Apoptotic cells enhance sphingosine-1-phosphate receptor 1 dependent macrophage migration

The lipid sphingosine-1-phosphate (S1P) is a chemokine for a variety of immune cells including lymphocytes and monocytes. Migration toward S1P is determined by the S1P receptor expression profile, with S1PR1/3 (where S1PR is S1P receptor) stimulating and S1PR2 attenuating migration. However, the impact and physiological significance of S1P-induced migration of macrophages is largely unclear. We observed that alternative activation of human macrophages, by IL-4 or apoptotic cells (ACs), enhanced S1PR1 expression. Moreover, ACs provoked macrophage migration toward S1P in an S1PR1-dependent manner as confirmed by pharmacological receptor inhibition and S1PR1-deficient murine macrophages. In a mouse model of resolving peritoneal inflammation, F4/80-driven deletion of S1PR1 reduced postinflammatory macrophage emigration from inflammatory sites. S1PR1 expression on macrophages might, therefore, be relevant for restoring tissue homeostasis during the resolution of inflammation.

Loss of Survivin influences liver regeneration and is associated with impaired Aurora B function

The chromosomal passenger complex (CPC) acts as a key regulator of mitosis, preventing asymmetric segregation of chromosomal material into daughter cells. The CPC is composed of three non-enzymatic components termed Survivin, the inner centromere protein (INCENP) and Borealin, and an enzymatic component, Aurora B kinase. Survivin is necessary for the appropriate separation of sister chromatids during mitosis and is involved in liver regeneration, but its role in regenerative processes is incompletely elucidated. Whether Survivin, which is classified as an inhibitor of apoptosis protein (IAP) based on domain composition, also has a role in apoptosis is controversial. The present study examined the in vivo effects of Survivin ablation in the liver and during liver regeneration after 70% hepatectomy in a hepatocyte-specific knockout mouse model. The absence of Survivin caused a reduction in the number of hepatocytes in the liver, together with an increase in cell volume, macronucleation and polyploidy, but no changes in apoptosis. During liver regeneration, mitosis of hepatocytes was associated with mislocalization of the members of the CPC, which were no longer detectable at the centromere despite an unchanged protein amount. Furthermore, the loss of survivin in regenerating hepatocytes was associated with reduced levels of phosphorylated Histone H3 at serine 28 and abolished phosphorylation of CENP-A and Hec1 at serine 55, which is a consequence of decreased Aurora B kinase activity. These data indicate that Survivin expression determines hepatocyte number during liver development and liver regeneration. Lack of Survivin causes mislocalization of the CPC members in combination with reduced Aurora B activity, leading to impaired phosphorylation of its centromeric target proteins and inappropriate cytokinesis.

Cardiovascular effects of sphingosine-1-phosphate (S1P)

Sphingosine-1-phosphate (S1P) regulates important functions in cardiac and vascular homeostasis. It has been implied to play causal roles in the pathogenesis of many cardiovascular disorders such as coronary artery disease, atherosclerosis, myocardial infarction, and heart failure. The majority of S1P in plasma is associated with high-density lipoproteins (HDL), and their S1P content has been shown to be responsible, at least in part, for several of the beneficial effects of HDL on cardiovascular risk. The attractiveness of S1P-based drugs for potential cardiovascular applications is increasing in the wake of the clinical approval of FTY720, but answers to important questions on the effects of S1P in cardiovascular biology and medicine must still be found. This chapter focuses on the current understanding of the role of S1P and its receptors in cardiovascular physiology, pathology, and disease.

[Congestive heart failure: reverse cardiac remodeling mediated by left ventricular assist devices]

Left ventricular assist devices (LVAD) are currently used to treat patients with terminal congestive heart failure as a bridge to transplantation or as destination therapy in individuals with contraindications for cardiac transplantation. The LVADs are pulsatile or non-pulsatile systems that transport blood from the left ventricle to the ascending aorta parallel to the circulation thus providing a profound volume and pressure reduction in the left ventricle. The use of LVADs is associated with a considerable decrease of cardiac hypertrophy and dilation with significantly improved cardiac performance in a small subset of patients. The underlying process is termed reverse cardiac remodelling and is characterized by a significant decrease in the size of cardiomyocytes and reversible regulation of numerous molecular systems in the myocardium.

Increase of ABCG2/BCRP+ side population stem cells in myocardium after ventricular unloading

BACKGROUND

A significant decrease in mean cardiomyocyte DNA content and increased numbers of diploid cardiomyocytes after unloading has been demonstrated, suggesting a numerical increase of cardiomyocytes. Despite a thorough search in that study, no mitoses explaining a potential net increase of cardiomyocytes has been observed. The heart harbors several stem cell populations, including c-kit (CD117)(+) stem cells and side population cells (SPC), which may proliferate after unloading and thus contribute to the generation of diploid cardiomyocytes. In this study we sought to determine, whether there is an increase of ABCG2(+) SPC and CD117(+) stem cells after unloading.

METHODS

In paired myocardial samples (prior to and after LVAD), the number of cells with immunoexpression of ABCG2, c-kit/CD117 and MEF-2 was assessed by immunohistochemistry. Their number was morphometrically determined and these data were correlated with the mean cardiomyocyte DNA content.

RESULTS

A significant increase of SPC and cells with coexpression of c-kit and MEF-2 after unloading was observed from 0.00013% in CHF to 0.0011%, and 0.013% to 0.035%, respectively after unloading (p = 0.001). A significant positive correlation between both SPC and cells with coexpression of c-kit and MEF-2 expression was observed (p = 0.007 and 0.01). No correlation was found between the number of SPC and the mean cardiomyocyte DNA content.

CONCLUSIONS

SPC are increased significantly in the myocardium after ventricular unloading, suggesting a role for stem cell proliferation during "reverse cardiac remodeling." These cells might proliferate and commit to different cell lineages, such as cardiomyocytes or endothelium, and thus ameliorate cardiac function.

Load-reducing therapy prevents development of arrhythmogenic right ventricular cardiomyopathy in plakoglobin-deficient mice

OBJECTIVES

We used a murine model of arrhythmogenic right ventricular cardiomyopathy (ARVC) to test whether reducing ventricular load prevents or slows development of this cardiomyopathy.

BACKGROUND

At present, no therapy exists to slow progression of ARVC. Genetically conferred dysfunction of the mechanical cell-cell connections, often associated with reduced expression of plakoglobin, is thought to cause ARVC.

METHODS

Littermate pairs of heterozygous plakoglobin-deficient mice (plako(+/-)) and wild-type (WT) littermates underwent 7 weeks of endurance training (daily swimming). Mice were randomized to blinded load-reducing therapy (furosemide and nitrates) or placebo.

RESULTS

Therapy prevented training-induced right ventricular (RV) enlargement in plako(+/-) mice (RV volume: untreated plako(+/-) 136 ± 5 μl; treated plako(+/-) 78 ± 5 μl; WT 81 ± 5 μl; p < 0.01 for untreated vs. WT and untreated vs. treated; mean ± SEM). In isolated, Langendorff-perfused hearts, ventricular tachycardias (VTs) were more often induced in untreated plako(+/-) hearts (15 of 25), than in treated plako(+/-) hearts (5 of 19) or in WT hearts (6 of 21, both p < 0.05). Epicardial mapping of the RV identified macro-re-entry as the mechanism of ventricular tachycardia. The RV longitudinal conduction velocity was reduced in untreated but not in treated plako(+/-) mice (p < 0.01 for untreated vs. WT and untreated vs. treated). Myocardial concentration of phosphorylated connexin43 was lower in plako(+/-) hearts with VTs compared with hearts without VTs and was reduced in untreated plako(+/-) compared with WT (both p < 0.05). Plako(+/-) hearts showed reduced myocardial plakoglobin concentration, whereas β-catenin and N-cadherin concentration was not changed.

CONCLUSIONS

Load-reducing therapy prevents training-induced development of ARVC in plako(+/-) mice.

Acute vasomotor paralysis and potential downstream effects of paclitaxel from stents implanted for saphenous vein aorto-coronary bypass stenosis

Implantation of bare metal stents (BMS) induces the release not only of particulate debris, but also of soluble vasoconstrictors which contribute to microvascular impairment. So this study aimed at addressing the potential attenuation of such vasoconstriction using paclitaxel eluting stents (PES). Using a distal protection/aspiration device, coronary arterial blood was retrieved before and during stent [n = 14 BMS, n = 14 PES, n = 3 sirolimus eluting stents (SES)] implantation in patients with saphenous vein aorto-coronary bypass stenosis and analyzed for plasma serotonin and thromboxane B(2) concentrations. The vasoconstriction of rat mesenteric arteries with intact (+E) and denuded (-E) endothelium in response to coronary arterial or aspirate plasma was quantified and normalized to that by potassium chloride (KCl(max) = 100%). Coronary arterial plasma before stent implantation induced a vasoconstriction of 30-43%, which was independent of endothelial integrity. Serotonin-release was 2.2 ± 0.5 μmol/l with BMS and 2.0 ± 0.4 μmol/l with PES, thromboxane B(2)-release was 26 ± 5 pg/ml with BMS and 22 ± 8 pg/ml with PES. BMS- and SES-aspirate plasma induced a vasoconstriction of 68 ± 18% (+E)/93 ± 14% (-E) and 81 ± 17% (+E)/124 ± 14% (-E), respectively. In contrast, PES-aspirate plasma induced only minor vasoconstriction of 8 ± 3% (+E)/12 ± 5% (-E). Addition of paclitaxel to BMS-aspirate plasma attenuated vasoconstriction. PES-aspirate induced microtubular condensation in immunofluorescence microscopy. Results indicate that aspirate from PES implantation attenuates vasoconstriction, possibly secondary to microtubular stabilization. Such acute downstream vascular paralysis could be beneficial in preventing a no-reflow phenomenon in patients undergoing stenting.

Vasoconstrictor Potential of Coronary Aspirate From Patients Undergoing Stenting of Saphenous Vein Aortocoronary Bypass Grafts and Its Pharmacological Attenuation

Rationale:

Stent implantation into atherosclerotic plaques releases, apart from particulate debris, soluble substances that contribute to impaired microvascular perfusion.

Objective:

To quantify the release of vasoconstrictors and to determine the efficacy of coronary dilators to attenuate their action.

Methods and Results:

Using a distal protection/aspiration device, coronary arterial blood was retrieved before and during stenting in 22 patients with severe saphenous vein aorto-coronary bypass stenoses. The release of catecholamines, endothelin, serotonin, thromboxane B 2 , and tumor necrosis factor (TNF)α was measured. The response of rat mesenteric arteries with intact (+E) and denuded (−E) endothelium to aspirate plasma was normalized to that by KCl. Responses to selective receptor blockade, adenosine, nitroprusside, and verapamil against the aspirate-induced constriction were determined. The coronary arterial plasma withdrawn before stenting induced 21±5% and the aspirate plasma after stenting induced 95±8% of maximum KCl-induced vasoconstriction. Serotonin, thromboxane B 2 , and TNFα release into aspirate plasma increased by 1.9±0.2 μmol/L, 25.6±3.1 pg/mL, and 19.7±6.1 pg/mL, respectively, during stenting. The aspirate-induced vasoconstriction was largely antagonized by selective serotonin receptor blockade, with little further antagonism by additional thromboxane receptor blockade. TNFα did not induce constriction per se but potentiated the constriction with serotonin and the thromboxane-analog U-46619 in arteries +E. The concentrations to induce half-maximal vasodilation were comparable for nitroprusside (+E, 3.3×10 −8 ; −E, 1.9×10 −8 mol/L) and verapamil (+E, 8.3×10 −8 ; −E, 7.8×10 −8 mol/L), and the vasoconstriction was eventually eliminated. The vasodilator response to adenosine was dependent on functional endothelium and weaker.

Conclusion:

Serotonin is the main coronary vasoconstrictor after stenting, and thromboxane and TNFα somewhat potentiate the serotonin response. Nitroprusside and verapamil are more potent than adenosine to attenuate the aspirate plasma-induced vasoconstriction, and they are not dependent on functional endothelium.

Sphingosine-1-phosphate receptor 3 promotes recruitment of monocyte/macrophages in inflammation and atherosclerosis

RATIONALE

The role of sphingosine-1-phosphate (S1P) and its receptors in the pathogenesis of atherosclerosis has not been investigated.

OBJECTIVE

We hypothesized that the S1P receptor 3 (S1P(3)) plays a causal role in the pathogenesis of atherosclerosis.

METHODS AND RESULTS

We examined atherosclerotic lesion development in mice deficient for S1P(3) and apolipoprotein (Apo)E. Although S1P(3) deficiency did not affect lesion size after 25 or 45 weeks of normal chow diet, it resulted in a dramatic reduction of the monocyte/macrophage content in lesions of S1P(3)(-/-)/ApoE(-/-) double knockout mice. To search for putative defects in monocyte/macrophage recruitment, we examined macrophage-driven inflammation during thioglycollate-induced peritonitis. Elicited peritoneal macrophages were reduced in S1P(3)-deficient mice and expressed lower levels of tumor necrosis factor-α and monocyte chemoattractant protein-1. Bone marrow-derived S1P(3)-deficient macrophages produced less MCP-1 in response to lipopolysaccharide stimulation. In vitro, S1P was chemotactic for wild-type but not S1P(3)-deficient peritoneal macrophages. In vivo, S1P concentration increased rapidly in the peritoneal cavity after initiation of peritonitis. Treatment with the S1P analog FTY720 attenuated macrophage recruitment to the peritoneum. Studies in bone marrow chimeras showed that S1P(3) in both hematopoietic and nonhematopoietic cells contributed to monocyte/macrophage accumulation in atherosclerotic lesions. Finally, S1P(3) deficiency increased the smooth muscle cell content of atherosclerotic lesions and enhanced neointima formation after carotid ligation arguing for an antiproliferative/antimigratory role of S1P(3) in the arterial injury response.

CONCLUSIONS

Our data suggest that S1P(3) mediates the chemotactic effect of S1P in macrophages in vitro and in vivo and plays a causal role in atherosclerosis by promoting inflammatory monocyte/macrophage recruitment and altering smooth muscle cell behavior.

Sphingosine 1-phosphate levels in plasma and HDL are altered in coronary artery disease

High-density lipoproteins (HDL) are the major plasma carriers for sphingosine 1-phosphate (S1P) in healthy individuals, but their S1P content is unknown for patients with coronary artery disease (CAD). The aim of the study was to determine whether the S1P levels in plasma and HDL are altered in coronary artery disease. S1P was determined in plasma and HDL isolated by ultracentrifugation from patients with myocardial infarction (MI, n = 83), stable CAD (sCAD, n = 95), and controls (n = 85). In our study, total plasma S1P levels were lower in sCAD than in controls (305 vs. 350 pmol/mL). However, normalization to HDL-cholesterol (a known determinant of plasma S1P) revealed higher normalized plasma S1P levels in sCAD than in controls (725 vs. 542 pmol/mg) and even higher ones in MI (902 pmol/mg). The S1P amount contained in isolated HDL from these individuals was lower in sCAD than in controls (S1P per protein in HDL: 132 vs. 153 pmol/mg). The amount of total plasma S1P bound to HDL was lower in sCAD and MI than in controls (sCAD: 204, MI: 222, controls: 335 pmol/mL), while the non-HDL-bound S1P was, accordingly, higher (sCAD: 84, MI: 81, controls: 10 pmol/mL). HDL-bound plasma S1P was dependent on the plasma HDL-C in all groups, but normalization to HDL-C still yielded lower HDL-bound plasma S1P in patients with sCAD than in controls (465 vs. 523 pmol/mg). The ratio of non-HDL-bound plasma S1P to HDL-C-normalized HDL-bound S1P was also higher in both sCAD (0.18 mg/mL) and MI (0.15 mg/mL) than in controls (0.02 mg/mL). Remarkably, levels of non-HDL-bound plasma S1P correlated with the severity of CAD symptoms as graded by Canadian Cardiovascular Score, and discriminated patients with MI and sCAD from controls. Furthermore, a negative association was present between non-HDL-bound plasma S1P and the S1P content of isolated HDL in controls, but was absent in sCAD and MI. Finally, MI patients with symptom duration of less than 12 h had the highest levels of total and normalized plasma S1P, as well as the highest levels of S1P in isolated HDL. The HDL-C-normalized plasma level of S1P is increased in sCAD and even further in MI. This may be caused by an uptake defect of HDL for plasma S1P in CAD, and may represent a novel marker of HDL dysfunction.

Erythrocytes serve as a reservoir for cellular and extracellular sphingosine 1-phosphate

Sphingosine 1-phosphate (S1P) in blood is phosphorylated, stored, and transported by red blood cells (RBC). Release of S1P from RBC into plasma is a regulated process that does not occur in plasma- or serum-free media. Plasma fractionation and incubations with isolated and recombinant proteins identified high density lipoprotein (HDL) and serum albumin (SA) as non-redundant endogenous triggers for S1P release from RBC. S1P bound to SA and HDL was able to stimulate the S1P(1) receptor in calcium flux experiments. The binding capability of acceptor molecules triggers S1P release, as demonstrated with the anti-S1P antibody Sphingomab. More S1P was extracted from RBC membranes by HDL than by SA. Blood samples from anemic patients confirmed a reduced capacity for S1P release in plasma. In co-cultures of RBC and endothelial cells (EC), we observed transcellular transportation of S1P as a second function of RBC-associated S1P in the absence of SA and HDL and during tight RBC-EC contact, mimicking conditions in tissue interstitium and capillaries. In contrast to S1P bound to SA and HDL, RBC-associated S1P was significantly incorporated by EC after S1P lyase (SGPL1) inhibition. RBC-associated S1P, therefore, has two functions: (1) It contributes to the cellular pool of SGPL1-sensitive S1P in tissues after transcellular transportation and (2) it helps maintain extracellular S1P levels via SA and HDL independently from SGPL1 activity.

Endothelial functions of sphingosine-1-phosphate

The biologically active sphingolipid sphingosine-1-phosphate (S1P) plays key functions in the immune, inflammatory, and cardiovascular systems. In the vasculature, S1P and its receptors are involved in vessel morphogenesis and angiogenesis during embryonic development and in the adult organism both under normal and pathological conditions. Via its actions on endothelial and smooth muscle cells, S1P regulates arterial tone, vascular permeability, and tissue perfusion. Elevated local S1P levels during inflammation induce endothelial adhesion molecules, recruit inflammatory cells, and activate dendritic cells. At the same time, S1P activates a negative feedback loop that consecutively seals endothelial cell-cell contacts, decreases vascular leakage, and inhibits cytokine-induced leukocyte adhesion. Thus S1P determines not only the build-up, magnitude, and duration of an inflammatory reaction but also the pace of its resolution. This review focuses on the role S1P plays in endothelial function, its receptors and signalling pathways, and the role its major carrier high-density lipoproteins (HDL) play in its bioavailability and transport. We will also discuss the potential of interfering with S1P-S1P receptor interactions for the treatment of endothelial disorders and vascular pathologies.

Hemodynamic support by left ventricular assist devices reduces cardiomyocyte DNA content in the failing human heart

BACKGROUND

Whether adult cardiomyocytes have the capacity to regenerate in response to injury and, if so, to what extent are still issues of intense debate. In human heart failure, cardiomyocytes harbor a polyploid genome. A unique opportunity to study the mechanism of polyploidization is provided through the setting of hemodynamic support by left ventricular assist devices. Hence, the cardiomyocyte DNA content, nuclear morphology, and number of nuclei per cell were assessed before and after left ventricular assist device support.

METHODS AND RESULTS

In 23 paired myocardial samples, cardiomyocyte ploidy was investigated by DNA image cytometry, flow cytometry, and in situ hybridization. Nuclear cross-sectional area and perimeters were measured morphometrically, and the binucleated cardiomyocytes were counted. The median of the cardiomyocyte DNA content and the number of polyploid cardiomyocytes both declined significantly from 6.79 c to 4.7 c and 40.2% to 23%, whereas a significant increase in diploid cardiomyocytes from 33.4% to 50.3% and in binucleated cardiomyocytes from 4.5% to 10% after unloading was observed.

CONCLUSIONS

The decrease in polyploidy and increase in diploidy after left ventricular assist device suggest a numeric increase in diploid cardiomyocytes (eg, through cell cycle progression with completion of mitosis or by increased stem cells). The cardiac regeneration that follows may serve as a morphological correlate of the recovery observed in some patients after unloading.

Coronary microembolization: from bedside to bench and back to bedside

Coronary microembolization from the erosion or rupture of a vulnerable atherosclerotic plaque occurs spontaneously in acute coronary syndromes and iatrogenically during percutaneous coronary interventions. Typical consequences of coronary microembolization are microinfarcts with an inflammatory response, contractile dysfunction, and reduced coronary reserve. Apart from transient elevations of creatine kinase and troponin, microemboli can be visualized by intracoronary Doppler and the resulting microinfarcts by late-enhancement nuclear magnetic resonance. Statins, antiplatelet agents, and coronary vasodilators protect against microembolization and microinfarction when started before percutaneous coronary interventions. Distal protection devices can retrieve atherothrombotic debris and prevent its embolization into the microcirculation, but their effect on clinical outcome has been disappointing so far, except for saphenous vein bypass grafts. Devices for aspiration of thrombi and thrombus-derived vasoconstrictor, thrombogenic, and inflammatory substances, however, reduce thrombus burden, improve perfusion, and provide protection in patients with acute myocardial infarction.

Ventricular unloading is associated with increased 20s proteasome protein expression in the myocardium

BACKGROUND

The ubiquitin-proteasome system (UPS) breaks down misfolded and normal proteins, including cell cycle regulatory proteins involved in cardiac hypertrophy. Because congestive heart failure (CHF) increases cardiomyocyte cellular mass, indicative of increased protein synthesis and/or impaired breakdown, and ventricular unloading decreases cardiac hypertrophy and changes regulation of multiple molecular systems ("reverse cardiac remodeling"), we tested the hypothesis that ventricular unloading alters myocardial UPS.

METHODS

In 23 paired myocardial specimens (before and after unloading) ubiquitin, 20S proteasome, and cyclin D1 were investigated immunohistochemically and morphometrically quantified in relation to cardiomyocyte hypertrophy, DNA content, nuclear profile area and perimeter, and cyclin D1 protein expression. Moreover, 20S proteasome plasma concentrations were measured by enzyme-linked immunoassay (ELISA).

RESULTS

In CHF, sarcoplasmic 20S proteasome protein expression was significantly decreased compared with controls, but significantly increased after unloading. In contrast, sarcoplasmic ubiquitin protein was increased in CHF but significantly decreased after unloading, and both variables were inversely correlated. Cardiomyocyte 20S proteasome expression correlated inversely with cell size, mean DNA content, and cyclin D1, whereas ubiquitin protein expression was positively correlated with these parameters. The 20S proteasome plasma concentration was significantly increased after unloading.

CONCLUSIONS

Our data indicate that: (1) the UPS is depressed in CHF; and (2) this is reversed by ventricular unloading and associated with decreased cardiomyocyte hypertrophy, mean DNA content, and cell cycle regulatory proteins. The findings support the view that the UPS is involved in both the pathogenesis of cardiac hypertrophy and "reverse cardiac remodeling" after ventricular unloading.