Comparison of amyloid deposition in two lines of transgenic mouse that model familial amyloidotic polyneuropathy, type I

We previously produced a transgenic mouse line designated MT-hMet30 by introducing the human mutant transthyretin (TTR) gene carrying the mouse metallothionein promoter, and showed that the presence of human variant TTR is sufficient for amyloid deposition in various tissues of these transgenic mice. However, the expression pattern of human mutant transthyretin gene in the mouse was different from that in man. To analyse pathologic processes, it is essential to establish a transgenic mouse line in which the development and tissue-specific expression of the human mutant TTR gene is the same as in man. Thus, we produced two additional transgenic mouse lines carrying the human mutant TTR gene containing either 0.6 kb (0.6-hMet30) or 6.0 kb (6.0- hMet30) of the upstream region. The expression levels of 6.0-hMet 30 gene in the liver and serum were the same as in man and about 10 times higher than those of 0.6-hMet30 gene in the liver and serum were the same as similar tissues to human patients except for the peripheral and autonomic nervous tissues. The amyloid deposition started earlier and was more extensive in 6.0-hMet30 than 0.6-hMet30 mice, suggesting that the serum levels of human mutant TTR are correlated with the occurrence and degree of amyloid deposition, to some extent. Neither amyloid deposition nor degenerative changes were observed in the peripheral and autonomic nervous systems despite the transgene expression in the choroid plexus of the 6.0-hMet30 mice. In the 6.0-hMet30 mice, amyloid deposition started at 9 months of age, although the serum level of human mutant TTR reached the adult level at 1 month. These results suggest that intrinsic environmental factors other than the mutant gene are involved in the late-onset deposition of amyloid fibrils. Transgenic mice described here should be useful for analysing such factors.