Proteolytic processing in lattice corneal dystrophy

Abstract

Purpose: Transforming growth factor beta-induced protein (TGFBIp) is a major component of the human corneal proteome. More than 40 different mutations, in the TBFBIp gene lead to various types of protein aggregates in the cornea including both amyloid deposits as well as non-amyloid deposits. Here we investigate the protein composition of two related lattice corneal dystrophy cases and investigate the role of the serine protease HtrA1 in the pathogenesis of this disease.

Methods: The amyloid corneal deposits from the two lattice corneal dystrophy cases were isolated from paraffin embedded tissues by laser capture microdissection. The collected material was treated with trypsin and analyzed by tandem mass spectrometry. Data were searched against the Swissprot database using the Mascot algorithm and processed using MS Data Miner software. Spectral counting of TGFBIp peptides was performed to expose any viabilities in in vivo TGFBIp processing. Furthermore, different genotypes of recombinant expressed TGFBIp was subjected to proteolysis by the serine protease HtrA1 and analyzed with SDS-PAGE and MS.

Results: Using Exponentially Modified Protein Abundance Index the most abundant proteins in the corneal deposits were compared to healthy corneal tissue. The amyloid deposits revealed accumulation of serum amyloid p component, clusterin, apolipoproteins A-IV and E and HtrA1. Further, spectral counting of TGFBIp peptides suggested an increased in vivo processing of TGFBIp associated with the amyloid deposits compared to healthy tissue. In vitro HtrA1 proteolysis of different TGFBIp genotypes showed preference for amyloid forming genotypes as seen in lattice corneal dystrophy.

Conclusions: The newly obtained insight into the plaque proteome associated with corneal dystrophies has provided new knowledge that may help illuminate the mechanism leading to these diseases.

Keywords: 480 cornea: basic science • 519 extracellular matrix • 662 proteolysis