Rapid Publication Expression of a Mutant Human Fibrillin Allele upon a Normal Human or Murine Genetic Background Recapitulates a Marfan Cellular Phenotype

The Marfan syndrome (MFS) is a connective tissue disorder inherited as an autosomal dominant trait and caused by mutations in the gene encoding fibrillin, a 350-kD glycopro-tein that multimerizes to form extracellular 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 func-tion of the wild-type protein encoded by the normal allele; or from a dynamic and variable interplay between these two pathogenetic mechanisms. We have now addressed this issue in a cell culture system. A mutant fibrillin allele from a patient with severe MFS was expressed in normal human and murine fibroblasts by stable transfection. Immunohisto-chemical analysis of the resultant cell lines revealed mark-edly diminished fibrillin deposition and disorganized micro-fibrillar architecture. Pulse-chase studies demonstrated nor-mal levels of fibrillin synthesis but substantially reduced deposition into the extracellular matrix. These data illus-trate that expression of a mutant fibrillin allele, on a back-ground of two normal alleles, is sufficient to disrupt normal microfibrillar assembly and reproduce the MFS cellular phenotype. This underscores the importance of the fibrillin amino-terminus in normal microfibrillar assembly and sug-gests that expression of the human extreme 5 ' fibrillin cod-ing sequence may be sufficient, in isolation, to produce an animal model of MFS. Lastly, this substantiation of a domi-nant-negative effect offers mutant allele knockout as a po-tential strategy for gene therapy. (J. Clin. Invest. 1995. 95:874-880.) Key words: Marfan syndrome * dominant-negative mutation * microfibril * extracellular matri