Immunohistochemical Localization of Glucocorticoid Pre-Receptors Along the Aqueous Pathway of Normal and Glaucomatous Dogs

Abstract

Purpose: : As individuals with primary glaucoma often have increased sensitivity to glucocorticoids (GC), we have begun to re-examine the role of GC in a colony of beagles with primary-open angle glaucoma (POAG), having studied the presence of GC receptors (GCR) in the anterior portion of their eyes. We have previously found a notable difference in their presence when compared to age-matched normals. The present study examines GC pre-receptors (GCPR), types I and II by immunohistochemistry to further understand the role of GC in individuals with this inherited disease.

Methods: : Paraffin-embedded specimens from the anterior uveas of 14 Beagles with inherited glaucoma (1-day to 13-yrs-old) and age-matched normal Beagles were sectioned and incubated with anti-human 11 beta-hydroxysteroid dehydrogenase type 1 (11bHSD1) polyclonal rabbit and anti-human 11 beta-hydroxysteroid dehydrogenase type 2 (11bHSD2) polyclonal rabbit Abs. 11bHSD1 is a prereceptor that regenerates active GCs, while 11bHSD2 converts GCs to their inert state. Specimens were incubated with secondary antibody with biotinylated link followed by peroxidase-labeled streptavidin and then by substrate-chromogen for light microscopy.

Results: : Among the glaucomatous dogs, the reaction for 11bHSD1 in cells of the nonpigmented epithelium (NPE) of the ciliary processes (CB) processes was considerably more intense and localized among the Beagles with later stages of POAG than the age-matched normals. Within the iridocorneal angle (ICA), the localization of 11bHSD1 within the trabecular meshwork (TM) and adjacent region was greater in affected animals than that of age-matched normals of all ages. There was little reaction for 11bHSD2 in cells of the NPE of the CB processes in either glaucomatous or age-matched normal dogs. In the ICA, the TM reacted positively for 11bHSD2 in the younger normal dogs, decreasing in dogs 6+ yrs old. The reverse trend was observed in the affected animals.

Conclusions: : Immuno-localization of both GCPRs was successfully observed in the canine eye. Changes in the apparent activity of the GCPRs appeared to occur mostly within the ICA rather than the CB, which differed markedly from our previous findings on the GCR, which changes mostly within NPE of the CB. Our findings collectively indicate that an increased sensitivity of GCs occurs within the aqueous humor pathway of the POAG dogs prior to IOP elevation.

Keywords: trabecular meshwork • ciliary processes • immunohistochemistry