bioRxiv. 2026 Mar 13. pii: 2026.03.12.711310. [Epub ahead of print]
Mitochondrial dysfunction and extracellular protein aggregation occur in neurodegenerative diseases such as Alzheimer's disease (AD). However, it remains unclear if these processes are functionally linked. Here, we identify a signaling pathway that is activated upon accumulation of aggregation-prone proteins in the extracellular space. We find that the transcription factor ATFS-1, which regulates the mitochondrial unfolded protein response, also regulates transcripts required for endosomal recycling, multiple plasma membrane-localized signaling receptors, and secreted proteins that bind aggregation-prone proteins in the extracellular space, including transthyretin and Aβ, and promote their degradation. Interestingly, Aβ(1-42) aggregation induces atfs-1 -dependent transcription by promoting degradation of the bZIP protein ZIP-3, which antagonizes ATFS-1. ZIP-3 accumulates in the cytosol when it is phosphorylated by kinases that function downstream of plasma membrane-localized signaling receptors, including the WNT and glutamate receptors. Upon ligand binding, the signaling receptors stimulate the cognate kinase, many of which we found phosphorylate ZIP-3, impeding ZIP-3 degradation, allowing it to antagonize atfs-1 -dependent transcription. However, accumulation of aggregation-prone proteins such as Aβ(1-42) causes endosomal swelling, which impairs endosomal recycling, instead diverting signaling receptors to lysosomes for degradation. In turn, the depletion of signaling receptors reduces the level of ZIP-3 phosphorylation, resulting in ZIP-3 degradation and activation of atfs-1 -dependent transcription, which promotes extracellular proteostasis. Our findings uncover an unexpected coupling between endocytic quality control and mitochondrial signaling, revealing a circuit that preserves extracellular proteostasis and promotes organismal resilience.