The impact of V30A mutation on transthyretin protein structural stability and cytotoxicity against neuroblastoma cells

Single point mutations in the transthyretin (TTR) gene may cause a hereditary neurodegenerative disease termed familial amyloidotic polyneuropathy (FAP) due to accelerated deposition of amyloid fibrils, resulting in peripheral and autonomic nervous system dysfunction. Recently, we found a Chinese FAP family involving a TTR V30A mutation. To understand the pathogenic mechanisms of this V30A TTR, we investigated the effects of this mutation on TTR quaternary and tertiary structural stabilities and cytotoxicities against neuroblastoma cells along with the most common variant V30M TTR and the wild-type (WT) TTR. Our results showed that the V30A mutation impaired the thermodynamic and kinetic stabilities of the TTR protein by increasing the extent and rate of tetramer dissociation and unfolded monomer and amyloid fibril formation, even to a greater extent than the V30M mutation under several experimental conditions. Further, an obviously cytotoxic effect of the V30A TTR on the human neuroblastoma cell line, IMR-32, was observed. The V30A TTR induced apoptosis and autophagy concomitant with the accumulation of reactive oxygen species (ROS) and DNA double-strand breaks, reflected in the induction of phosphor-H2A.X. These results suggest that the V30A mutation in the TTR gene promotes the formation of unfolded monomers and amyloid fibrils, which potentially contribute to the increased neurotoxicity and the pathology associated with this FAP family.