Author response: Ferredoxin 1 is essential for embryonic development and lipid homeostasis
Year: 2023
Type: peer-review
Abstract: Full text Figures and data Side by side Abstract Editor's evaluation Introduction Results Discussion Materials and methods Data availability References Decision letter Author response Article and author information Metrics Abstract Mammalian ferredoxin 1 and 2 (FDX1/2) belong to an evolutionary conserved family of iron-sulfur cluster containing proteins and act as electron shutters between ferredoxin reductase (FDXR) and numerous proteins involved in critical biological pathways. FDX1 is involved in biogenesis of steroids and bile acids, Vitamin A/D metabolism, and lipoylation of tricarboxylic acid (TCA) cycle enzymes. FDX1 has been extensively characterized biochemically but its role in physiology and lipid metabolism has not been explored. In this study, we generated Fdx1-deficient mice and showed that knockout of both alleles of the Fdx1 gene led to embryonic lethality. We also showed that like Fdxr+/-+/-, Fdx1+/-+/- had a shorter life span and were prone to steatohepatitis. However, unlike Fdxr+/-+/-, Fdx1+/-+/- were not prone to spontaneous tumors. Additionally, we showed that FDX1 deficiency led to lipid droplet accumulation possibly via the ABCA1-SREBP1/2 pathway. Specifically, untargeted lipidomic analysis showed that FDX1 deficiency led to alterations in several classes of lipids, including cholesterol, triacylglycerides, acylcarnitines, ceramides, phospholipids and lysophospholipids. Taken together, our data indicate that FDX1 is essential for mammalian embryonic development and lipid homeostasis at both cellular and organismal levels. Editor's evaluation The findings provided by Mohibi et al. are important to the field of lipid metabolism and cancer and provide insight for an in vivo role of FDX1. The evidence is solid, utilizing multiple modalities and both in vitro and in vivo lines of investigation. https://doi.org/10.7554/eLife.91656.sa0 Decision letter Reviews on Sciety eLife's review process Introduction Ferredoxin (FDX) proteins are a family of redox proteins present in all branches of life (Schulz et al., 2023). They contain iron-sulfur (Fe-S) clusters that aid in their function of transferring electrons from NADPH via ferredoxin reductase (FDXR) to systems involved in various biological processes including iron sulfur (Fe-S) cluster synthesis, steroidogenesis, bile acid production and vitamin metabolism. Mammalian cells contain two ferredoxins, FDX1 and FDX2, both of which are localized to mitochondria (Sheftel et al., 2010). Although they have high homology in primary and three-dimensional structures, they differ significantly in their substrate identity and function (Schulz et al., 2023). FDX2 is critical in the formation of Fe-S clusters in mitochondria by donating electrons to iron sulfur cluster assembly complex (Schulz et al., 2023). FDX1, on the other hand, donates its electrons to various cytochrome p450 systems present in mitochondria and is involved in production of steroid hormones from cholesterol (steroidogenesis), bile acid production, addition of heme α to Cytochrome c as well as Vitamin A/D metabolism (Schulz et al., 2023). Recently, FDX1 has been shown to regulate the process of lipoylation of tricarboxylic acid (TCA) cycle enzymes, especially pyruvate dehydrogenase (PDH) and a-ketoglutarate dehydrogenase (Schulz et al., 2023 ; Tsvetkov et al., 2022). Lipoylation is essential for the function of these enzymes. Moreover, FDX1 has emerged as the central player in the regulation of a new form of cell death, called cuproptosis (Tsvetkov et al., 2022; Tsvetkov et al., 2019). Lipids consist of a myriad group of biomolecules essential for various cellular processes, including membrane formation, energy storage and cellular signaling pathways (Snaebjornsson et al., 2020). Some vital lipids, such as triaclyglycerides (TAGs), cholesterol, cardiolipins (CLs) and phospholipids, are essential for cell survival. Due to the essential role of lipids in maintaining normal physiology, aberrant lipid homeostasis has been involved in various disease pathologies, including cancer, neurodegeneration, and cardiovascular diseases (Broadfield et al., 2021; Hoy et al., 2021; Snaebjornsson et al., 2020). Altered lipid metabolism is also linked with systemic inflammation and non-alcoholic steatohepatitis (NASH) (Carotti et al., 2020; Hoy et al., 2021; Pei et al., 2020; Singla et al., 2010). SREBP1/2 are considered master regulators of lipid metabolism and often associated with altered lipid homeostasis (Osborne and Espenshade, 2009; Shao and Espenshade, 2012). In physiological conditions, when intracellular cholesterol levels are depleted, SREBP1/2 are activated through the release of their N-terminal domains by proteolytic cleavage. The N-terminal domains are then translocated to nucleus where a set of genes involved in lipid metabolism are induced by SREBP1/2 (Osborne and Espenshade, 2009; Shao and Espenshade, 2012). However, in diseased conditions, SREBP1/2 are constitutively activated via various mechanisms, resulting in abnormal lipid production and accumulation (Osborne and Espenshade, 2009; Shao and Espenshade, 2012). SREBP1 is expressed as two isoforms, SREBP 1 a and 1 c, both of which are transcribed from the SREBF1 gene but through two separate promoters. SREBP-2 is encoded by the SREBF2 gene. SREBP-1c preferentially regulates genes for synthesis of fatty acids (FAs) and TAGs whereas SREBP-2 preferentially regulates genes for cholesterol synthetic pathway, including the mevalonate pathway (Brown and Goldstein, 1997). SREBP-1a has overlapping functions with both SREBP-1c and SREBP-2. FDXR transfers electrons from NADPH to FDX1, which then delivers the electrons to either COX15, lipoyl synthase or seven different mitochondrial cytochromes, thus supporting the biosynthesis of heme α, lipoic acid, steroid hormones, bile acid, and Vitamin A/D metabolism (Schulz et al., 2023). We previously showed an essential role of FDXR in mammalian embryonic development and lipid metabolism (Zhang et al., 2022; Zhang et al., 2017). As FDX1 is a substrate of FDXR in regulating steroidogenesis, we asked whether FDX1 is necessary for mammalian embryonic development and lipid metabolism. We showed that mice homozygous for Fdx1 deletion are embryonically lethal at embryonic day 10.5 (E10.5). We also showed that Fdx1+/- +/- have a short life span and are prone to steatohepatitis, but not to spontaneous tumors. Like FDXR, FDX1 was found to regulate lipid metabolism due to increased activation of the SREBP1/2 pathways. Moreover, untargeted lipidomic analysis showed that FDX1 loss leads to alterations in several classes of lipids. Results Fdx1-/- embryos die between E10.5 and E13.5 Although FDX1 has been extensively studied biochemically, its role in development and physiology has been unexplored. To determine physiological function of FDX1, we generated Fdx1 heterozygous mice using the knock-out first approach (Figure 1A and B). The Fdx1+/- +/- developed normally and were fertile. However, inter-breeding of Fdx1+/- +/- to obtain Fdx1-/- mice was unsuccessful. Out of the 67 pups obtained from the Fdx1+/- +/- inter-breeding, none were of the Fdx1-/- genotype (Figure 1C), suggesting complete loss of Fdx1 leads to embryonic lethality. To determine at what developmental stage the embryonic lethality occurs, we isolated embryos following timed pregnancies. We did not find any Fdx1-/- embryos at embryonic day 13.5 (E13.5) but found one at E10.5 (Figure 1C), suggesting Fdx1-KO is lethal for embryos between E10.5-E13.5. Although, the size of WT and Fdx1+/- +/- at E10.5 was comparable, Fdx1-/- embryos were small and abnormal (Figure 1D and E). Interestingly, this embryonic lethality is commensurate with that observed with the embryonic lethality of Fdxr-KO at E8.5 (Zhang et al., 2017). These results suggest that Fdx1 and Fdxr regulate similar processes required for mammalian embryonic development and survival. Figure 1 Download asset Open asset Fdx1 knock-out mouse are embryonically lethal. (A) Schematic diagram of the targeted Fdx1 gene locus and the cassette used to target the locus using a knock-out first approach. (B) Representative image of a PCR gel used to genotype WT and Fdx1+/- +/-. (C) The number and % of embryos and live off-springs from the intercrosses of Fdx1+/- +/-. (D) Representative images of WT, Fdx1+/-, and Fdx1-/- embryos obtained at embryonic day 10.5. The white dots seen in the pictures are the result of light reflection while taking the photos. (E) Agarose gel image of a PCR used to genotype WT, Fdx1+/-, and Fdx1-/- embryos shown in (D). Figure 1—source data 1 Unedited DNA gel images for Figure 1B and E. https://cdn.elifesciences.org/articles/91656/elife-91656-fig1-data1-v2.pdf Download elife-91656-fig1-data1-v2.pdf Mice deficient in Fdx1 have shorter lifespan and are prone to steatohepatitis/steatosis Although Fdx1-/- mice were embryonically lethal, Fdx1+/- +/- were viable. Thus, to study the effect of Fdx1 loss on the long-term survival as well as predisposition to tumors and other abnormalities, we generated a cohort of Fdx1+/- +/-. Since Fdxr catalyzes the transfer of an electron from NADPH to Fdx1, we compared the phenotypes between Fdx1+/- +/- and Fdxr+/- +/- from our previous studies (Zhang et al., 2022; Zhang et al., 2017). To minimize the number of animals used, the data for the WT mice were adapted from two previous studies (Yang et al., 2017; Zhang et al., 2017), as all the mice were derived from the same C57BL/6 background and maintained in the same facility. Moreover, to avoid any influences from sex differences, all the mice cohorts were kept at close to equal ratio of male:female mice. Previously, we found that Fdxr+/- +/- had a short life span compared to WT mice (Zhang et al., 2022; Zhang et al., 2017). Here, we found that the median lifespan for Fdx1+/- +/- (73 weeks) was significantly shorter than that for WT mice (117weeks) and even shorter than that for Fdxr+/- +/- (102weeks) (Figure 2A and Figure 2—source data 3). To examine if the Fdx1+/- +/- were tumor-prone, we performed histological analysis. Fdxr+/- (26 out of 29) mice were tumor-prone as compared to WT mice (11 out of 51) (p<0.00001 by Fisher's exact test). However, the overall incidence of spontaneous tumors was not statistically significant between Fdx1+/- +/- (11 out of 26) and WT mice (11 out of 51) (p=0.0673 by Fisher's exact test) (Figure 2B, Figure 2—source data 3). Nevertheless, like Fdxr+/- +/-, Fdx1+/- +/- showed significantly higher incidences of adenocarcinomas and sarcomas as compared to WT mice (Figure 2B–D). Out of the three Fdx1+/- mice that developed adenocarcinomas, two had lung adenocarcinomas and one had adenocarcinoma associated with the gastrointestinal tract (Figure 2D, Figure 2—source data 3C). Figure 2 Download asset Open asset Fdx1+/- +/- have shorter life-span and increased incidence of adenocarcinoma and steatohepatitis. (A) Kaplan-Meier survival curves of WT (n=56), Fdxr+/- (n=31), and Fdx1+/- (n=26) mice. (B) Tumor spectra and penetrance in WT, Fdxr+/-, and Fdx1+/- +/-. (C) The numbers and percentages of WT, Fdxr+/-, and Fdx1+/- +/- with adenocarcinoma. (D) Representative images of hematoxylin and eosin (H&E)-stained adenocarcinomas from Fdx1+/-mice. The images are of gastrointestinal tract-associated adenocarcinoma in mouse #5-20-1, whereas they are of lung adenocarcinoma in mice #10-21-20 and #7-24-14. (E) The numbers and percentages of WT, Fdxr+/-, and Fdx1+/- +/- with liver steatosis/steatohepatitis. (F) Representative images of hematoxylin and eosin (H&E)-stained WT and Fdx1+/- +/- showing steatosis in Fdx1-deficient mice. Figure 2—source data 1 Kaplan-Meier survival analysis for various mice cohorts in Figure 2A. https://cdn.elifesciences.org/articles/91656/elife-91656-fig2-data1-v2.docx Download elife-91656-fig2-data1-v2.docx Figure 2—source data 2 Analysis, graphs, and statistical significance for Figure 2C and E. https://cdn.elifesciences.org/articles/91656/elife-91656-fig2-data2-v2.xlsx Download elife-91656-fig2-data2-v2.xlsx Figure 2—source data 3 Wild type (WT) mice (n=56) - survival time, tumor spectrum, steatosis, inflammation, and other abnormalities (A); Fdxr+/- mice (n=31) - survival time, tumor spectrum and other abnormalities (B); Fdx1+/- mice (n=26) - survival time, tumor spectrum, steatosis, inflammation, and other abnormalities (C). https://cdn.elifesciences.org/articles/91656/elife-91656-fig2-data3-v2.xlsx Download elife-91656-fig2-data3-v2.xlsx Previously, we showed that mice deficient in Fdxr were prone to liver steatosis and inflammation (Figure 2E, Figure 2—source data 3A,B; Zhang et al., 2022; Zhang et al., 2017). Since Fdxr and Fdx1 are necessary for steroidogenesis/lipid metabolism, we next examined whether Fdx1+/- mice are susceptible to liver abnormalities. Indeed, we found that like Fdxr+/- +/-, Fdx1+/- +/- were highly prone to liver steatosis/steatohepatitis (Figure 2E–F, Figure 2—source data 3C). As steatohepatitis often leads to liver cirrhosis and eventually liver failure (Sanches et al., 2015), we conclude that the high incidence of steatosis/steatohepatitis are likely responsible for the shorter lifespan observed in Fdx1+/- +/-. Of note, we did not observe any variations in phenotypes based on any sex differences in our studies. Lack of FDX1 leads to altered lipid metabolism possibly via the ABCA1-SREBP1/2 pathway We previously showed that FDXR regulates lipid metabolism via SREBP1/2 pathways (Zhang et al., 2022). Given that FDX1 is a substrate of FDXR during steroidogenesis, FDX1 might be involved in lipid metabolism via the same pathway. To test this, we generated Fdx1+/- mouse embryo fibroblasts (+/-). As Fdx1+/- +/- are lethal at E10.5, we were only able to obtain Fdx1+/- +/-. As expected, the levels of Fdx1 protein in Fdx1+/- +/- were approximately half of that in WT MEFs (Figure 3A). To examine whether loss of FDX1 alters lipid metabolism, Nile Red (9-diethylamino-5H-benzo[a]phenoxazine-5-one) staining, which stains lipid droplets, was performed on these cells. We found intense Nile red staining in the cytoplasm of Fdx1+/- +/-, suggesting accumulation of lipid droplets in Fdx1-deficient MEFs as compared to WT MEFs (Figure 3B). Figure 3 Download asset Open asset Lack of FDX1 leads to altered lipid metabolism possibly via ABCA1-SREBP1/2 pathways in murine cells. (A) The levels of Fdx1 and Actin were measured in two sets of WT and Fdx1+/-+/-. (B) Lipid droplets were visualized with Nile Red staining (ex: 488 nm, em: 565 nm) in WT and Fdx1+/-+/- cultured in serum-free media for 4 hr. DAPI (ex: 358 nm, em: 461 nm) was used to stain nuclei. (C, G) The levels of Fdx1, Fdxr and Actin protein were measured by immunoblotting in isogenic control and two Fdx1+/-+/-83 B cells (D) or SCp2 cells (G). (D, I) Isogenic control and two Fdx1+/-+/-83B clones (clone#53 and #22) (E) or isogenic control and two Fdx1+/-+/-2 clones (clone#4 and #26) were cultured in serum-free media for 4 hr followed by Nile Red staining. DAPI was used to stain nuclei. (E) The levels of ABCA1, SREBP1/2, MVD, and Actin were measured in isogenic control and Fdx1+/-+/-83B cells cultured in serum-free media for 4 hr. (F, H) Quantification of Western blot bands from E (F) or G (H) using ImageJ. The graphs show relative fold change of the indicated proteins from at least three independent experiments. Data represent the mean ± SEM. Figure 3—source data 1 Unedited western blot images for Figure 3A, C, E and G. https://cdn.elifesciences.org/articles/91656/elife-91656-fig3-data1-v2.pdf Download elife-91656-fig3-data1-v2.pdf Figure 3—source data 2 ImageJ analysis and statistical significance for Figure 3F and H. https://cdn.elifesciences.org/articles/91656/elife-91656-fig3-data2-v2.xlsx Download elife-91656-fig3-data2-v2.xlsx To confirm the role of Fdx1 in lipid metabolism in other murine cells, we used CRISPR-Cas9 to knock-out Fdx1 in mouse FL83B hepatocytes and SCp2 mammary epithelial cells. Unfortunately, we were not able to obtain any Fdx1-KO clones in both cell lines, indicating a requirement of Fdx1 for cell survival (Figure 3C and G). Interestingly, along with the expected decrease in Fdx1 protein levels, we observed lower levels of Fdxr protein in Fdx1+/- +/- as compared to isogenic control cells, suggesting that Fdx1 regulates Fdxr expression (Figure 3G and H). Next, we performed Nile red staining to examine lipid droplet accumulation in these cells. We found that loss of Fdx1 led to increase in the accumulation of lipid droplets in the cytoplasm of FL83B and SCp2 cells (Figure 3D and I), consistent with the observation in MEFs that loss of Fdx1 leads to aberrant lipid metabolism. To investigate whether Fdx1 modulates lipid metabolism via the ABCA1-SREBP1/2 pathway, we cultured FL83B cells in serum-free medium, which mimics depletion of cholesterol response. First, we examined whether Fdx1 deficiency has an effect on the level of ABCA1, a cholesterol efflux pump, which is known to be regulated upon Fdxr deficiency (Yamauchi et al., 2015). We found that Fdx1 deficiency led to decreased expression of ABCA1 protein (Figure 3E and F). Moreover, the mature nuclear form of SREBP2 protein, which is known to be increased once ABCA1 expression is decreased (Moon et al., 2019), was increased upon Fdx1 deficiency (Figure 3E and F). Furthermore, we examined if Fdx1 deficiency affects the maturation of SREBP1, which is mainly involved in the fatty acid and triacylglyceride (TAG) synthesis (Shimano et al., 1997; Shimano et al., 1996). We found that the mature form of SREBP1 was only slightly increased in Fdx1-deficient cells (Figure 3E and F). As the maturation of SREBP2 was very robust in Fdx1-deficient cells, we further tested the induction of mevalonate decarboxylase (MVD), an SREBP2 target involved in ATP-dependent decarboxylation of mevalonate pyrophosphate to form isopentenyl pyrophosphate (Hinson et al., 1997; Michihara et al., 2001). We found that MVD was increased in Fdx1-deficient cells (Figure 3E and F), indicating that the mature nuclear form of SREBP2 protein induced by Fdx1 deficiency is transcriptionally active. Next, we used HCT116 human colorectal cancer cells to determine if the effect of FDX1 on lipid metabolism observed in murine cells is conserved in human cells. We again employed the CRISPR-Cas9 system to knock out the FDX1 gene in HCT116 cells (Zhang et al., 2017). Surprisingly, unlike murine cells, we were able to obtain complete knock-out of FDX1 in human cells (Figure 4A). Nevertheless, we found that like in murine cells, loss of FDX1 led to increased activation of the SREBP1/SREBP2 pathways in HCT116 cells (Figure 4B–C). Furthermore, lipid droplets were increased in the FDX1-KO HCT116 cells compared to isogenic control cells (Figure 4D). Since Nile Red is not specific to certain lipids and can recognize several intracellular neutral lipids, including TAGs (Greenspan et al., 1985) and sterol esters/cholesterol esters (CEs) (Genicot et al., 2005), in vitro enzymatic assays were performed to specifically measure the levels of TAGs and cholesterol in these cells. We found that the intracellular levels of both cholesterol and TAGs were significantly upregulated in FDX1-KO HCT116 cells compared to isogenic control cells (Figure 4E and F), confirming aberrant lipid metabolism upon loss of FDX1. Figure 4 with 1 supplement see all Download asset Open asset Lack of FDX1 leads to altered lipid metabolism possibly via SREBP1/2 pathways in human cells. (A) The levels of FDX1 and Actin protein were measured by immunoblotting in isogenic control and FDX1-/- HCT116 cells. (B) The levels of SREBP1/2, MVD, and Actin were measured in isogenic control and FDX1-/- HCT116 cells cultured in serum-free media for 4 hr. (C) Quantification of Western blot bands from (B) using ImageJ. The graph shows relative fold change of the indicated proteins from at least 3 independent experiments. Data represent the mean ± SEM. (D) Lipid droplets were visualized with Nile Red staining (ex: 488 nm, em: 565 nm) in isogenic control and two FDX1-/- HCT116 clones (clone#18 and #19) cultured in serum-free media for 4 hr. DAPI (ex: 358 nm, em: 461 nm) was used to stain nuclei. (E) Quantitative measurement of intracellular cholesterol esters. Isogenic control and FDX1-/- HCT116 cells were cultured in a 96-well plate. After 4 hr of fasting, the level of total cholesterol was measured with Cholesterol/Cholesterol Ester-GloTM assay kit according to manufacturer's instruction. Data represent the mean ± SD. (F) Quantitative measurement of intracellular triglycerides. Isogenic control and FDX1-/- HCT116 cells were cultured in a 96-well plate. After 4 hr of fasting, the level of total triglycerides was measured with Triglyceride-GloTM assay kit according to manufacturer's instruction. Data represent the mean ± SD. Figure 4—source data 1 Unedited western blot images for Figure 4A and B. https://cdn.elifesciences.org/articles/91656/elife-91656-fig4-data1-v2.pdf Download elife-91656-fig4-data1-v2.pdf Figure 4—source data 2 ImageJ analysis and statistical significance for Figure 4C. https://cdn.elifesciences.org/articles/91656/elife-91656-fig4-data2-v2.xlsx Download elife-91656-fig4-data2-v2.xlsx Figure 4—source data 3 Analysis, graphs, and statistical significance for Figure 4E and F. https://cdn.elifesciences.org/articles/91656/elife-91656-fig4-data3-v2.xlsx Download As loss of FDX1 lipid droplet we to investigate if of FDX1 decrease lipid droplet To test this, FDX1 was expressed the control of the in HCT116 cells. with led to robust of FDX1 in these cells (Figure supplement Next, we examined lipid droplet accumulation in these cells with or FDX1 induction using Nile red staining. We found that of FDX1 decreased lipid droplet accumulation (Figure supplement we that FDX1 is involved in lipid metabolism possibly via SREBP1/2 pathways in both murine and human cells. of FDX1 alters the in HCT116 cells As loss of FDX1 to lipid metabolism, we to examine which classes of lipids are altered by FDX1 this, untargeted lipidomic analysis was performed with isogenic control and FDX1-KO HCT116 cells. total of lipids were and by including cholesterol, fatty acids, various phospholipids and lysophospholipids. with the data measured by the enzymatic assay (Figure untargeted lipidomic analysis showed that the levels of cholesterol were highly increased in cells as compared to that in isogenic control cells (Figure and Figure supplement In loss of FDX1 led to a significant increase in the of and (Figure Figure supplement but a decrease in and (Figure Figure supplement the other hand, we did not observe any significant in the levels of fatty acids and (Figure Interestingly, while the level of TAGs was found to be increased by the enzymatic assay (Figure Figure supplement the level of TAGs was found to be decreased by untargeted lipidomic analysis (Figure Figure supplement suggesting that from other complex lipids have been by the enzymatic assay as TAGs and and 2020). these data indicate that FDX1-KO leads to significant alterations in lipid due to aberrant lipid metabolism. Figure with 1 supplement see all Download asset Open asset Lack of FDX1 leads to alterations in the lipid Isogenic control and FDX1-KO HCT116 cells were used for lipidomic analysis by The relative of a lipid was as mean ± and statistical significance was using (A) (B) (C) (D) (E) (F) (H) acids Figure data 1 lipid classes graphs and statistical significance for Figure Download Discussion an electron from FDXR to various protein FDX1 is to be involved in sterol and cholesterol side (Schulz et al., 2023). studies indicate that FDX1 a critical role in the regulation of via lipoylation of cycle (Schulz et al., Tsvetkov et al., 2022). Although FDX1 has been extensively characterized biochemically, its role in physiology and lipid metabolism has not been explored. In this study, we generated mice deficient in Fdx1 and showed that homozygous Fdx1 deletion led to embryonic lethality at We also showed that Fdx1+/- +/- had a short life span and developed steatohepatitis, which is similar to the phenotypes by Fdxr+/- +/-. Moreover, Fdx1 deficiency led to lipid droplet accumulation in both murine and human cells, possibly via the ABCA1-SREBP1/2 pathways. untargeted lipidomic analysis showed that FDX1 deficiency led to alterations in several classes of lipids, suggesting the role of FDX1 in lipid metabolism. The embryonic lethality by complete loss of Fdx1 is similar to what we previously showed by complete loss of the of which was in to iron (Zhang et al., 2017). However, as FDX1 is not a player in Fe-S cluster synthesis (Schulz et al., the lethality be due to of production by which is required for the of and Thus, Fdx1-/- embryos not be able to due to a However, mice with complete deletion of which is essential for production, can et al., we that other pathways be responsible for the lethality of Fdx1-/- Additionally, Fdx1-/- embryos developed we that FDX1 be required for embryo consistent with a observation that loss of FDX1 to in lipoylation of cycle and loss of (Schulz et al., Tsvetkov et al., 2022). We observed that Fdx1+/- +/- were not prone to spontaneous which is different from tumor-prone Fdxr+/- +/- (Zhang et al., 2022; Zhang et al., 2017). Nevertheless, Fdx1+/- +/- a higher incidence of adenocarcinomas and sarcomas compared to WT mice (Figure is that loss of Fdxr leads to decreased expression of tumor whereas loss of Fdx1 not have a significant effect on expression (Zhang et al., 2017). We also observed that murine cells deficient in both alleles of the Fdx1 gene are not which is consistent with the observation that Fdx1-KO embryos die between 10.5 and 13.5 (Figure However, both our and studies showed that FDX1-KO human cells are (Schulz et al., Tsvetkov et al., 2022; Zhang et al., 2017). is that human FDX2, but not murine be able to for loss of FDX1 for cell which is further investigation. and human cells deficient in FDX1 showed increased lipid accumulation possibly via activation of the ABCA1-SREBP1/2 which was again consistent with the loss of FDXR (Zhang et al., 2022). In to specific classes of lipids altered upon loss of FDX1, lipidomic analysis was performed and showed that the levels of cholesterol, phospholipids, and were significantly altered by the loss of FDX1. Thus, altered lipid metabolism is likely responsible for steatohepatitis observed in Fdx1-deficient mice. is a disease that with the accumulation of in the liver Shao et al., 2020; et al., 2010). The accumulation liver inflammation, to steatohepatitis, to as non-alcoholic steatohepatitis These data indicate that FDX1 is involved in cellular and physiological lipid homeostasis and that loss of FDX1 leads to development of in mice. Although previous studies showed that FDX1 is involved in cholesterol metabolism, the in this study a critical FDX1 regulates the metabolism of the various classes of lipids. Thus, further studies are to this lipid metabolism has emerged as a player in the of to the development and of various and
Source: eLife
Language: English
Subfield: Biochemistry
Domain: Life Sciences
Open Access status: gold
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