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.

Modulation of Amyloid Formation in Transgenic Worms.

Chris Link

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.