Characterization of an in vitro model off elastic fiber assembly

Elastic fibers consist of two morphologically distinct components: elastin and 10-nm fibrillin-containing microfibrils. During development, the microf ibrils form bundles that appear to act as a scaffold for the deposition, or ientation, and assembly of tropoelastin monomers into an insoluble elastic fiber. Although microfibrils can assemble independent of elastin, tropoelas tin monomers do not assemble without the presence of microfibrils. In the p resent study, immortalized ciliary body pigmented epithelial (PE) cells wer e investigated for their potential to serve as a cell culture model for ela stic fiber assembly. Northern analysis showed that the PE cells express mic rofibril proteins but do not express tropoelastin. Immunofluorescence stain ing and electron microscopy confirmed that the microfibril proteins produce d by the PE cells assemble into intact microfibrils. When the PE cells were transfected with a mammalian expression vector containing a bovine tropoel astin cDNA, the cells were found to express and secrete tropoelastin. Immun ofluorescence and electron microscopic examination of the transfected PE ce lls showed the presence of elastic fibers in the matrix. Biochemical analys is of this matrix showed the presence of cross-links that are unique to mat ure insoluble elastin. Together, these results indicate that the PE cells p rovide a unique, stable in vitro system in which to study elastic fiber ass embly.