MMP9 and Parkinson disease: Treatment with MMP-9 inhibitors attenuated the neuronal cell death induced by the dopaminergic neurotoxins 6-OHDA and MPP(+) [39], and mechanistic studies showed that both 6-OHDA and MPP(+) can induce MMP-9 promoter activity, suggesting that controlling MMP-9 expression may have therapeutic potential in PD [21].