Oxidation-dependent regulation of the selective autophagy receptor SQSTM1/p62

Abstract

Oxidative stress and impairment of autophagy can lead to the accumulation and aggregation of damaged proteins, a common feature of most age-related neurodegenerative disorders such as Alzheimer’s disease and Parkinson’s disease. SQSTM1/p62, a receptor and a substrate of selective autophagy, is implicated in the degradation of damaged and polyubiquitinated substrates. Importantly, p62 has been detected in many types of protein inclusions found in neurodegenerative diseases, together with other disease-related proteins. However, the mechanisms allowing p62 to selectively recruit and degrade autophagic substrates in conditions of oxidative stress remain unknown. The aim of this thesis work is to understand the mechanisms underlying the oligomerisation and the aggregation of p62 during oxidation, looking at post-translational modifications that can lead to the formation of protein aggregates. We found that p62 senses and is regulated by oxidative stress. In response to oxidation, two cysteine (Cys) residues C105 and C113 of p62 mediate the formation of disulphide-linked conjugates (DLC). The formation of p62 DLC was reduced upon antioxidants addition, while inhibitors of the antioxidant system enhanced their development. This feature was critical for the function of p62 as an autophagy receptor as well as for the accumulation of polyubiquitinated aggregates. Indeed, the accumulation and degradation of p62 and its substrates was impaired following mutation of the Cys residues implicated in DLC formation, while the interaction between p62 and polyubiquitinated substrates was not affected. Oxidation of p62 was also required for cell survival in conditions of oxidative stress, indicating the physiological importance of the correct function of p62 in selective autophagy. In addition, formation of p62 DLC was increased in ageing and age-related neurodegenerative diseases, possibly as a compensatory mechanism to protect cells in increased oxidative conditions. In conclusion, we reveal a new mechanism of p62 oligomerisation aiding the selective autophagy of dysfunctional proteins under oxidative stress conditions.