(The) mechanisms and dynamics of marginal glioblastoma invasion

Abstract

Glioblastoma (GBM) is a severely malignant cancer due to its deadliest invasion, leaving nonresectable clusters in brain tissues. While unraveling the exact mechanism of GBM invasion would be the key for developing the effective therapy, there have been no appropriate pre-clinical GBM models that recapitulate the human GBM. Here, we present a spontaneous mouse GBM model that features robust white matter invasion, typically observed in GBM patients. We then examined the brain-wide three dimensional (3D) landscape of GBM invasion along the white matter tract using tissue clearing. Transmission electron microscope (TEM) imaging highlights the existence of matrix-poor space between invading GBM cells and myelinated axon bundle. In vitro 3D invasion assay reveals GBM cells undergoing dynamic cycles of fast moving and stationary phases, accompanied by repeated long forward protrusion and rear contraction, atypical of mesenchymal crawling behavior. This saltatory migration mode demonstrates the GBM cells’ unique invasion phenotypes that resemble specific characteristics of the amoeboidal migration, unlike the universally accepted epithelial-to-mesenchymal transition (EMT)-driven invasion. Mechanistically, single-cell RNA sequencing (scRNA-seq) of spatially dissected regions pinpoints that Fyn kinase, a critical regulator of cytoskeletal structure, is expressed specifically in peripheral GBM cells. Moreover, transcriptomic signatures associated with microtubule organization are downregulated in GBM cells lacking Fyn. When Fyn is knocked out, the invasion in spontaneous GBM models is effectively suppressed, and rear contraction is severely impaired, emphasizing the pivotal role of Fyn-mediated microtubule remodeling. We also identify platelet-derived growth factor (PDGF-A) as a critical regulator for long forward protrusion in the saltatory mode of GBM migration. These findings on the well-known but poorly characterized GBM invasion manifest the Fyn and PDGF-A as the new molecular targets for treatment strategies against the aggressive GBM invasion along the white matter tract.