When TDP-43 fails to form groups in the neuron cell’s nucleus (dark blue, center), it is re-exported to the cytoplasm (bright purple). There, it interacts with the sensor molecule TBK1. The combined TDP-43 and TBK1 molecules create the bright whitish spot in the image above.
Image Credit: © Shohei Sakai et al., EMBO reports, 2026.
(CC BY 4.0)
Scientific Frontline: Extended "At a Glance" Summary: The TBK1-Interferon Beta-Immunoproteasome Pathway in ALS
The Core Concept: Researchers have identified a specific defense mechanism in motor neurons where the sensor molecule TBK1 triggers the production of interferon beta to activate an "immunoproteasome," a protein-digesting machine that breaks down dysfunctional, cytoplasm-bound TDP-43 proteins before they can form toxic aggregates associated with Amyotrophic Lateral Sclerosis (ALS).
Key Distinction/Mechanism: It was previously thought that faulty TDP-43 proteins were primarily cleared by autophagy (collection and digestion in vesicles). This new research demonstrates a parallel, perhaps dominant, pathway where non-paired TDP-43 in the cytoplasm interacts with TBK1, initiating an interferon beta signal that causes both the affected neuron and neighboring cells to ramp up immunoproteasome production for targeted protein degradation.
Major Frameworks/Components:
- TDP-43 Proteinopathy: The pathological hallmark of most ALS cases, where the TDP-43 protein mislocalizes from the nucleus to the cytoplasm and forms toxic aggregates.
- TBK1 Sensor Molecule: A known regulator of autophagy, now identified as the trigger for the interferon beta signaling cascade upon interacting with monomeric (non-paired) TDP-43.
- Interferon Beta Signaling: The molecular signal activated by TBK1 that instructs the cell (and neighboring cells) to produce immunoproteasomes.
- The Immunoproteasome: A specialized protein-degrading complex typically associated with immune cells responding to viral infections, now proven to be active in motor neurons to clear abnormal proteins.
Branch of Science: Neurobiology, Cellular Biology, Molecular Genetics.
Future Application: The discovery of this pathway opens new therapeutic avenues for ALS. While interferon beta itself may cause severe side effects, researchers are now looking to identify other compounds capable of safely activating the immunoproteasome directly within motor neurons to prevent TDP-43 aggregation.
Why It Matters: This research fundamentally alters the understanding of how motor neurons defend against the protein aggregations that cause ALS. By revealing that motor neurons utilize the immunoproteasome—a mechanism classically thought to be restricted to the immune system—scientists have a new, specific biological target for developing treatments to slow or halt the progression of this fatal neurodegenerative disorder.
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| TDP-43 in the cytoplasm (red) interacts with the sensor molecule TBK1 (blue), which activates the production of the signal molecule interferon beta (blue dots). This activates the production of the immunoproteasome (stripy barrel) in the affected and neighboring cells, which digests TDP-43 (red wiggly lines) into fragments (red dots), thus preventing the formation of aggregates (red bundle). Image Credit: © Shohei Sakai et al., EMBO reports, 2026 (CC BY 4.0) |
ALS is a disease in which, in most cases, a protein forms aggregates in neurons, leading to a rapid loss of motor control and death. A Nagoya University research team has discovered an unexpected defense mechanism in human neuron cell cultures and mice that neurons switch on to avoid these aggregations, offering a new potential path toward developing a treatment.
Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder that affects roughly 10,000 people in Japan. It is characterized by a rapid loss of control over the limbs and other body parts, and without a ventilator, patients have a life expectancy of two to five years after onset. In most cases, a specific protein is the root cause of the problem: TDP-43 is usually located in the neuron’s nucleus and has various roles in maintaining the cell’s health and function. However, in people with ALS, it aggregates in the cell’s cytoplasm.
Koji Yamanaka and his group at Nagoya University have been studying the role of TDP-43 for almost two decades. Yamanaka said, “Many people think that the problem starts when TDP-43 stops being transferred into the nucleus and accumulates in the cell’s cytoplasm. However, we could recently show that the protein, which usually operates in pairs or small groups, fails to form these groups under sudden stress, and so we think that the protein gets re-exported to the cytoplasm as some form of dysfunctional waste.” In the cytoplasm, healthy cells usually remove such waste proteins, but the mechanism has not been well understood.
Shohei Sakai joined Nagoya University as a graduate student several years ago specifically to work with Yamanaka, driven to contribute to finding a cure after a case in his family. Now a project assistant professor, he explained, “It is usually thought that these faulty proteins are removed by a process called ‘autophagy,’ where they are collected in small vesicles and digested. But in my experiments, inhibiting this process did not inhibit the removal of TDP-43.”
The ensuing research has been published in the journal EMBO Reports. In experiments on cultured neurons, including human stem cell-derived motor neurons, with supporting evidence from mice and patient tissue, the Nagoya group and their international collaborators found that motor neurons activate a protein-digesting machine called the “immunoproteasome” and traced the chain of events. Molecules of TDP-43 that have failed to pair up and have been exported into the cell’s cytoplasm physically interact with the sensor molecule “TBK1,” which is known to activate autophagy and is also associated with inherited ALS through gene mutations. In their experiments, however, Yamanaka, Sakai, and their team found that TBK1 also activates a signal mediated by “interferon beta” that can be perceived even by neighboring cells. Where this signal is received, neurons ramp up the production of the immunoproteasome, which then breaks down TDP-43 before it aggregates.
Importantly, the team also found that in motor neurons from spinal cord samples donated by human ALS patients postmortem, the receptor for the signal was present in significantly lower quantities than in samples from people without ALS.
When asked why his team was able to discover this pathway, first author Sakai said, “TBK1 is known to activate autophagy, and therefore, many researchers focused on this process as the possible means of TDP-43 clearance. We don’t claim that this is not the case, but we think this may have masked the parallel activation of the immunoproteasome.”
“Moreover, it is impressive that the immunoproteasome exists in motor neurons,” added Yamanaka. Usually, this protein-digesting machine is produced in immune cells in response to viral infections, where it is used to disassemble virus components and display them on the cell’s surface. Yamanaka noted, “This is a classical understanding of the immunoproteasome, but we found that motor neurons also have this system and ramp it up when they need to deal with abnormal proteins.”
The newly discovered pathway also offers a new route for developing a treatment approach. Yamanaka said, “In this pathway, the body uses interferon beta to activate the immunoproteasome, and the signal molecule has, in fact, been used in treatments for other conditions. But because it triggers many different reactions, its severe side effects cannot be ignored.” Interferon beta, therefore, does not seem to be a practical treatment option for ALS. He continued, “In our next project, we aim to identify other compounds that can activate the immunoproteasome in motor neurons.” Sakai added, “We need to know the true therapeutic potential of this pathway. But I wish that this result encourages more people to study ALS and treatment options.”
Funding: Funding Japan Society for the Promotion of Science (JP22J23468, JP25K23745, JP18H02740, JP19KK0214, JP22H00467, Overseas Challenge Program for Young Researchers), Japan Agency for Medical Research and Development (JP22ek0109426, JP24wm0425014, JP26wm0625301), Yukihiko Miyata Memorial Trust for ALS Research, Ikeda Rika Grant, WISE program (Nagoya University CIBoG), Wellcome Trust (221824/Z/20/Z), Motor Neuron Disease Association (Sreedharan/Apr24/2362-791)
Published in journal: EMBO reports
Authors: Shohei Sakai, Kotaro Oiwa, Yohei Iguchi, Izzet Mehmet Akcay, Seiji Watanabe, Okiru Komine, Noriko Nagata, Mai Horiuchi, Jemeen Sreedharan, Masahisa Katsuno, and Koji Yamanaka
Source/Credit: Nagoya University
Edited by: Scientific Frontline
Reference Number: nbio102026_01
