The linear ubiquitin E3 ligase-Relish pathway is involved in the regulation of proteostasis in Drosophila muscle during aging.

Linear ubiquitination is an atypic ubiquitination process that directly connects the N- and C-termini of ubiquitin and is catalyzed by HOIL-1-interacting protein (HOIP). It is involved in the immune response or apoptosis by activating the nuclear factor-κB pathway and is associated with polyglucosan body myopathy 1, an autosomal recessive disorder with progressive muscle weakness and cardiomyopathy. However, little is currently known regarding the function of linear ubiquitination in muscles. Here, we investigated the role of linear ubiquitin E3 ligase (LUBEL), a DrosophilaHOIP ortholog, in the development and aging of muscles. The muscles of the flies with down-regulation of LUBEL or its downstream factors, kenny and Relish, developed normally, and there were no obvious abnormalities in function in young flies. However, the locomotor activity of the LUBEL RNAi flies was reduced compared to age-matched control, while LUBEL RNAi did not affect the increased mitochondrial fusion or myofiber disorganization during aging. Interestingly, the accumulation of polyubiquitinated protein aggregation during aging decreased in muscles by silencing LUBEL, kenny, or Relish. Meanwhile, the levels of autophagy and global translation, which are implicated in the maintenance of proteostasis, did not change due to LUBEL down-regulation. In conclusion, we propose a new role of linear ubiquitination in proteostasis in the muscle aging.
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