Worm Breeder's Gazette 13(5): 85 (February 1, 1995)
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
Dept. of Biology, University of Denver, Denver, CO 80208
Although the identification of germline mutations in the amyloid precursor protein (APP) gene in some familial cases of Alzheimer's Disease has provided compelling evidence for a central role of b-amyloid in this disease, in the vast majority of cases no primary sequence changes are found. Because a number of lines of evidence suggest that the conversion of b-peptide (the initial proteolytic product of the APP gene) into insoluble, fibrillar b- amyloid is critical for the pathological effects of this protein, much recent work has focused on the mechanisms in the brain that enhance or inhibit this process. In vitro studies have demonstrated that some proteins (e.g., apolipoprotein E, anti-chymotrypsin) can enhance the formation of insoluble b- amyloid, while others ( e.g., transthyretin) can inhibit its formation. As described previously, I have constructed transgenic worms that express human peptide under control of the unc-54 promoter. These animals have muscle-specific anti-b immunoreactive deposits that bind the amyloid-specific dye thioflavine S. The dye reactivity of these deposits is particularly interesting, because it implies that the expressed b- peptide is forming insoluble amyloid deposits (something that has not yet been reported for transgenic mouse models). To determine if the in vitro amyloid-inhibiting effects of transthyretin can be observed in vivo, I have generated transgenic animals co-expressing b- peptide and transthyretin in muscle cells. This was accomplished by mating an inregrated unc-54/transthyretin transgenic strain to integrated unc-54 / b-1-42 transgenic strains, and dye-staining the resultant double transgene heterozygotes. These animals have greatly reduced (<15percent) numbers of dye-reactive deposits (compared to single transgene heterozygous controls), suggesting that transthyretin is inhibiting b- amyloid formation in this in vivo model. (Unfortunately, I have been unable to maintain double homozygous lines.) A trivial explanation for this result is that coexpression of the two transgenes simply reduces the amount of b- peptide made, which in turn reduces the number of deposits. Although the pattern of anti-transthyretin and anti-b- staining in these animals is indistinguishable from that of the respective singly transgenic animals, immunohistochemistry is probably not quantititative enough to rule out this trivial explanation. Transthyretin variants that fail to inhibit b- amyloid formation have recently been reported; repeating this experiment with such variants will presumably be a good control. It will also be interesting to see if the opposite result can be obtained co- expressing the "pathological chaperones" that may enhance b- amyloid formation.