HNF4 alpha contributes to glucose formation in aged rat hepatocytes

Abstract

Aging-dependent physiological conditions are attributed to parenchymal structural changes to cellular functions in aged organisms. Compared to the young animals, the primary hepatocytes from old rats showed a higher glucose output and a higher expression of the key gluconeogenesis-regulating enzyme, phosphoenol pyruvate carboxykinase (PEPCK). The primary hepatocytes from old rats showed a higher glucose output and a higher expression of the key gluconeogenesis-regulating enzyme, phosphoenol pyruvate carboxykinase (PEPCK), compared with those from the young animals. The in situ hybridization study showed increased PEPCK mRNA expression in the aged liver tissues. The livers from old rats showed loosened hexagonal hepatic lobular structures, increased collagen accumulation, and high expression of the hypoxia marker hypoxia-inducible factor 1 alpha (HIF1 alpha). Hypoxia increased the PEPCK mRNA and protein expression levels in accordance with the HIF1 alpha expression. PEPCK promoter luciferase reporter assay showed that hypoxia increased PEPCK through transcriptional activation. Furthermore, the hepatocyte nuclear factor a (HNF4 alpha) protein, but not the HNF4 alpha mRNA level, increased in parallel with the PEPCK mRNA expression under hypoxic conditions. Glucose production increased under hypoxic conditions, but this increment diminished by HNF4 alpha siRNA in young hepatocytes. Moreover, increased glucose production from old rat hepatocytes was reversed by the down-regulation of HNF4 alpha through a specific siRNA. This study suggests that the mild hypoxic conditions in response to aging-dependent hepatic structural changes may contribute to the induction of the gluconeogenic enzyme PEPCK through HNF4 alpha protein stabilization. (C) 2013 Elsevier Inc. All rights reserved.