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Mutant Presenilin 1 Dysregulates Exosomal Proteome Cargo Produced by Human-Induced Pluripotent Stem Cell Neurons.

ABSTRACT: The accumulation and propagation of hyperphosphorylated tau (p-Tau) is a neuropathological hallmark occurring with neurodegeneration of Alzheimer's disease (AD). Extracellular vesicles, exosomes, have been shown to initiate tau propagation in the brain. Notably, exosomes from human-induced pluripotent stem cell (iPSC) neurons expressing the AD familial A246E mutant form of presenilin 1 (mPS1) are capable of inducing tau deposits in the mouse brain after in vivo injection. To gain insights into the exosome proteome cargo that participates in propagating tau pathology, this study conducted proteomic analysis of exosomes produced by human iPSC neurons expressing A246E mPS1. Significantly, mPS1 altered the profile of exosome cargo proteins to result in (1) proteins present only in mPS1 exosomes and not in controls, (2) the absence of proteins in the mPS1 exosomes which were present only in controls, and (3) shared proteins which were upregulated or downregulated in the mPS1 exosomes compared to controls. These results show that mPS1 dysregulates the proteome cargo of exosomes to result in the acquisition of proteins involved in the extracellular matrix and protease functions, deletion of proteins involved in RNA and protein translation systems along with proteasome and related functions, combined with the upregulation and downregulation of shared proteins, including the upregulation of amyloid precursor protein. Notably, mPS1 neuron-derived exosomes displayed altered profiles of protein phosphatases and kinases involved in regulating the status of p-tau. The dysregulation of exosome cargo proteins by mPS1 may be associated with the ability of mPS1 neuron-derived exosomes to propagate tau pathology.

SUBMITTER: Podvin S

PROVIDER: S-EPMC8158845 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:IMPORTANCE:Although considerable effort has been expended developing drug candidates for Alzheimer disease, none have yet succeeded owing to the lack of efficacy or to safety concerns. One potential shortcoming of current approaches to Alzheimer disease drug discovery and development is that they rely primarily on transformed cell lines and animal models that substantially overexpress wild-type or mutant proteins. It is possible that drug development failures thus far are caused in part by the limits of these approaches, which do not accurately reveal how drug candidates will behave in naive human neuronal cells. OBJECTIVE:To analyze purified neurons derived from human induced pluripotent stem cells from patients carrying 3 different presenilin 1 (PS1) mutations and nondemented control individuals in the absence of any overexpression. We tested the efficacy of ?-secretase inhibitor and ?-secretase modulator (GSM) in neurons derived from both normal control and 3 PS1 mutations (A246E, H163R, and M146L). DESIGN, SETTING, AND PARTICIPANTS:Adult human skin biopsies were obtained from volunteers at the Alzheimer Disease Research Center, University of California, San Diego. Cell cultures were treated with ?-secretase inhibitor or GSM. Comparisons of total ?-amyloid (A?) and A? peptides 38, 40, and 42 in the media were made between vehicle- vs drug-treated cultures. MAIN OUTCOMES AND MEASURES:Soluble A? levels in the media were measured by enzyme-linked immunosorbent assay. RESULTS:As predicted, mutant PS1 neurons exhibited an elevated A?42:A?40 ratio (P < .05) at the basal state as compared with the nondemented control neurons. Treatment with a potent non-nonsteroidal anti-inflammatory druglike GSM revealed a new biomarker signature that differs from all previous cell types and animals tested. This new signature was the same in both the mutant and control neurons and consisted of a reduction in A?42, A?40, and A?38 and in the A?42:A?40 ratio, with no change in the total A? levels. CONCLUSIONS AND RELEVANCE:This biomarker discrepancy is likely due to overexpression of amyloid precursor protein in the transformed cellular models. Our results suggest that biomarker signatures obtained with such models are misleading and that human neurons derived from human induced pluripotent stem cells provide a unique signature that will more accurately reflect drug response in human patients and in cerebrospinal fluid biomarker changes observed during GSM treatment.

Project description:Accumulation and propagation of hyperphosphorylated Tau (p-Tau) is a common neuropathological hallmark associated with neurodegeneration of Alzheimer's disease (AD), frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17), and related tauopathies. Extracellular vesicles, specifically exosomes, have recently been demonstrated to participate in mediating Tau propagation in brain. Exosomes produced by human induced pluripotent stem cell (iPSC)-derived neurons expressing mutant Tau (mTau), containing the P301L and V337M Tau mutations of FTDP-17, possess the ability to propagate p-Tau pathology after injection into mouse brain. To gain an understanding of the mTau exosome cargo involved in Tau pathogenesis, these pathogenic exosomes were analyzed by proteomics and bioinformatics. The data showed that mTau expression dysregulates the exosome proteome to result in 1) proteins uniquely present only in mTau, and not control exosomes, 2) the absence of proteins in mTau exosomes, uniquely present in control exosomes, and 3) shared proteins which were significantly upregulated or downregulated in mTau compared with control exosomes. Notably, mTau exosomes (not control exosomes) contain ANP32A (also known as I1PP2A), an endogenous inhibitor of the PP2A phosphatase which regulates the phosphorylation state of p-Tau. Several of the mTau exosome-specific proteins have been shown to participate in AD mechanisms involving lysosomes, inflammation, secretases, and related processes. Furthermore, the mTau exosomes lacked a substantial portion of proteins present in control exosomes involved in pathways of localization, vesicle transport, and protein binding functions. The shared proteins present in both mTau and control exosomes represented exosome functions of vesicle-mediated transport, exocytosis, and secretion processes. These data illustrate mTau as a dynamic regulator of the biogenesis of exosomes to result in acquisition, deletion, and up- or downregulation of protein cargo to result in pathogenic mTau exosomes capable of in vivo propagation of p-Tau neuropathology in mouse brain.

Project description:OBJECTIVES:Alzheimer's disease (AD) is the most common neurodegenerative disease which is characterized by the formation of amyloid beta (A?) plaques and neurofibrillary tangles. These abnormal proteins induce disturbance in mitochondrial dynamics and defect in autophagy system. Since presenilin-1 (PS1) is a core component in ?-secretase complex, the mutations of PS1 gene cause the interference of ?-secretase activity and lead to the increased A?42 secretion. We aimed to characterize the patient-specific induced pluripotent stem cell (iPSC) line carrying PS1-S170F mutation. Furthermore, we tested whether disease-modifying drug can reduce AD pathology in the AD iPSC-derived neurons. MATERIALS AND METHODS:Mononuclear cells (MNCs) were isolated freshly from the peripheral blood of an autosomal dominant AD (ADAD) patient carrying presenilin-1 (PS1) mutation (Ser170Phe; PS1-S170F) and a cognitively normal control. We generated induced pluripotent stem cell (iPSC) lines, which were differentiated into functional cortical neurons. Then, we measured the markers indicative of AD pathogenesis using immunocytochemistry and Western blot. We also investigated the mitochondrial dynamics in the AD iPSC-derived neurons using Mito-tracker. RESULTS:We observed that both extracellular and intracellular A? levels were dramatically increased in the PS1-S170F iPSC-derived neurons, compared with the control iPSC-derived neurons. Furthermore, PS1-S170F iPSC-derived neurons showed high expression levels of p-Tau, which were detected both in the soma and neurites. The mitochondrial velocity in the PS1-S170F iPSC-derived neurons was much reduced, compared with that of the control. We also found a significant decrease of fusion-related protein Mfn1 (membrane proteins mitofusin 1) and an increase of fission-related protein DRP1 (dynamin-related protein 1) in the PS1-S170F iPSC-derived neurons. We further observed the defects of autophagy-related clearance in the PS1-S170F iPSC-derived neurons. Finally, we demonstrated the levels of A? and p-Tau can be dramatically reduced by the treatment of LY-2886721, a BACE1 inhibitor. CONCLUSIONS:Taken together, we have established and characterized the pathological features of an AD patient carrying PS1-S170F mutation using iPSC technology, which will be the first case on this mutation and this iPSC line will serve as a useful resource for studying AD pathogenesis and drug screening in the future.

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Mutant Presenilin 1 Dysregulates Exosomal Proteome Cargo Produced by Human-Induced Pluripotent Stem Cell Neurons.

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