In Vivo β-Secretase 1 Inhibition Leads to Brain Aβ Lowering and Increased α-Secretase Processing of Amyloid Precursor Protein without Effect on Neuregulin-1

Abstract

␤-Secretase (BACE) cleavage of amyloid precursor protein (APP) is one of the first steps in the production of amyloid ␤ peptide A␤42, the putative neurotoxic species in Alzheimer's disease. Recent studies have shown that BACE1 knockdown leads to hypomyelination, putatively caused by a decline in neuregulin (NRG)-1 processing. In this study, we have tested a potent cell-permeable BACE1 inhibitor (IC 50 ϳ 30 nM) by administering it directly into the lateral ventricles of mice, expressing human wild-type (WT)-APP, to determine the consequences of BACE1 inhibition on brain APP and NRG-1 processing. BACE1 inhibition, in vivo, led to a significant dose-and timedependent lowering of brain A␤40 and A␤42. BACE1 inhibition also led to a robust brain secreted (s)APP␤ lowering that was accompanied by an increase in brain sAPP␣ levels. Although an increase in full-length NRG-1 levels was evident in 15-day-old BACE1 homozygous knockout (KO) (Ϫ/Ϫ) mice, in agreement with previous studies, this effect was also observed in 15-dayold heterozygous (ϩ/Ϫ) mice, but it was not evident in 30-dayold and 2-year-old BACE1 KO (Ϫ/Ϫ) mice. Thus, BACE1 knockdown led to a transient decrease in NRG-1 processing in mice. Pharmacological inhibition of BACE1 in adult mice, which led to significant A␤ lowering, was without any significant effect on brain NRG-1 processing. Taken together, these results suggest that BACE1 is the major ␤-site cleavage enzyme for APP and that its inhibition can lower brain A␤ and redirect APP processing via the potentially nonamyloidogenic ␣-secretase pathway, without significantly altering NRG-1 processing.

A Noncompetitive BACE1 Inhibitor TAK-070 Ameliorates Aβ Pathology and Behavioral Deficits in a Mouse Model of Alzheimer's Disease

“…These profiles should be a merit of this compound, considering the long period of AD medication. The sustained efficacy of TAK-070 markedly differs from those documented in other BACE1 inhibitors (Sankaranarayanan et al, 2008) or on the higher efficacy of a compound in the presence of inhibitors of P-glycoprotein (Hussain et al, 2007), that determines exposure levels of compounds in brains.…”

“…However, there were pivotal differences: TAK-070 treatment affected neither the total number of arm entry in Y-maze test (Ohno et al, 2004) nor the swimming speed in Morris water maze test (Ohno et al, 2006), which were documented to be abnormal in BACE1-homozygous KO regardless of APP-transgenic background. Furthermore, BACE1-homozygous KO in nontransgenic background have been reported to show cognitively deteriorative (Ohno et al, 2004(Ohno et al, , 2006(Ohno et al, , 2007, schizophrenia-like (Savonenko et al, 2008), or hypomyelination (Hu et al, 2006;Sankaranarayanan et al, 2008) phenotypes, underscoring the necessity of BACE1 activity for physiological functions, probably due to multiplicity of substrates for BACE1 (for review, see Marks and Berg, 2008). Also in nontransgenic aged rats, TAK-070 ameliorated behavioral deficits in the water maze test (our unpublished observation).…”

“…Furthermore, cognitive deficits associated with synaptic degeneration have been documented in PS1/PS2 conditional KO mice with or without APP transgenic background (Saura et al, 2004(Saura et al, , 2005Chen et al, 2008). In contrast, BACE1 KO mice do not show such fatal phenotypes despite its complete ablation, except for partial hypomyelination at the developmental stage (Hu et al, 2006;Sankaranarayanan et al, 2008) or schizophrenialike behavior in homozygous BACE1 KO mice (Savonenko et al, 2008), whereas cognitive deficits are ameliorated on APP transgenic background (Ohno et al, 2004(Ohno et al, , 2006(Ohno et al, , 2007. Furthermore, it has been well documented that the protein levels or activities of BACE1 are upregulated in the brains of patients with sporadic AD (Stockley and O'Neill, 2007).…”

Robust Central Reduction of Amyloid-β in Humans with an Orally Available, Non-Peptidic β-Secretase Inhibitor

“…As noted above, the hypomyelination phenotype was not noted in BACE1 hemizygous mice expressing 50% of BACE1 in brain. In addition, pharmacologic inhibition achieved by direct central administration of a BACE1 inhibitor did not appear to alter Neuregulin-1 cleavage patterns in adult mouse brain (Sankaranarayanan et al, 2008), but functional deficits were not evaluated. Similarly, the deficits in behavioral cognitive tests, e.g., Morris water maze, Y maze, etc., observed in BACE knock-outs were not present in BACE1 hemizygous mice (Laird et al, 2005), suggesting that partial reduction in BACE1 activity may be better tolerated even when it already occurs during development.…”

Pharmacological applications of a novel neoepitope antibody to a modified amyloid precursor protein-derived beta-secretase product

“…Briefly, baculovirus expressed and purified truncated BACE1 (aa 1-460) (Shi et al, 2001) at 0.3 nmol/L was incubated at a range of concentrations with a previously characterized BACE1 inhibitor MRK-3 (Stachel et al, 2004;Sankaranarayanan et al, 2008;Wu et al, 2011) for 30 min at RT. After this preincubation, the BACE1 substrate (15 amino acid peptide with C-terminal biotin) was added at a final concentration of 300 nmol/L to the reaction buffer (50 mmol/L NaOAc, 0.01% BSA, 15 mmol/L EDTA, 0.2% CHAPS, 1 mmol/L Deferoxamine Mesylate and 10 μmol/L pepstatin A at pH 4.5) and incubated for 2 h at 37°C in a shaker at 40 rpm .…”