scholarly journals Why we need to understand the mechanics of developing cardiac sarcomeres in humans

2016 ◽  
Vol 594 (2) ◽  
pp. 255-255 ◽  
Author(s):  
R. John Solaro
Keyword(s):  
Cardiac Sarcomeres

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.

Ca2+-Dependence of Passive Properties of Cardiac Sarcomeres

2000 ◽  
pp. 353-370 ◽  
Author(s):  
Bruno D. Stuyvers ◽  
Masahito Miura ◽  
Henk E. D. J. ter Keurs
Keyword(s):  
Cardiac Sarcomeres

scholarly journals I-Band Titin in Cardiac Muscle Is a Three-Element Molecular Spring and Is Critical for Maintaining Thin Filament Structure

1999 ◽  
Vol 146 (3) ◽  
pp. 631-644 ◽  
Author(s):  
Wolfgang A. Linke ◽  
Diane E. Rudy ◽  
Thomas Centner ◽  
Mathias Gautel ◽  
Christian Witt ◽  
...  
Keyword(s):  
Cardiac Muscle ◽  
Thin Filament ◽  
Thick Filament ◽  
Cardiac Cells ◽  
Elastic Behavior ◽  
Unique Region ◽  
Cardiac Titin ◽  
Filament Structure ◽  
Pevk Domain ◽  
Cardiac Sarcomeres

In cardiac muscle, the giant protein titin exists in different length isoforms expressed in the molecule's I-band region. Both isoforms, termed N2-A and N2-B, comprise stretches of Ig-like modules separated by the PEVK domain. Central I-band titin also contains isoform-specific Ig-motifs and nonmodular sequences, notably a longer insertion in N2-B. We investigated the elastic behavior of the I-band isoforms by using single-myofibril mechanics, immunofluorescence microscopy, and immunoelectron microscopy of rabbit cardiac sarcomeres stained with sequence-assigned antibodies. Moreover, we overexpressed constructs from the N2-B region in chick cardiac cells to search for possible structural properties of this cardiac-specific segment. We found that cardiac titin contains three distinct elastic elements: poly-Ig regions, the PEVK domain, and the N2-B sequence insertion, which extends ∼60 nm at high physiological stretch. Recruitment of all three elements allows cardiac titin to extend fully reversibly at physiological sarcomere lengths, without the need to unfold Ig domains. Overexpressing the entire N2-B region or its NH2 terminus in cardiac myocytes greatly disrupted thin filament, but not thick filament structure. Our results strongly suggest that the NH2-terminal N2-B domains are necessary to stabilize thin filament integrity. N2-B–titin emerges as a unique region critical for both reversible extensibility and structural maintenance of cardiac myofibrils.

scholarly journals Mono- and Biallelic Protein-Truncating Variants in Alpha-Actinin 2 Cause Cardiomyopathy Through Distinct Mechanisms

2021 ◽  
Author(s):  
Malene E. Lindholm ◽  
David Jimenez-Morales ◽  
Han Zhu ◽  
Kinya Seo ◽  
David Amar ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Structural Changes ◽  
Affinity Purification ◽  
Protein Protein Interaction ◽  
Cellular Hypertrophy ◽  
C Terminus ◽  
Associated Proteins ◽  
Cardiac Sarcomeres ◽  
Affinity Purification Mass Spectrometry

Background: ACTN2 (alpha-actinin 2) anchors actin within cardiac sarcomeres. The mechanisms linking ACTN2 mutations to myocardial disease phenotypes are unknown. Here, we characterize patients with novel ACTN2 mutations to reveal insights into the physiological function of ACTN2. Methods: Patients harboring ACTN2 protein-truncating variants were identified using a custom mutation pipeline. In patient-derived iPSC-cardiomyocytes, we investigated transcriptional profiles using RNA sequencing, contractile properties using video-based edge detection, and cellular hypertrophy using immunohistochemistry. Structural changes were analyzed through electron microscopy. For mechanistic studies, we used coimmunoprecipitation for ACTN2, followed by mass-spectrometry to investigate protein-protein interaction, and protein tagging followed by confocal microscopy to investigate introduction of truncated ACTN2 into the sarcomeres. Results: Patient-derived iPSC-cardiomyocytes were hypertrophic, displayed sarcomeric structural disarray, impaired contractility, and aberrant Ca 2+ -signaling. In heterozygous indel cells, the truncated protein incorporates into cardiac sarcomeres, leading to aberrant Z-disc ultrastructure. In homozygous stop-gain cells, affinity-purification mass-spectrometry reveals an intricate ACTN2 interactome with sarcomere and sarcolemma-associated proteins. Loss of the C-terminus of ACTN2 disrupts interaction with ACTN1 and GJA1, 2 sarcolemma-associated proteins, which may contribute to the clinical arrhythmic and relaxation defects. The causality of the stop-gain mutation was verified using CRISPR-Cas9 gene editing. Conclusions: Together, these data advance our understanding of the role of ACTN2 in the human heart and establish recessive inheritance of ACTN2 truncation as causative of disease.

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.

scholarly journals Regulatory mechanism of length-dependent activation in skinned porcine ventricular muscle: role of thin filament cooperative activation in the Frank-Starling relation

2010 ◽  
Vol 136 (4) ◽  
pp. 469-482 ◽  
Author(s):  
Takako Terui ◽  
Yuta Shimamoto ◽  
Mitsunori Yamane ◽  
Fuyu Kobirumaki ◽  
Iwao Ohtsuki ◽  
...  
Keyword(s):  
Thin Filament ◽  
Linear Regression Analysis ◽  
Left Ventricular ◽  
Active Force ◽  
Force Measurements ◽  
Systematic Understanding ◽  
Cardiac Sarcomeres ◽  
Length Dependent Activation ◽  
Cooperative Activation

Cardiac sarcomeres produce greater active force in response to stretch, forming the basis of the Frank-Starling mechanism of the heart. The purpose of this study was to provide the systematic understanding of length-dependent activation by investigating experimentally and mathematically how the thin filament “on–off” switching mechanism is involved in its regulation. Porcine left ventricular muscles were skinned, and force measurements were performed at short (1.9 µm) and long (2.3 µm) sarcomere lengths. We found that 3 mM MgADP increased Ca2+ sensitivity of force and the rate of rise of active force, consistent with the increase in thin filament cooperative activation. MgADP attenuated length-dependent activation with and without thin filament reconstitution with the fast skeletal troponin complex (sTn). Conversely, 20 mM of inorganic phosphate (Pi) decreased Ca2+ sensitivity of force and the rate of rise of active force, consistent with the decrease in thin filament cooperative activation. Pi enhanced length-dependent activation with and without sTn reconstitution. Linear regression analysis revealed that the magnitude of length-dependent activation was inversely correlated with the rate of rise of active force. These results were quantitatively simulated by a model that incorporates the Ca2+-dependent on–off switching of the thin filament state and interfilament lattice spacing modulation. Our model analysis revealed that the cooperativity of the thin filament on–off switching, but not the Ca2+-binding ability, determines the magnitude of the Frank-Starling effect. These findings demonstrate that the Frank-Starling relation is strongly influenced by thin filament cooperative activation.

scholarly journals Incorporation of the A31P Cardiac Myosin Binding Protein C Missense Mutation Into Feline Cardiac Sarcomeres

2010 ◽  
Vol 98 (3) ◽  
pp. 554a
Author(s):  
Kristina L. Bezold ◽  
Elaine Hoye ◽  
Justin Shaffer ◽  
Aldrin Gomes ◽  
Mark Kittleson ◽  
...  
Keyword(s):  
Missense Mutation ◽  
Protein C ◽  
Binding Protein ◽  
Cardiac Myosin ◽  
Myosin Binding Protein ◽  
Myosin Binding Protein C ◽  
Myosin Binding ◽  
Cardiac Sarcomeres

scholarly journals HDAC4 and PCAF Bind to Cardiac Sarcomeres and Play a Role in Regulating Myofilament Contractile Activity

2008 ◽  
Vol 283 (15) ◽  
pp. 10135-10146 ◽  
Author(s):  
Mahesh P. Gupta ◽  
Sadhana A. Samant ◽  
Stephen H. Smith ◽  
Sanjeev G. Shroff
Keyword(s):  
Contractile Activity ◽  
Cardiac Sarcomeres

scholarly journals Restrictive Cardiomyopathy Troponin I R145W Mutation Does Not Perturb Myofilament Length-dependent Activation in Human Cardiac Sarcomeres

2016 ◽  
Vol 291 (41) ◽  
pp. 21817-21828 ◽  
Author(s):  
Alexey V. Dvornikov ◽  
Nikolai Smolin ◽  
Mengjie Zhang ◽  
Jody L. Martin ◽  
Seth L. Robia ◽  
...  
Keyword(s):  
Troponin I ◽  
Restrictive Cardiomyopathy ◽  
Cardiac Sarcomeres ◽  
Length Dependent Activation

scholarly journals Mono- and bi-allelic protein truncating variants in alpha-actinin 2 cause cardiomyopathy through distinct mechanisms

2020 ◽  
Author(s):  
Malene E Lindholm ◽  
David Jimenez-Morales ◽  
Han Zhu ◽  
Kinya Seo ◽  
David Amar ◽  
...  
Keyword(s):  
Human Heart ◽  
Gene Editing ◽  
Physiological Function ◽  
Affinity Purification ◽  
Disease Phenotypes ◽  
C Terminus ◽  
Associated Proteins ◽  
Cardiac Sarcomeres ◽  
Affinity Purification Mass Spectrometry

AbstractAlpha-actinin 2 (ACTN2) anchors actin within cardiac sarcomeres. The mechanisms linking ACTN2 mutations to myocardial disease phenotypes are unknown. Here, we characterize patients with novel ACTN2 mutations to reveal insights into the physiological function of ACTN2. Patient-derived iPSC-cardiomyocytes harboring ACTN2 protein-truncating variants were hypertrophic, displayed sarcomeric structural disarray, impaired contractility, and aberrant Ca2+-signaling. In heterozygous indel cells, the truncated protein incorporates into cardiac sarcomeres, leading to aberrant Z-disc structure. In homozygous stop-gain cells, affinity-purification mass spectrometry reveals an intricate ACTN2 interactome with sarcomere and sarcolemma-associated proteins. Loss of the C-terminus of ACTN2 disrupts interaction with ACTN1 and GJA1, two sarcolemma-associated proteins, that may lead to the clinical arrhythmic and relaxation defects. The causality of the stop-gain mutation was verified using CRISPR-Cas9 gene editing. Together, these data advance our understanding of the role of ACTN2 in the human heart and establish recessive inheritance of ACTN2 truncation as causative of disease.

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