Transthyretin is not expressed by dorsal root ganglia cells

Several mutations in transthyretin (TTR) are related to familial amyloidotic polyneuropathy (FAP), a neurodegenerative disorder caused by extracellular deposition of TTR fibrils, particularly in the peripheral nervous system (PNS). TTR is mainly synthesized by the liver and choroid plexus of the brain that contribute to the plasma and cerebrospinal fluid (CSF) pools of the protein, respectively. It has recently been reported that TTR is additionally expressed in the PNS, namely by peripheral glial cells of dorsal root ganglia (DRG). This lead to the hypothesis that TTR synthesis in the DRG might contribute to the PNS involvement in FAP. In this report we clarify this issue by showing that TTR synthesis is absent in both human and mouse DRG. Moreover, by using TTR KO mouse DRG as controls, we demonstrate that TTR-like immunoreactivity in the perineurium is an artifact. As such, and similarly to what has been previously shown in the central nervous system (CNS), TTR amplification by RT-PCR in the DRG most probably results from contamination by the meninges. In conclusion, TTR deposited in the PNS of FAP patients should still be regarded as having blood and/or CSF origin.