Cardiac thromboxane A2 receptor activation does not directly induce cardiomyocyte hypertrophy but does cause cell death that is prevented with gentamicin and 2-APB.

Chad D Touchberry,Hannah K Swan,Lori A Wetmore,Vladimir Tchikrizov,Shubra Srinivas,Christopher J Elmore,Adil S Akthar,Michael J Wacker,Neerupma Silswal

doi:10.1186/2050-6511-15-73

Abstract

BackgroundWe have previously shown that the thromboxane (TXA2) receptor agonist, U46619, can directly induce ventricular arrhythmias that were associated with increases in intracellular calcium in cardiomyocytes. Since TXA2 is an inflammatory mediator and induces direct calcium changes in cardiomyocytes, we hypothesized that TXA2 released during ischemia or inflammation could also cause cardiac remodeling.MethodsU46619 (0.1-10 μM) was applied to isolated adult mouse ventricular primary cardiomyocytes, mouse ventricular cardiac muscle strips, and cultured HL-1 cardiomyocytes and markers of hypertrophy and cell death were measured.ResultsWe found that TXA2 receptors were expressed in ventricular cardiomyocytes and were functional via calcium imaging. U46619 treatment for 24 h did not increase expression of pathological hypertrophy genes (atrial natriuretic peptide, β-myosin heavy chain, skeletal muscle α-actin) and it did not increase protein synthesis. There was also no increase in cardiomyocyte size after 48 h treatment with U46619 as measured by flow cytometry. However, U46619 (0.1-10 μM) caused a concentration-dependent increase in cardiomyocyte death (trypan blue, MTT assays, visual cell counts and TUNEL stain) after 24 h. Treatment of cells with the TXA2 receptor antagonist SQ29548 and inhibitors of the IP3 pathway, gentamicin and 2-APB, eliminated the increase in cell death induced by U46619.ConclusionsOur data suggests that TXA2 does not induce cardiac hypertrophy, but does induce cell death that is mediated in part by IP3 signaling pathways. These findings may provide important therapeutic targets for inflammatory-induced cardiac apoptosis that can lead to heart failure.

Highlights

We have previously shown that the thromboxane (TXA2) receptor agonist, U46619, can directly induce ventricular arrhythmias that were associated with increases in intracellular calcium in cardiomyocytes
There was a 3.2 fold higher expression of Thromoxane A2 receptor (TXA2R) in primary cardiomyocytes compared to HL-1 cardiomyocytes using β-actin as the reference gene and 2.7 fold higher expression using GAPDH as the reference gene
We have previously demonstrated that U46619 increases intracellular Ca2+ in rabbit cardiomyocytes [16] and have found that the cardiomyocytes from mice behave to U46619 treatment as to what we have previously reported in the rabbit

Summary

Introduction

We have previously shown that the thromboxane (TXA2) receptor agonist, U46619, can directly induce ventricular arrhythmias that were associated with increases in intracellular calcium in cardiomyocytes. TXA2 has Previously, while investigating the ability of the TXA2 mimetic (U46619) to stimulate peripheral sensory neurons involved in autonomic nervous system reflexes in the anesthetized rabbit [9], we noted that left atrial injections of U46619 induced ventricular arrhythmias These arrhythmias were independent of changes in coronary blood flow, systemic vasoconstriction, and without the induction of myocardial ischemia [10], which indicated that the effect was a direct action on the heart by U46619. To further elucidate the mechanisms responsible for these arrhythmias, we found that rabbit ventricular cardiomyocytes expressed TXA2 receptors (TXA2Rs) and antagonism of TXA2R eliminated the arrhythmias [10] It is well known in platelets and smooth muscle cells that stimulation of TXA2R activates phospholipase C (PLC), increases inositol trisphosphate (IP3) production, and releases Ca2+ from intracellular stores [11,12,13,14,15]. Because intracellular Ca2+ homeostasis is critical to normal heart function and disruption of intracellular Ca2+ triggers arrhythmias [20], and cardiac hypertrophy [21,22] and cell death [23], we wanted to investigate other potential roles TXA2 may play in the myocardium

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Conclusion