Hsp25 and -90 immunoreactivity in the normal rat eye

The distributions of heat shock protein (Hsp)25 and -90 in various regions of the rat eye are described to provide a basis for understanding their roles in normal, damaged, and diseased ocular tissues. This work complements the earlier examination of Hsp70 and Hsc70 (the constitutive form).

Eyes of adult male Sprague-Dawley rats were fixed in methacarn and embedded in paraffin. Sagittal sections (10 microm) through the optic nerve were stained with hematoxylin and eosin, or incubated with anti-Hsp90, anti-Hsp25, or control IgG. Bound antibody was visualized using an avidin-biotin-horseradish peroxidase detection system.

Hsp90 immunoreactivity was abundant in the retina, whereas only low levels of Hsp25 were detected there. In the optic nerve, the relative difference in immunoreactivity for the two Hsps was reversed, with Hsp25 being considerably greater than Hsp90. Both Hsps were detected at low levels in the retinal pigment epithelium (RPE), except for that portion within 250 microm of the optic disc, where Hsp25 and -90 immunoreactivities were increased. Similar to the optic nerve, the corneal epithelium showed greater staining for Hsp25 than for Hsp90, and basal cells contained the highest levels of immunoreactivity for both Hsps. In the ciliary body and iris, Hsp25 and -90 were abundant and similarly distributed in the epithelial and stromal layers.

Each of the ocular tissues had distinctive patterns of Hsp25 and -90 immunostaining. These results suggest that the various structures of the eye have unique requirements for the particular chaperoning and supportive functions of these two Hsp families.