VEGFR-3 and CD133 identify a population of CD34+ lymphatic/vascular endothelial precursor cells

Lymphangiogenesis and Inflammation-Looking for the "Missing Pieces" of the Puzzle

Several papers about lymphangiogenesis and inflammation focused on the detailed and complicated descriptions of the molecular pathways accompanying both non-tumor and tumor inflammatory-induced lymphatic vessel development. Many authors are tempted to present inflammatory-induced lymphangiogenesis in pathologic conditions neglecting the role of inflammatory cells during embryonic lymphatic vessel development. Some of the inflammatory cells are largely characterized in inflammatory-induced lymphangiogenesis, while others as mast cells, eosinophils, or plasma cells are less studied. No phenotypic characterization of inflammation-activated lymphatic endothelial cell is available in this moment. Another paradox is related to the existence of few papers regarding lymphangiogenesis inside lymphoid organs and for their related pathology. There are still several "missing pieces of such a big puzzle" of lymphangiogenesis and inflammation, with a direct impact on the ineffectiveness of the anti-inflammatory therapy as lymphangiogenesis inhibitors. The present paper will focus on the controversial issues of lymphangiogenesis and inflammation.

Long-term, regular remote ischemic preconditioning improves endothelial function in patients with coronary heart disease

Remote ischemic preconditioning (RIPre) can prevent myocardial injury. The purpose of this study was to assess the beneficial effects of long-term regular RIPre on human arteries. Forty patients scheduled for coronary artery bypass graft (CABG) surgery were assigned randomly to a RIPre group (n=20) or coronary heart disease (CHD) group (n=20). Twenty patients scheduled for mastectomy were enrolled as a control group. RIPre was achieved by occluding arterial blood flow 5 min with a mercury sphygmomanometer followed by a 5-min reperfusion period, and this was repeated 4 times. The RIPre procedure was repeated 3 times a day for 20 days. In all patients, arterial fragments discarded during surgery were collected to evaluate endothelial function by flow-mediated dilation (FMD), CD34⁺ monocyte count, and endothelial nitric oxide synthase (eNOS expression). Phosphorylation levels of STAT-3 and Akt were also assayed to explore the underlying mechanisms. Compared with the CHD group, long-term regular RIPre significantly improved FMD after 20 days (8.5±2.4 vs 4.9±4.2%, P<0.05) and significantly reduced troponin after CABG surgery (0.72±0.31 and 1.64±0.19, P<0.05). RIPre activated STAT-3 and increased CD34⁺ endothelial progenitor cell counts found in arteries. Long-term, regular RIPre improved endothelial function in patients with CHD, possibly due to STAT-3 activation, and this may have led to an increase in endothelial progenitor cells.

Aberrant lymphatic endothelial progenitors in lymphatic malformation development

Lymphatic malformations (LMs) are vascular anomalies thought to arise from dysregulated lymphangiogenesis. These lesions impose a significant burden of disease on affected individuals. LM pathobiology is poorly understood, hindering the development of effective treatments. In the present studies, immunostaining of LM tissues revealed that endothelial cells lining aberrant lymphatic vessels and cells in the surrounding stroma expressed the stem cell marker, CD133, and the lymphatic endothelial protein, podoplanin. Isolated patient-derived CD133+ LM cells expressed stem cell genes (NANOG, Oct4), circulating endothelial cell precursor proteins (CD90, CD146, c-Kit, VEGFR-2), and lymphatic endothelial proteins (podoplanin, VEGFR-3). Consistent with a progenitor cell identity, CD133+ LM cells were multipotent and could be differentiated into fat, bone, smooth muscle, and lymphatic endothelial cells in vitro. CD133+ cells were compared to CD133− cells isolated from LM fluids. CD133− LM cells had lower expression of stem cell genes, but expressed circulating endothelial precursor proteins and high levels of lymphatic endothelial proteins, VE-cadherin, CD31, podoplanin, VEGFR-3 and Prox1. CD133− LM cells were not multipotent, consistent with a differentiated lymphatic endothelial cell phenotype. In a mouse xenograft model, CD133+ LM cells differentiated into lymphatic endothelial cells that formed irregularly dilated lymphatic channels, phenocopying human LMs. In vivo, CD133+ LM cells acquired expression of differentiated lymphatic endothelial cell proteins, podoplanin, LYVE1, Prox1, and VEGFR-3, comparable to expression found in LM patient tissues. Taken together, these data identify a novel LM progenitor cell population that differentiates to form the abnormal lymphatic structures characteristic of these lesions, recapitulating the human LM phenotype. This LM progenitor cell population may contribute to the clinically refractory behavior of LMs.

ID3 contributes to the acquisition of molecular stem cell-like signature in microvascular endothelial cells: its implication for understanding microvascular diseases

While significant progress has been made to advance our knowledge of microvascular lesion formation, yet the investigation of how stem-like cells may contribute to the pathogenesis of microvascular diseases is still in its infancy. We assessed whether the inhibitor of DNA binding and differentiation 3 (ID3) contributes to the acquisition of a molecular stem cell-like signature in microvascular endothelial cells. The effects of stable ID3 overexpression and SU5416 treatment - a chemical inducer of microvascular lesions, had on the stemness signature were determined by flow cytometry, immunoblot, and immunohistochemistry. Continuous ID3 expression produced a molecular stemness signature consisting of CD133(+) VEGFR3(+) CD34(+) cells. Cells exposed to SU5416 showed positive protein expression of ID3, VEGFR3, CD34 and increased expression of pluripotent transcription factors Oct-4 and Sox-2. ID3 overexpressing cells supported the formation of a 3-D microvascular lesion co-cultured with smooth muscle cells. In addition, in vivo microvascular lesions from SuHx rodent model showed an increased expression of ID3, VEGFR3, and Pyk2 similar to SU5416 treated human endothelial cells. Further investigations into how normal and stem-like cells utilize ID3 may open up new avenues for a better understanding of the molecular mechanisms which are underlying the pathological development of microvascular diseases.

Cell-based therapy for therapeutic lymphangiogenesis

Lymphedema is a medically irreversible condition for which currently conservative and surgical therapies are either ineffective or impractical. The potential use of progenitor and stem cell-based therapies has offered a paradigm that may provide alternative treatment options for lymphatic disorders. Moreover, basic research, preclinical studies, as well as clinical trials have evaluated the therapeutic potential of various cell therapies in the field of lymphatic regeneration medicine. Among the available cell approaches, mesenchymal stem cells (MSCs) seem to be the most promising candidate mainly due to their abundant sources and easy availability as well as evitable ethical and immunological issues confronted with embryonic stem cells and induced pluripotent stem cells. In this context, the purpose of this review is to summarize various cell-based therapies for lymphedema, along with strengths and weaknesses of these therapies in the clinical application for lymphedema treatment. Particularly, we will highlight the use of MSCs for lymphatic regeneration medicine. In addition, the future perspectives of MSCs in the field of lymphatic regeneration will be discussed.

(Lymph)angiogenic influences on hematopoietic cells in acute myeloid leukemia

The purpose of this review is to provide an overview of the effect of (lymph)angiogenic cytokines on hematopoietic cells involved in acute myeloid leukemia (AML). Like angiogenesis, lymphangiogenesis occurs in pathophysiological conditions but not in healthy adults. AML is closely associated with the vasculature system, and the interplay between lymphangiogenic cytokines maintains leukemic blast survival in the bone marrow (BM). Once AML is induced, proangiogenic cytokines function as angiogenic or lymphangiogenic factors and affect hematopoietic cells, including BM-derived immune cells. Simultaneously, the representative cytokines, VEGFs and their receptors are expressed on AML blasts in vascular and osteoblast niches in both the BM and the peripheral circulation. After exposure to (lymph)angiogenic cytokines in leukemogenesis and infiltration, immune cell phenotypes and functions are affected. These dynamic behaviors in the BM reflect the clinical features of AML. In this review, we note the importance of lymphangiogenic factors and their receptors in hematopoietic cells in AML. Understanding the functional characterization of (lymph)angiogenic factors in the BM niche in AML will also be helpful in interrupting the engraftment of leukemic stem cells and for enhancing immune cell function by modulating the tumor microenvironment.

Intracellular NAMPT-NAD+-SIRT1 cascade improves post-ischaemic vascular repair by modulating Notch signalling in endothelial progenitors

AIMS

Intracellular nicotinamide phosphoribosyltransferase (NAMPT) is the rate-limiting enzyme for nicotinamide adenine dinucleotide (NAD(+)) biosynthesis. This study investigated the role of NAMPT-mediated NAD(+) signalling in post-ischaemic vascular repair.

METHODS AND RESULTS

Mouse hind-limb ischaemia up-regulated NAMPT expression and NAD(+) level in bone marrow (BM). Pharmacological inhibition of NAMPT by a chemical inhibitor FK866 impaired the mobilization of endothelial progenitor cells (EPCs) from BM upon ischaemic stress. Transgenic mice overexpressing NAMPT (Tg mice), but not H247A-mutant dominant-negative NAMPT (DN-Tg mice), exhibited enhanced capillary density, increased number of proliferating endothelial cells, improved blood flow recovery, and augmented collateral arterioles in the ischaemic limb. In cultured BM-derived EPCs, inhibition of NAMPT suppressed proliferation, migration, and tube formation, whereas overexpression of NAMPT induced opposite effects. The promoting effects of NAMPT on EPCs were abolished by silencing of sirtuin 1 (SIRT1), rather than silencing of SIRT2-7. Overexpression of NAMPT led to a SIRT1-depedent enhancement of Notch-1 intracellular domain deacetylation, which inhibited Delta-like ligand-4 (DLL4)-Notch signalling and thereby up-regulated of VEGFR-2 and VEGFR-3. Injection of recombinant VEGF induced a more pronounced EPC mobilization in Tg, but not in DN-Tg, mice. Furthermore, overexpression of NAMPT down-regulated Fringe family glycosyltransferases in a SIRT1-dependent manner, which rendered Notch more sensitive to the pro-angiogenic ligand Jagged1 rather than the anti-angiogenic ligand DLL4.

CONCLUSIONS

These results demonstrate that intracellular NAMPT-NAD(+)-SIRT1 cascade improves post-ischaemic neovascularization. The modulation of Notch signalling may contribute to the enhanced post-ischaemic neovascularization.

Hematopoietic stem cells in neonates: any differences between very preterm and term neonates?

Background

In the last decades, human full-term cord blood was extensively investigated as a potential source of hematopoietic stem and progenitor cells (HSPCs). Despite the growing interest of regenerative therapies in preterm neonates, only little is known about the biological function of HSPCs from early preterm neonates under different perinatal conditions. Therefore, we investigated the concentration, the clonogenic capacity and the influence of obstetric/perinatal complications and maternal history on HSPC subsets in preterm and term cord blood.

Methods

CD34+ HSPC subsets in UCB of 30 preterm and 30 term infants were evaluated by flow cytometry. Clonogenic assays suitable for detection of the proliferative potential of HSPCs were conducted. Furthermore, we analyzed the clonogenic potential of isolated HSPCs according to the stem cell marker CD133 and aldehyde dehydrogenase (ALDH) activity.

Results

Preterm cord blood contained a significantly higher concentration of circulating CD34+ HSPCs, especially primitive progenitors, than term cord blood. The clonogenic capacity of HSPCs was enhanced in preterm cord blood. Using univariate analysis, the number and clonogenic potential of circulating UCB HSPCs was influenced by gestational age, birth weight and maternal age. Multivariate analysis showed that main factors that significantly influenced the HSPC count were maternal age, gestational age and white blood cell count. Further, only gestational age significantly influenced the clonogenic potential of UCB HSPCs. Finally, isolated CD34+/CD133+, CD34+/CD133– and ALDH^high HSPC obtained from preterm cord blood showed a significantly higher clonogenic potential compared to term cord blood.

Conclusion

We demonstrate that preterm cord blood exhibits a higher HSPC concentration and increased clonogenic capacity compared to term neonates. These data may imply an emerging use of HSPCs in autologous stem cell therapy in preterm neonates.

Bone marrow-derived cells are implicated as a source of lymphatic endothelial progenitors in human breast cancer

Bone marrow-derived endothelial progenitor cells (EPCs) infiltrate into sites of neovascularization in adult tissues and mature into functional blood endothelial cells (BECs) during a process called vasculogenesis. Human marrow-derived EPCs have recently been reported to display a mixed myeloid and lymphatic endothelial cell (LEC) phenotype during inflammation-induced angiogenesis; however, their role in cancer remains poorly understood. We report the in vitro differentiation of human cord blood CD133⁺CD34⁺ progenitors into podoplanin⁺ cells expressing both myeloid markers (CD11b, CD14) and the canonical LEC markers vascular endothelium growth factor receptor 3 (VEGFR-3), lymphatic vessel endothelial hyaluronan receptor 1 (LYVE-1), and prospero homeobox 1 (PROX-1). These podoplanin⁺ cells displayed sprouting behavior comparable to that of LECs in vitro and a dual hemangiogenic and lymphangiogenic activity in vivo in an endothelial cell sprouting assay and corneal vascularization assay, respectively. Furthermore, these cells expressed vascular endothelium growth factor (VEGF) family members A, -C, and -D. Thus, bone-marrow derived EPCs stimulate hemangiogenesis and lymphangiogenesis through their ability to differentiate into LECs and to produce angiogenic factors. Importantly, plasma from patients with breast cancer induced differentiation of CD34⁺ cord blood progenitors into hemangiogenic and lymphangiogenic CD11b⁺ myeloid cells, whereas plasma from healthy women did not have this effect. Consistent with these findings, circulating CD11b⁺ cells from breast cancer patients, but not from healthy women, displayed a similar dual angiogenic activity. Taken together, our results show that marrow-derived EPCs become hemangiogenic and lymphangiogenic upon exposure to cancer plasma. These newly identified functions of bone-marrow derived EPCs are expected to influence the diagnosis and treatment of breast cancer.

Human podoplanin-positive monocytes and platelets enhance lymphangiogenesis through the activation of the podoplanin/CLEC-2 axis

Emerging studies suggested that murine podoplanin-positive monocytes (PPMs) are involved in lymphangiogenesis. The goal of this study was to demonstrate the therapeutic lymphangiogenesis of human PPMs by the interaction with platelets. Aggregation culture of human peripheral blood mononuclear cells (PBMCs) resulted in cellular aggregates termed hematospheres. During 5-day culture, PPMs expanded exponentially and expressed several lymphatic endothelial cell-specific markers including vascular endothelial growth factor receptor (VEGFR)-3 and well-established lymphangiogenic transcription factors. Next, we investigated the potential interaction of PPMs with platelets that had C-type lectin-like receptor-2 (CLEC-2), a receptor of podoplanin. In vitro coculture of PPMs and platelets stimulated PPMs to strongly express lymphatic endothelial markers and upregulate lymphangiogenic cytokines. Recombinant human CLEC-2 also stimulated PPMs through Akt and Erk signaling. Likewise, platelets in coculture with PPMs augmented secretion of a lymphangiogenic cytokine, interleukin (IL)-1-β, via podoplanin/CLEC-2 axis. The supernatant obtained from coculture was able to enhance the migration, viability, and proliferation of lymphatic endothelial cell. Local injection of hematospheres with platelets significantly increased lymphatic neovascularization and facilitated wound healing in the full-thickness skin wounds of nude mice. Cotreatment with PPMs and platelets augments lymphangiogenesis through podoplanin/CLEC-2 axis, which thus would be a promising novel strategy of cell therapy to treat human lymphatic vessel disease.

Adult neurogenesis and glial oncogenesis: when the process fails

Malignant brain tumors, including glioblastoma multiforme (GBM), are known for their high degree of invasiveness, aggressiveness, and lethality. These tumors are made up of heterogeneous cell populations and only a small part of these cells (known as cancer stem cells) is responsible for the initiation and recurrence of the tumor. The biology of cancer stem cells and their role in brain tumor growth and therapeutic resistance has been extensively investigated. Recent work suggests that glial tumors arise from neural stem cells that undergo a defective process of differentiation. The understanding of this process might permit the development of novel treatment strategies targeting cancer stem cells. In the present review, we address the mechanisms underlying glial tumor formation, paying special attention to cancer stem cells and the role of the microenvironment in preserving them and promoting tumor growth. Recent advancements in cancer stem cell biology, especially regarding tumor initiation and resistance to chemo- or radiotherapy, have led to the development of novel treatment strategies that focus on the niche of the stem cells that make up the tumor. Encouraging results from preclinical studies predict that these findings will be translated into the clinical field in the near future.

Id1 and NF-κB promote the generation of CD133+ and BMI-1+ keratinocytes and the growth of xenograft tumors in mice

Id1 and NF-κB are highly expressed in oral squamous cell carcinoma (OSCC). Whether they have a synergistic role in the carcinogenesis of OSCC is unclear. The current study was designed to demonstrate the synergy of both Id1 and NF-κB in the underlying disease mechanisms of OSCC using in vitro and in vivo animal models. Id1 and NF-κB strengthened the expression of both CD133 and BMI-1 in OSCC cell cultures. CD133(+) and BMI-1(+) keratinocytes from OSCC tissues and cell cultures initiated the growth of xenograft tumors in SCID/Beige mice. Id1 and NF-κB regulate the expression of CD133 and BMI-1 in an additive or synergistic manner in OSCC, which is associated with the generation of naïve and self-renewable keratinocytes and initiate the growth of xenograft tumors in vivo.

Aberrant expression of decoy receptor 3 in human breast cancer: relevance to lymphangiogenesis

BACKGROUND

Decoy receptor 3 (DcR3), a decoy receptor against Fas ligand belonging to the tumor necrosis factor receptor superfamily, is overexpressed in some forms of cancer. It was recently reported that DcR3 could protect endothelial cells from apoptosis, implying a potential role in the development of vessels, whereas its role in the lymphangiogenesis remains unclear. In the present study, we studied the DcR3 expression and its relationship with the lymphatic microvessel density (LMVD) to investigate if it played a role in the lymph metastasis of human breast cancer.

MATERIALS AND METHODS

Real-time polymerase chain reaction and immunohistochemistry were performed to measure the messenger RNA and protein expression of DcR3 in the breast cancer tissues, noncancerous counterparts, and axillary lymph node from 63 patients. LMVD in these specimens was assessed by counting the D2-40 labeled-microvessels. Furthermore, the correlations between DcR3 expression and LMVD and other clinicopathologic parameters were analyzed.

RESULTS

DcR3 was overexpressed in the breast cancer tissue of 58 patients (92.1%) and was also expressed in vascular endothelial cells and tumor cells in the lymph nodes. LMVD in cancer tissue and lymph nodes were both positively correlated to the aberrant expression of DcR3.

CONCLUSIONS

The relevance between DcR3 overexpression and LMVD revealed the existence of possible links between DcR3 and lymphangiogenesis. Based on these findings, it is important to further explore the regulation of lymphangiogenesis operated by the reverse tumor necrosis factor signaling of DcR3.

Productively infected murine Kaposi's sarcoma-like tumors define new animal models for studying and targeting KSHV oncogenesis and replication

Kaposi's sarcoma (KS) is an AIDS-defining cancer caused by the KS-associated herpesvirus (KSHV). KS tumors are composed of KSHV-infected spindle cells of vascular origin with aberrant neovascularization and erythrocyte extravasation. KSHV genes expressed during both latent and lytic replicative cycles play important roles in viral oncogenesis. Animal models able to recapitulate both viral and host biological characteristics of KS are needed to elucidate oncogenic mechanisms, for developing targeted therapies, and to trace cellular components of KS ontogeny. Herein, we describe two new murine models of Kaposi's sarcoma. We found that murine bone marrow-derived cells, whether established in culture or isolated from fresh murine bone marrow, were infectable with rKSHV.219, formed KS-like tumors in immunocompromised mice and produced mature herpesvirus-like virions in vivo. Further, we show in vivo that the histone deacetylase (HDAC) inhibitor suberoylanilide hydroxamic acid (SAHA/Vorinostat) enhanced viral lytic reactivation. We propose that these novel models are ideal for studying both viral and host contributions to KSHV-induced oncogenesis as well as for testing virally-targeted antitumor strategies for the treatment of Kaposi's sarcoma. Furthermore, our isolation of bone marrow-derived cell populations containing a cell type that, when infected with KSHV, renders a tumorigenic KS-like spindle cell, should facilitate systematic identification of KS progenitor cells.

CD34+ VEGFR-3+ progenitor cells have a potential to differentiate towards lymphatic endothelial cells

Endothelial progenitor cells (EPCs) play an important role in postnatal neovascularization. However, it is poorly understood whether EPCs contribute to lymphangiogenesis. Here, we assessed differentiation of a novel population of EPCs towards lymphatic endothelial cells and their lymphatic formation. CD34(+) VEGFR-3(+) EPCs were isolated from mononuclear cells of human cord blood by fluorescence-activated cell sorting. These cells expressed CD133 and displayed the phenotype of the endothelial cells. Cell colonies appeared at 7-10 days after incubation. The cells of the colonies grew rapidly and could be repeatedly subcultured. After induction with VEGF-C for 2 weeks, CD34(+) VEGFR-3(+) EPCs could differentiate into lymphatic endothelial cells expressing specific markers 5'-nucleotidase, LYVE-1 and Prox-1. The cells also expressed hyaluronan receptor CD44. The differentiated cells had properties of proliferation, migration and formation of lymphatic capillary-like structures in three-dimensional collagen gel and Matrigel. VEGF-C enhanced VEGFR-3 mRNA expression. After interfering with VEGFR-3 siRNA, the effects of VEGF-C were diminished. These results demonstrate that there is a population of CD34(+) VEGFR-3(+) EPCs with lymphatic potential in human cord blood. VEGF-C/VEGFR-3 signalling pathway mediates differentiation of CD34(+) VEGFR-3(+) EPCs towards lymphatic endothelial cells and lymphangiogenesis. Cord blood-derived CD34(+) VEGFR-3(+) EPCs may be a reliable source in transplantation therapy for lymphatic regenerative diseases.

Inhibition of lymphangiogenesis of endothelial progenitor cells with VEGFR-3 siRNA delivered with PEI-alginate nanoparticles

Lymphangiogenesis is implicated in lymphatic metastasis of tumor cells. Recently, growing evidences show that endothelial progenitor cells (EPCs) are involved in lymphangiogenesis. This study has investigated effects of VEGF-C/VEGFR-3 (vascular endothelial growth factor receptor-3) signaling pathway on EPC differentiation and effectiveness of inhibiting lymphatic formation of EPCs with VEGFR-3 siRNA delivered in PEI (polyethylenimine)-alginate nanoparticles. CD34⁺VEGFR-3⁺ EPCs were sorted from mononuclear cells of human cord blood. Under induction with VEGF-C, the cells differentiated toward lymphatic endothelial cells. The nanoparticles were formulated with 25 kDa branched PEI and alginate. The size and surface charge of PEI-alginate nanoparticles loading VEGFR-3 siRNA (N/P = 16) are 139.1 nm and 7.56 mV respectively. VEGFR-3 siRNA specifically inhibited expression of VEGFR-3 mRNA in the cells. After treatment with PEI-alginate/siRNA nanocomplexes, EPCs could not differentiate into lymphatic endothelial cells, and proliferation, migration and lymphatic formation of EPC-derived cells were suppressed significantly. These results demonstrate that VEGFR-3 signaling plays an important role in differentiation of CD34⁺VEGFR-3⁺ EPCs. VEGFR-3 siRNA delivered with PEI-alginate nanoparticles can effectively inhibit differentiation and lymphangiogenesis of EPCs. Inhibiting VEGFR-3 signaling with siRNA/nanocomplexes would be a potential therapy for suppression of tumor lymphangiogenesis and lymphatic metastasis.

Immunophenotypic comparison of heterogenous non-sorted versus sorted mononuclear cells from human umbilical cord blood: a novel cell enrichment approach

Human umbilical cord blood (hUCB) has been the preferred source of stem cells for the treatment of haematological malignancies and genetic disorders. This is primarily due to its non-invasiveness, high accessibility with relative ease of isolation. Still failures do prevail due to its heterogeneity and lesser frequency of MSC identified in UCB. This study, thus, employs a cell enrichment technology to improve its therapeutic efficacy. This was achieved by immunophenotypic comparison of stem cells isolated from the heterogenous non-sorted mononuclear cells (MNCs), linage depleted (Lin+ and Lin-) fractions obtained from magnetic activated cell sorter (MACS) and sorted MNCs obtained by fluorescent activated cell sorter (FACS). The markers under consideration were CD29, CD44, CD34, CD45, CD133, CD90 and CD117. FACS sorted MNCs were rich in naive stem cell population, whereas non-sorted MNCs and lineage depleted fractions were found to be rich in progenitors. Thus, we suggest that a combination therapy of both sorted population might serve as an alternative valuable tool in treating haematologic/genetic disorders. However, further research on cell enrichment technology might give a clue for improved cell based therapy in regenerative medicine.

Recruitment and retention of human autologous CD34+ CD117+ CD133+ bone marrow stem cells to infarcted myocardium followed by directed vasculogenesis: Novel strategy for cardiac regeneration

BACKGROUND

Ongoing clinical trials, in regenerative therapy of patients suffering from myocardial infarctions, rely primarily upon administration of bone marrow stem cells to the infarcted zones. Unfortunately, low retention of these cells, to the therapeutic delivery sites, reduces effectiveness of this strategy; thus it has been identified as the most critical problem for advancement of cardiac regenerative medicine.

SPECIFIC AIMS

The specific aim of this work was three-fold: (1) to isolate highly viable populations of human, autologous CD34+, CD117+, and CD133+ bone marrow stem cells; (2) to bioengineer heterospecific, tetravalent antibodies and to use them for recruiting of the stem cells to regenerated zones of infarcted myocardium; (3) to direct vasculogenesis of the retained stem cells with the defined factors.

PATIENTS METHODS

Cardiac tissue was biopsied from the hearts of the patients, who were receiving orthotopic heart transplants after multiple cardiac infarctions. This tissue was used to engineer fully human in vitro models of infarcted myocardium. Bone marrow was acquired from these patients. The marrow cells were sorted into populations of cells displaying CD34, CD117, and CD133. Heterospecific, tetravalent antibodies were bioengineered to bridge CD34, CD117, CD133 displayed on the stem cells with cardiac myosin of the infarcted myocardium. The sorted stem cells were administered to the infarcted myocardium in the in vitro models.

RESULTS

Administration of the bioengineered, heterospecific antibodies preceding administration of the stem cells greatly improved the stem cells' recruitment and retention to the infarcted myocardium. Treatment of the retained stem cells with vascular endothelial growth factor and angiopoietin efficiently directed their differentiation into endothelial cells, which expressed vascular endothelial cadherin, platelet / endothelial cell adhesion molecule, claudin, and occludin, while forming tight and adherens junctions.

CONCLUSIONS

This novel strategy improved retention of the patients' autologous bone marrow stem cells to the infarcted myocardium followed by directed vasculogenesis. Therefore, it is worth pursuing it in support of the ongoing clinical trials of cardiac regenerative therapy.

High levels of circulating CD34+/VEGFR3+ lymphatic/vascular endothelial progenitor cells is correlated with lymph node metastasis in patients with epithelial ovarian cancer

AIM

Lymph node metastasis is one of the predictive factors associated with poor prognosis of epithelial ovarian cancer. To clarify the role of CD34 and vascular endothelial growth factor receptor-3-positive (CD34+/VEGFR3+) lymphatic/vascular endothelial progenitor cells (LVEPC) in patients with lymph node metastasis and epithelial ovarian cancer progression, the levels of circulating CD34+/VEGFR3+ LVEPC in epithelial ovarian cancer patients were detected. We also tested the plasma protein levels of VEGF and stromal cell-derived factor to find out their possible relationships with lymph node metastasis in our epithelial ovarian cancer cohort.

MATERIAL AND METHODS

Peripheral blood samples were collected from 54 patients diagnosed as epithelial ovarian cancer, and 31 normal samples as control. The circulating levels of LVEPC were carried out by flow cytometry, and blood protein levels of biomarkers were measured by enzyme-linked immunosorbent assay (ELISA).

RESULTS

The level of circulating LVEPC was significantly higher in patients with ovarian cancer compared with that of healthy controls. There was also a statistically significant correlation between LVEPC levels and surgical staging of epithelial ovarian cancer (P < 0.01).

CONCLUSION

The circulating levels of bone marrow-derived LVEPC are significantly increased in epithelial ovarian cancer patients and these levels correlate with lymph node metastasis too.

Circulating endothelial progenitor cells in acromegaly

BACKGROUND

Endothelial progenitor cells (EPCs), involved in the repairing mechanisms of vascular damage, are positively correlated to insulin-like growth factor I (IGF-I) concentrations in healthy adults. However, the levels of EPCs and their role in acromegalic patients have never been investigated.

AIM

We conducted a cross-sectional study in order to assess the levels of the different phenotypes of circulating EPC in acromegalic patients.

SUBJECTS AND METHODS

The study was performed at the Endocrinology Unit of Federico II University and at the Unit of Metabolic Diseases and Endocrinology of the Second University of Naples. Fifty-five acromegalic patients and 65 healthy controls were studied. EPCs were assessed by flow cytometry and IGF-I by immunoradiometric assay.

RESULTS

Compared with subjects of the control group, acromegalic patients showed significantly higher levels of EPCs phenotypes expressing KDR antigen [KDR+, cells per 106 events, median and interquartile range, 44 (28-67) vs 23 (13-40), p=0.006; CD34+KDR+ 25 (18-38) vs 12 (8-17), p<0.001; CD133+KDR+ 17 (13-30) vs 8 (6-12), p<0.001; CD34+KDR+CD133+ 16 (12-25) vs 8 (6-10), p<0.001]. There was a positive correlations between CD34+KDR+CD133+ cells count and IGF-I in acromegaly group (r=0.79, p<0.001).

CONCLUSIONS

Acromegalic patients show higher circulating EPCs levels expressing KDR, positively correlated with IGF-I, suggesting a role for IGF-I in regulating the expression of this surface marker in the early phase of EPCs differentiation.

Targeting cancer stem cells: emerging role of Nanog transcription factor

The involvement of stemness factors in cancer initiation and progression has drawn much attention recently, especially after the finding that introducing four stemness factors in somatic cells is able to reprogram the cells back to an embryonic stem cell-like state. Following accumulating data revealing abnormal elevated expression levels of key stemness factors, like Nanog, Oct4, and Sox2, in several types of cancer stem cells; the importance and therapeutic potential of targeting these stemness regulators in cancers has turned to research focus. Nanog determines cell fate in both embryonic and cancer stem cells; activating Nanog at an inappropriate time would result in cancer stem cells rather than normal pluripotent stem cells or differentiated somatic cells. Upregulated Nanog is correlated with poor survival outcome of patients with various types of cancer. The discoveries of downstream regulatory pathways directly or indirectly mediated by Nanog indicate that Nanog regulates several aspects of cancer development such as tumor cell proliferation, self-renewal, motility, epithelial-mesenchymal transition, immune evasion, and drug-resistance, which are all defined features for cancer stem cells. The current review paper illustrates the central role of Nanog in the regulatory networks of cancer malignant development and stemness acquirement, as well as in the communication between cancer cells and the surrounding stroma. Though a more defined model is needed to test the therapeutic efficacy of targeting Nanog as a cancer treatment method, current animal experiments using siNanog or shNanog have shown the promising therapeutic potential of Nanog targeting in several types of cancer.

Myeloid cells and lymphangiogenesis

The lymphatic vascular system and the hematopoietic system are intimately connected in ontogeny and in physiology. During embryonic development, mammalian species derive a first lymphatic vascular plexus from the previously formed anterior cardinal vein, whereas birds and amphibians have a lymphatic vascular system of dual origin, composed of lymphatic endothelial cells (LECs) of venous origin combined with LECs derived from mesenchymal lymphangioblasts. The contribution of hematopoietic cells as building blocks of nascent lymphatic structures in mammals is still under debate. In contrast, the importance of myeloid cells to direct lymphatic vessel growth and function postnatally has been experimentally shown. For example, myeloid cells communicate with LECs via paracrine factors or cell-cell contacts, and they also can acquire lymphatic endothelial morphology and marker gene expression, a process reminiscent of developmental vasculogenesis. Here, we present an overview of the current understanding of how lymphatic vessels and the hematopoietic system, in particular myeloid cells, interact during embryonic development, in normal organ physiology, and in disease.

In vitro and in vivo properties of CD133 expressing cells from human lung cancer cell lines

Background

Tumor development is recently hypothesized to depend on a rare cell population with stem cell properties, such cells are called cancer stem cells (CSCs) or tumor-initiating cells (TICs). From various cancer tissues or cancer cell lines, CD133 expressing cells were found to define a unique CSC/TIC phenotype. To study whether that also could be the case in lung cancer, we examined different lung cancer cell lines for CD133 expression.

Results

Among the 4 cell lines studied, only the cell line LC-42 expressed CD133. Therefore, LC-42 was further characterized and studied with special emphasis on identifying the presence of CD133⁺ CSCs/TICs. FACS sorted CD133^high and CD133^dim subpopulations from LC-42 showed no differences in soft agar colony-forming capacity and spheres-forming capacity in serum-free cultures. LC-42 cells contained Side Population (SP), and only SP cells were able to form spheres. Furthermore, Nanog expression was significantly higher in SP than in non-SP. However, no difference was observed of CD133 expression in SP and non-SP. When CD133^high and CD133^dim cells were serially xeno-transplanted in NOD/SCID mice, both formed tumours similar to their parental LC-42 cells. There were no expression differences for NANOG, OCT4 and SOX2 examined immunohistochemically in the xenografts from both cell fractions.

Conclusion

Our data do not show a difference in tumorigenic potential of CD133^high and CD133^dim cells with respect to any of the parameters analyzed in vitro and in vivo, suggesting that CD133 expression is not restricted to cancer-initiating cells in the human lung cancer cell line LC-42.

BMP2 genetically engineered MSCs and EPCs promote vascularized bone regeneration in rat critical-sized calvarial bone defects

Current clinical therapies for critical-sized bone defects (CSBDs) remain far from ideal. Previous studies have demonstrated that engineering bone tissue using mesenchymal stem cells (MSCs) is feasible. However, this approach is not effective for CSBDs due to inadequate vascularization. In our previous study, we have developed an injectable and porous nano calcium sulfate/alginate (nCS/A) scaffold and demonstrated that nCS/A composition is biocompatible and has proper biodegradability for bone regeneration. Here, we hypothesized that the combination of an injectable and porous nCS/A with bone morphogenetic protein 2 (BMP2) gene-modified MSCs and endothelial progenitor cells (EPCs) could significantly enhance vascularized bone regeneration. Our results demonstrated that delivery of MSCs and EPCs with the injectable nCS/A scaffold did not affect cell viability. Moreover, co-culture of BMP2 gene-modified MSCs and EPCs dramatically increased osteoblast differentiation of MSCs and endothelial differentiation of EPCs in vitro. We further tested the multifunctional bone reconstruction system consisting of an injectable and porous nCS/A scaffold (mimicking the nano-calcium matrix of bone) and BMP2 genetically-engineered MSCs and EPCs in a rat critical-sized (8 mm) caviarial bone defect model. Our in vivo results showed that, compared to the groups of nCS/A, nCS/A+MSCs, nCS/A+MSCs+EPCs and nCS/A+BMP2 gene-modified MSCs, the combination of BMP2 gene -modified MSCs and EPCs in nCS/A dramatically increased the new bone and vascular formation. These results demonstrated that EPCs increase new vascular growth, and that BMP2 gene modification for MSCs and EPCs dramatically promotes bone regeneration. This system could ultimately enable clinicians to better reconstruct the craniofacial bone and avoid donor site morbidity for CSBDs.

[Lymphatic vascular system, development and lymph formation. Review]

The lymphatic vascular system is widely developed among vertebrates. Lymphatic vessels provide the interstitial fluid (20% of the body weight) drainage through interstitial prelymphatic channels, capillaries, precollectors and collectors flowing into the venous blood. Endothelial cells of capillaries are overlapped and fixed to interstitial collagen and elastic fibres by anchoring filaments facilitating the fluid transfer. Precollectors and collectors have valves controlling the lymph flux direction. In addition to external mechanisms, the lymphangions of collectors have contracting muscle cells driving the flow. Lymphatic endothelial cells are routinely identified by the expression of podoplanin, LYVE-1 and VEGFR3. In the embryo, prelymphatic endothelial cells emerge from the cardinal veins and migrate into the mesenchyma forming embryonic lymphatic sacs. Prox1, Sox18 and COUP-TFII play a major role in the endothelial speciation, VEGFC as VEGFD combined to VEGFR3 in cell migration and proliferation and FoxC2 in valves development. In cancer or inflammation, various factors secreted by cancer cells and/or inflammatory cells induce a neolymphangiogenesis. Recently it has been shown that cells from the bone marrow could be potential precursors for lymphatic endothelial cells.

Long chain lipid based tamoxifen NLC. Part I: preformulation studies, formulation development and physicochemical characterization

Tamoxifen citrate (Tmx) was formulated in nanostructured lipid carrier system (NLC) using long chain solid lipids (LCSL) and oils (LCO) with the aim to target lymphatic system to improve its bioavailability in plasma and lymphnode (initial sites for metastasis) and reduce its drug associated toxicity. Tamoxifen loaded NLC (Tmx-NLC) was formulated using solvent diffusion technique. Preformulation studies comprised evaluation of drug-excipients compatibility. Solubility of Tmx was screened in LCSL and LCO, surfactants and co-surfactants to identify NLC components. Surfactant co-surfactant combinations were studied for their ability to stabilize the system. Tmx-NLC was physicochemically characterized by TEM, DSC, XRD, and FTIR studies. Drug-excipients chemical compatibility study facilitated anticipation of excipients induced oxidative degradation of Tmx. Suitable storage condition below 30°C could stabilize Tmx. Tmx-NLC with >90% entrapment efficiency and 215.60 ± 7.98 nm particle size were prepared and freeze dried. Freeze dried Tmx-NLC could withstand various gastrointestinal tract (GI) media (pH 1.2, pH 3.5, pH 4.5, pH 6.8, pH 7.4). Dissolution profile of Tmx-NLC in various media showed sustained release pattern irrespective of pH of medium. No significant change in characteristics of Tmx-NLC was observed after 3 months of accelerated stability studies.

Novel anti(lymph)angiogenic treatment strategies for corneal and ocular surface diseases

The cornea is one of the few tissues which actively maintain an avascular state, i.e. the absence of blood and lymphatic vessels (corneal [lymph]angiogenic privilege). Nonetheless do several diseases interfere with this privilege and cause pathologic corneal hem- and lymphangiogenesis. The ingrowths of pathologic blood and lymphatic vessels into the cornea not only reduce transparency and thereby visual acuity up to blindness, but also significantly increases the rate of graft rejections after subsequent corneal transplantation. Therefore great interest exists in new strategies to target pathologic corneal (lymph)angiogenesis to promote graft survival. This review gives an overview on the vascular anatomy of the normal ocular surface, on the molecular mechanisms contributing to the corneal (lymph)angiogenic privilege and on the cellular and molecular mechanisms occurring during pathological neovascularization of the cornea. In addition we summarize the current preclinical and clinical evidence for three novel treatment strategies against ocular surface diseases based on targeting pathologic (lymph)angiogenesis: (a) modulation of the immune responses after (corneal) transplantation by targeting pathologic (lymph)angiogenesis prior to and after transplantation, (b) novel concepts against metastasis and recurrence of ocular surface tumors such as malignant melanoma of the conjunctiva by anti(lymph)angiogenic therapy and (c) new ideas on how to target ocular surface inflammatory diseases such as dry eye by targeting conjunctival and corneal lymphatic vessels. Based on compelling preclinical evidence and early data from clinical trials the novel therapeutic concepts of promoting graft survival, inhibiting tumor metastasis and dampening ocular surface inflammation and dry eye disease by targeting (lymph)angiogenesis are on their way to translation into the clinic.

Lymphatics in lymphangioleiomyomatosis and idiopathic pulmonary fibrosis

The primary function of the lymphatic system is absorbing and transporting macromolecules and immune cells to the general circulation, thereby regulating fluid, nutrient absorption and immune cell trafficking. Lymphangiogenesis plays an important role in tissue inflammation and tumour cell dissemination. Lymphatic involvement is seen in lymphangioleiomyomatosis (LAM) and idiopathic pulmonary fibrosis (IPF). LAM, a disease primarily affecting females, involves the lung (cystic destruction), kidney (angiomyolipoma) and axial lymphatics (adenopathy and lymphangioleiomyoma). LAM occurs sporadically or in association with tuberous sclerosis complex (TSC). Cystic lung destruction results from proliferation of LAM cells, which are abnormal smooth muscle-like cells with mutations in the TSC1 or TSC2 gene. Lymphatic abnormalities arise from infiltration of LAM cells into the lymphatic wall, leading to damage or obstruction of lymphatic vessels. Benign appearing LAM cells possess metastatic properties and are found in the blood and other body fluids. IPF is a progressive lung disease resulting from fibroblast proliferation and collagen deposition. Lymphangiogenesis is associated with pulmonary destruction and disease severity. A macrophage subset isolated from IPF bronchoalveolar lavage fluid (BALF) express lymphatic endothelial cell markers in vitro, in contrast to the same macrophage subset from normal BALF. Herein, we review lymphatic involvement in LAM and IPF.

Lung cancer-initiating cells: a novel target for cancer therapy

Lung cancer is a major public health problem causing more deaths than any other cancer. A better understanding of the biology of this disease and improvements in treatment are greatly needed. Increasing evidence supports the concept that a rare and specialized population of cancer cells, so-called cancer-initiating cells with stem cell-like characteristics, is responsible for tumor growth, maintenance, and recurrence. Cancer-initiating cells also exhibit characteristics that render them resistant to both radiation and chemotherapy, and therefore they are believed to play a role in treatment failure. This has led to the hypothesis that traditional therapies that indiscriminately kill tumor cells will not be as effective as therapies that selectively target cancer-initiating cells. Investigating putative cancer-initiating cells in lung cancer will greatly benefit the understanding of the origins of this disease and may lead to novel approaches to therapy by suggesting markers for use in either further isolating this population for study or for selectively targeting these cells. This review will discuss (1) lung cancer, (2) stem cells, and the role of cancer-initiating cells in tumorigenesis; (3) markers and functional characteristics associated with lung cancer-initiating cells; and (4) the potential to selectively target this subpopulation of tumor cells.

CD133-Positive Hematopoietic Stem Cells: From Biology to Medicine

Lifelong hematopoiesis is sustained by a very small number of hematopoietic stem cells capable of self-renewal and differentiation into multiple hematopoietic lineages. The sialomucin CD34 has been, and is currently, used for the identification and purification of primitive hematopoietic progenitors. Depending on the source of stem cells, CD34 may not be expressed on all progenitor cells. An alternative stem cell marker is prominin-1 (CD133), which is expressed on a subpopulation of CD34(+) cells as well as on CD34(-) progenitor cells derived from various sources including fetal liver and bone marrow, adult bone marrow, cord blood, and mobilized peripheral blood. CD133(+) stem cells can reconstitute myelo- and lymphopoiesis of lethally irradiated mice, and the characterization of the CD133 expression on stem cells provides some insights into the biology of the hierarchy and functional organization of human hematopoiesis. The availability of methods for clinical large-scale isolation of CD133(+) cells facilitates their use in autologous and allogeneic hematopoietic stem cell transplantation and possibly in other fields of regenerative medicine.

Recruitment and retention of human autologous CD34+ CD117+ CD133+ bone marrow stem cells to infarcted myocardium followed by directed vasculogenesis: Novel strategy for cardiac regeneration

Background

Ongoing clinical trials, in regenerative therapy of patients suffering from myocardial infarctions, rely primarily upon administration of bone marrow stem cells to the infarcted zones. Unfortunately, low retention of these cells, to the therapeutic delivery sites, reduces effectiveness of this strategy; thus it has been identified as the most critical problem for advancement of cardiac regenerative medicine.

Specific aims

The specific aim of this work was three-fold: (1) to isolate highly viable populations of human, autologous CD34+, CD117+, and CD133+ bone marrow stem cells; (2) to bioengineer heterospecific, tetravalent antibodies and to use them for recruiting of the stem cells to regenerated zones of infarcted myocardium; (3) to direct vasculogenesis of the retained stem cells with the defined factors.

Patients methods

Cardiac tissue was biopsied from the hearts of the patients, who were receiving orthotopic heart transplants after multiple cardiac infarctions. This tissue was used to engineer fully human in vitro models of infarcted myocardium. Bone marrow was acquired from these patients. The marrow cells were sorted into populations of cells displaying CD34, CD117, and CD133. Heterospecific, tetravalent antibodies were bioengineered to bridge CD34, CD117, CD133 displayed on the stem cells with cardiac myosin of the infarcted myocardium. The sorted stem cells were administered to the infarcted myocardium in the in vitro models.

Results

Administration of the bioengineered, heterospecific antibodies preceding administration of the stem cells greatly improved the stem cells’ recruitment and retention to the infarcted myocardium. Treatment of the retained stem cells with vascular endothelial growth factor and angiopoietin efficiently directed their differentiation into endothelial cells, which expressed vascular endothelial cadherin, platelet/endothelial cell adhesion molecule, claudin, and occludin, while forming tight and adherens junctions.

Conclusions

This novel strategy improved retention of the patients’ autologous bone marrow cells to the infarcted myocardium followed by directed vasculogenesis. Therefore, it is worth pursuing it in support of the ongoing clinical trials of cardiac regenerative therapy.

Pinocembrin, a major flavonoid in propolis, improves the biological functions of EPCs derived from rat bone marrow through the PI3K-eNOS-NO signaling pathway

The number and quality of endothelial progenitor cells (EPCs) are damaged to varying degrees in patients at risk for developing atherosclerosis. The improvement of the quantity and functions of EPCs can enhance repair of injured endothelial monolayer resulting in inhibiting atherosclerosis. The purpose of this study was to investigate the effect of pinocembrin (PIN), a major flavonoid in propolis on the differentiation and biological functions of EPCs and the potential mechanisms of these effects. Flow cytometry analysis revealed that PIN treatment increased the number of CD34(+), CD133(+), FLK-1(+), CD133(+)/FLK-1(+) and CD34(+)/FLK-1(+) mononuclear cells (MNCs) in the peripheral blood of apoE(-/-) mice compared to untreated control mice. In vitro PIN treatment significantly increased the number of CD34(+), CD133(+), FLK-1(+) and CD133(+)/FLK-1(+) MNCs derived from SD bone marrow compared to untreated controls by 42.1, 84.6, 165.9 and 23.1 %, respectively. Additionally, PIN can improve biological functions of EPCs, such as proliferation, migration, adhesion, and in vitro tube formation and NO release. All of these improvements were inhibited by LY294002, while L-NAME only inhibited the PIN-induced increase in EPC proliferation and adhesion. We conclude that PIN can both promote the differentiation of EPCs in vitro and ex vivo and improve the biological functions of EPCs. The PI3K-eNOS-NO signaling pathway may be involved in the PIN-induced increase in the proliferation and adhesion of EPCs.

Human skin cancer stem cells: a tale of mice and men

Carcinomas, cancers of epithelial tissues, are the commonest malignancies and cause the greatest cancer mortality worldwide. Among these, the incidence of keratinocyte-derived non-melanoma skin cancers (NMSC), by far the greatest, is increasing rapidly. Yet despite access to tumor tissue, acceptance of human NMSC as a model carcinoma has been hindered by the lack of a reliable xenograft model. Instead, we have relied on the murine two-step carcinogenesis protocol as a reproducible squamous cell carcinoma (SCC) model, but this differs from their human counterpart in cause, site, genetic basis and biological behaviour. By xeno-engraftment of primary human SCC, we were recently successful in demonstrating the presence of primary human SCC cancer stem cells or tumor-initiating cells. These findings once more align the study human SCC as the archetypal carcinoma model. In this review, we describe the evidence for the existence of tumor-initiating cells, with emphasis on skin cancer, limiting our discussions to primary human cancer studies where possible.

Role of bone marrow-derived lymphatic endothelial progenitor cells for lymphatic neovascularization

The lymphatic vasculature plays a pivotal role in maintaining tissue fluid homeostasis, immune surveillance, and lipid uptake in the gastrointestinal organs. Therefore, impaired function of the lymphatic vessels caused by genetic defects, infection, trauma, or surgery leads to the abnormal accrual of lymph fluid in the tissue and culminates in the swelling of affected tissues, known as lymphedema. Lymphedema causes impaired wound healing, compromised immune defense, and, in rare case, lymphangiosarcoma. Although millions of people suffer from lymphedema worldwide, no effective therapy is currently available. In addition, recent advances in cancer biology have disclosed an indispensable function of the lymphatic vessel in tumor growth and metastasis. Therefore, understanding the detailed mechanisms governing lymphatic vessel formation and function in pathophysiologic conditions is essential to prevent or treat these diseases. We review the developmental processes of the lymphatic vessels and postnatal lymphatic neovascularization, focusing on the role of recently identified bone marrow-derived podoplanin-expressing (podoplanin(+)) cells as lymphatic endothelial progenitor cells.

Generation of functional blood vessels from a single c-kit+ adult vascular endothelial stem cell

Adult vascular endothelial stem cells are shown to reside in the blood vessel wall endothelium. When isolated, these cells are capable of clonal expansion and generate functional blood vessels in vivo.

In adults, the growth of blood vessels, a process known as angiogenesis, is essential for organ growth and repair. In many disorders including cancer, angiogenesis becomes excessive. The cellular origin of new vascular endothelial cells (ECs) during blood vessel growth in angiogenic situations has remained unknown. Here, we provide evidence for adult vascular endothelial stem cells (VESCs) that reside in the blood vessel wall endothelium. VESCs constitute a small subpopulation within CD117+ (c-kit+) ECs capable of undergoing clonal expansion while other ECs have a very limited proliferative capacity. Isolated VESCs can produce tens of millions of endothelial daughter cells in vitro. A single transplanted c-kit-expressing VESC by the phenotype lin−CD31+CD105+Sca1+CD117+ can generate in vivo functional blood vessels that connect to host circulation. VESCs also have long-term self-renewal capacity, a defining functional property of adult stem cells. To provide functional verification on the role of c-kit in VESCs, we show that a genetic deficit in endothelial c-kit expression markedly decreases total colony-forming VESCs. In vivo, c-kit expression deficit resulted in impaired EC proliferation and angiogenesis and retardation of tumor growth. Isolated VESCs could be used in cell-based therapies for cardiovascular repair to restore tissue vascularization after ischemic events. VESCs also provide a novel cellular target to block pathological angiogenesis and cancer growth.

Angiogenesis—the growth of blood vessels—is essential for organ growth and repair, but also occurs during tumorigenesis and in certain inflammatory disorders. All blood vessels are lined by endothelial cells (ECs)—thin, flattened cells that form a continuous monolayer throughout the entire circulatory system. The cellular origin of new vascular ECs during blood vessel growth in angiogenic situations in adults is a matter of debate. New ECs could develop, in principle, from as yet undiscovered stem cells, as is well documented for the differentiated cells of skin or epithelia, or by the duplication of existing differentiated ECs. Here, we provide evidence for the existence of vascular endothelial stem cells (VESCs) that reside in the adult blood vessel wall endothelium. VESCs constitute a small subpopulation of ECs capable of clonal expansion, while other ECs have a very limited proliferative capacity. When isolated, these VESCs can produce tens of millions of endothelial daughter cells, and a single transplanted VESC can generate in vivo functional blood vessels that connect to host blood circulation. Isolated VESCs could be used in cell-based therapies for cardiovascular repair to restore tissue vascularization following ischemia and could also be pursued as a novel cellular target of inhibition to block pathological angiogenesis, for example during tumor growth.

Endothelial precursor cells promote angiogenesis in hepatocellular carcinoma

AIM: To investigate the role of bone marrow-derived endothelial progenitor cells (EPCs) in the angiogenesis of hepatocellular carcinoma (HCC).

METHODS: The bone marrow of HCC mice was reconstructed by transplanting green fluorescent protein (GFP) + bone marrow cells. The concentration of circulating EPCs was determined by colony-forming assays and fluorescence-activated cell sorting. Serum and tissue levels of vascular endothelial growth factor (VEGF) and colony-stimulating factor (CSF) were quantified by enzyme-linked immunosorbent assay. The distribution of EPCs in tumor and tumor-free tissues was detected by immunohistochemistry and real-time polymerase chain reaction. The incorporation of EPCs into hepatic vessels was examined by immunofluorescence and immunohistochemistry. The proportion of EPCs in vessels was then calculated.

RESULTS: The HCC model was successful established. The flow cytometry analysis showed the mean percentage of CD133CD34 and CD133VEGFR2 double positive cells in HCC mice was 0.45% ± 0.16% and 0.20% ± 0.09% respectively. These values are much higher than in the sham-operation group (0.11% ± 0.13%, 0.05% ± 0.11%, n = 9) at 14 d after modeling. At 21 d, the mean percentage of circulating CD133CD34 and CD133VEGFR2 cells is 0.23% ± 0.19%, 0.25% ± 0.15% in HCC model vs 0.05% ± 0.04%, 0.12% ± 0.11% in control. Compared to the transient increase observed in controls, the higher level of circulating EPCs were induced by HCC. In addition, the level of serum VEGF and CSF increased gradually in HCC, reaching its peak 14 d after modeling, then slowly decreased. Consecutive sections stained for the CD133 and CD34 antigens showed that the CD133+ and CD34+ VEGFR2 cells were mostly recruited to HCC tissue and concentrated in tumor microvessels. Under fluorescence microscopy, the bone-marrow (BM)-derived cells labeled with GFP were concentrated in the same area. The relative levels of CD133 and CD34 gene expression were elevated in tumors, around 5.0 and 3.8 times that of the tumor free area. In frozen liver sections from HCC mice, cells co-expressing CD133 and VEGFR2 were identified by immunohistochemical staining using anti-CD133 and VEGFR2 antibodies. In tumor tissue, the double-positive cells were incorporated into vessel walls. In immunofluorescent staining. These CD31 and GFP double positive cells are direct evidence that tumor vascular endothelial cells (VECs) come partly from BM-derived EPCs. The proportion of GFP CD31 double positive VECs (out of all VECs) on day 21 was around 35.3% ± 21.2%. This is much higher than the value recorded on day 7 group (17.1% ± 8.9%). The expression of intercellular adhesion molecule 1, vascular adhesion molecule 1, and VEGF was higher in tumor areas than in tumor-free tissues.

CONCLUSION: Mobilized EPCs were found to participate in tumor vasculogenesis of HCC. Inhibiting EPC mobilization or recruitment to tumor tissue may be an efficient strategy for treating HCC.

Lymphangiogenesis and cancer

Historically, lymphatic vessels were considered passive participants in tumor metastasis by simply providing channels for tumor cells to transit to draining lymph nodes. The discovery of several key lymphatic-specific molecular markers and an increased availability of in vitro and in vivo experimental systems to study lymphatic biology have however highlighted a much more complex, active role for the lymphatic vasculature in metastatic tumor spread. This review will briefly describe the lymphatic system and lymphangiogenesis and then focus on the role of the lymphatic system in cancer metastasis. The progression of our understanding from the lymphatic system as a somewhat passive conduit for metastasis to an active participant in metastatic tumor dissemination, regulated by a complex array of lymphangiogenic factors, chemokines, and immune cell subsets, will be described.

VEGFR-3 is expressed on megakaryocyte precursors in the murine bone marrow and plays a regulatory role in megakaryopoiesis

VEGFR-3 is a transmembrane receptor tyrosine kinase that is activated by its ligands VEGF-C and VEGF-D. Although VEGFR-3 has been linked primarily to the regulation of lymphangiogenesis, in the present study, we demonstrate a role for VEGFR-3 in megakaryopoiesis. Using a human erythroleukemia cell line and primary murine BM cells, we show that VEGFR-3 is expressed on megakaryocytic progenitor cells through to the promegakaryoblast stage. Functionally, specific activation of VEGFR-3 impaired the transition to polyploidy of CD41+ cells in primary BM cultures. Blockade of VEGFR-3 promoted endoreplication consistently. In vivo, long-term activation or blockade of VEGFR-3 did not affect steady-state murine megakaryopoiesis or platelet counts significantly. However, activation of VEGFR-3 in sublethally irradiated mice resulted in significantly elevated numbers of CD41+ cells in the BM and a significant increase in diploid CD41+ cells, whereas the number of polyploid CD41+ cells was reduced significantly. Moreover, activation of VEGFR-3 increased platelet counts in thrombopoietin-treated mice significantly and modulated 5-fluorouracil-induced thrombocytosis strongly, suggesting a regulatory role for VEGFR-3 in megakaryopoiesis.

Glioma revisited: from neurogenesis and cancer stem cells to the epigenetic regulation of the niche

Gliomas are the most incident brain tumor in adults. This malignancy has very low survival rates, even when combining radio- and chemotherapy. Among the gliomas, glioblastoma multiforme (GBM) is the most common and aggressive type, and patients frequently relapse or become refractory to conventional therapies. The fact that such an aggressive tumor can arise in such a carefully orchestrated organ, where cellular proliferation is barely needed to maintain its function, is a question that has intrigued scientists until very recently, when the discovery of the existence of proliferative cells in the brain overcame such challenges. Even so, the precise origin of gliomas still remains elusive. Thanks to new advents in molecular biology, researchers have been able to depict the first steps of glioma formation and to accumulate knowledge about how neural stem cells and its progenitors become gliomas. Indeed, GBM are composed of a very heterogeneous population of cells, which exhibit a plethora of tumorigenic properties, supporting the presence of cancer stem cells (CSCs) in these tumors. This paper provides a comprehensive analysis of how gliomas initiate and progress, taking into account the role of epigenetic modulation in the crosstalk of cancer cells with their environment.

Macrophage-mediated lymphangiogenesis: the emerging role of macrophages as lymphatic endothelial progenitors

It is widely accepted that macrophages and other inflammatory cells support tumor progression and metastasis. During early stages of neoplastic development, tumor-infiltrating macrophages (TAMs) mount an immune response against transformed cells. Frequently, however, cancer cells escape the immune surveillance, an event that is accompanied by macrophage transition from an anti-tumor to a pro-tumorigenic type. The latter is characterized by high expression of factors that activate endothelial cells, suppress immune response, degrade extracellular matrix, and promote tumor growth. Cumulatively, these products of TAMs promote tumor expansion and growth of both blood and lymphatic vessels that facilitate metastatic spread. Breast cancers and other epithelial malignancies induce the formation of new lymphatic vessels (i.e., lymphangiogenesis) that leads to lymphatic and subsequently, to distant metastasis. Both experimental and clinical studies have shown that TAMs significantly promote tumor lymphangiogenesis through paracrine and cell autonomous modes. The paracrine effect consists of the expression of a variety of pro-lymphangiogenic factors that activate the preexisting lymphatic vessels. The evidence for cell-autonomous contribution is based on the observed tumor mobilization of macrophage-derived lymphatic endothelial cell progenitors (M-LECP) that integrate into lymphatic vessels prior to sprouting. This review will summarize the current knowledge of macrophage-dependent growth of new lymphatic vessels with specific emphasis on an emerging role of macrophages as lymphatic endothelial cell progenitors (M-LECP).

Glioblastoma: therapeutic challenges, what lies ahead

Glioblastoma (GBM) is one of the most aggressive human cancers. Despite current advances in multimodality therapies, such as surgery, radiotherapy and chemotherapy, the outcome for patients with high grade glioma remains fatal. The knowledge of how glioma cells develop and depend on the tumor environment might open opportunities for new therapies. There is now a growing awareness that the main limitations in understanding and successfully treating GBM might be bypassed by the identification of a distinct cell type that has defining properties of somatic stem cells, as well as cancer-initiating capacity - brain tumor stem cells, which could represent a therapeutic target. In addition, experimental studies have demonstrated that the combination of antiangiogenic therapy, based on the disruption of tumor blood vessels, with conventional chemotherapy generates encouraging results. Emerging reports have also shown that microglial cells can be used as therapeutic vectors to transport genes and/or substances to the tumor site, which opens up new perspectives for the development of GBM therapies targeting microglial cells. Finally, recent studies have shown that natural toxins can be conjugated to drugs that bind to overexpressed receptors in cancer cells, generating targeted-toxins to selectively kill cancer cells. These targeted-toxins are highly effective against radiation- and chemotherapy-resistant cancer cells, making them good candidates for clinical trials in GBM patients. In this review, we discuss recent studies that reveal new possibilities of GBM treatment taking into account cancer stem cells, angiogenesis, microglial cells and drug delivery in the development of new targeted-therapies.

In vitro differentiation of bone marrow derived porcine mesenchymal stem cells to endothelial cells

Mesenchymal stem cells (MSCs) hold potential for the regeneration of damaged tissues in cardiovascular diseases. In this study, we investigated the potential of porcine MSCs to differentiate into endothelial cells (ECs) in vitro. The cultured bone marrow-derived cells were CD11b⁻CD34⁻CD44⁺CD45⁻CD90⁺ and showed mesodermal lineage differentiation, which is characteristic of MSCs. The MSCs were induced to differentiate into ECs using endothelial growth medium (EGM), with and without high concentrations of VEGF (EGM + VEGF; 50 ng/ml). Endothelial basal medium (EBM) without growth factors served as the control. The EC differentiation was assessed by the presence of vWF, ability to take up acetylated LDL, in vitro angiogenesis assay, flow cytometry and qPCR of EC markers vWF, VE-cadherin, PECAM-1, VEGF-R1 and VEGF-R2 after 10 days of stimulation. Cells cultured in EGM + VEGF medium demonstrated higher amounts of DiI-AcLDL-positive cells and enhanced the presence of vWF (90%), VE-Cadherin- (60%) and PECAM-1 (48%)-positive cells, than in EBM. These cells showed profuse sprouting of capillary tubes and closed polygon formation in the angiogenesis assay. There was 1.5-2-fold increase in the mRNA expression of endothelial markers in the cells stimulated with EGM + VEGF medium when compared to control. The results demonstrate the ability of porcine MSCs to differentiate into ECs under in vitro inducing conditions. The differentiated cells would provide new options for re-endothelialization following interventional procedures and tissue engineering.

Head and neck lymphatic tumors and bony abnormalities: a clinical and molecular review

Lymphatic malformations and lymphatic-derived tumors commonly involve the head and neck, where they may be associated with bony abnormalities and other systemic symptoms. The reasons for the association between these disorders and local skeletal changes are largely unknown, but such changes may cause significant disease-related morbidity. Ongoing work in molecular and developmental biology is beginning to uncover potential reasons for the bony abnormalities found in head and neck lymphatic disease; this article summarizes current knowledge on possible mechanisms underlying this association.