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MMP‐2, ‐3 and ‐9 levels and activity are not related to Aβ load in the frontal cortex in Alzheimer's disease

Matrix metalloproteinases (MMPs) ‐2, ‐3 and ‐9 are up‐regulated in several cell types on exposure to amyloid β peptide (Aβ) and have Aβ‐degrading activity in vitro. The aims of this study were to determine (i) the distribution of MMP‐2, ‐3 and ‐9 in the cerebral cortex in Alzheimer's disease (AD) and control brains; (ii) whether the levels and activity of these proteases are increased in AD; and (iii) whether their activity is related to Aβ load. In addition, we examined whether promoter polymorphisms in the MMP‐3 and ‐9 genes are associated with AD in the study cohort. Paraffin sections of frontal lobe from AD and control cases were immunostained for MMP‐2, ‐3 and ‐9 and tissue homogenates used for MMP activity assays. DNA from these cases was genotyped for the MMP‐3 5A/6A (‐1171) and MMP‐9 C‐1562T promoter polymorphisms. Immunohistochemistry revealed MMP‐3 in plaques and both MMP‐3 and ‐9 around scattered neurones. The levels and activity of all three MMPs were similar in AD and control brains and bore no relationship to Aβ load. Analysis of MMP‐3 ‐1171 5A/6A allele frequencies showed that the 6A allele (with reduced promoter activity) was associated with AD; the MMP‐9 C‐1562T polymorphism was not. The levels and activities of MMP‐2, ‐3 and ‐9 are not increased in the frontal cortex in AD and are not related to Aβ load. Our findings suggest that altered expression of these proteases does not make a significant contribution to the accumulation of Aβ in AD.