OPTN deficiency through CRISPR/Cas9 downregulates autophagy and mitophagy in a SOD1-G93A-expressing transgenic cell line

Abstract

Amyotrophic lateral sclerosis (ALS) is characterized by the loss of upper and lower motor neurons (MNs) and is the most common adult paralysis neurodegenerative disease. Dysregulated autophagy, which has been reported in the pathogenesis of familial ALS, has been found in superoxide dismutase 1 (SOD1) transgenic mice and cell lines. Optineurin (OPTN) is a signal regulator that coordinates many crucial cellular processes, including autophagy, mitophagy and aggrephagy. Recent studies have shown that OPTN gene mutations are correlated with ALS, glaucoma and Paget’s disease of the bone. Indeed, defects in autophagosome–lysosome fusion have been reported in patients with ALS-associated OPTN mutations. However, the exact function of OPTN in the pathology of ALS remains unknown. To determine the function of OPTN, we generated OPTN-knockdown cell lines from SOD1-G93A-expressing NSC34 cells with the clustered regularly interspaced short palindromic repeats/associated system 9 (CRISPR/Cas9) approach. In our research, we observed that the loss of OPTN resulted in the impairment of autophagy and mitophagy pathways. Moreover, the mitochondrial transmembrane potential was depolarized by LV-sgRNA-OPTN. On the basis of observations of live cells, the production of reactive oxygen species (ROS) was increased, the autophagic flux decreased, and the autophagic flux merged with that of mitochondria according to confocal live-cell imaging. A decreased LC3-II and an increased p62 levels indicated that autophagy pathway activation was decreased. The protein levels of VDAC1 and TBK1 decreased after OPTN knockdown, suggesting that mitophagy was blocked. Our results suggest that OPTN plays a pivotal role in regulating autophagy and mitophagy.