Targeting methionine metabolism in cancer: opportunities and challenges

Reprogramming of methionine metabolism is a conserved hallmark of tumorigenesis. Recent studies have revealed mechanisms regulating methionine metabolism within the tumor microenvironment (TME) that drive both cancer development and antitumor immunity evasion. In this review article we summarize advancements in our understanding of tumor regulation of methionine metabolism and therapies in development that target tumor methionine metabolism. We also delineate the challenges of methionine blockade therapies in cancer and discuss emerging strategies to address them.

Targeting EMSY-mediated methionine metabolism is a potential therapeutic strategy for triple-negative breast cancer

Cancer stem cells (CSCs) are the most intractable subpopulation of triple-negative breast cancer (TNBC) cells, which have been associated with a high risk of relapse and poor prognosis. However, eradication of CSCs continues to be difficult. Here, we integrate the multiomics data of a TNBC cohort (n = 360) to identify vital markers of CSCs. We discover that EMSY, inducing a BRCAness phenotype, is preferentially expressed in breast CSCs, promotes ALDH+ cells enrichment, and is positively correlated with poor relapse-free survival. Mechanistically, EMSY competitively binds to the Jmjc domain, which is critical for KDM5B enzyme activity, to reshape methionine metabolism, and to promote CSC self-renewal and tumorigenesis in an H3K4 methylation-dependent manner. Moreover, EMSY accumulation in TNBC cells sensitizes them to PARP inhibitors against bulk cells and methionine deprivation against CSCs. These findings indicate that clinically relevant eradication of CSCs could be achieved with a strategy that targets CSC-specific vulnerabilities in amino acid metabolism.

Analysis of clinical significance and molecular characteristics of methionine metabolism and macrophage-related patterns in hepatocellular carcinoma based on machine learning

BACKGROUND

Increasing evidence has indicated that abnormal methionine metabolic activity and tumour-associated macrophage infiltration are correlated with hepatocarcinogenesis. However, the relationship between methionine metabolic activity and tumour-associated macrophage infiltration is unclear in hepatocellular carcinoma, and it contributes to the occurrence and clinical outcome of hepatocellular carcinoma (HCC). Thus, we systematically analysed the expression patterns of methionine metabolism and macrophage infiltration in hepatocellular carcinoma using bioinformatics and machine learning methods and constructed novel diagnostic and prognostic models of HCC.

METHODS

In this study, we first mined the four largest HCC mRNA microarray datasets with patient clinical data in the GEO database, including 880 tissue mRNA expression datasets. Using GSVA analysis and the CIBERSORT and EPIC algorithms, we quantified the methionine metabolic activity and macrophage infiltration degree of each sample. WGCNA was used to identify the gene modules most related to methionine metabolism and tumour-associated macrophage infiltration in HCC. The KNN algorithm was used to cluster gene expression patterns in HCC. Random forest, logistic regression, Cox regression analysis and other algorithms were used to construct the diagnosis and prognosis model of HCC. The above bioinformatics analysis results were also verified by independent datasets (TCGA-LIHC, ICGC-JP and CPTAC datasets) and immunohistochemical fluorescence based on our external HCC panel. Furthermore, we carried out pancancer analysis to verify the specificity of the above model and screened a wide range of drug candidates.

RESULTS

We identified two methionine metabolism and macrophage infiltration expression patterns, and their prognoses were different in hepatocellular carcinoma. We constructed novel diagnostic and prognostic models of hepatocellular carcinoma with good diagnostic efficacy and differentiation ability.

CONCLUSIONS

Methionine metabolism is closely related to tumour-associated macrophage infiltration in hepatocellular carcinoma and can help in the clinical diagnosis and prognosis of HCC.

Pathological role of methionine in the initiation and progression of biliary atresia

Methionine (Met) is an essential amino acid, and its excessive dietary intake and/or its metabolism disturbance could lead to accumulation/depletion of hepatic Met and some of the key intermediates of these pathways, which would interfere normal liver function and would be associated with liver diseases. Biliary atresia (BA) is a life-threatening disease characterized by inflammatory fibrosclerosing changes of the intrahepatic and extrahepatic biliary systems and is the primary cause of obstructive neonatal cholestasis with a rapid course of liver failure. However, its pathogenesis remains unknown. Previous studies reported elevated Met level in patients with obstructive cholestasis, suggesting a potential link between Met and BA. This paper reviews the Met metabolism in normal conditions and its dysregulation under abnormal conditions, the possible causes of hypermethioninemia, and its connection to BA pathogenesis: Abnormal hepatic level of Met could lead to a perturbation of redox homeostasis and mitochondrial functions of hepatocytes, enhancement of viral infectivity, and dysregulation of innate and adaptative immune cells in response to infection/damage of the liver contributing to the initiation/progression of BA.

A novel methionine metabolism-related signature predicts prognosis and immunotherapy response in lung adenocarcinoma

Recent research revealed methionine metabolism as a key mediator of tumor initiation and immune evasion. However, the relationship between methionine metabolism and tumor microenvironment (TME) in lung adenocarcinoma (LUAD) remains unknown. Here, we comprehensively analyzed the genomic alterations, expression patterns, and prognostic values of 68 methionine-related regulators (MRGs) in LUAD. We found that most MRGs were highly prognostic based on 30 datasets including 5024 LUAD patients. Three distinct MRG modification patterns were identified, which showed significant differences in clinical outcomes and TME characteristics: The C2 subtype was characterized by higher immune score, while the C3 subtype had more malignant cells and worse survival. We developed a MethScore to measure the level of methionine metabolism in LUAD. MethScore was positively correlated with T-cell dysfunction and tumor-associated macrophages (TAMs), indicating a dysfunctional TME phenotype in the high MethScore group. In addition, two immunotherapy cohorts confirmed that patients with a lower MethScore exhibited significant clinical benefits. Our study highlights the important role of methionine metabolism in modeling the TME. Evaluating methionine modification patterns will enhance our understanding of TME characteristics and can guide more effective immunotherapy strategies.

NAD+ enhances the activity and thermostability of S-adenosyl-L-homocysteine hydrolase from Pyrococcus horikoshii OT3

S-Adenosyl-L-methionine (SAM) and S-adenosyl-L-homocysteine (SAH) are important biochemical intermediates. SAM is the major methyl donor for diverse methylation reactions in vivo. The SAM to SAH ratio serves as a marker of methylation capacity. Stable isotope-labeled SAM and SAH are used to measure this ratio with high sensitivity. SAH hydrolase (EC 3.13.2.1; SAHH), which reversibly catalyzes the conversion of adenosine and L-homocysteine to SAH, is used to produce labeled SAH. To produce labeled SAH with high efficiency, we focused on the SAHH of Pyrococcus horikoshii OT3, a thermophilic archaeon. We prepared recombinant P. horikoshii SAHH using Escherichia coli and investigated its enzymatic properties. Unexpectedly, the optimum temperature and thermostability of P. horikoshii SAHH were much lower than its optimum growth temperature. However, addition of NAD+ to the reaction mixture shifted the optimum temperature of P. horikoshii SAHH to a higher temperature, suggesting that NAD+ stabilizes the structure of the enzyme.

Oncogenes and Methionine Addiction of Cancer: Role of c-MYC

BACKGROUND/AIM

Methionine addiction is a general and fundamental hallmark of cancer cells, termed the Hoffman effect. Previously Vanhamme and Szpirer showed that methionine addiction could be induced by transfection of the activated HRAS1 gene to a normal cell line. In the present study, we investigated the role of the c-MYC oncogene in methionine addiction of cancer, by comparison of c-Myc expression and malignancy of methionine-addicted osteosarcoma cells and rare methionine-independent revertants, derived from the methionine-addicted cells.

MATERIALS AND METHODS

Methionine-independent revertant 143B osteosarcoma cells (143B-R) were derived from methionine-addicted parental 143B osteosarcoma cells (143B-P), by continuous culture in medium depleted of methionine by recombinant methioninase. To compare in vitro malignancy of methionine-addicted parental cells and methionine-independent revertant cells, the following experiments were performed: for 143B-P and 143B-R cells, cell proliferation capacity was measured with a cell-counting assay, and colony-formation capacity was determined on plastic and in soft agar, all in methionine-containing Dulbecco's Modified Eagle's Medium (DMEM). Tumor growth was measured in orthotopic xenograft nude-mouse models, to compare in vivo malignancy of 143B-P and 143B-R cells. c-MYC expression was examined with western immunoblotting and compared in 143B-P and 143B-R cells.

RESULTS

143B-R cells had reduced cell proliferation capacity, compared to 143B-P cells, in methionine-containing medium (p=0.003). 143B-R cells had reduced colony formation capacity on plastic (p=0.003) and in soft agar, compared to 143B-P cells in methionine-containing medium. 143B-R cells had reduced tumor growth in orthotopic xenograft nude-mouse models, compared to 143B-P cells, (p=0.002). These results demonstrate that 143B-R methionine-independent revertant cells lost malignancy. Expression of c-MYC was reduced in 143B-R methionine-independent revertant osteosarcoma cells, compared to 143B-P cells, (p=0.0007).

CONCLUSION

The present study demonstrated that c-MYC expression is linked to malignancy and methionine addiction of cancer cells. The present study on c-MYC, and the previous study on HRAS1, suggest that oncogenes may play a role in methionine addiction, which is a hallmark of all cancers, as well as in malignancy.

Phosphocholine cytidylyltransferase MoPct1 is crucial for vegetative growth, conidiation, and appressorium-mediated plant infection by Magnaporthe oryzae

Phosphatidylcholine (PC) plays crucial biological roles in eukaryotic cells. In Saccharomyces cerevisiae, apart from phosphatidylethanolamine (PE) methylation pathway, PC is also synthesized via CDP-choline pathway. Phosphocholine cytidylyltransferase Pct1 is the rate-limiting enzyme to catalyze the conversion from phosphocholine to CDP-choline in this pathway. Here, we report the identification and functional characterization of an ortholog of the budding yeast PCT1 in Magnaporthe oryzae, named MoPCT1. Targeted gene deletion mutants of MoPCT1 were impaired in vegetative growth, conidiation, appressorium turgor accumulation and cell wall integrity. Also, the mutants were severely compromised in appressorium-mediated penetration, infectious growth and pathogenicity. Western blot analysis revealed that cell autophagy was activated by the deletion of MoPCT1 under nutrient-rich conditions. Moreover, we found several key genes in PE methylation pathway, such as MoCHO2, MoOPI3, and MoPSD2, were significantly up-regulated in the ΔMopct1 mutants, indicating that a pronounced compensation effect exists between the two PC biosynthesis pathways in M. oryzae. Interestingly, in the ΔMopct1 mutants, histone H3 was hypermethylated and expression levels of several methionine cycling-related genes were significantly up-regulated, suggesting that MoPCT1 is involved in histone H3 methylation and methionine metabolism. Taken together, we conclude that the phosphocholine cytidylyltransferase coding gene MoPCT1 plays important roles in vegetative growth, conidiation and appressorium-mediated plant infection by M. oryzae.

Plant homocysteine, a methionine precursor and plant's hallmark of metabolic disorders

Homocysteine (Hcy) is a sulfur-containing non-proteinogenic amino acid, which arises from redox-sensitive methionine metabolism. In plants, Hcy synthesis involves both cystathionine β-lyase and S-adenosylhomocysteine hydrolase activities. Thus, Hcy itself is crucial for de novo methionine synthesis and S-adenosylmethionine recycling, influencing the formation of ethylene, polyamines, and nicotianamine. Research on mammalian cells has shown biotoxicity of this amino acid, as Hcy accumulation triggers oxidative stress and the associated lipid peroxidation process. In addition, the presence of highly reactive groups induces Hcy and Hcy derivatives to modify proteins by changing their structure and function. Currently, Hcy is recognized as a critical, independent hallmark of many degenerative metabolic diseases. Research results indicate that an enhanced Hcy level is also toxic to yeast and bacteria cells. In contrast, in the case of plants the metabolic status of Hcy remains poorly examined and understood. However, the presence of the toxic Hcy metabolites and Hcy over-accumulation during the development of an infectious disease seem to suggest harmful effects of this amino acid also in plant cells. The review highlights potential implications of Hcy metabolism in plant physiological disorders caused by environmental stresses. Moreover, recent research advances emphasize that recognizing the Hcy mode of action in various plant systems facilitates verification of the potential status of Hcy metabolites as bioindicators of metabolism disorders and thus may constitute an element of broadly understood biomonitoring.

Role of miRNAs in regulation of SA-mediated upregulation of genes involved in folate and methionine metabolism in foxtail millet

The effect of exogenous salicylic acid (SA) on folate metabolism and the related gene regulatory mechanisms is still unclear. In this study, the panicle of foxtail millet treated with different SA concentrations showed that 6 mM SA doubled the 5-methyltetrahydrofolate content compared to that of the control. An untargeted metabolomic analysis revealed that 275 metabolites were enriched in amino acid metabolic pathways. Significantly, the relative content of methionine (Met) after 6 mM SA treatment was 3.14 times higher than the control. Transcriptome analysis revealed that differentially expressed genes were mainly enriched in the folate and amino acid biosynthesis pathways (including Met, Cys, Pro, Ser et al.). The miRNA-mRNA interactions related to the folate and Met metabolic pathways were analyzed and several likely structural gene targets for miRNAs were identified, miRNA-seq analysis revealed that 33 and 51 miRNAs targeted 11 and 15 genes related to the folate and Met pathways, respectively. Eight key genes in the folate metabolism pathway were likely to be up-regulated by 14 new miRNAs and 20 new miRNAs up-regulated the 9 key genes in the Met metabolism pathway. The 6 miRNA-mRNA interactions related to the folate and Met metabolism pathways were verified by qRT-PCR, and consistent with the prediction. The results showed that DHFR1 gene expression level related to folate synthesis was directly up-regulated by Nov-m0139-3p with 3.8 times, but DHFR2 was down-regulated by Nov-m0731-5p with 0.62 times. The expression level of CYSC1 and APIP related to Met synthesis were up-regulated by Nov-m0461-5p and Nov-m0664-3p with 4.27 and 1.32 times, respectively. Our results suggested that exogenous SA could induce the folate and Met accumulated in the panicle of foxtail millet. The higher expression level of DHFR1, FTHFD, CYSC1 and APIP in the folate and Met metabolism pathway and their regulators, including Nov-m0139-3p, Nov-m0717-5p, Nov-m0461-5p and Nov-m0664-3p, could be responsible for these metabolites accumulation. This study lays the theoretical foundation for elucidating the post-transcription regulatory mechanisms of folate and Met metabolism.

Methionine metabolism controls the B cell EBV epigenome and viral latency

Epstein-Barr virus (EBV) subverts host epigenetic pathways to switch between viral latency programs, colonize the B cell compartment, and reactivate. Within memory B cells, the reservoir for lifelong infection, EBV genomic DNA and histone methylation marks restrict gene expression. But this epigenetic strategy also enables EBV-infected tumors, including Burkitt lymphomas, to evade immune detection. Little is known about host cell metabolic pathways that support EBV epigenome landscapes. We therefore used amino acid restriction, metabolomic, and CRISPR approaches to identify that an abundant methionine supply and interconnecting methionine and folate cycles maintain Burkitt EBV gene silencing. Methionine restriction, or methionine cycle perturbation, hypomethylated EBV genomes and de-repressed latent membrane protein and lytic gene expression. Methionine metabolism also shaped EBV latency gene regulation required for B cell immortalization. Dietary methionine restriction altered murine Burkitt xenograft metabolomes and de-repressed EBV immunogens in vivo. These results highlight epigenetic/immunometabolism crosstalk supporting the EBV B cell life cycle and suggest therapeutic approaches.

Effects on the Cell Barrier Function of L-Met and DL-HMTBA Is Related to Metabolic Characteristics and m6A Modification

Methionine is a substrate for protein synthesis and participates in many other biological events via its metabolism. We have previously demonstrated significant differences in the metabolism of L-methionine (L-Met) and its precursor DL-2-hydroxy-4-methylthiobutyric acid (DL-HMTBA) in IPEC-J2 cells. When DL–HMTBA is added to the diet, intracellular methionine (Met) sources also contain the natural form of L-Met. Then, what is the effect on Met metabolism when these two Met sources exist simultaneously? Moreover, the effects of metabolic differences on cell function remain unclear. In this study, it was found that when the proportion of L-Met to DL–HMTBA was ≤ 40%:60%, Met transmethylation was promoted and when the proportion of L-Met to DL-HMTBA was ≤ 85%:15%, Met trans-sulfuration and regeneration were improved. In addition, DL-HMTBA improved the cell barrier function when the ratio of L-Met to DL-HMTBA was ≤ 40%:60%. This finding may be due to the decrease in the proportion of S-adenosylmethionine to S-adenosylhomocysteine and mRNA N⁶-methyladenosine (m⁶A) levels, which increase the mRNA stability and protein expression of tight junction zona occludens-1. To sum up, the effects of L-Met and DL–HMTBA on Met metabolism, especially transmethylation, suggest that DL–HMTBA has the potential to influence the intestinal barrier function of animals through epigenetic processes.

A mitochondrial STAT3-methionine metabolism axis promotes ILC2-driven allergic lung inflammation

BACKGROUND

Group 2 innate lymphoid cells (ILC2s), the innate counterpart of T helper 2 cells (Th2), play a critical role in type 2 immune responses. However, the molecular regulatory mechanisms of ILC2s are still unclear.

OBJECTIVE

The aim of this study was to explore the importance of signal transducer and activator of transcription 3 (STAT3) to ILC2 function in allergic lung inflammation.

METHODS

Acute and chronic asthma models were established by intranasal administration of the protease allergen papain in Vav^icreStat3^fl/fl, Il5^tdtomato-creStat3^fl/fl, and Rorc^creStat3^fl/fl mice to verify the necessity of functional STAT3 for ILC2 allergic response. The intrinsic role of STAT3 in regulating ILC2 function was examined by generation of bone marrow chimera mice. The underlying mechanism was studied through confocal imaging, metabolomics analysis, and chromatin immunoprecipitation quantitative PCR.

RESULTS

STAT3 is essential for ILC2 effector function and promotes ILC2-driven allergic inflammation in the lung. Mechanistically, the alarmin cytokine interleukin (IL)-33 induces a non-canonical STAT3 phosphorylation at serine 727 in ILC2s, leading to translocation of STAT3 into the mitochondria. Mitochondrial STAT3 further facilitates adenosine triphosphate synthesis to fuel the methionine cycle and generation of S-adenosylmethionine, which supports the epigenetic reprogramming of type 2 cytokines in ILC2s. STAT3 deficiency, inhibition of STAT3 mitochondrial translocation, or blockade of methionine metabolism markedly dampened the ILC2 allergic response and ameliorated allergic lung inflammation.

CONCLUSION

The mitochondrial STAT3-methionine metabolism pathway is a key regulator that shapes ILC2 effector function through epigenetic regulation, and the related proteins or metabolites represent potential therapeutic targets for allergic lung inflammation.

Combined Analysis of the Effects of Exposure to Blue Light in Ducks Reveals a Reduction in Cholesterol Accumulation Through Changes in Methionine Metabolism and the Intestinal Microbiota

Monochromatic light is widely used in industry, medical treatment, and animal husbandry. Green-blue light has been found to stimulate the proliferation of satellite cells and the results of studies on the effects of blue light on poultry vary widely. It would be worthwhile to study the effect of blue light on poultry growth and how exposure to blue light affects metabolism and the intestinal microbiota. In this study, we irradiated Cherry Valley ducks with 460 nm wavelength light (blue light) for 3 weeks to explore the effects of blue light in comparison to those of white light (combined wavelength light) on animal growth and development. Our results showed that, under exposure to blue light, the body weight and average daily feed intake of ducks were decreased, but the leg muscle and relative length of the intestine were increased. Exposure to blue light chiefly enhanced the anti-inflammatory and antioxidant capacities of the animal and decreased lipid levels in serum and liver. Metabolomic analysis revealed that blue light heightened cysteine and methionine metabolism, and increased serum taurine and primary bile acid levels, as well as up-regulating the metabolites L-carnitine and glutamine. Treatment with blue light significantly increased the beta diversity of intestinal microbiota and the relative abundances of bile acid hydrolase-producing bacteria, especially Alistipes. These changes promote the synthesis of secondary bile acids to further enhance lipid metabolism in the host, thereby reducing cholesterol accumulation in ducks. These results should help us better understand the effects of exposure to blue light on metabolite levels and the intestinal microbiota, and suggest that it may be possible to use colored light to control the development of livestock and poultry.

Adenosine kinase deficiency presenting with tortuous cervical arteries: A risk factor for recurrent stroke

Adenosine kinase (ADK) deficiency is a very rare inborn error of methionine and adenosine metabolism. It is characterized by developmental delay, hypotonia, epilepsy, facial dysmorphism, failure to thrive, transient liver dysfunction with cholestasis, recurrent hypoglycemia, and cardiac defects. Only 26 cases (16 families) of ADK deficiency have been published since its identification in 2011. Vascular abnormalities in cervical arteries and cerebral stroke have never been reported in this condition. Here, we describe two patients with ADK deficiency and vascular tortuosity leading to stroke in one of them. ADK deficiency is a rare inborn error of methionine metabolism with a complex phenotype that might be associated with cerebrovascular abnormalities and stroke.

SRGN-Triggered Aggressive and Immunosuppressive Phenotype in a Subset of TTF-1-Negative Lung Adenocarcinomas

BACKGROUND

About 20% of lung adenocarcinoma (LUAD) is negative for the lineage-specific oncogene Thyroid transcription factor 1 (TTF-1) and exhibits worse clinical outcome with a low frequency of actionable genomic alterations. To identify molecular features associated with TTF-1-negative LUAD, we compared the transcriptomic and proteomic profiles of LUAD cell lines. SRGN, a chondroitin sulfate proteoglycan Serglycin, was identified as a markedly overexpressed gene in TTF-1-negative LUAD. We therefore investigated the roles and regulation of SRGN in TTF-1-negative LUAD.

METHODS

Proteomic and metabolomic analyses of 41 LUAD cell lines were done using mass spectrometry. The function of SRGN was investigated in 3 TTF-1-negative and 4 TTF-1-positive LUAD cell lines and in a syngeneic mouse model (n = 5 to 8 mice per group). Expression of SRGN in was evaluated in 94 and 105 surgically resected LUAD tumor specimens using immunohistochemistry. All statistical tests were two-sided.

RESULTS

SRGN was markedly overexpressed at mRNA and protein levels in TTF-1-negative LUAD cell lines (P < .001 for both mRNA and protein levels). Expression of SRGN in LUAD tumor tissue was associated with poor outcome (hazard ratio = 4.22, 95% confidential interval = 1.12 to 15.86; likelihood ratio test, P = .03), and with higher expression of Programmed cell death 1 ligand 1 (PD-L1) in tumor cells and higher infiltration of Programmed cell death protein 1 (PD-1)-positive lymphocytes. SRGN regulated expression of PD-L1, as well as proinflammatory cytokines including Interleukin-6 (IL-6), Interleukin-8 (IL-8), and C-X-C motif chemokine 1 (CXCL1) in LUAD cell lines, and increased migratory and invasive properties of LUAD cells and fibroblasts, and enhanced angiogenesis. SRGN was induced by DNA de-methylation resulting from Nicotinamide N-methyltransferase (NNMT)-mediated impairment of methionine metabolism.

CONCLUSION

Our findings suggest that SRGN plays a pivotal role in tumor-stromal interaction and reprogramming into an aggressive and immunosuppressive tumor microenvironment in TTF-1-negative LUAD.

SYVN1-MTR4-MAT2A Signaling Axis Regulates Methionine Metabolism in Glioma Cells

Methionine is one of the essential amino acids. How tumor cells adapt and adjust their signal transduction networks to avoid apoptosis in a methionine-restricted environment is worthy of further exploration. In this study, we investigated the molecular mechanism of glioma response to methionine restriction, providing a theoretical basis for new treatment strategies for glioma.

The effect of feeding adequate or deficient vitamin B6 or folic acid to breeders on methionine metabolism in 18-day-old chick embryos

Three isotopic tracers ([2,3,3-²H₃]-L-serine, [²H₁₁]-L-betaine, and [1-¹³C]-L-methionine) were administered by amnion injection into 18-day-old chick embryos to investigate the kinetics of methionine metabolism. The embryos utilized were from eggs collected from 34-week-old Cobb 500 broiler breeders that were fed either a control diet containing folic acid (1.25 mg/kg diet) and pyridoxine HCl (5 mg/kg diet) or diets devoid of supplemental pyridoxine or folic acid. Intermediate metabolites of methionine metabolism and polyamines were analyzed in 18-day-old chick embryos. There were no differences in hepatic [²H₂] methionine or [²H₃] cysteine enrichments or in physiological concentrations of sulfur amino acids for chick embryos from breeders fed the control diet and embryos from breeders fed diets containing no pyridoxine or folic acid. Supplementation of B₆ or folic acid did not affect the production of methionine and cysteine in chick embryos. However, breeders fed the control diet with both folic acid and pyridoxine supplementation produced embryos with a two-fold reduction of hepatic homocysteine and increased spermine compared with embryos from breeders fed diets containing no supplemental pyridoxine or folic acid (P < 0.05). Hepatic S-adenosylmethionine for embryos from breeders fed no supplemental B₆ was half the concentration compared with embryos from breeders fed the control diet. Embryos from breeders fed the control diet were utilized to determine the proportion of homocysteine going through remethylation and transsulfuration and also to determine the pathway of remethylation. Sixty-five percent of the methyl groups used for homocysteine remethylation from control embryos was via the MFMT pathway. Alternatively, 61% of homocysteine from control embryos was remethylated via the MFMT and the BHMT reactions and 39% of homocysteine was catabolized to cysteine via the transsulfuration pathway. These data show that in embryos, intermediate metabolites of methionine and polyamines increase in concentration when pyridoxine levels are provided in deficient concentrations to the breeder hen. In addition, this research demonstrates that folic acid deficient embryos conserve methionine, rather than catabolize it to cysteine.

Ontogeny of hepatic methionine catabolic enzyme activities (Transmethylation and Transsulphuration) and associated physiological amino acids in E10-21 chick embryos and D1-49 broilers

Developmental changes in hepatic methionine adenosyltransferase, cystathionine β-synthase, cystathionase, and glycine N-methyltransferase were determined in broiler chick embryos and hatched chicks by using radiometric and spectrometric methods. Hepatic free methionine, S-adenosylmethionine, S-adenosylhomocysteine, homocysteine, cystathionine, and cysteine levels were also investigated. Results showed an increase in hepatic MAT activity from E10 to E21 during embryogenesis, suggesting greater transmethylation rates throughout the rapid embryonic growth and development period. A strong positive correlation between embryo BW and MAT activity also supports this idea. The MAT specific activity continued to increase after hatching, but there was a negative correlation between chick BW and MAT activities from D1 to D49. This may indicate different MAT isozymes exist for chick embryo hepatic tissue compared to hepatic tissue of hatched chick and growing broilers. The developmental pattern of MAT isozymes could be critical for methionine metabolism to cope with the demand imposed on the embryo, chicks, and growing broilers. Additionally, the specific activity of hepatic CBS in chick embryos was determined to be lower compared to that observed in older broilers (35 and 49 days). Since liver CBS specific activity is at the lowest point from D1-7 in young chicks, the ability to convert adequate homocysteine to cysteine through transsulphuration may be limiting for cysteine synthesis at this time. Steady-state hepatic homocysteine levels in chick embryos and chicks may be a function of the rates of homocysteine formation, remethylation, and catabolism via the transsulphuration pathway. The present study indicates young chicks from D1 to D7 may have a limited ability for adequate transsulphuration; therefore, dietary cystine may be needed for optimum performance.

Betaine restores epigenetic control and supports neuronal mitochondria in the cuprizone mouse model of multiple sclerosis

Methionine metabolism is dysregulated in multiple sclerosis (MS). The methyl donor betaine is depleted in the MS brain where it is linked to changes in levels of histone H3 trimethylated on lysine 4 (H3K4me3) and mitochondrial impairment. We investigated the effects of replacing this depleted betaine in the cuprizone mouse model of MS. Supplementation with betaine restored epigenetic control and alleviated neurological disability in cuprizone mice. Betaine increased the methylation potential (SAM/SAH ratio), levels of H3K4me3, enhanced neuronal respiration, and prevented axonal damage. We show that the methyl donor betaine and the betaine homocysteine methyltransferase (BHMT) enzyme can act in the nucleus to repair epigenetic control and activate neuroprotective transcriptional programmes. ChIP-seq data suggest that BHMT acts on chromatin to increase the SAM/SAH ratio and histone methyltransferase activity locally to increase H3K4me3 and activate gene expression that supports neuronal energetics. These data suggest that the methyl donor betaine may provide neuroprotection in MS where mitochondrial impairment damages axons and causes disability.

One-Carbon Metabolism Regulates Embryonic Stem Cell Fate Through Epigenetic DNA and Histone Modifications: Implications for Transgenerational Metabolic Disorders in Adults

Human (h) and mouse (m) embryonic stem (ES) cells need specific amino acids to proliferate. mES cells require threonine (Thr) metabolism for epigenetic histone modifications. Thr is converted to glycine and acetyl CoA, and the glycine is metabolized specifically to regulate trimethylation of lysine (Lys) residue 4 in histone H3 (H3K4me3). DNA methylation and methylation of other H3 Lys residues remain unimpaired by Thr deprivation in mES cell culture medium. Similarly, hES cells require methionine (Met) to maintain the Met-SAM (S-adenosyl methionine) cycle of 1-carbon metabolism also for H3K4me3 formation. H3K4me3 is needed specifically to regulate and maintain both mES and hES cell proliferation and their pluripotent states. Better understanding of this regulation is essential since treatment of human diseases and disorders will increasingly involve hES cells. Furthermore, since ES cells are derived from their progenitor cells in preimplantation blastocysts, they serve as models of 1-carbon metabolism in these precursors of all mammalian tissues and organs. One-carbon metabolism challenges, such as a maternal low protein diet (LPD) during preimplantation blastocyst development, contribute to development of metabolic syndrome and related abnormalities in adults. These 1-carbon metabolism challenges result in altered epigenetic DNA and histone modifications in ES progenitor cells and the tissues and organs to which they develop. Moreover, the modified histones could have extracellular as well as intracellular effects, since histones are secreted in uterine fluid and influence early embryo development. Hence, the mechanisms and transgenerational implications of these altered epigenetic DNA and histone modifications warrant concerted further study.

Targeted Metabolic Profiling of Methionine Cycle Metabolites and Redox Thiol Pools in Mammalian Plasma, Cells and Urine

The concentration of thiol and thioether metabolites in plasma has diagnostic value in genetic diseases of B-vitamin metabolism linked to methionine utilization. Among these, cysteine/cystine (Cys/CSSC) and glutathione/oxidized glutathione (GSH/GSSG) act as cellular redox buffers. A new LC-MS/MS method was developed for the simultaneous detection of cystathionine (Cysta), methionine (Met), methionine sulfoxide (MSO), creatinine and the reduced and oxidized pairs of homocysteine (Hcy/HSSH), cysteine (Cys/CSSC) and glutathione (GSH/GSSG). A one-step thiol-blocking protocol with minimal sample preparation was established to determine redox thiol pairs in plasma and cells. The concentrations of diagnostic biomarkers Hcy, Met, Cysta, and Cys in a cohort of healthy adults (n = 53) agreed with reference ranges and published values. Metabolite concentrations were also validated in commercial samples of human, mouse, rat and Beagle dog plasma and by the use of a standardized ERNDIM quality control. Analysis of fibroblasts, endothelial and epithelial cells, human embryonic stem cells, and cancer cell lines showed cell specificity for both the speciation and concentration of thiol and thioether metabolites. This LC-MS/MS platform permits the fast and simultaneous quantification of 10 thiol and thioether metabolites and creatinine using 40 µL plasma, urine or culture medium, or 500,000 cells. The sample preparation protocols are directly transferable to automated metabolomic platforms.

Circulating Plasma Metabolomic Profiles Differentiate Rodent Models of Pulmonary Hypertension and Idiopathic Pulmonary Arterial Hypertension Patients

BACKGROUND

Pulmonary arterial hypertension (PAH) is a severe progressive disease with systemic metabolic dysregulation. Monocrotaline (MCT)-induced and hypoxia-induced pulmonary hypertension (PH) rodent models are the most widely used preclinical models, however, whether or not these preclinical models recapitulate metabolomic profiles of PAH patients remain unclear.

METHODS

In this study, a targeted metabolomics panel of 126 small molecule metabolites was conducted. We applied it to the plasma of the 2 preclinical rodent models of PH and 30 idiopathic pulmonary arterial hypertension (IPAH) patients as well as 30 healthy controls to comparatively assess the metabolomic profiles of PAH patients and rodent models.

RESULTS

Significantly different metabolomics profiling and pathways were shown among the 2 classical rodent models and IPAH patients. Pathway analysis demonstrated that methionine metabolism and urea cycle metabolism were the most significant pathway involved in the pathogenesis of hypoxia-induced PH model and MCT-induced model, respectively, and both of them were also observed in the dysregulated pathways in IPAH patients.

CONCLUSIONS

These 2 models may develop PAH through different metabolomic pathways and each of the 2 classical PH model resembles IPAH patients in certain aspects.

Alterations of Methionine Metabolism as Potential Targets for the Prevention and Therapy of Hepatocellular Carcinoma

Several researchers have analyzed the alterations of the methionine cycle associated with liver disease to clarify the pathogenesis of human hepatocellular carcinoma (HCC) and improve the preventive and the therapeutic approaches to this tumor. Different alterations of the methionine cycle leading to a decrease of S-adenosylmethionine (SAM) occur in hepatitis, liver steatosis, liver cirrhosis, and HCC. The reproduction of these changes in MAT1A-KO mice, prone to develop hepatitis and HCC, demonstrates the pathogenetic role of MAT1A gene under-regulation associated with up-regulation of the MAT2A gene (MAT1A:MAT2A switch), encoding the SAM synthesizing enzymes, methyladenosyltransferase I/III (MATI/III) and methyladenosyltransferase II (MATII), respectively. This leads to a rise of MATII, inhibited by the reaction product, with a consequent decrease of SAM synthesis. Attempts to increase the SAM pool by injecting exogenous SAM have beneficial effects in experimental alcoholic and non-alcoholic steatohepatitis and hepatocarcinogenesis. Mechanisms involved in hepatocarcinogenesis inhibition by SAM include: (1) antioxidative effects due to inhibition of nitric oxide (NO•) production, a rise in reduced glutathione (GSH) synthesis, stabilization of the DNA repair protein Apurinic/Apyrimidinic Endonuclease 1 (APEX1); (2) inhibition of c-myc, H-ras, and K-ras expression, prevention of NF-kB activation, and induction of overexpression of the oncosuppressor PP2A gene; (3) an increase in expression of the ERK inhibitor DUSP1; (4) inhibition of PI3K/AKT expression and down-regulation of C/EBPα and UCA1 gene transcripts; (5) blocking LKB1/AMPK activation; (6) DNA and protein methylation. Different clinical trials have documented curative effects of SAM in alcoholic liver disease. Furthermore, SAM enhances the IFN-α antiviral activity and protects against hepatic ischemia-reperfusion injury during hepatectomy in HCC patients with chronic hepatitis B virus (HBV) infection. However, although SAM prevents experimental tumors, it is not curative against already established experimental and human HCCs. The recent observation that the inhibition of MAT2A and MAT2B expression by miRNAs leads to a rise of endogenous SAM and strong inhibition of cancer cell growth could open new perspectives to the treatment of HCC.

In-Cell Synthesis of Bioorthogonal Alkene Tag S-Allyl-Homocysteine and Its Coupling with Reprogrammed Translation

In this study, we report our initial results on in situ biosynthesis of S-allyl-l-homocysteine (Sahc) by simple metabolic conversion of allyl mercaptan in Escherichia coli, which served as the host organism endowed with a direct sulfhydration pathway. The intracellular synthesis we describe in this study is coupled with the direct incorporation of Sahc into proteins in response to methionine codons. Together with O-acetyl-homoserine, allyl mercaptan was added to the growth medium, followed by uptake and intracellular reaction to give Sahc. Our protocol efficiently combined the in vivo synthesis of Sahc via metabolic engineering with reprogrammed translation, without the need for a major change in the protein biosynthesis machinery. Although the system needs further optimisation to achieve greater intracellular Sahc production for complete protein labelling, we demonstrated its functional versatility for photo-induced thiol-ene coupling and the recently developed phosphonamidate conjugation reaction. Importantly, deprotection of Sahc leads to homocysteine-containing proteins-a potentially useful approach for the selective labelling of thiols with high relevance in various medical settings.

The importance of methionine metabolism

T helper cells import the amino acid methionine to synthesize new proteins and to provide the methyl groups needed for the methylation of RNA and DNA that drives T cell proliferation and differentiation.

MicroRNA-203 impacts on the growth, aggressiveness and prognosis of hepatocellular carcinoma by targeting MAT2A and MAT2B genes

Hepatocellular carcinoma (HCC) is characterized by the down-regulation of the liver-specific methyladenosyltransferase 1A (MAT1A) gene, encoding the S-adenosylmethionine synthesizing isozymes MATI/III, and the up-regulation of the widely expressed methyladenosyltransferase 2A (MAT2A), encoding MATII isozyme, and methyladenosyltransferase 2B (MAT2B), encoding a β-subunit without catalytic action that regulates MATII enzymatic activity. Different observations showed hepatocarcinogenesis inhibition by miR-203. We found that miR-203 expression in HCCs is inversely correlated with HCC proliferation and aggressiveness markers, and with MAT2A and MAT2B levels. MiR-203 transfection in HepG2 and Huh7 liver cancer cells targeted the 3'-UTR of MAT2A and MAT2B, inhibiting MAT2A and MAT2B mRNA levels and MATα2 and MATβ2 protein expression. These molecular events were paralleled by an increase in SAM content and were associated with growth restraint and apoptosis, inhibition of cell migration and invasiveness, and suppression of the expression of CD133 and LIN28B stemness markers. In contrast, MAT2B transfection in the same cell lines led to a rise of both MATβ2 and MATα2 expression, associated with increases in cell growth, migration, invasion and overexpression of stemness markers and p-AKT. Altogether, our results indicate that the miR-203 oncosuppressor activity may at least partially depend on its inhibition of MAT2A and MAT2B and show, for the first time, an oncogenic activity of MAT2B linked to AKT activation.

Antigen receptor control of methionine metabolism in T cells

Immune activated T lymphocytes modulate the activity of key metabolic pathways to support the transcriptional reprograming and reshaping of cell proteomes that permits effector T cell differentiation. The present study uses high resolution mass spectrometry and metabolic labelling to explore how murine T cells control the methionine cycle to produce methyl donors for protein and nucleotide methylations. We show that antigen receptor engagement controls flux through the methionine cycle and RNA and histone methylations. We establish that the main rate limiting step for protein synthesis and the methionine cycle is control of methionine transporter expression. Only T cells that respond to antigen to upregulate and sustain methionine transport are supplied with methyl donors that permit the dynamic nucleotide methylations and epigenetic reprogramming that drives T cell differentiation. These data highlight how the regulation of methionine transport licenses use of methionine for multiple fundamental processes that drive T lymphocyte proliferation and differentiation.

Accumulation of Liver Lipids Induced by Vitamin B6 Deficiency Was Effectively Ameliorated by Choline and, to a Lesser Extent, Betaine

Despite previous studies suggesting that choline and betaine ameliorate lipid accumulation in rat livers, the relative effectiveness of the two nutrients is unclear. We examined the efficacy of dietary supplementation with choline or betaine in ameliorating lipid accumulation induced by vitamin B₆ (B₆) deficiency in the rat liver. Male Wistar rats were fed control, B₆-deficient, choline-supplemented B₆-deficient, betaine-supplemented B₆-deficient, or both choline and betaine-supplemented B₆-deficient diets (all containing 9 g of l-methionine (Met)/kg) for 35 d. Two experiments were performed, i.e., one using 17 mmol/kg diet choline bitartrate, betaine anhydrous, and the combination and another using 8.5 mmol/kg diet. Rats fed a B₆-deficient diet developed lipid accumulation in the liver with a reduction of plasma lipids induced by the disruption of Met metabolism. However, the addition of 17 mmol/kg diet choline or betaine was sufficient to ameliorate the disruptions of lipid and Met metabolism. Additionally, 8.5 mmol/kg diet choline ameliorated liver lipid deposition, while the same amount of betaine had no significant effects on liver or plasma lipid profiles. Supplementation with choline resulted in a higher liver betaine than that found using the same amount of betaine alone, although the overall liver betaine content was reduced in B₆-deficient rats. Our findings indicate that choline is more effective than betaine in ameliorating B₆ deficiency-related disruptions in Met metabolism and liver lipid accumulation by increasing liver betaine levels.

Alteration of S-adenosylhomocysteine levels affects lignin biosynthesis in switchgrass

Methionine (Met) synthesized from aspartate is a fundamental amino acid needed to produce S-adenosylmethionine (SAM) that is an important cofactor for the methylation of monolignols. As a competitive inhibitor of SAM-dependent methylation, the effect of S-adenosylhomocysteine (SAH) on lignin biosynthesis, however, is still largely unknown in plants. Expression levels of Cystathionine γ-synthase (PvCGS) and S-adenosylhomocysteine hydrolase 1 (PvSAHH1) were down-regulated by RNAi technology, respectively, in switchgrass, a dual-purpose forage and biofuel crop. The transgenic switchgrass lines were subjected to studying the impact of SAH on lignin biosynthesis. Our results showed that down-regulation of PvCGS in switchgrass altered the accumulation of aspartate-derived and aromatic amino acids, reduced the content of SAH, enhanced lignin biosynthesis and stunted plant growth. In contrast, down-regulation of PvSAHH1 raised SAH levels in switchgrass, impaired the biosynthesis of both guaiacyl and syringyl lignins and therefore significantly increased saccharification efficiency of cell walls. This work indicates that SAH plays a crucial role in monolignol methylation in switchgrass. Genetic regulation of either PvCGS or PvSAHH1 expression in switchgrass can change intracellular SAH contents and SAM to SAH ratios and therefore affect lignin biosynthesis. Thus, our study suggests that genes involved in Met metabolism are of interest as new valuable targets for cell wall bioengineering in future.

Genome-Scale Metabolic Model of Actinosynnema pretiosum ATCC 31280 and Its Application for Ansamitocin P-3 Production Improvement

Actinosynnema pretiosum ATCC 31280 is the producer of antitumor agent ansamitocin P-3 (AP-3). Understanding of the AP-3 biosynthetic pathway and the whole metabolic network in A. pretiosum is important for the improvement of AP-3 titer. In this study, we reconstructed the first complete Genome-Scale Metabolic Model (GSMM) Aspm1282 for A. pretiosum ATCC 31280 based on the newly sequenced genome, with 87% reactions having definite functional annotation. The model has been validated by effectively predicting growth and the key genes for AP-3 biosynthesis. Then we built condition-specific models for an AP-3 high-yield mutant NXJ-24 by integrating Aspm1282 model with time-course transcriptome data. The changes of flux distribution reflect the metabolic shift from growth-related pathway to secondary metabolism pathway since the second day of cultivation. The AP-3 and methionine metabolisms were both enriched in active flux for the last two days, which uncovered the relationships among cell growth, activation of methionine metabolism, and the biosynthesis of AP-3. Furthermore, we identified four combinatorial gene modifications for overproducing AP-3 by in silico strain design, which improved the theoretical flux of AP-3 biosynthesis from 0.201 to 0.372 mmol/gDW/h. Upregulation of methionine metabolic pathway is a potential strategy to improve the production of AP-3.

Deregulation of methionine metabolism as determinant of progression and prognosis of hepatocellular carcinoma

The under-regulation of liver-specific MAT1A gene codifying for S-adenosylmethionine (SAM) synthesizing isozymes MATI/III, and the up-regulation of widely expressed MAT2A, MATII isozyme occurs in hepatocellular carcinoma (HCC). MATα1:MATα2 switch strongly contributes to the fall in SAM liver content both in rodent and human liver carcinogenesis. SAM administration to carcinogen-treated animals inhibits hepatocarcinogenesis. The opposite occurs in Mat1a-KO mice, in which chronic SAM deficiency is followed by HCC development. This review focuses upon the changes, induced by the MATα1:MATα2 switch, involved in HCC development. In association with MATα1:MATα2 switch there occurs, in HCC, global DNA hypomethylation, decline of DNA repair, genomic instability, and deregulation of different signaling pathways such as overexpression of c-MYC (avian myelocytomatosis viral oncogene homolog), increase of polyamine (PA) synthesis and RAS/ERK (Harvey murine sarcoma virus oncogene homolog/extracellular signal-regulated kinase), IKK/NF-kB (I-k kinase beta/nuclear factor kB), PI3K/AKT, and LKB1/AMPK axes. Furthermore, a decrease in MATα1 expression and SAM level induces HCC cell proliferation and survival. SAM treatment in vivo and enforced MATα1 overexpression or MATα2 inhibition, in cultured HCC cells, prevent these changes. A negative correlation of MATα1:MATα2 and MATI/III:MATII ratios with cell proliferation and genomic instability and a positive correlation with apoptosis and global DNA methylation are present in human HCC. Altogether, these data suggest that the decrease of SAM level and the deregulation of MATs are potential therapeutic targets for HCC.

The Impairment of Methyl Metabolism From luxS Mutation of Streptococcus mutans

The luxS gene is present in a wide range of bacteria and is involved in many cellular processes. LuxS mutation can cause autoinducer(AI)-2 deficiency and methyl metabolism disorder. The objective of this study was to demonstrate that, in addition to AI-2-mediated quorum sensing (QS), methyl metabolism plays an important role in LuxS regulation in Streptococcus mutans. The sahH gene from Pseudomonas aeruginosa was amplified and introduced into the S. mutans luxS-null strain to complement the methyl metabolism disruption in a defective QS phenotype. The intracellular activated methyl cycle (AMC) metabolites [S-adenosylmethionine (SAM), S-adenosylhomocysteine (SAH), homocysteine (HCY), and methionine] were quantified in wild-type S. mutans and its three derivatives to determine the metabolic effects of disrupting the AMC. Biofilm mass and structure, acid tolerance, acid production, exopolysaccharide synthesis of multispecies biofilms and the transcriptional level of related genes were determined. The results indicated that SAH and SAM were relatively higher in S. mutans luxS-null strain and S. mutans luxS null strain with plasmid pIB169 when cultured overnight, and HCY was significantly higher in S. mutans UA159. Consistent with the transcriptional profile, luxS deletion-mediated impairment of biofilm formation and acid tolerance was restored to wild-type levels using transgenic SahH. These results also suggest that methionine methyl metabolism contributes to LuxS regulation in S. mutans to a significant degree.

Salt-Stress Response Mechanisms Using de Novo Transcriptome Sequencing of Salt-Tolerant and Sensitive Corchorus spp. Genotypes

High salinity is a major environmental stressor for crops. To understand the regulatory mechanisms underlying salt tolerance, we conducted a comparative transcriptome analysis between salt-tolerant and salt-sensitive jute (Corchorus spp.) genotypes in leaf and root tissues under salt stress and control conditions. In total, 68,961 unigenes were identified. Additionally, 11,100 unigenes (including 385 transcription factors (TFs)) exhibited significant differential expression in salt-tolerant or salt-sensitive genotypes. Numerous common and unique differentially expressed unigenes (DEGs) between the two genotypes were discovered. Fewer DEGs were observed in salt-tolerant jute genotypes whether in root or leaf tissues. These DEGs were involved in various pathways, such as ABA signaling, amino acid metabolism, etc. Among the enriched pathways, plant hormone signal transduction (ko04075) and cysteine/methionine metabolism (ko00270) were the most notable. Eight common DEGs across both tissues and genotypes with similar expression profiles were part of the PYL-ABA-PP2C (pyrabactin resistant-like/regulatory components of ABA receptors-abscisic acid-protein phosphatase 2C). The methionine metabolism pathway was only enriched in salt-tolerant jute root tissue. Twenty-three DEGs were involved in methionine metabolism. Overall, numerous common and unique salt-stress response DEGs and pathways between salt-tolerant and salt-sensitive jute have been discovered, which will provide valuable information regarding salt-stress response mechanisms and help improve salt-resistance molecular breeding in jute.

Characterization and Interrelations of One-Carbon Metabolites in Tissues, Erythrocytes, and Plasma in Mice with Dietary Induced Folate Deficiency

Studies on one-carbon metabolism for the assessment of folate deficiency have focused on either metabolites of folate metabolism or methionine cycle. To bridge the gap between deficiency markers in these pathways we designed a dietary induced folate deficiency study using male C57BL/6N mice. After weaning (3 weeks) mice were fed a defined control diet (1 week) before being fed a folate deficient diet (n = 6 mice) and the control diet (n = 6 mice) for 12 additional weeks. Thereafter, we determined total homocysteine in plasma and folate in erythrocytes as well as S-adenosylmethionine, S-adenosylhomocysteine, and six folate vitamers in tissues including 5-methyltetrahydrofolate, 5-formyltetrahydrofolate, 5,10-methenyltetrahydrofolate, tetrahydrofolate, 10-formylfolic acid, and folic acid by means of stable isotope dilution assays coupled with liquid chromatography tandem mass spectrometry. In all organs, except heart (mainly 5-mehtyltetrahydrofolate), tetrahydrofolate constitutes the main vitamer. Moreover, in liver tetrahydrofolate was most abundant followed by 5-methyltetrahydrofolate (heart: tetrahydrofolate), 5-formyltetrahydrofolate, and 5,10-methenyltetrahydrofolate. Because of the significant decrease (p < 0.05) of folate status and S-adenosylmethionine/S-adenosylhomocysteine ratio accompanied with increasing S-adenosylhomocysteine (p < 0.05), hepatocytes are most susceptible to folate deficiency. To the best of our knowledge, we herein present the first method for simultaneous quantitation of eight metabolites for both folate and methionine cycle in one tissue sample, tHcy in plasma, and erythrocyte folate to shed light on physiological interrelations of one-carbon metabolism.

Choline and betaine ameliorate liver lipid accumulation induced by vitamin B6 deficiency in rats

We investigated the efficacy of supplementing the diet with choline or betaine in ameliorating lipid accumulation induced by vitamin B₆ (B₆) deficiency in rat liver. Male Wistar rats were fed a control, B₆-deficient, choline-supplemented (2, 4, or 6 g choline bitartrate/kg diet) B₆-deficient diet or betaine-supplemented (1, 2, or 4 g betaine anhydrous/kg diet) B₆-deficient diet for 35 d; all diets contained 9 g L-methionine (Met)/kg diet. Choline or betaine supplementation attenuated liver lipid deposition and restored plasma lipid profiles to control levels. These treatments restored the disruptions in Met metabolism and the phosphatidylcholine (PC)/phosphatidylethanolamine (PE) ratio induced by B₆ deficiency in liver microsomes. These results suggest that choline and betaine ameliorated liver lipid accumulation induced by B₆ deficiency via recovery of Met metabolism and very low-density lipoprotein secretion by restoring the supply of PC derived from PE.

How tissue damage MET metabolism: Regulation of the systemic damage response

Living organisms experience tissue damage from both, the surrounding environment and from inside their bodies. Tissue repair/regeneration is triggered by local tissue injury to restore an injured, or lost, part of the body. Tissue damage results in a series of responses, not only locally but also systemically in distant tissues. In our recent publication, we established a "dual system" that induces spatiotemporal tissue damage simultaneously with gene manipulation in surrounding tissues. With this system, we demonstrated that appropriate regulation of methionine metabolism in the fat body is required for tissue repair in Drosophila wing discs, thus highlighting the importance of systemic damage response (SDR) in tissue repair. This "Extra View" aims to discuss our recent reports that propose methionine metabolism to be an essential part of SDR, together with related topics in several model organisms.

Changes in Methionine Metabolism and Histone H3 Trimethylation Are Linked to Mitochondrial Defects in Multiple Sclerosis

Mitochondrial changes, including decreased expression of electron transport chain subunit genes and impaired energetic, have been reported in multiple sclerosis (MS), but the mechanisms involved in these changes are not clear. To determine whether epigenetic mechanisms are involved, we measured the concentrations of methionine metabolites by liquid chromatography tandem mass spectrometry, histone H3 methylation patterns, and markers of mitochondrial respiration in gray matter from postmortem MS and control cortical samples. We found decreases in respiratory markers as well as decreased concentrations of the methionine metabolites S-adenosylmethionine, betaine, and cystathionine in MS gray matter. We also found expression of the enzyme betaine homocysteine methyltransferase in cortical neurons. This enzyme catalyzes the remethylation of homocysteine to methionine, with betaine as the methyl donor, and has previously been thought to be restricted to liver and kidney in the adult human. Decreases in the concentration of the methyl donor betaine were correlated with decreases in histone H3 trimethylation (H3K4me3) in NeuN+ neuronal nuclei in MS cortex compared with controls. Mechanistic studies demonstrated that H3K4me3 levels and mitochondrial respiration were reduced in SH-SY5Y cells after exposure to the nitric oxide donor sodium nitroprusside, and betaine was able to rescue H3K4me3 levels and respiratory capacity in these cells. Chromatin immunoprecipitation experiments showed that betaine regulates metabolic genes in human SH-SY5Y neuroblastoma cells. These data suggest that changes to methionine metabolism may be mechanistically linked to changes in neuronal energetics in MS cortex.

SIGNIFICANCE STATEMENT

For decades, it has been observed that vitamin B12 deficiency and multiple sclerosis (MS) share certain pathological changes, including conduction disturbances. In the present study, we have found that vitamin B12-dependent methionine metabolism is dysregulated in the MS brain. We found that concentrations of the methyl donor betaine are decreased in MS cortex and are correlated with reduced levels of the histone H3 methyl mark H3K4me3 in neurons. Cell culture and chromatin immunoprecipitation-seq data suggest that these changes may lead to defects in mitochondria and impact neuronal energetics. These data have uncovered a novel pathway linking methionine metabolism with mitochondrial respiration and have important implications for understanding mechanisms involved in neurodegeneration in MS.

Tissue nonautonomous effects of fat body methionine metabolism on imaginal disc repair in Drosophila

Regulatory mechanisms for tissue repair and regeneration within damaged tissue have been extensively studied. However, the systemic regulation of tissue repair remains poorly understood. To elucidate tissue nonautonomous control of repair process, it is essential to induce local damage, independent of genetic manipulations in uninjured parts of the body. Herein, we develop a system in Drosophila for spatiotemporal tissue injury using a temperature-sensitive form of diphtheria toxin A domain driven by the Q system to study factors contributing to imaginal disc repair. Using this technique, we demonstrate that methionine metabolism in the fat body, a counterpart of mammalian liver and adipose tissue, supports the repair processes of wing discs. Local injury to wing discs decreases methionine and S-adenosylmethionine, whereas it increases S-adenosylhomocysteine in the fat body. Fat body-specific genetic manipulation of methionine metabolism results in defective disc repair but does not affect normal wing development. Our data indicate the contribution of tissue interactions to tissue repair in Drosophila, as local damage to wing discs influences fat body metabolism, and proper control of methionine metabolism in the fat body, in turn, affects wing regeneration.

Disruption of Methionine Metabolism in Drosophila melanogaster Impacts Histone Methylation and Results in Loss of Viability

Histone methylation levels, which are determined by the action of both histone demethylases and methyltransferases, impact multiple biological processes by affecting gene expression activity. Methionine metabolism generates the major methyl donor S-adenosylmethionine (SAM) for histone methylation. The functions of methionine metabolic enzymes in regulating biological processes as well as the interaction between the methionine pathway and histone methylation, however, are still not fully understood. Here, we report that reduced levels of some enzymes involved in methionine metabolism and histone demethylases lead to lethality as well as wing development and cell proliferation defects in Drosophila melanogaster. Additionally, disruption of methionine metabolism can directly affect histone methylation levels. Reduction of little imaginal discs (LID) histone demethylase, but not lysine-specific demethylase 2 (KDM2) demethylase, is able to counter the effects on histone methylation due to reduction of SAM synthetase (SAM-S). Taken together, these results reveal an essential role of key enzymes that control methionine metabolism and histone methylation. Additionally, these findings are an indication of a strong connection between metabolism and epigenetics.

Chemical chaperone rescue of mutant human cystathionine beta-synthase

Missense mutations in the cystathionine beta-synthase (CBS) gene, such as I278T, are responsible for CBS deficiency, the most common inherited disorder in sulfur metabolism. Expression of human mutant CBS proteins in Saccharomyces cerevisiae reveals that most disease causing mutations severely inhibit enzyme activity and cannot support growth of yeast on cysteine-free media. Here, we show that the osmolyte chemical chaperones glycerol, trimethylamine-N-oxide, dimethylsulfoxide, proline or sorbitol, when added to yeast media, allows growth on cysteine-free media and causes increased enzyme activity from I278T and three other mutant CBS proteins. Rescuable mutants are ones that are predicted to cause a decrease in solvent accessible surface area. The increase in enzyme activity is associated with stabilization of the tetramer form of the enzyme. This effect is not specific to yeast, as addition of the chaperone glycerol resulted in increased I278T activity when the enzyme is produced either in Escherichia coli or in a coupled in vitro transcription/translation reaction. However, no stimulation of specific activity was observed when chaperones were added directly to purified I278T indicating that the presence of chemical chaperones is required during translation. We also found that by mixing different chaperones we could achieve rescue at significantly lower chaperone concentrations. Taken together, our data show that chemical chaperones present during the initial folding process can facilitate proper folding of several mutant CBS proteins and suggest it may be possible to treat some inborn errors of metabolism with agents that enhance proper protein folding.

Metabolic derangement of methionine and folate metabolism in mice deficient in methionine synthase reductase

Hyperhomocyst(e)inemia is a metabolic derangement that is linked to the distribution of folate pools, which provide one-carbon units for biosynthesis of purines and thymidylate and for remethylation of homocysteine to form methionine. In humans, methionine synthase deficiency results in the accumulation of methyltetrahydrofolate at the expense of folate derivatives required for purine and thymidylate biosynthesis. Complete ablation of methionine synthase activity in mice results in embryonic lethality. Other mouse models for hyperhomocyst(e)inemia have normal or reduced levels of methyltetrahydrofolate and are not embryonic lethal, although they have decreased ratios of AdoMet/AdoHcy and impaired methylation. We have constructed a mouse model with a gene trap insertion in the Mtrr gene specifying methionine synthase reductase, an enzyme essential for the activity of methionine synthase. This model is a hypomorph, with reduced methionine synthase reductase activity, thus avoiding the lethality associated with the absence of methionine synthase activity. Mtrr(gt/gt) mice have increased plasma homocyst(e)ine, decreased plasma methionine, and increased tissue methyltetrahydrofolate. Unexpectedly, Mtrr(gt/gt) mice do not show decreases in the AdoMet/AdoHcy ratio in most tissues. The different metabolite profiles in the various genetic mouse models for hyperhomocyst(e)inemia may be useful in understanding biological effects of elevated homocyst(e)ine.