Amyloid β-Protein (Aβ) 1–40 But Not Aβ1–42 Contributes to the Experimental Formation of Alzheimer Disease Amyloid Fibrils in Rat Brain

Abstract

Two major C-terminal variants ending at Val40 and Ala42 constitute the majority of amyloid ␤-protein (A␤), which undergoes postsecretory aggregation and deposition in the Alzheimer disease (AD) brain. To probe the differential pathobiology of the two A␤ variants, we used an in vivo paradigm in which freshly solubilized A␤1-40 or A␤1-42 was injected into rat brains, followed by examination using Congo red birefringence, A␤ immunohistochemistry, and electron microscopy. In the rat brain, soluble A␤ 1-40 and A␤1-42 formed aggregates, and the A␤1-40 but not the A␤1-42 aggregates showed Congo red birefringence. Electron microscopy revealed that the A␤1-40 aggregates contained fibrillar structures similar to the amyloid fibrils of AD, whereas the A␤1-42 aggregates contained nonfibrillar amorphous material. Preincubation of A␤1-42 solution in vitro led to the formation of birefringent aggregates, and after injection of the preincubated A␤1-42, the aggregates remained birefringent in the rat brain. Thus, a factor or factors might exist in the rat brain that inhibit the fibrillar assembly of soluble A␤1-42. To analyze the postsecretory processing of A␤, we used the same in vivo paradigm and showed that A␤1-40 and A␤1-42 were processed at their N termini to yield variants starting at pyroglutamate, and at their C termini to yield variants ending at Val40 and at Val39. Thus the normal rat brain could produce enzymes that mediate the conversion of A␤ 1-40/1-42 into processed variants similar to those in AD. This experimental paradigm may facilitate efforts to elucidate mechanisms of A␤ deposition evolving into amyloid plaques in AD.

Pyroglutamate Amyloid-β (Aβ): A Hatchet Man in Alzheimer Disease

“…This was further confirmed by the finding that A␤ pE3-42 constituted 25% of the total A␤ x-42 in plaques of AD brains (39). It was reported that unmodified A␤ and A␤ can be modified into A␤ pE3 after being injected into rat brain, indicating that rat brains harbor the enzymes required for N-terminal truncation and pyroglutamate formation (40).…”

“…Injection of A␤ 3-40 into wild-type rat cortex led to significant production of A␤ pE3-40 within 24 h, which was inhibited by co-application of a QC inhibitor (91). Oral administration of a QC inhibitor to Tg2576 and TASD-41 transgenic mice reduced A␤ pE3, A␤ 40 , and A␤ 42 levels. This was accompanied by a reduction in plaque load and gliosis in addition to improvements in contextual fear memory and spatial memory.…”

Quantitative Measurement of Changes in Amyloid-β(40) in the Rat Brain and Cerebrospinal Fluid following Treatment with the γ-Secretase Inhibitor LY-411575 [N2-[(2S)-2-(3,5-Difluorophenyl)-2-hydroxyethanoyl]-N1-[(7S)-5-methyl-6-oxo-6,7-dihydro-5H-dibenzo[b,d]azepin-7-yl]-l-alaninamide]

“…Evidence from clinical studies (Wang et al, 1999;Naslund et al, 2000), in vitro experiments (Lambert et al, 1998;Hartley et al, 1999;Chromy et al, 2003), and in vivo experiments (Shin et al, 1997;Hsia et al, 1999) suggest that the initial pathogenesis of AD is due to the build up of neurotoxic aggregates of the soluble A␤ peptide species A␤(1-40) and A␤(1-42). As a result, a number of therapeutic approaches for lowering amyloid are in progress, one of which is the use of ␥-secretase inhibitors (Hardy and Selkoe, 2002;Harrison et al, 2004b).…”

Neurofibrillary Tangles of Aβx-40 in Alzheimer’s Disease Brains

“…The antibodies used were: SAR-022 (anti-A␤ x-40 polyclonal antibody; Araclon Biotech, Zaragoza) at 1 : 500; SAR-031 (anti-A␤ x-42 polyclonal antibody; Araclon Biotech, Zaragoza) at 1 : 2000; 6E10 monoclonal antibody (anti-N-terminal region of A␤; Covance, London) at 1 : 2000; 4G8 monoclonal antibody (anti-central region of A␤; Covance, London) at 1 : 1000; and AT8 (antiPhospho-PHF-tau pSer202+Thr205; ThermoFisher Scientific, Waltham) at 1 : 200. The anti A␤ x-40 and anti A␤ x-42 antibodies were purified by antigenaffinity chromatography using the same A␤ fragment inoculated to the rabbits (A␤ [33][34][35][36][37][38][39][40] and A␤ [35][36][37][38][39][40][41][42] , respectively). As described elsewhere, they have practically no cross-reactivity (less than 1%) between their target A␤ species nor with A␤ 1-38 (<2%), A␤ 1-43 (<1%) [31].…”

“…Currently, it is generally accepted that A␤ 42 may be of particular relevance in triggering AD because it is more hydrophobic and prone to aggregate in vitro than A␤ 40 [37]. However, it should be considered that the aggregating behavior of the various A␤ species could be different in vivo than in vitro [38] and, in this line, it is also relevant to underline some studies pointing to the relevance of A␤ 40 in AD [39,40].…”