Phenyl Saligenin Phosphate Disrupts Cell Morphology and the Actin Cytoskeleton in Differentiating H9c2 Cardiomyoblasts and Human-Induced Pluripotent Stem-Cell-Derived Cardiomyocyte Progenitor Cells

We have previously shown that phenyl saligenin phosphate (PSP), an organophosphorus compound which is classed as a weak inhibitor of acetylcholinesterase, triggered cytotoxicity in mitotic and differentiated H9c2 cardiomyoblasts. The aim of this study was to assess whether sublethal concentrations of PSP could disrupt the morphology of differentiating rat H9c2 cardiomyoblasts and human-induced pluripotent stem-cell-derived cardiomyocyte progenitor cells (hiPSC-CMs) and to assess the underlying cytoskeletal changes. PSP-induced changes in protein expression were monitored via Western blotting, immunocytochemistry, and proteomic analysis. PSP-mediated cytotoxicity was determined by measuring MTT reduction, LDH release, and caspase-3 activity. Sublethal exposure to PSP (3 μM) induced morphological changes in differentiating H9c2 cells (7, 9, and 13 days), reflected by reduced numbers of spindle-shaped cells. Moreover, this treatment (7 days) attenuated the expression of the cytoskeletal proteins cardiac troponin I, tropomyosin-1, and α-actin. Further proteomic analysis identified nine proteins (e.g., heat shock protein 90-β and calumenin) which were down-regulated by PSP exposure in H9c2 cells. To assess the cytotoxic effects of organophosphorus compounds in a human cell model, we determined their effects on human-induced pluripotent stem-cell-derived cardiomyocyte progenitor cells. Chlorpyrifos and diazinon-induced cytotoxicity (48 h) was evident only at concentrations >100 μM. By contrast, PSP exhibited cytotoxicity in hiPSC-CMs at a concentration of 25 μM following 48 h exposure. Finally, sublethal exposure to PSP (3 μM; 7 days) induced morphological changes and decreased the expression of cardiac troponin I, tropomyosin-1, and α-actin in hiPSC-CMs. In summary, our data suggest cardiomyocyte morphology is disrupted in both cell models by sublethal concentrations of PSP via modulation of cytoskeletal protein expression.

Role of transglutaminase 2 in A1 adenosine receptor- and β2-adrenoceptor-mediated pharmacological pre- and post-conditioning against hypoxia-reoxygenation-induced cell death in H9c2 cells

Pharmacologically-induced pre- and post-conditioning represent attractive therapeutic strategies to reduce ischaemia/reperfusion injury during cardiac surgery and following myocardial infarction. We have previously reported that transglutaminase 2 (TG2) activity is modulated by the A₁ adenosine receptor and β₂-adrenoceptor in H9c2 cardiomyoblasts. The primary aim of this study was to determine the role of TG2 in A₁ adenosine receptor and β₂-adrenoceptor-induced pharmacological pre- and post-conditioning in the H9c2 cells. H9c2 cells were exposed to 8h hypoxia (1% O₂) followed by 18h reoxygenation, after which cell viability was assessed by monitoring mitochondrial reduction of MTT, lactate dehydrogenase release and caspase-3 activation. N⁶-cyclopentyladenosine (CPA; A₁ adenosine receptor agonist), formoterol (β₂-adrenoceptor agonist) or isoprenaline (non-selective β-adrenoceptor agonist) were added before hypoxia/reoxygenation (pre-conditioning) or at the start of reoxygenation following hypoxia (post-conditioning). Pharmacological pre- and post-conditioning with CPA and isoprenaline significantly reduced hypoxia/reoxygenation-induced cell death. In contrast, formoterol did not elicit protection. Pre-treatment with pertussis toxin (G_i/o-protein inhibitor), DPCPX (A₁ adenosine receptor antagonist) or TG2 inhibitors (Z-DON and R283) attenuated the A₁ adenosine receptor-induced pharmacological pre- and post-conditioning. Similarly, pertussis toxin, ICI 118,551 (β₂-adrenoceptor antagonist) or TG2 inhibition attenuated the isoprenaline-induced cell survival. Knockdown of TG2 using small interfering RNA (siRNA) attenuated CPA and isoprenaline-induced pharmacological pre- and post-conditioning. Finally, proteomic analysis following isoprenaline treatment identified known (e.g. protein S100-A6) and novel (e.g. adenine phosphoribosyltransferase) protein substrates for TG2. These results have shown that A₁ adenosine receptor and β₂-adrenoceptor-induced protection against simulated hypoxia/reoxygenation occurs in a TG2 and G_i/o-protein dependent manner in H9c2 cardiomyoblasts.