Role of phosphodiesterases in the development of takotsubo syndrome

Abstract Background/Purpose Takotsubo syndrome (TTS) is characterized by acute transient left ventricular dysfunction in the absence of obstructive coronary lesions. We identified a higher sensitivity to catecholamine-induced stress toxicity as mechanism associated with the TTS phenotype in our former study, but the pathogenesis of TTS is still not completely understood. In this study our aim was to prove the hypothesis of an altered phosphodiesterase (PDE)-dependent 3',5'-cyclic adenosine monophosphate (cAMP)-signaling in TTS in patient-specific induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs). Methods and results We generated functional TTS-iPSC-CMs and treated them with catecholamines to mimic a TTS-phenotype. To directly address the hypothesis that local cAMP dynamics might be altered in TTS, we used Förster resonance energy transfer (FRET) based cAMP sensors, which are specifically located in the cytosol or at the sarcoplasmic/endoplasmic reticulum calcium ATPase 2a (SERCA) micro domain. We demonstrated that β-adrenergic receptor (β-AR) stimulations resulted in stronger cytosolic FRET responses in TTS-CMs compared to controls. In contrast, no differences of cAMP level were observed in the SERCA-PLN micro domain between TTS- and control-iPSC-CMs. To analyze the interplay of β-AR signaling and specific PDE contribution to the cAMP signaling in TTS, specific PDE-inhibitors were used. We were able to show in the cytosol that after β-AR stimulation, the strong effects of the PDE4 family of control cells were significantly decreased in diseased TTS CMs, which is in line with previously described reduced PDE4 activity in failing mouse hearts. In contrast, the contribution of PDE3 to cytoplasmic cAMP degradation was increased in TTS (Figure 1 A). This is in line with increased PDE3A and down-regulated PDE4D protein expression in TTS-iPSC-CMs compared to control cells. Analysis of PDE-dependent cAMP level in the SERCA micro domain show also a significantly reduced PDE4 activity. But the dynamic cytosolic PDE contribution of PDE2 and PDE3 after catecholamine treatment in TTS is lost in SERCA micro domain (Figure1B). Conclusion Our data showed for the first time alterations of local cAMP signaling in healthy and diseased TTS-iPSC-CMs. We demonstrated an isozym shift from PDE4 in control to PDE3 and PDE2 in TTS and identified PDE4 as an important player in the β-adrenergic cAMP signaling in TTS. Therefore, PDE4 activators may be a possible new ther