Immunolocalization of βig-h3 Protein in 5q31-Linked Corneal Dystrophies and Normal Corneas

Abstract

To characterize the relation of the ␤ig-h3 protein to the diagnostic corneal deposits in the hereditary corneal dystrophies recently shown to have mutations in the βig-h3 gene on chromosome 5q31. Methods: Corneas with lattice, granular, mixed granularlattice ("Avellino"), and 2 types of Reis-Bü cklers dystrophy were diagnosed by the histochemical and ultrastructural characteristics of their abnormal aggregates. Dystrophic and normal corneas were compared for immunolocalization of ␤ig-h3 protein. Results: In normal corneas, immunoreactivity for ␤ig-h3 protein was strongest in the Bowman layer, and next strong along stromal interlamellar junctions and attachment sites of collagen to the Descemet membrane. Antibody binding was intense on all dystrophic aggregates, mimicking somewhat the normal protein distribution. Mixed granular-lattice dystrophy had the most variation in ␤ig-h3-immunopositive forms. The aggregates in both the "rod-shaped" Reis-Bü cklers type and the "curly fiber" Thiel-Behnke type were strongly stained for ␤ig-h3 protein, consistent with mutations on the βig-h3 gene. Conclusions: The marked immunopositivity for ␤ig-h3 protein in the abnormal deposits in these dystrophies indicates that ␤ig-h3 protein is a major component. The variety and quantity of immunopositive forms suggests that they consist primarily of the mutant protein, self-polymerizing and/or incorrectly binding to other corneal components. Variability of forms may relate to both the specific mutation and regional interactions of this protein.

Medical Applications of Transforming Growth Factor-

“…43 It appears that mutant βig-h3 protein self-polymerizes and/or incorrectly binds to other corneal components resulting in the abnormal deposits found in these dystrophies. 44 Hereditary hemorrhagic telangiectasia (HHT) type 1 or OslerWeber-Rendu disease is caused by mutations of endoglin. 10 In HHT type II, mutations of activin receptor-like kinase 1 (ALK1) have been identified.…”

TGFBI gene mutations in Brazilian patients with corneal dystrophy

“…15,20,21 Immunohistochemical studies demonstrated that the mutated keratoepithelin is a major component of the corneal deposits. [20][21][22] The keratoepithelin protein has four internal repeat domains and most of the mutations reported are located in the amino acid R124 or in the fourth fascilin-like domain.…”

Cytokeratin expression in corneal dystrophies

“…The transforming growth factor beta induced gene (TGFBI) on chromosome 5, responsible for the quality and quantity of keratoepithelin, has been related to several corneal dystrophies. The immunoreactivity of the keratoepithelin protein has been demonstrated in the dystrophic deposits of corneas with granular, Avellino, Reis-Buckler, lattice and Thiel-Behnke dystrophies, all related to the TGFBI gene suggesting that keratoepithelin is a major component of these deposits (1,7) . It has also been shown that the deposits contain keratoepithelin, together with nonkeratoepithelin proteins.…”

“…The inference is that mutated keratoepithelins, diffusing predominantly from the epithelium, coaggregate with an assortment of other proteins over a long period of time to form the deposits characteristic of the disorder (8) . Several substances reported to date include vimentin, immunoglobulin κ and λ light chains, microfibrillar protein lectinpositive carbohydrate, amyloid P protein, phospholipids, and epithelial proteins, such as the cytokeratins (3,(7)(8)(9) (Figure 1). Cytokeratins (CKs) are water-soluble proteins found in most celltypes having characteristics of epithelial cells (10) .…”