Relevance of the COPI complex for Alzheimer's disease progression in vivo

Abstract

Cellular trafficking and recycling machineries belonging to late secretory compartments have been associated with increased Alzheimer's disease (AD) risk. We have shown that coat protein complex I (COPI)-dependent trafficking, an early step in Golgi-to-endoplasmic reticulum retrograde transport, affects amyloid precursor protein subcellular localization, cell-surface expression, as well as its metabolism. We present here a set of experiments demonstrating that, by targeting subunit δ-COP function, the moderation of the COPI-dependent trafficking in vivo leads to a significant decrease in amyloid plaques in the cortex and hippocampus of neurological 17 mice crossed with the 2xTg AD mouse model. Remarkably, an improvement of the memory impairments was also observed. Importantly, human genetic association studies of different AD cohorts led to the identification of 12 SNPs and 24 mutations located in COPI genes linked to an increased AD risk. These findings further demonstrate in vivo the importance of early trafficking steps in AD pathogenesis and open new clinical perspectives.

Keywords: Alzheimer; COPI; EWAS studies; GWAS studies; human genetic.

Fig. 1.

Effect of δ-COP on Aβ production and protein trafficking. (A–C) Aβ40 measurements of N2a cells pretreated with control or δ-COP siRNAs and transfected with (A) APP-WT or (B) APP-SW or (C) nontransfected. OE, overexpressed. (D) Subcellular localization of various proteins in N2a-695 cells transfected with control siRNA or δ-COP siRNA by sucrose density gradient fractionation. The two main cellular fractions corresponding to the Golgi were analyzed by SDS/PAGE using different antibodies and used for the quantification studies indicated in Results. (E and F) Cell-surface protein measurement after (E) transfection with δ-COP siRNA using cell-surface biotinylation and (F) quantification. (*P < 0.05, **P < 0.01, two-tailed Student’s t test; n = 3. The results are shown as means ± SEM.)

Fig. 2.

Effect of partial inactivation of δ-COP on Aβ level in 2xTg AD mice. (A) Measurements of Aβ40 and Aβ42 in the hippocampus of age-matched 2xTg AD mice (AD/δ-COP WT vs. AD/δ-COP mut mice) (n = 6–11 per genotype; one outlier has been excluded among the 9-mo-old mice). (B) Analysis of APP and actin levels by Western blotting. (*P < 0.05, **P < 0.01, ****P < 0.0001, two- or one-tailed Student’s t test or Mann–Whitney test. The results are shown as means ± SEM.)

Fig. 3.

Effect of partial inactivation of δ-COP on amyloid plaque formation evaluated by immunohistochemistry in the hippocampus of 2xTg AD mice. (A) Representative images show amyloid plaques in the hippocampus of male mice at 9 mo (n = 6 per genotype). (Scale bar, 500 μm.) (B) Quantification of the number of plaques in the hippocampus (n = 6 per genotype). (**P < 0.01, ***P < 0.001, two- or one-tailed Student’s t test with or without Welch’s correction. The results are shown as means ± SEM.)

Fig. 4.

Effect of partial inactivation of δ-COP on amyloid plaque formation evaluated by immunohistochemistry in the piriform cortex of 2xTg AD mice. (A) Representative images show amyloid plaques in the piriform cortex (black boxes) of male mice at 9 mo (n = 6 per genotype). (B) Quantification of the number of plaques in the piriform cortex (n = 6 per genotype). (*P < 0.05, ***P < 0.001, two-tailed Student’s t test. The results are shown as means ± SEM.)

Fig. 5.

Effect of partial inactivation of δ-COP on memory in 2xTg AD mice. (A and B) Effect of δ-COP on novel object recognition in 9-mo-old male mice in (A) a WT or (B) an AD background. Measurement of time spent with a novel versus familiar object. (C) Measurement of the number of visits to the novel versus familiar object (n = 5–14 per genotype). (*P < 0.05, one-tailed Student’s t test or Mann–Whitney test; n.s., not significant. The results are shown as means ± SEM.)

Fig. S1.

Replicates of amyloid plaque immunostaining in 9-mo-old AD/δ-COP WT vs. AD/δ-COP mice. Representative images showing amyloid plaques in the brain. Amyloid plaque development was studied in both (A) the hippocampus and (B) the piriform cortex. (Scale bar, 500 μm.)