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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 human adipose tissueex vivo. mRNA expression of genes regulating cholesterol biosynthesis in adipocytes; (A) SREBF1, (B) SREBF2, (C) LDLR, and (D) HMGCR. Each group was a minimum of n = 5. Values are mean ± SEM. *P ≤ 0.05; **P ≤ 0.01, ***P ≤ 0.001, P value compared to control.
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Fig7: Effect of vitamin B12on human adipose tissueex vivo. mRNA expression of genes regulating cholesterol biosynthesis in adipocytes; (A) SREBF1, (B) SREBF2, (C) LDLR, and (D) HMGCR. Each group was a minimum of n = 5. Values are mean ± SEM. *P ≤ 0.05; **P ≤ 0.01, ***P ≤ 0.001, P value compared to control.

Mentions: The prevalence of serum B12 deficiency in this cohort of pregnant women at the time of delivery was 39.6%. Low B12 mothers had significantly higher BMI, cholesterol, LDL cholesterol, triglycerides, and homocysteine than normal B12 mothers (Table 2). To validate the findings from our cultured primary human adipocytes, we further performed the key experiments in maternal subcutaneous adipose tissue (ScAT) chosen from normal B12 (n = 5) and low B12 (n = 5) mothers. We observed that the mRNA expressions of cholesterol regulatory genes; SREBF1, SREBF2 and LDLR (Figure 7A,B,C), and cholesterol biosynthetic gene; and HMGCR (Figure 7D) were upregulated in adipose tissue from low B12 mothers compared to normal B12 mothers (Figure 7).Table 2


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 human adipose tissueex vivo. mRNA expression of genes regulating cholesterol biosynthesis in adipocytes; (A) SREBF1, (B) SREBF2, (C) LDLR, and (D) HMGCR. Each group was a minimum of n = 5. 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

Fig7: Effect of vitamin B12on human adipose tissueex vivo. mRNA expression of genes regulating cholesterol biosynthesis in adipocytes; (A) SREBF1, (B) SREBF2, (C) LDLR, and (D) HMGCR. Each group was a minimum of n = 5. Values are mean ± SEM. *P ≤ 0.05; **P ≤ 0.01, ***P ≤ 0.001, P value compared to control.
Mentions: The prevalence of serum B12 deficiency in this cohort of pregnant women at the time of delivery was 39.6%. Low B12 mothers had significantly higher BMI, cholesterol, LDL cholesterol, triglycerides, and homocysteine than normal B12 mothers (Table 2). To validate the findings from our cultured primary human adipocytes, we further performed the key experiments in maternal subcutaneous adipose tissue (ScAT) chosen from normal B12 (n = 5) and low B12 (n = 5) mothers. We observed that the mRNA expressions of cholesterol regulatory genes; SREBF1, SREBF2 and LDLR (Figure 7A,B,C), and cholesterol biosynthetic gene; and HMGCR (Figure 7D) were upregulated in adipose tissue from low B12 mothers compared to normal B12 mothers (Figure 7).Table 2

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