Glycosylation and Characterization of Human Transferrin in an End-Stage Kidney Disease.

Chronic kidney disease (CKD) is a global health concern affecting approximately one billion individuals worldwide. End-stage kidney disease (ESKD), the most severe form of CKD, is often accompanied by anemia. Peritoneal dialysis (PD), a common treatment for ESKD, utilizes the peritoneum for solute transfer but is associated with complications including protein loss, including transferrin (Tf) a key protein involved in iron transport. This study investigated Tf characteristics in ESKD patients compared to healthy individuals using lectin microarray, spectroscopic techniques and immunocytochemical analysis to assess Tf interaction with transferrin receptors (TfRs). ESKD patients exhibited altered Tf glycosylation patterns, evidenced by significant changes in lectin reactivity compared to healthy controls. However, structural analyses revealed no significant differences in the Tf secondary or tertiary structures between the two groups. A functional analysis demonstrated comparable Tf-TfR interaction in both PD and healthy samples. Despite significant alterations in Tf glycosylation, structural integrity and Tf-TfR interaction remained preserved in PD patients. These findings suggest that while glycosylation changes may influence iron metabolism, they do not impair Tf function. The study highlights the importance of a glucose-free dialysis solutions in managing anemia exacerbation in PD patients with poorly controlled anemia, potentially offering a targeted therapeutic approach to improve patient outcomes.

Gene expression of iron transporters, markers of vascularization and structural integrity in placenta of mothers with and without anemia.

OBJECTIVE: To compare the mRNA expression of placental iron transporters (TfR-1 and FPN), markers of placental vascularization (VEGF and sFLT1) and marker of structural integrity (LMN-A) in term women with and without iron deficiency anemia. MATERIALS AND METHODS: A total of 30 pregnant women were enrolled; 15 cases of iron deficiency anemia (Hb 7-10.9 gm/dL) and 15 gestational age matched healthy controls (Hb ≥ 11 gm/dL). Peripheral venous blood was collected for assessment of hemoglobin levels and serum iron profile. Placental tissue was used for assessing the mRNA expression of TfR-1, FPN, VEGF, sFLT-1 and LMN-A via real time PCR. RESULTS: Placental expression of TfR-1, VEGF and LMN-A was increased in pregnant women with anemia compared to healthy pregnant controls. Placental expression of sFLT-1 was decreased in pregnant women with anemia compared to healthy pregnant controls. There was no change in the placental expression of FPN. CONCLUSION: The increased expression of TfR-1, VEGF and LMN-A in cases of iron deficiency anemia are most likely to be compensatory in nature to help maintain adequate fetal iron delivery. WHAT DOES THIS STUDY ADDS TO THE CLINICAL WORK: Compensatory changes in the placenta aimed at buffering transport of iron to the fetus are seen in pregnant women with anemia compared to healthy pregnant controls.

Iron controls the development of airway hyperreactivity by regulating ILC2 metabolism and effector function.

Group 2 innate lymphoid cells (ILC2s) rapidly induce a type 2 inflammation in the lungs in response to allergens. Here, we focused on the role of iron, a critical nutritional trace element, on ILC2 function and asthma pathogenesis. We found that transferrin receptor 1 (TfR1) is rapidly up-regulated and functional during ILC2 activation in the lungs, and blocking transferrin uptake reduces ILC2 expansion and activation. Iron deprivation reprogrammed ILC2 metabolism, inducing a HIF-1α-driven up-regulation of glycolysis and inhibition of oxidative mitochondrial activity. Consequently, we observed that in vivo iron chelation or induction of hypoferremia reduced the development of airway hyperreactivity in experimental models of ILC2-driven allergic asthma. Human circulating ILC2s rapidly induced TfR1 during activation, whereas inhibition of iron uptake or iron deprivation reduced effector functions. Last, we found a negative relationship between circulating ILC2 TfR1 expression and airway function in cohorts of patients with asthma. Collectively, our studies define cellular iron as a critical regulator of ILC2 function.

MARK2 phosphorylates KIF13A at a 14-3-3 binding site to polarize vesicular transport of transferrin receptor within dendrites.

Neurons regulate the microtubule-based transport of certain vesicles selectively into axons or dendrites to ensure proper polarization of function. The mechanism of this polarized vesicle transport is still not fully elucidated, though it is known to involve kinesins, which drive anterograde transport on microtubules. Here, we explore how the kinesin-3 family member KIF13A is regulated such that vesicles containing transferrin receptor (TfR) travel only to dendrites. In experiments involving live-cell imaging, knockout of KIF13A, BioID assay, we found that the kinase MARK2 phosphorylates KIF13A at a 14-3-3 binding motif, strengthening interaction of KIF13A with 14-3-3 such that it dissociates from TfR-containing vesicles, which therefore cannot enter axons. Overexpression of KIF13A or knockout of MARK2 leads to axonal transport of TfR-containing vesicles. These results suggest a unique kinesin-based mechanism for polarized transport of vesicles to dendrites.

New Transferrin Receptor-Targeted Peptide-Doxorubicin Conjugates: Synthesis and In Vitro Antitumor Activity.

Poor selectivity to tumor cells is a major drawback in the clinical application of the antitumor drug doxorubicin (DOX). Peptide-drug conjugates (PDCs) constructed by modifying antitumor drugs with peptide ligands that have high affinity to certain overexpressed receptors in tumor cells are increasingly assessed for their possibility of tumor-selective drug delivery. However, peptide ligands composed of natural L-configuration amino acids have the defects of easy enzymatic degradation and insufficient biological stability. In this study, two new PDCs (LT7-SS-DOX and DT7-SS-DOX) were designed and synthesized by conjugating a transferrin receptor (TfR) peptide ligand LT7 (HAIYPRH) and its retro-inverso analog DT7 (hrpyiah), respectively, with DOX via a disulfide bond linker. Both conjugates exhibited targeted antiproliferative effects on TfR overexpressed tumor cells and little toxicity to TfR low-expressed normal cells compared with free DOX. Moreover, the DT7-SS-DOX conjugate possessed higher serum stability, more sustained reduction-triggered drug release characteristics, and stronger in vitro antiproliferative activity as compared to LT7-SS-DOX. In conclusion, the coupling of antitumor drugs with the DT7 peptide ligand can be used as a promising strategy for the further development of stable and efficient PDCs with the potential to facilitate TfR-targeted drug delivery.

Rocaglamide regulates iron homeostasis by suppressing hepcidin expression.

The anemia of inflammation (AI) is characterized by the presence of inflammation and abnormal elevation of hepcidin. Accumulating evidence has proved that Rocaglamide (RocA) was involved in inflammation regulation. Nevertheless, the role of RocA in AI, especially in iron metabolism, has not been investigated, and its underlying mechanism remains elusive. Here, we demonstrated that RocA dramatically suppressed the elevation of hepcidin and ferritin in LPS-treated mice cell line RAW264.7 and peritoneal macrophages. In vivo study showed that RocA can restrain the depletion of serum iron (SI) and transferrin (Tf) saturation caused by LPS. Further investigation showed that RocA suppressed the upregulation of hepcidin mRNA and downregulation of Fpn1 protein expression in the spleen and liver of LPS-treated mice. Mechanistically, this effect was attributed to RocA's ability to inhibit the IL-6/STAT3 pathway, resulting in the suppression of hepcidin mRNA and subsequent increase in Fpn1 and TfR1 expression in LPS-treated macrophages. Moreover, RocA inhibited the elevation of the cellular labile iron pool (LIP) and reactive oxygen species (ROS) induced by LPS in RAW264.7 cells. These findings reveal a pivotal mechanism underlying the roles of RocA in modulating iron homeostasis and also provide a candidate natural product on alleviating AI.

Imbalance of Iron Availability and Demand in Patients With Acute and Chronic Heart Failure.

BACKGROUND: Iron deficiency (ID) is a frequent comorbidity in patients with acute (AHF) and chronic heart failure (CHF) associated with morbidity and death. We aimed to better characterize iron homeostasis in patients with heart failure applying different biomarkers and to evaluate the accuracy of current ID definition by the European Society of Cardiology/American College of Cardiology/American Heart Association to indicate tissue iron availability and demand. METHODS AND RESULTS: We performed a retrospective cohort study investigating 277 patients with AHF and 476 patients with CHF between February 2021 and May 2022. Patients with AHF had more advanced ID than patients with CHF, reflected by increased soluble transferrin receptor and soluble transferrin receptor-ferritin index, and lower ferritin, serum iron, transferrin saturation, hepcidin, and reticulocyte hemoglobin. Decreased iron availability or increased tissue iron demand, reflected by increased soluble transferrin receptor-ferritin index and decreased reticulocyte hemoglobin, was found in 84.1% (AHF) and 28.0% (CHF) with absolute ID and in 50.0% (AHF) and 10.5% (CHF) with combined ID according to the current European Society of Cardiology/American College of Cardiology/American Heart Association-based ID definition. Low hepcidin expression as an indicator of systemic ID was found in 91.1% (AHF) and 80.4% (CHF) of patients with absolute ID and in 32.3% (AHF) and 18.8% (CHF) of patients with combined ID. ID definitions with higher specificity reduce the need for iron supplementation by 25.5% in patients with AHF and by 65.6% in patients with CHF. CONCLUSIONS: Our results suggest that the current European Society of Cardiology/American College of Cardiology/American Heart Association-based ID definition might overestimate true ID, particularly in CHF. More stringent thresholds for ID could more accurately identify patients with heart failure with reduced tissue iron availability who benefit from intravenous iron supplementation.

Exploring the complex dynamics of BMI, age, and physiological indicators in early adolescents.

BACKGROUND AND OBJECTIVES: To investigate the relationship between body mass index (BMI) and blood biochemical indicators in early adolescence, and to provide ideas for early prevention of diseases and explore possible disease-related predictors. METHODS: 3125 participants aged 10 ∼ 14 years were selected from China from the survey of "China Nutrition and Health Surveillance ( 2016 ∼ 2017 ) ". Employing advanced statistical methods, including generalized linear models, heatmaps, hierarchical clustering, and generalized additive models, the study delved into the associations between BMI and various biochemical indicators. RESULTS: In early adolescence, indicators including systolic pressure, diastolic pressure, weight, height, BMI, hemoglobin, blood uric acid, serum creatinine, albumin, vitamin A presented increasing trends with the increase of age ( P < 0.05 ), whereas LDL-C, vitamin D, and ferritin showed decreasing trends with the increase of age ( P < 0.05 ). The increase in hemoglobin and blood uric acid levels with age was more pronounced in males compared to females ( P < 0.05 ). BMI was positively correlated with blood glucose, hemoglobin, triglyceride, LDL-C, blood uric acid, serum creatinine, ferritin, transferrin receptor, hs-CRP, total protein, vitamin A ( P < 0.05 ). There was a significant BMI × age interaction in the correlation analysis with LDL-C, transferrin receptor, serum creatinine, and hs-CRP ( P < 0.05 ). BMI was a risk factor for hypertension, hypertriglyceridemia, low high density lipoprotein cholesterolemia, and metabolic syndrome in all age groups ( OR > 1, P < 0.05 ). CONCLUSIONS: High BMI was a risk factor for hypertension, hypertriglyceridemia, low high density lipoprotein cholesterolemia, and MetS in early adolescents. With the focus on energy intake beginning in early adolescence, the maintenance of a healthy weight warrants greater attention.

MEMO1 binds iron and modulates iron homeostasis in cancer cells.

Mediator of ERBB2-driven cell motility 1 (MEMO1) is an evolutionary conserved protein implicated in many biological processes; however, its primary molecular function remains unknown. Importantly, MEMO1 is overexpressed in many types of cancer and was shown to modulate breast cancer metastasis through altered cell motility. To better understand the function of MEMO1 in cancer cells, we analyzed genetic interactions of MEMO1 using gene essentiality data from 1028 cancer cell lines and found multiple iron-related genes exhibiting genetic relationships with MEMO1. We experimentally confirmed several interactions between MEMO1 and iron-related proteins in living cells, most notably, transferrin receptor 2 (TFR2), mitoferrin-2 (SLC25A28), and the global iron response regulator IRP1 (ACO1). These interactions indicate that cells with high-MEMO1 expression levels are hypersensitive to the disruptions in iron distribution. Our data also indicate that MEMO1 is involved in ferroptosis and is linked to iron supply to mitochondria. We have found that purified MEMO1 binds iron with high affinity under redox conditions mimicking intracellular environment and solved MEMO1 structures in complex with iron and copper. Our work reveals that the iron coordination mode in MEMO1 is very similar to that of iron-containing extradiol dioxygenases, which also display a similar structural fold. We conclude that MEMO1 is an iron-binding protein that modulates iron homeostasis in cancer cells.

Reducing neonatal Fc receptor binding enhances clearance and brain-to-blood ratio of TfR-delivered bispecific amyloid-ß antibody.

Recent development of amyloid-ß (Aß)-targeted immunotherapies for Alzheimer's disease (AD) have highlighted the need for accurate diagnostic methods. Antibody-based positron emission tomography (PET) ligands are well suited for this purpose as they can be directed toward the same target as the therapeutic antibody. Bispecific, brain-penetrating antibodies can achieve sufficient brain concentrations, but their slow blood clearance remains a challenge, since it prolongs the time required to achieve a target-specific PET signal. Here, two antibodies were designed based on the Aß antibody bapineuzumab (Bapi) - one monospecific IgG (Bapi) and one bispecific antibody with an antigen binding fragment (Fab) of the transferrin receptor (TfR) antibody 8D3 fused to one of the heavy chains (Bapi-Fab8D3) for active, TfR-mediated transport into the brain. A variant of each antibody was designed to harbor a mutation to the neonatal Fc receptor (FcRn) binding domain, to increase clearance. Blood and brain pharmacokinetics of radiolabeled antibodies were studied in wildtype (WT) and AD mice (AppNL-G-F). The FcRn mutation substantially reduced blood half-life of both Bapi and Bapi-Fab8D3. Bapi-Fab8D3 showed high brain uptake and the brain-to-blood ratio of its FcRn mutated form was significantly higher in AppNL-G-F mice than in WT mice 12 h after injection and increased further up to 168 h. Ex vivo autoradiography showed specific antibody retention in areas with abundant Aß pathology. Taken together, these results suggest that reducing FcRn binding of a full-sized bispecific antibody increases the systemic elimination and could thereby drastically reduce the time from injection to in vivo imaging.

Global distribution, cross-species transmission, and receptor binding of canine parvovirus-2: Risks and implications for humans.

For canine parvovirus -2 (CPV-2), a zoonotic virus capable of cross-species transmission in animals, the amino acid changes of capsid protein VP2 are key factors when binding to other species' transferrin receptors (TfR). CPV-2 variants can spread from felines and canines, for example, to Carnivora, Artiodactyla, and Pholidota species, and CPV-2c variants are essential to spread from Carnivora to Artiodactyla and Pholidota species in particular. In our study, a CPV-2a variant maintained a relatively stable trend, and the proportion of CPV-2c gradually rose from 1980 to 2021. The VP2 amino acid sequence analysis showed that five amino acid mutations at 426E/D, 305H/D, and 297S may be necessary for the virus to bind to different host receptors. Meanwhile, receptor-binding loop regions and amino acid sites 87 L, 93 N, 232I, and 305Y were associated with CPV-2 cross-species transmission. The homology of TfRs in different hosts infected with CPV-2 ranged from 77.2 % to 99.0 %, and from pig to feline, canine, and humans was 80.7 %, 80.4 %, and 77.2 %, respectively. The amino acid residues of TfRs involved in the viral binding in those hosts are highly conserved, which suggests that CPV-2 may be capable of pig-to-human transmission. Our analysis of the origin, evolutionary trend, cross-species transmission dynamics, and genetic characteristics of CPV-2 when binding to host receptors provides a theoretical basis for further research on CPV-2's mechanism of cross-species transmission and for establishing an early warning and monitoring mechanism for the possible threat of CPV-2 to animal-human public security.

Biomimetic peroxidase MOF-Fe promotes bone defect repair by inhibiting TfR2 and activating the BMP2 pathway.

BACKGROUND: Large bone defects pose a clinical treatment challenge; inhibiting transferrin receptor 2 (TfR2), which is involved in iron metabolism, can promote osteogenesis. Iron-based metal-organic frameworks (MOF-Fe) particles not only inhibit TfR2 but also serve as biomimetic catalysts to remove hydrogen peroxide in reactive oxygen species (ROS); excess ROS can disrupt the normal functions of osteoblasts, thereby hindering bone regeneration. This study explored the potential effects of MOF-Fe in increasing osteogenic activity and clearing ROS. METHODS: In vitro experiments were performed to investigate the osteogenic effects of MOF-Fe particles and assess their impact on cellular ROS levels. To further validate the role of MOF-Fe in promoting bone defect repair, we injected MOF-Fe suspensions into the femoral defects of SD rats and implanted MOF-Fe-containing hydrogel scaffolds in rabbit cranial defect models and observed their effects on bone healing. RESULTS: In vitro, the presence of MOF-Fe significantly increased the expression levels of osteogenesis-related genes and proteins compared to those in the control group. Additionally, compared to those in the untreated control group, the cells treated with MOF-Fe exhibited a significantly increased ability to remove hydrogen peroxide from ROS and generate oxygen and water within the physiological pH range. In vivo experiments further confirmed the positive effect of MOF-Fe in promoting bone defect repair. CONCLUSION: This study supports the application of MOF-Fe as an agent for bone regeneration, particularly for mitigating ROS and activating the bone morphogenetic protein (BMP) pathway, demonstrating its potential value.

Plasticity changes in iron homeostasis in hibernating Daurian ground squirrels (Spermophilus dauricus) may counteract chronically inactive skeletal muscle atrophy.

Disuse-induced muscular atrophy is frequently accompanied by iron overload. Hibernating animals are a natural animal model for resistance to disuse muscle atrophy. In this paper, we explored changes in skeletal muscle iron content of Daurian ground squirrels (Spermophilus dauricus) during different periods of hibernation as well as the regulatory mechanisms involved. The results revealed that compared with the summer active group (SA), iron content in the soleus muscle (SOL) decreased (- 65%) in the torpor group (TOR), but returned to normal levels in the inter-bout arousal (IBA); splenic iron content increased in the TOR group (vs. SA, + 67%), decreased in the IBA group (vs. TOR, - 37%). Expression of serum hepcidin decreased in the TOR group (vs. SA, - 22%) and returned to normal levels in the IBA groups; serum ferritin increased in the TOR group (vs. SA, + 31%), then recovered in the IBA groups. Soleus muscle transferrin receptor 1 (TfR1) expression increased in the TOR group (vs. SA, + 83%), decreased in the IBA group (vs. TOR, - 30%); ferroportin 1 increased in the IBA group (vs. SA, + 55%); ferritin increased in the IBA group (vs. SA, + 42%). No significant differences in extensor digitorum longus in iron content or iron metabolism-related protein expression were observed among the groups. Significantly, all increased or decreased indicators in this study returned to normal levels after the post-hibernation group, showing remarkable plasticity. In summary, avoiding iron overload may be a potential mechanism for hibernating Daurian ground squirrels to avoid disuse induced muscular atrophy. In addition, the different skeletal muscle types exhibited unique strategies for regulating iron homeostasis.

TFR1-Mediated Iron Metabolism Orchestrates Tumor Ferroptosis and Immunity in Non-Small Cell Lung Cancer.

This study aimed to investigate the underlying molecular mechanisms of transferrin receptor (TFR1) in non-small cell lung cancer (NSCLC). Histological analysis was performed using hematoxylin-eosin (HE) staining. The number of CD8+ T cell were determined by flow cytometry and immunofluorescence assays. mRNA levels were analyzed by qRT-PCR. Protein expression was detected by western blot. Ferroptosis was detected by using propidium iodide (PI) staining. Xenograft experiment was applied for determining tumor growth. The results showed that interferon (IFN)-γ plus iron dextran (FeDx) induced iron overload and the ferroptosis of NSCLC cells. Moreover, IFN-γ-mediated upregulation of TFR1 promoted ferritinophagy and tumor cell ferroptosis via blocking via blocking ferritin heavy chain 1 (FTH1)/ ferritin light chain (FTL) signaling. However, TFR1 knockout suppressed the ferroptosis of tumor cells. Furthermore, FeDx-mediated iron overload promoted the sensitivity of anti-programmed death ligand 1 (PD-L1) therapies. Clinically, TFR1 was downregulated in NSCLC patients. Low levels of TFR1 predicted decreased CD8+ T cells. Taken together, IFN-γ combined with iron metabolism therapies may provide a novel alternative for NSCLC.

Correlation between ferroptosis and adriamycin resistance in breast cancer regulated by transferrin receptor and its molecular mechanism.

Breast cancer is the most prevalent malignant tumor in women. Adriamycin (ADR) is a primary chemotherapy drug, but resistance limits its effectiveness. Ferroptosis, a newly identified cell death mechanism, involves the transferrin receptor (TFRC), closely linked with tumor cells. This study aimed to explore TFRC and ferroptosis's role in breast cancer drug resistance. Bioinformatics analysis showed that TFRC was significantly downregulated in drug-resistant cell lines, and patients with low TFRC expression might demonstrate a poor chemotherapeutic response to standard treatment. High expression of TFRC was positively correlated with most of the ferroptosis-related driver genes. The research findings indicate that ferroptosis markers were higher in breast cancer tissues than in normal ones. In chemotherapy-sensitive cases, Ferrous ion (Fe2+ ) and malondialdehyde (MDA) levels were higher than in resistant cases (all p < .05). TFRC expression was higher in breast cancer than in normal tissue, especially in the sensitive group (all p < .05). Cytological experiments showed increased hydrogen peroxide (H2 O2 ) after ADR treatment in both sensitive and resistant cells, with varying MDA changes (all p < .05). Elevating TFRC increased Fe2+ and MDA in ADR-resistant cells, enhancing their sensitivity to ADR. However, TFRC upregulation combined with ADR increased proliferation and invasiveness in resistant cell lines (all p < .05). In conclusion, ADR resistance to breast cancer is related to the regulation of iron ion-mediated ferroptosis by TFRC. Upregulation of TFRC in ADR-resistant breast cancer cells activates ferroptosis and reverses ADR chemotherapy resistance of breast cancer.

E3 ubiquitin ligase CHIP interacts with transferrin receptor 1 for degradation and promotes cell proliferation through inhibiting ferroptosis in hepatocellular carcinoma.

Hepatocellular carcinoma (HCC) is the major form of liver malignancy with high incidence and mortality. Identifying novel biomarkers and understanding regulatory mechanisms underlying the development and progression of HCC are critical for improving diagnosis, treatment and patient outcomes. Carboxyl terminus of Hsc-70-interacting protein (CHIP) is a well-described U-box-type E3 ubiquitin ligase which promotes the ubiquitination and degradation of numerous tumor-associated proteins. Recent studies have shown that CHIP can play as a tumor-suppressor gene or an oncogene in different kinds of malignancies. To date, the function and mechanism of CHIP in hepatocellular carcinoma remains largely unknown. Based on TCGA data, we found that compared with high CHIP expression, the overall survival of HCC patients with low expression of CHIP was better. In addition, CHIP overexpression markedly enhanced HCC cell proliferation and colony formation. Conversely, knockdown of CHIP restrained the proliferation and colony formation of HCC cells. Meanwhile, knockdown of CHIP decreased mitochondrial cristae or ruptured outer mitochondrial membrane, promoted the accumulation of Fe2+ and ferroptosis of HCC cells. Further research for the first time confirmed that CHIP interacts and degrades transferrin receptor 1 (TfR1) by ubiquitin-proteasome pathway, which leads to the inhibition of ferroptosis and promotes the proliferation of HCC cells. The analysis of proteomics data from CPTAC revealed a negative correlation between CHIP and TfR1 protein expression levels in HCC. These findings indicate that CHIP acts as a negative modulator of ferroptosis and functions as an oncogene in HCC.

Inhibition of Gpx4-mediated ferroptosis alleviates cisplatin-induced hearing loss in C57BL/6 mice.

Cisplatin-induced hearing loss is a common side effect of cancer chemotherapy in clinics; however, the mechanism of cisplatin-induced ototoxicity is still not completely clarified. Cisplatin-induced ototoxicity is mainly associated with the production of reactive oxygen species, activation of apoptosis, and accumulation of intracellular lipid peroxidation, which also is involved in ferroptosis induction. In this study, the expression of TfR1, a ferroptosis biomarker, was upregulated in the outer hair cells of cisplatin-treated mice. Moreover, several key ferroptosis regulator genes were altered in cisplatin-damaged cochlear explants based on RNA sequencing, implying the induction of ferroptosis. Ferroptosis-related Gpx4 and Fsp1 knockout mice were established to investigate the specific mechanisms associated with ferroptosis in cochleae. Severe outer hair cell loss and progressive damage of synapses in inner hair cells were observed in Atoh1-Gpx4-/- mice. However, Fsp1-/- mice showed no significant hearing phenotype, demonstrating that Gpx4, but not Fsp1, may play an important role in the functional maintenance of HCs. Moreover, findings showed that FDA-approved luteolin could specifically inhibit ferroptosis and alleviate cisplatin-induced ototoxicity through decreased expression of transferrin and intracellular concentration of ferrous ions. This study indicated that ferroptosis inhibition through the reduction of intracellular ferrous ions might be a potential strategy to prevent cisplatin-induced hearing loss.

Tetramethylpyrazine attenuates renal tubular epithelial cell ferroptosis in contrast-induced nephropathy by inhibiting transferrin receptor and intracellular reactive oxygen species.

Contrast-induced nephropathy (CIN) is a leading cause of hospital-acquired acute kidney injury (AKI). Recently, ferroptosis was reported to be crucial for AKI pathogenesis. Our previous studies indicated antioxidant tetramethylpyrazine (TMP) prevent CIN in vivo. However, whether ferroptosis is involved in TMP nephroprotective mechanism against CIN is unclear. In the present study, we investigated the role of renal tubular epithelial cell ferroptosis in TMP reno-protective effect against CIN and the molecular mechanisms by which TMP regulates ferroptosis. Classical contrast-medium, Iohexol, was used to construct CIN models in rats and HK-2 cells. Results showed that tubular cell injury was accompanied by ferroptosis both in vivo and in vitro, including the typical features of ferroptosis, Fe2+ accumulation, lipid peroxidation and decreased glutathione peroxidase 4 (GPX4). Ferroptosis inhibition by classic inhibitors Fer-1 and DFO promoted cell viability and reduced intracellular ROS production. Additionally, TMP significantly inhibited renal dysfunction, reduced AKI biomarkers, prevented ROS production, inhibited renal Fe2+ accumulation and increased GPX4 expression. Expressions of various proteins associated with iron ion metabolism, including transferrin receptor (TFRC), divalent metal transporter 1, iron-responsive element binding protein 2, ferritin heavy chain 1, ferroportin 1, and heat shock factor binding protein 1, were examined using mechanistic analyses. Among these, TFRC changes were the most significant after TMP pretreatment. Results of siRNA knockdown and plasmid overexpression of TFRC indicated that TFRC is essential for TMP to alleviate ferroptosis and reduce LDH release, Fe2+ accumulation and intracellular ROS. Our findings provide crucial insights about the potential of TMP in treating AKI associated with ferroptosis.

TFR1 knockdown alleviates iron overload and mitochondrial dysfunction during neural differentiation of Alzheimer's disease-derived induced pluripotent stem cells by interacting with GSK3B.

Iron metabolism disorders are implicated in the pathogenesis of Alzheimer's disease (AD). It was previously reported that transferrin receptor (TFR1) expression was upregulated in AD mouse model. However, the precise biological functions of TFR1 in AD progression remains unclear. Herein, we observed a gradual increase in TFR1 protein expression during the differentiation of AD patient-derived induced pluripotent stem cells (AD-iPS). TFR1 knockdown inhibited the protein expression of ferritin and ferritin heavy chain 1 (FTH1), enhanced the expression of ferroportin 1 (FPN1), and decreased intracellular levels of total iron, labile iron, and reactive oxygen species (ROS). Moreover, TFR1 knockdown improved mitochondrial membrane potential (MMP), increased adenosine triphosphate (ATP) content, downregulated mitochondrial fission proteins, and upregulated mitochondrial fusion proteins. TFR1 knockdown alleviated iron overload and mitochondrial dysfunction in neural cells differentiated from AD-iPS, while TFR1 overexpression showed the opposite results. Additionally, TFR1interacted with glycogen synthase kinase 3 beta (GSK3B) and promoted GSK3B expression. GSK3B overexpression reversed the inhibitory effects of TFR1 knockdown on iron overload and mitochondrial dysfunction in AD-iPS differentiated neural cells. In conclusion, TFR1 knockdown alleviated iron overload and mitochondrial dysfunction in neural cells differentiated from AD-iPS by promoting GSK3B expression. Our findings provide a potential therapeutic target for the treatment of AD.

Human transferrin receptor can mediate SARS-CoV-2 infection.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has been detected in almost all organs of coronavirus disease-19 patients, although some organs do not express angiotensin-converting enzyme-2 (ACE2), a known receptor of SARS-CoV-2, implying the presence of alternative receptors and/or co-receptors. Here, we show that the ubiquitously distributed human transferrin receptor (TfR), which binds to diferric transferrin to traffic between membrane and endosome for the iron delivery cycle, can ACE2-independently mediate SARS-CoV-2 infection. Human, not mouse TfR, interacts with Spike protein with a high affinity (KD ~2.95 nM) to mediate SARS-CoV-2 endocytosis. TfR knock-down (TfR-deficiency is lethal) and overexpression inhibit and promote SARS-CoV-2 infection, respectively. Humanized TfR expression enables SARS-CoV-2 infection in baby hamster kidney cells and C57 mice, which are known to be insusceptible to the virus infection. Soluble TfR, Tf, designed peptides blocking TfR-Spike interaction and anti-TfR antibody show significant anti-COVID-19 effects in cell and monkey models. Collectively, this report indicates that TfR is a receptor/co-receptor of SARS-CoV-2 mediating SARS-CoV-2 entry and infectivity by likely using the TfR trafficking pathway.