Iron–sulfur (Fe-S) clusters are ancient cofactors in cells and participate in diverse biochemical functions, including electron transfer and enzymatic catalysis. Although cell lines derived from individuals carrying mutations in the Fe-S cluster biogenesis pathway or siRNA-mediated knockdown of the Fe-S assembly components provide excellent models for investigating Fe-S cluster formation in mammalian cells, these experimental strategies focus on the consequences of prolonged impairment of Fe-S assembly. Here, we constructed and expressed dominant–negative variants of the primary Fe-S biogenesis scaffold protein iron–sulfur cluster assembly enzyme 2 (ISCU2) in human HEK293 cells. This approach enabled us to study the early metabolic reprogramming associated with loss of Fe-S–containing proteins in several major cellular compartments. Using multiple metabolomics platforms, we observed a ∼12-fold increase in intracellular citrate content in Fe-S–deficient cells, a surge that was due to loss of aconitase activity. The excess citrate was generated from glucose-derived acetyl-CoA, and global analysis of cellular lipids revealed that fatty acid biosynthesis increased markedly relative to cellular proliferation rates in Fe-S–deficient cells. We also observed intracellular lipid droplet accumulation in both acutely Fe-S–deficient cells and iron-starved cells. We conclude that deficient Fe-S biogenesis and acute iron deficiency rapidly increase cellular citrate concentrations, leading to fatty acid synthesis and cytosolic lipid droplet formation. Our findings uncover a potential cause of cellular steatosis in nonadipose tissues.
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This work was supported by the NICHD, National Institutes of Health (NIH), Intramural Research Program and the NCI/NIH Center for Cancer Research, NIAMS/NIH Grant R01 AR050597, NIDDK/NIH Grant 1U24DK097215-01A1, and NIEHS/NIH Grant 3R01ES022191-04S1.
NMR spectra were recorded at the Center for Environmental Systems Biochemistry, University of Kentucky, supported in part by NCI, National Institutes of Health, Cancer Center Support Grant P30 CA177558.
This article contains Table S1 and Figs. S1–S6.
Crooks, Daniel R.; Maio, Nunziata; Lane, Andrew N.; Jarnik, Michal; Higashi, Richard M.; Haller, Ronald G.; Yang, Ye; Fan, Teresa Whei-Mei; Linehan, W. Marston; and Rouault, Tracey A., "Acute Loss of Iron-Sulfur Clusters Results in Metabolic Reprogramming and Generation of Lipid Droplets in Mammalian Cells" (2018). Center for Environmental and Systems Biochemistry Faculty Publications. 4.