title: Vitamin B12 insufficiency induces cholesterol biosynthesis by limiting s-adenosylmethionine and modulating the methylation of SREBF1 and LDLR genes.
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.
authors.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.
authors.forename: Antonysunil
authors.initials: A
authors.lastname: Adaikalakoteswari
authors.affiliation: Centre for Diabetes, Blizard Institute, Queen Mary University of London, 4 Newark Street, London, E1 2AT UK ; Metabolic Research Laboratories, Wellcome Trust-MRC Institute of Metabolic Science, Level 4, University of Cambridge, Addenbrooke's Hospital, Box 289, Cambridge, CB2 0QQ UK.
authors.forename: Sarah
authors.initials: S
authors.lastname: Finer
authors.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.
authors.forename: Philip D
authors.initials: PD
authors.lastname: Voyias
authors.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.
authors.forename: Ciara M
authors.initials: CM
authors.lastname: McCarthy
authors.affiliation: Nuffield Department of Obstetrics and Gynaecology University of Oxford Level 3, John Radcliffe Hospital, Oxford, University of Oxford, Oxford, OX3 9DU UK.
authors.forename: Manu
authors.initials: M
authors.lastname: Vatish
authors.affiliation: Warwick Systems Biology, University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL UK.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Moore
authors.affiliation: Centre for Diabetes, Blizard Institute, Queen Mary University of London, 4 Newark Street, London, E1 2AT UK.
authors.forename: Melissa
authors.initials: M
authors.lastname: Smart-Halajko
authors.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.
authors.forename: Nahla
authors.initials: N
authors.lastname: Bawazeer
authors.affiliation: Biochemistry Department, College of Science, King Saud University, Riyadh, 11451 Saudi Arabia.
authors.forename: Nasser M
authors.initials: NM
authors.lastname: Al-Daghri
authors.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.
authors.forename: Philip G
authors.initials: PG
authors.lastname: McTernan
authors.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.
authors.forename: Sudhesh
authors.initials: S
authors.lastname: Kumar
authors.affiliation: Centre for Diabetes, Blizard Institute, Queen Mary University of London, 4 Newark Street, London, E1 2AT UK.
authors.forename: Graham A
authors.initials: GA
authors.lastname: Hitman
authors.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 ; iDEA Centre, George Eliot Hospital, Nuneton, CV10 7DJ UK.
authors.forename: Ponnusamy
authors.initials: P
authors.lastname: Saravanan
authors.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.
authors.forename: Gyanendra
authors.initials: G
authors.lastname: Tripathi
keywords: Adipocyte; Cholesterol; Folic acid; Homocysteine; Methylation; Vitamin B12