Aminopeptidase A contributes to biochemical, anatomical and cognitive defects in Alzheimer’s disease (AD) mouse model and is increased at early stage in sporadic AD brain

Abstract

One of the main components of senile plaques in Alzheimer’s disease (AD)-affected brain is the Aβ peptide species harboring a pyroglutamate at position three pE3-Aβ. Several studies indicated that pE3-Aβ is toxic, prone to aggregation and serves as a seed of Aβ aggregation. The cyclisation of the glutamate residue is produced by glutaminyl cyclase, the pharmacological and genetic reductions of which significantly alleviate AD-related anatomical lesions and cognitive defects in mice models. The cyclisation of the glutamate in position 3 requires prior removal of the Aβ N-terminal aspartyl residue to allow subsequent biotransformation. The enzyme responsible for this rate-limiting catalytic step and its relevance as a putative trigger of AD pathology remained yet to be established. Here, we identify aminopeptidase A as the main exopeptidase involved in the N-terminal truncation of Aβ and document its key contribution to AD-related anatomical and behavioral defects. First, we show by mass spectrometry that human recombinant aminopeptidase A (APA) truncates synthetic Aβ1-40 to yield Aβ2-40. We demonstrate that the pharmacological blockade of APA with its selective inhibitor RB150 restores the density of mature spines and significantly reduced filopodia-like processes in hippocampal organotypic slices cultures virally transduced with the Swedish mutated Aβ-precursor protein (βAPP). Pharmacological reduction of APA activity and lowering of its expression by shRNA affect pE3-42Aβ- and Aβ1-42-positive plaques and expressions in 3xTg-AD mice brains. Further, we show that both APA inhibitors and shRNA partly alleviate learning and memory deficits observed in 3xTg-AD mice. Importantly, we demonstrate that, concomitantly to the occurrence of pE3-42Aβ-positive plaques, APA activity is augmented at early Braak stages in sporadic AD brains. Overall, our data indicate that APA is a key enzyme involved in Aβ N-terminal truncation and suggest the potential benefit of targeting this proteolytic activity to interfere with AD pathology.

N-Truncated Aβ Starting at Position Four—Biochemical Features, Preclinical Models, and Potential as Drug Target in Alzheimer’s Disease

“…For example, N-truncated Aβ 5-X is mainly produced from the caspase-cleaved form of APP and not from full-length Aβ (Murayama et al, 2007 ). Another potential alternative may be the generation the Aβ4-x peptide, a sequential cleavage of full-length Aβ by aminopeptidase A, meprin-β or dipeptidyl-peptidases (Sevalle et al, 2009 ; Antonyan et al, 2018 ; Schlenzig et al, 2018 ; Valverde et al, 2021 ). At least theoretically, Aβ 4-x could be derived from Aβ 2-x or Aβ 3-x peptide ( Figure 1B ).…”

Dipeptidyl peptidase 4 contributes to Alzheimer’s disease–like defects in a mouse model and is increased in sporadic Alzheimer’s disease brains

“…S2 C ). It is of importance to note that our recent study indicated that synthetic pE3-Aβ could indeed alter dendritic morphology and mimic that triggered by APPswe expression ( 33 ). Overall, this set of data indicates that DPP4 contributes to the morphological alterations affecting spines in an ex vivo AD model.…”

“…2 ) showing that APA inhibitors enhanced the recovery of cellular flAβ. Furthermore, our recent work showed that the APA inhibitor RB150 and short hairpinRNA directed towards APA both rescue dendritic morphology, lower pE3-Aβ–positive and Aβ-positive plaques and loads, and improve memory defects in 3xTgAD mice ( 33 ). Interestingly, APA and DPP4 inhibitor–induced potentiation of flAβ recovery was additive, indicating that the two enzymes independently target flAβ.…”

Brain Renin–Angiotensin System as Novel and Potential Therapeutic Target for Alzheimer’s Disease

“…In this study, inhibition of AP-A with RB150 (described below) restored the density of mushroom dendritic spines and reduced filopodia-like immature spines in hippocampal organotypic slices. Moreover, the work showed increased AP-A activity in early cases of AD [ 85 ]. As discussed earlier in this review, environmental risk factors for AD, such as cholesterol metabolites have been shown to alter AP-A and AP-N expression and correlated with decreased spatial memory in mice [ 24 ].…”

“…In rats, it showed BP reduction activity from 2 to 15 h post-administration [ 89 ]. As mentioned before in this work, the proven activity of firibastat for neurodegeneration is based on the inhibition of aminopeptidase activity over Aβ, which decreases the abundance of toxic Aβ species and its effect on neuronal physiology [ 85 ]. We have also mentioned that vasoconstriction and reduction of glymphatic flow could promote protein aggregation in the brain; therefore firibastat, through the activity of EC33 in the brain, could potentially improve these risk factors that influence cognition directly by lowering AP-A activity and AngIII levels.…”