DYRK1A, a Novel Determinant of the Methionine-Homocysteine Cycle in Different Mouse Models Overexpressing this Down-Syndrome-Associated Kinase

a Novel Determinant of the Methionine-Homocysteine Cycle in Different Mouse Models Overexpressing this Down-Syndrome-Associated Kinase. PLoS ONE 4(10): e7540. doi:10.1371/journal.pone.0007540 DYRK1A, a Novel Determinant of the Methionine- Homocysteine Cycle in Different Mouse Models Overexpressing this Down-Syndrome-Associated Kinase Christophe Noll 0 Chris Planque 0 Cle mentine Ripoll 0 Fayc al Guedj 0 Anna Diez 0 Ve ronique Ducros 0 Nicole Belin 0 Arnaud Duchon 0 Jean-Louis Paul 0 Anne Badel 0 Be ne dicte de Freminville 0 Yann Grattau 0 Henri Ble haut 0 Yann Herault 0 Nathalie Janel 0 Jean-Maurice Delabar 0 Frank Beier, University of Western Ontario, Canada 0 1 University Paris Diderot-CNRS EAC 4413, Unit of Functional and Adaptive Biology (BFA), Paris, France, 2 De partement de Biologie Inte gre e, unite fonctionnelle de nutrition , CHU Grenoble, Grenoble, France, 3 UMR6218 CNRS, Immunology and Molecular Embryology, UPS44 , Institut de Transgenose, Orle ans, France, 4 AP-HP, H opital Europe en Georges Pompidou, Service de Biochimie, Paris, France, 5 Universite Paris-Sud, UMR 1154-INRA, Faculte de Pharmacie, Chatenay-Malabry, France , 6 UMR-S 973 , mole cule the rapeutique in silico, University Paris Diderot , Paris , France , 7 CHU-H opital Nord - Service de Ge ne tique , Saint Etienne , France , 8 Institut Je ro me Lejeune , Paris, France, 9 Fondation Je rome Lejeune, Paris , France Background: Hyperhomocysteinemia, characterized by increased plasma homocysteine level, is associated with an increased risk of atherosclerosis. On the contrary, patients with Down syndrome appear to be protected from the development of atherosclerosis. We previously found a deleterious effect of hyperhomocysteinemia on expression of DYRK1A, a Down-syndrome-associated kinase. As increased expression of DYRK1A and low plasma homocysteine level have been associated with Down syndrome, we aimed to analyze the effect of its over-expression on homocysteine metabolism in mice. Methodology/Principal Findings: Effects of DYRK1A over-expression were examined by biochemical analysis of methionine metabolites, real-time quantitative reverse-transcription polymerase chain reaction, and enzyme activities. We found that over-expression of Dyrk1a increased the hepatic NAD(P)H:quinone oxidoreductase and S-adenosylhomocysteine hydrolase activities, concomitant with decreased level of plasma homocysteine in three mice models overexpressing Dyrk1a. Moreover, these effects were abolished by treatment with harmine, the most potent and specific inhibitor of Dyrk1a. The increased NAD(P)H:quinone oxidoreductase and S-adenosylhomocysteine hydrolase activities were also found in lymphoblastoid cell lines from patients with Down syndrome. Conclusions/Significance: Our results might give clues to understand the protective effect of Down syndrome against vascular defect through a decrease of homocysteine level by DYRK1A over-expression. They reveal a link between the Dyrk1a signaling pathway and the homocysteine cycle. - Funding: This work was supported by an EU grant AnEUploidy and by the Fondation Jerome Lejeune. Christophe Noll and Faycal Guedj are supported by a fellowship from the Ministere de lEnseignement superieur et de la Recherche. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. . These authors contributed equally to this work. Homocysteine (Hcy) is a sulfur-containing amino acid formed during the intracellular conversion of methionine via the adenosylated compounds S-adenosylmethionine (SAM) and Sadenosylhomocysteine (SAH). The formation of SAM is catabolized by methionine adenosyl transferase (MAT). Once Hcy is formed, it may be recycled to methionine after remethylation by two different pathways. The first one involves methionine synthase (MS), an enzyme that uses vitamin B12 (cobalamin) as an essential cofactor and 5-methyltetrahydrofolate as the methyl donor. The 5-methyltetrahydrofolate is generated by 5, 10-methylene tetrahydrofolate reductase (MTHFR) [1]. The second pathway, which occurs in liver and kidney, involves the enzyme betainehomocysteine methyltransferase (BHMT). Hcy may also undergo condensation with serine to form cystathionine, which is catalyzed by the vitamin B6-dependent enzyme cystathionine beta synthase (CBS), the first enzyme involved in the transsulfuration pathway. Cystathionine is subsequently hydrolysed to form cysteine which can be, in turn, incorporated into protein or used to synthesize the antioxidant glutathione. Hcy can also turn back to SAH via reversal of the SAH hydrolase (SAHH) reaction [1]. Elevated plasma Hcy levels are well-recognized as an independant risk factor for atherosclerosis in the coronary, cerebrovascular and peripheral arterial circulation [2]. Conversely, although Down syndrome (DS) is associated with a great variety of phenotypes, the incidence of atherosclerotic vascular disease seems to be low [3,4]. Even if the coronary arteries of DS patients were not completely free of atherosclerosis, it was milder than in other mentally retarded patients and in control subjects of the same age [5]. Moreover, healthy old DS patients showed some classical biochemical risk factors for atherosclerosis but did not suffer from clinical cardiovascular alterations [6]. Because many genetic factors can be related to this reduction, the reasons for this apparent protection against atherosclerosis remain unclear. DYRK1A, which gene is localized on human chromosome 21, is a protein kinase that belongs to an evolutionarily conserved family of proteins known as DYRKs (dual-specificity tyrosine-(Y)phosphorylation regulated kinase) involved in diverse functions ranging from development, growth to apoptosis [79]. On the one hand, we recently reported a reduction of Dyrk1a protein level in liver of CBS-deficient mice, a murine model of hyperhomocysteinemia [10], suggesting a link between DYRK1A related pathways and the Hcy cycle. On the other hand, an increased expression of DYRK1A and low plasma Hcy levels have been associated with DS [6,1113]. To analyze further the relation between DYRK1A and Hcy metabolism, we used four transgenic models to demonstrate the effect of the over-expression of Dyrk1a on Hcy metabolism: a model of hyperhomocysteinemia due to CBS deficiency [14] and three models with duplications of increasing complexity and over-expression of Dyrk1a [15]: a BAC transgenic with one copy of the murine Dyrk1a gene; a YAC transgenic for a human chromosome 21 fragment carrying five genes including DYRK1A; a partial trisomy 16 mouse carrying an extra copy of a region of MMU16 syntenic for a region of HSA21 between Mrpl39 and Znf295 containing 138 genes (also including Dyrk1a) and considered to be a valid mouse model of human Down syndrome [16]. DYRK1A over-expression reduces the plasma Hcy leve (...truncated)