-
ESC Heart Failure Jun 2024Hypertrophic cardiomyopathy (HCM) is an autosomal dominant genetic cardiac disorder characterized by unexplained left ventricular hypertrophy. It can cause a wide...
AIMS
Hypertrophic cardiomyopathy (HCM) is an autosomal dominant genetic cardiac disorder characterized by unexplained left ventricular hypertrophy. It can cause a wide spectrum of clinical manifestations, ranging from asymptomatic to heart failure and sudden cardiac death (SCD). Approximately half of HCM cases are caused by variants in sarcomeric proteins, including α-tropomyosin (TPM1). In this study, we aimed to characterize the clinical and molecular phenotype of HCM in an Iranian pedigree with SCD.
METHODS AND RESULTS
The proband and available family members underwent comprehensive clinical evaluations, including echocardiography, cardiac magnetic resonance (CMR) imaging and electrocardiography (ECG). Whole-exome sequencing (WES) was performed in all available family members to identify the causal variant, which was validated, and segregation analysis was conducted via Sanger sequencing. WES identified a novel missense variant, c.761A>G:p.D254G (NM_001018005.2), in the TPM1 gene, in the proband, his father and one of his sisters. Bioinformatic analysis predicted it to be likely pathogenic. Clinical features in affected individuals were consistent with HCM.
CONCLUSIONS
The identification of a novel TPM1 variant in a family with HCM and SCD underscores the critical role of genetic screening in at-risk families. Early detection of pathogenic variants can facilitate timely intervention and management, potentially reducing the risk of SCD in individuals with HCM.
PubMed: 38874371
DOI: 10.1002/ehf2.14906 -
Bioactive Materials Aug 2024Bacteria can be programmed to deliver natural materials with defined biological and mechanical properties for controlling cell growth and differentiation. Here, we...
Bacteria can be programmed to deliver natural materials with defined biological and mechanical properties for controlling cell growth and differentiation. Here, we present an elastic, resilient and bioactive polysaccharide derived from the extracellular matrix of sp. BCCS 001. Specifically, it was methacrylated to generate a new photo crosslinkable hydrogel that we coined Pantoan Methacrylate or put simply PAMA. We have used it for the first time as a tissue engineering hydrogel to treat VML injuries in rats. The crosslinked PAMA hydrogel was super elastic with a recovery nearing 100 %, while mimicking the mechanical stiffness of native muscle. After inclusion of thiolated gelatin via a Michaelis reaction with acrylate groups on PAMA we could also guide muscle progenitor cells into fused and aligned tubes - something reminiscent of mature muscle cells. These results were complemented by sarcomeric alpha-actinin immunostaining studies. Importantly, the implanted hydrogels exhibited almost 2-fold more muscle formation and 50 % less fibrous tissue formation compared to untreated rat groups. inflammation and toxicity assays likewise gave rise to positive results confirming the biocompatibility of this new biomaterial system. Overall, our results demonstrate that programmable polysaccharides derived from bacteria can be used to further advance the field of tissue engineering. In greater detail, they could in the foreseeable future be used in practical therapies against VML.
PubMed: 38872731
DOI: 10.1016/j.bioactmat.2024.04.006 -
Gene Jun 2024The troponin complex plays a crucial role in regulating skeletal and cardiac contraction. Congenital myopathies can occur due to several mutations in genes that encode... (Review)
Review
BACKGROUND
The troponin complex plays a crucial role in regulating skeletal and cardiac contraction. Congenital myopathies can occur due to several mutations in genes that encode skeletal troponin. Moreover, there is limited information regarding the composition of skeletal troponin. This review specifically examines a comprehensive review of the TNNC gene mutations on cardiac and skeletal regulations.
MAIN BODY
Troponin C (TNNC) has been linked to a newly discovered inherited muscle disorder. Genetic variations in genes that encode skeletal troponin can impair the function of sarcomeres. Various treatment approaches have been employed to mitigate the impact of variations, including the use of troponin activators, the injection of wild-type protein via AAV gene therapy, and myosin modification to enhance muscle contraction. The processes responsible for the pathophysiological implications of the variations in genes that encode skeletal troponin are not fully understood.
CONCLUSION
This comprehensive review will contribute to the understanding of the relationship between human cardiomyopathy and TNNC mutations and will guide the development of therapy approaches.
PubMed: 38871035
DOI: 10.1016/j.gene.2024.148651 -
Development (Cambridge, England) Jun 2024Cofilin, an actin severing protein, plays key roles in muscle sarcomere addition and maintenance. Our previous work found that Drosophila cofilin (DmCFL) muscle...
Cofilin, an actin severing protein, plays key roles in muscle sarcomere addition and maintenance. Our previous work found that Drosophila cofilin (DmCFL) muscle knockdown causes progressive deterioration of muscle structure and function and produces features seen in nemaline myopathy (NM) caused by cofilin mutations. We hypothesized that disruption of actin cytoskeleton dynamics by DmCFL knockdown would impact other aspects of muscle development, and, thus, conducted an RNA sequencing analysis that unexpectedly revealed upregulated expression of numerous neuromuscular junction (NMJ) genes. We found that DmCFL is enriched in the muscle postsynaptic compartment and that DmCFL muscle knockdown causes F-actin disorganization in this subcellular domain prior to the sarcomere defects observed later in development. Despite NMJ gene expression changes, we found no significant changes in gross presynaptic Bruchpilot active zones or total postsynaptic glutamate receptor levels. However, DmCFL knockdown results in mislocalization of GluRIIA class glutamate receptors in more deteriorated muscles and strongly impaired NMJ transmission strength. These findings expand our understanding of cofilin's roles in muscle to include NMJ structural development and suggest that NMJ defects may contribute to NM pathophysiology.
PubMed: 38869008
DOI: 10.1242/dev.202558 -
Open Biology Jun 2024Hypertrophic cardiomyopathy (HCM) is a monogenic cardiac disorder commonly induced by sarcomere gene mutations. However, the mechanism for HCM is not well defined. Here,...
Hypertrophic cardiomyopathy (HCM) is a monogenic cardiac disorder commonly induced by sarcomere gene mutations. However, the mechanism for HCM is not well defined. Here, we generated transgenic MYH7 R453C and MYH6 R453C piglets and found both developed typical cardiac hypertrophy. Unexpectedly, we found serious fibrosis and cardiomyocyte loss in the ventricular of MYH7 R453C, not MYH6 R453C piglets, similar to HCM patients. Then, RNA-seq analysis and western blotting identified the activation of ERK1/2 and PI3K-Akt pathways in MYH7 R453C. Moreover, we observed an increased expression of fetal genes and an excess of reactive oxygen species (ROS) in MYH7 R453C piglet models, which was produced by Nox4 and subsequently induced inflammatory response. Additionally, the phosphorylation levels of Smad2/3, ERK1/2 and NF-kB p65 proteins were elevated in cardiomyocytes with the MYH7 R453C mutation. Furthermore, epigallocatechin gallate, a natural bioactive compound, could be used as a drug to reduce cell death by adjusting significant downregulation of the protein expression of Bax and upregulated Bcl-2 levels in the H9C2 models with MYH7 R453C mutation. In conclusion, our study illustrated that TGF-β/Smad2/3, ERK1/2 and Nox4/ROS pathways have synergistic effects on cardiac remodelling and inflammation in MYH7 R453C mutation.
Topics: Animals; Myosin Heavy Chains; Transforming Growth Factor beta; NADPH Oxidase 4; Reactive Oxygen Species; NF-kappa B; Signal Transduction; Swine; Myocytes, Cardiac; Humans; Cardiac Myosins; Disease Models, Animal; MAP Kinase Signaling System; Animals, Genetically Modified; Smad2 Protein; Mutation; Smad3 Protein; Ventricular Remodeling; Cardiomyopathy, Hypertrophic; Rats
PubMed: 38862020
DOI: 10.1098/rsob.230427 -
Cryobiology Jun 2024Victims of severe accidental hypothermia are frequently treated with catecholamines to counteract the hemodynamic instability associated with hypothermia-induced cardiac...
Victims of severe accidental hypothermia are frequently treated with catecholamines to counteract the hemodynamic instability associated with hypothermia-induced cardiac contractile dysfunction. However, we previously reported that the inotropic effects of epinephrine are diminished after hypothermia and rewarming (H/R) in an intact animal model. Thus, the goal of this study was to investigate the effects of Epi treatment on excitation-contraction coupling in isolated rat cardiomyocytes after H/R. In adult male rats, cardiomyocytes isolated from the left ventricle were electrically stimulated at 0.5 Hz and evoked cytosolic [Ca] and contractile responses (sarcomere length shortening) were measured. In initial experiments, the effects of varying concentrations of epinephrine on evoked cytosolic [Ca] and contractile responses at 37 °C were measured. In a second series of experiments, cardiomyocytes were cooled from 37 °C to 15 °C, maintained at 15 °C for 2 h, then rewarmed to 37 °C (H/R protocol). Immediately after rewarming, the effects of epinephrine treatment on evoked cytosolic [Ca] and contractile responses of cardiomyocytes were determined. At 37 °C, epinephrine treatment increased both cytosolic [Ca] and contractile responses of cardiomyocytes in a concentration-dependent manner peaking at 25-50 nM. The evoked contractile response of cardiomyocytes after H/R was reduced while the cytosolic [Ca] response was slightly elevated. The diminished contractile response of cardiomyocytes after H/R was not mitigated by epinephrine (25 nM) and epinephrine treatment reduced the exponential time decay constant (Tau), but did not increase the cytosolic [Ca] response. We conclude that epinephrine treatment does not mitigate H/R-induced contractile dysfunction in cardiomyocytes.
PubMed: 38857777
DOI: 10.1016/j.cryobiol.2024.104927 -
Biomedical Optics Express May 2024Aging induces cardiac remodeling, resulting in an increase in the risk of suffering heart diseases, including heart failure. Collagen deposition increases with age and,...
Aging induces cardiac remodeling, resulting in an increase in the risk of suffering heart diseases, including heart failure. Collagen deposition increases with age and, together with sarcomeric changes in cardiomyocytes, may lead to ventricular stiffness. Multiphoton (MP) microscopy is a useful technique to visualize and detect variations in cardiac structures in a label free fashion. Here, we propose a method based on MP imaging (both two-photon excitation fluorescence (TPEF) and second harmonic generation (SHG) modalities) to explore and objectively quantify age-related structural differences in various components of cardiac tissues. Results in transmural porcine left ventricle (LV) sections reveal significant differences when comparing samples from young and old animals. Collagen and myosin SHG signals in old specimens are respectively 3.8x and >6-fold larger than in young ones. Differences in TPEF signals from cardiomyocyte were ∼3x. Moreover, the increased amount of collagen in old specimens results in a more organized pattern when compared to young LV tissues. Since changes in collagen and myosin are associated with cardiac dysfunction, the technique used herein might be a useful tool to accurately predict and measure changes associated with age-related myocardium fibrosis, tissue remodeling and sarcomeric alterations, with potential implications in preventing heart disease.
PubMed: 38855691
DOI: 10.1364/BOE.509227 -
ArXiv May 2024Crossbridge binding, state transitions, and force in active muscle is dependent on the radial spacing between the myosin-containing thick filament and the...
Crossbridge binding, state transitions, and force in active muscle is dependent on the radial spacing between the myosin-containing thick filament and the actin-containing thin filament in the filament lattice. This radial lattice spacing has been previously shown through spatially explicit modeling and experimental efforts to greatly affect quasi-static, isometric, force production in muscle. It has recently been suggested that this radial spacing might also be able to drive differences in mechanical function, or net work, under dynamic oscillations like those which occur in muscles . However, previous spatially explicit models either had no radial spacing dependence, meaning the lattice spacing could not be investigated, or did include radial spacing dependence but could not reproduce net work during dynamic oscillations and only investigated isometric contractions. Here we show the first spatially explicit model to include radial crossbridge dependence which can produce mechanical function similar to real muscle. Using this spatially explicit model of a half sarcomere, we show that when oscillated at strain amplitudes and frequencies like those in the hawk moth , mechanical function (net work) does depend on the lattice spacing. In addition, since the trajectory of lattice spacing changes during dynamic oscillation can vary from organism to organism, we can prescribe a trajectory of lattice spacing changes in the spatially explicit half sarcomere model and investigate the extent to which the time course of lattice spacing changes can affect mechanical function. We simulated a half sarcomere undergoing dynamic oscillations and prescribed the Poisson's ratio of the lattice to be either 0 (constant lattice spacing) or 0.5 (isovolumetric lattice spacing changes). We also simulated net work using lattice spacing data taken from which has a variable Poisson's ratio. Our simulation results indicate that the lattice spacing can change the mechanical function of muscle, and that in some cases a 1 nm difference can switch the net work of the half sarcomere model from positive (motor-like) to negative (brake-like).
PubMed: 38855552
DOI: No ID Found -
BioRxiv : the Preprint Server For... May 2024, encoding cardiac myosin binding protein-C (cMyBP-C), is the most mutated gene known to cause hypertrophic cardiomyopathy (HCM). However, since little is known about...
BACKGROUND
, encoding cardiac myosin binding protein-C (cMyBP-C), is the most mutated gene known to cause hypertrophic cardiomyopathy (HCM). However, since little is known about the underlying etiology, additional studies are crucial to defining the underlying molecular mechanisms. Accordingly, this study aimed to investigate the molecular mechanisms underlying the pathogenesis of HCM associated with a polymorphic variant (D389V) in by using human-induced pluripotent stem cell (hiPSC)-derived cardiac organoids (hCOs).
METHODS
The hiPSC-derived cardiomyocytes (hiPSC-CMs) and hCOs were generated from human subjects to define the molecular, cellular, and functional changes caused by the variant. This variant is associated with increased fractional shortening and is highly prevalent in South Asian descendants. Recombinant C0-C2, N'-region of cMyBP-C (wildtype and D389V), and myosin S2 proteins were also utilized to perform binding and motility assays .
RESULTS
Confocal and electron microscopic analyses of hCOs generated from noncarriers (NC) and carriers of the variant revealed the presence of highly organized sarcomeres. Furthermore, functional experiments showed hypercontractility with increased contraction velocity, faster calcium cycling, and faster contractile kinetics in hCOs expressing than NC hCOs. Interestingly, significantly increased cMyBP-C phosphorylation in hCOs was observed, but without changes in total protein levels, in addition to higher oxidative stress and lower mitochondrial membrane potential (ΔΨm). Next, spatial mapping revealed the presence of endothelial cells, fibroblasts, macrophages, immune cells, and cardiomyocytes in the hCOs. The hypercontractile function was significantly improved after treatment with the myosin inhibitor mavacamten (CAMZYOS®) in hCOs. Lastly, various binding assays revealed a significant loss of affinity in the presence of with myosin S2 region as a likely mechanism for hypercontraction.
CONCLUSIONS
Conceptually, we showed the feasibility of assessing the functional and molecular mechanisms of HCM using highly translatable hCOs through pragmatic experiments that led to determining the hypercontractile phenotype, which was rescued by administration of a myosin inhibitor. mutations have been implicated in hypertrophic cardiomyopathy. D389V is a polymorphic variant of predicted to be present in 53000 US South Asians owing to the founder effect. D389V carriers have shown evidence of hyperdynamic heart, and human-induced pluripotent stem cells (hiPSC)-derived cardiomyocytes with D389V show cellular hypertrophy and irregular calcium transients. The molecular mechanism by which the D389V variant develops pathological cardiac dysfunction remains to be conclusively determined. The authors leveraged a highly translational cardiac organoid model to explore the role of altered cardiac calcium handling and cardiac contractility as a common pathway leading to pathophysiological phenotypes in patients with early HCM. The -mediated pathological pathway is first studied here by comparing functional properties using three-dimensional cardiac organoids differentiated from hiPSC and determining the presence of hypercontraction. Our data demonstrate that faster sarcomere kinetics resulting from lower binding affinity between D389V-mutated cMyBP-C protein and myosin S2, as evidenced by studies, could cause hypercontractility which was rescued by administration of mavacamten (CAMZYOS®), a myosin inhibitor. In addition, hypercontractility causes secondary mitochondrial defects such as higher oxidative stress and lower mitochondrial membrane potential (ΔΨm), highlighting a possible early adaptive response to primary sarcomeric changes. Early treatment of carriers with mavacamten may prevent or reduce early HCM-related pathology. A graphical abstract is available for this article.
PubMed: 38853909
DOI: 10.1101/2024.05.29.596463 -
BioRxiv : the Preprint Server For... Jun 2024We report the discovery of a new regulatory mechanism of the actomyosin system in muscle. We show that the weak binding of the myosin-nucleotide complex with unregulated...
UNLABELLED
We report the discovery of a new regulatory mechanism of the actomyosin system in muscle. We show that the weak binding of the myosin-nucleotide complex with unregulated F-actin is a cooperative process. Hundreds of myosin heads must work together for efficient force production in muscle, but the precise mechanism by which they coordinate remains elusive. It is known that myosin initially binds actin weakly, then transitions into a strongly bound state to produce force. Using the contiguous cooperative binding model, we interpreted our experimental results in terms of a cooperativity parameter defined as an increased probability for a myosin head to bind to the actin filament next to the already bound head. Considering the geometric organization of a sarcomere, we propose the formation of cross-bridge clusters composed of up to six myosin heads bound consecutively to actin. The cooperativity of weak actomyosin interaction may explain several challenging questions in muscle physiology, such as the role of myosin isoforms in mixed-isoform hybrid muscles, or the yield of supramaximal rate of force production in decorated skinned muscle fibers.
SIGNIFICANCE STATEMENT
Force in striated muscle results from myosin interacting with actin. Initially, myosin attaches weakly to the thin filament, transitioning to a strongly bound state, generating force. Our experiments show high cooperativity in myosin's weak interaction with unregulated actin filament. This cooperative behavior may facilitate the formation of cross-bridge clusters and the cooperative steps of myosin heads between clusters. Consequently, the thin- and thick-filament regulation could govern the spacing between cross-bridge clusters and influence the probability of a myosin head stepping along the thin filament during force development in muscle.
PubMed: 38853887
DOI: 10.1101/2024.05.28.596264