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

Tumor microenvironment restricts IL-10 induced multipotent progenitors to myeloid-lymphatic phenotype

Lymphangiogenesis is induced by local pro-lymphatic growth factors and bone marrow (BM)-derived myeloid-lymphatic endothelial cell progenitors (M-LECP). We previously showed that M-LECP play a significant role in lymphangiogenesis and lymph node metastasis in clinical breast cancer (BC) and experimental BC models. We also showed that differentiation of mouse and human M-LECP can be induced through sequential activation of colony stimulating factor-1 (CSF-1) and Toll-like receptor-4 (TLR4) pathways. This treatment activates the autocrine interleukin-10 (IL-10) pathway that, in turn, induces myeloid immunosuppressive M2 phenotype along with lymphatic-specific proteins. Because IL-10 is implicated in differentiation of numerous lineages, we sought to determine whether this pathway specifically promotes the lymphatic phenotype or multipotent progenitors that can give rise to M-LECP among other lineages. Analyses of BM cells activated either by CSF-1/TLR4 ligands in vitro or orthotopic breast tumors in vivo showed expansion of stem/progenitor population and coincident upregulation of markers for at least four lineages including M2-macrophage, lymphatic endothelial, erythroid, and T-cells. Induction of cell plasticity and multipotency was IL-10 dependent as indicated by significant reduction of stem cell markers and those for multiple lineages in differentiated cells treated with anti-IL-10 receptor (IL-10R) antibody or derived from IL-10R knockout mice. However, multipotent CD11b+/Lyve-1+/Ter-119+/CD3e+ progenitors detected in BM appeared to split into a predominant myeloid-lymphatic fraction and minor subsets expressing erythroid and T-cell markers upon establishing tumor residence. Each sub-population was detected at a distinct intratumoral site. This study provides direct evidence for differences in maturation status between the BM progenitors and those reaching tumor destination. The study results suggest preferential tumor bias towards expansion of myeloid-lymphatic cells while underscoring the role of IL-10 in early BM production of multipotent progenitors that give rise to both hematopoietic and endothelial lineages.

Lymph node metastases in breast cancer: Mechanisms and molecular imaging

Breast cancer is the most common malignant disease of women in the world. Breast cancer often metastasizes to axillary lymph nodes. Accurate assessment of the status of axillary lymph nodes is crucial to the staging and treatment of breast cancer. None of the methods used clinically for preoperative noninvasive examination of axillary lymph nodes can accurately identify cancer cells from a molecular level. In recent years, with the in-depth study of lymph node metastases, the mechanisms and molecular imaging of lymph node metastases in breast cancer have been reported. In this review, we highlight the new progress in the study of the main mechanisms of lymph node metastases in breast cancer. In addition, we analyze the advantages and disadvantages of traditional preoperative axillary lymph node imaging methods for breast cancer, and list molecular imaging methods that can accurately identify breast cancer cells in lymph nodes.

Lymphangiogenesis, a potential treatment target for myocardial injury

The lymphatic vascular system is crucial for the regulation of tissue fluid homeostasis, lipid metabolism, and immune function. Cardiac injury quickly leads to myocardial edema, cardiac lymphatic dysfunction, which ultimately results in myocardial fluid imbalance and cardiac dysfunction. Therefore, lymphangiogenesis-targeted therapy may improve the recovery of myocardial function post cardiac ischemia as observed in myocardial infarction (MI). Indeed, a promising strategy for the clinical treatment of MI relies on vascular endothelial growth factor-C (VEGF-C)-targeted therapy, which promotes lymphangiogenesis. However, much effort is needed to identify the mechanisms of lymphatic transport in response to heart disease. This article reviews regulatory factors of lymphangiogenesis, and discusses the effects of lymphangiogenesis on cardiac function after cardiac injury and its regulatory mechanisms. The involvement of stem cells on lymphangiogenesis was also discussed as stem cells could differentiate into lymphatic endothelial cells (LECs) and stimulate phenotype of LECs.

KSHV infection of endothelial precursor cells with lymphatic characteristics as a novel model for translational Kaposi's sarcoma studies

Kaposi's sarcoma herpesvirus (KSHV) is the etiologic agent of Kaposi's sarcoma (KS), a hyperplasia consisting of enlarged malformed vasculature and spindle-shaped cells, the main proliferative component of KS. While spindle cells express markers of lymphatic and blood endothelium, the origin of spindle cells is unknown. Endothelial precursor cells have been proposed as the source of spindle cells. We previously identified two types of circulating endothelial colony forming cells (ECFCs), ones that expressed markers of blood endothelium and ones that expressed markers of lymphatic endothelium. Here we examined both blood and lymphatic ECFCs infected with KSHV. Lymphatic ECFCs are significantly more susceptible to KSHV infection than the blood ECFCs and maintain the viral episomes during passage in culture while the blood ECFCs lose the viral episome. Only the KSHV-infected lymphatic ECFCs (K-ECFCLY) grew to small multicellular colonies in soft agar whereas the infected blood ECFCs and all uninfected ECFCs failed to proliferate. The K-ECFCLYs express high levels of SOX18, which supported the maintenance of high copy number of KSHV genomes. When implanted subcutaneously into NSG mice, the K-ECFCLYs persisted in vivo and recapitulated the phenotype of KS tumor cells with high number of viral genome copies and spindling morphology. These spindle cell hallmarks were significantly reduced when mice were treated with SOX18 inhibitor, SM4. These data suggest that KSHV-infected lymphatic ECFCs can be utilized as a KSHV infection model for in vivo translational studies to test novel inhibitors representing potential treatment modalities for KS.

CD34 positive cells as endothelial progenitor cells in biology and medicine

CD34 is a cell surface antigen expressed in numerous stem/progenitor cells including hematopoietic stem cells (HSCs) and endothelial progenitor cells (EPCs), which are known to be rich sources of EPCs. Therefore, regenerative therapy using CD34⁺ cells has attracted interest for application in patients with various vascular, ischemic, and inflammatory diseases. CD34⁺ cells have recently been reported to improve therapeutic angiogenesis in a variety of diseases. Mechanistically, CD34⁺ cells are involved in both direct incorporation into the expanding vasculature and paracrine activity through angiogenesis, anti-inflammatory, immunomodulatory, and anti-apoptosis/fibrosis roles, which support the developing microvasculature. Preclinical, pilot, and clinical trials have well documented a track record of safety, practicality, and validity of CD34⁺ cell therapy in various diseases. However, the clinical application of CD34⁺ cell therapy has triggered scientific debates and controversies in last decade. This review covers all preexisting scientific literature and prepares an overview of the comprehensive biology of CD34⁺ cells as well as the preclinical/clinical details of CD34⁺ cell therapy for regenerative medicine.

The Impact of Stem/Progenitor Cells on Lymphangiogenesis in Vascular Disease

Lymphatic vessels, as the main tube network of fluid drainage and leukocyte transfer, are responsible for the maintenance of homeostasis and pathological repairment. Recently, by using genetic lineage tracing and single-cell RNA sequencing techniques, significant cognitive progress has been made about the impact of stem/progenitor cells during lymphangiogenesis. In the embryonic stage, the lymphatic network is primarily formed through self-proliferation and polarized-sprouting from the lymph sacs. However, the assembly of lymphatic stem/progenitor cells also guarantees the sustained growth of lymphvasculogenesis to obtain the entire function. In addition, there are abundant sources of stem/progenitor cells in postnatal tissues, including circulating progenitors, mesenchymal stem cells, and adipose tissue stem cells, which can directly differentiate into lymphatic endothelial cells and participate in lymphangiogenesis. Specifically, recent reports indicated a novel function of lymphangiogenesis in transplant arteriosclerosis and atherosclerosis. In the present review, we summarized the latest evidence about the diversity and incorporation of stem/progenitor cells in lymphatic vasculature during both the embryonic and postnatal stages, with emphasis on the impact of lymphangiogenesis in the development of vascular diseases to provide a rational guidance for future research.

The Role of Podoplanin in the Immune System and Inflammation

Podoplanin is a small cell-surface mucin-like glycoprotein that participates in multiple physiological and pathological processes. Podoplanin exerts an important function in the immune response and is upregulated in fibroblasts, macrophages, T helper cells, and epithelial cells during inflammation. Herein, we summarize the latest knowledge on the functional expression of podoplanin in the immune system and review the contribution of podoplanin to several inflammatory diseases. Furthermore, we discuss podoplanin as a novel therapeutic target for various inflammatory diseases.

Endothelial Progenitor Cells in Coronary Artery Disease: From Bench to Bedside

Endothelial progenitor cells (EPCs) are a heterogeneous group of cells present in peripheral blood at various stages of endothelial differentiation. EPCs have been extensively investigated in patients with coronary artery disease (CAD), with controversial findings both on their role in atherosclerosis progression and in the process of neointimal growth after a percutaneous coronary intervention (PCI). Despite nearly 2 decades of experimental and clinical investigations, however, the significance of EPCs in clinical practice remains unclear and poorly understood. This review provides an update on the role of EPCs in the most common clinical scenarios that are experienced by cardiologists managing patients with CAD. We here summarize the main findings on the association of EPCs with cardiovascular risk factors, coronary atherosclerosis, and myocardial ischemia. We then discuss the potential effects of EPCs in post-PCI in-stent restenosis, as well as most recent findings with EPC-coated stents. Based on the mounting evidence of the relationship between levels of EPCs and several different adverse cardiovascular events, EPCs are emerging as novel predictive biomarkers of long-term outcomes in patients with CAD.

Subclinical Thyrotoxicosis and Cardiovascular Risk: Assessment of Circulating Endothelial Progenitor Cells, Proangiogenic Cells, and Endothelial Function

BACKGROUND

Subclinical thyrotoxicosis (SCT) is defined by low or undetectable thyroid-stimulating hormones and normal thyroid hormones. The treatment of SCT is uncertain despite being associated with increased cardiovascular risk (CVR) and mortality. Circulating endothelial progenitor cells (cEPCs) and circulating angiogenic cells (CACs) have been found to be reduced in conditions with CVR. We aimed to evaluate whether endothelial function and cEPC and CAC counts were reduced in SCT and to study the in vitro effect of triiodothyronine (T3) on proangiogenic cell (PAC) function from young healthy controls.

METHODS

cEPCs (quantified by flow cytometry, 20 SCT/20 controls), CACs following in vitro cultures (15 SCT/14 controls), paracrine function of CACs, endothelial function by flow-mediated dilation (FMD, 9 SCT/9 controls), and the effect of T3 on apoptosis and endothelial nitric oxide synthase (eNOS) expression in PACs were studied.

RESULTS

p < 0.001, CD133⁺/VEGFR-2⁺ 0.4 (0.0-0.7) vs. 0.6 (0.0-4.6), p = 0.009, CD34⁺/VEGFR-2⁺ 0.3 (0.0-1.0) vs. 0.7 (0.1-4.9), p = 0.002; while CAC count was similar. SCT predicted a lower cEPC count after adjustment for conventional CVR factors. FMD was lower in SCT subjects versus controls (% mean ± SD, 2.7 ± 2.3 vs. 6.1 ± 2.3, p = 0.005). In vitro studies showed T3 increased early apoptosis and reduced eNOS expression in PACs.

CONCLUSIONS

In conclusion, SCT is associated with reduced cEPC count and FMD, confirming increased CVR in SCT. Future outcome trials are required to examine if treatment of this subclinical hyperactive state improves cardiovascular outcome.

CLINICAL TRIAL REGISTRATION

http://www.controlled-trials.com/isrctn/, identifier ISRCTN70334066.

Lymphatic Endothelial Markers and Tumor Lymphangiogenesis Assessment in Human Breast Cancer

Metastasis via lymphatic vessels or blood vessels is the leading cause of death for breast cancer, and lymphangiogenesis and angiogenesis are critical prerequisites for the tumor invasion–metastasis cascade. The research progress for tumor lymphangiogenesis has tended to lag behind that for angiogenesis due to the lack of specific markers. With the discovery of lymphatic endothelial cell (LEC) markers, growing evidence demonstrates that the LEC plays an active role in lymphatic formation and remodeling, tumor cell growth, invasion and intravasation, tumor–microenvironment remodeling, and antitumor immunity. However, some studies have drawn controversial conclusions due to the variation in the LEC markers and lymphangiogenesis assessments used. In this study, we review recent findings on tumor lymphangiogenesis, the most commonly used LEC markers, and parameters for lymphangiogenesis assessments, such as the lymphatic vessel density and lymphatic vessel invasion in human breast cancer. An in-depth understanding of tumor lymphangiogenesis and LEC markers can help to illustrate the mechanisms and distinct roles of lymphangiogenesis in breast cancer progression, which will help in exploring novel potential predictive biomarkers and therapeutic targets for breast cancer.

Isolating and characterizing lymphatic endothelial progenitor cells for potential therapeutic lymphangiogenic applications

Lymphatic dysfunction is associated with the progression of several vascular disorders, though currently, there are limited strategies to promote new lymphatic vasculature (i.e., lymphangiogenesis) to restore lost lymphatic function. One promising approach to stimulate lymphangiogenesis involves delivering endothelial progenitor cells (EPCs), which are naturally involved in de novo blood vessel formation and have recently been identified to include a lymphatic subpopulation. However, the contribution of lymphatic EPCs in lymphangiogenesis is not clear and challenges with maintaining the activity of transplanted EPCs remain. Thus, the objective of this study was to isolate lymphatic EPCs from human umbilical cord blood and characterize their role in the initial stages of blood or lymphatic vasculature formation. Furthermore, this study also tested the applicability of alginate hydrogels to deliver lymphatic EPCs for a possible therapeutic application. We postulated and confirmed that blood and lymphatic EPC colonies could be isolated from human umbilical cord blood. Additionally, EPC populations responded to either angiogenic or lymphangiogenic growth factors and could stimulate their respective mature endothelial cells in vasculature models in vitro. Finally, lymphatic EPCs maintained their ability to promote lymphatic sprouts after prolonged interactions with the alginate hydrogel microenvironment. These results suggest EPCs have both a blood and a lymphatic population that have specific roles in promoting revascularization and highlight the potential of alginate hydrogels for the delivery of lymphatic EPCs. STATEMENT OF SIGNIFICANCE: Despite the potential therapeutic benefit of promoting lymphatic vasculature, lymphangiogenesis remains understudied. One appealing strategy for promoting lymphangiogenesis involves delivering lymphatic endothelial progenitor cells (EPCs), which are a subpopulation of EPCs involved in de novo vessel formation. Here, we investigate the role of isolated blood and lymphatic EPC subpopulations in promoting the early stages of vascularization and the utility of alginate hydrogels to deliver lymphatic EPCs. We determined that EPCs had two populations that expressed either blood or lymphatic markers, could stimulate their respective mature vasculature in tissue constructs and that alginate hydrogels maintained the therapeutic potential of lymphatic EPCs. We anticipate this work could support promising biomaterial applications of EPCs to promote revascularization, which could have many therapeutic applications.

Role of Podoplanin-Positive Cells in Cardiac Fibrosis and Angiogenesis After Ischemia

New insights into the cellular and extra-cellular composition of scar tissue after myocardial infarction (MI) have been identified. Recently, a heterogeneous podoplanin-expressing cell population has been associated with fibrogenic and inflammatory responses and lymphatic vessel growth during scar formation. Podoplanin is a mucin-like transmembrane glycoprotein that plays an important role in heart development, cell motility, tumorigenesis, and metastasis. In the adult mouse heart, podoplanin is expressed only by cardiac lymphatic endothelial cells; after MI, it is acquired with an unexpected heterogeneity by PDGFRα-, PDGFRβ-, and CD34-positive cells. Podoplanin may therefore represent a sign of activation of a cohort of progenitor cells during different phases of post-ischemic myocardial wound repair. Podoplanin binds to C-type lectin-like receptor 2 (CLEC-2) which is exclusively expressed by platelets and a variety of immune cells. CLEC-2 is upregulated in CD11b^high cells, including monocytes and macrophages, following inflammatory stimuli. We recently published that inhibition of the interaction between podoplanin-expressing cells and podoplanin-binding cells using podoplanin-neutralizing antibodies reduces but does not fully suppress inflammation post-MI while improving heart function and scar composition after ischemic injury. These data support an emerging and alternative mechanism of interactome in the heart that, when neutralized, leads to altered inflammatory response and preservation of cardiac function and structure. The overarching objective of this review is to assimilate and discuss the available evidence on the functional role of podoplanin-positive cells on cardiac fibrosis and remodeling. A detailed characterization of cell-to-cell interactions and paracrine signals between podoplanin-expressing cells and the other type of cells that compose the heart tissue is needed to open a new line of investigation extending beyond the known function of these cells. This review attempts to discuss the role and biology of podoplanin-positive cells in the context of cardiac injury, repair, and remodeling.

Co-culture of ASCs/EPCs and dermal extracellular matrix hydrogel enhances the repair of full-thickness skin wound by promoting angiogenesis

Background

The repair of large-scale full-thickness skin defects represents a challenging obstacle in skin tissue engineering. To address the most important problem in skin defect repair, namely insufficient blood supply, this study aimed to find a method that could promote the formation of vascularized skin tissue.

Method

The phenotypes of ASCs and EPCs were identified respectively, and ASCs/EPCs were co-cultured in vitro to detect the expression of dermal and angiogenic genes. Furthermore, the co-culture system combined with dermal extracellular matrix hydrogel was used to repair the full-scale skin defects in rats.

Result

The co-culture of ASCs/EPCs could increase skin- and angiogenesis-related gene expression in vitro. The results of in vivo animal experiments demonstrated that the ASCs/EPCs group could significantly accelerate the repair of skin defects by promoting the regeneration of vascularized skin.

Conclusion

It is feasible to replace traditional single-seed cells with the ASC/EPC co-culture system for vascularized skin regeneration. This system could ultimately enable clinicians to better repair the full-thickness skin defects and avoid donor site morbidity.

The co-culture of ASCs and EPCs promotes vascularized bone regeneration in critical-sized bone defects of cranial bone in rats

Background

The repair of critical-sized bone defect represents a challenging problem in bone tissue engineering. To address the most important problem in bone defect repair, namely insufficient blood supply, this study aimed to find a method that can promote the formation of vascularized bone tissue.

Method

The phenotypes of ASCs and EPCs were identified respectively, and ASCs/EPCs were co-cultured in vitro to detect the expression of osteogenic and angiogenic genes. Furthermore, the co-culture system combined with scaffold material was used to repair the critical-sized bone defects of the cranial bone in rats.

Results

The co-culture of ASCs/EPCs could increase osteogenesis and angiogenesis-related gene expression in vitro. The results of in vivo animal experiments demonstrated that the ASC/EPC group could promote bone regeneration and vascularization in the meantime and then significantly accelerate the repair of critical-sized bone defects.

Conclusion

It is feasible to replace traditional single seed cells with ASC/EPC co-culture system for vascularized bone regeneration. This system could ultimately enable clinicians to better repair the defect of craniofacial bone and avoid donor site morbidity.

Cell-Based Therapeutic Approaches for Cystic Fibrosis

Cystic Fibrosis (CF) is a chronic autosomal recessive disease caused by defects in the cystic fibrosis transmembrane conductance regulator gene (CFTR). Cystic Fibrosis affects multiple organs but progressive remodeling of the airways, mucus accumulation, and chronic inflammation in the lung, result in lung disease as the major cause of morbidity and mortality. While advances in management of CF symptoms have increased the life expectancy of this devastating disease, and there is tremendous excitement about the potential of new agents targeting the CFTR molecule itself, there is still no curative treatment. With the recent advances in the identification of endogenous airway progenitor cells and in directed differentiation of pluripotent cell sources, cell-based therapeutic approaches for CF have become a plausible treatment method with the potential to ultimately cure the disease. In this review, we highlight the current state of cell therapy in the CF field focusing on the relevant autologous and allogeneic cell populations under investigation and the challenges associated with their use. In addition, we present advances in induced pluripotent stem (iPS) cell approaches and emerging new genetic engineering methods, which have the capacity to overcome the current limitations hindering cell therapy approaches.

Anti-integrin αv therapy improves cardiac fibrosis after myocardial infarction by blunting cardiac PW1+ stromal cells

There is currently no therapy to limit the development of cardiac fibrosis and consequent heart failure. We have recently shown that cardiac fibrosis post-myocardial infarction (MI) can be regulated by resident cardiac cells with a fibrogenic signature and identified by the expression of PW1 (Peg3). Here we identify αV-integrin (CD51) as an essential regulator of cardiac PW1⁺ cells fibrogenic behavior. We used transcriptomic and proteomic approaches to identify specific cell-surface markers for cardiac PW1⁺ cells and found that αV-integrin (CD51) was expressed in almost all cardiac PW1⁺ cells (93% ± 1%), predominantly as the αVβ1 complex. αV-integrin is a subunit member of the integrin family of cell adhesion receptors and was found to activate complex of latent transforming growth factor beta (TGFβ at the surface of cardiac PW1⁺ cells. Pharmacological inhibition of αV-integrin reduced the profibrotic action of cardiac PW1⁺CD51⁺ cells and was associated with improved cardiac function and animal survival following MI coupled with a reduced infarct size and fibrotic lesion. These data identify a targetable pathway that regulates cardiac fibrosis in response to an ischemic injury and demonstrate that pharmacological inhibition of αV-integrin could reduce pathological outcomes following cardiac ischemia.

Parallels of Resistance between Angiogenesis and Lymphangiogenesis Inhibition in Cancer Therapy

Metastasis is the primary cause of cancer-related mortality. Cancer cells primarily metastasize via blood and lymphatic vessels to colonize lymph nodes and distant organs, leading to worse prognosis. Thus, strategies to limit blood and lymphatic spread of cancer have been a focal point of cancer research for several decades. Resistance to FDA-approved anti-angiogenic therapies designed to limit blood vessel growth has emerged as a significant clinical challenge. However, there are no FDA-approved drugs that target tumor lymphangiogenesis, despite the consequences of metastasis through the lymphatic system. This review highlights several of the key resistance mechanisms to anti-angiogenic therapy and potential challenges facing anti-lymphangiogenic therapy. Blood and lymphatic vessels are more than just conduits for nutrient, fluid, and cancer cell transport. Recent studies have elucidated how these vasculatures often regulate immune responses. Vessels that are abnormal or compromised by tumor cells can lead to immunosuppression. Therapies designed to improve lymphatic vessel function while limiting metastasis may represent a viable approach to enhance immunotherapy and limit cancer progression.

Lymphatic Endothelial Cell Progenitors in the Tumor Microenvironment

Tumor lymphatics play a key role in cancer progression as they are solely responsible for transporting malignant cells to regional lymph nodes (LNs), a process that precedes and promotes systemic lethal spread. It is broadly accepted that tumor lymphatic sprouting is induced mainly by soluble factors derived from tumor-associated macrophages (TAMs) and malignant cells. However, emerging evidence strongly suggests that a subset of TAMs, myeloid-lymphatic endothelial cell progenitors (M-LECP), also contribute to the expansion of lymphatics through both secretion of paracrine factors and a self-autonomous mode. M-LECP are derived from bone marrow (BM) precursors of the monocyte-macrophage lineage and characterized by unique co-expression of markers identifying lymphatic endothelial cells (LEC), stem cells, M2-type macrophages, and myeloid-derived immunosuppressive cells. This review describes current evidence for the origin of M-LECP in the bone marrow, their recruitment tumors and intratumoral trafficking, similarities to other TAM subsets, and mechanisms promoting tumor lymphatics. We also describe M-LECP integration into preexisting lymphatic vessels and discuss potential mechanisms and significance of this event. We conclude that improved mechanistic understanding of M-LECP functions within the tumor environment may lead to new therapeutic approaches to suppress tumor lymphangiogenesis and metastasis to lymph nodes.

Enhancement of cardiac lymphangiogenesis by transplantation of CD34+VEGFR-3+ endothelial progenitor cells and sustained release of VEGF-C

Impairment of cardiac lymphatic vessels leads to cardiac lymphedema. Recent studies have suggested that stimulation of lymphangiogenesis may reduce cardiac lymphedema. However, effects of lymphatic endothelial progenitor cells (LEPCs) on cardiac lymphangiogenesis are poorly understood. Therefore, this study investigated effectiveness of LEPC transplantation and VEGF-C release with self-assembling peptide (SAP) on cardiac lymphangiogenesis after myocardial infarction (MI). CD34⁺VEGFR-3⁺ EPCs isolated from rat bone marrow differentiated into lymphatic endothelial cells after VEGF-C induction. VEGF-C also stimulated the cells to incorporate into the lymphatic capillary-like structures. The functionalized SAP could adhere with the cells and released VEGF-C sustainedly. In the condition of hypoxia and serum deprivation or abdominal pouch assay, the SAP hydrogel protected the cells from apoptosis and necrosis. At 4 weeks after intramyocardial transplantation of the cells and VEGF-C loaded with SAP hydrogel in rat MI models, cardiac lymphangiogenesis was increased, cardiac edema and reverse remodeling were reduced, and cardiac function was improved significantly. Delivery with SAP hydrogel favored survival of the engrafted cells. VEGF-C released from the hydrogel promoted differentiation and incorporation of the cells as well as growth of pre-existed lymphatic vessels. Cardiac lymphangiogenesis was beneficial for elimination of the inflammatory cells in the infarcted myocardium. Moreover, angiogenesis and myocardial regeneration were enhanced after reduction of lymphedema. These results demonstrate that the combined delivery of LEPCs and VEGF-C with the functionalized SAP promotes cardiac lymphangiogenesis and repair of the infarcted myocardium effectively. This study represents a novel therapy for relieving myocardial edema in cardiovascular diseases.

CD133 in Breast Cancer Cells: More than a Stem Cell Marker

Initially correlated with hematopoietic precursors, the surface expression of CD133 was also found in epithelial and nonepithelial cells from adult tissues in which it has been associated with a number of biological events. CD133 is expressed in solid tumors as well, including breast cancer, in which most of the studies have been focused on its use as a surface marker for the detection of cells with stem-like properties (i.e., cancer stem cells (CSCs)). Differently with other solid tumors, very limited and in part controversial are the information about the significance of CD133 in breast cancer, the most common malignancy among women in industrialized countries. In this review, we summarize the latest findings about the implication of CD133 in breast tumors, highlighting its role in tumor cells with a triple negative phenotype in which it directly regulates the expression of proteins involved in metastasis and drug resistance. We provide updates about the prognostic role of CD133, underlining its value as an indicator of increased malignancy of both noninvasive and invasive breast tumor cells. The molecular mechanisms at the basis of the regulation of CD133 levels in breast tumors have also been reviewed, highlighting experimental strategies capable to restrain its level that could be taken into account to reduce malignancy and/or to prevent the progression of breast tumors.

Myeloid-Derived Lymphatic Endothelial Cell Progenitors Significantly Contribute to Lymphatic Metastasis in Clinical Breast Cancer

Lymphatic metastasis is a high-impact prognostic factor for mortality of breast cancer (BC) patients, and it directly depends on tumor-associated lymphatic vessels. We previously reported that lipopolysaccharide-induced inflammatory lymphangiogenesis is strongly promoted by myeloid-derived lymphatic endothelial cell progenitors (M-LECPs) derived from the bone marrow (BM). As BC recruits massive numbers of provascular myeloid cells, we hypothesized that M-LECPs, within this recruited population, are specifically programmed to promote tumor lymphatics that increase lymph node metastasis. In support of this hypothesis, high levels of M-LECPs were found in peripheral blood and tumor tissues of BC patients. Moreover, the density of M-LECPs and lymphatic vessels positive for myeloid marker proteins strongly correlated with patient node status. It was also established that tumor M-LECPs coexpress lymphatic-specific, stem/progenitor and M2-type macrophage markers that indicate their BM hematopoietic-myeloid origin and distinguish them from mature lymphatic endothelial cells, tumor-infiltrating lymphoid cells, and tissue-resident macrophages. Using four orthotopic BC models, we show that mouse M-LECPs are similarly recruited to tumors and integrate into preexisting lymphatics. Finally, we demonstrate that adoptive transfer of in vitro differentiated M-LECPs, but not naïve or nondifferentiated BM cells, significantly increased metastatic burden in ipsilateral lymph nodes. These data support a causative role of BC-induced lymphatic progenitors in tumor lymphangiogenesis and suggest molecular targets for their inhibition.

Podoplanin in Inflammation and Cancer

Podoplanin is a small cell-surface mucin-like glycoprotein that plays a crucial role in the development of the alveoli, heart, and lymphatic vascular system. Emerging evidence indicates that it is also involved in the control of mammary stem-cell activity and biogenesis of platelets in the bone marrow, and exerts an important function in the immune response. Podoplanin expression is upregulated in different cell types, including fibroblasts, macrophages, T helper cells, and epithelial cells, during inflammation and cancer, where it plays important roles. Podoplanin is implicated in chronic inflammatory diseases, such as psoriasis, multiple sclerosis, and rheumatoid arthritis, promotes inflammation-driven and cancer-associated thrombosis, and stimulates cancer cell invasion and metastasis through a variety of strategies. To accomplish its biological functions, podoplanin must interact with other proteins located in the same cell or in neighbor cells. The binding of podoplanin to its ligands leads to modulation of signaling pathways that regulate proliferation, contractility, migration, epithelial⁻mesenchymal transition, and remodeling of the extracellular matrix. In this review, we describe the diverse roles of podoplanin in inflammation and cancer, depict the protein ligands of podoplanin identified so far, and discuss the mechanistic basis for the involvement of podoplanin in all these processes.

Endothelial Progenitor Cells and Notch-1 Signaling as Markers of Alveolar Endothelium Regeneration in Pulmonary Emphysema

We studied the effects of elastase, cigarette smoke extract, D-galactosamine hydrochloride, and tyrosine kinase inhibitor SU5416 on endothelial progenitor cells and angiogenesis precursors, as well as on Notch-1 expression by immature endothelial cells. Simultaneously with pulmonary emphysema, different damaging factors with diverse mechanisms of action caused pathological changes in the microvascular network of the lungs and destroyed the alveolar endothelium in female C57Bl/6 mice. D-galactosamine hydrochloride disturbed mobilization of endothelial progenitor cells expressing VEGFR (CD45-CD309+) and angiogenesis progenitors (CD45-CD309+CD117+) and their migration into emphysema expanded lungs. Elastase inhibited VEGFR-expressing endothelial progenitor cells, while cigarette smoke extract inhibited cells with CD45-CD31+CD34+ phenotype. In pulmonary emphysema provoked by elastase or D-galactosamine hydrochloride, angiogenesis was provided by endothelial cells with CD45-CD31+CD34+ phenotype, whereas in emphysema modeled with SU5416 or cigarette smoke extract, it was provided by the endothelial VEGFR-expressing cells and mature CD31+ endothelial cells, respectively. Replenishment of immature endothelial cells damaged by elastase and SU5416 involved Notch-1+ angiogenesis precursors and Notch-1+ endothelial progenitor cells with VEGFR.

Multipotent Adult Progenitor Cells Support Lymphatic Regeneration at Multiple Anatomical Levels during Wound Healing and Lymphedema

Lymphatic capillary growth is an integral part of wound healing, yet, the combined effectiveness of stem/progenitor cells on lymphatic and blood vascular regeneration in wounds needs further exploration. Stem/progenitor cell transplantation also emerged as an approach to cure lymphedema, a condition caused by lymphatic system deficiency. While lymphedema treatment requires lymphatic system restoration from the capillary to the collector level, it remains undetermined whether stem/progenitor cells support a complex regenerative response across the entire anatomical spectrum of the system. Here, we demonstrate that, although multipotent adult progenitor cells (MAPCs) showed potential to differentiate down the lymphatic endothelial lineage, they mainly trophically supported lymphatic endothelial cell behaviour in vitro. In vivo, MAPC transplantation supported blood vessel and lymphatic capillary growth in wounds and restored lymph drainage across skin flaps by stimulating capillary and pre-collector vessel regeneration. Finally, human MAPCs mediated survival and functional reconnection of transplanted lymph nodes to the host lymphatic network by improving their (lymph)vascular supply and restoring collector vessels. Thus, MAPC transplantation represents a promising remedy for lymphatic system restoration at different anatomical levels and hence an appealing treatment for lymphedema. Furthermore, its combined efficacy on lymphatic and blood vascular growth is an important asset for wound healing.

Roles of circulating endothelial progenitor cells and endothelial cells in gastric carcinoma

The present study aimed to investigate the role of endothelial progenitor cells (EPCs) and endothelial cells (ECs) in the peripheral blood of patients with gastric cancer (GC), and to investigate vascular endothelial growth factor (VEGF) expression and microvessel density (MVD) in GC tissues. First, 6 ml peripheral blood with added anticoagulant was collected from each of the 42 patients with GC, followed by determination of the number of EPCs and ECs by flow cytometry using the surface markers cluster of differentiation (CD)34^brightCD133⁺CD31⁺CD45^dim and CD34^dimCD133⁻CD31^brightCD45⁻, respectively. VEGF expression in patients with GC was detected by the streptomycin avidin-peroxidase immunohistochemical method, and MVD was calculated using the marker CD34. EPC and EC levels were positively associated with VEGF expression level, as well as with MVD. VEGF expression was positive in 66.67% GC cases, and its level was significantly associated with tumor-node-metastasis (TNM) stage, invasion depth and lymph-node metastasis (P<0.05). VEGF expression level was also positively associated with MVD. MVD in GC was significantly larger than that in normal tissue (P<0.01), and it was significantly associated with TNM stage (P<0.05), invasion depth (P<0.01) and lymph-node metastasis (P<0.01). EPCs in the peripheral blood have an important role in GC development, and may be a promising indicator of GC diagnosis and prognosis.

Comparison and functional characterisation of peripheral blood mononuclear cells isolated from filarial lymphoedema and endemic normals of a South Indian population

OBJECTIVE

The underlying problem in lymphatic filariasis is irreversible swelling of the limbs (lymphoedema), which is a unique feature of lymphatic insufficiency. It is still unclear whether the natural ability of lymphatics to form functional lymphatic vasculature is achieved or attenuated in the lymphoedemal pathology. Clinical studies have clearly shown that circulating lymphatic progenitors (CLPs), a subset of bone marrow-derived mononuclear cells (PBMCs), contribute to post-natal lymph vasculogenesis. CLP-based revascularisation could be a promising strategy to bypass the endothelial disruption and damage incurred by the filarial parasites. Thus our aim was to compare and characterise the functional prowess of PBMCs in physiological and lymphoedemal pathology.

METHODS

PBMCs were isolated from venous blood sample from drug-naive endemic normals (EN) and drug-deprived filarial lymphoedema (FL) individuals using density gradient centrifugation. Adhesion, transwell migration and in vitro matrigel assays were employed to characterise the lymphvasculogenic potential of PBMCs. CLPs were phenotypically characterised using flow cytometry; expression levels of lymphatic markers and inflammatory cytokines were quantified using qRT-PCR and ELISA, respectively.

RESULTS

PBMCs from FL group display poor adherence to fibronectin (P = 0.040), reduced migration towards SDF-1α (P = 0.035), impaired tubular network (P = 0.004) and branching point (P = 0.048) formation. The PBMC mRNA expression of VEGFR3 (P = 0.039) and podoplanin (P = 0.050) was elevated, whereas integrin α9 (P = 0.046) was inhibited in FL individuals; additionally, the surface expression of CD34 (P = 0.048) was significantly reduced in the FL group compared to the EN group.

CONCLUSION

PBMCs from filarial lymphoedema show defective and dysregulated lymphvasculogenic function compared to endemic normals.

The role of bone marrow-derived endothelial progenitor cells and angiogenic responses in chronic obstructive pulmonary disease

Increased vascularity of the bronchial sub-mucosa is a cardinal feature of chronic obstructive pulmonary disease (COPD) and is associated with disease severity. Capillary engorgement, leakage, and vasodilatation can directly increase airway wall thickness resulting in airway luminal narrowing and facilitate inflammatory cell trafficking, thereby contributing to irreversible airflow obstruction, a characteristic of COPD. Airway wall neovascularisation, seen as increases in both the size and number of bronchial blood vessels is a prominent feature of COPD that correlates with reticular basement membrane thickening and airway obstruction. Sub-epithelial vascularization may be an important remodelling event for airway narrowing and airflow obstruction in COPD. Post-natal angiogenesis is a complex process, whereby new blood vessels sprouting from extant microvasculature, can arise from the proliferation of resident mature vascular endothelial cells (ECs). In addition, this may arise from increased turnover and lung-homing of circulating endothelial progenitor cells (EPCs) from the bone marrow (BM). Following lung-homing, EPCs can differentiate locally within the tissue into ECs, further contributing to vascular repair, maintenance, and expansion under pathological conditions, governed by a locally elaborated milieu of growth factors (GFs). In this article, we will review evidence for the role of BM-derived EPCs in the development of angiogenesis in the lug and discuss how this may relate to the pathogenesis of COPD.

Lymphatic endothelial progenitors originate from plastic myeloid cells activated by toll-like receptor-4

BACKGROUND

Myeloid-derived lymphatic endothelial cells (M-LECP) are induced by inflammation and play an important role in adult lymphangiogenesis. However, the mechanisms driving M-LECP differentiation are currently unclear. We previously showed that activation of Toll-like receptor-4 (TLR4) induces myeloid-lymphatic transition (MLT) of immortalized mouse myeloid cells. Here the goals were to assess the potential of different TLR4 ligands to induce pro-lymphatic reprogramming in human and mouse primary myeloid cells and to identify transcriptional changes regulating this process.

METHODOLOGY/PRINCIPAL FINDINGS

Human and mouse myeloid cells were reprogrammed to the lymphatic phenotype by TLR4 ligands including lipopolysaccharide (LPS), recombinant high mobility group box 1 protein (HMGB1), and paclitaxel. TLR4 induced similar MLT in cells from mice of different strains and immune status. Commonly induced genes were detected by transcriptional profiling in human and mouse myeloid cells from either immunocompetent or immunodeficient mice. Shared trends included: (1) novel expression of lymphatic-specific markers vascular endothelial growth factor receptor-3 (VEGFR-3), lymphatic vessel endothelial hyaluronan receptor-1 (LYVE-1) and podoplanin (PDPN) largely absent prior to induction; (2) lack of notable changes in blood vessel-specific markers; (3) transient expression of VEGFR-3, but sustained increase of vascular endothelial growth factor-C (VEGF-C) and a variety of inflammatory cytokines; (4) dependency of VEGFR-3 upregulation and other LEC genes on NF-κB; and (5) novel expression of lymphatic-specific (e.g., PROX1) and stem/progenitor (e.g., E2F1) transcription factors known for their roles in adult and embryonic vascular formation. M-LECP generated by TLR4 ligands in vitro were functional in vivo as demonstrated by significantly increased lymphatic vessel density and lymphatic metastasis detected in orthotopic breast cancer models.

CONCLUSIONS/SIGNIFICANCE

We established a novel TLR4-dependent protocol for in vitro production of functionally competent M-LECP from primary human or mouse myeloid cells and identified many potential regulators of this process. This information can be further exploited for research and therapeutic purposes.

Lymphatic Contribution to the Cellular Niche in Heterotopic Ossification

OBJECTIVE

The objective of this study was to determine the contribution of lymphatic tissue to heterotopic ossification (HO).

BACKGROUND

HO is the pathologic development of ectopic bone within soft tissues often following severe trauma. Characterization of the tissue niche supporting HO is critical to identifying therapies directed against this condition. Lymphangiogenesis is upregulated during incidents of trauma, thereby coincident with the niche supportive of HO. We hypothesized that lymphatic tissues play a critical role in HO formation.

METHODS

Mice underwent hindlimb Achilles' tendon transection and dorsal burn injury (burn/tenotomy) to induce HO. The popliteal and inguinal lymph nodes were excised ipsilateral to the tenotomy site. Flow cytometry and immunostaining were used to quantify and localize lymphoendothelium. MicroCT was used to quantify HO.

RESULTS

Enrichment of mature lymphatic tissues was noted 2 weeks after injury at the tendon transection sites when compared with the contralateral, intact tendon based on LYVE1+ tubules (10.9% vs 0.8%, P < 0.05). Excision of the inguinal and popliteal nodes with draining popliteal lymphatic vessel significantly decreased the presence of mature lymphoendothelium 2 weeks after injury (10.9% vs 3.3%, P < 0.05). Bone-cartilage-stromal progenitor cells (CD105+/AlphaV+/Tie2-/CD45-/CD90-/BP1-) were also significantly decreased after lymph node excision (10.2% vs 0.5%, P < 0.05). A significant decrease was noted in the volume of de novo HO present within the soft tissues (0.12 mm vs 0.02 mm).

CONCLUSION

These findings suggest that lymphatic vessels are intimately linked with the de novo formation bone within soft tissues following trauma, and their presence may facilitate bone formation.

Novel role of immature myeloid cells in formation of new lymphatic vessels associated with inflammation and tumors

Inflammation triggers an immune cell-driven program committed to restoring homeostasis to injured tissue. Central to this process is vasculature restoration, which includes both blood and lymphatic networks. Generation of new vessels or remodeling of existing vessels are also important steps in metastasis-the major cause of death for cancer patients. Although roles of the lymphatic system in regulation of inflammation and cancer metastasis are firmly established, the mechanisms underlying the formation of new lymphatic vessels remain a subject of debate. Until recently, generation of new lymphatics in adults was thought to occur exclusively through sprouting of existing vessels without help from recruited progenitors. However, emerging findings from clinical and experimental studies show that lymphoendothelial progenitors, particularly those derived from immature myeloid cells, play an important role in this process. This review summarizes current evidence for the existence and significant roles of myeloid-derived lymphatic endothelial cell progenitors (M-LECPs) in generation of new lymphatics. We describe specific markers of M-LECPs and discuss their biologic behavior in culture and in vivo, as well as currently known molecular mechanisms of myeloid-lymphatic transition (MLT). We also discuss the implications of M-LECPs for promoting adaptive immunity, as well as cancer metastasis. We conclude that improved mechanistic understanding of M-LECP differentiation and its role in adult lymphangiogenesis may lead to new therapeutic approaches for correcting lymphatic insufficiency or excessive formation of lymphatic vessels in human disorders.

The meaning of PIWI proteins in cancer development

Cancer is a histologically and genetically heterogeneous population of tumor cells that exhibits distinct molecular profiles determined by epigenetic alterations. P-element-induced wimpy testis (PIWI) proteins in complex with PIWI-interacting RNA (piRNA) have been previously demonstrated to be involved in epigenetic regulation in germline cells. Recently, reactivation of PIWI expression, primarily PIWI-like protein 1 and 2, through aberrant DNA methylation resulting in genomic silencing has been identified in various types of tumors. It has been suggested that the PIWI-piRNA complex contributes to cancer development and progression by promoting a stem-like state of cancer cells, or cancer stem cells (CSCs). It has been identified that CSCs represent the cells that have undergone epithelial-mesenchymal transition (EMT) and acquired metastatic capacities. However, the molecular association between the EMT process and the stem-cell state remains unclear. Further extensive characterization of CSCs in individual types of tumors is required to identify specific markers for the heterogeneous population of CSCs and therefore selectively target CSCs. Previous studies indicate a reciprocal regulation between PIWI proteins and a complex signaling network linking markers characterized for CSCs and transcription factors involved in EMT. In the present review, studies of PIWI function are summarized, and the potential involvement of PIWI proteins in cancer development and progression is discussed.

TIE-2 expressing monocytes in human cancers

Tumor-associated macrophages (TAM) are well known as a key player in the tumor microenvironment, which support cancer progression. More recently, a lineage of monocytes characterized by the expression of the TIE-2/Tek angiopoietin receptor identified a subset of circulating and tumor-associated monocytes endowed with proangiogenic activity. TIE-2 expressing monocytes (TEM) were found both in humans and mice. Here, we review the phenotypes and functions of TEM reported so far in human cancer and their potential use as markers of cancer progression and metastasis. Finally, we discuss the therapeutic approaches currently used or proposed to target TEM.

Endothelial progenitor cells in chronic obstructive pulmonary disease and emphysema

Endothelial injury is implicated in the pathogenesis of COPD and emphysema; however the role of endothelial progenitor cells (EPCs), a marker of endothelial cell repair, and circulating endothelial cells (CECs), a marker of endothelial cell injury, in COPD and its subphenotypes is unresolved. We hypothesized that endothelial progenitor cell populations would be decreased in COPD and emphysema and that circulating endothelial cells would be increased. Associations with other subphenotypes were examined. The Multi-Ethnic Study of Atherosclerosis COPD Study recruited smokers with COPD and controls age 50–79 years without clinical cardiovascular disease. Endothelial progenitor cell populations (CD34+KDR+ and CD34+KDR+CD133+ cells) and circulating endothelial cells (CD45dimCD31+CD146+CD133-) were measured by flow cytometry. COPD was defined by standard spirometric criteria. Emphysema was assessed qualitatively and quantitatively on CT. Full pulmonary function testing and expiratory CTs were measured in a subset. Among 257 participants, both endothelial progenitor cell populations, and particularly CD34+KDR+ endothelial progenitor cells, were reduced in COPD. The CD34+KDR+CD133+ endothelial progenitor cells were associated inversely with emphysema extent. Both endothelial progenitor cell populations were associated inversely with extent of panlobular emphysema and positively with diffusing capacity. Circulating endothelial cells were not significantly altered in COPD but were inversely associated with pulmonary microvascular blood flow on MRI. There was no consistent association of endothelial progenitor cells or circulating endothelial cells with measures of gas trapping. These data provide evidence that endothelial repair is impaired in COPD and suggest that this pathological process is specific to emphysema.

Efficient and robust differentiation of endothelial cells from human induced pluripotent stem cells via lineage control with VEGF and cyclic AMP

Blood vessels are essential components for many tissues and organs. Thus, efficient induction of endothelial cells (ECs) from human pluripotent stem cells is a key method for generating higher tissue structures entirely from stem cells. We previously established an EC differentiation system with mouse pluripotent stem cells to show that vascular endothelial growth factor (VEGF) is essential to induce ECs and that cyclic adenosine monophosphate (cAMP) synergistically enhances VEGF effects. Here we report an efficient and robust EC differentiation method from human pluripotent stem cell lines based on a 2D monolayer, serum-free culture. We controlled the direction of differentiation from mesoderm to ECs using stage-specific stimulation with VEGF and cAMP combined with the elimination of non-responder cells at early EC stage. This "stimulation-elimination" method robustly achieved very high efficiency (>99%) and yield (>10 ECs from 1 hiPSC input) of EC differentiation, with no purification of ECs after differentiation. We believe this method will be a valuable technological basis broadly for regenerative medicine and 3D tissue engineering.

Long-term Prediction of Cardiovascular Outcomes by Circulating CD34+ and CD34+CD133+ Stem Cells in Patients With Type 2 Diabetes

OBJECTIVE

Cardiovascular risk varies substantially in the population with diabetes, and biomarkers can improve risk stratification. Circulating stem cells predict future cardiovascular events and death, but data for the population with diabetes are scant. In this study we evaluated the ability of circulating stem cell levels to predict future cardiovascular outcomes and improve risk discrimination in patients with type 2 diabetes.

RESEARCH DESIGN AND METHODS

A cohort of 187 patients with type 2 diabetes was monitored for a median of 6.1 years. The primary outcome was time to a first cardiovascular event, defined as 3-point major adverse cardiovascular event (cardiovascular death, nonfatal myocardial infarction, or nonfatal stroke) plus hospitalization for cardiovascular causes. At baseline, we measured six stem/progenitor cell phenotypes in peripheral blood based on expression of CD34, CD133, and KDR.

RESULTS

The primary outcome occurred in 48 patients (4.5/100 patient-years). Patients with incident cardiovascular events had significantly lower CD34⁺ and CD34⁺CD133⁺ cells than those without. Higher rates of cardiovascular events occurred in patients with below median levels of CD34⁺ and CD34⁺CD133⁺. In Cox proportional hazards regression analyses, a reduced CD34⁺ (hazard ratio 2.21 [95% CI 1.14-4.29]) and CD34⁺CD133⁺ (2.98 [1.46-6.08]) cell count independently predicted future events. Addition of the CD34⁺ cell count to the reference model or the UK Prospective Diabetes Study risk engine improved C statistics, continuous net reclassification improvement, and/or integrated discrimination index.

CONCLUSIONS

In patients with type 2 diabetes, a reduced baseline level of circulating CD34⁺ stem cells predicts adverse cardiovascular outcomes up to 6 years later and improves risk stratification.

Multi-scale Modeling of the Cardiovascular System: Disease Development, Progression, and Clinical Intervention

Cardiovascular diseases (CVDs) are the leading cause of death in the western world. With the current development of clinical diagnostics to more accurately measure the extent and specifics of CVDs, a laudable goal is a better understanding of the structure-function relation in the cardiovascular system. Much of this fundamental understanding comes from the development and study of models that integrate biology, medicine, imaging, and biomechanics. Information from these models provides guidance for developing diagnostics, and implementation of these diagnostics to the clinical setting, in turn, provides data for refining the models. In this review, we introduce multi-scale and multi-physical models for understanding disease development, progression, and designing clinical interventions. We begin with multi-scale models of cardiac electrophysiology and mechanics for diagnosis, clinical decision support, personalized and precision medicine in cardiology with examples in arrhythmia and heart failure. We then introduce computational models of vasculature mechanics and associated mechanical forces for understanding vascular disease progression, designing clinical interventions, and elucidating mechanisms that underlie diverse vascular conditions. We conclude with a discussion of barriers that must be overcome to provide enhanced insights, predictions, and decisions in pre-clinical and clinical applications.

Differential expression of EBV proteins LMP1 and BHFR1 in EBV‑associated gastric and nasopharyngeal cancer tissues

Epstein-Barr virus (EBV) infection is associated with the development of T cell lymphoma, nasopharyngeal cancer (NPC), and EBV-associated gastric cancer (EBVaGC). This study assessed the expression of the EBV-associated proteins latent membrane protein 1 (LMP1) and BamHI-A rightward frame 1 (BARF1) in NPC and EBVaGC tissue specimens and determined their association with clinicopathological data, microvessel density (MVD) and micro-lymphatic vessel density (MLVD). This study collected 600 gastric cancer and 75 NPC tissue samples. EBV infection was assessed using in situ hybridization, and LMP1 and BARF1 expression was assessed using immunohistochemistry. The levels of MVD and MLVD were assessed using immunostaining of vascular endothelial growth factor (VEGF)-C, CD34, and lymphatic vessel endothelial receptor 1 (LYVE-1). Among the 600 gastric cancer cases, 30 were positive for EBV infection, which was shown to be associated with the age of patients (P=0.073), tumor differentiation (P<0.0001), tumor location (P<0.0001) and lymph node metastasis (P<0.0001). In these 30 EBVaGC cases, only one case was weakly positive for LMP1, but 17 cases were BARF1 positive. BARF1 expression was associated with lymph node metastasis of EBVaGC and the level of MLVD. Furthermore, 61 (81%) of 75 NPC patients were EBV positive, among which 38 cases were LMP-1 positive (62.3%) and LMP1 expression was associated with tumor-node-metastasis stage (P=0.011) and lymph node metastasis (P=0.041). MLVD was significantly higher in LMP1-positive cases than LMP1-negative cases. There were only 8 (13.3%) cases positive for BARF1 expression. In conclusion, EBV infection exhibits a role in gastric cancer and NPC development; however, expression of EBV-associated proteins LMP1 and BARF1 have differential functions during tumorigenesis of these two types of cancer.

Mobilization of lymphatic endothelial precursor cells and lymphatic neovascularization in primary Sjögren's syndrome

Although lymphatic neovascularization may be a key feature of chronic inflammation, it is almost unexplored in primary Sjögren's syndrome (pSS). A recent study revealed a pro‐lymphangiogenic function of interleukin (IL)‐17, a leading player in pSS pathogenesis. The aims of the study were to investigate lymphangiogenic mediators and lymphatic vasculature in pSS, as well as their possible association with IL‐17. Circulating lymphatic endothelial precursor cells (LEPCs) and Th17 cells were enumerated in pSS patients and healthy donors. VEGF‐C and IL‐17 levels were assessed in paired serum samples. Lymphatic vasculature, VEGF‐C/VEGF receptor (VEGFR)‐3 and IL‐17 were evaluated in pSS minor salivary glands (MSGs) and compared with normal and non‐specific chronic sialadenitis (NSCS) MSGs. Circulating LEPCs were expanded in pSS and correlated with circulating Th17 cells, IL‐17 and VEGF‐C. In pSS MSGs, a newly formed lymphatic capillary network was found within periductal inflammatory infiltrates and the number of interlobular lymphatic vessels was significantly increased compared with normal and NSCS MSGs. Strong VEGF‐C expression was detected in pSS ductal epithelial cells and periductal inflammatory cells. Numerous VEGFR‐3⁺ infiltrating mononuclear cells were exclusively observed in pSS MSGs. VEGFR‐3 expression was strongly increased in lymphatic capillaries of pSS MSGs. IL‐17⁺ inflammatory cells were preferentially observed around lymphatic vessels in pSS MSGs. This study supports the notion that lymphvasculogenesis and lymphangiogenesis are active in pSS, thereby unmasking a novel aspect of disease pathogenesis. In addition, our results suggest another possible pathogenic role of IL‐17 in pSS, further supporting its therapeutic targeting in this disease.

Breast Cancer-Associated Fibroblasts: Where We Are and Where We Need to Go

Cancers are heterogeneous tissues comprised of multiple components, including tumor cells and microenvironment cells. The tumor microenvironment has a critical role in tumor progression. The tumor microenvironment is comprised of various cell types, including fibroblasts, macrophages and immune cells, as well as extracellular matrix and various cytokines and growth factors. Fibroblasts are the predominant cell type in the tumor microenvironment. However, neither the derivation of tissue-specific cancer-associated fibroblasts nor markers of tissue-specific cancer-associated fibroblasts are well defined. Despite these uncertainties it is increasingly apparent that cancer-associated fibroblasts have a crucial role in tumor progression. In breast cancer, there is evolving evidence showing that breast cancer-associated fibroblasts are actively involved in breast cancer initiation, proliferation, invasion and metastasis. Breast cancer-associated fibroblasts also play a critical role in metabolic reprogramming of the tumor microenvironment and therapy resistance. This review summarizes the current understanding of breast cancer-associated fibroblasts.

PPAR Gamma and Angiogenesis: Endothelial Cells Perspective

We summarize the current knowledge concerning PPARγ function in angiogenesis. We discuss the mechanisms of action for PPARγ and its role in vasculature development and homeostasis, focusing on endothelial cells, endothelial progenitor cells, and bone marrow-derived proangiogenic cells.

Isolation and characterization of circulating lymphatic endothelial colony forming cells

RATIONALE

The identification of circulating endothelial progenitor cells has led to speculation regarding their origin as well as their contribution to neovascular development. Two distinct types of endothelium make up the blood and lymphatic vessel system. However, it has yet to be determined whether there are distinct lymphatic-specific circulating endothelial progenitor cells.

OBJECTIVE

This study aims to isolate and characterize the cellular properties and global gene expression of lymphatic-specific endothelial progenitor cells.

METHODS AND RESULTS

We isolated circulating endothelial colony forming cells (ECFCs) from whole peripheral blood. These cells are endothelial in nature, as defined by their expression of endothelial markers and their ability to undergo capillary morphogenesis in three-dimensional culture. A subset of isolated colonies express markers of lymphatic endothelium, including VEGFR-3 and Prox-1, with low levels of VEGFR-1, a blood endothelial marker, while the bulk of the isolated cells express high VEGFR-1 levels with low VEGFR-3 and Prox-1 expression. The different isolates have differential responses to VEGF-C, a lymphatic endothelial specific cytokine, strongly suggesting that there are lymphatic specific and blood specific ECFCs. Global analysis of gene expression revealed key differences in the regulation of pathways involved in cellular differentiation between blood and lymphatic-specific ECFCs.

CONCLUSION

These data indicate that there are two distinguishable circulating ECFC types, blood and lymphatic, which are likely to have discrete functions during neovascularization.

Detection and Clinical Significance of Circulating Tumor Cells in Colorectal Cancer--20 Years of Progress

Circulating tumor cells (CTC) may be defined as tumor- or metastasis-derived cells that are present in the bloodstream. The CTC pool in colorectal cancer (CRC) patients may include not only epithelial tumor cells, but also tumor cells undergoing epithelial-mesenchymal transition (EMT) and tumor stem cells. A significant number of patients diagnosed with early stage CRC subsequently relapse with recurrent or metastatic disease despite undergoing "curative" resection of their primary tumor. This suggests that an occult metastatic disease process was already underway, with viable tumor cells being shed from the primary tumor site, at least some of which have proliferative and metastatic potential and the ability to survive in the bloodstream. Such tumor cells are considered to be responsible for disease relapse in these patients. Their detection in peripheral blood at the time of diagnosis or after resection of the primary tumor may identify those early-stage patients who are at risk of developing recurrent or metastatic disease and who would benefit from adjuvant therapy. CTC may also be a useful adjunct to radiological assessment of tumor response to therapy. Over the last 20 years many approaches have been developed for the isolation and characterization of CTC. However, none of these methods can be considered the gold standard for detection of the entire pool of CTC. Recently our group has developed novel unbiased inertial microfluidics to enrich for CTC, followed by identification of CTC by imaging flow cytometry. Here, we provide a review of progress on CTC detection and clinical significance over the last 20 years.

The significance of lymphatic space invasion and its association with vascular endothelial growth factor-C expression in ovarian cancer

The aim of this study is to investigate the significance of lymphatic space invasion (LSI) and tumor VEGF-C expression in the lymphatic spread of ovarian cancer. By performing immunostaining using human ovarian cancer specimens, we first investigated the association between the extent of LSI and tumor VEGF-C expression, tumor lymphangiogenesis, or the lymphatic metastasis. Moreover, by performing in vitro and in vivo experiments, we elucidated the role of VEGF-C in tumor lymphangiogenesis and lymph node metastasis as well as its role as a therapeutic target in ovarian cancer. The presence of LSI was associated with lymph node metastasis in patients with ovarian cancer. VEGF-C overexpression was significantly associated with the increased LSI and LVD in ovarian cancer. VEGF-C stimulated the lymphangiogenesis in vitro, induced the new lymph vessel formation, and increased the lymph node metastasis in mice models of ovarian cancer. The attenuation of VEGF-C expression by the treatment with mTORC1 inhibitor significantly inhibited lymphangiogenesis, and decreased lymph node metastasis in mice models of ovarian cancer. The presence of LSI is an indicator of nodal metastasis and is associated with higher tumor VEGF-C expression and worse clinical outcome of ovarian cancer patients. VEGF-C plays a crucial role in tumor lymphangiogenesis and lymph node metastasis of ovarian cancer.

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.