Microenvironmental determinants of glioma cell behavior are incompletely understood. The age and neuroanatomical location predilections of glioma occurrence indicate important interactions between the cell of origin and its microenvironment and suggest dysregulation of mechanisms of neurodevelopment and/or plasticity. We recently showed active neurons exert a mitogenic effect on normal neural precursor and oligodendroglial precursor cells, the putative cellular origins for high-grade glioma (HGG). We now preliminarily demonstrate that active neurons similarly promote HGG proliferation in vivo using optogenetic control of cortical neuronal activity in a patient-derived pediatric glioblastoma orthotopic xenograft model. Activity-regulated mitogen(s) are secreted, as the conditioned medium from optogenetically stimulated cortical slices promoted proliferation of pediatric and adult patient-derived HGG cultures. The synaptic protein neuroligin-3 (NLGN3) was identified as the leading candidate mitogen; soluble NLGN3 was sufficient and necessary to promote robust HGG cell proliferation. NLGN3 induced PI3K pathway activity and feed-forward expression of NLGN3 in glioma cells, providing mechanistic insight into its surprising role as a mitogen. NLGN3 expression levels in human HGG negatively correlated with patient overall survival. These findings indicate the important role of active neurons in the brain tumor microenvironment and identify secreted neuroligin-3 as an unexpected mechanism promoting neuronal activity-regulated cancer growth. The proposed work aims to investigate further the direct interaction between NLNG3 and high-grade glioma cells. We will directly probe the necessity of NLGN3 in neuronal activity regulated glioma growth in an in vivo optogenetic model. Further, the research will identify mechanisms of secretion, receptor binding, and downstream signaling pathways. The proposed work highlights the previously under-recognized importance of neuronal activity in the glioma microenvironment, will result in a better mechanistic understanding of the newly identified glioma mitogen NLGN3, and may identify novel therapeutic targets to better treat these deadly brain tumors.
High-grade gliomas (HGG), the leading cause of brain tumor death in both children and adults, occur in a striking spatiotemporal pattern that highlights the critical importance of the tumor microenvironment. The finding that active neurons in the microenvironment contribute to glioma growth through the release of NLGN3 opens numerous doors to a deeper mechanistic understanding of the role this protein plays in health and disease. Such mechanisms may include, as we investigate here, activity-regulated secretion coupled with a positive feed-forward effect on expression and activation of oncogenic signaling pathways. Neuronal-glioma cell interactions, including NLGN3 secretion and subsequent signaling in glioma cells, thus represent a novel set of therapeutic targets for this group of devastating brain tumors.
| Venkatesh, Humsa; Monje, Michelle (2017) Neuronal Activity in Ontogeny and Oncology. Trends Cancer 3:89-112 |
| Venkatesh, Humsa S; Tam, Lydia T; Woo, Pamelyn J et al. (2017) Targeting neuronal activity-regulated neuroligin-3 dependency in high-grade glioma. Nature 549:533-537 |
