Aim: Biologically uncommon d-β-aspartic acid (d-β-Asp) accumulates in the body with age and is involved in the ageing process. In the present study, the localisation of d-β-Asp-containing proteins was investigated in surgical specimens with climatic droplet keratopathy (CDK), one of the ocular changes related to the ageing process.
Methods: Immunohistochemical localisation of d-β-Asp-containing proteins using polyclonal antibodies raised against d-β-Asp-containing peptides was examined in three corneas with CDK, three corneas with interstitial keratitis, six corneas with bullous keratopathy, and three corneas without any corneal diseases.
Results: Strong immunoreactivity to d-β-Asp-containing peptide was detected in all the surgical specimens with CDK. In contrast, no immunoreactivities to d-β-Asp-containing peptides were detected in the surgical specimens with bullous keratopathy, interstitial keratitis, or no corneal diseases.
Conclusions: CDK was regarded as aggregations of d-β-Asp-containing proteins. The formation of d-amino acids in protein causes the different side chain orientations and β-linkage of Asp residues elongates the main chain of proteins. Therefore, d-β-Asp formation will result in a partial unfolding of proteins leading to the aggregation of proteins seen in CDK.
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Competing interests: None.
Funding: This work is supported by the Ministry of Education, Science, Sports and Culture, Grant-in-Aid for Young Scientists, 18791259 (2006–2008) and for Scientific Research, 21592216 (2009–2011), Japan.
Ethics approval: Ethics approval was provided by Yuichi Kaji.
Patient consent: Obtained.