New Organoid May Allow for Deeper Study of Processes Leading to ALS
Using a new laboratory model of brain cells, researchers demonstrated that cells with mutations associated with amyotrophic lateral sclerosis (ALS) show early signs of DNA damage and other forms of cellular stress.
Results suggest that blocking these cellular stress processes may hold promise in treating ALS.
The study, “Human ALS/FTD brain organoid slice cultures display distinct early astrocyte and targetable neuronal pathology,” was published in Nature Neuroscience.
The biological processes that cause ALS are poorly understood, partly because scientists cannot collect samples of brain tissue from people at the earliest disease stages, before symptoms are evident. Rather, emphasis is on creating viable models of brain cells grown in lab dishes.
In recent years, a particular kind of cellular model, called an organoid, has come into increasing use. Organoids are meant to resemble a mini organ, with the cells grown in a three-dimensional structure that mimics how they would be arranged in human tissue.
“Organoids provide a suitable biological platform for assessing dynamic sequences of human-specific cellular events, especially those relevant to neurodegenerative disease research, in which many cell types are now implicated in pathogenesis [disease development],” the researchers wrote.
While organoids of the brain have been developed, a notable drawback of existing models is their short lifespan: the most long-lasting do not survive more than three months, making long-term experiments impossible.
“To come close to capturing this complexity [that of neurodegenerative diseases], we need models that are more long-lived and replicate the composition of those human brain cell populations in which disturbances typically occur, and this is what our approach offers,” András Lakatos, MD, PhD, a professor at the University of Cambridge and the study’s senior author, said in a press release.
Most brain organoids developed to date are also spherical in shape. The researchers realized that this shape likely contributed to these models’ limited survival.
“When the cells are clustered in larger spheres, those cells at the core may not receive sufficient nutrition, which may explain why previous attempts to grow organoids long term from patients’ cells have been difficult,” said Kornélia Szebényi, PhD, a Cambridge scientist and study co-author.
Instead, the researchers grew disk-shaped organoids. Since no cells were buried in the middle, all had ample access to nutrients.
This approach allowed the researchers to grow organoids in culture for 240 days — nearly eight months. These organoids contained neurons (nerve cells), as well as astrocytes, a type of cell that supports neuron health.
Using their technique, the scientists grew some organoids from healthy cells, and others using cells derived from patients with mutations in the C9ORF72 gene. Mutations in this gene are found in up to 40% of familial ALS cases, and about 7% of sporadic cases, but how these mutations cause the disease are incompletely understood.
Researchers analyzed single-cell gene expression profiles in the organoids over time. Gene expression essentially looks at how different genes are turned “on” or “off,” and is broadly indicative of the cell’s activity and health.
Results showed marked differences between healthy cells and cells with C9ORF72 mutations.
“Although these initial disturbances were subtle, we were surprised at just how early changes occurred in our human model of ALS,” Lakatos said. “This and other recent studies suggest that the damage may begin to accrue as soon as we are born. We will need more research to understand if this is in fact the case, or whether this process is brought forward in organoids by the artificial conditions in the dish.”
Specifically, results indicated high levels of DNA damage in ALS cells, as well as high levels of endoplasmic reticulum (ER) stress — a type of cellular stress that affects protein production.
“Overall, our findings predicted ER stress and DNA damage response as the main affected pathways in astroglia and neurons” with C9ORF72 mutations, the team wrote, noting a need for more research to tease apart the specific effects in different types of cells.
Treatment with GSK2606414, a blocker of ER stress, lessened these signs of cellular damage, the scientists noted.
“We currently have no very effective options for treating [ALS], and while there is much more work to be done following our discovery, it at least offers hope that it may in time be possible to prevent or to slow down the disease process,” Lakatos said.