Calreticulin Induces Dilated Cardiomyopathy

Background

Calreticulin, a Ca²⁺-buffering chaperone of the endoplasmic reticulum, is highly expressed in the embryonic heart and is essential for cardiac development. After birth, the calreticulin gene is sharply down regulated in the heart, and thus, adult hearts have negligible levels of calreticulin. In this study we tested the role of calreticulin in the adult heart.

Methodology/Principal Findings

We generated an inducible transgenic mouse in which calreticulin is targeted to the cardiac tissue using a Cre/loxP system and can be up-regulated in adult hearts. Echocardiography analysis of hearts from transgenic mice expressing calreticulin revealed impaired left ventricular systolic and diastolic function and impaired mitral valve function. There was altered expression of Ca²⁺ signaling molecules and the gap junction proteins, Connexin 43 and 45. Sarcoplasmic reticulum associated Ca²⁺-handling proteins (including the cardiac ryanodine receptor, sarco/endoplasmic reticulum Ca²⁺-ATPase, and cardiac calsequestrin) were down-regulated in the transgenic hearts with increased expression of calreticulin.

Conclusions/Significance

We show that in adult heart, up-regulated expression of calreticulin induces cardiomyopathy in vivo leading to heart failure. This is due to an alternation in changes in a subset of Ca²⁺ handling genes, gap junction components and left ventricle remodeling.     

Connective Tissue Growth Factor Overexpression in Cardiomyocytes Promotes Cardiac Hypertrophy and Protection against Pressure Overload

Connective tissue growth factor (CTGF) is a secreted protein that is strongly induced in human and experimental heart failure. CTGF is said to be profibrotic; however, the precise function of CTGF is unclear. We generated transgenic mice and rats with cardiomyocyte-specific CTGF overexpression (CTGF-TG). To investigate CTGF as a fibrosis inducer, we performed morphological and gene expression analyses of CTGF-TG mice and rat hearts under basal conditions and after stimulation with angiotensin II (Ang II) or isoproterenol, respectively. Surprisingly, cardiac tissues of both models did not show increased fibrosis or enhanced gene expression of fibrotic markers. In contrast to controls, Ang II treated CTGF-TG mice displayed preserved cardiac function. However, CTGF-TG mice developed age-dependent cardiac dysfunction at the age of 7 months. CTGF related heart failure was associated with Akt and JNK activation, but not with the induction of natriuretic peptides. Furthermore, cardiomyocytes from CTGF-TG mice showed unaffected cellular contractility and an increased Ca²⁺ reuptake from sarcoplasmatic reticulum. In an ischemia/reperfusion model CTGF-TG hearts did not differ from controls.Our data suggest that CTGF itself does not induce cardiac fibrosis. Moreover, it is involved in hypertrophy induction and cellular remodeling depending on the cardiac stress stimulus. Our new transgenic animals are valuable models for reconsideration of CTGF''s profibrotic function in the heart.     

Induction of Manganese Superoxide Dismutase by Nuclear Translocation and Activation of SIRT1 Promotes Cell Survival in Chronic Heart Failure

Oxidative stress plays a pivotal role in chronic heart failure. SIRT1, an NAD⁺-dependent histone/protein deacetylase, promotes cell survival under oxidative stress when it is expressed in the nucleus. However, adult cardiomyocytes predominantly express SIRT1 in the cytoplasm, and its function has not been elucidated. The purpose of this study was to investigate the functional role of SIRT1 in the heart and the potential use of SIRT1 in therapy for heart failure. We investigated the subcellular localization of SIRT1 in cardiomyocytes and its impact on cell survival. SIRT1 accumulated in the nucleus of cardiomyocytes in the failing hearts of TO-2 hamsters, postmyocardial infarction rats, and a dilated cardiomyopathy patient but not in control healthy hearts. Nuclear but not cytoplasmic SIRT1-induced manganese superoxide dismutase (Mn-SOD), which was further enhanced by resveratrol, and increased the resistance of C2C12 myoblasts to oxidative stress. Resveratrol''s enhancement of Mn-SOD levels depended on the level of nuclear SIRT1, and it suppressed the cell death induced by antimycin A or angiotensin II. The cell-protective effects of nuclear SIRT1 or resveratrol were canceled by the Mn-SOD small interfering RNA or SIRT1 small interfering RNA. The oral administration of resveratrol to TO-2 hamsters increased Mn-SOD levels in cardiomyocytes, suppressed fibrosis, preserved cardiac function, and significantly improved survival. Thus, Mn-SOD induced by resveratrol via nuclear SIRT1 reduced oxidative stress and participated in cardiomyocyte protection. SIRT1 activators such as resveratrol could be novel therapeutic tools for the treatment of chronic heart failure.     

IDH2 deficiency promotes mitochondrial dysfunction and cardiac hypertrophy in mice

Cardiac hypertrophy, a risk factor for heart failure, is associated with enhanced oxidative stress in the mitochondria, resulting from high levels of reactive oxygen species (ROS). The balance between ROS generation and ROS detoxification dictates ROS levels. As such, disruption of these processes results in either increased or decreased levels of ROS. In previous publications, we have demonstrated that one of the primary functions of mitochondrial NADP⁺-dependent isocitrate dehydrogenase (IDH2) is to control the mitochondrial redox balance, and thereby mediate the cellular defense against oxidative damage, via the production of NADPH. To explore the association between IDH2 expression and cardiac function, we measured myocardial hypertrophy, apoptosis, and contractile dysfunction in IDH2 knockout (idh2^−/−) and wild-type (idh2^+/+) mice. As expected, mitochondria from the hearts of knockout mice lacked IDH2 activity and the hearts of IDH2-deficient mice developed accelerated heart failure, increased levels of apoptosis and hypertrophy, and exhibited mitochondrial dysfunction, which was associated with a loss of redox homeostasis. Our results suggest that IDH2 plays an important role in maintaining both baseline mitochondrial function and cardiac contractile function following pressure-overload hypertrophy, by preventing oxidative stress.     

The potential role of Kv4.3 K+ channel in heart hypertrophy

Transient outward K⁺ current (I_to) plays a crucial role in the early phase of cardiac action potential repolarization. Kv4.3 K⁺ channel is an important component of I_to. The function and expression of Kv4.3 K⁺ channel decrease in variety of heart diseases, especially in heart hypertrophy/heart failure. In this review, we summarized the changes of cardiac Kv4.3 K⁺ channel in heart diseases and discussed the potential role of Kv4.3 K⁺ channel in heart hypertrophy/heart failure. In heart hypertrophy/heart failure of mice and rats, downregulation of Kv4.3 K⁺ channel leads to prolongation of action potential duration (APD), which is associated with increased [Ca²⁺]_i, activation of calcineurin and heart hypertrophy/heart failure. However, in canine and human, Kv4.3 K⁺ channel does not play a major role in setting cardiac APD. So, in addition to Kv4.3 K⁺ channel/APD/[Ca²⁺]_i pathway, there exits another mechanism of Kv4.3 K⁺ channel in heart hypertrophy and heart failure: downregulation of Kv4.3 K⁺ channels leads to CaMKII dissociation from Kv4.3–CaMKII complex and subsequent activation of the dissociated CaMKII, which induces heart hypertrophy/heart failure. Upregulation of Kv4.3 K⁺ channel inhibits CaMKII activation and its related harmful consequences. We put forward a new point-of-view that Kv4.3 K⁺ channel is involved in heart hypertrophy/heart failure independently of its electric function, and drugs inhibiting or upregulating Kv4.3 K⁺ channel might be potentially harmful or beneficial to hearts through CaMKII.     

The potential role of Kv4.3 K+ channel in heart hypertrophy

Transient outward K⁺ current (I_to) plays a crucial role in the early phase of cardiac action potential repolarization. Kv4.3 K⁺ channel is an important component of I_to. The function and expression of Kv4.3 K⁺ channel decrease in variety of heart diseases, especially in heart hypertrophy/heart failure. In this review, we summarized the changes of cardiac Kv4.3 K⁺ channel in heart diseases and discussed the potential role of Kv4.3 K⁺ channel in heart hypertrophy/heart failure. In heart hypertrophy/heart failure of mice and rats, downregulation of Kv4.3 K⁺ channel leads to prolongation of action potential duration (APD), which is associated with increased [Ca²⁺]_i, activation of calcineurin and heart hypertrophy/heart failure. However, in canine and human, Kv4.3 K⁺ channel does not play a major role in setting cardiac APD. So, in addition to Kv4.3 K⁺ channel/APD/[Ca²⁺]_i pathway, there exits another mechanism of Kv4.3 K⁺ channel in heart hypertrophy and heart failure: downregulation of Kv4.3 K⁺ channels leads to CaMKII dissociation from Kv4.3–CaMKII complex and subsequent activation of the dissociated CaMKII, which induces heart hypertrophy/heart failure. Upregulation of Kv4.3 K⁺ channel inhibits CaMKII activation and its related harmful consequences. We put forward a new point-of-view that Kv4.3 K⁺ channel is involved in heart hypertrophy/heart failure independently of its electric function, and drugs inhibiting or upregulating Kv4.3 K⁺ channel might be potentially harmful or beneficial to hearts through CaMKII.     

Global secretome analysis of resident cardiac progenitor cells from wild-type and transgenic heart failure mice: Why ambience matters

Resident cardiac progenitor cells (CPCs) have gained attention in cardiac regenerative medicine primarily due to their paracrine activity. In our current study we determined the role of pathological conditions such as heart failure on the autocrine-paracrine action of stem cell antigen-1 (Sca-1) expressing CPC. This comparative secretome profiling of Sca-1⁺ cells derived from transgenic heart failure (αMHC–cyclin-T1/Gαq overexpression [Cyc] cells) versus healthy (wild-type [Wt] cells) mice, achieved via mass-spectrometric quantification, enabled the identification of over 700 proteins. Our results demonstrate that the heart failure milieu caused a 2-fold enrichment of extracellular matrix proteins (ECM) like biglycan, versican, collagen XII, and angiogenic factors like heparan sulfate proteoglycan 2, plasminogen activator inhibitor 1 in the secretome. We further elucidated the direct influence of the secretome on the functional behavior of Sca-1 ⁺ cells via in vitro tube forming assay. Secreted factors present in the diseased milieu induced tube formation in Cyc cells (1.7-fold; p < 0.01) when compared with Wt cells after 24 hr of exposure. The presence of conditioned media moderately increased the proliferation of Cyc cells but had a more pronounced effect on Wt cells. Overall, these findings revealed global modifications in the secretory activity of adult Sca-1 ⁺ cells in the heart failure milieu. The secretion of ECM proteins and angiogenic factors, which are crucial for cardiac remodeling and recovery, was notably enriched in the supernatant of Cyc cells. Thus, during heart failure the microenvironment of Sca-1 ⁺ cells might favor angiogenesis and proliferation suggesting their potential to recover the damaged heart.     

CD117-positive Cells of the Heart: Progenitor Cells or Mast Cells?

Human cardiac stem/progenitor cells and their potential for repair of heart injury are a current hot topic of research. CD117 has been used frequently as a marker for identification of stem/progenitor cells in the heart. However, cardiac mast cells, which are also CD117⁺, have not been excluded by credible means when selecting putative cardiac progenitors by using CD117 as a marker. We evaluated the relationship between CD117⁺ cells and mast cells in the left ventricle of human hearts (n=5 patients, ages 1 week–75 years) with the well-established mast cell markers tryptase, toluidine blue, and thionine. A large number (85–100%) of CD117⁺ cells in the human heart were specifically identified as mast cells. In addition, mast cells showed weak or moderate CD45 immunostaining signals. These results indicate that the majority of CD117⁺ cells in the heart are mast cells and that these cells are distinctly positive for CD45, although staining was weak or moderate. These results strongly suggest that the newly reported CD117⁺/CD45^dim/moderate putative cardiac progenitor cells are mast cells. The significance of this observation in stem cell research of the heart is discussed. (J Histochem Cytochem 58:309–316, 2010)     

BEX1 is a critical determinant of viral myocarditis

Viral infection of the heart is a common but underappreciated cause of heart failure. Viruses can cause direct cardiac damage by lysing infected cardiomyocytes. Inflammatory immune responses that limit viral replication can also indirectly cause damage during infection, making regulatory factors that fine-tune these responses particularly important. Identifying and understanding these factors that regulate cardiac immune responses during infection will be essential for developing targeted treatments for virus-associated heart failure. Our laboratory has discovered Brain Expressed X-linked protein 1 (BEX1) as a novel stress-regulated pro-inflammatory factor in the heart. Here we report that BEX1 plays a cardioprotective role in the heart during viral infection. Specifically, we adopted genetic gain- and loss-of-function strategies to modulate BEX1 expression in the heart in the context of coxsackievirus B3 (CVB3)-induced cardiomyopathy and found that BEX1 limits viral replication in cardiomyocytes. Interestingly, despite the greater viral load observed in mice lacking BEX1, inflammatory immune cell recruitment in the mouse heart was profoundly impaired in the absence of BEX1. Overall, the absence of BEX1 accelerated CVB3-driven heart failure and pathologic heart remodeling. This result suggests that limiting inflammatory cell recruitment has detrimental consequences for the heart during viral infections. Conversely, transgenic mice overexpressing BEX1 in cardiomyocytes revealed the efficacy of BEX1 for counteracting viral replication in the heart in vivo. We also found that BEX1 retains its antiviral role in isolated cells. Indeed, BEX1 was necessary and sufficient to counteract viral replication in both isolated primary cardiomyocytes and mouse embryonic fibroblasts suggesting a broader applicability of BEX1 as antiviral agent that extended to viruses other than CVB3, including Influenza A and Sendai virus. Mechanistically, BEX1 regulated interferon beta (IFN-β) expression in infected cells. Overall, our study suggests a multifaceted role of BEX1 in the cardiac antiviral immune response.     

Coxsackievirus preferentially replicates and induces cytopathic effects in undifferentiated neural progenitor cells

Enteroviruses, including coxsackieviruses, exhibit significant tropism for the central nervous system, and these viruses are commonly associated with viral meningitis and encephalitis. Previously, we described the ability of coxsackievirus B3 (CVB3) to infect proliferating neuronal progenitor cells located in the neonatal subventricular zone and persist in the adult murine central nervous system (CNS). Here, we demonstrate that cultured murine neurospheres, which comprise neural stem cells and their progeny at different stages of development, were highly susceptible to CVB3 infection. Neurospheres, or neural progenitor and stem cells (NPSCs), isolated from neonatal C57BL/6 mice, supported high levels of infectious virus production and high viral protein expression levels following infection with a recombinant CVB3 expressing enhanced green fluorescent protein (eGFP) protein. Similarly, NPSCs isolated from neonatal actin-promoter-GFP transgenic mice (actin-GFP NPSCs) were highly susceptible to infection with a recombinant CVB3 expressing DsRed (Discosoma sp. red fluorescent protein). Both nestin-positive and NG2(+) progenitor cells within neurospheres were shown to preferentially express high levels of viral protein as soon as 24 h postinfection (p.i.). By day 3 p.i., viral protein expression and viral titers increased dramatically in NPSCs with resultant cytopathic effects (CPE) and eventual cell death. In contrast, reduced viral replication, lower levels of CPE, and diminished viral protein expression levels were observed in NPSCs differentiated for 5 or 16 days in the presence of fetal bovine serum (FBS). Despite the presence of CPE and high levels of cell death following early CVB3 infection, surviving neurospheres were readily observed and continued to express detectable levels of viral protein as long as 37 days after initial infection. Also, CVB3 infection of actin-GFP NPSCs increased the percentage of cells expressing neuronal class III β-tubulin following their differentiation in the presence of FBS. These results suggest that neural stem cells may be preferentially targeted by CVB3 and that neurogenic regions of the CNS may support persistent viral replication in the surviving host. In addition, normal progenitor cell differentiation may be altered in the host following infection.     

Cyclosporine A Treatment Inhibits Abcc6-Dependent Cardiac Necrosis and Calcification following Coxsackievirus B3 Infection in Mice

Coxsackievirus type B3 (CVB3) is a cardiotropic enterovirus. Infection causes cardiomyocyte necrosis and myocardial inflammation. The damaged tissue that results is replaced with fibrotic or calcified tissue, which can lead to permanently altered cardiac function. The extent of pathogenesis among individuals exposed to CVB3 is dictated by a combination of host genetics, viral virulence, and the environment. Here, we aimed to identify genes that modulate cardiopathology following CVB3 infection. 129S1 mice infected with CVB3 developed increased cardiac pathology compared to 129X1 substrain mice despite no difference in viral burden. Linkage analysis identified a major locus on chromosome 7 (LOD: 8.307, P<0.0001) that controlled the severity of cardiac calcification and necrosis following infection. Sub-phenotyping and genetic complementation assays identified Abcc6 as the underlying gene. Microarray expression profiling identified genotype-dependent regulation of genes associated with mitochondria. Electron microscopy examination showed elevated deposition of hydroxyapatite-like material in the mitochondrial matrices of infected Abcc6 knockout (Abcc6-/-) mice but not in wildtype littermates. Cyclosporine A (CsA) inhibits mitochondrial permeability transition pore opening by inhibiting cyclophilin D (CypD). Treatment of Abcc6 -/- mice with CsA reduced cardiac necrosis and calcification by more than half. Furthermore, CsA had no effect on the CVB3-induced phenotype of doubly deficient CypD-/-Abcc6-/- mice. Altogether, our work demonstrates that mutations in Abcc6 render mice more susceptible to cardiac calcification following CVB3 infection. Moreover, we implicate CypD in the control of cardiac necrosis and calcification in Abcc6-deficient mice, whereby CypD inhibition is required for cardioprotection.     

TRIF is a critical survival factor in viral cardiomyopathy

TRIF is a member of the innate immune system known to be involved in viral recognition and type I IFN activation. Because IFNs are thought to play an important role in viral myocarditis, we investigated the role of TRIF in induced myocarditis in mice. Whereas C57BL/6 (wild-type) mice showed only mild myocarditis, including normal survival postinfection with coxsackievirus group B serotype 3 (CVB3), infection of TRIF(-/-) mice led to the induction of cardiac remodeling, severe heart failure, and 100% mortality (p < 0.0001). These mice showed markedly reduced virus control in cardiac tissues and cardiomyocytes. This was accompained with dynamic cardiac cytokine activation in the heart, including a suppression of the antiviral cytokine IFN-β in the early viremic phase. TRIF(-/-) myocytes displayed a TLR4-dependent suppression of IFN-β, and pharmacological treatment of CVB3-infected TRIF(-/-) mice with murine IFN-β led to improved virus control and reduced cardiac inflammation. Additionally, this treatment within the viremic phase of myocarditis showed a significant long-term outcome indexed by reduced mortality (20 versus 100%; p < 0.001). TRIF is essential toward a cardioprotection against CVB3 infection.     

基因谱系示踪技术揭示小鼠Tbx18+心脏祖细胞向心系细胞分化的潜能

心脏祖细胞(cardiac progenitor cells,CPCs)的研究对阐明先天性心脏病的机制及治疗心血管疾病具有重要意义.哺乳动物的心脏组织由多种不同CPCs分化形成.转录因子Tbx18在发育中的心外膜中表达,对心脏的发育形成起重要的调节作用.为了在组织及活体细胞水平检测和阐明Tbx18+CPC的分化潜能,应用Cre-LoxP系统建立Tbx18+CPCs基因命运谱系示踪模型:Tbx18-Cre/Rosa26R-EYFP和Tbx18-Cre/Rosa26R-LacZ双杂合基因敲入小鼠.该双杂合基因敲入小鼠通过Cre的表达能有效地示踪Tbx18+细胞在胚胎和成年小鼠中的分化命运.Tbx18-Cre/Rosa26R-EYFP双杂合小鼠心脏能非常容易地利用流式细胞分选系统(FACS)分离出YFP+细胞,也可在倒置共聚焦显微镜下观察.应用X-gal染色分析其表达模式,揭示Tbx18命运谱系参与心房肌、室间隔、心室肌、冠状动脉、瓣膜等的形成.应用免疫荧光技术初步揭示Tbx18+CPCs向心脏肌钙蛋白T(cTNT)阳性心肌细胞和平滑肌肌球蛋白重链11(MYH11)阳性血管平滑肌细胞分化的潜能.心脏是一个由多种肌肉和非肌肉组织细胞构成的复杂器官.推测Tbx18可能在心脏祖细胞向肌源性细胞分化的信号通路中起重要调节作用.在上述研究中应用基因谱系示踪技术,验证Tbx18可作为一类CPCs的标志,为更深入揭示心脏祖细胞向心系细胞的分化潜能打下基础.     

Complement receptor 1 and 2 deficiency increases coxsackievirus B3-induced myocarditis, dilated cardiomyopathy, and heart failure by increasing macrophages, IL-1beta, and immune complex deposition in the heart

Complement and complement receptors (CR) play a central role in immune defense by initiating the rapid destruction of invading microorganisms, amplifying the innate and adaptive immune responses, and mediating solubilization and clearance of immune complexes. Defects in the expression of C or CR have been associated with loss of tolerance to self proteins and the development of immune complex-mediated autoimmune diseases such as systemic lupus erythematosus. In this study, we examined the role of CR on coxsackievirus B3 (CVB3)-induced myocarditis using mice deficient in CR1/2. We found that CR1/2 deficiency significantly increased acute CVB3 myocarditis and pericardial fibrosis resulting in early progression to dilated cardiomyopathy and heart failure. The increase in inflammation was not due to increased viral replication, which was not significantly altered in the hearts of CR1/2-deficient mice, but was associated with increased numbers of macrophages, IL-1beta levels, and immune complex deposition in the heart. The complement regulatory protein, CR1-related gene/protein Y (Crry), was increased on cardiac macrophage populations, while immature B220(low) B cells were increased in the spleen of CR1/2-deficient mice during acute CVB3-induced myocarditis. These results show that expression of CR1/2 is not necessary for effective clearance of CVB3 infection, but prevents immune-mediated damage to the heart.     

Activation of CaMKII via ER‐stress mediates coxsackievirus B3‐induced cardiomyocyte apoptosis

Cardiomyocyte apoptosis contributes to the development of coxsackievirus B3 (CVB3)‐induced myocarditis, but the mechanism for the apoptosis by CVB3 infection remains unclear. Here, we showed that CVB3‐induced endoplasmic reticulum (ER) stress response and apoptosis in cultured H9c2 cardiomyocytes. We found that Ca²⁺‐calmodulin‐dependent kinase II (CaMKII) was activated by ER stress‐dependent intracellular Ca²⁺ overload in the CVB3‐infected H9c2 cardiomyocytes. Treatment with an inhibitor of ER stress, 4‐phenylbutyric acid (4‐PBA), attenuated intracellular Ca²⁺ accumulation indirectly and reduced CaMKII activity. Inhibition of CaMKII with pharmacological inhibitor (KN‐93) or short hairpin RNA reduced CVB3‐induced H9c2 apoptosis and repressed cytochrome c release from mitochondria to cytoplasm; whereas overexpression of the activated mutant of CaMKII (CaMKII‐T287D) enhanced CVB3‐induced H9c2 apoptosis and mitochondrial cytochrome c release, which could be alleviated by blocking of mitochondrial Ca²⁺ uniporter or mitochondrial permeability transition pore. Further in vivo investigation revealed that blocking of CaMKII with KN‐93 prevented cardiomyocytes apoptosis and improved cardiac contractile function in CVB3‐infected mouse heart. Collectively, these findings provide a novel evidence that CaMKII plays a vital role in the promotion of CVB3‐induced cardiomyocyte apoptosis, which links ER stress and mitochondrial Ca²⁺ uptake.     

Rapidly progressive course of Trypanosoma cruzi infection in mice heterozygous for hexamethylene bis-acetamide inducible 1 (Hexim1) gene

Infection with Trypanosoma cruzi causes Chagas disease and results in myocardial inflammation and cardiomyopathy. Downregulated Hexim1 expression, as in Hexim1^+/? mice, reduces cardiac inflammation and fibrosis following ischemic stress. We asked whether reduced expression of Hexim1 would also afford protection against T. cruzi-induced cardiomyopathy. C57BL/6J (wild type – WT) and Hexim1^+/? mice were infected with sub-lethal doses of T. cruzi (Brazil strain), and cardiac function, serologic markers of inflammation and tissue pathology were examined. Infected Hexim1^+/? mice had compromised cardiac function, altered expression of both pro- and anti-inflammatory cytokines, and increased inflammation and fibrosis. Cardiac failure was evidenced by severely diminished heart rate, compensatory increase in respiratory rate, and abnormally high left ventricular mass with severe transmural inflammation. Lungs displayed intense peribronchial inflammation and fibrosis extending into the parenchyma. We also observed Smad3-serine²⁰⁸ phosphorylation in hearts and lungs of infected mice, suggesting increased TGF-β signaling pathway activity. This was more pronounced in Hexim1^+/? mice and correlated with increased fibrosis in these tissues. Conspicuous splenomegaly in the Hexim1^+/? mice most likely resulted from the observed extensive white pulp expansion. T. cruzi infection induced colonic dilatation and marked villous atrophy in both the WT and Hexim1^+/? mice but more so in the latter. The profound exacerbation of pathologic findings suggests a protective role for Hexim1 in T. cruzi infection.     

Cardiac-specific CGI-58 deficiency activates the ER stress pathway to promote heart failure in mice

Excess myocardial triacylglycerol accumulation (i.e., cardiac steatosis) impairs heart function, suggesting that enzymes promoting triacylglycerol metabolism exert essential regulatory effects on heart function. Comparative gene identification 58 (CGI-58) is a key enzyme that promotes the hydrolysis of triglycerides by activating adipose triglyceride lipase and plays a protective role in maintaining heart function. In this study, the effects of CGI-58 on heart function and the underlying mechanism were investigated using cardiac-specific CGI58-knockout mice (CGI-58^cko mice). Echocardiography and pathological staining were performed to detect changes in the structure and function of the heart. Proteomic profiling, immunofluorescent staining, western blotting, and real-time PCR were used to evaluate molecular changes. In CGI-58^cko mice, we detected cardiac hypertrophic remodeling and heart failure associated with excessive cardiac lipid accumulation, ROS production, and decreased expression of regulators of fatty acid metabolism. These changes were markedly attenuated in CGI-58^cko mice injected with rAAV9-CGI58. A quantitative proteomics analysis revealed significant increases in the expression of ER stress-related proteins and decreases in proteins related to fatty acid and amino acid metabolism in the hearts of CGI-58^cko mice. Furthermore, the inhibition of ER stress by the inhibitor 4-PBA improved mitochondrial dysfunction, reduced oxidative stress, and reversed cardiac remodeling and dysfunction in cultured cardiomyocytes or in CGI-58^cko mice. Our results suggested that CGI-58 is essential for the maintenance of heart function by reducing lipid accumulation and ER stress in cardiomyocytes, providing a new therapeutic target for cardiac steatosis and dysfunction.Subject terms: Heart failure, Heart failure     

Demonstration of suppressor cells in coxsackievirus group B, type 3 infected female Balb/c mice which prevent myocarditis

Coxsackievirus group B type 3 (CVB3) induces myocarditis in male Balb/c mice but produces little cardiac injury in females. Males develop cytolytic T lymphocytes (CTL) reactive to heart antigens which primarily cause the inflammation and cardiac injury observed in the disease. Infected female mice lack this CTL response because they rapidly produce suppressor cells inhibiting both cellular immunity and cardiac inflammation. Four lines of evidence demonstrate suppressor cells in females. First, females develop myocarditis when treated with low-dose cyclophosphamide under conditions known to preferentially eliminate suppressor cells but not other immune cells. Second, lymphocytes obtained from females at various times after infection prevent myocarditis when adoptively transferred into CVB3-infected males. Virus concentrations in the hearts of males receiving immune female cells and control males were equivalent. Thus protection did not result from accelerated virus elimination in recipient males. Third, CTL from CVB3 infected male mice could induce myocarditis in infected T-lymphocyte depleted but not in intact females suggesting the presence of an inhibitory T cell in the intact animals. Finally, male lymphocytes cultured on heart cell monolayers for 5 days generate significant cytolytic activity to myocyte targets. CTL generation could be inhibited by co-culture of the male cells with immune female lymphocytes. Nonimmune female cells were not inhibitory.