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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

GSCs inhibit SKN-1 activity in the intestine.(A) Representative images of SKN-1::green fluorescent protein (GFP) in intestinal nuclei; GFP channel (top), bright field (BF; bottom). (B) Accumulation of SKN-1::GFP in intestinal nuclei in GSC(−) animals. (C) skn-1-dependent activation of direct SKN-1 target genes (Robida-Stubbs et al., 2012) in response to GSC absence, detected by qRT-PCR. (D, E) Increased expression of gst-4p::GFP in the intestine of glp-1(ts) animals. Hypodermal gst-4p::GFP expression appeared to be unaffected. (D) Representative 10× images. (E) Intestinal gst-4p::GFP quantification. (F–H) GSCs regulate SKN-1 parallel to DAF-16 and DAF-12. In (H), SKN-1 target genes are assayed by qRT-PCR. glp-1(ts) refers to glp-1(e2141ts), and horizontal black lines indicate strains lacking GSCs. (C, H) Data are represented as mean ± SEM. n = 3 for qRT-PCR samples. (B, E–G) GFP quantification with high, medium, low scoring. Numbers above bars denote sample size. p < 0.05*; p < 0.01**; p < 0.001***.DOI:http://dx.doi.org/10.7554/eLife.07836.006
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fig2: GSCs inhibit SKN-1 activity in the intestine.(A) Representative images of SKN-1::green fluorescent protein (GFP) in intestinal nuclei; GFP channel (top), bright field (BF; bottom). (B) Accumulation of SKN-1::GFP in intestinal nuclei in GSC(−) animals. (C) skn-1-dependent activation of direct SKN-1 target genes (Robida-Stubbs et al., 2012) in response to GSC absence, detected by qRT-PCR. (D, E) Increased expression of gst-4p::GFP in the intestine of glp-1(ts) animals. Hypodermal gst-4p::GFP expression appeared to be unaffected. (D) Representative 10× images. (E) Intestinal gst-4p::GFP quantification. (F–H) GSCs regulate SKN-1 parallel to DAF-16 and DAF-12. In (H), SKN-1 target genes are assayed by qRT-PCR. glp-1(ts) refers to glp-1(e2141ts), and horizontal black lines indicate strains lacking GSCs. (C, H) Data are represented as mean ± SEM. n = 3 for qRT-PCR samples. (B, E–G) GFP quantification with high, medium, low scoring. Numbers above bars denote sample size. p < 0.05*; p < 0.01**; p < 0.001***.DOI:http://dx.doi.org/10.7554/eLife.07836.006

Mentions: We investigated whether the benefits of GSC absence simply require that SKN-1 be present or involve activation of SKN-1. SKN-1 accumulates in intestinal nuclei in response to certain stresses, or inhibition of mechanisms that include IIS, mTORC2, glycogen synthase kinase-3, translation elongation, and the ubiquitin ligase WDR-23 (An and Blackwell, 2003; Tullet et al., 2008; Choe et al., 2009; Park et al., 2009; Li et al., 2011; Robida-Stubbs et al., 2012). The levels of a SKN-1::GFP (green fluorescent protein) fusion in intestinal nuclei were also notably elevated in GSC(−) animals (Figure 2A,B). This was associated with increased expression of direct SKN-1 target genes, apparently through activation of their intestinal expression (Figure 2C–E). The KRI-1/KRIT1 ankyrin repeat protein and the TCER-1/TCERG1 transcription factor are required for GSC absence to induce DAF-16 nuclear accumulation and extend lifespan (Berman and Kenyon, 2006; Ghazi et al., 2009). In contrast, in GSC(−) animals SKN-1 nuclear accumulation was only partially or minimally affected by loss of kri-1 or tcer-1, respectively, but was abolished by knockdown of the pmk-1/p38 kinase (Figure 2F,G), which phosphorylates SKN-1 and under most circumstances is required for SKN-1 nuclear accumulation (Inoue et al., 2005). In GSC(−) animals, DAF-12 is needed for DAF-16 nuclear accumulation and activity (Berman and Kenyon, 2006; Kenyon, 2010; Antebi, 2013), and induces expression of the microRNAs mir-84 and mir-241, which target inhibitors of DAF-16 (Shen et al., 2012). In GSC(−) animals, daf-12 knockdown only mildly affected SKN-1::GFP accumulation (Figure 2G), and SKN-1 target gene induction was generally not impaired by daf-12 or mir-241;mir-84 mutations (Figure 2H). The absence of GSCs therefore activates SKN-1 in the intestine but through a different mechanism from DAF-16.10.7554/eLife.07836.006Figure 2.GSCs inhibit SKN-1 activity in the intestine.


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)

GSCs inhibit SKN-1 activity in the intestine.(A) Representative images of SKN-1::green fluorescent protein (GFP) in intestinal nuclei; GFP channel (top), bright field (BF; bottom). (B) Accumulation of SKN-1::GFP in intestinal nuclei in GSC(−) animals. (C) skn-1-dependent activation of direct SKN-1 target genes (Robida-Stubbs et al., 2012) in response to GSC absence, detected by qRT-PCR. (D, E) Increased expression of gst-4p::GFP in the intestine of glp-1(ts) animals. Hypodermal gst-4p::GFP expression appeared to be unaffected. (D) Representative 10× images. (E) Intestinal gst-4p::GFP quantification. (F–H) GSCs regulate SKN-1 parallel to DAF-16 and DAF-12. In (H), SKN-1 target genes are assayed by qRT-PCR. glp-1(ts) refers to glp-1(e2141ts), and horizontal black lines indicate strains lacking GSCs. (C, H) Data are represented as mean ± SEM. n = 3 for qRT-PCR samples. (B, E–G) GFP quantification with high, medium, low scoring. Numbers above bars denote sample size. p < 0.05*; p < 0.01**; p < 0.001***.DOI:http://dx.doi.org/10.7554/eLife.07836.006
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fig2: GSCs inhibit SKN-1 activity in the intestine.(A) Representative images of SKN-1::green fluorescent protein (GFP) in intestinal nuclei; GFP channel (top), bright field (BF; bottom). (B) Accumulation of SKN-1::GFP in intestinal nuclei in GSC(−) animals. (C) skn-1-dependent activation of direct SKN-1 target genes (Robida-Stubbs et al., 2012) in response to GSC absence, detected by qRT-PCR. (D, E) Increased expression of gst-4p::GFP in the intestine of glp-1(ts) animals. Hypodermal gst-4p::GFP expression appeared to be unaffected. (D) Representative 10× images. (E) Intestinal gst-4p::GFP quantification. (F–H) GSCs regulate SKN-1 parallel to DAF-16 and DAF-12. In (H), SKN-1 target genes are assayed by qRT-PCR. glp-1(ts) refers to glp-1(e2141ts), and horizontal black lines indicate strains lacking GSCs. (C, H) Data are represented as mean ± SEM. n = 3 for qRT-PCR samples. (B, E–G) GFP quantification with high, medium, low scoring. Numbers above bars denote sample size. p < 0.05*; p < 0.01**; p < 0.001***.DOI:http://dx.doi.org/10.7554/eLife.07836.006
Mentions: We investigated whether the benefits of GSC absence simply require that SKN-1 be present or involve activation of SKN-1. SKN-1 accumulates in intestinal nuclei in response to certain stresses, or inhibition of mechanisms that include IIS, mTORC2, glycogen synthase kinase-3, translation elongation, and the ubiquitin ligase WDR-23 (An and Blackwell, 2003; Tullet et al., 2008; Choe et al., 2009; Park et al., 2009; Li et al., 2011; Robida-Stubbs et al., 2012). The levels of a SKN-1::GFP (green fluorescent protein) fusion in intestinal nuclei were also notably elevated in GSC(−) animals (Figure 2A,B). This was associated with increased expression of direct SKN-1 target genes, apparently through activation of their intestinal expression (Figure 2C–E). The KRI-1/KRIT1 ankyrin repeat protein and the TCER-1/TCERG1 transcription factor are required for GSC absence to induce DAF-16 nuclear accumulation and extend lifespan (Berman and Kenyon, 2006; Ghazi et al., 2009). In contrast, in GSC(−) animals SKN-1 nuclear accumulation was only partially or minimally affected by loss of kri-1 or tcer-1, respectively, but was abolished by knockdown of the pmk-1/p38 kinase (Figure 2F,G), which phosphorylates SKN-1 and under most circumstances is required for SKN-1 nuclear accumulation (Inoue et al., 2005). In GSC(−) animals, DAF-12 is needed for DAF-16 nuclear accumulation and activity (Berman and Kenyon, 2006; Kenyon, 2010; Antebi, 2013), and induces expression of the microRNAs mir-84 and mir-241, which target inhibitors of DAF-16 (Shen et al., 2012). In GSC(−) animals, daf-12 knockdown only mildly affected SKN-1::GFP accumulation (Figure 2G), and SKN-1 target gene induction was generally not impaired by daf-12 or mir-241;mir-84 mutations (Figure 2H). The absence of GSCs therefore activates SKN-1 in the intestine but through a different mechanism from DAF-16.10.7554/eLife.07836.006Figure 2.GSCs inhibit SKN-1 activity in the intestine.

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