Yuanbiao Zhao1, Andrew S Riching1,2,3, Walter E Knight1,2,3, Congwu Chi1,2,3, Lindsey J Broadwell4,5, Yanmei Du1, Mostafa Abdel-Hafiz6, Amrut V Ambardekar1,3, David C Irwin7, Catherine Proenza8, Hongyan Xu9, Leslie A Leinwand5,10, Lori A Walker1, Kathleen C Woulfe1, Michael R Bristow1, Peter M Buttrick1, Kunhua Song1,2,3. 1. Division of Cardiology, Department of Medicine (Y.Z., A.S.R., W.E.K., C.C., Y.D., A.V.A., L.A.W., K.C.W., M.R.B., P.M.B., K.S.), University of Colorado Anschutz Medical Campus, Aurora. 2. Gates Center for Regenerative Medicine and Stem Cell Biology (A.S.R., W.E.K., C.C., K.S.), University of Colorado Anschutz Medical Campus, Aurora. 3. The Consortium for Fibrosis Research & Translation (A.S.R., W.E.K., C.C., A.V.A., K.S.), University of Colorado Anschutz Medical Campus, Aurora. 4. Department of Biochemistry (L.J.B.), University of Colorado Boulder. 5. BioFrontiers Institute (L.J.B., L.A.L.), University of Colorado Boulder. 6. Department of Bioengineering (M.A.-H.), University of Colorado Anschutz Medical Campus, Aurora. 7. Cardiovascular and Pulmonary Research Laboratory, Department of Medicine (D.C.I.), University of Colorado Anschutz Medical Campus, Aurora. 8. Department of Physiology and Biophysics (C.P.), University of Colorado Anschutz Medical Campus, Aurora. 9. Department of Population Health Sciences, Medical College of Georgia, Augusta University (H.X.). 10. Department of Molecular, Cellular, and Developmental Biology (L.A.L.), University of Colorado Boulder.
Abstract
BACKGROUND: Abnormalities in Ca2+ homeostasis are associated with cardiac arrhythmias and heart failure. Triadin plays an important role in Ca2+ homeostasis in cardiomyocytes. Alternative splicing of a single triadin gene produces multiple triadin isoforms. The cardiac-predominant isoform, mouse MT-1 or human Trisk32, is encoded by triadin exons 1 to 8. In humans, mutations in the triadin gene that lead to a reduction in Trisk32 levels in the heart can cause cardiac dysfunction and arrhythmias. Decreased levels of Trisk32 in the heart are also common in patients with heart failure. However, mechanisms that maintain triadin isoform composition in the heart remain elusive. METHODS: We analyzed triadin expression in heart explants from patients with heart failure and cardiac arrhythmias and in hearts from mice carrying a knockout allele for Trdn-as, a cardiomyocyte-specific long noncoding RNA encoded by the antisense strand of the triadin gene, between exons 9 and 11. Catecholamine challenge with isoproterenol was performed on Trdn-as knockout mice to assess the role of Trdn-as in cardiac arrhythmogenesis, as assessed by ECG. Ca2+ transients in adult mouse cardiomyocytes were measured with the IonOptix platform or the GCaMP system. Biochemistry assays, single-molecule fluorescence in situ hybridization, subcellular localization imaging, RNA sequencing, and molecular rescue assays were used to investigate the mechanisms by which Trdn-as regulates cardiac function and triadin levels in the heart. RESULTS: We report that Trdn-as maintains cardiac function, at least in part, by regulating alternative splicing of the triadin gene. Knockout of Trdn-as in mice downregulates cardiac triadin, impairs Ca2+ handling, and causes premature death. Trdn-as knockout mice are susceptible to cardiac arrhythmias in response to catecholamine challenge. Normalization of cardiac triadin levels in Trdn-as knockout cardiomyocytes is sufficient to restore Ca2+ handling. Last, Trdn-as colocalizes and interacts with serine/arginine splicing factors in cardiomyocyte nuclei and is essential for efficient recruitment of splicing factors to triadin precursor mRNA. CONCLUSIONS: These findings reveal regulation of alternative splicing as a novel mechanism by which a long noncoding RNA controls cardiac function. This study indicates potential therapeutics for heart disease by targeting the long noncoding RNA or pathways regulating alternative splicing.
BACKGROUND: Abnormalities in Ca2+ homeostasis are associated with cardiac arrhythmias and heart failure. Triadin plays an important role in Ca2+ homeostasis in cardiomyocytes. Alternative splicing of a single triadin gene produces multiple triadin isoforms. The cardiac-predominant isoform, mouse MT-1 or human Trisk32, is encoded by triadin exons 1 to 8. In humans, mutations in the triadin gene that lead to a reduction in Trisk32 levels in the heart can cause cardiac dysfunction and arrhythmias. Decreased levels of Trisk32 in the heart are also common in patients with heart failure. However, mechanisms that maintain triadin isoform composition in the heart remain elusive. METHODS: We analyzed triadin expression in heart explants from patients with heart failure and cardiac arrhythmias and in hearts from mice carrying a knockout allele for Trdn-as, a cardiomyocyte-specific long noncoding RNA encoded by the antisense strand of the triadin gene, between exons 9 and 11. Catecholamine challenge with isoproterenol was performed on Trdn-as knockout mice to assess the role of Trdn-as in cardiac arrhythmogenesis, as assessed by ECG. Ca2+ transients in adult mouse cardiomyocytes were measured with the IonOptix platform or the GCaMP system. Biochemistry assays, single-molecule fluorescence in situ hybridization, subcellular localization imaging, RNA sequencing, and molecular rescue assays were used to investigate the mechanisms by which Trdn-as regulates cardiac function and triadin levels in the heart. RESULTS: We report that Trdn-as maintains cardiac function, at least in part, by regulating alternative splicing of the triadin gene. Knockout of Trdn-as in mice downregulates cardiac triadin, impairs Ca2+ handling, and causes premature death. Trdn-as knockout mice are susceptible to cardiac arrhythmias in response to catecholamine challenge. Normalization of cardiac triadin levels in Trdn-as knockout cardiomyocytes is sufficient to restore Ca2+ handling. Last, Trdn-as colocalizes and interacts with serine/arginine splicing factors in cardiomyocyte nuclei and is essential for efficient recruitment of splicing factors to triadin precursor mRNA. CONCLUSIONS: These findings reveal regulation of alternative splicing as a novel mechanism by which a long noncoding RNA controls cardiac function. This study indicates potential therapeutics for heart disease by targeting the long noncoding RNA or pathways regulating alternative splicing.
Entities:
Keywords:
RNA, long noncoding; arrhythmias, cardiac; heart failure; myocytes, cardiac; splicing, alternative
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