MMP9 and Parkinson disease: The activation of microglia and astrocytes has been well-documented in PD following the release of the proinflammatory mediators interleukin-6 (IL-6), interleukin-IL-1 β (IL-1 β), tumor necrosis factor-alpha (TNF-α), and matrix metalloproteinase 9 (MMP9), as well as free oxygen radicals [4].