Activated SKN-1 alters the aging trajectories of long-lived Caenorhabditis elegans mutants.

In the presence of stressful environments, the SKN-1 cytoprotective transcription factor is activated to induce the expression of gene targets that can restore homeostasis. However, chronic activation of SKN-1 results in diminished health and a reduction of lifespan. Here, we demonstrate the necessity of modulating SKN-1 activity to maintain the longevity-promoting effects associated with genetic mutations that impair daf-2/insulin receptor signaling, the eat-2 model of dietary restriction, and glp-1-dependent loss of germ cell proliferation. A hallmark of animals with constitutive SKN-1 activation is the age-dependent loss of somatic lipids, and this phenotype is linked to a general reduction in survival in animals harboring the skn-1gf allele. Surprisingly, daf-2lf; skn-1gf double mutant animals do not redistribute somatic lipids, which suggests the insulin signaling pathway functions downstream of SKN-1 in the maintenance of lipid distribution. As expected, the eat-2lf allele, which independently activates SKN-1, continues to display somatic lipid depletion in older ages with and without the skn-1gf activating mutation. In contrast, the presence of the skn-1gf allele does not lead to somatic lipid redistribution in glp-1lf animals that lack a proliferating germline. Taken together, these studies support a genetic model where SKN-1 activity is an important regulator of lipid mobilization in response to nutrient availability that fuels the developing germline by engaging the daf-2/insulin receptor pathway.