Apolipoprotein E Isoforms Differentially Regulate Matrix Metallopeptidase 9 Function in Alzheimer’s Disease

Apolipoprotein E (APOE) is a major genetic risk factor for Alzheimer’s disease (AD) and has been shown to influence amyloid-β (Aβ) clearance from the brain in an isoform-specific manner. Our prior work showed Aβ transit across the blood-brain-barrier was reduced by apoE4, compared to other apoE isoforms, due to elevated lipoprotein receptor shedding in brain endothelia. Recently, we demonstrated matrix metallopeptidase 9 (MMP-9) induces lipoprotein receptor proteolysis in an apoE isoform-dependent manner, which impacts Aβ elimination from the brain. The current studies interrogated the relationship between apoE and MMP-9 and found apoE dose-dependently reduced MMP-9 activity in a cell-free assay, with apoE4 showing a significantly weaker ability to inhibit MMP-9 function than apoE2 or apoE3. Moreover, these effects may be due to the reduced binding affinity of apoE4 for MMP-9 compared to apoE2 and apoE3 as revealed by kinetic binding studies. Elevated MMP-9 expression and activity was observed in the cerebrovasculature of both human and animal AD brain specimens with an APOE4 genotype. The apoE isoforms also lead to altered levels of MMP-9 secreted from brain endothelia cultures (apoE2