It has long been understood that a protein called TDP-43 clumps together in brain cells of people with amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig’s Disease, and is associated with neuron death. This same protein is thought to cause muscle degeneration in patients with sporadic inclusion body myositis (sIBM), leading many researchers to think that TDP-43 is one of the causative factors in ALS and sIBM. Now researchers have found that a specific chemical modification called acetylation promotes TDP-43 clumping in animals. Using a natural anti-clumping method in mouse models, the scientists reversed protein clumping in muscle cells and prevented the sIBM-related muscle weakness.
The discovery, published in Nature Communications, has important implications for understanding ALS and sIBM, and for the creation of potential treatments down the road.
TDP-43 normally works in the cell nucleus and appears to have many important functions in regulating how genes are expressed. In people with sIBM, ALS, and a few other degenerative diseases, TDP-43 moves out of the nucleus and into the main volume of the cell, or cytoplasm, and then clumps together. The loss of TDP-43 from the nucleus leads to the failure of normal gene expression regulation. Many scientists suspect that this is the major reason why affected cells die. In ALS, motor neuron death leads to the brain’s inability to control voluntary muscles throughout the body. In sIBM, muscle degeneration leads to muscle weakness and impaired strength.
For the study, researchers examined the effect of acetylated TDP-43 in living animals. In this case, they sought to mimic sIBM in mice, in which TDP-43 clumps in muscle cells.
The team used a special method to inject acetylated TDP-43 proteins directly into mouse muscle cells. In contrast to ordinary TDP-43 proteins, these acetylated proteins quickly aggregated outside the nucleus. The aggregate-burdened cells showed multiple features that are also seen in human sIBM.
The researchers observed cellular markers indicating that the muscle cells were actively trying to get rid of the TDP-43 aggregates. The team found that they could boost these cell defense mechanisms and swiftly remove most of the aggregates by adding heat shock factor 1 (HSF1), a naturally occurring protein that is known to work as a master switch for anti-aggregation processes in cells.
The team now hopes to identify compounds suitable for use in oral drugs that have the same anti-clumping effect.
Reprinted from materials provided by the University of North Carolina Health Care.