Immunohistochemical Identification of L-kynurenine Aminotransferase III in Corpora Amylacea in the Human Retina and Optic Nerve

Abstract

Purpose: : Corpora amylacea (CAm) occur in optic nerve and retinal ageing and degeneration. Their rich acid polysaccharide content makes them best demonstrable by the PAS (periodic acid-Schiff) stain. Importantly, CAm contain, in addition to glucose polymers, ageing-, stress- and proinflammatory proteins also L-kynurenine amninotransferases I and II (KAT I and II) (Rejdak et al. 2007), the key enzymes of the L-kynurenine pathway and tryptophan metabolism in the CNS.This study is the first to examine immunoreactivity of the third isoform of L-kynurenine aminotransferase (KAT III) in the human retina and also CAm in the human retina and optic nerve.

Methods: : Immunohistochemistry was performed using polyclonal antibody against KAT III on sections of 23 human eyes enucleated for malignant uveal melanoma. Occurrence and location of KAT III -stained CAm was compared with PAS-stained sections.

Results: : Our studies revealed that KAT III is expressed in retinal ganglion cells in the human retina. Moreover, KAT III immunoreactivity was shown in CAm in the retina and optic nerve with similar location to PAS-stained sections. KAT III immunoreactivity was more pronounced in the retrolaminar part of the optic nerve. Occasionally there was no staining.

Conclusions: : Presence of KAT III in CAm in the human retina and optic nerve suggest that products of L-kynuenine pathway may be involved in mechanisms of retinal ageing and neurodegeneration leading to CAm formation.

Keywords: pathology: human