LPD-3 as a megaprotein brake for aging and insulin-mTOR signaling in C. elegans.

Insulin-mechanistic target of rapamycin (mTOR) signaling drives anabolic growth during organismal development; its late-life dysregulation contributes to aging and limits lifespans. Age-related regulatory mechanisms and functional consequences of insulin-mTOR remain incompletely understood. Here, we identify LPD-3 as a megaprotein that orchestrates the tempo of insulin-mTOR signaling during C. elegans aging. We find that an agonist insulin, INS-7, is drastically overproduced from early life and shortens lifespan in lpd-3 mutants. LPD-3 forms a bridge-like tunnel megaprotein to facilitate non-vesicular cellular lipid trafficking. Lipidomic profiling reveals increased hexaceramide species in lpd-3 mutants, accompanied by up-regulation of hexaceramide biosynthetic enzymes, including HYL-1. Reducing the abundance of HYL-1, insulin receptor/DAF-2 or mTOR/LET-363, normalizes INS-7 levels and rescues the lifespan of lpd-3 mutants. LPD-3 antagonizes SINH-1, a key mTORC2 component, and decreases expression with age. We propose that LPD-3 acts as a megaprotein brake for organismal aging and that its age-dependent decline restricts lifespan through the sphingolipid-hexaceramide and insulin-mTOR pathways. [Display omitted] • LPD-3, a megaprotein, regulates insulin-mTOR signaling during C. elegans aging • Agonist insulin INS-7 overproduction in early life shortens lpd-3 mutants' lifespan • LPD-3 aids phospholipid trafficking and appropriate balance with sphingolipids • Hexaceramide abundance, regulated by HYL-1, impacts lifespan via insulin-mTORC2 Pandey et al. identify LPD-3, a bridge-like lipid transfer protein, as a megaprotein "brake" critical for preventing insulin-mTOR hyperfunction during C. elegans aging. The underlying mechanism involves LPD-3's orchestration of the rheostat balance between the phospholipid and hexaceramide species that regulate C. elegans lifespan through the insulin-mTORC2 and mitochondrial pathways. [ABSTRACT FROM AUTHOR]