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Control of metabolic homeostasis by stress signaling is mediated by the lipocalin NLaz.

Hull-Thompson J, Muffat J, Sanchez D, Walker DW, Benzer S, Ganfornina MD, Jasper H - PLoS Genet. (2009)

Bottom Line: Loss of NLaz function reduces stress resistance and lifespan, while its over-expression represses growth, promotes stress tolerance and extends lifespan--phenotypes that are consistent with reduced IIS activity.Our results show that JNK-NLaz signaling antagonizes IIS and is critical for metabolic adaptation of the organism to environmental challenges.The JNK pathway and Lipocalins are structurally and functionally conserved, suggesting that similar interactions represent an evolutionarily conserved system for the control of metabolic homeostasis.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, University of Rochester, Rochester, New York, United States of America.

ABSTRACT
Metabolic homeostasis in metazoans is regulated by endocrine control of insulin/IGF signaling (IIS) activity. Stress and inflammatory signaling pathways--such as Jun-N-terminal Kinase (JNK) signaling--repress IIS, curtailing anabolic processes to promote stress tolerance and extend lifespan. While this interaction constitutes an adaptive response that allows managing energy resources under stress conditions, excessive JNK activity in adipose tissue of vertebrates has been found to cause insulin resistance, promoting type II diabetes. Thus, the interaction between JNK and IIS has to be tightly regulated to ensure proper metabolic adaptation to environmental challenges. Here, we identify a new regulatory mechanism by which JNK influences metabolism systemically. We show that JNK signaling is required for metabolic homeostasis in flies and that this function is mediated by the Drosophila Lipocalin family member Neural Lazarillo (NLaz), a homologue of vertebrate Apolipoprotein D (ApoD) and Retinol Binding Protein 4 (RBP4). Lipocalins are emerging as central regulators of peripheral insulin sensitivity and have been implicated in metabolic diseases. NLaz is transcriptionally regulated by JNK signaling and is required for JNK-mediated stress and starvation tolerance. Loss of NLaz function reduces stress resistance and lifespan, while its over-expression represses growth, promotes stress tolerance and extends lifespan--phenotypes that are consistent with reduced IIS activity. Accordingly, we find that NLaz represses IIS activity in larvae and adult flies. Our results show that JNK-NLaz signaling antagonizes IIS and is critical for metabolic adaptation of the organism to environmental challenges. The JNK pathway and Lipocalins are structurally and functionally conserved, suggesting that similar interactions represent an evolutionarily conserved system for the control of metabolic homeostasis.

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NLaz antagonizes IIS in larvae.(A–C) tGPH fluorescence [50] in larval fatbodies. (A) NLazCNW14/CNW14. (B) NLazNW5/NW5. Membrane localization of tGPH is increased in NLaz mutants compared to isogenic wild-type controls, indicating elevated PI3K activity. (C) Ratios of average membrane vs. nuclear fluorescence as determined using NIH ImageJ on images of fatbody cells of independent individuals. n = 6 for NLazCNW14/CNW14, n = 10 for NLazNW5/NW5. P value from Student's T test. (D) NLaz mutant third-instar larvae (homozygotes for NLazNW5/NW5) exhibit strongly decreased Glycogen stores compared to isogenic wild-type controls (NLazCNW14/CNW14). Glucose and Triglyceride levels do not differ in wild-type or NLaz mutant larvae. (E) Established Foxo target genes are induced in response to NLaz overexpression in the larval fatbody. Real-time PCR was performed to quantify dInR, dLip4, and hsp22 transcript levels in extracts of whole third-instar larvae. Transcript levels were normalized to actin5C and ratios of transcript levels in NLaz expressing larvae (pplG4/pplG4,tubGal80ts; UASNLaz/+) and in wildtype controls (pplG4/pplG4, tubGal80ts; +/+) are shown for control conditions (18°C) and after heat-shock. p-values from Student's Ttest. (F) Over-expression of NLaz in the fatbody results in elevated hemolymph glucose levels. Experiments were performed in larvae of the following genotypes: pplG4/+;+/+; pplG4/+; UASNlaz/+. (G) Comparison of adult sibling males of the following genotypes, reared at 29°C: pplG4; +/+. pplG4,NLazNW5/NW5;+/+; pplG4,NLazNW5/NW5;UASNlaz/+. Overall weight is increased in NLaz mutants. Size is decreased again in animals over-expressing NLaz in the fatbody. Fresh weight of males of the indicated genotypes.
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pgen-1000460-g006: NLaz antagonizes IIS in larvae.(A–C) tGPH fluorescence [50] in larval fatbodies. (A) NLazCNW14/CNW14. (B) NLazNW5/NW5. Membrane localization of tGPH is increased in NLaz mutants compared to isogenic wild-type controls, indicating elevated PI3K activity. (C) Ratios of average membrane vs. nuclear fluorescence as determined using NIH ImageJ on images of fatbody cells of independent individuals. n = 6 for NLazCNW14/CNW14, n = 10 for NLazNW5/NW5. P value from Student's T test. (D) NLaz mutant third-instar larvae (homozygotes for NLazNW5/NW5) exhibit strongly decreased Glycogen stores compared to isogenic wild-type controls (NLazCNW14/CNW14). Glucose and Triglyceride levels do not differ in wild-type or NLaz mutant larvae. (E) Established Foxo target genes are induced in response to NLaz overexpression in the larval fatbody. Real-time PCR was performed to quantify dInR, dLip4, and hsp22 transcript levels in extracts of whole third-instar larvae. Transcript levels were normalized to actin5C and ratios of transcript levels in NLaz expressing larvae (pplG4/pplG4,tubGal80ts; UASNLaz/+) and in wildtype controls (pplG4/pplG4, tubGal80ts; +/+) are shown for control conditions (18°C) and after heat-shock. p-values from Student's Ttest. (F) Over-expression of NLaz in the fatbody results in elevated hemolymph glucose levels. Experiments were performed in larvae of the following genotypes: pplG4/+;+/+; pplG4/+; UASNlaz/+. (G) Comparison of adult sibling males of the following genotypes, reared at 29°C: pplG4; +/+. pplG4,NLazNW5/NW5;+/+; pplG4,NLazNW5/NW5;UASNlaz/+. Overall weight is increased in NLaz mutants. Size is decreased again in animals over-expressing NLaz in the fatbody. Fresh weight of males of the indicated genotypes.

Mentions: To test this notion, we asked whether NLaz would affect other IIS-regulated processes in the fly. Indeed, we found elevated membrane localization of the reporter for PI3K activity, GFP-PH, in fatbody cells of NLaz mutant larvae, suggesting that Insulin signaling is increased in these cells in the absence of NLaz (Figure 6A–C; PI3K activity is indicative of Insulin signaling activity in flies and GFP-PH is widely used as a reliable reporter for this activity [50]). These larvae exhibited similar, albeit less general metabolic defects as adult NLaz mutants, with unaffected Glucose and Triglyceride levels, but complete loss of Glycogen stores (Figure 6D).


Control of metabolic homeostasis by stress signaling is mediated by the lipocalin NLaz.

Hull-Thompson J, Muffat J, Sanchez D, Walker DW, Benzer S, Ganfornina MD, Jasper H - PLoS Genet. (2009)

NLaz antagonizes IIS in larvae.(A–C) tGPH fluorescence [50] in larval fatbodies. (A) NLazCNW14/CNW14. (B) NLazNW5/NW5. Membrane localization of tGPH is increased in NLaz mutants compared to isogenic wild-type controls, indicating elevated PI3K activity. (C) Ratios of average membrane vs. nuclear fluorescence as determined using NIH ImageJ on images of fatbody cells of independent individuals. n = 6 for NLazCNW14/CNW14, n = 10 for NLazNW5/NW5. P value from Student's T test. (D) NLaz mutant third-instar larvae (homozygotes for NLazNW5/NW5) exhibit strongly decreased Glycogen stores compared to isogenic wild-type controls (NLazCNW14/CNW14). Glucose and Triglyceride levels do not differ in wild-type or NLaz mutant larvae. (E) Established Foxo target genes are induced in response to NLaz overexpression in the larval fatbody. Real-time PCR was performed to quantify dInR, dLip4, and hsp22 transcript levels in extracts of whole third-instar larvae. Transcript levels were normalized to actin5C and ratios of transcript levels in NLaz expressing larvae (pplG4/pplG4,tubGal80ts; UASNLaz/+) and in wildtype controls (pplG4/pplG4, tubGal80ts; +/+) are shown for control conditions (18°C) and after heat-shock. p-values from Student's Ttest. (F) Over-expression of NLaz in the fatbody results in elevated hemolymph glucose levels. Experiments were performed in larvae of the following genotypes: pplG4/+;+/+; pplG4/+; UASNlaz/+. (G) Comparison of adult sibling males of the following genotypes, reared at 29°C: pplG4; +/+. pplG4,NLazNW5/NW5;+/+; pplG4,NLazNW5/NW5;UASNlaz/+. Overall weight is increased in NLaz mutants. Size is decreased again in animals over-expressing NLaz in the fatbody. Fresh weight of males of the indicated genotypes.
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Related In: Results  -  Collection

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pgen-1000460-g006: NLaz antagonizes IIS in larvae.(A–C) tGPH fluorescence [50] in larval fatbodies. (A) NLazCNW14/CNW14. (B) NLazNW5/NW5. Membrane localization of tGPH is increased in NLaz mutants compared to isogenic wild-type controls, indicating elevated PI3K activity. (C) Ratios of average membrane vs. nuclear fluorescence as determined using NIH ImageJ on images of fatbody cells of independent individuals. n = 6 for NLazCNW14/CNW14, n = 10 for NLazNW5/NW5. P value from Student's T test. (D) NLaz mutant third-instar larvae (homozygotes for NLazNW5/NW5) exhibit strongly decreased Glycogen stores compared to isogenic wild-type controls (NLazCNW14/CNW14). Glucose and Triglyceride levels do not differ in wild-type or NLaz mutant larvae. (E) Established Foxo target genes are induced in response to NLaz overexpression in the larval fatbody. Real-time PCR was performed to quantify dInR, dLip4, and hsp22 transcript levels in extracts of whole third-instar larvae. Transcript levels were normalized to actin5C and ratios of transcript levels in NLaz expressing larvae (pplG4/pplG4,tubGal80ts; UASNLaz/+) and in wildtype controls (pplG4/pplG4, tubGal80ts; +/+) are shown for control conditions (18°C) and after heat-shock. p-values from Student's Ttest. (F) Over-expression of NLaz in the fatbody results in elevated hemolymph glucose levels. Experiments were performed in larvae of the following genotypes: pplG4/+;+/+; pplG4/+; UASNlaz/+. (G) Comparison of adult sibling males of the following genotypes, reared at 29°C: pplG4; +/+. pplG4,NLazNW5/NW5;+/+; pplG4,NLazNW5/NW5;UASNlaz/+. Overall weight is increased in NLaz mutants. Size is decreased again in animals over-expressing NLaz in the fatbody. Fresh weight of males of the indicated genotypes.
Mentions: To test this notion, we asked whether NLaz would affect other IIS-regulated processes in the fly. Indeed, we found elevated membrane localization of the reporter for PI3K activity, GFP-PH, in fatbody cells of NLaz mutant larvae, suggesting that Insulin signaling is increased in these cells in the absence of NLaz (Figure 6A–C; PI3K activity is indicative of Insulin signaling activity in flies and GFP-PH is widely used as a reliable reporter for this activity [50]). These larvae exhibited similar, albeit less general metabolic defects as adult NLaz mutants, with unaffected Glucose and Triglyceride levels, but complete loss of Glycogen stores (Figure 6D).

Bottom Line: Loss of NLaz function reduces stress resistance and lifespan, while its over-expression represses growth, promotes stress tolerance and extends lifespan--phenotypes that are consistent with reduced IIS activity.Our results show that JNK-NLaz signaling antagonizes IIS and is critical for metabolic adaptation of the organism to environmental challenges.The JNK pathway and Lipocalins are structurally and functionally conserved, suggesting that similar interactions represent an evolutionarily conserved system for the control of metabolic homeostasis.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, University of Rochester, Rochester, New York, United States of America.

ABSTRACT
Metabolic homeostasis in metazoans is regulated by endocrine control of insulin/IGF signaling (IIS) activity. Stress and inflammatory signaling pathways--such as Jun-N-terminal Kinase (JNK) signaling--repress IIS, curtailing anabolic processes to promote stress tolerance and extend lifespan. While this interaction constitutes an adaptive response that allows managing energy resources under stress conditions, excessive JNK activity in adipose tissue of vertebrates has been found to cause insulin resistance, promoting type II diabetes. Thus, the interaction between JNK and IIS has to be tightly regulated to ensure proper metabolic adaptation to environmental challenges. Here, we identify a new regulatory mechanism by which JNK influences metabolism systemically. We show that JNK signaling is required for metabolic homeostasis in flies and that this function is mediated by the Drosophila Lipocalin family member Neural Lazarillo (NLaz), a homologue of vertebrate Apolipoprotein D (ApoD) and Retinol Binding Protein 4 (RBP4). Lipocalins are emerging as central regulators of peripheral insulin sensitivity and have been implicated in metabolic diseases. NLaz is transcriptionally regulated by JNK signaling and is required for JNK-mediated stress and starvation tolerance. Loss of NLaz function reduces stress resistance and lifespan, while its over-expression represses growth, promotes stress tolerance and extends lifespan--phenotypes that are consistent with reduced IIS activity. Accordingly, we find that NLaz represses IIS activity in larvae and adult flies. Our results show that JNK-NLaz signaling antagonizes IIS and is critical for metabolic adaptation of the organism to environmental challenges. The JNK pathway and Lipocalins are structurally and functionally conserved, suggesting that similar interactions represent an evolutionarily conserved system for the control of metabolic homeostasis.

Show MeSH
Related in: MedlinePlus