Molecular mechanisms involved in the control of hepatic neoglucogenesis in animals submitted to a high-protein diet: Role of CREB and branched-chain amino acids

Abstract

Hepatic gluconeogenesis is vital for maintaining glycemic levels in different physiological situations. Previous work from our laboratory have demonstrated that animals adapted to a high protein (HP) diet, free of carbohydrates, are able to maintain glycemia, both in the fed and fasting state, due to the high hepatic gluconeogenic capacity, proven by the high incorporation of ¹tC of amino acids in glucose. In addition, animals adapted to the HP diet have high circulating levels of branched-chain amino acids (BCAA) and glucagon (main activator of CREB, cAMP response element binding protein). CREB induces PEPCK and G6Pase expression for glycemic control in fasting situations. BCAA and their ±-ketoacids (BCKAs) are also able to stimulate gluconeogenesis in hepatocytes, mainly by inhibiting AKT. However, very little is known about the molecular control of gluconeogenesis by these factors in animals adapted to the HP diet. In fact, the main aim of this work is to investigate the role of CREB, BCAA and their BCKAs in the control of hepatic gluconeogenesis in mice adapted to the HP diet. To achieve this goal, it will be evaluated in vivo the key regulatory proteins of the gluconeogenesis (PEPCK, G6Pase, AKT, CREB, SIK2, CRTC-2 and FoxO1) in the liver of control and HP fed mice, as well as CREB activity in vivo and in vitro, using CRE luc transgenic mice and primary culture of hepatocytes with adenovirus expressing dominant negative CREB (ACREB), as also in vitro experiments with isolated hepatocytes incubated with BCAA and BCKAs and gluconeogenic substrates in the presence or absence of glucagon. Thus, this study aims to contribute to the understanding of the participation of CREB, BCAA and BCKAs in the high hepatic gluconeogenic activity found in animals adapted to the HP diet, and may bring new knowledge about the participation of these transcriptional and nutritional factors in the control of this important metabolic pathway.