A newly developed method can help characterize the types of misfolded proteins present in patients with amyotrophic lateral sclerosis (ALS), according to findings in a thesis.
The recently published doctoral thesis, titled “Structural investigation of SOD1 aggregates in ALS: identification of prion strains using anti-peptide antibodies,” was written by doctoral student Johan Bergh, MD, at Umeå University in Sweden.
Most ALS patients have the sporadic form of the disease, while 10 percent have a genetic familial predisposition for the disease.
The first identified cause of ALS was mapped to mutations in the gene that provides instructions for the production of superoxide dismutase-1 (SOD1). The mutation causes the SOD1 protein to be misfolded and form aggregates.
Studies have found that SOD1 aggregates are present in the motor neurons of ALS patients, as well as mouse models that express human SOD1 (hSOD1).
Furthermore, studies have shown that SOD1 aggregates are also present in sporadic ALS patients, indicating that SOD1 likely plays a broader role in the disease.
Aiming to investigate how SOD1 contributes to ALS, researchers at Umeå University developed a panel of antibodies that cover and recognize 90 percent of the SOD1 protein. These antibodies were shown to be highly specific for misfolded SOD1.
Using these antibodies, researchers were able to purify hSOD1 from the central nervous system of terminally ill mice expressing hSOD1.
Through this method, they identified two different strains of aggregate hSOD1 that have distinct structural, molecular, and growth properties.
The two strains — denoted A and B — were also associated with differing disease progression.
“We’ve been able to identify two different types of protein aggregates with different structures and propagation abilities. One type gave rise to a more aggressive disease progression, which shows that these aggregates are the driving force in the development of ALS,” Bergh said in a press release.
To further investigate this, researchers added purified strain A and B hSOD1 into mice carrying a hSOD1 mutation.
Interestingly, mice inoculated with A or B aggregates developed premature signs of ALS and became terminally ill 200 days before the mice inoculated with the control preparation, which did not contain the aggregates.
Researchers found that each strain perpetuated the buildup of its own hSOD1 aggregate structure, which refers to when the misfolded protein causes the healthy protein to become deformed like itself. As a result, both A and B aggregates caused other hSOD1 proteins to become misfolded.
“Using the new method, we have shown and confirmed through animal models that the development of ALS follows the same principle as for other severe nervous disorders. Protein aggregates function as a template that healthy proteins stick to and cause the disease to spread,” Bergh said.
Mice that received the A and B strains had differing rates of disease progression, distribution of aggregates, and end-stage aggregate levels.
Bergh concludes that this novel method is a straightforward way to characterize aggregate strains in ALS, as well as in other neurodegenerative diseases.
“Through our new method, I hope that in the future, drugs will be developed specifically aimed at attacking these protein aggregates. Hopefully, research teams focusing on similar diseases will adopt the method. However, we are in an early phase, and developing drugs is a long-term process,” he said.