Abstract
Purpose :
Variants in Interphotoreceptor Matrix Proteoglycans (IMPG2) have been reported in retinitis pigmentosa patients. However, the molecular mechanisms underlying remain elusive due to lack of suitable disease models. This study aims to study the role of IMPG2 in the retina using a knockout out mouse model.
Methods :
To assess its in vivo functions of IMPG2 in the retina, we developed an Impg2 knockout (KO) mouse model using CRISPR-Cas9 technique. Electroretinogram tests were performed at 3 and 6 months of ages. Morphology of photoreceptors weas assayed by histopathological examination and immunostaining studies. Endoplasmic ER stress and autophagy in the retina was also evaluated.
Results :
Impg2 KO mice recapitulated RP phenotypes in patients, including attenuated ERG response and progressive degeneration of photoreceptors. Histopathological examination on KO mice showed irregularly arranged rod cells and mislocalized rhodopsin protein in the inner segment at 6 months of age. In additional to the pathological changes in rod cells, cone cells were also affected in KO retinas. KO retinas exhibited progressive death of cone cells and the proper elongation of cone cells was impaired. Further immunoblotting analysis revealed elevated expression of Endoplasmic Reticulum (ER) stress related proteins including C/EBP homologous protein (CHOP), immunoglobulin heavy chain binding protein (BIP) and protein disulfide isomerase (PDI) in Impg2 KO retinas. Increased gliosis and apoptotic cell death were also observed in the KO retinas. As autophagy is closely related with ER stress, we then check the autophagic flux in KO retinas. Results showed that the autophagy flux was impaired in KO retinas as revealed by increased expression of SQSTM1, LC3 and other proteins involved autophagy process.
Conclusions :
Our study demonstrated essential roles of Impg2 in the retina and provided a mouse model for mechanism investigation and therapy development for RP caused by variants in IMPG2 gene.
This is a 2020 ARVO Annual Meeting abstract.