The AAA-ATPase ATAD1 and its partners promote degradation of desmin intermediate filaments in muscle.

Maintenance of desmin intermediate filaments (IF) is vital for muscle plasticity and function, and their perturbed integrity due to accelerated loss or aggregation causes atrophy and myopathies. Calpain-1-mediated disassembly of ubiquitinated desmin IF is a prerequisite for desmin loss, myofibril breakdown, and atrophy. Because calpain-1 does not harbor a bona fide ubiquitin-binding domain, the precise mechanism for desmin IF disassembly remains unknown. Here, we demonstrate that the AAA-ATPase, ATAD1, is required to facilitate disassembly and turnover of ubiquitinated desmin IF. We identified PLAA and UBXN4 as ATAD1's interacting partners, and their downregulation attenuated desmin loss upon denervation. The ATAD1-PLAA-UBXN4 complex binds desmin filaments and promotes a release of phosphorylated and ubiquitinated species into the cytosol, presenting ATAD1 as the only known AAA-ATPase that preferentially acts on phosphorylated substrates. Desmin filaments disassembly was accelerated by the coordinated functions of Atad1 and calpain-1, which interact in muscle. Thus, by extracting ubiquitinated desmin from the insoluble filament, ATAD1 may expose calpain-1 cleavage sites on desmin, consequently enhancing desmin solubilization and degradation in the cytosol.