MMP9 and Alzheimer disease: MMP9, a member of the protein endopeptidase family, is an enzyme that helps remodel tissues by degrading extracellular matrix components.[21] In the brain, MMP9 is expressed in multiple cell types, and pre-MMP9 precursors are released from cells that are activated extracellularly.[22] In cerebrovascular diseases such as Alzheimer disease, elevated levels of MMP9 have been shown to be associated with various neurological and inflammatory disease states,[23–25] cerebral amyloid angiopathy,[26] ischemia,[27] and cerebral hemorrhage.[28] L1R2 expresses the receptor for IL1.