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

Antonysunil Adaikalakoteswari,Ponnusamy Saravanan,Sudhesh Kumar,Philip G Mcternan,Sarah Finer,Melissa Smart-Halajko,Graham A Hitman,Nahla Bawazeer,Jonathan Moore,Gyanendra Tripathi,Philip D Voyias,Ciara M Mccarthy,Nasser M Al-Daghri,Manu Vatish

doi:10.1186/s13148-015-0046-8

Abstract

BackgroundThe 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.ResultsThree 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.ConclusionsClinical 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.Electronic supplementary materialThe online version of this article (doi:10.1186/s13148-015-0046-8) contains supplementary material, which is available to authorized users.

Highlights

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
The results of the present study provide novel evidence that vitamin B12 plays a vital role in the biosynthesis of cholesterol through induction of SREBPs expression in human adipocytes and DNA hypomethylation due to limited availability of AdoMet
We have demonstrated that low vitamin B12 (a) is associated and independently predicted higher total cholesterol, LDL cholesterol, and cholesterol-to-HDL ratio in serum; (b) induced cholesterol biosynthesis and homocysteine in adipocytes; (c) increased expression of SREBPs and genes responsible for cholesterol biosynthesis; (d) reduced AdoMet-to-AdoHcy levels and caused hypomethylation of SREBF1 and LDL receptor (LDLR) genes in their regulatory regions leading to increased mRNA expression; and (e) increased expression of SREBs, LDLR, and hydroxy3-methylglutaryl-CoA reductase (HMGCR) in human adipose tissue

Summary

Introduction

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, as of yet, no direct mechanism has been investigated to confirm this. Studies in Zucker rats [11] and 3T3F442A cells [12] highlight that with an increase in triglyceride storage, cholesterol is redistributed from the plasma membrane to the surface of the lipid droplet and adipocyte cholesterol levels appear to increase in proportion to the triglyceride content [13]. There is accumulating evidence that adipose cholesterol imbalance is closely associated with adipocyte dysfunction and obesity-mediated metabolic complications and insulin resistance [9,13,14]

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