UNRAVELING A POSSIBLE CELLULAR MECHANISM BEHIND LEPTOMENINGEAL AMYLOIDOSIS USING AS MODEL A HIGHLY UNSTABLE TRANSTHYRETIN TETRAMER

Abstract

Transthyretin (TTR) is a 127‐residue homotetrameric β‐sheet‐rich protein that transports thyroxine in the blood and cerebrospinal fluid (CSF). In the present work we aimed to study A25T dissociation, aggregation and its role in leptomeningeal amyloidosis (LA). Using HPLC and native PAGE we monitored acrylodan‐labeled TTR aggregation in the plasma. The aggregates formed, when analyzed by AFM, Thioflavin T and Congo Red binding displayed amyloid structure. We solved the crystal structures of the wt and A25T and the comparative analysis shed light into the mechanism behind A25T highly amyloidogenicity: an expanded tetramer which is stabilized by a lower number of H‐bonds and hydrophobic interactions. Interestingly, in the presence of thyroxine and flufenamic acid (an anti‐inflammatory compound), two ligands of TTR, the structure of A25T was similar to that displayed by the wt protein. Since LA symptoms suggest a local inflammation, we questioned ourselves whether A25T aggregates can induce an inflammatory response in the CNS. Microglia primary cultures incubated for 48h with aggregates composed of A25T, underwent activation, phagocytosis (which could be blocked by cytochalasin D) and presented a significant nitric oxide and IL‐1 beta secretion. These results suggest that amyloid fibrils may have a role in LA pathogenesis, exacerbating tissue damage through inflammation.Support: CNPq and FAPERJ.