ABSTRACT: In late-onset sporadic Alzheimer’s disease (AD), the most prevalent and strongest risk factor is the ε4 allele of the apolipoprotein E (APOE4). To investigate the pathophysiological effects of the APOE4 genotype in the human cellular context, we generated isogenic iPSC-derived astrocytes bearing APOE4 alleles from APOE3 control iPSC. Next, to identify astrocytic APOE4-specific secreted proteomes, we performed a mass spectrometry using culture media from human astrocytes carrying APOE3 or APOE4.
Project description:APOE4 genotype is the strongest risk factor for the pathogenesis of sporadic Alzheimer’s disease (AD), but the detailed molecular mechanism of APOE4-mediated synaptic impairment remains to be determined in human cellular context. In this study, we generated human astrocyte model carrying APOE3 or APOE4 genotype using human induced pluripotent stem cells (iPSCs), in which isogenic APOE4 iPSCs were genome-edited from healthy control APOE3 iPSCs. By transcriptome analysis of human astrocytes between APOE genotypes, we showed the upregulation of an extracellular matrix glycoprotein in human APOE4 astrocytes, which may cause synaptic degeneration in concert with the equivocal reactive character and lipid change. Together, these results demonstrate novel negative impact of human APOE4 astrocyte on synaptic integrity and lead to a promising therapeutic intervention into APOE4-carriers.
Project description:Non-familial Alzheimer’s disease (AD) occurring before 65 years of age is commonly referred to as early-onset Alzheimer’s disease (EOAD) and constitutes ~5-6% of all Alzheimer’s disease (AD) cases. While EOAD exhibits the same clinicopathological changes such as amyloid plaques, neurofibrillary tangles (NFTs), brain atrophy, and cognitive decline as observed in the more prevalent late-onset AD (LOAD), EOAD patients tend to have more severe cognitive deficits, including visuospatial, language, and motor dysfunction. Patient-derived induced pluripotent stem cells (iPSCs) have been used to model and study penetrative, familial AD (FAD) mutations in APP, PSEN1, and PSEN2, but have been seldom used for sporadic forms of AD that display more heterogeneous disease manifestation. In this study, we sought to characterize iPSC-derived neurons from EOAD patients via RNA-sequencing. A modest difference in expression profiles between EOAD patients and non-demented control subjects resulted in a limited number of differentially expressed genes (DEGs). Based on this analysis, we provide evidence that iPSC-derived neuron model systems, likely due to the loss of EOAD-associated epigenetic signatures during the iPSC reprogramming, are not an ideal model system to study sporadic AD.
Project description:To explore the mechanistic basis of ApoE Ɛ4 vs ApoE Ɛ3 protein expression on endocytic pathways responsible for tau uptake in neurons and astrocytes and the maturation of neuronal networks, we have developed genotype matched co-cultures of iPSC derived astrocytes and neurons derived from isogenic triads of iPSC lines generated by the ADAPTED consortium (Schmid et al., 2019, 2020) . We show that isogenic iPSC derived APOE-E4 expressing astrocytes take up less extracellular tau than APOE-E3 or APOE null astrocytes, while isogenic neurons in monoculture take up equivalent amounts of tau primarily through macropinocytosis. Co-culture of neurons with genotype matched astrocytes increases the general uptake capacity of neurons by increasing the dependence of neuronal endocytosis on dynamin mediated pathways. Co-culture also enhances the emergence of spontaneous neuronal activity; however, the emergence of synchronous network activity is impaired by the expression of APOE-E4 genotype. We performed RNA-Seq on the astrocytes, neurons and co-cultures to understand the molecular pathway changes associated with different ApoE genotypes.
Project description:Here we elucidate the effect of Alzheimer’s disease (AD)-predisposing genetic backgrounds, APOE4, PSEN1ΔE9 and APPswe, on functionality of human microglia. We present a physiologically relevant high-yield protocol for producing human microglia-like cells (iMGLs) from induced pluripotent stem cells. Differentiation is directed with small molecules through primitive erythromyeloid progenitors to recreate microglial ontogeny from yolk sac. The iMGLs express microglial signature genes and respond to ADP with intracellular Ca2+ release distinguishing them from macrophages. Using 16 iPSC lines from healthy donors, AD patients and isogenic controls, we reveal that the APOE4 genotype has a profound impact on several aspects of microglial functionality whereas PSEN1ΔE9 and APPswe mutations trigger minor alterations. The APOE4 genotype impairs phagocytosis, migration and metabolic activity of iMGLs but exacerbates their cytokine secretion. This indicates that APOE4 iMGLs are fundamentally unable to mount normal microglial functionality in AD.
Project description:We have developed a panel of isogenic iPSC lines carrying MAPT splice-site mutations S305S, S305I or S305N, derived from four different donors. All three mutations significantly increased the proportion of 4R tau expression in iPSC-neurons and astrocytes, with up to 80% 4R transcripts in S305N neurons from as early as 4 weeks of differentiation.
Project description:We have developed a panel of isogenic iPSC lines carrying MAPT splice-site mutations S305S, S305I or S305N, derived from four different donors. All three mutations significantly increased the proportion of 4R tau expression in iPSC-neurons and astrocytes, with up to 80% 4R transcripts in S305N neurons from as early as 4 weeks of differentiation.
Project description:Duchenne Muscular Dystrophy (DMD) is a devastating genetic disease leading to degeneration of skeletal muscles and premature death. How dystrophin absence leads to muscle wasting remains unclear. Here, we describe an optimized protocol to differentiate human induced Pluripotent Stem Cells (iPSC) to a late myogenic stage. This allows to recapitulate classical DMD phenotypes (mislocalization of proteins of the Dystrophin glycoprotein associated complex (DGC), increased fusion, myofiber branching, force contraction defects and calcium hyperactivation) in isogenic DMD-mutant iPSC lines in vitro. Treatment of the myogenic cultures with prednisolone (the standard of care for DMD) can dramatically rescue force contraction, fusion and branching defects in DMD iPSC lines. This argues that prednisolone acts directly on myofibers, challenging the largely prevalent view that its beneficial effects are due to anti-inflammatory properties. Our work introduces a new human in vitro model to study the onset of DMD pathology and test novel therapeutic approaches.
Project description:Apolipoprotein E4 (APOE4) is the strongest genetic risk factor for late-onset Alzheimer’s disease (LOAD), leading to earlier age of clinical onset and exacerbating pathologies. There is a critical need to identify protective targets. Recently, a rare APOE variant, APOE3-R136S (Christchurch), was found to protect against early-onset AD in a PSEN1-E280A carrier. We sought to determine if the R136S mutation also protects against APOE4-driven effects in LOAD. We generated tauopathy mouse and human iPSC-derived neuron models carrying human APOE4 with the homozygous or heterozygous R136S mutation. We found that the homozygous R136S mutation rescued APOE4-driven Tau pathology, neurodegeneration, and neuroinflammation. The heterozygous R136S mutation partially protected against APOE4-driven neurodegeneration and neuroinflammation, but not Tau pathology. Single-nucleus RNA-sequencing revealed that the APOE4-R136S mutation increased disease-protective and diminished disease-associated cell populations in a gene dose-dependent manner. Thus, the APOE-R136S mutation protects against APOE4-driven AD pathologies, providing a target for therapeutic development against AD.
Project description:Microglia play a key role in the response to amyloid beta in Alzheimer’s disease (AD). In this context, the major transcriptional response of microglia is the upregulation of APOE, the strongest late-onset AD risk gene. Of its three isoforms, APOE2 is thought to be protective, while APOE4 increases AD risk. We hypothesised that the isoforms functionally alter microglia by shaping their transcriptomic and chromatin landscapes. We used RNA- and ATAC-sequencing to profile gene expression and chromatin accessibility of human microglia isolated from a xenotransplantation model of AD. We identified widespread transcriptomic and epigenomic differences which are dependent on APOE genotype, and are corroborated across the profiling assays.