Immunohistochemical identification of kynurenine aminotransferases in corpora amylacea in the human retina and optic nerve

Introduction: Corpora amylacea (CAm) occur in the optic nerve and in retinal ageing and degeneration. Cellular expression of L-kynurenine aminotransferases (KAT I and II) in the avian and rodent retina and its changes in retinal development and neurodegeneration have been documented. This study examines KAT I and II immunoreactivity in CAm in the human retina and optic nerve.

Material and methods: Immunohistochemistry was performed using polyclonal antibodies against KAT I and KAT II on sections of 23 human eyes enucleated for malignant uveal melanoma. Occurrence and location of KAT I- or KAT II-stained CAm was compared with PAS-stained sections.

Results: KAT I and KAT II expression in CAm has been shown in the retina and optic nerve with similar location to
PAS-stained sections. KAT I immunoreactivity was more intense than KAT II and its staining was more pronounced in the retrolaminar part of the optic nerve. Some of the CAm showed only faint KAT II expression and occasionally there was no staining. KAT II revealed no association of staining variability and localisation of CAm. Similarly to animal studies, in the human retina KAT I was observed on Müller cell endfeet while KAT II was expressed in retinal ganglion cells.

Conclusions: Presence of kynurenine aminotransferases in CAm in the human retina and optic nerve suggest that both enzymes may be involved in mechanisms of retinal ageing and neurodegeneration leading to CAm formation.