title: Experimentally Increasing the Compliance of Titin Through RNA Binding Motif-20 (RBM20) Inhibition Improves Diastolic Function In a Mouse Model of Heart Failure With Preserved Ejection Fraction.
abstract: BACKGROUND
  Left ventricular (LV) stiffening contributes to heart failure with preserved ejection fraction (HFpEF), a syndrome with no effective treatment options. Increasing the compliance of titin in the heart has become possible recently through inhibition of the splicing factor RNA binding motif-20. Here, we investigated the effects of increasing the compliance of titin in mice with diastolic dysfunction.
  
  
  METHODS
  Mice in which the RNA recognition motif (RRM) of one of the RNA binding motif-20 alleles was floxed and that expressed the MerCreMer transgene under control of the αMHC promoter (referred to as cRbm20ΔRRMmice) were used. Mice underwent transverse aortic constriction (TAC) surgery and deoxycorticosterone acetate (DOCA) pellet implantation. RRM deletion in adult mice was triggered by injecting raloxifene (cRbm20ΔRRM-raloxifene), with dimethyl sulfoxide (DMSO)-injected mice (cRbm20ΔRRM-DMSO) as the control. Diastolic function was investigated with echocardiography and pressure-volume analysis; passive stiffness was studied in LV muscle strips and isolated cardiac myocytes before and after elimination of titin-based stiffness. Treadmill exercise performance was also studied. Titin isoform expression was evaluated with agarose gels.
  
  
  RESULTS
  cRbm20ΔRRM-raloxifene mice expressed large titins in the hearts, called supercompliant titin (N2BAsc), which, within 3 weeks after raloxifene injection, made up ≈45% of total titin. TAC/DOCA cRbm20ΔRRM-DMSO mice developed LV hypertrophy and a marked increase in LV chamber stiffness as shown by both pressure-volume analysis and echocardiography. LV chamber stiffness was normalized in TAC/DOCA cRbm20ΔRRM-raloxifene mice that expressed N2BAsc. Passive stiffness measurements on muscle strips isolated from the LV free wall revealed that extracellular matrix stiffness was equally increased in both groups of TAC/DOCA mice (cRbm20ΔRRM-DMSO and cRbm20ΔRRM-raloxifene). However, titin-based muscle stiffness was reduced in the mice that expressed N2BAsc (TAC/DOCAcRbm20ΔRRM-raloxifene). Exercise testing demonstrated significant improvement in exercise tolerance in TAC/DOCA mice that expressed N2BAsc.
  
  
  CONCLUSIONS
  Inhibition of the RNA binding motif-20-based titin splicing system upregulates compliant titins, which improves diastolic function and exercise tolerance in the TAC/DOCA model. Titin holds promise as a therapeutic target for heart failure with preserved ejection fraction.
authors.affiliation: From Department of Cellular and Molecular Medicine and Sarver Molecular Cardiovascular Research Program, University of Arizona, Tucson.
authors.forename: Mei
authors.initials: M
authors.lastname: Methawasin
authors.affiliation: From Department of Cellular and Molecular Medicine and Sarver Molecular Cardiovascular Research Program, University of Arizona, Tucson.
authors.forename: Joshua G
authors.initials: JG
authors.lastname: Strom
authors.affiliation: From Department of Cellular and Molecular Medicine and Sarver Molecular Cardiovascular Research Program, University of Arizona, Tucson.
authors.forename: Rebecca E
authors.initials: RE
authors.lastname: Slater
authors.affiliation: From Department of Cellular and Molecular Medicine and Sarver Molecular Cardiovascular Research Program, University of Arizona, Tucson.
authors.forename: Vanessa
authors.initials: V
authors.lastname: Fernandez
authors.affiliation: From Department of Cellular and Molecular Medicine and Sarver Molecular Cardiovascular Research Program, University of Arizona, Tucson.
authors.forename: Chandra
authors.initials: C
authors.lastname: Saripalli
authors.affiliation: From Department of Cellular and Molecular Medicine and Sarver Molecular Cardiovascular Research Program, University of Arizona, Tucson. granzier@email.arizona.edu.
authors.forename: Henk
authors.initials: H
authors.lastname: Granzier
mesh_terms: D000818:Animals; D003187:Compliance; D064211:Connectin / Q000502:physiology; D003971:Diastole / Q000235:genetics* / Q000502:physiology; D004195:Disease Models, Animal; D017079:Exercise Tolerance / Q000235:genetics*; D006333:Heart Failure / Q000235:genetics* / Q000378:metabolism / Q000503:physiopathology; D017379:Hypertrophy, Left Ventricular / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D000071376:RNA-Binding Motifs / Q000235:genetics; D016601:RNA-Binding Proteins / Q000235:genetics*; D013318:Stroke Volume / Q000502:physiology; D016277:Ventricular Function, Left / Q000235:genetics* / Q000502:physiology
chemical_list: D064211:Connectin; C584322:RBM20 protein, mouse; D016601:RNA-Binding Proteins
keywords: compliance; diastole; heart failure