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Background: Transcriptional reconfiguration is central to heart failure, the most common cause of which is dilated cardiomyopathy (DCM). The effect of 3-dimensional chromatin topology on transcriptional dysregulation and pathogenesis in human DCM remains elusive. Methods: We generated a compendium of 3-dimensional epigenome and transcriptome maps from 101 biobanked human DCM and nonfailing heart tissues through highly integrative chromatin immunoprecipitation (H3K27ac [acetylation of lysine 27 on histone H3]), in situ high–throughput chromosome conformation capture, chromatin immunoprecipitation sequencing, assay for transposase-accessible chromatin using sequencing, and RNA sequencing. We used human induced pluripotent stem cell–derived cardiomyocytes and mouse models to interrogate the key transcription factor implicated in 3-dimensional chromatin organization and transcriptional regulation in DCM pathogenesis. Results: We discovered that the active regulatory elements (H3K27ac peaks) and their connectome (H3K27ac loops) were extensively reprogrammed in DCM hearts and contributed to transcriptional dysregulation implicated in DCM development. For example, we identified that nontranscribing NPPA-AS1 (natriuretic peptide A antisense RNA 1) promoter functions as an enhancer and physically interacts with the NPPA (natriuretic peptide A) and NPPB (natriuretic peptide B) promoters, leading to the cotranscription of NPPA and NPPB in DCM hearts. We revealed that DCM-enriched H3K27ac loops largely resided in conserved high-order chromatin architectures (compartments, topologically associating domains) and their anchors unexpectedly had equivalent chromatin accessibility. We discovered that the DCM-enriched H3K27ac loop anchors exhibited a strong enrichment for HAND1 (heart and neural crest derivatives expressed 1), a key transcription factor involved in early cardiogenesis. In line with this, its protein expression was upregulated in human DCM and mouse failing hearts. To further validate whether HAND1 is a causal driver for the reprogramming of enhancer–promoter connectome in DCM hearts, we performed comprehensive 3-dimensional epigenome mappings in human induced pluripotent stem cell–derived cardiomyocytes. We found that forced overexpression of HAND1 in human induced pluripotent stem cell–derived cardiomyocytes induced a distinct gain of enhancer–promoter connectivity and correspondingly increased the expression of their connected genes implicated in DCM pathogenesis, thus recapitulating the transcriptional signature in human DCM hearts. Electrophysiology analysis demonstrated that forced overexpression of HAND1 in human induced pluripotent stem cell–derived cardiomyocytes induced abnormal calcium handling. Furthermore, cardiomyocyte-specific overexpression of Hand1 in the mouse hearts resulted in dilated cardiac remodeling with impaired contractility/Ca 2+ handling in cardiomyocytes, increased ratio of heart weight/body weight, and compromised cardiac function, which were ascribed to recapitulation of transcriptional reprogramming in DCM. Conclusions: This study provided novel chromatin topology insights into DCM pathogenesis and illustrated a model whereby a single transcription factor (HAND1) reprograms the genome-wide enhancer–promoter connectome to drive DCM pathogenesis.

Introduction: Myocardial hypoxia & intestinal hyperpermeability (IH) are two important events commonly observed in the aftermath of a myocardial infarction (MI) event. Recent studies have shown that gut bacteria and their metabolites are able to leak into the systemic circulation due to post-MI IH. Hypothesis: We hypothesized that facultative anaerobic gut bacteria such as E. coli will be able to translocate and colonize the hypoxic heart post-MI. Methods: C57 mice were given an oral administration of 10e9 cfu of luciferase/GFP expressing E. coli Nissle (EcN). Permanent occlusion of LAD arteries was performed to induce MI. Mouse hearts were checked for presence of EcN using PCR at different timepoints (n=32), IHC (n=4), and siderophore-based PET imaging (n=2). Immunoblotting of heart tissue lysate was used to check for presence of GFP. Results: PCR amplification of DNA extracted from MI hearts of mice given oral EcN revealed cardiac presence of translocated EcN. IHC analysis further confirmed presence of EcN in the heart. Siderophore-based PET imaging & radionuclide-based biodistribution studies revealed significantly higher uptake in the MI heart vs. Sham corroborating EcN presence. Immunoblotting revealed presence of GFP in cardiac tissue of MI mice suggesting that bacterial products and proteins could potentially translocate through the gut-heart axis. Conclusion: MI induced IH & myocardial hypoxia contribute to the translocation of gut bacteria and colonization of the ischemic heart.

Introduction: Left ventricular (LV) diastolic dysfunction (LVDD) is often characterized by organ-level (global) metrics whose quantitative connections to mechanical remodeling events at the tissue and fiber levels remain poorly studied. Methods: We performed measurements in the LV at three length scales, namely, organ, tissue, and fiber, in two murine models of LVDD: (i) diabetic (db/db) (n=10) versus wild-type (WT; n=10) mice, and (ii) novel knock-in cardiac myosin binding protein-C (cMyBP-C) phospho-ablated (KI-3A; n=8) versus cMyBP-C phospho-mimetic (KI-3D, n=6) and WT (n=8) mice. Echocardiography was done in vivo. Left ventricular free wall (LVFW) specimens were harvested and passively stretched along with circumferential (C) and longitudinal (L) directions (schematically identified in Fig. 1c) in select mice. Passive tests were followed by activation-relaxation tests of the LVFW specimens at resting biaxial stretches. Active force-pCa measurements at resting stretch were carried out on the skinned papillary muscle fibers. Results: Both db/db and KI-3A mice demonstrated slow relaxation at the organ level indicated by increased E/e' (Figs. 1a-b). db/db LVFW specimens showed increased circumferential stiffness at the tissue level under biaxial passive stretching (p0.25). Biaxial activation-relaxation tests of LVFW specimens in knock-in mice (Fig. 1c shows the results for KI-3A mice) revealed that KI-3A mice relax significantly slower than KI-3D mice along the longitudinal direction (Fig. 1d). Fiber-level tests demonstrated that active force development was significantly enhanced in db/db mice (Fig. 1e) while it was significantly suppressed in KI-3A mice relative to KI-3D and WT mice (Fig. 1f). Conclusions: Although both db/db and KI-3A mice showed LVDD at the organ level, they demonstrated different mechanical alterations at the fiber and tissue fiber levels, suggesting that global metrics should be complemented with metrics characterizing the LV properties at the fiber and tissue levels to fully characterize LVDD.

Glycogen Synthase Kinase 3β (GSK-3β) can modulate myofilament function in vitro . However, it’s in vivo role, mechanism, and translational relevance are unknown, which we investigated here using inducible cardiomyocyte specific GSK-3β KO mice. Compared to tamoxifen-treated GSK-3β fl/fl Cre- mice (Con), skinned myocytes from KO mice had reduced calcium sensitivity at long sarcomere lengths (SL = 2.2 μm), but there were no differences at short SL (~1.9 μm). Thus, myocytes from KO mice did not sensitize to calcium with stretch, a mechanism called length dependent activation (LDA) that underlies the organ-level Frank-Starling law. LDA has been attributed to (1) phosphorylation of myofilament proteins, (2) altered lattice-spacing, and (3) changes to titin’s elastic properties. Using mass spectrometry and small energy x-ray diffraction we ruled out the first two mechanisms, however we did find that GSK-3β KO myocytes had decreased passive tension – indicating the loss of LDA was due to loss of titin as a length sensor. Interestingly, immunofluorescence showed that GSK-3β localized to the z-disc when phosphorylated at Y216 and, via mass spectrometry, phosphorylated primarily z-disc proteins including several sites on the structural protein Ablim-1, which we showed also localizes to the z-disc. These data suggested that GSK-3β’s effect on titin is likely through altering its ability to anchor to the z-disc through targeting of these z-disc proteins. To provide further evidence that GSK-3β is specifically altering LDA, we genetically removed a downstream effecter of LDA, cardiac myosin binding protein-C (cMyBP-C). In vitro treatment with exogenous GSK-3β was able to increase calcium sensitivity at long SLs in both KO and WT mice but had no effect on cMyBPC KO mice or mice lacking the c-terminal domains of cMyBPC that are known to be important for LDA. Lastly, we found that human heart failure patients had less myofilament GSK-3β compared to non-failing patients, and that these same samples had a depressed LDA. This work has identified a novel mechanism by which GSK-3β localizes to the myofilament to modulate LDA and indicates that z-disc localized GSK-3β may be a possible therapeutic target to restore the Frank-Starling mechanism in heart failure patients.

Rationale: Myosin binding protein-C ( MYBPC ) is a sarcomeric protein which regulates the force of contraction in striated muscles. Mutations in the MYBPC family of genes, slow skeletal( MYBPC1 ), fast skeletal ( MYBPC2 ) and cardiac ( MYBPC3 ) can result in cardiac and skeletal myopathies, yet their evolutionary pattern, pathogenicity and impact on MYBPC structure remain to be elucidated. Objective: To assess conserved and epigenetic patterns of MYBPC family mutations. Methods and Results: Leveraging a machine learning approach, the Genome Aggregation Database (gnomAD) provided 12353, 6227 and 5279 variants in MYBPC1 , MYBPC2 and MYBPC3 genes, respectively, followed by analysis with the Ensembl variant effector predictor. Missense variants comprised 62-68% of total variants in which the first and second nucleotide (nt) positions in the codons were highly altered, with G/A substitution nt substitution the most predominant. Arginine was the most mutated amino acid, important because most disease-causing mutations in MYBPC are arginine in origin. Domains C5 and C6of MYBPC were found to be hotspots for most mutations in the MYBPC family. A high percentage of truncated mutations in MYBPC3 cause cardiomyopathies. Arginine and glutamate were the top hits in MYBPC1 and MYBPC3, respectively, and tryptophan and tyrosine were the most common among the three paralogs changing to premature stop codons and causing protein truncations at the carboxy terminus. Conclusion: A heterogeneous epigenetic pattern was identified among the three MYBPC paralogs. Genomic databases using machine learning approaches can be used to diagnose and design therapeutics to treat muscle disorders caused by MYBPC mutations.

Missense variant Ile79Asn in human cardiac troponin T (HcTnT-I79N) tail region has been linked to familial hypertrophic cardiomyopathy (HCM), arrhythmia, and sudden cardiac death. It has been reported that inotropic stimulation with high extracellular Ca 2+ or isoproterenol led to diastolic dysfunction in both isolated and in vivo HcTnT-I79N mice hearts. Although HcTnT-I79N effects are acknowledged to be dependent on the inotropic state of the cardiac muscle, little is known about how this pathogenic variant affects the Frank-Starling law of the heart. To further investigate the functional and structural consequences of this deadly variant in a stretch-dependent manner, cardiac tissues were harvested from non-transgenic (NTg) control mice and transgenic mice bearing HcTnT-I79N. Left ventricular papillary muscle bundles were permeabilized and mounted for mechanical measurements. Sarcomere length (SL 1.9, 2.1 or 2.3 μm) was set at pCa 8 using HeNe laser diffraction and then Ca 2+ -dependence of isometric force, sinusoidal stiffness (SS, 0.2% PTP length oscillation) and rate of tension redevelopment ( k TR ) were measured. We observed that HcTnT-I79N tissue exhibited increased myofilament Ca 2+ -sensitivity of force, increased SS, slower k TR at all levels of Ca 2+ -activation, and diminished length-dependent activation (LDA). Small-angle X-ray diffraction revealed that HcTnT-I79N permeabilized cardiac muscles exhibit smaller myofilament lattice spacing at longer SLs (2.1 μm and 2.3 μm) compared to NTg. Using 3% Dextran T500 to osmotically compress the myofilament lattice (SL 2.1 μm), HcTnT-I79N showed no change in myofilament lattice spacing and little change in contractile indices associated with LDA. Interestingly, upon osmotic compression, HcTnT-I79N displayed a decrease in disordered relaxed state (DRX, ON state) of myosin and an increase in super-relaxed state (SRX, OFF state) of myosin. We conclude that altered cardiac myofilament performance, lack of responsiveness to osmotic compression, and reduced LDA observed with HcTnT-I79N are partially due to a combination of smaller myofilament lattice and disturbed ON and OFF states of myosin.

Rationale: Hypertrophic cardiomyopathy (HCM) is common inheritable heart disease. HCM is highly associated with arrhythmias and/or sudden death. Studies show that molecular defects in calcium handling impairing the cardiomyocyte contractility is a predominant cause. However, the pathophysiology underlying HCM with arrhythmias is not well understood, hindering the identification of novel therapies. Objective: To investigate the pathophysiological consequences of compound variants, consisting of Histidine Rich Calcium Binding Protein gene ( HRC S96A ) and an intronic 25bp deletion in cardiac myosin binding protein-C ( MYBPC3 Δ25bp ). Methods and Results: Clinical data revealed that co-segregation of HRC S96A and MYBPC3 ΔInt32 results in cardiac arrhythmia, heart failure, and sudden cardiac death in South Asians. To determine the cellular/molecular trigger underlying the pathophysiology of this dual variant, we used humanized, knock-in, heterozygous mouse models, including HRC S81A (equivalent to HRC S96A ) MYBPC3 Δ25bp , HRC S81A / MYBPC3 Δ25bp (double variant, DV), and wild-type controls. Echocardiography revealed a significant decrease in the percentage of ejection fraction and fractional shortening in DV mice, as well as the presence of diastolic dysfunction, at 12 weeks of age, compared to single-variant and wild-type mice. Electrocardiogram tracing of DV mice showed the presence of stress-induced arrhythmias, such as ventricular tachycardia after caffeine and epinephrine administration. Using isolated cardiomyocytes in vitro , Calcium transient experiments indicated a significant decrease in fractional shortening, Ca 2+ transient amplitude, and a higher number of after-contractions in cardiomyocytes from DV mice. DV mouse hearts showed increased phosphorylation of CaMKII and SR Ca 2+ leak by cardiomyocytes. Inclusion of the CaMKII inhibitor KN-93 rescued the increases in SR Ca 2+ leak and in aftercontractions. Conclusion: Impaired Ca 2+ -handling, owing to the HRC S96A variant, aggravates SR Ca 2+ leak and aftercontractions in MYBPC3 Δ25bp cardiomyocytes, subsequently triggering cardiac arrhythmias and sudden death in vivo .

Rationale: Cardiac m yosin binding protein-C regulates a ctomyosin interaction in striated muscle, but mutations in the MYBPC3 gene can lead to hypertrophic cardiomyopathy (HCM) as seen in some South Asians living in the USA carrying a novel variant wherein an aspartic acid is mutated to a valine at position 389 (D389V). Individuals and iPSC-derived cardiomyocytes carrying D389V display hypercontractility, indicating early onset of HCM. However, the mechanisms underlying the pathophysiology of this mutant in the context of HCM are unknown. Objective: To define the pathophysiological consequences D389V on myosin and cardiac function in vivo . Methods and Results: Compared with wild-type controls, our D389V knock-in homozygous mouse model showed decreased cardiac function by percentage of ejection fraction (-23%, PMYBPC3 domains (rC0C2 D389V ), cosedimentation and solid-phase binding assays showed significantly reduced binding rate of rC0C2 D389V to the myosin S2 region (-55% and -23%, Pin vitro actin motility over myosin increased 24% (PWT control, indicating a causal relationship between variant and decreased MYBPC3 binding to myosin. Human iPSC-derived D389V het cardiomyocytes display an increase in lipid peroxide and reactive oxygen species by +3- and +7-fold P Conclusion: D389V decreases interaction between MYBPC3 and myosin S2, causing reduced cardiac function and providing mechanistic evidence that it contributes to the etiology of HCM.

This article continues my previous thread examining early career viewpoints and turns the discussion to leadership training in the academic and pharmaceutical industries. Specifically, I will examine the characteristics of good leadership and leadership training required to succeed as a cardiovascular researcher in today’s competitive workplace.

Introduction: Hypertrophic cardiomyopathy (HCM) is a disease caused primarily by sarcomere gene mutations [like myosin-binding protein C3 ( MYBPC3 )], with several distinct phenotypes. Tissue-level inflammation has been reported in human HCM, tissue-specific neutrophil subsets, and their dysregulation cause inflammatory myopathies, and neutrophil extracellular traps (NETs) are associated with cardiac fibrosis in aged rodents. However, the mechanism(s) responsible for the broad phenotypic variability and changes observed over time transitioning from HCM to dilated cardiomyopathy (DCM) has not yet been elucidated. Objective: To determine the cardiac inflammatory signature of HCM and transition from HCM to DCM and its relationship to fibrosis and ventricular remodeling in an established MYBPC3 ( cMyBP-C t/t ) mouse model. Method and Results: Mixed-gender cMyBP-C +/+ (WT) and mutant mice ( cMyBP-C t/t ) underwent echocardiography and were euthanized at one, two and three months of age (n=8) and blood and hearts were harvested. Echocardiography and histopathology examination confirmed significant heart dysfunction and tissue remodeling in cMyBP-C t/t mice showing cardiac hypertrophy at one month of age (Left ventricular (LV) posterior wall systole 1.20 ±0.39 vs 1.51±0.49 and LV posterior wall diastole 0.96 ±0.22 vs 1.38 ±0.36 mm; * p ), and DCM phenotype (LV internal diameter systole 2.40 ±0.41 vs 3.67 ±0.25 and LV internal diameter diastole 3.44 ±0.29 vs 4.30 ±0.39 mm; * p ) along with myofibrillar loss and increased cardiac fibrosis at three months. Interestingly, LV dysfunction and hypertrophy resulted in a time-dependent increase in the activation of coagulation, as measured by plasma microvesicle tissue factor activity, thrombin antithrombin, and D-dimer. In silico analysis of RNA-Seq data from 3-months old cMyBP-C t/t mice heart revealed key genes and pathways associated with HCM, DCM, tissue remodeling, renin-angiotensin-aldosterone signaling, fibrosis, apoptosis, NETosis, and inflammation. Conclusions: The transition from HCM to a DCM phenotype involves proinflammatory and profibrotic signaling. Therapies directed at tissue-specific inflammation and NETs may be a novel and impactful strategy for HCM.

Introduction: Primary hypertension (PH) is a multifactorial disease influenced by genetic, epigenetic, and environmental factors. Despite the occurrence of PH-associated cardiovascular events in youth, the molecular mechanism(s) of target organ damage (TOD) are unknown. Objectives: (1) To identify an epigenetic signature and gene expression profiles in adolescents with low blood pressure (BP) and normal left ventricular mass (LVM) compared to those with high BP and high LVM; and (2) to determine novel gene targets and associated signaling pathways for future investigation and intervention. Methods and Results: A total of 397 participants (mean age 15.6 ±1.7 years, 59% male, 63% Caucasian) were enrolled across the distribution of BP. The average daytime ambulatory systolic BP recorded in healthy and hypertensive participants was 112 ±9.71 and 133 ±7.2 mmHg ( p ) respectively. Clinical measures revealed higher body mass index (26.8 ±7.02 vs 29.6 ±7.88 Kg/m 2 ; p ), and abnormal circulatory HDL (47.4 ±12.1 vs 43.4 ±11.7 mg/dL; p ), glucose (87.8 ±7.98 vs 90.8 ±8.17 mg/dL; p ), insulin (17.8 ±14.3 vs 23.7 ±19 μIU/dL; p ), creatinine (0.718 ±0.13 vs 0.727 ±0.17 mg/dL; p ), uric acid (5.4 ±1.63 vs 6.04 ±1.52 mg/dL; p ), CRP (1.35 ±1.8 vs 1.92 ±2.14 mg/dL; p ), and left ventricular hypertrophy (LVM/ht 2.7 ; 31.4 ±6.74 vs 33.5 ±7.15 g/m 2.7 ; p ), and arterial stiffness (Pulse wave velocity; 4.83 ±0.69 vs 5.35 ±0.92 m/sec; p ). Using peripheral blood mononuclear cells, mRNA-Seq, miRNA-Seq, and whole-genome DNA methylation analysis revealed master genes, and regulatory pathways related to BP regulation, tissue fibrosis and cardiovascular remodeling. Our study reveals a novel PH-associated TOD mechanism, showing angiogenesis inhibition mediated by VASH1 (Vasohibin-1) upregulation and downtrends in VASH2 (Vasohibin-2), VEGFC (Vascular endothelial growth factor C), HIF1α (Hypoxia-inducible factor 1-alpha), and IGF1 (Insulin Like Growth Factor 1). Moreover, VASH1 targeting miRNA hsa-miR-30e-5p is inversely regulated. Conclusion: Angiogenesis inhibition in the presence of common demographic and clinical intermediate-phenotypes may contribute to the development of TOD in hypertensive youth.

Background: Myocardial infarction leads to a massive loss of cardiomyocytes (CM) and cardiac remodeling, which results in reduced cardiac function and, ultimately, heart failure. Adult mammalian CMs cannot spontenously proliferate, and thus repair the cardiac injury, however in our previous study we showed that simultaneous knock down of Rb1 and Meis2 induced CM cell cycle activation that resulted in improved cardiac function. Moreover, most significant cardioprotective effects were due to CM mediated paracrine mechanisms including angiogenesis and CM cell survival. Thus, this study aims to identify these indirect cardioprotective pathways dependent on CM cell cycle. Methods and Results: We utilized genetically modified FUCCI mice, which allows identifying the cycling vs. non-cycling CM for transcriptome analysis. Adult mouse CM was isolated through the Langendorff heart perfusion method, using our modified isolation protocol, and cultured in the modified DMEM media. Adult CMs were transfected with equimolar (50uM each) combination of siRb1 and siMeis2 (siRNA-cocktail), cel-miR-67 served as control. CMs were harvested, and RNA isolation was performed on day seven after transfection. Rb1 and Meis2 knock-down were validated through CM proliferation analysis and RT-PCR based expression profiling for selected markers of proliferation, angiogenesis, cell survival, and structural genes. Our analysis showed a significant down-regulation of Rb1 and Meis2 after siRNA treatment.Further, we observed an up-regulation of pro-angiogenic and pro-survival genes without any significant alteration in the structural genes. After validating our samples, we performed a whole-genome transcriptome analysis using a high-throughput Illumina NextSeq platform. Our RNAseq analysis revealed the activation of pathways, which may induce the CM rejuvenation. The identified potential targets will be further validated through in vivo experiments. Conclusions: Our results suggest the activation of CM rejuvenation after knocking-down Rb1 and Meis2 to improve the cardioprotection after injury.

Although I currently lead a team of cardiovascular investigators at the University of Cincinnati, my beginnings were humble as I came from a farming family in a small village in the southernmost part of India. The path I traveled was arduous, and it involved significant struggles, but I’ve finally realized many of my career goals. My story recapitulates the essence of some of the common career hurdles that many early-career cardiovascular scientists must overcome these days, and in this article, these career hurdles are discussed, as well as some strategies to overcome them. This article presents common hurdles encountered by developing and early-career cardiovascular scientists and outlines some effective strategies to overcome these challenges. Students, whether at the undergraduate level or beyond, often do not establish clearly defined career goals, and even established long-term plans can encounter daunting, unforeseen stumbling blocks. It is convenient to blame our failure to succeed on a lack of resources, including family support or time constraints. Sometimes, however, our lack of success may simply depend on not being at the right place at the right time. Yet, fundamentally, it is the lack of resourcefulness, not resources, that poses the greatest barrier to achieving our goals. Resourcefulness is defined as the ability to find quick and clever ways to overcome difficulties. Resourcefulness involves optimizing the resources available to you by finding alternative ways to push forward. In the recesses of our minds, we all have an idea of our potential. In this sense, we are all obligated to create, make, or change our environment, academic, or otherwise so that we can achieve our potential. Therefore, we must all strive to find the environment that will best nourish our innate abilities. I grew up in a village named Pattiveeranpatti located in the state of Tamil Nadu in …

Background Myocardial infarction results in a large‐scale cardiomyocyte loss and heart failure due to subsequent pathological remodeling. Whereas zebrafish and neonatal mice have evident cardiomyocyte expansion following injury, adult mammalian cardiomyocytes are principally nonproliferative. Despite historical presumptions of stem cell–mediated cardiac regeneration, numerous recent studies using advanced lineage‐tracing methods demonstrated that the only source of cardiomyocyte renewal originates from the extant myocardium; thus, the augmented proliferation of preexisting adult cardiomyocytes remains a leading therapeutic approach toward cardiac regeneration. In the present study we investigate the significance of suppressing cell cycle inhibitors Rb1 and Meis2 to promote adult cardiomyocyte reentry to the cell cycle. Methods and Results In vitro experiments with small interfering RNA –mediated simultaneous knockdown of Rb1 and Meis2 in both adult rat cardiomyocytes, isolated from 12‐week‐old Fischer rats, and human induced pluripotent stem cell–derived cardiomyocytes showed a significant increase in cell number, a decrease in cell size, and an increase in mononucleated cardiomyocytes. In vivo, a hydrogel‐based delivery method for small interfering RNA –mediated silencing of Rb1 and Meis2 is utilized following myocardial infarction. Immunofluorescent imaging analysis revealed a significant increase in proliferation markers 5‐ethynyl‐2′‐deoxyuridine, PH 3, KI 67, and Aurora B in adult cardiomyocytes as well as improved cell survivability with the additional benefit of enhanced peri‐infarct angiogenesis. Together, this intervention resulted in a reduced infarct size and improved cardiac function post–myocardial infarction. Conclusions Silencing of senescence‐inducing pathways in adult cardiomyocytes via inhibition of Rb1 and Meis2 results in marked cardiomyocyte proliferation and increased protection of cardiac function in the setting of ischemic injury.

Rationale: Affecting 1 in 300 individuals, hypertrophic cardiomyopathy (HCM) is a genetic heart disease characterized by left ventricular hypertrophy, myocardial disarray, and sudden cardiac death. Often, HCM is associated with myocardial hypercontractility. The subfragment-2 (S2) of beta-myosin heavy chain contains a cluster of missense and deletion mutations associated with severe HCM. Interestingly, myosin S2 interacts with the C0-C2 region of cardiac myosin binding protein C (cMyBP-C) in a phosphorylation-dependent manner to regulate sarcomere contractility. However, the nature of myosin S2 and cMyBP-C interactions and the mechanism(s) by which mutations in myosin S2 cause HCM remain to be elucidated. Objective: To determine whether mutations in myosin S2 weaken its interaction with cMyBP-C, resulting in enhanced myofilament contractility. Methods and Results: Myosin S2 proteins (126 amino acids) containing three clinically relevant mutations (R870H, E924K, E930del, or wild type), and recombinant C0-C2 region of cMyBP-C were produced and purified by metal affinity chromatography. Solid-phase binding assays and isothermal calorimetry experiments revealed a significantly dampened binding to C0-C2 for these three mutants in myosin S2 (30% lower than wild type, p Conclusions: Mutations in myosin S2 result in reduced binding to cMyBP-C. Functionally, this would result in a greater attachment of cross-bridges, and thus enhance myofilament contractility. Strikingly, these mutations increase their affinity to cMyBP-C upon phosphorylation, demonstrating fundamental changes to the regulation of contractile function.

Rationale: Cardiac myosin binding protein-C (cMyBP-C) is heavily phosphorylated to regulate normal cardiac function under basal conditions. However, its phosphorylation level is significantly decreased in patients with heart failure and atrial fibrillation. Furthermore, decreased cMyBP-C phosphorylation causes reduced myofilament contractility and decreased calcium sensitivity. The impact of such decreases in cMyBP-C phosphorylation and myofilament calcium sensitivity on the overall calcium handling and potential induction of arrhythmogenesis is not known. Objective: To determine the necessity and sufficiency of cMyBP-C phosphorylation to regulate calcium cycling and contractility at the isolated cardiomyocyte level. Methods and Results: Contractile properties and calcium kinetics were measured in intact cardiomyocytes isolated from 3-month-old, mixed sex, mice expressing phospho-ablated (S273A/S282A/S302A) cMyBP-C (AAA) or phospho-mimetic (S273D/S282D/S302D) cMyBP-C (DDD) and nontransgenic (NTG) control mice. AAA cells displayed a significant decrease in fractional shortening compared to NTG and DDD cells (9.4% vs 12.8% in NTG, and 12.3% in DDD, pvs . NTG and DDD) and prolonged decay time of the calcium transient (26%, pvs NTG and DDD) when compared with NTG and DDD myocytes. Caffeine-induced calcium release in AAA myocytes indicated no change in SR calcium content, while sodium-calcium exchanger function, assessed as the time constant (τau) of calcium decline, was increased (89%, pvs NTG). However, these depressive effects in AAA myocytes were relieved by isoproterenol (100 nmol/L) stimulation. Furthermore, stress conditions (2 Hz + ISO) increased after-contractions in AAA cardiomyocytes (60% in AAA vs 13% in NTG, p Conclusion: Dephosphorylation of cMyBP-C is sufficient to reduce sarcomere contractility and impair calcium cycling resulting in spontaneous after-contractions and arrhythmias under stress conditions.

Background: Hypertrophic cardiomyopathy (HCM) affects at least 1 in 500 people worldwide, and results in the thickening of the ventricular walls and reduced cardiac function. Mutations in MYBPC3 , encoding cardiac myosin binding protein-C, are the most common cause of HCM. Previously, a highly prevalent 25bp deletion within intron 32 of MYBPC3 was described in the South Asian population. The MYBPC3 d25bp variant is present in approximately 100 million people, and encompasses a splicing branch point predicted to result in abnormal splicing of exon 33. Thus, there is a critical need to understand the mechanism by which MYBPC3 d25bp may cause cardiomyopathy. Methods: To determine the role of the 25bp deletion in vivo , knock-in humanized mice were created in which intron 32 was replaced with the human intron 32, with or without the MYBPC3 d25bp mutation. Mice were characterized at 3- and 6-months of age by echocardiography, histological, and protein analysis. The presence of aberrant exon splicing was also determined in mice carrying the MYBPC3 d25bp variant through RT-PCR and mini-gene assays. Finally, exon trapping experiments were performed to understand the mechanism behind exon skipping. Results: Under baseline conditions, MYBPC3 d25bp displayed no changes in cardiac function or morphology as measured by echocardiography (FS (%): NTG 35.3%, WT 32.8%, Het 33.7%), heart weight to body weight ratio, or histology. While exon 33 skipping was not detected by RT-PCR, the presence of an alternative splice site within exon 33 was identified in MYBPC3 d25bp mice. However, this did not affect the protein levels of cMyBP-C. Furthermore, mini-gene experiments demonstrated that the MYBPC3 d25bp mutation significantly reduced the percentage of correctly spliced transcripts (86.2% vs. 77.5%). Conclusions: These data demonstrate that the presence of the highly prevalent 25bp deletion is not sufficient to cause disease under baseline conditions. However, it is possible that the increased levels of aberrant splicing may increase the risk for developing HCM.

Introduction: Primary hypertension (PH) is a multifactorial disease mainly influenced by genetic, epigenetic and environmental dynamics. Despite the occurrence of PH-associated cardiovascular (CV) events in youth, we have acquired only a limited understanding of epigenetic and gene regulation of blood pressure (BP)-related target organ damage (TOD) in adolescents. Aims and Objectives: To define circulatory gene and miRNA expression levels and allied signaling pathways in hypertensive adolescents (Hyp) with TOD. Methods and Results: Three hundred adolescents of both genders aged 11 to 18 years participated in the AHA-funded Study of Hypertension in Pediatrics - Adult Hypertension Onset in Youth (SHIP AHOY) Project. Mean clinic SBP was 104.3 ±8.1 and 133.0 ± 8.2 mmHg in normal vs Hyp ( p ) and mean daytime ambulatory SBP was 115.7 ±11.4 and 128.9 ±6.4 mmHg in normal vs Hyp ( p ), respectively. Youth with PH also had higher BMI (22.33 ±3.67 vs 31.56 ±9.42; p< 0.05 ), elevated serum creatinine (0.73 ± 0.18 vs 0.92 ±0.12; p< 0.05 ), and left ventricular hypertrophy (LVM/ht 2.7 ; 25.4 ±1.8 vs 41.7 ±1.8; p< 0.05 ), and trend for increased arterial stiffness (PWV; 4.8 ±0.6 vs 5.8 ±2.0; p =0.18). mRNA and microRNA seq were performed using peripheral blood cells of 10 normal (mean 15.2 ±1.4 years; 50% male), and 10 Hyp patients (mean 15.5 ±1.5 years; 70% male). Seq data analysis revealed master genes (Fig. 1) and pathways that were differentially regulated in Hyp patients with TOD. Conclusions: PH in youth is associated with TOD that relates to a distinct gene expression profile. Knowledge of allied pathways may lead to new treatments in hypertensive youth to prevent future CV diseases.

Background: Heart failure is a devastating disease affecting nearly 5 million Americans. We recently identified the upregulation of fast skeletal myosin binding protein-C (fsMyBP-C) in models of heart failure. fsMyBP-C is a homologue of cardiac MyBP-C, which is normally expressed in the heart. This family of proteins regulate contractility by modulating thick and thin filament interactions. However, the functional role(s) of fsMyBP-C expression in the heart is unknown. Methods: To understand the role of fsMyBP-C expression in the heart, we generated cardiac specific transgenic mice expressing fsMyBP-C under the control of the alpha myosin heavy chain promoter. Mice underwent serial echocardiography to monitor cardiac function. Western blotting and qRT-PCR were performed to determine transgene expression levels. Additionally, fsMyBP-C localization in cardiomyocytes was established by immunofluorescence. Furthermore, to understand the temporal expression profiles of the MyBP-C homologues, we performed qRT-PCR on 9 muscle groups at different developmental stages in healthy mice. Results: qRT-PCR demonstrated an upregulation of the slow MyBP-C transcript in the developing heart, while fsMyBP-C transcript levels increased steadily following birth in WT mice. At 3 months of age, transgenic mice displayed a significant increase in ventricular dimensions compared to NTG littermates by echocardiography (LVID d : 3.72 ± 0.07 vs. 4.17 ± 0.09 mm, ps : 2.44 ± 0.09 vs. 2.81 ± 0.09, p Conclusion: Mice expressing fsMyBP-C in the heart display a mild hypertrophic phenotype at 3 months, with preserved function, possibly indicating compensated hypertrophy. Ongoing studies investigate cardiac function at later stages and cardiac specific conditional knockout of fsMyBP-C to determine the long-term effect of fsMyBP-C regulation in the heart.

The mechanisms by which truncating mutations in MYBPC3 (encoding cardiac myosin binding protein-C; cMyBPC) or myosin missense mutations cause hyper-contractility and poor relaxation in hypertrophic cardiomyopathy (HCM) are incompletely understood. Using genetic and biochemical approaches we explored how depletion of cMyBPC altered sarcomere function. We demonstrate that stepwise loss of cMyBPC resulted in reciprocal augmentation of myosin contractility. Direct attenuation of myosin function, via a damaging missense variant (F764L) that causes dilated cardiomyopathy (DCM) normalized the increased contractility from cMyBPC depletion. Depletion of cMyBPC also altered dynamic myosin conformations during relaxation - enhancing the myosin state that enables ATP hydrolysis and thin filament interactions while reducing the super relaxed conformation associated with energy conservation. MYK-461, a pharmacologic inhibitor of myosin ATPase, rescued relaxation deficits and restored normal contractility in mouse and human cardiomyocytes with MYBPC3 mutations. These data define dosage-dependent effects of cMyBPC on myosin that occur across all phases of the cardiac cycle as the pathophysiologic mechanisms by which MYBPC3 truncations cause HCM. Therapeutic strategies to attenuate cMyBPC activity may rescue depressed cardiac contractility in DCM patients, while inhibiting myosin by MYK-461 should benefit the substantial proportion of HCM patients with MYBPC3 mutations.

Background: Mutations in cardiac myosin binding protein C ( MYBPC3 ) account for more than one third of identified hypertrophic cardiomyopathy (HCM). Data from both human patients and mouse models suggest that cardiac fibrosis preceeds hypertrophy and cardiac dysfunction, implying that fibrosis related signaling may be one of the initial signs of developing cardiac disease. We wished to determine if cardiomyocyte-autonomous TGFβ signaling is sufficient to initiate pathogenic fibrosis in the heart in the context of a cMyBP-C-induced disease. Methods and Results: Neonatal rat ventricular cardiomyocytes (NRVMs) expressing either wild-type or Mybpc3 mutations were mediated by adenovirus for 48 hours. Both cells and culture medium (conditional medium) were harvested. The fibrotic effects of the conditional medium on neonatal rat ventricular fibroblasts (NRVFs) were determined using “fibrotic” gene promoters driving luciferase (luc) expression ( αSMA-luc , postn-luc and col1a1-luc ). TGFβ levels in the conditional medium were determined using ELISA assays. Expression of cMybpc3 mutations activated TGFβ promoter activity ( Tgfb1-luc , Tgfb2-luc and Tgfb3-luc ) in a TGFβ receptor(s) (TβRs) dependent manner. Upregulation of TGFβ was also confirmed in transgenic mice expressing a fragment of cMyBP-C (cMyBP-C 40kDa ) whose expression results in significant fibrosis and cardiac disease. To establish causality, we genetically ablated TGFβ receptors ( Tgfbr1 and Tgfbr2 ) in the cardiomyocytes of the cMybpc3 40kDa mice. TGFβ receptors ablation blocked the induction of TGFβ expression, alleviating cardiac fibrosis and decreasing cardiac hypertrophy. Cardiac function was significantly improved and survival of the cMyBP-C 40kDa mice was increased. Conclusions: Cardiomyocytes are a critical source of TGFβ in cMyBP-C 40kDa hearts during the initial stages of pathogenesis. Thus, TβRs ablation at the early stage completely prevent the progression of the pathological process in vivo .

Background: MYBPC3 encodes cardiac myosin binding protein-C, which regulates sarcomeric stability and contractility. Previous work described a prevalent 25bp deletion in intron 32, MYBPC3 Δ 25bp , in the South Asian population. Occurring in an estimated 100 million carriers, this variant may be associated with cardiomyopathy and heart failure. MYBPC3 Δ25bp encompasses a splicing branch point that could affect splicing of exon 32 to exon 33, potentially resulting in an aberrantly spliced MYBPC3 transcript where exon 33 is skipped entirely. However, the mechanism by which MYBPC3 Δ 25bp associates with disease remains unclear. Methods: To determine the consequence of the 25bp deletion in vivo , mice were engineered that replaced the endogenous Mybpc3 intron 32 with either the normal human intron 32 or human intron 32 containing the 25bp deletion ( Mybpc3 Δ 25bp ) . We characterized Mybpc3 splicing in mice carrying human intron-32 and human iPSC derived cardiomyocytes (hiPSC-CM) from patients heterozygous and homozygous for MYBPC3 Δ 25bp by RT-PCR and using mini-gene assays (across 5 different mouse and human gene segments encompassing exon 32 through exon 34). Results: Echocardiography of mice 3 months of age revealed no changes in cardiac function by fractional shortening (WT: 32.8%, Het: 34.2%, Homo: 36.7%). However, homozygous Mybpc3 Δ 25bp mice had significantly smaller hearts compared to heterozygous and wildtype (3.4 vs 3.71 and 4.25 mg/g p=0.001). Mybpc3 Δ 25bp heterozygous and homozygous mice displayed minimal alternative splicing in exon 33 at baseline. Similarly, transcripts from hiPSC-CM from heterozygous and homozygous MYBPC3 Δ 25bp carriers also show minimal alternative splicing. Mini gene assays suggest that the 25bp deletion does reduce the proportion (77.5% v. 86.2%) of normally spliced transcripts. Conclusions: Taken together, these data suggest that under baseline conditions, MYBPC3 Δ 25bp results in minimal alternative splicing in both human iPSC-CMs and humanized mice harboring the 25bp deletion. While increase aberrant splicing may increase risk of hypertrophic cardiomyopathy in variant-carrying individuals, ongoing studies will determine whether other factors or gene mutations modulate the pathogenicity of the MYBPC3 Δ25bp variant.

Background— Pharmacological activation of cGMP-dependent protein kinase G I (PKGI) has emerged as a therapeutic strategy for humans with heart failure. However, PKG-activating drugs have been limited by hypotension arising from PKG-induced vasodilation. PKGIα antiremodeling substrates specific to the myocardium might provide targets to circumvent this limitation, but currently remain poorly understood. Methods and Results— We performed a screen for myocardial proteins interacting with the PKGIα leucine zipper (LZ)–binding domain to identify myocardial-specific PKGI antiremodeling substrates. Our screen identified cardiac myosin–binding protein-C (cMyBP-C), a cardiac myocyte–specific protein, which has been demonstrated to inhibit cardiac remodeling in the phosphorylated state, and when mutated leads to hypertrophic cardiomyopathy in humans. GST pulldowns and precipitations with cGMP-conjugated beads confirmed the PKGIα–cMyBP-C interaction in myocardial lysates. In vitro studies demonstrated that purified PKGIα phosphorylates the cMyBP-C M-domain at Ser-273, Ser-282, and Ser-302. cGMP induced cMyBP-C phosphorylation at these residues in COS cells transfected with PKGIα, but not in cells transfected with LZ mutant PKGIα, containing mutations to disrupt LZ substrate binding. In mice subjected to left ventricular pressure overload, PKGI activation with sildenafil increased cMyBP-C phosphorylation at Ser-273 compared with untreated mice. cGMP also induced cMyBP-C phosphorylation in isolated cardiac myocytes. Conclusions— Taken together, these data support that PKGIα and cMyBP-C interact in the heart and that cMyBP-C is an anti remodeling PKGIα kinase substrate. This study provides the first identification of a myocardial-specific PKGIα LZ-dependent antiremodeling substrate and supports further exploration of PKGIα myocardial LZ substrates as potential therapeutic targets for heart failure.

Rationale: Cardiac myosin binding protein-C (cMyBP-C) is a thick filament-associated protein that has been suggested to regulate cardiac contraction via its amino terminal (N’) region. However, the necessity of the N’-C0-C1f region (domains C0 through C1 and the first 17 residues of the M-domain) of cMyBP-C in regulating cardiac function in vivo has not been elucidated. Hypothesis: The N’-C0-C1f region of cMyBP-C is critical for normal cardiac function in vivo . Methods and Results: Transgenic mice with 80±4% expression of a truncated cMyBP-C missing the N’-C0-C1f region (cMyBP-C 110kDa ) were generated and characterized at 3-months of age. cMyBP-C 110kDa animals exhibited cardiac hypertrophy as suggested by an increased heart weight to body weight ratio (5.0±0.1 mg/g NTG vs. 6.9±0.1 mg/g cMyBP-C 110kDa , p110kDa hearts compared to hearts from non-transgenic (NTG) littermates. Intriguingly, increased phosphorylation of cMyBP-C at Ser-282 and Ser-302, sites important for cMyBP-C’s regulation of actomyosin interactions, was observed in cMyBP-C 110kDa hearts compared to controls. Electron microscopy revealed normal sarcomere structure in cMyBP-C 110kDa hearts but with apparently weaker cMyBP-C stripes. Furthermore, the ability of cMyBP-C to slow actin-filament sliding within the C-zone of native thick filaments isolated from NTG hearts was lost on thick filaments from cMyBP-C 110kDa hearts. Short-axis M-mode echocardiography indicated a significant elevation in left ventricular internal diameter and a significant reduction in fractional shortening (31±5% NTG vs. 16±3% cMyBP-C 110kDa , p=0.0003) in cMyBP-C 110kDa hearts compared to controls. Finally, global longitudinal strain analysis revealed abnormal wall motion in cMyBP-C 110kDa hearts. Based upon these data, we propose that the N’-region of cMyBP-C is a critical regulator of actomyosin interactions and controls aberrant contraction kinetics within the cardiac sarcomere. Conclusion: The N’-C0-C1f region of cMyBP-C regulates cardiac contractility and is necessary for maintaining normal cardiac function in vivo .

Background The geometric organization of myocytes in the ventricular wall comprises the structural underpinnings of cardiac mechanical function. Cardiac myosin binding protein‐C ( MYBPC 3) is a sarcomeric protein, for which phosphorylation modulates myofilament binding, sarcomere morphology, and myocyte alignment in the ventricular wall. To elucidate the mechanisms by which MYBPC 3 phospho‐regulation affects cardiac tissue organization, we studied ventricular myoarchitecture using generalized Q‐space imaging ( GQI ). GQI assessed geometric phenotype in excised hearts that had undergone transgenic ( TG ) modification of phospho‐regulatory serine sites to nonphosphorylatable alanines ( MYBPC 3 AllP−/(t/t) ) or phospho‐mimetic aspartic acids ( MYBPC 3 AllP+/(t/t) ). Methods and Results Myoarchitecture in the wild‐type ( MYBPC 3 WT ) left‐ventricle ( LV ) varied with transmural position, with helix angles ranging from −90/+90 degrees and contiguous circular orientation from the LV mid‐myocardium to the right ventricle ( RV ). Whereas MYBPC 3 AllP+/(t/t) hearts were not architecturally distinct from MYBPC 3 WT , MYBPC 3 AllP−/(t/t) hearts demonstrated a significant reduction in LV transmural helicity. Null MYBPC 3 (t/t) hearts, as constituted by a truncated MYBPC 3 protein, demonstrated global architectural disarray and loss in helicity. Electron microscopy was performed to correlate the observed macroscopic architectural changes with sarcomere ultrastructure and demonstrated that impaired phosphorylation of MYBPC 3 resulted in modifications of the sarcomere aspect ratio and shear angle. The mechanical effect of helicity loss was assessed through a geometric model relating cardiac work to ejection fraction, confirming the mechanical impairments observed with echocardiography. Conclusions We conclude that phosphorylation of MYBPC 3 contributes to the genesis of ventricular wall geometry, linking myofilament biology with multiscale cardiac mechanics and myoarchitecture.

Background— Inflammation plays a critical role in adverse cardiac remodeling and heart failure. Therefore, approaches geared toward inhibiting inflammation may provide therapeutic benefits. We tested the hypotheses that genetic deletion of interleukin-10 (IL-10), a potent antiinflammatory cytokine, exacerbates pressure overload–induced adverse cardiac remodeling and hypertrophy and that IL-10 therapy inhibits this pathology. Methods and Results— Cardiac hypertrophy was induced in wild-type and IL-10 knockout mice by isoproterenol (ISO) infusion. ISO-induced left ventricular dysfunction and hypertrophic remodeling, including fibrosis and fetal gene expression, were further exaggerated in knockout mice compared with wild-type mice. Systemic recombinant mouse IL-10 administration markedly improved left ventricular function and not only inhibited but also reversed ISO-induced cardiac remodeling. Intriguingly, a very similar cardioprotective response of IL-10 was found in transverse aortic constriction–induced hypertrophy and heart failure models. In neonatal rat ventricular myocytes and H9c2 myoblasts, ISO activated nuclear factor-κB and inhibited signal transducers and activators of transcription 3 (STAT3) phosphorylation. Interestingly, IL-10 suppressed ISO-induced nuclear factor-κB activation and attenuated STAT3 inhibition. Moreover, pharmacological and genetic inhibition of STAT3 reversed the protective effects of IL-10, whereas ectopic expression of constitutively active STAT3 mimicked the IL-10 responses on the ISO effects, confirming that the IL-10–mediated inhibition of nuclear factor-κB is STAT3 dependent. Conclusion— Taken together, our results suggest IL-10 treatment as a potential therapeutic approach to limit the progression of pressure overload–induced adverse cardiac remodeling.

Rationale: Cardiac myosin-binding protein-C (cMyBP-C) phosphorylation at Ser-273, Ser-282, and Ser-302 regulates myocardial contractility. In vitro and in vivo experiments suggest the nonequivalence of these sites and the potential importance of Ser-282 phosphorylation in modulating the protein's overall phosphorylation and myocardial function. Objective: To determine whether complete cMyBP-C phosphorylation is dependent on Ser-282 phosphorylation and to define its role in myocardial function. We hypothesized that Ser-282 regulates Ser-302 phosphorylation and cardiac function during β-adrenergic stimulation. Methods and Results: Using recombinant human C1-M-C2 peptides in vitro, we determined that protein kinase A can phosphorylate Ser-273, Ser-282, and Ser-302. Protein kinase C can also phosphorylate Ser-273 and Ser-302. In contrast, Ca 2+ -calmodulin-activated kinase II targets Ser-302 but can also target Ser-282 at nonphysiological calcium concentrations. Strikingly, Ser-302 phosphorylation by Ca 2+ -calmodulin-activated kinase II was abolished by ablating the ability of Ser-282 to be phosphorylated via alanine substitution. To determine the functional roles of the sites in vivo, three transgenic lines, which expressed cMyBP-C containing either Ser-273-Ala-282-Ser-302 (cMyBP-C SAS ), Ala-273-Asp-282-Ala-302 (cMyBP-C ADA ), or Asp-273-Ala-282-Asp-302 (cMyBP-C DAD ), were generated. Mutant protein was completely substituted for endogenous cMyBP-C by breeding each mouse line into a cMyBP-C null (t/t) background. Serine-to-alanine substitutions were used to ablate the abilities of the residues to be phosphorylated, whereas serine-to-aspartate substitutions were used to mimic the charged state conferred by phosphorylation. Compared to control nontransgenic mice, as well as transgenic mice expressing wild-type cMyBP-C, the transgenic cMyBP-C SAS(t/t) , cMyBP-C ADA(t/t) , and cMyBP-C DAD(t/t) mice showed no increases in morbidity and mortality and partially rescued the cMyBP-C (t/t) phenotype. The loss of cMyBP-C phosphorylation at Ser-282 led to an altered β-adrenergic response. In vivo hemodynamic studies revealed that contractility was unaffected but that cMyBP-C SAS(t/t) hearts showed decreased diastolic function at baseline. However, the normal increases in cardiac function (increased contractility/relaxation) as a result of infusion of β-agonist was significantly decreased in all of the mutants, suggesting that competency for phosphorylation at multiple sites in cMyBP-C is a prerequisite for normal β-adrenergic responsiveness. Conclusions: Ser-282 has a unique regulatory role in that its phosphorylation is critical for the subsequent phosphorylation of Ser-302. However, each residue plays a role in regulating the contractile response to β-agonist stimulation.

Ischemic heart disease, which remains the leading cause of morbidity and mortality in the Western world, is invariably characterized by impaired cardiac function and disturbed Ca 2+ homeostasis. Because enhanced inhibitor-1 (I-1) activity has been suggested to preserve Ca 2+ cycling, we sought to define whether increases in I-1 activity in the adult heart may ameliorate contractile dysfunction and cellular injury in the face of an ischemic insult. To this end, we generated an inducible transgenic mouse model that enabled temporally controlled expression of active I-1 (T35D). Active I-1 expression in the adult heart elicited significant enhancement of contractile function, associated with preferential phospholamban phosphorylation and enhanced sarcoplasmic reticulum Ca 2+ -transport. Further phosphoproteomic analysis revealed alterations in proteins associated with energy production and protein synthesis, possibly to support the increased metabolic demands of the hyperdynamic hearts. Importantly, on ischemia/reperfusion-induced injury, active I-1 expression augmented contractile function and recovery. Further examination revealed that the infarct region and apoptotic as well as necrotic injuries were significantly attenuated by enhanced I-1 activity. These cardioprotective effects were associated with suppression of the endoplasmic reticulum stress response. The present findings indicate that increased I-1 activity in the adult heart enhances Ca 2+ cycling and improves mechanical recovery, as well as cell survival after an ischemic insult, suggesting that active I-1 may represent a potential therapeutic strategy in myocardial infarction.

Background— Cardiac myosin binding protein-C (cMyBP-C) is a thick-filament protein whose presence and phosphorylation by protein kinase A (PKA) regulates cross-bridge formation and kinetics in isolated myocardium. We tested the influence of cMyBP-C and its PKA-phosphorylation on contraction/relaxation kinetics in intact hearts and revealed its essential role in several classic properties of cardiac function. Methods and Results— Comprehensive in situ cardiac pressure–volume analysis was performed in mice harboring a truncation mutation of cMyBP-C (cMyBP-C (t/t) ) that resulted in nondetectable protein versus hearts re-expressing solely wild-type (cMyBP-C WT:(t/t) ) or mutated protein in which known PKA-phosphorylation sites were constitutively suppressed (cMyBP-C AllP-:(t/t) ). Hearts lacking cMyBP-C had faster early systolic activation, which then terminated prematurely, limiting ejection. Systole remained short at faster heart rates; thus, cMyBP-C (t/t) hearts displayed minimal rate-dependent decline in diastolic time and cardiac preload. Furthermore, prolongation of pressure relaxation by afterload was markedly blunted in cMyBP-C (t/t) hearts. All 3 properties were similarly restored to normal in cMyBP-C WT:(t/t) and cMyBP-C AllP-:(t/t) hearts, which supports independence of PKA-phosphorylation. However, the dependence of peak rate of pressure rise on preload was specifically depressed in cMyBP-C AllP-:(t/t) hearts, whereas cMyBP-C (t/t) and cMyBP-C AllP-:(t/t) hearts had similar blunted adrenergic and rate-dependent contractile reserve, which supports linkage of these behaviors to PKA-cMyBP-C modification. Conclusions— cMyBP-C is essential for major properties of cardiac function, including sustaining systole during ejection, the heart-rate dependence of the diastolic time period, and relaxation delay from increased arterial afterload. These are independent of its phosphorylation by PKA, which more specifically modulates early pressure rise rate and adrenergic/heart rate reserve.

The naked mole-rat (NMR) is the longest-lived rodent, with a maximum lifespan of >31 years. Unlike every other mammal studied to date, this species withstands cardiovascular structural and functional changes for at least 75% of its lifespan. Due to the intersection of oxidative stress, aging, and cardiovascular disease, we questioned if NMRs were more resistant to oxidative stress-induced cardiac dysfunction compared to short-lived mice. Echocardiography showed that 7 days after a 20 mg/kg dose of doxorubicin (DOX), mice had a 25% decline in fractional shortening (36 ± 1% to 27 ± 2%). In contrast, the fractional shortening of NMRs was unchanged with DOX treatment (27 ± 1%). Previously we observed that while basal cardiac function is low, NMRs have a robust cardiac reserve, displaying a 1.7 fold increase in fractional shortening under exercise-like conditions. DOX-treated NMRs had a significant reduction in their dobutamine response, signifying a diminished cardiac reserve. Intriguingly, we found no changes in phosphorylation or expression of myofilament proteins in the NMR heart with DOX treatment. Mice on the other hand, increased the phosphorylation of cardiac myosin binding protein-C and switched expression from predominantly α-myosin heavy chain to the β-isoform. Electron microscopy showed that DOX caused marked mitochondrial swelling and loss of cristae as well as massive cardiac myofibrillar disarray in mice. Conversely, DOX-treated NMRs had only slight alterations to myofilament structure. NMRs additionally had twofold higher levels of glutathione in their hearts, indicating a high antioxidant capacity. These findings reveal that long-lived NMRs are less susceptible to oxidative stress-induced cardiac dysfunction than mice. The NMR’s low basal cardiac function, unique regulation of myofilament proteins, and high glutathione levels may all be integral in the species’ ability to withstand oxidative damage and preserve cardiac function well into its third decade of life.

Rationale: Cardiac myosin binding protein-C (cMyBP-C) is a trans-filament protein that has been shown to regulate cardiac function via its amino terminal (N’) regions. However, it is unknown whether the first 271 residues (C0-C1f region) are necessary to regulate contractile function in vivo. Hypothesis: The N’-region of cMyBP-C is critical for proper cardiac function in vivo. Methods and Results: Transgenic mice with approximately 80% expression of mutant truncated cMyBP-C missing C0-C1f (cMyBP-C 110kDa ), compared to endogenous cMyBP-C, were generated and characterized at 3-months of age. cMyBP-C 110kDa hearts had significantly elevated heart weight/body weight ratio, fibrosis, nuclear area and collagen content compared to hearts from non-transgenic (NTG) littermates. Electron microscopic analysis revealed normal sarcomere structure in cMyBP-C 110kDa hearts but with apparently weaker cMyBP-C stripes. Furthermore, the ability of cMyBP-C to slow actin-filament sliding within the C-zone of native thick filaments isolated from NTG hearts was lost on thick filaments from cMyBP-C 110kDa hearts. Short axis M-mode echocardiography revealed a significant increase in left ventricular (LV) internal diameter during diastole in cMyBP-C 110kDa hearts. Importantly, cMyBP-C 110kDa hearts displayed a significant reduction in fractional shortening compared to hearts from NTG littermates. We further observed a decrease in the thickness of the LV interventricular septum and free wall during systole in cMyBP-C 110kDa hearts. Strain analysis using images acquired from ECG-Gated Kilohertz Visualization identified a significant deficit in global longitudinal strain in cMyBP-C 110kDa hearts compared to NTG hearts. Conclusion: The N’-region of cMyBP-C is indispensable for maintaining normal cardiac morphology and function and loss of this region promotes contractile dysfunction both at the molecular and tissue levels.

The role of cardiac myosin binding protein-C (cMyBP-C) phosphorylation in cardiac physiology or pathophysiology is unclear. To investigate the status of cMyBP-C phosphorylation in vivo, we determined its phosphorylation state in stressed and unstressed mouse hearts. cMyBP-C phosphorylation is significantly decreased during the development of heart failure or pathologic hypertrophy. We then generated transgenic (TG) mice in which the phosphorylation sites of cMyBP-C were changed to nonphosphorylatable alanines (MyBP-C AllP− ). A TG line showing &40% replacement with MyBP-C AllP− showed no changes in morbidity or mortality but displayed depressed cardiac contractility, altered sarcomeric structure and upregulation of transcripts associated with a hypertrophic response. To explore the effect of complete replacement of endogenous cMyBP-C with MyBP-C AllP− , the mice were bred into the MyBP-C (t/t) background, in which less than 10% of normal levels of a truncated MyBP-C are present. Although MyBP-C AllP− was incorporated into the sarcomere and expressed at normal levels, the mutant protein could not rescue the MyBP-C (t/t) phenotype. The mice developed significant cardiac hypertrophy with myofibrillar disarray and fibrosis, similar to what was observed in the MyBP-C (t/t) animals. In contrast, when the MyBP-C (t/t) mice were bred to a TG line expressing normal MyBP-C (MyBP-C WT ), the MyBP-C (t/t) phenotype was rescued. These data suggest that cMyBP-C phosphorylation is essential for normal cardiac function.

Introduction: Mutations in MYBPC3, encoding cardiac myosin binding protein-C (cMyBP-C), account for ~40% of hypertrophic cardiomyopathy (HCM) cases. MYBPC3 mutations are usually encode truncated proteins and are not found in tissue and are typically heterozygous (Het) in humans. Reduced protein levels occur in human HCM patients with these mutations, suggesting haploinsufficiency. However, it is unknown if cMyBP-C reduction causes or results from hypertrophy. Hypothesis: To test whether haploinsufficiency occurs following cardiac stress and if heterozygous MYBPC3 mice had worsened disease progression. Methods & Results: Transverse aortic constriction (TAC) was performed on 3 month old wild type (WT) and Het MYBPC3 truncation mutant mice which were allowed to hypertrophy for 4 or 12 weeks. Het TAC mice showed increased hypertrophy 12 weeks post-TAC compared to WT TAC controls. Het TAC hearts showed reduced ejection fraction compared to WT TAC at 4 and 12 weeks. MYBPC3 transcript levels were significantly reduced in sham and TAC Het hearts. cMyBP-C levels decreased in Het sham and TAC at 4 weeks but returned to baseline levels at 12 weeks. Het TAC myocytes showed higher Ca2+ sensitivity at 4 weeks, and impaired maximal force development. Het sham and TAC skinned cardiomyocytes showed reduced length dependent increases in Ca2+ sensitivity and maximal force development. RNA-Seq shows no alterations in proteasome of RNA-degradation pathways which have been suggested to play a role in the pathology of these mutations. Overexpression of WT cMyBP-C in the presence of truncated MYBPC3 rescued the decline in force observed in Het myocytes in the absence of stress. Conclusions: Heterozygous MYBPC3 truncation mutant carriers develop more profound hypertrophy and dysfunction following stress. Also, increased MYBPC3 expression reverses myocyte deficits in force generation in the presence of truncated alleles.

The naked mole-rat (NMR) is a mouse-sized rodent with a maximum longevity of >31 years. The species exhibits low basal heart rate (256 bpm) and cardiac output (7 ml/min) for its body size, as well as low fractional shortening (28%) for a rodent. However unlike other well-studied mammals, the NMR maintains cardiac reserve and diastolic function for at least 75% of its maximum lifespan - at ages equivalent to 90 year old humans. We questioned if this low basal cardiac function was due to NMR myofilament composition and function. NMR ventricles are comprised primarily of the β-myosin heavy chain isoform, which is associated with slowed myocardial contraction and increased efficiency. This is in stark contrast to mouse ventricles, which express predominately the α-isoform, and switch to the β-isoform upon experimental induction of heart failure. Compared to mice, NMR myofilament proteins such as cardiac troponin I and cardiac myosin binding protein-C display lower levels of phosphorylation. Such levels are indicative of decreased activation of myofilament proteins and may relate to the species’ low basal cardiac function. Both the NMR’s predominance of β-myosin heavy chain and the low basal level of myofilament phosphorylation present a phenotype much closer to that seen in human ventricles than in those of mice. Intriguingly, maximal force developed by skinned NMR cardiomyocytes is not significantly different to that of mouse cardiomyocytes (NMR: 70.9 ± 9.3mN/mm2 vs. mouse: 87.7 ± 0.6 mN/mm2). This is likely a reflection of the NMR’s ability to enhance cardiac function to the level of a mouse when stimulated, as is evident when both species are treated in vivo with dobutamine (3 μg/g i.p.). Such low basal cardiac function may put less overall strain on the heart over time and could be critical to the NMR’s ability to maintain cardiac function with age.

Protein kinase G I α (PKGIα) inhibits cardiac remodeling, and this effect requires the PKGIα leucine zipper (LZ) binding domain. However, PKGIα LZ-dependent cardiac substrates remain poorly understood. Clinical trials of PKGI activating drugs have been limited to date by hypotension arising from vascular PKGI activation. Therefore, we explored downstream PKGIα substrates in the heart which may inhibit remodeling, yet circumvent the hypotensive effects of systemic PKGI activation. A screen for PKGIα LZ-interacting proteins identified: 1)cardiac myosin binding protein-C (cMyBP-C) and 2) mixed lineage kinase 3 (MLK3). cMyBP-C is a cardiac myocyte protein known to inhibit remodeling when phosphorylated. Co-precipitations with cGMP-conjugated beads confirmed the PKGIα-cMyBP-C interaction. Purified PKGIα phosphorylated cMyBP-C in vitro at Ser-273, Ser-282, and Ser-302. cGMP induced cMyBP-C phosphorylation at these sites in COS cells transfected with WT PKGIα, but not in cells transfected with either LZ mutant PKGIα or kinase-inactive PKGIα. In hearts of 9 month old PKGIα Leucine Zipper mutant mice, which have LV hypertrophy (LVH) and diastolic dysfunction, we observed decreased phosphorylated cMyBP-C as well as decreased total cMyBP-C, compared with WT littermate hearts. We next tested the effect of MLK3, which interacts with PKGIα in the heart, on remodeling in vivo. We performed 7 day Transaortic Constriction (TAC) on MLK3 KO mice and WT littermates (n=5 shams, 8 TAC per genotype). MLK3 KO TAC mice had increased LVH (LV mass/tibia length 71.1 ± 2.7 g/cm KO TAC vs 62.1 ± 2.7 WT TAC; p These studies reveal 2 novel PKGIα anti-remodeling substrates, and they support that exploring PKGIα substrates in the heart may identify novel therapeutic targets to inhibit cardiac remodeling but avoid excessive PKGI induced vasodilation.

Background: Recently we have shown that IL-10, an anti-inflammatory cytokine, markedly inhibited the pressure overload-induced cardiac fibrosis, however, antifibrotic mechanisms of IL-10 are largely unknown. In most of organs, including heart, extracellular matrix (ECM) remodeling is primarily mediated by excessive proliferation of activated fibroblasts and myofibroblasts. Here we hypothesized that IL-10 inhibits stress-induced homing, proliferation and differentiation of nonresident bone marrow-derived fibroblast progenitor cells and therefore, attenuates cardiac remodeling and improves of heart function. Methods and Results: Cardiac hypertrophy was induced in Wild-type (WT) and IL-10-knockout (KO) mice by transverse aortic constriction (TAC). TAC-induced left ventricular (LV) dysfunction and fibrosis were further exaggerated in KO mice compared to WT. TAC significantly increased TGF-β, collagen Iα and IIIα genes expression. Systemic recombinant mouse IL-10 administration markedly improved LV function, inhibited TAC-induced cardiac fibrosis and fibrosis associated genes expression. To identify the role of fibroblast progenitor cells (FPCs), we measured the mobilization of FPCs (Prominin1 positive cells) from bone marrow to heart by FACs. Exacerbated mobilization of FPCs in peripheral blood and heart in IL-10 KO mice were found 3 and 7 days after aortic constriction. Bone marrow transplantation experiments were performed where WT-GFP positive marrow was transplanted in BM depleted IL-10 KO mice. TAC-induced mobilization was significantly reduced in WT-transplanted marrow as compare to TAC-IL-10 KO mice. To identify the role IL-10 on TGFβ-induced endothelial cells trans-differentiation to myofibroblasts, we treated aortic endothelial cells with IL-10 and TGFβ2 for 96 hrs. Both Immunocytochemistry and Western blot analysis results suggested that TGF-β2-induced EndMT was significantly inhibited by IL-10 treatment. To understand the mechanisms, we found that TGF-β2-induced Notch1 signaling was reduced by IL-10. Conclusion: Taken together our observations suggest that the anti-fibrotic effects of IL-10 treatment are mediated by reduced proliferation and differentiation of non-resident myofibroblasts.

Rationale: Cardiac myosin binding protein-C (cMyBP-C) phosphorylation is essential for normal heart function. We recently demonstrated a direct correlation between cMyBP-C dephosphorylation and its degradation during ischemia-reperfusion (I-R) injury. Strikingly, cMyBP-C phosphorylation protects the heart from I-R injury. However, the mechanism of cMyBP-C-mediated cardioprotection is unknown. Objective: To determine if preventing cMyBP-C proteolysis and cleavage confers cardioprotection during I-R injury. Methods and Results: cMyBP-C is a substrate for calpains and dephosphorylation makes cMyBP-C more susceptible to proteolysis. In patients with heart failure, such proteolysis leads to the cleavage and release of the predominant N'-fragment (40 kDa) in association with increased calpain activity. MS/MS analysis identified a cardiac-specific phosphorylation motif responsible for the release of the 40 kDa fragment, 272-TSLAGAGRR-280, which we term the calpain-targeted site (CTS). Next, we utilized cardiac-specific transgenic mice expressing cMyBP-C[[Unable to Display Character: △]]CTS in which CTS motif was ablated and bred into cMyBP-C null (t/t) mice. We hypothesized that ablation of the CTS motif would confer resistance to calpain-mediated proteolysis and thus protect the heart from I-R injury. An animal that transgenically expressed the normal cardiac isoform, cMyBP-CWT, served as a control. Histological, electron microscopic and immunofluorescence analyses confirm that cMyBP-C[[Unable to Display Character: ∆]]CTS incorporates normally into the cardiac sarcomere and results in complete rescue of the cMyBP-Ct/t phenotype, compared control groups. Moreover, echocardiography and in vivo hemodynamic studies revealed that cMyBP-C[[Unable to Display Character: ∆]]CTS:t/t mice have normal cardiac function, similar to control mice. Altogether, these data suggest that cMyBP-C[[Unable to Display Character: ∆]]CTS is benign. Compared to cMyBP-CWT, cMyBP-C[[Unable to Display Character: ∆]]CTS protein is protected from calpain-mediated degradation. Finally, we determined that ablation of the CTS reduced infarct size and preserved cMyBP-C stability and cardiac function during I-R injury. Conclusion: Our data suggest that preserving cMyBP-C stability by thwarting calpain-mediated proteolysis protects cardiac structure and function from I-R injury, as a supportive therapy.

Normal hearts increase contractile force in response to mechanical stretch caused by increasing volume. Although this phenomenon has been extensively studied from myofilaments’ spacing perspective, possible coupling of mechanical-sensing signaling to modulation of myofilament function remains unknown. Cardiac myosin binding protein-C (MyBPC3) is a component of heart muscle thick filament. Phosphorylation of MyBPC3 releases its inhibition on cross-bridge cycling to increase cardiac contractility. Thus, we postulate that mechanical stretch of the myocardium causes phosphorylation of MyBPC3 to increase contractility. We tested this hypothesis by performing static stretch of 20% from baseline on cultured neonatal rat cardiac myocytes (NRCM) at durations of 2, 5, 15, 30, and 60 minutes. NRCM culture provides the advantage of cells living in an environment free of adrenergic stimulation to avoid catecholamine stimulation mediated phosphorylation of MyBPC3. Site-specific phospho-serine antibodies were used to detect phosphorylation of rat equivalent of S282 and S302 of mouse MyBPC3. We used MyBPC3 antibody made from a different species than site-specific phospho-serine antibodies to account for loading. S282P transiently peaked after 5 minutes of stretch, whereas S302P continued to increase with time through 60 minutes (see figure ). Consequently, our data show that mechanical stretch alone can cause phosphorylation of MyBPC3 as a mechanism that couples different signaling pathways to myofilament function.