Supplementation of OAs ameliorates proteotoxicity and short life span caused by reduced UFA/SFA ratio at low temperatures.

(A) Images of hsp-16.1p::hsp-16.1::GFP [hsp-16.1::GFP] transgenic worms in wild-type and mdt-15(tm2182) [mdt-15(-)] backgrounds at 15 °C on control or OA-containing plates. Scale bar: 200 μm. (B) Quantification of hsp-16.1::GFP treated with OA at 15 °C. Images of the individual worms were obtained separately for the quantification (n ≥ 22 from three independent experiments, two-tailed Student t tests, ***p < 0.001). See S7 Table for the standard deviations of box plot data in this figure. (C) Images of polyQ::YFP (Q35::YFP) transgenic worms treated with OA in wild-type and mdt-15(-) backgrounds at 15 °C. Scale bar: 200 μm. (D) Quantification of the data in panel C (n ≥ 28 from three independent experiments, two-tailed Student t tests, **p < 0.01, ***p < 0.001). The data shown in Fig 6B are used in this panel for comparison. (E) Age-dependent increases in the paralysis of polyQ::YFP transgenic animals in mdt-15(-) and wild-type backgrounds at 15 °C. The transgenic worms were fed with OA for their whole life. The paralysis assays were performed 6 times by two independent researchers. Four repeats were performed with synchronized worms from L1 stage, and the other two repeats were performed with worms treated with OA from eggs. For five out of the six repeats, OA substantially suppressed the accelerated age-dependent paralysis in mdt-15(-) animals that expressed polyQ::YFP (S5 Table) (log-rank test, p = 0.3895 for wild-type control diet versus wild-type OA, p < 0.0001 for mdt-15(-) control diet versus mdt-15(-) OA). (F) Age-dependent increases in the paralysis of Aβ transgenic animals in wild-type and nhr-49(gk405) [nhr-49(-)] backgrounds under control or OA-treated conditions (log-rank test, p = 0.091 for wild-type control diet versus wild-type OA, p < 0.0001 for nhr-49(-) control diet versus nhr-49(-) OA). See S5 Table for statistical analysis and additional repeats of the paralysis assays. (G) Life-span curves of wild-type and mdt-15(-) animals under control or OA-treated conditions at 15 °C. We also showed that OA feeding partially suppressed the defects in the growth of mdt-15(-) animals (S6C Fig). See S4 Table for statistical analysis and additional repeats of the life-span assays and S6 Table for the Cox proportional hazard regression analysis. (H) A schematic model summarizing the current study. At low temperatures, wild-type MDT-15 up-regulates fat-7, which is crucial for maintaining lipidostasis and subsequently proteostasis, which lead to longevity. In mdt-15(-) mutants, the expression of fat-7 is low, and this in turn causes impaired lipidostasis and proteostasis leading to a very short life span at low temperature. GFP, green fluorescent protein; hsp, heat shock protein; MDT-15, Mediator 15; nhr, nuclear hormone receptor; OA, oleic acid; polyQ, polyglutamine; SFA, saturated fatty acid; UFA, unsaturated fatty acid; YFP, yellow fluorescent protein.