CRISPR screens in iPSC-derived neurons reveal principles of tau proteostasis

Abstract

A hallmark of age-associated neurodegenerative diseases is the aggregation of proteins. Aggregation of the protein tau defines tauopathies, which include Alzheimer's disease and frontotemporal dementia. Specific neuronal subtypes are selectively vulnerable to the accumulation of tau aggregates, and subsequent dysfunction and death. The mechanisms underlying cell type-selective vulnerability are unknown. To systematically uncover the cellular factors controlling the accumulation of tau aggregates in human neurons, we conducted a genome-wide CRISPRi-based modifier screen in iPSC-derived neurons. The screen uncovered expected pathways, including autophagy, but also unexpected pathways, including UFMylation and GPI anchor synthesis, that control tau oligomer levels. The E3 CUL5 ubiquitin ligase is a potent modifier of tau levels, and directly interacts with tau. Disruption of mitochondrial function increases tau oligomer levels and promotes proteasomal misprocessing of tau. These results reveal new principles of tau proteostasis in human neurons and pinpoint potential therapeutic targets for tauopathies.

Mono-UFMylation promotes misfolding-associated secretion of α-synuclein

“…Several recent studies have linked UFM1 and USP19 to the intercellular transfer of neurodegenerative disease-associated neurotoxic proteins. Specifically, in UFM1-deficient induced pluripotent stem cell-derived neurons and in USP19 KO mice, the seeding and propagation of misfolded Tau and α-Syn are inhibited (45)(46)(47). Although the underlying mechanisms are unclear, these studies and our work consolidate an emerging theme that the dynamics of protein aggregation may be influenced by a functional interplay between USP19 and UFM1 in either MAPS or a related UcPS process.…”

The UFMylation pathway is impaired in Alzheimer’s disease

“…The UFMylation pathway is implicated in a variety of biological processes known to be disrupted in AD, and deficiencies in this pathway have been linked to neurodevelopmental disorders [28][29][30]52]. In addition, the UFM1 pathway was very recently identified as potent modulator of tau aggregation upon seeding [26,53]. Therefore, the UFM1 pathway is of high relevance for AD.…”

A Massively Parallel CRISPR-Based Screening Platform for Modifiers of Neuronal Activity

“…20 These screens allow for unbiased identification of genes and mechanisms underlying cell type specific biological processes. Pooled CRISPR-based screens have been successfully deployed to elucidate neuronal phenotypes such as survival, 17,18,21 transcriptomic states, 17,18 oxidative damage, 18 lysosomal function, 18 and protein aggregation, 22 it has so far not been possible to use pooled CRISPR-based screens to uncover modifiers of neuronal activity. Here, we report a method to uncover modifiers of neuronal excitability in massively parallel screens.…”