MMP9 and glioblastoma: Karthikeyan et al. demonstrated how microglial cells exposed to GBM conditioned-medium exhibited a greater ability to migrate and attributed this phenotype to decreased levels of miR-146a and resulting upregulation of its target SMAD family member 4 (SMAD4), a critical node involved in the activation of the TGF-β pathway and genes such as matrix metallopeptidase 9 (MMP9), which facilitates tumor cell invasion [81].