Lysosomal control of proteostasis and reproductive capacity by conserved LMD-3 protein in <i>C. elegans</i>

Human female fertility declines markedly with age, a pattern mirrored in <i>C. elegans</i> fecundity. This shared vulnerability stems from evolutionarily conserved molecular pathways. A growing body of evidence links impaired proteostasis-the cell's ability to manage its proteins-to this age-related fertility drop in both species, although the underlying mechanisms are not fully understood. Here, we identify that LMD-3, a LysM domain protein, is a critical regulator of proteostasis and reproductive capacity in <i>C. elegans</i>. Deficiency of <i>lmd-3</i> leads to notable defects in oxidation resistance and constitutively high cellular stress responses. We demonstrate that LMD-3, localized to the lysosome, interacts with vitellogenin and a proton-pumping V-type ATPase via its TLDc domain to regulate lysosomal function and maintain yolk protein homeostasis. We also found that supplementing with vitamin B12 can restore fertility in <i>lmd-3</i> mutants by reducing oxidative stress and improving lysosomal function. These findings establish a model for studying reproductive health and finding potential therapeutic strategies.