Inflammatory Mediators in Glioma Microenvironment Play a Dual Role in Gliomagenesis and Mesenchymal Stem Cell Homing: Implication for Cellular Therapy

Glioblastoma is the most aggressive malignant primary brain tumor, with a dismal prognosis and a devastating overall survival. Despite aggressive surgical resection and adjuvant treatment, average survival remains approximately 14.6 months. The brain tumor microenvironment is heterogeneous, comprising multiple populations of tumor, stromal, and immune cells. Tumor cells evade the immune system by suppressing several immune functions to enable survival. Gliomas release immunosuppressive and tumor-supportive soluble factors into the microenvironment, leading to accelerated cancer proliferation, invasion, and immune escape. Mesenchymal stem cells (MSCs) isolated from bone marrow, adipose tissue, or umbilical cord are a promising tool for cell-based therapies. One crucial mechanism mediating the therapeutic outcomes often seen in MSC application is their tropism to sites of injury. Furthermore, MSCs interact with host immune cells to regulate the inflammatory response, and data points to the possibility of using MSCs to achieve immunomodulation in solid tumors. Interleukin 1β, interleukin 6, tumor necrosis factor α, transforming growth factor β, and stromal cell-derived factor 1 are notably up-regulated in glioblastoma and dually promote immune and MSC trafficking. Mesenchymal stem cells have widely been regarded as hypoimmunogenic, enabling this cell-based administration across major histocompatibility barriers. In this review, we will highlight (1) the bidirectional communication of glioma cells and tumor-associated immune cells, (2) the inflammatory mediators enabling leukocytes and transplantable MSC migration, and (3) review preclinical and human clinical trials using MSCs as delivery vehicles. Mesenchymal stem cells possess innate abilities to migrate great distances, cross the blood-brain barrier, and communicate with surrounding cells, all of which make them desirable "Trojan horses" for brain cancer therapy.

Biomaterial-engineering and neurobiological approaches for regenerating the injured cerebral cortex

The cerebral cortex is responsible for higher functions of the central nervous system (CNS), such as movement, sensation, and cognition. When the cerebral cortex is severely injured, these functions are irreversibly impaired. Although recent neurobiological studies reveal that the cortex has the potential for regeneration, therapies for functional recovery face some technological obstacles. Biomaterials have been used to evoke regenerative potential and promote regeneration in several tissues, including the CNS. This review presents a brief overview of new therapeutic strategies for cortical regeneration from the perspectives of neurobiology and biomaterial engineering, and discusses a promising technology for evoking the regenerative potential of the cerebral cortex.

DYRK1A-mediated Cyclin D1 Degradation in Neural Stem Cells Contributes to the Neurogenic Cortical Defects in Down Syndrome

Alterations in cerebral cortex connectivity lead to intellectual disability and in Down syndrome, this is associated with a deficit in cortical neurons that arises during prenatal development. However, the pathogenic mechanisms that cause this deficit have not yet been defined. Here we show that the human DYRK1A kinase on chromosome 21 tightly regulates the nuclear levels of Cyclin D1 in embryonic cortical stem (radial glia) cells, and that a modest increase in DYRK1A protein in transgenic embryos lengthens the G1 phase in these progenitors. These alterations promote asymmetric proliferative divisions at the expense of neurogenic divisions, producing a deficit in cortical projection neurons that persists in postnatal stages. Moreover, radial glial progenitors in the Ts65Dn mouse model of Down syndrome have less Cyclin D1, and Dyrk1a is the triplicated gene that causes both early cortical neurogenic defects and decreased nuclear Cyclin D1 levels in this model. These data provide insights into the mechanisms that couple cell cycle regulation and neuron production in cortical neural stem cells, emphasizing that the deleterious effect of DYRK1A triplication in the formation of the cerebral cortex begins at the onset of neurogenesis, which is relevant to the search for early therapeutic interventions in Down syndrome.

Cytotoxic effects of G(M1) ganglioside and amyloid β-peptide on mouse embryonic neural stem cells

AD (Alzheimer’s disease) is a neurodegenerative disease and the most common form of dementia. One of the pathological hallmarks of AD is the aggregation of extracellular Aβs (amyloid β-peptides) in senile plaques in the brain. The process could be initiated by seeding provided by an interaction between G_M1 ganglioside and Aβs. Several reports have documented the bifunctional roles of Aβs in NSCs (neural stem cells), but the precise effects of G_M1 and Aβ on NSCs have not yet been clarified. We evaluated the effect of G_M1 and Aβ-(1–40) on mouse NECs (neuroepithelial cells), which are known to be rich in NSCs. No change of cell number was detected in NECs cultured in the presence of either G_M1 or Aβ-(1–40). On the contrary, a decreased number of NECs were cultured in the presence of a combination of G_M1 and Aβ-(1–40). The exogenously added G_M1 and Aβ-(1–40) were confirmed to incorporate into NECs. The Ras–MAPK (mitogen-activated protein kinase) pathway, important for cell proliferation, was intact in NECs simultaneously treated with G_M1 and Aβ-(1–40), but caspase 3 was activated. NECs treated with G_M1 and Aβ-(1–40) were positive in the TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling) assay, an indicator of cell death. It was found that G_M1 and Aβ-(1–40) interacted in the presence of cholesterol and sphingomyelin, components of cell surface microdomains. The cytotoxic effect was found also in NSCs prepared via neurospheres. These results indicate that Aβ-(1–40) and G_M1 co-operatively exert a cytotoxic effect on NSCs, likely via incorporation into NEC membranes, where they form a complex for the activation of cell death signalling.