Innovative therapies are needed in the face of a lack of a comprehensive, in-depth understanding of the complex mechanisms underlying atrial fibrillation (AF). There is recognition of a need for deeper understanding and novel therapeutic approaches, especially in atrial cardiomyopathy (ACM). ACM is considered a separate entity characterized by structural, architectural, contractile, or electrophysiological changes, increasing the potential for clinical atrial pathology. Evidence indicating a role for ACM in atrial disorders is that, in some cases, thromboembolic risk and persistent AF continue despite treatments such as ablation of isolated regions of the pulmonary vein known to set off AF. Here we review a possible role for modifications at the level of atrial sarcomeres as a common mechanism inducing genetic and acquired AF/ACM. Our review indicates the likelihood that these modifications induce adverse signaling resulting in fibrosis, inflammation, neuro-humoral activity, and arrhythmias, in turn promoting atrial pathology. We discuss genetic and acquired ACM through the lens of a new era of understanding of sarcomere control mechanisms. This advanced understanding has not been thoroughly discussed previously in the case of atrial sarcomeres. Significant new evidence has revealed atrial sarcomere specific mechanisms with the potential for novel control of the pressure-volume relation that is vulnerable in ACM. These mechanisms in atrial sarcomeres have taken on new significance with the identification and clinical development of small-molecule sarcomere activators and inhibitors with possible use and further development in ACM therapy.
Background Atherosclerosis is driven by sustained recruitment and accumulation of monocytes and macrophages within arterial walls through chemokine-mediated pathways. Netrin-1, an immunomodulatory molecule originally identified in neural development, has emerged as a potential regulator of vascular inflammation, though its precise effects on chemokine-driven leukocyte migration remain undefined. Methods We investigated netrin-1 effects on macrophage migration in vitro using real-time impedance-based assays and assessed systemic effects in vivo through intravital microscopy and aortic sinus histology in an inflammation-induced model. Results Netrin-1 selectively inhibited CCL2-driven macrophage migration in vitro, reducing migration when combined with the chemokine compared to chemokine alone. In an acute inflammation mouse model, systemic netrin-1 pre-treatment showed a trend toward the decrease of monocyte adhesion and transmigration into the tissue while increasing rolling interactions, suggesting impaired firm adhesion and diapedesis. Importantly, hyperlipidaemic LDLR−/− mice presented enlarged aortic sinus after being fed a high-fat diet, and this enlargement was not observed when netrin-1 was continuously administered via osmotic minipumps. Conclusions Our data suggests that systemic netrin-1 selectively inhibits chemokine-driven monocyte migration in vitro, with potential implications for reducing vascular inflammatory cell recruitment, an important component of atherogenesis.
Rationale Although plexiform lesion (PL) formation in severe pulmonary arterial hypertension (PAH) is a therapeutic target, the mechanisms underlying their formation have not been fully elucidated. Objective To identify candidate proteins involved in PL formation by examining differentially expressed proteins (DEPs) in PAH lesions. Methods Proteomic remodeling was assessed before and after the formation of PLs in a SU5416 combined with hypoxia (SuHx) rat model of severe PAH using laser-capture microdissection coupled with mass spectrometry. Unobstructed pulmonary arteries with medial hypertrophy (UMHPAs) and PLs from SuHx rats were subjected to qualitative and quantitative proteomics, revealing DEPs between these structures. Results We identified 718 proteins with 58 DEPs, of which 31 were upregulated in UMHPAs and 27 were upregulated in PLs. Immunostaining confirmed that DEPs detected in our proteomic analysis were differentially expressed between UMHPAs and PLs. Among them, we focused on heterogeneous nuclear ribonucleoprotein A1 (hnRNPA1) as a candidate protein that may be associated with PL formation because of its strong association with cell proliferation. Small interfering RNA knockdown of hnRNPA1 in hypoxia-treated pulmonary artery smooth muscle cells reduced pyruvate kinase M2 expression and decreased proliferative capacity. Conclusions Several DEPs associated with PL formation but with unclear relevance to pulmonary artery remodeling in PAH were discovered. Among these, hnRNPA1, which was not detected in transcriptome analysis and whole lung analysis, may be important in PL formation.
Aims:Sodium-glucose cotransporter 2 inhibitors (SGLT2i) have demonstrated cardioprotective effects in heart failure (HF), yet the molecular mechanisms underlying these benefits remain incompletely understood. This study aimed to characterize cardioprotective effects of SGLT2i, changes of circulating growth and inflammatory factors, as well as adipose tissue gene expression, in subjects with advanced HF (stage D). Methods:27 subjects with HF undergoing cardiovascular surgery were included, comprising 17 subjects treated with SGLT2i and 10 untreated controls. Soluble factors were analysed using Luminex assay, and mRNA expression in subcutaneous (SAT) and epicardial adipose tissue (EAT) was assessed. Results:Subjects receiving SGLT2i exhibited a non-significant trend toward lower BNP concentrations (329.1 ± 78.7 vs. 514.2 ± 103.8 pmol/L, p = 0.079) and increased circulatory levels of anti-inflammatory IL-10 (7.2 ± 0.4 vs. 5.8 ± 0.7 pg/mL, p = 0.025) and cardioprotective TGF-α (3.5 ± 0.3 vs. 2.7 ± 0.4 pg/mL, p = 0.039). sVEGFR3 levels (82.3 ± 4.7 vs. 63.3 ± 3.9 pg/mL, p = 0.010) were higher in SGLT2i, suggesting altered lymphangiogenic signalling. Transcriptomic analysis showed lower expression of genes associated with inflammation (IL6, CCL2, CXCL2), cardiac hypertrophy (PKFP, NAMPT), fibrosis (TNC, TNFAIP3), and cellular senescence (ICAM1, CDKN1A), predominantly in SAT. Conclusions:SGLT2i therapy in advanced HF was associated with higher circulating IL-10, TGF-α and sVEGFR3 levels and with a more favourable adipose tissue gene expression profile characterized by lower expression of genes related to inflammation, fibrosis, and cellular senescence. These findings identify molecular pathways associated with SGLT2i therapy that warrant further mechanistic investigation.
Primary (genetic) cardiomyopathy comprises a heterogeneous group of predominantly monogenic (genetically determined) myocardial diseases-principally hypertrophic (HCM), dilated (DCM) and restrictive (RCM) phenotypes-and must be distinguished from secondary/acquired cardiomyopathies attributable to ischaemia, valvular disease, pressure overload, diabetes, infection or toxins. This review is restricted to primary cardiomyopathy; because organelle biology has been characterised far more extensively in secondary or acquired settings, evidence derived from such models (ischaemia-reperfusion, pressure overload, diabetes, sepsis, drug toxicity, neurodegenerative or non-cardiac injury models) is explicitly identified as such and treated as indirect, hypothesis-generating support rather than as direct evidence in primary cardiomyopathy. The pathophysiology of primary cardiomyopathy is tightly related to abnormal energy metabolism, protein homeostasis and calcium homeostasis. An increasing body of evidence suggests that organelle malfunction and abnormal inter-organelle interactions play a role in primary cardiomyopathy development. This review focuses on key organelles: mitochondrial dysfunction results in energy deprivation and oxidative imbalance; endoplasmic reticulum stress (ERS) impairs protein folding and calcium homeostasis; defects in the lysosome-mediated autophagy pathway exacerbate the accumulation of intracellular damaged material; Golgi fragmentation affects protein processing and trafficking; and cytoskeletal disruption compromises the structural integrity of myocardium. Furthermore, organelles create complex regulatory networks via structures like mitochondrial-associated ER membranes (MAMs), where imbalances such as aberrant calcium signalling and stress pathway cross-activation exacerbate pathological damage. While previous studies focus on individual proteins or organelles, the heart's high energy consumption and synchronized contraction require understanding cardiomyocytes as a dynamic, interdependent organelle ecosystem. Treating primary cardiomyopathy as a 'organelle network disease', in which organelles constitute a dynamic, interdependent ecosystem, provides a useful integrative paradigm for comprehending the causes. This review lays the groundwork for targeted therapy in primary cardiomyopathy by clarifying the functions of organelles.
Dilated cardiomyopathy (DCM) is a progressive heart muscle disease characterized by the enlargement of the heart's left ventricle. The aetiology of the disease can be genetic and/or environmental. Mutations in LMNA, the gene encoding for the nuclear lamina protein lamin A/C, are associated with approximately 6% of DCM, however, the role of the functionally related lamin B1 remains unknown. Lamin B1 provides structural integrity to the nucleus and regulates gene expression by restricting the accessibility and transcription of lamin B1 tethered genes. Our study focuses on the lamin B1 content and nuclear shape in human DCM. We first compare the levels of lamin B1 expression at the protein level in non-failing versus DCM diagnosed human hearts and then use an unbiased immunofluorescence and morphological phenotyping approach of cardiomyocyte nuclei to classify subpopulations of cells. This revealed that hearts diagnosed with DCM show a higher prevalence of nuclei within cardiomyocytes that were deformed and had a loss of lamin B1 signal. Using our unbiased analysis of the cardiomyocyte nuclei, we can separate non-failing from DCM donors. In conclusion, our study shows that lamin B1 loss in human cardiomyocytes is associated with nuclear shape deformation in dilated cardiomyopathy.
Heart failure is often accompanied by metabolic remodeling; however, the contribution of compartment-specific acetyl-CoA homeostasis to mitochondrial dysfunction remains unclear. Here, we identify acetyl-CoA synthetase 2 (ACSS2) as an important regulator of cytosolic acetyl-CoA homeostasis and mitochondrial integrity under chronic β-adrenergic stress.Chronic isoproterenol stimulation induced heart failure with reduced ejection fraction in mice and selectively suppressed myocardial ACSS2 expression, resulting in depletion of cytosolic acetyl-CoA without altering total cellular levels. Similar changes were observed in H9c2 cardiomyoblasts exposed to prolonged β-adrenergic stimulation. Genetic deletion of ACSS2 recapitulated this metabolic disturbance, leading to mitochondrial structural remodeling and impaired oxidative respiration without evidence of altered mitochondrial biogenesis.Mechanistically, ACSS2 deficiency was associated with compartment-specific alterations in protein acetylation, characterized by reduced cytosolic acetylation and increased mitochondrial acetylation. Mitochondrial dysfunction was reversible, as long-term supplementation with butyrate restored mitochondrial respiratory capacity.Conversely, cardiomyocyte-targeted ACSS2 overexpression preserved cytosolic acetyl-CoA levels and was associated with improved mitochondrial respiratory function and attenuated cardiac dysfunction in vivo under chronic β-adrenergic stress.Together, these findings suggest that ACSS2-dependent cytosolic acetyl-CoA homeostasis contributes to the maintenance of mitochondrial quality and cardiac resilience, highlighting the importance of metabolic compartmentalization in heart failure pathophysiology.
Anthracycline-induced cardiotoxicity remains a major limitation in cancer therapy, with substantial inter-individual variability in susceptibility, including documented sex differences. However, the molecular basis underlying these disparities remains incompletely understood. In this study, we employed large-scale data-independent acquisition proteomics in a long-latency rat model of doxorubicin-induced cardiomyopathy to characterize early cardiac proteomic remodeling. Longitudinal echocardiography demonstrated a significantly greater decline in fractional shortening in males compared to females. Early proteomic profiling identified 5184 proteins and revealed widespread remodeling across metabolic, mitochondrial, cytoskeletal, and stress-response pathways. While doxorubicin induced broad proteomic changes in both sexes, two-way limma-based sex-stratified analyses identified 430 proteins exhibiting significant sex-by-treatment interactions. Our results suggested that doxorubicin was associated with alterations in oxidative phosphorylation, fatty acid metabolism, and calcium handling pathways. A female-specific upregulation of mitochondrial proteins, including Sco1, Cox17, and Atp2a2, which may be associated with preserved energetics and Ca2+ handling, was detected. In contrast, male hearts demonstrated reduced Micu1 and RyR2 together with increased levels of Ppp1ca, findings that may indicate alterations in mitochondrial function and, excitation-contraction coupling. We also observed lower levels of calcineurin (Ppp3cb) in females. Baseline proteomic differences between sexes further implied distinct regulatory states that may shape the cardiac response to doxorubicin.Together, these findings suggest early proteomic remodeling upon doxorubicin treatment and represent candidate molecular targets that warrant functional validation in future studies. This work offers hypothesis-generating mechanistic insights into sex-specific responses to anthracycline-induced cardiomyopathy and underscores the importance of incorporating sex as a biological variable in cardio-oncology research.
Protein Arginine Methyltransferase (PRMT5) has emerged as a promising target for antineoplastic strategies. Given its oncogenic properties in promoting tumorigenesis and metastasis of several cancer entities, pharmacological approaches to inhibit the enzymatic activity of PRMT5 (PRMT5i) have gained particular attention. Among others, GSK3326595 is currently evaluated in clinical studies for the treatment of hematological malignancies. However, besides the pathophysiological relevance, PRMT5 is a ubiquitously expressed enzyme with essential cellular functions. Previous studies uncovered a substantial role in cardiomyocytes along with heart failure caused by loss of PRMT5 raising the question if PRMT5i may exert adverse effects on the cardiovascular system. Thus, we conducted comprehensive pharmacokinetic profiling of GSK3326595 in mice. We found that systemic administration leads to a homogenous distribution across organs and tissues. While major depression of hematopoiesis could be detected, we did not find detrimental impact on systolic function, cardiac morphology and homeostasis indicating differential pharmacodynamics on proliferating and postmitotic cells. In conclusion, systemic treatment with GSK3326595 shows no overt effects on the murine heart under the conditions tested in this study.
Hypertrophic cardiomyopathy (HCM) is the most common inherited cardiomyopathy. The pathognomonic finding is the thickening of the myocardial layer, usually of the left ventricular wall. This hypertrophy is often caused by variants in genes encoding sarcomeric proteins. Additionally, non-genetic factors contribute to the complex pathophysiology. Interestingly, these genetic and non-genetic factors result in quite uniform pathological changes, e.g., diastolic dysfunction and hypercontractility can be regarded as pathophysiological hallmarks of the disease. A potential explanation for this might be that embryological factors along with a first adaptive and later maladaptive myocardial remodeling prime myocardial hypertrophy. The present review compares the immature and mature myocardium to further assess the impact of embryological factors on the pathophysiology of HCM. According to the literature, there are differences between the immature and mature myocardium affected by sarcomeric variants at the molecular level. At the same time, the early postnatal period seems to be fundamental to sarcomeric alterations that later drive hypertrophy. Given the shared down-stream pathological changes, fetal-like reprogramming might be the pathophysiological molecular merging point of immature and mature myocardium finally driving the maladaptive hypertrophic remodeling in HCM. More research on such embryonic factors might allow for further HCM-specific targeted therapy.
Right ventricular (RV) failure is the leading cause of death in pulmonary artery hypertension (PAH) and treatments that preserve RV contractility are urgently required. β-adrenoceptor blockers (BB) are used clinically in left ventricular failure to improve β-adrenoceptor (AR) responsiveness but it is not known whether they confer the same benefits in RV failure. Here we tested this using the rat monocrotaline (MCT) model of PAH. When PAH was established, treatment commenced with β1AR-selective metoprolol (10 mg/kg/day; MCT + BB group) or vehicle (MCT group). In isolated RV myocytes from MCT, inotropic and lusitropic responses to β1AR stimulation were blunted vs. non-failing controls (CON), and this was recovered by BB treatment. Comparable effects on amplitude/kinetics of the Ca2+ transient were observed. The impact of RV failure and BB on β1AR responsiveness could be explained by altered expression of proteins of the βAR cascade and its regulatory domain, the caveola. Expression of β1AR, adenylyl cyclase 5/6, caveolin 1 & 3, and cavin 1 were decreased in RV from MCT, whereas G protein receptor kinase was increased. These changes were reversed by BB treatment, with the exception of caveolin 1. A computational model of cardiac myocyte β1AR signalling, incorporating observed changes in protein expression, showed that BB treatment recovered the β1AR-cAMP signals in caveolar and extra-caveolar compartments. Modelling indicated that recovery of adenylyl cyclase 5/6 was the main factor responsible for the beneficial impact of BB treatment on failing RV myocyte contractility. As RV function critically influences symptoms and mortality, this work supports the potential use of BB as a novel treatment for PAH-RV failure.
Genetic variants upstream of the paired-like homeodomain transcription factor 2 (PITX2) are the strongest risk variants associated with atrial fibrillation. However, the mechanisms downstream of PITX2 are not completely understood. Here, we explore the role of PITX2 in oxidative metabolism and stress as a unifying mechanism of arrhythmogenesis. Transcriptomic analysis of Pitx2c-deficient neonatal rat atrial myocytes indicates oxidative phosphorylation as the top dysregulated pathway. Extracellular flux analysis reveals a functional decrease in oxidative metabolism in Pitx2c-deficient atrial cardiomyocytes which was accompanied by an accumulation of mitochondrial-specific ROS. We additionally assessed cardiomyocyte calcium cycling and observed an increased frequency of pro-arrhythmogenic mechanisms including altered calcium traces. Further, we identified a role of PITX2C in the sarcomere, as Pitx2c-deficient atrial cardiomyocytes display altered Titin localization. Notably, we observe that antioxidant treatment with N-acetylcysteine partially attenuates arrhythmogenic phenotypes including abnormal calcium cycling and Titin organization in Pitx2c-deficient atrial cardiomyocytes. Together, these data suggest that PITX2C deficiency is associated with atrial metabolism defects that ramifies cardiomyocyte dysfunction through oxidative stress.
MicroRNAs are non-coding RNA sequences capable of transport outside the cell to regulate essential cellular processes. They are able to induce structural changes implicated in prevalent cardiovascular conditions such as heart failure, atherosclerosis and myocardial ischemia. SGLT2 inhibitors are newer anti-diabetic drugs used in the prevention and treatment of cardiovascular disease, which modulate metabolic pathways shared with microRNAs. Direct evidence linking a mechanistic relationship between microRNAs and SGLT2 inhibitors is limited. However, they share multiple pathways affecting key cellular processes implicated in cardiovascular disease progression, such as fibrosis and inflammation. This mini-review explores the effects of microRNAs on cardiac disease, with potential implications in cardiovascular disease management. Shared mechanisms between microRNAs and SGLT2 inhibitors and subsequent impact on heart failure development will be emphasized throughout. Certain microRNAs implicated in cardiovascular disease could potentially serve as diagnostic and therapeutic targets. Future use of microRNA-based technologies may include biomarker panels of circulating microRNAs and exosomal delivery of therapeutic microRNAs. However, these technologies are not fully developed, as the majority of relevant studies are preclinical. Possible future applications of biomarker panels in precision medicine include diagnosis and risk stratification of patients for cardiac disease progression, monitoring response to heart failure therapies, and identification of microRNA targets for modulation.
Background/objectives:Coronary arterial disease (CAD) poses a significant public health challenge, with tobacco as the most predominant modifiable risk factor in young individuals. Despite a strong correlation between tobacco use and CAD, many smokers remain CAD-free. This fact raises questions about the complex interplay between environmental and genetic factors that contribute to CAD. Objective:Identify genetic polymorphisms that may be responsible for CAD in smokers without the main cardiovascular risk factors. Methods:A small retrospective case-control association study included current smokers aged 35-50 with low-density lipoprotein (LDL) levels <100 mg/dL who were non-diabetic and non-hypertensive. A total of 134 individuals (83% male; mean age of 48.9 ± 8.4 years) were selected from the GENEMACOR population: 97 CAD patients defined as having at least 70% stenosis in one major coronary artery, and 37 controls without CAD. Nine genetic variants from 8 genes previously associated with CAD but not with traditional risk factors (TRFs) were genotyped using TaqMan real-time PCR: CDKN2B-AS1, TCF21, PHACTR1, MIA3, ADAMTS7, ZC3HC1, SMAD3, and GJA4. Bivariate analyses compared genotypic proportions between CAD and non-CAD groups, reporting odds ratios (ORs) and confidence intervals (CIs). Multivariate logistic regression evaluates variables independently associated with CAD. The Hardy-Weinberg equilibrium was tested. Results:The intronic PHACTR1 polymorphism rs12526453 C > T was significantly more prevalent in cases, with the dominant model presenting 86.6% in CAD smokers and 70.3% in non-CAD smokers (OR = 2.73; p = 0.028). After logistic regression, which included significant variables in the bivariate analysis, PHACTR1 rs12526453 remained in the model (OR = 3.02; p = 0.038), along with dyslipidemia (OR = 3.58; p = 0.004), obesity (OR = 4.39; p = 0.031), and a family history of CAD (OR = 5.56; p = 0.031). Conclusions:Our findings show that the PHACTR1 T allele is associated with an increased risk of CAD in smokers with a family history, dyslipidemia and obesity, in the absence of other major cardiovascular risk factors. These results support the concept that genetic susceptibility may modulate the vascular response to chronic inflammatory and oxidative stress. Further prospective and functional studies are warranted to clarify the underlying biological mechanisms and the potential clinical value of integrating genetic profiling into personalised cardiovascular risk stratification.
Cardiac aging reflects a convergence of intrinsic molecular damage and maladaptive stress responses that progressively erode myocardial resilience. Accumulating genomic instability, telomere dysfunction, chromatin remodeling, and metabolic dysregulation activate innate immune signaling and cellular senescence across cardiomyocytes, endothelial cells, fibroblasts, and immune cells. At the tissue level, these processes manifest as microvascular rarefaction, fibrosis, hypertrophy, neurovascular uncoupling, and impaired adaptive capacity, creating a substrate that overlaps extensively with cardiomyopathy, heart failure, and atrial fibrillation (AF). Importantly, senescence in the heart is not monolithic. Emerging multi-omics and spatial analyses reveal context-dependent senescence programs, including transient, injury-associated states that support angiogenesis and repair, alongside chronic senescent phenotypes that propagate inflammation and remodeling through the senescence-associated secretory phenotype (SASP). These observations indicate that senescence is not uniformly deleterious but rather comprises functionally heterogeneous responses within the aging myocardium. Non-cell autonomous interactions-spanning cardiomyocyte-fibroblast crosstalk, immune niche signaling, endothelial cell-neuronal axis, and systemic organ-to-heart communication-further amplify or constrain these trajectories. Advances in biomarker discovery, imaging, and circulating epigenetic signatures now enable biological aging of the heart to be quantified beyond chronological aging, although many circulating biomarkers are not cardiac-specific and may also reflect systemic inflammation, fibrosis, frailty, or generalized biological aging. In parallel, preclinical studies demonstrate that senolytic, senomorphic, metabolic, and nutrient-sensing-targeted interventions can partially restore cardiac homeostasis. Together, these insights suggest that cellular senescence may represent a key mechanism and a potentially targetable process in cardiac aging, with important implications for the prevention and treatment of age-related cardiovascular disease.
Sildenafil has been shown to decrease ventricular arrhythmias. We investigated whether sildenafil could similarly decrease atrial fibrillation (AF) burden through direct effects on atrial electrophysiology. In vivo electrophysiological studies were performed in 12 anaesthetised sheep before and after 10 mg intravenous sildenafil. Sildenafil decreased AF vulnerability by decreasing both AF incidence and duration. The antiarrhythmic actions of sildenafil were associated with increases in atrial effective refractory period and atrial wavelength, together with a decrease in alternans magnitude which were expected to limit both AF duration and incidence respectively. The antiarrhythmic effects of acute sildenafil should be confirmed in man.
Lactylation is a lactate-driven post-translational modification that directly modifies lysine residues on both histone and non-histone proteins, thereby linking energy metabolism to epigenetic regulation. Its levels are dynamically orchestrated by intracellular lactate availability, as well as by specific lactyltransferases and delactylases, including p300, histone deacetylases (HDACs), and sirtuin family members. The functional significance of lactylation is increasingly recognized in cardiovascular disease, particularly in the context of cardiac repair. Lactylation has been implicated in multiple facets of cardiac repair, including macrophage polarization, endothelial-to-mesenchymal transition, fibroblast activation, and cardiomyocyte survival. Dysregulation of lactylation across various cardiac cell types following myocardial injury suggests that modulating specific components of this modification pathway may offer therapeutic opportunities to influence repair outcomes. This review synthesizes current knowledge on the cell-specific functions of lactylation in cardiac repair and its regulatory networks, with the goal of identifying potential diagnostic markers and therapeutic targets.
Ischemic heart disease remains the leading cause of morbidity and mortality worldwide. While current therapies prolong survival, they do not address underlying tissue damage. Messenger RNA (mRNA)-based therapies offer a promising alternative for repair and regeneration. However, targeted and effective delivery to the injured heart remains challenging. Lipid nanoparticles (LNPs) have emerged as a compelling platform for delivering therapeutics, including mRNA, yet their cellular tropism following ischemic injury is not well understood. To investigate this, we used Ai9 lineage tracing mice to map LNP uptake across cardiac cell populations during inflammatory, proliferative, and scarring phases post-ischemia-reperfusion injury (IRI). Upon Cre delivery, tdTomato expression is induced. mRNA-LNPs encoding Cre recombinase were injected intravenously 1 hour post-reperfusion, and uptake assessed at 3, 14, and 28 days by high-dimensional flow cytometry and 3D microscopy. Three days post-IRI, myeloid cells predominantly expressed tdTomato, showing they are primary recipients of mRNA-LNPs. By days 14 and 28, the proportion of tdTomato-expressing cells was equivalent between myeloid cells and fibroblasts. Microscopy further revealed mRNA-LNP uptake by cardiomyocytes, particularly within the infarct zone and apex of the heart. We also examined dosing time, with mRNA-LNPs administered 1 h or 3 days post-IRI. Delayed administration shifted uptake from immune cells towards fibroblasts, pericytes, and endothelial cells. This is the first study presenting a high-resolution, temporal map of cell type-specific mRNA-LNP uptake in the injured heart, providing new mechanistic insight beyond prior biodistribution reports and inform the design of cell-specific therapeutic strategies to enhance cardiac repair and regeneration.
In hypertrophic cardiomyopathy (HCM), hypertrophy often disproportionately affects the interventricular septum, especially in the obstructive form (oHCM). The reasons for this septal predilection remain debated. Here, we review emerging evidence that septal hypertrophy in HCM represents a localised, load-driven remodelling response, an adaptive “retrofitting” of the heart's wall to withstand abnormal stress. Congenital differences in septal fibre architecture and chronic sarcomeric hypercontractility create a focal mechanical burden that predisposes the septum to near-isometric contraction (low septal mobility) and drives early hypertrophic remodelling. When present, systolic anterior motion of the mitral valve and left ventricular (LV) outflow tract obstruction (LVOTO) further amplify this load, increase wall stress, and accelerate this process. Analogous to earthquake engineering, where rigid buildings are retrofitted with dampers to absorb shocks, the septum adapts by accumulating viscoelastic elements (e.g., microtubules, titin, collagen) that thicken and stiffen the wall. This structural adaptation protects against further damage by limiting myocardial shortening and reducing wall tension (according to Laplace's law), albeit at the cost of diastolic dysfunction and energetic inefficiency. We integrate haemodynamic studies and new patient-specific computational modelling data to confirm this load-centric model. When LVOTO develops, the added external load activates the afterload-dependent compensation (Anrep effect), characterised by increased LV end-systolic pressure, enhanced contractility, prolonged ejection, and elevated myocardial work. Septal reduction (surgery/ablation) relieves the external load imposed by LVOTO, whereas myosin inhibition (mavacamten) reduces the internal load from sarcomere-level hypercontractility and can secondarily lessen dynamic obstruction. Both approaches therefore reduce septal stress (although not equally), but myosin inhibition acts earlier in the disease sequence. Computational models further demonstrate that removing the septal load yields a more homogeneous stress distribution and improves mechano-energetic efficiency in the ventricle. Thus, septal hypertrophy in HCM is best understood as a targeted, load-driven remodelling analogous to structural retrofitting. Reducing sarcomere-level hypercontractility and, when present, the added load from LVOTO addresses the key mechanical drivers of disease, halting the maladaptive cycle and potentially allowing reverse remodelling. This unifying framework, now corroborated by computational modelling, positions ventricular unloading as a central therapeutic strategy in HCM.
Pathological remodeling in cardiomyocytes during heart failure is driven by excessive activation of mTORC1. Preclinical studies in mice demonstrated that reducing mTORC1 activity protects against cardiac dysfunction and hypertrophic remodeling. However, clinical application of current mTOR inhibitors is limited by incomplete mTORC1 inhibition and off-target effects, including suppression of mTORC2-mediated pro-survival signaling. To address these challenges, the therapeutic effects of the third-generation bi-steric mTORC1 inhibitor RMC-6272 was tested in pressure overload induced heart failure models. The potency and selectivity of RMC-6272 were evaluated in isolated cardiomyocytes. Hypertrophy was induced by phenylephrine in vitro and aortic banding in vivo. Cardiomyocyte-specific mRNA translation changes were assessed in αMHC-Cre Ribo-tag mice. RMC-6272 demonstrated superior potency and specificity for mTORC1 compared to rapamycin and Torin1. RMC-6272 prevented pathological hypertrophic growth in vitro and suppressed mTORC1-dependent mRNA translation, particularly those encoding components of the translational machinery. Preventive RMC-6272 treatment preserved cardiac function under pressure overload, maintaining contractile dysfunction in mice. Therapeutic treatment improved function in established hypertrophy, demonstrating therapeutic potential even after disease onset.
