Early rhombic lip Protogenin+ve stem cells in a human-specific neurovascular niche initiate and maintain group 3 medulloblastoma.

We identify a population of Protogenin-positive (PRTG+ve) MYChigh NESTINlow stem cells in the four-week-old human embryonic hindbrain that subsequently localizes to the ventricular zone of the rhombic lip (RLVZ). Oncogenic transformation of early Prtg+ve rhombic lip stem cells initiates group 3 medulloblastoma (Gr3-MB)-like tumors. PRTG+ve stem cells grow adjacent to a human-specific interposed vascular plexus in the RLVZ, a phenotype that is recapitulated in Gr3-MB but not in other types of medulloblastoma. Co-culture of Gr3-MB with endothelial cells promotes tumor stem cell growth, with the endothelial cells adopting an immature phenotype. Targeting the PRTGhigh compartment of Gr3-MB in vivo using either the diphtheria toxin system or chimeric antigen receptor T cells constitutes effective therapy. Human Gr3-MBs likely arise from early embryonic RLVZ PRTG+ve stem cells inhabiting a specific perivascular niche. Targeting the PRTGhigh compartment and/or the perivascular niche represents an approach to treat children with Gr3-MB.

Colony stimulating factor-1 producing endothelial cells and mesenchymal stromal cells maintain monocytes within a perivascular bone marrow niche.

Macrophage colony stimulating factor-1 (CSF-1) plays a critical role in maintaining myeloid lineage cells. However, congenital global deficiency of CSF-1 (Csf1op/op) causes severe musculoskeletal defects that may indirectly affect hematopoiesis. Indeed, we show here that osteolineage-derived Csf1 prevented developmental abnormalities but had no effect on monopoiesis in adulthood. However, ubiquitous deletion of Csf1 conditionally in adulthood decreased monocyte survival, differentiation, and migration, independent of its effects on bone development. Bone histology revealed that monocytes reside near sinusoidal endothelial cells (ECs) and leptin receptor (Lepr)-expressing perivascular mesenchymal stromal cells (MSCs). Targeted deletion of Csf1 from sinusoidal ECs selectively reduced Ly6C- monocytes, whereas combined depletion of Csf1 from ECs and MSCs further decreased Ly6Chi cells. Moreover, EC-derived CSF-1 facilitated recovery of Ly6C- monocytes and protected mice from weight loss following induction of polymicrobial sepsis. Thus, monocytes are supported by distinct cellular sources of CSF-1 within a perivascular BM niche.

Life support for transitory exhausted CTLs.

Di Pilato et al. demonstrate that CXCR6 positions TCF-1- transitory CD8+ cytotoxic lymphocytes (CTLs) with perivascular CCR7+ dendritic cells (DCs) within the tumor stroma to receive IL-15 survival signals. The requirement for CXCR6 and its strong prediction of overall patient survival highlight the importance of continued CTL-DC interactions in sustaining tumor immunity.

TGFß1 Regulates Cellular Composition of In Vitro Cardiac Perivascular Niche Based on Cardiospheres.

The cardiac perivascular niche is a cellular microenvironment of a blood vessel. The principles of niche regulation are still poorly understood. We studied the effect of TGFß1 on cells forming the cardiac perivascular niche using 3D cell culture (cardiospheres). Cardiospheres contained progenitor (c-Kit), endothelial (CD31), and mural (αSMA) cells, basement membrane proteins (laminin) and extracellular matrix proteins (collagen I, fibronectin). TGFß1 treatment decreased the length of CD31+ microvasculature, VE cadherin protein level, and proportion of NG2+ cells, and increased proportion of αSMA+ cells and transgelin/SM22α protein level. We supposed that this effect is related to the stabilizing function of TGFß1 on vascular cells: decreased endothelial cell proliferation, as shown for HUVEC, and activation of mural cell differentiation.

Identification of vascular cues contributing to cancer cell stemness and function.

Glioblastoma stem cells (GSCs) reside close to blood vessels (BVs) but vascular cues contributing to GSC stemness and the nature of GSC-BVs cross talk are not fully understood. Here, we dissected vascular cues influencing GSC gene expression and function to perfusion-based vascular cues, as well as to those requiring direct GSC-endothelial cell (EC) contacts. In light of our previous finding that perivascular tumor cells are metabolically different from tumor cells residing further downstream, cancer cells residing within a narrow, < 60 µm wide perivascular niche were isolated and confirmed to possess a superior tumor-initiation potential compared with those residing further downstream. To circumvent reliance on marker expression, perivascular GSCs were isolated from the respective locales based on their relative state of quiescence. Combined use of these procedures uncovered a large number of previously unrecognized differentially expressed GSC genes. We show that the unique metabolic milieu of the perivascular niche dominated by the highly restricted zone of mTOR activity is conducive for acquisition of GSC properties, primarily in the regulation of genes implicated in cell cycle control. A complementary role of vascular cues including those requiring direct glioma/EC contacts was revealed using glioma/EC co-cultures. Outstanding in the group of glioma cells impacted by nearby ECs were multiple genes responsible for maintaining GSCs in an undifferentiated state, a large fraction of which also relied on Notch-mediated signaling. Glioma-EC communication was found to be bidirectional, evidenced by extensive Notch-mediated EC reprogramming by contacting tumor cells, primarily metabolic EC reprogramming.

Adventitial Cuffs: Regional Hubs for Tissue Immunity.

Inflammation must be effective, while limiting excessive tissue damage. To walk this line, immune functions are grossly compartmentalized by innate cells that act locally and adaptive cells that function systemically. But what about the myriad tissue-resident immune cells that are critical to this balancing act and lie on a spectrum of innate and adaptive immunity? We propose that mammalian perivascular adventitial 'cuffs' are conserved sites in multiple organs, enriched for these tissue-resident lymphocytes and dendritic cells, as well as lymphatics, nerves, and subsets of specialized stromal cells. Here, we argue that these boundary sites integrate diverse tissue signals to regulate the movement of immune cells and interstitial fluid, facilitate immune crosstalk, and ultimately act to coordinate regional tissue immunity.

Retraction fibers produced by fibronectin-integrin α5ß1 interaction promote motility of brain tumor cells.

Glioblastoma (GBM) is a refractory disease that has a highly infiltrative characteristic. Over the past decade, GBM perivascular niche (PVN) has been described as a route of dissemination. Here, we investigated that trailed membrane structures, namely retraction fibers (RFs), are formed by perivascular extracellular matrix (ECM) proteins. By using the anatomical GBM database, we validated that the ECM-related genes were highly expressed in the cells within the PVN where fibronectin (FN) induced RF formation. By disrupting candidates of FN-binding integrins, integrin α5ß1 was identified as the main regulator of RF formation. De novo RFs were produced at the trailing edge, and focal adhesions were actively localized in RFs, indicating that adhesive force makes RFs remain at the bottom surface. Furthermore, we observed that GBM cells more frequently migrated along the residual RFs formed by preceding cells in microfluidic channels in comparison to those in the channels without RFs, suggesting that the infiltrative characteristics GBM could be attributed to RFs formed by the preceding cells in concert with chemoattractant cues. Altogether, we demonstrated that shedding membrane structures of GBM cells are maintained by FN-integrin α5ß1 interaction and promoted their motility .

Chaperone-Mediated Autophagy in Pericytes: A Key Target for the Development of New Treatments against Glioblastoma Progression.

Glioblastoma (GB) cells physically interact with peritumoral pericytes (PCs) present in the brain microvasculature. These interactions facilitate tumor cells to aberrantly increase and benefit from chaperone-mediated autophagy (CMA) in the PC. GB-induced CMA leads to major changes in PC immunomodulatory phenotypes, which, in turn, support cancer progression. In this review, we focus on the consequences of the GB-induced up-regulation of CMA activity in PCs and evaluate how manipulation of this process could offer new strategies to fight glioblastoma, increasing the availability of treatments for this cancer that escapes conventional therapies. We finally discuss the use of modified PCs unable to increase CMA in response to GB as a cell therapy alternative to minimize undesired off-target effects associated with a generalized CMA inhibition.

Dormancy in the Tumor Microenvironment.

Tumor cells frequently disseminate to distant organ sites, where they encounter permissive or restrictive environments that enable them to grow and colonize or enter a dormant state. Tumor dormancy is not strictly defined, but generally describes a tumor cell that is non-proliferative or in a state of balanced equilibrium, in which the proliferation rate of the tumor cell or cells is equal to its rate of cell death. The mechanisms that regulate tumor cell entry into and exit from dormancy are poorly understood, but microenvironmental features as well as tumor cell intrinsic factors play an important role in mediating this transition. Upon homing to distant metastatic sites, tumor cells may disseminate into various niches, most frequently the perivascular, hematopoietic stem cell, or endosteal/osteogenic niche. Tumor cells sense the cytokines, growth factors, and chemo-attractants from each of these niches, and tumor cell expression of cognate ligands and receptors can determine whether a tumor cell enters or exits dormancy. In addition to the secreted factors and cell-cell interactions that regulate dormancy, the cellular milieu also impacts upon disseminated tumor cells to promote or restrain their growth in distant metastatic sites. In this chapter we will discuss the role of the osteogenic and perivascular niche on dormant tumor cells, as well as the impact of hypoxia (low oxygen tensions) and the immune system on the restriction and outgrowth of dormant, disseminated tumor cells.

Human bone perivascular niche-on-a-chip for studying metastatic colonization.

Eight out of 10 breast cancer patients die within 5 years after the primary tumor has spread to the bones. Tumor cells disseminated from the breast roam the vasculature, colonizing perivascular niches around blood capillaries. Slow flows support the niche maintenance by driving the oxygen, nutrients, and signaling factors from the blood into the interstitial tissue, while extracellular matrix, endothelial cells, and mesenchymal stem cells regulate metastatic homing. Here, we show the feasibility of developing a perfused bone perivascular niche-on-a-chip to investigate the progression and drug resistance of breast cancer cells colonizing the bone. The model is a functional human triculture with stable vascular networks within a 3D native bone matrix cultured on a microfluidic chip. Providing the niche-on-a-chip with controlled flow velocities, shear stresses, and oxygen gradients, we established a long-lasting, self-assembled vascular network without supplementation of angiogenic factors. We further show that human bone marrow-derived mesenchymal stem cells, which have undergone phenotypical transition toward perivascular cell lineages, support the formation of capillary-like structures lining the vascular lumen. Finally, breast cancer cells exposed to interstitial flow within the bone perivascular niche-on-a-chip persist in a slow-proliferative state associated with increased drug resistance. We propose that the bone perivascular niche-on-a-chip with interstitial flow promotes the formation of stable vasculature and mediates cancer cell colonization.

An Update on Glioblastoma Biology, Genetics, and Current Therapies: Novel Inhibitors of the G Protein-Coupled Receptor CCR5.

The mechanisms governing therapeutic resistance of the most aggressive and lethal primary brain tumor in adults, glioblastoma, have increasingly focused on tumor stem cells. These cells, protected by the periarteriolar hypoxic GSC niche, contribute to the poor efficacy of standard of care treatment of glioblastoma. Integrated proteogenomic and metabolomic analyses of glioblastoma tissues and single cells have revealed insights into the complex heterogeneity of glioblastoma and stromal cells, comprising its tumor microenvironment (TME). An additional factor, which isdriving poor therapy response is the distinct genetic drivers in each patient's tumor, providing the rationale for a more individualized or personalized approach to treatment. We recently reported that the G protein-coupled receptor CCR5, which contributes to stem cell expansion in other cancers, is overexpressed in glioblastoma cells. Overexpression of the CCR5 ligand CCL5 (RANTES) in glioblastoma completes a potential autocrine activation loop to promote tumor proliferation and invasion. CCL5 was not expressed in glioblastoma stem cells, suggesting a need for paracrine activation of CCR5 signaling by the stromal cells. TME-associated immune cells, such as resident microglia, infiltrating macrophages, T cells, and mesenchymal stem cells, possibly release CCR5 ligands, providing heterologous signaling between stromal and glioblastoma stem cells. Herein, we review current therapies for glioblastoma, the role of CCR5 in other cancers, and the potential role for CCR5 inhibitors in the treatment of glioblastoma.

Notch-inducing hydrogels reveal a perivascular switch of mesenchymal stem cell fate.

The fate of mesenchymal stem cells (MSCs) in the perivascular niche, as well as factors controlling their fate, is poorly understood. Here, we study MSCs in the perivascular microenvironment of endothelial capillaries by modifying a synthetic 3D biomimetic poly(ethylene glycol) (PEG)-hydrogel system in vitro We show that MSCs together with endothelial cells form micro-capillary networks specifically in soft PEG hydrogels. Transcriptome analysis of human MSCs isolated from engineered capillaries shows a prominent switch in extracellular matrix (ECM) production. We demonstrate that the ECM phenotypic switch of MSCs can be recapitulated in the absence of endothelial cells by functionalizing PEG hydrogels with the Notch-activator Jagged1. Moreover, transient culture of MSCs in Notch-inducing microenvironments reveals the reversibility of this ECM switch. These findings provide insight into the perivascular commitment of MSCs by use of engineered niche-mimicking synthetic hydrogels.

Role of growth factors in hematopoietic stem cell niche.

Hematopoietic stem cells (HSCs) produce new blood cells everyday throughout life, which is maintained by the self-renewal and differentiation ability of HSCs. This is not controlled by the HSCs alone, but rather by the complex and exquisite microenvironment surrounding the HSCs, which is called the bone marrow niche and consists of various bone marrow cells, growth factors, and cytokines. It is essential to understand the characteristic role of the stem cell niche and the growth factors in the niche formation. In this review, we describe the role of the bone marrow niche and factors for niche homeostasis, and also summarize the latest research related to stem cell niche.

Junctional Adhesion Molecule-C Mediates the Recruitment of Embryonic-Endothelial Progenitor Cells to the Perivascular Niche during Tumor Angiogenesis.

: The homing of Endothelial Progenitor Cells (EPCs) to tumor angiogenic sites has been described as a multistep process, involving adhesion, migration, incorporation and sprouting, for which the underlying molecular and cellular mechanisms are yet to be fully defined. Here, we studied the expression of Junctional Adhesion Molecule-C (JAM-C) by EPCs and its role in EPC homing to tumor angiogenic vessels. For this, we used mouse embryonic-Endothelial Progenitor Cells (e-EPCs), intravital multi-fluorescence microscopy techniques and the dorsal skin-fold chamber model. JAM-C was found to be expressed by e-EPCs and endothelial cells. Blocking JAM-C did not affect adhesion of e-EPCs to endothelial monolayers in vitro but, interestingly, it did reduce their adhesion to tumor endothelium in vivo. The most striking effect of JAM-C blocking was on tube formation on matrigel in vitro and the incorporation and sprouting of e-EPCs to tumor endothelium in vivo. Our results demonstrate that JAM-C mediates e-EPC recruitment to tumor angiogenic sites, i.e., coordinated homing of EPCs to the perivascular niche, where they cluster and interact with tumor blood vessels. This suggests that JAM-C plays a critical role in the process of vascular assembly and may represent a potential therapeutic target to control tumor angiogenesis.

The dystroglycan receptor maintains glioma stem cells in the vascular niche.

Glioblastomas (GBMs) are malignant central nervous system (CNS) neoplasms with a very poor prognosis. They display cellular hierarchies containing self-renewing tumourigenic glioma stem cells (GSCs) in a complex heterogeneous microenvironment. One proposed GSC niche is the extracellular matrix (ECM)-rich perivascular bed of the tumour. Here, we report that the ECM binding dystroglycan (DG) receptor is expressed and functionally glycosylated on GSCs residing in the perivascular niche. Glycosylated αDG is highly expressed and functional on the most aggressive mesenchymal-like (MES-like) GBM tumour compartment. Furthermore, we found that DG acts to maintain an MES-like state via tight control of MAPK activation. Antibody-based blockade of αDG induces robust ERK-mediated differentiation leading to reduced GSC potential. DG was shown to be required for tumour initiation in MES-like GBM, with constitutive loss significantly delaying or preventing tumourigenic potential in-vivo. These findings reveal a central role of the DG receptor, not only as a structural element, but also as a critical factor promoting MES-like GBM and the maintenance of GSCs residing in the perivascular niche.

Revealing the glioma cancer stem cell interactome, one niche at a time.

Glioblastoma (GBM) cancer stem cells (CSCs) are insidious. They extensively infiltrate brain tissue, resist radiotherapy and chemotherapy, and are thought to represent the ultimate drivers of disease progression. New research has identified CD109, a GPI-anchored protein, on a population of perivascular CSCs. Investigation of primary human tumour tissue suggests a role for CD109-expressing CSCs in the progression from low-grade to high-grade glioma, and animal modelling reveals a critical role for CD109 in the maintenance of the GBM CSC phenotype. Furthermore, CD109-expressing CSCs appear to drive the proliferation of adjacent non-stem tumour cells (NSTCs) in a rare example of CSC-NSTC cooperative interaction. With this Commentary, we highlight the newly revealed biology of CD109, and offer a synthesis of the published information on glioma CSCs in a variety of anatomical growth zones. We also discuss the landscape of interacting cells within GBM tumours, emphasizing the few reported examples of pro-tumourigenic, interactive tumour cell partnerships, as well as a variety of tumour cell-non-transformed neural cell interactions. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

The Multiaspect Functions of Periostin in Tumor Progression.

Extracellular matrix protein periostin is highly expressed in various tumors and plays a critical role in tumor development and progression. Periostin is mainly secreted by stromal cells such as cancer-associated fibroblasts, myofibroblasts, osteoblasts and bone marrow-derived mesenchymal stromal cells. But in some cases, tumor cells, especially cancer stem cells, can also produce periostin. Periostin has been shown to regulate multiple biological behaviors of tumor cells, including proliferation, survival, invasion, angiogenesis, metastasis and chemoresistance. Moreover, an excessive periostin deposition exerts a pivotal role in remodeling various tumor microenvironments, such as cancer stem cell niche, perivascular niche, premetastatic niche, immunosuppressive microenvironment, bone marrow microenvironment and other tumor growth-supportive microenvironments. In this review, we provide an update understanding of the multifaceted functions and mechanisms of periostin in tumor development and progression.

Hostile takeover: how tumours hijack pre-existing vascular environments to thrive.

An increasing body of evidence suggests that solid tumours do not require the generation of new blood vessels, i.e. angiogenesis, to successfully grow, and to colonize normal tissue. Instead, many tumour cells make the best use of what they find: pre-existing blood vessels of the host. In these cases, the host vasculature is incorporated by the growing tumour, resulting in a new organ consisting of malignant and non-malignant cell types. In consequence, pre-existing vessels are exploited by the tumour for optimal access to oxygen and nutrients. In this perspective article, the argument is made that tumour cells might gain even more: that is, access to the very special microenvironment of the perivascular niche. Here, specific cues for invasion, metastasis, survival, stem-like features, dormancy and, potentially, also immune escape exist - for non-malignant and malignant cells alike. The consequence of the hijacking of normal blood vessels and their perivascular niches by tumours is that antiangiogenic agents have little chance to work, and that tumour cells are better protected from the adverse effects of cytotoxic and targeted therapies. Thus, disturbing vascular hijacking could make tumours less resistant to established therapies. Concepts of how to do this are just starting to be explored. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

The multifaceted role of periostin in priming the tumor microenvironments for tumor progression.

Tumor microenvironment consists of tumor cells, stromal cells, extracellular matrix and a plethora of soluble components. The complex array of interactions between tumor cells and their surrounding tumor microenvironments contribute to the determination of the fate of tumor cells during tumorigenesis and metastasis. Matricellular protein periostin is generally absent in most adult tissues but is highly expressed in tumor microenvironments. Current evidence reveals that periostin plays a critical role in establishing and remodeling tumor microenvironments such as the metastatic niche, cancer stem cell niche, perivascular niche, pre-metastatic niche, fibrotic microenvironment and bone marrow microenvironment. Here, we summarize the current knowledge of the multifaceted role of periostin in the tumor microenvironments.