Abstract
The glaucoma-associated E50K mutation in optineurin (OPTN) is known to affect autophagy and cause the apoptosis of retinal ganglion cells (RGCs), but the pathogenic mechanism remains unclear. In this study, we investigated whether the OPTN (E50K) mutation caused TDP-43 aggregation by disrupting autophagy in vivo and in vitro. OPTN (E50K) mutant mice were generated and analysed for genotype and phenotype. Adeno-associated virus type 2 vectors containing either GFP only, GFP-tagged wild-type OPTN or GFP-tagged E50K-mutated OPTN were used to transfect R28 cells. Loss of RGCs decreased retinal thickness and visual impairment were observed in OPTN (E50K) mice compared with WT mice. Moreover, overexpression of E50K OPTN induced R28 cell apoptosis. Increased p62/SQSTM1 and LC3-II levels indicated that autophagic flux was inhibited and contributed to TDP-43 aggregation in vivo and in vitro. We found that rapamycin effectively reduced the aggregation of TDP-43 in OPTN (E50K) mice and decreased the protein levels of p62/SQSTM1 and the autophagic marker LC3-II. Moreover, rapamycin increased the RGC number and visual function of E50K mice. In addition, we also observed increased cytoplasmic TDP-43 in the spinal cord and motor dysfunction in 24-month-old OPTN (E50K) mice, indicating that TDP-43 accumulation may be the common pathological mechanism of glaucoma and amyotrophic lateral sclerosis (ALS). In conclusion, the disruption of autophagy by OPTN (E50K) affected the degradation of TDP-43 and may play an important role in OPTN (E50K)-mediated glaucomatous retinal neurodegeneration.
Highlights
Glaucoma is an important leading cause of progressive blindness worldwide
In the flash visual evoked potential (f-VEP) examination, the P2 amplitude measured for E50K mutant mice was 11.44 ± 0.8074 μV, which was significantly lower than the P2 amplitude measured for wild-type mice (15.42 ± 0.7107 μV, n = 19) (p < 0.01)
In the present study, we investigated the pathogenic mechanisms of E50K-induced retinal ganglion cells (RGCs) apoptosis in a 16month-old CRISPR/Cas9-mediated mouse model and an OPTN (E50K)-overexpressing R28 cell model
Summary
Glaucoma is an important leading cause of progressive blindness worldwide. Epidemiologically, normal-tension glaucoma (NTG) is more prevalent among Asian populations, including Japanese, Korean and Chinese populations, and 21% of patients with NTG have a family history of glaucoma, indicating a genetic predisposition to the disease[1,2]. One of the genes associated with NTG is optineurin (OPTN)[3,4], which encodes OPTN, an adaptor. As an ‘autophagy receptor’, OPTN binds ubiquitin or ubiquitinated aggregates and directs them to autophagosomes[7]. It contributes to the maturation of the autophagosome[8] and helps to degrade damaged organelles or abnormal proteins to maintain cellular homoeostasis[6]. The E50K mutation of OPTN is the most prevalent mutant form that is associated with NTG9; impaired autophagy has been found in E50K transgenic mice and. Several studies have suggested that OPTN has an important role in mitophagy[9,12,13]; the effect of E50K on protein metabolism is rarely reported
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