Sequestosome 1 (p62) mitigates hypoxia-induced cardiac dysfunction by stabilizing hypoxia-inducible factor 1α and nuclear factor erythroid 2-related factor 2

AIMS

Heart failure due to ischaemic heart disease (IHD) is a leading cause of mortality worldwide. A major contributing factor to IHD-induced cardiac damage is hypoxia. Sequestosome 1 (p62) is a multi-functional adaptor protein with pleiotropic roles in autophagy, proteostasis, inflammation, and cancer. Despite abundant expression in cardiomyocytes, the role of p62 in cardiac physiology is not well understood. We hypothesized that cardiomyocyte-specific p62 deletion evokes hypoxia-induced cardiac pathology by impairing hypoxia-inducible factor 1α (Hif-1α) and nuclear factor erythroid 2-related factor 2 (Nrf2) signalling.

METHODS AND RESULTS

Adult mice with germline deletion of cardiomyocyte p62 exhibited mild cardiac dysfunction under normoxic conditions. Transcriptomic analyses revealed a selective impairment in Nrf2 target genes in the hearts from these mice. Demonstrating the functional importance of this adaptor protein, adult mice with inducible depletion of cardiomyocyte p62 displayed hypoxia-induced contractile dysfunction, oxidative stress, and cell death. Mechanistically, p62-depleted hearts exhibit impaired Hif-1α and Nrf2 transcriptional activity. Because findings from these two murine models suggested a cardioprotective role for p62, mechanisms were evaluated using H9c2 cardiomyoblasts. Loss of p62 in H9c2 cells exposed to hypoxia reduced Hif-1α and Nrf2 protein levels. Further, the lack of p62 decreased Nrf2 protein expression, nuclear translocation, and transcriptional activity. Repressed Nrf2 activity associated with heightened Nrf2-Keap1 co-localization in p62-deficient cells, which was concurrent with increased Nrf2 ubiquitination facilitated by the E3 ligase Cullin 3, followed by proteasomal-mediated degradation. Substantiating our results, a gain of p62 in H9c2 cells stabilized Nrf2 and increased the transcriptional activity of Nrf2 downstream targets.

CONCLUSION

Cardiac p62 mitigates hypoxia-induced cardiac dysfunction by stabilizing Hif-1α and Nrf2.

Antigen presentation plays positive roles in the regenerative response to cardiac injury in zebrafish

In contrast to adult mammals, adult zebrafish can fully regenerate injured cardiac tissue, and this regeneration process requires an adequate and tightly controlled immune response. However, which components of the immune response are required during regeneration is unclear. Here, we report positive roles for the antigen presentation-adaptive immunity axis during zebrafish cardiac regeneration. We find that following the initial innate immune response, activated endocardial cells (EdCs), as well as immune cells, start expressing antigen presentation genes. We also observe that T helper cells, a.k.a. Cd4+ T cells, lie in close physical proximity to these antigen-presenting EdCs. We targeted Major Histocompatibility Complex (MHC) class II antigen presentation by generating cd74a; cd74b mutants, which display a defective immune response. In these mutants, Cd4+ T cells and activated EdCs fail to efficiently populate the injured tissue and EdC proliferation is significantly decreased. cd74a; cd74b mutants exhibit additional defects in cardiac regeneration including reduced cardiomyocyte dedifferentiation and proliferation. Notably, Cd74 also becomes activated in neonatal mouse EdCs following cardiac injury. Altogether, these findings point to positive roles for antigen presentation during cardiac regeneration, potentially involving interactions between activated EdCs, classical antigen-presenting cells, and Cd4+ T cells.

Pretreatment with interleukin-15 attenuates inflammation and apoptosis by inhibiting NF-κB signaling in sepsis-induced myocardial dysfunction

Sepsis-induced myocardial dysfunction (SIMD) is associated with poor prognosis and increased mortality in patients with sepsis. Cytokines are important regulators of both the initiation and progression of sepsis. Interleukin-15 (IL-15), a pro-inflammatory cytokine, has been linked to protective effects against myocardial infarction and myocarditis. However, the role of IL-15 in SIMD remains unclear. We established a mouse model of SIMD via cecal ligation puncture (CLP) surgery and a cell model of myocardial injury via lipopolysaccharide (LPS) stimulation. IL-15 expression was prominently upregulated in septic hearts as well as cardiomyocytes challenged with LPS. IL-15 pretreatment attenuated cardiac inflammation and cell apoptosis and improved cardiac function in the CLP model. Similar cardioprotective effects of IL-15 pretreatment were observed in vitro. As expected, IL-15 knockdown had the opposite effect on LPS-stimulated cardiomyocytes. Mechanistically, we found that IL-15 pretreatment reduced the expression of the pro-apoptotic proteins cleaved caspase-3 and Bax and upregulated the anti-apoptotic protein Bcl-2. RNA sequencing and Western blotting further confirmed that IL-15 pretreatment suppressed the activation of nuclear factor kappa B (NF-κB) signaling in mice with sepsis. Besides, the addition of NF-κB inhibitor can significantly attenuate cardiomyocyte apoptosis compared to the control findings. Our results suggest that IL-15 pretreatment attenuated the cardiac inflammatory responses and reduced cardiomyocyte apoptosis by partially inhibiting NF-κB signaling in vivo and in vitro, thereby improving cardiac function in mice with sepsis. These findings highlight a promising therapeutic strategy for SIMD.

The potential roles of exosomes in pathological cardiomyocyte hypertrophy mechanisms and therapy: A review

Pathological cardiac hypertrophy, characterized by the enlargement of cardiac muscle cells, leads to serious cardiac conditions and stands as a major global health issue. Exosomes, comprising small lipid bilayer vesicles, are produced by various cell types and found in numerous bodily fluids. They play a pivotal role in intercellular communication by transferring bioactive cargos to recipient cells or activating signaling pathways in target cells. Exosomes from cardiomyocytes, endothelial cells, fibroblasts, and stem cells are key in regulating processes like cardiac hypertrophy, cardiomyocyte survival, apoptosis, fibrosis, and angiogenesis within the context of cardiovascular diseases. This review delves into exosomes' roles in pathological cardiac hypertrophy, first elucidating their impact on cell communication and signaling pathways. It then advances to discuss how exosomes affect key hypertrophic processes, including metabolism, fibrosis, oxidative stress, and angiogenesis. The review culminates by evaluating the potential of exosomes as biomarkers and their significance in targeted therapeutic strategies, thus emphasizing their critical role in the pathophysiology and management of cardiac hypertrophy.

CAV3 alleviates diabetic cardiomyopathy via inhibiting NDUFA10-mediated mitochondrial dysfunction

BACKGROUND

The progression of diabetic cardiomyopathy (DCM) is noticeably influenced by mitochondrial dysfunction. Variants of caveolin 3 (CAV3) play important roles in cardiovascular diseases. However, the potential roles of CAV3 in mitochondrial function in DCM and the related mechanisms have not yet been elucidated.

METHODS

Cardiomyocytes were cultured under high-glucose and high-fat (HGHF) conditions in vitro, and db/db mice were employed as a diabetes model in vivo. To investigate the role of CAV3 in DCM and to elucidate the molecular mechanisms underlying its involvement in mitochondrial function, we conducted Liquid chromatography tandem mass spectrometry (LC-MS/MS) analysis and functional experiments.

RESULTS

Our findings demonstrated significant downregulation of CAV3 in the cardiac tissue of db/db mice, which was found to be associated with cardiomyocyte apoptosis in DCM. Importantly, cardiac-specific overexpression of CAV3 effectively inhibited the progression of DCM, as it protected against cardiac dysfunction and cardiac remodeling associated by alleviating cardiomyocyte mitochondrial dysfunction. Furthermore, mass spectrometry analysis and immunoprecipitation assays indicated that CAV3 interacted with NDUFA10, a subunit of mitochondrial complex I. CAV3 overexpression reduced the degradation of lysosomal pathway in NDUFA10, restored the activity of mitochondrial complex I and improved mitochondrial function. Finally, our study demonstrated that CAV3 overexpression restored mitochondrial function and subsequently alleviated DCM partially through NDUFA10.

CONCLUSIONS

The current study provides evidence that CAV3 expression is significantly downregulated in DCM. Upregulation of CAV3 interacts with NDUFA10, inhibits the degradation of lysosomal pathway in NDUFA10, a subunit of mitochondrial complex I, restores the activity of mitochondrial complex I, ameliorates mitochondrial dysfunction, and thereby protects against DCM. These findings indicate that targeting CAV3 may be a promising approach for the treatment of DCM.

Single-cell insights: pioneering an integrated atlas of chromatin accessibility and transcriptomic landscapes in diabetic cardiomyopathy

BACKGROUND

Diabetic cardiomyopathy (DCM) poses a growing health threat, elevating heart failure risk in diabetic individuals. Understanding DCM is crucial, with fibroblasts and endothelial cells playing pivotal roles in driving myocardial fibrosis and contributing to cardiac dysfunction. Advances in Multimodal single-cell profiling, such as scRNA-seq and scATAC-seq, provide deeper insights into DCM's unique cell states and molecular landscape for targeted therapeutic interventions.

METHODS

Single-cell RNA and ATAC data from 10x Multiome libraries were processed using Cell Ranger ARC v2.0.1. Gene expression and ATAC data underwent Seurat and Signac filtration. Differential gene expression and accessible chromatin regions were identified. Transcription factor activity was estimated with chromVAR, and Cis-coaccessibility networks were calculated using Cicero. Coaccessibility connections were compared to the GeneHancer database. Gene Ontology analysis, biological process scoring, cell-cell communication analysis, and gene-motif correlation was performed to reveal intricate molecular changes. Immunofluorescent staining utilized various antibodies on paraffin-embedded tissues to verify the findings.

RESULTS

This study integrated scRNA-seq and scATAC-seq data obtained from hearts of WT and DCM mice, elucidating molecular changes at the single-cell level throughout the diabetic cardiomyopathy progression. Robust and accurate clustering analysis of the integrated data revealed altered cell proportions, showcasing decreased endothelial cells and macrophages, coupled with increased fibroblasts and myocardial cells in the DCM group, indicating enhanced fibrosis and endothelial damage. Chromatin accessibility analysis unveiled unique patterns in cell types, with heightened transcriptional activity in myocardial cells. Subpopulation analysis highlighted distinct changes in cardiomyocytes and fibroblasts, emphasizing pathways related to fatty acid metabolism and cardiac contraction. Fibroblast-centered communication analysis identified interactions with endothelial cells, implicating VEGF receptors. Endothelial cell subpopulations exhibited altered gene expressions, emphasizing contraction and growth-related pathways. Candidate regulators, including Tcf21, Arnt, Stat5a, and Stat5b, were identified, suggesting their pivotal roles in DCM development. Immunofluorescence staining validated marker genes of cell subpopulations, confirming PDK4, PPARγ and Tpm1 as markers for metabolic pattern-altered cardiomyocytes, activated fibroblasts and endothelial cells with compromised proliferation.

CONCLUSION

Our integrated scRNA-seq and scATAC-seq analysis unveils intricate cell states and molecular alterations in diabetic cardiomyopathy. Identified cell type-specific changes, transcription factors, and marker genes offer valuable insights. The study sheds light on potential therapeutic targets for DCM.

METTL14-mediated N6-methyladenosine modification induces the ferroptosis of hypoxia/reoxygenation-induced cardiomyocytes

BACKGROUND

Hypoxia/reoxygenation (H/R) induces cardiomyocyte ferroptosis, a core remodeling event in myocardial ischemia/reperfusion injury. Methyltransferase-like 14 (METTL14) emerges as a writer of N6-methyladenosine (m6A) modification. This study was conducted to decipher the role of METTL14 in H/R-induced cardiomyocyte ferroptosis.

METHODS

Mouse cardiomyocytes HL-1 were cultured and underwent H/R treatment. The degree of ferroptosis after H/R treatment was appraised by the cell counting kit-8 assay, assay kits (ROS/GSH/Fe2+), and Western blotting (GPX4/ACSL4). The intracellular expressions of METTL14, pri-miR-146a-5p, miR-146a-5p, or adaptor protein phosphotyrosine interacting with PH domain and leucine zipper 1 (APPL1) were examined by real-time quantitative polymerase chain reaction or Western blotting, with m6A quantification analysis and RNA immunoprecipitation to determine the total m6A level and the expression of pri-miR-146a-5p bound to DiGeorge critical region 8 (DGCR8) and m6A-modified pri-miR-146a-5p. The binding of miR-146a-5p to APPL1 was testified by the dual-luciferase assay.

RESULTS

H/R treatment induced cardiomyocyte ferroptosis (increased ROS, Fe2+, and ACSL4 and decreased GSH and GPX4) and upregulated METTL14 expression. METTL14 knockdown attenuated H/R-induced cardiomyocyte ferroptosis. METTL14 induced the recognition of pri-miR-146a-5p by DGCR8 by increasing m6A modification on pri-miR-146a-5p, which promoted the conversion of pri-miR-146a-5p into miR-146a-5p and further repressed APPL1 transcription. miR-146a-5p upregulation or APPL1 downregulation limited the inhibitory effect of METTL14 downregulation on H/R-induced cardiomyocyte ferroptosis.

CONCLUSION

METTL14 promoted miR-146a-5p expression through the recognition and processing of pri-miR-146a-5p by DGCR8, which repressed APPL1 transcription and triggered H/R-induced cardiomyocyte ferroptosis.

Loss of TRIM29 mitigates viral myocarditis by attenuating PERK-driven ER stress response in male mice

Viral myocarditis, an inflammatory disease of the myocardium, is a significant cause of sudden death in children and young adults. The current coronavirus disease 19 pandemic emphasizes the need to understand the pathogenesis mechanisms and potential treatment strategies for viral myocarditis. Here, we found that TRIM29 was highly induced by cardiotropic viruses and promoted protein kinase RNA-like endoplasmic reticulum kinase (PERK)-mediated endoplasmic reticulum (ER) stress, apoptosis, and reactive oxygen species (ROS) responses that promote viral replication in cardiomyocytes in vitro. TRIM29 deficiency protected mice from viral myocarditis by promoting cardiac antiviral functions and reducing PERK-mediated inflammation and immunosuppressive monocytic myeloid-derived suppressor cells (mMDSC) in vivo. Mechanistically, TRIM29 interacted with PERK to promote SUMOylation of PERK to maintain its stability, thereby promoting PERK-mediated signaling pathways. Finally, we demonstrated that the PERK inhibitor GSK2656157 mitigated viral myocarditis by disrupting the TRIM29-PERK connection, thereby bolstering cardiac function, enhancing cardiac antiviral responses, and curbing inflammation and immunosuppressive mMDSC in vivo. Our findings offer insight into how cardiotropic viruses exploit TRIM29-regulated PERK signaling pathways to instigate viral myocarditis, suggesting that targeting the TRIM29-PERK axis could mitigate disease severity.

Design, Synthesis, and In Vivo Evaluation of Isosteviol Derivatives as New SIRT3 Activators with Highly Potent Cardioprotective Effects

Cardiovascular diseases (CVDs) persist as the predominant cause of mortality, urging the exploration of innovative pharmaceuticals. Mitochondrial dysfunction stands as a pivotal contributor to CVDs development. Sirtuin 3 (SIRT3), a prominent mitochondrial deacetylase known for its crucial role in protecting mitochondria against damage and dysfunction, has emerged as a promising therapeutic target for CVDs treatment. Utilizing isosteviol, a natural ent-beyerene diterpenoid, 24 derivatives were synthesized and evaluated in vivo using a zebrafish model, establishing a deduced structure-activity relationship. Among these, derivative 5v exhibited significant efficacy in doxorubicin-induced cardiomyopathy in zebrafish and murine models. Subsequent investigations revealed that 5v selectively elevated SIRT3 expression, leading to the upregulation of SOD2 and OPA1 expression, effectively preventing mitochondrial dysfunction, mitigating oxidative stress, and preserving cardiomyocyte viability. As a novel structural class of SIRT3 activators with robust therapeutic effects, 5v emerges as a promising candidate for further drug development.

BIN1 knockdown rescues systolic dysfunction in aging male mouse hearts

Cardiac dysfunction is a hallmark of aging in humans and mice. Here we report that a two-week treatment to restore youthful Bridging Integrator 1 (BIN1) levels in the hearts of 24-month-old mice rejuvenates cardiac function and substantially reverses the aging phenotype. Our data indicate that age-associated overexpression of BIN1 occurs alongside dysregulated endosomal recycling and disrupted trafficking of cardiac CaV1.2 and type 2 ryanodine receptors. These deficiencies affect channel function at rest and their upregulation during acute stress. In vivo echocardiography reveals reduced systolic function in old mice. BIN1 knockdown using an adeno-associated virus serotype 9 packaged shRNA-mBIN1 restores the nanoscale distribution and clustering plasticity of ryanodine receptors and recovers Ca2+ transient amplitudes and cardiac systolic function toward youthful levels. Enhanced systolic function correlates with increased phosphorylation of the myofilament protein cardiac myosin binding protein-C. These results reveal BIN1 knockdown as a novel therapeutic strategy to rejuvenate the aging myocardium.

Telomerase is essential for cardiac differentiation and sustained metabolism of human cardiomyocytes

Telomeres as the protective ends of linear chromosomes, are synthesized by the enzyme telomerase (TERT). Critically short telomeres essentially contribute to aging-related diseases and are associated with a broad spectrum of disorders known as telomeropathies. In cardiomyocytes, telomere length is strongly correlated with cardiomyopathies but it remains ambiguous whether short telomeres are the cause or the result of the disease. In this study, we employed an inducible CRISPRi human induced pluripotent stem cell (hiPSC) line to silence TERT expression enabling the generation of hiPSCs and hiPSC-derived cardiomyocytes with long and short telomeres. Reduced telomerase activity and shorter telomere lengths of hiPSCs induced global transcriptomic changes associated with cardiac developmental pathways. Consequently, the differentiation potential towards cardiomyocytes was strongly impaired and single cell RNA sequencing revealed a shift towards a more smooth muscle cell like identity in the cells with the shortest telomeres. Poor cardiomyocyte function and increased sensitivity to stress directly correlated with the extent of telomere shortening. Collectively our data demonstrates a TERT dependent cardiomyogenic differentiation defect, highlighting the CRISPRi TERT hiPSCs model as a powerful platform to study the mechanisms and consequences of short telomeres in the heart and also in the context of telomeropathies.

14-3-3 binding motif phosphorylation disrupts Hdac4-organized condensates to stimulate cardiac reprogramming

Cell fate conversion is associated with extensive post-translational modifications (PTMs) and architectural changes of sub-organelles, yet how these events are interconnected remains unknown. We report here the identification of a phosphorylation code in 14-3-3 binding motifs (PC14-3-3) that greatly stimulates induced cardiomyocyte (iCM) formation from fibroblasts. PC14-3-3 is identified in pivotal functional proteins for iCM reprogramming, including transcription factors and chromatin modifiers. Akt1 kinase and protein phosphatase 2A are the key writer and key eraser of the PC14-3-3 code, respectively. PC14-3-3 activation induces iCM formation with the presence of only Tbx5. In contrast, PC14-3-3 inhibition by mutagenesis or inhibitor-mediated code removal abolishes reprogramming. We discover that key PC14-3-3-embedded factors, such as histone deacetylase 4 (Hdac4), Mef2c, and Foxo1, form Hdac4-organized inhibitory nuclear condensates. PC14-3-3 activation disrupts Hdac4 condensates to promote cardiac gene expression. Our study suggests that sub-organelle dynamics regulated by a PTM code could be a general mechanism for stimulating cell reprogramming.

Differentiating the human heart: A focus on atrioventricular canal cardiomyocytes

Bioengineering of a functional human heart continues to face many challenges, including the production of distinct cardiac cell types. Now, in Cell Stem Cell, Ye et al.1 develop AVC-like cardiomyocytes through timing- and concentration-specific activation of canonical Wnt signaling.

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

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

miR-29b-3p regulates cardiomyocytes pyroptosis in CVB3-induced myocarditis through targeting DNMT3A

BACKGROUND

Viral myocarditis (VMC) is a disease resulting from viral infection, which manifests as inflammation of myocardial cells. Until now, the treatment of VMC is still a great challenge for clinicians. Increasing studies indicate the participation of miR-29b-3p in various diseases. According to the transcriptome sequencing analysis, miR-29b-3p was markedly upregulated in the viral myocarditis model. The purpose of this study was to investigate the role of miR-29b-3p in the progression of VMC.

METHODS

We used CVB3 to induce primary cardiomyocytes and mice to establish a model of viral myocarditis. The purity of primary cardiomyocytes was identified by immunofluorescence. The cardiac function of mice was detected by Vevo770 imaging system. The area of inflammatory infiltration in heart tissue was shown by hematoxylin and eosin (H&E) staining. The expression of miR-29b-3p and DNMT3A was detected by quantitative real time polymerase chain reaction (qRT-PCR). The expression of a series of pyroptosis-related proteins was detected by western blot. The role of miR-29b-3p/DNMT3A in CVB3-induced pyroptosis of cardiomyocytes was studied in this research.

RESULTS

Our data showed that the expression of miR-29b-3p was upregulated in CVB3-induced cardiomyocytes and heart tissues in mice. To explore the function of miR-29b-3p in CVB3-induced VMC, we conducted in vivo experiments by knocking down the expression of miR-29b-3p using antagomir. We then assessed the effects on mice body weight, histopathology changes, myocardial function, and cell pyroptosis in heart tissues. Additionally, we performed gain/loss-of-function experiments in vitro to measure the levels of pyroptosis in primary cardiomyocytes. Through bioinformatic analysis, we identified DNA methyltransferases 3A (DNMT3A) as a potential target gene of miR-29b-3p. Furthermore, we found that the expression of DNMT3A can be modulated by miR-29b-3p during CVB3 infection.

CONCLUSIONS

Our results demonstrate a correlation between the expression of DNMT3A and CVB3-induced pyroptosis in cardiomyocytes. These findings unveil a previously unidentified mechanism by which CVB3 induces cardiac injury through the regulation of miR-29b-3p/DNMT3A-mediated pyroptosis.

The redox-active defensive Selenoprotein T as a novel stress sensor protein playing a key role in the pathophysiology of heart failure

Maladaptive cardiac hypertrophy contributes to the development of heart failure (HF). The oxidoreductase Selenoprotein T (SELENOT) emerged as a key regulator during rat cardiogenesis and acute cardiac protection. However, its action in chronic settings of cardiac dysfunction is not understood. Here, we investigated the role of SELENOT in the pathophysiology of HF: (i) by designing a small peptide (PSELT), recapitulating SELENOT activity via the redox site, and assessed its beneficial action in a preclinical model of HF [aged spontaneously hypertensive heart failure (SHHF) rats] and against isoproterenol (ISO)-induced hypertrophy in rat ventricular H9c2 and adult human AC16 cardiomyocytes; (ii) by evaluating the SELENOT intra-cardiomyocyte production and secretion under hypertrophied stimulation. Results showed that PSELT attenuated systemic inflammation, lipopolysaccharide (LPS)-induced macrophage M1 polarization, myocardial injury, and the severe ultrastructural alterations, while counteracting key mediators of cardiac fibrosis, aging, and DNA damage and restoring desmin downregulation and SELENOT upregulation in the failing hearts. In the hemodynamic assessment, PSELT improved the contractile impairment at baseline and following ischemia/reperfusion injury, and reduced infarct size in normal and failing hearts. At cellular level, PSELT counteracted ISO-mediated hypertrophy and ultrastructural alterations through its redox motif, while mitigating ISO-triggered SELENOT intracellular production and secretion, a phenomenon that presumably reflects the extent of cell damage. Altogether, these results indicate that SELENOT could represent a novel sensor of hypertrophied cardiomyocytes and a potential PSELT-based new therapeutic approach in myocardial hypertrophy and HF.

Exosomal miR-9-5p derived from iPSC-MSCs ameliorates doxorubicin-induced cardiomyopathy by inhibiting cardiomyocyte senescence

Doxorubicin (DOX) is a chemotherapeutic agent widely used for tumor treatment. Nonetheless its clinical application is heavily limited by its cardiotoxicity. There is accumulated evidence that transplantation of mesenchymal stem cell-derived exosomes (MSC-EXOs) can protect against Dox-induced cardiomyopathy (DIC). This study aimed to examine the cardioprotective effects of EXOs isolated from human induced pluripotent stem cell-derived MSCs (iPSC-MSCs) against DIC and explore the potential mechanisms. EXOs were isolated from the cultural supernatant of human BM-MSCs (BM-MSC-EXOs) and iPSC-MSCs (iPSC-MSC-EXOs) by ultracentrifugation. A mouse model of DIC was induced by intraperitoneal injection of Dox followed by tail vein injection of PBS, BM-MSC-EXOs, or iPSC-MSC-EXOs. Cardiac function, cardiomyocyte senescence and mitochondrial dynamics in each group were assessed. In vitro, neonatal mouse cardiomyocytes (NMCMs) were subjected to Dox and treated with BM-MSC-EXOs or iPSC-MSC-EXOs. The mitochondrial morphology and cellular senescence of NMCMs were examined by Mitotracker staining and senescence-associated-β-galactosidase assay, respectively. Compared with BM-MSC-EXOs, mice treated with iPSC-MSC-EXOs displayed improved cardiac function and decreased cardiomyocyte mitochondrial fragmentation and senescence. In vitro, iPSC-MSC-EXOs were superior to BM-MSC-EXOs in attenuation of cardiomyocyte mitochondrial fragmentation and senescence caused by DOX. MicroRNA sequencing revealed a higher level of miR-9-5p in iPSC-MSC-EXOs than BM-MSC-EXOs. Mechanistically, iPSC-MSC-EXOs transported miR-9-5p into DOX-treated cardiomyocytes, thereby suppressing cardiomyocyte mitochondrial fragmentation and senescence via regulation of the VPO1/ERK signal pathway. These protective effects and cardioprotection against DIC were largely reversed by knockdown of miR-9-5p in iPSC-MSC-EXOs. Our results showed that miR-9-5p transferred by iPSC-MSC-EXOs protected against DIC by alleviating cardiomyocyte senescence via inhibition of the VPO1/ERK pathway. This study offers new insight into the application of iPSC-MSC-EXOs as a novel therapeutic strategy for DIC treatment.

Xinnaotongluo liquid protects H9c2 cells from H/R-induced damage by regulating MDM2/STEAP3

Xinnaotongluo liquid has been used to improve the clinical symptoms of patients with myocardial infarction. However, the molecular mechanism of Xinnaotongluo liquid is not completely understood. H9c2 cells exposed to hypoxia/reoxygenation (H/R) was used to simulate damage to cardiomyocytes in myocardial infarction in vitro. The biological indicators of H9c2 cells were measured by cell counting kit-8, enzyme linked immunoabsorbent assay, and western blot assay. In H/R-induced H9c2 cells, a markedly reduced murine double minute 2 (MDM2) was observed. However, the addition of Xinnaotongluo liquid increased MDM2 expression in H/R-induced H9c2 cells. And MDM2 overexpression strengthened the beneficial effects of Xinnaotongluo liquid on H9c2 cells from the perspective of alleviating oxidative damage, cellular inflammation, apoptosis and ferroptosis of H/R-induced H9c2 cells. Moreover, MDM2 overexpression reduced the protein expression of p53 and Six-Transmembrane Epithelial Antigen of Prostate 3 (STEAP3). Whereas, STEAP3 overexpression hindered the function of MDM2-overexpression in H/R-induced H9c2 cells. Our results insinuated that Xinnaotongluo liquid could protect H9c2 cells from H/R-induced damage by regulating MDM2/STEAP3, which provide a potential theoretical basis for further explaining the working mechanism of Xinnaotongluo liquid.

[Developmental toxicity of Cry1Ab protein in the embryonic stem-cell model]

OBJECTIVE

To evaluate the developmental toxicity of Cry1Ab protein by studying its effects on cell proliferation and differentiation ability using a developmental toxicity assessment model based on embryonic stem-cell.

METHODS

Cry1Ab protein was tested in seven dose groups (31.25, 62.50, 125.00, 250.00, 320.00, 1 000.00, and 2 000.00 μg/L) on mouse embryonic stem cells D3 (ES-D3) and 3T3 mouse fibroblast cells, with 5-fluorouracil (5-FU) used as the positive control and phosphate buffer saline (PBS) as the solvent control. Cell viability was detected by CCK-8 assay to calculate the 50% inhibitory concentration (IC50) of the test substance for different cells. Additionally, Cry1Ab protein was tested in five dose groups (125.00, 250.00, 320.00, 1 000.00, and 2 000.00 μg/L) on ES-D3 cells, with PBS as the solvent control and 5-FU used for model validation. After cell treatment, cardiac differentiation was induced using the embryonic bodies (EBs) culture method. The growth of EBs was observed under a microscope, and their diameters on the third and fifth days were measured. The proportion of EBs differentiating into beating cardiomyocytes was recorded, and the 50% inhibition concentration of differentiation (ID50) was calculated. Based on a developmental toxicity discrimination function, the developmental toxicity of the test substances was classified. Furthermore, at the end of the culture period, mRNA expression levels of cardiac differentiation-related markers (Oct3/4, GATA-4, Nkx2.5, and β-MHC) were quantitatively detected using real-time quantitative polymerase chain reaction (qPCR) in the collected EBs samples.

RESULTS

The IC50 of 5-FU was determined as 46.37 μg/L in 3T3 cells and 32.67 μg/L in ES-D3 cells, while the ID50 in ES-D3 cells was 21.28 μg/L. According to the discrimination function results, 5-FU was classified as a strong embryotoxic substance. There were no statistically significant differences in cell viability between different concentrations of Cry1Ab protein treatment groups and the control group in both 3T3 cells and ES-D3 cells (P>0.05). Moreover, there were no statistically significant differences in the diameter of EBs on the third and fifth days, as well as their morphology, between the Cry1Ab protein treatment groups and the control group (P>0.05). The cardiac differentiation rate showed no statistically significant differences between different concentrations of Cry1Ab protein treatment groups and the control group (P>0.05). 5-FU significantly reduced the mRNA expression levels of β-MHC, Nkx2.5, and GATA-4 (P < 0.05), showing a dose-dependent trend (P < 0.05), while the mRNA expression levels of the pluripotency-associated marker Oct3/4 exhibited an increasing trend (P < 0.05). However, there were no statistically significant differences in the mRNA expression levels of mature cardiac marker β-MHC, early cardiac differentiation marker Nkx2.5 and GATA-4, and pluripotency-associated marker Oct3/4 between the Cry1Ab protein treatment groups and the control group (P>0.05).

CONCLUSION

No developmental toxicity of Cry1Ab protein at concentrations ranging from 31.25 to 2 000.00 μg/L was observed in this experimental model.

HOIL-1L deficiency induces cell cycle alteration which causes immaturity of skeletal muscle and cardiomyocytes

HOIL-1L deficiency was recently reported to be one of the causes of myopathy and dilated cardiomyopathy (DCM). However, the mechanisms by which myopathy and DCM develop have not been clearly elucidated. Here, we sought to elucidate these mechanisms using the murine myoblast cell line C2C12 and disease-specific human induced pluripotent stem cells (hiPSCs). Myotubes differentiated from HOIL-1L-KO C2C12 cells exhibited deteriorated differentiation and mitotic cell accumulation. CMs differentiated from patient-derived hiPSCs had an abnormal morphology with a larger size and were excessively multinucleated compared with CMs differentiated from control hiPSCs. Further analysis of hiPSC-derived CMs showed that HOIL-1L deficiency caused cell cycle alteration and mitotic cell accumulation. These results demonstrate that abnormal cell maturation possibly contribute to the development of myopathy and DCM. In conclusion, HOIL-1L is an important intrinsic regulator of cell cycle-related myotube and CM maturation and cell proliferation.

CRISPR Activation Reverses Haploinsufficiency and Functional Deficits Caused by TTN Truncation Variants

BACKGROUND

TTN truncation variants (TTNtvs) are the most common genetic lesion identified in individuals with dilated cardiomyopathy, a disease with high morbidity and mortality rates. TTNtvs reduce normal TTN (titin) protein levels, produce truncated proteins, and impair sarcomere content and function. Therapeutics targeting TTNtvs have been elusive because of the immense size of TTN, the rarity of specific TTNtvs, and incomplete knowledge of TTNtv pathogenicity.

METHODS

We adapted CRISPR activation using dCas9-VPR to functionally interrogate TTNtv pathogenicity and develop a therapeutic in human cardiomyocytes and 3-dimensional cardiac microtissues engineered from induced pluripotent stem cell models harboring a dilated cardiomyopathy-associated TTNtv. We performed guide RNA screening with custom TTN reporter assays, agarose gel electrophoresis to quantify TTN protein levels and isoforms, and RNA sequencing to identify molecular consequences of TTN activation. Cardiomyocyte epigenetic assays were also used to nominate DNA regulatory elements to enable cardiomyocyte-specific TTN activation.

RESULTS

CRISPR activation of TTN using single guide RNAs targeting either the TTN promoter or regulatory elements in spatial proximity to the TTN promoter through 3-dimensional chromatin interactions rescued TTN protein deficits disturbed by TTNtvs. Increasing TTN protein levels normalized sarcomere content and contractile function despite increasing truncated TTN protein. In addition to TTN transcripts, CRISPR activation also increased levels of myofibril assembly-related and sarcomere-related transcripts.

CONCLUSIONS

TTN CRISPR activation rescued TTNtv-related functional deficits despite increasing truncated TTN levels, which provides evidence to support haploinsufficiency as a relevant genetic mechanism underlying heterozygous TTNtvs. CRISPR activation could be developed as a therapeutic to treat a large proportion of TTNtvs.

SIRT3 regulates cardiolipin biosynthesis in pressure overload-induced cardiac remodeling by PPARγ-mediated mechanism

Cardiac remodeling is the primary pathological feature of chronic heart failure (HF). Exploring the characteristics of cardiac remodeling in the very early stages of HF and identifying targets for intervention are essential for discovering novel mechanisms and therapeutic strategies. Silent mating type information regulation 2 homolog 3 (SIRT3), as a major mitochondrial nicotinamide adenine dinucleotide (NAD)-dependent deacetylase, is required for mitochondrial metabolism. However, whether SIRT3 plays a role in cardiac remodeling by regulating the biosynthesis of mitochondrial cardiolipin (CL) is unknown. In this study, we induced pressure overload in wild-type (WT) and SIRT3 knockout (SIRT3-/-) mice via transverse aortic constriction (TAC). Compared with WT mouse hearts, the hearts of SIRT3-/- mice exhibited more-pronounced cardiac remodeling and fibrosis, greater reactive oxygen species (ROS) production, decreased mitochondrial-membrane potential (ΔΨm), and abnormal mitochondrial morphology after TAC. Furthermore, SIRT3 deletion aggravated TAC-induced decrease in total CL content, which might be associated with the downregulation of the CL synthesis related enzymes cardiolipin synthase 1 (CRLS1) and phospholipid-lysophospholipid transacylase (TAFAZZIN). In our in vitro experiments, SIRT3 overexpression prevented angiotensin II (AngII)- induced aberrant mitochondrial function, CL biosynthesis disorder, and peroxisome proliferator-activated receptor gamma (PPARγ) downregulation in cardiomyocytes; meanwhile, SIRT3 knockdown exacerbated these effects. Moreover, the addition of GW9662, a PPARγ antagonist, partially counteracted the beneficial effects of SIRT3 overexpression. In conclusion, SIRT3 regulated PPARγ-mediated CL biosynthesis, maintained the structure and function of mitochondria, and thereby protected the myocardium against cardiac remodeling.

Naringenin protects against septic cardiomyopathy in mice by targeting HIF-1α

Myocardial dysfunction is a prevalent complication of sepsis (septic cardiomyopathy) with a high mortality rate and limited therapeutic options. Naringenin, a natural flavonoid compound with anti-inflammatory and antioxidant properties, holds promise as a potential treatment for sepsis-induced myocardial dysfunction. This study investigated the pharmacological effects of naringenin on septic cardiomyopathy. In vivo and in vitro experiments demonstrated that naringenin improved cardiomyocyte damage. Network pharmacology and database analysis revealed that HIF-1α is a key target protein of naringenin. Elevated expression of HIF-1α was observed in damaged cardiomyocytes, and the HIF-1α inhibitor effectively protected against LPS-induced cardiomyocyte damage. Molecular docking studies confirmed the direct binding between naringenin and HIF-1α protein. Importantly, our findings demonstrated that naringenin did not provide additional attenuation of cardiomyocyte injury on the biases of HIF-1α inhibitor treatment. In conclusion, this study proves that naringenin protects against septic cardiomyopathy through HIF-1α signaling. Naringenin is a promising therapeutic candidate for treating septic cardiomyopathy.

Long-Term Clinical-Pathologic Results of Enzyme Replacement Therapy in Prehypertrophic Fabry Disease Cardiomyopathy

BACKGROUND

The limited ability of enzyme replacement therapy (ERT) in removing globotriaosylceramide from cardiomyocytes is recognized for advanced Fabry disease cardiomyopathy (FDCM). Prehypertrophic FDCM is believed to be cured or stabilized by ERT. However, no pathologic confirmation is available. We report here on the long-term clinical-pathologic impact of ERT on prehypertrophic FDCM.

METHODS AND RESULTS

Fifteen patients with Fabry disease with left ventricular maximal wall thickness ≤10.5 mm at cardiac magnetic resonance required endomyocardial biopsy because of angina and ventricular arrhythmias. Endomyocardial biopsy showed coronary small-vessel disease in the angina cohort, and vacuoles in smooth muscle cells and cardiomyocytes ≈20% of the cell surface containing myelin bodies at electron microscopy. Patients received α-agalsidase in 8 cases, and β-agalsidase in 7 cases. Both groups experienced symptom improvement except 1 patients treated with α-agalsidase and 1 treated with β-agalsidase. After ERT administration ranging from 4 to 20 years, all patients had control cardiac magnetic resonance and left ventricular endomyocardial biopsy because of persistence of symptoms or patient inquiry on disease resolution. In 13 asymptomatic patients with FDCM, left ventricular maximal wall thickness and left ventricular mass, cardiomyocyte diameter, vacuole surface/cell surface ratio, and vessels remained unchanged or minimally increased (left ventricular mass increased by <2%) even after 20 years of observation, and storage material was still present at electron microscopy. In 2 symptomatic patients, FDCM progressed, with larger and more engulfed by globotriaosylceramide myocytes being associated with myocardial virus-negative lymphocytic inflammation.

CONCLUSIONS

ERT stabilizes storage deposits and myocyte dimensions in 87% of patients with prehypertrophic FDCM. Globotriaosylceramide is never completely removed even after long-term treatment. Immune-mediated myocardial inflammation can overlap, limiting ERT activity.

Protective effect and pharmacokinetics of dihydromyricetin nanoparticles on oxidative damage of myocardium

PURPOSE

This study aims to investigate the protective mechanism of dihydromyricetin PLGA nanoparticles (DMY-PLGA NPs) against myocardial ischemia-reperfusion injury (MIRI) in vitro and the improvement of oral bioavailability in vivo.

METHODS

DMY-PLGA NPs was prepared and characterized by emulsifying solvent volatilization, and the oxidative stress model of rat H9c2 cardiomyocyte induced by H2O2 was established. After administration, cell survival rate, lactate dehydrogenase (LDH), malondialdehyde (MDA) and superoxide dismutase (SOD) were detected, and the expressions of PGC1α and PPARα were detected by western blot (WB). At the same time, the pharmacokinetics in rats were studied to explore the improvement of bioavailability.

RESULTS

DMY-PLGA NPs can significantly increase cell survival rate, decrease LDH and MDA content, increase SOD content and PGC1α、PPARα protein expression. Compared with DMY, the peak time of DMY-PLGA NPs was extended (P<0.1), and the bioavailability was increased by 2.04 times.

CONCLUSION

DMY-PLGA NPs has a significant protective effect on H9c2 cardiomyocytes, which promotes the absorption of DMY and effectively improves bioavailability.

Elevated levels of alcohol dehydrogenase aggravate ethanol-evoked cardiac remodeling and contractile anomalies through FKBP5-yap-mediated regulation of ferroptosis and ER stress

Alcohol intake provokes severe organ injuries including alcoholic cardiomyopathy with hallmarks of cardiac remodeling and contractile defects. This study examined the toxicity of facilitated ethanol metabolism in alcoholism-evoked changes in myocardial morphology and contractile function, insulin signaling and various cell death domains using cardiac-selective overexpression of alcohol dehydrogenase (ADH). WT and ADH mice were offered an alcohol liquid diet for 12 weeks prior to assessment of cardiac geometry, function, ER stress, apoptosis and ferroptosis. Alcohol intake provoked pronounced glucose intolerance, cardiac remodeling and contractile anomalies with apoptosis, ER stress, and ferroptosis, the effects were accentuated by ADH with the exception of global glucose intolerance. Hearts from alcohol ingesting mice displayed dampened insulin-stimulated phosphorylation of insulin receptor (tyr1146) and IRS-1 (tyrosine) along with elevated IRS-1 serine phosphorylation, the effect was augmented by ADH. Alcohol challenge dampened phosphorylation of Akt and GSK-3β, and increased phosphorylation of c-Jun and JNK, the effects were accentuated by ADH. Alcohol challenge promoted ER stress, FK506 binding protein 5 (FKBP5), YAP, apoptosis and ferroptosis, the effects were exaggerated by ADH. Using a short-term ethanol challenge model (3 g/kg, i.p., twice in three days), we found that inhibition of FKBP5-YAP signaling or facilitated ethanol detoxification by Alda-1 alleviated ethanol cardiotoxicity. In vitro study revealed that the ethanol metabolite acetaldehyde evoked cardiac contractile anomalies, lipid peroxidation, and apoptosis, the effects of which were mitigated by Alda-1, inhibition of ER stress, FKBP5 and YAP. These data suggest that facilitated ethanol metabolism via ADH exacerbates alcohol-evoked myocardial remodeling, functional defects, and insulin insensitivity possibly through a FKBP5-YAP-associated regulation of ER stress and ferroptosis.

CHD4 and SMYD1 repress common transcriptional programs in the developing heart

Regulation of chromatin states is essential for proper temporal and spatial gene expression. Chromatin states are modulated by remodeling complexes composed of components that have enzymatic activities. CHD4 is the catalytic core of the nucleosome remodeling and deacetylase (NuRD) complex, which represses gene transcription. However, it remains to be determined how CHD4, a ubiquitous enzyme that remodels chromatin structure, functions in cardiomyocytes to maintain heart development. In particular, whether other proteins besides the NuRD components interact with CHD4 in the heart is controversial. Using quantitative proteomics, we identified that CHD4 interacts with SMYD1, a striated muscle-restricted histone methyltransferase that is essential for cardiomyocyte differentiation and cardiac morphogenesis. Comprehensive transcriptomic and chromatin accessibility studies of Smyd1 and Chd4 null embryonic mouse hearts revealed that SMYD1 and CHD4 repress a group of common genes and pathways involved in glycolysis, response to hypoxia, and angiogenesis. Our study reveals a mechanism by which CHD4 functions during heart development, and a previously uncharacterized mechanism regarding how SMYD1 represses cardiac transcription in the developing heart.

Distinct features of the regenerating heart uncovered through comparative single-cell profiling

Adult humans respond to heart injury by forming a permanent scar, yet other vertebrates are capable of robust and complete cardiac regeneration. Despite progress towards characterizing the mechanisms of cardiac regeneration in fish and amphibians, the large evolutionary gulf between mammals and regenerating vertebrates complicates deciphering which cellular and molecular features truly enable regeneration. To better define these features, we compared cardiac injury responses in zebrafish and medaka, two fish species that share similar heart anatomy and common teleost ancestry but differ in regenerative capability. We used single-cell transcriptional profiling to create a time-resolved comparative cell atlas of injury responses in all major cardiac cell types across both species. With this approach, we identified several key features that distinguish cardiac injury response in the non-regenerating medaka heart. By comparing immune responses to injury, we found altered cell recruitment and a distinct pro-inflammatory gene program in medaka leukocytes, and an absence of the injury-induced interferon response seen in zebrafish. In addition, we found a lack of pro-regenerative signals, including nrg1 and retinoic acid, from medaka endothelial and epicardial cells. Finally, we identified alterations in the myocardial structure in medaka, where they lack primordial layer cardiomyocytes and fail to employ a cardioprotective gene program shared by regenerating vertebrates. Our findings reveal notable variation in injury response across nearly all major cardiac cell types in zebrafish and medaka, demonstrating how evolutionary divergence influences the hidden cellular features underpinning regenerative potential in these seemingly similar vertebrates.

Extracellular Kir2.1C122Y Mutant Upsets Kir2.1-PIP2 Bonds and Is Arrhythmogenic in Andersen-Tawil Syndrome

BACKGROUND

Andersen-Tawil syndrome type 1 is a rare heritable disease caused by mutations in the gene coding the strong inwardly rectifying K+ channel Kir2.1. The extracellular Cys (cysteine)122-to-Cys154 disulfide bond in the channel structure is crucial for proper folding but has not been associated with correct channel function at the membrane. We evaluated whether a human mutation at the Cys122-to-Cys154 disulfide bridge leads to Kir2.1 channel dysfunction and arrhythmias by reorganizing the overall Kir2.1 channel structure and destabilizing its open state.

METHODS

We identified a Kir2.1 loss-of-function mutation (c.366 A>T; p.Cys122Tyr) in an ATS1 family. To investigate its pathophysiological implications, we generated an AAV9-mediated cardiac-specific mouse model expressing the Kir2.1C122Y variant. We employed a multidisciplinary approach, integrating patch clamping and intracardiac stimulation, molecular biology techniques, molecular dynamics, and bioluminescence resonance energy transfer experiments.

RESULTS

Kir2.1C122Y mice recapitulated the ECG features of ATS1 independently of sex, including corrected QT prolongation, conduction defects, and increased arrhythmia susceptibility. Isolated Kir2.1C122Y cardiomyocytes showed significantly reduced inwardly rectifier K+ (IK1) and inward Na+ (INa) current densities independently of normal trafficking. Molecular dynamics predicted that the C122Y mutation provoked a conformational change over the 2000-ns simulation, characterized by a greater loss of hydrogen bonds between Kir2.1 and phosphatidylinositol 4,5-bisphosphate than wild type (WT). Therefore, the phosphatidylinositol 4,5-bisphosphate-binding pocket was destabilized, resulting in a lower conductance state compared with WT. Accordingly, on inside-out patch clamping, the C122Y mutation significantly blunted Kir2.1 sensitivity to increasing phosphatidylinositol 4,5-bisphosphate concentrations. In addition, the Kir2.1C122Y mutation resulted in channelosome degradation, demonstrating temporal instability of both Kir2.1 and NaV1.5 proteins.

CONCLUSIONS

The extracellular Cys122-to-Cys154 disulfide bond in the tridimensional Kir2.1 channel structure is essential for the channel function. We demonstrate that breaking disulfide bonds in the extracellular domain disrupts phosphatidylinositol 4,5-bisphosphate-dependent regulation, leading to channel dysfunction and defects in Kir2.1 energetic stability. The mutation also alters functional expression of the NaV1.5 channel and ultimately leads to conduction disturbances and life-threatening arrhythmia characteristic of Andersen-Tawil syndrome type 1.

AKAP12 Upregulation Associates With PDE8A to Accelerate Cardiac Dysfunction

BACKGROUND

In heart failure, signaling downstream the β2-adrenergic receptor is critical. Sympathetic stimulation of β2-adrenergic receptor alters cAMP (cyclic adenosine 3',5'-monophosphate) and triggers PKA (protein kinase A)-dependent phosphorylation of proteins that regulate cardiac function. cAMP levels are regulated in part by PDEs (phosphodiesterases). Several AKAPs (A kinase anchoring proteins) regulate cardiac function and are proposed as targets for precise pharmacology. AKAP12 is expressed in the heart and has been reported to directly bind β2-adrenergic receptor, PKA, and PDE4D. However, its roles in cardiac function are unclear.

METHODS

cAMP accumulation in real time downstream of the β2-adrenergic receptor was detected for 60 minutes in live cells using the luciferase-based biosensor (GloSensor) in AC16 human-derived cardiomyocyte cell lines overexpressing AKAP12 versus controls. Cardiomyocyte intracellular calcium and contractility were studied in adult primary cardiomyocytes from male and female mice overexpressing cardiac AKAP12 (AKAP12OX) and wild-type littermates post acute treatment with 100-nM isoproterenol (ISO). Systolic cardiac function was assessed in mice after 14 days of subcutaneous ISO administration (60 mg/kg per day). AKAP12 gene and protein expression levels were evaluated in left ventricular samples from patients with end-stage heart failure.

RESULTS

AKAP12 upregulation significantly reduced total intracellular cAMP levels in AC16 cells through PDE8. Adult primary cardiomyocytes from AKAP12OX mice had significantly reduced contractility and impaired calcium handling in response to ISO, which was reversed in the presence of the selective PDE8 inhibitor (PF-04957325). AKAP12OX mice had deteriorated systolic cardiac function and enlarged left ventricles. Patients with end-stage heart failure had upregulated gene and protein levels of AKAP12.

CONCLUSIONS

AKAP12 upregulation in cardiac tissue is associated with accelerated cardiac dysfunction through the AKAP12-PDE8 axis.

Chronological-Programmed Black Phosphorus Hydrogel for Responsive Modulation of the Pathological Microenvironment in Myocardial Infarction

Electroactive hydrogels have garnered extensive interest as a promising approach to myocardial tissue engineering. However, the challenges of spatiotemporal-specific modulation of individual pathological processes and achieving nontoxic bioresorption still remain. Herein, inspired by the entire postinfarct pathological processes, an injectable conductive bioresorbable black phosphorus nanosheets (BPNSs)-loaded hydrogel (BHGD) was developed via reactive oxide species (ROS)-sensitive disulfide-bridge and photomediated cross-linking reaction. Significantly, the chronologically programmed BHGD hydrogel can achieve graded modulation during the inflammatory, proliferative, and maturation phases of myocardial infarction (MI). More details, during early infarction, the BHGD hydrogel can effectively reduce ROS levels in the MI area, inhibit cellular oxidative stress damage, and promote macrophage M2 polarization, creating a favorable environment for damaged myocardium repair. Meanwhile, the ROS-responsive structure can protect BPNSs from degradation and maintain good conductivity under MI microenvironments. Therefore, the BHGD hydrogel possesses tissue-matched modulus and conductivity in the MI area, facilitating cardiomyocyte maturation and electrical signal exchange, compensating for impaired electrical signaling, and promoting vascularization in infarcted areas in the maturation phase. More importantly, all components of the hydrogel degrade into nontoxic substances without adverse effects on vital organs. Overall, the presented BPNS-loaded hydrogel offers an expandable and safe option for clinical treatment of MI.

Polyploidy Promotes Hypertranscription, Apoptosis Resistance, and Ciliogenesis in Cancer Cells and Mesenchymal Stem Cells of Various Origins: Comparative Transcriptome In Silico Study

Mesenchymal stem cells (MSC) attract an increasing amount of attention due to their unique therapeutic properties. Yet, MSC can undergo undesirable genetic and epigenetic changes during their propagation in vitro. In this study, we investigated whether polyploidy can compromise MSC oncological safety and therapeutic properties. For this purpose, we compared the impact of polyploidy on the transcriptome of cancer cells and MSC of various origins (bone marrow, placenta, and heart). First, we identified genes that are consistently ploidy-induced or ploidy-repressed through all comparisons. Then, we selected the master regulators using the protein interaction enrichment analysis (PIEA). The obtained ploidy-related gene signatures were verified using the data gained from polyploid and diploid populations of early cardiomyocytes (CARD) originating from iPSC. The multistep bioinformatic analysis applied to the cancer cells, MSC, and CARD indicated that polyploidy plays a pivotal role in driving the cell into hypertranscription. It was evident from the upregulation of gene modules implicated in housekeeping functions, stemness, unicellularity, DNA repair, and chromatin opening by means of histone acetylation operating via DNA damage associated with the NUA4/TIP60 complex. These features were complemented by the activation of the pathways implicated in centrosome maintenance and ciliogenesis and by the impairment of the pathways related to apoptosis, the circadian clock, and immunity. Overall, our findings suggest that, although polyploidy does not induce oncologic transformation of MSC, it might compromise their therapeutic properties because of global epigenetic changes and alterations in fundamental biological processes. The obtained results can contribute to the development and implementation of approaches enhancing the therapeutic properties of MSC by removing polyploid cells from the cell population.

Focal Adhesion's Role in Cardiomyocytes Function: From Cardiomyogenesis to Mechanotransduction

Mechanotransduction refers to the ability of cells to sense mechanical stimuli and convert them into biochemical signals. In this context, the key players are focal adhesions (FAs): multiprotein complexes that link intracellular actin bundles and the extracellular matrix (ECM). FAs are involved in cellular adhesion, growth, differentiation, gene expression, migration, communication, force transmission, and contractility. Focal adhesion signaling molecules, including Focal Adhesion Kinase (FAK), integrins, vinculin, and paxillin, also play pivotal roles in cardiomyogenesis, impacting cell proliferation and heart tube looping. In fact, cardiomyocytes sense ECM stiffness through integrins, modulating signaling pathways like PI3K/AKT and Wnt/β-catenin. Moreover, FAK/Src complex activation mediates cardiac hypertrophic growth and survival signaling in response to mechanical loads. This review provides an overview of the molecular and mechanical mechanisms underlying the crosstalk between FAs and cardiac differentiation, as well as the role of FA-mediated mechanotransduction in guiding cardiac muscle responses to mechanical stimuli.

Thiamine-modified metabolic reprogramming of human pluripotent stem cell-derived cardiomyocyte under space microgravity

During spaceflight, the cardiovascular system undergoes remarkable adaptation to microgravity and faces the risk of cardiac remodeling. Therefore, the effects and mechanisms of microgravity on cardiac morphology, physiology, metabolism, and cellular biology need to be further investigated. Since China started constructing the China Space Station (CSS) in 2021, we have taken advantage of the Shenzhou-13 capsule to send human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) to the Tianhe core module of the CSS. In this study, hPSC-CMs subjected to space microgravity showed decreased beating rate and abnormal intracellular calcium cycling. Metabolomic and transcriptomic analyses revealed a battery of metabolic remodeling of hPSC-CMs in spaceflight, especially thiamine metabolism. The microgravity condition blocked the thiamine intake in hPSC-CMs. The decline of thiamine utilization under microgravity or by its antagonistic analog amprolium affected the process of the tricarboxylic acid cycle. It decreased ATP production, which led to cytoskeletal remodeling and calcium homeostasis imbalance in hPSC-CMs. More importantly, in vitro and in vivo studies suggest that thiamine supplementation could reverse the adaptive changes induced by simulated microgravity. This study represents the first astrobiological study on the China Space Station and lays a solid foundation for further aerospace biomedical research. These data indicate that intervention of thiamine-modified metabolic reprogramming in human cardiomyocytes during spaceflight might be a feasible countermeasure against microgravity.

HSPA12A maintains aerobic glycolytic homeostasis and Histone3 lactylation in cardiomyocytes to attenuate myocardial ischemia/reperfusion injury

Myocardial ischemia/reperfusion (MI/R) injury is a major cause of adverse outcomes of revascularization following myocardial infarction. Anaerobic glycolysis during myocardial ischemia is well studied, but the role of aerobic glycolysis during the early phase of reperfusion is incompletely understood. Lactylation of Histone H3 (H3) is an epigenetic indicator of the glycolytic switch. Heat shock protein A12A (HSPA12A) is an atypic member of the HSP70 family. In the present study, we report that, during reperfusion following myocardial ischemia, HSPA12A was downregulated and aerobic glycolytic flux was decreased in cardiomyocytes. Notably, HSPA12A KO in mice exacerbated MI/R-induced aerobic glycolysis decrease, cardiomyocyte death, and cardiac dysfunction. Gain- and loss-of-function studies demonstrated that HSPA12A was required to support cardiomyocyte survival upon hypoxia/reoxygenation (H/R) challenge and that its protective effects were mediated by maintaining aerobic glycolytic homeostasis for H3 lactylation. Further analyses revealed that HSPA12A increased Smurf1-mediated Hif1α protein stability, thus increasing glycolytic gene expression to maintain appropriate aerobic glycolytic activity to sustain H3 lactylation during reperfusion and, ultimately, improving cardiomyocyte survival to attenuate MI/R injury.

Protective effects of METRNL overexpression against pathological cardiac remodeling

At present, meteorin-like protein (METRNL) has been proven to be widely expressed in the myocardium and participates in the pathogenic process of various cardiovascular diseases. However, the effects of METRNL on pathological cardiac hypertrophy is still unknown. In the present study, we used a mouse model of transverse aortic constriction (TAC) surgery to mimic pathological cardiac hypertrophy and gene delivery system to overexpress METRNL in vivo. The results showed that METRNL overexpression improved TAC-induced pathological cardiac hypertrophy in mice and neonatal cardiomyocytes. In addition, METRNL overexpression diminished TAC-induced cardiac oxidative damage, inflammation and cardiomyocyte apoptosis. Moreover, the cardioprotective effect of METRNL overexpression was directly related to the activation of AMP-activated protein kinase (AMPK) and sirtuin1 (SIRT1). In summary, our data identified that METRNL may be a promising therapeutic target to mitigate pathological cardiac hypertrophy in the future.

Ginsenoside Rd Attenuates Myocardial Ischemia/Reperfusion Injury by Inhibiting Inflammation and Apoptosis through PI3K/Akt Signaling Pathway

Myocardial ischemia/reperfusion (I/R) injury is the leading cause of death worldwide. Ginsenoside Rd (GRd) has cardioprotective properties but its efficacy and mechanism of action in myocardial I/R injury have not been clarified. This study investigated GRd as a potent therapeutic agent for myocardial I/R injury. Oxygen-glucose deprivation and reperfusion (OGD/R) and left anterior descending (LAD) coronary artery ligation were used to establish a myocardial I/R injury model in vitro and in vivo. In vivo, GRd significantly reduced the myocardial infarct size and markers of myocardial injury and improved the cardiac function in myocardial I/R injury mice. In vitro, GRd enhanced cell viability and protected the H9c2 rat cardiomyoblast cell line from OGD-induced injury GRd. The network pharmacology analysis predicted 48 potential targets of GRd for the treatment of myocardial I/R injury. GO and KEGG enrichment analysis indicated that the cardioprotective effects of GRd were closely related to inflammation and apoptosis mediated by the PI3K/Akt signaling pathway. Furthermore, GRd alleviated inflammation and cardiomyocyte apoptosis in vivo and inhibited OGD/R-induced apoptosis and inflammation in cardiomyocytes. GRd also increased PI3K and Akt phosphorylation, suggesting activation of the PI3K/Akt pathway, whereas LY294002, a PI3K inhibitor, blocked the GRd-induced inhibition of OGD/R-induced apoptosis and inflammation in H9c2 cells. The therapeutic effect of GRd in vivo and in vitro against myocardial I/R injury was primarily dependent on PI3K/Akt pathway activation to inhibit inflammation and cardiomyocyte apoptosis. This study provides new evidence for the use of GRd as a cardiovascular drug.

Transient Receptor Potential Canonical 5 (TRPC5): Regulation of Heart Rate and Protection against Pathological Cardiac Hypertrophy

TRPC5 is a non-selective cation channel that is expressed in cardiomyocytes, but there is a lack of knowledge of its (patho)physiological role in vivo. Here, we examine the role of TRPC5 on cardiac function under basal conditions and during cardiac hypertrophy. Cardiovascular parameters were assessed in wild-type (WT) and global TRPC5 knockout (KO) mice. Despite no difference in blood pressure or activity, heart rate was significantly reduced in TRPC5 KO mice. Echocardiography imaging revealed an increase in stroke volume, but cardiac contractility was unaffected. The reduced heart rate persisted in isolated TRPC5 KO hearts, suggesting changes in basal cardiac pacing. Heart rate was further investigated by evaluating the reflex change following drug-induced pressure changes. The reflex bradycardic response following phenylephrine was greater in TRPC5 KO mice but the tachycardic response to SNP was unchanged, indicating an enhancement in the parasympathetic control of the heart rate. Moreover, the reduction in heart rate to carbachol was greater in isolated TRPC5 KO hearts. To evaluate the role of TRPC5 in cardiac pathology, mice were subjected to abdominal aortic banding (AAB). An exaggerated cardiac hypertrophy response to AAB was observed in TRPC5 KO mice, with an increased expression of hypertrophy markers, fibrosis, reactive oxygen species, and angiogenesis. This study provides novel evidence for a direct effect of TRPC5 on cardiac function. We propose that (1) TRPC5 is required for maintaining heart rate by regulating basal cardiac pacing and in response to pressure lowering, and (2) TRPC5 protects against pathological cardiac hypertrophy.

Hyaluronic acid stimulation of stem cells for cardiac repair: a cell-free strategy for myocardial infarct

BACKGROUND

Myocardial infarction (MI), a representative form of ischemic heart disease, remains a huge burden worldwide. This study aimed to explore whether extracellular vesicles (EVs) secreted from hyaluronic acid (HA)-primed induced mesenchymal stem cells (HA-iMSC-EVs) could enhance the cardiac repair after MI.

RESULTS

HA-iMSC-EVs showed typical characteristics for EVs such as morphology, size, and marker proteins expression. Compared with iMSC-EVs, HA-iMSC-EVs showed enhanced tube formation and survival against oxidative stress in endothelial cells, while reduced reactive oxygen species (ROS) generation in cardiomyocytes. In THP-1 macrophages, both types of EVs markedly reduced the expression of pro-inflammatory signaling players, whereas HA-iMSC-EVs were more potent in augmenting anti-inflammatory markers. A significant decrease of inflammasome proteins was observed in HA-iMSC-EV-treated THP-1. Further, phospho-SMAD2 as well as fibrosis markers in TGF-β1-stimulated cardiomyocytes were reduced in HA-iMSC-EVs treatment. Proteomic data showed that HA-iMSC-EVs were enriched with multiple pathways including immunity, extracellular matrix organization, angiogenesis, and cell cycle. The localization of HA-iMSC-EVs in myocardium was confirmed after delivery by either intravenous or intramyocardial route, with the latter increased intensity. Echocardiography revealed that intramyocardial HA-iMSC-EVs injections improved cardiac function and reduced adverse cardiac remodeling and necrotic size in MI heart. Histologically, MI hearts receiving HA-iMSC-EVs had increased capillary density and viable myocardium, while showed reduced fibrosis.

CONCLUSIONS

Our results suggest that HA-iMSC-EVs improve cardiac function by augmenting vessel growth, while reducing ROS generation, inflammation, and fibrosis in MI heart.

AP39, a novel mitochondria-targeted hydrogen sulfide donor ameliorates doxorubicin-induced cardiotoxicity by regulating the AMPK/UCP2 pathway

Doxorubicin (DOX) is a broad-spectrum, highly effective antitumor agent; however, its cardiotoxicity has greatly limited its use. Hydrogen sulfide (H2S) is an endogenous gaseous transmitter that exerts cardioprotective effects via the regulation of oxidative stress and apoptosis and maintenance of mitochondrial function, among other mechanisms. AP39 is a novel mitochondria-targeted H2S donor that, at appropriate concentrations, attenuates intracellular oxidative stress damage, maintains mitochondrial function, and ameliorates cardiomyocyte injury. In this study, DOX-induced cardiotoxicity models were established using H9c2 cells and Sprague-Dawley rats to evaluate the protective effect of AP39 and its mechanisms of action. Both in vivo and in vitro experiments showed that DOX induces oxidative stress injury, apoptosis, and mitochondrial damage in cardiomyocytes and decreases the expression of p-AMPK/AMPK and UCP2. All DOX-induced changes were attenuated by AP39 treatment. Furthermore, the protective effect of AP39 was significantly attenuated by the inhibition of AMPK and UCP2. The results suggest that AP39 ameliorates DOX-induced cardiotoxicity by regulating the expression of AMPK/UCP2.

AGO2 Protects Against Diabetic Cardiomyopathy by Activating Mitochondrial Gene Translation

BACKGROUND

Diabetes is associated with cardiovascular complications. microRNAs translocate into subcellular organelles to modify genes involved in diabetic cardiomyopathy. However, functional properties of subcellular AGO2 (Argonaute2), a core member of miRNA machinery, remain elusive.

METHODS

We elucidated the function and mechanism of subcellular localized AGO2 on mouse models for diabetes and diabetic cardiomyopathy. Recombinant adeno-associated virus type 9 was used to deliver AGO2 to mice through the tail vein. Cardiac structure and functions were assessed by echocardiography and catheter manometer system.

RESULTS

AGO2 was decreased in mitochondria of diabetic cardiomyocytes. Overexpression of mitochondrial AGO2 attenuated diabetes-induced cardiac dysfunction. AGO2 recruited TUFM, a mitochondria translation elongation factor, to activate translation of electron transport chain subunits and decrease reactive oxygen species. Malonylation, a posttranslational modification of AGO2, reduced the importing of AGO2 into mitochondria in diabetic cardiomyopathy. AGO2 malonylation was regulated by a cytoplasmic-localized short isoform of SIRT3 through a previously unknown demalonylase function.

CONCLUSIONS

Our findings reveal that the SIRT3-AGO2-CYTB axis links glucotoxicity to cardiac electron transport chain imbalance, providing new mechanistic insights and the basis to develop mitochondria targeting therapies for diabetic cardiomyopathy.

INO80-Dependent Remodeling of Transcriptional Regulatory Network Underlies the Progression of Heart Failure

BACKGROUND

Progressive remodeling of cardiac gene expression underlies decline in cardiac function, eventually leading to heart failure. However, the major determinants of transcriptional network switching from normal to failed hearts remain to be determined.

METHODS

In this study, we integrated human samples, genetic mouse models, and genomic approaches, including bulk RNA sequencing, single-cell RNA sequencing, chromatin immunoprecipitation followed by high-throughput sequencing, and assay for transposase-accessible chromatin with high-throughput sequencing, to identify the role of chromatin remodeling complex INO80 in heart homeostasis and dysfunction.

RESULTS

The INO80 chromatin remodeling complex was abundantly expressed in mature cardiomyocytes, and its expression further increased in mouse and human heart failure. Cardiomyocyte-specific overexpression of Ino80, its core catalytic subunit, induced heart failure within 4 days. Combining RNA sequencing, chromatin immunoprecipitation followed by high-throughput sequencing, and assay for transposase-accessible chromatin with high-throughput sequencing, we revealed INO80 overexpression-dependent reshaping of the nucleosomal landscape that remodeled a core set of transcription factors, most notably the MEF2 (Myocyte Enhancer Factor 2) family, whose target genes were closely associated with cardiac function. Conditional cardiomyocyte-specific deletion of Ino80 in an established mouse model of heart failure demonstrated remarkable preservation of cardiac function.

CONCLUSIONS

In summary, our findings shed light on the INO80-dependent remodeling of the chromatin landscape and transcriptional networks as a major mechanism underlying cardiac dysfunction in heart failure, and suggest INO80 as a potential preventative or interventional target.

Loss of Cardiac PFKFB2 Drives Metabolic, Functional, and Electrophysiological Remodeling in the Heart

BACKGROUND

Phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFK-2) is a critical glycolytic regulator responsible for upregulation of glycolysis in response to insulin and adrenergic signaling. PFKFB2, the cardiac isoform of PFK-2, is degraded in the heart in the absence of insulin signaling, contributing to diabetes-induced cardiac metabolic inflexibility. However, previous studies have not examined how the loss of PFKFB2 affects global cardiac metabolism and function.

METHODS AND RESULTS

To address this, we have generated a mouse model with a cardiomyocyte-specific knockout of PFKFB2 (cKO). Using 9-month-old cKO and control mice, we characterized the impacts of PFKFB2 on cardiac metabolism, function, and electrophysiology. cKO mice have a shortened life span of 9 months. Metabolically, cKO mice are characterized by increased glycolytic enzyme abundance and pyruvate dehydrogenase activity, as well as decreased mitochondrial abundance and beta oxidation, suggesting a shift toward glucose metabolism. This was supported by a decrease in the ratio of palmitoyl carnitine to pyruvate-dependent mitochondrial respiration in cKO relative to control animals. Metabolomic, proteomic, and Western blot data support the activation of ancillary glucose metabolism, including pentose phosphate and hexosamine biosynthesis pathways. Physiologically, cKO animals exhibited impaired systolic function and left ventricular dilation, represented by reduced fractional shortening and increased left ventricular internal diameter, respectively. This was accompanied by electrophysiological alterations including increased QT interval and other metrics of delayed ventricular conduction.

CONCLUSIONS

Loss of PFKFB2 results in metabolic remodeling marked by cardiac ancillary pathway activation. This could delineate an underpinning of pathologic changes to mechanical and electrical function in the heart.

Exploring the role of TRPM4 in calcium-dependent triggered activity and cardiac arrhythmias

Cardiac arrhythmias pose a major threat to a patient's health, yet prove to be often difficult to predict, prevent and treat. A key mechanism in the occurrence of arrhythmias is disturbed Ca2+ homeostasis in cardiac muscle cells. As a Ca2+-activated non-selective cation channel, TRPM4 has been linked to Ca2+-induced arrhythmias, potentially contributing to translating an increase in intracellular Ca2+ concentration into membrane depolarisation and an increase in cellular excitability. Indeed, evidence from genetically modified mice, analysis of mutations in human patients and the identification of a TRPM4 blocking compound that can be applied in vivo further underscore this hypothesis. Here, we provide an overview of these data in the context of our current understanding of Ca2+-dependent arrhythmias.

Protectin D1 Alleviates Myocardial Ischemia/Reperfusion Injury by Regulating PI3K/AKT Signaling Pathway

Myocardial ischemia/reperfusion (I/R) injury after the onset of acute myocardial infarction (AMI) can be life-threatening, and there is no effective strategy for therapeutic intervention. Here, we studied the potential of protectin D1 in protecting from I/R-induced cardiac damages and investigated the underlying mechanisms. An in vivo rat model of I/R after AMI induction was established through the ligation of the left anterior descending (LAD) artery to assess the cardiac functions and evaluate the protective effect of protectin D1. Protectin D1 protected against I/R-induced oxidative stress and inflammation in the rat model, improved the cardiac function, and reduced the infarct size in myocardial tissues. The beneficial effect of protectin D1 was associated with the up-regulation of miRNA-210 and the effects on PI3K/AKT signaling and HIF-1α expression. Together, our data suggest that protectin D1 could serve as a potential cardioprotective agent against I/R-associated cardiac defects.

Renalase mediates macrophage-to-fibroblast crosstalk to attenuate pressure overload-induced pathological myocardial fibrosis

A potential antifibrotic mechanism in pathological myocardial remodeling is the recruitment of beneficial functional subpopulations of macrophages or the transformation of their phenotype. Macrophages are required to activate molecular cascades that regulate fibroblast behavior. Identifying mediators that activate the antifibrotic macrophage phenotype is tantamount to identifying the button that retards pathological remodeling of the myocardium; however, relevant studies are inadequate. Circulating renalase (RNLS) is mainly of renal origin, and cardiac myocytes also secrete it autonomously. Our previous studies revealed that RNLS delivers cell signaling to exert multiple cardiovascular protective effects, including the improvement of myocardial ischemia, and heart failure. Here, we further investigated the potential mechanism by which macrophage phenotypic transformation is targeted by RNLS to mediate stress load-induced myocardial fibrosis. Mice subjected to transverse aortic constriction (TAC) were used as a model of myocardial fibrosis. The co-incubation of macrophages and cardiac fibroblasts was used to study intercellular signaling. The results showed that RNLS co-localized with macrophages and reduced protein expression after cardiac pressure overload. TAC mice exhibited improved cardiac function and alleviated left ventricular fibrosis when exogenous RNLS was administered. Flow sorting showed that RNLS is essential for macrophage polarization towards a restorative phenotype (M2-like), thereby inhibiting myofibroblast activation, as proven by both mouse RAW264.7 and bone marrow-derived macrophage models. Mechanistically, we found that activated protein kinase B is a major pathway by which RNLS promotes M2 polarization in macrophages. RNLS may serve as a prognostic biomarker and a potential clinical candidate for the treatment of myocardial fibrosis.

ATF6 protects against protein misfolding during cardiac hypertrophy

Cardiomyocytes activate the unfolded protein response (UPR) transcription factor ATF6 during pressure overload-induced hypertrophic growth. The UPR is thought to increase ER protein folding capacity and maintain proteostasis. ATF6 deficiency during pressure overload leads to heart failure, suggesting that ATF6 protects against myocardial dysfunction by preventing protein misfolding. However, conclusive evidence that ATF6 prevents toxic protein misfolding during cardiac hypertrophy is still pending. Here, we found that activation of the UPR, including ATF6, is a common response to pathological cardiac hypertrophy in mice. ATF6 KO mice failed to induce sufficient levels of UPR target genes in response to chronic isoproterenol infusion or transverse aortic constriction (TAC), resulting in impaired cardiac growth. To investigate the effects of ATF6 on protein folding, the accumulation of poly-ubiquitinated proteins as well as soluble amyloid oligomers were directly quantified in hypertrophied hearts of WT and ATF6 KO mice. Whereas only low levels of protein misfolding was observed in WT hearts after TAC, ATF6 KO mice accumulated increased quantities of misfolded protein, which was associated with impaired myocardial function. Collectively, the data suggest that ATF6 plays a critical adaptive role during cardiac hypertrophy by protecting against protein misfolding.

Cardioprotective Potential of Cymbopogon citratus Essential Oil against Isoproterenol-induced Cardiomyocyte Hypertrophy: Possible Involvement of NLRP3 Inflammasome and Oxidative Phosphorylation Complex Subunits

OBJECTIVE

Cymbopogon citratus (DC.) Stapf is a medicinal and edible herb that is widely used for the treatment of gastric, nervous and hypertensive disorders. In this study, we investigated the cardioprotective effects and mechanisms of the essential oil, the main active ingredient of Cymbopogon citratus, on isoproterenol (ISO)-induced cardiomyocyte hypertrophy.

METHODS

The compositions of Cymbopogon citratus essential oil (CCEO) were determined by gas chromatography-mass spectrometry. Cardiomyocytes were pretreated with 16.9 µg/L CCEO for 1 h followed by 10 µmol/L ISO for 24 h. Cardiac hypertrophy-related indicators and NLRP3 inflammasome expression were evaluated. Subsequently, transcriptome sequencing (RNA-seq) and target verification were used to further explore the underlying mechanism.

RESULTS

Our results showed that the CCEO mainly included citronellal (45.66%), geraniol (23.32%), and citronellol (10.37%). CCEO inhibited ISO-induced increases in cell surface area and protein content, as well as the upregulation of fetal gene expression. Moreover, CCEO inhibited ISO-induced NLRP3 inflammasome expression, as evidenced by decreased lactate dehydrogenase content and downregulated mRNA levels of NLRP3, ASC, CASP1, GSDMD, and IL-1β, as well as reduced protein levels of NLRP3, ASC, pro-caspase-1, caspase-1 (p20), GSDMD-FL, GSDMD-N, and pro-IL-1β. The RNA-seq results showed that CCEO inhibited the increase in the mRNA levels of 26 oxidative phosphorylation complex subunits in ISO-treated cardiomyocytes. Our further experiments confirmed that CCEO suppressed ISO-induced upregulation of mt-Nd1, Sdhd, mt-Cytb, Uqcrq, and mt-Atp6 but had no obvious effects on mt-Col expression.

CONCLUSION

CCEO inhibits ISO-induced cardiomyocyte hypertrophy through the suppression of NLRP3 inflammasome expression and the regulation of several oxidative phosphorylation complex subunits.