Wenli Guo

Disordered hepcidin-ferroportin signaling promotes breast cancer growth

Iron homeostasis is strictly governed in mammals; however, disordered iron metabolism (such as excess iron burden) is recognized as a risk factor for various types of diseases including cancers. Burgeoning evidence indicates that the central signaling of iron homeostasis, the hepcidin-ferroportin axis, is misregulated in cancers. Nonetheless, the mechanisms of misregulated expression of iron-related genes along this signaling in cancers remain largely unknown. In the current study, we found increased levels of serum hepcidin in breast cancer patients. Reduction of hepatic hepcidin through administration of heparin restrained tumorigenic properties of breast tumor cells. Mechanistic investigation revealed that increased iron, bone morphogenetic protein-6 (BMP6) and interleukin-6 (IL-6) jointly promoted the synthesis of hepatic hepcidin. Tumor hepcidin expression was marginally increased in breast tumors relative to adjacent tissues. In contrast, tumor ferroportin concentration was greatly reduced in breast tumors, especially in malignant tumors, compared to adjacent tissues. Elevation of ferroportin concentration inhibited cell proliferation in vitro and in vivo by knocking down tumor hepcidin expression. Additionally, increased IL-6 was demonstrated to jointly enhance the tumorigenic effects of iron through enforcing cell growth. Our combined data overall deciphered the machinery that altered the hepcidin-ferroportin signaling in breast cancers. Thus, targeting the hepcidin-ferroportin signaling would represent a promising therapeutics to restrain breast cancer growth.

Disordered signaling governing ferroportin transcription favors breast cancer growth

Iron is a necessary chemical element needed by all organisms. Iron metabolism is finely tuned in mammals, and the hepcidin-ferroportin (FPN) axis is the central signaling in governing systemic iron homeostasis. Deregulation of this signaling would lead to iron disorders and likely other diseases including cancers. Reduced FPN was previously found to correlate with poor prognosis in breast cancer patients. Nonetheless, the biological effects of abnormal FPN expression in tumor cells remain largely unexplored, and the mechanisms underlying misregulated expression of FPN in cancers keep elusive. In the current study, we scrutinized the effects of abnormal FPN on tumor growth and the molecular mechanisms of diminished tumor FPN. Downregulation of FPN significantly promoted breast cancer growth, whereas FPN upregulation impeded tumor growth. We demonstrated that the transcription factors Nrf2 (nuclear factor erythroid 2-like 2) and MZF-1 (myeloid zinc finger-1) synergistically transactivated FPN expression in breast cancer cells. Moreover, CpG island methylation at the FPN promoter was the reason of attenuated FPN expression. Downregulation of Nrf2 and MZF-1 and hypermethylation of the FPN promoter were concurrently associated with decreased FPN concentration in breast tumors. Taken together, our study highlighted the contribution of disordered iron metabolism to breast cancer growth, and also signified an oncogenic effect of misregulated ferroportin in breast cancers. This work represents a promising starting point to the possibility of restraining breast cancer through targeting FPN or its upstream regulatory factors.

Disruption of iron homeostasis and resultant health effects upon exposure to various environmental pollutants: A critical review

Environmental pollution has become one of the greatest problems in the world, and the concerns about environmental pollutants released by human activities from agriculture and industrial production have been continuously increasing. Although intense efforts have been made to understand the health effects of environmental pollutants, most studies have only focused on direct toxic effects and failed to simultaneously evaluate the long-term adaptive, compensatory and secondary impacts on health. Burgeoning evidence suggests that environmental pollutants may directly or indirectly give rise to disordered element homeostasis, such as for iron. It is crucially important to maintain concerted cellular and systemic iron metabolism. Otherwise, disordered iron metabolism would lead to cytotoxicity and increased risk for various diseases, including cancers. Thus, study on the effects of environmental pollutants upon iron homeostasis is urgently needed. In this review, we recapitulate the available findings on the direct or indirect impacts of environmental pollutants, including persistent organic pollutants (POPs), heavy metals and pesticides, on iron homeostasis and associated adverse health problems. In view of the unanswered questions, more efforts are warranted to investigate the disruptive effects of environmental pollutants on iron homeostasis and consequent toxicities.

Polychlorinated biphenyls (PCBs) inhibit hepcidin expression through an estrogen-like effect associated with disordered systemic iron homeostasis.

Polychlorinated biphenyls (PCBs), with 209 congeners, are a large family of persistent organic pollutants. PCBs elicit a wide range of toxicities, such as neurotoxicity, hepatoxicity, oncogenicity, and endocrine-disrupting effects. However, an understanding of the potential disruption of systematic iron metabolism by PCBs is still limited. To maintain iron homeostasis, the hepcidin-ferroportin (FPN) axis is critically important, and hepcidin is the central governor in guiding dietary iron absorption and iron egress from macrophages. Hepcidin is secreted by hepatocytes and binds to FPN to promote its degradation. Dysregulation of hepcidin gives rise to disordered iron homeostasis, associated with diverse diseases including anemia and β-thalassemia. Our previous study demonstrated that there is an estrogen response element (ERE) within the promoter of hepcidin gene and that its expression is regulated by estrogen. In the current study, we demonstrated that both PCB153 and PCB126 greatly suppress hepcidin expression in HepG2 cells, with a greater repression occurring in cells upon PCB126 treatment. Further studies uncovered that both PCB153 and PCB126 harbor estrogenic activity and that the estrogenic activity of PCB126 was stronger than that of PCB153 in HepG2 cells. Mechanistic investigation revealed that PCBs suppress hepcidin transcription through a functional ERE within the hepcidin promoter, analogous to the action of 17β-estradiol. Moreover, hepatic hepcidin was downregulated in wild-type mice upon PCB126 administration, coupled with elevated serum iron content as well as reduced hepatic and splenic iron mass. These changes were not replicated in hepcidin-deficient mice upon PCB administration. Additionally, hepatocytes were observed with severe accumulation of lipid droplets in the livers of mice challenged with PCB126, irrespective of the presence of hepcidin. To summarize, our results have deciphered a suppressive role of PCBs in restraining the expression of hepcidin through mimicking estrogenic activity and revealed a novel property of PCBs in disrupting systemic iron metabolism. This study also unearthed a PCB-mediated connection linking estrogen-like activity, iron effects, and lipid homeostasis.

Hepcidin deficiency undermines bone load-bearing capacity through inducing iron overload

Osteoporosis is one of the leading disorders among aged people. Bone loss results from a number of physiological alterations, such as estrogen decline and aging. Meanwhile, iron overload has been recognized as a risk factor for bone loss. Systemic iron homeostasis is fundamentally governed by the hepcidin-ferroportin regulatory axis, where hepcidin is the key regulator. Hepcidin deficiency could induce a few disorders, of which iron overload is the most representative phenotype. However, there was little investigation of the effects of hepcidin deficiency on bone metabolism. To this end, hepcidin-deficient (Hamp1(-/-)) mice were employed to address this issue. Our results revealed that significant iron overload was induced in Hamp1(-/-) mice. Importantly, significant decreases of maximal loading and maximal bending stress were found in Hamp1(-/-) mice relative to wildtype (WT) mice. Moreover, the levels of the C-telopeptide of type I collagen (CTX-1) increased in Hamp1(-/-) mice. Therefore, hepcidin deficiency resulted in a marked reduction of bone load-bearing capacity likely through enhancing bone resorption, suggesting a direct correlation between hepcidin deficiency and bone loss. Targeting hepcidin or the pathway it modulates may thus represent a therapeutic for osteopenia or osteoporosis.

Carbon Nanotubes Disrupt Iron Homeostasis and Induce Anemia of Inflammation through Inflammatory Pathway as a Secondary Effect Distant to Their Portal‐of‐Entry

Although numerous toxicological studies have been performed on carbon nanotubes (CNTs), a few studies have investigated their secondary and indirect effects beyond the primary target tissues/organs. Here, a cascade of events are investigated: the initiating event and the subsequent key events necessary for the development of phenotypes, namely CNT-induced pro-inflammatory effects on iron homeostasis and red blood cell formation, which are linked to anemia of inflammation (AI). A panel of CNTs are prepared including pristine multiwall CNTs (P-MWCNTs), aminated MWCNTs (MWCNTs-NH2 ), polyethylene glycol MWCNTs (MWCNTs-PEG), polyethyleneimine MWCNTs (MWCNTs-PEI), and carboxylated MWCNTs (MWCNTs-COOH). It has been demonstrated that all CNT materials provoke inflammatory cytokine interleukin-6 (IL-6) production and stimulate hepcidin induction, associated with disordered iron homeostasis, irrespective of exposure routes including intratracheal, intravenous, and intraperitoneal administration. Meanwhile, PEG and COOH modifications can ameliorate the activation of IL-6-hepcidin signaling. Long-term exposure of MWCNTs results in AI and extramedullary erythropoiesis. Thus, an adverse outcome pathway is identified: MWCNT exposure leads to inflammation, hepatic hepcidin induction, and disordered iron metabolism. Together, the combined data depict the hazardous secondary toxicity of CNTs in incurring anemia through inflammatory pathway. This study will also open a new avenue for future investigations on CNT-induced indirect and secondary adverse effects.

An important role of the hepcidin–ferroportin signaling in affecting tumor growth and metastasis

Epidemiological and experimental studies have suggested that deregulated hepcidin-ferroportin (FPN) signaling is associated with the increased risk of cancers. However, the effects of deregulated hepcidin-FPN signaling on tumor behaviors such as metastasis and epithelial to mesenchymal transition (EMT) have not been closely investigated. In this study, LL/2 cancer cells were found to exhibit an impaired propensity to home into lungs, and a reduced ability to develop tumors was also demonstrated in lungs of Hamp1(-/-) mice. Moreover, hepatic hepcidin deficiency was found to considerably favor tumor-free survival in Hamp1(-/-) mice, compared with wild-type mice. These data thus underscored a contributive role of hepatic hepcidin in promoting lung cancer cell homing and fostering tumor progression. To explore the role of FPN in regulating tumor progression, we genetically engineered 4T1 cells with FPN over-expression upon induction by doxycycline. With this cell line, it was discovered that increased FPN expression reduced cell division and colony formation in vitro, without eliciting significant cell death. Analogously, FPN over-expression impeded tumor growth and metastasis to lung and liver in mice. At the molecular level, FPN over-expression was identified to undermine DNA synthesis and cell cycle progression. Importantly, FPN over-expression inhibited EMT, as reflected by the significant decrease of representative EMT markers, such as Snail1, Twist1, ZEB2, and vimentin. Additionally, there was also a reduction of lactate production in cells upon induction of FPN over-expression. Together, our results highlighted a crucial role of the hepcidin-FPN signaling in modulating tumor growth and metastasis, providing new evidence to understand the contribution of this signaling in cancers.

Icariin regulates systemic iron metabolism by increasing hepatic hepcidin expression through Stat3 and Smad1/5/8 signaling

Systemic iron homeostasis is strictly controlled under normal conditions to ensure a balance between the absorption, utilization, storage and recycling of iron. The hepcidin-ferroportin (FPN) axis is of critical importance in the maintenance of iron homeostasis. Hepcidin deficiency gives rise to enhanced dietary iron absorption, as well as to increased iron release from macrophages, and this in turn results in iron accumulation in the plasma and organs, and is associated with a range of tissue pathologies. Low hepcidin levels have been demonstrated in most forms of hereditary hemochromatosis (HH), as well as in β-thalassemia. Therapies that increase hepcidin concentrations may potentially play a role in the treatment of these iron overload-related diseases. To date, natural compounds have not been extensively investigated for this purpose, to the best of our knowledge. Thus, in the present study, we screened natural compounds that have the potential to regulate hepcidin expression. By performing hepcidin promoter-luciferase assay, RT-qPCR and animal experiments, we demonstrated that icariin and berberine were potent stimulators of hepcidin transcription. Mechanistic experiments indicated that icariin and berberine increased hepcidin expression by activating the signal transducer and activator of transcription 3 (Stat3) and Smad1/5/8 signaling pathways. The induction of hepcidin was confirmed in mice following icariin administration, coupled with associated changes in serum and tissue iron concentrations. In support of these findings, the icariin analogues, epimedin A, B and C, also increased hepatic hepcidin expression. However, these changes were not observed in hepcidin-deficient [Hamp1-/- or Hamp1‑knockout (KO)] mice following icariin administration, thereby verifying hepatic hepcidin as the target of icariin. Although berberine exhibited a robust capacity to promote hepcidin expression in vitro, it failed to alter hepcidin expression in mice. Taken together, the findings of the present study suggest that icariin exhibits a robust capacity to increase hepatic hepcidin expression and to modulate systemic iron homeostasis. The present study therefore highlights the significance of using natural compounds to ameliorate iron disorders through the regulation of hepcidin expression.

Establishment of a novel orthotopic model of breast cancer metastasis to the lung

Breast cancer is the second leading cause of cancer-related death among women, and distant metastasis is responsible for the death of ~90% of these patients. However, despite recent advances, the underlying mechanisms responsible for breast cancer metastasis remain elusive. A great impediment to this is the lack of appropriate orthotopic models of breast cancer metastasis to distant organs. In the present study, we established a novel orthotopic model of breast cancer metastasis to the lungs in mice, where metastatic sublines of 4T1 cells revealed enhanced metastatic propensity to the lungs. All mice (100%) developed lung metastasis upon orthotopic implantation of a metastatic subline of 4T1 cells, in contrast to 10% of mice with lung metastasis for a subline derived from primary tumors and 60% of mice with lung metastasis for parental 4T1 cells. At the molecular level, significant epithelial-mesenchymal transition was characterized in these metastatic sublines, which is likely at least partially, responsible for the enhanced metastasis. These established cell lines provide a novel platform to study the relevant molecular basis of metastasis and metastasis-specific therapeutics.

Synergistic hepatotoxicity by cadmium and chlorpyrifos: Disordered hepatic lipid homeostasis

Due to its extensive application, chlorpyrifos (CPF) has contaminated a diverse range of environmental substrates, fruits and vegetables. A number of studies have suggested that CPF may incur adverse effects on human health, including neurotoxicity, hepatotoxicity and endocrine disruption. Additionally, cadmium (Cd) is one of the most prevalent environmental heavy metals, as a result of considerable use in a wide spectrum of industrial fields. Exposure to Cd can cause several lesions in various organs, including the liver, kidneys and lungs. CPF and Cd often co-exist in the environment, food and crops, however, their joint exposure and potential synergistic toxicity are largely neglected and unrecognized. Our previous study characterized an interaction between CPF and Cd, which may occur via bonding between Cd2+ and the nitrogen atom in the pyridine ring of CPF, or the chelation between one Cd2+ and two CPF molecules. Our previous study also identified increased hepatotoxicity induced by CPF and Cd together compared with the individual compounds. In the present study, the effects of the concomitant exposure of CPF and Cd on lipid metabolism in hepatocytes was investigated. The results demonstrated an accumulation of lipids in hepatocytes, induced by the CPF and Cd complex, which was fundamentally distinct from its parental chemicals. Notably, the molecular mechanism by which the CPF-Cd complex significantly induced hepatic lipogenesis was revealed, elevating the concentrations of sterol regulatory element-binding protein-1 and fatty acid synthase. These findings pave the way for future studies in recognizing synergistic biological effects between pollutants.