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Updated: Jun 12, 2026
Investigating the Pathogenesis of MYH7 Mutation Gly823Glu in Familial Hypertrophic Cardiomyopathy using a Mouse Model
Published on: August 8, 2022
Familial hypertrophic cardiomyopathy can be characterized by a specific pattern of orientation fluctuations of actin
J Borejdo1, D Szczesna-Cordary, P Muthu
1Department of Molecular Biology and Immunology and Center for Commercialization of Fluorescence Technologies, University of North Texas Health Science Center, 3500 Camp Bowie Boulevard, Fort Worth, Texas 76107, USA. Julian.Borejdo@unthsc.edu
Insights
Familial hypertrophic cardiomyopathy (FHC) can be identified by observing actin molecule fluctuations in heart muscle. This new method distinguishes healthy hearts from those with R58Q and D166V mutations.
Area of Science:
- Cardiology
- Biophysics
- Molecular Biology
Background:
- Familial hypertrophic cardiomyopathy (FHC) is linked to mutations in the myosin regulatory light chain (RLC).
- Inefficient energy utilization in cardiac muscle is the suspected cause of FHC.
- Distinguishing between FHC phenotypes caused by specific RLC mutations (R58Q, D166V) is crucial for understanding disease mechanisms.
Purpose of the Study:
- To develop a simple method for characterizing FHC phenotypes caused by RLC mutations.
- To analyze actin molecule dynamics in working ex vivo heart myofibrils from healthy and FHC hearts.
- To differentiate between wild-type (WT) and FHC hearts using a novel biophysical approach.
Main Methods:
- Observing single actin molecules labeled with fluorescent dye in working ex vivo heart myofibrils.
- Utilizing confocal microscopy to analyze actin molecule orientation fluctuations within a small volume.
- Measuring polarized fluorescence intensity fluctuations and analyzing their probability distribution histograms.
Main Results:
- Histograms of actin molecule fluctuations in WT hearts (rigor) showed Gaussian curves.
- Histograms of contracting WT and FHC hearts exhibited peaked and asymmetric distributions, suggesting a multi-step contraction process.
- Statistically significant differences were observed in fluctuation histograms between contracting FHC (R58Q, D166V) and WT hearts.
Conclusions:
- A novel method using polarized fluorescence intensity fluctuations of sparsely labeled actin molecules can distinguish between healthy and FHC hearts.
- The observed differences in actin dynamics provide insights into the altered cardiac muscle function in FHC.
- This technique offers a potential diagnostic tool for identifying specific FHC mutations.
Abstract:
A single-point mutation in the gene encoding the ventricular myosin regulatory light chain (RLC) is sufficient to cause familial hypertrophic cardiomyopathy (FHC). Most likely, the underlying cause of this disease is an inefficient energy utilization by the mutated cardiac muscle. We set out to devise a simple method to characterize two FHC phenotypes caused by the R58Q and D166V mutations in RLC. The method is based on the ability to observe a few molecules of actin in working ex vivo heart myofibril. Actin is labeled with extremely diluted fluorescent dye, and a small volume within the I-band ( approximately 10(-16) L), containing on average three actin molecules, is observed by confocal microscopy. During muscle contraction, myosin cross-bridges deliver cyclic impulses to actin. As a result, actin molecules undergo periodic fluctuations of orientation. We measured these fluctuations by recording the parallel and perpendicular components of fluorescent light emitted by an actin-bound fluorophore. The histograms of fluctuations of fluorescent actin molecules in wild-type (WT) hearts in rigor were represented by perfect Gaussian curves. In contrast, histograms of contracting heart muscle were peaked and asymmetric, suggesting that contraction occurred in at least two steps. Furthermore, the differences between histograms of contracting FHC R58Q and D166V hearts versus corresponding contracting WT hearts were statistically significant. On the basis of our results, we suggest a simple new method of distinguishing between healthy and FHC R58Q and D166V hearts by analyzing the probability distribution of polarized fluorescence intensity fluctuations of sparsely labeled actin molecules.
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