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Gary Hin-Fai Yam, Kaijie Wang, Li Huang, Larry Baum, Chi-Pui Pang; Chemical Chaperone Trimethylamine N-oxide Alleviated Amyloid Aggregation By Corneal Dystrophy-causing Transforming Growth Factor Beta-induced Protein. Invest. Ophthalmol. Vis. Sci. 2012;53(14):4208.
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© ARVO (1962-2015); The Authors (2016-present)
Mutations in human transforming growth factor beta-induced protein (TGFBIp, or Bigh3p) are linked to protein deposits in corneal epithelial and stromal tissue, leading to visually impaired corneal dystrophy. This study investigated the effect of common mutants on amyloid beta peptide aggregation in vitro and the potential correction by small molecule chemical chaperones.
Recombinant FLAG/myc-tagged wildtype or mutant (R124C, R124H, R124L, R124S and R555W) TGFBIp was over-expressed in human embryonic kidney epithelial HEK293 cells for 48 hours. The cell-free medium containing secreted TGFBIp was incubated with amyloid beta 1-40 (Aβ40) peptides in the presence or absence of a chemical osmolyte, trimethylamine N-oxide (TMAO, 15 to 100 mM). Protein aggregates harvested by ultracentrifugation were denatured and immunoblotted for Aβ peptide (mouse monoclonal 6E10) and FLAG (for TGFBI). Effect of TMAO on chemical and morphological properties of Aβ aggregation was examined by Congo red binding assay and transmission electron microscopy (TEM), respectively. Aβ40 scrambled peptide was used as control.
Cell free media containing R124 TGFBIp accelerated Aβ aggregation within 12 hours of incubation, whereas wildtype and R555 mutant had similar Aβ aggregation only after 24 hours. These aggregates were presented in gel as high molecular-weight aggregates (HMA, >150 kDa), medium molecular-weight aggregates (MMA, 80-100 kDa), small molecular-weight aggregates (SMA, 40-50 kDa) and oligomers (<20 kDa). Western blot and Congo red binding analyses showed that TMAO dose-dependently suppressed R124-induced Aβ aggregation. By TEM, TMAO reduced the fibrillar aggregates caused by Aβ and R124H TGFBIp.
Our result demonstrated that mutant TGFBIp promoted fibril aggregate formation of Aβ40 peptides, and this was alleviated by TMAO. This novel finding of a chemical chaperone to reduce amyloid deposition by mutant TGFBIp may represent a potential chemical-based therapeutic intervention for corneal dystrophy.
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