Protein aggregation by aldehydes derived from cholesterol oxidation

Redoxoma Highlights by Sayuri Miyamoto

Cholesterol is present at a high concentration in the central nervous system. Our brain produces most of its own cholesterol since blood lipoproteins cannot cross the blood-brain barrier. Being one of the major lipids present in myelin, cholesterol is critical for adequate transmission of neural electrical signals and proper neuronal function. A number of studies have shown alterations in cholesterol levels in neurodegenerative diseases. Yet mechanistic aspects connecting cholesterol with neurodegenerative diseases are yet incompletely elucidated.studies have shown alterations in cholesterol levels in neurodegenerative diseases

A hallmark of neurodegenerative diseases is the accumulation of toxic protein clumps or aggregates and increased features of oxidative stress. Amyotrophic lateral sclerosis (ALS) is a complex neurodegenerative disease in which neurons from both spinal cord and brain are affected. To date pathological mechanisms leading to progressive motor neuron degeneration still remains to be clarified.

In order to get some new insights into ALS disease mechanism, we investigated whether cholesterol oxidation could have any connection with this devastating disease. Cholesterol can be oxidized by enzymatic and non-enzymatic mechanisms to generate oxidized derivatives collectively known as oxysterols. An interesting feature of cholesterol oxidation by free radicals and particularly by singlet oxygen is the production of reactive products bearing an aldehyde group (secosterol A and B), which are highly prone to bind to proteins.

Using ALS rat model having SOD1 mutation, we first investigated the presence of cholesterol aldehydes in brain, spinal cord and blood plasma of these animals. Interestingly, cholesterol aldehydes were ubiquitously present in all analyzed tissues. Of note, increased aldehyde levels were detected in the blood plasma of symptomatic animals compared to non-symptomatic ones, suggesting that cholesterol oxidation might be exacerbated during disease progression.

cholesterol aldehydes could irreversibly modify SOD1 proteins, enhancing their propensity to aggregateThese results stimulated us to conduct a series of in vitro studies to deeply characterize cholesterol aldehyde's effect on protein aggregation. Using SOD1 as a model, it was possible to demonstrate that aldehydes accelerate SOD1 aggregation producing large amorphous aggregates. Furthermore, extensive mass spectrometry analysis of the modified protein revealed that aldehydes bind to specific lysine residues located mostly at the electrostatic loop as well as some residues at the protein dimer interface. Collectively, these results reinforced our hypothesis that cholesterol aldehydes could irreversibly modify SOD1 proteins, enhancing their propensity to aggregate during the course of the disease. Now we are further exploring the potential role of cholesterol aldehyde-induced protein aggregation in vivo.

Related article:

• L. S. Dantas, A. B. Chaves-Filho, F. R. Coelho, T. C. Genaro-Mattos, K. A. Tallman, N. A. Porter, O. Augusto, S. Miyamoto. Cholesterol secosterol aldehyde adduction and aggregation of Cu,Zn-superoxide dismutase: Potential implications in ALS Redox Biology, 19: 105–15, 2018 | doi: 10.1016/j.redox.2018.08.007

Sayuri Miyamoto, Ph.D. Assistant Professor at Department of Biochemistry,
Institute of Chemistry, University of São Paulo, Brazil