The cancer stem cell hypothesis in spontaneous canine gliomas: from tumors to neurogenesis in the adult dog

Cancer stem cells (CSCs) can originate both the transformation of normal stem cells as progenitors or from more differentiated cells that have acquired capacity for self-renewal. The hypothesis of the CSCs proposes that a specific subpopulation of cancer stem cells is responsible for maintaining the tumor. This hypothesis has been demonstrated in a wide variety of human tumors and canines, including gliomas. Nestin, a specific intermediate filament cytoskeleton and CD133 a cell membrane glycoprotein related with polarization, migration and interaction between cells and the extracellular matrix; both are used as markers for the detection and study of neural stem cells. In the present study, a total of 20 canine brain tumors were examined and diagnosed histologically as gliomas, according to the international classification of tumors of the central nervous system in humans. They were then studied by immunohistochemistry (IHC) using Nestin and CD133 as markers of neural precursors; Neu-N, doublecortin (DCx) and βIII tubulin as neuronal markers; glial fibrillary acidic protein (GFAP), vimentin, S-100 protein and protein Olig2 as glial markers and Ki67 as a marker for cell proliferation. These tumors are characterized as neuropathologically: Oligodendogliomas (Grade II), anaplastic oligodendrogliomas (Grade III), Mixed glioma (grade II) and glioblastomas (grade IV). IHC evaluation showed more positive for Nestin and CD133 in high-grade tumors. Olig2 was expressed in most tumors, whereas positivity for GFAP was higher in the mixed glioma and glioblastomas. Differentiated neuron markers were negative in all tumors, while in some high grade gliomas DCX positivity was detected. Our results agree with the hypothesis of the CSCs, confirming the presence of undifferentiated neural precursors in canine gliomas, increasing their number in higher grade tumors. Subsequently, the potential for expansion in vitro of cells extracted from areas of the center and periphery of canine gliomas were cultured in vitro by assaying neurospheres in order to assess the ability of proliferation, expansion and survival of the neural progenitors that are part of the canine glial tumors canines. Neurospheres of all samples corresponding to the center of the tumor indicating the existence of neural precursors in tumors of all grades of glioma were obtained canine. Furthermore, the amount of cells capable of proliferating was increased in higher grade tumors, indicating the possible influence of these neural precursors in malignant gliomas canine behavior. The neural precursors isolated from all samples with expandability were able to differentiate into neural three lines indicating their multipotentiality. These results demonstrated the involvement of neural progenitors in canine gliomas, according to the second criterion demonstration of the hypothesis of CSCs. In parallel neural stem cells from normal postnatal adult dog brain phases were studied. The cytoarchytecture of its main niche it was studied in the adult brain. This corresponds to previous niche subventricular zone (SVZ) which has been widely described in human and murine species. By histological, immunohistochemical, ultrastructural and cell culture studies, the presence of multipotent neural cells in SVZ was confirmed canine, which reside in neurogenic niches and is structurally and cellularlly similar to those described in other mammalian species. Moreover, the architecture of these components is similar to that described in humans, probably related with complexity similar brain structures, which could be related to adult neurogenesis related processes. Finally, chains of migratory neuroblasts associated with vascular structures outside the SVZ indicating high migration capability and adaptability of resident neural stem cells in the brain of adult and comparable dog with similar events described in other mammalian species were identified including human species. The results of the studies conducted in this thesis conclude that the dog can be a relevant animal model in future related to the identification of new therapeutic targets in the field of comparative oncology studies, as well as a model to consider in studies and the progress of studies related to neurogenesis in the adult individual.