FHL2 expression and variants in hypertrophic cardiomyopathy

Structural domain in the Titin N2B-us region binds to FHL2 in a force-activation dependent manner

Titin N2B unique sequence (N2B-us) is a 572 amino acid sequence that acts as an elastic spring to regulate muscle passive elasticity. It is thought to lack stable tertiary structures and is a force-bearing region that is regulated by mechanical stretching. In this study, the conformation of N2B-us and its interaction with four-and-a-half LIM domain protein 2 (FHL2) are investigated using AlphaFold2 predictions and single-molecule experimental validation. Surprisingly, a stable alpha/beta structural domain is predicted and confirmed in N2B-us that can be mechanically unfolded at forces of a few piconewtons. Additionally, more than twenty FHL2 LIM domain binding sites are predicted to spread throughout N2B-us. Single-molecule manipulation experiments reveals the force-dependent binding of FHL2 to the N2B-us structural domain. These findings provide insights into the mechano-sensing functions of N2B-us and its interactions with FHL2.

Nesprin-2 is a novel scaffold protein for telethonin and FHL-2 in the cardiomyocyte sarcomere

Nesprins comprise a family of multi-isomeric scaffolding proteins, forming the linker of nucleoskeleton-and-cytoskeleton complex with lamin A/C, emerin and SUN1/2 at the nuclear envelope. Mutations in nesprin-1/-2 are associated with Emery-Dreifuss muscular dystrophy (EDMD) with conduction defects and dilated cardiomyopathy (DCM). We have previously observed sarcomeric staining of nesprin-1/-2 in cardiac and skeletal muscle, but nesprin function in this compartment remains unknown. In this study, we show that specific nesprin-2 isoforms are highly expressed in cardiac muscle and localize to the Z-disc and I band of the sarcomere. Expression of GFP-tagged nesprin-2 giant spectrin repeats 52 to 53, localized to the sarcomere of neonatal rat cardiomyocytes. Yeast two-hybrid screening of a cardiac muscle cDNA library identified telethonin and four-and-half LIM domain (FHL)-2 as potential nesprin-2 binding partners. GST pull-down and immunoprecipitation confirmed the individual interactions between nesprin-2/telethonin and nesprin-2/FHL-2, and showed that nesprin-2 and telethonin binding was dependent on telethonin phosphorylation status. Importantly, the interactions between these binding partners were impaired by mutations in nesprin-2, telethonin, and FHL-2 identified in EDMD with DCM and hypertrophic cardiomyopathy patients. These data suggest that nesprin-2 is a novel sarcomeric scaffold protein that may potentially participate in the maintenance and/or regulation of sarcomeric organization and function.

Single-cell transcriptomics in MI identify Slc25a4 as a new modulator of mitochondrial malfunction and apoptosis-associated cardiomyocyte subcluster

Myocardial infarction (MI) is the leading cause of premature death. The death of cardiomyocytes (CMs) and the dysfunction of the remaining viable CMs are the main pathological factors contributing to heart failure (HF) following MI. This study aims to determine the transcriptional profile of CMs and investigate the heterogeneity among CMs under hypoxic conditions. Single-cell atlases of the heart in both the sham and MI groups were developed using single-cell data (GSE214611) downloaded from Gene Expression Omnibus (GEO) database ( https://www.ncbi.nlm.nih.gov/geo/ ). The heterogeneity among CMs was explored through various analyses including enrichment, pseudo time, and intercellular communication analysis. The marker gene of C5 was identified using differential expression analysis (DEA). Real-time polymerase chain reaction (RT-PCR), bulk RNA-sequencing dataset analysis, western blotting, immunohistochemical and immunofluorescence staining, Mito-Tracker staining, TUNEL staining, and flow cytometry analysis were conducted to validate the impact of the marker gene on mitochondrial function and cell apoptosis of CMs under hypoxic conditions. We identified a cell subcluster named C5 that exhibited a close association with mitochondrial malfunction and cellular apoptosis characteristics, and identified Slc25a4 as a significant biomarker of C5. Furthermore, our findings indicated that the expression of Slc25a4 was increased in failing hearts, and the downregulation of Slc25a4 improved mitochondrial function and reduced cell apoptosis. Our study significantly identified a distinct subcluster of CMs that exhibited strong associations with ventricular remodeling following MI. Slc25a4 served as the hub gene for C5, highlighting its significant potential as a novel therapeutic target for MI.

Unraveling the role of the FHL family in cardiac diseases: Mechanisms, implications, and future directions

Heart diseases are a major cause of morbidity and mortality worldwide. Understanding the molecular mechanisms underlying these diseases is essential for the development of effective diagnostic and therapeutic strategies. The FHL family consists of five members: FHL1, FHL2, FHL3, FHL4, and FHL5/Act. These members exhibit different expression patterns in various tissues including the heart. FHL family proteins are implicated in cardiac remodeling, regulation of metabolic enzymes, and cardiac biomechanical stress perception. A large number of studies have explored the link between FHL family proteins and cardiac disease, skeletal muscle disease, and ovarian metabolism, but a comprehensive and in-depth understanding of the specific molecular mechanisms targeting FHL on cardiac disease is lacking. The aim of this review is to explore the structure and function of FHL family members, to comprehensively elucidate the mechanisms by which they regulate the heart, and to explore in depth the changes in FHL family members observed in different cardiac disorders, as well as the effects of mutations in FHL proteins on heart health.

Neonatal Cardiac Arrest Following Lacosamide Treatment: A Case Report

BACKGROUND

Lacosamide is an antiepileptic drug with US Food and Drug Administration approval for the treatment of partial-onset seizures in patients older than one month. Lacosamide works by selective enhancement of proteins that induce preferential slow promotion of sodium channels to the hyperpolarized inactive state. Lacosamide is generally well-tolerated; however, clinical and nonclinical studies have linked its use with cardiac side effects including PR prolongation and atrioventricular (AV) block.

RESULTS

We present the case of a three-week-old female neonatal patient born at 25 weeks' gestation who developed second-degree AV heart block and cardiac arrest after initiating lacosamide therapy. The patient was being treated for neonatal seizure complicated by intraventricular hemorrhage (grade II) and electrolyte disturbances with phenobarbital, levetiracetam, and phenytoin. Before addition of lacosamide therapy, the patient had an unremarkable electrocardiogram and no known cardiac risk factors for lacosamide. After medication discontinuation, the patient experienced no reoccurring episodes or other cardiac events.

CONCLUSION

Use of lacosamide for neonatal populations is currently under evaluation. This is the first report of adverse cardiac event (AV block) in the setting of neonatal lacosamide use. Risk of future adverse cardiac events should be evaluated when determining the safety and efficacy of lacosamide in the neonatal population.

Cardioprotective effects of Moku-boi-to and its impact on AngII-induced cardiomyocyte hypertrophy

Cardiomyocyte hypertrophy, induced by elevated levels of angiotensin II (AngII), plays a crucial role in cardiovascular diseases. Current therapeutic approaches aim to regress cardiac hypertrophy but have limited efficacy. Widely used Japanese Kampo medicines are highly safe and potential therapeutic agents. This study aims to explore the impact and mechanisms by which Moku-boi-to (MBT), a Japanese Kampo medicine, exerts its potential cardioprotective benefits against AngII-induced cardiomyocyte hypertrophy, bridging the knowledge gap and contributing to the development of novel therapeutic strategies. By evaluating the effects of six Japanese Kampo medicines with known cardiovascular efficiency on AngII-induced cardiomyocyte hypertrophy and cell death, we identified MBT as a promising candidate. MBT exhibited preventive effects against AngII-induced cardiomyocyte hypertrophy, cell death and demonstrated improvements in intracellular Ca2+ signaling regulation, ROS production, and mitochondrial function. Unexpectedly, experiments combining MBT with the AT1 receptor antagonist losartan suggested that MBT may target the AT1 receptor. In an isoproterenol-induced heart failure mouse model, MBT treatment demonstrated significant effects on cardiac function and hypertrophy. These findings highlight the cardioprotective potential of MBT through AT1 receptor-mediated mechanisms, offering valuable insights into its efficacy in alleviating AngII-induced dysfunction in cardiomyocytes. The study suggests that MBT holds promise as a safe and effective prophylactic agent for cardiac hypertrophy, providing a deeper understanding of its mechanisms for cardioprotection against AngII-induced dysfunction.

The roles of FHL2 in cancer

LIM domain protein 2, also known as LIM protein FHL2, is a member of the LIM-only family. Due to its LIM domain protein characteristics, FHL2 is capable of interacting with various proteins and plays a crucial role in regulating gene expression, cell growth, and signal transduction in muscle and cardiac tissue. In recent years, mounting evidence has indicated that the FHLs protein family is closely associated with the development and occurrence of human tumors. On the one hand, FHL2 acts as a tumor suppressor by down-regulating in tumor tissue and effectively inhibiting tumor development by limiting cell proliferation. On the other hand, FHL2 serves as an oncoprotein by up-regulating in tumor tissue and binding to multiple transcription factors to suppress cell apoptosis, stimulate cell proliferation and migration, and promote tumor progression. Therefore, FHL2 is considered a double-edged sword in tumors with independent and complex functions. This article reviews the role of FHL2 in tumor occurrence and development, discusses FHL2 interaction with other proteins and transcription factors, and its involvement in multiple cell signaling pathways. Finally, the clinical significance of FHL2 as a potential target in tumor therapy is examined.

Myofilament-associated proteins with intrinsic disorder (MAPIDs) and their resolution by computational modeling

The cardiac sarcomere is a cellular structure in the heart that enables muscle cells to contract. Dozens of proteins belong to the cardiac sarcomere, which work in tandem to generate force and adapt to demands on cardiac output. Intriguingly, the majority of these proteins have significant intrinsic disorder that contributes to their functions, yet the biophysics of these intrinsically disordered regions (IDRs) have been characterized in limited detail. In this review, we first enumerate these myofilament-associated proteins with intrinsic disorder (MAPIDs) and recent biophysical studies to characterize their IDRs. We secondly summarize the biophysics governing IDR properties and the state-of-the-art in computational tools toward MAPID identification and characterization of their conformation ensembles. We conclude with an overview of future computational approaches toward broadening the understanding of intrinsic disorder in the cardiac sarcomere.

Signaling network model of cardiomyocyte morphological changes in familial cardiomyopathy

Familial cardiomyopathy is a precursor of heart failure and sudden cardiac death. Over the past several decades, researchers have discovered numerous gene mutations primarily in sarcomeric and cytoskeletal proteins causing two different disease phenotypes: hypertrophic (HCM) and dilated (DCM) cardiomyopathies. However, molecular mechanisms linking genotype to phenotype remain unclear. Here, we employ a systems approach by integrating experimental findings from preclinical studies (e.g., murine data) into a cohesive signaling network to scrutinize genotype to phenotype mechanisms. We developed an HCM/DCM signaling network model utilizing a logic-based differential equations approach and evaluated model performance in predicting experimental data from four contexts (HCM, DCM, pressure overload, and volume overload). The model has an overall prediction accuracy of 83.8%, with higher accuracy in the HCM context (90%) than DCM (75%). Global sensitivity analysis identifies key signaling reactions, with calcium-mediated myofilament force development and calcium-calmodulin kinase signaling ranking the highest. A structural revision analysis indicates potential missing interactions that primarily control calcium regulatory proteins, increasing model prediction accuracy. Combination pharmacotherapy analysis suggests that downregulation of signaling components such as calcium, titin and its associated proteins, growth factor receptors, ERK1/2, and PI3K-AKT could inhibit myocyte growth in HCM. In experiments with patient-specific iPSC-derived cardiomyocytes (MLP-W4R;MYH7-R723C iPSC-CMs), combined inhibition of ERK1/2 and PI3K-AKT rescued the HCM phenotype, as predicted by the model. In DCM, PI3K-AKT-NFAT downregulation combined with upregulation of Ras/ERK1/2 or titin or Gq protein could ameliorate cardiomyocyte morphology. The model results suggest that HCM mutations that increase active force through elevated calcium sensitivity could increase ERK activity and decrease eccentricity through parallel growth factors, Gq-mediated, and titin pathways. Moreover, the model simulated the influence of existing medications on cardiac growth in HCM and DCM contexts. This HCM/DCM signaling model demonstrates utility in investigating genotype to phenotype mechanisms in familial cardiomyopathy.

Insulin and Insulin-Like Growth Factor 1 Signaling Preserves Sarcomere Integrity in the Adult Heart

Insulin and insulin-like growth factor 1 (IGF1) signaling is transduced by insulin receptor substrate 1 (IRS1) and IRS2. To elucidate physiological and redundant roles of insulin and IGF1 signaling in adult hearts, we generated mice with inducible cardiomyocyte-specific deletion of insulin and IGF1 receptors or IRS1 and IRS2. Both models developed dilated cardiomyopathy, and most mice died by 8 weeks post-gene deletion. Heart failure was characterized by cardiomyocyte loss and disarray, increased proapoptotic signaling, and increased autophagy. Suppression of autophagy by activating mTOR signaling did not prevent heart failure. Transcriptional profiling revealed reduced serum response factor (SRF) transcriptional activity and decreased mRNA levels of genes encoding sarcomere and gap junction proteins as early as 3 days post-gene deletion, in concert with ultrastructural evidence of sarcomere disruption and intercalated discs within 1 week after gene deletion. These data confirm conserved roles for constitutive insulin and IGF1 signaling in suppressing autophagic and apoptotic signaling in the adult heart. The present study also identifies an unexpected role for insulin and IGF1 signaling in regulating an SRF-mediated transcriptional program, which maintains expression of genes encoding proteins that support sarcomere integrity in the adult heart, reduction of which results in rapid development of heart failure.

ACTN2 Mutant Causes Proteopathy in Human iPSC-Derived Cardiomyocytes

Genetic variants in α-actinin-2 (ACTN2) are associated with several forms of (cardio)myopathy. We previously reported a heterozygous missense (c.740C>T) ACTN2 gene variant, associated with hypertrophic cardiomyopathy, and characterized by an electro-mechanical phenotype in human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs). Here, we created with CRISPR/Cas9 genetic tools two heterozygous functional knock-out hiPSC lines with a second wild-type (ACTN2wt) and missense ACTN2 (ACTN2mut) allele, respectively. We evaluated their impact on cardiomyocyte structure and function, using a combination of different technologies, including immunofluorescence and live cell imaging, RNA-seq, and mass spectrometry. This study showed that ACTN2mut presents a higher percentage of multinucleation, protein aggregation, hypertrophy, myofibrillar disarray, and activation of both the ubiquitin-proteasome system and the autophagy-lysosomal pathway as compared to ACTN2wt in 2D-cultured hiPSC-CMs. Furthermore, the expression of ACTN2mut was associated with a marked reduction of sarcomere-associated protein levels in 2D-cultured hiPSC-CMs and force impairment in engineered heart tissues. In conclusion, our study highlights the activation of proteolytic systems in ACTN2mut hiPSC-CMs likely to cope with ACTN2 aggregation and therefore directs towards proteopathy as an additional cellular pathology caused by this ACTN2 variant, which may contribute to human ACTN2-associated cardiomyopathies.

CMYA5 is a novel interaction partner of FHL2 in cardiac myocytes

Four-and-a-half LIM domains protein 2 (FHL2) is an anti-hypertrophic adaptor protein that regulates cardiac myocyte signalling and function. Herein, we identified cardiomyopathy-associated 5 (CMYA5) as a novel FHL2 interaction partner in cardiac myocytes. In vitro pull-down assays demonstrated interaction between FHL2 and the N- and C-terminal regions of CMYA5. The interaction was verified in adult cardiac myocytes by proximity ligation assays. Immunofluorescence and confocal microscopy demonstrated co-localisation in the same subcellular compartment. The binding interface between FHL2 and CMYA5 was mapped by peptide arrays. Exposure of neonatal rat ventricular myocytes to a CMYA5 peptide covering one of the FHL2 interaction sites led to an increase in cell area at baseline, but a blunted response to chronic phenylephrine treatment. In contrast to wild-type hearts, loss or reduced FHL2 expression in Fhl2-targeted knockout mouse hearts or in a humanised mouse model of hypertrophic cardiomyopathy led to redistribution of CMYA5 into the perinuclear and intercalated disc region. Taken together, our results indicate a direct interaction of the two adaptor proteins FHL2 and CMYA5 in cardiac myocytes, which might impact subcellular compartmentation of CMYA5.

QiShenYiQi Pill Ameliorates Cardiac Fibrosis After Pressure Overload-Induced Cardiac Hypertrophy by Regulating FHL2 and the Macrophage RP S19/TGF-β1 Signaling Pathway

Purpose: Heart failure (HF) is a leading cause of morbidity and mortality worldwide, and it is characterized by cardiac hypertrophy and fibrosis. However, effective treatments are not available to block cardiac fibrosis after cardiac hypertrophy. The QiShenYiQi pill (QSYQ) is an effective treatment for chronic HF. However, the underlying mechanism remains unclear.

Methods: In the present study, a pressure overload-induced cardiac hypertrophy model was established in rats by inducing ascending aortic stenosis for 4 weeks. QSYQ was administered for 6 weeks, and its effects on cardiac fibrosis, myocardial apoptosis, RP S19 release, macrophage polarization, TGF-β1 production, and TGF-β1/Smad signaling were analyzed. In vitro studies using H9C2, Raw264.7, and RDF cell models were performed to confirm the in vivo study findings and evaluate the contribution to the observed effects of the main ingredients of QSYQ, namely, astragaloside IV, notoginsenoside R1, 3,4-dihydroxyl-phenyl lactic acid, and Dalbergia odorifera T. C. Chen oil. The role of four-and-a-half LIM domains protein 2 (FHL2) in cardiac fibrosis and QSYQ’s effects were assessed by small interfering RNAs (siRNAs).

Results: QSYQ ameliorated cardiac fibrosis after pressure overload-induced cardiac hypertrophy and attenuated cardiomyocyte apoptosis, low FHL2 expression, and TGF-β1 release by the injured myocardium. QSYQ also inhibited the following: release of RP S19 from the injured myocardium, activation of C5a receptors in monocytes, polarization of macrophages, and release of TGF-β1. Moreover, QSYQ downregulated TGF-βR-II expression induced by TGF-β1 in fibroblasts and inhibited Smad protein activation and collagen release and deposition.

Conclusion: The results showed that QSYQ inhibited myocardial fibrosis after pressure overload, which was mediated by RP S19-TGF-β1 signaling and decreased FHL2, thus providing support for QSYQ as a promising therapy for blocking myocardial fibrosis.

miR-377 Inhibits Proliferation and Differentiation of Bovine Skeletal Muscle Satellite Cells by Targeting FHL2

Non-coding RNAs, especially microRNAs (miRNAs), play an important role in skeletal muscle growth and development. miR-377 regulates many basic biological processes and plays a key role in tumor cell proliferation, migration and apoptosis. Nevertheless, the function of miR-377 during skeletal muscle development and how it regulates skeletal muscle satellite cells (SMSCs) remains unclear. In the present study, we proposed to elucidate the regulatory mechanism of miR-377 in the proliferation and differentiation of bovine primary SMSCs. Our results showed that miR-377 can significantly inhibit the proliferation of SMSCs. In addition, we found that miR-377 can reduce myotube formation and restrain skeletal myogenic differentiation. Moreover, the results obtained from the biosynthesis and dual luciferase experiments showed that FHL2 was the target gene of miR-377. We further probed the function of FHL2 in muscle development and found that FHL2 silencing significantly suppressed the proliferation and differentiation of SMSCS, which is contrary to the role of miR-377. Furthermore, FHL2 interacts with Dishevelled-2 (Dvl2) to enable Wnt/β-catenin signaling pathway, consequently regulating skeletal muscle development. miR-377 negatively regulates the Wnt/β-catenin signaling pathway by targeting FHL2-mediated Dvl2. Overall, these findings demonstrated that miR-377 regulates the bovine SMSCs proliferation and differentiation by targeting FHL2 and attenuating the Wnt/β-catenin signaling pathway.

Adverse effects of PM2.5 on cardiovascular diseases

As an air pollutant, fine particulate matter with a diameter  ≤ 2.5 μm (PM_2.5) can enter the body through the respiratory tract and cause adverse cardiovascular effects. Here, the effects of PM_2.5 on atherosclerosis, hypertension, arrhythmia, myocardial infarction are summarized from the perspective researches of human epidemiology, animal, cell and molecule. The results of this review should be proved useful as a scientific basis for the prevention and treatment of cardiovascular disease caused by PM_2.5.

Understanding the molecular basis of cardiomyopathy

Inherited cardiomyopathies are a major cause of mortality and morbidity worldwide and can be caused by mutations in a wide range of proteins located in different cellular compartments. The present review is based on Dr. Ju Chen's 2021 Robert M. Berne Distinguished Lectureship of the American Physiological Society Cardiovascular Section, in which he provided an overview of the current knowledge on the cardiomyopathy-associated proteins that have been studied in his laboratory. The review provides a general summary of the proteins in different compartments of cardiomyocytes associated with cardiomyopathies, with specific focus on the proteins that have been studied in Dr. Chen's laboratory.

Striated muscle proteins are regulated both by mechanical deformation and by chemical post-translational modification

All cells sense force and build their cytoskeleton to optimize function. How is this achieved? Two major systems are involved. The first is that load deforms specific protein structures in a proportional and orientation-dependent manner. The second is post-translational modification of proteins as a consequence of signaling pathway activation. These two processes work together in a complex way so that local subcellular assembly as well as overall cell function are controlled. This review discusses many cell types but focuses on striated muscle. Detailed information is provided on how load deforms the structure of proteins in the focal adhesions and filaments, using α-actinin, vinculin, talin, focal adhesion kinase, LIM domain-containing proteins, filamin, myosin, titin, and telethonin as examples. Second messenger signals arising from external triggers are distributed throughout the cell causing post-translational or chemical modifications of protein structures, with the actin capping protein CapZ and troponin as examples. There are numerous unanswered questions of how mechanical and chemical signals are integrated by muscle proteins to regulate sarcomere structure and function yet to be studied. Therefore, more research is needed to see how external triggers are integrated with local tension generated within the cell. Nonetheless, maintenance of tension in the sarcomere is the essential and dominant mechanism, leading to the well-known phrase in exercise physiology: "use it or lose it."

How (Epi)Genetic Regulation of the LIM-Domain Protein FHL2 Impacts Multifactorial Disease

Susceptibility to complex pathological conditions such as obesity, type 2 diabetes and cardiovascular disease is highly variable among individuals and arises from specific changes in gene expression in combination with external factors. The regulation of gene expression is determined by genetic variation (SNPs) and epigenetic marks that are influenced by environmental factors. Aging is a major risk factor for many multifactorial diseases and is increasingly associated with changes in DNA methylation, leading to differences in gene expression. Four and a half LIM domains 2 (FHL2) is a key regulator of intracellular signal transduction pathways and the FHL2 gene is consistently found as one of the top hyper-methylated genes upon aging. Remarkably, FHL2 expression increases with methylation. This was demonstrated in relevant metabolic tissues: white adipose tissue, pancreatic β-cells, and skeletal muscle. In this review, we provide an overview of the current knowledge on regulation of FHL2 by genetic variation and epigenetic DNA modification, and the potential consequences for age-related complex multifactorial diseases.

Ouabain worsens diastolic sarcomere length in myocytes from a cardiomyopathy mouse model

Diastolic dysfunction is a major feature of hypertrophic cardiomyopathy (HCM). Data from patient tissue and animal models associate increased Ca²⁺ sensitivity of myofilaments with altered Na⁺ and Ca²⁺ ion homeostasis in cardiomyocytes with diastolic dysfunction. In this study, we tested the acute effects of ouabain on ventricular myocytes of an HCM mouse model. The effects of ouabain on contractility and Ca²⁺ transients were tested in intact adult mouse ventricular myocytes (AMVMs) of Mybpc3-targeted knock-in (KI) and wild-type (WT) mice. Concentration-response assessment of contractile function revealed low sensitivity of AMVMs to ouabain (10 μM) compared to literature data on human cardiomyocytes (100 nM). Three hundred μM ouabain increased contraction amplitude (WT ~1.8-fold; KI ~1.5-fold) and diastolic intracellular Ca²⁺ in both WT and KI (+12-18%), but further decreased diastolic sarcomere length in KI cardiomyocytes (-5%). Western Blot analysis of whole heart protein extracts revealed 50% lower amounts of Na⁺/K⁺ ATPase (NKA) in KI than in WT. Ouabain worsened the diastolic phenotype of KI cardiomyocytes at concentrations which did not impair WT diastolic function. Ouabain led to an elevation of intracellular Ca²⁺, which was poorly tolerated in KI showing already high cytosolic Ca²⁺ at baseline due to increased myofilament Ca²⁺ sensitivity. Lower amounts of NKA in KI could amplify the need to exchange excessive intracellular Na⁺ for Ca²⁺ and thereby explain the general tendency to higher diastolic Ca²⁺ in KI.

Identifying Methylation Patterns in Dental Pulp Aging: Application to Age-at-Death Estimation in Forensic Anthropology

Age-at-death estimation constitutes one of the key parameters for identification of human remains in forensic investigations. However, for applications in forensic anthropology, many current methods are not sufficiently accurate for adult individuals, leading to chronological age estimates erring by ±10 years. Based on recent trends in aging studies, DNA methylation has great potential as a solution to this problem. However, there are only a few studies that have been published utilizing DNA methylation to determine age from human remains. The aim of the present study was to expand the range of this work by analyzing DNA methylation in dental pulp from adult individuals. Healthy erupted third molars were extracted from individuals aged 22–70. DNA from pulp was isolated and bisulfite converted. Pyrosequencing was the chosen technique to assess DNA methylation. As noted in previous studies, we found that ELOVL2 and FHL2 CpGs played a role in age estimation. In addition, three new markers were evaluated—NPTX2, KLF14, and SCGN. A set of CpGs from these five loci was used in four different multivariate regression models, providing a Mean Absolute Error (MAE) between predicted and chronological age of 1.5–2.13 years. The findings from this research can improve age estimation, increasing the accuracy of identification in forensic anthropology.

Volume Load-Induced Right Ventricular Failure in Rats Is Not Associated With Myocardial Fibrosis

Background

Right ventricular (RV) function and failure are key determinants of morbidity and mortality in various cardiovascular diseases. Myocardial fibrosis is regarded as a contributing factor to heart failure, but its importance in RV failure has been challenged. This study aims to assess whether myocardial fibrosis drives the transition from compensated to decompensated volume load-induced RV dysfunction.

Methods

Wistar rats were subjected to aorto-caval shunt (ACS, n = 23) or sham (control, n = 15) surgery, and sacrificed after 1 month, 3 months, or 6 months. Echocardiography, RV pressure-volume analysis, assessment of gene expression and cardiac histology were performed.

Results

At 6 months, 6/8 ACS-rats (75%) showed clinical signs of RV failure (pleural effusion, ascites and/or liver edema), whereas at 1 month and 3 months, no signs of RV failure had developed yet. Cardiac output has increased two- to threefold and biventricular dilatation occurred, while LV ejection fraction gradually decreased. At 1 month and 3 months, RV end-systolic elastance (Ees) remained unaltered, but at 6 months, RV Ees had decreased substantially. In the RV, no oxidative stress, inflammation, pro-fibrotic signaling (TGFβ1 and pSMAD2/3), or fibrosis were present at any time point.

Conclusions

In the ACS rat model, long-term volume load was initially well tolerated at 1 month and 3 months, but induced overt clinical signs of end-stage RV failure at 6 months. However, no myocardial fibrosis or increased pro-fibrotic signaling had developed. These findings indicate that myocardial fibrosis is not involved in the transition from compensated to decompensated RV dysfunction in this model.

A high-throughput screening identifies ZNF418 as a novel regulator of the ubiquitin-proteasome system and autophagy-lysosomal pathway

The ubiquitin-proteasome system (UPS) and autophagy-lysosomal pathway (ALP) are two major protein degradation pathways in eukaryotic cells. Initially considered as two independent pathways, there is emerging evidence that they can work in concert. As alterations of UPS and ALP function can contribute to neurodegenerative disorders, cancer and cardiac disease, there is great interest in finding targets that modulate these catabolic processes. We undertook an unbiased, total genome high-throughput screen to identify novel effectors that regulate both the UPS and ALP. We generated a stable HEK293 cell line expressing a UPS reporter (Ub^G76V-mCherry) and an ALP reporter (GFP-LC3) and screened for genes for which knockdown increased both Ub^G76V-mCherry intensity and GFP-LC3 puncta. With stringent selection, we isolated 80 candidates, including the transcription factor ZNF418 (ZFP418 in rodents). After screen validation with Zfp418 overexpression in HEK293 cells, we evaluated Zfp418 knockdown and overexpression in neonatal rat ventricular myocytes (NRVMs). Endogenous and overexpressed ZFP418 were localized in the nucleus. Subsequent experiments showed that ZFP418 negatively regulates UPS and positively regulates ALP activity in NRVMs. RNA-seq from Zfp418 knockdown revealed altered gene expression of numerous ubiquitinating and deubiquitinating enzymes, decreased expression of autophagy activators and initiators and increased expression of autophagy inhibitors. We found that ZPF418 activated the promoters of Dapk2 and Fyco1, which are involved in autophagy. RNA-seq from Zfp418 knockdown revealed accumulation of several genes involved in cardiac development and/or hypertrophy. In conclusion, our study provides evidence that ZNF418 activates the ALP, inhibits the UPS and regulates genes associated with cardiomyocyte structure/function.

Abbreviations: ACTN2, actinin alpha 2; ALP, autophagy-lysosomal pathway; COPB1, COPI coat complex subunit beta 1; DAPK2, death associated protein kinase 2; FYCO1, FYVE and coiled-coil domain autophagy adaptor 1; HEK293, human embryonic kidney cells 293; HTS, high-throughput screen; LC3, microtubule associated protein 1 light chain 3; NRVMs, neonatal rat ventricular myocytes; RNA-seq, RNA sequencing; RPS6, ribosomal protein S6; TNNI3, troponin I, cardiac 3; UPS, ubiquitin-proteasome system; shRNA, short hairpin RNA; SQSTM1/p62, sequestosome 1; VPS28, VPS28 subunit of ESCRT-I; ZNF418/ZFP418, zinc finger protein 418.

Mechanosensing through Direct Binding of Tensed F-Actin by LIM Domains

Mechanical signals transmitted through the cytoplasmic actin cytoskeleton must be relayed to the nucleus to control gene expression. LIM domains are protein-protein interaction modules found in cytoskeletal proteins and transcriptional regulators. Here, we identify three LIM protein families (zyxin, paxillin, and FHL) whose members preferentially localize to the actin cytoskeleton in mechanically stimulated cells through their tandem LIM domains. A minimal actin-myosin reconstitution system reveals that representatives of all three families directly bind F-actin only in the presence of mechanical force. Point mutations at a site conserved in each LIM domain of these proteins disrupt tensed F-actin binding in vitro and cytoskeletal localization in cells, demonstrating a common, avidity-based mechanism. Finally, we find that binding to tensed F-actin in the cytoplasm excludes the cancer-associated transcriptional co-activator FHL2 from the nucleus in stiff microenvironments. This establishes direct force-activated F-actin binding as a mechanosensing mechanism by which cytoskeletal tension can govern nuclear localization.

Proteomic Analysis of Myocardia Containing the Obscurin R4344Q Mutation Linked to Hypertrophic Cardiomyopathy

Obscurin is a giant cytoskeletal protein with structural and regulatory roles encoded by the OBSCN gene. Recently, mutations in OBSCN were associated with the development of different forms of cardiomyopathies, including hypertrophic cardiomyopathy (HCM). We previously reported that homozygous mice carrying the HCM-linked R4344Q obscurin mutation develop arrhythmia by 1-year of age under sedentary conditions characterized by increased heart rate, frequent incidents of premature ventricular contractions, and episodes of spontaneous ventricular tachycardia. In an effort to delineate the molecular mechanisms that contribute to the observed arrhythmic phenotype, we subjected protein lysates prepared from left ventricles of 1-year old R4344Q and wild-type mice to comparative proteomics analysis using tandem mass spectrometry; raw data are available via ProteomeXchange with identifier PXD017314. We found that the expression levels of proteins involved in cardiac function and disease, cytoskeletal organization, electropotential regulation, molecular transport and metabolism were significantly altered. Moreover, phospho-proteomic evaluation revealed changes in the phosphorylation profile of Ca²⁺ cycling proteins, including sAnk1.5, a major binding partner of obscurin localized in the sarcoplasmic reticulum; notably, this is the first report indicating that sAnk1 undergoes phosphorylation. Taken together, our findings implicate obscurin in diverse cellular processes within the myocardium, which is consistent with its multiple binding partners, localization in different subcellular compartments, and disease association.

Multi-ancestry GWAS of the electrocardiographic PR interval identifies 202 loci underlying cardiac conduction

The electrocardiographic PR interval reflects atrioventricular conduction, and is associated with conduction abnormalities, pacemaker implantation, atrial fibrillation (AF), and cardiovascular mortality. Here we report a multi-ancestry (N = 293,051) genome-wide association meta-analysis for the PR interval, discovering 202 loci of which 141 have not previously been reported. Variants at identified loci increase the percentage of heritability explained, from 33.5% to 62.6%. We observe enrichment for cardiac muscle developmental/contractile and cytoskeletal genes, highlighting key regulation processes for atrioventricular conduction. Additionally, 8 loci not previously reported harbor genes underlying inherited arrhythmic syndromes and/or cardiomyopathies suggesting a role for these genes in cardiovascular pathology in the general population. We show that polygenic predisposition to PR interval duration is an endophenotype for cardiovascular disease, including distal conduction disease, AF, and atrioventricular pre-excitation. These findings advance our understanding of the polygenic basis of cardiac conduction, and the genetic relationship between PR interval duration and cardiovascular disease.

Genetic Dissection of Hypertrophic Cardiomyopathy with Myocardial RNA-Seq

Hypertrophic cardiomyopathy (HCM) is an inherited disorder of the myocardium, and pathogenic mutations in the sarcomere genes myosin heavy chain 7 (MYH7) and myosin-binding protein C (MYBPC3) explain 60%–70% of observed clinical cases. The heterogeneity of phenotypes observed in HCM patients, however, suggests that novel causative genes or genetic modifiers likely exist. Here, we systemically evaluated RNA-seq data from 28 HCM patients and 9 healthy controls with pathogenic variant identification, differential expression analysis, and gene co-expression and protein–protein interaction network analyses. We identified 43 potential pathogenic variants in 19 genes in 24 HCM patients. Genes with more than one variant included the following: MYBPC3, TTN, MYH7, PSEN2, and LDB3. A total of 2538 protein-coding genes, six microRNAs (miRNAs), and 1617 long noncoding RNAs (lncRNAs) were identified differentially expressed between the groups, including several well-characterized cardiomyopathy-related genes (ANKRD1, FHL2, TGFB3, miR-30d, and miR-154). Gene enrichment analysis revealed that those genes are significantly involved in heart development and physiology. Furthermore, we highlighted four subnetworks: mtDNA-subnetwork, DSP-subnetwork, MYH7-subnetwork, and MYBPC3-subnetwork, which could play significant roles in the progression of HCM. Our findings further illustrate that HCM is a complex disease, which results from mutations in multiple protein-coding genes, modulation by non-coding RNAs and perturbations in gene networks.

Mix and (mis-)match - The mechanosensing machinery in the changing environment of the developing, healthy adult and diseased heart

The composition and the stiffness of cardiac microenvironment change during development and/or in heart disease. Cardiomyocytes (CMs) and their progenitors sense these changes, which decides over the cell fate and can trigger CM (progenitor) proliferation, differentiation, de-differentiation or death. The field of mechanobiology has seen a constant increase in output that also includes a wealth of new studies specific to cardiac or cardiomyocyte mechanosensing. As a result, mechanosensing and transduction in the heart is increasingly being recognised as a main driver of regulating the heart formation and function. Recent work has for instance focused on measuring the molecular, physical and mechanical changes of the cellular environment - as well as intracellular contributors to the passive stiffness of the heart. On the other hand, a variety of new studies shed light into the molecular machinery that allow the cardiomyocytes to sense these properties. Here we want to discuss the recent work on this topic, but also specifically focus on how the different components are regulated at various stages during development, in health or disease in order to highlight changes that might contribute to disease progression and heart failure.

CRISPR/Cas9 editing in human pluripotent stem cell-cardiomyocytes highlights arrhythmias, hypocontractility, and energy depletion as potential therapeutic targets for hypertrophic cardiomyopathy

Aims

Sarcomeric gene mutations frequently underlie hypertrophic cardiomyopathy (HCM), a prevalent and complex condition leading to left ventricle thickening and heart dysfunction. We evaluated isogenic genome-edited human pluripotent stem cell-cardiomyocytes (hPSC-CM) for their validity to model, and add clarity to, HCM.

Methods and results

CRISPR/Cas9 editing produced 11 variants of the HCM-causing mutation c.C9123T-MYH7 [(p.R453C-β-myosin heavy chain (MHC)] in 3 independent hPSC lines. Isogenic sets were differentiated to hPSC-CMs for high-throughput, non-subjective molecular and functional assessment using 12 approaches in 2D monolayers and/or 3D engineered heart tissues. Although immature, edited hPSC-CMs exhibited the main hallmarks of HCM (hypertrophy, multi-nucleation, hypertrophic marker expression, sarcomeric disarray). Functional evaluation supported the energy depletion model due to higher metabolic respiration activity, accompanied by abnormalities in calcium handling, arrhythmias, and contraction force. Partial phenotypic rescue was achieved with ranolazine but not omecamtiv mecarbil, while RNAseq highlighted potentially novel molecular targets.

Conclusion

Our holistic and comprehensive approach showed that energy depletion affected core cardiomyocyte functionality. The engineered R453C-βMHC-mutation triggered compensatory responses in hPSC-CMs, causing increased ATP production and αMHC to energy-efficient βMHC switching. We showed that pharmacological rescue of arrhythmias was possible, while MHY7: MYH6 and mutant: wild-type MYH7 ratios may be diagnostic, and previously undescribed lncRNAs and gene modifiers are suggestive of new mechanisms.

Landscape of heart proteome changes in a diet-induced obesity model

Obesity is a pandemic associated with a high incidence of cardiovascular disease; however, the mechanisms are not fully elucidated. Proteomics may provide a more in-depth understanding of the pathophysiological mechanisms and contribute to the identification of potential therapeutic targets. Thus, our study evaluated myocardial protein expression in healthy and obese rats, employing two proteomic approaches. Male Wistar rats were established in two groups (n = 13/group): control diet and Western diet fed for 41 weeks. Obesity was determined by the adipose index, and cardiac function was evaluated in vivo by echocardiogram and in vitro by isolated papillary muscle analysis. Proteomics was based on two-dimensional gel electrophoresis (2-DE) along with mass spectrometry identification, and shotgun proteomics with label-free quantification. The Western diet was efficient in triggering obesity and impaired contractile function in vitro; however, no cardiac dysfunction was observed in vivo. The combination of two proteomic approaches was able to increase the cardiac proteomic map and to identify 82 differentially expressed proteins involved in different biological processes, mainly metabolism. Furthermore, the data also indicated a cardiac alteration in fatty acids transport, antioxidant defence, cytoskeleton, and proteasome complex, which have not previously been associated with obesity. Thus, we define a robust alteration in the myocardial proteome of diet-induced obese rats, even before functional impairment could be detected in vivo by echocardiogram.

Novel Therapies for Prevention and Early Treatment of Cardiomyopathies

Heritable cardiomyopathies are a class of heart diseases caused by variations in a number of genetic loci. Genetic variants on one allele lead to either a degraded protein, which causes a haploinsufficiency of that protein, or a nonfunctioning protein that subverts the molecular system within which the protein works. Over years, both of these mechanisms eventually lead to diseased heart tissue and symptoms of a failing heart. Most cardiomyopathy treatments repurpose heart failure drugs to manage these symptoms and avoid adverse outcomes. There are few therapies that correct the underlying pathogenic genetic or molecular mechanism. This review will reflect on this unmet clinical need in genetic cardiomyopathies and consider a variety of therapies that address the mechanism of disease rather than patient symptoms. These therapies are genetic, targeting a defective gene or transcript, or ameliorating a genetic insufficiency. However, there are also a number of small molecules under exploration that modulate downstream faulty protein products affected in cardiomyopathies.

miR-340-FHL2 axis inhibits cell growth and metastasis in ovarian cancer

Although increasing evidence indicated that deregulation of microRNAs (miRNAs) contributed to tumor initiation and progression, but little is known about the biological role of miR-340 in ovarian cancer (OC). In this study, we found that miR-340 expression was downregulated in OC tissues compared with its expression in normal ovarian epithelium and endometrium, and treatment with 5-aza-2′-deoxycytidine (5-Aza-dC) or trichostatin A (TSA) increased miR-340 expression in OC cells. In addition, ectopic miR-340 expression inhibited OC cell growth and metastasis in vitro and in vivo. Four and a half LIM domains protein 2 (FHL2) was confirmed as a direct target of miR-340 and silencing FHL2 mimicked the effects of miR-340 in OC cells. Further mechanistic study showed that miR-340 inhibited the Wnt/β-catenin pathway by targeting FHL2, as well as downstream cell cycle and epithelial-to-mesenchymal transition (EMT) signals in OC cells. Moreover, the greatest association between miR-340 and FHL2 was found in 481 ovarian serous cystadenocarcinoma tissues via pan-cancer analysis. Finally, we revealed that lower miR-340 or higher FHL2 was associated with poor OC patient outcomes. Our findings indicate that the miR-340-FHL2 axis regulates Wnt/β-catenin signaling and is involved in tumorigenesis in OC. Therefore, manipulating the expression of miR-340 or its target genes is a potential strategy in OC therapy.

The role of FHL2 in wound healing and inflammation

The 4-and-a-half LIM domain protein 2 (FHL2) is a multifunctional adaptor protein that can interact with cell surface receptors, cytosolic adaptor and structural proteins, kinases, and nuclear transcription factors. It is involved in numerous functional activities, including the epithelial-mesenchymal transition, cell proliferation, apoptosis, adhesion, migration, structural stability, and gene expression. Despite this, FHL2-knockout (KO) mice are viable and fertile with no obvious abnormalities, rather suggesting a high capacity for fine-tuning adjustment and functional redundancy of FHL2. Indeed, challenging FHL2-KO cells or mice provided numerous evidences for the great functional significance of FHL2. In recent years, several reviews have been published describing the high capacity of FHL2 to bind diverse proteins as well as the versatile functions of FHL2, emphasizing in particular its role in cardiovascular diseases and carcinogenesis. Here, we view the function of FHL2 from a different perspective. We summarize the published data demonstrating the impact of FHL2 on wound healing and inflammation. FHL2 seems to be involved in numerous steps of these extremely complex and multidirectional but tightly regulated tissue remodeling processes, supporting tissue repair and coordinating inflammation. Deficiency of FHL2 not only slows down ongoing wound healing but also often turns it into a chronic condition.-Wixler, V. The role of FHL2 in wound healing and inflammation.

Deficiency of Fhl2 leads to delayed neuronal cell migration and premature astrocyte differentiation

The four and a half LIM domains protein 2 (Fhl2) is an adaptor protein capable of mediating protein-protein interactions. Here, we report for the first time phenotypic changes in the brain of Fhl2-deficient mice. We showed that Fhl2 is expressed in neural stem cells, precursors and mature cells of neuronal lineage. Moreover, Fhl2 deficiency leads to delayed neuroblast migration in vivo, premature astroglial differentiation of neural stem cells (NSCs) in vitro, and a gliosis-like accumulation of glial fibrillary acidic protein (GFAP)-positive astrocytes in vivo that substantially increases with age. Collectively, Fhl2-deficiency in the brain interrupts the maintenance and the balanced differentiation of adult NSCs, resulting in preferentially glial differentiation and early exhaustion of the NSC pool required for adult neurogenesis.

S100A4 as a Target of the E3-Ligase Asb2β and Its Effect on Engineered Heart Tissue

Background: S100A4 has recently emerged as an important player in cardiac disease, affecting phenotype development in animal models of myocardial infarction and pathological cardiac hypertrophy, albeit it is unclear whether S100A4 exerts a detrimental or beneficial function. The goal of the current study was to analyze S100A4 expression in models of cardiac pathology, investigate its degradation by the ubiquitin-proteasome system (UPS), and furthermore examine the functional effects of S100A4 levels in a 3D model of engineered heart tissue (EHT).

Methods and Results: S100A4 mRNA and protein levels were analyzed in different models of cardiac pathology via quantitative RT-PCR and Western blot, showing a higher S100A4 steady-state protein concentration in hearts of Mybpc3-knock-in (KI) hypertrophic cardiomyopathy (HCM) mice. COS-7 cells co-transfected with plasmids encoding mutant (MUT) Asb2β lacking the E3 ligase activity in combination with V5-tagged S100A4 plasmid presented higher S100A4-V5 protein steady-state concentrations than cells co-transfected with the Asb2β wild type (WT) plasmid. This effect was blunted by treatment with the specific proteasome inhibitor epoxomicin. Adeno-associated virus serotype 6 (AAV6)-mediated S100A4 overexpression in a 3D model of EHT did not affect contractile parameters. Immunofluorescence analysis showed a cytosolic and partly nuclear expression pattern of S100A4. Gene expression analysis in EHTs overexpressing S100A4-V5 showed markedly lower steady-state concentrations of genes involved in cardiac fibrosis and pathological cardiac hypertrophy.

Conclusion: We showed that S100A4 protein level is higher in cardiac tissue of Mybpc3-KI HCM mice probably as a result of a lower degradation by the E3 ligase Asb2β. While an overexpression of S100A4 did not alter contractile parameters in EHTs, downstream gene expression analysis points toward modulation of signaling cascades involved in fibrosis and hypertrophy.

Mutant Muscle LIM Protein C58G causes cardiomyopathy through protein depletion

Cysteine and glycine rich protein 3 (CSRP3) encodes Muscle LIM Protein (MLP), a well-established disease gene for Hypertrophic Cardiomyopathy (HCM). MLP, in contrast to the proteins encoded by the other recognised HCM disease genes, is non-sarcomeric, and has important signalling functions in cardiomyocytes. To gain insight into the disease mechanisms involved, we generated a knock-in mouse (KI) model, carrying the well documented HCM-causing CSRP3 mutation C58G.

In vivo phenotyping of homozygous KI/KI mice revealed a robust cardiomyopathy phenotype with diastolic and systolic left ventricular dysfunction, which was supported by increased heart weight measurements. Transcriptome analysis by RNA-seq identified activation of pro-fibrotic signalling, induction of the fetal gene programme and activation of markers of hypertrophic signalling in these hearts. Further ex vivo analyses validated the activation of these pathways at transcript and protein level. Intriguingly, the abundance of MLP decreased in KI/KI mice by 80% and in KI/+ mice by 50%. Protein depletion was also observed in cellular studies for two further HCM-causing CSRP3 mutations (L44P and S54R/E55G). We show that MLP depletion is caused by proteasome action. Moreover, MLP C58G interacts with Bag3 and results in a proteotoxic response in the homozygous knock-in mice, as shown by induction of Bag3 and associated heat shock proteins.

In conclusion, the newly generated mouse model provides insights into the underlying disease mechanisms of cardiomyopathy caused by mutations in the non-sarcomeric protein MLP. Furthermore, our cellular experiments suggest that protein depletion and proteasomal overload also play a role in other HCM-causing CSPR3 mutations that we investigated, indicating that reduced levels of functional MLP may be a common mechanism for HCM-causing CSPR3 mutations.

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We present a mouse model for non-sarcomeric hypertrophic cardiomyopathy (HCM).

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Homozygous Muscle LIM Protein (MLP) C58G mice have systolic and diastolic dysfunction.

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MLP C58G is depleted via proteasomal pathways.

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Protein depletion is also a hallmark of further HCM causing MLP mutations.

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MLP C58G interacts with Bag3 and causes a proteotoxic response.

Four and a half LIM domain protein signaling and cardiomyopathy

Four and a half LIM domain (FHL) protein family members, FHL1 and FHL2, are multifunctional proteins that are enriched in cardiac muscle. Although they both localize within the cardiomyocyte sarcomere (titin N2B), they have been shown to have important yet unique functions within the context of cardiac hypertrophy and disease. Studies in FHL1-deficient mice have primarily uncovered mitogen-activated protein kinase (MAPK) scaffolding functions for FHL1 as part of a novel biomechanical stretch sensor within the cardiomyocyte sarcomere, which acts as a positive regulator of pressure overload-mediated cardiac hypertrophy. New data have highlighted a novel role for the serine/threonine protein phosphatase (PP5) as a deactivator of the FHL1-based biomechanical stretch sensor, which has implications in not only cardiac hypertrophy but also heart failure. In contrast, studies in FHL2-deficient mice have primarily uncovered an opposing role for FHL2 as a negative regulator of adrenergic-mediated signaling and cardiac hypertrophy, further suggesting unique functions targeted by FHL proteins in the "stressed" cardiomyocyte. In this review, we provide current knowledge of the role of FHL1 and FHL2 in cardiac muscle as it relates to their actions in cardiac hypertrophy and cardiomyopathy. A specific focus will be to dissect the pathways and protein-protein interactions that underlie FHLs' signaling role in cardiac hypertrophy as well as provide a comprehensive list of FHL mutations linked to cardiac disease, using evidence gained from genetic mouse models and human genetic studies.

Nebivolol Desensitizes Myofilaments of a Hypertrophic Cardiomyopathy Mouse Model

Background: Hypertrophic cardiomyopathy (HCM) patients often present with diastolic dysfunction and a normal to supranormal systolic function. To counteract this hypercontractility, guideline therapies advocate treatment with beta-adrenoceptor and Ca²⁺ channel blockers. One well established pathomechanism for the hypercontractile phenotype frequently observed in HCM patients and several HCM mouse models is an increased myofilament Ca²⁺ sensitivity. Nebivolol, a commonly used beta-adrenoceptor antagonist, has been reported to lower maximal force development and myofilament Ca²⁺ sensitivity in rabbit and human heart tissues. The aim of this study was to evaluate the effect of nebivolol in cardiac muscle strips of an established HCM Mybpc3 mouse model. Furthermore, we investigated actions of nebivolol and epigallocatechin-gallate, which has been shown to desensitize myofilaments for Ca²⁺ in mouse and human HCM models, in cardiac strips of HCM patients with a mutation in the most frequently mutated HCM gene MYBPC3.

Methods and Results: Nebivolol effects were tested on contractile parameters and force-Ca²⁺ relationship of skinned ventricular muscle strips isolated from Mybpc3-targeted knock-in (KI), wild-type (WT) mice and cardiac strips of three HCM patients with MYBPC3 mutations. At baseline, KI strips showed no difference in maximal force development compared to WT mouse heart strips. Neither 1 nor 10 μM nebivolol had an effect on maximal force development in both genotypes. 10 μM nebivolol induced myofilament Ca²⁺ desensitization in WT strips and to a greater extent in KI strips. Neither 1 nor 10 μM nebivolol had an effect on Ca²⁺ sensitivity in cardiac muscle strips of three HCM patients with MYBPC3 mutations, whereas epigallocatechin-gallate induced a right shift in the force-Ca²⁺ curve.

Conclusion: Nebivolol induced a myofilament Ca²⁺ desensitization in both WT and KI strips, which was more pronounced in KI muscle strips. In human cardiac muscle strips of three HCM patients nebivolol had no effect on myofilament Ca²⁺ sensitivity.

The novel cardiac z-disc protein CEFIP regulates cardiomyocyte hypertrophy by modulating calcineurin signaling

The z-disc is a structural component at the lateral borders of the sarcomere and is important for mechanical stability and contractility of both cardiac and skeletal muscles. Of note, the sarcomeric z-disc also represents a nodal point in cardiomyocyte function and signaling. Mutations of numerous z-disc proteins are associated with cardiomyopathies and muscle diseases. To identify additional z-disc proteins that might contribute to cardiac disease, we employed an in silico screen for cardiac-enriched cDNAs. This screen yielded a previously uncharacterized protein named cardiac-enriched FHL2-interacting protein (CEFIP), which exhibited a heart- and skeletal muscle-specific expression profile. Importantly, CEFIP was located at the z-disc and was up-regulated in several models of cardiomyopathy. We also found that CEFIP overexpression induced the fetal gene program and cardiomyocyte hypertrophy. Yeast two-hybrid screens revealed that CEFIP interacts with the calcineurin-binding protein four and a half LIM domains 2 (FHL2). Because FHL2 binds calcineurin, a phosphatase controlling hypertrophic signaling, we examined the effects of CEFIP on the calcineurin/nuclear factor of activated T-cell (NFAT) pathway. These experiments revealed that CEFIP overexpression further enhances calcineurin-dependent hypertrophic signal transduction, and its knockdown repressed hypertrophy and calcineurin/NFAT activity. In summary, we report on a previously uncharacterized protein CEFIP that modulates calcineurin/NFAT signaling in cardiomyocytes, a finding with possible implications for the pathogenesis of cardiomyopathy.

Autophagy Induced FHL2 Upregulation Promotes IL-6 Production by Activating the NF-κB Pathway in Mouse Aortic Endothelial Cells after Exposure to PM2.5

Epidemiological and clinical studies have increasingly shown that fine particulate matter (PM2.5) is associated with cardiovascular morbidity and mortality, which share the common feature of PM2.5-induced vascular inflammation; however, the underlying mechanisms of how PM2.5 triggers increased inflammatory response in vascular endothelial cells are not well understood. After treating mouse aortic endothelial cells (MAECs) with different concentrations of PM2.5, we assessed interleukin (IL)-6 and four and a half LIM domains 2 (FHL2) expression in cell supernatant by enzyme-linked immunosorbent assay and Western blot, respectively, as well as activation of nuclear factor (NF)-κB and immune-response signaling pathways. Additionally, changes in pathway activation, IL-6 expression, and autophagy were evaluated under PM2.5 exposure, following FHL2 knockdown with small interfering RNA. Our results indicated that PM2.5 exposure induced FHL2 expression and IL-6 secretion, as well as activation of pathways associated with immune response. Additionally, following FHL2 knockdown, the activation of NF-κB-related pathways and IL-6 secretion was inhibited under PM2.5 exposure, although the Akt- and p38-signaling pathways were not affected. Furthermore, PM2.5 exposure induced autophagy, whereas autophagy inhibition eventually inhibited PM2.5-induced FHL2 expression. These findings suggested a novel link between autophagy induced FHL2 upregulation and IL-6 production in MAECs under PM2.5 exposure.

Diltiazem prevents stress-induced contractile deficits in cardiomyocytes, but does not reverse the cardiomyopathy phenotype in Mybpc3-knock-in mice

KEY POINTS

Hypertrophic cardiomyopathy (HCM) is the most common inherited cardiac illness and can lead to diastolic dysfunction, sudden cardiac death and heart failure. Treatment of HCM patients is empirical and current pharmacological treatments are unable to stop disease progression or reverse hypertrophy. In this study, we tested if the non-dihydropyridine Ca²⁺ channel blocker diltiazem, which previously showed potential to stop disease progression, can improve the phenotype of a HCM mouse model (Mybpc3-targeted knock-in), which is based on a mutation commonly found in patients. Diltiazem improved contractile function of isolated ventricular cardiomyocytes acutely, but chronic application did not improve the phenotype of adult mice with a fully developed HCM. Our study shows that diltiazem has beneficial effects in HCM, but long-term treatment success is likely to depend on characteristics and cause of HCM and onset of treatment.

ABSTRACT

Left ventricular hypertrophy, diastolic dysfunction and fibrosis are the main features of hypertrophic cardiomyopathy (HCM). Guidelines recommend β-adrenoceptor or Ca²⁺ channel antagonists as pharmacological treatment. The Ca²⁺ channel blocker diltiazem recently showed promising beneficial effects in pre-clinical HCM, particularly in patients carrying MYBPC3 mutations. In the present study we evaluated whether diltiazem could ameliorate or reverse the disease phenotype in cells and in vivo in an Mybpc3-targeted knock-in (KI) mouse model of HCM. Sarcomere shortening and Ca²⁺ transients were measured in KI and wild-type (WT) cardiomyocytes in basal conditions (1-Hz pacing) and under stress conditions (30 nm isoprenaline, 5-Hz pacing) with or without pre-treatment with 1 μm diltiazem. KI cardiomyocytes exhibited lower diastolic sarcomere length (dSL) at baseline, a tendency to a stronger positive inotropic response to isoprenaline than WT, a marked reduction of dSL and a tendency towards arrhythmias under stress conditions. Pre-treatment of cardiomyocytes with 1 μm diltiazem reduced the drop in dSL and arrhythmia frequency in KI, and attenuated the positive inotropic effect of isoprenaline. Furthermore, diltiazem reduced the contraction amplitude at 5 Hz but did not affect diastolic Ca²⁺ load and Ca²⁺ transient amplitude. Six months of diltiazem treatment of KI mice did not reverse cardiac hypertrophy and dysfunction, activation of the fetal gene program or fibrosis. In conclusion, diltiazem blunted the response to isoprenaline in WT and KI cardiomyocytes and improved diastolic relaxation under stress conditions in KI cardiomyocytes. This beneficial effect of diltiazem in cells did not translate in therapeutic efficacy when applied chronically in KI mice.

Epigallocatechin-3-Gallate Accelerates Relaxation and Ca2+ Transient Decay and Desensitizes Myofilaments in Healthy and Mybpc3-Targeted Knock-in Cardiomyopathic Mice

Background: Hypertrophic cardiomyopathy (HCM) is the most common inherited cardiac muscle disease with left ventricular hypertrophy, interstitial fibrosis and diastolic dysfunction. Increased myofilament Ca²⁺ sensitivity could be the underlying cause of diastolic dysfunction. Epigallocatechin-3-gallate (EGCg), a catechin found in green tea, has been reported to decrease myofilament Ca²⁺ sensitivity in HCM models with troponin mutations. However, whether this is also the case for HCM-associated thick filament mutations is not known. Therefore, we evaluated whether EGCg affects the behavior of cardiomyocytes and myofilaments of an HCM mouse model carrying a gene mutation in cardiac myosin-binding protein C and exhibiting both increased myofilament Ca²⁺ sensitivity and diastolic dysfunction. Methods and Results: Acute effects of EGCg were tested on fractional sarcomere shortening and Ca²⁺ transients in intact ventricular myocytes and on force-Ca²⁺ relationship of skinned ventricular muscle strips isolated from Mybpc3-targeted knock-in (KI) and wild-type (WT) mice. Fractional sarcomere shortening and Ca²⁺ transients were analyzed at 37°C under 1-Hz pacing in the absence or presence of EGCg (1.8 μM). At baseline and in the absence of Fura-2, KI cardiomyocytes displayed lower diastolic sarcomere length, higher fractional sarcomere shortening, longer time to peak shortening and time to 50% relengthening than WT cardiomyocytes. In WT and KI neither diastolic sarcomere length nor fractional sarcomere shortening were influenced by EGCg treatment, but relaxation time was reduced, to a greater extent in KI cells. EGCg shortened time to peak Ca²⁺ and Ca²⁺ transient decay in Fura-2-loaded WT and KI cardiomyocytes. EGCg did not influence phosphorylation of phospholamban. In skinned cardiac muscle strips, EGCg (30 μM) decreased Ca²⁺ sensitivity in both groups. Conclusion: EGCg hastened relaxation and Ca²⁺ transient decay to a larger extent in KI than in WT cardiomyocytes. This effect could be partially explained by myofilament Ca²⁺ desensitization.

Inferring chronological age from DNA methylation patterns of human teeth

OBJECTIVE

Current methods to determine chronological age from modern and ancient remains rely on both morphological and molecular approaches. However, low accuracy and the lack of standardized protocols make the development of alternative methods for the estimation of individual's age even more urgent for several research fields, such as biological anthropology, biodemography, forensics, evolutionary genetics, and ancient DNA studies. Therefore, the aim of this study is to identify genomic regions whose DNA methylation level correlates with age in modern teeth.

METHODS

We used MALDI-TOF mass spectrometry to analyze DNA methylation levels of specific CpGs located in the ELOVL2, FHL2, and PENK genes. We considered methylation data from cementum, dentin and pulp of 21 modern teeth (from 17 to 77 years old) to construct a mathematical model able to exploit DNA methylation values to predict age of the individuals.

RESULTS

The median difference between the real age and that estimated using DNA methylation values is 1.20 years (SD = 1.9) if DNA is recovered from both cementum and pulp of the same modern teeth, 2.25 years (SD = 2.5) if DNA is recovered from dental pulp, 2.45 years (SD = 3.3) if DNA is extracted from cementum and 7.07 years (SD = 7.0) when DNA is recovered from dentin only.

DISCUSSION

We propose for the first time the evaluation of DNA methylation at ELOVL2, FHL2, and PENK genes as a powerful tool to predict age in modern teeth for anthropological applications. Future studies are needed to apply this method also to historical and relatively ancient human teeth.

Corresponding morphological and molecular indicators of crude oil toxicity to the developing hearts of mahi mahi

Crude oils from distinct geological sources worldwide are toxic to developing fish hearts. When oil spills occur in fish spawning habitats, natural resource injury assessments often rely on conventional morphometric analyses of heart form and function. The extent to which visible indicators correspond to molecular markers for cardiovascular stress is unknown for pelagic predators from the Gulf of Mexico. Here we exposed mahi (Coryphaena hippurus) embryos to field-collected crude oil samples from the 2010 Deepwater Horizon disaster. We compared visible heart defects (edema, abnormal looping, reduced contractility) to changes in expression of cardiac-specific genes that are diagnostic of heart failure in humans or associated with loss-of-function zebrafish cardiac mutants. Mahi exposed to crude oil during embryogenesis displayed typical symptoms of cardiogenic syndrome as larvae. Contractility, looping, and circulatory defects were evident, but larval mahi did not exhibit downstream craniofacial and body axis abnormalities. A gradation of oil exposures yielded concentration-responsive changes in morphometric and molecular responses, with relative sensitivity being influenced by age. Our findings suggest that 1) morphometric analyses of cardiac function are more sensitive to proximal effects of crude oil-derived chemicals on the developing heart, and 2) molecular indicators reveal a longer-term adverse shift in cardiogenesis trajectory.

Protein-protein interactions of the LIM-only protein FHL2 and functional implication of the interactions relevant in cardiovascular disease

FHL2 belongs to the LIM-domain only proteins and contains four and a half LIM domains, each of which are composed of two zinc finger structures. FHL2 exhibits specific interaction with proteins exhibiting diverse functions, including transmembrane receptors, transcription factors and transcription co-regulators, enzymes, and structural proteins. The function of these proteins is regulated by FHL2, which modulates intracellular signal transduction pathways involved in a plethora of cellular tasks. The present review summarizes the current knowledge on the protein interactome of FHL2 and provides an overview of the functional implication of these interactions in apoptosis, migration, and regulation of nuclear receptor function. FHL2 was originally identified in the heart and there is extensive literature available on the role of FHL2 in the cardiovascular system, which is also summarized in this review.

The E3 ubiquitin ligase Asb2β is downregulated in a mouse model of hypertrophic cardiomyopathy and targets desmin for proteasomal degradation

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is an autosomal-dominant disease with mutations in genes encoding sarcomeric proteins. Previous findings suggest deregulation of the ubiquitin proteasome system (UPS) in HCM in humans and in a mouse model of HCM (Mybpc3-targeted knock-in (KI) mice). In this study we investigated transcript levels of several muscle-specific E3 ubiquitin ligases in KI mice and aimed at identifying novel protein targets.

METHODS AND RESULTS

Out of 9 muscle-specific E3 ligases, Asb2β was found with the lowest mRNA level in KI compared to wild-type (WT) mice. After adenoviral-mediated Asb2β transduction of WT neonatal mouse cardiomyocytes with either a WT or inactive Asb2β mutant, desmin was identified as a new target of Asb2β by mass spectrometry, co-immunoprecipitation and immunoblotting. Immunofluorescence analysis revealed a co-localization of desmin with Asb2β at the Z-disk of the sarcomere. Knock-down of Asb2β in cardiomyocytes resulted in higher desmin protein levels. Furthermore, desmin levels were higher in ventricular samples of HCM mice and patients than controls.

CONCLUSIONS

This study identifies desmin as a new Asb2β target for proteasomal degradation in cardiomyocytes and suggests that accumulation of desmin could contribute to UPS impairment in HCM mice and patients.

I-1-deficiency negatively impacts survival in a cardiomyopathy mouse model

AIMS

Hypertrophic cardiomyopathy (HCM) is characterized by left ventricular hypertrophy, diastolic dysfunction and increased interstitial fibrosis. Current treatment is based on beta-adrenoceptor (AR) and calcium channel blockers. Since mice deficient of protein phosphatase-1 inhibitor-1 (I-1), an amplifier in beta-AR signalling, were protected from pathological adrenergic stimulation in vivo, we hypothesized that I-1 ablation could result in an improved outcome in a HCM mouse model.

METHODS AND RESULTS

We crossed mice deficient of I-1 with homozygous myosin-binding protein C knock-out (Mybpc3 KO) mice exhibiting cardiac dilatation and reduced survival. Unexpectedly, survival time was shorter in double I-1/Mybpc3 KO than in single Mybpc3 KO mice. Longitudinal echocardiographic assessment revealed lower fractional area change, and higher diastolic left ventricular inner dimensions and end-diastolic volumes in Mybpc3 KO than in WT mice. In comparison to Mybpc3 KO, double I-1/Mybpc3 KO presented higher left ventricular end-diastolic volumes, inner dimensions and ventricular surface areas with increasing differences over time. Phosphorylation levels of PKA-downstream targets and mRNA levels of hypertrophic markers did not differ between I-1/Mybpc3 KO and single Mybpc3 KO mice, except a trend towards higher beta-myosin heavy chain levels in double I-1/Mybpc3 KO.

CONCLUSION

The data indicate that interference with beta-AR signalling has no long-term benefit in this severe MYBPC3-related cardiomyopathy mouse model.

Research priorities in sarcomeric cardiomyopathies

The clinical variability in patients with sarcomeric cardiomyopathies is striking: a mutation causes cardiomyopathy in one individual, while the identical mutation is harmless in a family member. Moreover, the clinical phenotype varies ranging from asymmetric hypertrophy to severe dilatation of the heart. Identification of a single phenotype-associated disease mechanism would facilitate the design of targeted treatments for patient groups with different clinical phenotypes. However, evidence from both the clinic and basic knowledge of functional and structural properties of the sarcomere argues against a 'one size fits all' therapy for treatment of one clinical phenotype. Meticulous clinical and basic studies are needed to unravel the initial and progressive changes initiated by sarcomere mutations to better understand why mutations in the same gene can lead to such opposing phenotypes. Ultimately, we need to design an 'integrative physiology' approach to fully realize patient/gene-tailored therapy. Expertise within different research fields (cardiology, genetics, cellular biology, physiology, and pharmacology) must be joined to link longitudinal clinical studies with mechanistic insights obtained from molecular and functional studies in novel cardiac muscle systems. New animal models, which reflect both initial and more advanced stages of sarcomeric cardiomyopathy, will also aid in achieving these goals. Here, we discuss current priorities in clinical and preclinical investigation aimed at increasing our understanding of pathophysiological mechanisms leading from mutation to disease. Such information will provide the basis to improve risk stratification and to develop therapies to prevent/rescue cardiac dysfunction and remodelling caused by sarcomere mutations.