Functional Study Of ASRGL1 In Retinitis Pigmentosa

Retinitis pigmentosa(RP)is an inherited disease of retina characterized by degeneration of retinal pigment epithelial cells and photoreceptor cells,caused retina to atrophy eventually.There are about 1.5 million patients with RP worldwide,and about 400,000 in China.About 100 causative genes have been identified and novel causative genes and mutations are now being reported annually.Some of pathogenic genes,such as ARL2,RHO,and IMPG2,have been constructed animal models to dig into the functions and mechanisms in RP.Asparaginase-like 1(ASRGL1)is a newly discovered pathogenic gene in patients with RP,and it is of great significance to explore the function and potential molecular mechanism in RP.As a member of the N-terminal nucleophilic hydrolase superfamily,ASRGL1 can catalyze the hydrolysis of L-asparagine and iso-asparagine dipeptides.Polypeptides containing iso-asparagine have important effects on substrate recognition and conversion of several proteases,which can as protease inhibitor under some circumstances.Formation of iso-asparagine peptide bonds can lead to the damage of non-enzymatic proteins,because of the kink formed in the protein skeleton.And the kink can disrupt the normal folding of amino acids,resulting in loss of protein function or change of hydrolytic activity,and ultimately lead to metabolic dysfunction.In brief,ASRGL1 plays an important physiological role in the removal of peptides containing iso-asparagine and the return of amino acids to the metabolic pool.Mutations in the ASRGL1 gene have been reported in patients with RP.However,the function and underlying mechanism have not been studied in RP,and corresponding animal model of the disease is lacking.We established an Asrgl1 knockout mouse models by the CRISPR-Cas9 technique to evaluate the roles and potential molecular mechanism of Asrgl1 in the retina.The Asrgl1 knockout mice reproduced the phenotype of RP patients including the reduction of A-waves and B-waves in electroretinogram(ERG)and progressive degradation of rod and cone photoreceptors.In addition,increased apoptotic cell and gliosis were also observed in the retinas of Asrgl1-KO mice.The histological examination of Asrgl1 knockout mice at 12 months of age revealed irregularly shortened rod cells and dislocation of rhodopsin protein.And impaired cone cell elongation and progressive cone cell death.Thus,Asrgl1 is extremely significant to maintain the function and morphology of retinal cells,and this study offers fresh idea and models for research of RP caused by Asrgl1 mutations.