Bone Marrow-derived Precursor Cells Research Articles

Sequence and TLR9 independent increase of TRACP expression by antisense DNA and siRNA molecules

Reactive oxygen species generating activity of tartrate-resistant acid phosphatase (TRACP) has been suggested to have several functions in TRACP expressing bone resorbing osteoclasts, macrophages, and dendritic cells. This work aimed to study the TRACP knock down phenotype in osteoclasts by using antisense DNA and RNA interference methods. Unexpectedly, both TRACP specific DNA oligonucleotides and siRNA molecules extensively increased the TRACP expression in human osteoclasts and monocytes. Toll-like receptor 9 (TLR9) is an immunity sensor for CpG motifs in DNA. We cultured bone marrow-derived osteoclast precursor cells from wild-type and TLR9−/− mice with CpG and non-CpG DNA oligonucleotides, and observed that the increased TRACP expression was sequence and TLR9 independent. In contrast, cells with increased TRACP activity showed decreased activity of tartrate-sensitive acid phosphatases. Conclusion: DNA oligonucleotides and RNA molecules extensively increase TRACP expression in monocyte-macrophage lineage. These results suggest a potential role of TRACP in pathogen recognition and in innate immunity.

TREM2-Transduced Myeloid Precursors Mediate Nervous Tissue Debris Clearance and Facilitate Recovery in an Animal Model of Multiple Sclerosis

BackgroundIn multiple sclerosis, inflammation can successfully be prevented, while promoting repair is still a major challenge. Microglial cells, the resident phagocytes of the central nervous system (CNS), are hematopoietic-derived myeloid cells and express the triggering receptor expressed on myeloid cells 2 (TREM2), an innate immune receptor. Myeloid cells are an accessible source for ex vivo gene therapy. We investigated whether myeloid precursor cells genetically modified to express TREM2 affect the disease course of experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis.Methods and FindingsEAE was induced in mice by immunization with a myelin autoantigen. Intravenous application of TREM2-transduced bone marrow–derived myeloid precursor cells at the EAE peak led to an amelioration of clinical symptoms, reduction in axonal damage, and prevention of further demyelination. TREM2-transduced myeloid cells applied intravenously migrated into the inflammatory spinal cord lesions of EAE-diseased mice, showed increased lysosomal and phagocytic activity, cleared degenerated myelin, and created an anti-inflammatory cytokine milieu within the CNS.ConclusionsIntravenously applied bone marrow–derived and TREM2-tranduced myeloid precursor cells limit tissue destruction and facilitate repair within the murine CNS by clearance of cellular debris during EAE. TREM2 is a new attractive target for promotion of repair and resolution of inflammation in multiple sclerosis and other neuroinflammatory diseases.

Obliterative vasculopathy in systemic sclerosis: endothelial precursor cells as novel targets for therapy

Evaluation of: Kuwana M, Kaburaki J, Okazaki Y et al. Increase in circulating endothelial precursors by atorvastatin in patients with systemic sclerosis. Arthritis Rheum. 54(6), 1946–1951 (2006).Systemic sclerosis (SSc) is associated with a progressive obliterative vasculopathy that accounts for serious clinical manifestations of the disease, and has, to date, no effective treatment. Vascular obliteration is accompanied by defective vasculogenesis due to impaired production, mobilization or function of bone marrow-derived vascular precursor cells. Statins enhance vascular precursor cell production in chronic cardiovascular diseases and may also have a therapeutic role in SSc. This paper evaluates the results from a recent open-label clinical trial of atorvastatin that support this notion. Larger controlled trials are now needed to critically evaluate the efficacy of statins for repairing vascular damage, enhancing vasculogenesis, and attenuating the burden of chronic vasculopathy in SSc.

Stem cell therapy in end-stage ischaemic heart failure: a catheter-based therapeutic strategy targeting myocardial viability

Recent evidence that the adult heart can repair itself through the proliferation of cardiac precursor cells and the recruitment and engraftment of bone marrow-derived precursor cells has stimulated interest in stem cell therapy for cardiac diseases. Although preclinical studies have shown the efficacy of stem cell treatment, numerous controversies exist, and many basic questions still await answers. Meanwhile, clinical trials of stem cell therapy continue to advance. Our group has focused on using stem cells to treat patients with end-stage ischaemic heart failure who are ineligible for surgical or percutaneous revascularization. The preliminary results of the phase I trial are encouraging but need to be reproduced before larger randomized trials can be attempted. This review covers some of the most important clinical developments in targeted, transendocardially delivered stem cell therapy for end-stage ischaemic heart failure.

Vascular Progenitor Cells Lineage Controversies

The discovery that vascular progenitor cells in peripheral blood can differentiate into endothelial and vascular smooth muscle cells has lead to a major re-evaluation of many traditionally held beliefs about vascular biology. For instance concepts of vascular regeneration and repair previously considered limited to proliferation of existing differentiated cells within the vessel wall have been expanded to include potential for postnatal vasculogenesis from blood-derived, adventitial tissue-derived and bone marrow-derived precursor cells. The significance of these data lays not only in the development of a novel understanding of vascular biology but also in the new insights provided in vascular disease in general and atherosclerosis research in particular. The mechanisms underlying the mobilization, target tissue integration and differentiation of these cells are now being elucidated. Paramount in this endeavour is a more precise understanding of the lineage of various progenitor cell types and development of experimental systems which can rigorously test vascular lineage questions.

Antioxidant α-lipoic acid inhibits osteoclast differentiation by reducing nuclear factor-κB DNA binding and prevents in vivo bone resorption induced by receptor activator of nuclear factor-κB ligand and tumor necrosis factor-α

The relationship between oxidative stress and bone mineral density or osteoporosis has recently been reported. As bone loss occurring in osteoporosis and inflammatory diseases is primarily due to increases in osteoclast number, reactive oxygen species (ROS) may be relevant to osteoclast differentiation, which requires receptor activator of nuclear factor-κB ligand (RANKL). Tumor necrosis factor-α (TNF-α) frequently present in inflammatory conditions has a profound synergy with RANKL in osteoclastogenesis. In this study, we investigated the effects of α-lipoic acid (α-LA), a strong antioxidant clinically used for some time, on osteoclast differentiation and bone resorption. At concentrations showing no growth inhibition, α-LA potently suppressed osteoclastogenesis from bone marrow-derived precursor cells driven either by a high-dose RANKL alone or by a low-dose RANKL plus TNF-α (RANKL/TNF-α). α-LA abolished ROS elevation by RANKL or RANKL/TNF-α and inhibited NF-κB activation in osteoclast precursor cells. Specifically, α-LA reduced DNA binding of NF-κB but did not inhibit IKK activation. Furthermore, α-LA greatly suppressed in vivo bone loss induced by RANKL or TNF-α in a calvarial remodeling model. Therefore, our data provide evidence that ROS plays an important role in osteoclast differentiation through NF-κB regulation and the antioxidant α-lipoic acid has a therapeutic potential for bone erosive diseases.

Differential expression of angiopoietin-1 and angiopoietin-2 may enhance recruitment of bone marrow-derived endothelial precursor cells into brain tumors

Objectives: Angiogenesis is necessary for sustained neoplastic development. The angiopoietins Ang-1 and Ang-2 have been implicated in the regulation of this process; recent reports have suggested that a net gain in Ang-2 activity may be an initiating factor for tumor angiogenesis. We examined the recruitment of bone marrow-derived endothelial precursor cells into developing tumor neovasculature, and the spatial relationship between these cells and angiopoietin (Ang-1 and Ang-2) expression.Methods: For this study T-cell depleted knockout mice (RAG-2/KO-5.2) were lethally irradiated and their bone marrow was reconstituted by bone marrow cells (BMCs) from transgenic mice (C57BL/Ka-Thy1.1) expressing green fluorescent protein (GFP). Rat glioma cells (RT-2/RAG) were then injected into the transplanted animals to form solid brain tumors. The animals were killed and their brains were analysed using immunohistochemistry and fluorescence-activated cell sorting.Results: We found that BMCs migrated preferentially into the tumor when compared to adjacent healthy brain parenchyma. Furthermore, GFP+/CD34+ cells represented up to 8% of endothelial-like cells within the walls of tumor blood vessels. In the tumor, significant colocalization of Ang-2 with GFP+/CD34+ cells was noted (>80%), but colocalization with Ang-1 never exceeded 20%. In normal tissue directly surrounding the tumor, GFP+/CD34+ cells colocalized strongly with both angiopoietins (>75% and >70% for Ang-1 and Ang-2, respectively).Discussion: The relative increase in angiopoietin-2 activity in brain tumors may result in the creation of a pro-angiogenic environment that enhances the recruitment of putative bone marrow-derived endothelial precursor cells into the tumor's developing vascular tree.

Circulating Mononuclear Cells With a Dual, Macrophage-Fibroblast Phenotype Contribute Robustly to Hypoxia-Induced Pulmonary Adventitial Remodeling

Chronic hypoxic pulmonary hypertension, especially in the young, is characterized by striking fibroproliferative changes in the adventitia of both large and small pulmonary arteries. These changes are thought to contribute significantly to high pulmonary vascular resistance and, in some instances, to cor pulmonale. It has long been assumed that the resident pulmonary artery fibroblasts are the primary contributors to adventitial thickening and fibrosis. However, there is evidence that circulating mononuclear cells of a myeloid origin, which have the capability of exhibiting fibroblast-like properties, can be chemotactically recruited to sites of tissue injury and participate in the repair process. 1 Quan TE Cowper S Wu S-P et al. Circulating fibrocytes: collagen-secreting cells of the peripheral blood. J Biochem Cell Biol. 2004; 36: 598-606 Crossref PubMed Scopus (482) Google Scholar In fact, bone marrow-derived fibroblast precursor cells have recently been suggested 2 Hashimoto N Jin H Liu T et al. Bone marrow-derived progenitor cells in pulmonary fibrosis. J Clin Invest. 2004; 113: 243-252 Crossref PubMed Scopus (638) Google Scholar to be major contributors to lung fibrosis following bleomycin-induced injury. However, whether circulating precursor cells with the potential to exhibit fibroblast-like properties contribute to adventitial thickening under hypoxic conditions is unknown. We recently demonstrated 3 Davie NJ Crossno JT Frid MG et al. Hypoxia-induced pulmonary artery adventitial remodeling and neovascularization: contribution of progenitor cells. Am J Physiol Lung Cell Mol Physiol. 2004; 286: L668-L678 Crossref PubMed Scopus (197) Google Scholar the presence of hematopoietic precursor cells expressing cKit marker in the adventitia of chronically hypoxic animals. We therefore tested the hypothesis that, in hypoxia-induced pulmonary hypertension, circulating mononuclear cells contribute to pulmonary artery adventitial thickening and fibrosis.

Osteoclasts direct bystander killing of cancer cells in vitro

Cytosine deaminase (CD) catalyzes the deamination of 5-fluorocytosine (5FC) to produce the highly toxic chemotherapeutic agent 5-fluorouracil (5FU). A unique feature of the CD/5FC enzyme/prodrug system is its ability to kill adjacent cells via bystander killing. Bystander killing of cancer cells can be mediated by non-cancerous accessory cells transduced with the CD gene; one type of non-cancerous accessory cell found in primary bone cancer and breast cancer metastases to bone is the osteoclast. This manuscript determines if osteoclast precursor cells, transduced with the CD gene, can function as a gene delivery system capable of killing cancer cells. An osteoclast precursor cell line (RAW 264.7, RAW) and authentic bone marrow-derived osteoclast precursor cells were transduced with a retroviral vector containing the cytosine deaminase fusion gene (NCD) composed of the human nerve growth factor receptor and CD genes. RAW cells and bone marrow-derived osteoclast precursor cells transduced with NCD expressed NCD protein and converted 5FC to 5FU. Treatment of NCD-transduced osteoclast precursor cells with the 5FC prodrug resulted in significant killing in vitro. NCD-transduced osteoclasts were co-cultured with either DsRed2-labeled sarcoma cells (2472-DSR) or green fluorescent protein (GFP)-labeled breast cancer cells (GFP-4T1). Treatment of the NCD osteoclast/tumor cell co-cultures with 5FC resulted in bystander killing of 2472-DSR cells ( P < 0.006) and GFP-4T1 cells ( P < 0.004). These findings demonstrate that NCD-transduced osteoclasts can promote killing of cancer cells and introduce the exciting possibility for developing osteoclast-mediated, CD-based treatment of primary bone cancers and breast cancer metastases to bone.

Unsatisfactory gene transfer into bone-resorbing osteoclasts with liposomal transfection systems

BackgroundBone-resorbing osteoclasts are multinucleated cells that are formed via fusion of their hematopoietic stem cells. Many of the details of osteoclast formation, activation and motility remain unsolved. Therefore, there is an interest among bone biologists to transfect the terminally differentiated osteoclasts and follow their responses to the transgenes in vitro. Severe difficulties in transfecting the large, adherent osteoclasts have been encountered, however, making the use of modern cell biology tools in osteoclast research challenging. Transfection of mature osteoclasts by non-viral gene transfer systems has not been reported.ResultsWe have systematically screened the usefulness of several commercial DNA transfection systems in human osteoclasts and their mononuclear precursor cell cultures, and compared transfection efficacy to adenoviral DNA transfection. None of the liposome-based or endosome disruption-inducing systems could induce EGFP-actin expression in terminally differentiated osteoclasts. Instead, a massive cell death by apoptosis was found with all concentrations and liposome/DNA-ratios tested. Best transfection efficiencies were obtained by adenoviral gene delivery. Marginal DNA transfection was obtained by just adding the DNA to the cell culture medium. When bone marrow-derived CD34-positive precursor cells were transfected, some GFP-expression was found at the latest 24 h after transfection. Large numbers of apoptotic cells were found and those cells that remained alive, failed to form osteoclasts when cultured in the presence of RANKL and M-CSF, key regulators of osteoclast formation. In comparison, adenoviral gene delivery resulted in the transfection of CD34-positive cells that remained GFP-positive for up to 5 days and allowed osteoclast formation.ConclusionOsteoclasts and their precursors are sensitive to liposomal transfection systems, which induce osteoclast apoptosis. Gene transfer to mononuclear osteoclast precursors or differentiated osteoclasts was not possible with any of the commercial transfection systems tested. Osteoclasts are non-dividing, adherent cells that are difficult to grow as confluent cultures, which may explain problems with transfection reagents. Large numbers of αvβ3 integrin on the osteoclast surface allows adenovirus endocytosis and infection proceeds in dividing and non-dividing cells efficiently. Viral gene delivery is therefore currently the method of choice for osteoclast transfection.

Breast tumors induce the recruitment of AC133+KDR+ endothelial precursor cells mobilized by plasma vascular endothelial growth factor

Recent evidence has demonstrated the importance of bone marrow-derived endothelial precursor cells (EPC) in the contribution to postnatal physiological and pathological neovascularization, and in tumor growth and angiogenesis. These cells are recruited undifferentiated; in response to systemic or chemoattractive signals, such as vascular endothelial growth factor (VEGF), they lodge in the growing or lesioned tissue and differentiate into endothelial cells in response to local stimuli and cell–cell interactions. The extent and the significance of the EPC contribution for the growing of most tumors, including breast carcinomas, are still not defined. We analysed the peripheral blood mononuclear cells (PBMNC) of 48 breast cancer patients and found that 16.7% of them have circulating EPC. These cells were detected by RT-PCR expression of AC133 and kinase domain receptor (KDR). Furthermore, using an ELISA assay, we also found an association between circulating AC133+KDR+ cells and VEGF plasma levels in these patients. We also found AC133 and KDR positivity in breast carcinoma tissues. To our knowledge, this is the first report addressing the recruitment of EPC to breast tumors. Strategies to impair the mobilization and incorporation of EPC into tumors may interfere with the growth of these tumors.

Quantum dots spectrally distinguish multiple species within the tumor milieu in vivo

A solid tumor is an organ composed of cancer and host cells embedded in an extracellular matrix and nourished by blood vessels. A prerequisite to understanding tumor pathophysiology is the ability to distinguish and monitor each component in dynamic studies. Standard fluorophores hamper simultaneous intravital imaging of these components. Here, we used multiphoton microscopy techniques and transgenic mice that expressed green fluorescent protein, and combined them with the use of quantum dot preparations. We show that these fluorescent semiconductor nanocrystals can be customized to concurrently image and differentiate tumor vessels from both the perivascular cells and the matrix. Moreover, we used them to measure the ability of particles of different sizes to access the tumor. Finally, we successfully monitored the recruitment of quantum dot-labeled bone marrow-derived precursor cells to the tumor vasculature. These examples show the versatility of quantum dots for studying tumor pathophysiology and creating avenues for treatment.

Noninvasive MR imaging of magnetically labeled stem cells to directly identify neovasculature in a glioma model

AbstractBone marrow-derived endothelial precursor cells incorporate into neovasculature and have been successfully used as vehicles for gene delivery to brain tumors. To determine whether systemically administered Sca1+ bone marrow cells labeled with superparamagnetic iron oxide nanoparticles can be detected by in vivo magnetic resonance imaging in a mouse brain tumor model, mouse Sca1+ cells were labeled in vitro with ferumoxides-poly-l-lysine complexes. Labeled or control cells were administered intravenously to glioma-bearing severe combined immunodeficient (SCID) mice. Magnetic resonance imaging (MRI) was performed during tumor growth. Mice that received labeled cells demonstrated hypointense regions within the tumor that evolved over time and developed a continuous dark hypointense ring at a consistent time point. This effect was not cleared by administration of a gadolinium contrast agent. Histology showed iron-labeled cells around the tumor rim in labeled mice, which expressed CD31 and von Willebrand factor, indicating the transplanted cells detected in the tumor have differentiated into endothelial-like cells. These results demonstrate that MRI can detect the incorporation of magnetically labeled bone marrow-derived precursor cells into tumor vasculature as part of ongoing angiogenesis and neovascularization. This technique can be used to directly identify neovasculature in vivo and to facilitate gene therapy by noninvasively monitoring these cells as gene delivery vectors. (Blood. 2005;105:420-425)

Utilization of bone marrow-derived endothelial cell precursors in spontaneous prostate tumors varies with tumor grade.

Id1 and Id3 genes are required for vascularization, growth, and metastasis of xenograft tumors. In Id-deficient mice, tumor transplantation and proangiogenic factors fail to mobilize and recruit circulating endothelial precursor cells (CEPs) and hematopoietic cells, leading to defective tumor angiogenesis in various models. To investigate the requirement of Id genes and bone marrow incorporation in spontaneous prostate tumors, we crossbred Id mutant mice with the transgenic adenocarcinoma of the mouse prostate (TRAMP) mice. Id1-/- Id3+/- TRAMP mice display delayed tumor growth at 24 weeks compared with wild-type TRAMP mice. Id1 and Id3 were strongly expressed in the endothelial cells of poorly differentiated prostate adenocarcinoma but not in the vasculature of well-differentiated tumors, a finding that is corroborated in human prostate tumor samples. In Id-deficient TRAMP mice, the poorly differentiated tumors show extensive hemorrhage, whereas well-differentiated tumors exhibit none. Transplantation with Id wild-type bone marrow significantly reduced the hemorrhage in poorly differentiated prostate adenocarcinomas with bone marrow-derived endothelial cells contributing to 14% of the tumor blood vessels. However, in well-differentiated prostate adenocarcinomas, there was little evidence of bone marrow-derived endothelial cell incorporation. These differences in the expression of Id genes, the effects of Id loss, and the recruitment of bone marrow-derived endothelial precursor cells in tumor vasculature between well-differentiated and poorly differentiated prostate adenocarcinoma suggest that tumor angiogenesis varies depending on the tumor grade.

Role of bone marrow derived precursor cells in wound healing

Abstract Introduction: Neovascularization, necessary for wound healing, involves angiogenesis and vasculogenesis. Bone marrow-derived endothelial progenitor cells (EPCs) are key to vasculogenesis. We hypothesized ischemic wounds have a deficit of EPCs. Methods: EPCs were quantified using LacZ-Tie-2 transgenic mice, where beta-galactosidase (beta-gal) is expressed by the Tie-2 promoter. Wild type mice were transplanted with bone marrow from LacZ-Tie-2 mice. 4 wks later, chimeric mice underwent unilateral femoral artery ligation and bilateral 3mm punch-biopsy of hindlimbs. Ischemia was monitored with laser Doppler. Wound closure was assessed for 14 d with digital imaging. 5 mice/group were sacrificed on postoperative day 3 to harvest: wound, skeletal muscle, un-wounded adjacent skin, and remote skin. EPC counts were quantified by beta-gal staining in serial cross sections. Results: We observed significantly decreased EPCs in ischemic wounds, without a difference in the overall cellularity. Significantly higher numbers of EPCs were observed in the ischemic muscle. As expected, ischemic wounds showed significantly decreased healing rates. Non-ischemic healing wounds had significantly increased EPCs. EPC numbers showed a three-fold increase in ischemic hindlimb skeletal muscle with or without overlying wounds. Conclusions: Ischemic wounds suffer from significantly reduced EPC numbers at day 3 post-wounding and these wounds show delayed healing. Conversely, increased numbers of EPCs are observed in non-ischemic healing wounds. To our knowledge, this is the first report demonstrating an early EPC deficit in ischemic wounds thus targeting vasculogenesis as a potential key component of delay wound healing in ischemia.

Effects of Lactobacillus helveticus fermented milk on bone cells in vitro

Milk fermented with Lactobacillus helveticus ( L. helveticus) contains small peptides such as isoleucyl-prolyl-proline (IPP) and valyl-prolyl-proline (VPP), which inhibit the angiotensin converting enzyme (ACE). We investigated the effects of L. helveticus fermented milk whey ( Lh-whey) and its components, sour milk whey, calcium and IPP and VPP peptides, on bone cells in vitro. An osteoblast assay was performed by determining the amount of deposited calcium as an index of bone formation in cultures of mouse osteoblasts formed from bone marrow-derived osteoblast precursor cells. An osteoclast assay was performed by determining the activity of tartrate-resistant acid phosphatase released into the culture medium in cultures of mouse osteoclasts formed from bone marrow-derived osteoclast precursor cells. The Lh-whey increased bone formation 1.3–1.4 times with the 1 × 10 −5, 1 × 10 −4 and 1 × 10 −3 solutions. The IPP and VPP peptides also demonstrated a significant 5-fold activation of bone formation in in vitro osteoblast cultures, whereas the sour milk whey and calcium had no effect. No significant effects were observed on osteoclasts in vitro with any of the study products. L. helveticus fermented milk whey contains bioactive components that increase osteoblastic bone formation in vitro. The effect may be due to the ACE-inhibitory IPP and VPP peptides, which showed a similar effect to that of the L. helveticus fermented milk whey.

Induction of vasculogenesis in breast cancer models.

Recently, there have been reports of postnatal vasculogenesis in cases of ischaemia models. The aim of the present study is to provide evidence of postnatal vasculogenesis in breast-cancer–bearing mice. Based on cell surface antigen expression, we isolated endothelial precursor cells from bone marrow, peripheral blood and tumour-infiltrating cells from mice that had received six human breast cancer xenografts. In all three areas (bone marrow, peripheral blood and tumour-infiltrating cells), endothelial precursor cell population was elevated in all transplanted mice. Differentiation and migration activities of endothelial precursor cells were measured by comparing levels of the endothelial precursor cell maturation markers Flk-1, Flt-1, Tie2, VE-cadherin and CD31 among these three areas. The endothelial precursor cell population was 14% or greater in the gated lymphocyte-size fraction of the inflammatory breast cancer xenograft named WIBC-9, which exhibits a hypervascular structure and de novo formation of vascular channels, namely vasculogenic mimicry (Shirakawa et al, 2001). In vitro, bone marrow-derived endothelial precursor cells from four human breast cancer xenografts proliferated and formed multiple clusters of spindle-shaped attaching cells on a vitronectin-coated dish. The attaching cells, which incorporated DiI-labelled acetylated low-density lipoprotein (DiI-acLDL) and were negative for Mac-1. The putative bone marrow derived endothelial precursor cell subset, which was double positive of CD34 and Flk-1, and comparative bone marrow derived CD34 positive with Flk-1 negative subset were cultured. The former subset incorporated DiI-acLDL and were integrated with HUVECs. Furthermore, they demonstrated significantly higher levels of murine vascular endothelial growth factor and interleukin-8 in culture supernatant on time course by enzyme-linked immunosorbent assay. These findings constitute direct evidence that breast cancer induces postnatal vasculogenesis in vivo.British Journal of Cancer (2002) 87, 1454–1461. doi:10.1038/sj.bjc.6600610 www.bjcancer.com© 2002 Cancer Research UK

Dermatological aspects of angiogenesis.

Neovascularization is vital for the growth of tumours, providing a lifeline for sustenance and waste disposal. Tumour vessels can grow by sprouting, intussusception or by incorporating bone marrow-derived endothelial precursor cells into growing vessels. Recent advances in vascular biology have identified some key factors that control vascular growth, and have led to the hypothesis that in normal tissues vascular quiescence is maintained by the dominant influence of endogenous angiogenesis inhibitors over angiogenic stimuli. In contrast, increased secretion of angiogenic factors and the down-regulation of endogenous angiogenesis inhibitors induce tumour angiogenesis. Vascular quiescence in the skin seems to be primarily maintained by a balance between the endogenous angiogenesis inhibitors thrombospondin 1 and thrombospondin 2 and the potent proangiogenic factor vascular endothelial growth factor A. Inhibiting tumour growth by controlling angiogenesis is an intriguing approach with great potential for the treatment of vascular tumours such as haemangioma, Kaposi's sarcoma and solid cutaneous tumours such as squamous cell carcinoma, melanoma and basal cell carcinoma. In this review, the role of angiogenesis and more recent topics such as lymphangiogenesis in cutaneous tumour growth, invasion and metastasis will be discussed.

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.

Angiogenesis in hematologic malignancies.

Angiogenesis, defined as the blood vessel generation from preexisting blood vessels, was found to play an important role in the progression of solid tumors. In addition, bone marrow-derived endothelial precursor cells may contribute to tumor angiogenesis. Recently angiogenesis induction was described in several hematologic neoplasms as leukemia, lymphoma, myelodysplastic syndrome and multiple myeloma (MM). Clinical angiogenesis research also termed as angiodiagnosis has established the prognostic relevance of markers of angiogenesis e.g., microvessel density and circulating levels of angiogenic peptides. Development of antiangiogenic treatment for hematologic neoplasms has recently been sparked by the success of Thalidomide (Thal) which has antiangiogenic properties in MM. Antiangiogenic treatment strategies are now being tested in clinical trials on several types of hematologic neoplasms.