Network Organization of the Huntingtin Proteomic Interactome in Mammalian Brain

Abstract

SUMMARY We used affinity-purification mass spectrometry to identify 747 candidate proteins that are complexed with Huntingtin (Htt) in distinct brain regions and ages in Huntington’s disease (HD) and wildtype mouse brains. To gain a systems-level view of the Htt interactome, we applied Weighted Gene Correlation Network Analysis (WGCNA) to the entire proteomic dataset to unveil a verifiable rank of Htt-correlated proteins and a network of Htt-interacting protein modules, with each module highlighting distinct aspects of Htt biology. Importantly, the Htt-containing module is highly enriched with proteins involved in 14-3-3 signaling, microtubule-based transport, and proteostasis. Top-ranked proteins in this module were validated as novel Htt interactors and genetic modifiers in an HD Drosophila model. Together, our study provides a compendium of spatiotemporal Htt-interacting proteins in the mammalian brain, and presents a conceptually novel approach to analyze proteomic interactome datasets to build in vivo protein networks in complex tissues such as the brain.

Proteostasis impairment in protein-misfolding and -aggregation diseases

“…Inclusions disappear when huntingtin expression is blocked [108]. Multiple lines of evidence suggest that polyQ expanded proteins titrate chaperones away from their clients, leading to proteostasis impairment [44,74,100,109,110]. Conversely, overexpression of various chaperones, such as members of the Hsp70 system, suppresses polyQ toxicity [3, 69,75].…”

Dysregulation of 14‐3‐3 proteins in neurodegenerative diseases with Lewy body or Alzheimer pathology

“…We have shown that 14‐3‐3 overexpression, particularly 14‐3‐3 θ , is protective in neurotoxin, α syn, and LRRK2 models of PD, while 14‐3‐3 inhibition promotes toxicity in these models 5, 15, 16, 17. 14‐3‐3s also interact with proteins implicated in other neurodegenerative disorders, including beta‐amyloid (A β ), tau, superoxide dismutase, and huntingtin 18, 19, 20, 21, 22. 14‐3‐3s colocalize with these aggregation‐prone proteins in neurofibrillary tangles and plaques of Alzheimer's disease (AD), Huntington's disease (HD) inclusion bodies, and inclusions observed in amyotrophic lateral sclerosis (ALS) 20, 23, 24, 25…”

Experimental Models for Identifying Modifiers of Polyglutamine-Induced Aggregation and Neurodegeneration

“…Recently, proteomic studies to identify HTT-associated proteins have also been done in the context of full-length HTT expressed in mouse brain, using affinity purificationmass spectrometry [112,113]. Using subcellular fractionation of brain homogenates, one study found molecular chaperones as mutant HTT interactors, in support of previous findings and highlighting the central role of these folding machineries as HTT modifiers [112].…”

“…Interestingly, although the majority of HTT interactors were relatively conserved across different brain tissue and age, brain region-and developmental stage-specific interactors were also found, suggesting that some of these proteins might contribute to the selective neuronal susceptibility and age-dependent degeneration observed in HD patients. A comparison to other proteomic datasets reported previously [53,111,115] showed greater overlap among HTT datasets than between HTT and ataxia datasets, suggesting that unique protein-protein interactions may contribute to specific pathogenic mechanisms in different, but related, polyQ-mediated diseases [113].…”

“…Interestingly, components of the translational machinery were also identified as mutant HTT interacting proteins, providing a novel molecular pathway for HTT-mediated toxicity. In another study distinct regions of WT and BACHD mouse brains of different ages were used to identify 747 HTT interacting proteins [113], of which several had previously been found as HTT interactors or as modifiers of mHTT toxicity [53,114]. A subset of these protein hits was also shown to act as genetic modifiers of mHTT-induced neurodegeneration in a Drosophila model.…”