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Vitamin B12 insufficiency induces cholesterol biosynthesis by limiting s-adenosylmethionine and modulating the methylation of SREBF1 and LDLR genes.

Adaikalakoteswari A, Finer S, Voyias PD, McCarthy CM, Vatish M, Moore J, Smart-Halajko M, Bawazeer N, Al-Daghri NM, McTernan PG, Kumar S, Hitman GA, Saravanan P, Tripathi G - Clin Epigenetics (2015)

Bottom Line: The induction of cholesterol biosynthesis was associated with reduced s-adenosylmethionine (AdoMet)-to-s-adenosylhomocysteine (AdoHcy) ratio, also known as methylation potential (MP).We therefore studied whether reduced MP could lead to hypomethylation of genes involved in the regulation of cholesterol biosynthesis.This finding was further confirmed by the addition of the methylation inhibitor, 5-aza-2'-deoxycytidine, which resulted in increased SREBF1 and LDLR expressions and cholesterol accumulation in vitamin B12-sufficient conditions.

View Article: PubMed Central - PubMed

Affiliation: Division of Metabolic and Vascular Health, Clinical Sciences Research Laboratories, Warwick Medical School, University Hospital Coventry and Warwickshire, University of Warwick, Clifford Bridge Road, Coventry, CV2 2DX UK.

ABSTRACT

Background: The dietary supply of methyl donors such as folate, vitamin B12, betaine, methionine, and choline is essential for normal growth, development, and physiological functions through the life course. Both human and animal studies have shown that vitamin B12 deficiency is associated with altered lipid profile and play an important role in the prediction of metabolic risk, however, as of yet, no direct mechanism has been investigated to confirm this.

Results: Three independent clinical studies of women (i) non-pregnant at child-bearing age, (ii) in early pregnancy, and (iii) at delivery showed that low vitamin B12 status was associated with higher total cholesterol, LDL cholesterol, and cholesterol-to-HDL ratio. These results guided the investigation into the cellular mechanisms of induced cholesterol biosynthesis due to vitamin B12 deficiency, using human adipocytes as a model system. Adipocytes cultured in low or no vitamin B12 conditions had increased cholesterol and homocysteine levels compared to control. The induction of cholesterol biosynthesis was associated with reduced s-adenosylmethionine (AdoMet)-to-s-adenosylhomocysteine (AdoHcy) ratio, also known as methylation potential (MP). We therefore studied whether reduced MP could lead to hypomethylation of genes involved in the regulation of cholesterol biosynthesis. Genome-wide and targeted DNA methylation analysis identified that the promoter regions of SREBF1 and LDLR, two key regulators of cholesterol biosynthesis, were hypomethylated under vitamin B12-deficient conditions, and as a result, their expressions and cholesterol biosynthesis were also significantly increased. This finding was further confirmed by the addition of the methylation inhibitor, 5-aza-2'-deoxycytidine, which resulted in increased SREBF1 and LDLR expressions and cholesterol accumulation in vitamin B12-sufficient conditions. Finally, we observed that the expression of SREBF1, LDLR, and cholesterol biosynthesis genes were increased in adipose tissue of vitamin B12 deficient mothers compared to control group.

Conclusions: Clinical data suggests that vitamin B12 deficiency is an important metabolic risk factor. Regulation of AdoMet-to-AdoHcy levels by vitamin B12 could be an important mechanism by which it can influence cholesterol biosynthesis pathway in human adipocytes.

No MeSH data available.


Related in: MedlinePlus

Effect of vitamin B12on methylation index. AdoMet and AdoHcy was measured in cell pellets collected from the adipocytes cultured in customised media, control, LB, and NoB. (A) AdoMet, (B) AdoHcy, and (C) AdoMet-to-AdoHcy ratio. Normalized for cell number and expressed as pmol per 1 × 106 cells. All experiments were performed as triplicates. Values are mean ± SEM. *P ≤ 0.05; **P ≤ 0.01, ***P ≤ 0.001, P value compared to control.
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Fig5: Effect of vitamin B12on methylation index. AdoMet and AdoHcy was measured in cell pellets collected from the adipocytes cultured in customised media, control, LB, and NoB. (A) AdoMet, (B) AdoHcy, and (C) AdoMet-to-AdoHcy ratio. Normalized for cell number and expressed as pmol per 1 × 106 cells. All experiments were performed as triplicates. Values are mean ± SEM. *P ≤ 0.05; **P ≤ 0.01, ***P ≤ 0.001, P value compared to control.

Mentions: To test whether vitamin B12 deficiency impairs the cellular methylation potential (AdoMet/AdoHcy), intracellular AdoMet and AdoHcy were determined (Figure 5A,B). AdoMet and AdoHcy are the substrate and product of essential methyltransferase reactions. We found that adipocytes treated in B12 deficient conditions showed significantly decreased AdoMet, increased AdoHcy, and decreased AdoMet/AdoHcy (Figure 5C). A decrease in AdoMet/AdoHcy is predictive of reduced methylation potential (MP) and confirms that DNA methylation is likely to be affected in adipocytes cultured in deficient B12 conditions.Figure 5


Vitamin B12 insufficiency induces cholesterol biosynthesis by limiting s-adenosylmethionine and modulating the methylation of SREBF1 and LDLR genes.

Adaikalakoteswari A, Finer S, Voyias PD, McCarthy CM, Vatish M, Moore J, Smart-Halajko M, Bawazeer N, Al-Daghri NM, McTernan PG, Kumar S, Hitman GA, Saravanan P, Tripathi G - Clin Epigenetics (2015)

Effect of vitamin B12on methylation index. AdoMet and AdoHcy was measured in cell pellets collected from the adipocytes cultured in customised media, control, LB, and NoB. (A) AdoMet, (B) AdoHcy, and (C) AdoMet-to-AdoHcy ratio. Normalized for cell number and expressed as pmol per 1 × 106 cells. All experiments were performed as triplicates. Values are mean ± SEM. *P ≤ 0.05; **P ≤ 0.01, ***P ≤ 0.001, P value compared to control.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4356060&req=5

Fig5: Effect of vitamin B12on methylation index. AdoMet and AdoHcy was measured in cell pellets collected from the adipocytes cultured in customised media, control, LB, and NoB. (A) AdoMet, (B) AdoHcy, and (C) AdoMet-to-AdoHcy ratio. Normalized for cell number and expressed as pmol per 1 × 106 cells. All experiments were performed as triplicates. Values are mean ± SEM. *P ≤ 0.05; **P ≤ 0.01, ***P ≤ 0.001, P value compared to control.
Mentions: To test whether vitamin B12 deficiency impairs the cellular methylation potential (AdoMet/AdoHcy), intracellular AdoMet and AdoHcy were determined (Figure 5A,B). AdoMet and AdoHcy are the substrate and product of essential methyltransferase reactions. We found that adipocytes treated in B12 deficient conditions showed significantly decreased AdoMet, increased AdoHcy, and decreased AdoMet/AdoHcy (Figure 5C). A decrease in AdoMet/AdoHcy is predictive of reduced methylation potential (MP) and confirms that DNA methylation is likely to be affected in adipocytes cultured in deficient B12 conditions.Figure 5

Bottom Line: The induction of cholesterol biosynthesis was associated with reduced s-adenosylmethionine (AdoMet)-to-s-adenosylhomocysteine (AdoHcy) ratio, also known as methylation potential (MP).We therefore studied whether reduced MP could lead to hypomethylation of genes involved in the regulation of cholesterol biosynthesis.This finding was further confirmed by the addition of the methylation inhibitor, 5-aza-2'-deoxycytidine, which resulted in increased SREBF1 and LDLR expressions and cholesterol accumulation in vitamin B12-sufficient conditions.

View Article: PubMed Central - PubMed

Affiliation: Division of Metabolic and Vascular Health, Clinical Sciences Research Laboratories, Warwick Medical School, University Hospital Coventry and Warwickshire, University of Warwick, Clifford Bridge Road, Coventry, CV2 2DX UK.

ABSTRACT

Background: The dietary supply of methyl donors such as folate, vitamin B12, betaine, methionine, and choline is essential for normal growth, development, and physiological functions through the life course. Both human and animal studies have shown that vitamin B12 deficiency is associated with altered lipid profile and play an important role in the prediction of metabolic risk, however, as of yet, no direct mechanism has been investigated to confirm this.

Results: Three independent clinical studies of women (i) non-pregnant at child-bearing age, (ii) in early pregnancy, and (iii) at delivery showed that low vitamin B12 status was associated with higher total cholesterol, LDL cholesterol, and cholesterol-to-HDL ratio. These results guided the investigation into the cellular mechanisms of induced cholesterol biosynthesis due to vitamin B12 deficiency, using human adipocytes as a model system. Adipocytes cultured in low or no vitamin B12 conditions had increased cholesterol and homocysteine levels compared to control. The induction of cholesterol biosynthesis was associated with reduced s-adenosylmethionine (AdoMet)-to-s-adenosylhomocysteine (AdoHcy) ratio, also known as methylation potential (MP). We therefore studied whether reduced MP could lead to hypomethylation of genes involved in the regulation of cholesterol biosynthesis. Genome-wide and targeted DNA methylation analysis identified that the promoter regions of SREBF1 and LDLR, two key regulators of cholesterol biosynthesis, were hypomethylated under vitamin B12-deficient conditions, and as a result, their expressions and cholesterol biosynthesis were also significantly increased. This finding was further confirmed by the addition of the methylation inhibitor, 5-aza-2'-deoxycytidine, which resulted in increased SREBF1 and LDLR expressions and cholesterol accumulation in vitamin B12-sufficient conditions. Finally, we observed that the expression of SREBF1, LDLR, and cholesterol biosynthesis genes were increased in adipose tissue of vitamin B12 deficient mothers compared to control group.

Conclusions: Clinical data suggests that vitamin B12 deficiency is an important metabolic risk factor. Regulation of AdoMet-to-AdoHcy levels by vitamin B12 could be an important mechanism by which it can influence cholesterol biosynthesis pathway in human adipocytes.

No MeSH data available.


Related in: MedlinePlus