Cerebrospinal fluid levels of phosphorylated tau and Aβ1-38/Aβ1-40/Aβ1-42 in Alzheimer's disease with PS1 mutations

Genetics, Functions, and Clinical Impact of Presenilin-1 (PSEN1) Gene

Presenilin-1 (PSEN1) has been verified as an important causative factor for early onset Alzheimer's disease (EOAD). PSEN1 is a part of γ-secretase, and in addition to amyloid precursor protein (APP) cleavage, it can also affect other processes, such as Notch signaling, β-cadherin processing, and calcium metabolism. Several motifs and residues have been identified in PSEN1, which may play a significant role in γ-secretase mechanisms, such as the WNF, GxGD, and PALP motifs. More than 300 mutations have been described in PSEN1; however, the clinical phenotypes related to these mutations may be diverse. In addition to classical EOAD, patients with PSEN1 mutations regularly present with atypical phenotypic symptoms, such as spasticity, seizures, and visual impairment. In vivo and in vitro studies were performed to verify the effect of PSEN1 mutations on EOAD. The pathogenic nature of PSEN1 mutations can be categorized according to the ACMG-AMP guidelines; however, some mutations could not be categorized because they were detected only in a single case, and their presence could not be confirmed in family members. Genetic modifiers, therefore, may play a critical role in the age of disease onset and clinical phenotypes of PSEN1 mutations. This review introduces the role of PSEN1 in γ-secretase, the clinical phenotypes related to its mutations, and possible significant residues of the protein.

A Pathogenic Presenilin-1 Val96Phe Mutation from a Malaysian Family

Presenilin-1 (PSEN1) is one of the causative genes for early onset Alzheimer's disease (EOAD). Recently, emerging studies have reported several novel PSEN1 mutations among Asians. In this study, a PSEN1 Val96Phe mutation was discovered in two siblings from Malaysia with a strong family history of disease. This is the second report of PSEN1 Val96Phe mutation among EOAD patients in Asia and in the world. Patients presented symptomatic changes in their behaviors and personality, such as apathy and withdrawal in their 40s. Previous cellular studies with COS1 cell lines revealed the mutation increased the amyloid-β42 (Aβ42) productions. In the present study, whole-exome sequencing was performed on the two siblings with EOAD, and they were analyzed against the virtual panel of 100 genes from various neurodegenerative diseases. In silico modeling was also performed on PSEN1 Val96Phe mutation. This mutation was located on the first transmembrane helix of PSEN1 protein, resulting significant intramolecular stresses in the helices. This helical domain would play a significant role in γ-secretase cleavage for the increased Aβ42 productions. Several other adjacent mutations were reported in this helical domain, including Ile83Thr or Val89Leu. Our study suggested that perturbations in TMI-HLI-TMII regions could also be associated with C-terminal fragment accumulation of APP and enhanced amyloid productions.

Cerebral Microbleeds, Cerebrospinal Fluid, and Neuroimaging Markers in Clinical Subtypes of Alzheimer's Disease

Lobar cerebral microbleeds (CMBs) in Alzheimer's disease (AD) are associated with cerebral amyloid angiopathy (CAA) due to vascular amyloid beta (Aβ) deposits. However, the relationship between lobar CMBs and clinical subtypes of AD remains unknown. Here, we enrolled patients with early- and late-onset amnestic dominant AD, logopenic variant of primary progressive aphasia (lvPPA) and posterior cortical atrophy (PCA) who were compatible with the AD criteria. We then examined the levels of cerebrospinal fluid (CSF) biomarkers [Aβ1-42, Aβ1-40, Aβ1-38, phosphorylated tau 181 (P-Tau), total tau (T-Tau), neurofilament light chain (NFL), and chitinase 3-like 1 protein (YKL-40)], analyzed the number and localization of CMBs, and measured the cerebral blood flow (CBF) volume by ^99mTc-ethyl cysteinate dimer single photon emission computerized tomography (^99mTc ECD-SPECT), as well as the mean cortical standard uptake value ratio by ¹¹C-labeled Pittsburgh Compound B-positron emission tomography (¹¹C PiB-PET). Lobar CMBs in lvPPA were distributed in the temporal, frontal, and parietal lobes with the left side predominance, while the CBF volume in lvPPA significantly decreased in the left temporal area, where the number of lobar CMBs and the CBF volumes showed a significant inversely correlation. The CSF levels of NFL in lvPPA were significantly higher compared to the other AD subtypes and non-demented subjects. The numbers of lobar CMBs significantly increased the CSF levels of NFL in the total AD patients, additionally, among AD subtypes, the CSF levels of NFL in lvPPA predominantly were higher by increasing number of lobar CMBs. On the other hand, the CSF levels of Aβ1-38, Aβ1-40, Aβ1-42, P-Tau, and T-Tau were lower by increasing number of lobar CMBs in the total AD patients. These findings may suggest that aberrant brain hypoperfusion in lvPPA was derived from the brain atrophy due to neurodegeneration, and possibly may involve the aberrant microcirculation causing by lobar CMBs and cerebrovascular injuries, with the left side dominance, consequently leading to a clinical phenotype of logopenic variant.

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.

Fluid Biomarkers and APOE Status of Early Onset Alzheimer's Disease Variants: A Systematic Review and Meta-Analysis

BACKGROUND

Numerous studies have reported on cerebrospinal fluid (CSF) and blood biomarkers of Alzheimer's disease (AD); however, to date, none has compared biomarker patterns across the early-onset subtypes, i.e., early onset sporadic AD (EOsAD) and autosomal dominant AD (ADAD), qualitatively and quantitatively.

OBJECTIVE

To compare the fluid biomarker patterns in early-onset subtypes of AD; EOsAD and ADAD.

METHODS

Six scientific databases were searched for peer-reviewed research publications. The total number of individuals used in all the meta-analysis were 2,427, comprised of 1,337 patients and 1,090 controls.

RESULTS

In the subset of EOsAD cases without APP, PSEN1/PSEN2 mutations, CSF Aβ42 and tau levels were higher when compared to the EOsAD group as a whole. Prevalence of the APOEɛ4 allele was more elevated in EOsAD relative to controls, and not significantly elevated in ADAD cases.

CONCLUSION

Established CSF biomarkers confirmed quantitative differences between variants of EOAD. EOsAD is enriched with APOEɛ4, but the level is not higher than generally reported in late-onset AD. The results prompt further exploration of the etiopathogenesis of EOsAD, which accounts for ∼4-10% of all AD cases, but the reasons for the early onset remain poorly understood.

Systematic validation of variants of unknown significance in APP, PSEN1 and PSEN2

Alzheimer’s disease (AD) is a neurodegenerative disease that is clinically characterized by progressive cognitive decline. More than 200 pathogenic mutations have been identified in amyloid-β precursor protein (APP), presenilin 1 (PSEN1) and presenilin 2 (PSEN2). Additionally, common and rare variants occur within APP, PSEN1, and PSEN2 that may be risk factors, protective factors, or benign, non-pathogenic polymorphisms. Yet, to date, no single study has carefully examined the effect of all of the variants of unknown significance reported in APP, PSEN1 and PSEN2 on Aβ isoform levels in vitro. In this study, we analyzed Aβ isoform levels by ELISA in a cell-based system in which each reported pathogenic and risk variant in APP, PSEN1, and PSEN2 was expressed individually. In order to classify variants for which limited family history data is available, we have implemented an algorithm for determining pathogenicity using available information from multiple domains, including genetic, bioinformatic, and in vitro analyses. We identified 90 variants of unknown significance and classified 19 as likely pathogenic mutations. We also propose that five variants are possibly protective. In defining a subset of these variants as pathogenic, individuals from these families may eligible to enroll in observational studies and clinical trials.

Histidine 131 in presenilin 1 is the pH-sensitive residue that causes the increase in Aβ42 level in acidic pH

Alzheimer disease (AD) is the most common neurodegenerative disease worldwide. The pathological hallmark of AD is the presence of senile plaques in the brain, which are accumulations of amyloid-β peptide (Aβ) ending at the 42nd residue (i.e. Aβ42), which is produced through multistep cleavage by γ-secretase. Thus, methods to regulate γ-secretase activity to attenuate the production of Aβ42 are in urgent demand towards the development of treatments for AD. We and others have demonstrated that γ-secretase activity is affected by its localization and ambient environment. In particular, an increase in Aβ42 production is correlated with the intracellular transport of γ-secretase and endosomal maturation-dependent luminal acidification. In this study, we focused on the mechanism by which γ-secretase affects Aβ42 production together with alterations in pH. Histidine is known to function as a pH sensor in many proteins, to regulate their activities through the protonation state of the imidazole side chain. Among the histidines facing the luminal side of presenilin (PS) 1, which is the catalytic subunit of γ-secretase, point mutations at H131 had no effect on the Aβ42 production ratio in an acidic environment. We also observed an increase in Aβ42 ratio when histidine was introduced into N137 of PS2, which is the corresponding residue of H131 in PS1. These results indicated that H131 serves as the pH sensor in PS1, which contains γ-secretase, to regulate Aβ42 production depending on the luminal pH. Our findings provide new insights into therapeutic strategies for AD targeting endosomes or the intracellular transport of γ-secretase.

Extracellular Vesicle as a Source of Alzheimer's Biomarkers: Opportunities and Challenges

Alzheimer’s disease (AD) is a chronic progressive neurodegenerative disease characterized by memory decline and cognitive dysfunction. Although the primary causes of AD are not clear, it is widely accepted that the accumulation of amyloid beta (Aβ) and consecutive hyper-phosphorylation of tau, synaptic loss, oxidative stress and neuronal death might play a vital role in AD pathogenesis. Recently, it has been widely suggested that extracellular vesicles (EVs), which are released from virtually all cell types, are a mediator in regulating AD pathogenesis. Clinical evidence for the diagnostic performance of EV-associated biomarkers, particularly exosome biomarkers in the blood, is also emerging. In this review, we briefly introduce the biological function of EVs in the central nervous system and discuss the roles of EVs in AD pathogenesis. In particular, the roles of EVs associated with autophagy and lysosomal degradation systems in AD proteinopathy and in disease propagation are discussed. Next, we summarize candidates for biochemical AD biomarkers in EVs, including proteins and miRNAs. The accumulating data brings hope that the application of EVs will be helpful for early diagnostics and the identification of new therapeutic targets for AD. However, at the same time, there are several challenges in developing valid EV biomarkers. We highlight considerations for the development of AD biomarkers from circulating EVs, which includes the standardization of pre-analytical sources of variability, yield and purity of isolated EVs and quantification of EV biomarkers. The development of valid EV AD biomarkers may be facilitated by collaboration between investigators and the industry.

Genetic Markers of Alzheimer's Disease

Alzheimer's disease is a complex and heterogeneous, severe neurodegenerative disorder and the predominant form of dementia, characterized by cognitive disturbances, behavioral and psychotic symptoms, progressive cognitive decline, disorientation, behavioral changes, and death. Genetic background of Alzheimer's disease differs between early-onset familial Alzheimer's disease, other cases of early-onset Alzheimer's disease, and late-onset Alzheimer's disease. Rare cases of early-onset familial Alzheimer's diseases are caused by high-penetrant mutations in genes coding for amyloid precursor protein, presenilin 1, and presenilin 2. Late-onset Alzheimer's disease is multifactorial and associated with many different genetic risk loci (>20), with the apolipoprotein E ε4 allele being a major genetic risk factor for late-onset Alzheimer's disease. Genetic and genomic studies offer insight into many additional genetic risk loci involved in the genetically complex nature of late-onset Alzheimer's disease. This review highlights the contributions of individual loci to the pathogenesis of Alzheimer's disease and suggests that their exact contribution is still not clear. Therefore, the use of genetic markers of Alzheimer's disease, for monitoring development, time course, treatment response, and prognosis of Alzheimer's disease, is still far away from the clinical application, because the contribution of genetic variations to the relative risk of developing Alzheimer's disease is limited. In the light of prediction and prevention of Alzheimer's disease, a novel approach could be found in the form of additive genetic risk scores, which combine additive effects of numerous susceptibility loci.

Autophagy and Alzheimer's Disease: From Molecular Mechanisms to Therapeutic Implications

Alzheimer’s disease (AD) is the most common cause of progressive dementia in the elderly. It is characterized by a progressive and irreversible loss of cognitive abilities and formation of senile plaques, composed mainly of amyloid β (Aβ), and neurofibrillary tangles (NFTs), composed of tau protein, in the hippocampus and cortex of afflicted humans. In brains of AD patients the metabolism of Aβ is dysregulated, which leads to the accumulation and aggregation of Aβ. Metabolism of Aβ and tau proteins is crucially influenced by autophagy. Autophagy is a lysosome-dependent, homeostatic process, in which organelles and proteins are degraded and recycled into energy. Thus, dysfunction of autophagy is suggested to lead to the accretion of noxious proteins in the AD brain. In the present review, we describe the process of autophagy and its importance in AD. Additionally, we discuss mechanisms and genes linking autophagy and AD, i.e., the mTOR pathway, neuroinflammation, endocannabinoid system, ATG7, BCL2, BECN1, CDK5, CLU, CTSD, FOXO1, GFAP, ITPR1, MAPT, PSEN1, SNCA, UBQLN1, and UCHL1. We also present pharmacological agents acting via modulation of autophagy that may show promise in AD therapy. This review updates our knowledge on autophagy mechanisms proposing novel therapeutic targets for the treatment of AD.

Generation of Rabbit Monoclonal Antibody to Amyloid-β38 (Aβ38): Increased Plasma Aβ38 Levels in Down Syndrome

Secreted soluble amyloid-β (Aβ)38 is the second most prominent Aβ form next to Aβ40, and is found in cerebrospinal fluid (CSF) and blood. Recent studies have shown the importance of quantitation of CSF Aβ38 levels in combination with those of Aβ40 and Aβ42 to support the diagnosis of Alzheimer's disease (AD), and other neurodegenerative diseases, and to facilitate drug discovery studies. However, the availability of reliable and specific Aβ38 monoclonal antibody is limited. Our first aim was to generate and partially characterize rabbit monoclonal antibody (RabmAb) to Aβ38. The antibody was specific to Aβ38, since it did not react with Aβ37, Aβ39, Aβ40, or Aβ42 in ELISA or immunoblotting. The antibody was sensitive enough to measure Aβ38 levels in plasma. Our second aim was to quantitate Aβ38 levels in plasma from older Down syndrome (DS) persons and age-matched controls. Persons with DS (35 years and older) have neuropathological changes characteristic of AD. Studies have shown that plasma Aβ40 and Aβ42 levels are higher in older persons with DS than in controls. However, none examined Aβ38 levels in DS. Our quantitation data showed that, like Aβ40 and Aβ42 plasma levels, Aβ38 plasma levels were higher in DS than in controls. Longitudinal studies will determine whether plasma Aβ38 levels in combination with levels of Aβ40 and Aβ42 are useful to predict early signs of AD in DS.

Autosomal Dominant Alzheimer Disease: A Unique Resource to Study CSF Biomarker Changes in Preclinical AD

Our understanding of the pathogenesis of Alzheimer disease (AD) has been greatly influenced by investigation of rare families with autosomal dominant mutations that cause early onset AD. Mutations in the genes coding for amyloid precursor protein (APP), presenilin 1 (PSEN-1), and presenilin 2 (PSEN-2) cause over-production of the amyloid-β peptide (Aβ) leading to early deposition of Aβ in the brain, which in turn is hypothesized to initiate a cascade of processes, resulting in neuronal death, cognitive decline, and eventual dementia. Studies of cerebrospinal fluid (CSF) from individuals with the common form of AD, late-onset AD (LOAD), have revealed that low CSF Aβ42 and high CSF tau are associated with AD brain pathology. Herein, we review the literature on CSF biomarkers in autosomal dominant AD (ADAD), which has contributed to a detailed road map of AD pathogenesis, especially during the preclinical period, prior to the appearance of any cognitive symptoms. Current drug trials are also taking advantage of the unique characteristics of ADAD and utilizing CSF biomarkers to accelerate development of effective therapies for AD.

CSF levels of Aβ1-38/Aβ1-40/Aβ1-42 and (11)C PiB-PET studies in three clinical variants of primary progressive aphasia and Alzheimer's disease

Primary progressive aphasia (PPA) is a cognitive syndrome characterized by progressive and isolated language impairments due to neurodegenerative diseases. Recently, an international group of experts published a Consensus Classification of the three PPA clinical variants (naPPA, svPPA and lvPPA). We analyzed 24 patients with PPA by cognitive functions, neuroimaging (MRI, (99 m)Tc ECD-SPECT, (11)C PiB-PET and FDG-PET) and cerebrospinal fluid (CSF) analysis (ptau-181, Aβ1-42, Aβ1-40 and Aβ1-38), to elucidate relationships between neuroimaging studies and biochemical findings in the three PPA clinical variants. Cognitive and speech functions were measured by mini-mental state examination and standard language test of aphasia. The patients with lvPPA showed significant decreases in CSF Aβ1-42 and ratios of Aβ1-42/Aβ1-40 and Aβ1-42/Aβ1-38, and significant increases in CSF ptau-181 and ratios of ptau-181/Aβ1-42 and ptau-181/Aβ1-38; these findings were similar to those of patients with Alzheimer's disease (AD). We observed a higher frequency of the ApoE ε4 allele in the lvPPA patients relative to the two other PPA variants. In (11)C PiB-PET of lvPPA patients, PiB positive findings were detected in cortices of frontal, temporal and parietal lobes and the posterior cingulate, where massive Aβ may accumulate due to AD. Our results of AD-CSF markers including Aβ1-38 and (11)C PiB-PET in the lvPPA patients demonstrate a common pathological mechanism with the occurrence of AD.

Longitudinal change in CSF biomarkers in autosomal-dominant Alzheimer's disease

Clinicopathological evidence suggests that the pathology of Alzheimer's disease (AD) begins many years before the appearance of cognitive symptoms. Biomarkers are required to identify affected individuals during this asymptomatic ("preclinical") stage to permit intervention with potential disease-modifying therapies designed to preserve normal brain function. Studies of families with autosomal-dominant AD (ADAD) mutations provide a unique and powerful means to investigate AD biomarker changes during the asymptomatic period. In this biomarker study, we collected cerebrospinal fluid (CSF), plasma, and in vivo amyloid imaging cross-sectional data at baseline in individuals from ADAD families enrolled in the Dominantly Inherited Alzheimer Network. Our study revealed reduced concentrations of CSF amyloid-β1-42 (Aβ1-42) associated with the presence of Aβ plaques, and elevated concentrations of CSF tau, ptau181 (phosphorylated tau181), and VILIP-1 (visinin-like protein-1), markers of neurofibrillary tangles and neuronal injury/death, in asymptomatic mutation carriers 10 to 20 years before their estimated age at symptom onset (EAO) and before the detection of cognitive deficits. When compared longitudinally, however, the concentrations of CSF biomarkers of neuronal injury/death within individuals decreased after their EAO, suggesting a slowing of acute neurodegenerative processes with symptomatic disease progression. These results emphasize the importance of longitudinal, within-person assessment when modeling biomarker trajectories across the course of the disease. If corroborated, this pattern may influence the definition of a positive neurodegenerative biomarker outcome in clinical trials.

Neonatal exposure to a moderate dose of ionizing radiation causes behavioural defects and altered levels of tau protein in mice

Medical use of ionizing radiation (IR) has great benefits for treatment and diagnostic imaging, but procedures as computerized tomography (CT) may deliver a significant radiation dose to the patient. Recently, awareness has been raised about possible non-cancer consequences from low dose exposure to IR during critical phases of perinatal and/or neonatal brain development. In the present study neonatal NMRI mice were whole body irradiated with a single dose of gamma radiation (0; 350 and 500 mGy) on postnatal day 10 (PND 10). At 2 and 4 months of age, mice of both sexes were observed for spontaneous behaviour in a novel home environment. The neuroproteins CaMKII, GAP-43, synaptophysin and total tau in male mouse cerebral cortex and hippocampus were analysed 24h post-irradiation and in adults at 6 months of age exposed to 0 or 500 mGy on PND 10. A significantly dose-response related deranged spontaneous behaviour in 2- and 4-month-old mice was observed, where both males and females displayed a modified habituation, indicating reduced cognitive function. The dose of 350 mGy seems to be a tentative threshold. Six-month-old male mice showed a significantly increased level of total tau in cerebral cortex after irradiation to 500 mGy compared to controls. This demonstrates that a single moderate dose of IR, given during a defined critical period of brain development, is sufficient to cause persistently reduced cognitive function. Moreover, an elevation of tau protein was observed in male mice displaying reduced cognitive function.

Developmental exposure to the polybrominated diphenyl ether PBDE 209: Neurobehavioural and neuroprotein analysis in adult male and female mice

Polybrominated diphenyl ethers (PBDEs), used as flame retardants in polymer products, are reported to cause developmental neurotoxic effects in mammals. The present study have investigated neurotoxic effects arising from neonatal exposure to PBDE 209, including alterations in sex differences, spontaneous behaviour, learning and memory, neuroproteins and altered susceptibility of the cholinergic system in adults. Three-day-old NMRI mice, of both sexes, were exposed to PBDE 209 (2,2',3,3',4,4',5,5',6,6'-decaBDE at 0, 1.4, 6.0 and 14.0μmol/kg b.w.). At adult age (2-7 months) a similar developmental neurotoxic effects in both male and female mice were seen, including lack of or reduced habituation to a novel home environment, learning and memory defects, modified response to the cholinergic agent's paraoxon (males) and nicotine (females) indicating increased susceptibility of the cholinergic system. The behavioural defects were dose-response related and persistent. In mice of both sexes and showing behavioural defects, neuroprotein tau was increased.

Relative ratio and level of amyloid-β 42 surrogate in cerebrospinal fluid of familial Alzheimer disease patients with presenilin 1 mutations

BACKGROUND

Presenilin 1 (PS1) mutations associated with familial Alzheimer disease (FAD) generally increase the amyloid-β 42 (Aβ42) to Aβ40 ratio secreted in cultured cells. Some of these mutants reduce the secretion of Aβ40 rather than increase that of Aβ42. Since it has been difficult to estimate Aβ42 secretion in brains of PS1-FAD patients due to substantial Aβ42 accumulation, it remains unknown whether the enhanced Aβ42 to Aβ40 ratio in brains of FAD patients is caused by elevated Aβ42 secretion or by reduced secretion of Aβ40.

OBJECTIVE/METHODS

Cerebrospinal fluids (CSF) of PS1-FAD patients and neurological control patients (controls) were collected. Levels of CSF amyloid precursor-like protein-1-derived Aβ-like peptide (APL1β), including APL1β28, an Aβ42 surrogate marker, were quantified by liquid chromatography tandem mass spectrometry, and Aβ42 secretion in the brain was estimated.

RESULTS

The relative ratio of CSF APL1β28 to total APL1β was higher in PS1-FAD patients than in controls. Importantly, CSF APL1β28 was not significantly higher. However, C-terminally shorter CSF APL1β25 and APL1β27 were significantly lower in PS1-FAD patients and, as expected, so were CSF Aβ40 and Aβ42.

CONCLUSION

A higher relative ratio of the CSF Aβ42 surrogate in PS1-FAD patients is not due to its increase in CSF, suggesting that massive Aβ42 accumulation in the PS1-FAD brain occurs without an apparent increase in Aβ42 secretion.