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Cell Metab. 2009 May;9(5):440-8. doi: 10.1016/j.cmet.2009.04.004.

IRE-1 and HSP-4 contribute to energy homeostasis via fasting-induced lipases in C. elegans.

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Research Center for Functional Cellulomics, Department of Biological Sciences, Seoul National University, Seoul, Korea.


The endoplasmic reticulum (ER) is an organelle associated with lipid metabolism. However, the involvement of the ER in nutritional status-dependent energy homeostasis is largely unknown. We demonstrate that IRE-1, an ER protein known to be involved in the unfolded protein response, and HSP-4, an ER chaperone, regulate expression of the novel fasting-induced lipases FIL-1 and FIL-2, which induce fat granule hydrolysis upon fasting in C. elegans. RNAi and ectopic expression experiments demonstrated that FIL-1 and FIL-2 are both necessary and sufficient for fasting-induced fat granule breakdown. Failure of ire-1 and hsp-4 mutant animals to hydrolyze fat granules during starvation impaired their motility, which was rescued by glucose supplementation, implicating the importance of ire-1/hsp-4-dependent lipolysis for energy supply from stored fat during fasting. These data suggest that the ER-resident proteins IRE-1 and HSP-4 are key nutritional sensors that modulate expression of inducible lipases to maintain whole-body energy homeostasis in C. elegans.

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