Amyloid β-Protein Is Degraded by Cellular Angiotensin-converting Enzyme (ACE) and Elevated by an ACE Inhibitor

Abstract

Human genetic data have associated angiotensin-converting enzyme (ACE) with Alzheimer disease (AD), and purified ACE has been reported to cleave synthetic amyloid ␤-protein (A␤) in vitro. Whether deficiency in ACE activity, arising from genetic alteration or pharmacological inhibition, can decrease A␤ degradation and allow A␤ accumulation in intact cells is unknown. We cloned ACE from human neuroblastoma cells and showed that it had posttranslational processing and enzymatic activity typical of the endogenous protease. Cellular expression of ACE promoted degradation of naturally secreted A␤40 and A␤42, leading to significant clearance of both species. Using site-directed mutagenesis, we determined that both active sites within ACE contribute to A␤ clearance, and an ACE construct bearing mutations in each catalytic domain had no effect on A␤ levels. Pharmacological inhibition of ACE with a widely prescribed drug, captopril, promoted the accumulation of cell-derived A␤ in the media of ␤-amyloid precursor-protein expressing cells. Together, these results show that ACE can lower the levels of secreted A␤ in living cells and that this effect is blocked by inhibiting the protease's activity with an ACE inhibitor. This work, combined with the genetic studies, supports the hypothesis that ACE may modulate the susceptibility to and progression of AD via degradation of A␤. Our data encourage further analyses of the ACE gene for disease association and raise the question of whether currently prescribed ACE inhibitors could elevate cerebral A␤ levels in humans. An early and pathogenically important feature of Alzheimer disease (AD)2 is the progressive accumulation and deposition of the amyloid ␤-protein (A␤) in brain regions serving memory and cognition. Biochemical, cell biological, animal modeling, genetic, and emerging clinical data all suggest that A␤ is an upstream initiator of the disease process and its associated neuropathology (1-4). Although no proven diseasemodifying treatments are currently available, recent efforts to treat AD have focused on both decreasing the production of A␤ and enhancing its clearance from the brain. One little studied approach to A␤ clearance is augmenting the degradation of the peptide by various proteases expressed in the brain. Thus far, the metalloproteases neprilysin (NEP) (5), insulin-degrading enzyme (IDE) (6), and the endothelin-converting enzymes 1 and 2 (7) have each been implicated as A␤-degrading proteases in the mammalian brain. The serine protease plasmin has been implicated in A␤ degradation in vitro (8), although genetic plasmin deficiency did not promote accumulation of murine A␤ in vivo (9). Supporting a role for therapeutic regulation of A␤-degrading proteases, the overexpression of IDE or NEP in a murine model of AD decreased cerebral A␤ levels and produced significant attenuation of A␤-associated neuropathology (10).Somatic angiotensin-converting enzyme (ACE) is a zinc metalloprotease containing two homologous regions, termed the N-and C-domains, each of which is prot...

Angiotensin-Converting Enzyme Converts Amyloid β-Protein 1–42 (Aβ1–42) to Aβ1–40, and Its Inhibition Enhances Brain Aβ Deposition

“…A recent in vivo study also shows that ACE inhibitors at doses similar to those used clinically do not increase the levels of brain A␤s (Eckman et al, 2006). Previous studies using purified human seminal plasma ACE and cultured cells showed that ACE degrades A␤s and ACE inhibition increases A␤ levels in APP-and ACE-transfected cells (Hu et al, 2001;Hemming and Selkoe, 2005;Oba et al, 2005). However, these findings seem to disagree with those of in vivo studies.…”

Phosphorylation of Amyloid-β Peptide at Serine 8 Attenuates Its Clearance via Insulin-degrading and Angiotensin-converting Enzymes

“…However, recent large genome-wide association studies did not identify ACE as a significant genetic risk factor (68 -70). However, recombinant ACE is capable of cleaving both A␤40 and A␤42 in vitro and thereby decreases A␤ aggregation and toxicity (71)(72)(73). We also observed efficient cleav- age of A␤ by ACE.…”

A GPCR/secretase complex regulates β- and γ-secretase specificity for Aβ production and contributes to AD pathogenesis

“…Accumulated Aβ can be removed by Aβ-degrading enzymes, such as neprilysin (NEP) [14], insulin-degrading enzyme (IDE) [15], endothelin-converting enzyme [16] and angiotensinconverting enzyme [17]. All these protease activities respond elaborately to diverse genetic and biochemical mediations.…”