Project Summary/Abstract
Heterozygous truncating variants in the essential sarcomere protein titin (TTNtv) are the most common genetic
cause of dilated cardiomyopathy (DCM), dilatation and contractile dysfunction of one or both ventricles of the
heart. DCM often progresses to heart failure (HF), a devastating disorder associated with high morbidity and
mortality including death in 50% within 5 years after the first HF hospitalization. While an exact mechanism of
how TTNtv leads to pathogenesis of DCM is still under investigation, insufficient amount of TTN protein caused
by TTNtv significantly disrupts cardiac physiology and contributes to development of DCM. To define therapeutic
strategies for DCM caused by dominant truncating variants in TTN (TTNtv DCM), Dr. Kim first developed an
efficient model system: isogenic wild-type (WT) and mutant human induced pluripotent stem cell-derived
cardiomyocytes (hiPSC-CMs) carrying heterozygous TTNtv. TTNtv/+ hiPSC-CMs have decreased TTN
expression and impaired contractility, similar to human patients with DCM. Additionally, by comparative analyses
of sequence conservation and transcriptional activation signals during cardiomyocyte differentiation of hiPSCs,
Dr. Kim identified a transcriptional enhancer of TTN, when deleted from WT hiPSC-CMs, markedly reduced TTN
expression and disrupted sarcomere formation and function. Furthermore, Dr. Kim’s preliminary work
demonstrated that transcriptional activity of the TTN enhancer can be increased by modifying its sequences and
by directing clustered regularly interspaced short palindromic repeats (CRISPR)-mediated activator to the TTN
locus in human cells. Based on these preliminary data, Dr. Kim formed the hypothesis that increasing TTN gene
expression by modulating endogenous TTN regulatory elements and by introducing exogenous transcriptional
activators will improve function of cardiomyocytes in TTNtv DCM model systems. In this proposal, Dr. Kim plans
to test her hypothesis in three specific aims. In Specific Aim 1, Dr. Kim will identify regulatory genetic elements
of TTN gene expression, which are currently unknown. In Specific Aim 2, Dr. Kim will modulate regulatory
elements of TTN via genome editing to augment TTN expression. In Specific Aim 3, Dr. Kim plans to assess
effects of increased TTN expression in TTNtv DCM model systems. This work will take place in the Division of
Cardiovascular Medicine at Brigham and Women’s Hospital (BWH), a core teaching hospital of Harvard Medical
School (HMS). Dr. Kim will perform the research under the mentorship of Dr. Christine Seidman, the Thomas W.
Smith Professor of Medicine at HMS and director of Cardiovascular Genetics Center at BWH, and Dr. Jonathan
Seidman, the Henrietta B. and Frederick H. Bugher Foundation Professor of Genetics at HMS. Dr. Kim’s goal is
to become an R01-funded independent clinician-scientist with expertise in genetics of cardiomyopathy. Dr. Kim
plans to use her K08 award to strengthen her skills and knowledge in gene regulation and genome editing, which
will serve as a foundation for her R01 application where she will apply genetic engineering technologies to
develop therapeutic strategies for DCM.