In vivo stabilization of mutant human transthyretin in transgenic mice

Transthyretin (TTR) is a 55 kD homotetrameric serum protein transporter of retinol binding protein charged with retinol and thyroxine (T4). The highly amyloidogenic human TTR variant in which leucine at position 55 is replaced by proline (L55P TTR) is responsible for aggressive fatal amyloiclosis with peripheral and autonomic neuropathy, cardiornyopathy and nephropathy. Mice bearing one or two copies of a 19.2 kB human genomic fragment containing the entire coding sequence and the known control regions of the L55P TTR transgene, failed to develop TTR amyloiclosis even though their sera contained mutant human TTR. The frequency of TTR tissue deposition was increased when the L55P'rTR transgene was bred onto a murine TTR-null background. Denaturation of sera from the transgenic animals and murine TTR-knockouts expressing the human L55P TTR transgene revealed that the T7R tetramer was much more stable in the presence of the murine protein because the =R circulates as hybrid hurnan/murine heterotetramers. Intraperitoneal administration of diflunisal, a non-steroidal anti-inflammatory drug that binds to TTR in its T4-binding site and inhibits fibril formation in vitro, to human L55P TTR transgenic animals in which die murine TTR gene had been silenced, also stabilizes the circulating mutant protein to in vitro urea denaturation.