Serum and liver iron differently regulate the bone morphogenetic protein 6 (BMP6)-SMAD signaling pathway in mice

The bone morphogenetic protein 6 (BMP6)-SMAD signaling pathway is a central regulator of hepcidin expression and systemic iron balance. However, the molecular mechanisms by which iron is sensed to regulate BMP6-SMAD signaling and hepcidin expression are unknown. Here we examined the effects of circulating and tissue iron on Bmp6-Smad pathway activation and hepcidin expression in vivo after acute and chronic enteral iron administration in mice. We demonstrated that both transferrin saturation and liver iron content independently influence hepcidin expression. Although liver iron content is independently positively correlated with hepatic Bmp6 messenger RNA (mRNA) expression and overall activation of the Smad1/5/8 signaling pathway, transferrin saturation activates the downstream Smad1/5/8 signaling cascade, but does not induce Bmp6 mRNA expression in the liver. Hepatic inhibitory Smad7 mRNA expression is increased by both acute and chronic iron administration and mirrors overall activation of the Smad1/5/8 signaling cascade. In contrast to the Smad pathway, the extracellular signal-regulated kinase 1 and 2 (Erk1/2) mitogen-activated protein kinase (Mapk) signaling pathway in the liver is not activated by acute or chronic iron administration in mice. CONCLUSION: Our data demonstrate that the hepatic Bmp6-Smad signaling pathway is differentially activated by circulating and tissue iron to induce hepcidin expression, whereas the hepatic Erk1/2 signaling pathway is not activated by iron in vivo.     

Increased adipose tissue expression of hepcidin in severe obesity is independent from diabetes and NASH

BACKGROUNDS & AIMS: Hepcidin is an acute-phase response peptide. We have investigated the possible involvement of hepcidin in massive obesity, a state of chronic low-grade inflammation. Three groups of severely obese patients with or without diabetes or nonalcoholic steatohepatitis were investigated. METHODS: Hepcidin expression was studied in liver and adipose tissue of these patients. Hepcidin regulation was investigated in vitro by adipose tissue explant stimulation studies. RESULTS: Hepcidin was expressed not only in the liver but also at the messenger RNA (mRNA) and the protein levels in adipose tissue. Moreover, mRNA expression was increased in adipose tissue of obese patients. The presence of diabetes or NASH did not modify the hepcidin expression levels in liver and adipose tissue. In adipose tissue, mRNA expression correlated with indexes of inflammation, interleukin-6, and C-reactive protein. Interleukin-6 also promoted in vitro hepcidin expression. A low transferrin saturation ratio was observed in 68% of the obese patients; moreover, 24% of these patients presented with anemia. The observed changes in iron status could be due to the role of hepcidin as a negative regulator of intestinal iron absorption and macrophage iron efflux. Interestingly, a feedback control mechanism on hepcidin expression related to low transferrin saturation occurred in the liver but not in the adipose tissue. CONCLUSIONS: Hepcidin is a proinflammatory adipokine and may play an important role in hypoferremia of inflammation in obese condition.     

Autocrine formation of hepcidin induces iron retention in human monocytes

Hepcidin, a master regulator of iron homeostasis, is produced in small amounts by inflammatory monocytes/macrophages. Chronic immune activation leads to iron retention within monocytes/macrophages and the development of anemia of chronic disease (ACD). We questioned whether monocyte-derived hepcidin exerts autocrine regulation toward cellular iron metabolism. Monocyte hepcidin mRNA expression was significantly induced within 3 hours after stimulation with LPS or IL-6, and hepcidin mRNA expression was significantly higher in monocytes of ACD patients than in controls. In ACD patients, monocyte hepcidin mRNA levels were significantly correlated to serum IL-6 concentrations, and increased monocyte hepcidin mRNA levels were associated with decreased expression of the iron exporter ferroportin and iron retention in these cells. Transient transfection experiments using a ferroportin/EmGFP fusion protein construct demonstrated that LPS inducible hepcidin expression in THP-1 monocytes resulted in internalization and degradation of ferroportin. Transfection of monocytes with siRNA directed against hepcidin almost fully reversed this lipopolysaccharide-mediated effect. Using ferroportin mutation constructs, we found that ferroportin is mainly targeted by hepcidin when expressed on the cell surface. Our results suggest that ferroportin expression in inflammatory monocytes is negatively affected by autocrine formation of hepcidin, thus contributing to iron sequestration within monocytes as found in ACD.     

Analysis of hepcidin expression: in situ hybridization and quantitative polymerase chain reaction from paraffin sections

AIM: To establish methods for quantitative polymerase chain reaction (PCR) for hepcidin using RNAs isolated from paraffin-embedded sections and in situ hybridization of hepatocellular carcinoma (HCC). METHODS: Total RNA from paraffin-embedded sections was isolated from 68 paraffin-embedded samples of HCC. Samples came from 54 male and 14 female patients with a mean age of 66.8 ± 7.8 years. Quantitative PCR was performed. Immunohistochemistry and in situ hybridization for hepcidin were also performed. RESULTS: Quantitative PCR for hepcidin using RNAs isolated from paraffin-embedded sections of HCC was performed successfully. The expression level of hepcidin mRNA in cancer tissues was significantly higher than that in non-cancer tissues. A method of in situ hybridization for hepcidin was established successfully, and this demonstrated that hepcidin mRNA was expressed in non-cancerous tissue but absent in cancerous tissue. CONCLUSION: We have established novel methods for quantitative PCR for hepcidin using RNAs isolated from paraffin-embedded sections and in situ hybridization of HCC.     

Hepcidin levels in humans are correlated with hepatic iron stores, hemoglobin levels, and hepatic function

Hepcidin, a key regulator of iron metabolism, is synthesized by the liver. Hepcidin binds to the iron exporter ferroportin to regulate the release of iron into plasma from macrophages, hepatocytes, and enterocytes. We analyzed liver samples from patients undergoing hepatic surgery for cancer or receiving liver transplants and analyzed correlations between clinical parameters and liver hepcidin mRNA and urinary hepcidin concentrations. Despite the many potential confounding influences, urinary hepcidin concentrations significantly correlated with hepatic hepcidin mRNA concentrations, indicating that hepcidin quantification in urine is a valid approach to evaluate hepcidin expression. Moreover, we found in humans that hepcidin levels correlated with hepatic iron stores and hemoglobin levels and may also be affected by hepatic dysfunction.     

Expression of insulin-like growth factor system components in colorectal tissue and its relation with serum IGF levels

ContextThe insulin-like growth factor (IGF)-system has been implicated in colorectal tumor carcinogenesis. Although both tumor expression levels and serum concentrations of IGF-system components are related to colorectal cancer risk, it is unknown whether IGF levels in tissue and serum are correlated.ObjectiveThe objective of this study was to determine expression levels of various IGF-system components in different locations of the colorectum, and to investigate whether normal tissue IGF expression levels are correlated with serum IGF-I and IGF-II concentrations.DesignBiopsies from macroscopically normal mucosa at four locations in the colorectum (ascending, transverse, sigmoid colon, and rectum) and a fasting serum sample were obtained from 48 asymptomatic patients at increased risk of colorectal cancer. Expression levels of IGF-I, IGF-II, IGF-IR, IGF-IIR, and IGFBP-3 messenger RNA (mRNA) in tissue were quantitatively evaluated using real-time RT-PCR. Expression of IGF-IR protein in the ascending colon and rectum tissue specimens was assessed semi-quantitatively by immunohistochemistry. Serum IGF-I and IGF-II concentrations were determined using immunometric assays.ResultsWith the exception of IGF-IIR, mRNA levels of all the IGF-system components investigated, as well as IGF-IR protein expression, were significantly higher in the rectum compared with the ascending colon (p ? 0.001). Serum IGF-I and IGF-II concentrations did not correlate with any of the parameters studied in colorectal tissues.ConclusionsOur results indicate that in humans IGF-system components are differentially expressed in the colorectum. Moreover, our findings suggest that local and circulating components of the IGF-system are differentially regulated. However, due to large intra-individual variation in mRNA expression, we cannot formally exclude undetected but existing routes of co-regulation.     

Liver hepcidin mRNA correlates with iron stores, but not inflammation, in patients with chronic hepatitis C

PURPOSE: Liver iron is frequently elevated in chronic hepatitis C and may contribute to liver injury. The pathophysiology behind this phenomenon may involve hepcidin, a gene that is up-regulated in the liver by inflammation and iron. Inappropriately low hepcidin is important to the pathophysiology of hereditary hemochromatosis. However, the role of hepcidin in the iron loading of patients with hepatitis C is unknown. SUBJECTS AND METHODS: To determine whether liver hepcidin mRNA correlates with markers of hepatic inflammation and iron status in patients with hepatitis C, we extracted total RNA from liver biopsy specimens of patients with chronic hepatitis C and quantified hepcidin mRNA. Liver hepcidin mRNA levels were then correlated with aspartate aminotransferase, alanine aminotransferase, ferritin, viral load, fibrosis, hepatic iron concentration, and Hepatic Activity Index (HAI). RESULTS: Among patients with hepatitis C, there was a significant correlation of hepcidin mRNA expression in the liver with hepatic iron concentration and serum ferritin (r = 0.72, P = 0.006, and r = 0.60, P = 0.01, respectively). Hepcidin mRNA expression in the liver did not correlate with aspartate aminotransferase, alanine aminotransferase, HAI, or viral load. No differences in hepcidin mRNA were found based on viral genotype or the presence of fibrosis. CONCLUSION: In contrast to other inflammatory states, hepcidin mRNA expression in the liver was independent of markers of inflammation in hepatitis C. Instead, our results suggest that iron stores in patients with hepatitis C regulate hepcidin expression and that iron loading in chronic hepatitis C is not due to inappropriate hepcidin expression.     

Regulation of TMPRSS6 by BMP6 and iron in human cells and mice

Mutations in transmembrane protease, serine 6 (TMPRSS6), encoding matriptase-2, are responsible for the familial anemia disorder iron-refractory iron deficiency anemia (IRIDA). Patients with IRIDA have inappropriately elevated levels of the iron regulatory hormone hepcidin, suggesting that TMPRSS6 is involved in negatively regulating hepcidin expression. Hepcidin is positively regulated by iron via the bone morphogenetic protein (BMP)-SMAD signaling pathway. In this study, we investigated whether BMP6 and iron also regulate TMPRSS6 expression. Here we demonstrate that, in vitro, treatment with BMP6 stimulates TMPRSS6 expression at the mRNA and protein levels and leads to an increase in matriptase-2 activity. Moreover, we identify that inhibitor of DNA binding 1 is the key element of the BMP-SMAD pathway to regulate TMPRSS6 expression in response to BMP6 treatment. Finally, we show that, in mice, Tmprss6 mRNA expression is stimulated by chronic iron treatment or BMP6 injection and is blocked by injection of neutralizing antibody against BMP6. Our results indicate that BMP6 and iron not only induce hepcidin expression but also induce TMPRSS6, a negative regulator of hepcidin expression. Modulation of TMPRSS6 expression could serve as a negative feedback inhibitor to avoid excessive hepcidin increases by iron to help maintain tight homeostatic balance of systemic iron levels.     

Expression and significance of CD44s, CD44v6, and nm23 mRNA in human cancer

AIM: To investigate the relationship between the expression levels of nm23 mRNA, CD44s, and CD44v6,and oncogenesis, development and metastasis of human gastric adenocarcinoma, colorectal adenocarcinoma,intraductal carcinoma of breast, and lung cancer.METHODS: Using tissue microarray by immuhistochemical (IHC) staining and in situ hybri-dization (ISH), we examined the expression levels of nm23mRNA, CD44s, and CD44v6 in 62 specimens of human gastric adenocarcinoma and 62 specimens of colorectal adenocarcinoma; the expression of CD44s and CD44v6in 120 specimens of intraductal carcinoma of breast and 20 specimens of normal breast tissue; the expression of nm23 mRNA in 72 specimens of human lung cancer and 23 specimens of normal tissue adjacent to cancer.RESULTS: The expression of nm23 mRNA in the tissues of gastric and colorectal adenocarcinoma was not significantly different from that in the normal tissues adjacent to cancer (P＞0.05), and was not associated with the invasion of tumor and the pathology grade of adenocarcinoma (P＞0.05). However, the expression of nm23 mRNA was correlated negatively to the lymph node metastasis of gastric and colorectal adenocarcinoma (r = -0.49, P＜0.01; r = -4.93, P＜0.01). The expression of CD44s in the tissues of gastric and colorectal adenocarcinoma was significantly different from that in the normal tissues adjacent to cancer (P＜0.05;P＜0.01). CD44v6 was expressed in the tissues of gastric and colorectal adenocarcinoma only, the expression of CD44v6 was significantly associated with the lymph node metastasis, invasion and pathological grade of the tumor (r = 0.47, P＜0.01; r = 5.04, P＜0.01). CD44sand CD44v6 were expressed in intraductal carcinoma of breast, the expression of CD44s and CD44v6 was significantly associated with lymph node metastases and invasion (P＜0.01). However, neither of them was expressed in the normal breast tissue. In addition, the expression of CD44v6 was closely related to the degree of cell differentiation of intraductal carcinoma of breast (x2= 5.68, P＜0.05). The expressional level of nm23mRNA was closely related to the degree of cell differentiation (P＜0.05) and lymph node metastasis (P＜0.01), but the expression of nm23 gene was not related to sex, age, and type of histological classification (P＞0.05).CONCLUSION: Patients with overexpression of CD44s and CD44v6 and low expression of nm23 mRNA have a higher lymph node metastatic rate and invasion. In addition, overexpression of CD44v6 is closely related to the degree of cell differentiation. Detection of the three genes is able to provide a reliable index to evaluate the invasion and metastasis of tumor cells.     

Hepcidin and Cytokines in Anaemia

Hepcidin is a cytokine-induced antibacterial protein which is produced in the liver, circulates in the blood, and is excreted in the urine. It is a major regulator of iron balance in the intestinal mucosa, and appears to have a significant role in the pathogenesis of haemochromatosis and related disorders. Hepcidin appears to be a major contributor to the hypoferraemia associated with inflammation. Serum ferritin concentration is strongly correlated with hepcidin protein levels in either urine or serum, and certain patients with hepatic adenomas exhibit a microcytic, hypoferraemic hepcidin-dependent anaemia. For these reasons, it has been proposed that hepcidin is a primary factor in the pathogenesis of the anaemia of chronic disease (ACD), a cytokine-mediated anaemia commonly encountered in clinical practice and characterized by hypoferraemia with adequate reticuloendothelial iron stores. However, the pathogenetic basis of ACD is not entirely due to changes in iron metabolism, but also involves abnormalities in red cell survival and the erythropoietic response to anaemia. In this review, the evidence for involvement of hepcidin as a major mediator of ACD is evaluated. Hepcidin appears to be a major factor in the systemic iron abnormalities seen in ACD; whether it contributes to the other aspects of the pathogenesis of the syndrome requires further investigation.     

Hepcidin and cytokines in anaemia

Hepcidin is a cytokine-induced antibacterial protein which is produced in the liver, circulates in the blood, and is excreted in the urine. It is a major regulator of iron balance in the intestinal mucosa, and appears to have a significant role in the pathogenesis of haemochromatosis and related disorders. Hepcidin appears to be a major contributor to the hypoferraemia associated with inflammation. Serum ferritin concentration is strongly correlated with hepcidin protein levels in either urine or serum, and certain patients with hepatic adenomas exhibit a microcytic, hypoferraemic hepcidin-dependent anaemia. For these reasons, it has been proposed that hepcidin is a primary factor in the pathogenesis of the anaemia of chronic disease (ACD), a cytokine-mediated anaemia commonly encountered in clinical practice and characterized by hypoferraemia with adequate reticuloendothelial iron stores. However, the pathogenetic basis of ACD is not entirely due to changes in iron metabolism, but also involves abnormalities in red cell survival and the erythropoietic response to anaemia. In this review, the evidence for involvement of hepcidin as a major mediator of ACD is evaluated. Hepcidin appears to be a major factor in the systemic iron abnormalities seen in ACD; whether it contributes to the other aspects of the pathogenesis of the syndrome requires further investigation.     

Iron transferrin regulates hepcidin synthesis in primary hepatocyte culture through hemojuvelin and BMP2/4

The peptide hormone hepcidin is the principal regulator of systemic iron homeostasis. We examined the pathway by which iron stimulates the production of hepcidin. In humans who ingested 65 mg of iron, the increase in transferrin saturation preceded by hours the increase in urinary hepcidin excretion. Increases in urinary hepcidin concentrations were proportional to the increment in transferrin saturation. Paradoxically, in previous studies in primary hepatocytes and cell lines, hepcidin response to iron or iron transferrin was not observed. We now report that freshly isolated murine primary hepatocytes responded to holotransferrin but not apotransferrin by increasing hepcidin mRNA. Hepcidin increase was not due to contamination of the transferrin preparations by endotoxin, a potent pathologic stimulus of hepcidin synthesis. Using this culture system, we showed that holotransferrin concentrations regulate hepcidin mRNA concentrations through a hemojuvelin/BMP2/4-dependent pathway. Although BMP9 is known to be expressed in the liver and potently increased the basal concentrations of hepcidin mRNA, it did not interact with hemojuvelin, and interference with its signaling pathway did not affect iron regulation. Fresh primary hepatocytes constitute a sufficient system for the regulation of hepcidin by physiologic iron stimuli and will greatly facilitate studies of major disorders of iron homeostasis.     

Expression of ST13 in colorectal cancer and adjacent normal tissues

AIM: To investigate the in situ expression of suppression of tumorigenecity 13 (ST13) mRNA in both colorectal cancer and adjacent normal tissues, METHODS: Colorectal cancer cell lines SW1116, SW620 and CoLo205 were enrolled to confirm the feasibility of the in situ hybridization procedure. Seven colorectal cancer and adjacent normal tissues were included for RNA-RNA in situ hybridization. RESULTS: The expression of ST13 in the seven normal colon tissues was positive and the positive signals appeared in mucosal cells. Only three of the seven colorectal cancer tissues had positive hybridization signals that appeared in adenocarcinoma cells. CONCLUSION: The expression of ST13 decreases in colorectal cancer tissue compared with that in adjacent normal tissue. ST13 is mostly expressed in colorectal epithelia and adenocarcinoma cells.