Researchers at the Brigham and Women’s Hospital have developed a technology that rapidly converts stem cells to brain cells with protein structures characteristic of Parkinson’s disease (PD), helping scientists study the disorder’s unique, highly variable disease pathology in a petri dish.
The new approach enables the transformation from stem cells to brain cells to occur reproducibly within weeks, and also allows researchers to develop models that reflect the diverse protein misfolding pathologies that can occur in the brain in that timeframe. The team, headed by Vikram Khurana, MD, PhD, chief of the Movement Disorders Division at BWH and principal investigator within the Ann Romney Center for Neurologic Diseases at BWH, suggest the model may in future aid development of personalized diagnostic and treatment methods for Parkinson’s disease.
“We sought to assess how quickly we could make human brain cells in the lab that give us a window into key processes occurring in the brains of patients with Parkinson’s disease and related disorders like multiple system atrophy and Lewy body dementia,” said Khurana. “And, unlike previous models, we wanted to do this in a short enough timeframe for these models to be useful for high-throughput genetic and drug screens and easy enough for many labs to use across academia and industry.”
Senior author Khurana and colleagues reported on the development of the inclusionopathy models, in Neuron, in a paper, titled “Rapid iPSC inclusionopathy models shed light on formation, consequence and molecular subtype of α-synuclein inclusions.” In their paper the team concluded “These scalable models hold promise for biological and drug discovery and as personalized medicine tools in neurodegenerative proteinopathies.”
PD is a progressive and degenerative brain condition. Individuals with the disease often struggle with slowed movement, tremors, muscle stiffness, and speech impairment, among other health complications. PD, along with other neurodegenerative conditions, such as Alzheimer’s disease, causes protein build-up in neurons, leading to protein misfolding and impaired cell function. The authors explained, “Neurodegenerative diseases—such as Alzheimer’s disease (AD), Parkinson’s disease (PD), or frontotemporal dementias—are named “proteinopathies” because their hallmark pathology is widespread protein-rich inclusions within various neuronal and glial subtypes of the central nervous system (CNS.)” Current PD therapies can alleviate some symptoms but do not address the root cause of the protein misfolding.
Induced pluripotent stem cell (iPSC)-derived CNS models present a potential patient-specific model system for visualizing inclusion formation in real time, the team continued. Existing “Parkinson’s in a dish” models can effectively transform stem cells into brain cells, but not within a reasonable timeframe to study patient-specific cellular pathologies to guide tailored treatment strategies. “… current human iPSC models have limited tractability, often requiring lengthy differentiation,” the investigators stated. “Mature inclusions do not form in a reasonable time frame.”
This is important because patients with PD are diverse and a one-size-fits-all treatment strategy may not work for some patients. “The problem is that the way protein clusters form in PD looks different in different patients, and even in different brain cells of the same patient,” said Khurana. “This begs the question: how do we model this complexity in the dish? And how do we do it fast enough for it to be practical for diagnostics and drug discovery?”
To create their new model Khurana’s lab used what are known as PiggyBac vectors to introduce transcription factors, and rapidly turn stem cells into different types of brain cells. They then introduced aggregation-prone proteins like alpha-synuclein (α-synuclein; αS), which is central to the formation of protein clusters in PD and related disorders, in nerve cells. Using CRISPR-Cas9 and other screening systems, they identified diverse types of inclusions forming in the cells, some of them protective and some of them toxic. To prove relevance to disease, they used their stem-cell models to discover similar inclusions in brains tissue from deceased patients. “These models shed light on the dynamic nature of αS inclusions, important molecular interactions within them, and subtypes of potential biological relevance in postmortem brain,” they wrote.
The technology will enable new approaches for classifying protein pathologies in patients and determining which of these pathologies might be the best drug targets, the scientists suggest. They acknowledge that the technology does have limitations that will need addressing. One limitation is that the technology currently generates immature neurons. The researchers aim to replicate this model with mature neurons to model the effects of aging on the protein aggregates that form. And while the new system can rapidly create both neurons and key inflammatory glial cells in the brain, the reported work only examined these cells individually. The team is now combining these cell types together to study the inflammatory responses to the protein aggregation process that might be important for PD progression.
The authors concluded, “We anticipate that the rapid and scalable iPSC inclusionopathy models described here will contribute to molecular-level understanding of inclusion subclasses and their distinct biological consequences. They will enable systematic mapping of genetic and physical interactions of different αS conformers (or “strains”) in distinct CNS cell types and co-cultures and modeling of mixed proteinaceous pathologies.”
Co-first author Alain Ndayisaba, MD, research fellow in the Department of Neurology at BWH, commented on the clinical applications that are already underway in the lab. “In one key application, we are utilizing this technology to identify candidate radiotracer molecules to help us visualize alpha-synuclein aggregation pathologies in the brains of living patients we see in the clinic.”
Added co-first author Isabel Lam, PhD, also a research fellow in the Department of Neurology at BWH, “This technology will pave the way for rapidly developing ‘personalized stem cell models’ from individual patients. These models are already being used to efficiently test new diagnostic and treatment strategies ‘in a dish’ before jumping into clinical trials so we target the right drug to the right patient.”
The authors further wrote, These models now offer a path to a patient-specific model incorporating both “host” cells and proteinaceous strains amplifiable from patient tissue and body fluids. Diagnostics like radiotracers or therapeutics like antibodies can now, in principle, be readily tested in stem-cell models derived from individual patients.”
