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. 2011 Oct 26;31(43):15384-90.
doi: 10.1523/JNEUROSCI.2986-11.2011.

Impaired β-amyloid secretion in Alzheimer's disease pathogenesis

Davide Tampellini  1 , Nawreen Rahman, Michael T Lin, Estibaliz Capetillo-Zarate, Gunnar K Gouras
Affiliations

Impaired β-amyloid secretion in Alzheimer's disease pathogenesis

Davide Tampellini et al. J Neurosci. .

Abstract

A central question in Alzheimer's disease (AD) research is what role β-amyloid peptide (Aβ) plays in synaptic dysfunction. Synaptic activity increases Aβ secretion, potentially inhibiting synapses, but also decreases intraneuronal Aβ, protecting synapses. We now show that levels of secreted Aβ fall with time in culture in neurons of AD-transgenic mice, but not wild-type mice. Moreover, the ability of synaptic activity to elevate secreted Aβ and reduce intraneuronal Aβ becomes impaired in AD-transgenic but not wild-type neurons with time in culture. We demonstrate that synaptic activity promotes an increase in the Aβ-degrading protease neprilysin at the cell surface and a concomitant increase in colocalization with Aβ42. Remarkably, AD-transgenic but not wild-type neurons show reduced levels of neprilysin with time in culture. This impaired ability to secrete Aβ and reduce intraneuronal Aβ has important implications for the pathogenesis and treatment of AD.

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Figures

Figure 1.
Figure 1.
Decreased Aβ secretion in AD-transgenic (Tg) but not wild-type (WT) neurons with time in culture. A, Levels of Aβ1–40 and Aβ1–42 were assayed by ELISA in media of AD-transgenic or wild-type neurons. While wild-type neurons secrete comparable amounts of Aβ peptides at 12 and 19 DIV (n = 6; left), AD-transgenic neurons showed decreased levels of Aβ1–40 and Aβ1–42 in media at 19 compared with 12 DIV (n = 10; *p < 0.05, **p < 0.01; right). B, Levels of intraneuronal Aβ42 were increased by 46 ± 17% in AD-transgenic neurites at 19 compared with 12 DIV (n = 4; p < 0.05). C, D, Levels of intraneuronal Aβ42 were unchanged in wild-type neurons at 19 compared with 12 DIV, as quantified by confocal immunofluorescence (C) and ELISA (D) (n = 4). E, Left, Levels of αCTFs were decreased by 52 ± 2%, while levels of βCTFs and full-length APP were unchanged in AD-transgenic neurons at 19 compared with 12 DIV (n = 4; p < 0.01). Right, Levels of αCTFs were decreased by 32 ± 9% (n = 5; p < 0.05), while levels of βCTFs (longer exposure) showed a trend for a 49 ± 16% decrease (p = 0.074) in wild-type neurons at 19 compared with 12 DIV. F, At 19 DIV, AD-transgenic neurons failed to enhance secretion of both Aβ1–40 and Aβ1–42 during g-LTP (n = 6, right). In contrast, wild-type neurons were still able to increase Aβ1–40 and Aβ1–42 secretion during g-LTP (n = 4; *p < 0.05, left). Conc., Concentration. Scale bars, 50 μm.
Figure 2.
Figure 2.
Impaired ability for synaptic activity to reduce intraneuronal Aβ42 and protect synapses in AD-transgenic neurons with time in culture. A, g-LTP reduced levels of intraneuronal Aβ42 by 23 ± 4% in wild-type (WT; left) but not AD-transgenic (Tg; right) neurons at 19 DIV, as determined by confocal immunofluorescence (n = 4; p < 0.01). B, Aβ1–42 ELISA of lysates from g-LTP compared with untreated neurons at 19 DIV revealed reduced levels of Aβ1–42 in wild-type but not in AD-transgenic neurons (n = 4; *p < 0.05). C, Western blot of cell lysates demonstrated reduced levels of intraneuronal Aβ in g-LTP-treated compared with -untreated AD-transgenic neurons at 12 (lanes 1 and 2, longer exposure) but not 19 (lanes 3 and 4) DIV (n = 3). D, PSD-95 puncta increased in g-LTP-activated AD-transgenic neurons at 19 DIV, although they failed to reach wild-type levels (n = 5; **p < 0.01). E, Wild-type neurons (12 DIV) showed a 74 ± 21% greater relative colocalization of neprilysin with the MVB/late endosomal marker tumor susceptibility gene 101 (TSG101) than the early endosomal marker early endosomal antigen-1 (EEA1) (n = 3; p < 0.01). Conc., Concentration. Scale bars: A, D, E, 50 μm; E, inset, 10 μm.
Figure 3.
Figure 3.
Synaptic activation increases neprilysin surface levels and colocalization with Aβ42. A, g-LTP increased levels of surface neprilysin by 37 ± 7% in g-LTP-treated compared with -untreated wild-type neurons at 12 DIV (n = 6; p < 0.01). B, g-LTP also increased levels of surface neprilysin in g-LTP-treated compared with untreated AD-transgenic neurons at 12 DIV (n = 3; p < 0.01). C, g-LTP increased the relative colocalization of neprilysin with Aβ42 by 54 ± 21% at the cell surface in AD-transgenic neurons at 12 DIV (n = 3; p < 0.01). Scale bars: A–C, 50 μm; C, insets, 10 μm.
Figure 4.
Figure 4.
Decreased levels of neprilysin in AD-transgenic neurons with time in culture. A, Levels of neprilysin were decreased by 18 ± 8% in 19 compared with 12 DIV AD-transgenic neurons (n = 4; *p < 0.05; scale bar, 50 μm). In contrast, 19 compared with 12 DIV wild-type neurons did not show a decrease of neprilysin. B, The number of AICD-positive nuclei was decreased by 27 ± 6% in 19 compared with 12 DIV AD-transgenic neurons (n = 3; p < 0.05). C, The ability to secrete Aβ falls with time in culture in AD-transgenic neurons. Neprilysin levels fall with time in culture, suggesting a mechanism for progressive intracellular Aβ accumulation and loss of synaptic proteins (PSD-95) in aged AD-transgenic neurons. D, Synaptic activity enhances Aβ secretion, leads to neprilysin recruitment to the cell surface, and increases colocalization of neprilysin with Aβ42.
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References

    1. Almeida CG, Tampellini D, Takahashi RH, Greengard P, Lin MT, Snyder EM, Gouras GK. Beta-amyloid accumulation in APP mutant neurons reduces PSD-95 and GluR1 in synapses. Neurobiol Dis. 2005;20:187–198. - PubMed
    1. Almeida CG, Takahashi RH, Gouras GK. Beta-amyloid accumulation impairs multivesicular body sorting by inhibiting the ubiquitin-proteasome system. J Neurosci. 2006;26:4277–4288. - PMC - PubMed
    1. Billings LM, Oddo S, Green KN, McGaugh JL, LaFerla FM. Intraneuronal Abeta causes the onset of early Alzheimer's disease-related cognitive deficits in transgenic mice. Neuron. 2005;45:675–688. - PubMed
    1. Brody DL, Magnoni S, Schwetye KE, Spinner ML, Esparza TJ, Stocchetti N, Zipfel GJ, Holtzman DM. Amyloid-beta dynamics correlate with neurological status in the injured human brain. Science. 2008;321:1221–1224. - PMC - PubMed
    1. Cataldo AM, Petanceska S, Terio NB, Peterhoff CM, Durham R, Mercken M, Mehta PD, Buxbaum J, Haroutunian V, Nixon RA. Abeta localization in abnormal endosomes: association with earliest Abeta elevations in AD and Down syndrome. Neurobiol Aging. 2004;25:1263–1272. - PubMed

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