Abstract 1279 Characterization of Adenosine-to-Inosine RNA editing in the human heart.

Background & Purpose:
Adenosine-to-Inosine (A-to-I) RNA editing regulates the secondary structure, stability, and alternative splicing of RNAs. The editing enzymes ADAR1 and ADAR2 mediate this process and alterations in RNA editing have been associated with several human diseases. The extent of A-to-I RNA editing, the underlying mechanisms, and the potential consequences for the healthy and failing human heart remain unclear.

Methods & Results:
Using next generation sequencing, we analyzed RNA editing in human heart samples of heart failure (HF) patients (n=20) and controls (n=10). We identified A-to-I RNA editing as the major type of RNA editing in the human heart. In failing hearts, RNA editing, which was mainly occurring in intronic Alu elements of protein-coding genes, was reduced. In HF, we identified 166 upregulated circRNAs, with the majority showing reduced RNA editing in the host gene (88.3%). Consistently, we observed reduced ADAR2 protein levels in HF patients (-68.2%). Reduction of ADAR2 in vitro resulted in elevated circRNA levels as well as reduced cell size in induced pluripotent stem cell-derived cardiomyocytes (-19.2%). Using the top edited mRNA of AKAP13, we examined the formation of circRNAs in the human heart. We identified the interaction of ADAR2 with Alu elements, such as in flanking intronic regions of circAKAP13. A knockdown of ADAR2 in vitro led to upregulation of circAKAP13, which was in line with our observations in HF patients.

Conclusion:
Out data suggests that ADAR2 reduces the formation of double-stranded structures in AKAP13 pre-mRNA, thereby reducing the stability of Alu elements and circularization of the resulting circRNA. This study describes a novel role of RNA editing in alternative splicing of mRNAs regulating circRNA formation in the human heart and contributes to a better mechanistic understanding of A-to-I RNA editing in cardiac diseases.

Clin Res Cardiol (2022). https://doi.org/10.1007/s00392-022-02002-5
Characterization of Adenosine-to-Inosine RNA editing in the human heart.
K. E. Kokot¹, J. Kneuer¹, D. John², S. Rebs³, M. Möbius-Winkler¹, M. Müller⁴, M. Andritschke¹, S. Gaul¹, B. N. Sheikh⁵, J. Haas⁶, H. Thiele⁷, O. J. Müller⁸, S. Hille⁸, F. Leuschner⁶, S. Dimmeler², K. Streckfuß-Bömeke³, B. Meder⁶, U. Laufs¹, J.-N. Boeckel¹
¹Klinik und Poliklinik für Kardiologie, Universitätsklinikum Leipzig, Leipzig; ²Zentrum für Molekulare Medizin, Institut für Kardiovaskuläre Regeneration, Goethe Universität Frankfurt am Main, Frankfurt am Main; ³Institut für Pharmakologie und Toxikologie, Universitätsklinikum Würzburg, Würzburg; ⁴Agnes Wittenborg Institut für translationale Herz-Kreislaufforschung, Herz- und Diabeteszentrum NRW, Bad Oeynhausen; ⁵Helmholtz Institute for Metabolic, Obesity and Vascular Research (HI-MAG) of the Helmholtz Zentrum München at the University of Leipzig and University Hospital Leipzig, Leipzig, Germany, Leipzig; ⁶Klinik für Innere Med. III, Kardiologie, Angiologie u. Pneumologie, Universitätsklinikum Heidelberg, Heidelberg; ⁷Klinik für Innere Medizin/Kardiologie, Herzzentrum Leipzig - Universität Leipzig, Leipzig; ⁸Klinik für Innere Medizin III, Schwerpunkt Kardiologie und Angiologie, Universitätsklinikum Schleswig-Holstein, Kiel;
Background & Purpose: Adenosine-to-Inosine (A-to-I) RNA editing regulates the secondary structure, stability, and alternative splicing of RNAs. The editing enzymes ADAR1 and ADAR2 mediate this process and alterations in RNA editing have been associated with several human diseases. The extent of A-to-I RNA editing, the underlying mechanisms, and the potential consequences for the healthy and failing human heart remain unclear. Methods & Results: Using next generation sequencing, we analyzed RNA editing in human heart samples of heart failure (HF) patients (n=20) and controls (n=10). We identified A-to-I RNA editing as the major type of RNA editing in the human heart. In failing hearts, RNA editing, which was mainly occurring in intronic Alu elements of protein-coding genes, was reduced. In HF, we identified 166 upregulated circRNAs, with the majority showing reduced RNA editing in the host gene (88.3%). Consistently, we observed reduced ADAR2 protein levels in HF patients (-68.2%). Reduction of ADAR2 in vitro resulted in elevated circRNA levels as well as reduced cell size in induced pluripotent stem cell-derived cardiomyocytes (-19.2%). Using the top edited mRNA of AKAP13, we examined the formation of circRNAs in the human heart. We identified the interaction of ADAR2 with Alu elements, such as in flanking intronic regions of circAKAP13. A knockdown of ADAR2 in vitro led to upregulation of circAKAP13, which was in line with our observations in HF patients. Conclusion: Out data suggests that ADAR2 reduces the formation of double-stranded structures in AKAP13 pre-mRNA, thereby reducing the stability of Alu elements and circularization of the resulting circRNA. This study describes a novel role of RNA editing in alternative splicing of mRNAs regulating circRNA formation in the human heart and contributes to a better mechanistic understanding of A-to-I RNA editing in cardiac diseases.
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