title: Serine protease HtrA1 accumulates in corneal transforming growth factor beta induced protein (TGFBIp) amyloid deposits.
abstract: OBJECTIVE
  Specific mutations in the transforming growth factor beta induced (TGFBI) gene are associated with lattice corneal dystrophy (LCD) type 1 and its variants. In this study, we performed an in-depth proteomic analysis of human corneal amyloid deposits associated with the heterozygous A546D mutation in TGFBI.
  
  
  METHODS
  Corneal amyloid deposits and the surrounding corneal stroma were procured by laser capture microdissection from a patient with an A546D mutation in TGFBI. Proteins in the captured corneal samples and healthy corneal stroma were identified with liquid chromatography-tandem mass spectrometry and quantified by calculating exponentially modified Protein Abundance Index values. Mass spectrometry data were further compared for identifying enriched regions of transforming growth factor beta induced protein (TGFBIp/keratoepithelin/βig-h3) and detecting proteolytic cleavage sites in TGFBIp.
  
  
  RESULTS
  A C-terminal fragment of TGFBIp containing residues Y571-R588 derived from the fourth fasciclin 1 domain (FAS1-4), serum amyloid P-component, apolipoprotein A-IV, clusterin, and serine protease HtrA1 were significantly enriched in the amyloid deposits compared to the healthy cornea. The proteolytic cleavage sites in TGFBIp from the diseased cornea are in accordance with the activity of serine protease HtrA1. We also identified small amounts of the serine protease kallikrein-14 in the amyloid deposits.
  
  
  CONCLUSIONS
  Corneal amyloid caused by the A546D mutation in TGFBI involves several proteins associated with other varieties of amyloidosis. The proteomic data suggest that the sequence 571-YHIGDEILVSGGIGALVR-588 contains the amyloid core of the FAS1-4 domain of TGFBIp and point at serine protease HtrA1 as the most likely candidate responsible for the proteolytic processing of amyloidogenic and aggregated TGFBIp, which explains the accumulation of HtrA1 in the amyloid deposits. With relevance to identifying serine proteases, we also found glia-derived nexin (protease-nexin 1) in the amyloid deposits, making this serine protease inhibitor a good candidate for the physiologically relevant inhibitor of one of the amyloid-associated serine proteases in the cornea and probably in other tissues. Noteworthy, the present results are in accordance with our findings from a previous study of corneal amyloid deposits caused by the V624M mutation in TGFBI, suggesting a common mechanism for lattice corneal dystrophies (LCDs) associated with mutations in the TGFBIp FAS1-4 domain.
authors.affiliation: Institute of Chemical Engineering, Biotechnology and Environmental Technology, Faculty of Engineering, University of Southern Denmark, Odense, Denmark.
authors.forename: Henrik
authors.initials: H
authors.lastname: Karring
authors.forename: Ebbe Toftgaard
authors.initials: ET
authors.lastname: Poulsen
authors.forename: Kasper
authors.initials: K
authors.lastname: Runager
authors.forename: Ida B
authors.initials: IB
authors.lastname: Thøgersen
authors.forename: Gordon K
authors.initials: GK
authors.lastname: Klintworth
authors.forename: Peter
authors.initials: P
authors.lastname: Højrup
authors.forename: Jan J
authors.initials: JJ
authors.lastname: Enghild
mesh_terms: D000368:Aged; D000595:Amino Acid Sequence; D016000:Cluster Analysis; D003315:Cornea / Q000378:metabolism* / Q000473:pathology*; D003317:Corneal Dystrophies, Hereditary / Q000378:metabolism / Q000473:pathology; D003319:Corneal Stroma / Q000378:metabolism / Q000473:pathology; D016326:Extracellular Matrix Proteins / Q000737:chemistry / Q000378:metabolism*; D005260:Female; D000074289:High-Temperature Requirement A Serine Peptidase 1; D006801:Humans; D042282:Microdissection; D008969:Molecular Sequence Data; D058225:Plaque, Amyloid / Q000378:metabolism*; D011480:Protease Inhibitors / Q000378:metabolism; D017434:Protein Structure, Tertiary; D059748:Proteolysis; D040901:Proteomics; D016415:Sequence Alignment; D012697:Serine Endopeptidases / Q000378:metabolism*; D053719:Tandem Mass Spectrometry; D016212:Transforming Growth Factor beta / Q000737:chemistry / Q000378:metabolism*; D014357:Trypsin / Q000378:metabolism; D000099222:betaIG-H3 Protein
chemical_list: D016326:Extracellular Matrix Proteins; D000074289:High-Temperature Requirement A Serine Peptidase 1; D011480:Protease Inhibitors; D012697:Serine Endopeptidases; D016212:Transforming Growth Factor beta; D014357:Trypsin; D000099222:betaIG-H3 Protein; C474012:HTRA1 protein, human