A protein called S100A6 may help toxic clumps of SOD1 build up in the form of ALS tied to SOD1 mutations by getting in the way of the cell's protein-clearing machinery, according to a study conducted in mouse and cell models. ALS News Today reported the findings, which were published in Metabolic Brain Disease. The work points to S100A6 as both a possible biomarker and a candidate target for therapies designed to help cells clear abnormal proteins.
Why it matters
ALS is a progressive neurological condition in which the motor neurons that control movement are damaged and eventually die, leading to worsening muscle weakness and other symptoms. Mutations in SOD1 account for roughly 10% to 20% of familial ALS cases and 1% to 2% of sporadic cases, per ALS News Today. These mutations can cause the SOD1 protein to fold incorrectly and gather into toxic clumps inside cells.
Cells normally deal with unwanted or damaged proteins through autophagy, a recycling process, and a specialized form of it called aggrephagy removes protein clumps specifically. When aggrephagy falters, clumps can accumulate and harm motor neurons. How exactly this breakdown happens in ALS has remained unclear, which is the gap the new study set out to address. If a single protein like S100A6 proves to be a driver of that failure, it could offer a measurable marker of disease and a target for treatment.
How the researchers narrowed the search
The team, based in China, worked from publicly available data on gene activity in the spinal cords of SOD1-G93A mice, a widely used model of SOD1-linked ALS. The primary dataset covered eight SOD1-G93A mice and eight controls, and a second dataset of six SOD1-G93A mice and three controls was used to check the results.
Comparing the two groups, the researchers found 524 genes whose activity levels differed significantly. Of those, 49 were flagged as possible participants in aggrephagy. Applying several machine-learning approaches, they cut the list to three genes: Ctsb, Kif11 and S100a6. Two of them, Ctsb and S100a6, showed consistently elevated activity in both datasets and were carried forward for closer study.
Ctsb carries the instructions for cathepsin B, an enzyme that helps break down material inside lysosomes, the cell's recycling centers. S100a6 encodes S100A6, a calcium-binding protein involved in a range of cellular functions. Lab work confirmed that both genes were more active and both proteins more abundant in the spinal cords of SOD1-G93A mice and in lab-grown mouse cells engineered to resemble motor neurons producing mutant SOD1.
Testing S100A6's role in clump formation
The team concentrated on S100A6, which earlier research had already connected to autophagy and SOD1 clumping. In the motor neuron-like cells, raising S100A6 levels disrupted autophagy, increased the formation of SOD1 clumps and lowered cell viability. Lowering S100A6 produced the reverse: autophagy recovered and clumps decreased.
The researchers then asked whether restarting autophagy could offset the effects of too much S100A6. They treated cells with rapamycin, a compound that switches autophagy on, and found the treatment substantially reversed the signs of impaired autophagy and cut SOD1 clumping. Taken together, ALS News Today reports, the experiments suggest S100A6 may allow abnormal SOD1 clumps to accumulate by interfering with autophagy.
The team also examined whether Ctsb and S100a6 might work as biomarkers. A computer model built on their expression patterns showed some ability to tell SOD1-G93A samples apart from controls in the training dataset. The researchers cautioned, however, that the datasets were small and that neither gene has been assessed as a biomarker in body fluids or clinical samples from people with ALS.
They further noted that the SOD1-G93A model represents only one genetic form of the disease and may not capture the full range of ALS in patients, so larger studies, including work with human samples, are needed to confirm the results. In their paper, the researchers described Ctsb and S100a6 as potential aggrephagy-related biomarkers in the SOD1-G93A model and said they had experimentally validated S100a6 as a key negative regulator of autophagy that drives SOD1 aggregation. They concluded that the findings underscore the importance of aggrephagy in ALS, laying groundwork for early diagnostic tools built on this mechanism and for future research into targeted treatments.
What to watch: whether follow-up studies in human samples confirm S100A6's role and establish it as a usable biomarker or drug target.
