Za. Eldadah et al., EXPRESSION OF A MUTANT HUMAN FIBRILLIN ALLELE UPON A NORMAL HUMAN OR MURINE GENETIC BACKGROUND RECAPITULATES A MARFAN CELLULAR PHENOTYPE, The Journal of clinical investigation, 95(2), 1995, pp. 874-880
The Marfan syndrome (MFS) is a connective tissue disorder inherited as
an autosomal dominant trait and caused by mutations in the gene encod
ing fibrillin, a 350-kD glycoprotein that multimerizes to form extrace
llular microfibrils. It has been unclear whether disease results from
a relative deficiency of wild-type fibrillin; from a dominant-negative
effect, in which mutant fibrillin monomers disrupt the function of th
e wild-type protein encoded by the normal allele; or from a dynamic an
d variable interplay between these two pathogenetic mechanisms. We hav
e now addressed this issue in a cell culture system. A mutant fibrilli
n allele from a patient with severe MFS was expressed in normal human
and murine fibroblasts by stable transfection. Immunohistochemical ana
lysis of the resultant cell lines revealed markedly diminished fibrill
in deposition and disorganized microfibrillar architecture. Pulse-chas
e studies demonstrated normal levels of fibrillin synthesis but substa
ntially reduced deposition into the extracellular matrix. These data i
llustrate that expression of a mutant fibrillin allele, on a backgroun
d of two normal alleles, is sufficient to disrupt normal microfibrilla
r assembly and reproduce the MFS cellular phenotype. This underscores
the importance of the fibrillin amino-terminus in normal microfibrilla
r assembly and suggests that expression of the human extreme 5' fibril
lin coding sequence may be sufficient, in isolation, to produce an ani
mal model of MFS. Lastly, this substantiation of a dominant-negative e
ffect offers mutant allele knockout as a potential strategy for gene t
herapy.