Purpose: Biologically uncommon D-β-aspartic acid (D-β-Asp) accumulates in the body with age and is involved in the aging process. In the present study, the localization of D-β-Asp-containing proteins was investigated in surgical specimens with climatic droplet keratopathy (CDK), one of the ocular changes related to the aging process.
Methods: Immunohistochemical localization 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.