A novel proteotoxic stress associated mechanism for macular corneal dystrophy

Macular corneal dystrophy is a rare autosomal recessive eye disease affecting primarily the corneal stroma. Abnormal accumulation of proteoglycan aggregates has been observed intra- and extracellularly in the stromal layer. In addition to the stromal keratocytes and corneal lamellae, deposits are also present in the basal epithelial cells, endothelial cells and Descemet's membrane. Misfolding of proteins has a tendency to gather into aggregating deposits. We studied interaction of molecular chaperones and proteasomal clearance in macular dystrophy human samples and in human corneal HCE-2 epithelial cells. Seven cases of macular corneal dystrophy and four normal corneal buttons collected during corneal transplantation were examined for their expression patterns of heat shock protein 70, ubiquitin protein conjugates and SQSTM1/p62. In response to proteasome inhibition the same proteins were analyzed by western blotting. Slit-lamp examination, in vivo confocal cornea microscopy and transmission electron microscopy were used for morphological analyses. Heat shock protein 70, ubiquitin protein conjugates and SQSTM1/p62 were upregulated in both the basal corneal epithelial cells and the stromal keratocytes in macular corneal dystrophy samples that coincided with an increased expression of the same molecules under proteasome inhibition in the HCE-2 cells in vitro. We propose a novel regulatory mechanism that connects the molecular chaperone and proteasomal clearance system in the pathogenesis of macular corneal dystrophy.