Gene expression of colony-stimulating factors and stem cell factor after myocardial infarction in the mouse

Cardiomyocyte-GSK-3β deficiency induces cardiac progenitor cell proliferation in the ischemic heart through paracrine mechanisms

Cardiomyopathy is an irreparable loss and novel strategies are needed to induce resident cardiac progenitor cell (CPC) proliferation in situ to enhance the possibility of cardiac regeneration. Here, we sought to identify the potential roles of glycogen synthase kinase-3β (GSK-3β), a critical regulator of cell proliferation and differentiation, in CPC proliferation post-myocardial infarction (MI). Cardiomyocyte-specific conditional GSK-3β knockout (cKO) and littermate control mice were employed and challenged with MI. Though cardiac left ventricular chamber dimension and contractile functions were comparable at 2 weeks post-MI, cKO mice displayed significantly preserved LV chamber and contractile function versus control mice at 4 weeks post-MI. Consistent with protective phenotypes, an increased percentage of c-kit-positive cells (KPCs) were observed in the cKO hearts at 4 and 6 weeks post-MI which was accompanied by increased levels of cardiomyocyte proliferation. Further analysis revealed that the observed increased number of KPCs in the ischemic cKO hearts was mainly from a cardiac lineage, as the majority of identified KPCs were negative for the hematopoietic lineage marker, CD45. Mechanistically, cardiomyocyte-GSK-3β profoundly suppresses the expression and secretion of growth factors, including basic-fibroblast growth factor, angiopoietin-2, erythropoietin, stem cell factor, platelet-derived growth factor-BB, granulocyte colony-stimulating factor, and vascular endothelial growth factor, post-hypoxia. In conclusion, our findings strongly suggest that loss of cardiomyocyte-GSK-3β promotes cardiomyocyte and resident CPC proliferation post-MI. The induction of cardiomyocyte and CPC proliferation in the ischemic cKO hearts is potentially regulated by autocrine and paracrine signaling governed by dysregulated growth factors post-MI. A strategy to inhibit cardiomyocyte-GSK-3β could be helpful for the promotion of in situ cardiac regeneration post-ischemic injury.

Slow Ca²⁺ sparks de-synchronize Ca²⁺ release in failing cardiomyocytes: evidence for altered configuration of Ca²⁺ release units?

In heart failure, cardiomyocytes exhibit slowing of the rising phase of the Ca(2+) transient which contributes to the impaired contractility observed in this condition. We investigated whether alterations in ryanodine receptor function promote slowing of Ca(2+) release in a murine model of congestive heart failure (CHF). Myocardial infarction was induced by left coronary artery ligation. When chronic CHF had developed (10 weeks post-infarction), cardiomyocytes were isolated from viable regions of the septum. Septal myocytes from SHAM-operated mice served as controls. Ca(2+) transients rose markedly slower in CHF than SHAM myocytes with longer time to peak (CHF=152 ± 12% of SHAM, P<0.05). The rise time of Ca(2+) sparks was also increased in CHF (SHAM=9.6 ± 0.6 ms, CHF=13.2 ± 0.7 ms, P<0.05), due to a sub-population of sparks (≈20%) with markedly slowed kinetics. Regions of the cell associated with these slow spontaneous sparks also exhibited slowed Ca(2+) release during the action potential. Thus, greater variability in spark kinetics in CHF promoted less uniform Ca(2+) release across the cell. Dyssynchronous Ca(2+) transients in CHF additionally resulted from T-tubule disorganization, as indicated by fast Fourier transforms, but slow sparks were not associated with orphaned ryanodine receptors. Rather, mathematical modeling suggested that slow sparks could result from an altered composition of Ca(2+) release units, including a reduction in ryanodine receptor density and/or distribution of ryanodine receptors into sub-clusters. In conclusion, our findings indicate that slowed, dyssynchronous Ca(2+) transients in CHF result from alterations in Ca(2+) sparks, consistent with rearrangement of ryanodine receptors within Ca(2+) release units.

Hematopoietic cytokines for cardiac repair: mobilization of bone marrow cells and beyond

Hematopoietic cytokines, traditionally known to influence cellular proliferation, differentiation, maturation, and lineage commitment in the bone marrow, include granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage colony-stimulating factor, stem cell factor, Flt-3 ligand, and erythropoietin among others. Emerging evidence suggests that these cytokines also exert multifarious biological effects on diverse nonhematopoietic organs and tissues. Although the precise mechanisms remain unclear, numerous studies in animal models of myocardial infarction (MI) and heart failure indicate that hematopoietic cytokines confer potent cardiovascular benefits, possibly through mobilization and subsequent homing of bone marrow-derived cells into the infarcted heart with consequent induction of myocardial repair involving multifarious mechanisms. In addition, these cytokines are also known to exert direct cytoprotective effects. However, results from small-scale clinical trials of G-CSF therapy as a single agent after acute MI have been discordant and largely disappointing. It is likely that cardiac repair following cytokine therapy depends on a number of known and unknown variables, and further experimental and clinical studies are certainly warranted to accurately determine the true therapeutic potential of such therapy. In this review, we discuss the biological features of several key hematopoietic cytokines and present the basic and clinical evidence pertaining to cardiac repair with hematopoietic cytokine therapy.

Cytokines and myocardial regeneration: a novel treatment option for acute myocardial infarction

The regenerative capacity of the myocardium and its blood vessels has now been well demonstrated. The cytokines granulocyte colony-stimulating factor, erythropoietin, and stem cell factor may play a role in helping to stimulate cell regeneration under normal physiologic conditions and in patients with myocardial injury. After an ischemic insult, cytokines are released into the peripheral circulation and signal for the mobilization of stem cells. In experimental cardiac injury models, the addition of cytokines has been shown to improve myocardial function with and without the concurrent use of stem cell therapy. Preliminary studies in humans using cytokine therapy alone for treating myocardial infarction have been disappointing. Future studies in patients with myocardial injury need to examine the use of various combinations of cytokines, with and without the addition of intravascular stem cell infusions or direct stem cell injections.

Slowing of cardiomyocyte Ca2+ release and contraction during heart failure progression in postinfarction mice

Deterioration of cardiac contractility during congestive heart failure (CHF) is believed to involve decreased function of individual cardiomyocytes and may include reductions in contraction magnitude and/or kinetics. We examined the progression of in vivo and in vitro alterations in contractile function in CHF mice and investigated underlying alterations in Ca(2+) homeostasis. Following induction of myocardial infarction (MI), mice with CHF were examined at early (1 wk post-MI) and chronic (10 wk post-MI) stages of disease development. Sham-operated mice served as controls. Global and local left ventricle function were assessed by echocardiography in sedated animals ( approximately 2% isoflurane). Excitation-contraction coupling was examined in cardiomyocytes isolated from the viable septum. CHF progression between 1 and 10 wk post-MI resulted in increased mortality, development of hypertrophy, and deterioration of global left ventricular function. Local function in the noninfarcted myocardium also declined, as posterior wall shortening velocity was reduced in chronic CHF (1.2 +/- 0.1 vs. 1.9 +/- 0.2 cm/s in sham). Parallel alterations occurred in isolated cardiomyocytes since contraction and Ca(2+) transient time to peak values were prolonged in chronic CHF (115 +/- 6 and 158 +/- 11% sham values, respectively). Surprisingly, contraction and Ca(2+) transient magnitudes in CHF were larger than sham values at both time points, resulting from increased sarcoplasmic reticulum Ca(2+) content and greater Ca(2+) influx via L-type channels. We conclude that, in mice with CHF following myocardial infarction, declining myocardial function involves slowing of cardiomyocyte contraction without reduction in contraction magnitude. Corresponding alterations in Ca(2+) transients suggest that slowing of Ca(2+) release is a critical mediator of CHF progression.

Mouse surgical models in cardiovascular research

Mouse models that mimic human diseases are important tools for investigating underlying mechanisms in many disease states. Although the demand for these models is high, there are few schools or courses available for surgeons to obtain the necessary skills. Researchers are usually exposed to brief descriptions of the procedures in scientific journals, which they then attempt to reproduce by trial and error. This often leads to a number of mistakes and unnecessary loss of animals. This chapter provides comprehensive details of three major surgical procedures currently employed in cardiovascular research: aortic constriction (of both ascending and transverse portions), pulmonary artery banding, and myocardial infarction (including ischemia-reperfusion). It guides the reader through the entire procedure, from the preparation of the animal for surgery until its full recovery, and includes a list of all necessary tools and devices. Due consideration has been given to the pitfalls and possible complications in the course of surgery. Adhering to our recommendations should improve reproducibility of the models and bring the number of the animal subjects to the minimum.

Direct injection of kit ligand-2 lentivirus improves cardiac repair and rescues mice post-myocardial infarction

Myocardial infarction (MI) and subsequent adverse remodeling cause heart failure. Previously we demonstrated a role for Kit ligand (KL) in improving cardiac function post-MI. KL has two major isoforms; KL-1 is secreted whereas KL-2 is predominantly membrane bound. We demonstrate here first that KL-2-deficient mice have worse survival and an increased heart/bodyweight ratio post-MI compared to mice with reduced c-Kit receptor expression. Next we synthesized recombinant lentiviral vectors (LVs) that engineered functional expression of murine KL-1 and KL-2. For in vivo analyses, we directly injected these LVs into the left ventricle of membrane-bound KL-deficient Sl/Sl(d) or wild-type (WT) mice undergoing MI. Control LV/enGFP injection led to measurable reporter gene expression in hearts. Injection of LV/KL-2 attenuated adverse left ventricular remodeling and dramatically improved survival post-MI in both Sl/Sl(d) and WT mice (from 12 to 71% and 35 to 73%, respectively, versus controls). With regard toward beginning to understand the possible salutary mechanisms involved in this effect, differential staining patterns of Sca-1 and Ly49 on peripheral blood (PB) cells from therapeutically treated animals was found. Our data show that LV/KL-2 gene therapy is a promising treatment for MI.

Macrophage colony stimulating factor expression in human cardiac cells is upregulated by tumor necrosis factor-alpha via an NF-kappaB dependent mechanism

INTRODUCTION

Macrophage colony stimulating factor (M-CSF) is a key factor for monocyte and macrophage survival and proliferation. M-CSF has been implicated in cardiac healing and repair after myocardial infarction.

METHODS AND RESULTS

We show by immunohistochemistry and Western blotting analysis that M-CSF protein is present in human heart tissue. Cultured human adult cardiac myocytes (HACM) and human adult cardiac fibroblasts (HACF) isolated from human myocardial tissue constitutively express M-CSF. When HACM and HACF were treated with tumor necrosis factor-alpha (TNF-alpha) M-CSF protein production and M-CSF mRNA expression, determined by ELISA or by using RT-PCR, respectively, was significantly increased. To determine a possible role of nuclear factor kappaB (NF-kappaB) and activating protein 1 (AP-1) in M-CSF regulation, blockers to both pathways and an adenovirus overexpressing a dominant negative (dn) form of IkappaB kinase 2 (IKK2) were used. Only the NF-kappaB blocker dimethylfumarate and the dn IKK2, but not januskinase inhibitor-1 (JNK-I), were able to block the TNF-alpha-induced increase in M-CSF production in these cells, suggesting that the induction of M-CSF through TNF-alpha is mainly dependent on the activation of the NF-kappaB pathway. The monocyte activation marker CD11b was significantly increased after incubating U937 cells with conditioned medium from HACM or HACF as determined by FACS analysis.

CONCLUSIONS

Our in vitro data taken together with our immunohistochemistry data suggest that human cardiac cells constitutively express M-CSF. This expression of M-CSF in the human heart and its upregulation by TNF-alpha might contribute to monocyte and macrophage survival and differentiation.

Crystallization and preliminary X-ray diffraction of human interleukin-7 bound to unglycosylated and glycosylated forms of its alpha-receptor

The interleukin-7 (IL-7) signaling pathway plays an essential role in the development, proliferation and homeostasis of T and B cells in cell-mediated immunity. Understimulation and overstimulation of the IL-7 signaling pathway leads to severe combined immunodeficiency, autoimmune reactions, heart disease and cancers. Stimulation of the IL-7 pathway begins with IL-7 binding to its alpha-receptor, IL-7R alpha. Protein crystals of unglycosylated and glycosylated complexes of human IL-7-IL-7R alpha extracellular domain (ECD) obtained using a surface entropy-reduction approach diffract to 2.7 and 3.0 A, respectively. Anomalous dispersion methods will be used to solve the unglycosylated IL-7-IL-7R alpha ECD complex structure and this unglycosylated structure will then serve as a model in molecular-replacement attempts to solve the structure of the glycosylated IL-7-alpha-receptor complex.

Increased cardiomyocyte function and Ca2+ transients in mice during early congestive heart failure

End-stage heart failure is believed to involve depressed cardiomyocyte contractility and Ca2+ transients. However, the time course of these alterations is poorly understood. We examined alterations in myocyte excitation-contraction coupling in a mouse model of early congestive heart failure (CHF) following myocardial infarction. One week after myocardial infarction was induced by ligation of the left coronary artery, CHF mice were selected based on established criteria (increased left atrial diameter, increased lung weight). Sham-operated animals (SHAM) served as controls. Echocardiographic measurements showed decreased global function in early CHF relative to SHAM, but increased local function in viable regions of the myocardium which deteriorated with time. Cardiomyocytes isolated from the non-infarcted septum also exhibited larger contractions in early CHF than SHAM (CHF=219.6+/-15.3% of SHAM values, P<0.05; 1 Hz field stimulation), and relaxation was more rapid (time to 50% relaxation=82.9+/-5.5% of SHAM values, P<0.05). Ca2+ transients (fluo-4 AM) were larger and decayed more rapidly in CHF than SHAM during both field stimulation (1 Hz) and voltage-clamp steps. Sarcoplasmic reticulum (SR) Ca2+ content was increased. Western blots showed that while SR Ca2+ ATPase (SERCA) expression was unaltered in CHF, phospholamban (PLB) was downregulated (60+/-11% of SHAM values, P<0.05). Thus, an increased SERCA/PLB ratio in CHF may promote SR Ca2+ re-uptake. Additionally, peak L-type Ca2+ current and Na+/Ca2+ exchanger expression were increased in CHF, suggesting increased sarcolemmal Ca2+ flux. Thus, in early CHF, alterations in Ca2+ homeostasis improve cardiomyocyte contractility which may compensate for loss of function in the infarction area.

Non-canonical Wnt signaling enhances differentiation of Sca1+/c-kit+ adipose-derived murine stromal vascular cells into spontaneously beating cardiac myocytes

Recent reports have described a stem cell population termed stromal vascular cells (SVCs) derived from the stromal vascular fraction of adipose tissue, which are capable of intrinsic differentiation into spontaneously beating cardiomyocytes in vitro. The objective of this study was to further define the cardiac lineage differentiation potential of SVCs in vitro and to establish methods for enriching SVC-derived beating cardiac myocytes. SVCs were isolated from the stromal vascular fraction of murine adipose tissue. Cells were cultured in methylcellulose-based murine stem cell media. Analysis of SVC-derived beating myocytes included Western blot and calcium imaging. Enrichment of acutely isolated SVCs was carried out using antibody-tagged magnetic nanoparticles, and pharmacologic manipulation of Wnt and cytokine signaling. Under initial media conditions, spontaneously beating SVCs expressed both cardiac developmental and adult protein isoforms. Functionally, this specialized population can spontaneously contract and pace under field stimulation and shows the presence of coordinated calcium transients. Importantly, this study provides evidence for two independent mechanisms of enriching the cardiac differentiation of SVCs. First, this study shows that differentiation of SVCs into cardiac myocytes is augmented by non-canonical Wnt agonists, canonical Wnt antagonists, and cytokines. Second, SVCs capable of cardiac lineage differentiation can be enriched by selection for stem cell-specific membrane markers Sca1 and c-kit. Adipose-derived SVCs are a unique population of stem cells that show evidence of cardiac lineage development making them a potential source for stem cell-based cardiac regeneration studies.

Increase in circulating bone marrow progenitor cells after myocardial infarction

BACKGROUND

Most circulating blood cells expressing the marker CD34 are bone marrow progenitor cells. These cells differentiate into cardiomyocytes, endothelial and smooth muscle cells after myocardial infarction in vivo. Mobilization of bone marrow progenitor cells into the peripheral blood after myocardial infarction may supply these cells to the heart. Rise in CD34+ cell concentrations following myocardial infarction would support the existence of myocardial-initiated mobilization.

METHODS

Serial measurements of circulating CD34+ cells were made in 42 consecutive patients presenting with first ST-elevation myocardial infarction. Measurement of serum concentrations of monocyte chemoattractant protein-1, stromal derived factor-1, hepatocyte growth factor, interleukin-17 and thrombopoietin was also performed. Samples were drawn on day 1 after myocardial infarction, and on days 4, 8 and 12. Levels of CD34+ cells and cytokines were also measured in 15 controls.

RESULTS

By day 8, the mean concentration of CD34+ cells rose by 74% above mean control level of 2527 cells/ml, and 41% above day 1 mean (P=0.02). This rise was sustained on day 12 (P=0.05). On day 1, there was a 9.3-fold rise in hepatocyte growth factor above the control level of 589 pg/ml (P=0.002). Hepatocyte growth factor levels declined from the day 1 mean of 6061 to 1485 pg/ml on day 12 (P=0.002). No significant change in stromal derived factor-1, interleukin-17, monocyte chemoattractant protein-1 and thrombopoietin was observed. Elevations in CD34+ cells and hepatocyte growth factor were not related to infarction size as estimated on echocardiography.

CONCLUSIONS

Elevation in the concentration of circulating CD34+ cells after myocardial infarction suggests that myocardial initiated bone marrow progenitor cell mobilization exists in humans. The cytokines studied in our protocol are not likely to play a direct role in bone marrow progenitor cell mobilization.

Reactive oxygen species drives myocardial angiogenesis?

Neovascularization, the natural physiological process of formation of new blood vessels, is extremely important for ameliorating the function of the heart that undergoes ischemic stress. This process is potentially important for the treatment of ischemic heart and limb diseases, which includes formation of capillaries (angiogenesis) and collateral arteries. Ischemia or coronary artery occlusion induces vascular endothelial growth factor (VEGF) in the experimental rat myocardial infarction model, and this molecule encourages development of coronary collateral circulation and retention of the blood supply to the ischemic area. Restoration of the blood supply to the ischemic area prevents cardiomyocyte death and cardiac remodeling. Among the various triggers and enhancers of angiogenesis, hypoxic or ischemic preconditioning, as well as pharmacologic agents such as statin and resveratrol, have been identified as important stimuli for the induction of new vessel growth. It has already been demonstrated that the VEGF family and its receptor system is the fundamental regulator in the redox cell signaling of angiogenesis. This review article will focus on the role of reactive oxygen species in the process of myocardial angiogenesis.

T-tubule disorganization and reduced synchrony of Ca2+ release in murine cardiomyocytes following myocardial infarction

In cardiac myocytes, initiation of excitation-contraction coupling is highly localized near the T-tubule network. Myocytes with a dense T-tubule network exhibit rapid and homogeneous sarcoplasmic reticulum (SR) Ca(2+) release throughout the cell. We examined whether progressive changes in T-tubule organization and Ca(2+) release synchrony occur in a murine model of congestive heart failure (CHF). Myocardial infarction (MI) was induced by ligation of the left coronary artery, and CHF was diagnosed by echocardiography (left atrial diameter >2.0 mm). CHF mice were killed at 1 or 3 weeks following MI (1-week CHF, 3-week CHF) and cardiomyocytes were isolated from viable regions of the septum, excluding the MI border zone. Septal myocytes from SHAM-operated mice served as controls. T-tubules were visualized by confocal microscopy in cells stained with di-8-ANEPPS. SHAM cells exhibited a regular striated T-tubule pattern. However, 1-week CHF cells showed slightly disorganized T-tubule structure, and more profound disorganization occurred in 3-week CHF with irregular gaps between adjacent T-tubules. Line-scan images of Ca(2+) transients (fluo-4 AM, 1 Hz) showed that regions of delayed Ca(2+) release occurred at these gaps. Three-week CHF cells exhibited an increased number of delayed release regions, and increased overall dyssynchrony of Ca(2+) release. A common pattern of Ca(2+) release in 3-week CHF was maintained between consecutive transients, and was not altered by forskolin application. Thus, progressive T-tubule disorganization during CHF promotes dyssynchrony of SR Ca(2+) release which may contribute to the slowing of SR Ca(2+) release in this condition.

Versican is induced in infiltrating monocytes in myocardial infarction

Versican, a large chondroitin sulfate proteoglycan, plays a role in conditions such as wound healing and tissue remodelling. To test the hypothesis that versican expression is transiently upregulated and plays a role in the infarcted heart, we examined its expression in a rat model of myocardial infarction. Northern blot analysis demonstrated increased expression of versican mRNA. Quantitative real-time RT-PCR analysis revealed that versican mRNA began to increase as early as 6 h and reached its maximal level 2 days after coronary artery ligation. Versican mRNA then gradually decreased, while the mRNA of decorin, another small proteoglycan, increased thereafter. Versican mRNA was localized in monocytes, as indicated by CD68-positive staining, around the infarct tissue. The induction of versican mRNA was accelerated by ischemia/reperfusion (I/R), which was characterized by massive cell infiltration and enhanced inflammatory response. To examine the alteration of versican expression in monocytes/macrophages, we isolated human peripheral blood mononuclear cells and stimulated them with granulocyte/macrophage colony-stimulating factor (GM-CSF). Stimulation of mononuclear cells with GM-CSF increased the expression of versican mRNA as well as cytokine induction. The production of versican by monocytes in the infarct area represents a novel finding of the expression of an extracellular matrix gene by monocytes in the infarcted heart. We suggest that upregulation of versican in the infarcted myocardium may have a role in the inflammatory reaction, which mediates subsequent chemotaxis in the infarcted heart.

Alveolar hypoxia induces left ventricular diastolic dysfunction and reduces phosphorylation of phospholamban in mice

Chronic obstructive pulmonary disease (COPD) may lead to pulmonary hypertension (PH) and reduced function of the right ventricle (RV). However, COPD patients may also develop left ventricular (LV) diastolic dysfunction. We hypothesized that alveolar hypoxia induces LV diastolic dysfunction and changes in proteins governing Ca(2+) removal from cytosol during diastole. Mice exposed to 10% oxygen for 1, 2, or 4 wk were compared with controls. Cardiac hemodynamics were assessed with Doppler echocardiography and a microtransducer catheter under general anesthesia. The pulmonary artery blood flow acceleration time was shorter and RV pressure was higher after 4 wk of hypoxia compared with controls (both P < 0.05). In the RV and LV, 4 wk of hypoxia induced a prolongation of the time constant of isovolumic pressure decay (51% RV, 43% LV) and a reduction in the maximum rate of decline in pressure compared with control (42% RV, 42% LV, all P < 0.05), indicating impaired relaxation and diastolic dysfunction. Alveolar hypoxia induced a 38%, 47%, and 27% reduction in Ser16-phosphorylated phospholamban (PLB) in the RV after 1, 2, and 4 wk of hypoxia, respectively, and at the same time points, Ser16-phosphorylated PLB in the LV was downregulated by 32%, 34%, and 25% (all P < 0.05). The amounts of PLB and sarco(endo)plasmic reticulum Ca(2+) ATPase (SERCA2a) were not changed. In conclusion, chronic alveolar hypoxia induces hypophosphorylation of PLB at Ser16, which might be a mechanism for impaired relaxation and diastolic dysfunction in both the RV and LV.

Treatment with granulocyte colony-stimulating factor ameliorates chronic heart failure

Chronic heart failure remains a leading cause of mortality. Although granulocyte colony-stimulating factor (G-CSF) is reported to have a beneficial affect on postinfarction cardiac remodeling and dysfunction when administered before the onset of or at the acute stage of myocardial infarction (MI), its effect on established heart failure is unknown. We show here that subcutaneous administration of G-CSF greatly improves the function of murine hearts failing due to a large, healed MI. G-CSF changed the geometry of the infarct scar from elongated and thin to short and thick, induced hypertrophy among surviving cardiomyocytes, and reduced myocardial fibrosis. Expression of G-CSF receptor was confirmed in failing hearts and was upregulated by G-CSF treatment. G-CSF treatment also led to activation of signal transducer and activator of transcription-3 and induction of GATA-4 and various sarcomeric proteins such as myosin heavy chain, troponin I and desmin. Expression of metalloproteinase-2 and -9 was also increased in G-CSF-treated hearts, while that of tumor necrosis factor-alpha, angiotensin II type 1 receptor (AT1) and transforming growth factor-beta1 was reduced. Although activation of Akt was noted in G-CSF-treated hearts, vessel density was unchanged, and apoptosis was too rare to exert a meaningful effect. No bone marrow-derived cardiomyocytes or vascular cells were detected in the failing hearts of green fluorescent protein chimeric mice. Finally, beneficial effects of G-CSF on cardiac function were found persisting long after discontinuing the treatment (2 weeks). Collectively, these findings suggest G-CSF administration could be an effective approach to treating chronic heart failure following a large MI.

Reduced immune responses to an aseptic inflammation in mice with congestive heart failure

We previously found that mice with congestive heart failure (CHF) were anemic, had decreased bone marrow haematopoiesis and functionally impaired neutrophilic granulocytes despite normal blood concentrations of these cells. We now asked if CHF-mice could mount an adequate immune response when challenged with an acute inflammation. A postinfarction heart failure was induced in mice. Six weeks later the mice had developed CHF. At that time a sterile peritonitis was induced by injection of a casein digest. Five hours after this injection a marked neutrophilia had developed. Specimens were then obtained from peritoneal washings, bone marrow and blood. Total bone marrow cell numbers were halved in CHF-peritonitis mice compared with sham-peritonitis mice. Bone marrow colony-forming cell numbers in CHF-peritonitis mice were only 14% of those in sham-peritonitis mice. The mobilization of leucocytes to the blood was much lower in CHF-peritonitis mice than in sham-peritonitis mice (5.6 vs. 8.1 million cells/mL), as was the peritoneal influx of these cells (1.6 vs. 4.1 million cells). A profound decline (>50%) in the functional activity, determined with various in vitro assays, was evident for both neutrophilic granulocytes and lymphocytes from CHF-peritonitis mice. Heart failure after myocardial infarction in mice may severely compromise their ability to combat an inflammatory challenge.

Daily administration of interleukin-18 causes myocardial dysfunction in healthy mice

Although increased levels of circulating interleukin (IL)-18 have been demonstrated in patients with cardiovascular diseases, the functional consequences of chronically increased circulating IL-18 with respect to myocardial function have not been defined. Thus we aimed to examine the effects of chronic IL-18 exposure on left ventricular (LV) function in healthy mice. Moreover, to clarify whether IL-18 has direct effects on the cardiomyocyte, we examined effects of IL-18 on cardiomyocytes in vitro. After 7 days of daily intraperitoneal injections of 0.5 microg IL-18 in healthy mice, a 40% (P < 0.05) reduction in the LV maximal positive derivative, a 25% (P < 0.05) reduction in the LV maximal rate of pressure decay, and a 2.8-fold (P < 0.001) increase in the LV end-diastolic pressure were measured, consistent with myocardial dysfunction. Furthermore, we measured a 75% (P < 0.05) reduction in beta-adrenergic responsiveness to isoproterenol. IL-18 induced myocardial hypertrophy, and there was a 2.9-fold increase (P < 0.05) in atrial natriuretic peptide mRNA expression in the LV myocardium. In vitro examinations of isolated adult rat cardiomyocytes being stimulated with IL-18 (0.1 microg/ml) exhibited an increase in peak Ca2+ transients (P < 0.05) and in diastolic Ca2+ concentrations (P < 0.05). In conclusion, this study shows that daily administration of IL-18 in healthy mice causes LV myocardial dysfunction and blunted beta-adrenergic responsiveness to isoproterenol. A direct effect of IL-18 on the cardiomyocyte in vitro was demonstrated, suggesting that IL-18 reduces the responsiveness of the myofilaments to Ca2+. Finally, induction of myocardial hypertrophy by IL-18 indicates a role for this cytokine in myocardial remodeling.

Echocardiographic parameters discriminating myocardial infarction with pulmonary congestion from myocardial infarction without congestion in the mouse

Our aim was to establish parameters describing systolic and diastolic function in mice after myocardial infarction (MI) that distinguish MI with pulmonary congestion from MI without congestion. Echocardiography, left ventricular (LV) catheterization, and infarct size measurements were performed on days 3, 5, 7, and 14 after ligation of the left coronary artery in C57BL/6 mice. Sham-operated mice were used as controls (Sham). MI mice with lung weight normalized to tibial length >125% of the average in the corresponding Sham group were considered to have pulmonary congestion (MIchf). MI mice with a smaller increase were called MI nonfailing (MInf). An infarct >40% of total LV circumference measured in two-dimensional long axis distinguished MIchf from MInf on both an average and an individual basis. Mean maximum rate of rise of LV pressure, LV fractional shortening, and posterior wall shortening velocity were significantly lower in MIchf compared with Sham at all time points and to MInf at 7 days. The diastolic parameters mitral flow deceleration velocity, LV end-diastolic pressure, and maximum rate of decline in LV pressure (LVdP/dtmin) discriminated the MIchf groups from Sham at all time points. Mitral flow deceleration velocity and LVdP/dtmin separated MIchf from MInf at 7 days. In addition to distinguishing all the groups on an average basis, left atrial diameter distinguished all MIchf animals from Sham and MInf. In conclusion, significantly increased left atrial diameter and infarct size >40% of total LV circumference may serve as major criteria for heart failure with pulmonary congestion after MI in mice.

Hemodynamic forces regulate mural macrophage infiltration in experimental aortic aneurysms

Blood flow (BF) and wall shear stress (WSS) influence reactive oxygen species production and oxidative stress in abdominal aortic aneurysm (AAA) disease. To gain further insight into the mechanisms of hemodynamic influences on AAA inflammation, we examined aneurysm macrophage density, chemotaxis and survival under varying aortic flow conditions. Rat AAAs were created via porcine pancreatic elastase (PPE) infusion. In selected cohorts, AAA flow was increased via left common femoral arteriovenous fistula (AVF) creation (HF-AAA) or decreased by left common iliac ligation (LF-AAA). WSS was highest in HF-AAA (10.4 +/- 2.3 dyn/cm(2) vs. 2.4 +/- 0.4 and 0.5 +/- 0.2 for NF- and LF-AAA, respectively, P < 0.001) 7 days after PPE infusion, with reduced medial macrophage density and increased apoptosis. Adventitial macrophage density was not significantly influenced by flow. Monocyte chemoattractant protein-1 (MCP-1) and granulocyte-macrophage colony-stimulating factor (GM-CSF) gene expression correlated with observed macrophage densities in the media and adventitia. Luminal flow conditions regulate AAA inflammation in part via influences on medial macrophage density. Hemodynamic forces may modulate AAA inflammation and diameter enlargement via direct regulation of intimal macrophage adhesion, transmural migration or survival.

Mouse cardiac surgery: comprehensive techniques for the generation of mouse models of human diseases and their application for genomic studies

Mouse models mimicking human diseases are important tools in trying to understand the underlying mechanisms of many disease states. Several surgical models have been described that mimic human myocardial infarction (MI) and pressure-overload-induced cardiac hypertrophy. However, there are very few detailed descriptions for performing these surgical techniques in mice. Consequently, the number of laboratories that are proficient in performing cardiac surgical procedures in mice has been limited. Microarray technologies measure the expression of thousands of genes simultaneously, allowing for the identification of genes and pathways that may potentially be involved in the disease process. The statistical analysis of microarray experiments is highly influenced by the amount of variability in the experiment. To keep the number of required independent biological replicates and the associated costs of the study to a minimum, it is critical to minimize experimental variability by optimizing the surgical procedures. The aim of this publication was to provide a detailed description of techniques required to perform mouse cardiac surgery, such that these models can be utilized for genomic studies. A description of three major surgical procedures has been provided: 1) aortic constriction, 2) pulmonary artery banding, 3) MI (including ischemia-reperfusion). Emphasis has been placed on technical procedures with the inclusion of thorough descriptions of all equipment and devices employed in surgery, as well as the application of such techniques for expression profiling studies. The cardiac surgical techniques described have been, and will continue to be, important for elucidating the molecular mechanisms of cardiac hypertrophy and failure with high-throughput technology.

Evaluation of a new fiber-optic pressure recording system for cardiovascular measurements in mice

We have tested a new fiber-optic pressure recording system, Samba, with a thin fiber [outer diameter (OD) = 0.25 mm] and a pressure sensor (length and OD = 0.42 mm) attached to the end. The accuracy of the system tested in vitro was good, with a coefficient of variation of 2.54% at 100 mmHg. The drift was <0.45 mmHg/h, and the temperature sensitivity was approximately 0.07 mmHg/1 degrees C between 22 and 37 degrees C. The frequency response characteristics were similar to a 1.4-Fr Millar catheter (0-200 Hz). Introduction of the Samba sensor from the right carotid artery into the left ventricle in six mice caused no drop in mean aortic pressure, whereas introduction of a 1.4-Fr Millar catheter (OD = 0.47 mm; n = 6) caused a pressure drop from 91.6 +/- 9.2 to 65.1 +/- 6.2 mmHg; P < 0.05. Thus the Samba sensor system may represent a new alternative to assess hemodynamic variables in the murine cardiovascular system.

Adult cardiac stem cells--where do we go from here?

A potential treatment for cardiovascular disease involves the transplantation of a patient's bone marrow stem cells into the heart of that same patient. In order to maximize the potential benefits to select patient populations, the continued clinical development of this technology will require a comprehensive understanding of the role(s) of the transplanted cells in the repair of damaged heart tissue as well as an understanding of which types of cardiac injury can be repaired by this approach. The widespread application of cardiovascular stem cell therapies, however, will likely be based on pharmacological approaches to enhance the capacity of endogenous bone marrow stem cells to provide for the replacement of cardiac muscle and vascular cells after myocardial injury.

Auto Repair on the Aging Stem Cell Superhighway

Adult bone marrow stem cells offer the potential for rejuvenation of diseased or damaged tissues and organs. The greatest need for such a treatment in older individuals is to counter age-associated predisposition to cardiovascular diseases. Unfortunately, changes in senescent vascular function might limit the recruitment of bone marrow-derived precursor cells. In order to provide the patient with the conduits required to deliver bone marrow cells to damaged tissues, it is essential to develop strategies to overcome these limitations. This effort will require novel approaches to reverse aging-associated vascular dysfunction, including reharnessing the potential of stem cells from the aging bone marrow for vascular repair.