Phosphatidylcholine Extends Lifespan via DAF-16 and Reduces Amyloid-Beta-Induced Toxicity in Caenorhabditis elegans

Abstract

Phosphatidylcholine is one of the major phospholipids comprising cellular membrane and is known to have several health-promoting activities, including the improvement of brain function and liver repair. In this paper, we examine the in vivo effect of dietary supplementation with phosphatidylcholine on the response to environmental stressors and aging in C. elegans. Treatment with phosphatidylcholine significantly increased the survival of worms under oxidative stress conditions. However, there was no significant difference in response to stresses caused by heat shock or ultraviolet irradiation. Oxidative stress is believed to be one of the major causal factors of aging. Then, we examined the effect of phosphatidylcholine on lifespan and age-related physiological changes. Phosphatidylcholine showed a lifespan-extending effect and a reduction in fertility, possibly as a tradeoff for long lifespan. Age-related decline of motility was also significantly delayed by supplementation with phosphatidylcholine. Interestingly, the expressions of well-known longevity-assuring genes, hsp-16.2 and sod-3, were significantly upregulated by dietary intervention with phosphatidylcholine. DAF-16, a transcription factor modulating stress response genes, was accumulated in the nucleus by phosphatidylcholine treatment. Increase of the ROS level with phosphatidylcholine suggests that the antioxidant and lifespan-extending effects are due to the hormetic effect of phosphatidylcholine. Phosphatidylcholine also showed a protective effect against amyloid beta-induced toxicity in Alzheimer's disease model animals. Experiments with long-lived mutants revealed that the lifespan-extending effect of phosphatidylcholine specifically overlapped with that of reduced insulin/IGF-1-like signaling and required DAF-16. These findings showed the antioxidant and antiaging activities of phosphatidylcholine for the first time in vivo. Further studies focusing on the identification of underlying cellular mechanisms involved in the antiaging effect will increase the possibility of using phosphatidylcholine for the development of antiaging therapeutics.

Figure 1

Effect of phosphatidylcholine on resistance to oxidative stress and lifespan. Sixty age-synchronized worms pretreated with phosphatidylcholine were placed under (a) oxidative stress, (b) heat shock, and (c) UV irradiation conditions. Survival of worms was monitored at indicated times after stress. (d) Lifespan was compared between the untreated control and worms treated with phosphatidylcholine. Error bar indicates standard error. PC: phosphatidylcholine.

Figure 2

Effect of phosphatidylcholine on reproduction. (a) Total number of progeny produced during a gravid period was compared between the untreated control and phosphatidylcholine-treated groups. (b) Time course distribution of progeny produced during a gravid period. Number of progeny was recorded every day until there was no progeny produced. Data indicate a mean of 10 individual worms. Error bar indicates standard error. PC: phosphatidylcholine; ^∗statistically significant (P < 0.05).

Figure 3

Effect of phosphatidylcholine on age-related decline in motility. (a) Relative distribution of worms in different locomotive phases was calculated in the untreated control and phosphatidylcholine-treated groups at indicated days. Phase 1, worms moving spontaneously without any stimuli; Phase 2, worms moving the whole body in response to mechanical stimuli; Phase 3, worms moving only the head part in response to mechanical stimuli; (b) the number of trashing was counted individually (n = 15) at indicated days after laying eggs. PC: phosphatidylcholine; ^∗statistically significant (P < 0.05).

Figure 4

Cellular distribution of DAF-16 and GFP expressions of downstream targets of DAF-16. (a) Subcellular localization was classified as three categories: cytosolic, fluorescence was spread in cytosol; intermediate, GFP can be found both in cytosol and nucleus; and nucleus, clear localization of GFP into the nucleus. (b) Relative distribution of DAF-16 was compared between the untreated control and 100 mg/l phosphatidylcholine-treated groups. (c) Age-synchronized 3-day-old worms were treated with each concentration of phosphatidylcholine for 7 d. Then, worms were observed on confocal microscopy. (d) Change in the expression level was determined using a fluorescence multireader. Fluorescence intensity of PC-treated worms is expressed as the ratio of fluorescence intensity determined in the untreated control. Error bar indicates standard error. PC: phosphatidylcholine; ^∗statistically significant (P < 0.05).

Figure 5

Effect of phosphatidylcholine on the cellular ROS level. The cellular ROS level was measured in an individual worm at indicated days after laying eggs. Error bar indicates standard error. PC: phosphatidylcholine; ^∗statistically significant (P < 0.05).

Figure 6

Effect of phosphatidylcholine on Aβ-induced toxicity. (a) Paralyzed worms were counted every hour after human Aβ induction in muscle tissues. (b) Effect of daf-16 knockdown on reduced susceptibility to Aβ-induced toxicity was determined using RNAi. PC: phosphatidylcholine; EV: empty vector.

Figure 7

The underlying mechanism involved in the lifespan-extending effect of phosphatidylcholine. Survival curve was compared between the untreated control and phosphatidylcholine-treated groups in three long-lived mutants, (a) age-1, (b) clk-1, and (c) eat-2. (d) Requirement of DAF-16 on lifespan extension by phosphatidylcholine. EV: empty vector; PC: 100 mg/l of phosphatidylcholine.