scholarly journals Moderate Calcium Channel Dysfunction in Adult Mice with Inducible Cardiomyocyte-specific Excision of the cacnb2 Gene

2011 ◽  
Vol 286 (18) ◽  
pp. 15875-15882 ◽  
Author(s):  
Marcel Meissner ◽  
Petra Weissgerber ◽  
Juan E. Camacho Londoño ◽  
Jean Prenen ◽  
Sabine Link ◽  
...  

The major L-type voltage-gated calcium channels in heart consist of an α1C (CaV1.2) subunit usually associated with an auxiliary β subunit (CaVβ2). In embryonic cardiomyocytes, both the complete and the cardiac myocyte-specific null mutant of CaVβ2 resulted in reduction of L-type calcium currents by up to 75%, compromising heart function and causing defective remodeling of intra- and extra-embryonic blood vessels followed by embryonic death. Here we conditionally excised the CaVβ2 gene (cacnb2) specifically in cardiac myocytes of adult mice (KO). Upon gene deletion, CaVβ2 protein expression declined by >96% in isolated cardiac myocytes and by >74% in protein fractions from heart. These latter protein fractions include CaVβ2 proteins expressed in cardiac fibroblasts. Surprisingly, mice did not show any obvious impairment, although cacnb2 excision was not compensated by expression of other CaVβ proteins or changes of CaV1.2 protein levels. Calcium currents were still dihydropyridine-sensitive, but current density at 0 mV was reduced by <29%. The voltage for half-maximal activation was slightly shifted to more depolarized potentials in KO cardiomyocytes when compared with control cells, but the difference was not significant. In summary, CaVβ2 appears to be a much stronger modulator of L-type calcium currents in embryonic than in adult cardiomyocytes. Although essential for embryonic survival, CaVβ2 down-regulation in cardiomyocytes is well tolerated by the adult mice.

2000 ◽  
Vol 279 (6) ◽  
pp. H2916-H2926 ◽  
Author(s):  
Can G. Pham ◽  
Alice E. Harpf ◽  
Rebecca S. Keller ◽  
Hoa T. Vu ◽  
Shaw-Yung Shai ◽  
...  

Alterations in the extracellular matrix occur during the cardiac hypertrophic process. Because integrins mediate cell-matrix adhesion and β1D-integrin (β1D) is expressed exclusively in cardiac and skeletal muscle, we hypothesized that β1D and focal adhesion kinase (FAK), a proximal integrin-signaling molecule, are involved in cardiac growth. With the use of cultured ventricular myocytes and myocardial tissue, we found the following: 1) β1D protein expression was upregulated perinatally; 2) α1-adrenergic stimulation of cardiac myocytes increased β1D protein levels 350% and altered its cellular distribution; 3) adenovirally mediated overexpression of β1D stimulated cellular reorganization, increased cell size by 250%, and induced molecular markers of the hypertrophic response; and 4) overexpression of free β1D cytoplasmic domains inhibited α1-adrenergic cellular organization and atrial natriuretic factor (ANF) expression. Additionally, FAK was linked to the hypertrophic response as follows: 1) coimmunoprecipitation of β1D and FAK was detected; 2) FAK overexpression induced ANF-luciferase; 3) rapid and sustained phosphorylation of FAK was induced by α1-adrenergic stimulation; and 4) blunting of the α1-adrenergically modulated hypertrophic response was caused by FAK mutants, which alter Grb2 or Src binding, as well as by FAK-related nonkinase, a dominant interfering FAK mutant. We conclude that β1D and FAK are both components of the hypertrophic response pathway of cardiac myocytes.


2005 ◽  
Vol 79 (5) ◽  
pp. 2979-2987 ◽  
Author(s):  
Michael J. Stewart ◽  
Kathleen Smoak ◽  
Mary Ann Blum ◽  
Barbara Sherry

ABSTRACT Viral myocarditis is an important human disease, with a wide variety of viruses implicated. Cardiac myocytes are not replenished yet are critical for host survival and thus may have a unique response to infection. Previously, we determined that the extent of reovirus induction of beta interferon (IFN-β) and IFN-β-mediated protection in primary cardiac myocyte cultures was inversely correlated with the extent of reovirus-induced cardiac damage in a mouse model. Surprisingly, and in contrast, the IFN-β response did not determine reovirus replication in skeletal muscle cells. Here we compared the IFN-β response in cardiac myocytes to that in primary cardiac fibroblast cultures, a readily replenished cardiac cell type. We compared basal and reovirus-induced expression of IFN-β, IRF-7 (an interferon-stimulated gene [ISG] that further induces IFN-β), and another ISG (561) in the two cell types by using real-time reverse transcription-PCR. Basal IFN-β, IRF-7, and 561 expression was higher in cardiac myocytes than in cardiac fibroblasts. Reovirus T3D induced greater expression of IFN-β in cardiac myocytes than in cardiac fibroblasts but equivalent expression of IRF-7 and 561 in the two cell types (though fold induction for IRF-7 and 561 was higher in fibroblasts than in myocytes because of the differences in basal expression). Interestingly, while reovirus replicated to equivalent titers in cardiac myocytes and cardiac fibroblasts, removal of IFN-β resulted in 10-fold-greater reovirus replication in the fibroblasts than in the myocytes. Together the data suggest that the IFN-β response controls reovirus replication equivalently in the two cell types. In the absence of reovirus-induced IFN-β, however, reovirus replicates to higher titers in cardiac fibroblasts than in cardiac myocytes, suggesting that the higher basal IFN-β and ISG expression in myocytes may play an important protective role.


2017 ◽  
Vol 121 (suppl_1) ◽  
Author(s):  
David Barbosa ◽  
Melanie Wehmöller ◽  
Maximilian R Spinner ◽  
Ulrich Rüther ◽  
Margriet Ouwens

Fibrosis, which occurs in various heart diseases like acute myocardial ischemia and pressure overload, is triggered by the differentiation of fibroblasts into myofibroblasts. Dysregulation of this reparative mechanism results in excessive collagen accumulation leading to cardiac stiffness and impaired heart function. The aim of this study was to determine whether the rhubarb anthraquinone Rhein, a drug already used as treatment for chondroarthritis, prevents the transdifferentiation of cardiac fibroblasts. We observed that Rhein pre-treatment ameliorates the cardiac function and reduces adverse remodeling after acute myocardial infarction in mice, in vivo . In primary human cardiac fibroblasts, Rhein incubation dose-dependently inhibited the TGF-β-mediated upregulation of α-SMA, the master marker for myofibrolasts, and prevented the contraction of fibroblast-populated collagen gel lattices upon TGF-β stimulation. Further, Rhein reduced TGFβ-R1 expression in primary human cardiac fibroblast, resulting in decreased SMAD2 phosphorylation and blunting of the fibrogenic response. Furthermore, Rhein stabilized protein levels of SMAD7, a key inhibitor of TGF-β signaling. Collectively, these data show for the first time that Rhein administration prevents cardiac fibrosis in vivo and in vitro by blunting the TGF-β signaling pathway, and identify Rhein as potential therapeutic treatment to prevent excessive fibrosis and adverse remodeling in cardiac pathologies.


2020 ◽  
Vol 41 (Supplement_2) ◽  
Author(s):  
V Montiel ◽  
R Bella ◽  
L Michel ◽  
E Robinson ◽  
J.C Jonas ◽  
...  

Abstract Background Pathological remodeling of the myocardium has long been known to involve oxidant signaling, but so far, strategies using systemic anti-oxidants have generally failed to prevent it. Aquaporins are a family of transmembrane water channels with thirteen isoforms currently known. Some isoforms have been implicated in oxidant signaling. AQP1 is the most abundant aquaporin in cardiovascular tissues but its specific role in cardiac remodeling remains unknown. Purpose We tested the role of AQP1 as a key regulator of oxidant-mediated cardiac remodeling amenable to targeted pharmacological therapy. Methods We used mice with genetic deletion of Aqp1 (and wild-type littermate), as well as primary isolates from the same mice and human iPSC/Engineered Heart Tissue to test the role of AQP1 in pro-hypertrophic signaling. Human cardiac myocyte-specific (PCM1+) expression of AQP's and genes involved in hypertrophic remodeling was studied by RNAseq and bioinformatic GO pathway analysis. Results RNA sequencing from human cardiac myocytes revealed that the archetypal AQP1 is a major isoform. AQP1 expression correlates with the severity of hypertrophic remodeling in patients with aortic stenosis. The AQP1 channel was detected at the plasma membrane of human and mouse cardiac myocytes from hypertrophic hearts, where it colocalizes with the NADPH oxidase-2 (NOX2) and caveolin-3. We show that hydrogen peroxide (H2O2), produced extracellularly, is necessary for the hypertrophic response of isolated cardiac myocytes and that AQP1 facilitates the transmembrane transport of H2O2 through its water pore, resulting in activation of oxidant-sensitive kinases in cardiac myocytes. Structural analysis of the amino acid residues lining the water pore of AQP1 supports its permeation by H2O2. Deletion of Aqp1 or selective blockade of AQP1 intra-subunit pore (with Bacopaside II) inhibits H2O2 transport in mouse and human cells and rescues the myocyte hypertrophy in human induced pluripotent stem cell-derived engineered heart muscle. This protective effect is due to loss of transmembrane transport of H2O2, but not water, through the intra-subunit pore of AQP1. Treatment of mice with clinically-approved Bacopaside extract (CDRI08) inhibitor of AQP1 attenuates cardiac hypertrophy and fibrosis. Conclusion We provide the first demonstration that AQP1 functions as an aqua-peroxiporin in primary rodent and human cardiac parenchymal cells. We show that cardiac hypertrophy is mediated by the transmembrane transport of H2O2 through the AQP1 water channel. Our studies open the way to complement the therapeutic armamentarium with specific blockers of AQP1 for the prevention of adverse remodeling in many cardiovascular diseases leading to heart failure. Funding Acknowledgement Type of funding source: Public grant(s) – National budget only. Main funding source(s): FRS-FNRS, Welbio


1998 ◽  
Vol 18 (12) ◽  
pp. 7243-7258 ◽  
Author(s):  
Madhu Gupta ◽  
Radovan Zak ◽  
Towia A. Libermann ◽  
Mahesh P. Gupta

ABSTRACT The expression of the α-myosin heavy chain (MHC) gene is restricted primarily to cardiac myocytes. To date, several positive regulatory elements and their binding factors involved in α-MHC gene regulation have been identified; however, the mechanism restricting the expression of this gene to cardiac myocytes has yet to be elucidated. In this study, we have identified by using sequential deletion mutants of the rat cardiac α-MHC gene a 30-bp purine-rich negative regulatory (PNR) element located in the first intronic region that appeared to be essential for the tissue-specific expression of the α-MHC gene. Removal of this element alone elevated (20- to 30-fold) the expression of the α-MHC gene in cardiac myocyte cultures and in heart muscle directly injected with plasmid DNA. Surprisingly, this deletion also allowed a significant expression of the α-MHC gene in HeLa and other nonmuscle cells, where it is normally inactive. The PNR element required upstream sequences of the α-MHC gene for negative gene regulation. By DNase I footprint analysis of the PNR element, a palindrome of two high-affinity Ets-binding sites (CTTCCCTGGAAG) was identified. Furthermore, by analyses of site-specific base-pair mutation, mobility gel shift competition, and UV cross-linking, two different Ets-like proteins from cardiac and HeLa cell nuclear extracts were found to bind to the PNR motif. Moreover, the activity of the PNR-binding factor was found to be increased two- to threefold in adult rat hearts subjected to pressure overload hypertrophy, where the α-MHC gene is usually suppressed. These data demonstrate that the PNR element plays a dual role, both downregulating the expression of the α-MHC gene in cardiac myocytes and silencing the muscle gene activity in nonmuscle cells. Similar palindromic Ets-binding motifs are found conserved in the α-MHC genes from different species and in other cardiac myocyte-restricted genes. These results are the first to reveal a role of the Ets class of proteins in controlling the tissue-specific expression of a cardiac muscle gene.


Biosystems ◽  
2007 ◽  
Vol 90 (3) ◽  
pp. 707-715 ◽  
Author(s):  
Takeru Hachiro ◽  
Koichi Kawahara ◽  
Rie Sato ◽  
Yoshiko Yamauchi ◽  
Daisuke Matsuyama

Circulation ◽  
2014 ◽  
Vol 130 (suppl_2) ◽  
Author(s):  
John E Baker ◽  
Jidong Su ◽  
Stacy Koprowski ◽  
Anuradha Dhanasekaran ◽  
Tom P Aufderheide ◽  
...  

Thrombopoietin confers immediate protection against injury caused by ischemia/reperfusion in the rat heart at a dose that does not increase platelet levels. Eltrombopag is a small molecule agonist of the thrombopoietin receptor; the physiological target of thrombopoietin. Administration of thrombopoietin and eltrombopag result in a dose- and time-dependent increase in platelet counts in patients with thrombocytopenia. However, the ability of eltrombopag and thrombopoietin to immediately protect human cardiac myocytes against injury and the mechanisms underlying myocyte protection are not known. Human cardiac myocytes (7500 cells, n=10/group) were treated with eltrombopag (0.1- 30.0 μM) or thrombopoietin ( 0.1 - 30.0 ng/ml) and then subjected to 5 hours of hypoxia (95% N 2 /5%CO 2 ) and 16 hours of reoxygenation to determine their ability to confer resistance to necrotic and apoptotic myocardial injury . The thrombopoietin receptor (c-Mpl) was detected in unstimulated human cardiac myocytes by western blotting. Eltrombopag and thrombopoietin confer immediate protection to human cardiac myocytes against injury from hypoxia/reoxygenation by decreasing necrotic and apoptotic cell death in a concentration-dependent manner with an optimal concentration of 3 μM for eltrombopag and 1.0 ng/ml for thrombopoietin. The extent of protection conferred to cardiac myocytes with eltrombopag is equivalent to that of thrombopoietin. Eltrombopag and thrombopoietin activate multiple pro-survival pathways; inhibition of JAK-2 (AG-490, 10 μM), p38 MAPK (SB203580, 10 μM), p44/42 MAPK (PD98059, 10 μM), Akt/PI 3 kinase (Wortmannin, 100 nM), and src kinase (PP1, 20 μM) prior to and during hypoxia abolished cardiac myocyte protection by eltrombopag and thrombopoietin. These inhibitors had no effect on hypoxia/reoxygenation injury in myocytes when used alone. Eltrombopag and thrombopoietin may represent important and potent agents for immediately and substantially increasing protection of human cardiac myocytes, and may offer long-lasting benefit through activation of pro-survival pathways during ischemia.


Hypertension ◽  
2013 ◽  
Vol 62 (suppl_1) ◽  
Author(s):  
Dilyara Lauer ◽  
Svetlana Slavic ◽  
Manuela Sommerfeld ◽  
Christa Thöne-Reineke ◽  
Yuliya Sharkovska ◽  
...  

Aims: A selective nonpeptide agonist for the angiotensin AT2 receptor compound 21 (C21) improved cardiac functions 7 days after myocardial infarction (MI). Here, we aimed to investigate what are the cellular mechanisms underlying cardiac protection in the late stage after MI. Methods and Results: MI was induced in Wistar rats by permanent ligation of the left coronary artery. Treatment with C21 (0.03mg/kg i.p. daily) started 6h after MI and continued for 6 weeks. Hemodynamic parameters were measured via transthoracic Doppler echocardiography and intracardiac Samba catheter. The expression of MMP9, TIMP1, TGF-β1 and collagen content were determined in left ventricle. Anti-proteolytic effects were additionally studied in primary cardiac fibroblasts. C21 significantly improved systolic and diastolic function 6 weeks after MI in comparison with the vehicle group as shown by ejection fraction (71.2±4.7 % vs. 53.4±7.0%; p<0.001), fractional shortening (40.8±2.3% vs. 30.9±3.1%; p<0.05), LVIDs (4.4±0.5mm vs. 5.2±0.8mm; p<0.05), LV EDP (16.9±1.2mmHg vs. 22.1±1.4mmHg; p<0.05), E/A ratio, dP/dt max and dP/dt min (p<0.05). Moreover, C21 improved arterial stiffness parameter (AIx) (18±1.2% vs. 25%±1.8, p<0.05) and reduced collagen content (15%; p<0.05) in postinfarcted myocardium. TIMP1 protein expression in the left ventricle was strongly up-regulated (17.7-fold; p<0.05) whereas MMP9 and TGF-β1 were significantly down-regulated (1.5-fold, p<0.05; 3.4-fold p<0.001, respectively) in the treated group. In cardiac fibroblasts, C21 primarily induced TIMP1 expression followed by attenuated MMP9 secretion and TGF-β1 down-regulation. Conclusion: C21 improves heart function in the late stage after MI and prevents cardiac remodeling. Activation of TIMP1 and subsequent inhibition of MMP9-mediated proteolysis as well as down-regulation of TGF-β1 followed by decreased collagen accumulation may attenuate disintegration of the extracellular matrix and reduce fibrosis.


2012 ◽  
Vol 111 (suppl_1) ◽  
Author(s):  
Shirin Doroudgar ◽  
Mirko Völkers ◽  
Donna J Thuerauf ◽  
Ashley Bumbar ◽  
Mohsin Khan ◽  
...  

The endoplasmic reticulum (ER) is essential for protein homeostasis, or proteostasis, which governs the balance of the proteome. In addition to secreted and membrane proteins, proteins bound for many other cellular locations are also made on ER-bound ribosomes, emphasizing the importance of protein quality and quantity control in the ER. Unlike cytosolic E3 ubiquitin ligases studied in the heart, synoviolin/Hrd1, which has not been studied in the heart, is an ER transmembrane E3 ubiquitin ligase, which we found to be upregulated upon protein misfolding in cardiac myocytes. Given the strategic location of synoviolin in the ER membrane, we addressed the hypothesis that synoviolin is critical for regulating the balance of the proteome, and accordingly, myocyte size. We showed that in vitro, adenovirus-mediated overexpression of synoviolin decreased cardiac myocyte size and protein synthesis, but unlike atrophy-related ubiquitin ligases, synoviolin did not increase global protein degradation. Furthermore, targeted gene therapy using adeno-associated virus 9 (AAV9) showed that overexpression of synoviolin in the left ventricle attenuated maladaptive cardiac hypertrophy and preserved cardiac function in mice subjected to trans-aortic constriction (AAV9-control TAC = 22.5 ± 6.2% decrease in EF vs. AAV9-synoviolin TAC at 6 weeks post TAC; P<0.001), and decreased mTOR activity. Since calcium is a major regulator of cardiac myocyte size, we examined the effects of synoviolin gain- or loss-of-function, using AAV9-synoviolin, or an miRNA designed to knock down synoviolin, respectively. While synoviolin gain-of-function did not affect calcium handling in isolated adult myocytes, synoviolin loss-of-function increased calcium transient amplitude (P<0.01), prolonged spark duration (P<0.001), and increased spark width (P<0.001). Spark frequency and amplitude were unaltered upon synoviolin gain- or loss-of-function. Whereas SR calcium load was unaltered by synoviolin loss-of-function, SERCA-mediated calcium removal was reduced (P<0.05). In conclusion, our studies suggest that in the heart, synoviolin is 1) a critical component of proteostasis, 2) a novel determinant of cardiac myocyte size, and 3) necessary for proper calcium handling.


Author(s):  
Dihan Fan ◽  
Hanrong Wu ◽  
Huashan Peng ◽  
Kaichao Pan ◽  
Rongxue Wu

Cardiovascular disease (CVD) is one of the contributing factors to more than one-third of human mortality and the leading cause of death worldwide. Cardiac myocyte death is a fundamental process in cardiac pathologies caused by various heart diseases, including myocardial infarction. Thus, strategies for replacing fibrotic tissue in the infarcted region with functional myocardium have long been a goal of cardiovascular research. This review focuses primarily on induced-pluripotent stem cells (iPSCs), which have emerged as perhaps the most promising source of cardiomyocytes for both therapeutic applications and drug testing. We also briefly summarize other stems- and progenitor-cell populations that have been used for regenerative myocardial therapy and attempt to generate cardiomyocytes directly from cardiac fibroblasts (i.e., transdifferentiation), which, if successful, may enable the pool of endogenous cardiac fibroblasts to be used as an in-situ source of cardiomyocytes for myocardial repair.


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