University of Michigan researchers have developed a new method to study the behavior of protein and RNA molecules inside biomolecular condensates, which are small structures within cells that help regulate cellular functions. The research focuses on a protein called fused in sarcoma (FUS), which is known to form aggregates in patients with neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS) and frontotemporal dementia.
The team, led by chemistry professor Nils Walter, found that the movement of molecules within these condensates slows down in very small regions they call nanodomains. As these condensates age, the nanodomains move toward the surface of the droplet. This process was observed using advanced fluorescence microscopy techniques after overcoming challenges related to keeping the droplets still during imaging.
Researchers also tested drugs used for ALS treatment on these condensates. They observed that these drugs may speed up the movement of nanodomains to the surface, leading to faster formation of fibrils—structures thought to protect neurons by absorbing smaller toxic aggregates associated with disease progression.
“There is a lot of hope that by manipulating these condensates, we can use them for medical purposes, such as slowing neurodegenerative disease, making them a repository for drugs that can be released slowly over time, or sequestering unwanted proteins such as those that are cancer- or virus-related by inducing them to form condensates,” said Walter, who directs the Center for RNA Biomedicine at U-M. “Understanding how they form—and what develops inside of them as they age—is essential for finding ways to influence the process beneficially.”
The study highlights how FUS plays a key role in managing RNA metabolism in cells and responds to stress conditions by condensing. Mutations in FUS can cause it to accumulate abnormally and are linked with both cancers and neurodegenerative diseases like ALS.
Walter explained some technical hurdles: “If you make a condensate and put it on a microscope slide, it can roll over the surface or wiggle back and forth. If that happens, then the particle tracking gets messed up,” he said. “So you have to immobilize the condensates on the surface, but you have to do that in a very judicial way. For example, if you have too many anchors on the surface of the condensate, it just flattens out. It becomes a pancake.”
By optimizing this process and using HILO microscopy, researchers were able to observe individual molecule movements within droplets and watch fibril formation around FUS condensates under drug treatment.
“But what our findings mean overall is that, for the first time, we see these nanodomains as potential seeds to these fibers,” Walter said. “Maybe the drugs we used, edaravone and especially riluzole, have another effect beyond those known, by helping the condensates to fibralize faster and protect the neuron.”
Walter noted growing interest in this area: “The field of phase condensation has exploded. There are many of these phase condensates in cells that either accelerate reactions or sequester things away so they cannot wreak havoc,” he said. “There’s a lot of biology being learned in a fast-moving area of biology.”
The research was supported by funding from national agencies including NIH and NSF as well as private foundations.
