Interleukin-6 stimulates circulating blood-derived endothelial progenitor cell angiogenesis in vitro

The cutaneous vascular system in chronic skin inflammation

The blood and lymphatic vasculature have an important role in skin homeostasis. Angiogenesis and lymphangiogenesis-the growth of new vessels from existing ones-have received tremendous interest because of their role in promoting cancer spread. However, there is increasing evidence that both vessel types also have a major role in acute and chronic inflammatory disorders. Vessels change their phenotype during inflammation (vascular remodeling). In inflamed skin, vascular remodeling consists of a hyperpermeable, enlarged network of vessels with increased blood flow, and influx of inflammatory cells. During chronic inflammation, the activated endothelium expresses adhesion molecules, cytokines, and other molecules that lead to leukocyte rolling, attachment, and migration into the skin. Recent studies reveal that inhibition of blood vessel activation exerts potent anti-inflammatory properties. Thus, anti-angiogenic drugs might be used to treat inflammatory conditions. In particular, topical application of anti-angiogenic drugs might be ideally suited to circumvent the adverse effects of systemic therapy with angiogenesis inhibitors. Our recent results indicate that stimulation of lymphatic vessel growth and function unexpectedly represents a new approach for treating chronic inflammatory disorders.

The angiogenic capacity from ligamentum flavum subsequent to inflammation: a critical component of the pathomechanism of hypertrophy

STUDY DESIGN

In vitro study about angiogenic potentiality of ligamentum flavum (LF) cells using coculture of human lumbar LF cells and activated macropage-like THP-1 cells.

OBJECTIVE

To test our hypothesis that activated LF, which was exposed to inflammation, induces angiogenesis, thus resulting in hypertrophy.

SUMMARY OF BACKGROUND DATA

Inflammatory reactions after mechanical stress produce fibrosis and scarring of the LF that result in hypertrophy, a major pathological feature of spinal stenosis. This study evaluated the roles of LF cells in the pathomechanism of hypertrophy, focusing on angiogenesis.

METHODS

To determine their response to the inflammatory reaction, human LF cells were cocultured with phorbol myristate acetate-stimulated macrophage-like THP-1 cells. The conditioned media were assayed for tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6, IL-8, vascular endothelial growth factor (VEGF), and transforming growth factor (TGF)-β1. Naïve and macrophage-exposed LF cells that responded to TNF-α/IL-1β were compared using the same outcome measures. Hypertrophied LF tissue was stained by TGF-β1 primary antibody using immunohistochemical method.

RESULTS

Larger quantities of IL-6, IL-8, and VEGF were secreted by cocultured cells than by macrophages alone and LF cells alone combined. Prior macrophage exposure increased the secretion of IL-8 and VEGF in response to TNF-α/IL-1β stimulation whereas IL-6 production was increased in response to IL-1β. The coculture appeared to increase TGF-β1 secretion but the level was lower than that for macrophage-like cells alone and LF cells alone combined.

CONCLUSION

LF cells interact with macrophage-like cells to produce angiogenesis-related factors except TGF-β1. Activated LF cells that have been exposed to macrophage, can impact the inducement of angiogenesis-related factors, suggesting that fibrosis and scarring during inflammatory reaction is the major pathomechanism of LF hypertrophy.

Effect of tocopherol supplementation during last trimester of pregnancy on mRNA abundances of interleukins and angiogenesis in ovine placenta and uterus

BACKGROUND

Interleukins (IL) play an important role in angiogenesis. Tocopherol possesses immunomodulating effect in addition to antioxidant property. The objective of this study was to determine whether gamma tocopherol's (gT) angiogenic activity in placental network is enhanced via promoting interleukins.

METHODS

Pregnant ewes (N=18) were supplemented, orally, with 500 mg of alpha tocopherol (aT; N=6) or 1,000 mg of gT (N=7) or placebo (CON; N=5) once daily from 107 to 137 days post breeding. Uterine and placental tissue samples were obtained at the end of supplementation to evaluate relative mRNA expressions of IL-1b, IL-6, IL-8, Tumor Necrosis Factor (TNF) alpha, Vascular Endothelial Growth Factor (VEGF), kinase insert domain receptor (KDR; VGFR2; a type III receptor tyrosine kinase), and soluble fms-like tyrosine kniase-1 (sFlt1 or sVEGFR1) in uterus, caruncle and cotyledon.

RESULTS

Oral supplementation of gT increased IL-6, IL-8, KDR and VEGF mRNA abundances whereas sFlt1 mRNA abundance was suppressed in uterus, caruncle and cotyledon, compared to aT and placebo treated ewes (P<0.05). The TNF alpha and IL-1b mRNA abundances were suppressed in uterus, caruncle and cotyledon but TNF alpha is higher in gT group compared to aT group (P<0.05), whereas IL-1b was similar between treatment groups (P>0.1).

CONCLUSIONS

Gamma tocopherol supplementation increased IL-6, IL-8, and KDR mRNA abundances and suppressed sFlt1 and TNFalpha mRNA abundances thereby increased VEGF mRNA expression and angiogenesis in placental vascular network during late gestation. It is plausible that the angiogenic effect of gamma tocopherol in placental vascular network is exerted via an alternate path by enhancing IL-6 and IL-8.

Vascular effects of glycoprotein130 ligands--part I: pathophysiological role

The vessel wall is no longer considered as only an anatomical barrier for blood cells but is recognized as an active endocrine organ. Dysfunction of the vessel wall occurs in various disease processes including atherosclerosis, hypertension, peripheral artery disease, aneurysms, and transplant and diabetic vasculopathies. Different cytokines were shown to modulate the behavior of the cells, which constitute the vessel wall such as immune cells, endothelial cells and smooth muscle cells. Glycoprotein 130 (gp130) is a common cytokine receptor that controls the activity of a group of cytokines, namely, interleukin (IL)-6, oncostatin M (OSM), IL-11, ciliary neurotrophic factor (CNTF), leukemia inhibitory factor (LIF), cardiotrophin-1 (CT-1), cardiotrophin-like cytokine (CLC), IL-27, and neuropoietin (NP). Gp130 and associated cytokines have abundantly diverse functions. Part I of this review focuses on the pathophysiological functions of gp130 ligands. We specifically describe vascular effects of these molecules and discuss the respective underlying molecular and cellular mechanisms.

Angiogenesis in peritoneal dialysis

Long-term exposure to peritoneal dialysis fluid induces morphological alterations, including angiogenesis, leading to a loss of ultrafiltration (UF) capacity. We discuss the effect of different factors in peritoneal dialysis (PD) on angiogenesis. In addition, we describe the process of angiogenesis and the possible role of different cell types in the peritoneum upon PD contributing to new blood vessel formation. Furthermore, we review several interventions used in our rat PD exposure model to decrease angiogenesis in PD. Moreover, we show new data on the use of sunitinib to inhibit angiogenesis in this rat model. Although various interventions seem to be promising, well-randomised clinical trials showing absolute prevention of angiogenesis and UF failure are, yet, still missing. To make real progress in PD treatment, the aim should be to prevent angiogenesis as well as peritoneal fibrosis and PD-induced inflammation.

Adrenomedullin augments the angiogenic potential of late outgrowth endothelial progenitor cells

The therapeutic utility of endothelial progenitor cells (EPCs) in cardiovascular disease is potentially hampered by their low numbers in the circulation, impaired functional activity, and inhibitory factors in the recipient. These obstacles can possibly be circumvented by the use of proangiogenic cytokines and peptides. We sought to examine the effect of the endogenous vasoactive peptide adrenomedullin (AM) on the angiogenic potential of late outgrowth EPCs and their release of proangiogenic and proinflammatory cytokines/chemokines. Human peripheral blood mononuclear cells were cultured until the appearance of typical late outgrowth EPC colonies. The effect of AM on EPC proliferation was assessed using a colorimetric MTS proliferation assay while differentiation and formation of tubular structures in an EPC/fibroblast coculture or matrigel assay was used to assess the angiogenic potential of the cells. Finally, the release and mRNA transcripts of cytokines/chemokines were quantified in stimulated vs. nonstimulated EPCs using real-time PCR and a bead-based multiplex assay. The cultured EPCs possessed an endothelial phenotype and expressed the AM receptor (calcitonin receptor-like receptor/receptor activity modifying protein-2). AM stimulation induced proliferation of EPCs compared with controls ( P < 0.05). Furthermore, AM produced a 36% and 80% increase in the formation of tubular networks in the EPC/fibroblast coculture and matrigel assay, respectively ( P < 0.05). These effects seemed to be mediated through the phosphatidylinositol 3-kinase/Akt signaling pathway. AM did not seem to significantly influence the release or production of IL-6, IL-8, VEGF, stromal cell-derived factor 1, or the expression of CXCR-4 or VEGF receptor 2. In conclusion, adrenomedullin augmented the growth and angiogenic properties of late outgrowth EPCs, but did not influence their paracrine properties.

Novel Endothelial Biomarkers: Implications for Periodontal Disease and CVD

Endothelial cells are actively involved in various aspects of vascular biology and different stages of atherosclerosis. Endothelial function is increasingly used as an important outcome measure in cardiovascular research. Endothelial progenitor cells (EPCs) are closely linked to endothelial function, and their biomarkers have received much attention. EPCs may not only serve as a pool of progenitor cells and possess the capacity to repair the damaged vasculature, but also act as potent effectors in systemic inflammation, suggesting that EPCs may play a critical role in maintaining endothelial function and the progression of cardiovascular disease (CVD). Emerging evidence shows an association of periodontal infections (gingivitis and periodontitis) with endothelial dysfunction, while the relevant mechanisms remain unknown. Our recent finding of the association of periodontitis with EPCs warrants their utilization as additional biomarkers in future studies on periodontal medicine. This review starts with a brief account on the current understanding of the nature of periodontal infections and their link with systemic inflammation and endothelial dysfunction. The paper also provides an update on endothelial biology and function as well as the novel biomarkers of EPCs and concludes with clinical studies on periodontal diseases and CVD.

Hypoxic/normoxic preconditioning increases endothelial differentiation potential of human bone marrow CD133+ cells

CD133+ cells are hemangioblasts that have capacity to generate into both hematopoietic and endothelial cells (ECs). Hypoxia/normoxia has shown to be the regulator of the balance between stemness and differentiation. In this study we performed Agilent's whole human genome oligo microarray analysis and examined the differentiation potential of the bone-marrow-derived CD133+ cells after hypoxic/normoxic preconditioning of CD133+ cells. Results showed that there was no significant increase in erythroid colony forming unit (CFU-E) and CFU-granulocyte, erythrocyte, monocyte, and megakaryocyte formation with cells treated under hypoxia/normoxia. However, a significant increment of EC forming unit at 24 h (143.2 +/- 8.0%) compared to 0 h (100 +/- 11.4%) was observed in CFU-EC analysis. Reverse transcription-polymerase chain reaction and immunostaining analysis showed that the differentiated cells diminished hematopoietic stem cell surface markers and acquired the gene markers and functional phenotype of ECs. The transcriptome profile revealed a cluster of 232 downregulated and 498 upregulated genes in cells treated for 24 h under hypoxia. The upregulated genes include angiogenic genes, angiogenic growth factor genes, angiogenic cytokine and chemokine genes, as well as angiogenic-positive regulatory genes, including FGFBP1, PDGFB, CCL15, CXCL12, CXCL6, IL-6, PTN, EREG, ERBB2, EDG5, FGF3, FHF2, GDF15, JUN, L1CAM, NRG1, NGFR, and PDGFB. On the other hand, angiogenesis inhibitors and related genes, including IL12A, MLLT7, STAB1, and TIMP2, are downregulated. Taken together, hypoxic/normoxic preconditioning may lead to the differentiation of CD133+ cells toward endothelial lineage, which may improve the current clinical trial studies.

Human umbilical cord blood plasma can replace fetal bovine serum for in vitro expansion of functional human endothelial colony-forming cells

BACKGROUND AIMS

A hierarchy of endothelial colony-forming cells (ECFC) with different levels of proliferative potential has been identified in human circulating blood and blood vessels. ECFC has recently become an attractive target for new vascular regenerative therapies; however, in vitro expansion of ECFC typically depends on the presence of fetal bovine serum (FBS) or fetal calf serum (FCS) in the culture medium, which is not appropriate for its therapeutic application.

METHODS

To identify optimal conditions for in vitro expansion of ECFC, the effects of human endothelial serum-free medium (SFM) supplemented with six pro-angiogenic cytokines and human umbilical cord blood plasma (HCP) were investigated. The in vitro morphology, proliferation, surface antigen expression and in vivo vessel-forming ability were utilized for examining the effects of medium on ECFC.

RESULTS

This novel formulation of endothelial cell culture medium allows us, for the first time, to isolate and expand human ECFC efficiently in vitro with a low concentration of HCP (1.5%) and without bovine serum additives. In this serum-reduced medium (SRM), human ECFC colony yields remained quantitatively similar to those cultured in a high concentration (10%) of bovine serum-supplemented medium. SRM-cultured ECFC displayed a robust clonal proliferative ability in vitro and human vessel-forming capacity in vivo.

CONCLUSIONS

The present study provides a novel method for the expansion of human ECFC in vitro and will help to advance approaches for using the cells in human therapeutic trials.

Enhancement of wound healing by human multipotent stromal cell conditioned medium: the paracrine factors and p38 MAPK activation

Wound healing can be improved by transplanting mesenchymal stem cells (MSCs). In this study, we have demonstrated the benefits of the conditioned medium derived from human MSCs (CM-MSC) in wound healing using an excisional wound model. CM-MSC accelerated wound closure with increased reepithelialization, cell infiltration, granulation formation, and angiogenesis. Notably, CM-MSC enhanced epithelial and endothelial cell migration, suggesting the contribution of increased cell migration to wound healing enhanced by CM-MSC. Cytokine array, ELISA analysis, and quantitative RT-PCR revealed high levels of IL-6 in CM-MSC. Moreover, IL-6 added to the preconditioned medium enhanced both cell migration and wound healing, and antibodies against IL-6 blocked the increase in cell motility and wound closure by CM-MSC. The IL-6 secretory pathway of MSCs was inhibited by SB203580, an inhibitor of p38 MAPK or siRNA against p38 MAPK, suggesting IL-6 secretion by MSCs is mediated through the activation of p38 MAPK. Inactivation of p38 MAPK also reduced the expression and production of IL-8 and CXCL1 by MSCs, both of which were also demonstrated to enhance cell migration and wound closure. Thus, our data suggest MSCs promote wound healing through releasing a repertoire of paracrine factors via activation of p38 MAPK, and the CM-MSC may be applied to enhance wound healing.

Endothelial progenitor cells in patients on extracorporeal maintenance dialysis therapy

BACKGROUND

Chronic renal failure patients have a high cardiovascular disease burden, low numbers and impaired function of endothelial progenitor cells (EPCs). We hypothesized that enhanced uraemic toxin removal restores EPCs in haemodialysis patients.

METHODS

In a prospective, randomized, cross-over trial, 18 patients were subjected to 4 weeks of each low-flux haemodialysis, high-flux haemodialysis and haemodiafiltration differing in uraemic toxin removal. EPCs were determined at baseline and at the end of each 4-week period. A cohort of 16 healthy volunteers served as control. EPCs were studied after culture on fibronectin (CFU-Hill) and collagen-1 (ECFC).

RESULTS

Dialysis patients had a lower number of ECFCs than in healthy controls (P < 0.001) and a reduced fraction of vital ECFCs (P < 0.05), whereas the formation of endothelial cell colonies (ECCs) was increased (P < 0.05). Different middle molecular uraemic toxin removal had no effects on EPC numbers. The number of prototypical EPCs (CD34( +)/VEGFR2-KDR( +)/CD45( -) ECFCs) was similar between patients and controls. Correlations of plasma C-reactive protein with ECC count, CFU-Hill colony count and CD34( +)/VEGFR2-KDR( +)/CD45( -) subpopulation of both ECFC and CFU-Hill cells were observed.

CONCLUSIONS

Different middle molecule removal has no effect on EPCs. Reduced vitality and enhanced ECC formation suggest growth induction of impaired EPCs in chronic renal failure and are associated with inflammation.

The detrimental effects of IFN-α on vasculogenesis in lupus are mediated by repression of IL-1 pathways: potential role in atherogenesis and renal vascular rarefaction

Systemic lupus erythematosus (SLE) is characterized by increased vascular risk due to premature atherosclerosis independent of traditional risk factors. We previously proposed that IFN-α plays a crucial role in premature vascular damage in SLE. IFN-α alters the balance between endothelial cell apoptosis and vascular repair mediated by endothelial progenitor cells (EPCs) and myeloid circulating angiogenic cells (CACs). In this study, we demonstrate that IFN-α promotes an antiangiogenic signature in SLE and control EPCs/CACs, characterized by transcriptional repression of IL-1α and β, IL-1R1, and vascular endothelial growth factor A, and upregulation of IL-1R antagonist and the decoy receptor IL-1R2. IL-1β promotes significant improvement in the functional capacity of lupus EPCs/CACs, therefore abrogating the deleterious effects of IFN-α. The beneficial effects from IL-1 are mediated, at least in part, by increases in EPC/CAC proliferation, by decreases in EPC/CAC apoptosis, and by preventing the skewing of CACs toward nonangiogenic pathways. IFN-α induces STAT2 and 6 phosphorylation in EPCs/CACs, and JAK inhibition abrogates the transcriptional antiangiogenic changes induced by IFN-α in these cells. Immunohistochemistry of renal biopsies from patients with lupus nephritis, but not anti-neutrophil cytoplasmic Ab-positive vasculitis, showed this pathway to be operational in vivo, with increased IL-1R antagonist, downregulation of vascular endothelial growth factor A, and glomerular and blood vessel decreased capillary density, compared with controls. Our study introduces a novel putative pathway by which type I IFNs may interfere with vascular repair in SLE through repression of IL-1-dependent pathways. This could promote atherosclerosis and loss of renal function in this disease.

Role of the renin angiotensin system on bone marrow-derived stem cell function and its impact on skeletal muscle angiogenesis

Autologous bone marrow cell (BMC) transplantation has been shown as a potential approach to treat various ischemic diseases. However, under many conditions BMC dysfunction has been reported, leading to poor cell engraftment and a failure of tissue revascularization. We have previously shown that skeletal muscle angiogenesis induced by electrical stimulation (ES) is impaired in the SS/Mcwi rats and that this effect is related to a dysregulation of the renin angiotensin system (RAS) that is normalized by the replacement of chromosome 13 derived from the Brown Norway rat (SS-13(BN)/Mcwi consomic rats). The present study explored bone marrow-derived endothelial cell (BM-EC) function in the SS/Mcwi rat and its impact on skeletal muscle angiogenesis induced by ES. SS/Mcwi rats were randomized to receive BMC from: SS/Mcwi; SS-13(BN)/Mcwi; SS/Mcwi rats infused with saline or ANG II (3 ng kg(-1) min(-1)). BMC were injected in the stimulated tibialis anterior muscle of SS/Mcwi rats. Vessel density was evaluated in unstimulated and stimulated muscles after 7 days of ES. BMC isolated from SS/Mcwi or SS/Mcwi rats infused with saline failed to restore angiogenesis induced by ES. However, BMC isolated from SS-13(BN)/Mcwi and SS/Mcwi rats infused with ANG II effectively restored the angiogenesis response in the SS/Mcwi recipient. Furthermore, ANG II infusion increased the capacity of BM-EC to induce endothelial cell tube formation in vitro and slightly increased VEGF protein expression. This study suggests that dysregulation of the RAS in the SS/Mcwi rat contributes to impaired BM-EC function and could impact the angiogenic therapeutic potential of BMC.

Early outgrowth EPCs generation is reduced in patients with Buerger's disease

BACKGROUND

Buerger's disease often shows poor collateral artery generation (i.e. neovascularization) in the ischemic limbs. However, the etiology has not yet been clarified. Circulating endothelial progenitor cells (EPCs) derived from bone marrow contribute to neovascularization in the multi-step process which includes the following capacities; mobilization, differentiation, adhesion, migration, invasion and secretion.

MATERIALS AND METHODS

We assessed EPCs capacities in vitro and ex vivo in age- and sex-matched controls (n = 12) and patients with Buerger's disease (n = 12), derived from peripheral blood-derived mononuclear cells (PB-MNCs).

RESULTS

In the flow cytometry analysis, the numbers of circulating EPC (CD34(+)/KDR(+) or CD133(+)/KDR(+) PB-MNC) were similar between controls and patients with Buerger's disease. Next, we cultured PB-MNC to obtain EPCs. The number of early outgrowth EPCs was significantly decreased in patients with Buerger's disease (p < 0.005), indicating the reduced generation of early outgrowth EPCs in Buerger's disease. However, adhesion, migration, invasion and secretion capacities were not impaired in patients with Buerger's disease.

CONCLUSIONS

The early outgrowth EPCs generation is reduced in patients with Buerger's disease.

Adipocytokines in atherothrombosis: focus on platelets and vascular smooth muscle cells

Visceral obesity is a relevant pathological condition closely associated with high risk of atherosclerotic vascular disease including myocardial infarction and stroke. The increased vascular risk is related also to peculiar dysfunction in the endocrine activity of adipose tissue responsible of vascular impairment (including endothelial dysfunction), prothrombotic tendency, and low-grade chronic inflammation. In particular, increased synthesis and release of different cytokines, including interleukins and tumor necrosis factor-α (TNF-α), and adipokines—such as leptin—have been reported as associated with future cardiovascular events. Since vascular cell dysfunction plays a major role in the atherothrombotic complications in central obesity, this paper aims at focusing, in particular, on the relationship between platelets and vascular smooth muscle cells, and the impaired secretory pattern of adipose tissue.

Enhanced progenitor cell recruitment and endothelial repair after selective endothelial injury of the mouse kidney

Primary and/or secondary injury of the renal microvascular endothelium is a common finding in various renal diseases. Besides well-known endothelial repair mechanisms, including endothelial cell (EC) proliferation and migration, homing of extrinsic cells such as endothelial progenitor cells (EPC) and hematopoietic stem cells (HSC) has been shown in various organs and may contribute to microvascular repair. However, these mechanisms have so far not been studied after selective microvascular injury in the kidney. The present study investigated the time course of EPC and HSC stimulation and homing following induction of selective EC injury in the mouse kidney along with various angiogenic factors potentially involved in EC repair and progenitor cell stimulation. Erythropoietin was used to stimulate progenitor cells in a therapeutic approach. We found that selective EC injury leads to a marked stimulation of EPCs, HSCs, and various angiogenic factors to orchestrate microvascular repair. Angiogenic factors started to increase as early as 30 min after disease induction. Progenitor cells could be first detected in the circulation and the spleen before they selectively homed to the diseased kidney. Injection of a high dose of erythropoietin 2 h after disease induction markedly attenuated vascular injury through nonhemodynamic mechanisms, possibly involving vascular endothelial growth factor release.

Interleukin-6 in bone metastasis and cancer progression

The bone and bone marrow are among the most frequent sites of cancer metastasis. It is estimated that 350,000 patients die with bone metastases annually in the United States. The ability of tumor cells to colonize the bone marrow and invade the bone is the result of close interactions between tumor cells and the bone marrow microenvironment. In this article, we review the contribution of interleukin-6 (IL-6) produced in the bone marrow microenvironment to bone metastasis. This cytokine has a strong pro-tumorigenic activity due to its multiple effects on bone metabolism, tumor cell proliferation and survival, angiogenesis, and inflammation. These effects are mediated by several signaling pathways, in particular the Janus kinase/signal transducer and transcription activator (JAK/STAT-3), Ras/mitogen activated protein kinase (MAPK), and phosphoinositol-3 kinase (PI3K)-protein kinase B/Akt (PkB/Akt), which are activated by IL-6 and amplified in the presence of soluble IL-6 receptor (sIL-6R). Supporting the role of IL-6 in human cancer is the observation of elevated serum levels of IL-6 and sIL-6R in patients with bone metastasis and their association with a poor clinical outcome. Over the last decade several large (monoclonal antibodies) and small (inhibitors of IL-6 mediated signaling) molecules that inhibit IL-6 activity in preclinical models have been developed. Several of these inhibitors are now undergoing phases I and II clinical trials, which will determine their inclusion in the list of effective targeted agents in the fight against cancer.

Endothelial progenitor cell transplantation improves long-term stroke outcome in mice

OBJECTIVE

Endothelial progenitor cells (EPCs) play an important role in tissue repairing and regeneration in ischemic organs, including the brain. However, the cause of EPC migration and the function of EPCs after ischemia are unclear. In this study, we demonstrated the effects of EPCs on ischemic brain injury in a mouse model of transient middle cerebral artery occlusion (tMCAO).

METHODS

Circulating human EPCs were characterized with immunofluorescent staining and flow cytometry. EPCs (1 x 10(6)) were injected into nude mice after 1 hour of tMCAO. Histological analysis and behavioral tests were performed from day 0 to 28 days after tMCAO.

RESULTS

EPCs were detected in ischemic brain regions 24 hours after tMCAO. EPC transplantation significantly reduced ischemic infarct volume at 3 days after tMCAO compared with control animals (p < 0.05). CXCR4 was expressed in the majority of EPCs, and stromal-derived factor-1 (SDF-1) induced EPC migration, which was blocked by pretreated EPCs with AMD3100 in vitro. SDF-1 was upregulated in ischemic brain. Compared with control animals, injecting AMD3100-pretreated EPCs resulted in a larger infarct volume 3 days after tMCAO, suggesting that SDF-1-mediated signaling was involved in EPC-mediated neuroprotection. In addition, EPC transplantation reduced mouse cortex atrophy 4 weeks after tMCAO and improved neurobehavioral outcomes (p < 0.05). EPC injection potently increased angiogenesis in the peri-infarction area (p < 0.05).

INTERPRETATION

We conclude that systemic delivery of EPCs protects the brain against ischemic injury, promotes neurovascular repair, and improves long-term neurobehavioral outcomes. Our data suggest that SDF-1-mediated signaling plays a critical role in EPC-mediated neuroprotection.

The role of hypoxia in 2-butoxyethanol-induced hemangiosarcoma

To understand the molecular mechanisms underlying compound-induced hemangiosarcomas in mice, and therefore, their human relevance, a systems biology approach was undertaken using transcriptomics and Causal Network Modeling from mice treated with 2-butoxyethanol (2-BE). 2-BE is a hemolytic agent that induces hemangiosarcomas in mice. We hypothesized that the hemolysis induced by 2-BE would result in local tissue hypoxia, a well-documented trigger for endothelial cell proliferation leading to hemangiosarcoma. Gene expression data from bone marrow (BM), liver, and spleen of mice exposed to a single dose (4 h) or seven daily doses of 2-BE were used to develop a mechanistic model of hemangiosarcoma. The resulting mechanistic model confirms previous work proposing that 2-BE induces macrophage activation and inflammation in the liver. In addition, the model supports local tissue hypoxia in the liver and spleen, coupled with increased erythropoeitin signaling and erythropoiesis in the spleen and BM, and suppression of mechanisms that contribute to genomic stability, events that could be contributing factors to hemangiosarcoma formation. Finally, an immunohistochemistry method (Hypoxyprobe) demonstrated that tissue hypoxia was present in the spleen and BM. Together, the results of this study identify molecular mechanisms that initiate hemangiosarcoma, a key step in understanding safety concerns that can impact drug decision processes, and identified hypoxia as a possible contributing factor for 2-BE-induced hemangiosarcoma in mice.

Time-dependent mobilization of circulating progenitor cells during strenuous exercise in healthy individuals

Exercise stimulates the release of hematopoietic and endothelial progenitor cells (EPC) from the bone marrow. However, no data are available concerning the time frame of EPC release during strenuous exercise. The aim of the present study was to investigate the time-dependent release of progenitor cells during strenuous exercise. Eighteen healthy young men cycled for 4 h continuously at 70% of their individual anaerobic threshold. Peripheral blood was drawn at 16 predefined time points during and after finishing cycling. A significant rise in heart rate and leukocytes was obvious, whereas lactate levels and hematocrit did not change. The amount of circulating progenitor cells, EPCs, mature endothelial cells (mECs), and microparticles, quantified by flow cytometry, showed a significant time-dependent increase at 210/240 min. In addition a very early rise in VEGF and later increase in IL-6, both measured by ELISA, were evident. All observed changes were normalized 24 h after finishing the test. In conclusion, strenuous activity in healthy individuals leads to a time-dependent increase in mECs, PCs, and EPCs that may be related to VEGF and IL-6.

Retinal endothelial cell apoptosis stimulates recruitment of endothelial progenitor cells

PURPOSE

Bone marrow-derived endothelial progenitor cells (EPCs) contribute to vascular repair although it is uncertain how local endothelial cell apoptosis influences their reparative function. This study was conducted to determine how the presence of apoptotic bodies at sites of endothelial damage may influence participation of EPCs in retinal microvascular repair.

METHODS

Microlesions of apoptotic cell death were created in monolayers of retinal microvascular endothelial cells (RMECs) by using the photodynamic drug verteporfin. The adhesion of early-EPCs to these lesions was studied before detachment of the apoptotic cells or after their removal from the wound site. Apoptotic bodies were fed to normal RMECs and mRNA levels for adhesion molecules were analyzed.

RESULTS

Endothelial lesions where apoptotic bodies were left attached at the wound site showed a fivefold enhancement in EPC recruitment (P < 0.05) compared with lesions where the apoptotic cells had been removed. In intact RMEC monolayers exposed to apoptotic bodies, expression of ICAM, VCAM, and E-selectin was upregulated by 5- to 15-fold (P < 0.05-0.001). EPCs showed a characteristic chemotactic response (P < 0.05) to conditioned medium obtained from apoptotic bodies, whereas analysis of the medium showed significantly increased levels of VEGF, IL-8, IL-6, and TNF-alpha when compared to control medium; SDF-1 remained unchanged.

CONCLUSIONS

The data indicate that apoptotic bodies derived from retinal capillary endothelium mediate release of proangiogenic cytokines and chemokines and induce adhesion molecule expression in a manner that facilitates EPC recruitment.

Interleukin-1beta augments angiogenic responses of murine endothelial progenitor cells in vitro

Endothelial progenitor cells (EPCs) may provide novel opportunities for therapeutic angiogenesis after ischemic diseases. However, it is unclear how the angiogenic potential of EPCs might be affected by an inflammatory environment. We examine how the potent cytokine interleukin-1beta (IL-1beta) affects angiovasculogenic responses in EPCs in culture. Mononuclear cells isolated from mouse spleen were plated on fibronectin-coated wells and grown in EGM-2 MV media. Endothelial progenitor cells were phenotyped using multiple markers (UEA-Lectin, ac-LDL, CD133, CD34, vWillebrand Factor, Flk-1) and to identify the IL-1 Receptor-I. We quantified cell and colony counts and performed MTT (3-(4,5-dimethylthiazol-2-yl)2,5-diphenyl-tetrazolium bromide) and Matrigel assays, in vitro, under control and IL-1beta (10 ng/mL) conditions. Endothelial progenitor cells exposed to IL-1beta increased in the number of cells and colonies compared with untreated cells, without any effect on cell metabolic integrity. Furthermore, IL-1beta treatment augmented EPC angiogenic function, significantly increasing the number of vessel-like structures in the Matrigel assay. An early phosphorylation of ERK1/2 occurred after IL-1beta stimulation, and this pathway was inhibited if IL-1 Receptor-I was blocked. Our results suggest that IL-1beta is a potent stimulator of in vitro angiogenesis through ERK signaling in mouse EPCs. Further studies are warranted to assess how interactions between proinflammatory environments and EPC responses may be leveraged to enhance therapeutic angiogenesis.

Ambivalent aspects of interleukin-6 in cerebral ischemia: inflammatory versus neurotrophic aspects

Interleukin-6 (IL-6) is pleiotropic cytokine involved in many central nervous system disorders including stroke, and elevated serum IL-6 has been found in acute stroke patients. IL-6 is implicated in the inflammation, which contributes to both injury and repair process after cerebral ischemia. However, IL-6 is one of the neurotrophic cytokines sharing a common receptor subunit, gp130, with other neurotrophic cytokines, such as leukemia inhibitory factor (LIF) and ciliary neurotrophic factor. The expression of IL-6 is most prominently identified in neurons in the peri-ischemic regions, and LIF expression shows a similar pattern. The direct injection of these cytokines into the brain after ischemia can reduce ischemic brain injury. The cytokine receptors are localized on the neuron surface, suggesting that neurons are the cytokine target. The major IL-6 downstream signaling pathway is JAK-STAT, and Stat3 activation occurs mainly in neurons during postischemic reperfusion. Further investigation is necessary to clarify the exact role of Stat3 signaling in neuroprotection. Taken together, the information suggests that IL-6 plays a double role in cerebral ischemia, as an inflammatory mediator during the acute phase and as a neurotrophic mediator between the subacute and prolonged phases.