Mutations In Presenilin Research Articles

Aβ43 levels determine the onset of pathological amyloid deposition

About 2% of Alzheimer's disease (AD) cases have early onset (FAD) and are caused by mutations in either Presenilins (PSEN1/2) or amyloid-β precursor protein (APP). PSEN1/2 catalyze production of Aβ peptides of different length from APP. Aβ peptides are the major components of amyloid plaques, a pathological lesion that characterizes AD. Analysis of mechanisms by which PSEN1/2 and APP mutations affect Aβ peptide compositions lead to the implication of the absolute or relative increase in Aβ42 in amyloid-β plaques formation. Here, to elucidate the formation of pathogenic Aβ cocktails leading to amyloid pathology, we utilized FAD rat knock-in models carrying the Swedish APP (Apps allele) and the PSEN1 L435F (Psen1LF allele) mutations. To accommodate the differences in the pathogenicity of rodent and human Aβ, these rat models are genetically engineered to express human Aβ species as both the Swedish mutant allele and the WT rat allele (called Apph) have been humanized in the Aβ-coding region. Analysis of the eight possible FAD mutant permutations indicates that the CNS levels of Aβ43, rather than absolute or relative increases in Aβ42, determine the onset of pathological amyloid deposition in FAD knock-in rats. Notably, Aβ43 was found in amyloid plaques in late onset AD and mild cognitive impairment cases, suggesting that the mechanisms initiating amyloid pathology in FAD knock-in rat reflect disease mechanisms driving amyloid pathology in late onset AD. This study helps clarifying the molecular determinants initiating amyloid pathology and supports therapeutic interventions targeting Aβ43 in AD.

Presenilin-1 (PSEN1) Mutations: Clinical Phenotypes beyond Alzheimer's Disease.

Presenilin 1 (PSEN1) is a part of the gamma secretase complex with several interacting substrates, including amyloid precursor protein (APP), Notch, adhesion proteins and beta catenin. PSEN1 has been extensively studied in neurodegeneration, and more than 300 PSEN1 mutations have been discovered to date. In addition to the classical early onset Alzheimer's disease (EOAD) phenotypes, PSEN1 mutations were discovered in several atypical AD or non-AD phenotypes, such as frontotemporal dementia (FTD), Parkinson's disease (PD), dementia with Lewy bodies (DLB) or spastic paraparesis (SP). For example, Leu113Pro, Leu226Phe, Met233Leu and an Arg352 duplication were discovered in patients with FTD, while Pro436Gln, Arg278Gln and Pro284Leu mutations were also reported in patients with motor dysfunctions. Interestingly, PSEN1 mutations may also impact non-neurodegenerative phenotypes, including PSEN1 Pro242fs, which could cause acne inversa, while Asp333Gly was reported in a family with dilated cardiomyopathy. The phenotypic diversity suggests that PSEN1 may be responsible for atypical disease phenotypes or types of disease other than AD. Taken together, neurodegenerative diseases such as AD, PD, DLB and FTD may share several common hallmarks (cognitive and motor impairment, associated with abnormal protein aggregates). These findings suggested that PSEN1 may interact with risk modifiers, which may result in alternative disease phenotypes such as DLB or FTD phenotypes, or through less-dominant amyloid pathways. Next-generation sequencing and/or biomarker analysis may be essential in clearly differentiating the possible disease phenotypes and pathways associated with non-AD phenotypes.

Inhibitory, But Not Excitatory Synapses Are Reduced in the Hippocampus of the Six-Month-Old Alzheimer’s Disease Model Mouse

Abstract Alzheimer’s disease (AD) is a devastating neurodegenerative disorder and the most common cause of elderly dementia. One of the main features of AD diseased brain are amyloid plaques, pathological depositions made of β-amyloid peptide, derived from β- amyloid precursor protein (APP). To assess how AD pathology affects synapses in the hippocampus, brain region to be one of the earliest with obvious pathological changes, we examined APPPS1 mice, transgeneticaly expressing human APP mutation (“Swedish mutation”) and human presenilin-1 mutation under the neuron-specific promoter, which develop AD symptoms early in life. We analyzed inhibitory and excitatory synapses using immunoflourescent staining and laser scanning confocal microscopy. In APPPS1 mice, inhibitory synaptic terminals labeled with vesicular inhibitory transmitter transporter (VGAT) were reduced in CA1 and CA3 regions of the hippocampus in APPPS1 mice compared to controls. This was true for both parvalbumin-positive and parvalbumin-negative terminals. On the other hand, excitatory synapses, coming from either hippocampal or entorhinal projections were similar between the genotypes. We conclude that first changes in the hippocampus caused by amyloid pathology affect inhibitory, but not excitatory synapses.

A Novel Presenilin-1 Mutation Associated with Dementia and Spastic Paraplegia (P5-6.004)

A Novel Presenilin-1 Mutation Associated with Dementia and Spastic Paraplegia (P5-6.004)

Differential and substrate-specific inhibition of γ-secretase by the C-terminal region of ApoE2, ApoE3, and ApoE4

Aberrant low γ-secretase activity is associated with most of the presenilin mutations that underlie familial Alzheimer's disease (fAD). However, the role of γ-secretase in the more prevalent sporadic AD (sAD) remains unaddressed. Here, we report that human apolipoprotein E (ApoE), the most important genetic risk factor of sAD, interacts with γ-secretase and inhibits it with substrate specificity in cell-autonomous manners through its conserved C-terminal region (CT). This ApoE CT-mediated inhibitory activity is differentially compromised in different ApoE isoforms, resulting in an ApoE2>ApoE3>ApoE4 potency rank order inversely correlating to their associated AD risk. Interestingly, in an AD mouse model, neuronal ApoE CT migrates to amyloid plaques in the subiculum from other regions and alleviates the plaque burden. Together, our data reveal a hidden role of ApoE as a γ-secretase inhibitor with substrate specificity and suggest that this precision γ-inhibition by ApoE may protect against the risk of sAD.

Clinical and genetic characteristics in a central-southern Chinese cohort of early-onset Alzheimer's disease.

Mutations in the presenilin-1 (PSEN1), presenilin-2 (PSEN2), and amyloid precursor protein (APP) genes have been commonly identified in early-onset Alzheimer's disease (EOAD). Some of the mutations in the three causative genes, especially the PSEN1 gene, result in variable phenotypes and exhibit clinical heterogeneity among EOAD families. Using next-generation sequencing (NGS), we performed genetic screening in a Chinese cohort of 18 patients with EOAD, consisting of five familial EOAD and 13 sporadic cases. We identified two likely pathogenic PSEN1 mutations (one novel) and a novel APP mutation in three cases of EOAD, where two are familial and one is sporadic, respectively. In addition, we detected a few variants of uncertain significance (VUS) in several genes, including not only the two known variants in PSEN2 (p.H169N and p.V214L) but also genes causal of other types of dementia or previously identified as risk factors for AD, suggesting the possible involvement of multiple genes in the etiopathology of AD. The patients carrying PSEN1 mutations had an earlier mean age at the onset than those with PSEN2 or APP variants. The initial symptoms varied greatly among patients in the EOAD cohort, from progressive memory impairment and epilepsy to uncommon motor symptoms such as involuntary tremors in the upper extremities. In conclusion, our study provides further evidence of the genetic profile of patients with EOAD from China and expands the mutation spectrum of both PSEN1 and APP. In addition, our results highlight the clinical heterogeneity in patients with EOAD and mutations in PSEN1, PSEN2, and APP and suggest strong effects of genetic variants on clinical phenotypes. Future functional studies are needed to clarify the interaction between AD-causative gene mutations and phenotypic heterogeneity.

Presenilin 1 deficiency impairs Aβ42-to-Aβ40- and angiotensin-converting activities of ACE.

Alzheimer's disease (AD) is associated with amyloid β-protein 1-42 (Aβ42) accumulation in the brain. Aβ42 and Aβ40 are the major two species generated from amyloid precursor protein. We found that angiotensin-converting enzyme (ACE) converts neurotoxic Aβ42 to neuroprotective Aβ40 in an ACE domain- and glycosylation-dependent manner. Presenilin 1 (PS1) mutations account for most of cases of familial AD and lead to an increased Aβ42/40 ratio. However, the mechanism by which PSEN1 mutations induce a higher Aβ42/40 ratio is unclear. We over expressed human ACE in mouse wild-type and PS1-deficient fibroblasts. The purified ACE protein was used to analysis the Aβ42-to-Aβ40- and angiotensin-converting activities. The distribution of ACE was determined by Immunofluorescence staining. We found that ACE purified from PS1-deficient fibroblasts exhibited altered glycosylation and significantly reduced Aβ42-to-Aβ40- and angiotensin-converting activities compared with ACE from wild-type fibroblasts. Overexpression of wild-type PS1 in PS1-deficient fibroblasts restored the Aβ42-to-Aβ40- and angiotensin-converting activities of ACE. Interestingly, PS1 mutants completely restored the angiotensin-converting activity in PS1-deficient fibroblasts, but some PS1 mutants did not restore the Aβ42-to-Aβ40-converting activity. We also found that the glycosylation of ACE in adult mouse brain differed from that of embryonic brain and that the Aβ42-to-Aβ40-converting activity in adult mouse brain was lower than that in embryonic brain. PS1 deficiency altered ACE glycosylation and impaired its Aβ42-to-Aβ40- and angiotensin-converting activities. Our findings suggest that PS1 deficiency and PSEN1 mutations increase the Aβ42/40 ratio by reducing the Aβ42-to-Aβ40-converting activity of ACE.

Effects of presenilin-1 familial Alzheimer’s disease mutations on γ-secretase activation for cleavage of amyloid precursor protein

Presenilin-1 (PS1) is the catalytic subunit of γ-secretase which cleaves within the transmembrane domain of over 150 peptide substrates. Dominant missense mutations in PS1 cause early-onset familial Alzheimer’s disease (FAD); however, the exact pathogenic mechanism remains unknown. Here we combined Gaussian accelerated molecular dynamics (GaMD) simulations and biochemical experiments to determine the effects of six representative PS1 FAD mutations (P117L, I143T, L166P, G384A, L435F, and L286V) on the enzyme-substrate interactions between γ-secretase and amyloid precursor protein (APP). Biochemical experiments showed that all six PS1 FAD mutations rendered γ-secretase less active for the endoproteolytic (ε) cleavage of APP. Distinct low-energy conformational states were identified from the free energy profiles of wildtype and PS1 FAD-mutant γ-secretase. The P117L and L286V FAD mutants could still sample the “Active” state for substrate cleavage, but with noticeably reduced conformational space compared with the wildtype. The other mutants hardly visited the “Active” state. The PS1 FAD mutants were found to reduce γ-secretase proteolytic activity by hindering APP residue L49 from proper orientation in the active site and/or disrupting the distance between the catalytic aspartates. Therefore, our findings provide mechanistic insights into how PS1 FAD mutations affect structural dynamics and enzyme-substrate interactions of γ-secretase and APP.

Alzheimer's Disease: An Updated Overview of Its Genetics.

Alzheimer's disease (AD) is the most common neurodegenerative disease in the world. It is classified as familial and sporadic. The dominant familial or autosomal presentation represents 1-5% of the total number of cases. It is categorized as early onset (EOAD; <65 years of age) and presents genetic mutations in presenilin 1 (PSEN1), presenilin 2 (PSEN2), or the Amyloid precursor protein (APP). Sporadic AD represents 95% of the cases and is categorized as late-onset (LOAD), occurring in patients older than 65 years of age. Several risk factors have been identified in sporadic AD; aging is the main one. Nonetheless, multiple genes have been associated with the different neuropathological events involved in LOAD, such as the pathological processing of Amyloid beta (Aβ) peptide and Tau protein, as well as synaptic and mitochondrial dysfunctions, neurovascular alterations, oxidative stress, and neuroinflammation, among others. Interestingly, using genome-wide association study (GWAS) technology, many polymorphisms associated with LOAD have been identified. This review aims to analyze the new genetic findings that are closely related to the pathophysiology of AD. Likewise, it analyzes the multiple mutations identified to date through GWAS that are associated with a high or low risk of developing this neurodegeneration. Understanding genetic variability will allow for the identification of early biomarkers and opportune therapeutic targets for AD.

Alzheimer's disease-related presenilin 1 M146L mutation disrupts SERCA2a regulation and increases propensity of Ca waves in ventricular cardiomyocytes.

Presenilin 1 (PS1) is a transmembrane protein expressed in the endoplasmic reticulum (ER) of different cell types. It has been shown that Ca mishandling due to PS1 mutations contributes to the Alzheimer's disease (AD)-related neurodegeneration. PS1 is also expressed in the heart. Several clinical studies revealed that PS1 mutations are associated with cardiomyopathies. We previously showed that PS1 interacts with the cardiac ER Ca ATPase (SERCA2a) and regulates its function. Here, we studied the role of AD-related PS1M146L mutation in regulation of intracellular Ca homeostasis. Fluorescent resonance energy transfer (FRET) experiments in HEK293 cells transfected with fluorescently labeled SERCA2a and PS1M146L revealed that the mutation does not disrupt the interaction between these two proteins. Measurements of SERCA2a-mediated Ca transport showed that at low ER Ca loads ([Ca]ER≤0.15 mM), both PS1WT and PS1M146L enhance ER Ca uptake by a similar level (∼40%) compared to control (no PS1 expression). At high ER Ca loads ([Ca]ER≥0.35 mM), however, PS1WT reduced ER Ca uptake and ER Ca load, whereas PS1M146L was less effective in regulating SERCA2a function. We used in vivo gene delivery in mouse cardiac wall to study the effect of PS1WT and PS1M146L overexpression on Ca regulation in ventricular myocytes. We found that both PS1WT and PS1M146L localized predominantly at the sarcoplasmic reticulum. Analysis of cytosolic Ca dynamics revealed that PS1WT overexpression in cardiomyocytes increases diastolic Ca and decreases Ca transient amplitudes. In contrast, PS1M146L expression increased propensity of spontaneous Ca waves. These results illustrate that the lack of SERCA2a regulation by PS1M146L at high ER Ca loads can lead to ER Ca overload and Ca waves. These defects in Ca regulation might contribute to the onset of cardiomyopathies in patients with PS1 mutations.

Analysis of Non-Amyloidogenic Mutations in APP Supports Loss of Function Hypothesis of Alzheimer's Disease.

Proteolytic processing of amyloid precursor protein (APP) plays a critical role in pathogenesis of Azheimer's disease (AD). Sequential cleavage of APP by β- and γ-secretases leads to generation of Aβ40 (non-amyloidogenic) and Aβ42 (amyloidogenic) peptides. Presenilin-1 (PS1) or presenilin-2 (PS2) act as catalytic subunits of γ-secretase. Multiple familial AD (FAD) mutations in APP, PS1, or PS2 affect APP proteolysis by γ-secretase and influence levels of generated Aβ40 and Aβ42 peptides. The predominant idea in the field is the "amyloid hypothesis" that states that the resulting increase in Aβ42:Aβ40 ratio leads to "toxic gain of function" due to the accumulation of toxic Aβ42 plaques and oligomers. An alternative hypothesis based on analysis of PS1 conditional knockout mice is that "loss of function" of γ-secretase plays an important role in AD pathogenesis. In the present paper, we propose a mechanistic hypothesis that may potentially reconcile these divergent ideas and observations. We propose that the presence of soluble Aβ peptides in endosomal lumen (and secreted to the extracellular space) is essential for synaptic and neuronal function. Based on structural modeling of Aβ peptides, we concluded that Aβ42 peptides and Aβ40 peptides containing non-amyloidogenic FAD mutations in APP have increased the energy of association with the membranes, resulting in reduced levels of soluble Aβ in endosomal compartments. Analysis of PS1-FAD mutations also revealed that all of these mutations lead to significant reduction in both total levels of Aβ produced and in the Aβ40/Aβ42 ratio, suggesting that the concentration of soluble Aβ in the endosomal compartments is reduced as a result of these mutations. We further reasoned that similar changes in Aβ production may also occur as a result of age-related accumulation of cholesterol and lipid oxidation products in postsynaptic spines. Our analysis more easily reconciled with the "loss of γ-secretase function" hypothesis than with the "toxic gain of Aβ42 function" idea. These results may also explain why inhibitors of β- and γ- secretase failed in clinical trials, as these compounds are also expected to significantly reduce soluble Aβ levels in the endosomal compartments.

Unraveling Presenilin 2 Functions in a Knockout Zebrafish Line to Shed Light into Alzheimer’s Disease Pathogenesis

Mutations in presenilin 2 (PS2) have been causally linked to the development of inherited Alzheimer's disease (AD). Besides its role as part of the γ-secretase complex, mammalian PS2 is also involved, as an individual protein, in a growing number of cell processes, which result altered in AD. To gain more insight into PS2 (dys)functions, we have generated a presenilin2 (psen2) knockout zebrafish line. We found that the absence of the protein does not markedly influence Notch signaling at early developmental stages, suggesting a Psen2 dispensable role in the γ-secretase-mediated Notch processing. Instead, loss of Psen2 induces an exaggerated locomotor response to stimulation in fish larvae, a reduced number of ER-mitochondria contacts in zebrafish neurons, and an increased basal autophagy. Moreover, the protein is involved in mitochondrial axonal transport, since its acute downregulation reduces in vivo organelle flux in zebrafish sensory neurons. Importantly, the expression of a human AD-linked mutant of the protein increases this vital process. Overall, our results confirm zebrafish as a good model organism for investigating PS2 functions in vivo, representing an alternative tool for the characterization of new AD-linked defective cell pathways and the testing of possible correcting drugs.

Temporal Appearance of Enhanced Innate Anxiety in Alzheimer Model Mice

The prevalence of Alzheimer's disorder (AD) is increasing worldwide, and the co-morbid anxiety is an important, albeit often neglected problem, which might appear early during disease development. Animal models can be used to study this question. Mice, as prey animals, show an innate defensive response against a predator odor, providing a valuable tool for anxiety research. Our aim was to test whether the triple-transgenic mice model of AD shows signs of innate anxiety, with specific focus on the temporal appearance of the symptoms. We compared 3xTg-AD mice bearing human mutations of amyloid precursor protein, presenilin 1, and tau with age-matched controls. First, separate age-groups (between 2 and 18 months) were tested for the avoidance of 2-methyl-2-thiazoline, a fox odor component. To test whether hypolocomotion is a general sign of innate anxiety, open-field behavior was subsequently followed monthly in both sexes. The 3xTg-AD mice showed more immobility, approached the fox odor container less often, and spent more time in the avoidance zone. This effect was detectable already in two-month-old animals irrespective of sex, not visible around six months of age, and was more pronounced in aged females than males. The 3xTg-AD animals moved generally less. They also spent less time in the center of the open-field, which was detectable mainly in females older than five months. In contrast to controls, the aged 3xTg-AD was not able to habituate to the arena during a 30-min observation period irrespective of their sex. Amyloid beta and phospho-Tau accumulated gradually in the hippocampus, amygdala, olfactory bulb, and piriform cortex. In conclusion, the early appearance of predator odor- and open space-induced innate anxiety detected already in two-month-old 3xTg-AD mice make this genetically predisposed strain a good model for testing anxiety both before the onset of AD-related symptoms as well as during the later phase. Synaptic dysfunction by protein deposits might contribute to these disturbances.

Apolipoprotein E4 inhibits γ-secretase activity via binding to the γ-secretase complex.

The mechanisms of amyloid accumulation in familial Alzheimer's disease (FAD) and sporadic AD (SAD) are controversial. In FAD, mutations in presenilin (PSEN) impair γ-secretase activity and lead to abnormal amyloid β-protein (Aβ) production, thereby increasing the Aβ42/40 ratio. SAD is postulated to be caused by decreased Aβ clearance of apolipoprotein E4 (APOE4), the strongest risk factor for SAD. However, whether intracellular APOE4 affects Aβ production is unclear. Using APOE3 and APOE4 knock-in (KI) mouse brain and primary cultured fibroblasts from these mice, in this study, we demonstrated that APOE3 and APOE4 bind to the γ-secretase complex and isoform-dependently regulate its activity and Aβ production. We found that Aβ40 levels and γ-secretase activity were higher in APOE knockout mouse brain than in wild-type mouse brain. APOE4-KI fibroblasts had significant lower Aβ levels and γ-secretase activity but higher Aβ42/40 ratio compared with APOE3-KI cells, indicating that APOE4-KI reduces Aβ production by inhibiting γ-secretase activity. Interestingly, the levels of γ-secretase complex bound to APOE4 are higher than those bound to APOE3, and the levels of γ-secretase complex in the brain and fibroblasts of APOE4-KI mice were higher than those of APOE3-KI mice. Taken together, our findings demonstrate that intracellular APOE4 inhibits Aβ production, more preferentially inhibits Aβ40 production, and thereby induces an increase in the Aβ42/40 ratio via binding to the γ-secretase complex. These results suggest a novel mechanism in which intracellular APOE4 contributes to the pathogenesis of SAD by inhibiting γ-secretase activity.

Mutational Screening in Exon 6 of the PSEN2 Gene in Iranian Patients with Late-Onset Alzheimer's Disease

Background and Aims: One of the most important genes involved in Alzheimer's disease (AD) is the presenilin2 (PSEN2) gene, which is one of the main constituents of the gamma-secretase complex. Mutations in this gene promote the formation of amyloid plaques resulting in AD. The study aimed to evaluate the mutation variant in exon 6 of the PSEN2 gene in patients with Late-Onset Alzheimer's disease (LOAD). Due to the important role of the PSEN2 gene in the formation of beta-amyloid aggregates and the investigation involves an association between PSEN2 mutations and their pathogenicity in LOAD progression, we presented this exon as a more efficient alternative.&#x0D; Materials and Methods: The thirty patients with LOAD and 16 healthy subjects as a control group were involved in this experimental study. DNA was extracted from blood samples and purified. The desired gene fragment was propagated using polymerase chain reaction and the products were electrophoresed and the results were analyzed.&#x0D; Result: A novel mutation was found in PSEN2 IVS6 + 30 G → C at the intron region of exon 6 in 20 cases of patients suffering from LOAD and 12 subjects in control cohort. In this mutation a guanine base was substituted by cytosine base which this position was 30 nucleotides separated from coding region.&#x0D; Conclusions: The novel mutation was identified in both studied groups. These findings reveal no relationship between PSEN2 mutation and pathogenicity of LOAD disease. However, further studies are required to find the role of PSEN2 mutation in LOAD progression.

The transcriptomic landscape of neurons carrying PSEN1 mutations reveals changes in extracellular matrix components and non-coding gene expression

Alzheimer's disease (AD) is a progressive and irreversible brain disorder, which can occur either sporadically, due to a complex combination of environmental, genetic, and epigenetic factors, or because of rare genetic variants in specific genes (familial AD, or fAD). A key hallmark of AD is the accumulation of amyloid beta (Aβ) and Tau hyperphosphorylated tangles in the brain, but the underlying pathomechanisms and interdependencies remain poorly understood. Here, we identify and characterise gene expression changes related to two fAD mutations (A79V and L150P) in the Presenilin-1 (PSEN1) gene. We do this by comparing the transcriptomes of glutamatergic forebrain neurons derived from fAD-mutant human induced pluripotent stem cells (hiPSCs) and their individual isogenic controls generated via precision CRISPR/Cas9 genome editing. Our analysis of Poly(A) RNA-seq data detects 1111 differentially expressed coding and non-coding genes significantly altered in fAD. Functional characterisation and pathway analysis of these genes reveal profound expression changes in constituents of the extracellular matrix, important to maintain the morphology, structural integrity, and plasticity of neurons, and in genes involved in calcium homeostasis and mitochondrial oxidative stress. Furthermore, by analysing total RNA-seq data we reveal that 30 out of 31 differentially expressed circular RNA genes are significantly upregulated in the fAD lines, and that these may contribute to the observed protein-coding gene expression changes. The results presented in this study contribute to a better understanding of the cellular mechanisms impacted in AD neurons, ultimately leading to neuronal damage and death.

Mixed Pathologies in a Subject with a Novel PSEN1 G206R Mutation.

There are more than 300 presenilin-1 (PSEN1) mutations identified but a thorough postmortem neuropathological assessment of the mutation carriers is seldom performed. To assess neuropathological changes (NC) in a 73-year-old subject with the novel PSEN1 G206R mutation suffering from cognitive decline in over 20 years. To compare these findings with an age- and gender-matched subject with sporadic Alzheimer's disease (sAD). The brains were assessed macro- and microscopically and the proteinopathies were staged according to current recommendations. The AD neuropathological change (ADNC) was more extensive in the mutation carrier, although both individuals reached a high level of ADNC. The transactive DNA binding protein 43 pathology was at the end-stage in the index subject, a finding not previously described in familial AD. This pathology was moderate in the sAD subject. The PSEN1 G206R subject displayed full-blown alpha-synuclein pathology, while this proteinopathy was absent in the sAD case. Additionally, the mutation carrier displayed pronounced neuroinflammation, not previously described in association with PSEN1 mutations. Our findings are exceptional, as the PSEN1 G206R subject displayed an end-stage pathology of every common proteinopathy. It is unclear whether the observed alterations are caused by the mutation or are related to a cross-seeding mechanisms. The pronounced neuroinflammation in the index patient can be reactive to the extensive NC or a contributing factor to the proteinopathies. Thorough postmortem neuropathological and genetic assessment of subjects with familial AD is warranted, for further understanding of a dementing illness.

Spatial dysregulation of Rho GTPases in Alzheimer’s Disease brain in human and in transgenic mouse model

AbstractBackgroundAlzheimer disease (AD) is histopathologically characterized by brain accumulation of amyloid plaques, neurofibrillary tangle formation, and loss of synapses. The small GTPases of Rho family such as RhoA, Rac1 and Cdc42 play an important role in neural plasticity by regulating synaptic actin and spine dynamics. However, the functions of these proteins in AD are paradoxical. To understand their contributions in AD pathogenesis, it is important to investigate the relationship between the expression of Rho GTPases and their functional states in signaling.MethodWe characterized the spatial dysregulation of Rho GTPases in human AD brains and that of aged Triple Transgenic (3xTg‐AD) mouse model carrying mutations in amyloid precursor protein, tau protein, and presenilin. For human brains, the paraffin‐embedded tissues were collected from age and gender matched AD and Non‐Dementia (ND) patients. Phosphorylated Rho GTPase antibodies were used as signaling indicators for immunofluorescence microscopyResultWe observed altered phospho‐RhoA (S188) and phospho‐Rac/Cdc42(S71) expression and distribution in human, wild type (WT), and 3xTg‐AD mouse brains. In the CA3 region and dentate gyrus (DG), pRac/Cdc42 immunostaining showed decreased punctate staining in WT compared to 3xTg‐AD mice. For CA3 pRhoA immunostaining scored a slightly higher level of expression in WT compared to 3xTg‐AD. In the CA2 region, pRac/Cdc42 immunostaining was perinuclear in WT and diffused in 3xTg‐AD, whereas the pRhoA immunostaining pattern was similar between WT and 3xTg‐AD. In the CA1 region, pRac/Cdc42 immunostaining showed perinuclear as well as dendritic localization in WT and 3xTg‐AD, while pRhoA immunostaining between WT and 3xTg‐AD was similar. In human brains,there was no significant difference in pRhoA in cortex between ND and AD whereas pRac/Cdc42 was slightly reduced in AD cortex. However, while Rac signaling was reduced, Cdc42 signaling was increased in ND compared to AD cortex. On the other hand, Rac signaling is decreased in ND DG compared to AD whereas the differences in Cdc42 signaling in DG were not significant.ConclusionSmall GTPases of Rho family are differentially dysregulated in expression, distribution, and functional states in different areas of the brain in AD patients as well as in AD mouse brains

Reproductive health data and its relationship to baseline brain imaging and cognitive measurements in cognitively unimpaired female PSEN1 E280A mutation carriers and non‐carriers from the API ADAD Trial

AbstractBackgroundThe impact of sex steroid hormones on Alzheimer’s disease (AD) remains to be further clarified. Research suggests that shorter reproductive span, late menarcheal age, early menopause, oophorectomies and hysterectomies, are associated with increased dementia risk. We examined reproductive health and its associations with brain imaging and cognitive measurements in unimpaired female Presenilin 1 (PSEN1) E280A mutation carriers and non‐carriers from the Alzheimer’s Prevention Initiative Autosomal Dominant AD (API ADAD) Trial (NCT01998841).MethodA total of 151 cognitively unimpaired 30‐53 year‐old females (101 PSEN1 mutation carriers and 50 non‐carriers) were included. Reproductive health data (i.e., menarcheal age, number of pregnancies, deliveries, miscarriages, and living children) from all participants were examined, as well as the extent to which menarcheal age was related to age‐adjusted baseline 1) cortical amyloid plaque burden (florbetapir PET), 2) Precuneus cerebral glucose metabolism (fluorodeoxyglucose PET), 3) hippocampal volume (3TMRI), and 4) the API ADAD preclinical cognitive composite score, which includes the MMSE Orientation score, CERAD Word List Delayed Recall and Constructional Praxis, Multilingual Naming Test and Raven’s Progressive Matrices subset. We examined associations with the cognitive and brain imaging measures corrected for multiple comparisons (Bonferroni).ResultCarrier and non‐carrier females did not differ on number of pregnancies, deliveries, miscarriages, or living children. Female carriers had a significantly younger menarcheal age than non‐carriers (12.8 ±1.5 versus 13.7±1.6 years, p = 0.007, Bonferroni). Among carrier females, older menarcheal age was associated with lower scores on the Raven’s test (Bonferroni: r = ‒0.28,p =0.035). Menarcheal age was not associated with scores on the cognitive composite or other individual subtests, or with brain imaging measures.ConclusionOur findings suggest reproductive health data did not differ between carrier and non‐carrier females, except for a slightly younger menarcheal age compared to non‐carriers, and that menarcheal age may have a very limited impact on brain pathology and function at preclinical stages of ADAD. Longitudinal studies with larger samples are needed to clarify the extent to which earlier menarcheal age may be related to changes in cognitive function in mutation carrier females transitioning from preclinical to clinical stages.

GENE REPLACEMENT OF MUTANT PRESENILIN1 NORMALIZES GAMMA‐SECRETASE FUNCTION IN MODELS OF AUTOSOMAL DOMINANT ALZHEIMER'S DISEASE

AbstractBackgroundParos Bio is developing an AAV gene therapy for the treatment of Autosomal Dominant Alzheimer’s Disease (ADAD), an early onset form of AD (onset at &lt;65 years of age). ADAD is mainly caused by mutations in the presenilin 1 (PSEN1) gene, which encodes the catalytic subunit of γ‐secretase complex and is responsible for the cleavage of amyloid precursor protein (APP). This cleavage produces Aβ of varying lengths, with longer peptides like Aβ42 being more prone to aggregation than shorter peptides such as Aβ40. Of the &gt;150 distinct, 100% penetrant PSEN1 mutations associated with ADAD, most lead to a partial or nearly complete loss of g‐secretase function, resulting in decreased production of Aβ40 and an increase in the ratio of Aβ42:Aβ40. Aggregation of Aβ peptides into amyloid plaques in the brain is a hallmark of ADAD.MethodParos Bio is employing a gene replacement approach to normalize g‐secretase function. Using an AAV vector, Paros has successfully expressed a functional copy of PSEN1 in mouse and patient‐derived cellular models of presenilin dysfunction.ResultWe have demonstrated that introduction of wildtype PSEN1 in mouse models and patient‐derived cell lines effectively normalizes g‐secretase function. Our AAV vector can be broadly distributed in brain tissue and provides attractive expression of PSEN1.ConclusionParos Bio has developed a vector that enables broad expression of WT PSEN1 and is capable of normalizing g‐secretase function in in vitro and in vivo models of ADAD.