Transthyretin oligomers induce calcium influx via voltage-gated calcium channels

The deposition of transthyretin (TTR) amyloid in the PNS is a major pathological feature of familial amyloidotic polyneuropathy. The aim of the present study was to examine whether TTR could disrupt cytoplasmic Ca2+ homeostasis and to determine the role of TTR aggregation in this process. The aggregation of amyloidogenic TTR was examined by solution turbidity, dynamic light scattering and atomic force microscopy. A nucleation-dependent polymerization process was observed in which TTR formed low molecular weight aggregates (oligomers < 100 nm in diameter) before the appearance of mature fibrils. TTR rapidly induced an increase in the concentration of intracellular Ca2+ ([Ca2+](i)) when applied to SH-SY5Y human neuroblastoma cells. The greatest effect on [Ca2+](i) was induced by a preparation that contained the highest concentration of TTR oligomers. The TTR-induced increase in [Ca2+](i) was due to an influx of extracellular Ca2+, mainly via L- and N-type voltage-gated calcium channels (VGCCs). These results suggest that increasing [Ca2+](i) via VGCCs may be an important early event which contributes to TTR-induced cytotoxicity, and that TTR oligomers, rather than mature fibrils, may be the major cytotoxic form of TTR.