Cross-species comparison of genomewide gene expression profiles reveals induction of hypoxia-inducible factor-responsive genes in iron-deprived intestinal epithelial cells

Comparison of apical and basolateral Cu treatment for iron-related gene regulation during deferoxamine induced iron deficiency

BACKGROUND

Intestinal copper transporter (Atp7a) mutant-brindled mice with systemic Cu deficiency had elevated Cu levels in enterocyte cells without any perturbation of iron-regulating genes, suggesting that blood Cu level might be important for intestinal iron homeostasis during iron deficiency (ID). We hypothesized that the blood Cu level and polarization (apical and basolateral) of enterocyte cells might be important regulators for the compensatory response on the regulation of genes in enterocyte cells during iron deficiency.

METHODS

We grew Caco-2 cells on a bicameral cell culture plate to mimic the human intestine system and on a regular tissue culture plate. Iron deficiency was induced by deferoxamine (DFO). The cells were treated with Cu and Cu with Fe following mRNA expressions of DMT1, FPN, TFR, and ANKRD37 were analyzed.

RESULTS

Our main finding was that basolateral treatment of Cu significantly reduced mRNA expressions of iron-regulated genes, including DMT1, FPN, TFR, and ANKRD37, compared to DFO-treated and DFO with apical Cu-treated groups in both bicameral and regular tissue culture plates.

CONCLUSIONS

Cu level in the basolateral side of Caco-2 cells significantly influenced the intracellular gene regulation in DFO-induced iron-deficient condition, and polarization of the cells might be important factor gene regulation in enterocyte cells.

The Effect of Ankaferd Blood Stopper on Colonic Inflammation: An In Vitro Study in RAW 264.7 and Caco-2 Cells

Ankaferd Blood Stopper (ABS) is a medicinal plant extract that has anti-inflammatory effect. Inflammatory bowel disease is a pathological condition that directly affects colon health and increases the risk of colon cancer. Especially inflammation is an important factor in the formation and progression of this disease. The aim of the study was to investigate the protective effect of ABS on colonic inflammation. Caco-2 and RAW 264.7 cells were used as a model of in vitro colonic inflammation. RAW 264.7 cells were treated with lipopolysaccharide for 12 h to induce inflammation, and an inflammatory medium (IM) was obtained. Caco-2 cells were treated with 15 μL/mL ABS for 4 h, then incubated with IM. The cells also were incubated with 15 μL/mL ABS and IM together for 12 h. Tumor necrosis factor alpha (TNF-α) protein levels were targeted in testing inflammatory condition and cyclooxygenase-2 (COX-2) mRNA level was used as a marker gene to show the possible anti-inflammatory effect of ABS in Caco-2 cells. TNF-α level was 26.1-fold higher than the control group. IM caused 3.2-fold increase in COX-2 expression in Caco-2 cells. Pretreatment of Caco-2 cells with ABS resulted in 3.3-fold decrease in COX-2 mRNA levels relative to IM group. Furthermore, COX-2 mRNA level reduced 4.7-fold when ABS and conditional medium were given at the same time. ABS has suppressive effect on COX-2 mRNA expression in Caco-2 cells. These results suggest that ABS might have protective and therapeutic effect for colonic inflammation.

The development of lentil derived protein–iron complexes and their effects on iron deficiency anemia in vitro

Lentil derived proteins have the capacity to chelate iron minerals and hydrolysed protein–iron complexes have functional properties on iron deficiency anemia in in vitro by influencing mRNA levels of iron regulating genes.

Intersection of Iron and Copper Metabolism in the Mammalian Intestine and Liver

Iron and copper have similar physiochemical properties; thus, physiologically relevant interactions seem likely. Indeed, points of intersection between these two essential trace minerals have been recognized for many decades, but mechanistic details have been lacking. Investigations in recent years have revealed that copper may positively influence iron homeostasis, and also that iron may antagonize copper metabolism. For example, when body iron stores are low, copper is apparently redistributed to tissues important for regulating iron balance, including enterocytes of upper small bowel, the liver, and blood. Copper in enterocytes may positively influence iron transport, and hepatic copper may enhance biosynthesis of a circulating ferroxidase, ceruloplasmin, which potentiates iron release from stores. Moreover, many intestinal genes related to iron absorption are transactivated by a hypoxia-inducible transcription factor, hypoxia-inducible factor-2α (HIF2α), during iron deficiency. Interestingly, copper influences the DNA-binding activity of the HIF factors, thus further exemplifying how copper may modulate intestinal iron homeostasis. Copper may also alter the activity of the iron-regulatory hormone hepcidin. Furthermore, copper depletion has been noted in iron-loading disorders, such as hereditary hemochromatosis. Copper depletion may also be caused by high-dose iron supplementation, raising concerns particularly in pregnancy when iron supplementation is widely recommended. This review will cover the basic physiology of intestinal iron and copper absorption as well as the metabolism of these minerals in the liver. Also considered in detail will be current experimental work in this field, with a focus on molecular aspects of intestinal and hepatic iron-copper interplay and how this relates to various disease states. © 2018 American Physiological Society. Compr Physiol 8:1433-1461, 2018.

Investigation of the influence of high glucose on molecular and genetic responses: an in vitro study using a human intestine model

Background

Dietary glucose consumption has increased worldwide. Long-term high glucose intake contributes to the development of obesity and type 2 diabetes mellitus (T2DM). Obese people tend to eat glucose-containing foods, which can lead to an addiction to glucose, increased glucose levels in the blood and intestine lumen, and exposure of intestinal enterocytes to high dietary glucose. Recent studies have documented a role for enterocytes in glucose sensing. However, the molecular and genetic relationship between high glucose levels and intestinal enterocytes has not been determined. We aimed to identify relevant target genes and molecular pathways regulated by high glucose in a well-established in vitro epithelial cell culture model of the human intestinal system (Caco-2 cells).

Methods

Cells were grown in a medium containing 5.5 and 25 mM glucose in a bicameral culture system for 21 days to mimic the human intestine. Transepithelial electrical resistance was used to control monolayer formation and polarization of the cells. Total RNA was isolated, and genome-wide mRNA expression profiles were determined. Molecular pathways were analyzed using the DAVID bioinformatics program. Gene expression levels were confirmed by quantitative reverse transcription polymerase chain reaction (RT-qPCR).

Results

Microarray gene expression data demonstrated that 679 genes (297 upregulated, 382 downregulated) were affected by high glucose treatment. Bioinformatics analysis indicated that intracellular protein export (p = 0.0069) and ubiquitin-mediated proteolysis (p = 0.024) pathways were induced, whereas glycolysis/gluconeogenesis (p < 0.0001), pentose phosphate (p = 0.0043), and fructose-mannose metabolism (p = 0.013) pathways were downregulated, in response to high glucose. Microarray analysis of gene expression showed that high glucose significantly induced mRNA expression levels of thioredoxin-interacting protein (TXNIP, p = 0.0001) and lipocalin 15 (LCN15, p = 0.0016) and reduced those of ATP-binding cassette, sub-family A member 1 (ABCA1, p = 0.0004), and iroquois homeobox 3 (IRX3, p = 0.0001).

Conclusions

To our knowledge, this is the first investigation of high glucose-regulated molecular responses in an intestinal enterocyte model. Our findings identify new target genes that may be important in the intestinal glucose absorption and metabolism during high glucose consumption.

Evaluation of the iron regulatory protein-1 interactome

The interactions of iron regulatory proteins (IRPs) with mRNAs containing an iron-responsive element (IRE) is a major means through which intracellular iron homeostasis is maintained and integrated with cellular function. Although IRE-IRP interactions have been proposed to modulate the expression of a diverse number of mRNAs, a transcriptome analysis of the interactions that form within the native mRNA structure and cellular environment has not previously been described. An RNA-CLIP study is described here that identified IRP-1 interactions occurring within a primary cell line expressing physiologically relevant amounts of mRNA and protein. The study suggests that only a small subset of the previously proposed IREs interact with IRP-1 in situ. Identifying authentic IRP interactions is not only important to a greater understanding of iron homeostasis and its integration with cell biology but also to the development of novel therapeutics that can compensate for iron imbalances.

Ankaferd Influences mRNA Expression of Iron-Regulated Genes During Iron-Deficiency Anemia

Ankaferd Blood Stopper (ABS) comprises a mixture of plants and stops bleeding via forming a protein network by erythroid aggregation. Bleeding causes reduction of iron levels in body. It has been indicated that ABS contains significant amount of iron. Thus, we investigated the biological activity of ABS-derived iron on iron-regulated genes during iron-deficiency anemia (IDA). IDA We selected Caco-2 and HepG2 cell lines as in vitro models of human intestine and liver, respectively. Iron deficiency anemia was induced by deferoxamine. The cells were treated with ferric ammonium citrate (FAC) and ABS. Messenger RNA levels of iron-regulated genes were analyzed by quantitative reverse transcription polymerase chain reaction to elucidate whether iron in ABS behaved similar to inorganic iron (FAC) during IDA. The results showed that ABS-derived iron influenced transcriptions of iron-regulated marker genes, including divalent metal transporter (Dmt1), transferrin receptor (TfR), ankyrin repeat domain 37 (Ankrd37), and hepcidin (Hamp) in IDA-induced Caco-2 and HepG2 cells. Our results suggest that when ABS is used to stop tissue bleeding, it might have an ability to reduce levels of IDA.

Mechanistic and regulatory aspects of intestinal iron absorption

Iron is an essential trace mineral that plays a number of important physiological roles in humans, including oxygen transport, energy metabolism, and neurotransmitter synthesis. Iron absorption by the proximal small bowel is a critical checkpoint in the maintenance of whole-body iron levels since, unlike most other essential nutrients, no regulated excretory systems exist for iron in humans. Maintaining proper iron levels is critical to avoid the adverse physiological consequences of either low or high tissue iron concentrations, as commonly occurs in iron-deficiency anemia and hereditary hemochromatosis, respectively. Exquisite regulatory mechanisms have thus evolved to modulate how much iron is acquired from the diet. Systemic sensing of iron levels is accomplished by a network of molecules that regulate transcription of the HAMP gene in hepatocytes, thus modulating levels of the serum-borne, iron-regulatory hormone hepcidin. Hepcidin decreases intestinal iron absorption by binding to the iron exporter ferroportin 1 on the basolateral surface of duodenal enterocytes, causing its internalization and degradation. Mucosal regulation of iron transport also occurs during low-iron states, via transcriptional (by hypoxia-inducible factor 2α) and posttranscriptional (by the iron-sensing iron-regulatory protein/iron-responsive element system) mechanisms. Recent studies demonstrated that these regulatory loops function in tandem to control expression or activity of key modulators of iron homeostasis. In health, body iron levels are maintained at appropriate levels; however, in several inherited disorders and in other pathophysiological states, iron sensing is perturbed and intestinal iron absorption is dysregulated. The iron-related phenotypes of these diseases exemplify the necessity of precisely regulating iron absorption to meet body demands.

Molecular mediators governing iron-copper interactions

Given their similar physiochemical properties, it is a logical postulate that iron and copper metabolism are intertwined. Indeed, iron-copper interactions were first documented over a century ago, but the homeostatic effects of one on the other has not been elucidated at a molecular level to date. Recent experimental work has, however, begun to provide mechanistic insight into how copper influences iron metabolism. During iron deficiency, elevated copper levels are observed in the intestinal mucosa, liver, and blood. Copper accumulation and/or redistribution within enterocytes may influence iron transport, and high hepatic copper may enhance biosynthesis of a circulating ferroxidase, which potentiates iron release from stores. Moreover, emerging evidence has documented direct effects of copper on the expression and activity of the iron-regulatory hormone hepcidin. This review summarizes current experimental work in this field, with a focus on molecular aspects of iron-copper interplay and how these interactions relate to various disease states.

Silencing the Menkes copper-transporting ATPase (Atp7a) gene in rat intestinal epithelial (IEC-6) cells increases iron flux via transcriptional induction of ferroportin 1 (Fpn1)

The Menkes copper-transporting ATPase (Atp7a) gene is induced in rat duodenum during iron deficiency, consistent with copper accumulation in the intestinal mucosa and liver. To test the hypothesis that ATP7A influences intestinal iron metabolism, the Atp7a gene was silenced in rat intestinal epithelial (IEC-6) cells using short hairpin RNA (shRNA) technology. Perturbations in intracellular copper homeostasis were noted in knockdown cells, consistent with the dual roles of ATP7A in pumping copper into the trans-Golgi (for cuproenzyme synthesis) and exporting copper from cells. Intracellular iron concentrations were unaffected by Atp7a knockdown. Unexpectedly, however, vectorial iron ((59)Fe) transport increased (∼33%) in knockdown cells grown in bicameral inserts and increased further (∼70%) by iron deprivation (compared with negative control shRNA-transfected cells). Additional experiments were designed to elucidate the molecular mechanism of increased transepithelial iron flux. Enhanced iron uptake by knockdown cells was associated with increased expression of a ferrireductase (duodenal cytochrome b) and activity of a cell-surface ferrireductase. Increased iron efflux from knockdown cells was likely mediated via transcriptional activation of the ferroportin 1 gene (by an unknown mechanism). Moreover, Atp7a knockdown significantly attenuated expression of an iron oxidase [hephaestin (HEPH); by ∼80%] and membrane ferroxidase activity (by ∼50%). Cytosolic ferroxidase activity, however, was retained in knockdown cells (75% of control cells), perhaps compensating for diminished HEPH activity. This investigation has thus documented alterations in iron homeostasis associated with Atp7a knockdown in enterocyte-like cells. Alterations in copper transport, trafficking, or distribution may underlie the increase in transepithelial iron flux noted when ATP7A activity is diminished.

Transcription factors Sp1 and Hif2α mediate induction of the copper-transporting ATPase (Atp7a) gene in intestinal epithelial cells during hypoxia

Genes with G/C-rich promoters were up-regulated in the duodenal epithelium of iron-deficient rats including those encoding iron (e.g. Dmt1 and Dcytb) and copper (e.g. Atp7a and Mt1) metabolism-related proteins. It was shown previously that an intestinal copper transporter (Atp7a) was co-regulated with iron transport-related genes by a hypoxia-inducible transcription factor, Hif2α. In the current study, we sought to test the role of Sp1 in transcriptional regulation of Atp7a expression during iron deprivation/hypoxia. Initial studies in IEC-6 cells showed that mithramycin, an Sp1 inhibitor, reduced expression of Atp7a and iron transport-related genes (Dmt1, Dcytb, and Fpn1) and blocked their induction by CoCl2, a hypoxia mimetic. Consistent with this, overexpression of Sp1 increased endogenous Atp7a mRNA and protein expression and stimulated Atp7a, Dmt1, and Dcytb promoter activity. Site-directed mutagenesis and functional analysis of a basal Atp7a promoter construct revealed four functional Sp1 binding sites that were necessary for Hif2α-mediated induction of promoter activity. Furthermore, chromatin immunoprecipitation (ChIP) assays confirmed that Sp1 specifically interacts with the Atp7a promoter in IEC-6 cells and in rat duodenal enterocytes. This investigation has thus revealed a novel aspect of Atp7a gene regulation in which Sp1 may be necessary for the HIF-mediated induction of gene transcription during iron deficiency/hypoxia. Understanding regulation of Atp7a expression may help further clarify the physiological role of copper in the maintenance of iron homeostasis. Furthermore, this Sp1/Hif2α regulatory mechanism may have broader implications for understanding the genetic response of the intestinal epithelium to maintain whole-body iron homeostasis during states of deficiency.

Investigation of iron metabolism in mice expressing a mutant Menke's copper transporting ATPase (Atp7a) protein with diminished activity (Brindled; Mo (Br) (/y) )

During iron deficiency, perturbations in copper homeostasis have frequently been documented. Previous studies in iron-deprived rats demonstrated that enterocyte and hepatic copper levels increase and a copper transporter (the Menkes Copper ATPase; Atp7a) is induced in the duodenal epithelium in parallel to iron transport-related genes (e.g. Dmt1, Dcytb, Fpn1). Moreover, two ferroxidase proteins involved in iron homeostasis, hephaestin expressed in enterocytes and ceruloplasmin, produced and secreted into blood by the liver, are copper-dependent enzymes. We thus aimed to test the hypothesis that Atp7a function is important for the copper-related compensatory response of the intestinal epithelium to iron deficiency. Accordingly, iron homeostasis was studied for the first time in mice expressing a mutant Atp7a protein with minimal activity (Brindled [Mo^Br/y]). Mutant mice were rescued by perinatal copper injections, and, after a 7–8 week recovery period, were deprived of dietary iron for 3 weeks (along with WT littermates). Adult Mo^Br/y mice displayed copper-deficiency anemia but had normal iron status; in contrast, iron-deprived Mo^Br/y mice were iron deficient and more severely anemic with partial amelioration of the copper-deficient phenotype. Intestinal iron absorption in both genotypes (WT and Mo^Br/y) increased ∼3-fold when mice consumed a low-iron diet and ∼6-fold when mice were concurrently bled. WT mice exhibited no alterations in copper homeostasis in response to iron deprivation or phlebotomy. Conversely, upregulation of iron absorption was associated with increased enterocyte and liver copper levels and serum ferroxidase (ceruloplasmin) activity in Mo^Br/y mice, typifying the response to iron deprivation in many mammalian species. We thus speculate that a copper threshold exists that is necessary to allow appropriate regulate of iron absorption. In summary, Mo^Br/y mice were able to adequately regulate iron absorption, but unlike in WT mice, concurrent increases in enterocyte and liver copper levels and serum ferroxidase activity may have contributed to maintenance of iron homeostasis.

Copper stabilizes the Menkes copper-transporting ATPase (Atp7a) protein expressed in rat intestinal epithelial cells

Iron deficiency decreases oxygen tension in the intestinal mucosa, leading to stabilization of hypoxia-inducible transcription factor 2α (Hif2α) and subsequent upregulation of genes involved in iron transport [e.g., divalent metal transporter (Dmt1) and ferroportin 1 (Fpn1)]. Iron deprivation also alters copper homeostasis, reflected by copper accumulation in the intestinal epithelium and induction of an intracellular copper-binding protein [metallothionein (Mt)] and a copper exporter [Menkes copper ATPase (Atp7a)]. Importantly, Atp7a is also a Hif2α target. It was, however, previously noted that Atp7a protein expression was induced more strongly than mRNA in the duodenum of iron-deprived rats, suggesting additional regulatory mechanisms. The current study was thus designed to decipher mechanistic aspects of Atp7a regulation during iron deprivation using an established in vitro model of the mammalian intestine, rat intestinal epithelial (IEC-6) cells. Cells were treated with an iron chelator and/or copper loaded to mimic the in vivo situation. IEC-6 cells exposed to copper showed a dose-dependent increase in Mt expression, confirming intracellular copper accumulation. Iron chelation with copper loading increased Atp7a mRNA and protein levels; however, contrary to our expectation, copper alone increased only protein levels. This suggested that copper increased Atp7a protein levels by a posttranscriptional regulatory mechanism. Therefore, to determine if Atp7a protein stability was affected, the translation inhibitor cycloheximide was utilized. Experiments in IEC-6 cells revealed that the half-life of the Atp7a protein was ~41 h and, furthermore, that intracellular copper accumulation increased steady-state Atp7a protein levels. This investigation thus reveals a novel mechanism of Atp7a regulation in which copper stabilizes the protein, possibly complementing Hif2α-mediated transcriptional induction during iron deficiency.

Serum ceruloplasmin protein expression and activity increases in iron-deficient rats and is further enhanced by higher dietary copper intake

Increases in serum and liver copper content are noted during iron deficiency in mammals, suggesting that copper-dependent processes participate during iron deprivation. One point of intersection between the 2 metals is the liver-derived, multicopper ferroxidase ceruloplasmin (Cp) that is important for iron release from certain tissues. The current study sought to explore Cp expression and activity during physiologic states in which hepatic copper loading occurs (eg, iron deficiency). Weanling rats were fed control or low iron diets containing low, normal, or high copper for ∼ 5 weeks, and parameters of iron homeostasis were measured. Liver copper increased in control and iron-deficient rats fed extra copper. Hepatic Cp mRNA levels did not change; however, serum Cp protein was higher during iron deprivation and with higher copper consumption. In-gel and spectrophotometric ferroxidase and amine oxidase assays demonstrated that Cp activity was enhanced when hepatic copper loading occurred. Interestingly, liver copper levels strongly correlated with Cp protein expression and activity. These observations support the possibility that liver copper loading increases metallation of the Cp protein, leading to increased production of the holo enzyme. Moreover, this phenomenon may play an important role in the compensatory response to maintain iron homeostasis during iron deficiency.

Hypoxia-inducible factor-2α mediates the adaptive increase of intestinal ferroportin during iron deficiency in mice

BACKGROUND & AIMS

Iron deficiency and iron overload affect over a billion people worldwide. Dietary iron absorption in the small intestine is required for systemic iron homeostasis. Ferroportin (FPN) is the only characterized, mammalian, basolateral iron exporter. Despite the importance of FPN in maintaining iron homeostasis, its in vivo mechanisms of regulation are unclear.

METHODS

Systemic iron homeostasis was assessed in mice with intestine-specific disruption of genes encoding the von Hippel-Lindau tumor suppressor protein (Vhl), hypoxia-inducible factor (HIF)-1α, HIF-2α, and aryl hydrocarbon nuclear translocator (ARNT).

RESULTS

We observed biphasic regulation of Fpn during iron deficiency. Fpn was rapidly induced under conditions of low iron, which required the transcription factor HIF-2α. Targeted disruption of HIF-2α in the intestine inhibited Fpn induction in mice with low iron, through loss of transcriptional activation. Analysis of the Fpn promoter and in vivo chromatin immunoprecipitation assays demonstrated that HIF-2α directly binds to the Fpn promoter and induces its expression, indicating a mechanism of transcriptional regulation of Fpn following changes in systemic levels of iron. During chronic iron deficiency, FPN protein levels also increased, via increased stability through a HIF-2α-independent pathway.

CONCLUSIONS

In mice, expression of the gene that encodes Fpn and its protein levels are regulated by distinct pathways to provide a rapid and sustained response to acute and chronic iron deficiency. Therapies that target FPN might be developed for patients with iron-related disorders.

The role of iron in learning and memory

Iron deficiency (ID) is the most common nutrient deficiency, affecting 2 billion people and 30% of pregnant women and their offspring. Early life ID affects at least 3 major neurobehavioral domains, including speed of processing, affect, and learning and memory, the latter being particularly prominent. The learning and memory deficits occur while the infants are iron deficient and persist despite iron repletion. The neural mechanisms underlying the short- and long-term deficits are being elucidated. Early ID alters the transcriptome, metabolome, structure, intracellular signaling pathways, and electrophysiology of the developing hippocampus, the brain region responsible for recognition learning and memory. Until recently, it was unclear whether these effects are directly due to a lack of iron interacting with important transcriptional, translational, or post-translational processes or to indirect effects such as hypoxia due to anemia or stress. Nonanemic genetic mouse models generated by conditionally altering expression of iron transport proteins specifically in hippocampal neurons in late gestation have led to a greater understanding of iron's role in learning and memory. The learning deficits in adulthood likely result from interactions between direct and indirect effects that contribute to abnormal hippocampal structure and plasticity.

Transcriptional regulation of the Menkes copper ATPase (Atp7a) gene by hypoxia-inducible factor (HIF2{alpha}) in intestinal epithelial cells

Iron homeostasis-related genes (e.g., Dmt1 and Dcytb) are upregulated by hypoxia-inducible factor 2α (HIF2α) during iron deficiency in the mammalian intestine. Menkes copper ATPase (Atp7a) gene expression is also strongly induced in the duodenum of iron-deficient rats. The current study was thus designed to test the hypothesis that Atp7a is regulated by HIF2α. Rat intestinal epithelial (IEC-6) cells were utilized to model the intestinal epithelium, and CoCl(2) and 1% O(2) were applied to mimic hypoxia in vitro. Both treatments significantly increased endogenous Atp7a mRNA levels; mRNA induction with CoCl(2) treatment was blunted by a transcriptional inhibitor. The rat Atp7a promoter was thus cloned and studied. Various sized promoter constructs were inserted into a luciferase reporter vector and transfected into cells. A -224/+88 bp construct had full activity and was induced by CoCl(2); this promoter fragment was thus utilized for subsequent analyses. Interestingly, this region contains three phylogenetically conserved, putative hypoxia response elements (HRE; 5'-NCGTGN-3'). It was further noted that HIF2α overexpression caused a significant upregulation of promoter activity while HIF1α overexpression had little effect. To determine whether Atp7a is a direct HIF target, three putative HREs were deleted individually or in combination; all were shown to be essential for transcriptional induction. Chromatin immunoprecipitation studies also demonstrated that HIF2α binds to the Atp7a promoter region. Lastly, Atp7a and HIF2α protein levels were shown to be increased by both treatments. In conclusion, the Atp7a gene is upregulated by direct interaction with HIF2α, demonstrating coordinate regulation with genes related to intestinal iron homeostasis.