IMMUNOCYTOCHEMICAL COLOCALIZATION OF CLUSTERIN IN APOPTOTIC PHOTORECEPTOR CELLS IN RETINAL DEGENERATION SLOW RDS MUTANT MOUSE RETINAS

In the rds mutant mouse the photoreceptor cells differentiate normally for the first few postnatal days, with the inner segments projecting an extended cilium. However, outer segments fail to form and only rudi mentary disks and opsin-laden vesicles assemble at the tip of the cili um. These are shed into the interphotoreceptor space where they are ph agocytosed by the retinal pigment epithelial cells. In this animal mod el, the photoreceptors undergo a slow degeneration via apoptosis leadi ng to eventual loss of the entire photoreceptor population. Since incr eased expression of clusterin has been implicated in apoptosis, we stu died the expression of clusterin in the rds mutant mouse retina and co mpared it to normal BALB/c retinas. Small intestinal microvillus epith elium was used as a positive control tissue for apoptosis. Immunocytoc hemistry revealed the presence of clusterin in the ganglion cell, inne r nuclear and outer plexiform layers and in the retinal pigment epithe lium of both the rds and the BALB/c retinas. Interestingly, scattered clusterin-positive cells were observed in the outer nuclear layer (onl ) of dystrophic retinas. Since the increased presence of clusterin pro tein in the onl of dystrophic retina may indicate dying photoreceptor cells due to apoptosis, we utilized a co-localization procedure for ap optotic nuclei and clusterin. For apoptosis we utilized an in situ 3' end labeling of fragmented DNA (TUNEL) and immunohistochemistry for cl usterin using brown and red colored substrates respectively. Small int estine tissue sections were also included as positive controls for apo ptosis. Our results show that clusterin is co-localized with apoptotic nuclei both in the onl of rds mutant retinas as well as in the small intestine epithelial cells undergoing cell turnover and exfoliation. T hese results are of interest since overexpression of clusterin is also observed in other neuro-degenerative diseases such as Alzheimer's and Pick's disease. (C) 1996 Academic Press. Inc.