Previous studies suggest that neuronal activity may guide the development of synaptic connections in the central nervous system through mechanisms involving glutamate receptors and GTPase-dependent modulation of the actin cytoskeleton. Here we demonstrate by in vivo time-lapse imaging of optic tectal cells in Xenopus laevis tadpoles that enhanced visual activity driven by a light stimulus promotes dendritic arbor growth. The stimulus-induced dendritic arbor growth requires glutamate-receptor-mediated synaptic transmission, decreased RhoA activity and increased Rac and Cdc42 activity. The results delineate a role for Rho GTPases in the structural plasticity driven by visual stimulation in vivo.

Reactive astrocytes are integral to the glioma microenvironment. Connexin43 (Cx43) is a major gap junction protein in astrocytes and its expression is enhanced significantly in glioma-associated astrocytes, especially at the peri-tumoral region. Although downregulation of Cx43-mediated intercellular communication is associated with increased malignancy in tumor cells, the role of Cx43 in stromal cells in glioma progression is not defined. Using a mouse model consisting of syngeneic intracranial implantation of GL261 glioma cells into Nestin-Cre:Cx43(fl/fl) mice where Cx43 was eliminated in astrocytes, we demonstrate a role of astrocytic Cx43 in the dissemination of glioma cells from the tumor core. To determine whether heterocellular communication between astrocytes and glioma cells is essential for reduced invasion in the absence of astrocytic Cx43, we abolished channel formation between glioma cells and astrocytes by either knocking down Cx43 in glioma cells with short hairpin RNA (shRNA) or overexpressing a dominant-negative channel-defective Cx43-T154A mutant in these cells. Although Cx43shRNA in glioma cells reduced invasion, expression of Cx43-T154A had no effect on glioma invasion, suggesting tumoral Cx43 may influence motility independently from its channel function. Alteration in astrocytic Cx43 function, such as by replacing the wild-type allele with a C-terminal truncated Cx43 mutant exhibiting reduced intercellular coupling, is sufficient to reduce glioma spreading into the brain parenchyma. Our results reveal a novel role of astrocytic Cx43 in the formation of an invasive niche and raise the possibility to control glioma progression by manipulating the microenvironment.

The invasiveness of high-grade glioma is the primary reason for poor survival following treatment. Interaction between glioma cells and surrounding astrocytes are crucial to invasion. We investigated the role of gap junction mediated miRNA transfer in this context. By manipulating gap junctions with a gap junction inhibitor, siRNAs, and a dominant negative connexin mutant, we showed that functional glioma-glioma gap junctions suppress glioma invasion while glioma-astrocyte and astrocyte-astrocyte gap junctions promote it in an in vitro transwell invasion assay. After demonstrating that glioma-astrocyte gap junctions are permeable to microRNA, we compared the microRNA profiles of astrocytes before and after co-culture with glioma cells, identifying specific microRNAs as candidates for transfer through gap junctions from glioma cells to astrocytes. Further analysis showed that transfer of miR-5096 from glioma cells to astrocytes is through gap junctions; this transfer is responsible, in part, for the pro-invasive effect. Our results establish a role for glioma-astrocyte gap junction mediated microRNA signaling in modulation of glioma invasive behavior, and that gap junction coupling among astrocytes magnifies the pro-invasive signaling. Our findings reveal the potential for therapeutic interventions based on abolishing alteration of stromal cells by tumor cells via manipulation of microRNA and gap junction channel activity.

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