The serine protease HtrA1 cleaves misfolded transforming growth factor β–induced protein (TGFBIp) and induces amyloid formation

• Published in: The Journal of biological chemistry 2019-08, Vol.294 (31), p.11817-11828
• Main Authors: Poulsen, Ebbe Toftgaard, Nielsen, Nadia Sukusu, Scavenius, Carsten, Mogensen, Emilie Hage, Risør, Michael W., Runager, Kasper, Lukassen, Marie V., Rasmussen, Casper B., Christiansen, Gunna, Richner, Mette, Vorum, Henrik, Enghild, Jan J.
• Format: Article
• Language: English
• Subjects: Aged, 80 and over; amyloid; Amyloid - metabolism; BIGH3; Chromatography, High Pressure Liquid; cornea; Cornea - metabolism; Corneal Diseases - metabolism; Corneal Diseases - pathology; corneal dystrophy; Extracellular Matrix Proteins - chemistry; Extracellular Matrix Proteins - genetics; Extracellular Matrix Proteins - metabolism; eye disorder; granular corneal dystrophy (GCD); High-Temperature Requirement A Serine Peptidase 1 - genetics; High-Temperature Requirement A Serine Peptidase 1 - metabolism; high-temperature requirement protein A1 (HtrA1); HTRA1; Humans; lattice corneal dystrophy (LCD); Molecular Bases of Disease; Mutagenesis, Site-Directed; Peptides - analysis; Peptides - metabolism; protease; Protein Domains; Protein Folding; protein misfolding; protein turnover; proteolytic processing; Recombinant Proteins - biosynthesis; Recombinant Proteins - genetics; Recombinant Proteins - isolation & purification; Tandem Mass Spectrometry; Transforming Growth Factor beta - chemistry; Transforming Growth Factor beta - genetics; Transforming Growth Factor beta - metabolism; transforming growth factor β–induced protein (TGFBIp)
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.RA119.009050

The serine protease high-temperature requirement protein A1 (HtrA1) is associated with protein-misfolding disorders such as Alzheimer's disease and transforming growth factor β–induced protein (TGFBIp)–linked corneal dystrophy. In this study, using several biochemical and biophysical approaches, including recombinant protein expression, LC-MS/MS and 2DE analyses, and thioflavin T (ThT) fluorescence assays for amyloid fibril detection, and FTIR assays, we investigated the role of HtrA1 both in normal TGFBIp turnover and in corneal amyloid formation. We show that HtrA1 can cleave WT TGFBIp but prefers amyloidogenic variants. Corneal TGFBIp is extensively processed in healthy people, resulting in C-terminal degradation products spanning the FAS1-4 domain of TGFBIp. We show here that HtrA1 cleaves the WT FAS1-4 domain only inefficiently, whereas the amyloidogenic FAS1-4 mutations transform this domain into a considerably better HTRA1 substrate. Moreover, HtrA1 cleavage of the mutant FAS1-4 domains generated peptides capable of forming in vitro amyloid aggregates. Significantly, these peptides have been previously identified in amyloid deposits in vivo, supporting the idea that HtrA1 is a causative agent for TGFBIp-associated amyloidosis in corneal dystrophy. In summary, our results indicate that TGFBIp is an HtrA1 substrate and that some mutations in the gene encoding TGFBIp cause aberrant HtrA1-mediated processing that results in amyloidogenesis in corneal dystrophies.