A Novel Mouse Model for Late-Onset Retinal Degeneration (L-ORD) Develops RPE Abnormalities Due to the Loss of C1qtnf5/Ctrp5.

Late-onset retinal degeneration (L-ORD) is an autosomal dominant macular dystrophy resulting from mutations in the gene CTRP5/C1QTNF5. A mouse model (Ctrp5+/-) for the most common S163R developed many features of human clinical disease. We generated a novel homozygous Ctrp5 gene knock-out (Ctrp5-/-) mouse model to further study the mechanism of L-ORD. The retinal morphology of these mice was evaluated by retinal imaging, light microscopy, and transmission electron microscopy (TEM) at 6, 11, and 18.5 mo. Expression of Ctrp5 was analyzed using immunostaining and qRT-PCR. The Ctrp5-/- mice showed lack of both Ctrp5 transcript and protein. Presence of a significantly larger number of autofluorescent spots was observed in Ctrp5-/- mice compared to the WT (P < 0.0001) at 19 mo. Increased RPE stress with vacuolization and thinning was observed as early as 6 mo in Ctrp5-/- mice. Further, ultrastructural analyses revealed a progressive accumulation of basal laminar sub-RPE deposits in Ctrp5-/- mice from 11 mo. The Ctrp5-/- mice shared retinal and RPE pathology that matches with that previously described for Ctrp5+/- mice suggesting that pathology in these mice results from the loss of functional CTRP5 and that the presence of CTRP5 is critical for normal RPE and retinal function.