Mouse Cardiomyocytes Research Articles

S14-Phosphorylated RPN6 Mediates Proteasome Activation by PKA and Alleviates Proteinopathy.

A better understanding of the regulation of proteasome activities can facilitate the search for new therapeutic strategies. A cell culture study shows that PKA (cAMP-dependent protein kinase or protein kinase A) activates the 26S proteasome by pS14-Rpn6 (serine14-phosphorylated Rpn6), but this discovery and its physiological significance remain to be established in vivo. Male and female mice with Ser14 of Rpn6 (regulatory particle non-ATPase 6) mutated to Ala (S14A [Rpn6/Psmd11S14A]) or Asp (S14D) to respectively block or mimic pS14-Rpn6 were created and used along with cells derived from them. cAMP/PKA were manipulated pharmacologically. Ubiquitin-proteasome system functioning was evaluated with the GFPdgn (green fluorescence protein with carboxyl fusion of the CL1 degron) reporter mouse and proteasomal activity assays. Impact of S14A and S14D on proteotoxicity was tested in mice and cardiomyocytes overexpressing the misfolded protein R120G-CryAB (R120G [arginine120 to glycine missense mutant alpha B-crystallin]). PKA activation increased pS14-Rpn6 and 26S proteasome activities in wild-type but not S14A embryonic fibroblasts (mouse embryonic fibroblasts), adult cardiomyocytes, and mouse hearts. Basal 26S proteasome activities were significantly greater in S14D myocardium and adult mouse cardiomyocytes than in wild-type counterparts. S14D::GFPdgn mice displayed significantly lower myocardial GFPdgn protein but not mRNA levels than GFPdgn mice. In R120G mice, a classic model of cardiac proteotoxicity, basal myocardial pS14-Rpn6 was significantly lower compared with nontransgenic littermates, which was not always associated with reduction of other phosphorylated PKA substrates. Cultured S14D neonatal cardiomyocytes displayed significantly faster proteasomal degradation of R120G than wild-type neonatal cardiomyocytes. Compared with R120G mice, S14D/S14D::R120G mice showed significantly greater myocardial proteasome activities, lower levels of total and K48-linked ubiquitin conjugates, and of aberrant CryAB (alpha B-crystallin) protein aggregates, less fetal gene reactivation, and cardiac hypertrophy, and delays in cardiac malfunction. This study establishes in animals that pS14-Rpn6 mediates the activation of 26S proteasomes by PKA and that the reduced pS14-Rpn6 is a key pathogenic factor in cardiac proteinopathy, thereby identifying a new therapeutic target to reduce cardiac proteotoxicity.

Stress-enhanced cardiac lncRNA Morrbid protects hearts from acute myocardial infarction.

Myeloid RNA regulator of Bim-induced death (Morrbid) is a newly identified leukocyte-specific long noncoding RNA (lncRNA). However, the expression and biological functions of Morrbid in cardiomyocytes and heart disease are currently unclear. This study was meant to determine the role of cardiac Morrbid in acute myocardial infarction (AMI) and to identify the potential cellular and molecular mechanisms involved. We found that both human and mouse cardiomyocytes could express a significant amount of Morrbid and that its expression was increased in cardiomyocytes with hypoxia or oxidative stress as well as in mouse hearts with AMI. Overexpression of Morrbid reduced the myocardial infarct size and cardiac dysfunction, whereas the infarct size and cardiac dysfunction deteriorated in cardiomyocyte-specific Morrbid-KO (Morrbidfl/fl/Myh6-Cre) mice. We identified that Morrbid had a protective effect against hypoxia- or H2O2-induced apoptosis; this was also confirmed in vivo in mouse hearts after AMI. We further discovered that serpine1 was a direct target gene of Morrbid that was involved in the Morrbid-mediated protective effect on cardiomyocytes. In summary, we have found, for the first time to our knowledge, that the cardiac Morrbid is a stress-enhanced lncRNA that protects hearts from AMI via antiapoptosis through its target gene serpine1. Morrbid may be a novel promising therapeutic target for ischemic heart diseases such as AMI.

Ibrutinib impairs IGF-1-dependent activation of intracellular Ca handling in isolated mouse ventricular myocytes.

The Bruton tyrosine kinase (BTK) inhibitor Ibrutinib is associated with a higher incidence of cardiotoxic side effects including heart failure (HF). Ibrutinib is capable of inhibiting PI3K/Akt signaling in neonatal rat ventricular cardiomyocytes when stimulated with insulin-like growth factor 1 (IGF-1). We therefore hypothesized that Ibrutinib might disrupt IGF-1-mediated activation of intracellular Ca handling in adult mouse cardiomyocytes by inhibiting PI3K/Akt signaling. Isolated ventricular myocytes (C57BL6/J) were exposed to IGF-1 at 10 nmol/L in the presence or absence of Ibrutinib (1 µmol/L) or Acalabrutinib (10 µmol/L; cell culture for 24 ± 2 h). Intracellular Ca handling was measured by epifluorescence (Fura-2 AM) and confocal microscopy (Fluo-4 AM). Ruptured-patch whole-cell voltage-clamp was used to measure ICa. Levels of key cardiac Ca handling proteins were investigated by immunoblots. IGF-1 significantly increased Ca transient amplitudes by ∼83% as compared to vehicle treated control cells. This was associated with unaffected diastolic Ca, enhanced SR Ca loading and increased ICa. Co-treatment with Ibrutinib attenuated both the IGF-1-mediated increase in SR Ca content and in ICa. IGF-1 treated cardiomyocytes had significantly increased levels of pS473Akt/Akt and SERCA2a expression as compared to cells concomitantly treated with IGF-1 and Ibrutinib. SR Ca release (as assessed by Ca spark frequency) was unaffected by either treatment. In order to test for potential off-target effects, second generation BTK inhibitor Acalabrutinib with greater BTK selectivity and lower cardiovascular toxicity was tested for IGF1-mediated activation of intracellular Ca handling. Acalabrutinib induced similar effects on Ca handling in IGF-1 treated cultured myocytes as Ibrutinib in regard to decreased Ca transient amplitude and slowed Ca transient decay, hence implying a functional class effect of BTK inhibitors in cardiac myocytes. Inhibition of BTK by Ibrutinib impairs IGF-1-dependent activation of intracellular Ca handling in adult ventricular mouse myocytes in the face of disrupted Akt signaling and absent SERCA2a upregulation.

The Effect and Mechanism of POSTN and Its Alternative Splicing on the Apoptosis of Myocardial Cells in Acute Myocardial Infarction: A Study in Vitro

Our study aimed to investigate key molecular targets in the pathogenesis of AMI, and provide new strategy for the treatment. In this work, the myocardial ischemia and hypoxia model was constructed by using HL-1 mouse cardiomyocytes. The over-expressing POSTN wild-type, mutant and negative control lentiviruses (GV492-POSTNWT,GV492-POSTN-MUT, GV492-NC) was conducted and transfected. Cardiomyocytes were examined for cell proliferation and apoptosis to explore the effects of POSTN and its alternative splicing. The endoplasmic reticulum stess-related apoptosis proteins were selected and detected. We found that POSTN could promote the proliferation of normal and hypoxic cardiomyocytes and inhibit their apoptosis. The mechanism by which POSTN inhibited cardiomyocyte apoptosis may be through inhibiting the GRP78-eIF2α-ATF4-CHOP pathway of endoplasmic reticulum stress. Alternative splicing of POSTN could inhibit the apoptosis of ischemic and hypoxic cardiomyocytes, and its mechanism needs to be confirmed by further studies. We drawed the conclusion that POSTN might be a potential therapeutic target for AMI.

MiRNA-103-3p-Hlf regulates apoptosis and autophagy by targeting hepatic leukaemia factor in heart failure.

Cardiomyocyte apoptosis is an important factor leading to the occurrence and development of heart failure (HF), which is associated with high mortality of patients with cardiovascular diseases. This study aims to investigate the underlying mechanisms of HF in terms of expression and regulation patterns using bioinformatics and experimental validation. Two HF datasets were collected: a dataset GSE112056 downloaded from the GEO database (including mRNA and miRNA sequencing data) and another is the laboratory-owned mRNA dataset. Differential mRNAs and miRNAs in the two datasets were screened using the raw Bayesian approach method. Gene Ontology was used to perform functional enrichment analysis of the differential mRNAs and co-expression network analysis of the differential mRNAs, combined with nuclear transcription factors in the differential miRNAs and mRNAs for target gene prediction. A HF cell model was constructed using mouse cardiomyocytes (HL-1), and the role and mechanism of miRNA-103-3p-Hlf (hepatic leukaemia factor) in the process of HF was verified by cell transfection, luciferase reporter gene, WB, and qPCR. We found that Hlf gene expression was decreased in the HF model group and strongly correlated with FYCO1 (FYVE and coiled-coil domain-containing protein 1) gene, a phenomenon enriched in apoptotic autophagy-related pathways. MiR-103-3p expression was up-regulated in the HF model group, and its targeting correlation with Hlf was confirmed by luciferase activity assay. In the HL-1 cell model, miR-103-3p significantly promoted apoptosis and inhibited autophagy in HL-1 cells (all P<0.05), and overexpression of the Hlf gene reversed this phenomenon, inhibiting apoptosis and promoting autophagy in HL-1 cells (all P<0.05). MiR-103-3p affects myocardial cells apoptosis and autophagy by targeting Hlf, playing as a potential therapeutic biomarker for HF progression.

Cardiomyocytes from female compared to male mice have larger ryanodine receptor clusters and higher calcium spark frequency.

Sex differences in cardiac physiology are receiving increased attention as it has become clear that men and women have different aetiologies of cardiac disease and require different treatments. There are experimental data suggesting that male cardiomyocytes exhibit larger Ca2+ transients due to larger Ca2+ sparks and a higher excitation-contraction coupling gain; in addition, they exhibit a larger response to adrenergic stimulation with isoprenaline (ISO). Here, we studied whether there are sex differences relating to structural organization of the transverse tubular network and ryanodine receptors (RyRs). Surprisingly, we found that female cardiomyocytes exhibited a higher spark frequency in a range of spark magnitudes. While overall RyR expression and phosphorylation were the same, female cardiomyocytes had larger but fewer RyR clusters. The density of transverse t-tubules was the same, but male cardiomyocytes had more longitudinal t-tubules. The Ca2+ transients were similar in male and female cardiomyocytes under control conditions and in the presence of ISO. The synchrony of the Ca2+ transients was similar between sexes as well. Overall, our data suggest subtle sex differences in the Ca2+ influx and efflux pathways and their response to ISO, but these differences are balanced, resulting in similar Ca2+ transients in field-stimulated male and female cardiomyocytes. The higher spark frequency in female cardiomyocytes is related to the organization of RyRs into larger, but fewer clusters. KEY POINTS: During a heartbeat, the force of contraction depends on the amplitude of the calcium transient, which in turn depends on the amount of calcium released as calcium sparks through ryanodine receptors in the sarcoplasmic reticulum. Previous studies suggest that cardiomyocytes from male compared to female mice exhibit larger calcium sparks, larger sarcoplasmic reticulum calcium release and greater response to adrenergic stimulation triggering a fight-or-flight response. In contrast, we show that cardiomyocytes from female mice have a higher spark frequency during adrenergic stimulation and similar spark morphology. The higher spark frequency is related to the organization of ryanodine receptors into fewer, but larger clusters in female compared to male mouse cardiomyocytes. Despite subtle sex differences in cardiomyocyte structure and calcium fluxes, the differences are balanced, leading to similar calcium transients in cardiomyocytes from male and female mice.

Abstract P3142: Engineering A Genetically Encoded Enhancer Of L-type Ca 2+ Currents

L-type calcium channels (LTCC) play a crucial role as they serve as vital portals for Ca 2+ entry into cardiac myocytes, neurons, and other physiological systems. Altered LTCC function is linked to various pathologies including cardiac arrhythmias and neurodevelopmental disorders. In particular, genetic studies have identified loss-of-function mutations in Ca V 1.2 channels in patients with shortened QT interval and Brugada Syndrome, as well as neuropsychiatric disorders. Given the broad physiological importance of LTCC in various tissues, conventional pharmacological agonists of LTCC may yield off-target effects and toxicity. Therefore, new approaches to upregulate LTCC function in a cell-type dependent manner is sought after. To do so, we here develop a genetically encoded enhancer of calcium channels (GeeCC, “geek”) by leveraging both a cardiac specific L-type channel modulator, leucine rich repeat containing protein 10 (Lrrc10), and selective nanobodies that target the LTCC complex. Specifically, Lrrc10 co-expression markedly upregulates LTCC currents. Furthermore, mutations in Lrrc10 are linked to cardiac diseases, including cardiomyopathies. Through extensive structure-function analysis, we identified a minimal action domain within Lrrc10 that is critical for functional modulation of LTCC. However, as this segment alone has a low affinity for the channel complex, its expression alone yielded minimal changes in Ca 2+ current amplitude. However, fusion of this Lrrc10 domain to a nanobody (nb.F3) that targets the Ca 2+ channel beta subunit resulted in a significant increase in the LTCC current amplitude. In depth analysis revealed exquisite selectivity of GeeCC for Ca V 1.2/Ca V 1.3 channels. In mouse cardiomyocytes, deployment of GeeCC via adenovirus enhances endogenous L-type currents when compared to uninfected controls or cardiomyocytes infected with nanobodies alone. Additionally, in neurons, co-expression of GeeCC enhanced excitation-transcription coupling. In all, we have developed a genetically-encoded approach to selectively enhance L-type currents. This strategy may enable new insights into cardiovascular and neuronal physiology and pathophysiology, and may have potential therapeutic applications.

Abstract P3083: Trim29 Deficiency Ameliorates Viral Myocarditis By Reducing Perk Mediated Er Stress And Ros Responses

Infections by viruses including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) could cause viral myocarditis. Endoplasmic reticulum (ER) stress is associated with several metabolic diseases such as cardiovascular disease, diabetes and cancer. However, the immune mechanisms of ER stress regulation in controlling the pathogenesis of viral myocarditis are unclear. Here, we found that knockdown or knockout of TRIM29 significantly inhibited PERK (Protein kinase RNA-like endoplasmic reticulum kinase) mediated ER stress and apoptosis induced by cardiotropic viruses CVB3 (coxsackievirus B3) or EMCV (encephalomyocarditis virus) in human and mouse cardiomyocytes. Additionally, TRIM29 deficiency relieved ROS (Reactive oxygen species) mediated STING (Stimulator of interferon genes) inhibition to produce more type I interferon for restricting cardiotropic viruses in cardiomyocytes. Importantly, cardiomyocytes specific TRIM29 deficiency exhibited dramatic protective effects on cardiac damage, cardiac dysfunction, viral replication and promoted survival in CVB3-induced viral myocarditis model in vivo . Mechanistically, TRIM29 was shown to interact with PERK and catalyze SUMOylation for maintaining its stability, thereby promoting PERK mediated ER stress and ROS responses to induce pathogenesis of viral myocarditis. Our results indicate that TRIM29 loss-of-function in cardiomyocytes ameliorates viral myocarditis by reducing PERK mediated ER stress response and unleashing ROS-suppressed interferon response. Our data suggest the TRIM29-PERK axis is a potential therapeutic target for viral myocarditis and other ER stress-associated cardiovascular disease.

Abstract P2158: In Vivo Dissection Of A CRISPR/Cas9-Mediated Precise Genome Editing Mechanism

Genomic sequencing has uncovered many genetic variations that interfere with development and function. Our inability to make precise and permanent genome edits limits our ability to treat genetic disorders. However, CRISPR/Cas9 has been demonstrated to be a potent tool for genome editing, with enormous therapeutic potential. Furthermore, the use of adeno-associated virus (AAV) to deliver CRISPR/Cas9 components, as well as a donor template for homology directed repair (HDR; AAV-HDR), has shown impressive editing efficiencies, particularly in vitro . In comparison, in vivo studies have shown more modest editing efficiencies, with large variation between target loci. Thus, to employ this strategy therapeutically it is imperative to establish a robust understanding of the underlying mechanism, which can then be exploited to improve efficiency. Thus far, the absence of high-throughput tools that enable systematic analysis has hindered efforts to explore and enhance AAV-HDR efficiency. Here we employ two novel high-throughput methodologies for measuring in vivo AAV-HDR editing efficiency in cardiomyocytes of Cas9-expressing mice. In our first approach we analyze the locus-dependent variability of AAV-HDR efficiency, with the goal of identifying the genomic characteristics of high-efficiency loci. In the second approach, we utilize a high-throughput pooled CRISPR KO screen to identify the DNA-repair factors required for efficient gene editing. This approach has uncovered several novel regulators of cardiac AAV-HDR, which we are currently working on characterizing. Collectively these studies will provide insights into the molecular mechanism of AAV-HDR, and we anticipate that these advances will promote development of AAV-HDR based therapies.

Abstract P3098: Immune Suppression Ameliorates A Mouse Model Of Lmna-related Cardiomyopathy With Nuclear Envelope Rupture

Lamin A/C (encoded by the LMNA gene) are the components of the nuclear lamina, a protein meshwork providing the structural integrity to the nuclear membrane. Dilated cardiomyopathy (DCM) caused by LNNA gene mutations is the second most common familial DCM in adults and associated with severe prognosis and high mortality. Despite decades of investigations into cell autonomous impacts of LMNA mutations, LMNA-DCM lacks effective treatments except for heart transplantation. Here, we identify cell non-autonomous effects of LMNA mutations and demonstrate the efficacy of targeting immune activities in mouse models of LMNA-DCM. We induced Lmna gene deletion specifically in cardiomyocytes in adult mice and tracked molecular, cellular, and physiological alterations in the heart at a high temporal resolution. We identified frequent localized nuclear envelope rupture, with the concomitant exposure of nuclear DNA to the cytoplasm, as the earliest direct consequence of Lamin A/C protein reduction in cardiomyocytes. Surprisingly, nuclear envelope rupture did accompany cardiomyocyte cell death or extensive transcriptional changes or cytosolic DNA sensing pathway activation within the cardiomyocytes. Instead, it coincided with extensive proinflammatory signaling activation within the cardiac macrophage population. This was followed by extensive fibrosis and structural and functional alterations of the heart, culminating in DCM and death. Treatment of LMNA-DCM mice with the immunosuppressant Dexamethasone suppressed fibrosis, profoundly improved the cardiac structure and function, and conferred a two-fold lifespan extension after Lmna gene deletion. This work suggested that immune activation is the major pathological component of LMNA-DCM and an effective target for treating LMNA-DCM patients.

Abstract P2132: The Raf Kinase Inhibitor Protein Protects Mitochondria From Ischemic Stress

Background: The Raf kinase inhibitor protein (RKIP) increases cardiac inotropy without detrimental remodeling and even protects from the development of heart failure in response to chronic pressure overload or catecholamines. These RKIP effects are mediated via simultaneous and persistent activation of cardiac β1- and β2-adrenergic receptors (βAR). Hypothesis: Since an intact mitochondrial function is central for the energy supply and cardiomyocyte health, which are parameters that had been proven to be positively influenced by RKIP in the heart, we here aimed to analyze the impact of RKIP and βAR signaling on mitochondria. Methods and Results: Electron microscopy, respiration measurements and confocal analysis of the mitochondrial membrane potential (mtMP) revealed that the mitochondria of RKIP knockout mice are of smaller size and abnormal shape, show a reduced ADP-stimulated respiration and a hyperpolarized mtMP compared to WT mitochondria. And, expression levels of several respiratory proteins were reduced. In contrast, mitochondrial content in RKIP-tg mouse hearts was enhanced, mitochondrial function maintained, and expression of proteins involved in respiratory complexes and mitochondria-related transcription (e.g. Tfam, NRF-1) was enhanced. To evaluate the stress resistance of RKIP-tg hearts, we subjected isolated cardiomyocytes or hearts of RKIP-tg or WT, respectively, to ischemia/reperfusion (I/R) stress. I/R effectively decreased the mtMP in WT cardiomyocytes and impaired ADP-stimulated respiration of isolated WT mitochondria after ex vivo I/R. In contrast, RKIP-tg mitochondria were protected from mtMP collapse and impaired respiration after I/R. To understand this protective RKIP-mediated effect and whether βAR are involved, we analyzed mtMP in neonatal cardiomyocytes of β2AR knockout mice, upon application of different βAR ligands, pertussis toxin and inhibitors of the PI3K or AKT. These experiments suggest a RKIP-mediated mitochondrial protection via β2AR/Gi/PI3Kα/pAKT signaling. Discussion: Our study shows that RKIP-βAR signaling protects mitochondria from I/R stress suggesting βAR modulation as a potential therapeutic strategy to protect the myocardium in ischemic conditions.

Abstract P1147: Cardinal Is A Nuclear Lncrna That Represses SRF/TCF-mediated Gene Transcription By Co-occupying SRF/TCF-bound Gene Promoters In The Heart

LncRNAs are an emerging class of co-transcriptional regulators important for balancing gene expression networks in the heart during development and disease. We recently characterized a cardiac-specific lncRNA named CARDINAL, which is transcribed adjacent to the SRF-coactivator myocardin. Myocardin, and members of the ternary complex factor (TCF) family (Elk1-4), compete for interaction with SRF to balance opposing transcriptional networks in the heart. Previously we showed that CARDINAL forms a stable complex with SRF and can repress SRF/TCF-mediated gene transcription, suggesting CARDINAL functions as an RNA cofactor for SRF. Here we show using RNAscope in situ hybridization that CARDINAL is a nuclear lncRNA in both mouse and human cardiomyocytes. To identify CARDINAL-regulated genes, we performed Chromatin Isolation by RNA Purification (ChIRP) using anti-sense oligonucleotides specific to endogenous CARDINAL in HL-1 cardiomyocytes, followed by deep sequencing. CARDINAL transcripts were localized at ~100 genes, with the majority (76%) of CARDINAL peaks occupying the transcriptional start site (TSS) of gene promoters. Strikingly, the majority of CARDINAL ChIRP peaks overlapped with SRF-bound ChIP peaks in the cardiac genome. Homer motif analyses of CARDINAL peaks identified enrichment for the SRF CArG box and TCF binding motifs for Elk1 and Elk4. Consistent with our previous findings, CARDINAL peaks were localized to canonical SRF/TCF-regulated genes, including Egr1, Elk4, and components of the AP-1 complex, such as c-Fos, Junb, and Jund. These findings highlight CARDINAL, similar to its protein coding neighbor gene myocardin, as a co-regulator of SRF-dependent gene transcription. CARDINAL, however, in contrast to myocardin, can repress SRF/TCF-dependent gene transcription, which is likely mediated by its unique ability to co-occupy SRF/TCF-bound gene promoters.

Abstract P1183: Phosphorylation Signatures Of Human Heart Failure: Characterizing Dilated Cardiomyopathy-associated Signaling Pathways At The Cardiomyocyte Intercalated Disc

Heart failure remains a highly prevalent condition with diverse etiology, yet the underlying signaling mechanisms are not fully understood. Despite the profound effects of post-translational protein modifications on downstream signaling, limited studies have investigated the cardiac phosphoproteome in human heart failure. We hypothesized that a combined proteomic and phosphoproteomic analysis of human dilated (DCM) and ischemic (ICM) cardiomyopathy would reveal novel etiology-associated disease pathways. Integrative analyses of left ventricular explants from DCM patients ( n =4) vs. non-failing controls ( n =4), and left ventricular infarct vs. non-infarct, and peri-infarct vs. non-infarct regions of ICM patients ( n =4) identified 5,570 unique proteins with 13,624 corresponding phosphorylation sites. Each pair-wise comparison revealed shared and etiology-specific signatures, with a unique DCM-associated enrichment of cell-cell adhesion pathways. We focused our attention on αT-catenin (CTNNA3) as a cardiomyocyte intercalated disc candidate phosphoprotein with a unique cluster of 4 hyperphosphorylated sites in DCM hearts ( P &lt;0.0001). Overexpression of non-phosphorylatable hCTNNA3 in ex vivo isolated adult mouse cardiomyocytes showed internalized protein expression and weaker cell-cell adhesion vs. wildtype (WT) and phospho-mimetic forms. We established an in vivo mouse model using recombinant adeno-associated virus 9 (rAAV9) harboring hCTNNA3-WT, hCTNNA3-phospho-null, or empty rAAV9 control. Phospho-null CTNNA3 mice developed left ventricular dilation and contractile dysfunction (% EF; 51.25±1.17 phospho-null vs. 62.07±1.20 WT vs. 66.76±1.42 empty; n ≥10) with impaired left ventricular conduction velocity (cm/s; 36.83±1.10 phospho-null vs. 47.74±2.04 WT; n =6), by echocardiography and ex vivo optical mapping. Loss of CTNNA3 phosphorylation led to intercalated disc remodeling with internalization and dissociation of CTNNA3, connexin 43, N-cadherin, β-catenin, and plakophilin 2 from the adherens junction, using high-resolution confocal imaging. Together these findings reveal a compensatory role for αT-catenin phosphorylation in maintaining cardiomyocyte intercalated disc organization in human DCM.

Abstract P1115: Epicardial Signaling Regulates Myocardial Contractility Via Mirna

Background: A congenital left ventricular aneurysm is a rare cardiac malformation that maycause heartfailure, ventricular wall rupture, ventricular arrythmia or sudden cardiac death. However, mechanisms of congenital left ventricular aneurysm are not known. Paracrinesignals from cardiomyocytes, such as a cardiokine, prokineticin-2, can activate EPDCsdifferentiation in adult heart to promote neovascularization. How the reciprocal interaction viaprokineticin and miRs from epicardium to cardiomyocytes affect heart growth and function,and how EMT-related events contributecardiomyocyte proliferation and function areunknown. MicroRNA (miR124) has an important role in the adult heart, however, its role incardiac development is unknown. Results: Here in this study, by deletion of a prokineticin-2 receptor PKR1 through epicardialcell linage tracing at the different developmental stages of mice embryos, we found that thesemice exhibited ventricular rupture and embryonic lethality. Indeed, miR-124 was significantlyupregulated in PKR1 -deficient epicardial cells both in vitro and in vivo , whereas ectopicexpression of these miRs in epicardial cells resulted in the reduced expression of SNAI2 andsubsequently led to impaired EMT and EMT-related events such impaired migration andincreased apoptosis. Wild type mice cardiomyocytes that were cultured in condition mediumderived from PKR1-deficient epicardial cells had a lower beating rate and contractility. Treatment of the cardiomyocytes with miR-124mimic exhibited the same phenotype, that wasrestored by miR-124 inhibitor, indicating involvement of mir124 in epicardium-cardiomyocyte communication and regulation of cardiomyocyte contractility. Conclusion: These finding reveals a key signaling pathway in which a cardiokine,prokineticin-2 promotes EMT to form EPDCs and their migration in an autocrine manner, andsupports myocardial growth and contractility through repressing miR124. Our study mayprovide novel insight in etiology of congenital defects and new strategies to promotemyocardial regeneration.

Abstract P3037: MicroRNA-205 Is Required For Normal Cell Cycle And Cardiac Growth In The Neonatal Mouse Heart.

After birth, most newborn mouse cardiomyocytes (CM) undergo a final cycle of cell division in the absence of cytokinesis, which leads to binucleation. The majority of subsequent increases in cardiac mass are attributable to cardiomyocyte hypertrophy, as a negligible number of new CM are created after birth. Mice with a heart-specific deletion of Dicer, a crucial enzyme necessary for microRNA maturation, die by the fifth postnatal day in spite of having normal cardiac morphology and function at birth. Despite the significance of this phenomenon, little is known about the molecular/genetic foundation for the change from hyperplastic to hypertrophic-based myocardial expansion that occurs in the neonatal mouse heart. We hypothesize that a microRNA is required for the normal transition from fetal to adult heart during the neonatal period. Heart microRNA profiles (3 arrays/time point) were measured from RNA was isolated from E19, 1, 3, 5, 7, 10, and 35-day-old mouse hearts (9 hearts/time point pooled). Bioinformatic analysis identified microRNA-205 as a possible participant in the cardiac transitional program. We observed a transient 20-fold increase in miR205 expression between postnatal days 1 and 5, with levels returning to baseline by day 10. In-situ hybridization revealed miR-205 expression is restricted to the heart's epicardium.We next generated mice with a CM-specific deletion of miR205 using MHCcre targeting of a floxed-miR205 allele. Mice lacking miR-205 in their CM appear normal at birth. Elevated cell cycle markers (Ki67 &amp; phospho-pH3) were detected at postnatal day-14 with 20% larger hearts at postnatal day 14, and adult hearts measuring up to 50% larger than controls. In contrast, a CM-specific miR205 over-expression mouse model resulted in more CM being present at both 5-day and 14-day post-birth. Interestingly, no difference in cell-cycle markers or heart size was observed. miR205 directly targets YAP within the evolutionarily conserved hippo pathway, which regulates organ size. YAP protein expression is significantly increased in hearts lacking miR205. Both of the miR205-heart models present with altered Hippo signaling kinetics after birth. We conclude that miR205 regulates postnatal heart size by directly modulating the Hippo pathway.

Abstract P2070: The Microprotein Another-Regulin Regulates Serca2a In Response To Neurohormonal Signaling

Objective: Calcium (Ca 2+ ) regulation is a key component of proper heart function and is largely controlled by the sarco/endoplsmic reticulum Ca 2+ ATPase 2a (SERCA2a). Ca 2+ dysregulation is a hallmark feature of heart failure, yet few advances have been made to reestablish Ca 2+ homeostasis during disease. Another-regulin (ALN) inhibits SERCA2a, though little is known about how ALN functions in heart physiology and disease. Here, we determine a mechanism by which ALN is regulated via phosphorylation at serine 19 (S19), resulting in dissociation from SERCA2a. Methods and Results: ALN phosphorylation at S19 was confirmed via Phos-tag gel migration assay and site directed mutagenesis (SDM), whereby serine to alanine (S19A) mutation abolished the migrational shift which was confirmed with a custom S19 phospho-specific antibody. Effects of S19 phosphorylation on ALN-SERCA2a affinity were investigated using co-immunoprecipitation (IP) and fluorescence resonance energy transfer (FRET) in HEK293 cells. In addition to phosphodeficient S19A, SDM was used to mutate S19 to phosphomimetic aspartate (S19D) and glutamate (S19E). IPs of SERCA2a and hemagglutinin (HA)-tagged ALN WT, S19A, S19D, or S19E revealed less interaction between SERCA2a and ALN-S19D/E, suggesting S19 phosphorylation causes ALN dissociation from SERCA2a. Acceptor sensitization and fluorescence lifetime measurements show that ALN-S19D decreases ALN/SERCA2a binding affinity. To investigate signaling upstream of ALN phosphorylation, adult mouse cardiomyocytes were stimulated with various agonists and levels of pALN measured. Phosphorylation was significantly induced with the neurohormonal stimuli endothelin-1 and phenylephrine compared to DMSO and the β-adrenergic stimulus isoproterenol, suggesting Gαq/PKC pathway involvement. In addition, pALN levels are elevated in whole heart lysates of mice subject to transverse aortic constriction which is a model of pathological hypertension. Conclusions: These results indicate that ALN is phosphorylated at S19 in response to neurohormonal stimuli, resulting in dissociation from SERCA2. Future directions will investigate the impact of ALN phosphorylation on SERCA2 activity and heart function.

Abstract P3161: Engineering Mesenchymal Stem Cell-derived Extracellular Vesicles To Enhance Their Therapeutic Efficacy In Cardiovascular Disease

Background: Extracellular vesicles derived from cardiosphere-derived cells (CDC-EVs) have demonstrated the ability to regulate cardiomyocyte apoptosis and induce cardiomyocyte proliferation in pre-clinical models of acute MI. While CDC-EVs exhibit cardioprotective effects, they require invasive intramyocardial injections to achieve therapeutic efficacy, detracting from their translatability. Mesenchymal stem cells (MSC) also generate cardioprotective EVs (MSC-EVs), which have demonstrated therapeutic efficacy in models of cardiac disease following intravenous administration. However, MSC-EVs lack several of the cardioprotective miRs expressed by CDC-EVs, including miR146a, which has been shown to modulate cardiomyocyte apoptosis. The objective of our current study was to determine the effect of enriching MSC-EVs with cardioprotective CDC-EV miRNA on cardiomyocyte apoptosis. Methods: MSCs were transfected with miR-146a-5p mimics using Trans-IT TKO in serum free growth media. EVs were isolated using a combination of ultrafiltration and size exclusion chromatography (SEC) and characterized by size, morphology and expression of surface markers. RT-PCR was performed on EV samples to quantify miR-146a expression. Primary neonatal mouse cardiomyocytes were treated with MSC-EVs, miR-146a loaded MSC-EVs, CDC-EVs or matched volume vehicle control. Cardiomyocyte apoptosis was assessed by a TUNEL assay. Results: Treatment with miR-146a loaded MSC EVs reduced cardiomyocyte apoptosis compared with cardiomyocytes treated with unmodified MSC exosomes (14±1% vs. 31±3%) (mean ± SEM, p=0.001, one-way ANOVA). miR-146a loaded MSC-EVs and CDC-EVs demonstrated a similar level of reduction in cardiomyocyte apoptosis (14±1% vs. 15±1%). There was no difference in the level of apoptosis between cardiomyocytes treated with unmodified MSC exosomes and cardiomyocytes treated with vehicle control (31±3% vs. 27±1%) (mean ± SEM, p=0.366, one-way ANOVA). Conclusion: Engineering MSC-EVs to express miR-146a enhances their ability to reduce cardiomyocyte apoptosis in vitro . This highlights the potential of cargo engineering as a means to improve the therapeutic efficacy of EVs for cardiovascular disease.

T-tubule recovery after detubulation in isolated mouse cardiomyocytes.

Remodeling of cardiac t-tubules in normal and pathophysiological conditions is an important process contributing to the functional performance of the heart. While it is well documented that deterioration of t-tubule network associated with various pathological conditions can be reversed under certain conditions, the mechanistic understanding of the recovery process is essentially lacking. Accordingly, in this study we investigated some aspects of the recovery of t-tubules after experimentally-induced detubulation. T-tubules of isolated mouse ventricular myocytes were first sealed using osmotic shock approach, and their recovery under various experimental conditions was then characterized using electrophysiologic and imaging techniques. The data show that t-tubule recovery is a strongly temperature-dependent process involving reopening of previously collapsed t-tubular segments. T-tubule recovery is slowed by (1) metabolic inhibition of cells, (2) reducing influx of extracellular Ca2+ as well as by (3) both stabilization and disruption of microtubules. Overall, the data show that t-tubule recovery is a highly dynamic process involving several central intracellular structures and processes and lay the basis for more detailed investigations in this area.

FAM210A regulates mitochondrial translation and maintains cardiac mitochondrial homeostasis.

Mitochondria play a vital role in cellular metabolism and energetics and support normal cardiac function. Disrupted mitochondrial function and homeostasis cause a variety of heart diseases. Fam210a (family with sequence similarity 210 member A), a novel mitochondrial gene, is identified as a hub gene in mouse cardiac remodelling by multi-omics studies. Human FAM210A mutations are associated with sarcopenia. However, the physiological role and molecular function of FAM210A remain elusive in the heart. We aim to determine the biological role and molecular mechanism of FAM210A in regulating mitochondrial function and cardiac health in vivo. Tamoxifen-induced αMHCMCM-driven conditional knockout of Fam210a in the mouse cardiomyocytes induced progressive dilated cardiomyopathy and heart failure, ultimately causing mortality. Fam210a deficient cardiomyocytes exhibit severe mitochondrial morphological disruption and functional decline accompanied by myofilament disarray at the late stage of cardiomyopathy. Furthermore, we observed increased mitochondrial reactive oxygen species production, disturbed mitochondrial membrane potential, and reduced respiratory activity in cardiomyocytes at the early stage before contractile dysfunction and heart failure. Multi-omics analyses indicate that FAM210A deficiency persistently activates integrated stress response, resulting in transcriptomic, translatomic, proteomic, and metabolomic reprogramming, ultimately leading to pathogenic progression of heart failure. Mechanistically, mitochondrial polysome profiling analysis shows that FAM210A loss of function compromises mitochondrial mRNA translation and leads to reduced mitochondrial-encoded proteins, followed by disrupted proteostasis. We observed decreased FAM210A protein expression in human ischaemic heart failure and mouse myocardial infarction tissue samples. To further corroborate FAM210A function in the heart, AAV9-mediated overexpression of FAM210A promotes mitochondrial-encoded protein expression, improves cardiac mitochondrial function, and partially rescues murine hearts from cardiac remodelling and damage in ischaemia-induced heart failure. These results suggest that FAM210A is a mitochondrial translation regulator to maintain mitochondrial homeostasis and normal cardiomyocyte contractile function. This study also offers a new therapeutic target for treating ischaemic heart disease.

LncRNA Miat knockdown protects against pirarubicin-induced cardiotoxicity by targeting miRNA-129-1-3p.

Pirarubicin (THP) is a widely used antitumor drug in clinical practice, but its cardiotoxicity limits its use. The aim of this study was to investigate the protective effect and mechanism of knockdown of lncRNA Miat in THP-induced cardiotoxicity. The extent of damage to immortalized cardiomyocytes in mice was assessed by CCK8, TUNEL, ROS, Ca2+ , RT-qPCR, and Western blot. The relative levels of Miat in THP-treated cardiomyocytes (HL-1) were measured. The protective effect of Miat on THP-treated HL-1 was assessed. The binding relationship between lncRNA Miat and mmu-miRNA-129-1-3p was verified by a dual luciferase reporter gene assay. The protective role of Miat/miRNA-129-1-3p in THP-induced HL-1 was explored by performing a rescue assay. THP reduced cell viability, induced apoptosis, triggered oxidative stress and calcium overload. Expression of Miat in HL-1 was significantly elevated after THP treatment. Miat knockdown significantly alleviated the cardiotoxicity of THP. MiR-129-1-3p is a direct target of Miat. Knockdown of miR-129-1-3p reversed the protective effect of Miat knockdown on HL-1. Miat knockdown can alleviate THP-induced cardiomyocyte injury by regulating miR-129-1-3p.