Role of Saturation and Length of Fatty Acids of Phosphatidylserine in the Aggregation of Transthyretin.

The progressive accumulation of transthyretin (TTR), a small protein that transports thyroxine, in various organs and tissues is observed upon transthyretin amyloidosis, a severe pathology that affects the central, peripheral, and autonomic nervous systems. Once expressed in the liver and choroid plexus, TTR is secreted into the bloodstream and cerebrospinal fluid. In addition to thyroxine, TTR interacts with a large number of molecules, including retinol-binding protein and lipids. In this study, we examined the extent to which phosphatidylserine (PS), a phospholipid that is responsible for the recognition of apoptotic cells by macrophages, could alter the stability of TTR. Using thioflavin T assay, we investigated the rates of TTR aggregation in the presence of PS with different lengths and saturation of fatty acids (FAs). We found that all analyzed lipids decelerated the rate of TTR aggregation. We also used a set of biophysical methods to investigate the extent to which the presence of PS altered the morphology and secondary structure of TTR aggregates. Our results showed that the length and saturation of fatty acids in PS uniquely altered the morphology and secondary structure of TTR fibrils. As a result, TTR fibrils that were formed in the presence of PS with different lengths and saturation of FAs exerted significantly lower cell toxicity compared with the TTR aggregates grown in the lipid-free environment. These findings help to reveal the role of PS in transthyretin amyloidosis and determine the role of the length and saturation of FAs in PS on the morphology and secondary structure of TTR fibrils.