Phylogenetic and sequence analyses of insect transferrins suggest that only transferrin 1 has a role in iron homeostasis

Iron is essential to life,but surprisingly little is known about how iron is managed in nonvertebrate animals.In mammals,the well-characterized transferrins bind iron and are involved in iron transport or immunity,whereas other members of the transferrin family do not have a role in iron homeostasis.In insects,the functions of transferrins are still poorly understood.The goals of this project were to identify the transferrin genes in a diverse set of insect species,resolve the evolutionary relationships among these genes,and predict which of the transferrins are likely to have a role in iron homeostasis.Our phylogenetic analysis of transferrins from 16 orders of insects and two orders of noninsect hexapods demonstrated that there are four orthologous groups of insect transferrins.Our analysis suggests that transferrin 2 arose prior to the origin of insects,and transferrins/,i,and 4 arose early in insect evolution.Primary sequence analysis of each of the insect transferrins was used to predict signal peptides,carboxyl-terminal transmembrane regions,GPI-anchors,and iron binding.Based on this analysis,we suggest that transferrins 2,and 4 are unlikely to play a major role in iron homeostasis.In contrast,the transferrin 1 orthologs are predicted to be secreted,soluble,iron-binding proteins.We conclude that transferrin 1 orthologs are the most likely to play an important role in iron homeostasis.Interestingly,it appears that the louse,aphid,and thrips lineages have lost the transferrin 1 gene and,thus,have evolved to manage iron without transferrins.

Serum nutritional predictive biomarkers and risk assessment for anastomotic leakage after laparoscopic surgery in rectal cancer patients

BACKGROUND Anastomotic leakage(AL)is one of the severest complications after laparoscopic surgery for middle/low rectal cancer,significantly impacting patient outcomes.Identifying reliable predictive factors for AL remains a clinical challenge.Serum nutritional biomarkers have been implicated in surgical outcomes but are un-derexplored as predictive tools for AL in this setting.Our study hypothesizes that preoperative serum levels of prealbumin(PA),albumin(ALB),and transferrin(TRF),along with surgical factors,can accurately predict AL risk.AIM To determine the predictive value of preoperative serum nutritional biomarkers for rectal cancer AL following laparoscopic surgery.METHODS In the retrospective cohort study carried out at a tertiary cancer center,we examined 560 individuals who underwent laparoscopic procedures for rectal cancer from 2018 to 2022.Preoperative serum levels of PA,ALB,and TRF were measured.We employed multivariate logistic regression to determine the independent risk factors for AL,and a predictive model was constructed and evaluated using receiver operating characteristic curve analysis.RESULTS AL occurred in 11.96%of cases,affecting 67 out of 560 patients.Multivariate analysis identified PA,ALB,and TRF as the independent risk factor,each with an odds ratio of 2.621[95%confidence interval(CI):1.582-3.812,P=0.012],3.982(95%CI:1.927-4.887,P=0.024),and 2.109(95%CI:1.162-2.981,P=0.031),respectively.Tumor location(<7 cm from anal verge)and intraoperative bleeding≥300 mL also increased AL risk.The predictive model demonstrated an excellent accuracy,achieving an area under the receiver operating characteristic curve of 0.942,a sensitivity of 0.844,and a specificity of 0.922,demonstrating an excellent ability to discriminate.CONCLUSION Preoperative serum nutritional biomarkers,combined with surgical factors,reliably predict anastomotic leakage risk after rectal cancer surgery,highlighting their importance in preoperative assessment.

Cervical cancer with transferrin receptor has a poor prognosis and is associated with immune infiltration, according to a comprehensive bioinformatics study

Background:The molecular mechanism underlying the involvement of the Transferrin receptor(TFRC)in cervical cancer remains poorly understood.This study aims to elucidate the role of TFRC in cervical cancer by analyzing data from The Cancer Genome Atlas(TCGA)and Genotype-Tissue Expression(GTEx)databases.Methods:TFRC protein expression was obtained from Human Protein Altas(HPA).All datas were collected from TCGA and GTEx.In this study,we analyzed the expression of TFRC in cervical cancer and its clinical significance.Through Kyoto Encyclopedia of Genes and Genomes(KEGG)and Gene set enrichment analyses(GSEA),investigated the related molecular pathways of TFRC.The relationship between TFRC and immune infiltration was then examined.The prognosis of different immune cell subsets was then analyzed after dividing cervical cancer patients into high and low expression of TFRC groups.Results:TFRC is highly expressed in various tumor tissues compared to control normal tissues,including cervical cancer.An increased expression of TFRC was associated with higher Tumor(T)and Node(N)stage,as well as a higher clinical stage.Kaplan–Meier(KM)survival analysis investigated that higher TFRC expression patients have a poor overall survival(OS),disease specific survival(DSS)and progress free interval(PFI).Both KEGG and GSEA enriched signaling pathway by high TFRC and low TFRC groups.There was a significant negative linear correlation between TFRC expression and immune infiltration.TFRC affects the prognosis of cervical cancer patients through immune pathway.Conclusions:Cervical cancer patients with TFRC expression may have a worse prognosis.

Expression of HIF-1α and Its Target Genes in the Nanorana parkeri Heart：Implications for High Altitude Adaptation

Hypoxia-inducible factor 1 alpha（HIF-1α） and its target genes vascular endothelial growth factor（VEGF） and transferrins（TF） play an important role in native endothermic animals＇ adaptation to the high altitude environments. For ectothermic animals – especially frogs – it remains undetermined whether HIF-1α and its target genes（VEGF and TF） play an important role in high altitude adaptation, too. In this study, we compared the gene sequences and expression of HIF-1α and its target genes（VEGF and TF） between three Nanorana parkeri populations from different altitudes（3008 m a.s.l., 3440 m a.s.l. and 4312 m a.s.l.）. We observed that the c DNA sequences of HIF-1A exhibited high sequence similarity（99.38%） among the three altitudinally separated populations; but with increasing altitude, the expression of HIF-1A and its target genes（VEGF and TF） increased significantly. These results indicate that HIF-1α plays an important role in N. parkeri adaptation to the high altitude, similar to its role in endothermic animals.

Gc、Tf和C_3表型的同步检测

血清蛋白多态性的同步检测可节省检材、简化操作步骤、省时省力.本文用醋酸纤维素薄膜电泳免疫固定法同步检测血清型特异成份（Group-Specific component,Gc）、转铁蛋白（Transferrin,Tf）和补体第三成份（Complment 3,C3）的表型,调查了成都地区汉族116名无亲缘关系的健康献血员的表型频率,现将结果报导如下:

Expression of transferrin in hematoma brain tissue at different stages after intra cerebral hemorrhage in rats

Objective: To explore the expression of transferrin(Tf) and transferrin receptor(Tf R) in hematoma brain tissue at different stage after intracerebral hemorrhage(ICH) in rats. Methods: ICH rats model were established by collagenase method, and rats were sacrificed at 24 h, 72 h, 7 d and 14 d after operation. The levels of Tf and Tf R in different periods of rats were detected by immunohistochemical method, and correlation between two groups was analyzed. Results: Tf, Tf R-positive cells at each time after operation in observation group were significantly higher than that in control group(P<0.05). Tf, Tf R-positive cells began to increase from 24 h after the operation and reached the peak 72 h-7 d after surgery, but then gradually decreased. Tf was mainly expressed in nucleus and cytoplasm of neurons and glial cells around the hematoma, but Tf R was mainly expressed in nucleus and cytoplasm of neurons and choroid plexus endothelial cells. Correlation analysis showed that the Tf-positive cell was significantly positively correlated with Tf R-positive cell expression(r=0.447, P=0.022). Conclusions: Tf and Tf R were important transporters in brain tissue excessive load iron transport after ICH, and detecting the expression levels of the two indicators can provide a reference for prognosis treatmentin ICH.

Construction of single chain Fv antibody against transferrin receptor and its protein fusion with alkaline phosphatase

AIM: To construct fusion protein of a single-chain antibody (scFv) against transferrin receptor (TfR) with alkaline phosphatase(AP). METHODS: The VH-linker-VL,namely scFv gene,was prepared by amplifying the VH and VL genes from plasmid pGEM-T-VH and pGEM-T-VL with splicing overlap extension polymerase chain reaction (SOE PCR). After the ScFv gene was modified by 5/71 and Not I,it was subcloned into the secretory expression vector pUC19/119, and then was transformed into E.coli TG1.The positive colonies were screened by colony PCR and their expressions were induced by IPTG.ScFv gene was gained by digesting ScFv expression vector pUC19/119 with 5/71 and NotI restriction enzymes, then subcloned into expression vector pDAP2, followed by transformation in E.coli TG1.The positive colonies were selected by bacterial colony PCR.The expression of fusion protein (scFv-AP) was induced by IPTG.Its activity was detected by enzyme immunoassay. The molecular weights of scFv and scFv-AP were measured by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). RESULTS: The product of SOE PCR formed a band of 700 bp in agarose gel electrophoresis. SDS-PAGE demonstrated the molecular weight of scFv was 27 ku.Immunofluorescent assay (IFA) demonstrated its reactivity with TfR.The molecular weight of scFv-AP was 75 ku.Enzyme immunoassay showed that scFv-AP could specifically bind to human TfR and play AP activity. CONCLUSION: We have successfully prepared the anti-human TfR scFv and constructed the fusion protein of scFv and AP.It is promising for immunological experiments.

Transferrin receptor and ferritin-H are developmentally regulated in oligodendrocyte lineage cells

Iron is an essential trophic element that is required for cell viability and differentiation, especially in oligodendrocytes, which consume relatively high rates of energy to produce myelin. Multiple iron metabolism proteins are expressed in the brain including transferrin receptor and ferritin-H. However, it is still unknown whether they are developmentally regulated in oligodendrocyte lineage cells for myelination. Here, using an in vitro cultured differentiation model of oligodendrocytes, we found that both transferrin receptor and ferritin-H are significantly upregulated during oligodendrocyte maturation, implying the essential role of iron in the development of oligodendrocytes. Additional different doses of Fe3＋ in the cultured medium did not affect oligodendrocyte precursor cell maturation or ferritin-H expression but decreased the expression of the transferrin receptor. These results indicate that upregulation of both transferrin receptor and ferritin-H contributes to maturation and myelination of oligodendrocyte precursor cells.

Retinol-binding protein, acute phase reactants and Helicobacter pylori infection in patients with gastric adenocarcinoma

AIM： To determine the serum levels of c-reactive protein （CRP）, transferrin （TRF）, a2-macroglobulin （A2M）, ceruloplasmin （CER）, al-acid glycoprotein （AAG）, prealbumin （P-ALB） and retinol-binding protein （RBP） in gastric carcinoma patients and to explore their possible correlation with underlying Helicobacter pylori （H pylon） infection. METHODS： We measured the serum levels of CRP, TRF, A2M, CER, AAG, P-ALB, and RBP in 153 preoperative patients （93 males; mean age： 63.1±11.3 years） with non-cardia gastric adenocarcinoma and 19 healthy subjects. RESULTS： The levels of CRP, CER, RBP, and AAG in cancer patients were significantly higher than those in healthy controls （P〈0.0001）, while no difference was found regarding the TRF, P-ALB, and A2M levels. Cancer patients with H py/ori infection had significantly lower RBP values compared to non-infected ones （P〈0.0001） and also higher values of CRP and AAG （P = 0.09 andP = 0.08, respectively）. CONCLUSION： High serum levels of CRP, CER and AAG in cancer patients do not seem to be related to H pylori infection. Retinol-binding protein seems to discriminate between infected and non-infected patients with gastric carcinoma. Further studies are needed to explore if it is directly involved in the pathogenesis of the disease or is merely an epiphenomenon.

Study on The Method of Quantitative Analysis of Serum Ferritin and Soluble Transferrin Receptor with Protein Microarray Technology

Objective To establish and evaluate a protein serum ferritin （SF） and soluble transferrin receptor microarray method for combined measurement of （sTfR）. Methods Microarrayer was used to print both anti-SF antibodies I and anti-sTfR antibodies I on each protein microarray. Anti-SF antibodies II and anti-sTfR antibodies II were used as detection antibodies and goat antibodies coupled to Cy3 were used as antibodies Ill. The detection conditions of the quantitative analysis method for simultaneous measurement of SF and sTfR with protein microarray were optimized and evaluated. The protein microarray was compared with commercially available traditional tests with 26 serum samples. Results By comparison experiment, mouse monoclonal antibodies were chosen as the probes and contact printing was chosen as the printing method. The concentrations of SF and sTfR probes were 0.5 mg/mL and 0.5 mg/mL respectively, while those of SF and sTfR detection antibodies were 5 μg/mL and 0.36 μg/mL respectively. Intra- and inter-assay variability was between 3.26% and 18.38% for all tests. The regression coefficients comparing protein microarray with traditional test assays were better than 0.81 for SF and sTfR. Conclusion The present study has established a protein microarray method for combined measurement of SF and sTfR.

TfR1 Extensively Regulates the Expression of Genes Associated with Ion Transport and Immunity

Transferrin receptor 1(TfR1),encoded by the TFRC gene,is the gatekeeper of cellular iron uptake for cells.A variety of molecular mechanisms are at work to tightly regulate TfR1 expression,and abnormal TfR1 expression has been associated with various diseases.In the current study,to determine the regulation pattern of TfR1,we cloned and overexpressed the human TFRC gene in HeLa cells.RNA-sequencing(RNA-seq)was used to analyze the global transcript levels in overexpressed(OE)and normal control(NC)samples.A total of 1669 differentially expressed genes(DEGs)were identified between OE and NC.Gene ontology(GO)analysis was carried out to explore the functions of the DEGs.It was found that multiple DEGs were associated with ion transport and immunity.Moreover,the regulatory network was constructed on basis of DEGs associated with ion transport and immunity,highlighting that TFRC was the node gene of the network.These results together suggested that precisely controlled TfR1 expression might be not only essential for iron homeostasis,but also globally important for cell physiology,including ion transport and immunity.

DL-3-n-butylphthalide alleviates motor disturbance by suppressing ferroptosis in a rat model of Parkinson’s disease

DL-3-n-butylphthalide(NBP)-a compound isolated from Apium graveolens seeds-is protective against brain ischemia via various mechanisms in humans and has been approved for treatment of acute ischemic stroke.NBP has shown recent potential as a treatment for Parkinson’s disease.However,the underlying mechanism of action of NBP remains poorly understood.In this study,we established a rat model of Parkinson’s disease by intraperitoneal injection of rotenone for 28 successive days,followed by intragastric injection of NBP for 14-28 days.We found that NBP greatly alleviated rotenone-induced motor disturbance in the rat model of Parkinson’s disease,inhibited loss of dopaminergic neurons and aggregation ofα-synuclein,and reduced iron deposition in the substantia nigra and iron content in serum.These changes were achieved by alterations in the expression of the iron metabolism-related proteins transferrin receptor,ferritin light chain,and transferrin 1.NBP also inhibited oxidative stress in the substantia nigra and protected mitochondria in the rat model of Parkinson’s disease.Our findings suggest that NBP alleviates motor disturbance by inhibition of iron deposition,oxidative stress,and ferroptosis in the substantia nigra.

Metabolically based liver damage pathophysiology in patients with urea cycle disorders-A new hypothesis

The underlying pathophysiology of liver dysfunction in urea cycle disorders(UCDs) is still largely elusive. There is some evidence that the accumulation of urea cycle(UC) intermediates are toxic for hepatocyte mitochondria. It is possible that liver injury is directly caused by the toxicity of ammonia. The rarity of UCDs, the lack of checking of iron level in these patients, superficial knowledge of UC and an underestimation of the metabolic role of fumaric acid, are the main reasons that are responsible for the incomprehension of the mechanism of liver injury in patients suffering from UCDs. Owing to our routine clinical practice to screen for iron overload in severely ill neonates, with the focus on the newborns suffering from acute liver failure, we report a case of citrullinemia with neonatal liver failure and high blood parameters of iron overload. We hypothesize that the key is in the decreased-deficient fumaric acid production in the course of UC in UCDs that causes several sequentially intertwined metabolic disturbances with final result of liver iron overload. The presented hypothesis could be easily tested by examining the patients suffering from UCDs, for liver iron overload. This could be easily performed in countries with a high population and comprehensive national register for inborn errors of metabolism. Conclusion: Providing the hypothesis is correct, neonatal liver damage in patients having UCD can be prevented by the supplementation of pregnant women with fumaric or succinic acid, prepared in the form of iron supplementation pills. After birth, liverdamage in patients having UCDs can be prevented by supplementation of these patients with zinc fumarate or zinc succinylate, as well.

Transferrin receptor 1 plays an important role in muscle development and denervation-induced muscular atrophy

Previous studies demonstrate an accumulation of transferrin and transferrin receptor 1(TfR1) in regenerating peripheral nerves.However, the expression and function of transferrin and TfR1 in the denervated skeletal muscle remain poorly understood.In this study, a mouse model of denervation was produced by complete tear of the left brachial plexus nerve.RNA-sequencing revealed that transferrin expression in the denervated skeletal muscle was upregulated, while TfR1 expression was downregulated.We also investigated the function of TfR1 during development and in adult skeletal muscles in mice with inducible deletion or loss of TfR1.The ablation of TfR1 in skeletal muscle in early development caused severe muscular atrophy and early death.In comparison, deletion of TfR1 in adult skeletal muscles did not affect survival or glucose metabolism, but caused skeletal muscle atrophy and motor functional impairment, similar to the muscular atrophy phenotype observed after denervation.These findings suggest that TfR1 plays an important role in muscle development and denervation-induced muscular atrophy.This study was approved by the Institutional Animal Care and Use Committee of Beijing Institute of Basic Medical Sciences, China(approval No.SYXK 2017-C023) on June 1, 2018.

Binding Constants for Terbium(Ⅲ) with Chicken Apoovotransferrin

The binding of Tb 3+ to chicken apoovotransferrin was studied by monitoring the fluorescent intensity of Tb 3+ at 549 nm. The conditional equilibrium constants for the complexation of Tb 3+ by chicken apoovotransferrin in 0 1 mol/L hepes, at pH 7 4 and room temperature were measured. The successive macroscopic binding constants are lg K 1=9 08±0 12 and lg K 2=7 36±0 22. The molar fluorescence enhancement of Tb 3+ apoovotransferrin complex is (2 06±0 14)×10 4 mol -1 ·L. The fluorescence quenching experiment and the titration of N terminal monoferric ovotransferrin showed that Tb 3+ has a preference for being bound to the N terminal binding site of apoovotransferrin.

Non-HFE haemochromatosis

Non-HFE hereditary haemochromatosis （HH） refers to a genetically heterogeneous group of iron overload disorders that are unlinked to mutations in the HFE gene. The four main types of non-HFE HH are caused by mutations in the hemojuvelin, hepcidin, transferrin receptor 2 and ferroportin genes. Juvenile haemochromatosis is an autosomal recessive disorder and can be caused by mutations in either hemojuvelin or hepcidin. Ar~ adult onset form of HH similar to HFE-HH is caused by homozygosity for mutations in transferrin receptor 2. The autosomal dominant iron overload disorder ferroportin disease is caused by mutations in the iron exporter ferroportin. The clinical characteristics and molecular basis of the various types of non-HFE haemochromatosis are reviewed. The study of these disorders and the molecules involved has been invaluable in improving our understanding of the mechanisms involved in the regulation of iron metabolism.

Iron metabolism imbalance at the time of listing increases overall and infectious mortality after liver transplantation

BACKGROUND Liver transplantation(LT)is the best treatment for patients with liver cancer or end stage cirrhosis,but it is still associated with a significant mortality.Therefore identifying factors associated with mortality could help improve patient management.The impact of iron metabolism,which could be a relevant therapeutic target,yield discrepant results in this setting.Previous studies suggest that increased serum ferritin is associated with higher mortality.Surprisingly iron deficiency which is a well described risk factor in critically ill patients has not been considered.AIM To assess the impact of pre-transplant iron metabolism parameters on posttransplant survival.METHODS From 2001 to 2011,553 patients who underwent LT with iron metabolism parameters available at LT evaluation were included.Data were prospectively recorded at the time of evaluation and at the time of LT regarding donor and recipient.Serum ferritin(SF)and transferrin saturation(TS)were studied as continuous and categorical variable.Cox regression analysis was used to determine mortality risks factors.Follow-up data were obtained from the local and national database regarding causes of death.RESULTS At the end of a 95-mo median follow-up,196 patients were dead,38 of them because of infections.In multivariate analysis,overall mortality was significantly associated with TS>75%[HR:1.73(1.14;2.63)],SF<100μg/L[HR:1.62(1.12;2.35)],hepatocellular carcinoma[HR:1.58(1.15;2.26)],estimated glomerular filtration rate(CKD EPI Cystatin C)[HR:0.99(0.98;0.99)],and packed red blood cell transfusion[HR:1.05(1.03;1.08)].Kaplan Meier curves show that patients with low SF(<100μg/L)or high SF(>400μg/L)have lower survival rates at 36 mo than patients with normal SF(P=0.008 and P=0.016 respectively).Patients with TS higher than 75%had higher mortality at 12 mo(91.4%±1.4%vs 84.6%±3.1%,P=0.039).TS>75%was significantly associated with infection related death[HR:3.06(1.13;8.23)].CONCLUSION Our results show that iron metabolism imbalance(either deficiency or overload)is associated with post-transplant overall and infectious mortality.Impact of iron supplementation or depletion should be assessed in prospective study.

Transferrin and Its Isoforms from Normal Human Serum Revealed by Several Analytical Techniques

Transferrin（TF） and its isoforms have been widely reported via various analytical techniques, including a noticeable increased number of isoforms with low content of sialic acid（asialo-, monosialo-, and disialo-transferrin） and asialo-TF as well as disialo-TF, with one or several oligosaccharides released in human serum transferrin（hTf）. Here, hTf has been purified by native gradient polyacrylamide gel electrophoresis（PAGEso） before use. The hTf extracted with the electron-transfer approach showed a single subunit band（77.1 Da） in the SDS-PAGE gel, but it exhibited two bands in the native and denatured isoelectric focusing（IEF） gels, namely, hTf-2Fe^3＋ and apo-hTf, without finding any other transferrin isoforms. A reversed phase HPLC（RP-HPLC） equipped with a C18 column effectively separated hTf and its polymers and combined off-line techniques, including peptide mass fingerprinting（PMF）, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry（MALDI-TOF-MS） and database search, and identified the high homology among hTf, apo-hTf, and their isoforms. Moreover, the elution solution consisting of acetonitrile and formic acid could easily denature both hTf and apo-hTf to form various isoforms during separation with HPLC, indicating that chemical factors lead to the formation of various isoforms in transferrin, artificially, during extraction and separation. The authors claimed that only two transferrin isoforms existed in the NHS, namely, hTf-2Fe^3＋ and apo-hTf, which could be employed in biomarkers, to distinguish the healthy population from many disease sufferers, such as, carbohydrate-deficient transferrin（CDT）

miR-126、Transferrin、miR-133b、miR-342和Cystatin C对2型糖尿病肾病的诊断价值

目的探讨miR-126、Transferrin、miR-133b、miR-342和Cystatin C对2型糖尿病肾病的诊断价值。方法选取2型糖尿病肾病患者30例为糖尿病肾病组,2型糖尿病非肾病患者30例为糖尿病非肾病组,同时选取健康体检者30例为对照组,检测3组受试者血清中miR-126和Transferrin的水平,尿中miR-133b、miR-342和Cystatin C的水平。用ROC曲线下面积分析miR-126、Transferrin、miR-133b、miR-342和Cystatin C对2型糖尿病肾病的诊断价值。结果糖尿病肾病患者的miR-126的相对表达量明显低于糖尿病非肾病患者和健康体检者(P<0.05),而其miR-133b和miR-342的相对表达量、Cystatin C和Transferrin的表达量明显高于糖尿病非肾病患者和健康体检者(P <0. 05)。糖尿病非肾病患者miR-126的相对表达量明显低于健康体检者(P <0.05),而其miR-133b的相对表达量和Cystatin C和Transferrin的表达量明显高于健康体检者(P<0.05)。2型糖尿病肾病患者与非2型糖尿病肾病人员的miR-126、miR-133b、miR-342、Cystatin C和Transferrin的灵敏度分别为96%、83%、70%、77%、83%;特异性分别为41%、75%、82%、88%、80%。四项联合检测的灵敏度为97%、特异性为77%,准确率为83%。结论 miR-126、Transferrin、miR-133b、miR-342和Cystatin C可作为诊断2型糖尿病肾病的潜在标志物。

Function of the hemochromatosis protein HFE:Lessons from animal models

Hereditary hemochromatosis （HH） is caused by chronic hyperabsorption of dietary iron. Progressive accumulation of excess iron within tissue parenchymal cells may lead to severe organ damage. The most prevalent type of HH is linked to mutations in the HFE gene, encoding an atypical major histocompatibility complex class I molecule. Shortly after its discovery in 1996, the hemochromatosis protein HFE was shown to physically interact with transferrin receptor 1 （TfR1） and impair the uptake of transferrin-bound iron in cells. However, these findings provided no clue why HFE mutations associate with systemic iron overload. It was later established that all forms of HH result from misregulation of hepcidin expression. This liverderived circulating peptide hormone controls iron efflux from duodenal enterocytes and reticuloendothelial macrophages by promoting the degradation of the iron exporter ferroportin. Recent studies with animal models of HH uncover a crucial role of HFE as a hepatocyte iron sensor and upstream regulator of hepcidin. Thus, hepatocyte HFE is indispensable for signaling to hepcidin, presumably as a constituent of a larger ironsensing complex. A working model postulates that the signaling activity of HFE is silenced when the protein is bound to TfR1. An increase in the iron saturation of plasma transferrin leads to displacement of TfR1 from HFE and assembly of the putative iron-sensing complex. In this way, iron uptake by the hepatocyte is translated into upregulation of hepcidin, reinforcing the concept that the liver is the major regulatory site for systemic iron homeostasis, and not merely an iron storage depot.