ER remodelling is a feature of ageing and depends on ER-phagy.

The endoplasmic reticulum (ER) comprises an array of subdomains, each defined by a characteristic structure and function. Although altered ER processes are linked to age-onset pathogenesis, it is unclear whether shifts in ER structure or dynamics underlie these functional changes. Here we establish ER structural and functional remodelling as a conserved feature of ageing across yeast, Caenorhabditis elegans and mammals. Focusing on C. elegans as the exemplar of metazoan ageing, we reveal striking age-related reductions in ER volume across diverse tissues and a morphological shift from rough sheets to tubular ER. This morphological transition corresponds with large-scale shifts in ER proteome composition from protein synthesis to lipid metabolism, a phenomenon conserved in mammalian tissues. We show that Atg8 and ULK1-dependent ER-phagy drives age-associated ER remodelling through tissue-specific factors, including the previously uncharacterized ER-phagy regulator TMEM-131 and the IRE-1-XBP-1 branch of the unfolded protein response. Providing support for a model where ER remodelling is adaptive, diverse lifespan-extending paradigms downscale and remodel ER morphology throughout life. Furthermore, mTOR-dependent lifespan extension in yeast and worms requires ER-phagy, indicating that ER remodelling is a proactive and protective response during ageing. These results reveal ER-phagy and ER dynamics as pronounced, underappreciated mechanisms of both normal ageing and age-delaying interventions.