Amyloid precursor protein secretases as therapeutic targets for traumatic brain injury

Abstract

Amyloid-beta (Abeta) peptides, found in Alzheimer's disease brain, accumulate rapidly after traumatic brain injury (TBI) in both humans and animals. Here we show that blocking either beta- or gamma-secretase, enzymes required for production of Abeta from amyloid precursor protein (APP), can ameliorate motor and cognitive deficits and reduce cell loss after experimental TBI in mice. Thus, APP secretases are promising targets for treatment of TBI.

Figure 1

Bace1 ablation protects against TBI-induced cell loss and behavioral deficits in vivo. (a) Quantification of Aβ_x-40 in the ipsilateral cortex 1 d, 3 d and 7 d after controlled cortical contusion injury, as outlined in the Supplementary Methods online. *P < 0.05 and ***P < 0.001 versus sham control by analysis of variance (ANOVA), Neuman-Keuls post-hoc test. Data are means ± s.e.m.; n = 4. (b) Western blot analysis of the amyloid-related proteins APP, sAPP-α, BACE1 and presenilin-1 (PS-1) after TBI in nontransgenic mice. Blots are representative of three separate experiments. (c) Fine motor coordination test on a beam walk apparatus. Deficits in coordination are recorded as foot faults. *P < 0.05, **P < 0.01 and ***P < 0.001 by ANOVA, Newman-Keuls post-hoc test. Data are means ± s.e.m.; n = 8. (d) Spatial learning in a Morris water maze. Each trial is the average of four individual tests, and four trials were performed with the escape latency to the platform being recorded. **P < 0.01 versus uninjured Bace1^+/+ and ++P < 0.01 versus injured Bace1^+/+ by ANOVA, Newman-Keuls post-hoc test. Data are means ± s.e.m. n = 5 for Bace1^+/+ and n = 8 for TBI groups. (e) T2-weighted MRI images from TBI mice 21 d after injury. Representative images from three different mice in each group. Lesions of the left hemisphere appear white on the images (scale bar, 1mm). (f) Representative images of H&E-stained sections, highlighting hippocampal sparing in injured Bace1^−/− mice. Scale bar, 500 μm. (g) Hippocampal volume, as assessed by comparing tissue remaining in the ipsilateral side with the contralateral hippocampus. **P < 0.01 by Mann-Whitney U test, n = 5. (h) Lesion volume 21 d after injury. *P < 0.05 by Student’s t test; data are means ± s.e.m., n = 5. All procedures were reviewed and approved by the Georgetown University Animal Care and Use Committee.

Figure 2

Chronic γ-secretase inhibition protects against TBI-induced cell loss and behavioral deficits in vivo. (a) Fine motor coordination test on a beam walk apparatus. Deficits in coordination are recorded as foot faults. ***P < 0.001 by ANOVA, Newman-Keuls post-hoc test. Data are means ± s.e.m. n = 11 for vehicle and n = 8 for DAPT. (b) Spatial learning in a Morris water maze. *P < 0.05, **P < 0.01 and ***P < 0.001 versus vehicle sham by ANOVA, Newman-Keuls post-hoc test. Data are means ± s.e.m. n = 6 for sham groups, n = 11 for vehicle-treated TBI mice and n = 8 for DAPT-treated TBI mice. (c) Swim speed measures from the water maze test in b. (d) Successive T2-weighted MRI slices showing the depth of lesion volume in 21 d CCI-injured mice. The top panels show a vehicle-treated mouse with the lesion clearly visible through eight consecutive 0.5-mm slices (region of hyperintensity in the upper left region of the brain). The bottom panels show the extent of injury in a mouse chronically treated with DAPT. Scale bar, 2 mm; representative images shown, n = 6. (e) Representative H&E-stained sections showing the extent of tissue sparing in DAPT-treated mice. Subcortical white matter tracts are spared in DAPT treated mice (arrowhead). Scale bar, 750 μm. (f) Quantification of lesion volume. **P < 0.01 by Student’s t test. Data are means ± s.e.m. n = 4. (g) Representative images of NeuN-stained CA1 neurons showing neuronal damage in mice after TBI. Scale bar, 100 μm. (h) Stereological cell counts comparing NeuN-positive cells from the ipsilateral (Ipsi) CA1 region of the hippocampus to the contralateral (Contra) CA1 of vehicle and DAPT-treated TBI mice. *P < 0.05 and +P < 0.05 by ANOVA, Newman-Keuls post-hoc test. Data are means ± s.e.m., n = 3.