Exploration of Amyotrophic Lateral Sclerosis (ALS) biology has found new momentum through innovative research led by Brian McCabe, Bernard Schneider, and Sabine Liebscher. Their work, funded by Target ALS, sheds light on novel therapeutic avenues, blending basic biological inquiry with advanced technological innovations.
The Science Behind the Discovery
Lab director and Professor in the EPFL Brain Mind Institute Brian McCabe’s quest began with a simple yet profound question: What role does TDP-43 dysfunction play in ALS? The protein is aggregated and dysfunctional in 97% of ALS cases, but the upstream and downstream biology is still poorly understood. To answer this question, McCabe’s Switzerland-based lab started with TDP-43-null Drosophila melanogaster (fruit flies). These flies not only had significantly reduced lifespan, but also displayed a striking loss of premotor central synapses. Further genetic screening, made possible by decades of genetic discovery and understanding in Drosophila, revealed that this synapse loss was linked to improper activation of the phosphatidyl serine (PtdSer)-dependent synapse engulfment pathway, a mechanism typically involved in adolescent synaptic pruning. This reactivation of adolescent synaptic pruning pathways resonated with findings from other neurodegenerative diseases (NDDs), suggesting the group was on the right path. They quickly followed up on these results by replacing the TDP-43 null flies with humanized TDP-43 mutant flies, to begin to assess whether this biology might also occur in people with ALS.
“Our starting point for this project was to create new models for ALS using genome editing, specifically CRISPR-Cas9 technology,” explained Brian. “We used human gene replacement, or HGR technology, to swap the Drosophila gene with the human version, incorporating ALS-associated mutations.” This approach revealed specific motor deficits, but what truly surprised the team was the discovery that these motor deficits were linked to the loss of inhibitory synapses specifically in the fly’s ventral nerve cord (spinal cord equivalent). “That unexpected finding by my student Marine sparked our interest in understanding why these synapses were being eliminated,” Brian explained. The team then identified PtdSer (a specific lipid) on neurons that phagocytic cells in Drosophila recognize, triggering synapse elimination. “Once we knew the mechanism, the next step was clear: could we prevent these cells from targeting the synapses to protect them? Could that delay ALS progression?” This led to the development of a novel ‘MASK peptide,’ a small protein that is able to physically cover, or mask, the PtdSer signal on a vulnerable synapse, now in its second iteration with a third in development.
Recognizing the potential for therapeutic breakthroughs, Brian assembled a stellar team: Bernard Schneider, a specialist in gene therapy and viral vector technologies, and Sabine Liebscher, an expert in in vivo imaging and mouse behavior. Together, they aimed to explore if similar synaptic loss occurred in other ALS models beyond those in Drosophila, including mouse models of familial ALS (fALS) and human tissue from sporadic ALS (sALS) and fALS patients. They also aimed to target and prevent this loss with the MASK peptide in mammalian models. Brian explained, “Bernard’s group has vectorized this MASK therapeutic and allowed for its expression in the mammalian CNS, and Sabine is able to look in vivo at target engagement in the cortex.”
Their consortium achieved remarkable results in just two years:
- Identification of specific loss of inhibitory central motor system synapses in Drosophila TDP-43 knockout models, humanized Drosophila, and SOD1G93A mice. “That was a good day, when Greta, a post-doc in my lab, saw that SOD1 mice also have a loss of inhibitory synapses. It was not predicted, and it was surprising,” Brian recalled. “Those are very good days when you get a result, showing that you are on the right track. That keeps you motivated through the other days.”
- Demonstrated that hMFG-MASK, when expressed from astrocytes using an AAV-mediated approach, could alter synaptic density in ALS mouse models, thanks to Sabine’s advanced in vivo 2-photon imaging. “We’re looking at the motor cortex, a part of the nervous system that is compromised in ALS but is really understudied and its role in ALS pathophysiology is not well understood. The data is pointing to stabilization and prevention of ongoing synaptic loss when MASK is expressed, driving a slowly progressive increase in synapse density” shared Sabine. This clear demonstration of target engagement—observing individual synapses in real-time within the living brain using the group’s emerging candidate therapeutic—stands as a testament to technological innovation.
- Showed that intrathecal administration of AAV-MASK improved motor function in SOD1G93A mice, assessed through Schneider’s machine learning-driven swimming assays, developed with assistance of the group of Mackenzie Mathis at EPFL. “The idea here was to have an approach which would be less investigator-dependent, but also an approach that potentially could highlight neuroprotective effects on motor function at an early stage of the disease. Now we have an algorithm which has been improving over the years. The behavioral test itself also was improved, and that allowed us to basically show that the MASK protein seems to improve motor function, at least in its first version,” Bernard explained.
The group’s third-year plans focus on:
- Optimizing the MASK peptide to specifically target synapses. Bernard and Sabine’s labs are already working with a second version of the MASK peptide that Brian’s lab developed. “Version 3 is in the pipeline,” said Brian. The goal is to make sure that when the MASK peptide is injected in the nervous system, it’s able to home in on the synapses where PtdSer might be expressed.
- Refining AAV delivery for potential therapeutic applications. Bernard commented, “I think there is always a question whether we might also see side effects of disrupting synapse elimination and whether preventing the elimination might actually be perturbing the circuit. And I think that one positive surprise is that at least so far, we have not seen anything negative in the animals. This remains an approach which is highly, highly experimental.” As the third year begins, his lab is testing a new injection technique (intracerebroventricular) of the AAV construct that he hopes will provide better coverage of MASK peptide across the central nervous system, including the motor cortex. “We will also cover a longer period of the disease progression,” he added. Although their initial results injecting the peptide in adult mice were promising, testing delivery in animals earlier on in disease progression may show enhanced therapeutic efficacy of the approach.
- Confirming biological consistency across various ALS models and human tissues. The group is actively analyzing human postmortem tissue to confirm that inhibitory synapse loss occurs in premotor circuits in people with ALS. “We don’t know yet if this is true in human patient tissues. We’re doing those experiments right now,” said Brian.
Target ALS is excited to continue to support this work that began with mechanistic interrogation of biology in fruit flies and now, in its third year, has the potential to accumulate preclinical data to enter the ALS therapeutic clinical pipeline.
The Mystery of Inhibitory Synapse Vulnerability
A lingering question in their research is why inhibitory synapses are particularly vulnerable in ALS. The research team was surprised that the loss of inhibitory synapses was much more pronounced than excitatory synapse reduction in both the ventral nerve cord of TDP-43 null Drosophila and the spinal motor neurons of SOD1G93A mice. Their finding aligns with previous studies, such as those conducted in the FUSΔNLS mouse model. In a 2021 Nature Communications paper, Sabine partnered with Luc Dupuis’s lab to show evidence for transcriptional and structural defects in both inhibitory and excitatory cortical motor neuron synapses in FUSΔNLS mice, with more pronounced defects in inhibitory synapse ultrastructure. The question of whether this predominant loss or damage of inhibitory synapses occurs in human ALS patient tissue is still being explored by Brian, Bernard, and Sabine’s team. Understanding why inhibitory synapses are particularly vulnerable in premotor circuits might also shed light on the biology that drives synapse vulnerability across ALS and other NDDs. The team speculated that the pronounced vulnerability of inhibitory synapses may be linked to PtdSer, the lipid molecule the team identified, which appears necessary for synapse elimination in Drosophila models and was sufficient to rescue synapse elimination in SOD1G93A mice. “Our guess is that these inhibitory synapses might have higher levels of this lipid, making them more susceptible,” they explained, though this remains unconfirmed. Despite this insight, Brian acknowledged the challenges in this line of research, noting, “Imaging this particular lipid at subsets of synapses is difficult. We speculate there must be a molecule specific to inhibitory synapses regulating this process, but we haven’t identified it yet.”
Sabine also discussed the potential connection between their work and the broader concept of cortical hyperexcitability in ALS, a symptom of ALS targeted by several emerging candidate therapeutics. She mentioned the known structural and functional disruption of inhibitory interneurons in the spinal cord and cortex in ALS, but acknowledged that in this project, she is measuring inhibitory postsynapses of upper motor neurons themselves. “It could be that the synapse loss we’re observing is inherent to the motor neuron itself, so cell-autonomously dysregulated, or it could be mirroring deficits happening on the input interneuron or between multiple upstream interneurons,” she explained. Both scenarios are plausible, and the complexity of premotor and other neural circuits—where interneurons vary widely and inhibit each other—makes it difficult to pinpoint the exact mechanism.
Sabine noted that this complexity, and the uncertainty around which synapses and cells are directly damaged, challenges the notion of simply boosting inhibition as a universal treatment strategy to target cortical hyperexcitability. “Overall the standard treatment Riluzole only exerts a transient effect on cortical hyperexcitability. Neural circuits are plastic and they can adapt to a given stimulation or reduction of excitation. We may need to better account for homeostatic effects in our treatment strategies. It’s also not clear whether targeting cortical hyperexcitability at a late stage of the disease would be beneficial, or if interventions need to occur much earlier,” she added. She emphasized the importance of considering ALS heterogeneity when developing therapeutics and designing clinical trials, suggesting that treatment strategies might need to be tailored not only to specific ALS subtypes but also to different stages of the disease. The group rigorously considered these potential pitfalls as they conducted their first two years of work. “And so the question for us was, since synapse removal happens apparently very early on in disease, would this masking approach, by the time we actually start intervention, could it still be fruitful? And sure enough, the data we have so far actually argues in that direction. So we could stabilize or prevent the ongoing synaptic loss. And we could also see that there was a slow but progressive increase in synapse density. So we believe that indeed, once we shield synapses, the newly formed become more stable.” She added in her thoughts about the applicability of this approach across multiple ALS subtypes. “We are currently investigating synapse loss and the effect of MASK in two different models, FUSΔNLS and SOD1 mice, to see whether this represents a generalizable effect. Ideally, we want to have a treatment, a strategy that is applicable to all forms of ALS.”
Reflecting on their overall research goals, Sabine said, “If the idea is that increased brain activity results from severed inhibitory connections, then pinpointing and trying to prevent the loss of these synapses might help correct cortical hyperexcitability.” Although the group may not ultimately be able to understand why inhibitory synapses are vulnerable in ALS during the course of their Target ALS funded project, their ability to rigorously measure target engagement and functional outputs in mouse models will allow them to determine if preventing loss of these synapses is a viable therapeutic strategy. The work by this consortium is testament to the power of breaking down barriers and removing silos to encourage breakthroughs in ALS research, bringing together the incredible genetic toolkit of Drosophila melanogaster with rapid technological advancement in mammalian ALS models. Their research aligns with Target ALS’s goals as we work together to transform ALS into a manageable disease and a world where Everyone Lives.
The Power of Collaboration
Brian, Bernard, and Sabine emphasized in our discussion the importance of Target ALS’ commitment to funding collaborative work. The group came together specifically to apply for the 2022 Basic Biology RFA offered at Target ALS. Sabine reflected, “I fondly remember long discussions we had in particular on Bernard’s machine learning, how to interpret this and that, how to make sense of these parameters, because that’s a completely new field that Bernard is entering now that could, I think, be used for patients at some point.” For all of Target ALS’ consortia grant opportunities, we encourage funded groups to troubleshoot, brainstorm, and think as a team. Discussing the technological development that Sabine and her lab have achieved in the last two years, she added, “The classical assessments we undertake to look at synapses can only tell us so much. The question is, which synapses do we protect with our masking peptide? Are there more synapses being formed and would these new synapses then also live longer? These are questions we can only answer using the in vivo imaging technology. And for all of this, Target ALS has been very helpful and instrumental.”
Brian added insights about how Target ALS’ collaborative vision allowed Sabine and Bernard to “take a risk” on his Drosophila work. “This is a new technology, genome engineering humanized fruit flies,” he said. “People will be skeptical. We said that we think there’s selective synapse loss, we have phenotypes in flies. But the Target ALS funding has enabled us to pursue this with Bernard and Sabine across model systems and in human tissues. And it has pushed technology development.” He went on to explain how the collaboration has allowed the team to work much faster than each lab in isolation. “It has allowed us to move faster than we really predicted and to get to interesting discoveries with unexpected results popping up, which I hope in the end will pay off for something that’s going to make an impact on the disease for patients.”
Bernard called out the networking opportunities afforded to groups who receive Target ALS funding. “I felt that there was a sense of a community, which is very important,” he said of his initial impressions upon receiving the Target ALS grant. He added that Target ALS funding is unique in that it has enabled the group to pursue high risk high reward research, like advanced technological development to test an underexplored disease hypothesis. “I think we don’t have so many sources of funding in the world that allow us to take such risks. And this is something which I really highly appreciate with Target ALS.”
One of Target ALS’ core values is “radical collaboration.” This funded group embodies this value, seeing the opportunity to bring together seemingly disparate research foci in the service of answering an important biological question. We look forward to seeing their progress together in the year to come.
The Minds Behind the Mission
Brian McCabe’s journey into ALS research is rooted in his background as a basic neuroscientist with a focus on the motor system, particularly neuromuscular junction synapses and the factors that influence their development and maintenance. “When I started my own lab, we became interested in another disease called spinal muscular atrophy (SMA), and we built models to study it,” he explained. Initially, his motivation was to gain deeper insights into how neural circuits and synapses function through the lens of disease models. However, as his work with SMA evolved and eventually expanded to ALS, his perspective shifted. “I also think there is a possibility to apply the most cutting-edge research tools that we use for basic neuroscience to disease investigation,” he noted.
What drives Brian today is the intersection of fundamental neuroscience with translational research, particularly the potential to make a tangible impact on patients’ lives. “This disease in particular is cruel and fast. If there’s a possibility that our research tools can in some way help patients, of course, this is a strong motivator,” he said. He finds inspiration in the collaborative nature of ALS research, where basic science meets clinical application. Reflecting on colleagues like Sabine, who bridges clinical practice and laboratory research, Brian highlighted the power of this interdisciplinary approach. “This mix of basic research, cutting-edge neuroscience, and the translational angle of discoveries—that’s the most interesting aspect for me. The ability to apply new or different ideas to translation is super exciting, and I hope it will benefit both the patients and the funders who support this research.”
It’s his deep belief in the transformative power of science that keeps Brian motivated when it comes to ALS research. Having witnessed firsthand the dramatic progress in spinal muscular atrophy (SMA)—which shifted from being the leading genetic killer of children to a condition with effective treatments—he remains optimistic about the potential for similar breakthroughs in ALS. “I’m long on basic research,” he explained. “I think this is one of the great endeavors of humanity, to push back the veil of ignorance in biology and disease. I know we’re at a time where people are skeptical about science, but science has helped us overcome some of the horrors of diseases like smallpox and polio. And I firmly believe it will help us overcome ALS.” His unwavering motivation stems from the conviction that persistent, dedicated research is the only path to achieving those transformative breakthroughs. “The only way we will do that is if we keep working on it,” he added.
Bernard Schneider’s passion for ALS research links back to his broader commitment to tackling diseases that profoundly affect humanity. “What drove my interest in ALS is the interest to work on disease and to possibly find solutions for problems that affect humankind,” he reflected. This motivation has been a consistent thread throughout his scientific career. While ALS is undeniably devastating, Bernard finds the underlying mechanisms and scientific questions it raises both complex and fascinating. “As nasty as the disease is, the mechanisms are fascinating. The questions we come up with are really fascinating.”
From a translational perspective, Bernard sees ALS as a uniquely compelling challenge. “I believe it is going to be one of, if not the first neurodegenerative diseases for which we may have a real impact on disease progression,” he explained. Because of the aggressive nature of ALS, there is additional incentive to accelerate solutions and discover therapies. Beyond scientific curiosity, Bernard is driven by the urgent, unmet clinical need. “The fact that the disease is so devastating is also a major motivation for everything I’ve been doing in this field.” His journey with ALS research began in the 1990s during his PhD, where he first encountered the field in a lab already dedicated to ALS studies. “I always remain fascinated by this field, and I’m very happy if I can even give a very tiny contribution at some point,” he said.
What keeps Bernard motivated in his ALS research is the remarkable pace of technological advancement, despite the often slow and frustrating process of translating scientific discoveries into clinical therapies. “It is slow in terms of reaching therapeutic effects and really demonstrating that we can have a real impact on the disease. The clinical translation also takes so much time. This is, I agree, a bit frustrating,” he admitted. However, his optimism is fueled by the transformative progress in scientific tools and techniques. “What is really fast, though, is the development of new technologies. Everything we can do nowadays compared to 10 or 20 years ago is absolutely remarkable,” Bernard explained. The ability to manipulate DNA and RNA, along with advancements at multiple levels of biomedical research, convinces him that it’s only a matter of time before these breakthroughs lead to meaningful treatments. “That keeps me very motivated because I think it’s evidence that one day it will have an impact. I think it’s just a question of time.”
As an educator, Bernard has also witnessed the evolution of the neurodegeneration field firsthand. Reflecting on the past 15 years of teaching, he recalled, “When I started, I had nothing else to say except that we had no treatments for any of these diseases. But year after year, there’s more positive progress to share.” While the advancements may not always be dramatic, they signal steady momentum. Bernard remains hopeful that ALS will soon benefit from the same wave of therapeutic progress, emphasizing that even without blockbuster treatments like in cancer, the growing body of research and investment is paving the way for breakthroughs. “I see that there is something happening,” he said. “And for this, I’m very hopeful that something will also happen for ALS.”
Sabine Liebscher’s inspiration to pursue ALS research is grounded in her background as a medical doctor and her encounters with patients. “Simply put, it’s the patients I met and meet that keep me going,” she shared. From her early days in medical school, she knew she wanted to contribute to understanding disease mechanisms and identifying effective treatment strategies—a motivation that remains as strong today as when she first began her journey in medicine. Her passion for bridging the gap between clinical observations and basic scientific discoveries has shaped her career, driving her to unravel the complexities of ALS. Her work is centered on the investigation of neural circuits and how alterations within these delicate networks cause disease symptoms and fuel the degenerative process. “ALS is a complex disease involving many different types of neurons but also glia in the brain and spinal cord. With our research we try to understand how molecular alterations or typical pathological hallmarks of ALS affect the function of individual neurons and entire neural networks to than cause the degeneration of motor neurons. To do so, we watch the brain in action in our model mice and later strive to validate our findings in humans.”
Reflecting on moments where she felt her work made a difference, Sabine highlighted a collaborative effort that brought together clinicians and neurophysiologists to translate findings from mouse models to ALS patients. “I am very happy and proud of this effort,” she said, referencing the study published in Science Translational Medicine in 2024. This project, led by her together with colleagues Caroline Rouaux and Véronique Marchand-Pauvert, provided novel insights into cortical hyperexcitability in ALS, paving the way for improved diagnostics and emphasizing the role of neural circuit mechanisms in the disease. While progress in ALS research can feel incremental—“like baby steps,” as she described—Sabine remains energized by each new piece of data, eager to integrate it into the larger puzzle of ALS pathology.
What keeps her hopeful is the rapid evolution of the field, fueled by significant funding and technological advancements. “Thanks to major funding in recent years, the field has exploded. It’s hard to even keep track of all the new developments,” she noted. Innovations in sequencing, molecular tools, imaging technologies, iPSCs, novel mouse models, big data, and AI have dramatically accelerated ALS research. Sabine is particularly optimistic about emerging clinical trials and the potential of antisense oligonucleotide (ASO) therapies, such as Tofersen for SOD1-related ALS, which she describes as “game-changers.” She also believes that the key to future breakthroughs may lie in combination therapies, akin to strategies used in cancer treatment, where multi-target approaches could offer more effective outcomes.
For Sabine, collaboration is at the heart of scientific progress. “Forget about the borders and hurdles of traditional academic research and the prestige of individual labs. Let’s join forces, approach problems from many different angles, and merge expertise,” she urged. Organizations like Target ALS play a crucial role by not only providing funding but also fostering collaboration through meetings, data sharing, and biobanking initiatives. Sabine is equally excited about the transformative role of AI in research, noting its potential to accelerate discoveries and uncover new ideas, even if it won’t fully replace traditional lab models. To aspiring ALS researchers, she offered an encouraging message: “It’s an exciting time. The field has grown and attracts researchers from many disciplines. Insights from other neurodegenerative diseases are incredibly valuable, and there’s ample reason to be optimistic and hopeful.”
A Hopeful Horizon
This trio exemplifies the fusion of basic science and translational research, driven by curiosity, resilience, and a shared commitment to making a difference. Their work not only brings us closer to effective ALS therapies but also highlights the importance of supporting foundational biological research. As McCabe aptly put it, “Not all research is translational yet, but without basic science, there’s nothing to translate.”
Their journey is a testament to the power of perseverance, collaboration, and the relentless pursuit of knowledge—paving the way for hope in the fight against ALS.
