α 1A -Adrenoceptors activate mTOR signalling and glucose uptake in cardiomyocytes

The capacity of G protein-coupled receptors to modulate mechanistic target of rapamycin (mTOR) activity is a newly emerging paradigm with the potential to link cell surface receptors with cell survival. Cardiomyocyte viability is linked to signalling pathways involving Akt and mTOR, as well as increased glucose uptake and utilization. Our aim was to determine whether the α 1A -adrenoceptor (AR) couples to these protective pathways, and increased glucose uptake. We characterised α 1A -AR signalling in CHO-K1 cells co-expressing the human α 1A -AR and GLUT4 (CHOα 1A GLUT4myc) and in neonatal rat ventricular cardiomyocytes (NRVM), and measured glucose uptake, intracellular Ca 2+ mobilization, and phosphorylation of mTOR, Akt, 5′ adenosine monophosphate-activated kinase (AMPK) and S6 ribosomal protein (S6rp). In both systems, noradrenaline and the α 1A -AR selective agonist A61603 stimulated glucose uptake by parallel pathways involving mTOR and AMPK, whereas another α 1 -AR agonist oxymetazoline increased glucose uptake predominantly by mTOR. All agonists promoted phosphorylation of mTOR at Ser2448 and Ser2481, indicating activation of both mTORC1 and mTORC2, but did not increase Akt phosphorylation. In CHOα 1A GLUT4myc cells, siRNA directed against rictor but not raptor suppressed α 1A -AR mediated glucose uptake. We have thus identified mTORC2 as a key component in glucose uptake stimulated by α 1A -AR agonists. Our findings identify a novel link between the α 1A -AR, mTORC2 and glucose uptake, that have been implicated separately in cardiomyocyte survival. Our studies provide an improved framework for examining the utility of α 1A -AR selective agonists as tools in the treatment of cardiac dysfunction.