Abstract 2885: Connexin 43-dependent miRNA transfer drives perivascular glioma invasion through dysregulation of astrocytes
Authors: McCutcheon Sean , Spray David C. 
Published: July 2021

Abstract
Background: Glioblastoma multiforme (GBM) invasion occurs along vasculature, and intercellular communication between glioma cells and the astrocyte endfoot may manipulate astrocytes to repress cell-matrix adhesion through transfer of miRNAs. Intercellular communication, specifically through Connexin 43 (Cx43) gap junction (GJ) channels, has been confoundingly demonstrated to both limit and facilitate GBM invasion. In solid tumors, Cx43 between tumor cells is correlated with a low invasion and the GJs have long been postulated to be required for growth control. By contrast, functional Cx43 channels between GBM and non-cancerous cells is correlated with high invasiveness, and GJs have been proposed to provide the pathway through which GBM drives surrounding astrocytes into a tumor-permissive state. How GJs participate in the transfer of genetic regulatory molecules from GBM to astrocytes is incompletely understood and might involve direct diffusion through Cx43 channels, GJ-facilitated exosomal transfer, and biased GJ endocytosis. In this study we examine astrocyte miRNA expression after contact with GBM and used an ex vivo assay to assess Cx43-dependent invasion.
Methods: Immortalized wild-type (WT) and connexin 43 (Cx43) knockout (KO) murine astrocytes were co-cultured for 24 hours with U87 GBM cells expressing cytosolic GFP. Cells were separated by FACS and collected for miRNAseq. For ex vivo invasion model, 350µm whole brain coronal slices (from WT and GFAP-Cre Cx43-/- C57BL/6J mice) were obtained via vibratome in high-sucrose ACSF and cultured for &gt;12 hours in 20% serum recovery medium. At that time, 250-350µm U87 spheroids (4-8 per slice) expressing cytosolic mCherry (either WT or CRISPR-generated Cx43 KO U87 cell lines) were injected into the cerebral cortex. Slices were cultured for up to 72 hours, fixed, and cleared by SeeDB protocol. Invasion was imaged by confocal microscopy at 10x. Extent of perivascular invasion by the injected tumor spheroids was quantified using Sholl analysis to compare number and lengths of branches.
Results: miRNASeq identified a cohort of &gt;10 miRNAs that were upregulated in WT astrocytes, but not KO astrocytes, co-cultured with GBM. Some of these miRNAs are known to have elevated expression in GBM and have predicted cell adhesion protein targets. GBM pervascular invasion was substantially lower for WT-U87 spheroids in GFAP-Cre Cx43-/- slice when compared to WT-U87 in WT slice or Cx43 KO U87 in Cx43-/- slice.
Conclusions: Specific miRNAs are transferred via Cx43-mediated mechanisms from GBM to astrocytes and may play a role in astrocyte-matrix adhesion at the endfoot, creating an opening for GBM invasion. Initial slice culture data indicate that functional GBM-GBM GJs inhibit peritumoral outgrowth, whereas astrocyte-GBM GJs are critical for invasion, presumably facilitating remodeling of host tissue by the miRNAs to accommodate invading GBM.
Citation Format: Sean McCutcheon, David C. Spray. Connexin 43-dependent miRNA transfer drives perivascular glioma invasion through dysregulation of astrocytes [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2885.