Dysregulation of Exosome Cargo by Mutant Tau Expressed in Human-induced Pluripotent Stem Cell (iPSC) Neurons Revealed by Proteomics Analyses

Abstract

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.

Outside-in induction of the IFITM3 trafficking system by infections, including SARS-CoV-2, in the pathobiology of Alzheimer’s disease

“…On its own right, IFITM3 induction is not restricted to intracellular cascades. IFITM3 has been previously shown to be a mutant-tau exclusive cargo in AD exosomes 33 , whereas IFITM3-loaded exosome trafficking from infected to non-infected cells has been shown to confer resistance to DENV infection 34 . On these premises, IFITM3, exosomal hyperphosphorylated tau 35 and Αβ-ΝΑ may constitute a feed-forward signal expanding from a primary site of neuroinfection (i.e.…”

Human Induced Pluripotent Stem Cell-Derived Exosomes as a New Therapeutic Strategy for Various Diseases

“…This suggests that exosomes are sufficient to cause the long-distance propagation of tau pathology and neurodegeneration in vivo. To further understand the dysregulation of pathogenic exosomes, they were analyzed using proteomics and bioinformatics in the study of Podvin et al [ 62 ]. They found that the expression of the P301L and V337M mutations of tau in human iPSC neurons results in the recruitment of distinct proteins to exosomes.…”

Exosomes as Emerging Biomarker Tools in Neurodegenerative and Neuropsychiatric Disorders—A Proteomics Perspective

“…Table 2 summarizes some of the exosome proteins used as biomarkers in studies of neurodegeneration. A recent quantitative proteomics study exploring the differential expression of proteins in exosomes derived from iPSC neurons transfected with mutant Tau (P301L and V337M) (mTau) showed significant alteration in protein expression compared to control exosomes [ 89 ]. Proteomic analyses identified 347 and 574 proteins in mTau and control exosomes, respectively.…”

“…Eighteen proteins were unique to mTau exosomes, wheras 245 proteins were found only in control exosomes. Proteins unique to mTau exosomes included acidic nuclear phosphoprotein 32 family member A (ANP32A), AP-2 complex subunit α-1 (AP2A1), and V-type proton ATPase catalytic subunit A, that have been shown to be involved in synaptic dysfunction, memory loss and neuropathology [ 89 ]. Studies of exosome-mediated secretion of phosphorylated Tau from human neuroblastoma cells have shed light onto the possible role of exosomes in Tau pathophysiology in AD [ 90 ].…”