Long way up: rethink diseases in light of phase separation and phase transition

Abstract

Biomolecular condensation, driven by multivalency, serves as a fundamental mechanism within cells, facilitating the formation of distinct compartments, including membraneless organelles that play essential roles in various cellular processes. Perturbations in the delicate equilibrium of condensation, whether resulting in gain or loss of phase separation, have robustly been associated with cellular dysfunction and physiological disorders. As ongoing research endeavors wholeheartedly embrace this newly acknowledged principle, a transformative shift is occurring in our comprehension of disease. Consequently, significant strides have been made in unraveling the profound relevance and potential causal connections between abnormal phase separation and various diseases. This comprehensive review presents compelling recent evidence that highlight the intricate associations between aberrant phase separation and neurodegenerative diseases, cancers, and infectious diseases. Additionally, we provide a succinct summary of current efforts and propose innovative solutions for the development of potential therapeutics to combat the pathological consequences attributed to aberrant phase separation.

Keywords: aberrant phase separation; compartments; diseases; gain or loss of phase separation; multivalency; therapeutics.

Figure 1.

Gain and loss of phase separation and their potential links with diseases. Top: genomic variants, post translation modifications (PTM), stress, or other abnormal conditions coupled with acquiring further phase separation ability (LLPS enhancement, liquid to gel/glass/solid transition), termed gain of phase separation (GoPS). Bottom: on the other side, original physiological LLPS partially or totally lose phase separation, termed loss of phase separation (LoPS). Nevertheless, the causality between gain and loss of phase separation with disease is still elusive.

Figure 2.

Aberrant phase separation with neurodegenerative diseases. (A) Liquid–liquid phase separation of FUS in healthy and gain of phase separation in FTD, ALS diseases. (B) RNA and PTM promote Tau protein from liquid droplet to hydrogel transition in Alzheimer disease. (C) Continuous accumulation of α-Synuclein causes the formation of fiber in Parkinson’s disease.

Figure 3.

Loss of phase separation in p62-participated protein quality control. (A) Left: schematic of p62-WT, polyubiquitin chain, p62ΔPB1 and Paget’s disease of bone (PDB) mutation of p62-M404V/M404T/G411S. PB1: Phox 1 and Bem1p domain for oligomerization. UBA: ubiquitin associated domain for ubiquitin binding. Right: multivalent assembly of p62 with polyubiquitin chain contribute to p62 liquid–liquid phase separation. (B) p62ΔPB1 loses phase separation with polyubiquitin chain due to valency deficiency. (C) PDB related mutations of p62 compromise physical interaction with polyubiquitin chain and hence loss of phase separation.

Figure 4.

Aberrant phase separation and cancer. (A) Cancer-related mutants of ENL form condensates within nucleus and promote recruitment and transcription of elongation. (B) EWS-FLI1 fusion protein in diseases acquires phase separation ability and disturbs downstream gene regulation. (C) Cancer related mutations of SPOP compromise its phase separation with substrates.

Figure 5.

Representative examples for disturbed phase separation and condensate formation in virus infection. (A) Rabies virus N and P proteins assemble into Negri bodies as liquid-like viral factories. (B) Influenza A virus ribonucleoproteins form liquid inclusion at endoplasmic reticulum exit sites. (C) SARS CoV-2 nucleocapsid protein forms condensates with viral genomic RNA.

Figure 6.

Potential therapeutic intervention targeting aberrant phase separation via high-content screening. Utilizing cell-based or/and protein-based high-content screening, it is conceivable to identify small molecular compounds directly targeting aberrant phase separation (LoPS/GoPS) via physical interactions with components within condensates in vitro or phenotypic screening for effects on condensates in cellular. Hit compounds can be further evaluated as any lead compounds that are towards clinical utilization. (PCC, preclinical candidate; SAR, structure–activity relationships; R&D, research and development).