title: Inhibition of Foxo1 function is associated with improved fasting glycemia in diabetic mice.
abstract: Excessive hepatic glucose production is a contributing factor to fasting hyperglycemia in diabetes. Insulin suppresses hepatic glucose production by inhibiting the expression of two gluconeogenic enzymes, phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G-6-Pase). The forkhead transcription factor Foxo1 has been implicated as a mediator of insulin action in regulating hepatic gluconeogenesis, and a Foxo1 mutant (Foxo1-Delta256), devoid of its carboxyl domain, has been shown to interfere with Foxo1 function and inhibit gluconeogenic gene expression in cultured cells. To study the effect of Foxo1-Delta256 on glucose metabolism in animals, the Foxo1-Delta256 cDNA was delivered to the livers of mice by adenovirus-mediated gene transfer. Hepatic Foxo1-Delta256 production resulted in inhibition of gluconeogenic activity, as evidenced by reduced PEPCK and G-6-Pase expression in the liver. Mice treated with the Foxo1-Delta256 vector exhibited significantly reduced blood glucose levels. In contrast, blood glucose levels in control vector-treated animals remained unchanged, which coincided with the lack of alterations in the expression levels of PEPCK and G-6-Pase. When tested in diabetic db/db mice, hepatic production of Foxo1-Delta256 was shown to reduce fasting hyperglycemia. Furthermore, we showed that hepatic Foxo1 expression was deregulated as a result of insulin resistance in diabetic mice and that Foxo1-Delta256 interfered with Foxo1 function via competitive binding to target promoters. These results demonstrated that functional inhibition of Foxo1, caused by hepatic expression of its mutant, is associated with reduced hepatic gluconeogenic activity and improved fasting glycemia in diabetic mice.
authors.affiliation: Carl C. Icahn Institute for Gene Therapy and Molecular Medicine, Mount Sinai School of Medicine, One Gustave L. Levy Place, New York, NY 10029, USA.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Altomonte
authors.forename: Anja
authors.initials: A
authors.lastname: Richter
authors.forename: Sonal
authors.initials: S
authors.lastname: Harbaran
authors.forename: Jenny
authors.initials: J
authors.lastname: Suriawinata
authors.forename: Jun
authors.initials: J
authors.lastname: Nakae
authors.forename: Swan N
authors.initials: SN
authors.lastname: Thung
authors.forename: Marcia
authors.initials: M
authors.lastname: Meseck
authors.forename: Domenico
authors.initials: D
authors.lastname: Accili
authors.forename: Hengjiang
authors.initials: H
authors.lastname: Dong
mesh_terms: D000818:Animals; D001786:Blood Glucose / Q000032:analysis / Q000378:metabolism*; D006528:Carcinoma, Hepatocellular / Q000235:genetics / Q000378:metabolism*; D003924:Diabetes Mellitus, Type 2 / Q000378:metabolism*; D005215:Fasting / Q000378:metabolism; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors; D005786:Gene Expression Regulation; D005943:Gluconeogenesis / Q000502:physiology; D005947:Glucose / Q000378:metabolism*; D008099:Liver / Q000378:metabolism*; D051379:Mice / Q000235:genetics; D016297:Mutagenesis, Site-Directed; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism*; D014162:Transfection / Q000379:methods; D014407:Tumor Cells, Cultured
chemical_list: D001786:Blood Glucose; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors; C467200:Foxo1 protein, mouse; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; D005947:Glucose