Immunohistochemical localisation of d- -aspartic acid-containing proteins in climatic droplet keratopathy

AIM: Biologically uncommon D-beta-aspartic acid (D-beta-Asp) accumulates in the body with age and is involved in the ageing process. In the present study, the localisation of D-beta-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-beta-Asp-containing proteins using polyclonal antibodies raised against D-beta-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-beta-Asp-containing peptide was detected in all the surgical specimens with CDK. In contrast, no immunoreactivities to D-beta-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-beta-Asp-containing proteins. The formation of D-amino acids in protein causes the different side chain orientations and beta-linkage of Asp residues elongates the main chain of proteins. Therefore, D-beta-Asp formation will result in a partial unfolding of proteins leading to the aggregation of proteins seen in CDK.