Samuel H. Cheshier

Wnt-mediated self-renewal of neural stem/progenitor cells

In this work we have uncovered a role for Wnt signaling as an important regulator of stem cell self-renewal in the developing brain. We identified Wnt-responsive cells in the subventricular zone of the developing E14.5 mouse brain. Responding cell populations were enriched for self-renewing stem cells in primary culture, suggesting that Wnt signaling is a hallmark of self-renewing activity in vivo. We also tested whether Wnt signals directly influence neural stem cells. Using inhibitors of the Wnt pathway, we found that Wnt signaling is required for the efficient cloning and expansion of single-cell derived populations that are able to generate new stem cells as well as neurons, astrocytes, and oligodendrocytes. The addition of exogenous Wnt3a protein enhances clonal outgrowth, demonstrating not only a critical role for the Wnt pathway for the regulation of neurogenesis but also its use for the expansion of neural stem cells in cell culture and in tissue engineering.

BET Bromodomain Inhibition of MYC-Amplified Medulloblastoma

Purpose: MYC-amplified medulloblastomas are highly lethal tumors. Bromodomain and extraterminal (BET) bromodomain inhibition has recently been shown to suppress MYC-associated transcriptional activity in other cancers. The compound JQ1 inhibits BET bromodomain-containing proteins, including BRD4. Here, we investigate BET bromodomain targeting for the treatment of MYC-amplified medulloblastoma. Experimental Design: We evaluated the effects of genetic and pharmacologic inhibition of BET bromodomains on proliferation, cell cycle, and apoptosis in established and newly generated patient- and genetically engineered mouse model (GEMM)-derived medulloblastoma cell lines and xenografts that harbored amplifications of MYC or MYCN. We also assessed the effect of JQ1 on MYC expression and global MYC-associated transcriptional activity. We assessed the in vivo efficacy of JQ1 in orthotopic xenografts established in immunocompromised mice. Results: Treatment of MYC-amplified medulloblastoma cells with JQ1 decreased cell viability associated with arrest at G1 and apoptosis. We observed downregulation of MYC expression and confirmed the inhibition of MYC-associated transcriptional targets. The exogenous expression of MYC from a retroviral promoter reduced the effect of JQ1 on cell viability, suggesting that attenuated levels of MYC contribute to the functional effects of JQ1. JQ1 significantly prolonged the survival of orthotopic xenograft models of MYC-amplified medulloblastoma (P < 0.001). Xenografts harvested from mice after five doses of JQ1 had reduced the expression of MYC mRNA and a reduced proliferative index. Conclusion: JQ1 suppresses MYC expression and MYC-associated transcriptional activity in medulloblastomas, resulting in an overall decrease in medulloblastoma cell viability. These preclinical findings highlight the promise of BET bromodomain inhibitors as novel agents for MYC-amplified medulloblastoma. Clin Cancer Res; 20(4); 912–25. ©2013 AACR.

Epigenetic targeting of Hedgehog pathway transcriptional output through BET bromodomain inhibition

Hedgehog signaling drives oncogenesis in several cancers, and strategies targeting this pathway have been developed, most notably through inhibition of Smoothened (SMO). However, resistance to Smoothened inhibitors occurs by genetic changes of Smoothened or other downstream Hedgehog components. Here we overcome these resistance mechanisms by modulating GLI transcription through inhibition of bromo and extra C-terminal (BET) bromodomain proteins. We show that BRD4 and other BET bromodomain proteins regulate GLI transcription downstream of SMO and suppressor of fused (SUFU), and chromatin immunoprecipitation studies reveal that BRD4 directly occupies GLI1 and GLI2 promoters, with a substantial decrease in engagement of these sites after treatment with JQ1, a small-molecule inhibitor targeting BRD4. Globally, genes associated with medulloblastoma-specific GLI1 binding sites are downregulated in response to JQ1 treatment, supporting direct regulation of GLI activity by BRD4. Notably, patient- and GEMM (genetically engineered mouse model)-derived Hedgehog-driven tumors (basal cell carcinoma, medulloblastoma and atypical teratoid rhabdoid tumor) respond to JQ1 even when harboring genetic lesions rendering them resistant to Smoothened antagonists. Altogether, our results reveal BET proteins as critical regulators of Hedgehog pathway transcriptional output and nominate BET bromodomain inhibitors as a strategy for treating Hedgehog-driven tumors with emerged or a priori resistance to Smoothened antagonists.

Glioblastoma Multiforme: Exploratory Radiogenomic Analysis by Using Quantitative Image Features

PURPOSE To derive quantitative image features from magnetic resonance (MR) images that characterize the radiographic phenotype of glioblastoma multiforme (GBM) lesions and to create radiogenomic maps associating these features with various molecular data. MATERIALS AND METHODS Clinical, molecular, and MR imaging data for GBMs in 55 patients were obtained from the Cancer Genome Atlas and the Cancer Imaging Archive after local ethics committee and institutional review board approval. Regions of interest (ROIs) corresponding to enhancing necrotic portions of tumor and peritumoral edema were drawn, and quantitative image features were derived from these ROIs. Robust quantitative image features were defined on the basis of an intraclass correlation coefficient of 0.6 for a digital algorithmic modification and a test-retest analysis. The robust features were visualized by using hierarchic clustering and were correlated with survival by using Cox proportional hazards modeling. Next, these robust image features were correlated with manual radiologist annotations from the Visually Accessible Rembrandt Images (VASARI) feature set and GBM molecular subgroups by using nonparametric statistical tests. A bioinformatic algorithm was used to create gene expression modules, defined as a set of coexpressed genes together with a multivariate model of cancer driver genes predictive of the modules expression pattern. Modules were correlated with robust image features by using the Spearman correlation test to create radiogenomic maps and to link robust image features with molecular pathways. RESULTS Eighteen image features passed the robustness analysis and were further analyzed for the three types of ROIs, for a total of 54 image features. Three enhancement features were significantly correlated with survival, 77 significant correlations were found between robust quantitative features and the VASARI feature set, and seven image features were correlated with molecular subgroups (P < .05 for all). A radiogenomics map was created to link image features with gene expression modules and allowed linkage of 56% (30 of 54) of the image features with biologic processes. CONCLUSION Radiogenomic approaches in GBM have the potential to predict clinical and molecular characteristics of tumors noninvasively. Online supplemental material is available for this article.

Intracarotid Injection of Fluorescence Activated Cell-Sorted CD49d-Positive Neural Stem Cells Improves Targeted Cell Delivery and Behavior After Stroke in a Mouse Stroke Model

Background and Purpose— Intravascular delivery of neural stem cells (NSCs) after stroke has been limited by the low efficiency of transendothelial migration. Vascular cell adhesion molecule-1 is an endothelial adhesion molecule known to be upregulated early after stroke and is responsible for the firm adhesion of inflammatory cells expressing the surface integrin, CD49d. We hypothesize that enriching for NSCs that express CD49d and injecting them into the carotid artery would improve targeted cell delivery to the injured brain. Methods— Mouse NSCs were analyzed for the expression of CD49d by fluorescence activated cell sorting. A CD49d-enriched (CD49d+) (>95%) and -depleted (CD49d–; <5%) NSC population was obtained by cell sorting. C57/Bl6 mice underwent left-sided hypoxia–ischemia surgery and were assigned to receive 3×105 CD49d+, CD49d– NSCs, or vehicle injection into the left common carotid artery 48 hours after stroke. Behavioral recovery was measured using a rotarod for 2 weeks after cell injection. Results— Fluorescence activated cell sorting analysis revealed 25% CD49d+ NSCs. In a static adhesion assay, NSCs adhered to vascular cell adhesion molecule-1 in a dose-dependent manner. Significantly more NSCs were found in the cortex, the hippocampus, and the subventricular zone in the ischemic hemisphere in animals receiving CD49d+ NSCs as compared with CD49d– NSCs (P<0.05). Animals treated with CD49d+ cells showed a significantly better behavioral recovery as compared with CD49d– and vehicle-treated animals. Conclusions— We show that enrichment of NSCs by fluorescence activated cell sorting for the surface integrin, CD49d, and intracarotid delivery promotes cell homing to the area of stroke in mice and improves behavioral recovery.

Cerebrospinal fluid and plasma oxytocin concentrations are positively correlated and negatively predict anxiety in children

The neuropeptide oxytocin (OXT) exerts anxiolytic and prosocial effects in the central nervous system of rodents. A number of recent studies have attempted to translate these findings by investigating the relationships between peripheral (e.g., blood, urinary and salivary) OXT concentrations and behavioral functioning in humans. Although peripheral samples are easy to obtain in humans, whether peripheral OXT measures are functionally related to central OXT activity remains unclear. To investigate a possible relationship, we quantified OXT concentrations in concomitantly collected cerebrospinal fluid (CSF) and blood samples from child and adult patients undergoing clinically indicated lumbar punctures or other CSF-related procedures. Anxiety scores were obtained in a subset of child participants whose parents completed psychometric assessments. Findings from this study indicate that plasma OXT concentrations significantly and positively predict CSF OXT concentrations (r=0.56, P=0.0064, N=27). Moreover, both plasma (r=−0.92, P=0.0262, N=10) and CSF (r=−0.91, P=0.0335, N=10) OXT concentrations significantly and negatively predicted trait anxiety scores, consistent with the preclinical literature. Importantly, plasma OXT concentrations significantly and positively (r=0.96, P=0.0115, N=10) predicted CSF OXT concentrations in the subset of child participants who provided behavioral data. This study provides the first empirical support for the use of blood measures of OXT as a surrogate for central OXT activity, validated in the context of behavioral functioning. These preliminary findings also suggest that impaired OXT signaling may be a biomarker of anxiety in humans, and a potential target for therapeutic development in individuals with anxiety disorders.

Hematopoietic stem cells: challenges to expectations

The past year provided a number of challenges to our expectations regarding hematopoietic stem cell (HSC) biology. Evidence has emerged that HSCs arise intraembryonically before they can be detected in the yolk sac. A number of genes that may regulate the formation, self-renewal, or differentiation of HSC have been identified. New markers for purifying HSCs have also been described. Although different groups have attributed different properties to HSCs, it now appears that the differences may be explained by variations in assay conditions rather than by differences in the HSCs themselves. Finally, insights have emerged into the complexity of the regulation of HSC proliferation and adhesion properties.

New vessel formation in the central nervous system during tumor growth, vascular malformations, and Moyamoya

In the normal adult brain, blood vessel formation is tightly down-regulated. However, pathologic processes such as brain tumors can increase the proportion of endothelial cells involved in angiogenesis. When this process is initiated, a complex series of timed events result in new vessel formation. In this review, we will describe the process of angiogenesis in the central nervous system. We will discuss the roles of Vascular Endothelial Growth Factor (VEGF), Fibroblast Growth Factor (FGF), Angiopoietins, Platelet Derived Growth Factor (PDGF), and integrins in angiogenesis. We will also look into their significance in disease processes such as neoplasms, arteriovenous malformations (AVM), and Moyamoya disease.

Usp16 contributes to somatic stem-cell defects in Down’s syndrome

Down’s syndrome results from full or partial trisomy of chromosome 21. However, the consequences of the underlying gene–dosage imbalance on adult tissues remain poorly understood. Here we show that in Ts65Dn mice, which are trisomic for 132 genes homologous to genes on human chromosome 21, triplication of Usp16 reduces the self-renewal of haematopoietic stem cells and the expansion of mammary epithelial cells, neural progenitors and fibroblasts. In addition, Usp16 is associated with decreased ubiquitination of Cdkn2a and accelerated senescence in Ts65Dn fibroblasts. Usp16 can remove ubiquitin from histone H2A on lysine 119, a critical mark for the maintenance of multiple somatic tissues. Downregulation of Usp16, either by mutation of a single normal Usp16 allele or by short interfering RNAs, largely rescues all of these defects. Furthermore, in human tissues overexpression of USP16 reduces the expansion of normal fibroblasts and postnatal neural progenitors, whereas downregulation of USP16 partially rescues the proliferation defects of Down’s syndrome fibroblasts. Taken together, these results suggest that USP16 has an important role in antagonizing the self-renewal and/or senescence pathways in Down’s syndrome and could serve as an attractive target to ameliorate some of the associated pathologies.

Hematopoietic Stem Cell–Derived Pericytic Cells in Brain Tumor Angio-Architecture

Bone marrow-derived cells are recruited into tumor vasculature in response to angiogenic signals, and some of the cells within the newly forming tumor vessels are hematopoietic stem cells (HSCs) in origin. Previous studies suggest that bone marrow-derived pericytes are associated with newly formed vessels in tumors. In this study, we used an orthotopic rat glioma model (RT-2/RAG) to examine the contribution of long-term hematopoietic stem cell (LT-HSC)-derived pericytic cells to brain tumor angiogenesis. Mice (RAG-2/KO5.2) were lethally irradiated, and their hematopoietic cells were repopulated by transplantation of double fluorescence-activated cell-sorted LT-HSCs that express green fluorescent protein (GFP+). RT-2/RAG cells were then injected into the striatum of the chimeric mice 6 weeks post-transplantation. The animals were sacrificed 9 days after tumor implantation, and the incorporation and lineage-specific marker expression profile of the GFP+ cells within the growing tumor and tumor periphery were analyzed. LT-HSC-derived GFP+ cells were noted to incorporate onto the surface of tumor vessels within the perivascular space. LT-HSC-derived GFP+ cells express the pericyte progenitor marker, platelet-derived growth factor receptor-beta (PDGFR beta), as well as mature perictyte markers such as nerve/glial antigen 2 proteoglycan (NG2), alpha-smooth muscle actin (alpha SMA), and desmin. These LT-HSC-derived cells may represent a population of progenitor or committed pericytes within the neovascular tree and may play a role in shaping the angio-architecture in the vascular niche of brain tumors.