Epigallocatechin Gallate Remodels Fibrils of Lattice Corneal Dystrophy Protein, Facilitating Proteolytic Degradation and Preventing Formation of Membrane-Permeabilizing Species

Abstract

Lattice corneal dystrophy is associated with painful recurrent corneal erosions and amyloid corneal opacities induced by transforming growth factor β-induced protein (TGFBIp) that impairs vision. The exact mechanism of amyloid fibril formation in corneal dystrophy is unknown but has been associated with destabilizing mutations in the fourth fasciclin 1 (Fas1-4) domain of TGFBIp. The green tea compound epigallocatechin gallate (EGCG) has been found to inhibit fibril formation of various amyloidogenic proteins in vitro. In this study, we investigated the effect of EGCG as a potential treatment in lattice corneal dystrophy (LCD) using Fas1-4 with the naturally occurring LCD-inducing A546T mutation. A fewfold molar excess of EGCG was found to inhibit fibril formation in vitro by directing Fas1-4 A546T into stable EGCG-bound protein oligomers. Incubation with 2 molar equiv of EGCG led to a 4-fold reduction in the aggregates' membrane disruptive potential, potentially indicative of significantly lower cytotoxicity with regard to corneal erosions. EGCG did not induce oligomer formation by wild-type Fas1-4, indicating that treatment with EGCG would not interfere with the native function of the wild-type protein. Addition of EGCG to 10-day-old fibrils reduced fibril content in a dose-dependent manner. Proteinase K was found to reduce the light scattering of nontreated fibrils by 31% but reduced that of fibrils treated with 8 molar equiv of EGCG by 85%. This suggests that EGCG remodeling of fibril structure can facilitate aggregate removal by endogenous proteases and thus alleviate the protein deposits' light scattering symptoms.