Matrix Metalloproteinase-9 Degrades Amyloid-β Fibrils in Vitro and Compact Plaques in Situ

Abstract

The pathological hallmark of Alzheimer disease is the senile plaque principally composed of tightly aggregated amyloid-␤ fibrils (fA␤), which are thought to be resistant to degradation and clearance. In this study, we explored whether proteases capable of degrading soluble A␤ (sA␤) could degrade fA␤ as well. We demonstrate that matrix metalloproteinase-9 (MMP-9) can degrade fA␤ and that this ability is not shared by other sA␤-degrading enzymes examined, including endothelinconverting enzyme, insulin-degrading enzyme, and neprilysin. fA␤ was decreased in samples incubated with MMP-9 compared with other proteases, assessed using thioflavin-T. Furthermore, fA␤ breakdown with MMP-9 but not with other proteases was demonstrated by transmission electron microscopy. Proteolytic digests of purified fA␤ were analyzed with matrix-assisted laser desorption ionization time-of-flight mass spectrometry to identify sites of A␤ that are cleaved during its degradation. Only MMP-9 digests contained fragments (A␤ 1-20 and A␤ 1-30 ) from fA␤ 1-42 substrate; the corresponding cleavage sites are thought to be important for ␤-pleated sheet formation. To determine whether MMP-9 can degrade plaques formed in vivo, fresh brain slices from aged APP/PS1 mice were incubated with proteases. MMP-9 digestion resulted in a decrease in thioflavin-S (ThS) staining. Consistent with a role for endogenous MMP-9 in this process in vivo, MMP-9 immunoreactivity was detected in astrocytes surrounding amyloid plaques in the brains of aged APP/PS1 and APPsw mice, and increased MMP activity was selectively observed in compact ThS-positive plaques. These findings suggest that MMP-9 can degrade fA␤ and may contribute to ongoing clearance of plaques from amyloid-laden brains.

Clearance of Amyloid Beta Plaques from Brain of Alzheimeric Rats by Lavandula angustifolia

“…Although the animals were received Aβ intracerebroventricularly, however, via plasma clearance of Aβ, the extract can help to decrease the Aβ level in brain. Since systemic clearance of Aβ, especially by the liver, could determine the plasma levels of Aβ available for transport into the brain across the blood-brain barrier [9,15] it can be concluded that the lavender may undergo the liver clearance of Aβ. However, probable direct effect of the medicine on the Aβ plaques in the brain requires crossing the blood-brain barrier.…”

“…Also phagocytosis of Aβ plaques by microglia can restrict its accumulation in the brain [13]. Microglia also secrete proteolytic enzymes that degrade Aβ, such as insulin-degrading enzyme, neprilysin, matrix metalloproteinase 9, and plasminogen, further suggesting a neuroprotective role for these cells in AD [14,15]. However, persistent Aβ accumulation despite increasing microglial numbers suggests that the ability of microglia to clear Aβ may decrease with age and progression of AD pathology [13].…”

Intracerebral Transplantation of Bone Marrow-Derived Mesenchymal Stem Cells Reduces Amyloid-Beta Deposition and Rescues Memory Deficits in Alzheimer's Disease Mice by Modulation of Immune Responses

“…In fact, sometimes the activated microglia in BM-MSCtreated mice contained Ab (data not shown). Microglia secrete proteolytic enzymes that degrade Ab, such as insulin-degrading enzyme (IDE), neprilysin (NEP), matrix metalloproteinase 9 (MMP-9), and plasminogen [21,22].…”

Therapeutic Potential of Amyloid β-Degrading Enzymes in Alzheimer‘s Disease

“…The proteolytic efficiency with which plasmin degrades fibrillar Aβ, however, is approximately 1% of that for freshly dissolved (i.e., largely monomeric) Aβ [17]. A recent study demonstrated that MMP-2 and -9 degrade Aβ fibrils in vitro [19]. However, the ability of plasmin or MMPs to degrade Aβ aggregates in AD-related animal models remains to be established.…”

“…Known Aβ-degrading enzymes include neprilysin (NEP), insulin-degrading enzyme (IDE), matrix metalloproteinases (MMPs), endothelincoverting enzyme (ECE), angiotensin-converting enzyme, the plasmin system and CatB [14][15][16][17][18][19][20]. Studies in knockout mice demonstrated that NEP, IDE, ECEs and MMP-2 or -9 are involved in degrading endogenous murine Aβ [16,21,22].…”