Presenilin-1 knockin mice reveal loss-of-function mechanism for familial Alzheimer's disease.
ABSTRACT: Presenilins play essential roles in memory formation, synaptic function, and neuronal survival. Mutations in the Presenilin-1 (PSEN1) gene are the major cause of familial Alzheimer's disease (FAD). How PSEN1 mutations cause FAD is unclear, and pathogenic mechanisms based on gain or loss of function have been proposed. Here, we generated Psen1 knockin (KI) mice carrying the FAD mutation L435F or C410Y. Remarkably, KI mice homozygous for either mutation recapitulate the phenotypes of Psen1(-/-) mice. Neither mutation altered Psen1 mRNA expression, but both abolished ?-secretase activity. Heterozygosity for the KI mutation decreased production of A?40 and A?42, increased the A?42/A?40 ratio, and exacerbated A? deposition. Furthermore, the L435F mutation impairs hippocampal synaptic plasticity and memory and causes age-dependent neurodegeneration in the aging cerebral cortex. Collectively, our findings reveal that FAD mutations can cause complete loss of Presenilin-1 function in vivo, suggesting that clinical PSEN mutations produce FAD through a loss-of-function mechanism.
Project description:Familial forms of Alzheimer's disease (FAD) are caused by mutations in the gene encoding amyloid precursor protein, whose processing can result in formation of ?-amyloid (A?). FAD can also result from mutations in the presenilin 1/2 (PSEN1/2) genes, whose protein products partially compose the ?-secretase complex that cleaves A? from amyloid precursor protein fragments. Psen1 KO mice and knock-in (KI) mice with homozygous FAD-associated L435F mutations (Psen1LF/LF ) are embryonic and perinatally lethal, precluding a more rigorous examination of the effect of Alzheimer's disease-causing Psen1 mutations on neurodegeneration. Given that the rat is a more suitable model organism with regard to surgical interventions and behavioral testing, we generated a rat KI model of the Psen1LF mutation. In this study, we focused on young Psen1LF rats to determine potential early pathogenic changes caused by this mutation. We found that, unlike Psen1LF/LF mice, Psen1LF/LF rats survive into adulthood despite loss of ?-secretase activity. Consistent with loss of ?-secretase function, Psen1LF/LF rats exhibited low levels of A?38, A?40, and A?42 peptides. In contrast, levels of A?43, a longer and potentially more amyloidogenic A? form, were significantly increased in Psen1LF/LF and Psen1LF/w rats. The longer survival of these KI rats affords the opportunity to examine the effect of homozygous Psen1 Alzheimer's disease-associated mutations on neurodegeneration in older animals.
Project description:Presenilin (PSEN) pathogenic mutations cause familial Alzheimer's disease (AD [FAD]) in an autosomal-dominant manner. The extent to which the healthy and diseased alleles influence each other to cause neurodegeneration remains unclear. In this study, we assessed ?-secretase activity in brain samples from 15 nondemented subjects, 22 FAD patients harboring nine different mutations in PSEN1, and 11 sporadic AD (SAD) patients. FAD and control brain samples had similar overall ?-secretase activity levels, and therefore, loss of overall (endopeptidase) ?-secretase function cannot be an essential part of the pathogenic mechanism. In contrast, impaired carboxypeptidase-like activity (?-secretase dysfunction) is a constant feature in all FAD brains. Significantly, we demonstrate that pharmacological activation of the carboxypeptidase-like ?-secretase activity with ?-secretase modulators alleviates the mutant PSEN pathogenic effects. Most SAD cases display normal endo- and carboxypeptidase-like ?-secretase activities. However and interestingly, a few SAD patient samples display ?-secretase dysfunction, suggesting that ?-secretase may play a role in some SAD cases. In conclusion, our study highlights qualitative shifts in amyloid-? (A?) profiles as the common denominator in FAD and supports a model in which the healthy allele contributes with normal A? products and the diseased allele generates longer aggregation-prone peptides that act as seeds inducing toxic amyloid conformations.
Project description:Mutations in presenilin 1 (PSEN1) or presenilin 2 (PSEN2), the catalytic subunit of ?-secretase, cause familial Alzheimer's disease (fAD). We hypothesized that mutations in PSEN1 reduce Notch signaling and alter neurogenesis. Expression data from developmental and adult neurogenesis show relative enrichment of Notch and ?-secretase expression in stem cells, whereas expression of APP and ?-secretase is enriched in neurons. We observe premature neurogenesis in fAD iPSCs harboring PSEN1 mutations using two orthogonal systems: cortical differentiation in 2D and cerebral organoid generation in 3D. This is partly driven by reduced Notch signaling. We extend these studies to adult hippocampal neurogenesis in mutation-confirmed postmortem tissue. fAD cases show mutation-specific effects and a trend toward reduced abundance of newborn neurons, supporting a premature aging phenotype. Altogether, these results support altered neurogenesis as a result of fAD mutations and suggest that neural stem cell biology is affected in aging and disease.
Project description:Mutations in presenilin-1 (PSEN1), encoding the catalytic subunit of the amyloid precursor protein-processing enzyme ?-secretase, cause familial Alzheimer's disease. However, the mechanism of disease is yet to be fully understood and it remains contentious whether mutations exert their effects predominantly through gain or loss of function. To address this question, we generated an isogenic allelic series for the PSEN1 mutation intron 4 deletion; represented by control, heterozygous and homozygous mutant induced pluripotent stem cells in addition to a presenilin-1 knockout line. Induced pluripotent stem cell-derived cortical neurons reveal reduced, yet detectable amyloid-beta levels in the presenilin-1 knockout line, and a mutant gene dosage-dependent defect in amyloid precursor protein processing in PSEN1 intron 4 deletion lines, consistent with reduced processivity of ?-secretase. The different effects of presenilin-1 knockout and the PSEN1 intron 4 deletion mutation on amyloid precursor protein-C99 fragment accumulation, nicastrin maturation and amyloid-beta peptide generation support distinct consequences of familial Alzheimer's diseaseassociated mutations and knockout of presenilin-1 on the function of ?-secretase.
Project description:Alzheimer's disease (AD) is the most common age-related neurodegenerative disorder in which learning, memory and cognitive functions decline progressively. Familial forms of AD (FAD) are caused by mutations in amyloid precursor protein (<i>APP</i>), presenilin 1 (<i>PSEN1</i>) and presenilin 2 (<i>PSEN2</i>) genes. Presenilin 1 (PS1) and its homologue, presenilin 2 (PS2), represent, alternatively, the catalytic core of the ?-secretase complex that, by cleaving APP, produces neurotoxic amyloid beta (A?) peptides responsible for one of the histopathological hallmarks in AD brains, the amyloid plaques. Recently, <i>PSEN1</i> FAD mutations have been associated with a loss-of-function phenotype. To investigate whether this finding can also be extended to <i>PSEN2</i> FAD mutations, we studied two processes known to be modulated by PS2 and altered by FAD mutations: Ca<sup>2+</sup> signaling and mitochondrial function. By exploiting neurons derived from a <i>PSEN2</i> knock-out (PS2-/-) mouse model, we found that, upon IP<sub>3</sub>-generating stimulation, cytosolic Ca<sup>2+</sup> handling is not altered, compared to wild-type cells, while mitochondrial Ca<sup>2+</sup> uptake is strongly compromised. Accordingly, PS2-/- neurons show a marked reduction in endoplasmic reticulum-mitochondria apposition and a slight alteration in mitochondrial respiration, whereas mitochondrial membrane potential, and organelle morphology and number appear unchanged. Thus, although some alterations in mitochondrial function appear to be shared between PS2-/- and FAD-PS2-expressing neurons, the mechanisms leading to these defects are quite distinct between the two models. Taken together, our data appear to be difficult to reconcile with the proposal that FAD-PS2 mutants are loss-of-function, whereas the concept that PS2 plays a key role in sustaining mitochondrial function is here confirmed.
Project description:Mitochondrial dysfunction and subsequent metabolic deregulation is observed in neurodegenerative diseases and aging. Mutations in the presenilin (PSEN) encoding genes (PSEN1 and PSEN2) cause most cases of familial Alzheimer's disease (AD); however, the underlying mechanism of pathogenesis remains unclear. Here, we show that mutations in the C. elegans gene encoding a PSEN homolog, sel-12 result in mitochondrial metabolic defects that promote neurodegeneration as a result of oxidative stress. In sel-12 mutants, elevated endoplasmic reticulum (ER)-mitochondrial Ca2+ signaling leads to an increase in mitochondrial Ca2+ content which stimulates mitochondrial respiration resulting in an increase in mitochondrial superoxide production. By reducing ER Ca2+ release, mitochondrial Ca2+ uptake or mitochondrial superoxides in sel-12 mutants, we demonstrate rescue of the mitochondrial metabolic defects and prevent neurodegeneration. These data suggest that mutations in PSEN alter mitochondrial metabolic function via ER to mitochondrial Ca2+ signaling and provide insight for alternative targets for treating neurodegenerative diseases.
Project description:Hidradenitis suppurativa (HS), or acne inversa, is a chronic inflammatory skin disorder characterized clinically with acne-like lesions in apocrine gland-bearing skin, follicular occlusion and recurrent inflammation. Thirty-four unique mutations in patients with HS have been found in three genes encoding the ?-secretase complex: nicastrin (NCSTN), presenilin 1 (PSEN1), presenilin enhancer 2 (PSENEN) and in POGLUT1, an endoplasmic reticulum O-glucosyltransferase involved in Notch signaling. We have carried out a system review and have performed a functional analysis of the 34 unique reported HS-linked mutations in NCSTN, PSEN1, PSENEN and POGLUT1. We have also examined the effects of the HS-linked PSEN1-P242LfsX11 mutation on cytokine and chemokine expression in macrophages. Mutations in NCSTN are predicted to cause loss of function, to result in loss of transmembrane (TM) domain, to affect NCSTN substrate recruitment sites, to cause loss or creation of new ligand binging sites and to alter post-translational modifications and disulfide bonds. PSEN1-P242LfsX11 occurs at the opposite side of TM5 from Alzheimer's disease-linked PSEN1 mutations. All of the PSENEN mutations occur on TM regions that are predicted to disrupt membrane function. POGLUT1 mutations lead to an early termination of protein synthesis and are predicted to affect ligand binding function. In addition, PSEN1-P242LfsX11 mediates cytokine and chemokine expression and prolongs tumor necrosis factor ? production on the inflammatory processes in THP-1 cells and phorbol-12-myristate-13-acetate-differentiated macrophages in response to lipopolysaccharide stimulation. These in silico analyses are instructive for functional studies of the HS-linked mutations. The PSEN1-P242LfsX11 mutation mediates cytokine and chemokine expression in macrophages.
Project description:Alzheimer's disease (AD) is a neurodegenerative disorder characterized by progressive memory loss and cognitive disturbance as a consequence of the loss of cholinergic neurons in the brain, neuritic plaques and hyperphosphorylation of TAU protein. Although the underlying mechanisms leading to these events are unclear, mutations in presenilin 1 (PSEN1), e.g., E280A (PSEN1 E280A), are causative factors for autosomal dominant early-onset familial AD (FAD). Despite advances in the understanding of the physiopathology of AD, there are no efficient therapies to date. Limitations in culturing brain-derived live neurons might explain the limited effectiveness of AD research. Here, we show that mesenchymal stromal (stem) cells (MSCs) can be used to model FAD, providing novel opportunities to study cellular mechanisms and to establish therapeutic strategies. Indeed, we cultured MSCs with the FAD mutation PSEN1 E280A and wild-type (WT) PSEN1 from umbilical cords and characterized the transdifferentiation of these cells into cholinergic-like neurons (ChLNs). PSEN1 E280A ChLNs but not WT PSEN1 ChLNs exhibited increased intracellular soluble amyloid precursor protein (sAPPf) fragments and extracellular A?42 peptide and TAU phosphorylation (at residues Ser202/Thr205), recapitulating the molecular pathogenesis of FAD caused by mutant PSEN1. Furthermore, PSEN1 E280A ChLNs presented oxidative stress (OS) as evidenced by the oxidation of DJ-1Cys106-SH into DJ-1Cys106-SO3 and the detection of DCF-positive cells and apoptosis markers such as activated pro-apoptosis proteins p53, c-JUN, PUMA and CASPASE-3 and the concomitant loss of the mitochondrial membrane potential and DNA fragmentation. Additionally, mutant ChLNs displayed Ca2+ flux dysregulation and deficient acetylcholinesterase (AChE) activity compared to control ChLNs. Interestingly, the inhibitor JNK SP600125 almost completely blocked TAU phosphorylation. Our findings demonstrate that FAD MSC-derived cholinergic neurons with the PSEN1 E280A mutation provide important clues for the identification of targetable pathological molecules.
Project description:Alzheimer's disease (AD) is an insidious and progressive disease with a genetically complex and heterogenous etiology. More than 200 fully penetrant mutations in the amyloid beta-protein precursor (APP), presenilin 1 (or PSEN1), and presenilin 2 (PSEN2) have been linked to early-onset familial AD (FAD). 177 PSEN1 FAD mutations have been identified so far and account for more than approximately 80% of all FAD mutations. All PSEN1 FAD mutations can increase the Abeta42:Abeta40 ratio with seemingly different and incompletely understood mechanisms. A recent study has shown that the 286 amino acid N-terminal fragment of APP (N-APP), a proteolytic product of beta-secretase-derived secreted form of APP (sAPPbeta), could bind the death receptor, DR6, and lead to neurodegeneration. Here we asked whether PSEN1 FAD mutations lead to neurodegeneration by modulating sAPPbeta levels. All four different PSEN1 FAD mutations tested (in three mammalian cell lines) did not alter sAPPbeta levels. Therefore PS1 mutations do not appear to contribute to AD pathogenesis via altered production of sAPPbeta.
Project description:Presenilin 1 (PSEN1) encodes the catalytic subunit of ?-secretase, and PSEN1 mutations are the most common cause of early onset familial Alzheimer's disease (FAD). In order to elucidate pathways downstream of PSEN1, we characterized neural progenitor cells (NPCs) derived from FAD mutant PSEN1 subjects. Thus, we generated induced pluripotent stem cells (iPSCs) from affected and unaffected individuals from two families carrying PSEN1 mutations. PSEN1 mutant fibroblasts, and NPCs produced greater ratios of A?42 to A?40 relative to their control counterparts, with the elevated ratio even more apparent in PSEN1 NPCs than in fibroblasts. Molecular profiling identified 14 genes differentially-regulated in PSEN1 NPCs relative to control NPCs. Five of these targets showed differential expression in late onset AD/Intermediate AD pathology brains. Therefore, in our PSEN1 iPSC model, we have reconstituted an essential feature in the molecular pathogenesis of FAD, increased generation of A?42/40, and have characterized novel expression changes.