# The mechanisms of cardiac thin filament regulation in health and disease.

> **NIH NIH R01** · OLD DOMINION UNIVERSITY · 2024 · $150,980

## Abstract

Project Summary
Cardiomyopathies are the most common genetic cardiovascular disease worldwide. The presence of cardiac
troponin variants accounts for at least 15% of all familial cardiomyopathy cases. Cardiac muscle contraction is
regulated by free intracellular Ca2+ concentration via two thin filament regulatory proteins – tropomyosin and
troponin complex. Ca2+ binding to troponin displaces tropomyosin from myosin-binding sites and allows formation
of myosin cross-bridges, which on their own contribute to thin filament activation. Troponin complex is composed
of Ca2+ sensing troponin C, actin-binding troponin I, and Tm-bound troponin T. For decades, the helical approach
to electron microscopy reconstruction of the thin filament eliminated information on the structure of the Tn
complex. Hence, the complex interactions among components of the thin filament remained unknown. We
developed cryo-EM non-helical algorithm to the reconstruction of native cardiac thin filaments to reveal the
structure of the whole troponin complex at physiological Ca2+ levels. We show that the thin filament is comprised
of an array of Ca2+-free and Ca2+-bound non-equivalent troponin complexes with short-range cooperativity
between adjacent units. Troponin variants associated with inherited cardiomyopathies affect thin filament Ca2+-
dependent activation. We hypothesize that: (1) dilated (DCM) or hypertrophic (HCM) cardiomyopathy variants in
troponin affect thin filament regulation by: (a) altering the equilibrium between Ca2+-free and Ca2+-bound troponin
complexes via conformational changes in Ca2+-sensing troponin C unit; and/or (b) altering the distribution of
Ca2+-free and Ca2+-bound troponin complexes by changing communication between the adjacent troponins
along and across the thin filament. To test our hypothesis we chose 4 strategically located mutations. In Aim 1
we will utilize pathogenic variants in troponin C located in distal parts of Ca2+-sensing troponin N-lobe to evaluate
how they affect the equilibrium between Ca2+-free and Ca2+-bound troponin complexes, and if they affect
communication between troponin units that may curb activating effect of rigor myosin-S1. In Aim 2 we will focus
on highly penetrant pathogenic variants in troponin T located in N-terminus of troponin T, which stabilizes the
interaction between tropomyosin cables belonging to adjacent troponin units. We will evaluate how these
mutations affect the communication between neighboring troponins and activation by myosin-S1. To reveal how
distal parts of the troponin complex (Ca2+ sensing troponin C and N-terminus of troponin T) communicate, we
will use a Ca2+ sensitizer, which binds to troponin C to revert effects of a troponin T variant. Our multidisciplinary,
multi-PI approach with collective expertise in structural, functional and computational methods will reveal how
the complex interactions between components of the thin filament make heartbeats possible. Successful
execution of the aims ...

## Key facts

- **NIH application ID:** 11123745
- **Project number:** 6R01HL160966-04
- **Recipient organization:** OLD DOMINION UNIVERSITY
- **Principal Investigator:** P. Bryant Chase
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $150,980
- **Award type:** 6
- **Project period:** 2022-01-01 → 2025-12-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/11123745

## Citation

> US National Institutes of Health, RePORTER application 11123745, The mechanisms of cardiac thin filament regulation in health and disease. (6R01HL160966-04). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/11123745. Licensed CC0.

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