Cardiac Myocyte Nuclei Research Articles

Abstract P319: Eliminating Cardiotoxicity In Alpha1-adrenergic Receptor Antagonists

Introduction: Alpha-1 adrenergic receptor (α1-AR) antagonists (α1-blockers) are efficacious antihypertensives, but ALLHAT found that doxazosin (Dzn) doubled the risk of heart failure (HF). We previously demonstrated that α1-ARs, specifically the α1A-AR, protect the heart, explaining the worse outcomes with Dzn in ALLHAT. Interestingly, α1-ARs localize to and signal at the nucleus in cardiac myocytes (CM), whereas α1-ARs localize to the sarcolemma in smooth muscle (SM). Hypothesis: We hypothesize that a membrane impermeant α1-blocker would inhibit α1-ARs in SM, reducing blood pressure, but preserve protective α1-signaling in CMs, preventing HF. Methods: We developed an α1A-AR homology model to define the structural basis of α1-blocker binding and modified existing α1-blocker structure to reduce cardiotoxicity. Using this model, we designed 30 compounds, synthesized 9 in gram quantities, and tested 2 compounds. Results and Conclusions: Binding assays identified 2 novel high affinity α1-ligands; α1705 (IC50 = 5.2 [CI:3.5,7.6] nM, n=3) and α1707 (5.8 [CI:4.2,8.1] nM, n=3) (Dzn: 7.7 [CI:6.3,9.2] nM, n=6). Uptake assays in cultured CM indicated uptake of Prazosin (10 μM Prz: 230 nM in CMs detected by mass spectrometry), whereas α1705 and α1707 were not detected. In HEK cells expressing α1A-AR at the cell surface, Prz, α1705, and α1707 (all 2 μM) inhibited Ca2+ transients (90%, 76%, 88%) induced by the α1A agonist A61603 (20 μM). In CM, A61603 increased ERK phosphorylation (1.55±0.04 fold, n=7, P<0.0001), a survival signal, which was blocked by Prz (1.21±0.06 fold, n=7, P=NS), but not α1705 (1.72±0.13 fold, n=7, P<0.001). Further, A61603 (20 μM) inhibited H202-induced CM death (-17.4±7.6%, n=5), which was reversed by Prz (30.9±15.4%, n=5, P=0.035), but not α1705 (-0.94±11.6%, n=5, P=NS). In DOCA-salt hypertensive mice, infusion of Prz or α1705 (2 mg/kg/d, 3 d) lowered systolic pressure (Cont: +18.9 mmHg, n=1; Prz: 6.4±3.2 mmHg, n=3, α1705: -6.1±5.6 mmHg, n=3), and while Prz was detected in CMs following 4 d, α1705 was not. In conclusion, we have developed a novel membrane impermeant α1-blocker with reduced cardiotoxicity that could improve hypertension outcomes, especially in patients suffering from chronic kidney disease or benign prostatic hyperplasia.

SERCA Activity Controls the Systolic Calcium Increase in the Nucleus of Cardiac Myocytes.

In cardiomyocytes, nuclear calcium is involved in regulation of transcription and, thus, remodeling. The cellular mechanisms regulating nuclear calcium, however, remain elusive. Therefore, the aim of this study was to identify and characterize the factors that regulate nuclear calcium in cardiomyocytes. We focused on the roles of (1) the cytoplasmic calcium transient (CaT), (2) the sarcoplasmic/endoplasmic reticulum calcium ATPase (SERCA), and (3) intracellular calcium stores for nuclear calcium handling. Experiments were performed on rat ventricular myocytes loaded with Fluo-4/AM. Subcellularly resolved CaTs were visualized using confocal microscopy. The cytoplasmic CaT was varied by reducing extracellular calcium (from 1.5 to 0.3 mM) or by exposure to isoprenaline (ISO, 10 nM). SERCA was blocked by thapsigargin (5 μM). There was a strict linear dependence of the nucleoplasmic CaT on the cytoplasmic CaT over a wide range of calcium concentrations. Increasing SERCA activity impaired, whereas decreasing SERCA activity augmented the systolic calcium increase in the nucleus. Perinuclear calcium store load, on the other hand, did not change with either 0.3 mM calcium or ISO and was not a decisive factor for the nucleoplasmic CaT. The results indicate, that the nucleoplasmic CaT is determined largely by the cytoplasmic CaT via diffusion of calcium through nuclear pores. They identify perinuclear SERCA activity, which limits the systolic calcium increase in the nucleus, as a novel regulator of the nuclear CaT in cardiac myocytes.

Nuclear calcineurin is a sensor for detecting Ca2+ release from the nuclear envelope via IP3R.

In continuously beating cells like cardiac myocytes, there are rapid alterations of cytosolic Ca2+ levels. We therefore hypothesize that decoding Ca2+ signals for hypertrophic signaling requires intracellular Ca2+ microdomains that are partly independent from cytosolic Ca2+. Furthermore, there is a need for a Ca2+ sensor within these microdomains that translates Ca2+ signals into hypertrophic signaling. Recent evidence suggested that the nucleus of cardiac myocytes might be a Ca2+ microdomain and that calcineurin, once translocated into the nucleus, could act as a nuclear Ca2+ sensor. We demonstrate that nuclear calcineurin was able to act as a nuclear Ca2+ sensor detecting local Ca2+ release from the nuclear envelope via IP3R. Nuclear calcineurin mutants defective for Ca2+ binding failed to activate NFAT-dependent transcription. Under hypertrophic conditions Ca2+ transients in the nuclear microdomain were significantly higher than in the cytosol providing a basis for sustained calcineurin/NFAT-mediated signaling uncoupled from cytosolic Ca2+. Measurements of nuclear and cytosolic Ca2+ transients in IP3 sponge mice showed no increase of Ca2+ levels during diastole as we detected in wild-type mice. Nuclei, isolated from ventricular myocytes of mice after chronic Ang II treatment, showed an elevation of IP3R2 expression which was dependent on calcineurin/NFAT signaling and persisted for 3weeks after removal of the Ang II stimulus. These data provide an explanation how Ca2+ and calcineurin might regulate transcription in cardiomyocytes in response to neurohumoral signals independently from their role in cardiac contraction control. KEY MESSAGES: • Calcineurin acts as an intranuclear Ca2+ sensor to promote NFAT activity. • Nuclear Ca2+ in cardiac myocytes increases via IP3R2 upon Ang II stimulation. • IP3R2 expression is directly dependent on calcineurin/NFAT.

30-Year-Old Man With Outside-of-Hospital Cardiac Arrest

30-Year-Old Man With Outside-of-Hospital Cardiac Arrest

Transplantation of cardiac stem cells overexpressing integrin-linked kinase improves cardiac function in a rat model of acute myocardial infarction

Objective: To investigate the effect of cardiac stem cells (CSC) overexpressing integrin-linked kinase (ILK-CSC) transplantation on cardiac function after myocardial infarction (MI) and related mechanism. Methods: CSCs were isolated from the hearts of neonatal Sprague-Dawley (SD) rats and ILK-CSC were established by transfecting recombinant adenoviral vector harboring human wild-type ILK cDNA. Forty 8-week-old rats were randomly divided into 4 groups (n=10 each group): sham group, MI plus saline injection group(saline group), MI plus CSC transfected with null vector injection group (Ad-null-CSC group), and MI plus ILK-CSC injection group(ILK-CSC group). MI was induced through coronary artery ligation, and after 15 minutes, 30 μl saline, Ad-null-CSC (1×10(5) cells/30 μl) or ILK-CSC (1×10(5) cells/30 μl) were injected into the hearts of MI rats at 3 different points in infracted zone and infarct border zone. After 4 weeks, left ventricular (LV) function was examined by echocardiography, LV fibrosis was detected by HE and Masson staining, and myocardial protein expression of Ki-67 and p-H3 was evaluated by immuohistochemistry and mRNA expression of cyclinD1 and PCNA was detected by real-time RT-PCR. Results: (1) Thirty-seven rats (sham group=10, saline group=8, Ad-null-CSC group=9 and ILK-CSC group=10) survived at 4 weeks after operation. Left ventricular end-systolic dimension (LVESD, P=0.009) and left ventricular end-diastolic dimension (LVEDD, P=0.002) were significantly increased, and left ventricular ejection fraction(LVEF, P=0.006) was decreased in saline group compared with those of sham group.In Ad-null-CSC group LVESD (P=0.005) and LVEDD (P=0.003) were decreased, but LVEF remained unchanged (P=0.113) compared with those of saline group. LVESD (P=0.004) and LVEDD (P=0.000 1) of ILK-CSC group were significantly decreased, and LVEF (P=0.004) was significantly increased compared with those of Ad-null-CSC group. (2) LV histology and myocardial fibrosis: there were marked myocyte loss and significant increase of myocardial fibrosis in the saline group((70.6±5.1) %, P=0.002) and Ad-null-CSC group((57.7±3.4) %, P=0.001) compared with sham group ((8.2±2.2) %), while the fibrosis was significantly attenuated post injection of ILK-CSC ((30.6±7.0)%, P=0.005 vs. Ad-null-CSC). (3) Protein levels of mitotic genes: the results of immuohistochemistry showed that the brown positive particles were presented in the nuclei of cardiac myocytes in saline, Ad-null-CSC and ILK-CSC groups, but they were negative in sham group. The protein expression of Ki-67 (P=0.007) and phosphohistone-H3 (p-H3) (P=0.003) in ILK-CSC group was significantly higher than in Ad-null-CSC group. (4) mRNA levels of mitotic genes: the results of real-time RT-PCR showed that the mRNA levels of cyclinD1 and proliferating cell nuclear antigen (PCNA) in saline and Ad-null-CSC groups were similar as in sham group (all P>0.05). However, in ILK-CSC group they were significantly increased compared with those in Ad-null-CSC group (cyclinD1, P=0.003; PCNA, P=0.004). Conclusion: Our results suggest that myocardial transplantation of CSC overexpressing ILK improves cardiac function in the post-MI rats, and this beneficial effect may be related to the enhanced proliferation of cardiac myocytes and attenuated myocardial fibrosis.

Compartmentalized Gαq-Signaling in Adult Cardiac Myocytes

Gαq-coupled G-protein receptors (Gq-receptors), including α1-adrenergic and angiotensin receptors (α1-AR, AT-R), activate cardiac signaling pathways controlling hypertrophy, cell survival/death, and inotropy. Early studies in cell and animal models established the convention that Gq-signaling exacerbates heart failure (HF). However, clinically, AT-R antagonists improve HF outcomes, whereas α1-AR antagonists worsen HF, suggesting Gq-receptors are functionally unique. Our work indicates that α1-ARs are unique cardiac Gq-receptors by inducing cardioprotection and localizing to the nucleus in adult cardiac myocytes, suggesting that subcellular localization might form the mechanistic basis for unique Gq-receptor function. Here, we test the hypothesis that α1-ARs and AT-Rs localize to and initiate proximal signaling in distinct subcellular compartments. Using a novel fluorescent α1-ligand that improves the dynamics of defining receptor localization, we detected α1-ARs only at the nucleus in adult cardiac myocytes and isolated nuclei. Conversely, using a fluorescent AT-R ligand, we detected AT-Rs at the sarcolemma and the t-tubules. To measure proximal Gq-receptor signaling, we employed a fluorescent probe, GFP-PHD, that binds phosphatidylinositol-4,5-bisphosphate (PIP2) in the membrane and is released when phospholipase Cβ (PLCβ) cleaves PIP2. In adult cardiac myocytes, GFP-PHD localized to the sarcolemma and t-tubules, but not the nucleus, consistent with previous reports. Angiotensin, but not phenylephrine, induced movement of GFP-PHD off of the sarcolemma and t-tubules. The failure to detect GFP-PHD at the nucleus indicates that either PIP2 is excluded from nuclear membranes or that the probe fails to target the nucleus. Addition of a nuclear localization sequence to GFP-PHD (NLS-GFP-PHD) produced nuclear localization of GFP-PHD suggesting the presence of PIP2 in nuclear membranes in adult cardiac myocytes. Phenylephrine, and to a lesser extent, angiotensin induced movement of NLS-GFP-PHD off the nuclear membrane. In summary, our data demonstrate that α1-ARs and AT-Rs localize to and initiate proximal signaling in unique subcellular compartments.

Curcumin Analogue GO-Y030 Significantly Improves Pressure Overload-induced Heart Failure in Vivo

Signals activated by increased hemodynamic overload to the heart finally reach the nuclei of cardiac myocytes and induce maladaptive hypertrophy in them. Nuclear acetylation, which is controlled by histone deacetylases and the intrinsic histone acetyltransferase p300, is a critical event in this process. We previously found that a natural p300 HAT inhibitor, curcumin, can inhibit cardiomyocyte hypertrophy and the development of heart failure in vivo. However, curcumin is insoluble in water, and its bioavailability is low. Therefore, a more efficient system for heart failure therapy is desirable for actual clinical practice. To overcome this limitation, we recently synthesized a curcumin analog, GO-Y030, which possesses stronger anti-cancer activity than curcumin. However, the effect of GO-Y030 on heart failure is still unclear. The purpose of this study was to determine whether GO-Y030 inhibits p300-HAT activity and can be used as a therapeutic agent for heart failure.

Estrogen receptor profiling and activity in cardiac myocytes

Estrogen signaling appears critical in the heart. However a mechanistic understanding of the role of estrogen in the cardiac myocyte is lacking. Moreover, there are multiple cell types in the heart and multiple estrogen receptor (ER) isoforms. Therefore, we studied expression, localization, transcriptional and signaling activity of ERs in isolated cardiac myocytes. We found only ERα RNA (but no ERβ RNA) in cardiac myocytes using two independent methods. The vast majority of full-length ERα protein (ERα66) localizes to cardiac myocyte nuclei where it is competent to activate transcription. Alternate isoforms of ERα encoded by the same genomic locus (ERα46 and ERα36) have differential transcriptional activity in cardiac myocytes but also primarily localize to nuclei. In contrast to other reports, no ERα isoform is competent to activate MAPK or PI3K signaling in cardiac myocytes. Together these data support a role for ERα at the level of transcription in cardiac myocytes.

Deciphering the Epigenetic Code of Cardiac Myocyte Transcription.

Epigenetic mechanisms are crucial for cell identity and transcriptional control. The heart consists of different cell types, including cardiac myocytes, endothelial cells, fibroblasts, and others. Therefore, cell type-specific analysis is needed to gain mechanistic insight into the regulation of gene expression in cardiac myocytes. Although cytosolic mRNA represents steady-state levels, nuclear mRNA more closely reflects transcriptional activity. To unravel epigenetic mechanisms of transcriptional control, cell type-specific analysis of nuclear mRNA and epigenetic modifications is crucial. The aim was to purify cardiac myocyte nuclei from hearts of different species by magnetic- or fluorescent-assisted sorting and to determine the nuclear and cellular RNA expression profiles and epigenetic marks in a cardiac myocyte-specific manner. Frozen cardiac tissue samples were used to isolate cardiac myocyte nuclei. High sorting purity was confirmed for cardiac myocyte nuclei isolated from mice, rats, and humans. Deep sequencing of nuclear RNA revealed a major fraction of nascent, unspliced RNA in contrast to results obtained from purified cardiac myocytes. Cardiac myocyte nuclear and cellular RNA expression profiles showed differences, especially for metabolic genes. Genome-wide maps of the transcriptional elongation mark H3K36me3 were generated by chromatin-immunoprecipitation. Transcriptome and epigenetic data confirmed the high degree of cardiac myocyte-specificity of our protocol. An integrative analysis of nuclear mRNA and histone mark occurrence indicated a major impact of the chromatin state on transcriptional activity in cardiac myocytes. This study establishes cardiac myocyte-specific sorting of nuclei as a universal method to investigate epigenetic and transcriptional processes in cardiac myocytes of different origins. These data sets provide novel insight into cardiac myocyte transcription.

Transgenic systems for unequivocal identification of cardiac myocyte nuclei and analysis of cardiomyocyte cell cycle status.

Even though the mammalian heart has been investigated for many years, there are still uncertainties in the fields of cardiac cell biology and regeneration with regard to exact fractions of cardiomyocytes (CMs) at different developmental stages, their plasticity after cardiac lesion and also their basal turnover rate. A main shortcoming is the accurate identification of CM and the demonstration of CM division. Therefore, an in vivo model taking advantage of a live reporter-based identification of CM nuclei and their cell cycle status is needed. In this technical report, we describe the generation and characterization of embryonic stem cells and transgenic mice expressing a fusion protein of human histone 2B and the red fluorescence protein mCherry under control of the CM specific αMHC promoter. This fluorescence label allows unequivocal identification and quantitation of CM nuclei and nuclearity in isolated cells and native tissue slices. In ventricles of adults, we determined a fraction of <20 % CMs and binucleation of 77–90 %, while in atria a CM fraction of 30 % and a binucleation index of 14 % were found. We combined this transgenic system with the CAG-eGFP-anillin transgene, which identifies cell division and established a novel screening assay for cell cycle-modifying substances in isolated, postnatal CMs. Our transgenic live reporter-based system enables reliable identification of CM nuclei and determination of CM fractions and nuclearity in heart tissue. In combination with CAG-eGFP-anillin-mice, the cell cycle status of CMs can be monitored in detail enabling screening for proliferation-inducing substances in vitro and in vivo.Electronic supplementary materialThe online version of this article (doi:10.1007/s00395-015-0489-2) contains supplementary material, which is available to authorized users.

Circulation Research “In This Issue” Anthology

<i>Circulation Research</i> “In This Issue” Anthology

Abstract 304: Crystal Structure Of Fak/mef2 Complex Reveals The Role Of Fak In The Regulation Of Mef2 Transcription Factor.

Members of MEF2 (Myocyte Enhancer Factor 2) family of transcription factors are major regulators of cardiac development and homeostasis. Their functions are regulated at several levels, including the association with a variety of protein partners. We have previously shown that FAK (Focal Adhesion Kinase) regulates the stretch-induced activation of MEF2 in cardiomyocytes. But, the molecular mechanisms, involved in this process, are unclear. Here, we integrated biochemical, imaging and structural analyses to characterize a novel interaction between MEF2 and FAK. An association between MEF2 and FAK was detected by co-immunoprecipitation in the extracts of stretched cardiomyocytes (10%, 60Hz, 2 hours). MEF2 and FAK staining were co-localized in the nuclei of stretched cells. Pull down assays indicated that the Focal Adhesion Targeting (FAT) domain is sufficient to confer FAK interaction with MEF2. Gene reporter assays indicated that the interaction with FAK enhances the MEF2C transcriptional activity in cultured cardiomyocytes. Also, we present a 2.9-Å X-ray crystal structure for the FAK_FAT domain bound to MEF2C (1-95), comprised by the MADS box/MEF2 domain. The structural information, when used in combination with biochemical studies, small-angle X-ray scattering (SAXS) data and reporter gene assay, lead to a mechanistic model describing how FAK binds to MEF2C and stimulates its transcription function in cardiomyocytes. We further validated this model by showing that the binding of FAK to MEF2C is essential for the hypertrophy of cardiomyocyte in response to mechanical stress. Our results present FAK as a new positive regulator of MEF2, implicated in the fine control of the signal transduction between focal adhesions and the nucleus of cardiac myocytes during mechanical stress.

Cardiac Alpha1-Adrenergic Receptors: Novel Aspects of Expression, Signaling Mechanisms, Physiologic Function, and Clinical Importance

Adrenergic receptors (AR) are G-protein-coupled receptors (GPCRs) that have a crucial role in cardiac physiology in health and disease. Alpha1-ARs signal through Gαq, and signaling through Gq, for example, by endothelin and angiotensin receptors, is thought to be detrimental to the heart. In contrast, cardiac alpha1-ARs mediate important protective and adaptive functions in the heart, although alpha1-ARs are only a minor fraction of total cardiac ARs. Cardiac alpha1-ARs activate pleiotropic downstream signaling to prevent pathologic remodeling in heart failure. Mechanisms defined in animal and cell models include activation of adaptive hypertrophy, prevention of cardiac myocyte death, augmentation of contractility, and induction of ischemic preconditioning. Surprisingly, at the molecular level, alpha1-ARs localize to and signal at the nucleus in cardiac myocytes, and, unlike most GPCRs, activate "inside-out" signaling to cause cardioprotection. Contrary to past opinion, human cardiac alpha1-AR expression is similar to that in the mouse, where alpha1-AR effects are seen most convincingly in knockout models. Human clinical studies show that alpha1-blockade worsens heart failure in hypertension and does not improve outcomes in heart failure, implying a cardioprotective role for human alpha1-ARs. In summary, these findings identify novel functional and mechanistic aspects of cardiac alpha1-AR function and suggest that activation of cardiac alpha1-AR might be a viable therapeutic strategy in heart failure.

Abstract 18006: Nuclear Calcineurin is a Sensor for Detecting Ca2+ Release From the Nuclear Envelope via InsP3R

Background: Recent evidence demonstrates that not only NFAT, but also calcineurin (CN) is translocated to the nucleus upon hypertrophic stimulation. It was also shown that calpain-mediated degradation caused a constitutive active CN. We hypothesised 1) that nuclear CN is an intranuclear Ca2+ sensor, 2) that the nucleus in cardiac myocytes is a Ca2+ microdomain largely independent of cytosolic Ca2+ alterations and that 3) inhibition of nuclear translocation of CN is a therapeutic strategy to prevent hypertrophy. Methods: Employing a transgene mouse model with conditional calpastatin overexpression (resulting in calpain inhibition), different adenoviral CN mutants and confocal microscopy in isolated adult cardiac myocytes we investigated CN translocation and nuclear Ca2+ transients. Assessment of cardiac function in transgenic animals was performed by MRI. Results: We could demonstrate that chronic Ang II stimulation of mice caused calpain-mediated degradation of CN resulting in a constitutive active CN with nuclear translocation. The constitutive active CN in the nucleus escaped degradation by the UPS and sustained an ongoing hypertrophic response, even after removal of Ang II. Transgenic inhibition of calpain by calpastatin overexpression prevented proteolysis of CN and allowed for relocation of CN from the nucleus back to the cytosol and regression of hypertrophy after removal of Ang II. Inhibition of the interaction between CN and the transport protein importin ß1 by an inhibitory peptide prevented nuclear translocation of activated CN. The synthetic peptide prevented myocardial hypertrophy in vivo. We were able to demonstrate that Ang II increases nuclear Ca2+ transients via nuclear InsP3 receptors. We also showed that Ca2+ levels are constantly elevated during diastole (up to 0.2 μM) in Ang II stimulated cardiac myocytes and that CN is able to act as nuclear Ca2+ sensor detecting this local Ca2+ release from the nuclear envelope via InsP3R. Nuclear CN mutants that are defective for Ca2+ activation failed to activate NFAT dependent transcription. Conclusion: These results provide an explanation how Ca2+ and CN can regulate transcription in cardiac myocytes in response to neurohumoral signals apart from Ca2+ changes in contraction regulation.

Components of the interleukin-33/ST2 system are differentially expressed and regulated in human cardiac cells and in cells of the cardiac vasculature

Interleukin-33 (IL-33) is a recently described member of the IL-1 family of cytokines, which was identified as a ligand for the ST2 receptor. Components of the IL-33/ST2 system were shown to be expressed in normal and pressure overloaded human myocardium, and soluble ST2 (sST2) has emerged as a prognostic biomarker in myocardial infarction and heart failure. However, expression and regulation of IL-33 in human adult cardiac myocytes and fibroblasts was not tested before. In this study we found that primary human adult cardiac fibroblasts (HACF) and human adult cardiac myocytes (HACM) constitutively express nuclear IL-33 that is released during cell necrosis. Tumor necrosis factor (TNF)-α, interferon (IFN)-γ and IL-1β significantly increased both IL-33 protein and IL-33 mRNA expression in HACF and HACM as well as in human coronary artery smooth muscle cells (HCASMC). The nuclear factor-κB (NF-κB) inhibitor dimethylfumarate inhibited TNF-α- and IL-1β-induced IL-33 production as well as nuclear translocation of p50 and p65 NF-κB subunits in these cells. Mitogen-activated protein/extracellular signal-regulated kinase inhibitor U0126 abrogated TNF-α-, IFN-γ-, and IL-1β-induced and Janus-activated kinase inhibitor I reduced IFN-γ-induced IL-33 production. We detected IL-33 mRNA in human myocardial tissue from patients undergoing heart transplantation (n=27) where IL-33 mRNA levels statistically significant correlated with IFN-γ (r=0.591, p=0.001) and TNF-α (r=0.408, p=0.035) mRNA expression. Endothelial cells in human heart expressed IL-33 as well as ST2 protein. We also reveal that human cardiac and vascular cells have different distribution patterns of ST2 isoforms (sST2 and transmembrane ST2L) mRNA expression and produce different amounts of sST2 protein. Both human macrovascular (aortic and coronary artery) and heart microvascular endothelial cells express specific mRNA for both ST2 isoforms (ST2L and sST2) and are a source for sST2 protein, whereas cardiac myocytes, cardiac fibroblasts and vascular SMC express only minor amounts of ST2 mRNA and do not secrete detectable amounts of sST2 antigen. In accordance with the cellular distribution of ST2 receptor, human cardiac fibroblasts and myocytes as well as HCASMC did not respond to treatment with IL-33, as recombinant human IL-33 did not induce NF-κB p50 and p65 subunits nuclear translocation or increase IL-6, IL-8, and monocyte chemoattractant protein (MCP-1) level in HACF, HACM and HCASMC. In summary, we found that endothelial cells seem to be the source of sST2 and the target for IL-33 in the cardiovascular system. IL-33 is expressed in the nucleus of human adult cardiac fibroblasts and myocytes and released during necrosis. Proinflammatory cytokines TNF-α, IFN-γ and IL-1β increase IL-33 in these cells in vitro, and IL-33 mRNA levels correlated with TNF-α and IFN-γ mRNA expression in human myocardial tissue.

Type 1 diabetes mellitus abrogates compensatory augmentation of myocardial neuregulin-1β/ErbB in response to myocardial infarction resulting in worsening heart failure

BackgroundDiabetes mellitus (DM) patients surviving myocardial infarction (MI) exhibit a substantially higher incidence of subsequent heart failure (HF). Neuregulin (NRG)-1 and erythroblastic leukemia viral oncogene homolog (ErbB) receptors have been shown to play a critical role in maintenance of cardiac function. However, whether myocardial NRG-1/ErbB is altered during post-MI HF associated with DM remains unknown. The aim of this study was to determine the impact of type 1 DM on the myocardial NRG-1/ErbB system following MI in relation to residual left ventricular (LV) function.MethodsType 1 DM was induced in rats via administration of streptozotocin (65 mg/kg, i.p.). Control rats were injected with citrate buffer (vehicle) only. Two weeks after induction of type 1 DM, MI was produced in DM and non-DM rats by ligation of the left coronary artery. Sham MI rats underwent the same surgical procedure with the exception that the left coronary artery was not ligated. At 4 weeks after surgery, residual in vivo LV function was assessed via echocardiography. Myocardial protein expression of NRG-1β, ErbB2 and ErbB4 receptors, and MDM2 (a downstream signaling pathway induced by NRG-1 that has been implicated in cell survival) was assessed in the remaining, viable LV myocardium by Western blotting. Changes in ErbB receptor localization in the surviving LV myocardium of diabetic and non-diabetic post-MI rats was determined using immunohistochemistry techniques.ResultsAt 4 weeks post-MI, echocardiography revealed that LV fractional shortening (FS) and LV ejection fraction (EF) were significantly lower in the DM + MI group compared to the MI group (LVFS: 17.9 ± 0.7 vs. 25.2 ± 2.2; LVEF: 35.5 ± 1.4 vs. 47.5 ± 3.5, respectively; P < 0.05), indicating an increased functional severity of HF among the DM + MI rats. Up-regulation of NRG-1β and ErbB2 protein expression in the MI group was abrogated in the DM + MI group concurrent with degradation of MDM2, a downstream negative regulator of p53. ErbB2 and ErbB4 receptors re-localized to cardiac myocyte nuclei in failing type 1 diabetic post-MI hearts.ConclusionsType 1 DM prevents compensatory up-regulation of myocardial NRG-1/ErbB after MI coincident with an increased severity of HF.

Mild Electrical Pulse Current Stimulation Upregulates S100A4 and Promotes Cardiogenesis in MSC and Cardiac Myocytes Coculture Monolayer

Parietal endoderm-secreted S100A4 promotes early cardiomyogenesis in embryoid bodies [1]. After an acute ischemic event, S100A4 protein appears in cardiac myocytes only in the border zone in rat and human hearts [2]. In wound research, a large outward current of 4 μA/cm(2) was always measured at the wound edges of rat cornea and human skin [3]. We hypothesize that a special electrical circumstance at the border zone may contribute to the phenomenon. An electric stimulation system was designed to give the cells electric pulse current stimulation (EPCS), the feature of the signal is pulse polarity altered one after another, rectangular 2 ms, 2 Hz, 40 μA. This intensity of stimulation is proved to be safe to cardiac myocytes (both in structure and beating behavior compared with the cardiac myocytes which do not receive stimulation) and MSCs (in cell vitality, proliferation, cell cycle, and gap junction generation potential) through our previous work. Canine MSCs are capable of generating voltage-sensitive Ca(2+) channel and Na(+) channels and generating the Ca(2+) handling system during differentiation. We found that CD44 was reduced in the MSCs monolayer treated with EPCS, compared with non-stimulated MSCs; and EPCS MSCs (3 h/day, 6 h/day, 5 days) showed an 14.04 ± 3.44 and 14.55 ± 3.97 % reduction in CD44, compared with the cotemporary MSCs; these reveal that CD44 reduction amplitude is not correlated with time for EPCS disposure and CD29 (integrin β1) expression is not affected by EPCS exposure. EPCS was given to the MSCs and cardiac myocytes coculture monolayer (ratio 3:1) for different time (1, 3, and 6 h/day) for 4 days to see the biological effects. Gap junction protein and troponin T show an increase after EPCS. We found that the gap junction protein Cx43 increased with treating time-in the EPCS group, it exhibited 1.5 and 1.7 fold in the 3 h/day group and 6 h/day group (P < 0.01), and troponin T exhibited to about 3.6 and 4.4 fold in the 3 h/day group (P < 0.01) and 6 h/day group (P < 0.05). Since coculture was used as stimuli, immunofluorescence was used to visualize the changes during EPCS for the purpose of elucidating the impact of EPCS on cardiac myocytes and MSCs. We found that after 5 days exposure, EPCS can enhance the expression of S100A4, which is 2.33 fold in cardiac myocytes (P < 0.01) and 1.99 fold in MSCs (P < 0.01) in gray value. A significant increasing expression of the myocyte enhancer factor (MEF) and GATA4 is detected in neonatal rat cardiac myocytes (P < 0.01) compared with cotemporary coculture monolayer in the control group. Also, EPCS can trigger the assembly of MEF2c in the nuclei. In addition, more cardiac myocytes were found to have two nuclei. But MSCs fail to active MEF2C transcriptional factor like that in cardiac myocytes after EPCS exposure. The elevation of MEF2 in both cytoplasm and nuclei of cardiac myocytes can always make a clear distinction of the cardiac myocytes and MSCs in coculture. Some factors show strong upregulation tendency with EPCS in both cardiac myocytes and MSCs-these include the troponin T (P < 0.01) and Cx43 (P < 0.05) in cardiac myocytes, and troponin T (P < 0.01) and Cx43 (P < 0.01) in MSCs. Collagen I expression is not affected with EPCS. In conclusion, mild EPCS can upregulate the secretion of S100A4 in both cardiac myocytes and MSCs, which is a factor supporting the cardiomyogenesis and angiogenesis; it further triggers the development of neonatal rat cardiac myocytes through upregulation of MEF2C and GATA4, the number of cardiac myocytes with two nuclei increases with EPCS, but this phenomenon does not appear in MSCs. Despite this, Cx43 and troponin T in both cardiac myocytes and MSCs are very sensitive to EPCS. EPCS can act as an effective and multi-targeted physical intervention method in cardiomyogenesis.

Isolation of Cardiomyocyte Nuclei from Post-mortem Tissue

Identification of cardiomyocyte nuclei has been challenging in tissue sections as most strategies rely only on cytoplasmic marker proteins1. Rare events in cardiac myocytes such as proliferation and apoptosis require an accurate identification of cardiac myocyte nuclei to analyze cellular renewal in homeostasis and in pathological conditions2. Here, we provide a method to isolate cardiomyocyte nuclei from post mortem tissue by density sedimentation and immunolabeling with antibodies against pericentriolar material 1 (PCM-1) and subsequent flow cytometry sorting. This strategy allows a high throughput analysis and isolation with the advantage of working equally well on fresh tissue and frozen archival material. This makes it possible to study material already collected in biobanks. This technique is applicable and tested in a wide range of species and suitable for multiple downstream applications such as carbon-14 dating3, cell-cycle analysis4, visualization of thymidine analogues (e.g. BrdU and IdU)4, transcriptome and epigenetic analysis.

Isolation of cardiomyocyte nuclei from post-mortem tissue.

Identification of cardiomyocyte nuclei has been challenging in tissue sections as most strategies rely only on cytoplasmic marker proteins(1). Rare events in cardiac myocytes such as proliferation and apoptosis require an accurate identification of cardiac myocyte nuclei to analyze cellular renewal in homeostasis and in pathological conditions(2). Here, we provide a method to isolate cardiomyocyte nuclei from post mortem tissue by density sedimentation and immunolabeling with antibodies against pericentriolar material 1 (PCM-1) and subsequent flow cytometry sorting. This strategy allows a high throughput analysis and isolation with the advantage of working equally well on fresh tissue and frozen archival material. This makes it possible to study material already collected in biobanks. This technique is applicable and tested in a wide range of species and suitable for multiple downstream applications such as carbon-14 dating(3), cell-cycle analysis(4), visualization of thymidine analogues (e.g. BrdU and IdU)(4), transcriptome and epigenetic analysis.

Localization and ERK signaling of α1‐adrenergic subtypes in HeLa cells

G‐protein coupled receptors (GPCRs), like α1‐adrenergic receptors (α1‐AR), are thought to localize to and signal at the plasma membrane, but many GPCRs localize to and signal at the nucleus in several cell types, including neurons, hepatocytes, and cardiac myocytes. Interestingly, α1‐ARs show differential localization based on cell type: nuclear in cardiac myocytes, but plasma membrane/intracellular in most cell lines and smooth muscle cells. Here, we examined receptor localization, oligomerization and signaling using HeLa cells as a cell model where α1‐ARs are not primarily at the nucleus. In HeLa cells, the α1A‐AR localized to the plasma membrane and nucleus, whereas the α1B‐AR localized intracellularly. Interestingly, co‐expression of both subtypes induced receptor hetero‐oligomer formation and produced a unique nuclear co‐localization. Activation of either subtype induced phosphorylation of ERK, which was unchanged by the membrane impermeant α1‐antagonist CGP‐12177a or the nuclear export inhibitor leptomycin B. These results suggest that, in contrast to other cells an intracellular, non‐nuclear α1‐AR population signals in HeLa cells. Signaling from intracellular α1‐AR and the localization differences between cell types could have implications in the treatment of hypertension and benign prostate hyperplasia. This work was supported by grants from NIH (TDO, CDW) and PhRMA Foundation (CDW).