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-adrenoceptor (AR) couples to these protective pathways, and increased glucose uptake. We characterised α-AR signalling in CHO-K1 cells co-expressing the human α-AR and GLUT4 (CHOαGLUT4myc) and in neonatal rat ventricular cardiomyocytes (NRVM), and measured glucose uptake, intracellular Ca mobilization, and phosphorylation of mTOR, Akt, 5' adenosine monophosphate-activated kinase (AMPK) and S6 ribosomal protein (S6rp). In both systems, noradrenaline and the α-AR selective agonist A61603 stimulated glucose uptake by parallel pathways involving mTOR and AMPK, whereas another α-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 CHOαGLUT4myc cells, siRNA directed against rictor but not raptor suppressed α-AR mediated glucose uptake. We have thus identified mTORC2 as a key component in glucose uptake stimulated by α-AR agonists. Our findings identify a novel link between the α-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-AR selective agonists as tools in the treatment of cardiac dysfunction.

The adenosine A 1 receptor is a therapeutic target based on its ability to provide cardioprotection during episodes of myocardial ischemia and reperfusion injury. However, the clinical translation of A 1 R agonists has been hindered by dose-limiting adverse effects (bradycardia and hypotension). Previously, we demonstrated that the bitopic agonist VCP746 (1), consisting of an adenosine pharmacophore linked to an allosteric moiety, can stimulate cardioprotective A 1 R signaling effects in the absence of unwanted bradycardia. This study maps the structure−activity relationships of 1 through modifications to the linker moiety. Derivatives differing in the flexibility, length, and nature of the linker were assessed, which revealed that the linker is tolerant of several modifications including added rigidity. Ligands featuring 1,4-disubstituted 1,2,3-triazoles were the most biased of the novel analogues but also displayed sub-nanomolar potency in a cAMP accumulation assay at the A 2B R. To our knowledge, 10 is the most potent A 2B R agonist published to date.

Heart failure remains a leading cause of morbidity and mortality worldwide. Current treatment for patients with heart failure include drugs targeting G protein‐coupled receptors such as β‐adrenoceptor antagonists (β‐blockers) and angiotensin II type 1 receptor antagonists (or angiotensin II receptor blockers). However, many patients progress to advanced heart failure with persistent symptoms, despite treatment with available therapeutics that have been shown to reduce mortality and mortality. GPCR targets currently being explored for the development of novel heart failure therapeutics include adenosine receptor, formyl peptide receptor, relaxin/insulin‐like family peptide receptor, vasopressin receptor, endothelin receptor and the glucagon‐like peptide 1 receptor. Many GPCR drug candidates are limited by insufficient efficacy and/or dose‐limiting unwanted effects. Understanding the current challenges hindering successful clinical translation and the potential to overcome existing limitations will facilitate the future development of novel heart failure therapeutics.

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Background: There has been convincing evidence that cardiac α 1A -adrenoceptors (α 1A -ARs) increase in expression and have an enhanced compensatory role during advanced heart failure (O'Connell et al, 2014). Mechanistic target of rapamycin (mTOR) signalling is involved in many critical cellular processes, and implicated in early development, normal function and stress responses of cardiomyocytes. However, it remains unclear whether mTOR is involved in the signalling mechanisms underlying α 1A -AR-mediated cardioprotective effects. This study aims to elucidate the ability of α 1A -ARs to enhance cardiomyocyte viability via mTOR signalling. Methods: Neonatal rat ventricular myocytes (NRVMs) were incubated under normoxic or hypoxic (1% O 2 ) conditions.Whole-cell radioligand binding assay was performed using [ 3 H]-prazosin. Cell viability was measured by propidium iodide staining and caspase 3/7 assay. Glucose uptake was measured using [ 3 H]-2-deoxy-glucose. Activation of cardioprotective signalling proteins were examined using AlphaScreen SureFire and In-Cell Western assays.Results: Stimulation of α 1A -AR with A61603 increased Ca 2+ mobilisation and glucose uptake in NRVMs, but failed to phosphorylate Akt which is a key protein for insulin-mediated glucose uptake. A61603 (100 nM) significantly decreased the percentage of apoptotic cells under hypoxic conditions (Control 22.0 ± 2.0%, A61603 11.9 ± 1.0%). Hypoxia significantly increased the abundance of α 1 -AR protein (Bmax normoxic 62.3 ± 3.2 fmol/mg, hypoxic 102.5 ± 14.6 fmol/mg protein). The general mTOR complex 1/2 inhibitor KU-0063794 (1 µM) significantly inhibited α 1A -ARmediated glucose uptake by 69% and cell survival by 69% in hypoxic NRVMs, whereas the mTOR complex 1 inhibitor rapamycin (10 nM) had no effect, suggesting that mTOR complex 2 has a key role. Conclusion: These findings indicate that α 1A -ARs are proportionally increased in hypoxia, mediate protective signalling in hypoxic NRVMs, increase Akt-independent glucose uptake and promote cell survival via mTORC2.