"iDoctor – Medical Blog"

Publication year: 2011
Source: Journal of Molecular and Cellular Cardiology, Available online 19 December 2011

William M. Chilian, Marc S. Penn, Yuh Fen Pung, Feng Dong, Maritza Mayorga, …

The coronary collateral circulation is critically important as an adaptation of the heart to prevent the damage from ischemic insults. In their native state, collaterals in the heart would be classified as part of the microcirculation, existing as arterial-arterial anastomotic connections in the range of 30 to 100 μM in diameter. However, these vessels also show a propensity to remodel into components of the macrocirculation and can become arteries larger than a 1000 μM in diameter. This process of outward remodelling is critically important in the adaptation of the heart to ischemia because the resistance to blood flow is inversely related to the fourth power of the diameter of the vessel. Thus, an expansion of a vessel from 100 to 1000 μM would reduce resistance (in this part of the circuit) to a negligible amount and enable delivery of flow to the region at risk. Our goal in this review is to highlight the voids in understanding this adaptation to ischemia—the growth of the coronary collateral circulation. In doing so we discuss the controversies and unknown aspects of the causal factors that stimulate growth of the collateral circulation, the role of genetics, and the role of endogenous stem and progenitor cells in the context of the normal, physiological situation and under more pathological conditions of ischemic heart disease or with some of the underlying risk factors, e.g., diabetes. The major conclusion of this review is that there are many gaps in our knowledge of coronary collateral growth and this knowledge is critical before the potential of stimulating collateralization in the hearts of patients can be realized. This article is part of a Special Issue entitled Coronary Blood Flow SI Review Article.

Highlights

► This review focuses on what is not known about coronary collateral growth. ► This review raises fundamental questions about the regulation of coronary collateral growth. ► We present a schematic that we hope will facilitate the goal of therapeutic collateral growth.

Publication year: 2011
Source: Journal of Molecular and Cellular Cardiology, Available online 19 December 2011

Guangdong Yang, Hongzhu Li, Guanghua Tang, Lingyun Wu, Kexin Zhao, …

The physiological and pathological roles of hydrogen sulfide (H2S) in the regulation of cardiovacular functions have been recogenized. Vascular smooth muscle cells (SMCs) express cystathionine gamma-lyase (CSE) and produce significant amount of H2S. Although growing evidence demonstated the anti-atherosclerotic effect of H2S, less is known about the contribution of the endogenous CSE/H2S pathway to the development of vascular remodeling. This study investigated the roles of the CSE/H2S pathway on SMC migration and neoimtimal formation by using CSE knockout (KO) mice. SMCs and aortic explants isolated from CSE KO mice exhibited more migration and outgrowth compared with that from wild-type (WT) mice, and exogenously applied NaHS (a H2S donor) at 100 μM significantly inhibited SMC migration and outgrowth. SMCs became more elongated and spread in the absence of CSE, and fibronectin significantly stimulated adhesion and migration of SMCs from CSE KO mice (KO-SMCs) in comparison with SMCs from WT mice (WT-SMCs). The expressions of α5- and β1-integrins were significantly higher in KO-SMCs, and functional blocking of α5β1-integrin effectively abrogated KO-SMC migration. CSE deficiency also enhanced matrix metalloproteinase-2 (MMP-2) expression, and the selective blocking of MMP-2 decreased KO-SMC migration. NaHS treatment decreased both the expressions of α5- and β1-integrins and MMP-2. We further found that the expressions of α5- and β1-integrins as well as MMP-2, were stimulated by fibronectin, and that the blockage of α5β1-integrin reduced but overexpression of α5β1-integrin induced MMP-2 expression in both WT-SMCs and KO-SMCs. We also noticed that CSE deficiency in mice led to increased neointima formation in carotid arteries 4 weeks after ligation, which were attenuated by NaHS administration. In conclusion, inhibition of SMC migration by H2S may be a novel target for the treatment of vascular occlusive disorder.

Highlights

► Cystathionine gamma-lyase deficiency induces smooth muscle cell migration. ► H2S inhibits the expressions of α5β1-integrin and MMP-2. ► Cystathionine gamma-lyase induces neointima formation in mice. ► H2S attenuates neointima formation in mice.

Publication year: 2011
Source: Journal of Molecular and Cellular Cardiology, Available online 20 December 2011

Ku-Chung Chen, Yi-Chu Liao, I-Chung Hsieh, Yung-Song Wang, Ching-Yu Hu, …

MicroRNA-29b has been reported to epigenetically regulate proatherogenic genes in response to oxLDL. Since transcription factors and epigenetic regulations are important mechanisms to regulate gene expression, we investigated whether these mechanisms are involved in oxLDL-induced microRNA-29b upregulation. First, we confirmed microRNA-29b expression was increased in the aorta of mice fed with a high-fat diet, which was consistent with our previous in vitro findings. Next, we found that oxLDL only activated the microRNA-29b-1/microRNA-29a cluster gene on chromosome 7 but not the other distinct microRNA-29b gene located on chromosome 1. Using the promoter reporter assay and chromatin immunoprecipitation, activator protein-1 (AP-1) was shown to bind to the microRNA-29b-1 promoter. We further identified the signaling pathway of LOX-1/Ca/ROS/ERK/c-Fos was involved in oxLDL-mediated microRNA-29b overexpression after treating with the MAPTAM (Cachelator), NAC (ROS scavenger), U0126 (ERK inhibitor) and c-Fos (one of the AP-1 proteins) shRNA, respectively. To investigate epigenetic regulations, we found microRNA-29b promoter contained no CpG islands for DNA methylation. Therefore we investigated whether histone modifications influence microRNA-29b promoter activity. We showed that down-regulation of HDAC1 and the modifications on histone 3 lysine 4 (H3K4) and H3K9 significantly affected microRNA-29b expression. Furthermore, knockdown of c-Fos expression attenuated the effect of oxLDL-induced histone modifications on the microRNA-29b gene expression. Taken together, our data suggest that both transcription factor activation and histone modifications are important regulatory mechanisms of oxLDL-induced atherogenic process. This article is part of a Special Issue entitled OxLDL causes both epigenetic modification and signaling regulation on the microRNA-29b gene: Novel mechanisms for cardiovascular diseases.

Highlights

► In this study we studied mechanisms of oxLDL-upregulated miR-29b. ► OxLDL activated miR-29b from microRNA-29b-1/microRNA-29a cluster gene. ► The LOX-1/Ca/ROS/ERK/c-Fos involved in oxLDL-mediated miR-29b overexpression. ► OxLDL-downregulated HDAC1 affected miR-29b expression. ► OxLDL-mediated histone 3 lysine 4 (H3K4) and H3K9 regulated miR-29b expression.

Publication year: 2011
Source: Journal of Molecular and Cellular Cardiology, Available online 24 November 2011

Xi Shi, Chen Yan, Sergiy M. Nadtochiy, Jun-Ichi Abe, Paul S. Brookes, …

Publication year: 2011
Source: Journal of Molecular and Cellular Cardiology, Available online 29 November 2011

Takeshi Onizuka, Shinsuke Yuasa, Dai Kusumoto, Kenichiro Shimoji, Toru Egashira, …

The efficient induction of cardiomyocyte differentiation from embryonic stem (ES) cells is crucial for cardiac regenerative medicine. Although Wnts play important roles in cardiac development, complex questions remain as to when, how and what types of Wnts are involved in cardiogenesis. We found that Wnt2 was strongly up-regulated during cardiomyocyte differentiation from ES cells. Therefore, we investigated when and how Wnt2 acts in cardiogenesis during ES cell differentiation. Wnt2 was strongly expressed in the early developing murine heart. We applied this embryonic Wnt2 expression pattern to ES cell differentiation, to elucidate Wnt2 function in cardiomyocyte differentiation. Wnt2 knockdown revealed that intrinsic Wnt2 was essential for efficient cardiomyocyte differentiation from ES cells. Moreover, exogenous Wnt2 increased cardiomyocyte differentiation from ES cells. Interestingly, the effects on cardiogenesis of intrinsic Wnt2 knockdown and exogenous Wnt2 addition were temporally restricted. During cardiomyocyte differentiation from ES cells, Wnt2 didn’t activate canonical Wnt pathway but utilizes JNK/AP-1 pathway which is required for cardiomyocyte differentiation from ES cells. Therefore we conclude that Wnt2 plays strong positive stage-specific role in cardiogenesis through non-canonical Wnt pathway in murine ES cells.

Highlights

► The effects on cardiogenesis of intrinsic Wnt2 were temporally restricted. ► During cardiac differentiation, Wnt2 didn’t activate canonical pathway but JNK/AP-1 pathway. ► Wnt2 plays strong positive stage-specific role in cardiogenesis.

Publication year: 2011
Source: Journal of Molecular and Cellular Cardiology, Available online 1 December 2011

Kobra Haghighi, Tracy Pritchard, Julie Bossuyt, Jason R. Waggoner, Qunying Yuan, …

Depressed Ca-handling in cardiomyocytes is frequently attributed to impaired sarcoplasmic reticulum (SR) function in human and experimental heart failure. Phospholamban (PLN) is a key regulator of SR and cardiac function, and PLN mutations in humans have been associated with dilated cardiomyopathy (DCM). We previously reported the deletion of the highly conserved amino acid residue arginine 14 (nucleic acids 39, 40 and 41) in DCM patients. This basic amino acid is important in maintaining the upstream consensus sequence for PKA phosphorylation of Ser 16 in PLN. To assess the function of this mutant PLN, we introduced the PLN-R14Del in cardiac myocytes of the PLN null mouse. Transgenic lines expressing mutant PLN-R14Del at similar protein levels to wild types exhibited no inhibition of the initial rates of oxalate-facilitated SR Ca uptake compared to PLN-knockouts (PLN-KO). The contractile parameters and Ca-kinetics also remained highly stimulated in PLN-R14Del cardiomyocytes,similar to PLN-KO,and isoproterenol did not further stimulate these hyper-contractile basal parameters. Consistent with the lack of inhibition on SR Ca-transport and contractility, confocal microscopy indicated that the PLN-R14Del failed to co-localize with SERCA2a.Moreover, PLN-R14Del did not co-immunoprecipitate with SERCA2a (as did WT-PLN), but rather co-immunoprecipitated with the sarcolemmal Na/K-ATPase (NKA) and stimulated NKA activity. In addition, studies in HEK cells indicated significant fluorescence resonance energy transfer between PLN-R14Del-YFP and NKAα1-CFP, but not with the NKA regulator phospholemman.Despite the enhanced cardiac function in PLN-R14Del hearts (as in PLN-knockouts), there was cardiac hypertrophy (unlike PLN-KO)coupled with activation of Akt and the MAPK pathways. Thus, human PLN-R14Del is misrouted to the sarcolemma, in the absence of endogenous PLN, and alters NKA activity, leading to cardiac remodeling.

Publication year: 2011
Source: Journal of Molecular and Cellular Cardiology, Available online 1 December 2011

Gregory T. Bass, Karen A. Ryall, Ashwin Katikapalli, Brooks E. Taylor, Stephen T. Dang, …

Cardiac hypertrophy is controlled by a complex signal transduction and gene regulatory network, containing multiple layers of crosstalk and feedback. While numerous individual components of this network have been identified, understanding how these elements are coordinated to regulate heart growth remains a challenge. Past approaches to measure cardiac myocyte hypertrophy have been manual and often qualitative, hindering the ability to systematically characterize the network’s higher-order control structure and identify therapeutic targets. Here, we develop and validate an automated image analysis approach for objectively quantifying multiple hypertrophic phenotypes from immunofluorescence images. This approach incorporates cardiac myocyte-specific optimizations and provides quantitative measures of myocyte size, elongation, circularity, sarcomeric organization, and cell-cell contact. As a proof-of-concept, we examined the hypertrophic response to α-adrenergic, β-adrenergic, tumor necrosis factor (TNFα), insulin-like growth factor-1 (IGF-1), and fetal bovine serum pathways. While all five hypertrophic pathways increased myocyte size, other hypertrophic metrics were differentially regulated, forming a distinct phenotype signature for each pathway. Sarcomeric organization was uniquely enhanced by α-adrenergic signaling. TNFα and α-adrenergic pathways markedly decreased cell circularity due to increased myocyte protrusion. Surprisingly, adrenergic and IGF-1 pathways differentially regulated myocyte-myocyte contact, potentially forming a feed-forward loop that regulates hypertrophy. Automated image analysis unlocks a range of new quantitative phenotypic data, aiding dissection of the complex hypertrophic signaling network and enabling myocyte-based high-content drug screening.

Highlights

► Automated image analysis method for cardiac myocyte hypertrophy ► New quantitative measure of sarcomeric organization ► TNFα and α-adrenergic signaling have opposite effects on myocyte elongation. ► Sarcomeric organization is uniquely enhanced by α-adrenergic signaling. ► α- and β-adrenergic pathways enhance myocyte-myocyte contact.

Publication year: 2011
Source: Journal of Molecular and Cellular Cardiology, Available online 1 December 2011

Eun Young Kim, Li Chen, Yanlin Ma, Wei Yu, Jiang Chang, …

Sumoylation is a posttranslational modification implicated in a variety of cellular activities, and its role in a number of human pathogeneses such as cleft lip/palate has been well documented. However, the importance of the SUMO conjugation pathway in cardiac development and functional disorders is newly emerging. We previously reported that knockout of SUMO-1 in mice led to congenital heart diseases (CHDs). To further investigate the effects of imbalanced SUMO conjugation on heart development and function and its underlying mechanisms, we generated transgenic (Tg) mice with cardiac-specific expression of SENP2, a SUMO-specific protease that deconjugates sumoylated proteins, to evaluate the impact of desumoylation on heart development and function. Overexpression of SENP2 resulted in premature death of mice with CHDs—atrial septal defects (ASDs) and/or ventricular septal defects (VSDs). Immunobiochemistry revealed diminished cardiomyocyte proliferation in SENP2-Tg mouse hearts compared with that in wild type (WT) hearts. Surviving SENP2-Tg mice showed growth retardation, and developed cardiomyopathy with impaired cardiac function with aging. Cardiac-specific overexpression of the SUMO-1 transgene reduced the incidence of cardiac structural phenotypes in the sumoylation defective mice. Moreover, cardiac overexpression of SENP2 in the mice with Nkx2.5 haploinsufficiency promoted embryonic lethality and severity of CHDs, indicating the functional interaction between SENP2 and Nkx2.5 in vivo. Our findings indicate the indispensability of a balanced SUMO pathway for proper cardiac development and function.

Highlights

► We studied the effect of de-sumoylation on heart development in a transgenic model. ► Increased desumoylation by overexpressed SENP2 in heart caused cardiac defects and dysfunction. ► SENP2 overexpression also caused defect in cardiomyocyte proliferation. ► SUMO-1 overexpression rescued cardiac structural phenotypes in SENP2-Tg mice. ► Balanced SUMO conjugation is essential for normal heart development and function.

Publication year: 2011
Source: Journal of Molecular and Cellular Cardiology, Available online 1 December 2011

Feng Hua Yang, W. Glen Pyle

The Z-disc protein CapZ has historically been classified as a structural element, anchoring sarcomeric actin. Our previous work expanded its role to include signal transduction, as CapZ transgenic myofilaments are less sensitive to protein kinase C (PKC). Myocardial PKC has paradoxical effects, mediating both preconditioning and ischemia-reperfusion (IR) injury. Our objective was to determine how decreased CapZ affects IR injury and cardiac preconditioning. Mouse hearts were subjected to 20 min global ischemia and 60 min reperfusion. Some hearts were preconditioned with intermittent IR (IPC). Left ventricular function was assessed and myocardial tissue collected post-IR for molecular analysis and tissue staining. Post-ischemic function was significantly better and infarct size smaller in CapZ transgenic hearts, as compared to wildtype. IPC decreased IR damage in both wildtype and CapZ transgenic hearts, although CapZ transgenic hearts performed significantly better than wildtype. Immunoblotting revealed increased myofilament-associated PKC-α and -ε following IR in wildtype hearts, but no change in PKC-δ or -ζ. By contrast, post-IR myofilament-associated PKC-α was significantly higher in CapZ transgenic mice but the rise in PKC-ε was attenuated. Both PKC-δ and PKC-ζ decreased in CapZ transgenic myofilaments following IR. IPC increased myofilament-associated PKC-α and -ε, while decreasing PKC-δ in wildtype hearts. Preconditioned CapZ IPC hearts showed attenuated increases in myofilament PKC-α and -ε, but also a significant decrease in myofilament PKC-δ and -ζ. These data demonstrate significant differences in post-IR myofilament PKC in untreated and preconditioned CapZ transgenic mice. CapZ reduction did not dramatically affect post-IR myofilament function, nor did preconditioning. These results demonstrate that CapZ deficiency decreases IR injury, while providing enhanced cardioprotection with IPC. The cardioprotected phenotype of CapZ transgenic mice is associated with an altered translocation of PKC-isoforms to cardiac myofilaments.

Highlights

► We examined post-ischemic heart function in CapZ transgenic mice ► CapZ transgenic mice were subjected to acute ischemia-reperfusion ► Reduced CapZ protein increased post-ischemic function compared to wildtype ► Protein kinase C activation was altered in CapZ transgenic mice

Publication year: 2011
Source: Journal of Molecular and Cellular Cardiology, Available online 15 November 2011

Simone Barbara Kreutmayer, Barbara Messner, Michael Knoflach, Blair Henderson, Harald Niederegger, …