Decreased Insulin Secretion and Accumulation of Triglyceride in β Cells Overexpressing a Dominant-negative Form of AMP-activated Protein Kinase

Abstract

Adenosine 5’ -monophosphate-activated protein kinase (AMPK) has been implicated in the regulation of energy metabolism, although its role in the pancreatic β cells remains unclear. In the present, we have overexpressed a dominant negative form of AMPKα1 subunit (Asp57Ala) tagged with c-myc epitope (AMPKα1-DN) in INS-1D cells with an adenoviral vector. After 48 h of adenoviral infection, overexpression of AMPKα1-DN in INS-1D cells was confirmed by Western blot analysis with anti-c-myc antibody. Phosphorylation of the Thr172 in AMPKα1/α2 subunit was progressively decreased in parallel with increasing number of adenoviral titers. Glucose-stimulated insulin secretion in response to 30 mmol/L glucose was decreased in INS-1D cells overexpressing AMPKα1-DN as compared to control cells infected with adeno- LacZ vector. Neither cellular insulin content nor insulin mRNA level was changed between the two groups. Phosphorylation of acetyl-CoA carboxylase (ACC), a down-stream substrate of AMPK, was decreased, indicating that ACC activity was increased, due to the decreased AMPK activity. In fact, intracellular triglyceride content was increased as compared to control cells. The β-oxidation of palmitate was decreased at 30 mmol/L glucose. Insulin secretion in response to potassium chloride or glibenclamide was also decreased as compared to control cells. In conclusion, suppression of AMPK activity in β-cells inhibited insulin secretion in response to glucose, potassium chloride or glibenclamide without altering insulin content. Accumulation of triglyceride subsequent to the activation of ACC by suppression of AMPK activity, was suggested to be, at least in part, responsible for the impaired insulin secretion through so called lipotixicity mechanism.