Glioblastoma (GBM), the most aggressive primary intracranial tumor in adults, carries a median survival time of only 12–18 months despite advances in surgery, chemotherapy, and radiotherapy. GBM cells migrate through brain tissue by deforming and squeezing between narrow extracellular spaces, including junctions between cells and regions surrounding blood vessels and white matter tracts. Brain tissue is notable in exhibiting significant viscoelastic stress relaxation (SR), and it remains poorly understood how SR cues are processed by the intracellular motility machinery, including actin-binding proteins, to control 3D invasion. Here, we applied engineered viscoelastic hyaluronic acid (HA) hydrogels to investigate the interplay between SR and the actin-severing protein cofilin-1 (CFL1) on GBM 3D invasion. Following our recent publication, we fabricated variably crosslinked high-molecular weight and RGD peptide-conjugated HA hydrogels with matched elastic moduli but exhibiting either fast or slow or SR rates. We then knocked down CFL1 in cultured GBM cells, implanted spheroids of these cells in fast- and slow-relaxing viscoelastic HA matrices, and quantified 3D cell invasion speed relative to non-targeting controls. In fast-relaxing matrices, CFL1 depletion suppressed invasion, whereas in slow-relaxing matrices, CFL1 knockdown did not strongly affect invasion. By contrast, we showed in a previous study that CFL1 knockdown speeds invasion in purely elastic HA hydrogels, which may be regarded as representing the infinitely slowly relaxing limit. In other words, stress relaxation surprisingly reverses the effect of CFL1 on invasion dynamics, with CFL1 suppression stimulating invasion in purely elastic matrices and suppressing invasion in rapidly stress-relaxing matrices. We describe our efforts to dissect the mechanisms underlying this result, including the possibility that SR shifts the mode of 3D invasion and the associated contributions of actin polymerization and bundling.
Ford et al. (Sun,) studied this question.