Minimal contribution of marrow-derived endothelial precursors to tumor vasculature

During embryogenesis, vascular and hemopoietic cells originate from a common precursor, the hemangioblast. Recent evidence suggests the existence of endothelial precursors in adult bone marrow cells, but it is unclear whether those precursors have a role in tumor neovascularization. In this report, we demonstrate that murine bone marrow contains endothelial progenitors, which arise from a cell with self-renewing capacity, and can integrate into tumor microvasculature, albeit at a very low frequency. A transgenic double-reporter strategy allowed us to demonstrate definitively that tumor bone marrow-derived endothelial cells arise by transdifferentiation of marrow progenitors rather than by cell fusion. Single cell transplants showed that a common precursor contributes to both the hemopoietic and endothelial lineages, thus demonstrating the presence of an adult hemangioblast. Furthermore, we demonstrate that increased vascular endothelial growth factor (VEGF)-A secretion by tumor cells, as well as activation of VEGF receptor-2 in bone marrow cells does not alter the mobilization and incorporation of marrow-derived endothelial progenitors into tumor vasculature. Finally, in human umbilical cord blood cells, we show that endothelial precursors make up only approximately 1 in 10(7) mononuclear cells but are highly enriched in the CD133+ cell population. By ruling out cell fusion, we clearly demonstrate the existence of an adult hemangioblast, but the differentiation of marrow stem cells toward the endothelial lineage is an extremely rare event. Furthermore, we show that VEGF-A stimulation of hemopoietic cells does not significantly alter this process.     

Contribution of bone marrow-derived endothelial cells to human tumor vasculature

It has been shown that bone marrow-derived stem cells can form a major fraction of the tumor endothelium in mouse tumors. To determine the role of such cells in human tumor angiogenesis, we studied six individuals who developed cancers after bone marrow transplantation with donor cells derived from individuals of the opposite sex. By performing fluorescence in situ hybridization (FISH) with sex chromosome-specific probes in conjunction with fluorescent antibody staining, we found that such stem cells indeed contributed to tumor endothelium, but at low levels, averaging only 4.9% of the total. These results illustrate substantial differences between human tumors and many mouse models with respect to angiogenesis and have important implications for the translation of experimental antiangiogenic therapies to the clinic.     

Characteristics of bone marrow-derived endothelial progenitor cells in aged mice

Evidence for dysfunction of endothelial repair in aged mice was sought by studying the pattern of induced differentiation, quantity, and function of bone marrow-derived endothelial progenitor cells (EPCs) in aged mice. The CD117-positive stem cell population was separated from bone marrow by magnetic activated cell-sorting system (MACS), and EPCs were defined by demonstrating the expression of CD117+CD34+Flk-1+ by flow cytometry. After 7 days of culture, the number of clones formed was counted, and proliferation and migration of EPCs were analyzed by MTT[3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide] assay and modified Boyden chamber assay. The results demonstrated that compared to the control group, the quantity of bone marrow-derived CD117+ stem cells and EPCs, as well as the proliferation, migration, the number of clones formed, and phagocytotic function of EPCs were significantly reduced in aged mice. There were no significant differences in the morphology and induced differentiation pattern of EPCs between the aged mouse group and the control group. Authors suggest that the dysfunction of EPCs may serve as a surrogate parameter of vascular function in old mice.     

Cilostazol activates function of bone marrow-derived endothelial progenitor cell for re-endothelialization in a carotid balloon injury model

Background

Cilostazol(CLZ) has been used as a vasodilating anti-platelet drug clinically and demonstrated to inhibit proliferation of smooth muscle cells and effect on endothelial cells. However, the effect of CLZ on re-endothelialization including bone marrow (BM)-derived endothelial progenitor cell (EPC) contribution is unclear. We have investigated the hypothesis that CLZ might accelerate re-endothelialization with EPCs.

Methodology/Principal Findings

Balloon carotid denudation was performed in male Sprague-Dawley rats. CLZ group was given CLZ mixed feed from 2weeks before carotid injury. Control group was fed normal diet. CLZ accelerated re-endothelialization at 2 weeks after surgery and resulted in a significant reduction of neointima formation 4 weeks after surgery compared with that in control group. CLZ also increased the number of circulating EPCs throughout the time course. We examined the contribution of BM-derived EPCs to re-endothelialization by BM transplantation from Tie2/lacZ mice to nude rats. The number of Tie2-regulated X-gal positive cells on injured arterial luminal surface was increased at 2 weeks after surgery in CLZ group compared with that in control group. In vitro, CLZ enhanced proliferation, adhesion and migration activity, and differentiation with mRNA upregulation of adhesion molecule integrin αvβ3, chemokine receptor CXCR4 and growth factor VEGF assessed by real-time RT-PCR in rat BM-derived cultured EPCs. In addition, CLZ markedly increased the expression of SDF-1α that is a ligand of CXCR4 receptor in EPCs, in the media following vascular injury.

Conclusions/Significance

CLZ promotes EPC mobilization from BM and EPC recruitment to sites of arterial injury, and thereby inhibited neointima formation with acceleration of re-endothelialization with EPCs as well as pre-existing endothelial cells in a rat carotid balloon injury model. CLZ could be not only an anti-platelet agent but also a promising tool for endothelial regeneration, which is a key event for preventing atherosclerosis or restenosis after vascular intervention.     

Directing bone marrow-derived stromal cell function with mechanics

Because bone marrow-derived stromal cells (BMSCs) are able to generate many cell types, they are envisioned as source of regenerative cells to repair numerous tissues, including bone, cartilage, and ligaments. Success of BMSC-based therapies, however, relies on a number of methodological improvements, among which better understanding and control of the BMSC differentiation pathways. Since many years, the biochemical environment is known to govern BMSC differentiation, but more recent evidences show that the biomechanical environment is also directing cell functions. Using in vitro systems that aim to reproduce selected components of the in vivo mechanical environment, it was demonstrated that mechanical loadings can affect BMSC proliferation and improve the osteogenic, chondrogenic, or myogenic phenotype of BMSCs. These effects, however, seem to be modulated by parameters other than mechanics, such as substrate nature or soluble biochemical environment. This paper reviews and discusses recent experimental data showing that despite some knowledge limitation, mechanical stimulation already constitutes an additional and efficient tool to drive BMSC differentiation.     

间充质干细胞体外调控骨髓造血前体细胞向单核系分化

研究间充质干细胞(MSC)能否在体外调控造血。体外分离培养人骨髓来源的MSC,RT-PCR检测其造血生长因子的表达,并以其为饲养层细胞,接种骨髓单个核细胞(MNC),观察生长情况,并通过形态学观察和流式细胞术分析,鉴定细胞来源和分化方向。结果显示,MSC构成性表达SCF、Flt3L和M-CSF,不表达C-CSF和GM-CSF,在骨髓MNC和MSC共培养体系中,大约2周左右可以看到大量的圆形细胞粘附在梭型MSC上生长,细胞胞体为圆形,胞浆较丰富,胞核为圆形、半月型或肾型,部分细胞呈典型的单核细胞形态,流式细胞术分析该类细胞表达CDl4,不表达CDl5、CD41、glycophorin A、CD5和CDl9。表明不需要添加外源性造血生长因子,间充质干细胞能在体外调控骨髓造血前体细胞向单核系分化,其定向分化可能与MSC分泌造血生长因子及MSC与造血细胞间相互作用有关。     

CCR2 mediates the uptake of bone marrow-derived fibroblast precursors in angiotensin II-induced cardiac fibrosis

Angiotensin II plays an important role in the development of cardiac hypertrophy and fibrosis, but the underlying cellular and molecular mechanisms are not completely understood. Recent studies have shown that bone marrow-derived fibroblast precursors are involved in the pathogenesis of cardiac fibrosis. Since bone marrow-derived fibroblast precursors express chemokine receptor, CCR2, we tested the hypothesis that CCR2 mediates the recruitment of fibroblast precursors into the heart, causing angiotensin II-induced cardiac fibrosis. Wild-type and CCR2 knockout mice were infused with angiotensin II at 1,500 ng·kg(-1)·min(-1). Angiotensin II treatment resulted in elevated blood pressure and cardiac hypertrophy that were not significantly different between wild-type and CCR2 knockout mice. Angiotensin II treatment of wild-type mice caused prominent cardiac fibrosis and accumulation of bone marrow-derived fibroblast precursors expressing the hematopoietic markers, CD34 and CD45, and the mesenchymal marker, collagen I. However, angiotensin II-induced cardiac fibrosis and accumulation of bone marrow-derived fibroblast precursors in the heart were abrogated in CCR2 knockout mice. Furthermore, angiotensin II treatment of wild-type mice increased the levels of collagen I, fibronectin, and α-smooth muscle actin in the heart, whereas these changes were not observed in the heart of angiotensin II-treated CCR2 knockout mice. Functional studies revealed that the reduction of cardiac fibrosis led to an impairment of cardiac systolic function and left ventricular dilatation in angiotensin II-treated CCR2 knockout mice. Our data demonstrate that CCR2 plays a pivotal role in the pathogenesis of angiotensin II-induced cardiac fibrosis through regulation of bone marrow-derived fibroblast precursors.     

The characteristics of bone marrow-derived endothelial progenitor cells and their effect on glioma

ABSTRACT: BACKGROUND: EPCs were isolated primarily in 1997 by Asahara et al and recent studies indicate that bone-marrow-derived EPCs contribute little to the endothelium of tumor vessels. Tumors of the CNS system demonstrate various features of angiogenesis. METHODS: EPCs derived from rat bone marrow were isolated and cultured in M199 medium without any induced factors. EPCs derived from rat bone marrow were studied using immunohistochemical staining, Flow cytometry and culture under three-dimensional condition to determine EPCs' characteristics in vitro. We also established an animal model by injecting EPCs marked with Hoechst 33342 into the back of BALB/c nude mouse and performed hematoxylin-eosin (HE) and immunofluorescent staining to study EPCs' features in vivo. To research effect of EPCs on glioma, animals bearing tumors model with C6 glioma were established. About 27day after injected, we performed immunohistochemical staining and Immunofluorescence staining. RESULTS: Our results showed that EPCs derived from rat bone marrow appeared typical morphological characteristics and were positive of CD34, CD133, KDR and CD31 antigens at different time in vitro under the special M199 medium without any induced factors. The percentage of cells that expressed CD133 decreased gradually. In brief, the present study showed that EPCs derived from rat bone marrow differentiated into ECs in medium 199 without any induced factors and formed tubular structures in three-dimensional circumstances. Animal experiments suggested that EPCs differentiated into ECs and other else non-endothelial cells, and that EPCs contributed to growth of glioma. DISCUSSION: These findings provides some novel findings about biological characteristics of EPCs in vivo and ex vivo, and an update on the effect of EPCs on glioma and which would be helpful for the overall understanding of EPCs and make EPCs to be implied on the clinical therapy.     

Establishment and characterization of mouse bone marrow-derived mast cell hybridomas

Interleukin (IL)-3-dependent mouse bone marrow-derived mast cells (BMMCs) are an important model for studying the function of mucosal-type mast cells. In the present study, BMMCs were successfully immortalized by cell fusion using a hypoxanthine-aminopterin-thymidine medium-sensitive variant of P815 mouse mastocytoma (P815-6TgR) as a partner cell line. The established mouse mast cell hybridomas (MMCHs) expressed α, β, and γ subunits of high-affinity immunoglobulin E (IgE) receptor (FcεRI) and possessed cytoplasmic granules devoid of or partially filled with electron-dense material. Four independent MMCH clones continuously proliferated without supplemental exogenous IL-3 and showed a degranulation response on stimulation with IgE+antigen. Furthermore, histamine synthesis and release by degranulation were confirmed in MMCH-D5, a MMCH clone that showed the strongest degranulation response. MMCH-D5 exhibited elevated levels of IL-3, IL-4, IL-13, granulocyte-macrophage colony-stimulating factor, tumor necrosis factor (TNF)-α, and cyclooxygenase 2, and production of prostaglandin D(2) and leukotriene C(4) in response to IgE-induced stimulation. MMCH clones also expressed Toll-like receptors (TLRs) 1, 2, 4, and 6 and showed elevated levels of TNF-α expression in response to stimulation with TLR2 and TLR4 ligands. The MMCHs established using this method should be suitable for studies on FcεRI- and TLR-mediated effector functions of mast cells.     

VEGF contributes to postnatal neovascularization by mobilizing bone marrow-derived endothelial progenitor cells.

Vascular endothelial growth factor (VEGF) has been shown to promote neovascularization in animal models and, more recently, in human subjects. This feature has been assumed to result exclusively from its direct effects on fully differentiated endothelial cells, i.e. angiogenesis. Given its regulatory role in both angiogenesis and vasculogenesis during fetal development, we investigated the hypothesis that VEGF may modulate endothelial progenitor cell (EPC) kinetics for postnatal neovascularization. Indeed, we observed an increase in circulating EPCs following VEGF administration in vivo. VEGF-induced mobilization of bone marrow-derived EPCs resulted in increased differentiated EPCs in vitro and augmented corneal neovascularization in vivo. These findings thus establish a novel role for VEGF in postnatal neovascularization which complements its known impact on angiogenesis.     

Prostaglandin E2 promotes endothelial differentiation from bone marrow-derived cells through AMPK activation

Prostaglandin E2 (PGE2) has been reported to modulate angiogenesis, the process of new blood vessel formation, by promoting proliferation, migration and tube formation of endothelial cells. Endothelial progenitor cells are known as a subset of circulating bone marrow mononuclear cells that have the capacity to differentiate into endothelial cells. However, the mechanism underlying the stimulatory effects of PGE2 and its specific receptors on bone marrow-derived cells (BMCs) in angiogenesis has not been fully characterized. Treatment with PGE2 significantly increased the differentiation and migration of BMCs. Also, the markers of differentiation to endothelial cells, CD31 and von Willebrand factor, and the genes associated with migration, matrix metalloproteinases 2 and 9, were significantly upregulated. This upregulation was abolished by dominant-negative AMP-activated protein kinase (AMPK) and AMPK inhibitor but not protein kinase, a inhibitor. As a functional consequence of differentiation and migration, the tube formation of BMCs was reinforced. Along with altered BMCs functions, phosphorylation and activation of AMPK and endothelial nitric oxide synthase, the target of activated AMPK, were both increased which could be blocked by EP4 blocking peptide and simulated by the agonist of EP4 but not EP1, EP2 or EP3. The pro-angiogenic role of PGE2 could be repressed by EP4 blocking peptide and retarded in EP4(+/-) mice. Therefore, by promoting the differentiation and migration of BMCs, PGE2 reinforced their neovascularization by binding to the receptor of EP4 in an AMPK-dependent manner. PGE2 may have clinical value in ischemic heart disease.     

Cell density-dependent proliferation of the murine bone marrow-derived stromal cell lines

Proliferation of three murine marrow-derived stromal cell lines, LC1, LC2, and LC3, depended on initial cell density. For LC2 and LC3, the cell density-dependence was negated by conditioned-media, indicating growth dependence on a soluble growth factor. For LC1, conditioned-media failed to stimulate proliferation, suggesting growth dependence on direct cell-cell contact.     

In vitro interactions between rat bone marrow-derived endothelial progenitor cells and hepatic stellate cells

Transplantation of bone marrow (BM)-derived endothelial progenitor cells (EPCs) has been reported to improve liver fibrosis, but there is no direct evidence for the mechanism of improvement. We investigated the mechanism in vitro by coculturing BM-derived EPCs with activated hepatic stellate cells (HSCs) to mimic the hepatic environment. EPCs and HSCs were cultured alone and indirectly cocultured at a 1:1 ratio in a Transwell system. The characteristics of HSCs and EPCs were examined at different time points. An invasion assay showed the time-dependent effect on degradation of the extracellular matrix (ECM) layer in EPCs cultured alone. Real-time PCR and enzyme-linked immunosorbent assay analysis revealed that EPCs served as a source of matrix metalloproteinase-9 (MMP-9), and MMP-9 expression levels significantly increased during the 2 d of coculture. CFSE labeling showed that EPCs inhibited proliferation of HSCs. Annexin-V/PI staining, erminal deoxynucleotidyl transferase X-dUTP nick end labeling analysis, and (cleaved) caspase-3 activity revealed that EPCs promoted HSC apoptosis. However, the proliferation and apoptosis of EPCs were unaffected by cocultured HSCs. Coculturing increased the expression of inducible nitric oxide synthase, vascular endothelial growth factor, and hepatocyte growth factor (HGF) in EPCs, promoted differentiation of EPCs, and reduced the expression of types I and III collagens and transforming growth factor beta 1. Knockdown of HGF expression attenuated EPC-induced activation of HSC apoptosis and profibrotic ability. These findings demonstrated that BM-derived EPCs could degrade ECM, promoting activated HSC apoptosis, suppressing proliferation and profibrotic ability of activated HSCs. HGF secretion by EPCs plays a key role in inducing activated HSC apoptosis and HSC profibrotic ability.     

Multi-organ, multi-lineage engraftment by a single bone marrow-derived stem cell

Purification of rare hematopoietic stem cell(s) (HSC) to homogeneity is required to study their self-renewal, differentiation, phenotype, and homing. Long-term repopulation (LTR) of irradiated hosts and serial transplantation to secondary hosts represent the gold standard for demonstrating self-renewal and differentiation, the defining properties of HSC. We show that rare cells that home to bone marrow can LTR primary and secondary recipients. During the homing, CD34 and SCA-1 expression increases uniquely on cells that home to marrow. These adult bone marrow cells have tremendous differentiative capacity as they can also differentiate into epithelial cells of the liver, lung, GI tract, and skin. This finding may contribute to clinical treatment of genetic disease or tissue repair.     

Celastrol inhibits vasculogenesis by suppressing the VEGF-induced functional activity of bone marrow-derived endothelial progenitor cells

Bone marrow (BM)-derived endothelial progenitor cells (EPCs) play a critical role in tumor vasculogenesis because they provide both instructive (release of pro-angiogenic cytokines, such as VEGF) and structural (vessel incorporation and stabilization) functions. Celastrol, derived from Trypterygium wilfordii Hook F., a traditional Chinese medicine plant, has been studied for its antitumorigenic properties, but its mechanism of action is not well understood. The aims of this study are to investigate the effects of Celastrol on VEGF-induced functional activity of BM-EPCs and to identify any mechanisms associated with this process. Here, we show that Celastrol attenuates VEGF secretion in BM-EPCs in vitro. This attenuation, in turn, inhibits the in vitro VEGF-induced cell viability, cell-cell adhesion, cell-ECM adhesion, migration response and vascular tube formation of BM-EPCs. Additionally, Celastrol inhibits the phosphorylation of VEGFR2, endothelial nitric oxide synthase (eNOS), and Akt to attenuate cell functions. Taken together, the present study demonstrates that Celastrol decreases Akt/eNOS signaling in BM-EPCs in vitro. These findings identify novel mechanisms that regulate EPC function and may provide new insights for the medicinal use of Celastrol.     

Impact of parathyroid hormone on bone marrow-derived stem cell mobilization and migration

Parathyroid hormone (PTH) is well-known as the principal regulator of calcium homeostasis in the human body and controls bone metabolism via actions on the survival and activation of osteoblasts. The intermittent administration of PTH has been shown to stimulate bone production in mice and men and therefore PTH administration has been recently approved for the treatment of osteoporosis. Besides to its physiological role in bone remodelling PTH has been demonstrated to influence and expand the bone marrow stem cell niche where hematopoietic stem cells, capable of both self-renewal and differentiation, reside. Moreover, intermittent PTH treatment is capable to induce mobilization of progenitor cells from the bone marrow into the bloodstream. This novel function of PTH on modulating the activity of the stem cell niche in the bone marrow as well as on mobilization and regeneration of bone marrow-derived stem cells offers new therapeutic options in bone marrow and stem cell transplantation as well as in the field of ischemic disorders.     

Adenoviral expression of vascular endothelial growth factor splice variants differentially regulate bone marrow-derived mesenchymal stem cells

Bone marrow-derived mesenchymal stem cells (MSCs) are being explored for clinical applications, and genetic engineering represents a useful strategy for boosting the therapeutic potency of MSCs. Vascular endothelial growth factor (VEGF)-based gene therapy protocols have been used to treat tissue ischemia, and a combined VEGF/MSC therapeutics is appealing due to their synergistic paracrine actions. However, multiple VEGF splice variants exhibit differences in their mitogenicity, chemotactic efficacy, receptor interaction, and tissue distribution, and the differential regulatory effects of multiple VEGF isoforms on the function of MSCs have not been characterized. We expressed three rat VEGF-A splice variants VEGF120, 164, and 188 in MSCs using adenoviral vectors, and analyzed their effects on MSC proliferation, differentiation, survival, and trophic factor production. The three VEGF splice variants exert common and differential effects on MSCs. All three expressed VEGFs are potent in promoting MSC proliferation. VEGF120 and 188 are more effective in amplifying expression of multiple growth factor and cytokine genes. VEGF164 on the other hand is more potent in promoting expression of genes associated with MSC remodeling and endothelial differentiation. The longer isoform VEGF188, which is preferentially retained by proteoglycans, facilitates bone morphogenetic protein-7 (BMP7)-mediated MSC osteogenesis. Under serum starvation condition, virally expressed VEGF188 preferentially enhances serum withdrawal-mediated cell death involving nitric oxide production. This work indicates that seeking the best possible match of an optimal VEGF isoform to a given disease setting can generate maximum therapeutic benefits and minimize unwanted side effects in combined stem cell and gene therapy.