Presenilin Research Articles

FAD mutants decrease brain neovascularization and neuronal survival by targeting angiogenic mechanisms of PS1/γ‐secretase

AbstractBackgroundThe cerebrovascular system is central to neuronal survival and function and emerging evidence suggests that vascular brain abnormalities are involved in the development of neurodegenerative disorders such as Alzheimer’s disease (AD). Angiogenesis, the generation of new blood vessels from existing vasculature, is crucial throughout adult life for maintaining brain blood circulation and for reparative mechanisms of toxic insults such as ischemia. Angiogenesis is controlled by growth factors including the Vascular Endothelial Growth Factor (VEGF). By binding to its receptor (VEGFR2), VEGF regulates extension of new blood vessels in damaged areas and maintains blood supply to tissues and organs. FAD variants of Presenilin1 (PS1), the catalytic subunit of γ‐secretase induce Familial AD (FAD) and can serve as systems where mechanisms of AD‐like neurodegeneration can be studied.MethodsMouse brain endothelial cells (ECs) expressing knock‐in PS1 FAD mutants were isolated and cultured and effects of PS1/γ‐secretase on angiogenic functions and processing of VEGFR2 were performed as in literature. VEGF‐induced phosphorylation of kinases downstream of VEGFR2 were determined on WBs. Middle cerebral artery occlusion (MCAO) was performed in mice as in literature. Isolated brains were sectioned using a mouse brain matrix and slices were stained with TTC and fixed with 4% PFA to detect infarct area. Cerebral blood flow (CBF) was assessed using perfusion MRI (pMRI) as in literature. Neurons were stained with anti‐NeuN and positive neurons in lesioned and contralateral areas were countedResultsPS1/γ‐secretase process VEGFR2 and regulate crucial functions of the brain VEGF/VEGFR2 system including receptor dimerization, internalization and downstream angiogenic signaling. Importantly, PS1 FAD mutants decrease the VEGF‐induced activation and angiogenic signaling of VEGFR2 and reduce brain neovascularization suggesting mechanisms by which PS1 FAD mutants may cause neuronal dysfunction and death. In this presentation we discuss the importance of the PS1/γ‐secretase on the VEGFA/VEGFR2‐mediated angiogenenic signaling and brain neovascularization and test effects of PS1FAD mutants in brain neoangiogenesis and neuronal survival.ConclusionsThe PS1/γ‐secretase system regulates brain angiogenesis and neovascularization by activating properties of the VEGF/VEGFR2 system. PS1 FAD mutants decrease brain angiogenesis, neovascularization and neuronal survival by targeting angiogenic mechanisms of PS1 and γ‐secretase.

Levels of nicastrin species are increased in Alzheimer’s disease cerebrospinal fluid

AbstractBackgroundPrevious studies demonstrated that presenilin‐1 (PS1), the active component of the intramembrane γ‐secretase complex, can be detected as soluble heteromeric aggregates in cerebrospinal fluid (CSF). The γ‐secretase components, APH‐1 (anterior pharynx‐defective 1) and PEN‐2 (presenilin enhancer 2), co‐exist within these CSF complexes, while nicastrin is not detected. Nicastrin plays a role in the complex regulation, and substrate recognition, being the unique γ‐secretase component that is a Type I, single‐pass transmembrane protein. Here, we aim to characterize and compare the levels of CSF nicastrin in Alzheimer’s disease (AD) and non‐AD control patients.MethodNicastrin levels were analyzed in the CSF by western blotting using antibodies against the ectodomain and the intracellular domain to identify the different species of the protein that are present in human CSF. Core AD CSF biomarkers (Aβ1‐42, T‐tau, and p‐Tau) were determined. We also assessed whether CSF nicastrin and PS1 are present in extracellular vesicles (EVs).ResultWe show that nicastrin is present in CSF as full‐length species of 130, 110, and 105 kDa. We demonstrated that nicastrin full‐length species are increased in AD patients (n = 21) in comparison with non‐AD controls (n = 21), and that the levels of the three species positively correlated with T‐tau and p‐Tau levels in AD patients. Nicastrin was also found to be present in EVs, different from PS1.ConclusionThe increased levels of nicastrin in the CSF of AD patients confirmed the potential alteration of γ‐secretase subunits during pathology progression. Further studies are required to evaluate whether these proteins could act as biomarkers to facilitate AD diagnosis and/or prognosis.

Assessing the functional effect of the Presenilin‐1 G206A variant on age of onset of Alzheimer Disease in the Puerto Rican population

AbstractBackgroundThe variant G206A in Presenilin‐1 (PSEN1) gene has been identified almost exclusively in Alzheimer Disease (AD) Puerto Rican families. This variant represents a founder effect on the African background. The G206A variant associates with extreme variability in age of onset (AOO), ranging from 30 to 90 years. In contrast, other variants at the same amino acid of PSEN1 (G206N, G206S) have a tighter range of AOO (30‐35 years). We aim to identify the molecular mechanisms involved in the AOO variability between G206A carriers through functional analysis of induced pluripotent stem cells (iPSCs).MethodGenotyping data were phased using SHAPEIT to identify local ancestry and RFMix to estimate genetic ancestry. p‐Tau181 levels were tested from plasma using Simoa (Quanterix HD‐X). iPSCs of G206A carriers with different AOO were reprogrammed using non‐integrating Sendai virus. These clonal lines were assessed for pluripotency and chromosomal stability Isogenic construction of G206A iPSC lines is currently in progress.ResultWe screened for G206A carriers using whole genome from 896 individuals (182 families) and identified 43 carriers (39 AD and 4 cognitively unimpaired <65 years) from 8 families and 3 isolated cases. 55% of AD G206A carriers had AOO <65. A single African haplotype was identified in all G206Acarriers. We observed higher pTau181 levels in AD G206A carriers with early age of onset, compared to those with late onset. Association analysis did not identify APOE4 or SYNJ1 polymorphisms as contributing to the differences in AOO within G206A carriers. To perform functional studies, we selected three with early (<65) and three with late (>65) AOO AD peripheral blood mononuclear cells (PBMCs)that were reprogrammed into iPSC lines. G‐band Karyotype, factor loss analyses, genetic finger printing, immunocytochemistry (ICC) and qRT‐PCR for intracellular and surface pluripotency markers was confirmed in the iPSC lines.ConclusionThe PSEN1 G206A variant, originating in African ancestry haplotype revealing a founder effect, is an important contributor to AD in an underserved population. Understanding the role of the G206A variant in AD pathogenesis and the factors that influence its effect on AOO will provide insight on AD pathogenesis, age of onset variation and identification of potential novel therapeutic targets.

A novel Presenilin 2 mutation in two siblings with predominantly amnestic, early‐onset Alzheimer’s disease

AbstractBackgroundFamilial, early‐onset Alzheimer’s Disease (AD) is a rare form of dementia resulting from autosomal dominant mutations in the amyloid precursor protein (APP), presenilin‐1 (PSEN1), or presenilin‐2 (PSEN2) genes with phenotypic diversity. PSEN2 mutations are rare and vary widely in age of onset.MethodCase report and literature review.ResultWe report a novel PSEN2 variant (c.359T>G, p.Ile120Ser) that has been clearly segregated in two siblings in their fifties, presenting as predominantly amnestic AD. One of the siblings was also heterozygous in the PSEN1 gene (c.118_120del, p.Asp40del). There was no evidence of C9orf72 repeat expansion in either sibling. A third sibling has also started manifesting cognitive impairments. Their strong family history of cognitive dysfunction suggests that the PSEN2 mutation is pathogenic, and the causative variant has never been reported in Medline and the Alzgene genetic database of PSEN2.ConclusionAs there are numerous PSEN2 mutations still incompletely characterized, there remains a need to systematically report patients either with familial or sporadic presentation and very early age of onset and classify their pathogenicity accordingly. Providing information about the genetic bases of AD can help allay the stress of patients and families about their diagnosis, individual risks, and possible care planning.

A systematic evaluation of cortical GABA levels in transgenic mouse models of amyloid

AbstractBackgroundRodent models that overexpress mutations in the amyloid precursor protein (APP) and presenilin 1 (PSEN1) genes have been widely applied in Alzheimer’s disease (AD) research. These models classically present amyloid plaque deposition in cortical and hippocampal areas and neurotransmission changes. Although amyloid‐related glutamatergic abnormalities have been extensively described, little is known about its effects on the GABAergic system. Thus, we aimed to examine GABA levels in the cortex of two transgenic amyloid mouse models.MethodWe systematically reviewed the literature following the PRISMA 2020 guidelines. PubMed and Web of Science databases were searched for studies reporting GABA levels in the cortex of APPswe/PSEN1dE9 and Tg2576 mice. We opted to evaluate only animals with mature amyloid plaques in their cortices, according to each mouse model previous characterization.ResultThe search identified 3576 papers. Seven records met the inclusion criteria (Tg2576: n = 21, mean age ± standard deviation (SD) = 14.7 ± 3.7 months; controls: n = 21; APPswe/PSEN1dE9: n = 25, mean age ± SD = 8.5 ± 4.1 months; controls: n = 25). Five out of seven results reported non‐significant differences in the GABA levels in multiple cortical regions, such as the frontal, pre‐frontal, and rhinal cortices of the Tg2576 mouse model, but two studies described that GABA is significantly decreased. Furthermore, all studies with the APP/PSEN1 model consistently reported decreased cortical GABA levels. Figure 1 provides a summary of our findings.ConclusionOur results suggest that APP and PSEN1 mutations may contribute to the decrease in the levels of GABA in cortical regions of amyloid models. Future meta‐analyses and clinical studies are needed to ascertain the consistency of the reported results.

Tau pathology is associated with neuropsychiatric symptoms in a cohort of individuals of predominantly Mexican descent at risk for autosomal‐dominant Alzheimer’s disease

AbstractBackgroundNeuropsychiatric symptoms are common in Alzheimer’s disease (AD), causing significant suffering and diminished quality of life for both individuals and caregivers. The goal of this study was to investigate the relationship between tau pathology in vivo and neuropsychiatric symptoms within a cohort of individuals of predominantly Mexican ancestry at risk for fully penetrant autosomal dominant AD (ADAD) caused by mutations in PSEN1 and APP genes (Figure 1).MethodParticipants from the Estudio de la Enfermedad de Alzheimer en Jalisciences (EEAJ) cohort were selected based on availability of demographic variables, mutation carrier status, tau PET scans (flortaucipir), and completion of the neuropsychiatric inventory (NPI). Linear regression models were used to investigate whether regional tau PET standard uptake value ratio (SUVR) predicted total score on the NPI. Models were adjusted for age, sex, and mutation carrier status. Participants were characterized as carriers if they possessed one of the following ADAD mutations: PSEN1 A431E, PSEN1 I180F, or APP V717I. Analyses were done with and without outliers. The 12‐item total NPI score was used for all analyses. The primary brain regions of interest (i.e., medial orbitofrontal, caudal anterior cingulate, rostral anterior cingulate, parahippocampal, precuneus, and lateral occipital) were selected based on previous findings. Additional analyses were conducted only on individuals who were carriers of 1 of the ADAD mutations.ResultThe sample consisted of 31 participants (45% women, mean age±SD = 37.1±11.7 years, 71% ADAD mutation carriers [81% PSEN1 A431E, 16% PSEN1 I180F, and 3% APP V717I carriers]). A significant relationship was found between regional tau pathology and neuropsychiatric symptoms for all six brain regions (Table 1), all p’s < 0.01. Within all regression models, regional tau pathology explained between 24% to 49% of the variance in neuropsychiatric symptoms. Sub‐set analyses completed on the ADAD mutation carriers sample exhibited similar results (Table 2). No significant results were found for non‐carriers.ConclusionRegional tau pathology within six distinct brain regions is strongly associated with neuropsychiatric symptoms in a cohort of individuals of predominantly Mexican ancestry at risk for fully penetrant ADAD caused by mutations in PSEN1 and APP genes.

Tau pathology is associated with neuropsychiatric symptoms in a cohort of individuals of predominantly Mexican descent at risk for autosomal‐dominant Alzheimer’s disease

AbstractBackgroundNeuropsychiatric symptoms are common in Alzheimer’s disease (AD), causing significant suffering and diminished quality of life for both individuals and caregivers. The goal of this study was to investigate the relationship between tau pathology in vivo and neuropsychiatric symptoms within a cohort of individuals of predominantly Mexican ancestry at risk for fully penetrant autosomal dominant AD (ADAD) caused by mutations in PSEN1 and APP genes (Figure 1).MethodParticipants from the Estudio de la Enfermedad de Alzheimer en Jalisciences (EEAJ) cohort were selected based on availability of demographic variables, mutation carrier status, tau PET scans (flortaucipir), and completion of the neuropsychiatric inventory (NPI). Linear regression models were used to investigate whether regional tau PET standard uptake value ratio (SUVR) predicted total score on the NPI. Models were adjusted for age, sex, and mutation carrier status. Participants were characterized as carriers if they possessed one of the following ADAD mutations: PSEN1 A431E, PSEN1 I180F, or APP V717I. Analyses were done with and without outliers. The 12‐item total NPI score was used for all analyses. The primary brain regions of interest (i.e., medial orbitofrontal, caudal anterior cingulate, rostral anterior cingulate, parahippocampal, precuneus, and lateral occipital) were selected based on previous findings. Additional analyses were conducted only on individuals who were carriers of 1 of the ADAD mutations.ResultThe sample consisted of 31 participants (45% women, mean age±SD = 37.1±11.7 years, 71% ADAD mutation carriers [81% PSEN1 A431E, 16% PSEN1 I180F, and 3% APP V717I carriers]). A significant relationship was found between regional tau pathology and neuropsychiatric symptoms for all six brain regions (Table 1), all p’s < 0.01. Within all regression models, regional tau pathology explained between 24% to 49% of the variance in neuropsychiatric symptoms. Sub‐set analyses completed on the ADAD mutation carriers sample exhibited similar results (Table 2). No significant results were found for non‐carriers.ConclusionRegional tau pathology within six distinct brain regions is strongly associated with neuropsychiatric symptoms in a cohort of individuals of predominantly Mexican ancestry at risk for fully penetrant ADAD caused by mutations in PSEN1 and APP genes.

Production of a PSEN1 genetically engineered marmoset model of early‐onset Alzheimer’s Disease

AbstractBackgroundThe lack of an adequate animal model of Alzheimer’s disease (AD) that mirrors the natural onset and progression of the human disorder has been a substantial barrier to basic and translational research into AD. Consequently, many fundamental questions remain about the key mechanisms that initiate the disease and the factors that promote its progression. While rodents are valuable AD models, nonhuman primates (NHPs) offer many advantages and have greater translational relevance. The common marmoset (Callithrix jacchus) is a small, prolific New World NHP that is amenable to genetic engineering and is rapidly becoming a valuable model organism, especially for neuroscience research.MethodWe used CRISPR/Cas9 technology to generate marmosets with C410Y or A426P point mutations in the PSEN1 gene. In humans, these mutations lead to familial early‐onset autosomal dominant Alzheimer’s Disease. Briefly, we designed, synthesized, and injected CRISPR/Cas9 reagents into single‐cell embryos that were subsequently transferred to synchronized recipient females. One adult C410Y founder animal was bred to a wild‐type mate.ResultTo date, we have produced seven live‐born marmosets harboring the PSEN1 C410Y (3 males, 1 female) or A426P (1 male, 2 females) mutations. One male founder animal, a compound heterozygote harboring C410Y and 1bp insertion PSEN1 alleles, has successfully sired three litters and transmitted the C410Y substitution (n = 6) and the 1bp insertion (n = 5) alleles to F1 offspring. We are currently characterizing the founders and F1 offspring using fluid‐based biomarkers, non‐invasive neuroimaging, and behavioral assessment to identify early markers of disease progression.ConclusionCRISPR/Cas9 gene editing was used to successfully establish a line of genetically engineered marmosets expected to model early‐onset AD. This nonhuman primate model will bridge the rodent‐to‐human translational gap and enable detailed studies of the early‐life molecular determinants of AD pathogenesis.

Neurophysiological alterations in mice and humans carrying mutations in APP and PSEN1 genes

AbstractBackgroundStudies in animal models of Alzheimer’s disease (AD) have provided valuable insights into the molecular and cellular processes underlying neuronal network dysfunction, but whether and how AD‐related neurophysiological alterations translate between mice and men remains uncertain.MethodWe characterized neurophysiological alterations in mice and humans carrying AD mutations in the APP and/or PSEN1 genes, focusing on early changes. Longitudinal local field potential recordings were peformed in 3‐12‐month‐old APP/PS1 mice and cross‐sectional magnetoencephalography recordings in pre‐symptomatic human APP and PSEN1 mutation carriers. Recordings were acquired of the left hippocampus, frontal and parietal cortex. We performed spectral activity and functional connectivity analyses and results were compared with wildtype control mice and healthy age‐matched human subjects.ResultAPP/PS1 mice showed increased aboslute power, especially at higher frequencies (beta and gamma) and predominantly between 3 and 6 months of age. Relative power showed an overall shift from lower to higher fequencies over almost the entire recording period and across all three brain regions. There was a trend for reduced peak frequency in APP/PS1 mice at 3‐4 months of age. Human mutation carriers did not show changes in power except for an increase in relative theta power in the hippocampus. Parietal cortex and hippocampal peak frequency were reduced in human mutation carriers. In both models, significant alteration in functional connectivity were detected in theta, alpha, beta and gamma frequency bands, but the exact frequency range and direction of change differed for APP/PS1 mice and human mutation carriers (Table 1).ConclusionIn conclusion, both mice and humans carrying APP and/or PSEN1 mutations show abnormal neurophysiological activity, but several measures do not translate one‐to‐one between species. Alterations in spectral characteristics and functional connectivity in mice should be interpreted with care and may be due to overexpression of amyloid in combination with absence of tau pathology in cholinergic degeneration. Future studies should explore whether changes in brain activity in other AD mouse models provide better translation to the human AD continuum.

A novel humanized Tau‐FAD mice represent a robust model for studying AD‐related dysfunction

AbstractBackgroundFamilial AD (FAD) mice expressing mutant forms of the Amyloid β protein (Aβ) precursor (APP) and presenilin‐1 (PS1) have been key models for AD research. While other studies combined FAD and the Tau protein, none, except 3xTgAD, have been made freely available or characterized well. As APP and Tau are linked in 3xTgAD mice, one cannot evaluate their contribution. This study combined the popular hTau strain lacking mouse Mapt and expressed human wild‐type MAPT with FAD.MethodWe generated HTAP by crossing hTau mice in C57BL6/J (JAX #005491) with FAD mutant APP‐PS1 (MMRRC #034833‐JAX) and HTAP2 with 5xFAD (#032882‐JAX). While hTau hyperphosphorylates Tau at 3 mo, the FAD models deposit Aβ after 5 mo. We compared mouse spatial memory with either a radial arm water maze or a Barnes maze. We also compared the levels of norepinephrine in the hippocampus, cortex, and striatum of HTAP2 with the parental C57BL6/J mice by HPLC analysisResultHTAP and HTAP2 mice deposit plaques similar to parental FAD mice and hTau hyperphosphorylated Tau. The combined HTAP mice showed hyperphosphorylated Tau, but the structures appeared distorted. We noted that after 7 months of age, HTAP mice performed poorly in the radial arm water maze compared to wild‐type, FAD, and hTau mice. We observed a similar deficit in HTAP2 in the Barnes Maze. HTAP2 mice showed a significant drop in norepinephrine in all evaluated brain regions, reminiscent of early AD‐related changes.ConclusionHTAP/2 mice have exacerbated behavioral deficits, suggesting that it is a more robust model for studying AD‐related dysfunction. However, these mice still perform well in activities of daily living, such as grooming and feeding. Such novel tau mice, which contain the human MAPT gene, would accelerate our ongoing studies on human microRNAs that target human 3'UTR MAPT mRNA without interference from the host Mapt gene. We propose that this system may better represent the behavioral deficits in AD.

Midpoint baseline results of the Longitudinal Early‐Onset Alzheimer’s Disease Study (LEADS)

AbstractBackgroundFewer than 5% of patients with Alzheimer’s disease are diagnosed between 40‐64 years old, making “early‐onset Alzheimer’s disease” (EOAD) an uncommon phenomenon (Zu et al., 2015). To date, only basic knowledge on EOAD is known, no uniform criteria for EOAD have been implemented, and sample sizes in research have been small. The Longitudinal Early‐Onset Alzheimer’s Disease Study (LEADS) aims to provide a comprehensive understanding of EOAD symptomology, with the current project profiling baseline clinical, cognitive, and basic genetic characteristics of the cohort nearing the data‐collection mid‐point.MethodData from 371 participants undergoing the LEADS protocol were compared based on diagnostic group classification (cognitively normal [CN], amyloid‐positive EOAD, and amyloid‐negative Early‐Onset non‐Alzheimer’s disease [EOnonAD]). Because LEADS focuses on sporadic early‐onset dementia, impaired individuals with genetic mutations in Amyloid Precursor Protein (APP), Presenilin‐1 (PSEN1) or Presenilin‐2 (PSEN2), Microtubule Associated Protein Tau (MAPT), Chromosome 9 Open Reading Frame 72 (C9ORF72), or Granulin Precursor aka Progranulin (GRN) were excluded.ResultDemographic characteristics for each group are shown in Table 1. After adjusting for age, education, and sex, EOAD performed worse than CN for all domains (ps<.001, η2s = 0.05‐0.66), and worse than EOnonAD for all domains except language (ps<.001, η2s = 0.06‐0.29). As shown in Table 2, EOAD showed worse performance on Episodic Memory (z = ‐2.38), followed by Speed Attention (z = ‐1.93) and Executive domains (z = ‐1.43) relative to CN. An amnestic presentation was common among impaired participants, with several clinical phenotypes present. The EOAD group possessed a significantly greater proportion of apolipoprotein ε4 homozygous participants than the EOnonAD group (p = .01, Cohen’s w = 0.15), and a trend of greater proportions of ε4 heterozygous participants than both CN and EOnonAD (ps = .05‐.07, Cohen’s ws = 0.11; Table 3). Finally, LEADS participants generally consented at high rates to optional trial procedures like lumbar puncture (60%) and genetic disclosure (89%).ConclusionThis work represents the best baseline characterization of sporadic EOAD in the U.S. to date. Early‐onset dementia presents with widespread cognitive impairment, characterized by several known clinical phenotypes. Apolipoprotein ε4 allele carrier status appears to remain important in EOAD. Future investigation will explore many potential associations between EOAD and cognition, neuropsychiatric symptoms, genetics, and imaging.

Clinical Manifestations.

In recent years, there has been an increase in the number of case reports of families with autosomal dominant Alzheimer's disease (ADAD) in Latin America (LA). Nevertheless, little is known about the clinical phenotypes and demographic characteristics of mutations in each country. Past literature has proved that variants in LA have different and unique characteristics than those reported in Asia, North America, and Europe. Clinical heterogeneity in ADAD supports the need to study clinical phenotypes, especially in preclinical stages, to develop cognitive and clinical markers of the disease. We aimed to describe clinical and cognitive characteristics at baseline assessment of an Argentina PSEN1 p.M146L family enrolled at DIAN. Fifteen Dian Participants living in Buenos Aires and its suburbs and in Taco Pozo, a rural and isolated community from the Province of Salta, positive for the PSEN1 p.M146L mutation, were recruited. DNA was obtained from peripheral blood leukocytes according to standard protocols. In addition, exon 5 of the PSEN1 gene was PCR-amplified, and Sanger sequencing was performed. NACC Uniform Data Set clinical assessment, including the 2.0 UDS Neuropsychological Battery, was administered. Two groups were used to compare cognitive data: Patients with CDR:0 (n:10) and patients with CDR>0 (n:5). The mean age at symptom onset reported in this cohort was 42,90 (SD: 4,62). Significant differences were found in several cognitive measures: Logical Memory Immediate, TMT B and Digit Backward (<0,001); MMSE, Category Fluency Animals, TMT A and Digit Symbol(<0,05). In neurological signs, paraplegia was reported in one of the patients. As expected, differences in neuropsychological tests showed a prevalence of memory deficits, however, dysexecutive symptoms were also present for this mutation. Paraplegia in PSEN1 p.M146L has not been reported in the literature so far. Ongoing longitudinal work will be important in tracking changes in this cohort. Other characteristics, proper of underrepresented groups, such as socioeconomic status, education, race, and ethnicity, deserve appropriate follow-up. Future studies are planned, comparing urban and rural populations in this cohort with the same mutation.

Rare A360T Mutation Alters GSK3β(Ser9) Binding in the Cytosolic Loop of Presenilin 1, Influencing β-Catenin Nuclear Localization and Pro-Death Gene Expression in Alzheimer’s Disease Case

Presenilin 1 (PS1) forms, via its large cytosolic loop, a trimeric complex with N-cadherin and β-catenin, which is a key component of Wnt signaling. PS1 undergoes phosphorylation at 353 and 357 serines upon enhanced activity and elevated levels of the GSK3β isoform. PS1 mutations surrounding these serines may alter the stability of the β-catenin complex. Such mutations are found in some cases of familial early-onset Alzheimer’s disease (fEOAD), but their functional impact remains obscure. One of such variants of PS1, the A360T substitution, is located close to GSK3β-targeted serine residues. This variant was recently demonstrated in the French population, but more detail is needed to understand its biological effects. To assess the significance of this variant, we employed functional studies using a fibroblast cell line from an Alzheimer’s disease case (a female proband) carrying the A360T mutation. Based on functional transcriptomic, cellular, and biochemical assays, we demonstrated atypically impaired β-catenin/GSK3β signaling in the A360T patient’s fibroblasts. In detail, this was characterized by a decreased level of active cytosolic β-catenin and bound by PS1, an increased level of nuclear β-catenin, an increased level of inhibited GSK3β phosphorylated on Ser9, and enhanced interaction of GSK3β(Ser9) with PS1. Based on the transcriptomic profile of the A360T fibroblasts, we proposed a dysregulated transcriptional activity of β-catenin, exemplified by increased expression of various cyclin-dependent kinases and cyclins, such as cyclin D1, potentially inducing neurons’ cell cycle re-entry followed by apoptosis. The A360T cells did not exhibit significant amyloid pathology. Therefore, cell death in this PS1 cytosolic loop mutation may be attributed to impaired β-catenin/GSK3β signaling rather than amyloid deposition per se. We further estimated the biological and clinical relevance of the A360T variant by whole exome sequencing (WES). WES was performed on DNA from the blood of an A360T female proband, as well as an unrelated male patient carrying the A360T mutation and his mutation-free daughter (both unavailable for the derivation of the fibroblast cell lines). WES confirmed the highest-priority AD causality of the A360T variant in PS1 and also profiled the pathways and processes involved in the A360T case, highlighting the greatest importance of altered Wnt signaling.

Clearance of β-amyloid mediated by autophagy is enhanced by MTORC1 inhibition but not AMPK activation in APP/PSEN1 astrocytes.

Proteostasis mechanisms mediated by macroautophagy/autophagy are altered in neurodegenerative diseases such as Alzheimer disease (AD) and their recovery/enhancement has been proposed as a therapeutic approach. From the two central nodes in the anabolism-catabolism balance, it is generally accepted that mechanistic target of rapamycin kinase complex 1 (MTORC1)_ activation leads to the inhibition of autophagy, whereas adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) has the opposite role. In AD, amyloid beta (Aβ) production disturbs the optimal neuronal/glial proteostasis. As astrocytes are essential for brain homeostasis, the purpose of this work was to analyze if the upregulation of autophagy in this cell type, either by MTORC1 inhibition or AMPK activation, could modulate the generation/degradation of β-amyloid. By using primary astrocytes from amyloid beta precursor protein (APP)/Presenilin 1 (PSEN1) mouse model of AD, we confirmed that MTORC1 inhibition reduced Aβ secretion through moderate autophagy induction. Surprisingly, pharmacologically increased activity of AMPK did not enhance autophagy but had different effects on Aβ secretion. Conversely, AMPK inhibition did not affect autophagy but reduced Aβ secretion. These puzzling data were confirmed through the overexpression of different mutant AMPK isoforms: while only the constitutively active AMPK increased autophagy, all versions augmented Aβ secretion. We conclude that AMPK has a significantly different role in primary astrocytes than in other reported cells, similar to our previous findings in neurons. Our data support that perhaps only a basal AMPK activity is needed to maintain autophagy whereas the increased activity, either physiologically or pharmacologically, has no direct effect on autophagy-dependent amyloidosis. These results shed light on the controversy about the therapeutic effect of AMPK activation on autophagy induction.

Lipophorin receptors genetically modulate neurodegeneration caused by reduction of Psn expression in the aging Drosophila brain.

Mutations in the Presenilin (PSEN) genes are the most common cause of early-onset familial Alzheimer's disease (FAD). Studies in cell culture, in vitro biochemical systems, and knockin mice showed that PSEN mutations are loss-of-function mutations, impairing γ-secretase activity. Mouse genetic analysis highlighted the importance of Presenilin (PS) in learning and memory, synaptic plasticity and neurotransmitter release, and neuronal survival, and Drosophila studies further demonstrated an evolutionarily conserved role of PS in neuronal survival during aging. However, molecular pathways that interact with PS in neuronal survival remain unclear. To identify genetic modifiers that modulate PS-dependent neuronal survival, we developed a new DrosophilaPsn model that exhibits age-dependent neurodegeneration and increases of apoptosis. Following a bioinformatic analysis, we tested top ranked candidate genes by selective knockdown (KD) of each gene in neurons using two independent RNAi lines in Psn KD models. Interestingly, 4 of the 9 genes enhancing neurodegeneration in Psn KD flies are involved in lipid transport and metabolism. Specifically, neuron-specific KD of lipophorin receptors, lpr1 and lpr2, dramatically worsens neurodegeneration in Psn KD flies, and overexpression of lpr1 or lpr2 does not alleviate Psn KD-induced neurodegeneration. Furthermore, lpr1 or lpr2 KD alone also leads to neurodegeneration, increased apoptosis, climbing defects, and shortened lifespan. Lastly, heterozygotic deletions of lpr1 and lpr2 or homozygotic deletions of lpr1 or lpr2 similarly lead to age-dependent neurodegeneration and further exacerbate neurodegeneration in Psn KD flies. These findings show that LpRs modulate Psn-dependent neuronal survival and are critically important for neuronal integrity in the aging brain.

Molecular Dynamics Activation of γ-Secretase for Cleavage of the Notch1 Substrate.

γ-Secretase is an intramembrane aspartyl protease complex that cleaves the transmembrane domain of over 150 peptide substrates, including amyloid precursor protein (APP) and the Notch family of receptors, via two conserved aspartates D257 and D385 in the presenilin-1 (PS1) catalytic subunit. However, while the activation of γ-secretase for cleavage of APP has been widely studied, the cleavage of Notch by γ-secretase remains poorly explored. Here, we combined Gaussian accelerated molecular dynamics (GaMD) simulations and mass spectrometry (MS) analysis of proteolytic products to present the first dynamic models for cleavage of Notch by γ-secretase. MS showed that γ-secretase cleaved the WT Notch at Notch residue G34, while cleavage of the L36F mutant Notch occurred at Notch residue C33. Initially, we prepared our simulation systems starting from the cryoEM structure of Notch-bound γ-secretase (PDB: 6IDF) and failed to capture the proper cleavages of WT and L36F Notch by γ-secretase. We then discovered an incorrect registry of the Notch substrate in the PS1 active site through alignment of the experimental structure of Notch-bound (PDB: 6IDF) and APP-bound γ-secretase (PDB: 6IYC). Every residue of the APP substrate was systematically mutated to the corresponding Notch residue to prepare a resolved model of Notch-bound γ-secretase complexes. GaMD simulations of the resolved model successfully captured γ-secretase activation for proper cleavages of both WT and L36F mutant Notch. Our findings presented here provided mechanistic insights into the structural dynamics and enzyme-substrate interactions required for γ-secretase activation for cleavage of Notch and other substrates.

Abstract 11680: Presenilin 1 Deletion in Smooth Muscle Cells Ameliorates Hypermuscularization and Stenosis in Elastin Aortopathy

Introduction: Smooth muscle cell (SMC) accumulation is central to the pathogenesis of elastin-defective arterial diseases, such as atherosclerosis, pulmonary hypertension and supravalvular aortic stenosis (SVAS). We previously demonstrated that elastin deficiency activates the Notch pathway in aortic SMCs, resulting in hypermuscularization and stenosis. Activation of Notch is catalyzed by the enzyme gamma-secretase, but the role of specific catalytic subunits presenilin (PSEN)-1 or PSEN-2 in elastin aortopathy is not defined. Psen1 (-/-) mice die shortly after birth with intracranial hemorrhage and bone abnormalities, while Psen2 (-/-) mice are viable. Methods: Western blot and qRT-PCR for PSEN-1 and -2 were performed on human aortic SMCs in culture and wildtype and elastin null aortas at postnatal day (P) 0.5. Genetic deletion of cell type-specific Psen1 and/or global Psen2 was performed on the elastin mutant background. For SMC- or endothelial cell (EC)-specific Psen1 deletion, pregnant dams were injected with tamoxifen at embryonic days 14.5 and 15.5, and elastin mutant pups carrying no Cre, Acta2-CreER T2 , or Cdh5-CreER T2 were analyzed at P0.5. Results: PSEN-1 and -2 are upregulated in aortic SMCs with elastin deficiency in human and mouse. Global Psen2 deletion partially attenuates Notch downstream gene expression and SMC proliferation, mitigating elastin aortopathy while Psen1 deletion in SMCs more significantly inhibits this aortopathy and improves survival of elastin null pups. In contrast, Psen1 deletion in ECs does not improve aortic disease. The combination of global Psen2 deletion and SMC-specific Psen1 deletion has additive rescue effects on elastin aortopathy. In addition, SMC-specific Psen1 deletion rescues hypermuscularization in newborns heterozygous for the elastin null gene, which genetically mimics human SVAS. Conclusions: Elastin insufficiency in SMCs leads to upregulation of PSEN-1 and -2, which induce Notch signaling and SMC proliferation. Among PSEN subunits and vascular cell types, SMC PSEN-1 plays the major role in elastin aortopathy. Selective inhibition of SMC PSEN-1 may be an attractive therapeutic strategy for SVAS to improve efficacy and mitigate off-target effects of gamma-secretase blockade.

An In Silico Study for Expanding the Utility of Cannabidiol in Alzheimer's Disease Therapeutic Development.

Cannabidiol (CBD), a major non-psychoactive component of the cannabis plant, has shown therapeutic potential in Alzheimer's disease (AD). In this study, we identified potential CBD targets associated with AD using a drug-target binding affinity prediction model and generated CBD analogs using a genetic algorithm combined with a molecular docking system. As a result, we identified six targets associated with AD: Endothelial NOS (ENOS), Myeloperoxidase (MPO), Apolipoprotein E (APOE), Amyloid-beta precursor protein (APP), Disintegrin and metalloproteinase domain-containing protein 10 (ADAM10), and Presenilin-1 (PSEN1). Furthermore, we generated CBD analogs for each target that optimize for all desired drug-likeness properties and physicochemical property filters, resulting in improved pIC50 values and docking scores compared to CBD. Molecular dynamics (MD) simulations were applied to analyze each target's CBD and highest-scoring CBD analogs. The MD simulations revealed that the complexes of ENOS, MPO, and ADAM10 with CBD exhibited high conformational stability, and the APP and PSEN1 complexes with CBD analogs demonstrated even higher conformational stability and lower interaction energy compared to APP and PSEN1 complexes with CBD. These findings demonstrated the capable binding of the six identified targets with CBD and the enhanced binding stability achieved with the developed CBD analogs for each target.

Taking it to the extreme: The search for determinants of cognitive vulnerability and resilience in children with autosomal dominant Alzheimer’s disease

Abstract:Presenilin-1 (PSEN1) mutations predispose individuals to develop autosomal-dominant Alzheimer's disease (ADAD) in middle adulthood. While the pathogenesis of ADAD may be different from late-onset sporadic AD (e.g., differences in disease etiology, age of disease onset, etc), these conditions share many characteristics, including similar abnormalities in amyloid and tau biomarkers, brain structure and brain activity, and clinical features (Quiroz et al., 2010, Quiroz et al., 2011, Quiroz et al. 2018). Biomarker investigations of families with ADAD have already shed light on the trajectory of some AD-related brain changes, especially prior to the onset of clinical symptoms.We have been studying a Colombian kindred with a genetic form of AD caused by a single genetic mutation in the PSEN1 (E280A), which serves as a unique model for preclinical AD. Because of a well-defined age at clinical onset, and near 100% penetrance, this kindred provides important information about the time course and relationships between physiological mechanisms and cognitive changes, and in so doing, it has yielded new insights about presymptomatic AD that will enhance future prevention trials for AD, including primary prevention trials.The well-characterized clinical trajectory of these PSEN1 E280A mutation carriers allow us to examine brain function in children, more than three decades before the average age of onset of mild cognitive impairment (MCI) and dementia in this cohort (45 years for MCI, 50 years for dementia). This is giving us the unique opportunity to characterize the cognitive and behavioral profiles of children genetically determined to develop dementia in their forties, and is helping us improve our understanding of the impact of ADAD mutations in early life cognitive and brain functioning, as well as its potential impact on learning, academic performance and educational attainment. We previously studied 20 PSEN1 E280A carriers and 20 non-carriers aged 9 to 17 years from the Colombian ADAD cohort and showed that mutation-carrying children were distinguished from non-carriers by plasma biomarker findings consistent with Aß1-42 overproduction, as well as by increased functional connectivity of the posterior cingulate cortex with medial temporal lobe regions (Quiroz et al 2015). More recently, we used the WISC-IV, a measure of general intellectual abilities to examine cognitive abilities in these children. We reported in 265 children with the E280A mutation and 1089 non-carriers that they did not differ on any of the WISC-IV indices. Surprisingly, male carriers performed slightly worse than female carriers on working memory (mean difference = -4.97; P = .001) (Fox-Fuller et al., 2021). Some of our ongoing work includes comprehensive examinations of social, educational and developmental histories along with functional brain networks, as markers of synaptic dysfunction in individuals with ADAD, as this is particularly relevant to understanding the impact of PSEN1 mutations on the developing brain and subsequent neurodegenerative changes seen later in life, without the confounds of aging and age-related comorbidities that often exist in late-onset sporadic AD.Disclosures: Financial: Dr. Quiroz receives a consulting fee from Biogen. Non-Financial: Dr. Quiroz is a Hispanic Neuropsychological Society Member-At-Large and serves as the INS Teleneuropsychology Special Interest Group Chair

Alzheimer's disease as a viral disease: Revisiting the infectious hypothesis.

Alzheimer's disease (AD) represents the most frequent type of dementia in elderly people. Two major forms of the disease exist: sporadic - the causes of which have not yet been fully understood - and familial - inherited within families from generation to generation, with a clear autosomal dominant transmission of mutations in Presenilin 1 (PSEN1), 2 (PSEN2) or Amyloid Precursors Protein (APP) genes. The main hallmark of AD consists of extracellular deposits of amyloid-beta (Aβ) peptide and intracellular deposits of the hyperphosphorylated form of the tau protein. An ever-growing body of research supports the viral infectious hypothesis of sporadic forms of AD. In particular, it has been shown that several herpes viruses (i.e., HHV-1, HHV-2, HHV-3 or varicella zoster virus, HHV-4 or Epstein Barr virus, HHV-5 or cytomegalovirus, HHV-6A and B, HHV-7), flaviviruses (i.e., Zika virus, Dengue fever virus, Japanese encephalitis virus) as well as Human Immunodeficiency Virus (HIV), hepatitis viruses (HAV, HBV, HCV, HDV, HEV), SARS-CoV2, Ljungan virus (LV), Influenza A virus and Borna disease virus, could increase the risk of AD. Here, we summarized and discussed these results. Based on these findings, significant issues for future studies are also put forward.