Progress of Brain Amyloid Deposition in Familial Alzheimer's Disease with Taiwan D678H APP Mutation

Endoplasmic reticulum stress induces Alzheimer's disease-like phenotypes in the neuron derived from the induced pluripotent stem cell with D678H mutation on amyloid precursor protein

Alzheimer's disease (AD), a progressive neurodegenerative disorder, is mainly caused by the interaction of genetic and environmental factors. The impact of environmental factors on the genetic mutation in the amyloid precursor protein (APP) is not well characterized. We hypothesized that Endoplasmic Reticulum (ER) stress would promote disease for the patient carrying the APP D678H mutation. Therefore, we analyzed the impact of a familial AD mutation on amyloid precursor protein (APP D678H) under ER stress. Induced pluripotent stem cell (iPSC) from APP D678H mutant carrier was differentiated into neurons, which were then analyzed for AD-like changes. Immunocytochemistry and whole-cell patch-clamp recording revealed that the derived neurons on day 28 after differentiation showed neuronal markers and electrophysiological properties similar to those of mature neurons. However, the APP D678H mutant neurons did not have significant alterations in the levels of amyloid-β (Aβ) and phosphorylated tau (pTau) compared to its isogenic wild-type neuron. Only under ER stress, the neurons with the APP D678H mutation had more Aβ and pTau via immune detection assays. The higher level of Aβ in the APP D678H mutant neurons was probably due to the increased level of β-site APP cleaving enzyme (BACE1) and decreased level of Aβ degrading enzymes under ER stress. Increased Aβ and pTau under ER stress reduced the N-methyl-D-aspartate receptor (NMDAR) in Western blot analysis and altered electrophysiological properties in the mutant neurons. Our study provides evidence that the interaction between genetic mutation and ER stress would induce AD-like changes.

Mutational analysis in familial Alzheimer's disease of Han Chinese in Taiwan with a predominant mutation PSEN1 p.Met146Ile

Mutations in PSEN1, PSEN2, or APP genes are known to be causative for autosomal dominant Alzheimer’s disease (ADAD). While more than 400 mutations were reported worldwide, predominantly PSEN1, over 40 mutations have been reported in Han Chinese and were associated with earlier onset and more affected family members. Between 2002 and 2018, 77 patients in the neurological clinic of Taipei Veterans General Hospital with a history suggestive of ADAD were referred for mutational analysis. We retrospectively collected demographics, initial symptoms, neurological features and inheritance. We identified 16 patients with PSEN1 and 1 with APP mutation. Among the mutations identified, PSEN1 p.Pro117Leu, p.Met146Ile, p.Gly206Asp, p.Gly209Glu, p.Glu280Lys and p.Leu286Val and APP p.Asp678His were known pathogenic mutations; PSEN1 p.His131Arg and p.Arg157Ser were classified as likely pathogenic and variance of unknown significance respectively. The mean age at onset was 46.2 ± 6.2 years in patients with mutation found. PSEN1 p.Met146Ile, occurred in 56.2% (9/16) of patients with PSEN1 mutations, was the most frequent mutation in the cohort. The additional neurological features occurring in 9 PSEN1 p.Met146Ile index patients were similar with the literature. We found patients with genetic diagnoses were more likely to have positive family history, younger age at onset and less brain white matter hyperintensity.

Tau PET With 18F-THK-5351 Taiwan Patients With Familial Alzheimer's Disease With the APP p.D678H Mutation

Background: Brain ¹⁸F-AV-45 amyloid positron emission tomography (PET) in Taiwanese patients with familial Alzheimer's disease with the amyloid precursor protein (APP) p.D678H mutation tends to involve occipital and cerebellar cortical areas. However, tau pathology in patients with this specific Taiwan mutation remains unknown. In this study, we aimed to study the Tau PET images in these patients.

Methods: Clinical features, brain magnetic resonance imaging/computed tomography (MRI/CT), and brain ¹⁸F-THK-5351 PET were recorded in five patients with the APP p.D678H mutation and correlated with brain ¹⁸F-AV-45 PET images. We also compared the tau deposition patterns among five patients with familial mild cognitive impairment (fMCI), six patients with sporadic amnestic mild cognitive impairment (sMCI), nine patients with mild to moderate dementia due to Alzheimer's disease (AD), and 12 healthy controls (HCs). All of the subjects also received brain ¹⁸F-AV-45 PET.

Results: The nine patients with sAD and six patients with sMCI had a positive brain AV-45 PET scans, while the 12 HCs had negative brain AV-45 PET scans. All five patients with fMCI received a tau PET scan with the age at onset ranging from 46 to 53 years, in whom increased standard uptake value ratio (SUVR) of ¹⁸F-THK-5351 was noted in all seven brain cortical areas compared with the HCs. In addition, the SUVRs of ¹⁸F-THK-5351 were increased in the frontal, medial parietal, lateral parietal, lateral temporal, and occipital areas (P < 0.001) in the patients with sAD compared with the HCs. The patients with fMCI had a significant higher SUVR of ¹⁸F-THK-5351 in the cerebellar cortex compared to the patients with sMCI. The correlations between regional SUVR and Mini-Mental State Examination score and between regional SUVR and clinical dementia rating (sum box) scores within volumes of interest of Braak stage were statistically significant.

Conclusion: Tau deposition was increased in the patients with fMCI compared to the HCs. Increased regional SUVR in the cerebellar cortical area was a characteristic finding in the patients with fMCI. As compared between amyloid and tau PET, the amyloid deposition is diffuse, but tau deposition is limited to the temporal lobe in the patients with fMCI.