Platelet-derived growth factor (PDGF) signaling, through the ligand PDGF-A and its receptor PDGFRA, is important for the growth and maintenance of oligodendrocyte progenitor cells (OPCs) in the central nervous system (CNS). PDGFRA signaling is downregulated prior to OPC differentiation into mature myelinating oligodendrocytes. By contrast, PDGFRA is often genetically amplified or mutated in many types of gliomas, including diffuse midline glioma (DMG) where OPCs are considered the most likely cell-of-origin. The cellular and molecular changes that occur in OPCs in response to unregulated PDGFRA expression, however, are not known.Here, we created a conditional knock-in (KI) mouse that overexpresses wild type (WT) human PDGFRA (hPDGFRA) in prenatal Olig2-expressing progenitors, and examined in vivo cellular and molecular consequences.The KI mice exhibited stunted growth, ataxia, and a severe loss of myelination in the brain and spinal cord. When combined with the loss of p53, a tumor suppressor gene whose activity is decreased in DMG, the KI mice failed to develop tumors but still exhibited hypomyelination. RNA-sequencing analysis revealed decreased myelination gene signatures, indicating a defect in oligodendroglial development. Mice overexpressing PDGFRA in prenatal GFAP-expressing progenitors, which give rise to a broader lineage of cells than Olig2-progenitors, also developed myelination defects.Our results suggest that embryonic overexpression of hPDGFRA in Olig2- or GFAP-progenitors is deleterious to OPC development and leads to CNS hypomyelination.
Abstract Diffuse intrinsic pontine glioma (DIPG) is an incurable brain tumor that arises in the pons of children. Recent studies using single cell RNA-seq and enhancer analysis of DIPG tumor cells, together with analysis of the developing human pons, strongly suggest that an oligodendrocyte progenitor cell is the most likely cell-of-origin for DIPG. Here we describe a novel mouse model by expressing PDGF-B, with H3.3K27M or H3.3 wild-type in Olig2-expressing progenitors via injection into the 4th ventricle using Olig2-tva-cre;p53fl/fl mice. H3.3K27M tumors have high rate of Ki-67, Sox2, and Olig2 positivity and show a higher rate of leptomeningeal dissemination than H3.3 wild-type tumors (95.2％ vs 68.8%, p=0.0303) and mice harboring H3.3K27M tumors demonstrate a significantly shorter survival period than those harboring H3.3 wild-type tumors (31 days vs. 37 days, p=0.0473). While there is not any difference in survival between mice harboring PDGF-B; p53 wild-type; H3.3K27M tumors and those harboring PDGF-B; p53 wild-type; H3.3 wild-type tumors at the 6-month endpoint, we found that H3.3K27M tumors show a higher rate of high-grade glioma than H3.3 wild-type tumors (100% vs. 41.7%, p=0.0017). RNA-seq analysis identified 25 significantly differentially expressed genes with 23 upregulated and 2 downregulated genes in the PDGF-B; p53 null; H3.3K27M tumors compared with the H3.3 wild-type tumors. Phox2b, which is the most upregulated gene in the PDGF-B; p53 null; H3.3K27M tumors, was validated by qRT-PCR and expressed only in brainstem tumors and not expressed in tumors located in any other areas. IHC with Phox2b also revealed positivity in PDGF-B; p53 null; H3.3K27M tumors located only in the brainstem. Ongoing work includes validation of other significant differentially expressed genes as well as elucidation of their role in K27M-mediated gliomagenesis.
Abstract Significant progress has been made molecularly defining pediatric high-grade gliomas (pHGG), including diffuse midline gliomas (DMG), yet little progress has been made with respect to delineating the inflammatory microenvironment. We utilize molecularly defined human samples and immunocompetent genetic mouse models to study how tumor location and genetic driver mutations influence the tumor microenvironment (TME). We report human DMGs have a significant enrichment of Elane+ neutrophils compared to their hemispheric counterparts. We validate this utilizing the RCAS-Tva mouse model, which histologically and genetically recapitulates human pHGGs. Using this model we demonstrate each distinct pHGG/DMG entity confers unique transcriptional identities as made evident by NanoString RNA expression profiles and whole-tumor single-cell RNA sequencing. H3.3WT DMGs and H3.3K27M DMGs cluster together and have high expression of inflammatory genes such as Ptprc, Trem2, Lag3, and Cd274 while H3.3WT and H3.3G34R hemispheric tumors, and H3.1K27M DMGs cluster together with low expression of these genes. Several genes were found to significantly correlate with median survival in human bulk RNA sequencing data including IL13RA2. Flow cytometry and immunohistochemistry demonstrate H3WT DMGs are enriched for monocytes and lymphocytes while H3.3K27M DMGs are enriched for microglia. Genetic perturbations were made to prevent TAM or neutrophil infiltration, including targeting Ccl3, Cxcl1, and Ccl8/12. Only Ccl8/12 knockout resulted in significant extension of survival in H3K27M DMGs, which was met with an increase in CD4+ and CD8+ T-cells and decreased neutrophil infiltration. CD4+ T-cell depletion and anti-PD1 therapy was performed to further study the role of lymphocyte infiltration in DMGs. Lastly, CCR1/CCR5 inhibitors were utilized to abrogate TAM infiltration in DMGs, resulting in decreased microglia infiltration and significant survival extension comparable to radiation therapy. Together, this work provides the foundation for developing or improving immunotherapies designed at specific subgroups of pHGG and DMGs, such as CAR-T-cell, oncolytic viral therapy, and checkpoint blockade.
<p>Graph depicting fold change of Abcg2, Abcb1a, and Abcb1b transcripts of nestin-expressing brainstem progenitors, ABC KO tumor cell-lines, and ABC WT tumor cell-lines</p>
Abstract Many immunotherapies act by enhancing T cell killing of tumor cells. CD8+ cytotoxic T cells recognize antigens presented by class I major histocompatibility complex (MHC-I) proteins on tumor cells. Here we show that medulloblastomas lacking the p53 tumor suppressor do not express surface MHC-I and are therefore resistant to immune rejection. Mechanistically, this is because p53 regulates expression of the peptide transporter Tap1 and the aminopeptidase Erap1, which are required for MHC-I trafficking to the cell surface. Treatment with tumor necrosis factor (TNF) or lymphotoxin beta receptor agonist (LTβRag) rescues expression of Erap1, Tap1 and MHC-I on p53-mutant tumor cells. In vivo, TNF treatment prolongs survival and markedly augments the efficacy of the immune checkpoint inhibitor anti-PD-1. These studies identify p53 as a key regulator of immune evasion in vivo, and suggest that TNF could be used to enhance sensitivity of p53-mutant tumors to immunotherapy.
// Sridevi Yadavilli 1 , Joseph Scafidi 2 , Oren J. Becher 3 , Amanda M. Saratsis 4 , Rebecca L. Hiner 5 , Madhuri Kambhampati 1 , Santi Mariarita 6 , Tobey J. MacDonald 7 , Kari-Elise Codispoti 8 , Suresh N. Magge 9 , Jyoti K. Jaiswal 1,10 , Roger J. Packer 11 and Javad Nazarian 1,10 1 Research Center for Genetic Medicine, Children’s National Health System, Washington, DC, USA 2 Department of Neurology and Center for Neuroscience Research, Children’s National Health System, Washington, DC, USA 3 Department of Pediatrics and Pathology, Preston Robert Tisch Brain Tumor Center, Duke University Medical Center, Durham, NC, USA 4 Division of Neurosurgery, Ann & Robert H. Lurie Children’s Hospital of Chicago, Chicago, IL, USA 5 Human Oncology and Pathogenesis Program, Memorial Sloan-Kettering Cancer Center, NY, USA 6 Department of Pathology and Lab Medicine, The Children’s Hospital of Philadelphia, Philadelphia, PA, USA 7 Department of Pediatrics, Emory University School of Medicine, Atlanta, GA, USA 8 Department of Pathology, Children’s National Health System, Washington, DC, USA 9 Division of Neurosurgery, Children’s National Health System, Washington, DC, USA 10 Department of Integrative Systems Biology, George Washington University School of Medicine and Health Sciences, Washington, DC, USA 11 Brain Tumor Institute, Center for Neuroscience and Behavioral Medicine, Children’s National Health System, Washington, DC, USA Correspondence to: Javad Nazarian, email: // Keywords : DIPG, NG2, PDGF, histone 3, glioma Received : March 04, 2015 Accepted : March 11, 2015 Published : March 30, 2015 Abstract Diffuse intrinsic pontine gliomas (DIPGs) have a dismal prognosis and are poorly understood brain cancers. Receptor tyrosine kinases stabilized by neuron-glial antigen 2 (NG2) protein are known to induce gliomagenesis. Here, we investigated NG2 expression in a cohort of DIPG specimens (n= 50) . We demonstrate NG2 expression in the majority of DIPG specimens tested and determine that tumors harboring histone 3.3 mutation express the highest NG2 levels. We further demonstrate that microRNA 129-2 (miR129-2) is downregulated and hypermethylated in human DIPGs, resulting in the increased expression of NG2. Treatment with 5-Azacytidine, a methyltransferase inhibitor, results in NG2 downregulation in DIPG primary tumor cells in vitro . NG2 expression is altered (symmetric segregation) in mitotic human DIPG and mouse tumor cells. These mitotic cells co-express oligodendrocyte (Olig2) and astrocyte (glial fibrillary acidic protein, GFAP) markers, indicating lack of terminal differentiation. NG2 knockdown retards cellular migration in vitro, while NG2 expressing neurospheres are highly tumorigenic in vivo, resulting in rapid growth of pontine tumors. NG2 expression is targetable in vivo using miR129-2 indicating a potential avenue for therapeutic interventions. This data implicates NG2 as a molecule of interest in DIPGs especially those with H3.3 mutation.
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