Coronary Artery In Mice Research Articles

Role of PI3k/Akt pathway in cytoprotective effect of erythropoietin and erythropoietin derivatives in ischaemic human myotubes

Naoxintong capsules (NXT), a traditional Chinese Medical preparation, are widely used for treatment of cardiovascular diseases, while the mechanism is still unclear.Myocardial infarction (MI) was induced by ligation of the left coronary artery in mice. Echocardiographic measurements were performed to do physiological assessments of left ventricle (LV) function. Histological and immunohistochemical staining was used to determine infarct size, capillary density, tissue endothelial nitric oxide synthase (eNOS) expression. Bone Marrow Transplantation (BMT) model and flow cytometric (FCM) analyses were applied to assay endothelial progenitor cells (EPCs) mobilization. Quantitative Real-Time Reverse Transcription Polymerase Chain Reaction (qRT-PCR), Western blotting and enzyme-linked immunosorbent assay (ELISA) were performed to detect the expressions of vascular endothelial growth factor (VEGF), kinase domain region (KDR), phosphorylated-Akt (p-Akt), phosphorylated-eNOS (p-eNOS).NXT administration reduced myocardium fibrosis and increased myocardium capillary density in response to MI. NXT increased circulating Sca1+/ Fetal liver kinase 1 (Flk1)+ mononuclear cells (MNCs) and soluble Kit ligand (sKitL) of bone marrow (BM) in response to MI. In mice transplanted with green fluorescent protein (GFP) BM cells, NXT increased the numbers of GFP-positive cells at the border zone of the ischemic region in MI-induced mice. NXT increased the numbers of eNOS-expressing BM-derived cells in tissues, which was involved in increased the expressions of VEGF, KDR, p-eNOS, p-Akt in the myocardium.NXT-mediated recovery in MI-induced mice was involved in mobilization and incorporation of bone marrow–derived EPCs/circulating angiogenic cells (CACs) leading to enhancement of neovascularization via VEGF/eNOS signaling.

Statins Inhibit NADPH Oxidase Activity by Interference with Membrane Raft Clustering Independent of Rac1 Inactivation in Endothelial Cells

Statins, the inhibitor of 3‐hydroxy‐3‐methylglutaryl coenzyme A (HMG‐CoA) reductase, inhibit mevalonate pathway to block cholesterol biosynthesis, thereby lowering plasma cholesterol and being used for prevention and treatment of atherosclerotic diseases. Our previous studies have shown that statins including pravastatin and simvastatin interfere with the formation of OxLDL‐induced membrane raft (MR)‐redox signaling platforms in human coronary arterial endothelial cells (HCAECs) and in mouse coronary arterial endothelium. However, it remains unknown how statins produce this action that is independent of plasma cholesterol lowering. Here, we tested a hypothesis that inhibition of enhanced MR clustering is essential for the inhibitory effect of statins on Rac1 and NADPH oxidase (NOX) activity. We first demonstrated that statins had no effect on protein expression of NOX subunits, gp91phox or p47phox and Rac1 in HCAECs and mRNA levels of gp91phox or p47phox in coronary arteries of mice, confirming that statins primarily inhibit NADPH oxidase activation rather than alter their gene expression. Overexpression of oncogenic Rac1 in HCAECs was unable to reverse the inhibitory effects of statins on OxLDL‐induced MR clustering suggesting that the effect of statins on MR clustering does not require Rac1 activation. Electron spin resonance spectrometry demonstrated that incubation of HCAECs with sphingomyelinase, a strong stimulator of MR clustering significantly increased O2•− production, which was abolished by pravastatin and simvastatin or by a MR disruptor methyl‐β‐cyclodextrin. Taken together, these results indicate that statins inhibit NOX activity by interference with MR clustering independent of Rac1 activation. This action of statins on MR clustering may be associated with reduction of cholesterol in cell membrane of ECs (supported by NIH grants HL057244, HL091464 and HL075316).

Protective Role of ADAMTS13 for Myocardium in Mouse Model of Experimental Myocardial Infarction.

AbstractAbstract 2175The metalloprotease ADAMTS13 regulates the size of von Willebrand factor (VWF) multimers, controlling excessive VWF functions and preventing thrombotic occlusion of microvasculature. We previously reported that ADAMTS13 deficiency aggravated the extent of brain ischemic stroke in a mouse model of middle cerebral arterial occlusion, suggesting the relevant role of ADAMTS13 in the pathophysiology of brain stroke (Fujioka, et al. Blood, 2010; 115: 1650). These results raised the possibility that the functional regulation of VWF by ADAMTS13 could also play a role in coronary ischemic events such as myocardial infarction. To address this issue, we have used a mouse model of experimental myocardial infarction. The left anterior descending coronary artery in mice was ligated at 2 mm downstream from the origin under thoracotomy with ventilator-assisted respiration, and the cardiac function was evaluated with M-mode echocardiography after 7 days of operation. We compared 20 wild-type (WT) mice and 20 Adamts13 −/− (KO) mice, all of which were 12–14 weeks of age, healthy and fertile. Significantly (p < 0.01) decreased ejection fraction (EF; 44.0±6.7%) and increased left ventricular end-diastolic diameter (LVDd; 4.68±0.69 mm) of KO mice, as compared to WT (EF; 62.7±13.0% and LVDd; 3.77±0.56 mm, respectively), revealed that cardiac functions were apparently more impaired in KO mice. In addition, these reduced cardiac functions observed in KO mice were improved to an extent comparable to those of WT mice by the bolus injection of recombinant human ADAMTS13 (rhADAM; 3 μg/mouse, n=20) just after the operation (KO mice + rhADAM, EF; 58.2.±9.9% and LVDd; 3.16±0.52 mm). Consistent with echocardiography data, histological studies demonstrated the significantly (p < 0.01) higher infarct ratio in myocardium of KO mice (WT; 37.3±18.4%, KO; 59.1±16.3%, KO + rhADAM; 33.7±24.4%). Our results indicate that ADAMTS13, as seen in the case of brain ischemic stroke, plays a protective role for myocardium in coronary artery ischemia, improving myocardial functions and the severity of heart failure. Proper functional regulation of VWF-dependent thrombotic or inflammatory responses by ADAMTS13 could reduce thrombotic occlusion of microvasculature including leukocyte plugging, contributing to better local microcirculation which is crucial for tissue or organ functions. Disclosures:No relevant conflicts of interest to declare.

Retinoic Acid Signalling Is Activated in the Postischemic Heart and May Influence Remodelling

BackgroundAll-trans retinoic acid (atRA), an active derivative of vitamin A, regulates cell differentiation, proliferation and cardiac morphogenesis via transcriptional activation of retinoic acid receptors (RARs) acting on retinoic acid response elements (RARE).We hypothesized that the retinoic acid (RA) signalling pathway is activated in myocardial ischemia and postischemic remodelling.Methods and FindingsMyocardial infarction was induced through ligating the left coronary artery in mice. In vivo cardiac activation of the RARs was measured by imaging RARE-luciferase reporter mice, and analysing expression of RAR target genes and proteins by real time RT-PCR and western blot. Endogenous retinoids in postinfarcted hearts were analysed by triple-stage liquid chromatography/tandem mass spectrometry. Cardiomyocytes (CM) and cardiofibroblasts (CF) were isolated from infarcted and sham operated RARE luciferase reporter hearts and monitored for RAR activity and expression of target genes. The effect of atRA on CF proliferation was evaluated by EdU incorporation. Myocardial infarction increased thoracic RAR activity in vivo (p<0.001), which was ascribed to the heart through ex vivo imaging (p = 0.002) with the largest signal 1 week postinfarct. This was accompanied by increased cardiac gene and protein expression of the RAR target genes retinol binding protein 1 (p = 0.01 for RNA, p = 0,006 for protein) and aldehyde dehydrogenase 1A2 (p = 0.04 for RNA, p = 0,014 for protein), while gene expression of cytochrome P450 26B1 was downregulated (p = 0.007). Concomitantly, retinol accumulated in the infarcted zone (p = 0.02). CM and CF isolated from infarcted hearts had higher luminescence than those from sham operated hearts (p = 0.02 and p = 0.008). AtRA inhibited CF proliferation in vitro (p = 0.02).ConclusionThe RA signalling pathway is activated in postischemic hearts and may play a role in regulation of damage and repair during remodelling.

Combined therapy with cardioprotective cytokine administration and antiapoptotic gene transfer in postinfarction heart failure

We hypothesized that therapy, composed of antiapoptotic soluble Fas (sFas) gene transfer, combined with administration of the cardioprotective cytokine granulocyte colony-stimulating factor (G-CSF), would markedly mitigate cardiac remodeling and dysfunction following myocardial infarction (MI). On the 3rd day after MI induced by ligating the left coronary artery in mice, four different treatments were initiated: saline injection (Group C, n = 26); G-CSF administration (Group G, n = 27); adenoviral transfer of sFas gene (Group F, n = 26); and the latter two together (Group G+F, n = 26). Four weeks post-MI, Group G+F showed better survival than Group C (96 vs. 65%, P < 0.05) and the best cardiac function among the four groups. In Group G, the infarct scar was smaller and less fibrotic, whereas in Group F the scar was thicker, without a reduction in area, and contained abundant myofibroblasts and vascular cells; Group G+F showed both phenotypes. G-CSF exerted a beneficial effect on infarct tissue dynamics through antifibrotic and proliferative effects on granulation tissue; however, it also exerts an adverse proapoptotic effect that leads to thinning of the infarct scar. sFas appeared to offset the latter drawback. In vitro study using cultured myofibroblasts derived from the infarct tissue revealed that G-CSF increased proliferating activity of those cells accompanying activation of Akt and signal transducer and activator of transcription 3, while accelerating Fas-mediated apoptosis with increasing Bax-to-Bcl-2 ratio. The results suggest that combined use of G-CSF administration and sFas gene therapy is a potentially powerful tool against post-MI heart failure.

Intrinsic Gating for Small-Animal Computed Tomography

A projection-based method of intrinsic cardiac gating in small-animal computed tomography imaging is presented. In this method, which operates without external ECG monitoring, the gating reference signal is derived from the raw data of the computed tomography projections. After filtering, the derived gating reference signal is used to rearrange the projection images retrospectively into data sets representing different time points in the cardiac cycle during expiration. These time-stamped projection images are then used for tomographic reconstruction of different phases of the cardiac cycle. Intrinsic gating was evaluated in mice and rats and compared with extrinsic retrospective gating. An excellent agreement was achieved between ECG-derived gating signal and self-gating signal (coverage probability for a difference between the 2 measurements to be less than 5 ms was 89.2% in mice and 85.9% in rats). Functional parameters (ventricular volumes and ejection fraction) obtained from the intrinsic and the extrinsic data sets were not significantly different. The ease of use and reliability of intrinsic gating were demonstrated via a chemical stress test on 2 mice, in which the system performed flawlessly despite an increased heart rate. Because of intrinsic gating, the image quality was improved to the extent that even the coronary arteries of mice could be visualized in vivo despite a heart rate approaching 430 bpm. Feasibility of intrinsic gating for functional imaging and assessment of cardiac wall motion abnormalities was successfully tested in a mouse model of myocardial infarction. Our results demonstrate that self-gating using advanced software postprocessing of projection data promises to be a valuable tool for rodent computed tomography imaging and renders ECG gating with external electrodes superfluous.

Increased inflammatory response and neovascularization in reperfused vs. nonreperfused murine myocardial infarction

Introduction Fundamental knowledge of the inflammatory response after myocardial infarction (MI) is indispensable for intervention toward cardiac regeneration. Although reperfusion is preferred as clinical therapy, for basic research, also permanent ligation MI models are widely used. Methods In this report, we pathohistologically compared the kinetics of the inflammatory and angiogenic response after MI induced by permanent ligation or ligation followed by reperfusion of the left anterior descending coronary artery in mice. Results Permanent ligation resulted in a higher mortality rate accompanied by increased left ventricular dilatation and more progressive wall thinning. However, reperfused infarcts showed higher inflammatory cell influx. Neutrophil numbers were higher after reperfusion post-MI, although their presence was prolonged after ligation. Also, the number of macrophages after reperfusion was continuously higher, but the course of macrophage influx was comparable in both models. The number of lymphocytes was low in both models. Only the peak in myofibroblast numbers at 7 days was higher after ligation than after reperfusion. Moreover, cardiomyocyte remnants were cleared faster, and collagen deposition started earlier after reperfusion. In addition, reperfusion resulted in an increased angiogenic response, as was reflected in increased numbers of medium-sized and large vessels at 7 and 14 days post-MI. Conclusion We show less adverse remodeling together with a higher presence of inflammatory cells and enhanced neovascularization in reperfused MI. These differences between nonreperfused and reperfused MI should be taken into consideration for experimental use of MI models.

71 Infarct healing and arrhythmias affected by gap junction remodelling in Cx43-deficient mice

Changes in gap junctions have been implicated in anatomic substrates of ventricular tachycardia (VT) in patients with healed myocardial infarcts (MI) but the exact role of altered cell-cell coupling has been difficuk to define. To determine the potential value of mouse models to identify gene products critical in arrhythmogenesis following MI, we ligated the coronary artery in mice (C57BL/6J) heterozygous for a connexin43 (Cx43) null allele (Cx43+/-) (n=30) and wildtype mice (Cx43+/+) (n=23) and characterized ventricular remodeling by histology. Spontaneous arrhythmias were observed for 1 week then hearts were analyzed with extrastimulus protocol for inducing ventricular tachycardia. In histology we determined whether diminished coupling affects infarct healing and post-MI remodeling. Ventricular sections were examined histologically 1 and 10 weeks after infarction. Specific morphological features were evaluated including whether infarcts were transmural or non-transmural, and the presence or absence of ventricular aneurysmal dilatation, patchy interstitial fibrosis at infarct border zones, and surviving subendocardial myocytes. A layer of surviving subendocardial myocytes was seen more frequently in hearts in which VT could be induced but the occurrence of this feature was similar in Cx43+/- and +/+ hearts. The other features of post-infarct remodeling pertinent to development of arrhythmias and contractile dysfunction in hearts with healed infarcts were also observed with equal frequency in Cx43 +/- and +/+ hearts. Thus, reduced basal coupling does not by itself significantly alter infarct healing or post-MI remodeling. Infarct healing in mice closely resembles human ischemic heart disease.

Inhibition of cyclooxygenase-2 improves cardiac function after myocardial infarction in the mouse

Cyclooxygenase (COX)-2 is expressed in the heart in animal models of ischemic injury. Recent studies have suggested that COX-2 products are involved in inflammatory cell infiltration and fibroblast proliferation in the heart. Using a mouse model, we questioned whether 1). myocardial infarction (MI) in vivo induces COX-2 expression chronically, and 2). COX-2 inhibition reduces collagen content and improves cardiac function in mice with MI. MI was produced by ligation of the left anterior descending coronary artery in mice. Two days later, mice were treated with 3 mg/kg NS-398, a selective COX-2 inhibitor, or vehicle in drinking water for 2 wk. After the treatment period, mice were subjected to two-dimensional M-mode echocardiography to determine cardiac function. Hearts were then analyzed for determination of infarct size, interstitial collagen content, brain natriuretic peptide (BNP) mRNA, myocyte cross-sectional area, and immunohistochemical staining for transforming growth factor (TGF)-beta and COX-2. COX-2 protein, detected by immunohistochemistry, was increased in MI versus sham hearts. MI resulted in increased left ventricular systolic and diastolic dimension and decreased ejection fraction, fractional shortening, and cardiac output. NS-398 treatment partly reversed these detrimental changes. Myocyte cross-sectional area, a measure of hypertrophy, was decreased by 30% in the NS-398 versus vehicle group, but there was no effect on BNP mRNA. The interstitial collagen fraction increased from 5.4 +/- 0.4% in sham hearts to 10.4 +/- 0.9% in MI hearts and was decreased to 7.9 +/- 0.6% in NS-398-treated hearts. A second COX-2 inhibitor, rofecoxib (MK-0966), also decreased myocyte cross-sectional area and interstitial collagen fraction. TGF-beta, a key regulator of collagen synthesis, was increased in MI hearts. NS-398 treatment reduced TGF-beta immunostaining by 40%. NS-398 treatment had no effect on infarct size. These results suggest that COX-2 products contribute to cardiac remodeling and functional deficits after MI. Thus selected inhibition of COX-2 may be a therapeutic target for reducing myocyte damage after MI.

Echocardiographic evaluation of ventricular remodeling in a mouse model of myocardial infarction

Gene-targeting in mice is a powerful tool to define molecular mechanisms of ischemic heart disease that determine infarct size, postinfarct left ventricular (LV) remodeling, and arrhythmogenesis. Coronary ligation in mice is becoming a widely used model of myocardial infarction (MI), but the pathophysiologic consequences of MI in mice and its relevance to human MI have not been fully elucidated. To characterize structural and functional changes during evolving MI, we analyzed 2-dimensional-based reconstruction of the left ventricle by noninvasive echocardiography obtained 1 day and 1 week after surgical ligation of the left anterior descending coronary artery in mice. Sequential 2-dimensional short-axis cineloops of the left ventricle were used to measure LV mass, and LV volumes at end-diastole and end-systole. Echocardiographic infarct size was estimated by measuring the volume of akinetic LV segments. Histologic infarct size was measured by planimetry of 9 transverse sections of each heart. There was close correlation between the 2 methods (31% ± 20% of LV mass and 34% ± 17% of LV area, respectively; y =.83x + 7.9, r = 0.96, P <.01). LV volumes at end diastole increased significantly between 1 day and 1 week (51 ± 17 μL vs 78 ± 46 μL, respectively, P <.05). The relative change in LV volumes at end diastole varied as a function of infarct size (r = 0.93, P <.01). LV mass and the extent of hypertrophy of noninfarcted segments also varied with infarct size (r = 0.92, P <.01; r = 0.90, P <.01, respectively). Thus, echocardiography is an accurate noninvasive tool for determination of infarct size and quantitative characterization of postinfarct remodeling in the mouse model of MI. Alterations in cardiac structure and function after coronary ligation in mice closely resemble pathophysiologic changes in human ischemic heart disease. (J Am Soc Echocardiogr 2002;15:601-9.)

Heart fatty acid binding protein and cardiac troponin T plasma concentrations as markers for myocardial infarction after coronary artery ligation in mice.

Ligation of the main left coronary artery in mice serves as a model for myocardial infarction (MI). We tested whether plasma concentrations of heart-type fatty acid-binding protein (H-FABP) and/or cardiac troponin T (cTnT) discriminate between infarcted and sham-operated mice and allow estimation of infarct size. Mice were subjected to coronary artery ligation or sham surgery and release curves of H-FABP and cTnT were determined. At 4 h after surgery the mean (+/-SD) H-FABP plasma concentration was 461+/-134 microg/l (n=10) in MI and 185+/-51 microg/l (n=6; P<0.001) in sham-operated mice. By 24 h after surgery H-FABP levels had returned to normal in both groups. cTnT plasma concentrations increased up to 48 h after MI to 13.5+/-6.2 microg/l (n=6; P<0.001) compared with 0.031+/-0.063 microg/l (n=7) in sham-operated mice. Linear regression analysis revealed a significant correlation between plasma H-FABP at 4 h and infarct size assessed 7 days after surgery. Plasma cTnT did not correlate significantly with infarct size. In conclusion, plasma cTnT concentration at 48 h after infarction can be used to distinguish MI from sham mice, whereas H-FABP concentration at 4 h can be used for stratification of animals according to infarct size.