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Dysregulated Hepatic Methionine Metabolism Drives Homocysteine Elevation in Diet-Induced Nonalcoholic Fatty Liver Disease.

Pacana T, Cazanave S, Verdianelli A, Patel V, Min HK, Mirshahi F, Quinlivan E, Sanyal AJ - PLoS ONE (2015)

Bottom Line: SAH hydrolase protein levels decreased significantly (p <0.01).The protein levels of protein arginine methytransferase 1 (PRMT1) increased significantly, but its products, monomethylarginine (MMA) and asymmetric dimethylarginine (ADMA), decreased significantly.Although gene expression of the DNA methyltransferase Dnmt3a decreased, the global DNA methylation was unaltered.

View Article: PubMed Central - PubMed

Affiliation: Div. of Gastroenterology, Hepatology and Nutrition, Dept. of Internal Medicine, Virginia Commonwealth University School of Medicine, Richmond, VA, 23298, United States of America.

ABSTRACT
Methionine metabolism plays a central role in methylation reactions, production of glutathione and methylarginines, and modulating homocysteine levels. The mechanisms by which these are affected in NAFLD are not fully understood. The aim is to perform a metabolomic, molecular and epigenetic analyses of hepatic methionine metabolism in diet-induced NAFLD. Female 129S1/SvlmJ;C57Bl/6J mice were fed a chow (n = 6) or high-fat high-cholesterol (HFHC) diet (n = 8) for 52 weeks. Metabolomic study, enzymatic expression and DNA methylation analyses were performed. HFHC diet led to weight gain, marked steatosis and extensive fibrosis. In the methionine cycle, hepatic methionine was depleted (30%, p< 0.01) while s-adenosylmethionine (SAM)/methionine ratio (p< 0.05), s-adenosylhomocysteine (SAH) (35%, p< 0.01) and homocysteine (25%, p< 0.01) were increased significantly. SAH hydrolase protein levels decreased significantly (p <0.01). Serine, a substrate for both homocysteine remethylation and transsulfuration, was depleted (45%, p< 0.01). In the transsulfuration pathway, cystathionine and cysteine trended upward while glutathione decreased significantly (p< 0.05). In the transmethylation pathway, levels of glycine N-methyltransferase (GNMT), the most abundant methyltransferase in the liver, decreased. The phosphatidylcholine (PC)/ phosphatidylethanolamine (PE) ratio increased significantly (p< 0.01), indicative of increased phosphatidylethanolamine methyltransferase (PEMT) activity. The protein levels of protein arginine methytransferase 1 (PRMT1) increased significantly, but its products, monomethylarginine (MMA) and asymmetric dimethylarginine (ADMA), decreased significantly. Circulating ADMA increased and approached significance (p< 0.06). Protein expression of methionine adenosyltransferase 1A, cystathionine β-synthase, γ-glutamylcysteine synthetase, betaine-homocysteine methyltransferase, and methionine synthase remained unchanged. Although gene expression of the DNA methyltransferase Dnmt3a decreased, the global DNA methylation was unaltered. Among individual genes, only HMG-CoA reductase (Hmgcr) was hypermethylated, and no methylation changes were observed in fatty acid synthase (Fasn), nuclear factor of kappa light polypeptide gene enhancer in B-cells 1 (Nfκb1), c-Jun, B-cell lymphoma 2 (Bcl-2) and Caspase 3. NAFLD was associated with hepatic methionine deficiency and homocysteine elevation, resulting mainly from impaired homocysteine remethylation, and aberrancy in methyltransferase reactions. Despite increased PRMT1 expression, hepatic ADMA was depleted while circulating ADMA was increased, suggesting increased export to circulation.

No MeSH data available.


Related in: MedlinePlus

Transsulfuration pathway: depletion of serine limits the ability to replete glutathione in diet-induced NAFLD.(A) HFHC diet for 52 weeks resulted only in modest non-significant increase in cystathionine (CST) and cysteine (Cys) levels in spite of homocysteine accumulation and decrease in glutathione levels. (B) mRNA expression of cystathionine β-synthase (Cbs) and γ-glutamylcysteine synthetase (γ-Gcs) decreased but the protein levels of CBS and GCS did not significantly change. (C) Glutathione (GSH) was depleted (p< 0.05), likely as a result of oxidative stress, while cysteinyl-glycine, a catabolic product of GSH, remained unchanged (C). Data are represented as mean ± SEM.
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pone.0136822.g002: Transsulfuration pathway: depletion of serine limits the ability to replete glutathione in diet-induced NAFLD.(A) HFHC diet for 52 weeks resulted only in modest non-significant increase in cystathionine (CST) and cysteine (Cys) levels in spite of homocysteine accumulation and decrease in glutathione levels. (B) mRNA expression of cystathionine β-synthase (Cbs) and γ-glutamylcysteine synthetase (γ-Gcs) decreased but the protein levels of CBS and GCS did not significantly change. (C) Glutathione (GSH) was depleted (p< 0.05), likely as a result of oxidative stress, while cysteinyl-glycine, a catabolic product of GSH, remained unchanged (C). Data are represented as mean ± SEM.

Mentions: Another mechanism to remove homocysteine is through the transsulfuration pathway by conversion of homocysteine to cystathionine by cystathionine β-synthase. Cystathionine is then converted to cysteine for GSH synthesis via γ-glutamylcysteine synthetase. There was a modest non-significant increase in the levels of cystathionine and cysteine in mice on the HFHC diet (Fig 2A). However, this was not proportional to the increase in homocysteine and the homocysteine:cystathionine and homocysteine:cysteine ratios trended downwards in obese mice with NAFLD. This could be influenced by the depletion of the substrate serine, which is also needed to convert cystathionine from homocysteine, as noted above. Both cystathionine β-synthase and γ-glutamylcysteine synthetase mRNA levels decreased significantly in mice with NAFLD (Fig 2B). The protein levels of these enzymes also trended down but these changes were not significant. There was a significant decrease in the glutathione levels (p< 0.05) (Fig 2C) which is an indication of oxidative stress. The levels of cysteinyl-glycine remained unchanged. The ratio of reduced to oxidized glutathione trended upward, suggesting enhanced formation of glutathione to replete glutathione stores.


Dysregulated Hepatic Methionine Metabolism Drives Homocysteine Elevation in Diet-Induced Nonalcoholic Fatty Liver Disease.

Pacana T, Cazanave S, Verdianelli A, Patel V, Min HK, Mirshahi F, Quinlivan E, Sanyal AJ - PLoS ONE (2015)

Transsulfuration pathway: depletion of serine limits the ability to replete glutathione in diet-induced NAFLD.(A) HFHC diet for 52 weeks resulted only in modest non-significant increase in cystathionine (CST) and cysteine (Cys) levels in spite of homocysteine accumulation and decrease in glutathione levels. (B) mRNA expression of cystathionine β-synthase (Cbs) and γ-glutamylcysteine synthetase (γ-Gcs) decreased but the protein levels of CBS and GCS did not significantly change. (C) Glutathione (GSH) was depleted (p< 0.05), likely as a result of oxidative stress, while cysteinyl-glycine, a catabolic product of GSH, remained unchanged (C). Data are represented as mean ± SEM.
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4556375&req=5

pone.0136822.g002: Transsulfuration pathway: depletion of serine limits the ability to replete glutathione in diet-induced NAFLD.(A) HFHC diet for 52 weeks resulted only in modest non-significant increase in cystathionine (CST) and cysteine (Cys) levels in spite of homocysteine accumulation and decrease in glutathione levels. (B) mRNA expression of cystathionine β-synthase (Cbs) and γ-glutamylcysteine synthetase (γ-Gcs) decreased but the protein levels of CBS and GCS did not significantly change. (C) Glutathione (GSH) was depleted (p< 0.05), likely as a result of oxidative stress, while cysteinyl-glycine, a catabolic product of GSH, remained unchanged (C). Data are represented as mean ± SEM.
Mentions: Another mechanism to remove homocysteine is through the transsulfuration pathway by conversion of homocysteine to cystathionine by cystathionine β-synthase. Cystathionine is then converted to cysteine for GSH synthesis via γ-glutamylcysteine synthetase. There was a modest non-significant increase in the levels of cystathionine and cysteine in mice on the HFHC diet (Fig 2A). However, this was not proportional to the increase in homocysteine and the homocysteine:cystathionine and homocysteine:cysteine ratios trended downwards in obese mice with NAFLD. This could be influenced by the depletion of the substrate serine, which is also needed to convert cystathionine from homocysteine, as noted above. Both cystathionine β-synthase and γ-glutamylcysteine synthetase mRNA levels decreased significantly in mice with NAFLD (Fig 2B). The protein levels of these enzymes also trended down but these changes were not significant. There was a significant decrease in the glutathione levels (p< 0.05) (Fig 2C) which is an indication of oxidative stress. The levels of cysteinyl-glycine remained unchanged. The ratio of reduced to oxidized glutathione trended upward, suggesting enhanced formation of glutathione to replete glutathione stores.

Bottom Line: SAH hydrolase protein levels decreased significantly (p <0.01).The protein levels of protein arginine methytransferase 1 (PRMT1) increased significantly, but its products, monomethylarginine (MMA) and asymmetric dimethylarginine (ADMA), decreased significantly.Although gene expression of the DNA methyltransferase Dnmt3a decreased, the global DNA methylation was unaltered.

View Article: PubMed Central - PubMed

Affiliation: Div. of Gastroenterology, Hepatology and Nutrition, Dept. of Internal Medicine, Virginia Commonwealth University School of Medicine, Richmond, VA, 23298, United States of America.

ABSTRACT
Methionine metabolism plays a central role in methylation reactions, production of glutathione and methylarginines, and modulating homocysteine levels. The mechanisms by which these are affected in NAFLD are not fully understood. The aim is to perform a metabolomic, molecular and epigenetic analyses of hepatic methionine metabolism in diet-induced NAFLD. Female 129S1/SvlmJ;C57Bl/6J mice were fed a chow (n = 6) or high-fat high-cholesterol (HFHC) diet (n = 8) for 52 weeks. Metabolomic study, enzymatic expression and DNA methylation analyses were performed. HFHC diet led to weight gain, marked steatosis and extensive fibrosis. In the methionine cycle, hepatic methionine was depleted (30%, p< 0.01) while s-adenosylmethionine (SAM)/methionine ratio (p< 0.05), s-adenosylhomocysteine (SAH) (35%, p< 0.01) and homocysteine (25%, p< 0.01) were increased significantly. SAH hydrolase protein levels decreased significantly (p <0.01). Serine, a substrate for both homocysteine remethylation and transsulfuration, was depleted (45%, p< 0.01). In the transsulfuration pathway, cystathionine and cysteine trended upward while glutathione decreased significantly (p< 0.05). In the transmethylation pathway, levels of glycine N-methyltransferase (GNMT), the most abundant methyltransferase in the liver, decreased. The phosphatidylcholine (PC)/ phosphatidylethanolamine (PE) ratio increased significantly (p< 0.01), indicative of increased phosphatidylethanolamine methyltransferase (PEMT) activity. The protein levels of protein arginine methytransferase 1 (PRMT1) increased significantly, but its products, monomethylarginine (MMA) and asymmetric dimethylarginine (ADMA), decreased significantly. Circulating ADMA increased and approached significance (p< 0.06). Protein expression of methionine adenosyltransferase 1A, cystathionine β-synthase, γ-glutamylcysteine synthetase, betaine-homocysteine methyltransferase, and methionine synthase remained unchanged. Although gene expression of the DNA methyltransferase Dnmt3a decreased, the global DNA methylation was unaltered. Among individual genes, only HMG-CoA reductase (Hmgcr) was hypermethylated, and no methylation changes were observed in fatty acid synthase (Fasn), nuclear factor of kappa light polypeptide gene enhancer in B-cells 1 (Nfκb1), c-Jun, B-cell lymphoma 2 (Bcl-2) and Caspase 3. NAFLD was associated with hepatic methionine deficiency and homocysteine elevation, resulting mainly from impaired homocysteine remethylation, and aberrancy in methyltransferase reactions. Despite increased PRMT1 expression, hepatic ADMA was depleted while circulating ADMA was increased, suggesting increased export to circulation.

No MeSH data available.


Related in: MedlinePlus