Molecular Basis of Takotsubo Syndrome

Abstract

IntroductionTakotsubo syndrome (TTS), also known as the “Broken Heart Syndrome” or “Apical Ballooning Syndrome is defined by its characteristic anomaly: when the heart contracts during systole, the apex of the heart dilates as the base of the heart contracts. Severe TTS can lead to cardiogenic shock and death in 3–4% of patients. There is no standard medical therapy for TTS because the mechanism underlying the development of the syndrome is unknown. Our goal is to determine the molecular mechanisms of TTS as a first step towards better treatment plans and outcomes.MethodsOur model of TTS is a Kv1.5 null mouse, with compromised coronary metabolic dilation, subjected to transaortic constriction (TAC). Two weeks after TAC, when Kv1.5 null mouse showed profound apical ballooning during ventricular contraction (echocardiography), myocardial blood flow (MBF) was measured by contrast echocardiography in the base and apex of the left ventricle of mice under control conditions and during acute administration of norepinephrine to increase cardiac work. Hearts were collected and gene expression (RNA deep sequencing) in both the apex and the base were performed and followed by bioinformatic analysis. Wild type (WT) and unstressed Kv1.5 null mice were used as controls. To increase the scientific rigor, we purposefully analyzed RNA expression from different animals with Real‐Time‐PCR, to confirm the sequencing data.ResultsA total of 3875 genes were identified by differentially expressed between TTS vs unstressed Kv1.5 null hearts. Gene Set Enrichment Analysis shows many families of genes downregulated (metabolism) and upregulated (inflammation, hypoxia, apoptosis) in the apical (ballooning) area of the heart in TTS (compared to the base of the heart). RT‐qPCR revealed significant upregulation of the genes for Postn, Lox, and C920009B18Rik (p<0.01) and down‐regulation of the genes Ucp3, Acaa2, Pfkb1, Mir133a‐2 (p<0.05). These significant changes in expression were also shown in the apex of TTS hearts as compared to the apex of control Kv1.5 null hearts (p<0.01). We also found that in the mice with TTS, MBF was lower in the apex than in the base.ConclusionOur results suggest that the apex of the heart in TTS is receiving insufficient perfusion compared to the base, which may be one of the root problems in TTS. There is significant upregulation of structural genes in the apex of TTS hearts versus their bases and the apexes of normal hearts, whereas there is a significant downregulation of genes playing roles in metabolism. This confirms the importance of these specific genes in the development of the anomaly shown in TTS.