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Fat body Ire1 regulates lipid homeostasis through the Xbp1s-FoxO axis in Drosophila.

ABSTRACT: The endoplasmic reticulum (ER)-resident transmembrane protein kinase/RNase Ire1 is a conserved sensor of the cellular unfolded protein response and has been implicated in lipid homeostasis, including lipid synthesis and transport, across species. Here we report a novel catabolic role of Ire1 in regulating lipid mobilization in Drosophila. We found that Ire1 is activated by nutrient deprivation, and, importantly, fat body-specific Ire1 deficiency leads to increased lipid mobilization and sensitizes flies to starvation, whereas fat body Ire1 overexpression results in the opposite phenotypes. Genetic interaction and biochemical analyses revealed that Ire1 regulates lipid mobilization by promoting Xbp1s-associated FoxO degradation and suppressing FoxO-dependent lipolytic programs. Our results demonstrate that Ire1 is a catabolic sensor and acts through the Xbp1s-FoxO axis to hamper the lipolytic response during chronic food deprivation. These findings offer new insights into the conserved Ire1 regulation of lipid homeostasis.

SUBMITTER: Zhao P

PROVIDER: S-EPMC8333185 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Phenotypic plasticity, the ability for a single genotype to generate different phenotypes in response to environmental conditions, is biologically ubiquitous, and yet almost nothing is known of the developmental mechanisms that regulate the extent of a plastic response. In particular, it is unclear why some traits or individuals are highly sensitive to an environmental variable while other traits or individuals are less so. Here we elucidate the developmental mechanisms that regulate the expression of a particularly important form of phenotypic plasticity: the effect of developmental nutrition on organ size. In all animals, developmental nutrition is signaled to growing organs via the insulin-signaling pathway. Drosophila organs differ in their size response to developmental nutrition and this reflects differences in organ-specific insulin-sensitivity. We show that this variation in insulin-sensitivity is regulated at the level of the forkhead transcription factor FOXO, a negative growth regulator that is activated when nutrition and insulin signaling are low. Individual organs appear to attenuate growth suppression in response to low nutrition through an organ-specific reduction in FOXO expression, thereby reducing their nutritional plasticity. We show that FOXO expression is necessary to maintain organ-specific differences in nutritional-plasticity and insulin-sensitivity, while organ-autonomous changes in FOXO expression are sufficient to autonomously alter an organ's nutritional-plasticity and insulin-sensitivity. These data identify a gene (FOXO) that modulates a plastic response through variation in its expression. FOXO is recognized as a key player in the response of size, immunity, and longevity to changes in developmental nutrition, stress, and oxygen levels. FOXO may therefore act as a more general regulator of plasticity. These data indicate that the extent of phenotypic plasticity may be modified by changes in the expression of genes involved in signaling environmental information to developmental processes.

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Fat body Ire1 regulates lipid homeostasis through the Xbp1s-FoxO axis in Drosophila.

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