Computational simulation of hypertrophic cardiomyopathy mutations in Troponin I: Influence of increased myofilament calcium sensitivity on isometric force, ATPase and [Ca2+]i

2007 ◽  
Vol 40 (9) ◽  
pp. 2044-2052 ◽  
Author(s):  
Aya Kataoka ◽  
Carolyn Hemmer ◽  
P. Bryant Chase
Keyword(s):  
Hypertrophic Cardiomyopathy ◽  
Troponin I ◽  
Isometric Force ◽  
Computational Simulation ◽  
Calcium Sensitivity ◽  
Myofilament Calcium Sensitivity ◽  
Cardiomyopathy Mutations

Abstract 219: Histidine Substituted Cardiac Troponin I (a164h) Improves Survival And Protects Cardiac Contractility During Acute Hypoxia In The Aged Murine Heart.

Circulation ◽  
2007 ◽  
Vol 116 (suppl_16) ◽  
Author(s):  
Nathan Palpant ◽  
Sharlene Day ◽  
Kimber Converso ◽  
Joseph Metzger
Keyword(s):  
Cardiac Troponin ◽  
Troponin I ◽  
Acute Hypoxia ◽  
Cardiac Contractility ◽  
Systolic Pressure ◽  
Calcium Sensitivity ◽  
The Elderly ◽  
Cardiac Troponin I ◽  
Pump Failure ◽  
Myofilament Calcium Sensitivity

Contractile dysfunction associated with ischemia is a significant cause of morbidity and mortality particularly in the elderly. Strategies designed to protect the aged heart from ischemia-mediated pump failure are needed. We have generated transgenic (Tg) mice expressing a modified form of adult cardiac troponin I, the Ca ++ -activated molecular switch of the myofilament. Consonant with the fetal isoform, this transgene encodes a histidine substitution (A164H) in the critical switch domain of TnI thus increasing myofilament calcium sensitivity in a pH-dependent manner. We hypothesized that aged mice (24 months), intrinsically susceptible to myocardial dysfunction, would retain improved cardiac contractility at baseline and during an acute hypoxic challenge by means of myofilament-mediated calcium sensitization. Methods/Results: At baseline, by echocardiography, Tg hearts had increased systolic function, with a 26% higher mean ejection fraction compared to nontransgenic (Ntg) mice: 75 ± 3% [Tg: n = 13] vs. 63 ± 4% [Ntg: n = 12], P < 0.05, with no differences in diastolic function between the groups. To study the effects of acute hypoxia on cardiac hemodynamics mice underwent microconductance Millar catheterization while ventilated with 12% oxygen. Aged Tg mice had improved survival compared to Ntg mice: time to pump failure (65% of baseline peak systolic pressure) 11.59 ± 1.25 min. [Tg: n = 3] vs. 4.11 ± 1.90 min. [Ntg: n = 3], P < 0.05. After four minutes of hypoxia, Tg mice had markedly improved cardiac contractility compared to Ntg mice with increased stroke volume (30.05 ± 4.49 uL [Tg] vs. 13.23 ± 3.21 uL [Ntg], P < 0.05), end systolic pressure (106.09 ± 11.81 mmHg [Tg] vs. 64.49 ± 4.05 mmHg [Ntg], P < 0.05) and rate of positive left ventricular pressure development (12958.66 ± 2544.68 mmHg/sec [Tg] vs. 5717.00 ± 745.67 mmHg/sec [Ntg], P = 0.05). Conclusion: An alteration in myofilament calcium sensitivity via a pH-responsive histidine button in cardiac troponin I augments baseline heart function in Tg mice over their lifetime. During acute hypoxia, cTnI A164H improves survival in aged mice by maintaining cardiac contractility, and thus holds promise for the design of gene therapeutics to treat pump failure associated with acute ischemic events in the elderly.

High-throughput assessment of calcium sensitivity in skinned cardiac myocytes

2001 ◽  
Vol 281 (2) ◽  
pp. H969-H974 ◽  
Author(s):  
Chee Chew Lim ◽  
Michiel H. B. Helmes ◽  
Douglas B. Sawyer ◽  
Mohit Jain ◽  
Ronglih Liao
Keyword(s):  
Cardiac Myocytes ◽  
High Throughput ◽  
High Throughput Screening ◽  
Rapid Determination ◽  
Isometric Force ◽  
Calcium Sensitivity ◽  
Pharmacological Agents ◽  
Length Changes ◽  
Myofilament Calcium Sensitivity ◽  
High Degree

Isolated permeabilized cardiac myocytes have been used in the study of myofilament calcium sensitivity through measurement of the isometric force-pCa curve. Determining this force-pCa relationship in skinned myocytes is relatively expensive and carries a high degree of variability. We therefore attempted to establish an alternative high-throughput method to measure calcium sensitivity in cardiac myocytes. With the use of commercially available software that allows for precise measurement of sarcomere spacing, we measured sarcomere length changes in unloaded skinned cardiac myocytes over a range of calcium concentrations. With the use of this technique, we were able to accurately detect acute increases or decreases in myofilament calcium sensitivity after exposure to 10 mM caffeine or 5 mM 2,3-butanedione monoxime, respectively. This technique allows for the simple and rapid determination of myofilament calcium sensitivity in cardiac myocytes in a reproducible and inexpensive manner and could be used for high-throughput screening of pharmacological agents and/or transgenic mouse models for changes in myofilament calcium sensitivity.

Frequency-dependent acceleration of relaxation involves decreased myofilament calcium sensitivity

2007 ◽  
Vol 292 (5) ◽  
pp. H2212-H2219 ◽  
Author(s):  
Kenneth D. Varian ◽  
Paul M. L. Janssen
Keyword(s):  
Intracellular Calcium ◽  
Calcium Concentration ◽  
Troponin I ◽  
Zealand White Rabbit ◽  
Calcium Sensitivity ◽  
Intracellular Calcium Concentration ◽  
Calcium Handling ◽  
Force Frequency ◽  
Frequency Dependent ◽  
Myofilament Calcium Sensitivity

The force-frequency relationship is an intrinsic modulator of cardiac contractility and relaxation. Force of contraction increases with frequency, while simultaneously a frequency-dependent acceleration of relaxation occurs. While frequency dependency of calcium handling and sarcoplasmic reticulum calcium load have been well described, it remains unknown whether frequency-dependent changes in myofilament calcium sensitivity occur. We hypothesized that an increase in heart rate that results in acceleration of relaxation is accompanied by a proportional decrease in myofilament calcium sensitivity. To test our hypothesis, ultrathin right ventricular trabeculae were isolated from New Zealand White rabbit hearts and iontophorically loaded with the calcium indicator bis-fura 2. Twitch and intracellular calcium handling parameters were measured and showed a robust increase in twitch force, acceleration of relaxation, and rise in both diastolic and systolic intracellular calcium concentration with increased frequency. Steady-state force-intracellular calcium concentration relationships were measured at frequencies 1, 2, 3, and 4 Hz at 37°C using potassium-induced contractures. EC50 significantly and gradually increased with frequency, from 475 ± 64 nM at 1 Hz to 1,004 ± 142 nM at 4 Hz ( P < 0.05) and correlated with the corresponding changes in half relaxation time. No significant changes in maximal active force development or in the myofilament cooperativity coefficient were found. Myofilament protein phosphorylation was assessed using Pro-Q Diamond staining on protein gels of trabeculae frozen at either 1 or 4 Hz, revealing troponin I and myosin light chain-2 phosphorylation associated with the myofilament desensitization. We conclude that myofilament calcium sensitivity is substantially and significantly decreased at higher frequencies, playing a prominent role in frequency-dependent acceleration of relaxation.

scholarly journals Myofilament Calcium Sensitivity: Consequences of the Effective Concentration of Troponin I

2016 ◽  
Vol 7 ◽  
Author(s):  
Jalal K. Siddiqui ◽  
Svetlana B. Tikunova ◽  
Shane D. Walton ◽  
Bin Liu ◽  
Meredith Meyer ◽  
...  
Keyword(s):  
Troponin I ◽  
Calcium Sensitivity ◽  
Effective Concentration ◽  
Myofilament Calcium Sensitivity

Human-based computational and experimental investigation of disease mechanisms in mutation-specific hypertrophic cardiomyopathy

EP Europace ◽  
2021 ◽  
Vol 23 (Supplement_3) ◽  
Author(s):  
F Margara ◽  
Y Psaras ◽  
B Rodriguez ◽  
CN Toepfer ◽  
A Bueno-Orovio
Keyword(s):  
Hypertrophic Cardiomyopathy ◽  
In Silico ◽  
Calcium Transient ◽  
Calcium Sensitivity ◽  
Human Cardiomyocytes ◽  
Calcium Affinity ◽  
Myofilament Calcium Sensitivity ◽  
Vitro Data ◽  
In Vitro Data

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – EU funding. Main funding source(s): European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement 764738. British Heart Foundation Intermediate Basic Science Fellowship (FS/17/22/32644). Background The pathogenic TNNI3R21C/+ variant causes malignant hypertrophic cardiomyopathy (HCM) with high incidence of sudden cardiac death, even in individuals absent of hypertrophy. There is evidence to support a known biophysical defect in the protein, yet the cellular mechanisms that precipitate adverse clinical outcomes remain unclear. Purpose We aim to computationally model and map the TNNI3R21C/+ cellular phenotype observed in induced pluripotent stem cell derived cardiomyocytes (iPSC-CMs) to human disease, thereby explaining the key mechanisms driving HCM in TNNI3R21C/+ variant carriers.  Methods Wild-type (WT) and TNNI3R21C/+ iPSC-CMs were characterised by calcium transient analysis and direct sarcomere tracking to assess cellular contraction and relaxation. In-vitro data was used to inform the in-silico modelling of human cardiomyocytes. We constructed an in-silico population of WT adult cardiomyocytes and used it to transform the in-vitro data into corresponding adult phenotypes by means of a novel iPSC-to-adult data mapping. We tested the hypothesis that the abnormal TNNI3R21C/+ phenotype observed in iPSC-CMs would be explained by alterations in calcium affinity of troponin and increased myofilament calcium sensitivity.  Results Analysis of in-vitro iPSC-CM data showed that TNNI3R21C/+ cells exhibit increased contractility with slowed relaxation when compared to WT. They also exhibited a faster rise in the calcium transient with a slowed calcium decay in comparison to WT. The in-silico adult TNNI3R21C/+ phenotype from the iPSC-to-adult mapping replicated the abnormalities observed in iPSC-CMs. The WT in-silico population accurately covered the ranges of electromechanical biomarkers providing a representative cohort of physiological variability. The TNNI3R21C/+ calcium phenotype could be recovered by our in-silico mutant models. Simulation results suggest that calcium abnormalities in TNNI3R21C/+ are a direct consequence of abnormal calcium buffering by thin filaments, mediated by increases in calcium affinity of troponin and myofilament calcium sensitivity. The TNNI3R21C/+ phenotype could not be recovered if these two factors were considered in isolation. Corresponding contractility analyses of in-silico models showed that the calcium level changes caused by the TNNI3R21C/+ phenotype are associated with hypercontractility and diastolic dysfunction, well-known hallmarks of HCM, which were also observed in the iPSC-CM model of disease. Conclusions This study showcases human-based computational and experimental methodologies that unearth direct mechanistic explanations of phenotypes driven by the TNNI3R21C/+ HCM variant. We show that the TNNI3R21C/+ HCM-causing mutation exhibits multifactorial remodelling of troponin calcium affinity and myofilament calcium sensitivity. Unearthing mechanistic pathways in mutation-specific HCM will be key to develop effective pharmacological interventions for a wide variety of understudied variants.

scholarly journals Mavacamten rescues increased myofilament calcium sensitivity and dysregulation of Ca2+ flux caused by thin filament hypertrophic cardiomyopathy mutations

2020 ◽  
Vol 318 (3) ◽  
pp. H715-H722 ◽  
Author(s):  
Alexander J. Sparrow ◽  
Hugh Watkins ◽  
Matthew J. Daniels ◽  
Charles Redwood ◽  
Paul Robinson
Keyword(s):  
Hypertrophic Cardiomyopathy ◽  
Cardiac Troponin ◽  
Thin Filament ◽  
Troponin I ◽  
Troponin T ◽  
Thick Filament ◽  
Calcium Sensitivity ◽  
Calcium Handling ◽  
Cellular Models

Thin filament hypertrophic cardiomyopathy (HCM) mutations increase myofilament Ca2+ sensitivity and alter Ca2+ handling and buffering. The myosin inhibitor mavacamten reverses the increased contractility caused by HCM thick filament mutations, and we here test its effect on HCM thin filament mutations where the mode of action is not known. Mavacamten (250 nM) partially reversed the increased Ca2+ sensitivity caused by HCM mutations Cardiac troponin T (cTnT) R92Q, and cardiac troponin I (cTnI) R145G in in vitro ATPase assays. The effect of mavacamten was also analyzed in cardiomyocyte models of cTnT R92Q and cTnI R145G containing cytoplasmic and myofilament specific Ca2+ sensors. While mavacamten rescued the hypercontracted basal sarcomere length, the reduced fractional shortening did not improve with mavacamten. Both mutations caused an increase in peak systolic Ca2+ detected at the myofilament, and this was completely rescued by 250 nM mavacamten. Systolic Ca2+ detected by the cytoplasmic sensor was also reduced by mavacamten treatment, although only R145G increased cytoplasmic Ca2+. There was also a reversal of Ca2+ decay time prolongation caused by both mutations at the myofilament but not in the cytoplasm. We thus show that mavacamten reverses some of the Ca2+-sensitive molecular and cellular changes caused by the HCM mutations, particularly altered Ca2+ flux at the myofilament. The reduction of peak systolic Ca2+ as a consequence of mavacamten treatment represents a novel mechanism by which the compound is able to reduce contractility, working synergistically with its direct effect on the myosin motor. NEW & NOTEWORTHY Mavacamten, a myosin inhibitor, is currently in phase-3 clinical trials as a pharmacotherapy for hypertrophic cardiomyopathy (HCM). Its efficacy in HCM caused by mutations in thin filament proteins is not known. We show in reductionist and cellular models that mavacamten can rescue the effects of thin filament mutations on calcium sensitivity and calcium handling although it only partially rescues the contractile cellular phenotype and, in some cases, exacerbates the effect of the mutation.

scholarly journals Increased myofilament calcium sensitivity is associated with decreased cardiac troponin I phosphorylation in the diabetic rat heart

2021 ◽  
Author(s):  
Angela C. Greenman ◽  
Gary M. Diffee ◽  
Amelia S. Power ◽  
Gerard T. Wilkins ◽  
Olivia M. S. Gold ◽  
...  
Keyword(s):  
Cardiac Troponin ◽  
Rat Heart ◽  
Troponin I ◽  
Calcium Sensitivity ◽  
Cardiac Troponin I ◽  
Diabetic Rat ◽  
Myofilament Calcium Sensitivity

Rescue of tropomyosin-induced familial hypertrophic cardiomyopathy mice by transgenesis

2007 ◽  
Vol 293 (2) ◽  
pp. H949-H958 ◽  
Author(s):  
Ganapathy Jagatheesan ◽  
Sudarsan Rajan ◽  
Natalia Petrashevskaya ◽  
Arnold Schwartz ◽  
Greg Boivin ◽  
...  
Keyword(s):  
Hypertrophic Cardiomyopathy ◽  
Thin Filament ◽  
Calcium Sensitivity ◽  
Contractile Proteins ◽  
Familial Hypertrophic Cardiomyopathy ◽  
Physiological Effects ◽  
Calcium Response ◽  
Normal Morphology ◽  
Filament Protein ◽  
Myofilament Calcium Sensitivity

Familial hypertrophic cardiomyopathy (FHC) is a disease caused by mutations in contractile proteins of the sarcomere. Our laboratory developed a mouse model of FHC with a mutation in the thin filament protein α-tropomyosin (TM) at amino acid 180 (Glu180Gly). The hearts of these mice exhibit dramatic systolic and diastolic dysfunction, and their myofilaments demonstrate increased calcium sensitivity. The mice also develop severe cardiac hypertrophy, with death ensuing by 6 mo. In an attempt to normalize calcium sensitivity in the cardiomyofilaments of the hypertrophic mice, we generated a chimeric α-/β-TM protein that decreases calcium sensitivity in transgenic mouse cardiac myofilaments. By mating mice from these two models together, we tested the hypothesis that an attenuation of myofilament calcium sensitivity would modulate the severe physiological and pathological consequences of the FHC mutation. These double-transgenic mice “rescue” the hypertrophic phenotype by exhibiting a normal morphology with no pathological abnormalities. Physiological analyses of these rescued mice show improved cardiac function and normal myofilament calcium sensitivity. These results demonstrate that alterations in calcium response by modification of contractile proteins can prevent the pathological and physiological effects of this disease.

Familial hypertrophic cardiomyopathy mutations in troponin I (K183Δ, G203S, K206Q) enhance filament sliding

2003 ◽  
Vol 14 (2) ◽  
pp. 117-128 ◽  
Author(s):  
Jan Köhler ◽  
Ying Chen ◽  
Bernhard Brenner ◽  
Albert M. Gordon ◽  
Theresia Kraft ◽  
...  
Keyword(s):  
Hypertrophic Cardiomyopathy ◽  
Troponin I ◽  
Isometric Force ◽  
Familial Hypertrophic Cardiomyopathy ◽  
In Vitro Assays ◽  
Maximum Speed ◽  
Exchange Method ◽  
In Vitro Motility ◽  
Maximum Isometric Force

A major cause of familial hypertrophic cardiomyopathy (FHC) is dominant mutations in cardiac sarcomeric genes. Linkage studies identified FHC-related mutations in the COOH terminus of cardiac troponin I (cTnI), a region with unknown function in Ca2+ regulation of the heart. Using in vitro assays with recombinant rat troponin subunits, we tested the hypothesis that mutations K183Δ, G203S, and K206Q in cTnI affect Ca2+ regulation. All three mutants enhanced Ca2+ sensitivity and maximum speed ( smax) of filament sliding of in vitro motility assays. Enhanced smax (pCa 5) was observed with rabbit skeletal and rat cardiac (α-MHC or β-MHC) heavy meromyosin (HMM). We developed a passive exchange method for replacing endogenous cTn in permeabilized rat cardiac trabeculae. Ca2+ sensitivity and maximum isometric force did not differ between preparations exchanged with cTn(cTnI,K206Q) or wild-type cTn. In both trabeculae and motility assays, there was no loss of inhibition at pCa 9. These results are consistent with COOH terminus of TnI modulating actomyosin kinetics during unloaded sliding, but not during isometric force generation, and implicate enhanced cross-bridge cycling in the cTnI-related pathway(s) to hypertrophy.

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