Photocontrollable Probe Spatiotemporally Induces Neurotoxic Fibrillar Aggregates and Impairs Nucleocytoplasmic Trafficking

Engineered droplet-forming peptide as photocontrollable phase modulator for fused in sarcoma protein

The assembly and disassembly of biomolecular condensates are crucial for the subcellular compartmentalization of biomolecules in the control of cellular reactions. Recently, a correlation has been discovered between the phase transition of condensates and their maturation (aggregation) process in diseases. Therefore, modulating the phase of condensates to unravel the roles of condensation has become a matter of interest. Here, we create a peptide-based phase modulator, JSF1, which forms droplets in the dark and transforms into amyloid-like fibrils upon photoinitiation, as evidenced by their distinctive nanomechanical and dynamic properties. JSF1 is found to effectively enhance the condensation of purified fused in sarcoma (FUS) protein and, upon light exposure, induce its fibrilization. We also use JSF1 to modulate the biophysical states of FUS condensates in live cells and elucidate the relationship between FUS phase transition and FUS proteinopathy, thereby shedding light on the effect of protein phase transition on cellular function and malfunction.

Degradation of neurodegenerative disease-associated TDP-43 aggregates and oligomers via a proteolysis-targeting chimera

BACKGROUND

Amyotrophic lateral sclerosis (ALS) associated with TAR DNA-binding protein 43 (TDP-43) aggregation has been considered as a lethal and progressive motor neuron disease. Recent studies have shown that both C-terminal TDP-43 (C-TDP-43) aggregates and oligomers were neurotoxic and pathologic agents in ALS and frontotemporal lobar degeneration (FTLD). However, misfolding protein has long been considered as an undruggable target by applying conventional inhibitors, agonists, or antagonists. To provide this unmet medical need, we aim to degrade these misfolding proteins by designing a series of proteolysis targeting chimeras (PROTACs) against C-TDP-43.

METHODS

By applying filter trap assay, western blotting, and microscopy imaging, the degradation efficiency of C-TDP-43 aggregates was studied in Neuro-2a cells overexpressing eGFP-C-TDP-43 or mCherry-C-TDP-43. The cell viability was characterized by alarmarBlue assay. The beneficial and disaggregating effects of TDP-43 PROTAC were examined with the YFP-C-TDP-43 transgenic C. elegans by motility assay and confocal microscopy. The impact of TDP-43 PROTAC on C-TDP-43 oligomeric intermediates was monitored by fluorescence lifetime imaging microscopy and size exclusion chromatography in the Neuro-2a cells co-expressing eGFP-C-TDP-43 and mCherry-C-TDP-43.

RESULTS

Four PROTACs with different linker lengths were synthesized and characterized. Among these chimeras, PROTAC 2 decreased C-TDP-43 aggregates and relieved C-TDP-43-induced cytotoxicity in Neuro-2a cells without affecting endogenous TDP-43. We showed that PROTAC 2 bound to C-TDP-43 aggregates and E3 ligase to initiate ubiquitination and proteolytic degradation. By applying advanced microscopy, it was further shown that PROTAC 2 decreased the compactness and population of C-TDP-43 oligomers. In addition to cellular model, PROTAC 2 also improved the motility of transgenic C. elegans by reducing the C-TDP-43 aggregates in the nervous system.

CONCLUSIONS

Our study demonstrated the dual-targeting capacity of the newly-designed PROTAC 2 against both C-TDP-43 aggregates and oligomers to reduce their neurotoxicity, which shed light on the potential drug development for ALS as well as other neurodegenerative diseases.

Nanoscopic Insights of Amphiphilic Peptide against the Oligomer Assembly Process to Treat Huntington's Disease

Finding an effective therapeutic regimen is an urgent demand for various neurodegenerative disorders including Huntington's disease (HD). For the difficulties in observing the dynamic aggregation and oligomerization process of mutant Huntingtin (mHtt) in vivo, the evaluation of potential drugs at the molecular protein level is usually restricted. By combing lifetime-based fluorescence microscopies and biophysical tools, it is showcased that a designed amphiphilic peptide, which targets the mHtt at an early stage, can perturb the oligomer assembly process nanoscopically, suppress the amyloid property of mHtt, conformationally transform the oligomers and/or aggregates of mHtt, and ameliorate mHtt-induced neurological damage and aggregation in cell and HD mouse models. It is also found that this amphiphilic peptide is able to transport to the brain and rescue the memory deficit through intranasal administration, indicating its targeting specificity in vivo. In summary, a biophotonic platform is provided to investigate the oligomerization/aggregation process in detail that offers insight into the design and effect of a targeted therapeutic agent for Huntington's disease.

Harnessing biomolecular condensates in living cells

As part of the 'Central Dogma' of molecular biology, the function of proteins and nucleic acids within a cell is determined by their primary sequence. Recent work, however, has shown that within living cells the role of many proteins and RNA molecules can be influenced by the physical state in which the molecule is found. Within living cells, both protein and RNA molecules are observed to condense into non-membrane-bound yet distinct structures such as liquid droplets, hydrogels and insoluble aggregates. These unique intracellular organizations, collectively termed biomolecular condensates, have been found to be vital in both normal and pathological conditions. Here, we review the latest studies that have developed molecular tools attempting to recreate artificial biomolecular condensates in living cells. We will describe their design principles, implementation and unique characteristics, along with limitations. We will also introduce how these tools can be used to probe and perturb normal and pathological cell functions, which will then be complemented with discussions of remaining areas for technological advance under this exciting theme.

Chemical modification of proteins with photocleavable groups

In this work, we describe methods for synthesizing and incorporating a wide range of photocleavable groups into proteins. These are based on the di-methoxyl nitro phenyl ethyl (DMNPE) group. Using a common ketone starting material, we have modified the DMNPE core with different peptides and small molecules. We describe how these can be incorporated into DMNPE either by solution or solid phase methods. In addition, we show how the ketone group can be effectively converted into a hydrazone group and ultimately into a diazo. The potential pitfall of azine formation is also delineated, as are the strategies for avoiding this side product. We then show how these modified diazo groups can then be reacted with the carboxyl groups of the protein to make the final ester product. Finally, we show how the ultimate product can be purified, and the products identified using 280 and 345nm ratios, as well as ESI-MS characterization. The combined methods should allow the incorporation of many possible photocleavable groups into a range of proteins, and allow the ultimate properties of the modified protein to be subsequently toggled with light.