Identification of Microglial Cell Molecular Markers During Chick Embryo Brain Development and Human Xenograft Tumor Formation

Abstract

Glioblastoma (GBM) is the most aggressive and invasive human brain tumor, which despite advancement in surgery and immunology, only 10% of patients survive 18 months after diagnosis. The Galileo lab studies GBM, focusing on the role of the protein L1CAM on increasing the motility, proliferation, and invasiveness of GBM cells using in vitro cell tracking and a novel xenograft chick embryo brain tumor model. The work here focused on microglial cells, which are resident brain immune system cells that are not well understood. Studies in rodents and GBM patients showed that microglia play a critical role in promoting GBM growth via an activation of complex network of cytokines, chemokines and other metabolic factors that occur in the extracellular matrix. In the context of brain tumors, microglia promote neuroinflammation, which induces the BBB breakdown and inhibits antitumor immune responses. The first aim for my project was to find biomarkers that specifically identify microglial cells in normal chick embryo brain during development. The second aim was to use those markers in xenograft tumors in the chick embryo brain to look for any proinflammatory changes in microglial cells. Chick embryo brains were fixed, frozen, and cut into serial cryostat sections or fixed and vibratome sectioned, followed by immunofluorescent staining using antibodies or lectins that specifically identified microglial cells and endothelial cells in other model organisms. The optimal staining protocol required overnight primary antibody/lectin with 0.1% Triton X‐100 detergent and 5% normal goat serum in phosphate buffered saline. The antibodies and lectins investigated included Isolectin B4, Tomato (Lycopersicon esculentum) lectin, anti‐ferritin, anti‐laminin and CD45. Immunofluorescence analysis revealed CD45 to stain microglial cells with the most specificity. CD45 staining reveal microglial cell morphology to progressively change from a compact ameboid shape (E5) into ramified branched shape (E12 and E15). In addition to the increased quantity of ramified microglial cells in chick brain with xenograft human tumors, the microglia also appeared to be localized near endothelia. Further investigations are needed to verify the increased presence of reactive microglial cells and their interaction with tumor cells and angiogenesis.Support or Funding InformationThis work was supported by the Delaware INBRE program, with a grant from the National Institute of General Medical Sciences‐NIGMS (8 P20 GM103446‐16) from the National Institutes of Health, a grant to DSG from the National Cancer Institute, and a generous gift from Pamela S. Simpson ‘97 Translational Cancer Research Fund. I would like to thank Tyler Hellmig and Emily Kollenbroich for their guidance.