Daniela Liccardo, Federica Marzano, Nazareno Paolocci, Giuseppe Rengo, Alessandro Cannavo
Background:The G protein-coupled receptor (GPCR) kinase 2 (GRK2) is upregulated in the ischemic myocardium, accounting for myocyteβ-adrenergic receptor (βAR) desensitization/downregulation, apoptosis, and perturbed metabolism. The toll-like receptor 4 (TLR4),induces GRK2 inhibition in leukocytes and macrophage while prothymosin alpha (PTα) is a pro-survival protein in cardiomyocytes that, in the retina and neuronal cells,is a damage-associated molecular pattern (DAMPs)able to bind TLR4. Herein, we tested whether PTα-dependent beneficial effects in cardiomyocytes implies TLR4 activation and GRK2 down-regulation. Methods:Weusedneonatal rat ventricular myocytes (NRVMs) underwent simulated ischemia (SI) or SI/reperfusion (SI/R). Results:We found that GRK2 protein levels plummeted after SI, returning at baseline levels in reperfused injured cardiomyocytes.Conversely, PTα treatment of NRVMsprevented GRK2 upregulation either after SI/R(in a TLR4-dependentmanner) or chronic adrenergic receptor stimulation. In I/R challenged NRVMs, we observed an increased mitochondrial translocation of GRK2, which was inhibited by PTα treatment. PTα markedly blunted cardiomyocyte apoptotic rate, increased cell survival, and improved mitochondrial function. We crowned these in vitro findings with in vivo studies, delivering PTα intramyocardially to WT C57Bl6 mice subjected to 30 min ischemia followed by 24 hours reperfusion. Control (vehicle-treated) I/R mice exhibited markedly elevated GRK2 and apoptotic rates, effects ostensibly attenuated inPTα-treated I/R mice. Conclusions:The PTα/TLR4 axisis anovel strategyto blockGRK2 and prevent cardiomyocytes damage after ischemia. Thus, present findings offer new avenues to offset chronic post-ischemic myocyte loss that remains a clinically relevant unmet clinical milestone.
Published Date: 2020-10-30; Received Date: 2020-10-16