MMP9 and concussion: Of note, in comparison to those with no mTBI history who engaged in breacher training, in SMs with mTBI we found elevated expression of genes THBS1, MMP9, and PIK3R6. The THBS1 gene encodes Thrombospondin-1 (TSP-1), a multifunctional extracellular matrix glycoprotein involved in inflammatory and angiogenic processes, and was elevated at both the post and follow-up blast exposure timepoints in SMs with mTBI history.