The microtubule cytoskeleton in cardiac mechanics and heart failure

Dysfunctional cardiomyocyte signalling and heart disease

Cardiomyocyte signalling pathways are central to maintaining the structural and functional integrity of the heart. Dysregulation of these pathways contributes to the onset and progression of heart diseases, including heart failure, arrhythmias and cardiomyopathies. This review focuses on very recent work on dysfunctional cardiomyocyte signalling and its role in the pathophysiology of heart disease. We discuss key pathways, including immune signalling within cardiomyocytes, signalling associated with microtubule dysfunction, Hippo-yes-associated protein signalling and adenosine monophosphate-activated protein kinase signalling, highlighting how aberrations in their regulation lead to impaired cardiomyocyte functions and pinpointing the potential therapeutic opportunities in these pathways. This review underscores the complexity of cardiomyocyte signalling networks and emphasises the need for further dissecting signalling pathways to prevent cardiomyocyte dysfunction.

Alternative mRNA splicing in anthracycline-induced cardiomyopathy - a COG-ALTE03N1 report

BACKGROUND

Anthracycline-induced cardiomyopathy is a well-established adverse consequence in childhood cancer survivors. Altered mRNA expression in the peripheral blood has been found at the level of genes and pathways among anthracycline-exposed childhood cancer survivors with and without cardiomyopathy. However, the role of aberrant alternative splicing in anthracycline-induced cardiomyopathy remains unexplored. The present study examined if transcript-specific events, due to alternative splicing occur in anthracycline-exposed childhood cancer survivors with and without cardiomyopathy.

METHODS

Participants were anthracycline-exposed childhood cancer survivors with cardiomyopathy (cases) matched with anthracycline-exposed childhood cancer survivors without cardiomyopathy (controls; matched on primary cancer diagnosis, year of diagnosis, and race/ethnicity). mRNA sequencing was performed on total RNA from peripheral blood in 32 cases and 32 matched controls. Event-level splicing tool, rMATS (replicate Multivariate Analysis of Transcript Splicing) was used for quantitative profiling of alternative splicing events.

RESULTS

A total of 45 alternative splicing events in 36 genes were identified. Using a prioritization strategy to filter the alternative splicing events, intron retention in RPS24 and skipped exon of PFND5 showed differential expression of altered transcripts.

CONCLUSIONS

We identified specific alternative splicing events in anthracycline-exposed childhood cancer survivors with and without cardiomyopathy. Our findings suggest that differential alternative splicing events can provide additional insight into the peripheral blood transcriptomic landscape of anthracycline-induced cardiomyopathy.

Lactobacillus Restructures the Micro/Mycobiome to Combat Inflammation-Mediated Right Ventricular Dysfunction in Pulmonary Arterial Hypertension

BACKGROUND

Inflammation suppresses right ventricular (RV) function in pulmonary arterial hypertension (PAH). In particular, we showed GP130 (glycoprotein-130) signaling promotes pathological microtubule remodeling and RV dysfunction in rodent PAH. Emerging data demonstrate the intestinal microbiome regulates systemic inflammation, but the impact of modulating the gut microbiome on the GP130-microtubule axis in RV failure is unknown.

METHODS

Two weeks following monocrotaline injection, rats were administered daily Lactobacillus rhamnosus (4×107 colony-forming units) via oral gavage for 10 days. Next-generation metagenomics and internal transcribed spacer 2 sequencing delineated fecal bacterial and fungal compositions. SomaScan proteomics measured levels of 7596 serum proteins. RV immunoblots quantified protein abundances. Light or super resolution confocal microscopy assessed RV, lung, and jejunal morphology. Echocardiography and invasive closed-chest pressure-volume loops evaluated PAH severity and RV function. The relationship between Lactobacillus abundance and RV function was assessed in 65 patients with PAH.

RESULTS

Lactobacillus administration restructured both the intestinal micro- and mycobiome. The alteration in the gut ecosystem improved intestinal health as demonstrated by increased jejunal villus length and glycocalyx thickness and diminished intestinal permeability biomarkers. Serum proteomics revealed Lactobacillus modulated systemic inflammation and decreased circulating GP130 ligands. Lactobacillus-mediated suppression of GP130 signaling blunted pathological microtubule remodeling in RV cardiomyocytes. Microtubule-associated phenotypes, including RV cardiomyocyte and nuclear hypertrophy, transverse tubule integrity, and connexin-43 localization, were all corrected with Lactobacillus. These cellular changes manifested as improved RV function despite no significant alteration in PAH severity. Finally, patients with PAH and detectable fecal Lactobacillus had superior RV function despite similar mean pulmonary arterial pressure and pulmonary vascular resistance as compared with those without detectable Lactobacillus.

CONCLUSIONS

Lactobacillus supplementation restructures the gut micro/mycobiome, restores intestinal health, dampens systemic inflammation, and reduces GP130 ligands and associated RV cardiomyocyte microtubule remodeling. These data identify a novel microbiome-inflammation-microtubule axis that has therapeutic relevance for RV dysfunction.

Identification of Mitochondrial and Succinylation Modification-Related Gene Signature in Ischemic Stroke

Ischemic stroke (IS) is a leading cause of death and disability worldwide, often associated with immune dysregulation, mitochondrial dysfunction, and altered protein succinylation. This study aimed to identify mitochondrial and succinylation-related gene signatures with diagnostic potential in IS. Differentially expressed genes (DEGs) associated with IS were identified using transcriptome expression profiles from merged GSE16561 and GSE58294 GEO datasets. Functional enrichment and WGCNA identified hub genes. Mitochondrial and succinylation-related gene expression was assessed via ssGSEA. Feature genes were selected using machine learning. A prognostic nomogram was constructed. PPI networks were generated using GeneMANIA. Immune infiltration was assessed through ssGSEA. Drug-gene interactions were explored using DGIdb. qRT-PCR validation was performed on blood samples from IS patients and controls. We identified 317 DEGs enriched in immune response and inflammation pathways in 108 IS patients and 47 healthy controls using data from the merged datasets. WGCNA identified 101 hub genes in the yellow module and 65 in the brown module. Seven overlapping genes related to mitochondrial and succinylation processes were identified. Feature gene analysis revealed six key genes (MRPL41, NGRN, SLC25A42, SPTLC2, TUBB, and TXN) with robust diagnostic potential across both the merged and individual datasets (all AUCs > 0.7). Nomogram integration demonstrated predictive reliability. Feature genes exhibited significant correlations with immune cell infiltration. qRT-PCR validation confirmed the differential expression of four feature genes. TUBB and TXN showed interactions with various drugs. Mitochondrial and succinylation-related genes have diagnostic significance in IS, providing insights into disease pathogenesis and clinical applications.

The Contractile Function of Ventricular Cardiomyocytes Is More Sensitive to Acute 17β-Estradiol Treatment Compared to Atrial Cardiomyocytes

17β-estradiol (E2) is the most active metabolite of estrogen with a wide range of physiological action on cardiac muscle. Previous studies have reported E2 effects predominantly for the ventricles, while the E2 impact on the atria has been less examined. In this study, we focused on the direct E2 effects on atrial and ventricular contractility at the cellular and molecular levels. Single atrial and ventricular cardiomyocytes (CM) from adult (24 weeks-old) female Wistar rats were incubated with 10 nM E2 for 15 min. Sarcomere length and cytosolic [Ca2+]i transients were measured in mechanically non-loaded CM, and the tension-length relationship was studied in CM mechanically loaded by carbon fibers. The actin-myosin interaction and sarcomeric protein phosphorylation were analyzed using an in vitro motility assay and gel electrophoresis with Pro-Q Diamond phosphoprotein stain. E2 had chamber-specific effects on the contractile function of CM with a pronounced influence on ventricular CM. The characteristics of [Ca2+]i transients did not change in both atrial and ventricular CM. However, in ventricular CM, E2 reduced the amplitude and maximum velocity of sarcomere shortening and decreased the slope of the passive tension-length relationship that was associated with increased TnI and cMyBP-C phosphorylation. E2 treatment accelerated the cross-bridge cycle of both atrial and ventricular myosin that was associated with increased phosphorylation of the myosin essential light chain. This study shows that E2 impairs the mechanical function of the ventricular myocardium while atrial contractility remains mostly preserved. Hormonal replacement therapy (HRT) with estrogen is by far the most effective therapy for treating climacteric symptoms experienced during menopause. Here we found a chamber specificity of myocardial contractile function to E2 that should be taken into account for the potential side effects of HRT.

Sudden cardiac death, arrhythmogenic cardiomyopathy and intercalated disc pathology due to reduced filamin C protein levels: a matter of life and death

Mutations in the human FLNC gene encoding filamin C (FLNc) cause a broad spectrum of sporadic and familial cardiomyopathies and myopathies. We report on the genetic, clinical, morphological and biochemical findings in a German family harboring an FLNC variant that leads to severe cardiac disease comprising sudden cardiac death and arrhythmogenic cardiomyopathy. Genetic analysis identified a novel heterozygous FLNC variant in exon 16 (NM_001458.4:c.2495_2498delAGTA, het; p.K832TfsX45) in i) the index patient suffering from dilated cardiomyopathy necessitating heart transplantation, ii) a son, who died from sudden cardiac death, iii) a second son, who survived an episode of sudden cardiac arrest and iv) a third son affected by isolated skeletal muscle myopathy. FLNc protein levels were markedly reduced in cardiac tissue obtained from the index patient, implying that the p.K832TfsX45 FLNc variant most probably caused nonsense-mediated decay of the corresponding mRNA. Morphological analysis of the diseased cardiac tissue revealed extensive fibrotic remodeling, and marked degenerative changes of the contractile apparatus of cardiomyocytes and severe structural alterations of intercalated discs. Connexin-43 signal intensity at intercalated discs was diminished and FLNc labelling of myofibrils was attenuated or even absent. Proteome analyses demonstrated complex alterations of extracellular matrix and intercalated disc proteins. Our findings demonstrate that this novel, truncating FLNC mutation likely leads to haploinsufficiency, thereby causing a deleterious sequence of degenerative changes of cardiac tissue with extensive fibrotic remodeling and intercalated disc pathology as the structural basis for FLNC-related cardiomyopathy with life-threatening cardiac arrhythmias.

Tubulin targeting agents and their implications in non-cancer disease management

Microtubules act as molecular 'tracks' for the intracellular transport of accessory proteins, enabling them to assemble into various larger structures, such as spindle fibres formed during the cell cycle. Microtubules provide an organisational framework for the healthy functioning of various cellular processes that work through the process of dynamic instability, driven by the hydrolysis of GTP. In this role, tubulin proteins undergo various modifications, and in doing so modulate various healthy or pathogenic physiological processes within cells. In this review, we provide a detailed update of small molecule chemical agents that interact with tubulin, along with their implications, specifically in non-cancer disease management.

Inhibition of Bif-1 confers cardio-protection in myocardial infarction

Myocardial infarction (MI) remains a major cause of chronic heart failure. Endoplasmic reticulum (ER) stress is an emerging therapeutic strategy to prevent adverse remodeling of the infarcted heart. However, little is known about how Bax-interacting protein 1 (Bif-1), a member of the endophilin B family, is involved in mediating cardiac ER stress in ischemic heart disease. Here, a combination of a left anterior descending coronary artery ligation mouse model and an adenovirus-based transfection strategy was used to investigate the effect of Bif-1 on cardiac remodeling and function after MI. 4-Phenylbutyric acid (4-PBA) was used to understand the role of ER stress in cardiac remodeling. To discover the molecular mechanism, an RNA sequencing study was performed. We found that Bif-1 expression was highly elevated in the heart infarct border zone post-MI and neonatal rat cardiomyocytes treated with oxygen and glucose deprivation. Adenovirus-based knockdown of Bif-1 protected the heart from MI as demonstrated by attenuated maladaptive remodeling and preserved contractile function. ER stress inhibition by 4-PBA alleviated the adverse effects of Bif-1 overexpression on cardiac structure and function. Furthermore, we explored the underlying mechanism by RNA sequencing and identified Bif-1 as a molecule involved in cardiac lipid metabolism. In conclusion, our study identifies Bif-1 as a negative regulator of cardiac protection in MI. Inhibition of Bif-1 alleviates ER stress, which may restore lipid metabolism homeostasis to preserve cardiac function post-MI. Therefore, Bif-1 is a potential novel therapeutic target for ischemic heart disease.NEW & NOTEWORTHY Our study demonstrated that Bif-1 contributes to adverse cardiac remodeling and dysfunction following MI by promoting ER stress. Pharmacological inhibition of ER stress ameliorates cardiac remodeling and dysfunction. In addition, we identified Bif-1 as a negative regulator of cardiac lipid metabolism post-MI, as shown by elevated expression of Acox1, Pla2g7, Acsbg1, Acsl5, Ch25h, and Bcat1 in the heart. These findings suggest that Bif-1 plays a crucial role in cardiac decline post-MI.

Diversity of microtubule arrays in animal cells at a glance

Microtubules are cytoskeletal filaments important for various cellular processes such as intracellular transport, cell division, polarization and migration. Microtubule organization goes hand in hand with cellular function. Motile cells, such as immune cells or fibroblasts, contain microtubule asters attached to the centrosome and the Golgi complex, whereas in many other differentiated cells, microtubules form linear arrays or meshworks anchored at membrane-bound organelles or the cell cortex. Over the past decade, new developments in cell culture, genome editing and microscopy have greatly advanced our understanding of complex microtubule arrays. In this Cell Science at a Glance article and the accompanying poster, we review the diversity of microtubule arrays in interphase animal cells. We describe microtubule network geometries present in various differentiated cells, explore the variety in microtubule-organizing centers responsible for these geometries, and discuss examples of microtubule reorganization in response to functional changes and their interplay with cell motility and tissue development.

17β-Estradiol Counteracts Pathological Microtubule Remodeling To Enhance Cardiac Function

The female-predominate sex hormone 17β-estradiol exerts cardioprotective effects via multiple mechanisms. Available data demonstrate 17β-estradiol modulates microtubule dynamics in vitro, but its effects on pathogenic microtubule remodeling in pressure-overloaded cardiomyocytes are unexplored. Here, we show 17β-estradiol directly blunts microtubule polymerization in vitro, counteracts endothelin-mediated microtubule remodeling in iPSC-cardiomyocytes, and mitigates microtubule stabilization in pulmonary artery banded right ventricular cardiomyocytes. 17β-estradiol treatment blunts cardiomyocyte and nuclear hypertrophy, restores t-tubule architecture, and prevents mislocalization of connexin-43 in RV cardiomyocytes of pulmonary artery banded rats. These cellular phenotypes are paired with significant improvements in RV function. Thus, we propose 17β-estradiol exerts cardioprotective effects via direct modulation of microtubules in addition to its well ascribed signaling functions.

The Role of the MTUS1 Gene in the Development of Left Ventricular Noncompaction Cardiomyopathy-A Case Report

BACKGROUND/OBJECTIVES

The microtubule-associated scaffold protein 1 (MTUS1) gene affects the microtubule stability and cell polarity in the heart and could thus lead to the development of left ventricular noncompaction (LVNC). Pathological gene variants in MTUS1 are associated with pathological phenotypes in both cell cultures and animal models. However, the literature lacks human studies on the specific effects of the MTUS1 gene in heart disease, particularly in congenital LVNC.

METHODS

We present a case of a male infant, diagnosed with LVNC, who passed away at the age of 8 months due to end-stage heart failure. In the investigation process of the etiology of LVNC, whole-genome sequencing using next-generation sequencing was performed in the patient and his first-degree family members.

RESULTS

Genetic analysis identified two heterozygous variants in the MTUS1 gene (NM_001363059.2:c.87C>G and NM_001363059.2:c.2449+421_2288-425del) in the presented patient. The first variant introduced an early stop codon, while the second caused the deletion of an entire exon, both of which significantly altered the protein structure. The older brother of the patient, at the age of 5 years, was a carrier of both variants; however, he was asymptomatic and without signs of heart disease on cardiac ultrasonography.

CONCLUSIONS

Although, in theory, defects in the MTUS1 gene may contribute to the development of LVNC, our observations indicate that MTUS1 variants alone are not sufficient to cause LVNC or lead to any significant developmental disorder. Additional factors, whether genetic or environmental, are likely necessary for the clinical manifestation of LVNC.

Mechanism-based myofilament manipulation to treat diastolic dysfunction in HFpEF

Heart failure with preserved ejection fraction (HFpEF) is a major public health challenge, affecting millions worldwide and placing a significant burden on healthcare systems due to high hospitalization rates and limited treatment options. HFpEF is characterized by impaired cardiac relaxation, or diastolic dysfunction. However, there are no therapies that directly treat the primary feature of the disease. This is due in part to the complexity of normal diastolic function, and the challenge of isolating the mechanisms responsible for dysfunction in HFpEF. Without a clear understanding of the mechanisms driving diastolic dysfunction, progress in treatment development has been slow. In this review, we highlight three key areas of molecular dysregulation directly underlying impaired cardiac relaxation in HFpEF: altered calcium sensitivity in the troponin complex, impaired phosphorylation of myosin-binding protein C (cMyBP-C), and reduced titin compliance. We explore how targeting these pathways can restore normal relaxation, improve diastolic function, and potentially provide new therapeutic strategies for HFpEF treatment. Developing effective HFpEF therapies requires precision targeting to balance systolic and diastolic function, avoiding both upstream non-specificity and downstream rigidity. This review highlights three rational molecular targets with a strong mechanistic basis and potential for therapeutic success.

Mechanisms of mitotic inhibition in human aorta endothelial cells: Molecular and morphological in vitro spectroscopic studies

Mitotic inhibitors are drugs commonly used in chemotherapy, but their nonspecific and indiscriminate distribution throughout the body after intravenous administration can lead to serious side effects, particularly on the cardiovascular system. In this context, our investigation into the mechanism of the cytotoxic effects on endothelial cells of mitotic inhibitors widely used in cancer treatment, such as paclitaxel (also known as Taxol) and Vinca alkaloids, holds significant practical implications. Understanding these mechanisms can lead to more targeted and less harmful cancer treatments. Human aorta endothelial cells (HAECs) were incubated with selected mitotic inhibitors in a wide range of concentrations close to those in human plasma during anticancer therapy. The analysis of single cells imaged by Raman spectroscopy allowed for visualization of the nuclear, cytoplasmic, and perinuclear areas to assess biochemical changes induced by the drug's action. The results showed significant changes in the morphology and molecular composition of the nucleus. Moreover, an effect of a given drug on the cytoplasm was observed, which can be related to its mechanism of action (MoA). Raman data supported by fluorescence microscopy measurements identified unique changes in DNA form and proteins and revealed drug-induced inflammation of endothelial cells. The primary goal of mitotic inhibitors is based on the impairment of tubulin formation and the inhibition of the mitosis process. While all three drugs affect microtubules and disrupt cell division, they do so through different MoA, i.e., Vinca alkaloids inhibit microtubule formation, whereas paclitaxel stabilizes microtubules. To sum up, the work shows how a specific drug can interact with endothelial cells.

Endothelial Unfolded Protein Response-Mediated Cytoskeletal Effects

The endothelial semipermeable monolayers ensure tissue homeostasis, are subjected to a plethora of stimuli, and their function depends on cytoskeletal integrity and remodeling. The permeability of those membranes can fluctuate to maintain organ homeostasis. In cases of severe injury, inflammation or disease, barrier hyperpermeability can cause irreparable damage of endothelium-dependent issues, and eventually death. Elucidation of the signaling regulating cytoskeletal structure and barrier integrity promotes the development of targeted pharmacotherapies towards disorders related to the impaired endothelium (e.g., acute respiratory distress syndrome, sepsis). Recent reports investigate the role of unfolded protein response in barrier function. Herein we review the cytoskeletal components, the unfolded protein response function; and their interrelations on health and disorder. Moreover, we emphasize on unfolded protein response modulators, since they ameliorate illness related to endothelial leak.

Remodelling of T-Tubules and Associated Calcium Handling Dysfunction in Heart Failure: Mechanisms and Therapeutic Insights

In cardiomyocytes, transverse tubules (T-tubules) are sarcolemmal invaginations that facilitate excitation-contraction coupling and diastolic function. The clinical significance of T-tubules has become evident in that their remodelling is recognised as a hallmark feature of heart failure (HF) and a key contributor to disrupted Ca2+ homeostasis, compromised cardiac function, and arrhythmogenesis. Further investigations have revealed that T-tubule remodelling is particularly pronounced in HF with reduced ejection fraction (HFrEF), but not in HF with preserved ejection fraction, implying that T-tubule remodelling may play a crucial pathophysiologic role in HFrEF. While research on the functional importance of T-tubules is ongoing, T-tubule remodelling has been found to be reversible. That finding has triggered a surge in studies aimed at identifying specific therapeutic approaches for HFrEF. This review discusses the functional importance of T-tubules and their microdomains, the pathophysiology of T-tubule remodelling, and the potential mechanisms of current HFrEF therapeutic approaches in reversing T-tubule alterations. We also highlight discrepancies regarding the roles of T-tubule proteins in the recovery process across studies to offer valuable insights for future research.

Force-sensing protein expression in response to cardiovascular mechanotransduction

Force-sensing biophysical cues in microenvironment, including extracellular matrix performances, stretch-mediated mechanics, shear stress and flow-induced hemodynamics, have a significant influence in regulating vascular morphogenesis and cardiac remodeling by mechanotransduction. Once cells perceive these extracellular mechanical stimuli, Piezo activation promotes calcium influx by forming integrin-adhesion-coupling receptors. This induces robust contractility of cytoskeleton structures to further transmit biomechanical alternations into nuclei by regulating Hippo-Yes associated protein (YAP) signaling pathway between cytoplasmic and nuclear translocation. Although biomechanical stimuli are widely studied in cardiovascular diseases, the expression of force-sensing proteins in response to cardiovascular mechanotransduction has not been systematically concluded. Therefore, this review will summarize the force-sensing Piezo, cytoskeleton and YAP proteins to mediate extracellular mechanics, and also give the prominent emphasis on intrinsic connection of these mechanical proteins and cardiovascular mechanotransduction. Extensive insights into cardiovascular mechanics may provide some new strategies for cardiovascular clinical therapy.

Rapid onset fibrotic remodeling and ventricular dysfunction induced by phenylephrine involve targeted reprogramming of myocyte and fibroblast transcriptomes

Catecholamine dysregulation is a common feature of multiple acute and chronic cardiac conditions, including heart failure. To investigate the role of altered α-adrenergic stimulation on cardiac function, we developed a short-term exposure model, administering phenylephrine subcutaneously to mice for one week. Compared to vehicle-injected controls, phenylephrine-treated animals exhibited increased ejection fraction, decreased chamber size, diastolic dysfunction and ventricular hypertrophy in the absence of hypertension. Remarkably, these animals developed extensive fibrotic remodeling of the tissue that plateaued at 24 hours and myocyte hypertrophy localized to regions of fibrotic deposition after 3 days of treatment. Transcriptome analyses of purified myocyte and fibroblast populations from these hearts revealed an unexpected role for myocytes in the production of extracellular matrix. Comparison with other models of cardiac stress, including pressure overload hypertrophy and cytokine activation of fibroblasts, identified stimulus-specific transcriptional circuits associated with cardiac pathology. Given the rapid, robust fibrotic response that preceded myocyte hypertrophy, intercellular communication analyses were conducted to investigate fibroblast to myocyte signaling, identifying potential crosstalk between these cells. These studies thoroughly describe and phenotypically characterize a new model of short-term catecholamine stress and provide an atlas of transcriptional remodeling in myocytes and fibroblasts.

Chronic Activation of Tubulin Tyrosination Improves Heart Function

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is the most common cardiac genetic disorder caused by sarcomeric gene variants and associated with left ventricular hypertrophy and diastolic dysfunction. The role of the microtubule network has recently gained interest with the findings that microtubule detyrosination (dTyr-MT) is markedly elevated in heart failure. Acute reduction of dTyr-MT by inhibition of the detyrosinase (VASH [vasohibin]/SVBP [small VASH-binding protein] complex) or activation of the tyrosinase (TTL [tubulin tyrosine ligase]) markedly improved contractility and reduced stiffness in human failing cardiomyocytes and thus posed a new perspective for HCM treatment. In this study, we tested the impact of chronic tubulin tyrosination in an HCM mouse model (Mybpc3 knock-in), in human HCM cardiomyocytes, and in SVBP-deficient human engineered heart tissues (EHTs).

METHODS

Adeno-associated virus serotype 9-mediated TTL transfer was applied in neonatal wild-type rodents, in 3-week-old knock-in mice, and in HCM human induced pluripotent stem cell-derived cardiomyocytes.

RESULTS

We show (1) TTL for 6 weeks dose dependently reduced dTyr-MT and improved contractility without affecting cytosolic calcium transients in wild-type cardiomyocytes; (2) TTL for 12 weeks reduced the abundance of dTyr-MT in the myocardium, improved diastolic filling, compliance, cardiac output, and stroke volume in knock-in mice; (3) TTL for 10 days normalized cell area in HCM human induced pluripotent stem cell-derived cardiomyocytes; (4) TTL overexpression activated transcription of tubulins and other cytoskeleton components but did not significantly impact the proteome in knock-in mice; (5) SVBP-deficient EHTs exhibited reduced dTyr-MT levels, higher force, and faster relaxation than TTL-deficient and wild-type EHTs. RNA sequencing and mass spectrometry analysis revealed distinct enrichment of cardiomyocyte components and pathways in SVBP-deficient versus TTL-deficient EHTs.

CONCLUSIONS

This study provides the first proof of concept that chronic activation of tubulin tyrosination in HCM mice and in human EHTs improves heart function and holds promise for targeting the nonsarcomeric cytoskeleton in heart disease.

Microtubule forces drive nuclear damage in LMNA cardiomyopathy

Nuclear homeostasis requires a balance of forces between the cytoskeleton and nucleus. Mutations in the LMNA gene, which encodes the nuclear envelope proteins lamin A/C, disrupt this balance by weakening the nuclear lamina. This results in nuclear damage in contractile tissues and ultimately muscle disease. Intriguingly, disrupting the LINC complex that connects the cytoskeleton to the nucleus has emerged as a promising strategy to ameliorate LMNA-associated cardiomyopathy. Yet how LINC complex disruption protects the cardiomyocyte nucleus remains unclear. To address this, we developed an assay to quantify the coupling of cardiomyocyte contraction to nuclear deformation and interrogated its dependence on the nuclear lamina and LINC complex. We found that, surprisingly, the LINC complex was mostly dispensable for transferring contractile strain to the nucleus, and that increased nuclear strain in lamin A/C-deficient cardiomyocytes was not rescued by LINC complex disruption. Instead, LINC complex disruption eliminated the cage of microtubules encircling the nucleus. Disrupting microtubules was sufficient to prevent nuclear damage and rescue cardiac function induced by lamin A/C deficiency. We computationally simulated the stress fields surrounding cardiomyocyte nuclei and show how microtubule forces generate local vulnerabilities that damage lamin A/C-deficient nuclei. Our work pinpoints localized, microtubule-dependent force transmission through the LINC complex as a pathological driver and therapeutic target for LMNA-cardiomyopathy.

Citrinin disrupts microtubule assembly in cardiac cells: Impact on mitochondrial organization and function

Citrinin (CTN) is a mycotoxin commonly present in various foods and feeds worldwide, as well as dietary supplements in Asian countries, but the risks and cellular mechanisms associated with its cardiotoxicity remains unclear. In this study, RNA-seq analysis of CTN-treated H9c2 cardiac cells demonstrated significant perturbations in pathways related to microtubule cytoskeleton and mitochondrial network organization. CTN disrupted microtubule polymerization and downregulated mRNA levels of microtubule-assembling genes, Map2 and Tpx2, in H9c2 cardiac cells. Additionally, CTN interfered with the distribution of mitochondrial network along the microtubules, leading to the accumulation of dysfunctional mitochondria characterized by elevated superoxide levels and reduced membrane potential. This disruption also caused the buildup of lysosomes and ubiquitinated proteins, which hindered waste clearance in microtubule-disassembled H9c2 cells. Molecular docking analysis indicated that CTN could bind to the colchicine binding site on β-tubulin, thereby mimicking the microtubule-disrupting effect of colchicine. This study provides morphological, transcriptomic, and mechanistic evidence to elucidate the cardiotoxic mechanisms of CTN, which involve the dysregulated microtubule network, subsequent mitochondrial mislocalization, and impaired proteolysis of damaged proteins/organelles in cardiac cells. Our findings may enhance the fundamental understanding and facilitate future risk assessment of CTN.

Microtubules and cardiovascular diseases: insights into pathology and therapeutic strategies

Microtubules, complex cytoskeletal structures composed of tubulin proteins in eukaryotic cells, have garnered recent attention in cardiovascular research. Investigations have focused on the post-translational modifications of tubulin, including acetylation and detyrosination. Perturbations in microtubule homeostasis have been implicated in various pathological processes associated with cardiovascular diseases such as heart failure, ischemic heart disease, and arrhythmias. Thus, elucidating the intricate interplay between microtubule dynamics and cardiovascular pathophysiology is imperative for advancing preventive and therapeutic strategies. Several natural compounds have been identified to potentially modulate microtubules, thereby exerting regulatory effects on cardiovascular diseases. This review synthesizes current literature to delineate the roles of microtubules in cardiovascular diseases and assesses the potential of natural compounds in microtubule-targeted therapies.

Genetically Encoded Microtubule Binders for Single-Cell Interrogation of Cytoskeleton Dynamics and Protein Activity

Microtubule (MT) dynamics is tightly regulated by microtubule-associated proteins (MAPs) and various post-translational modifications (PTMs) of tubulin. Here, we introduce OligoMT and OligoTIP as genetically encoded oligomeric MT binders designed for real-time visualization and manipulation of MT behaviors within living cells. OligoMT acts as a reliable marker to label the MT cytoskeleton, while OligoTIP allows for live monitoring of the growing MT plus-ends. These engineered MT binders have been successfully utilized to label the MT network, monitor cell division, track MT plus-ends, and assess the effect of tubulin acetylation on the MT stability at the single-cell level. Moreover, OligoMT and OligoTIP can be repurposed as biosensors for quantitative assessment of drug actions and for reporting enzymatic activity. Overall, these engineered MT binders hold promise for advancing the mechanistic dissection of MT biology and have translational applications in cell-based high-throughput drug discovery efforts.

Lactobacillus Restructures the Micro/Mycobiome to Combat Glycoprotein-130 Associated Microtubule Remodeling and Right Ventricular Dysfunction in Pulmonary Arterial Hypertension

Emerging data demonstrate systemic and local inflammation regulate right ventricular (RV) adaption in preclinical and human pulmonary arterial hypertension (PAH). Pathological RV inflammation is targetable as antagonism of glycoprotein-130 (GP130) signaling counteracts pathological microtubule remodeling and improves RV function in rodents. Microtubules control several aspects of cardiomyocyte biology including cellular and nuclear size/structure, t-tubule homeostasis, and the proper localization of connexin-43. The intestinal microbiome regulates systemic inflammation, but the impact of the gut microbiome on the GP130-microtubule axis in RV failure is unknown. Here, we examined how the anti-inflammatory bacteria, Lactobacillus , modulated cellular and physiological RV phenotypes in preclinical and clinical PAH. Lactobacillus supplementation restructured the gut micro/mycobiome, suppressed systemic inflammation, combatted pathological GP130-mediated RV cardiomyocyte microtubule remodeling, and augmented RV function in rodent PAH. Moreover, Lactobacillus was associated with superior RV adaption in human PAH. These data further support the hypothesis that inflammation negatively impacts RV adaption in PAH, and identify the gut microbiome as a potentially targetable regulator of RV function in PAH.

Embryonic Exposure to Organophosphate Flame Retardants (OPFRs) Differentially Induces Cardiotoxicity in Rare Minnow (Gobiocypris rarus)

Organophosphorus flame retardants (OPFRs) such as triphenyl phosphate (TPHP) and tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) were reported to impair cardiac function in fish. However, limited information is available regarding their cardiotoxic mechanisms. Using rare minnow (Gobiocypris rarus) as a model, we found that both TPHP and TDCIPP exposures decreased heart rate at 96 h postfertilization (hpf) in embryos. Atropine (an mAChR antagonist) can significantly attenuate the bradycardia caused by TPHP, but only marginally attenuated in TDCIPP treatment, suggesting that TDCIPP-induced bradycardia is independent of mAChR. Unlike TDCIPP, although TPHP-induced bradycardia could be reversed by transferring larvae to a clean medium, the inhibitory effect of AChE activity persisted compared to 96 hpf, indicating the existence of other bradycardia regulatory mechanisms. Transcriptome profiling revealed cardiotoxicity-related pathways in treatments at 24 and 72 hpf in embryos/larvae. Similar transcriptional alterations were also confirmed in the hearts of adult fish. Further studies verified that TPHP and TDCIPP can interfere with Na+/Ca2+ transport and lead to disorders of cardiac excitation-contraction coupling in larvae. Our findings provide useful clues for unveiling the differential cardiotoxic mechanisms of OPFRs and identifying abnormal Na+/Ca2+ transport as one of a select few known factors sufficient to impair fish cardiac function.

Role of Microtubule Network in the Passive Anisotropic Viscoelasticity of Healthy Right Ventricle

Cardiomyocytes are viscoelastic and key determinants of right ventricle (RV) mechanics. Intracellularly, microtubules are found to impact the viscoelasticity of isolated cardiomyocytes or trabeculae; whether they contribute to the tissue-level viscoelasticity is unknown. Our goal was to reveal the role of the microtubule network in the passive anisotropic viscoelasticity of the healthy RV. Equibiaxial stress relaxation tests were conducted in healthy RV free wall (RVFW) under early (6%) and end (15%) diastolic strain levels, and at sub- and physiological stretch rates. The viscoelasticity was assessed at baseline and after the removal of microtubule network. Furthermore, a quasi-linear viscoelastic (QLV) model was applied to delineate the contribution of microtubules to the relaxation behavior of RVFW. After removing the microtubule network, RVFW elasticity and viscosity were reduced at the early diastolic strain level and in both directions. The reduction in elasticity was stronger in the longitudinal direction, whereas the degree of changes in viscosity were equivalent between directions. There was insignificant change in RVFW viscoelasticity at late diastolic strain level. Finally, the modeling showed that the tissue's relaxation strength was reduced by the removal of the microtubule network, but the change was present only at a later time scale. These new findings suggest a critical role of cytoskeleton filaments in RVFW passive mechanics in physiological conditions.

FGF13 deficiency ameliorates calcium signaling abnormality in heart failure by regulating microtubule stability

Calcium signaling abnormality in cardiomyocytes, as a key mechanism, is closely associated with developing heart failure. Fibroblast growth factor 13 (FGF13) demonstrates important regulatory roles in the heart, but its association with cardiac calcium signaling in heart failure remains unknown. This study aimed to investigate the role and mechanism of FGF13 on calcium mishandling in heart failure. Mice underwent transaortic constriction to establish a heart failure model, which showed decreased ejection fraction, fractional shortening, and contractility. FGF13 deficiency alleviated cardiac dysfunction. Heart failure reduces calcium transients in cardiomyocytes, which were alleviated by FGF13 deficiency. Meanwhile, FGF13 deficiency restored decreased Cav1.2 and Serca2α expression and activity in heart failure. Furthermore, FGF13 interacted with microtubules in the heart, and FGF13 deficiency inhibited the increase of microtubule stability during heart failure. Finally, in isoproterenol-stimulated FGF13 knockdown neonatal rat ventricular myocytes (NRVMs), wildtype FGF13 overexpression, but not FGF13 mutant, which lost the binding site of microtubules, promoted calcium transient abnormality aggravation and Cav1.2 downregulation compared with FGF13 knockdown group. Generally, FGF13 deficiency improves abnormal calcium signaling by inhibiting the increased microtubule stability in heart failure, indicating the important role of FGF13 in cardiac calcium homeostasis and providing new avenues for heart failure prevention and treatment.

The long noncoding RNA CARDINAL attenuates cardiac hypertrophy by modulating protein translation

One of the features of pathological cardiac hypertrophy is enhanced translation and protein synthesis. Translational inhibition has been shown to be an effective means of treating cardiac hypertrophy, although system-wide side effects are common. Regulators of translation, such as cardiac-specific long noncoding RNAs (lncRNAs), could provide new, more targeted therapeutic approaches to inhibit cardiac hypertrophy. Therefore, we generated mice lacking a previously identified lncRNA named CARDINAL to examine its cardiac function. We demonstrate that CARDINAL is a cardiac-specific, ribosome-associated lncRNA and show that its expression was induced in the heart upon pathological cardiac hypertrophy and that its deletion in mice exacerbated stress-induced cardiac hypertrophy and augmented protein translation. In contrast, overexpression of CARDINAL attenuated cardiac hypertrophy in vivo and in vitro and suppressed hypertrophy-induced protein translation. Mechanistically, CARDINAL interacted with developmentally regulated GTP-binding protein 1 (DRG1) and blocked its interaction with DRG family regulatory protein 1 (DFRP1); as a result, DRG1 was downregulated, thereby modulating the rate of protein translation in the heart in response to stress. This study provides evidence for the therapeutic potential of targeting cardiac-specific lncRNAs to suppress disease-induced translational changes and to treat cardiac hypertrophy and heart failure.

Low-Dose Colchicine Ameliorates Doxorubicin Cardiotoxicity Via Promoting Autolysosome Degradation

BACKGROUND

The only clinically approved drug that reduces doxorubicin cardiotoxicity is dexrazoxane, but its application is limited due to the risk of secondary malignancies. So, exploring alternative effective molecules to attenuate its cardiotoxicity is crucial. Colchicine is a safe and well-tolerated drug that helps reduce the production of reactive oxygen species. High doses of colchicine have been reported to block the fusion of autophagosomes and lysosomes in cancer cells. However, the impact of colchicine on the autophagy activity within cardiomyocytes remains inadequately elucidated. Recent studies have highlighted the beneficial effects of colchicine on patients with pericarditis, postprocedural atrial fibrillation, and coronary artery disease. It remains ambiguous how colchicine regulates autophagic flux in doxorubicin-induced heart failure.

METHODS AND RESULTS

Doxorubicin was administered to establish models of heart failure both in vivo and in vitro. Prior studies have reported that doxorubicin impeded the breakdown of autophagic vacuoles, resulting in damaged mitochondria and the accumulation of reactive oxygen species. Following the administration of a low dose of colchicine (0.1 mg/kg, daily), significant improvements were observed in heart function (left ventricular ejection fraction: doxorubicin group versus treatment group=43.75%±3.614% versus 57.07%±2.968%, P=0.0373). In terms of mechanism, a low dose of colchicine facilitated the degradation of autolysosomes, thereby mitigating doxorubicin-induced cardiotoxicity.

CONCLUSIONS

Our research has shown that a low dose of colchicine is pivotal in restoring the autophagy activity, thereby attenuating the cardiotoxicity induced by doxorubicin. Consequently, colchicine emerges as a promising therapeutic candidate to improve doxorubicin cardiotoxicity.

Mammalian Diaphanous1 signalling in neurovascular complications of diabetes

Over the past few decades, diabetes gradually has become one of the top non-communicable disorders, affecting 476.0 million in 2017 and is predicted to reach 570.9 million people in 2025. It is estimated that 70 to 100% of all diabetic patients will develop some if not all, diabetic complications over the course of the disease. Despite different symptoms, mechanisms underlying the development of diabetic complications are similar, likely stemming from deficits in both neuronal and vascular components supplying hyperglycaemia-susceptible tissues and organs. Diaph1, protein diaphanous homolog 1, although mainly known for its regulatory role in structural modification of actin and related cytoskeleton proteins, in recent years attracted research attention as a cytoplasmic partner of the receptor of advanced glycation end-products (RAGE) a signal transduction receptor, whose activation triggers an increase in proinflammatory molecules, oxidative stressors and cytokines in diabetes and its related complications. Both Diaph1 and RAGE are also a part of the RhoA signalling cascade, playing a significant role in the development of neurovascular disturbances underlying diabetes-related complications. In this review, based on the existing knowledge as well as compelling findings from our past and present studies, we address the role of Diaph1 signalling in metabolic stress and neurovascular degeneration in diabetic complications. In light of the most recent developments in biochemical, genomic and transcriptomic research, we describe current theories on the aetiology of diabetes complications, highlighting the function of the Diaph1 signalling system and its role in diabetes pathophysiology.

Association between Hypertrophic Cardiomyopathy and Variations in Sarcomere Gene and Calcium Channel Gene in Adults

INTRODUCTION

Calcium channel gene variations have been reported to be associated with hypertrophic cardiomyopathy (HCM) in family, but the relationship between calcium channel gene variations and HCM remains undefined in the population.

METHODS

A total of 719 HCM unrelated patients were initially enrolled. Finally, 371 patients were identified based on inclusion and exclusion criteria, including 145 patients with gene negative, 28 patients with a single rare calcium channel gene variation (calcium gene variation), 162 patients with a single pathogenic/likely pathogenic sarcomere gene variation (sarcomere gene variation) and 36 patients with a single pathogenic/likely pathogenic sarcomere gene variation and a single rare calcium channel gene variation (double gene variations). Then the demographic, electrocardiographic, echocardiographic, and follow-up data were collected.

RESULTS

Patients with double gene variations were at an earlier age and had more percent of family history of HCM, and had thicker walls, higher left ventricular outflow tract pressure gradient, more pathological Q waves, and more bundle branch blocks as compared with those with single sarcomere gene variation. During the follow-up period, patients with double gene variations had more primary endpoints than the other three groups (p = 0.0013). Multivariate analysis showed that double gene variations were the independent predictor of primary endpoint events in patients (HR: 4.82, 95% CI: 1.77-13.2; p = 0.002).

CONCLUSION

We found that patients with double gene variations had more severe HCM phenotype and prognosis. The pathogenesis effects of sarcomere gene variation and calcium channel gene variation may be cumulative in HCM populations.

Comparative analysis of ventricular stiffness across species

Investigating ventricular diastolic properties is crucial for understanding the physiological cardiac functions in organisms and unraveling the pathological mechanisms of cardiovascular disorders. Ventricular stiffness, a fundamental parameter that defines ventricular diastolic functions in chordates, is typically analyzed using the end-diastolic pressure-volume relationship (EDPVR). However, comparing ventricular stiffness accurately across chambers of varying maximum volume capacities has been a long-standing challenge. As one of the solutions to this problem, we propose calculating a relative ventricular stiffness index by applying an exponential approximation formula to the EDPVR plot data of the relationship between ventricular pressure and values of normalized ventricular volume by the ventricular weight. This article reviews the potential, utility, and limitations of using normalized EDPVR analysis in recent studies. Herein, we measured and ranked ventricular stiffness in differently sized and shaped chambers using ex vivo ventricular pressure-volume analysis data from four animals: Wistar rats, red-eared slider turtles, masu salmon, and cherry salmon. Furthermore, we have discussed the mechanical effects of intracellular and extracellular viscoelastic components, Titin (Connectin) filaments, collagens, physiological sarcomere length, and other factors that govern ventricular stiffness. Our review provides insights into the comparison of ventricular stiffness in different-sized ventricles between heterologous and homologous species, including non-model organisms.

Role of the microtubule network in the passive anisotropic viscoelasticity of right ventricle with pulmonary hypertension progression

Cardiomyocytes are viscoelastic and contribute significantly to right ventricle (RV) mechanics. Microtubule, a cytoskeletal protein, has been shown to regulate cardiomyocyte viscoelasticity. Additionally, hypertrophied cardiomyocytes from failing myocardium have increased microtubules and cell stiffness. How the microtubules contribute to the tissue-level viscoelastic behavior in RV failure remains unknown. Our aim was to investigate the role of the microtubules in the passive anisotropic viscoelasticity of the RV free wall (RVFW) during pulmonary hypertension (PH) progression. Equibiaxial stress relaxation tests were conducted in the RVFW from healthy and PH rats under early (6%) and end (15%) diastolic strains, and at sub- (1Hz) and physiological (5Hz) stretch-rates. The RVFW viscoelasticity was also measured before and after the depolymerization of microtubules at 5Hz. In intact tissues, PH increased RV viscosity and elasticity at both stretch rates and strain levels, and the increase was stronger in the circumferential than longitudinal direction. At 6% of strain, the removal of microtubules reduced elasticity, viscosity, and the ratio of viscosity to elasticity in both directions and for both healthy and diseased RVs. However, at 15% of strain, the effect of microtubules was different between groups - both viscosity and elasticity were reduced in healthy RVs, but in the diseased RVs only the circumferential viscosity and the ratio of viscosity to elasticity were reduced. These data suggest that, at a large strain with collagen recruitment, microtubules play more significant roles in healthy RV tissue elasticity and diseased RV tissue viscosity. Our findings suggest cardiomyocyte cytoskeletons are critical to RV passive viscoelasticity under pressure overload. STATEMENT OF SIGNIFICANCE: This study investigated the impact of microtubules on the passive anisotropic viscoelasticity of the right ventricular (RV) free wall at healthy and pressure-overloaded states. We originally found that the microtubules contribute significantly to healthy and diseased RV viscoelasticity in both (longitudinal and circumferential) directions at early diastolic strains. At end diastolic strains (with the engagement of collagen fibers), microtubules contribute more to the tissue elasticity of healthy RVs and tissue viscosity of diseased RVs. Our findings reveal the critical role of microtubules in the anisotropic viscoelasticity of the RV tissue, and the altered contribution from healthy to diseased state suggests that therapies targeting microtubules may have potentials for RV failure patients.

The cardiomyocyte origins of diastolic dysfunction: cellular components of myocardial "stiffness"

The impaired ability of the heart to relax and stretch to accommodate venous return is generally understood to represent a state of "diastolic dysfunction" and often described using the all-purpose noun "stiffness." Despite the now common qualitative usage of this term in fields of cardiac patho/physiology, the specific quantitative concept of stiffness as a molecular and biophysical entity with real practical interpretation in healthy and diseased hearts is sometimes obscure. The focus of this review is to characterize the concept of cardiomyocyte stiffness and to develop interpretation of "stiffness" attributes at the cellular and molecular levels. Here, we consider "stiffness"-related terminology interpretation and make links between cardiomyocyte stiffness and aspects of functional and structural cardiac performance. We discuss cross bridge-derived stiffness sources, considering the contributions of diastolic myofilament activation and impaired relaxation. This includes commentary relating to the role of cardiomyocyte Ca2+ flux and Ca2+ levels in diastole, the troponin-tropomyosin complex role as a Ca2+ effector in diastole, the myosin ADP dissociation rate as a modulator of cross bridge attachment and regulation of cross-bridge attachment by myosin binding protein C. We also discuss non-cross bridge-derived stiffness sources, including the titin sarcomeric spring protein, microtubule and intermediate filaments, and cytoskeletal extracellular matrix interactions. As the prevalence of conditions involving diastolic heart failure has escalated, a more sophisticated understanding of the molecular, cellular, and tissue determinants of cardiomyocyte stiffness offers potential to develop imaging and molecular intervention tools.

Considering impact of age and sex on cardiac cytoskeletal components

The cardiac cytoskeletal components are integral to cardiomyocyte function and are responsible for contraction, sustaining cell structure, and providing scaffolding to direct signaling. Cytoskeletal components have been implicated in cardiac pathology; however, less attention has been paid to age-related modifications of cardiac cytoskeletal components and how these contribute to dysfunction with increased age. Moreover, significant sex differences in cardiac aging have been identified, but we still lack a complete understanding to the mechanisms behind these differences. This review summarizes what is known about how key cardiomyocyte cytoskeletal components are modified because of age, as well as reported sex-specific differences. Thorough consideration of both age and sex as integral players in cytoskeletal function may reveal potential avenues for more personalized therapeutics.

Microtubule destabilization with colchicine increases the work output of myocardial slices

Cardiac microtubules have recently been implicated in mechanical dysfunction during heart failure. However, systemic intolerance and non-cardiac effects of microtubule-depolymerizing compounds have made it challenging to determine the effect of microtubules on myocardial performance. Herein, we leverage recent advancements in living myocardial slices to develop a stable working preparation that recapitulates the complexity of diastole by including early and late phases of diastolic filling. To determine the effect of cardiac microtubule depolymerization on diastolic performance, myocardial slices were perfused with oxygenated media to maintain constant isometric twitch forces for more than 90 min. Force-length work loops were collected before and after 90 min of treatment with either DMSO (vehicle) or colchicine (microtubule depolymerizer). A trapezoidal stretch was added prior to the beginning of ventricular systole to mimic late-stage-diastolic filling driven by atrial systole. Force-length work loops were obtained at fixed preload and afterload, and tissue velocity was obtained during diastole as an analog to trans-mitral Doppler. In isometric twitches, microtubule destabilization accelerated force development, relaxation kinetics, and decreased end diastolic stiffness. In work loops, microtubule destabilization increased stroke length, myocardial output, accelerated isometric contraction and relaxation, and increased the amplitude of early filling. Taken together, these results indicate that the microtubule destabilizer colchicine can improve diastolic performance by accelerating isovolumic relaxation and early filling leading to increase in myocardial work output.

Ion channel trafficking implications in heart failure

Heart failure (HF) is recognized as an epidemic in the contemporary world, impacting around 1%-2% of the adult population and affecting around 6 million Americans. HF remains a major cause of mortality, morbidity, and poor quality of life. Several therapies are used to treat HF and improve the survival of patients; however, despite these substantial improvements in treating HF, the incidence of HF is increasing rapidly, posing a significant burden to human health. The total cost of care for HF is USD 69.8 billion in 2023, warranting a better understanding of the mechanisms involved in HF. Among the most serious manifestations associated with HF is arrhythmia due to the electrophysiological changes within the cardiomyocyte. Among these electrophysiological changes, disruptions in sodium and potassium currents' function and trafficking, as well as calcium handling, all of which impact arrhythmia in HF. The mechanisms responsible for the trafficking, anchoring, organization, and recycling of ion channels at the plasma membrane seem to be significant contributors to ion channels dysfunction in HF. Variants, microtubule alterations, or disturbances of anchoring proteins lead to ion channel trafficking defects and the alteration of the cardiomyocyte's electrophysiology. Understanding the mechanisms of ion channels trafficking could provide new therapeutic approaches for the treatment of HF. This review provides an overview of the recent advances in ion channel trafficking in HF.

Chronic activation of tubulin tyrosination in HCM mice and human iPSC-engineered heart tissues improves heart function

Rationale: Hypertrophic cardiomyopathy (HCM) is the most common cardiac genetic disorder caused by sarcomeric gene variants and associated with left ventricular (LV) hypertrophy and diastolic dysfunction. The role of the microtubule network has recently gained interest with the findings that -α-tubulin detyrosination (dTyr-tub) is markedly elevated in heart failure. Acute reduction of dTyr-tub by inhibition of the detyrosinase (VASH/SVBP complex) or activation of the tyrosinase (tubulin tyrosine ligase, TTL) markedly improved contractility and reduced stiffness in human failing cardiomyocytes, and thus poses a new perspective for HCM treatment. Objective: In this study, we tested the impact of chronic tubulin tyrosination in a HCM mouse model ( Mybpc3 -knock-in; KI), in human HCM cardiomyocytes and in SVBP-deficient human engineered heart tissues (EHTs). Methods and Results: AAV9-mediated TTL transfer was applied in neonatal wild-type (WT) rodents and 3-week-old KI mice and in HCM human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes. We show that i) TTL for 6 weeks dose-dependently reduced dTyr-tub and improved contractility without affecting cytosolic calcium transients in WT cardiomyocytes; ii) TTL for 12 weeks improved diastolic filling, cardiac output and stroke volume and reduced stiffness in KI mice; iii) TTL for 10 days normalized cell hypertrophy in HCM hiPSC-cardiomyocytes; iv) TTL induced a marked transcription and translation of several tubulins and modulated mRNA or protein levels of components of mitochondria, Z-disc, ribosome, intercalated disc, lysosome and cytoskeleton in KI mice; v) SVBP-deficient EHTs exhibited reduced dTyr-tub levels, higher force and faster relaxation than TTL-deficient and WT EHTs. RNA-seq and mass spectrometry analysis revealed distinct enrichment of cardiomyocyte components and pathways in SVBP-KO vs. TTL-KO EHTs. Conclusion: This study provides the first proof-of-concept that chronic activation of tubulin tyrosination in HCM mice and in human EHTs improves heart function and holds promise for targeting the non-sarcomeric cytoskeleton in heart disease.

Titin takes centerstage among cytoskeletal contributions to myocardial passive stiffness

Both diastolic filling and systolic pumping of the heart are dependent on the passive stiffness characteristics of various mechanical elements of myocardium. However, the specific contribution from each element, including the extracellular matrix, actin filaments, microtubules, desmin intermediate filaments, and sarcomeric titin springs, remains challenging to assess. Recently, a mouse model allowing for precise and acute cleavage of the titin springs was used to remove one mechanical element after the other from cardiac fibers and record the effect on passive stiffness. It became clear that the stiffness contribution from each element is context-dependent and varies depending on strain level and the force component considered (elastic or viscous); elements do not act in isolation but in a tensegral relationship. Titin is a substantial contributor under all conditions and dominates the elastic forces at both low and high strains. The contribution to viscous forces is more equally shared between microtubules, titin, and actin. However, the extracellular matrix substantially contributes to both force components at higher strain levels. Desmin filaments may bear low stiffness. These insights enhance our understanding of how different filament networks contribute to passive stiffness in the heart and offer new perspectives for targeting this stiffness in heart failure treatment.

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.

MEK1-ERK1/2 signaling regulates the cardiomyocyte non-sarcomeric actin cytoskeletal network

During select pathological conditions, the heart can hypertrophy and remodel in either a dilated or concentric ventricular geometry, which is associated with lengthening or widening of cardiomyocytes, respectively. The mitogen-activated protein kinase kinase 1 (MEK1) and extracellular signal-related kinase 1 and 2 (ERK1/2) pathway has been implicated in these differential types of growth such that cardiac overexpression of activated MEK1 causes profound concentric hypertrophy and cardiomyocyte thickening, while genetic ablation of the genes encoding ERK1/2 in the mouse heart causes dilation and cardiomyocyte lengthening. However, the mechanisms by which this kinase signaling pathway controls cardiomyocyte directional growth as well as its downstream effectors are poorly understood. To investigate this, we conducted an unbiased phosphoproteomic screen in cultured neonatal rat ventricular myocytes treated with an activated MEK1 adenovirus, the MEK1 inhibitor U0126, or an eGFP adenovirus control. Bioinformatic analysis identified cytoskeletal-related proteins as the largest subset of differentially phosphorylated proteins. Phos-tag and traditional Western blotting were performed to confirm that many cytoskeletal proteins displayed changes in phosphorylation with manipulations in MEK1-ERK1/2 signaling. From this, we hypothesized that the actin cytoskeleton would be changed in vivo in the mouse heart. Indeed, we found that activated MEK1 transgenic mice and gene-deleted mice lacking ERK1/2 protein had enhanced non-sarcomeric actin expression in cardiomyocytes compared with wild-type control hearts. Consistent with these results, cytoplasmic β- and γ-actin were increased at the subcortical intracellular regions of adult cardiomyocytes. Together, these data suggest that MEK1-ERK1/2 signaling influences the non-sarcomeric cytoskeletal actin network, which may be important for facilitating the growth of cardiomyocytes in length and/or width.NEW & NOTEWORTHY Here, we performed an unbiased analysis of the total phosphoproteome downstream of MEK1-ERK1/2 kinase signaling in cardiomyocytes. Pathway analysis suggested that proteins of the non-sarcomeric cytoskeleton were the most differentially affected. We showed that cytoplasmic β-actin and γ-actin isoforms, regulated by MEK1-ERK1/2, are localized to the subcortical space at both lateral membranes and intercalated discs of adult cardiomyocytes suggesting how MEK1-ERK1/2 signaling might underlie directional growth of adult cardiomyocytes.

Integrative Proteomic Analysis Reveals the Cytoskeleton Regulation and Mitophagy Difference Between Ischemic Cardiomyopathy and Dilated Cardiomyopathy

Ischemic cardiomyopathy (ICM) and dilated cardiomyopathy (DCM) are the two primary etiologies of end-stage heart failure. However, there remains a dearth of comprehensive understanding the global perspective and the dynamics of the proteome and phosphoproteome in ICM and DCM, which hinders the profound comprehension of pivotal biological characteristics as well as differences in signal transduction activation mechanisms between these two major types of heart failure. We conducted high-throughput quantification proteomics and phosphoproteomics analysis of clinical heart tissues with ICM or DCM, which provided us the system-wide molecular insights into pathogenesis of clinical heart failure in both ICM and DCM. Both protein and phosphorylation expression levels exhibit distinct separation between heart failure and normal control heart tissues, highlighting the prominent characteristics of ICM and DCM. By integrating with omics results, Western blots, phosphosite-specific mutation, chemical intervention, and immunofluorescence validation, we found a significant activation of the PRKACA-GSK3β signaling pathway in ICM. This signaling pathway influenced remolding of the microtubule network and regulated the critical actin filaments in cardiac construction. Additionally, DCM exhibited significantly elevated mitochondria energy supply injury compared to ICM, which induced the ROCK1-vimentin signaling pathway activation and promoted mitophagy. Our study not only delineated the major distinguishing features between ICM and DCM but also revealed the crucial discrepancy in the mechanisms between ICM and DCM. This study facilitates a more profound comprehension of pathophysiologic heterogeneity between ICM and DCM and provides a novel perspective to assist in the discovery of potential therapeutic targets for different types of heart failure.

Physiological roles of chloride ions in bodily and cellular functions

Physiological roles of Cl-, a major anion in the body, are not well known compared with those of cations. This review article introduces: (1) roles of Cl- in bodily and cellular functions; (2) the range of cytosolic Cl- concentration ([Cl-]c); (3) whether [Cl-]c could change with cell volume change under an isosmotic condition; (4) whether [Cl-]c could change under conditions where multiple Cl- transporters and channels contribute to Cl- influx and efflux in an isosmotic state; (5) whether the change in [Cl-]c could be large enough to act as signals; (6) effects of Cl- on cytoskeletal tubulin polymerization through inhibition of GTPase activity and tubulin polymerization-dependent biological activity; (7) roles of cytosolic Cl- in cell proliferation; (8) Cl--regulatory mechanisms of ciliary motility; (9) roles of Cl- in sweet/umami taste receptors; (10) Cl--regulatory mechanisms of with-no-lysine kinase (WNK); (11) roles of Cl- in regulation of epithelial Na+ transport; (12) relationship between roles of Cl- and H+ in body functions.

Liquid-Liquid Phase Separation Sheds New Light upon Cardiovascular Diseases

Liquid-liquid phase separation (LLPS) is a biophysical process that mediates the precise and complex spatiotemporal coordination of cellular processes. Proteins and nucleic acids are compartmentalized into micron-scale membrane-less droplets via LLPS. These droplets, termed biomolecular condensates, are highly dynamic, have concentrated components, and perform specific functions. Biomolecular condensates have been observed to organize diverse key biological processes, including gene transcription, signal transduction, DNA damage repair, chromatin organization, and autophagy. The dysregulation of these biological activities owing to aberrant LLPS is important in cardiovascular diseases. This review provides a detailed overview of the regulation and functions of biomolecular condensates, provides a comprehensive depiction of LLPS in several common cardiovascular diseases, and discusses the revolutionary therapeutic perspective of modulating LLPS in cardiovascular diseases and new treatment strategies relevant to LLPS.

NAP1L1 is a novel microtubule-associated protein

Microtubule-associated proteins (MAPs) regulate assembly and stability of microtubules (MTs) during cell cytokinesis, cell migration, neuronal growth, axon guidance, and synapse formation. Using data mining of the Human Protein Atlas database and experimental screening, we identified nucleosome assembly protein 1 like 1 (NAP1L1) as a new MAP. The Human Protein Atlas and PubMed database screening identified 99 potential new MAPs. Twenty candidate proteins that highly co-localized with MTs were exogenously expressed with green fluorescent protein (GFP) or hemagglutinin (HA) tags in tissue culture cells and MTs were co-stained for immunofluorescent microscopy. We found that NAP1L1 is mainly localized in the cytosol with MTs during interphase. Using bacterially expressed recombinant NAP1L1 fragments and purified MTs, we biochemically mapped the MT-binding site on the N-terminal region (1-72aa) and the central region (164-269aa) of NAP1L1. NAP1L1 dimerizes through the long helix region (73-163aa), and full-length NAP1L1 induces the formation of thick MTs, indicating that NAP1L1 has the ability to bundle MTs in cells. Analysis of publicly available RNA-seq data of NAP1L1 depleted cells suggested that NAP1L1 is involved in cell adhesion and migration in agreement with the function of NAP1L1 as a MAP.

Nucleus Mechanosensing in Cardiomyocytes

Cardiac muscle contraction is distinct from the contraction of other muscle types. The heart continuously undergoes contraction-relaxation cycles throughout an animal's lifespan. It must respond to constantly varying physical and energetic burdens over the short term on a beat-to-beat basis and relies on different mechanisms over the long term. Muscle contractility is based on actin and myosin interactions that are regulated by cytoplasmic calcium ions. Genetic variants of sarcomeric proteins can lead to the pathophysiological development of cardiac dysfunction. The sarcomere is physically connected to other cytoskeletal components. Actin filaments, microtubules and desmin proteins are responsible for these interactions. Therefore, mechanical as well as biochemical signals from sarcomeric contractions are transmitted to and sensed by other parts of the cardiomyocyte, particularly the nucleus which can respond to these stimuli. Proteins anchored to the nuclear envelope display a broad response which remodels the structure of the nucleus. In this review, we examine the central aspects of mechanotransduction in the cardiomyocyte where the transmission of mechanical signals to the nucleus can result in changes in gene expression and nucleus morphology. The correlation of nucleus sensing and dysfunction of sarcomeric proteins may assist the understanding of a wide range of functional responses in the progress of cardiomyopathic diseases.

New Mechanical Markers for Tracking the Progression of Myocardial Infarction

The mechanical properties of soft tissues can often be strongly correlated with the progression of various diseases, such as myocardial infarction (MI). However, the dynamic mechanical properties of cardiac tissues during MI progression remain poorly understood. Herein, we investigate the rheological responses of cardiac tissues at different stages of MI (i.e., early-stage, mid-stage, and late-stage) with atomic force microscopy-based microrheology. Surprisingly, we discover that all cardiac tissues exhibit a universal two-stage power-law rheological behavior at different time scales. The experimentally found power-law exponents can capture an inconspicuous initial rheological change, making them particularly suitable as markers for early-stage MI diagnosis. We further develop a self-similar hierarchical model to characterize the progressive mechanical changes from subcellular to tissue scales. The theoretically calculated mechanical indexes are found to markedly vary among different stages of MI. These new mechanical markers are applicable for tracking the subtle changes of cardiac tissues during MI progression.