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Lipid-mediated regulation of SKN-1/Nrf in response to germ cell absence.

Steinbaugh MJ, Narasimhan SD, Robida-Stubbs S, Moronetti Mazzeo LE, Dreyfuss JM, Hourihan JM, Raghavan P, Operaña TN, Esmaillie R, Blackwell TK - Elife (2015)

Bottom Line: Surprisingly, SKN-1 is activated by signals from this fat, which appears to derive from unconsumed yolk that was produced for reproduction.We conclude that SKN-1 plays a direct role in maintaining lipid homeostasis in which it is activated by lipids.This SKN-1 function may explain the importance of mammalian Nrf proteins in fatty liver disease and suggest that particular endogenous or dietary lipids might promote health through SKN-1/Nrf.

View Article: PubMed Central - PubMed

Affiliation: Research Division, Joslin Diabetes Center, Boston, United States.

ABSTRACT
In Caenorhabditis elegans, ablation of germline stem cells (GSCs) extends lifespan, but also increases fat accumulation and alters lipid metabolism, raising the intriguing question of how these effects might be related. Here, we show that a lack of GSCs results in a broad transcriptional reprogramming in which the conserved detoxification regulator SKN-1/Nrf increases stress resistance, proteasome activity, and longevity. SKN-1 also activates diverse lipid metabolism genes and reduces fat storage, thereby alleviating the increased fat accumulation caused by GSC absence. Surprisingly, SKN-1 is activated by signals from this fat, which appears to derive from unconsumed yolk that was produced for reproduction. We conclude that SKN-1 plays a direct role in maintaining lipid homeostasis in which it is activated by lipids. This SKN-1 function may explain the importance of mammalian Nrf proteins in fatty liver disease and suggest that particular endogenous or dietary lipids might promote health through SKN-1/Nrf.

No MeSH data available.


Related in: MedlinePlus

Analysis of the intestinal lipid droplet marker DHS-3::GFP, and TAG levels.skn-1 RNAi increases DHS-3::GFP intensity in both wild-type and GSC(−) animals, whereas sbp-1 RNAi decreases DHS-3::GFP intensity. (A) 10× slide-mounted DHS-3::GFP images. White arrows indicate intestine-specific expression. (B, C) COPAS Biosorter quantification of DHS-3::GFP in live day-1 adult worms. (B) Representative 10× inverted scope images of worms suspended in M9 buffer used for COPAS scoring. (C) Graph of mean DHS-3::GFP fluorescence, assayed by COPAS. Numbers above bars denote sample size. Asterisks directly above bars indicate p values relative to WT or RNAi control. Asterisks above black lines denote effect of RNAi in glp-1(ts) background. RNAi was started from egg stage, and animals were raised at 25°C. (D) TAG levels are significantly elevated in skn-1 mutants. Data are represented as mean ± SEM. p < 0.01**; p < 0.001***.DOI:http://dx.doi.org/10.7554/eLife.07836.013
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fig5s2: Analysis of the intestinal lipid droplet marker DHS-3::GFP, and TAG levels.skn-1 RNAi increases DHS-3::GFP intensity in both wild-type and GSC(−) animals, whereas sbp-1 RNAi decreases DHS-3::GFP intensity. (A) 10× slide-mounted DHS-3::GFP images. White arrows indicate intestine-specific expression. (B, C) COPAS Biosorter quantification of DHS-3::GFP in live day-1 adult worms. (B) Representative 10× inverted scope images of worms suspended in M9 buffer used for COPAS scoring. (C) Graph of mean DHS-3::GFP fluorescence, assayed by COPAS. Numbers above bars denote sample size. Asterisks directly above bars indicate p values relative to WT or RNAi control. Asterisks above black lines denote effect of RNAi in glp-1(ts) background. RNAi was started from egg stage, and animals were raised at 25°C. (D) TAG levels are significantly elevated in skn-1 mutants. Data are represented as mean ± SEM. p < 0.01**; p < 0.001***.DOI:http://dx.doi.org/10.7554/eLife.07836.013

Mentions: Given that SKN-1 increases both lifespan and stress resistance in GSC(−) animals, its effects on lipid metabolism should also be beneficial. If the elevated fat storage in GSC(−) animals reflects simply elevated production and storage of ‘good’ lipids, we might expect skn-1 to support this fat production. We investigated whether SKN-1 affects fat storage in WT and GSC(−) animals by oil red O (ORO) staining of fixed animals, a method that reliably indicates fat accumulation (O'Rourke et al., 2009). Remarkably, ablation of skn-1 by either mutation or RNAi significantly increased lipid levels in either WT or GSC(−) day-1 adults, so that glp-1(ts);skn-1(−) animals exhibited markedly high levels of ORO staining (Figure 5B,C, and Figure 5—figure supplement 1A,B). As an independent method of assessing fat accumulation in the intestine, we examined levels of the predicted short-chain FA dehydrogenase DHS-3 (Zhang et al., 2012). Proteomic and microscopy analyses have shown that DHS-3 localizes almost exclusively to intestinal lipid droplets (Figure 5—figure supplement 2A) and marks the vast majority of these lipid droplets in vivo (Zhang et al., 2012; Na et al., 2015). Consistent with ORO staining, lack of skn-1 increased accumulation of a DHS-3::GFP fusion in the intestine in WT and GSC(−) animals, without affecting expression of the dhs-3 mRNA (Figure 5—figure supplements 2B,C, 3). An analysis of total triglyceride levels also indicated that SKN-1 reduces the overall level of fat accumulation (Figure 5—figure supplement 2D).


Lipid-mediated regulation of SKN-1/Nrf in response to germ cell absence.

Steinbaugh MJ, Narasimhan SD, Robida-Stubbs S, Moronetti Mazzeo LE, Dreyfuss JM, Hourihan JM, Raghavan P, Operaña TN, Esmaillie R, Blackwell TK - Elife (2015)

Analysis of the intestinal lipid droplet marker DHS-3::GFP, and TAG levels.skn-1 RNAi increases DHS-3::GFP intensity in both wild-type and GSC(−) animals, whereas sbp-1 RNAi decreases DHS-3::GFP intensity. (A) 10× slide-mounted DHS-3::GFP images. White arrows indicate intestine-specific expression. (B, C) COPAS Biosorter quantification of DHS-3::GFP in live day-1 adult worms. (B) Representative 10× inverted scope images of worms suspended in M9 buffer used for COPAS scoring. (C) Graph of mean DHS-3::GFP fluorescence, assayed by COPAS. Numbers above bars denote sample size. Asterisks directly above bars indicate p values relative to WT or RNAi control. Asterisks above black lines denote effect of RNAi in glp-1(ts) background. RNAi was started from egg stage, and animals were raised at 25°C. (D) TAG levels are significantly elevated in skn-1 mutants. Data are represented as mean ± SEM. p < 0.01**; p < 0.001***.DOI:http://dx.doi.org/10.7554/eLife.07836.013
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Related In: Results  -  Collection

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fig5s2: Analysis of the intestinal lipid droplet marker DHS-3::GFP, and TAG levels.skn-1 RNAi increases DHS-3::GFP intensity in both wild-type and GSC(−) animals, whereas sbp-1 RNAi decreases DHS-3::GFP intensity. (A) 10× slide-mounted DHS-3::GFP images. White arrows indicate intestine-specific expression. (B, C) COPAS Biosorter quantification of DHS-3::GFP in live day-1 adult worms. (B) Representative 10× inverted scope images of worms suspended in M9 buffer used for COPAS scoring. (C) Graph of mean DHS-3::GFP fluorescence, assayed by COPAS. Numbers above bars denote sample size. Asterisks directly above bars indicate p values relative to WT or RNAi control. Asterisks above black lines denote effect of RNAi in glp-1(ts) background. RNAi was started from egg stage, and animals were raised at 25°C. (D) TAG levels are significantly elevated in skn-1 mutants. Data are represented as mean ± SEM. p < 0.01**; p < 0.001***.DOI:http://dx.doi.org/10.7554/eLife.07836.013
Mentions: Given that SKN-1 increases both lifespan and stress resistance in GSC(−) animals, its effects on lipid metabolism should also be beneficial. If the elevated fat storage in GSC(−) animals reflects simply elevated production and storage of ‘good’ lipids, we might expect skn-1 to support this fat production. We investigated whether SKN-1 affects fat storage in WT and GSC(−) animals by oil red O (ORO) staining of fixed animals, a method that reliably indicates fat accumulation (O'Rourke et al., 2009). Remarkably, ablation of skn-1 by either mutation or RNAi significantly increased lipid levels in either WT or GSC(−) day-1 adults, so that glp-1(ts);skn-1(−) animals exhibited markedly high levels of ORO staining (Figure 5B,C, and Figure 5—figure supplement 1A,B). As an independent method of assessing fat accumulation in the intestine, we examined levels of the predicted short-chain FA dehydrogenase DHS-3 (Zhang et al., 2012). Proteomic and microscopy analyses have shown that DHS-3 localizes almost exclusively to intestinal lipid droplets (Figure 5—figure supplement 2A) and marks the vast majority of these lipid droplets in vivo (Zhang et al., 2012; Na et al., 2015). Consistent with ORO staining, lack of skn-1 increased accumulation of a DHS-3::GFP fusion in the intestine in WT and GSC(−) animals, without affecting expression of the dhs-3 mRNA (Figure 5—figure supplements 2B,C, 3). An analysis of total triglyceride levels also indicated that SKN-1 reduces the overall level of fat accumulation (Figure 5—figure supplement 2D).

Bottom Line: Surprisingly, SKN-1 is activated by signals from this fat, which appears to derive from unconsumed yolk that was produced for reproduction.We conclude that SKN-1 plays a direct role in maintaining lipid homeostasis in which it is activated by lipids.This SKN-1 function may explain the importance of mammalian Nrf proteins in fatty liver disease and suggest that particular endogenous or dietary lipids might promote health through SKN-1/Nrf.

View Article: PubMed Central - PubMed

Affiliation: Research Division, Joslin Diabetes Center, Boston, United States.

ABSTRACT
In Caenorhabditis elegans, ablation of germline stem cells (GSCs) extends lifespan, but also increases fat accumulation and alters lipid metabolism, raising the intriguing question of how these effects might be related. Here, we show that a lack of GSCs results in a broad transcriptional reprogramming in which the conserved detoxification regulator SKN-1/Nrf increases stress resistance, proteasome activity, and longevity. SKN-1 also activates diverse lipid metabolism genes and reduces fat storage, thereby alleviating the increased fat accumulation caused by GSC absence. Surprisingly, SKN-1 is activated by signals from this fat, which appears to derive from unconsumed yolk that was produced for reproduction. We conclude that SKN-1 plays a direct role in maintaining lipid homeostasis in which it is activated by lipids. This SKN-1 function may explain the importance of mammalian Nrf proteins in fatty liver disease and suggest that particular endogenous or dietary lipids might promote health through SKN-1/Nrf.

No MeSH data available.


Related in: MedlinePlus