families are well-characterized in terms of function and substrate specificity, regulation across most thioesterase families is poorly understood. Here, we characterized a TE6 thioesterase from the bacterium Neisseria meningitidis Structural analysis with X-ray crystallographic diffraction data to 2.0-Å revealed that each protein subunit harbors a hot dog-fold and that the TE6 enzyme forms a hexamer with D3 symmetry. An assessment of thioesterase activity against a range of acyl-CoA substrates revealed the greatest activity against acetyl-CoA, and structure-guided mutagenesis of putative active site residues identified Asn²⁴ and Asp³⁹ as being essential for activity. Our structural analysis revealed that six GDP nucleotides bound the enzyme in close proximity to an intersubunit disulfide bond interactions that covalently link thioesterase domains in a double hot dog dimer. Structure-guided mutagenesis of residues within the GDP-binding pocket identified Arg⁹³ as playing a key role in the nucleotide interaction and revealed that GDP is required for activity. All mutations were confirmed to be specific and not to have resulted from structural perturbations by X-ray crystallography. This is the first report of a bacterial GDP-regulated thioesterase and of covalent linkage of thioesterase domains through a disulfide bond, revealing structural similarities with ADP regulation in the human ACOT12 thioesterase.

The anti-inflammatory and anti-glycative effects of rosmarinic acid in the livers of type 1 diabetic mice

Background: Rosmarinic acid (RA) is a polyphenol present in members of the Lamiaceae family. In this study, yhe anti-inflammatory and anti-glycative effects of RA in the livers of type 1 diabetic mice were examined.

Methods: The diabetic mice were divided into three groups: diabetic mice with 0, low dose RA (25 mg/ml), and high dose RA (50 mg/ml). One group of non-diabetic mice was used as a control for comparison. RA was supplied via daily 200 μL oral injections for 9 weeks. The level of interleukin (IL)-6, the tumor necrosis factor (TNF)-alpha, the prostaglandin E₂ (PGE₂), and the activity of cyclooxygenase (COX)-2 in the livers were measured. The hepatic receptor of advanced glycative endproduct (RAGE), the sorbitol levels, and the glyoxalase 1 (GLO-1) activity were also determined.

Results: Compared with diabetic group that received no RA, the groups with RA supplements at both levels of dosages had increased body weight and had both decreased water intake and feed intake (p < 0.05). RA intake was found to reduce plasma glucose level and elevate plasma insulin level when compared with the diabetic group that received no RA (p < 0.05). RA treatments lowered the hepatic level of IL-6, TNF-alpha, and PGE₂, as well as the activity of COX-2 (p < 0.05). RA administration also decreased hepatic RAGE and sorbitol levels, and GLO-1 activity when compared with the diabetic group that received no RA (P < 0.05).

Conclusion: These findings support the conclusion that rosmarinic acid (RA) could be a potent protective agent for the liver against diabetic injury.

Glyoxalase 1 copy number variation in patients with well differentiated gastro-entero-pancreatic neuroendocrine tumours (GEP-NET)

Background

The glyoxalase-1 gene (GLO1) is a hotspot for copy-number variation (CNV) in human genomes. Increased GLO1 copy-number is associated with multidrug resistance in tumour chemotherapy, but prevalence of GLO1 CNV in gastro-entero-pancreatic neuroendocrine tumours (GEP-NET) is unknown.

Methods

GLO1 copy-number variation was measured in 39 patients with GEP-NET (midgut NET, n = 25; pancreatic NET, n = 14) after curative or debulking surgical treatment. Primary tumour tissue, surrounding healthy tissue and, where applicable, additional metastatic tumour tissue were analysed, using real time qPCR. Progression and survival following surgical treatment were monitored over 4.2 ± 0.5 years.

Results

In the pooled GEP-NET cohort, GLO1 copy-number in healthy tissue was 2.0 in all samples but significantly increased in primary tumour tissue in 43% of patients with pancreatic NET and in 72% of patients with midgut NET, mainly driven by significantly higher GLO1 copy-number in midgut NET. In tissue from additional metastases resection (18 midgut NET and one pancreatic NET), GLO1 copy number was also increased, compared with healthy tissue; but was not significantly different compared with primary tumour tissue. During mean 3 - 5 years follow-up, 8 patients died and 16 patients showed radiological progression. In midgut NET, a high GLO1 copy-number was associated with earlier progression. In NETs with increased GLO1 copy number, there was increased Glo1 protein expression compared to non-malignant tissue.

Conclusions

GLO1 copy-number was increased in a large percentage of patients with GEP-NET and correlated positively with increased Glo1 protein in tumour tissue. Analysis of GLO1 copy-number variation particularly in patients with midgut NET could be a novel prognostic marker for tumour progression.

Hormesis enables cells to handle accumulating toxic metabolites during increased energy flux

Energy production is inevitably linked to the generation of toxic metabolites, such as reactive oxygen and carbonyl species, known as major contributors to ageing and degenerative diseases. It remains unclear how cells can adapt to elevated energy flux accompanied by accumulating harmful by-products without taking any damage. Therefore, effects of a sudden rise in glucose concentrations were studied in yeast cells. This revealed a feedback mechanism initiated by the reactive dicarbonyl methylglyoxal, which is formed non-enzymatically during glycolysis. Low levels of methylglyoxal activate a multi-layered defence response against toxic metabolites composed of prevention, detoxification and damage remission. The latter is mediated by the protein quality control system and requires inducible Hsp70 and Btn2, the aggregase that sequesters misfolded proteins. This glycohormetic mechanism enables cells to pre-adapt to rising energy flux and directly links metabolic to proteotoxic stress. Further data suggest the existence of a similar response in endothelial cells.

•

Low-dose MG induces tolerance towards toxic levels of MG and ROS in yeast cells.

•

This preconditioning effect is mediated via a multi-layered defence mechanism.

•

The hormetic defence is composed of prevention, detoxification and damage remission.

•

Low MG induces the PQS including protein sorting and handling via HSPs.

Methylglyoxal-induced dicarbonyl stress in aging and disease: first steps towards glyoxalase 1-based treatments

Dicarbonyl stress is the abnormal accumulation of dicarbonyl metabolites leading to increased protein and DNA modification contributing to cell and tissue dysfunction in aging and disease. It is produced by increased formation and/or decreased metabolism of dicarbonyl metabolites. MG (methylglyoxal) is a dicarbonyl metabolite of relatively high flux of formation and precursor of the most quantitatively and functionally important spontaneous modifications of protein and DNA clinically. Major MG-derived adducts are arginine-derived hydroimidazolones of protein and deoxyguanosine-derived imidazopurinones of DNA. These are formed non-oxidatively. The glyoxalase system provides an efficient and essential basal and stress-response-inducible enzymatic defence against dicarbonyl stress by the reduced glutathione-dependent metabolism of methylglyoxal by glyoxalase 1. The GLO1 gene encoding glyoxalase 1 has low prevalence duplication and high prevalence amplification in some tumours. Dicarbonyl stress contributes to aging, disease and activity of cytotoxic chemotherapeutic agents. It is found at a low, moderate and severe level in obesity, diabetes and renal failure respectively, where it contributes to the development of metabolic and vascular complications. Increased glyoxalase 1 expression confers multidrug resistance to cancer chemotherapy and has relatively high prevalence in liver, lung and breast cancers. Studies of dicarbonyl stress are providing improved understanding of aging and disease and the basis for rational design of novel pharmaceuticals: glyoxalase 1 inducers for obesity, diabetes and cardiovascular disease and glyoxalase 1 inhibitors for multidrug-resistant tumours. The first clinical trial of a glyoxalase 1 inducer in overweight and obese subjects showed improved glycaemic control, insulin resistance and vascular function.

Multiple roles of glyoxalase 1-mediated suppression of methylglyoxal glycation in cancer biology-Involvement in tumour suppression, tumour growth, multidrug resistance and target for chemotherapy

Glyoxalase 1 (Glo1) is part of the glyoxalase system in the cytoplasm of all human cells. It catalyses the glutathione-dependent removal of the endogenous reactive dicarbonyl metabolite, methylglyoxal (MG). MG is formed mainly as a side product of anaerobic glycolysis. It modifies protein and DNA to form mainly hydroimidazolone MG-H1 and imidazopurinone MGdG adducts, respectively. Abnormal accumulation of MG, dicarbonyl stress, increases adduct levels which may induce apoptosis and replication catastrophe. In the non-malignant state, Glo1 is a tumour suppressor protein and small molecule inducers of Glo1 expression may find use in cancer prevention. Increased Glo1 expression is permissive for growth of tumours with high glycolytic activity and is thereby a biomarker of tumour growth. High Glo1 expression is a cause of multi-drug resistance. It is produced by over-activation of the Nrf2 pathway and GLO1 amplification. Glo1 inhibitors are antitumour agents, inducing apoptosis and necrosis, and anoikis. Tumour stem cells and tumours with high flux of MG formation and Glo1 expression are sensitive to Glo1 inhibitor therapy. It is likely that MG-induced cell death contributes to the mechanism of action of current antitumour agents. Common refractory tumours have high prevalence of Glo1 overexpression for which Glo1 inhibitors may improve therapy.

Glyoxalase Goes Green: The Expanding Roles of Glyoxalase in Plants

The ubiquitous glyoxalase enzymatic pathway is involved in the detoxification of methylglyoxal (MG), a cytotoxic byproduct of glycolysis. The glyoxalase system has been more extensively studied in animals versus plants. Plant glyoxalases have been primarily associated with stress responses and their overexpression is known to impart tolerance to various abiotic stresses. In plants, glyoxalases exist as multigene families, and new roles for glyoxalases in various developmental and signaling pathways have started to emerge. Glyoxalase-based MG detoxification has now been shown to be important for pollination responses. During self-incompatibility response in Brassicaceae, MG is required to target compatibility factors for proteasomal degradation, while accumulation of glyoxalase leads to MG detoxification and efficient pollination. In this review, we discuss the importance of glyoxalase systems and their emerging biological roles in plants.

Methylglyoxal-Glyoxalase 1 Balance: The Root of Vascular Damage

The highly reactive dicarbonyl methylglyoxal (MGO) is mainly formed as byproduct of glycolysis. Therefore, high blood glucose levels determine increased MGO accumulation. Nonetheless, MGO levels are also increased as consequence of the ineffective action of its main detoxification pathway, the glyoxalase system, of which glyoxalase 1 (Glo1) is the rate-limiting enzyme. Indeed, a physiological decrease of Glo1 transcription and activity occurs not only in chronic hyperglycaemia but also with ageing, during which MGO accumulation occurs. MGO and its advanced glycated end products (AGEs) are associated with age-related diseases including diabetes, vascular dysfunction and neurodegeneration. Endothelial dysfunction is the first step in the initiation, progression and clinical outcome of vascular complications, such as retinopathy, nephropathy, impaired wound healing and macroangiopathy. Because of these considerations, studies have been centered on understanding the molecular basis of endothelial dysfunction in diabetes, unveiling a central role of MGO-Glo1 imbalance in the onset of vascular complications. This review focuses on the current understanding of MGO accumulation and Glo1 activity in diabetes, and their contribution on the impairment of endothelial function leading to diabetes-associated vascular damage.

Glyoxalase 1-knockdown in human aortic endothelial cells - effect on the proteome and endothelial function estimates

Methylglyoxal (MG), an arginine-directed glycating agent, is implicated in diabetic late complications. MG is detoxified by glyoxalase 1 (GLO1) of the cytosolic glyoxalase system. The aim was to investigate the effects of MG accumulation by GLO1-knockdown under hyperglycaemic conditions in human aortic endothelial cells (HAECs) hypothesizing that the accumulation of MG accounts for the deleterious effects on vascular function. SiRNA-mediated knockdown of GLO1 was performed and MG concentrations were determined. The impact of MG on the cell proteome and targets of MG glycation was analysed, and confirmed by Western blotting. Markers of endothelial function and apoptosis were assessed. Collagen content was assayed in cell culture supernatant. GLO1-knockdown increased MG concentration in cells and culture medium. This was associated with a differential abundance of cytoskeleton stabilisation proteins, intermediate filaments and proteins involved in posttranslational modification of collagen. An increase in fibrillar collagens 1 and 5 was detected. The extracellular concentration of endothelin-1 was increased following GLO1-knockdown, whereas the phosphorylation and amount of eNOS was not influenced by GLO1-knockdown. The expression of ICAM-1, VCAM-1 and of MCP-1 was elevated and apoptosis was increased. MG accumulation by GLO1-knockdown provoked collagen expression, endothelial inflammation and dysfunction and apoptosis which might contribute to vascular damage.

A Caenorhabditis elegans Model Elucidates a Conserved Role for TRPA1-Nrf Signaling in Reactive α-Dicarbonyl Detoxification

Reactive α-dicarbonyls (α-DCs), like methylglyoxal (MGO), accumulate with age and have been implicated in aging and various age-associated pathologies, such as diabetic complications and neurodegenerative disorders like Alzheimer's and Parkinson's diseases. Evolutionarily conserved glyoxalases are responsible for α-DC detoxification; however, their core biochemical regulation has remained unclear. We have established a Caenorhabditis elegans model, based on an impaired glyoxalase (glod-4/GLO1), to broadly study α-DC-related stress. We show that, in comparison to wild-type (N2, Bristol), glod-4 animals rapidly exhibit several pathogenic phenotypes, including hyperesthesia, neuronal damage, reduced motility, and early mortality. We further demonstrate TRPA-1/TRPA1 as a sensor for α-DCs, conserved between worms and mammals. Moreover, TRPA-1 activates SKN-1/Nrf via calcium-modulated kinase signaling, ultimately regulating the glutathione-dependent (GLO1) and co-factor-independent (DJ1) glyoxalases to detoxify α-DCs. Interestingly, this pathway is in stark contrast to the TRPA-1 activation and the ensuing calcium flux implicated in cold sensation in C. elegans, whereby DAF-16/FOXO gets activated via complementary kinase signaling. Finally, a phenotypic drug screen using C. elegans identified podocarpic acid as a novel activator of TRPA1 that rescues α-DC-induced pathologies in C. elegans and mammalian cells. Our work thus identifies TRPA1 as a bona fide drug target for the amelioration of α-DC stress, which represents a viable option to address aging-related pathologies in diabetes and neurodegenerative diseases.

Dicarbonyls and glyoxalase in disease mechanisms and clinical therapeutics

The reactive dicarbonyl metabolite methylglyoxal (MG) is the precursor of the major quantitative advanced glycation endproducts (AGEs) in physiological systems - arginine-derived hydroimidazolones and deoxyguanosine-derived imidazopurinones. The glyoxalase system in the cytoplasm of cells provides the primary defence against dicarbonyl glycation by catalysing the metabolism of MG and related reactive dicarbonyls. Dicarbonyl stress is the abnormal accumulation of dicarbonyl metabolites leading to increased protein and DNA modification contributing to cell and tissue dysfunction in ageing and disease. It is produced endogenously by increased formation and/or decreased metabolism of dicarbonyl metabolites. Dicarbonyl stress contributes to ageing, disease and activity of cytotoxic chemotherapeutic agents. It contributes to ageing through age-related decline in glyoxalase 1 (Glo-1) activity. Glo-1 has a dual role in cancer as a tumour suppressor protein prior to tumour development and mediator of multi-drug resistance in cancer treatment, implicating dicarbonyl glycation of DNA in carcinogenesis and dicarbonyl-driven cytotoxicity in mechanism of action of anticancer drugs. Glo-1 is a driver of cardiovascular disease, likely through dicarbonyl stress-driven dyslipidemia and vascular cell dysfunction. Dicarbonyl stress is also a contributing mediator of obesity and vascular complications of diabetes. There are also emerging roles in neurological disorders. Glo-1 responds to dicarbonyl stress to enhance cytoprotection at the transcriptional level through stress-responsive increase of Glo-1 expression. Small molecule Glo-1 inducers are in clinical development for improved metabolic, vascular and renal health and Glo-1 inhibitors in preclinical development for multidrug resistant cancer chemotherapy.

Dicarbonyl stress in clinical obesity

The glyoxalase system in the cytoplasm of cells provides the primary defence against glycation by methylglyoxal catalysing its metabolism to D-lactate. Methylglyoxal is the precursor of the major quantitative advanced glycation endproducts in physiological systems - arginine-derived hydroimidazolones and deoxyguanosine-derived imidazopurinones. Glyoxalase 1 of the glyoxalase system was linked to anthropometric measurements of obesity in human subjects and to body weight in strains of mice. Recent conference reports described increased weight gain on high fat diet-fed mouse with lifelong deficiency of glyoxalase 1 deficiency, compared to wild-type controls, and decreased weight gain in glyoxalase 1-overexpressing transgenic mice, suggesting a functional role of glyoxalase 1 and dicarbonyl stress in obesity. Increased methylglyoxal, dicarbonyl stress, in white adipose tissue and liver may be a mediator of obesity and insulin resistance and thereby a risk factor for development of type 2 diabetes and non-alcoholic fatty liver disease. Increased methylglyoxal formation from glyceroneogenesis on adipose tissue and liver and decreased glyoxalase 1 activity in obesity likely drives dicarbonyl stress in white adipose tissue increasing the dicarbonyl proteome and related dysfunction. The clinical significance will likely emerge from on-going clinical evaluation of inducers of glyoxalase 1 expression in overweight and obese subjects. Increased transcapillary escape rate of albumin and increased total body interstitial fluid volume in obesity likely makes levels of glycation of plasma protein unreliable indicators of glycation status in obesity as there is a shift of albumin dwell time from plasma to interstitial fluid, which decreases overall glycation for a given glycemic exposure.

Proteomics analysis reveals distinct involvement of embryo and endosperm proteins during seed germination in dormant and non-dormant rice seeds

Seed germination is a complex trait which is influenced by many genetic, endogenous and environmental factors, but the key event(s) associated with seed germination are still poorly understood. In present study, the non-dormant cultivated rice Yannong S and the dormant Dongxiang wild rice seeds were used as experimental materials, we comparatively investigated the water uptake, germination time course, and the differential proteome of the effect of embryo and endosperm on germination of these two types of seeds. A total of 231 and 180 protein spots in embryo and endosperm, respectively, showed a significant change in abundance during germination. We observed that the important proteins associated with seed germination included those involved in metabolism, energy production, protein synthesis and destination, storage protein, cell growth and division, signal transduction, cell defense and rescue. The contribution of embryo and endosperm to seed germination is different. In embryo, the proteins involved in amino acid activation, sucrose cleavage, glycolysis, fermentation and protein synthesis increased; in endosperm, the proteins involved in sucrose cleavage and glycolysis decreased, and those with ATP and CoQ synthesis and proteolysis increased. Our results provide some new knowledge to understand further the mechanism of seed germination.

Methylglyoxal can mediate behavioral and neurochemical alterations in rat brain

Diabetes is associated with loss of cognitive function and increased risk for Alzheimer's disease (AD). Advanced glycation end products (AGEs) are elevated in diabetes and AD and have been suggested to act as mediators of the cognitive decline observed in these pathologies. Methylglyoxal (MG) is an extremely reactive carbonyl compound that propagates glycation reactions and is, therefore, able to generate AGEs. Herein, we evaluated persistent behavioral and biochemical parameters to explore the hypothesis that elevated exogenous MG concentrations, induced by intracerebroventricular (ICV) infusion, lead to cognitive decline in Wistar rats. A high and sustained administration of MG (3μmol/μL; subdivided into 6days) was found to decrease the recognition index of rats, as evaluated by the object-recognition test. However, MG was unable to impair learning-memory processes, as shown by the habituation in the open field (OF) and Y-maze tasks. Moreover, a single high dose of MG induced persistent alterations in anxiety-related behavior, diminishing the anxiety-like parameters evaluated in the OF test. Importantly, MG did not alter locomotion behavior in the different tasks performed. Our biochemical findings support the hypothesis that MG induces persistent alterations in the hippocampus, but not in the cortex, related to glyoxalase 1 activity, AGEs content and glutamate uptake. Glial fibrillary acidic protein and S100B content, as well as S100B secretion (astroglial-related parameters of brain injury), were not altered by ICV MG administration. Taken together, our data suggest that MG interferes directly in brain function and that the time and the levels of exogenous MG determine the different features that can be seen in diabetic patients.

Proteomic Analysis Reveals Different Involvement of Embryo and Endosperm Proteins during Aging of Yliangyou 2 Hybrid Rice Seeds

Seed aging is a process that results in a delayed germination, a decreased germination percentage, and finally a total loss of seed viability. However, the mechanism of seed aging is poorly understood. In the present study, Yliangyou 2 hybrid rice (Oryza sativa L.) seeds were artificially aged at 100% relative humidity and 40°C, and the effect of artificial aging on germination, germination time course and the change in protein profiles of embryo and endosperm was studied to understand the molecular mechanism behind seed aging. With an increasing duration of artificial aging, the germination percentage and germination rate of hybrid rice seeds decreased. By comparing the protein profiles from the seeds aged for 0, 10 and 25 days, a total of 91 and 100 protein spots were found to show a significant change of more than 2-fold (P < 0.05) in abundance, and 71 and 79 protein spots were identified, in embryos and endosperms, respectively. The great majority of these proteins increased in abundance in embryos (95%) and decreased in abundance in endosperms (99%). In embryos, most of the identified proteins were associated with energy (30%), with cell defense and rescue (28%), and with storage protein (18%). In endosperms, most of the identified proteins were involved in metabolism (37%), in energy (27%), and in protein synthesis and destination (11%). The most marked change was the increased abundance of many glycolytic enzymes together with the two fermentation enzymes pyruvate decarboxylase and alcohol dehydrogenase in the embryos during aging. We hypothesize that the decreased viability of hybrid rice seeds during artificial aging is caused by the development of hypoxic conditions in the embryos followed by ethanol accumulation.

Proteome Analysis of Poplar Seed Vigor

Seed vigor is a complex property that determines the seed’s potential for rapid uniform emergence and subsequent growth. However, the mechanism for change in seed vigor is poorly understood. The seeds of poplar (Populus × Canadensis Moench), which are short-lived, were stored at 30°C and 75±5% relative humidity for different periods of time (0–90 days) to obtain different vigor seeds (from 95 to 0% germination). With decreasing seed vigor, the temperature range of seed germination became narrower; the respiration rate of the seeds decreased markedly, while the relative electrolyte leakage increased markedly, both levelling off after 45 days. A total of 81 protein spots showed a significant change in abundance (≥ 1.5-fold, P < 0.05) when comparing the proteomes among seeds with different vigor. Of the identified 65 proteins, most belonged to the groups involved in metabolism (23%), protein synthesis and destination (22%), energy (18%), cell defense and rescue (17%), and storage protein (15%). These proteins accounted for 95% of all the identified proteins. During seed aging, 53 and 6 identified proteins consistently increased and decreased in abundance, respectively, and they were associated with metabolism (22%), protein synthesis and destination (22%), energy (19%), cell defense and rescue (19%), storage proteins (15%), and cell growth and structure (3%). These data show that the decrease in seed vigor (aging) is an energy-dependent process, which requires protein synthesis and degradation as well as cellular defense and rescue.

Penicillium chrysogenum as a model system for studying cellular effects of methylglyoxal

Background

α-oxoaldehydes are formed as toxic by-products during metabolic activity. The biologically most important compound of this class, methylglyoxal, results from spontaneous phosphate elimination from dihydroxyacetone phosphate and glyceraldehyde 3-phosphate which are intermediate glycolysis products. Methylglyoxal-mediated modification of lipids, nucleic acids and proteins is known to lead to the formation of advanced glycation end products. These modifications contribute to the aetiology of severe diseases like diabetes and neurodegenerative disorders. By using simple model organisms it is possible to conveniently study the effects of methylglyoxal on cellular processes. Here, results are presented on the effects of methylglyoxal on mycelium growth, stationary phase entry (monitored by autophagy induction), mitochondrial morphology and protein composition in the filamentous fungus Penicillium chrysogenum.

Results

Methylglyoxal leads to growth rate reduction of this fungus so that the entry into the stationary phase is delayed. Mitochondrial morphology is not changed by methylglyoxal. However, rapamycin-mediated fragmentation of mitochondria is prevented by methylglyoxal. Furthermore, three proteins are identified that are present in lower abundance when methylglyoxal is added to the growth medium (aldo-keto reductase [Pc22g04850], 5-methyl-tetrahydropteroyl-triglutamate-homocysteine S-methyltransferase [Pc22g18630] and NAD-dependent formate dehydrogenase [Pc12g04310]).

Conclusions

The presented results contribute to the understanding of cellular pathways and mechanisms that are affected by the ubiquitous α-oxoaldehyde methylglyoxal.

Advanced glycation end products and schizophrenia: A systematic review

Oxidative stress has become an exciting area of research on schizophrenia, which is a highly prevalent condition that affects approximately 1% of the worldwide population. Advanced glycation end products (AGEs), which are considered metabolic biomarkers of increased oxidative stress, have a pathogenic role in the development and progression of different oxidative stress-based diseases including atherosclerosis, diabetes, neurodegenerative disorders and schizophrenia. AGE formation and accumulation as well as the activation of its receptor (RAGE) can lead to signaling through several inflammatory signaling pathways and further damaging effects. This systematic review is based on a search conducted in July 2014 in which 6 studies were identified that met our criteria. In this work, we describe how recent methodological advances regarding the role of AGEs may contribute to a better understanding of the pathophysiology of schizophrenia and provide a different approach in the comprehension of the relationship between cardiovascular disease and schizophrenia. These latest findings may lead to new directions for future research on novel diagnostic and treatment strategies.

A fluorogenic assay for methylglyoxal

MG (methylglyoxal) is a potent glycating agent and an endogenous reactive dicarbonyl metabolite formed in all live cells and organisms. It is an important precursor of AGEs (advanced glycation end-products) and is implicated in aging and disease. MG is assayed by derivatization by 1,2-diaminobenzene derivatives in cell extracts. Such assays are not applicable to high sample throughput, subcellular, live-cell and in vivo estimations. The use of fluorogenic probes designed for NO (nitric oxide) detection in biological samples and living cells has inadvertently provided probes for the detection of dicarbonyls such as MG. We describe the application of DAF-2 (4,5-diaminofluorescein) and DAR-1 (4,5-diaminorhodamine) for the detection of MG in cell-free systems and application for high-throughput assay of glyoxalase activity and assay of glucose degradation products in peritoneal dialysis fluids. DAF-2 and DAR-1, as for related BODIPY probes, do not have sufficient sensitivity to detect MG in live cells. Care will also be required to control for NO and dehydroascorbate co-detection and interference from peroxidase catalysing the degradation of probes to MG and glyoxal. Fluorogenic detection of MG, however, has great potential to facilitate the assay of MG and to advance towards that capability of imaging this product in live cells in vitro and small animals in vivo.

Measurement of glyoxalase activities

Glyoxalase I catalyses the isomerization of the hemithioacetal formed non-enzymatically from methylglyoxal and glutathione to S-D-lactoylglutathione. The activity of glyoxalase I is conventionally measured spectrophotometrically by following the increase in A240 for which the change in molar absorption coefficient Δε240=2.86 mM⁻¹·cm⁻¹. The hemithioacetal is pre-formed in situ by incubation of methylglyoxal and glutathione in 50 mM sodium phosphate buffer (pH 6.6) at 37°C for 10 min. The cell extract is then added, the A240 is monitored over 5 min, and the initial rate of increase in A240 and hence glyoxalase I activity deduced with correction for blank. Glyoxalase I activity is given in units per mg of protein or cell number where one unit is the amount of enzyme that catalyses the formation of 1 μmol of S-D-lactoylglutathione per min under assay conditions. Glyoxalase II catalyses the hydrolysis of S-D-lactoylglutathione to D-lactate and glutathione. Glyoxalase II activity is also measured spectrophotometrically by following the decrease in A240 for which the change in molar absorption coefficient Δε240=-3.10 mM⁻¹·cm⁻¹. It is given in units per mg of protein or cell number where one unit is the amount of enzyme that catalyses the hydrolysis of 1 μmol of S-D-lactoylglutathione per min under assay conditions. Glyoxalase I and glyoxalase II activity measurements have been modified for use with a UV-transparent microplate for higher sample throughput.

Genetic analysis of the glyoxalase system in schizophrenia

Recent reports suggest that carbonyl stress might affect a subset of schizophrenia patients suffering from severe symptoms. Carbonyl stress protection is achieved by the glyoxalase system consisting of two enzymes, glyoxalase 1 and 2, which in humans are encoded by the genes GLO1 and HAGH, respectively. Glyoxalase 1 and 2 catalyze the detoxification of reactive alpha-oxoaldehydes such as glyoxal and methylglyoxal, which are particularly damaging components of carbonyl stress. Here, we investigated the role of the glyoxalase system in schizophrenia by performing association analyses of common genetic variants (n=12) in GLO1 and HAGH in a Japanese sample consisting of 2012 schizophrenia patients and 2170 healthy controls. We detected a nominally significant association with schizophrenia (p=0.020) of rs11859266, a SNP in the intronic region of HAGH. However, rs11859266 did not survive multiple testing (empirical p=0.091). The variants in HAGH, rs11859266 and rs3743852, showed significant associations with schizophrenia in males at allelic and genotype levels, which remained persistent after multiple testing with the exception of rs3743852 for the genotype model. We further measured the mRNA expression of both genes in postmortem brain, but did not detect any changes in transcript expression levels between case and control samples or in sex-specific comparisons. Therefore, our findings suggest that an explanation of elevated carbonyl stress in a substantial part (reported as ~20%) of patients with schizophrenia will require the examination of a much larger cohort to detect risk alleles with weak effect size and/or other risk factors.

Dicarbonyl stress in cell and tissue dysfunction contributing to ageing and disease

Dicarbonyl stress is the abnormal accumulation of dicarbonyl metabolites leading to increased protein and DNA modification contributing to cell and tissue dysfunction in ageing and disease. Enzymes metabolising dicarbonyls, glyoxalase 1 and aldoketo reductases, provide an efficient and stress-response enzyme defence against dicarbonyl stress. Dicarbonyl stress is produced by increased formation and/or decreased metabolism of dicarbonyl metabolites, and by exposure to exogenous dicarbonyls. It contributes to ageing, disease and activity of cytototoxic chemotherapeutic agents.

Carbonyl stress and schizophrenia

Appropriate biological treatment and psychosocial support are essential to achieve and maintain recovery for patients with schizophrenia. Despite extensive efforts to clarify the underlying disease mechanisms, the main cause and pathophysiology of schizophrenia remain unclear. This is due in large part to disease heterogeneity, which results in biochemical differences within a single disease entity. Other factors include variability across clinical symptoms and disease course, along with varied risk factors and treatment responses. Although schizophrenia's positive symptoms are largely managed through treatment with atypical antipsychotics, new classes of drugs are needed to address the unmet medical need for improving cognitive dysfunction and promoting recovery of negative symptoms in these patients. Accumulation of toxic reactive dicarbonyls, such as methylglyoxal, are typical indicators of carbonyl stress, and result in the modification of proteins and the formation of advanced glycation end products, such as pentosidine. In June 2010, we reported on idiopathic carbonyl stress in a subpopulation of schizophrenia patients, leading to a failure of metabolic systems with plasma pentosidine accumulation and serum pyridoxal depletion. Our findings suggest two markers, pentosidine and pyridoxal, as beneficial for distinguishing a specific subgroup of schizophrenics. We believe that this information, derived from in vitro and in vivo studies, is beneficial in the search for personalized and hopefully more effective treatment regimens in schizophrenia. Here, we define a subtype of schizophrenia based on carbonyl stress and the potential for using carbonyl stress as a biomarker in the challenge of overcoming heterogeneity in schizophrenia treatment.

Differential response to α-oxoaldehydes in tamoxifen resistant MCF-7 breast cancer cells

Tamoxifen is the standard adjuvant endocrine therapy for estrogen-receptor positive premenopausal breast cancer patients. However, tamoxifen resistance is frequently observed under therapy. A tamoxifen resistant cell line has been generated from the estrogen receptor positive mamma carcinoma cell line MCF-7 and was analyzed for putative differences in the aldehyde defence system and accumulation of advanced glycation end products (AGE). In comparison to wt MCF-7 cells, these tamoxifen resistant cells were more sensitive to the dicarbonyl compounds glyoxal and methylglyoxal and displayed increased caspase activity, p38-MAPK- and IκBα-phosphorylation. However, mRNA accumulation of the aldehyde- and AGE-defence enzymes glyoxalase-1 and -2 (GLO1, GLO2) as well as fructosamine-3-kinase (FN3K) was not significantly altered. Tamoxifen resistant cells contained less free sulfhydryl-groups (glutathione) suggesting that the increased sensitivity towards the dicarbonyls was due to a higher sensitivity towards reactive oxygen species which are associated with dicarbonyl stress. To further analyse, if these data are of more general importance, key experiments were replicated with tamoxifen resistant MCF-7 cell lines from two independent sources. These cell lines were also more sensitive to aldehydes, especially glyoxal, but were different in their cellular signalling responses to the aldehydes. In conclusion, glyoxalases and other aldehyde defence enzymes might represent a promising target for the therapy of tamoxifen resistant breast cancers.

Copy number variation of glyoxalase I

The glyoxalase I gene GLO1 is a hotspot for copy number variation in the human and mouse genomes. The additional copies are often functional, giving rise to 2–4-fold increased glyoxalase I expression and activity. The prevalence of GLO1 copy number increase in the human population appears to be approximately 2% and may be linked to a risk of obesity, diabetes and aging. Increased GLO1 copy number has been found in human tumour cell lines and primary human tumours. The minimum common copy number increase region was approximately 1 Mb and it contained GLO1 and seven other genes. The increased copy number was generally functional, being associated with increased glyoxalase I protein and multidrug resistance in cancer chemotherapy. Glo1 duplication in the mouse genome is found within approximately 0.5 Mb of duplicated DNA. It was claimed to be linked to anxiety phenotypes, but other related discordant findings have doubted the association with glyoxalase I and further investigation is required.

Measurement of glyoxalase gene expression

The glyoxalase system is an important component of the enzymatic defence against glycation, preventing particularly quantitatively and functionally important glycation of protein and DNA by methylglyoxal. Expression of genes encoding Glo1 (glyoxalase I) and Glo2 (glyoxalase II) may be induced or suppressed, and rates of proteolysis of Glo1 and Glo2 proteins may change in health and disease. Quantitative assessment of glyoxalase gene expression at the mRNA and protein levels has become a key part of glyoxalase system characterization. For mRNA, there is the common technique of real-time RT (reverse transcription)–PCR and direct quantification of mRNA copy number by the Nanostring™ method. For glyoxalase protein quantification, there is the commonly used Western blotting, and also immunoassay and, in proteome-wide studies, quantitative proteomics and proteome dynamics. We provide protocols for the common methods below and briefly review their application.