Cardiac Myosin Binding Protein Research Articles

Generation of induced pluripotent stem cells from an individual with early onset and severe hypertrophic cardiomyopathy linked to MYBPC3: c.772G > A mutation.

Hypertrophic cardiomyopathy (HCM) is frequently caused by mutations in the MYPBC3 gene, which encodes the cardiac myosin-binding protein C (cMyBP-C). Most pathogenic variants in MYPBC3 are either nonsense mutations or result in frameshifts, suggesting that the primary disease mechanism involves reduced functional cMyBP-C protein levels within sarcomeres. However, a subset of MYPBC3 variants are missense mutations, and the molecular mechanisms underlying their pathogenicity remain elusive. Upon in vitro differentiation into cardiomyocytes, induced pluripotent stem cells (iPSCs) derived from HCM patients represent a valuable resource for disease modeling. In this study, we generated twoiPSC lines from peripheral blood mononuclear cells (PBMCs) of a female with early onset and severe HCM linked to the MYBPC3: c.772G > A variant. Although this variant was initially classified as a missense mutation, recent studies indicate that it interferes with splicing and results in a frameshift. The generated iPSC lines exhibit a normal karyotype and display hallmark characteristics of pluripotency, including the ability to undergo trilineage differentiation. These novel iPSCs expand the existing repertoire of MYPBC3-mutated cell lines, broadening the spectrum of resources for exploring how diverse mutations induce HCM. They additionally offer a platform to study potential secondary genetic elements contributing to the pronounced disease severity observed in this individual.

Sex-specific cardiovascular remodeling leads to a divergent sex-dependent development of heart failure in aged hypertensive rats.

The prevalence of heart failure with preserved ejection fraction (HFpEF) is continuously rising and predominantly affects older women often hypertensive and/or obese or diabetic. Indeed, there is evidence on sex differences in the development of HF. Hence, we studied cardiovascular performance dependent on sex and age as well as pathomechanisms on a cellular and molecular level. We studied 15-week- and 1-year-old female and male hypertensive transgenic rats carrying the mouse Ren-2 renin gene (TG) and compared them to wild-type (WT) controls at the same age. We tracked blood pressure and cardiac function via echocardiography. After sacrificing the 1-year survivors we studied vascular smooth muscle and endothelial function. Isolated single skinned cardiomyocytes were used to determine passive stiffness and Ca2+-dependent force. In addition, Western blots were applied to analyse the phosphorylation status of sarcomeric regulatory proteins, titin and of protein kinases AMPK, PKG, CaMKII as well as their expression. Protein kinase activity assays were used to measure activities of CaMKII, PKG and angiotensin-converting enzyme (ACE). TG male rats showed significantly higher mortality at 1 year than females or WT male rats. Left ventricular (LV) ejection fraction was specifically reduced in male, but not in female TG rats, while LV diastolic dysfunction was evident in both TG sexes, but LV hypertrophy, increased LV ACE activity, and reduced AMPK activity as evident from AMPK hypophosphorylation were specific to male rats. Sex differences were also observed in vascular and cardiomyocyte function showing different response to acetylcholine and Ca2+-sensitivity of force production, respectively cardiomyocyte functional changes were associated with altered phosphorylation states of cardiac myosin binding protein C and cardiac troponin I phosphorylation in TG males only. Cardiomyocyte passive stiffness was increased in TG animals. On a molecular level titin phosphorylation pattern was altered, though alterations were sex-specific. Thus, also the reduction of PKG expression and activity was more pronounced in TG females. However, cardiomyocyte passive stiffness was restored by PKG and CaMKII treatments in both TG sexes. Here we demonstrated divergent sex-specific cardiovascular adaptation to the over-activation of the renin-angiotensin system in the rat. Higher mortality of male TG rats in contrast to female TG rats was observed as well as reduced LV systolic function, whereas females mainly developed HFpEF. Though both sexes developed increased myocardial stiffness to which an impaired titin function contributes to a sex-specific molecular mechanism. The functional derangements of titin are due to a sex-specific divergent regulation of PKG and CaMKII systems.

Insights into the Novel Cardiac Biomarker in Acute Heart Failure: Mybp-C.

(1) Background: Given its high cardiac specificity and its capacity to directly assess the cardiac function, cardiac myosin-binding protein (MyBP-C) is a promising biomarker in patients with acute heart failure (AHF). The aim of our study was to investigate the clinical utility of this novel marker for diagnosis and short-term prognosis in subjects with AHF. (2) Methods: We measured plasma levels of MyBP-C at admission in 49 subjects (27 patients admitted with AHF and 22 controls). (3) Results: The plasma concentration of MyBP-C was significantly higher in patients with AHF compared to controls (54.88 vs. 0.01 ng/L, p < 0.001). For 30-day prognosis, MyBP-C showed significantly greater AUC (0.972, p < 0.001) than NT-proBNP (0.849, p = 0.001) and hs-TnI (0.714, p = 0.047). In a multivariate logistic regression analysis, an elevated level of MyBP-C was the best independent predictor of 30-day mortality (OR = 1.08, p = 0.039) or combined death/recurrent 30-days rehospitalization (OR = 1.12, p = 0.014). (4) Conclusions: Our data show that circulating MyBP-C is a sensitive and cardiac-specific biomarker with potential utility for the accurate diagnosis and prognosis of AHF.

Detecting Polymorphism of Myosin-binding Protein C3 Gene in Persian Breed Cat With and Without Hypertrophic Cardiomyopathy

Background: In cats, hypertrophic cardiomyopathy (HCM) stands out as a prevailing heart disease. The mutations in the gene that encodes cardiac myosin-binding protein C (MYBPC3) have been detected in the Ragdoll and Maine Coon breeds. Objectives: HCM is believed to be hereditary in other breeds, too. Methods: Blood samples were collected for DNA extraction from 2 unaffected and 7 affected Persian breed cats with HCM. Besides accomplishing conventional polymerase chain reaction, DNA sequencing was performed. The sequence changes were utilized to detect single nucleotide polymorphisms in the MYBPC3 gene and predict amino acid substitutions based on the Acc. No. XM_019812396.1 and comparisons with the literature on identified breed variants and control samples. Results: Although many single nucleotide polymorphisms were found in the affected and unaffected Persian cats, no causative mutation for HCM was observed. Conclusion: In this breed, HCM does not seem to be caused solely by mutations in this cardiac gene. Potential cardiac genes should be investigated to uncover other genetic reasons for this cardiac disease in the Persian cat breed.

Translating myosin-binding protein C and titin abnormalities to whole-heart function using a novel calcium-contraction coupling model

Mutations in cardiac myosin-binding protein C (cMyBP-C) or titin may respectively lead to hypertrophic (HCM) or dilated (DCM) cardiomyopathies. The mechanisms leading to these phenotypes remain unclear because of the challenge of translating cellular abnormalities to whole-heart and system function.We developed and validated a novel computer model of calcium-contraction coupling incorporating the role of cMyBP-C and titin based on the key assumptions: 1) tension in the thick filament promotes cross-bridge attachment mechanochemically, 2) with increasing titin tension, more myosin heads are unlocked for attachment, and 3) cMyBP-C suppresses cross-bridge attachment.Simulated stationary calcium-tension curves, isotonic and isometric contractions, and quick release agreed with experimental data. The model predicted that a loss of cMyBP-C function decreases the steepness of the calcium-tension curve, and that more compliant titin decreases the level of passive and active tension and its dependency on sarcomere length. Integrating this cellular model in the CircAdapt model of the human heart and circulation showed that a loss of cMyBP-C function resulted in HCM-like hemodynamics with higher left ventricular end-diastolic pressures and smaller volumes. More compliant titin led to higher diastolic pressures and ventricular dilation, suggesting DCM-like hemodynamics.The novel model of calcium-contraction coupling incorporates the role of cMyBP-C and titin. Its coupling to whole-heart mechanics translates changes in cellular calcium-contraction coupling to changes in cardiac pump and circulatory function and identifies potential mechanisms by which cMyBP-C and titin abnormalities may develop into HCM and DCM phenotypes. This modeling platform may help identify distinct mechanisms underlying clinical phenotypes in cardiac diseases.

Protein Kinase D Plays a Crucial Role in Maintaining Cardiac Homeostasis by Regulating Post-Translational Modifications of Myofilament Proteins.

Protein kinase D (PKD) enzymes play important roles in regulating myocardial contraction, hypertrophy, and remodeling. One of the proteins phosphorylated by PKD is titin, which is involved in myofilament function. In this study, we aimed to investigate the role of PKD in cardiomyocyte function under conditions of oxidative stress. To do this, we used mice with a cardiomyocyte-specific knock-out of Prkd1, which encodes PKD1 (Prkd1loxP/loxP; αMHC-Cre; PKD1 cKO), as well as wild type littermate controls (Prkd1loxP/loxP; WT). We isolated permeabilized cardiomyocytes from PKD1 cKO mice and found that they exhibited increased passive stiffness (Fpassive), which was associated with increased oxidation of titin, but showed no change in titin ubiquitination. Additionally, the PKD1 cKO mice showed increased myofilament calcium (Ca2+) sensitivity (pCa50) and reduced maximum Ca2+-activated tension. These changes were accompanied by increased oxidation and reduced phosphorylation of the small myofilament protein cardiac myosin binding protein C (cMyBPC), as well as altered phosphorylation levels at different phosphosites in troponin I (TnI). The increased Fpassive and pCa50, and the reduced maximum Ca2+-activated tension were reversed when we treated the isolated permeabilized cardiomyocytes with reduced glutathione (GSH). This indicated that myofilament protein oxidation contributes to cardiomyocyte dysfunction. Furthermore, the PKD1 cKO mice exhibited increased oxidative stress and increased expression of pro-inflammatory markers interleukin (IL)-6, IL-18, and tumor necrosis factor alpha (TNF-α). Both oxidative stress and inflammation contributed to an increase in microtubule-associated protein 1 light chain 3 (LC3)-II levels and heat shock response by inhibiting the mammalian target of rapamycin (mTOR) in the PKD1 cKO mouse myocytes. These findings revealed a previously unknown role for PKD1 in regulating diastolic passive properties, myofilament Ca2+ sensitivity, and maximum Ca2+-activated tension under conditions of oxidative stress. Finally, we emphasized the importance of PKD1 in maintaining the balance of oxidative stress and inflammation in the context of autophagy, as well as cardiomyocyte function.

Troponin Structural Dynamics in the Native Cardiac Thin Filament Revealed by Cryo Electron Microscopy

Cardiac muscle contraction occurs due to repetitive interactions between myosin thick and actin thin filaments (TF) regulated by Ca2+ levels, active cross-bridges, and cardiac myosin-binding protein C (cMyBP-C). The cardiac TF (cTF) has two nonequivalent strands, each comprised of actin, tropomyosin (Tm), and troponin (Tn). Tn shifts Tm away from myosin-binding sites on actin at elevated Ca2+ levels to allow formation of force-producing actomyosin cross-bridges. The Tn complex is comprised of three distinct polypeptides – Ca2+-binding TnC, inhibitory TnI, and Tm-binding TnT. The molecular mechanism of their collective action is unresolved due to lack of comprehensive structural information on Tn region of cTF. C1 domain of cMyBP-C activates cTF in the absence of Ca2+ to the same extent as rigor myosin. Here we used cryo-EM of native cTFs to show that cTF Tn core adopts multiple structural conformations at high and low Ca2+ levels and that the two strands are structurally distinct. At high Ca2+ levels, cTF is not entirely activated by Ca2+ but exists in either partially or fully activated state. Complete dissociation of TnI C-terminus is required for full activation. In presence of cMyBP-C C1 domain, Tn core adopts a fully activated conformation, even in absence of Ca2+. Our data provide a structural description for the requirement of myosin to fully activate cTFs and explain increased affinity of TnC to Ca2+ in presence of active cross-bridges. We suggest that allosteric coupling between Tn subunits and Tm is required to control actomyosin interactions.

N-Terminal Fragment of Cardiac Myosin Binding Protein C Modulates Cooperative Mechanisms of Thin Filament Activation in Atria and Ventricles.

Cardiac myosin binding protein C (cMyBP-C) is one of the essential control components of the myosin cross-bridge cycle. The C-terminal part of cMyBP-C is located on the surface of the thick filament, and its N-terminal part interacts with actin, myosin, and tropomyosin, affecting both kinetics of the ATP hydrolysis cycle and lifetime of the cross-bridge, as well as calcium regulation of the actin-myosin interaction, thereby modulating contractile function of myocardium. The role of cMyBP-C in atrial contraction has not been practically studied. We examined effect of the N-terminal C0-C1-m-C2 (C0-C2) fragment of cMyBP-C on actin-myosin interaction using ventricular and atrial myosin in an in vitro motility assay. The C0-C2 fragment of cMyBP-C significantly reduced the maximum sliding velocity of thin filaments on both myosin isoforms and increased the calcium sensitivity of the actin-myosin interaction. The C0-C2 fragment had different effects on the kinetics of ATP and ADP exchange, increasing the affinity of ventricular myosin for ADP and decreasing the affinity of atrial myosin. The effect of the C0-C2 fragment on the activation of the thin filament depended on the myosin isoforms. Atrial myosin activates the thin filament less than ventricular myosin, and the C0-C2 fragment makes these differences in the myosin isoforms more pronounced.

Assessment of Cardiac Myosin-binding Protein C Levels in Coronavirus Disease 2019

Assessment of Cardiac Myosin-binding Protein C Levels in Coronavirus Disease 2019

Clinical Utility of Soluble Lectin Type Oxidized Low-Density Lipoprotein Receptor as a Biomarker for Myocardial Infarction and Stable Angina.

Background and objectives Endothelial soluble lectin-type oxidized low-density lipoprotein receptor 1 (sLOX-1) recognizes oxidized low-density lipoprotein (LDL) and triggers downstream signaling leading to atherosclerosis. The objective of this study was to demonstrate the utility of sLOX-1 as a biomarker for detecting acute myocardial infarction (MI) and stable angina (SA) and to develop a diagnostic algorithm for distinguishing coronary vasospasm from coronary plaque rupture. Methods We enrolled 62 patients who underwent diagnostic coronary angiography (CAG) and 30 healthy controls (21 men and nine women) and measured sLOX-1, troponin I, and cardiac myosin-binding protein C (c-MyBPC) using commercial kits. Results Patients with MI exhibited higher sLOX-1 levels (301.55 ± 196.16 pg/ml) than patients with stable angina (220.76 ± 103.65 pg/ml) and healthy controls (121.14 ± 77.10, F: 10.55, p<0.001). Although higher troponin I levels were detected in MI patients (263.00 ± 493.00 vs. 3.19 ± 2.15 ng/ml, p=0.0019), no significant elevation was observed in SA patients (1.91 ± 0.79 ng/ml). Plasma sLOX-1 levels showed a positive association with age (r=0.37, p=0.003), but not with gender (r=0.04, p=0.75). Troponin I showed no association with age (r=0.12, p=0.36) or gender (r=0.06, p=0.62). Receiver operating characteristic (ROC) curves revealed that among the three biomarkers, troponin-I showed a higher area under the curve (AUC) (AUC: 0.941), followed by sLOX-1 (AUC: 0.888), while c-MyBPC showed no clinical utility in the detection of MI (AUC: 0.666). Conclusions A marked elevation of sLOX-1 can detect MI and differentiate the presence or absence of plaque rupture, along with diagnosing stable angina.

Cardiac myosin-binding protein C N-terminal interactions with myosin and actin filaments: Opposite effects of phosphorylation and M-domain mutations

N-terminal cardiac myosin-binding protein C (cMyBP-C) domains (C0-C2) bind to thick (myosin) and thin (actin) filaments to coordinate contraction and relaxation of the heart. These interactions are regulated by phosphorylation of the M-domain situated between domains C1 and C2. In cardiomyopathies and heart failure, phosphorylation of cMyBP-C is significantly altered. We aimed to investigate how cMyBP-C interacts with myosin and actin. We developed complementary, high-throughput, C0-C2 FRET-based binding assays for myosin and actin to characterize the effects due to 5 HCM-linked variants or functional mutations in unphosphorylated and phosphorylated C0-C2. The assays indicated that phosphorylation decreases binding to both myosin and actin, whereas the HCM mutations in M-domain generally increase binding. The effects of mutations were greatest in phosphorylated C0-C2, and some mutations had a larger effect on actin than myosin binding. Phosphorylation also altered the spatial relationship of the probes on C0-C2 and actin. The magnitude of these structural changes was dependent on C0-C2 probe location (C0, C1, or M-domain). We conclude that binding can differ between myosin and actin due to phosphorylation or mutations. Additionally, these variables can change the mode of binding, affecting which of the interactions in cMyBP-C N-terminal domains with myosin or actin take place. The opposite effects of phosphorylation and M-domain mutations is consistent with the idea that cMyBP-C phosphorylation is critical for normal cardiac function. The precision of these assays is indicative of their usefulness in high-throughput screening of drug libraries for targeting cMyBP-C as therapy.

Abstract 17019: The Missense W792R Mutation in C6 Domain of Cardiac Myosin Binding Protein-C Alters Morphology and Contractility in Mouse Myocardium

Background: Mutations in cardiac myosin binding protein C (cMyBP-C) are a common cause of hypertrophic cardiomyopathy (HCM) in humans. While many known cMyBP-C mutations lead to haploinsufficiency, others lead to amino acid substitutions which may impact protein function in unique ways The W792R mutation introduces a charge change and is known to be pathogenic in humans. This mutation, located remotely from both the regulatory amino terminus, and the C-terminus, has an unknown impact on the final protein structure and function. Goal: Generate a murine knock-in model to fully characterize the impact of the W792R mutation on cardiac morphology and function in vivo. Methods: We generated a W792R knock-in (KI) mouse and produced heterozygous (HT) and homozygous (KI) offspring, and wild-type (WT) littermate controls. We performed histology, RNA and protein expression analyses, and mechanics on isolated trabeculae at postnatal day 12 (KI n=5; HT n=3; and LC n=4). One-way ANOVA used to compare KI and HT to WT samples, with p-values &lt; ; 0.05 as significant. Results: The KI mice did not live past ~20 days old with massive hypertrophy, dilated atrium, myofibrillar disarray and fibrosis. Full-length mutant protein was expressed and incorporated into the sarcomere. Survival and morphology in the HT was similar to WT. Post-natal day 10 KI mice demonstrated severely enlarged atria and ventricles, interstitial fibrosis, a trend towards increased Ca 2+ sensitivity (pCA 50 KI 5.8 vs HT 5.65 vs LC 5.67 mM; p &gt; 0.05), a trend towards increased cross-bridge cycling kinetics (k tr KI 24.00 + 2.42 vs HT 24.33 + 1.08 vs LC 21.25 + 0.87; p &gt; 0.05) and increased levels of β-myosin heavy chain expression compared to both LC and HT mice. Conclusions: In our mouse HCM model, homozygous expression of the W792R-cMyBP-C mutation recapitulates severe human HCM and provides mechanistic insights into the pathology of this mutation. The trend towards accelerated crossbridge kinetics suggest that the W792R mutation disrupts the inhibitory effects of cMyBP-C on myosin-actin binding implicating the potential application of current myosin ATPase inhibitors in the treatment of patients carrying this mutation. Ongoing work will expand sample sizes to evaluate significance of findings.

Abstract 11841: Gene Therapy Improves Pathological Cardiac Remodeling in Human Hypertrophic Cardiomyopathy Gene Variant Knock-In Mice

Introduction: Some patients with hypertrophic cardiomyopathy (HCM) has been reported to develop ventricular systolic dysfunction, called the dilated phase of HCM (d-HCM). Although d-HCM is associated with increased morbidity and mortality, precise mechanism for the development of the pathological cardiac remodeling and gene-targeted therapy are still under investigation. It has been shown that cardiac myosin binding protein C (Mybpc3) missense mutation (R820Q) is associated with familial HCM and d-HCM. Methods and Results: We generated a knock-in mouse model, carrying the R820Q mutation of Mybpc3 (MyBP-KI mice). MyBP KI mice spontaneously developed cardiac hypertrophy and mild systolic dysfunction at 8 weeks of age, reproducing the d-HCM phenotype, while their littermate control mice showed normal cardiac mass and function. Transcriptome analysis by RNA-seq showed that, in addition to upregulation of heart failure-related fetal genes, mitochondria-related gene sets (oxidative phosphorylation and fatty acid metabolism) were suppressed in MyBP-KI mice compared to control mice. We examined adeno-associated virus (AAV)-mediated gene therapy on MyBP-KI mice. AAV vectors with wild type Mybpc3 controlled by the cardiac troponin T promoter were administered intravenously to MyBP-KI mice that began to develop hypertrophy at 8 weeks of age. Echocardiography and cardiac catheter examinations showed that the deterioration of cardiac function over time was significantly suppressed by AAV gene therapy. Overexpression of fetal genes of cardiomyocyte was significantly suppressed, mitochondrial gene abnormalities were also significantly attenuated, and histological myocardial fibrosis was also significantly suppressed by administration of AAV harboring wild type Mybpc3. Conclusions: Our MyBP-KI mice spontaneously recapitulated human d-HCM phenotype. Gene therapy with AAV, even when administered at a stage when cardiac remodeling has already begun to progress, successfully suppressed cardiac dysfunction at the genetic level and prevented the transition to d-HCM.

Abstract 12927: Impact of AAV- MYBPC3 Gene Transfer on Heart Structure and Function in Human and Mouse Models of Hypertrophic Cardiomyopathy

Background: Hypertrophic cardiomyopathy (HCM) is a life-threatening inherited heart disease characterized by left ventricular hypertrophy and diastolic dysfunction. The most common cause of HCM is genetic variants in MYBPC3 , encoding cardiac myosin binding protein C (cMyBP-C), a sarcomeric protein with structural and regulatory roles. The majority of MYBPC3 gene variants are truncating leading to protein haploinsufficiency. Hypothesis: Transfer of a functional copy of MYBPC3 to heart muscle deficient in cMyBP-C will lead to sustained improvements in cardiac function. Aims: To determine whether BMN 293 (AAV-hMYBPC3) can restore cMyBP-C levels in the sarcomere and halt and/or reverse disease progression in non-clinical models of genetic HCM due to MYPBC3 deficiency. Methods: BMN 293 is an adeno-associated virus (AAV) vector that encodes wild-type human MYBPC3 under the control of a cardiomyocyte-selective promoter. We transduced human iPSC-derived cardiomyocytes and engineered heart tissues (EHTs) carrying a compound heterozygous truncating MYBPC3 mutation (MYBPC3 -/- ) with BMN 293 and assessed cMyBP-C levels and contractile parameters. We also systemically administered BMN 293 to MYBPC3 -/- mice and assessed cardiac distribution of human cMyBP-C by molecular and histological methods and determined its impact on left ventricular hypertrophy and function by echocardiography and other imaging techniques. Results: BMN 293 transduction of human iPSC MYBPC3 -/- cardiomyocytes and EHTs resulted in high levels of human MYBPC3 mRNA and cMyBP-C protein, correct incorporation of cMyBP-C into the sarcomere, and complete normalization of contractile kinetics. BMN 293 was well tolerated in MYBPC3 -/- mice and resulted in uniform restoration of cMyBP-C expression throughout the heart and significant correction of structural and functional cardiac abnormalities. Conclusions: A single IV infusion of BMN 293 to MYBPC3 -/- mice resulted in early and sustained reduction in left ventricular hypertrophy and durable improvements in diastolic function.

MDM2 Regulation of HIF Signaling Causes Microvascular Dysfunction in Hypertrophic Cardiomyopathy.

Microvasculature dysfunction is a common finding in pathologic remodeling of the heart and is thought to play an important role in the pathogenesis of hypertrophic cardiomyopathy (HCM), a disease caused by sarcomere gene mutations. We hypothesized that microvascular dysfunction in HCM was secondary to abnormal microvascular growth and could occur independent of ventricular hypertrophy. We used multimodality imaging methods to track the temporality of microvascular dysfunction in HCM mouse models harboring mutations in the sarcomere genes Mybpc3 (cardiac myosin binding protein C3) or Myh6 (myosin heavy chain 6). We performed complementary molecular methods to assess protein quantity, interactions, and post-translational modifications to identify mechanisms regulating this response. We manipulated select molecular pathways in vivo using both genetic and pharmacological methods to validate these mechanisms. We found that microvascular dysfunction in our HCM models occurred secondary to reduced myocardial capillary growth during the early postnatal time period and could occur before the onset of myocardial hypertrophy. We discovered that the E3 ubiquitin protein ligase MDM2 (murine double minute 2) dynamically regulates the protein stability of both HIF1α (hypoxia-inducible factor 1 alpha) and HIF2α (hypoxia-inducible factor 2 alpha)/EPAS1 (endothelial PAS domain protein 1) through canonical and noncanonical mechanisms. The resulting HIF imbalance leads to reduced proangiogenic gene expression during a key period of myocardial capillary growth. Reducing MDM2 protein levels by genetic or pharmacological methods normalized HIF protein levels and prevented the development of microvascular dysfunction in both HCM models. Our results show that sarcomere mutations induce cardiomyocyte MDM2 signaling during the earliest stages of disease, and this leads to long-term changes in the myocardial microenvironment.

Hemodialysis and biomarkers of myocardial infarction- a cohort study.

End-stage renal disease is associated with a high risk of cardiovascular disease. We compared the concentration and prognostic ability of high sensitivity cardiac troponin T (hs-cTnT) and I (hs-cTnI) and cardiac myosin-binding protein C (cMyC) among stable hemodialysis patients. Patients were sampled before and after hemodialysis. We measured hs-cTnI, hs-cTnT and cMyC and used Cox regressions to assess the association between quartiles of concentrations and all-cause mortality and a combination of cardiovascular events and all-cause mortality during follow-up. A total of 307 patients were included, 204 males, mean age 66 years (SD 14). Before dialysis, 299 (99 %) had a hs-cTnT concentration above the 99th percentile, compared to 188 (66 %) for cMyC and 35 (11 %) for hs-cTnI. Hs-cTnT (23 %, p<0.001) and hs-cTnI (15 %, p=0.049) but not cMyC (4 %,p=0.256) decreased during dialysis. Follow-up was a median of 924days (492-957days); patients in the 3rd and 4th quartiles of hs-cTnT (3rd:HR 3.0, 95 % CI 1.5-5.8, 4th:5.2, 2.7-9.8) and the 4th quartile of hs-cTnI (HR 3.8, 2.2-6.8) had an increased risk of mortality. Both were associated with an increased risk of the combined endpoint for patients in the3rd and 4th quartiles. cMyC concentrations were not associated with risk of mortality or cardiovascular event. Hs-cTnT was above the 99th percentile in almost all patients. This was less frequent for hs-cTnI and cMyC. High cTn levels were associated with a 3-5-fold higher mortality. This association was not present for cMyC. These findings are important for management of hemodialysis patients.

The inter-chamber differences in the contractile function between left and right atrial cardiomyocytes in atrial fibrillation in rats.

The left and right atria (LA, RA) work under different mechanical and metabolic environments that may cause an intrinsic inter-chamber diversity in structure and functional properties between atrial cardiomyocytes (CM) in norm and provoke their different responsiveness to pathological conditions. In this study, we assessed a LA vs. RA difference in CM contractility in paroxysmal atrial fibrillation (AF) and underlying mechanisms. We investigated the contractile function of single isolated CM from LA and RA using a 7-day acetylcholine (ACh)-CaCl2 AF model in rats. We compared auxotonic force, sarcomere length dynamics, cytosolic calcium ([Ca2+]i) transients, intracellular ROS and NO production in LA and RA CM, and analyzed the phosphorylation levels of contractile proteins and actin-myosin interaction using an in vitro motility assay. AF resulted in more prominent structural and functional changes in LA myocardium, reducing sarcomere shortening amplitude, and velocity of sarcomere relengthening in mechanically non-loaded LA CM, which was associated with the increased ROS production, decreased NO production, reduced myofibrillar content, and decreased phosphorylation of cardiac myosin binding protein C and troponin I. However, in mechanically loaded CM, AF depressed the auxotonic force amplitude and kinetics in RA CM, while force characteristics were preserved in LA CM. Thus, inter-atrial differences are increased in paroxysmal AF and affected by the mechanical load that may contribute to the maintenance and progression of AF.

Divalent ions as mediators of carbonylation in cardiac myosin binding protein C

The dosing and efficacy of chemotherapeutic drugs can be limited by toxicity caused by off-pathway reactions. One hypothesis for how such toxicity arises is via metal-catalyzed oxidative damage of cardiac myosin binding protein C (cMyBP-C) found in cardiac tissue. Previous research indicates that metal ion mediated reactive oxygen species induce high levels of protein carbonylation, changing the structure and function of this protein. In this work, we use long timescale all-atom molecular dynamics simulations to investigate the ion environment surrounding the C0 and C1 subunits of cMyBP-C responsible for actin binding. We show that divalent cations are co-localized with protein carbonylation-prone amino acid residues and that carbonylation of these residues can lead to site-specific interruption to the actin-cMyBP-C binding.

Development of T-ARMS-PCR to Detect MYBPC3 Gene Variation in Hypertrophic Cardiomyopathy (HCM) Patients

Hypertrophic cardiomyopathy (HCM) is a common and complex, genetically inherited, cardiovascular disorder. It is typically inherited in an autosomal dominant manner with variable penetrance and mutable expression. Mutations in MYBPC3 gene is one of the genetic causes of HCM. Only 0.2% of general population suffers from HCM. The MYBPC3 gene provides instructions for making cardiac myosin binding protein C, which is imperative for the maintenance and regulation of normal cardiac functions. This study aims to explore the reported SNP rs1052373 from exon 30 of MYBPC3 gene in the population of Punjab, Pakistan. The reported SNP rs1052373 was analysed using Tetra Amplification Refractory Mutation System Polymerase Chain Reaction (T-ARMS-PCR) to find the allelic frequency in the selected population. T-ARMS-PCR is a cost effective, flexible, rapid, and accurate tool for genotyping. The specific sequences of MYBPC3 gene from exons 30 and 31 and introns 29, 30, and 31 were retrieved from NCBI (https://www.ncbi.nlm.nih.gov/). A tetra primer designing tool known as Primer 1 (http://primer1.soton.ac.uk/primer1.html) was used to design the primers for the targeted region of MYBPC3 gene. In this study, the genotyping of previously reported SNP rs1052373 showed variation in the disease group, giving CC, CT, and TT genotypes with the frequency of 0.04. The genotyping analysis of rs1052373 showed that the allelic frequency of homozygous condition T/T was 0.02 and the allelic frequency of heterozygous condition C/T was 0.02 in disease group as compared to the control group. In the latter, the homozygous T/T and heterozygous C/T genotypes were not observed in any individuals. All the individuals in control group carried homozygous C/C genotype. While, the frequency of homozygous C/C genotype was 0.96 in disease group. The findings of this study would help to find novel molecular markers for HCM diagnosis.

Multi-marker panel in patients with NSTEMI: pillars of pathogenesis and diagnostics

Aim. Assessment within the multi-marker panel applied to patients with NSTEMI of admission levels of the main markers of cardiovascular pathology in order to disentangle the pathogenetic interface and identify diagnostic predictors. Material and methods. The research was carried out on a group of 87 patients with NSTEMI, exposed to angioplasty, in which the admission values of 2 morphofunctional markers of endothelial dysfunction were determined, as well as the serum levels of 53 biochemical markers with reference to: inflammation, oxidative stress, endothelial dysfunction, cell injury, hemostasis disorder, myocardial and extracellular matrix (ECM) remodeling. The control group has consisted of 40 apparently healthy people. Results. The analysis of the multi-makrer panel revealed significant deviations of the majority of the explored markers compared to the control level. Endothelial dysfunction was marked by the increase of thickness of the medial-intima complex of the carotid artery and the decrease of the flow-mediated dilation of brachial artery in association with a 7694% raise of endothelial cell fragments (EF), phospholipase A2 (PhA2) and angiopoietin 2 (Ang 2). Among 16 markers of inflammation, the elevation of myeloperoxidase (MPO) by 156% is remarkable as a specific marker of NETosis. Activated oxidative stress is the result of the impairment of the antioxidant defense, and hemostasis disorder must be underlined by double increase of fibrin monomers (FM). From a pathogenetic point of view, the multiple increase (more than 8 times) of cardiac myosin-binding protein (cMyBP-C) is important and understandable, and the markers of myocardial and ECM remodeling basically demonstrated an activation of several types of metalloproteinases. Conclusion. From the spectrum of the multi-marker panel applied to patients with NSTEMI, markers with plausible diagnostic value due to inteligibly reflected pathogenetic mechanism are highlighted as: MPO, PhA2, Ang 2, EF, FM, and cMyBP-C.