Structural remodeling of tumor microtubes in IDH1 mutation shapes microRNA transfer in glioma

Tumor microtubes (TMs) are actin- and tubulin-based protrusions interconnecting glioma cells into multicellular networks linked to tumor aggressiveness, but the molecular signals exchanged through them and the impact of IDH1 mutation on TM function remain poorly defined. Using isogenic U87 glioma cells expressing wild-type IDH1 (U87^IDH-WT) or the IDH1-R132H mutant (U87^IDH-R132H), we combined quantitative immunofluorescence, RT-qPCR, fluorescent microRNA transfection, vertical co-culture with primary normal human astrocytes, and live-cell time-lapse imaging to analyze TM architecture, connexin-43 (Cx43) enrichment, and intercellular trafficking of the oncogenic miR-21 and tumor-suppressive miR-340. Cell viability, apoptosis, and proliferation were assessed by XTT, caspase-3/7 activity, and Ki-67 immunostaining. The IDH1-R132H mutation was associated with significant reductions in TM number, length, diameter, and Cx43 enrichment, indicating profound network remodeling. Despite these structural changes, TMs mediated intercellular microRNA transfer. miR-21 was overexpressed in glioma cells compared with astrocytes and promoted glioma cell survival while inducing apoptosis in astrocytes; TM-mediated miR-21 transfer was visualized between glioma cells, from glioma cells to astrocytes, and between astrocytes themselves. In contrast, miR-340 was downregulated in glioma cells, and its direct transfection markedly inhibited proliferation without astrocyte toxicity; fluorescent miR-340 was also detected within TMs and recipient glioma cells. Together, these findings identify TMs as structural features shaped by IDH1 mutation and as conduits for intercellular exchange of both oncogenic and tumor-suppressive microRNAs, providing a framework for understanding TM-mediated communication and its potential therapeutic exploitation in glioma.