Adeno-associated virus gene therapy with cholesterol 24-hydroxylase reduces the amyloid pathology before or after the onset of amyloid plaques in mouse models of Alzheimer's disease

Abstract

The development of Alzheimer's disease (AD) is closely connected with cholesterol metabolism. Cholesterol increases the production and deposition of amyloid-beta (Abeta) peptides that result in the formation of amyloid plaques, a hallmark of the pathology. In the brain, cholesterol is synthesized in situ but cannot be degraded nor cross the blood-brain barrier. The major exportable form of brain cholesterol is 24S-hydroxycholesterol, an oxysterol generated by the neuronal cholesterol 24-hydroxylase encoded by the CYP46A1 gene. We report that the injection of adeno-associated vector (AAV) encoding CYP46A1 in the cortex and hippocampus of APP23 mice before the onset of amyloid deposits markedly reduces Abeta peptides, amyloid deposits and trimeric oligomers at 12 months of age. The Morris water maze (MWM) procedure also demonstrated improvement of spatial memory at 6 months, before the onset of amyloid deposits. AAV5-wtCYP46A1 vector injection in the cortex and hippocampus of amyloid precursor protein/presenilin 1 (APP/PS) mice after the onset of amyloid deposits also reduced markedly the number of amyloid plaques in the hippocampus, and to a less extent in the cortex, 3 months after the injection. Our data demonstrate that neuronal overexpression of CYP46A1 before or after the onset of amyloid plaques significantly reduces Abeta pathology in mouse models of AD.

Figures

Figure 1

Injections of AAV5-CYP46A1 vector in cerebral cortex and hippocampus of APP23 mice increase the level of 24S-hydroxycholesterol. (a) Representative expression of the wild-type (wtCYP46A1) and mutant (mtCYP46A1) forms of human CYP46A1 protein in the brain of 12-month-old APP23 mice after injection of adeno-associated vector (AAV) vector at 3 months. DG, dentate gyrus; Sbcl, subiculum; CA, Cornu Ammonis. Bar = 200 µmol/l. (b) Immunolabeling of hemaglutinin (HA)-tagged wtCYP46A1 protein in neurons (NeuN, nuclear staining, left panel) and co-localization with the endoplasmic reticulum Grp78 Bip marker (right panel). HA-tagged mtCYP46 protein has identical subcellular localization (data not shown). Bar = 200 µmol/l. (c) Cholesterol and 24S-hydroxycholesterol concentrations in the cerebral cortex and hippocampus of 12-month-old APP23 mice injected with AAV5-wtCYP46A1 or AAV5-mtCYP46A1 vectors (n = 5 mice per group). No difference in 24S-hydroxycholesterol and cholesterol content was observed between noninjected and AAV5-mtCYP46A1-injected APP23 mice. (d) Quantitative expression of murine 3-hydroxy-3-methylglutaryl-coenzyme A reductase (Hmgcr), sterol-binding protein 2 (Srebp2), acyl-coenzyme A: cholesterol acyltransferase 1 (Acat1), low-density lipoprotein–related protein 1 (Lrp1), lecithin:cholesterol acyltransferase (Lcat), and Niemann–Pick disease C1 (Npc1) genes in APP23 mice at 12 months after cerebral injections of AAV5-wtCYP46A1 or AAV5-mtCYP46A1 vectors (n = 5 mice per group). (Mann–Whitney U-test) ***P < 0.0005; NS, non significant.

Figure 2

Intracerebral delivery of CYP46A1 at 3 months markedly reduces amyloid pathology in APP23 mice at 12 months. (a) Representative immunostaining of amyloid deposits with NT2 antibody in 12-month-old APP23 mice injected with AAV5-mtCYP46A1 (upper panel) or AAV5-wtCYP46A1 (lower panel) vectors at 3 months. Bar = 200 µmol/l. (b) Stereological analyses of amyloid deposits number and surface in the cortex and hippocampus of APP23 mice injected with AAV5-mtCYP46A1 or AAV5-wtCYP46A1 vectors at 12 months (three different section levels per mouse, with three to five slices per level, n = 5 mice per group). (c) Aβ40 and Aβ42 peptide concentrations in the pooled cerebral cortex and hippocampus of 12-month-old APP23 mice injected with AAV5-wtCYP46A1 or AAV5-mtCYP46A1 vectors. Aβ peptides were quantified using enzyme-linked immunosorbent assay after a solubilization step in 5 mol/l guanidine–HCl (n = 5 mice per group). (d) Quantification at 12 months of mono-, tri-, hexa-, and dodecamers of Aβ peptides by western blotting after extraction in 10 mmol/l Tris–HCl (Tris), 10 mmol/l Tris–HCl/2% Triton (Triton) and 10 mmol/l Tris–HCl/0.5% SDS (SDS) buffers (n = 5 mice per group). (e) Representative western blot of full length APP (APPfl), BACE1, PSEN1, and CTFs (C83, C99, and AICD) in pooled cerebral cortex and hippocampus samples from 12-month-old APP23 mice injected with AAV5-wtCYP46A1 and AAV5-mtCYP46A1 vectors (n = 5 mice per group). (f) Quantification at 12 months of α- and β-secretase C-terminal fragments (C83 and C99) in pooled cerebral cortex and hippocampus samples from 12-month-old APP23 mice injected with AAV5-wtCYP46A1 and AAV5-mtCYP46A1 vectors. The amounts of C-terminal fragments are normalized to ACTIN level (n = 5 mice per group). AU, arbitrary unit. (Mann–Whitney U-test). *P < 0.05; **P < 0.005.

Figure 3

Decreased microgliosis and improvement of cognitive performances in APP23 mice treated with AAV5-wtCYP46A1 vector. (a,b) Number of Iba-1 and glial fibrillary acidic protein-positive cells in the cortex, hippocampus, and cerebellum of APP23 mice at 12 months after injections of AAV5-wtCYP46A1 or AAV5-mutCYP46A1 vectors at 3 months. The cerebellum is not affected by amyloid deposits and was thus chosen as a control brain region. Bar = 100 µmol/l. (n = 5 mice per group; three section levels per mouse were analyzed). (Mann–Whitney U-test). *P < 0.05; NS, not significant. (c) Path length, (d) escape latency, and (e) swim speed curves during the acquisition phase of the Morris water maze procedure in 6-month-old APP23 mice treated with the AAV5-wtCYP46A1 (n = 5, open circles) or AAV-mutCYP46A1 (control) vectors (n = 4, filled circles) at 3 months. Data points represent mean (± SEM) summed results of four daily trials. (f) The proportion of total time spent in each quadrant of the Morris water maze during probe trial in APP23 mice treated with the control versus the therapeutic vectors. Bars represent mean (SEM) percentage of total time in a specific quadrant.

Figure 4

Intracerebral delivery of CYP46A1 at 3 months reduces amyloid deposits at 6 months in APP/PS mice. (a) Representative immunostaining of amyloid deposits with NT2 antibody in 3-month-old APP/PS mice (age of injection). (b) Representative immunostaining of amyloid deposits and stereological analyses of amyloid deposits in the cortex and hippocampus of 6-month-old APP/PS mice injected with AAV5-mtCYP46A1 (right panel) or AAV5-wtCYP46A1 (left panel) vectors (three different section levels per mouse, with three to five slices per level, n = 5 mice per group). Bar = 200 µmol/l. (Mann–Whitney U-test) *P < 0.05.

Figure 5

Quantification of C-terminal fragments in N2a-APP17 cells expressing the cholesterol 24-hydroxylase gene and measurement of cholesterol, APP and PSEN1 in detergent-resistant membrane (DRM). (a) Representative western blot and quantification of α, β- and γ-secretase C-terminal fragments (C83, C99, and AICD) in crude extracts from N2a-APP17, N2a-APP-CYP-A, and N2a-APP-CYP-B cells. Black bars: N2a-APP17; gray bars: N2a-APP-CYP-A; white bars: N2a-APP-CYP-B. The amounts of C-terminal fragments are normalized to ACTIN level; AU, arbitrary unit. (b) Cholesterol content in DRMs isolated after iodixanol gradient ultracentrifugation from N2a-APP17, N2a-APP-CYP-A, and N2a-APP-CYP-B cells. As expected, highest content of cholesterol is found in flotillin-2 (FLOT-2) positive fractions from N2a-APP17 cells. Black bars: N2a-APP17; gray bars: N2a-APP-CYP-A; white bars: N2a-APP-CYP-B. (c) Protein blot analysis of APP, PSEN1, and ACTIN in N2a-APP17, N2a-APP-CYP-A, and N2a-APP-CYP-B cells. The percentages of APP and PSEN1 associated with FLOT-2 positive fractions 1 and 4 are shown on the right. All experiments were done in triplicate. (analysis of variance and post hoc Student's t-test) *P < 0.05; **P < 0.005; NS, non significant.