Animal Model Cysteine 10 Is a Key Residue in Amyloidogenesis of Human Transthyretin Val30Met

Type I familial amyloidotic polyneuropathy (FAP), a systemic amyloidosis, is characterized by aggregation of variant transthyretin (TTR Val30Met) into stable, insoluble fibrils. This aggregation is caused by genetic and environmental factors. Genetic factors have been studied extensively. However, little is known about environmental or physiological factors involved in the disease process, and their identification may be important for development of effective treatment. Xray crystallography of normal and amyloidogenic human TTR Val30Met in type I FAP showed that the SH side chain of cysteine at position 10 (Cys10) forms a hydrogen bond with Gly57 in normal TTR but not in TTR Val30Met. This result suggests a crucial role for the free Cys10 residue and possible involvement of physiological factors affecting Cys residue reactivity in TTR amyloidogenesis. To analyze amyloidogenesis in vivo , our group generated murine FAP models by transgenic technology, with human TTR Val30Met. The three lines of transgenic mice expressed amyloidogenic mutant TTR (Cys10/Met30), wild-type TTR (Cys10/Val30), and artificial Cys-free mutant TTR (Ser10/Met30). Histochemical investigation showed deposition of amyloid derived from human TTR only in amyloidogenic mutant TTR (Cys10/Met30) mice. Thus, the SH residue in Cys10 plays a crucial role in TTR Val30Met amyloidogenesis in vivo. These data suggest the possibility of innovative treatment via physiological factors modulating Cys10 residue reactivity. (Am J Pathol 2004, 164:337–345) Type I familial amyloidotic polyneuropathy (FAP) is caused by deposition of stable and insoluble protein fibrils called amyloid. The formation of amyloid fibrils is initiated by overproduction, mutation, or abnormal processing of amyloidogenic proteins. In the case of FAP, mutant transthyretin (TTR) is involved in amyloid fibril formation. Type I FAP, caused by the substitution Val to Met at position 30 of TTR (TTR Val30Met), predominates over other types of FAP in Japan, Portugal, Sweden, and the United States. This disorder has an autosomal dominant inheritance and eventually leads to death. TTR is a homotetrameric plasma protein that under normal conditions carries thyroxine (T4) and retinol with retinol-binding protein. It is mainly synthesized by the liver and choroid plexuses; trace amounts are also found in the retina of the eye, the pancreas, and other tissues. Amyloid formation is a complicated process involving not only genetic but also various physiological (and environmental) factors. The process leading from the amyloidogenic protein to the resultant amyloid fibrils is a primary focus of amyloid research; genes and genetic factors responsible for the disease have also been extensively studied. Important approaches have been used in an attempt to understand this process such as structural biology, in vitro study, and animal model. We previously used a structural biology approach in our previous investigations. Our fine three-dimensional structure analysis of human mutant TTR by X-ray crystallography showed that the Cys10 residue in TTR Val30Met is free from an internal hydrogen bond and suggested that Cys10 may play a crucial role in TTR amyloidogenesis. This result implies that physiological factors affecting reactivity of the cysteine residue may be involved