Reactive astrocytes release reactive oxygen species and nitrogen, tumor necrosis factor-α, matrix metalloproteinase-9 and other cytokines, which have direct neurotoxicity.[42] There is a growing consensus that glial cell-mediated inflammation is a major contributor to the degenerative process and cognitive loss in AD.[43] Astrocytes and their released cytokines can be used as new biomarkers for AD and provide new targets for AD treatment. Here, MMP9 is linked to Alzheimer disease.