Differentiation drives widespread rewiring of the neural stem cell chaperone network

Abstract

<jats:title>Summary</jats:title><jats:p>Neural stem and progenitor cells (NSPCs) are critical for continued cellular replacement in the adult brain. Life-long maintenance of a functional NSPC pool necessitates stringent mechanisms to preserve a pristine proteome. We find that the NSPCs chaperone network robustly maintains misfolded protein solubility and stress resilience through high levels of the ATP-dependent chaperonin TRiC/CCT. Strikingly, NSPC differentiation rewires the cellular chaperone network, reducing TRiC/CCT levels and inducing those of the ATP-independent small heat shock proteins (sHSPs). This switches the proteostasis strategy in neural progeny cells to promote sequestration of misfolded proteins into protective inclusions. The chaperone network of NSPCs is more effective than that of differentiated cells, leading to improved management of proteotoxic stress and amyloidogenic proteins. However, NSPC proteostasis is impaired by brain aging. The less efficient chaperone network of differentiated neural progeny may contribute to their enhanced susceptibility to neurodegenerative diseases characterized by aberrant protein misfolding and aggregation.</jats:p>

Turnover and replication analysis by isotope labeling (TRAIL) reveals the influence of tissue context on protein and organelle lifetimes

“…It is possible that protein damage occurs more rapidly in some tissues than in others, perhaps linked to the variable rate of production of reactive oxygen species and other damaging agents during normal cellular metabolism. A second, non-exclusive possibility is that the activity and/or selectivity of protein folding and/or degradation machineries varies across cell types and tissues 51 . Intriguingly, in vivo reporters of the proteasome and of autophagy do suggest variable flux across tissues 50,52 .…”

“…Consistent with our findings, protein lifetimes have also been found to differ significantly between non-dividing cell types in culture 16 , as well as in the same cell type (fibroblasts) isolated from different mammals 17 . One potential explanation for these differences could be variation in the composition and activity of protein folding chaperones, the ubiquitin-proteasome system, and/or the autophagy machinery across tissues [49][50][51] .…”

Impairment of lipid homoeostasis causes accumulation of protein aggregates in the lysosome

“…In one model of aggresome formation, misfolded and aggregated proteins are poly-ubiquitinated, transported along microtubules, and coalesced into perinuclear aggresomes, which are then detected by autophagy receptors to induce autophagosome formation, eventually delivering the cargo to the lysosomes for degradation 26 . ProteoStat staining was initially reported to colocalize with mono-/poly-ubiquitinated proteins, p62, and LC3, and has been increasingly used as a general reporter for protein aggregation 12,13,15,16 . To our surprise, we did not see colocalization of MG132-induced ProteoStat puncta with mono-/poly-ubiquinated proteins (Fig S2E).…”

“…Like Thioflavin T, ProteoStat fluorescence increases when rotationally confined by binding to cross-beta sheets in amyloidal structures. The dye has recently been used in studies to visualize aggregated proteins in mouse NSCs and in C. elegans 12,13,15,16 . To verify that ProteoStat can be used to report changes in proteostasis in human cell cultures, we inhibited proteasomes in K562, U2OS, and A549 cells and stained them for microscopy or flow cytometry analysis.…”

“…To uncover novel components and pathways that regulate endogenous protein homeostasis, we applied CRISPR interference (CRISPRi) technology to perform unbiased, genome-wide screens on K562 cells using an aggresome-staining dye, ProteoStat. ProteoStat is known to label both experimentally induced aggresomes and aggregates that accumulate with age in the CNS of mammals [12][13][14][15] . Our screens uncovered a link between lysosomal lipid homeostasis and proteostasis.…”