Figure 1.

Role of MMP9 in Depression. During inflammation, pro-inflammatory cytokines such as NF-κβ, IL1β, and IL6 stimulate the synthesis of MMP9. MMP9 can impair the integrity of BBB via the degradation of basement membrane of the BBB and tight junction proteins, allowing the entry of inflammatory cytokines and other neurotoxic substances into the brain, which leads to neuroinflammation. Neuroinflammation leads to depression through neuronal damage induced by oxidative stress and reduced availability of neurotransmitters. BBB: Blood-brain barrier; GFAP, Glial fibrillary acidic protein; IL, Interleukin; MMP9, Matrix metalloproteinase 9; TJPs, Tight junction proteins; TNF-α, Tumor necrosis factor alpha.