M-class hypertrophic cardiomyopathy cardiac actin mutations increase calcium sensitivity of regulated thin filaments

2019 ◽  
Vol 519 (1) ◽  
pp. 148-152 ◽  
Author(s):  
Grace Zi Teng ◽  
Zeeshan Shaikh ◽  
Haidun Liu ◽  
John F. Dawson
Keyword(s):  
Hypertrophic Cardiomyopathy ◽  
Calcium Sensitivity ◽  
Thin Filaments ◽  
Cardiac Actin

scholarly journals Facilitated Cross-Bridge Interactions with Thin Filaments by Familial Hypertrophic Cardiomyopathy Mutations inα-Tropomyosin

2011 ◽  
Vol 2011 ◽  
pp. 1-12 ◽  
Author(s):  
Fang Wang ◽  
Nicolas M. Brunet ◽  
Justin R. Grubich ◽  
Ewa A. Bienkiewicz ◽  
Thomas M. Asbury ◽  
...  
Keyword(s):  
Hypertrophic Cardiomyopathy ◽  
Molecular Mechanisms ◽  
Helical Structure ◽  
Familial Hypertrophic Cardiomyopathy ◽  
Maximum Speed ◽  
Sliding Speed ◽  
Thin Filaments ◽  
In Vitro Motility ◽  
Cardiac Sarcomeres

Familial hypertrophic cardiomyopathy (FHC) is a disease of cardiac sarcomeres. To identify molecular mechanisms underlying FHC pathology, functional and structural differences in three FHC-related mutations in recombinantα-Tm (V95A, D175N, and E180G) were characterized using both conventional and modified in vitro motility assays and circular dichroism spectroscopy. Mutant Tm's exhibited reducedα-helical structure and increased unordered structure. When thin filaments were fully occupied by regulatory proteins, little or no motion was detected at pCa 9, and maximum speed (pCa 5) was similar for all tropomyosins. Ca2+-responsiveness of filament sliding speed was increased either by increasedpCa50(V95A), reduced cooperativityn(D175N), or both (E180G). When temperature was increased, thin filaments with E180G exhibited dysregulation at temperatures ~10°C lower, and much closer to body temperature, than WT. When HMM density was reduced, thin filaments with D175N required fewer motors to initiate sliding or achieve maximum sliding speed.

Modulation of Striated Muscle Function is Reflected by Thick Filament Structure.

2000 ◽  
Vol 6 (S2) ◽  
pp. 76-77
Author(s):  
Rhea J.C. Levine ◽  
Irina Kulakovskaya ◽  
H. Lee Sweeney ◽  
Saul Winegrad ◽  
Zhaohui Yang
Keyword(s):  
Structural Changes ◽  
Striated Muscle ◽  
Contractile Function ◽  
Thick Filament ◽  
Calcium Sensitivity ◽  
Thin Filaments ◽  
Calcium Dependent ◽  
Regulation Of Activity ◽  
Myosin Binding ◽  
Tissue Specimens

In mammalian skeletal and cardiac muscles, regulation of activity occurs when calcium binds to troponin on thin filaments, which ultimately results in exposure of myosin-binding sites on actin. However, modulation of contractile function, affecting such parameters as calcium sensitivity, the rate of rise of tension, the expression of maximum tension and/or the rate of onset of relaxation, is also calcium dependent. It is, in part, a property of the thick filament itself and its component myosin and/or accessory proteins. Among these are phosphorylation of myosin regulatory light chains or light chain 2 (RLCs; LC2) and in cardiac, but not skeletal fibers, phosphorylation of myosin-binding protein C (MyBP-C).Gentle methods of separating thick filaments from small tissue specimens, subjected to various experimental protocols designed to explore the functional parameters of such modulatory activities, allow examination of any accompanying structural changes.

Hypertrophic cardiomyopathy-related β-myosin mutations cause highly variable calcium sensitivity with functional imbalances among individual muscle cells

2005 ◽  
Vol 288 (3) ◽  
pp. H1242-H1251 ◽  
Author(s):  
Sebastian E. Kirschner ◽  
Edgar Becker ◽  
Massimo Antognozzi ◽  
Hans-Peter Kubis ◽  
Antonio Francino ◽  
...  
Keyword(s):  
Hypertrophic Cardiomyopathy ◽  
Muscle Cells ◽  
Calcium Sensitivity ◽  
Cardiac Myosin ◽  
Adaptive Responses ◽  
Selective Treatment ◽  
Normal Response ◽  
Individual Muscle ◽  
Marked Variability ◽  
Slow Twitch

Disease-causing mutations in cardiac myosin heavy chain (β-MHC) are identified in about one-third of families with hypertrophic cardiomyopathy (HCM). The effect of myosin mutations on calcium sensitivity of the myofilaments, however, is largely unknown. Because normal and mutant cardiac MHC are also expressed in slow-twitch skeletal muscle, which is more easily accessible and less subject to the adaptive responses seen in myocardium, we compared the calcium sensitivity (pCa50) and the steepness of force-pCa relations (cooperativity) of single soleus muscle fibers from healthy individuals and from HCM patients of three families with selected myosin mutations. Fibers with the Arg723Gly and Arg719Trp mutations showed a decrease in mean pCa50, whereas those with the Ile736Thr mutation showed slightly increased mean pCa50 with higher active forces at low calcium concentrations and residual active force even under relaxing conditions. In addition, there was a marked variability in pCa50 between individual fibers carrying the same mutation ranging from an almost normal response to highly significant differences that were not observed in controls. While changes in mean pCa50 may suggest specific pharmacological treatment (e.g., calcium antagonists), the observed large functional variability among individual muscle cells might negate such selective treatment. More importantly, the variability in pCa50 from fiber to fiber is likely to cause imbalances in force generation and be the primary cause for contractile dysfunction and development of disarray in the myocardium.

scholarly journals Cardiac actin changes in the actomyosin interface have different effects on myosin duty ratio

2018 ◽  
Vol 96 (1) ◽  
pp. 26-31 ◽  
Author(s):  
Haidun Liu ◽  
Mary Henein ◽  
Maria Anillo ◽  
John F. Dawson
Keyword(s):  
Cardiovascular Disease ◽  
Hypertrophic Cardiomyopathy ◽  
Left Ventricle ◽  
Duty Ratio ◽  
Actomyosin Atpase ◽  
In Vitro Motility ◽  
Cardiac Actin ◽  
Myosin Binding ◽  
Cardiac Sarcomeres

Hypertrophic cardiomyopathy (HCM) is an inherited cardiovascular disease (CD) that commonly causes an increased size of cardiomyocytes in the left ventricle. The proteins myosin and actin interact in the myocardium to produce contraction through the actomyosin ATPase cycle. The duty ratio (r) of myosin is the proportion of the actomyosin ATPase cycle that myosin is bound to actin and does work. A common hypothesis is that HCM mutations increase contraction in cardiac sarcomeres; however, the available data are not clear on this connection. Based on previous work with human α-cardiac actin (ACTC), we hypothesize that HCM-linked ACTC variants with alterations near the myosin binding site have an increased r, producing more force. Myosin duty ratios using human ACTC variant proteins were calculated with myosin ATPase activity and in-vitro motility data. We found no consistent changes in the duty ratio of the ACTC variants, suggesting that other factors are involved in the development of HCM when ACTC variants are present.

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 Micromechanical Thermal Assays of Ca2+-Regulated Thin-Filament Function and Modulation by Hypertrophic Cardiomyopathy Mutants of Human Cardiac Troponin

2012 ◽  
Vol 2012 ◽  
pp. 1-13 ◽  
Author(s):  
Nicolas M. Brunet ◽  
Goran Mihajlović ◽  
Khaled Aledealat ◽  
Fang Wang ◽  
Peng Xiong ◽  
...  
Keyword(s):  
Hypertrophic Cardiomyopathy ◽  
Temperature Regime ◽  
Cardiac Troponin ◽  
Thin Filament ◽  
Familial Hypertrophic Cardiomyopathy ◽  
High Activation ◽  
Thin Filaments ◽  
Wide Range ◽  
Bridge Number ◽  
Regulated Thin Filament

Microfabricated thermoelectric controllers can be employed to investigate mechanisms underlying myosin-driven sliding of Ca2+-regulated actin and disease-associated mutations in myofilament proteins. Specifically, we examined actin filament sliding—with or without human cardiac troponin (Tn) and α-tropomyosin (Tm)—propelled by rabbit skeletal heavy meromyosin, when temperature was varied continuously over a wide range (∼20–63C°). At the upper end of this temperature range, reversible dysregulation of thin filaments occurred at pCa 9 and 5; actomyosin function was unaffected. Tn-Tm enhanced sliding speed at pCa 5 and increased a transition temperature (Tt) between a high activation energy (Ea) but low temperature regime and a lowEabut high temperature regime. This was modulated by factors that alter cross-bridge number and kinetics. Three familial hypertrophic cardiomyopathy (FHC) mutations, cTnI R145G, cTnI K206Q, and cTnT R278C, cause dysregulation at temperatures ∼5–8C°lower; the latter two increased speed at pCa 5 at all temperatures.

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