Heart failure (HF) is a major cause of death, yet understanding of the underlying mechanisms is still limited and treatment options are few at best. This proposal focuses on the elastic protein titin, a recently revealed major player in heart failure, and addresses the basic biology of the poorly understood but clinically important A-band segment of the molecule, the mechanistic basis of its contribution to heart failure, and its potential as a therapeutic target. Titin, the largest known protein, comprises the third myofilament of muscle and spans from the Z-disk to the M-band of the sarcomere. Titin?s I-band region is known to function as a complex molecular spring that is a dominant contributor to passive myocardial stiffness. The A-band segment is the least well- studied part of titin and its functions are largely obscure. Yet several recent landmark sequencing studies in large groups of patients revealed that the A-band segment of titin is particularly important in familial dilated cardiomyopathy (DCM), a common type of heart failure with a prevalence of up to 1:250. Many of the DCM mutations in TTN are truncation variants (TTNtv), most of these are found in the A-band segment of titin, with a phenotype that appears to be more severe the closer the mutation occurs to titin?s C-terminus.
In Aim 1 we propose to critically examine the biology of the A-band segment of titin with a focus on where most disease- causing mutations are located, titin?s D-zone and C-zone. Mouse models were created for this purpose in which these regions within the A-band segment of titin were targeted. We propose to study in these models the ultrastructure of the A-band region of the sarcomere, transcript and protein expression (titin, cMyBP-C) and posttranslational-modification (PTMs), as well as heart function. Pilot studies with a novel C-zone deletion model reveal deranged thick filament length and the development of DCM, which provides a unique opportunity to study mechanisms of titin-based DCM. Additional models will be investigated in Aim 2 in which disease-causing TTNtvs were introduced in different regions of titin?s A-band segment. These models will be studied at baseline and when stressed; the severity of their phenotype will be studied as a function of the location of the TTNtv. In parallel, protein expression and structural and functional studies will be conducted on biopsies from DCM patients with TTNtvs.
Aim 3 will investigate the new concept in the titin field that TTN is a modifier gene in which disease severity can be explained by a combination of mutations in TTN and other genes. This will be studied by crossing the TTNtv models with mice that carry clinically relevant mutations in other sarcomeric genes. Finally, through excision of the mutated titin exons, we will test the therapeutic potential of exon skipping for treating titin-based DCM. With its basic science and translational goals and its in-depth and integrative approach, this application seeks to continue our track record of cutting edge titin research. Powerful techniques and novel mouse models are in place and pilot data are supportive of our guiding hypotheses. The proposed research is likely to enhance insights in the function of titin titin, including its potential as a therapeutic target.

Public Health Relevance

Heart failure is a major cause of death, yet understanding the underlying mechanisms is still limited and treatment options are few at best. Recent studies revealed that the gene that encodes the giant protein titin is a major cause of dilated cardiomyopathy (DCM) but the mechanistic basis is unknown. This will be addressed in this proposal in an in-depth and critical fashion using novel animal models and innovative approaches. Our long-term goal is to establish whether titin is a therapeutic target for DCM.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
5R01HL115988-06
Application #
9610710
Study Section
Special Emphasis Panel (ZRG1)
Program Officer
Adhikari, Bishow B
Project Start
2013-03-01
Project End
2021-11-30
Budget Start
2018-12-01
Budget End
2019-11-30
Support Year
6
Fiscal Year
2019
Total Cost
Indirect Cost
Name
University of Arizona
Department
Physiology
Type
Schools of Medicine
DUNS #
806345617
City
Tucson
State
AZ
Country
United States
Zip Code
85721
Jeong, Mark Y; Lin, Ying H; Wennersten, Sara A et al. (2018) Histone deacetylase activity governs diastolic dysfunction through a nongenomic mechanism. Sci Transl Med 10:
Ma, Weikang; Gong, Henry; Kiss, Balázs et al. (2018) Thick-Filament Extensibility in Intact Skeletal Muscle. Biophys J 115:1580-1588
Methawasin, Mei; Granzier, Henk (2018) Softening the Stressed Giant Titin in Diabetes Mellitus. Circ Res 123:315-317
Oates, Emily C; Jones, Kristi J; Donkervoort, Sandra et al. (2018) Congenital Titinopathy: Comprehensive characterization and pathogenic insights. Ann Neurol 83:1105-1124
Tonino, Paola; Kiss, Balazs; Strom, Josh et al. (2017) The giant protein titin regulates the length of the striated muscle thick filament. Nat Commun 8:1041
Methawasin, Mei; Granzier, Henk (2017) Response by Methawasin and Granzier to Letter Regarding Article, ""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 Frac Circulation 135:e681-e682
Kellermayer, Dalma; Smith 3rd, John E; Granzier, Henk (2017) Novex-3, the tiny titin of muscle. Biophys Rev 9:201-206
Bull, Mathew; Methawasin, Mei; Strom, Joshua et al. (2016) Alternative Splicing of Titin Restores Diastolic Function in an HFpEF-Like Genetic Murine Model (Ttn?IAjxn). Circ Res 119:764-72
Methawasin, Mei; Strom, Joshua G; Slater, Rebecca E et al. (2016) 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. Circulation 134:1085-1099
Pappas, Christopher T; Mayfield, Rachel M; Henderson, Christine et al. (2015) Knockout of Lmod2 results in shorter thin filaments followed by dilated cardiomyopathy and juvenile lethality. Proc Natl Acad Sci U S A 112:13573-8

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