Early formation of mature amyloid‐β protein deposits in a mutant APP transgenic model depends on levels of Aβ_1–42

Abstract

The main objective of the present study was to develop an alternative singly-transgenic (tg) hAPP model where amyloid deposition will occur at an earlier age. For this purpose, we generated lines of tg mice expressing hAPP751 cDNA containing the London (V717I) and Swedish (K670M/N671L) mutations under the regulatory control of the murine (m)Thy-1 gene (mThy1-hAPP751). In the brains of the highest (line 41) and intermediate (lines 16 and 11) expressers, high levels of hAPP expression were found in neurons in layers 4-5 of the neocortex, hippocampal CA1 and olfactory bulb. As early as 3-4 months of age, line 41 mice developed mature plaques in the frontal cortex, whereas at 5-7 months plaque formation extended to the hippocampus, thalamus and olfactory region. Ultrastructural and double-immunolabeling analysis confirmed that most plaques were mature and contained dystrophic neurites immunoreactive with antibodies against APP, synaptophysin, neurofilament and tau. In addition, a decrease in the number of synaptophysin-immunoreactive terminals was most prominent in the frontal cortex of mice from line 41. Mice from line 11 developed diffuse amyloid deposits at 11 months of age, whereas mice from line 16 did not show evidence of amyloid deposition. Analysis of Abeta by ELISA showed that levels of Abeta(1-40) were higher in mice that did not show any amyloid deposits (line 16), whereas Abeta(1-42) was the predominant species in tg animals from the lines showing plaque formation (lines 41 and 11). Taken together this study indicates that early onset plaque formation depends on levels of Abeta(1-42).

Neprilysin Gene Transfer Reduces Human Amyloid Pathology in Transgenic Mice

“…The first expressed mutant human amyloid precursor protein cDNA (hAPP V717F ) under the control of the platelet-derived growth factor promoter (PDAPP minigene) (Masliah et al, 1996). The second expressed double-mutant hAPP London (V717I) and Swedish (K670M/ N671L) under the control of the murine Thy1 regulatory sequences (Rockenstein et al, 2001). A total of 13 PD-hAPP tg mice from line J9M, aged 12-20 months, and 13 mThy1-hAPP from line 41 (TASD41), aged 11-14 months, were injected with 3 l of the lentiviral preparations (1.5 ϫ 10 7 TU) into the frontal cortex and hippocampus (using a 5 l Hamilton syringe, 0.25 l/min).…”

“…Additional double-immunolabeling experiments were performed to ascertain colocalization of lentiviral neprilysin expression and amyloid plaques. For this purpose, vibratome sections were incubated with antibodies against A␤ (3D6) and Nep (56C6) (Research Diagnostics) and visualized with Tyramide Red (for Nep) and FITC (for A␤), followed by analysis with the LSCM as described previously (Rockenstein et al, 2001).…”

Neprilysin-2 Is an Important β-Amyloid Degrading Enzyme

“…This issue was addressed with the use of APPtg mice, which dramatically overproduce A␤. 20 In combination with the APP transgene, NEP2 deficiency produced more dramatic elevation in A␤ 40 levels, strongly supporting a role for NEP2 in A␤ regulation (Figure 2). Although no elevations in A␤ were seen in the cerebral cortex of NEP2 KO mice ( Figure 1), a dramatic increase in plaque deposition was observed in the cerebral cortex of APP transgenic/NEP2 KO mice (Figure 3).…”

“…APPtg/NEP2 KO mice were created by cross-breeding NEP2 KO mice (129 background) with APPtg mice (TASD41 line, received from the laboratory of Dr. Eliezer Masliah) (Blk/Sw background). 20 These mice are propagated by breeding heterozygous APP transgenic mice having either wild-type or NEP2…”

“…Ϫ/Ϫ mice were crossbred with an APP transgenic (APPtg) mouse line (TASD41) 20 to generate APPtg/NEP2 Ϫ/Ϫ mice. The APP transgenic line produced approximately an 80-fold increase in A␤ 40 levels, as can be observed by comparing the levels of A␤ in the hippocampus from normal APPtg/NEP2 ϩ/ϩ mice ( Figure 2B) to wild-type NEP2 ϩ/ϩ mice ( Figure 1B).…”