Abstract 16681: Hepatic Nuclear Factor 4 Alpha is the Major Regulator of Alanine:Glyoxylate Aminotransferase 2 Expression - A Novel Link Between Diabetes and Impaired Metabolism of Nitric Oxide and Lipids
Background: Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, is elevated in numerous diseases associated with impairment in nitric oxide (NO) production, including atherosclerosis, hypertension, dyslipidemia and diabetes mellitus. ADMA can be hydrolysed by dimethylarginine dimethylaminohydrolase (DDAH) or metabolized through an alternative pathway by alanine:glyoxylate aminotransferase 2 (AGXT2). Recent findings suggest that AGXT2 plays an important role in regulation of lipid metabolism, insulin resistance and blood pressure. The goal of this study was to determine the mechanisms of regulation of AGXT2 expression.
Methods and Results: We identified a putative hepatic nuclear factor 4 alpha (HNF4a) binding site in the conserved region of the murine Agxt2 promoter. A series of murine Agxt2 promoter/luciferase reporter constructs with mutations in the putative HNF4a binding site was expressed in murine hepatic cell line Hepa 1-6 and luciferase activity in the cell lysates was measured. The mutated constructs showed a 74% decrease in the reporter activity as compared to the intact construct (p<0.001). The binding of HNF4a to the Agxt2 promoter region was confirmed by chromatin immunoprecipitation. siRNA-mediated knockdown of Hnf4a in Hepa 1-6 cells led to 40% (p<0.001) reduction in Hnf4a mRNA levels and 50% (p<0.001) reduction in Agxt2 mRNA levels. To test, whether Hnf4a regulates Agxt2 expression in vivo we measured the mRNA levels and activity of AGXT2 in liver-specific Hnf4a knockout mice and found 90% (p<0.001) decrease in liver Agxt2 expression and 85% (p<0.01) decrease in liver Agxt2 activity upon loss of HNF4a.
Conclusions: We have identified HNF4a as the major regulator of Agxt2 expression. Previous studies have shown an association between HNF4a polymorphisms and increased risk of type 2 diabetes. Our current findings therefore suggest a potential link between type 2 diabetes and AGXT2-mediated impairment in metabolism of nitric oxide and lipids. We are currently investigating the levels of AGXT2 metabolites in plasma of the diabetic patients with inborn HNF4a deficiency to determine to which extent our findings from the experimental models could be translated into humans.
Author Disclosures: A.A. Kolobov: None. D.V. Burdin: None. A.V. Demyanov: None. A.A. Soshnev: None. C. Brocker: None. N. Samusik: None. S. Brilloff: None. J. Martens-Lobenhoffer: None. T. Reetz: None. R. Maas: None. S.M. Bode-Böger: None. F. Gonzalez: None. N. Weiss: None. R.N. Rodionov: None.
- © 2014 by American Heart Association, Inc.