Abstract 513: Metabolic Switch and Hypertrophy of Cardiomyocytes Following Angiotensin-treatment are Prevented by Activation of AMP-activated Protein Kinase
Angiotensin II mediates left ventricular hypertrophy, but its consequences on cardiomyocyte metabolism and energy supply are not understood. Here we investigated its effect on glucose and fatty acid utilization and the potential role of AMP-activated protein kinase (AMPK), a key regulator of metabolism and proliferation.
METHODS / RESULTS: Neonatal rat cardiomyocytes and H9C2 cells were stimulated with Ang II with or without pre-incubation with the AMPK-stimulator AICAR. Western-blot analysis was performed for phosphorylation of AMPK, the key metabolic regulators GLUT4 and acetyl-CoA-Carboxylase (ACC) as well as the mTOR-regulator Tuberin-2 (TSC). Hypertrophic response was quantified as incorporation of radioactive labelled Leucine by scintillation counting, metabolic effects by uptake of labelled glucose and palmitic acid, and expression of the fetal gene program was evaluated by RT-PCR. Ang II stimulated Leucine-incorporation to 170 ±13% of control. Western blot showed a time- and concentration-dependent depression of AMPK-phosphorylation. This was paralleled by a significant translocation of GLUT4 to the cell membrane and increased glucose-uptake whereas (P)ACC and fatty-acid uptake remained unchanged. TSC-phosphorylation was decreased to 51 ±9%, indicating decreased inhibition of mTOR, and the expression of fetal genes (ANF, β-MHC, MLC) was elevated. Pre-incubation with AICAR inhibited Angiotensin-induced hypertrophy nearly to standard level and reversed the effects on fetal gene program and the considered metabolic parameters: GLUT4-translocation was reduced to 50 ±11%, but ACC-phosphorylation and TSC-phosphorylation were elevated to 260 ±23%. In C57/B6 mice a short-term increase in afterload correspondingly decreased phosphorylation of AMPK and ACC to 22±9% and 36±10% respectively, TSC remained unchanged. p<0.05 for all results.
CONCLUSIONS: Angiotensin-induced hypertrophy of cardiomyocytes is accompanied by decreased activation of AMPK, increased glucose-uptake and decreased mTOR-inhibition, representing a metabolic switch to a favour of glucose-uptake. Stimulation with the AMPK-activator AICAR reverses these metabolic changes and inhibits hypertrophy as quantified by Leucine-incorporation.