Abstract Body: Background: Recent evidence suggests that cystic fibrosis affects multiple organs independent of lung function. Myocardial cystic fibrosis transmembrane regulator (CFTR) channels are normally inactive but it is activated in response to catecholamine stress.
Method/Result: In 2 mouse models of homozygous CFTR mutations (S489X; F508d), we demonstrate increased susceptibility to ventricular tachycardia (VT) in response to epinephrine, and this is associated with prolonged QTc intervals. The Ingenuity Pathway Analysis of mouse cardiac proteomics data revealed increased caveolin-1 (cav-1) signaling among the top pathways affected in CF mutant hearts. In CF mouse and pig hearts, and human induced pluripotent stem cells-derived cardiomyocytes (iPS-CM), we found increased ER stress, ATF4, Cav-1 and -3, and decreased ERG proteins. Genetic deletion of Cav-1 or ATF4 in cardiomyocytes, or treatment with TUDCA, prevented stress-induced VT in both CF mouse models, in parallel with restoration of ERG channel (a K+ channel contributing to IKr, which is mutated in Long QT syndrome 2, LQT2). The inducible polymorphic VT was confirmed in CF mutant piglets, which also showed increased Cav-1 and decreased ERG. We performed whole-cell patch clamp and found a substantial decrease of Ikr (hERG current) but preserved INa in iPS-CM from CF F508d patients compared with those from isogenic controls. The decreased Ikr can be corrected by long-term treatment of Trikafta (CF correctors + potentiator) or Cav-1 siRNA, or ATF4-siRNA. Mechanistically, CF-iPS-CM display deranged caveolae-mediated endocytosis, with increased caveolar internalization of hERG. Suppression of Cav-1 restored membranous hERG in CF-iPS-CM. Suppression of ATF4 by siRNA attenuated the deranged caveolae-endocytosis, restored membrane localization and the current of hERG (Ikr). We confirm the clinical significance by a retrospective analysis of EKG in 126 CF patients (61M, 65F) in our Epic medical record. There is a significant QTc prolongation in CF patients compared with matched controls: Male: CF 447.8±4.5 vs cont. 429.2±2.5; Females: CF 454.0±3.5 vs cont.437.5±2.4 msec. The QTc interval is independent of lung function. Finally, immunostaining of autopsy heart sections from 7 CF decedents showed upregulation of Cav-1/-3 and loss of hERG.
Conclusion: We elucidated a novel mechanism of arrhythmia in CF through ATF4 regulation of caveolin-endocytosis of hERG in CF-related Long QT2 and inducible VT.