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Hepatic ALT isoenzymes are elevated in gluconeogenic conditions including diabetes and suppressed by insulin at the protein level
Author(s) -
Qian Kun,
Zhong Shao,
Xie Keming,
Yu Daozhan,
Yang Rongze,
Gong DaWei
Publication year - 2015
Publication title -
diabetes/metabolism research and reviews
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.307
H-Index - 110
eISSN - 1520-7560
pISSN - 1520-7552
DOI - 10.1002/dmrr.2655
Subject(s) - gluconeogenesis , medicine , endocrinology , insulin , downregulation and upregulation , gene isoform , insulin resistance , isozyme , alanine transaminase , biology , carbohydrate metabolism , aspartate transaminase , diabetes mellitus , chemistry , metabolism , enzyme , biochemistry , alkaline phosphatase , gene
Background Alanine transaminase (ALT) plays an important role in gluconeogenesis by converting alanine into pyruvate for glucose production. Early studies have shown that ALT activities are upregulated in gluconeogenic conditions and may be implicated in the development of diabetes. ALT consists of two isoforms, ALT1 and ALT2, with distinctive subcellular and tissue distributions. Whether and how they are regulated are largely unknown. Methods By using Western blotting analysis, we measured hepatic ALT isoforms at the protein level in obese and diabetic animals and in Fao hepatoma cells treated with dexamethasone and insulin. In addition, we measured glucose output in Fao cells over‐expressing ALT1 and ALT2. Results Both ALT isoforms in the liver were increased in diabetic Goto‐Kakizaki rats and during fasting. However, in ob/ob mice, only ALT2, but not ALT1, protein levels were elevated, and the increase of ALT2 was correlated with that of ALT activity. We further demonstrated that, in vitro , both ALT1 and ALT2 were induced by glucocorticoid dexamethasone, but suppressed by insulin in Fao cells. Finally, we showed that the over‐expression of ALT1 and ALT2 in Fao cells directly increased glucose output. Conclusions We have shown the similarity and difference in the regulation of ALT isoforms in gluconeogenic conditions at the protein level, supporting that ALT isoenzymes play an important role in glucose metabolism and may be implicated the development of insulin resistance and diabetes. Copyright © 2015 John Wiley & Sons, Ltd.