title: Molecular and cellular effects of vitamin B12 in brain, myocardium and liver through its role as co-factor of methionine synthase.
abstract: Vitamin B12 (cobalamin, cbl) is a cofactor of methionine synthase (MTR) in the synthesis of methionine, the precursor of the universal methyl donor S-Adenosylmethionine (SAM), which is involved in epigenomic regulatory mechanisms. We have established a neuronal cell model with stable expression of a transcobalamin-oleosin chimer and subsequent decreased cellular availability of vitamin B12, which produces reduced proliferation, increased apoptosis and accelerated differentiation through PP2A, NGF and TACE pathways. Anti-transcobalamin antibody or impaired transcobalamin receptor expression produce also impaired proliferation in other cells. Consistently, the transcription, protein expression and activity of MTR are increased in proliferating cells of skin and intestinal epitheliums, in rat intestine crypts and in proliferating CaCo2 cells, while MTR activity correlates with DNA methylation in rat intestine villi. Exposure to nitrous oxide in animal models identified impairment of MTR reaction as the most important metabolic cause of neurological manifestations of B12 deficiency. Early vitamin B12 and folate deprivation during gestation and lactation of a 'dam-progeny' rat model developed in our laboratory is associated with long-lasting disabilities of behavior and memory capacities, with persisting hallmarks related to increased apoptosis, impaired neurogenesis and altered plasticity. We found also an epigenomic deregulation of energy metabolism and fatty acids beta-oxidation in myocardium and liver, through imbalanced methylation/acetylation of PGC-1alpha and decreased expression of SIRT1. These nutrigenomic effects display similarities with the molecular mechanisms of fetal programming. Beside deficiency, B12 loading increases the expression of MTR through internal ribosome entry sites (IRES) and down-regulates MDR-1 gene expression. In conclusion, vitamin B12 influences cell proliferation, differentiation and apoptosis in brain. Vitamin B12 and folate combined deficiency impairs fatty acid oxidation and energy metabolism in liver and heart through epigenomic mechanisms related to imbalanced acetylation/methylation. Some but not all of these effects reflect the upstream role of vitamin B12 in SAM synthesis.
authors: Inserm U954, Department of Nutrition-Genetics-Environmental Risk Exposure, University of Lorraine and University Hospital of Nancy, Vandoeuvre-lès-Nancy, France. jean-louis.gueant@medecine.uhp-nancy.fr
authors: Jean-Louis
authors: JL
authors: Guéant
authors: Maatem
authors: M
authors: Caillerez-Fofou
authors: Shyuefang
authors: S
authors: Battaglia-Hsu
authors: Jean-Marc
authors: JM
authors: Alberto
authors: Jean-Noel
authors: JN
authors: Freund
authors: Isabelle
authors: I
authors: Dulluc
authors: Charles
authors: C
authors: Adjalla
authors: Florence
authors: F
authors: Maury
authors: Carole
authors: C
authors: Merle
authors: Jean-Pierre
authors: JP
authors: Nicolas
authors: Fares
authors: F
authors: Namour
authors: Jean-Luc
authors: JL
authors: Daval
mesh_terms: D013766:5-Methyltetrahydrofolate-Homocysteine S-Methyltransferase / Q000378:metabolism*; D000818:Animals; D001921:Brain / Q000378:metabolism*; D006801:Humans; D008099:Liver / Q000378:metabolism*; D009206:Myocardium / Q000378:metabolism*; D014805:Vitamin B 12 / Q000378:metabolism*
chemical_list: D013766:5-Methyltetrahydrofolate-Homocysteine S-Methyltransferase; D014805:Vitamin B 12