A Mouse Model with Ablated Asparaginase and Isoaspartyl Peptidase 1 () Develops Early Onset Retinal Degeneration (RD) Recapitulating the Human Phenotype.

We previously identified a homozygous G178R mutation in human () through whole-exome analysis responsible for early onset retinal degeneration (RD) in patients with cone-rod dystrophy. The mutant G178R ASRGL1 expressed in Cos-7 cells showed altered localization, while the mutant ASRGL1 in lacked the autocatalytic activity needed to generate the active protein. To evaluate the effect of impaired ASRGL1 function on the retina in vivo, we generated a mouse model with c.578_579insAGAAA (NM_001083926.2) mutation () through the CRISPR/Cas9 methodology. The expression of ASGRL1 and its asparaginase activity were undetectable in the retina of mice. The ophthalmic evaluation of mice showed a significant and progressive decrease in scotopic electroretinographic (ERG) response observed at an early age of 3 months followed by a decrease in photopic response around 5 months compared with age-matched wildtype mice. Immunostaining and RT-PCR analyses with rod and cone cell markers revealed a loss of cone outer segments and a significant decrease in the expression of , , and at 3 months in mice compared with age-matched wildtype mice. Importantly, the retinal phenotype of mice is consistent with the phenotype observed in patients harboring the G178R mutation in confirming a critical role of ASRGL1 in the retina and the contribution of mutations in retinal degeneration.