טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentAllon Gilad
SubjectEstablishment and Characterization of a Line of
Prcd-Knockout Mice as a Model for Hereditary
Retinal Dystrophy in Humans
DepartmentDepartment of Medicine
Supervisor Professor Tamar Ben-Yosef
Full Thesis textFull thesis text - English Version


Abstract

PRCD is a unique component of photoreceptor outer segment discs in the eye's retina. PRCD mutations cause an autosomal recessive progressive blinding disease, named retinitis pigmentosa (RP), in both humans and dogs. However, the retinal function of PRCD is currently unknown. To facilitate the study of PRCD's role in the retina and the pathophysiology associated with PRCD mutations, we generated Prcd-knockout mice.

Mice homozygous for the knockout allele exhibit progressive retinal degeneration. In 5-weeks old Prcd-knockout mice electroretinographic (ERG) responses are comparable to those of wild-type (WT) littermates. However, at the age of 20-weeks, both scotopic and photopic ERG responses of Prcd-knockout mice are significantly reduced.  At this age, retinal thickness in Prcd-knockout mice is significantly reduced, as indicated by histological analysis. Specific measurement of each retinal layer indicated significant thinning of the retina. This thinning mainly affected the outer nuclear layer, indicating loss of photoreceptors. Electron Microscopy indicated severe and progressive damage to POS in the KO mice. Based on both electrophysiological and histological analyses (performed at the ages of 5 weeks, 10 weeks, 20 weeks and 30 weeks), retinal degeneration in Prcd-knockout mice is progressive.

In PRCD-mutant dogs, homeostasis of photoreceptor outer segments (POS) was reported to be altered. We therefore decided to study the possible involvement of PRCD in phagocytosis of POS discs by retinal pigment epithelium (RPE) cells. For this purpose we used 6-weeks old Prcd-knockout mice, prior to photoreceptor degeneration. Retinas of knockout mice and WT controls were harvested at 9AM and at 1PM, and immunostained for two distinct markers: (a) rhodopsin, which is a unique POS component, and in the RPE marks phagocytosed POS discs; and (b) LAMP1, a phagosome-specific marker. Quantification of signals from both markers indicated that in knockout retinas, phagocytosis of POS discs by the RPE was severely impaired.

In summary, Prcd-knockout mice are a good model for RP caused by PRCD mutations in humans. Moreover, our data suggest that PRCD is involved in phagocytosis of shed POS discs. This study has important implications for understanding the function of PRCD in the retina, as well as for future development of treatment modalities for PRCD-deficiency in humans.