Amyloid β peptide cleavage by kallikrein 7 attenuates fibril growth and rescues neurons from Aβ-mediated toxicity in vitro

Abstract

The gradual accumulation and assembly of β-amyloid (Aβ) peptide into neuritic plaques is a major pathological hallmark of Alzheimer disease (AD). Proteolytic degradation of Aβ is an important clearance mechanism under normal circumstances, and it has been found to be compromised in those with AD. Here, the extended substrate specificity and Aβ-degrading capacity of kallikrein 7 (KLK7), a serine protease with a unique chymotrypsin-like specificity, was characterized. Preferred peptide substrates of KLK7 identified using a bacterial display substrate library were found to exhibit a consensus motif of RXΦ(Y/F)↓(Y/F)↓(S/A/G/T) or RXΦ(Y/F)↓(S/T/A) (Φ=hydrophobic), which is remarkably similar to the hydrophobic core motif of Aβ (K16L17V18F19F20 A21) that is largely responsible for aggregation propensity. KLK7 was found to cleave after both Phe residues within the core of Aβ42 in vitro, thereby inhibiting Aβ fibril formation and promoting the degradation of preformed fibrils. Finally, the treatment of Aβ oligomer preparations with KLK7, but not inactive pro-KLK7, significantly reduced Aβ42-mediated toxicity to rat hippocampal neurons to the same extent as the known Aβ-degrading protease insulin-degrading enzyme (IDE). Taken together, these results indicate that KLK7 possesses an Aβ-degrading capacity that can ameliorate the toxic effects of the aggregated peptide in vitro.

Unraveling Comparative Anti-Amyloidogenic Behavior of Pyrazinamide and D-Cycloserine: A Mechanistic Biophysical Insight

“…The aggregated/amyloid fibrils are toxic to neurons; though pre-amyloid fibrils or oligomers are believed to be more cytotoxic [ 53 , 54 ]. Thus, the cytotoxicity of 120 h aged HEWL fibrils were examined on two cell lines i.e., PC-12 and SH-SY5Y by MTT reduction assay at 24 h ( Fig 10A and 10B ).…”

Dysregulated Metabolism of the Amyloid‐β Protein and Therapeutic Approaches in Alzheimer Disease

“…In addition, gene expression databases demonstrate that KLK7 is also expressed in the brain, lungs, and esophagus. Recently, we as well as others identified KLK7 as a novel Aβ‐degrading enzyme that is secreted from human astrocytoma cell lines and murine astrocytes [Shropshire et al, ; Tomita, ]. KLK7 degrades Aβ monomers, oligomers, and fibrils.…”

Involvement of Kallikrein-Related Peptidases in Normal and Pathologic Processes

“…Besides KLK6, the kallikrein-related peptidases 7 and 10 show decreased and increased levels, respectively, in cerebrospinal fluid of AD patients [ 39 ]. Recently, Shropshire and collaborators observed that KLK7 is able to cleave the core of A β in vitro, inhibiting A β aggregation and reducing neuronal toxicity [ 186 ]. This result may open new opportunities towards treatments for AD.…”