Identification and expression analysis of hepcidin-like cDNAs from pigeon (Columba livia)

Hepcidin cDNA evolution in vertebrates

Hepcidin, belonging to the β-defensin family, was isolated for the first time from plasma and human urine. It is a cationic peptide, rich in cysteine bound with four disulfide bridges, which plays a major role in innate immunity and iron homeostasis. Some vertebrate species have multiple hepcidin homolog genes and each contains only one copy that functions as an iron regulator except hepcidin sequences in the pigeon (Columba livia). The aim of this chapter is to investigate the molecular evolution of several hepcidin gene from searches of the literature and public genomic databases from 17 different species, all among the vertebrates.

An improved genome assembly for Larimichthys crocea reveals hepcidin gene expansion with diversified regulation and function

Larimichthys crocea (large yellow croaker) is a type of perciform fish well known for its peculiar physiological properties and economic value. Here, we constructed an improved version of the L. crocea genome assembly, which contained 26,100 protein-coding genes. Twenty-four pseudo-chromosomes of L. crocea were also reconstructed, comprising 90% of the genome assembly. This improved assembly revealed several expansions in gene families associated with olfactory detection, detoxification, and innate immunity. Specifically, six hepcidin genes (LcHamps) were identified in L. crocea, possibly resulting from lineage-specific gene duplication. All LcHamps possessed similar genomic structures and functional domains, but varied substantially with respect to expression pattern, transcriptional regulation, and biological function. LcHamp1 was associated specifically with iron metabolism, while LcHamp2s were functionally diverse, involving in antibacterial activity, antiviral activity, and regulation of intracellular iron metabolism. This functional diversity among gene copies may have allowed L. crocea to adapt to diverse environmental conditions.

Expression and cellular localization of hepcidin mRNA and protein in normal rat brain

Background

Hepcidin is a peptide hormone belonging to the defensin family of cationic antimicrobial molecules that has an essential role in systemic iron homeostasis. The peptide is synthesised by hepatocytes and transported in the circulation to target tissues where it regulates the iron export function of the ferrous iron permease, ferroportin. In the brain hepcidin protein has been identified using immuno-histochemistry and mRNA by real-time PCR but not by in situ hybridisation raising the question of whether there is measurable transcription of the hepcidin gene in the central nervous system. Alternatively hepcidin could be transported as a hormone to the brain via the circulation.

Results

By RT-PCR hepcidin mRNA was present at low level throughout normal rat brain while in situ hybridisation to detect low-abundant mRNA revealed that transcripts were restricted to endothelium of blood vessels and choroid plexus. In contrast, hepcidin protein analysed by immuno-histochemistry was highly expressed in blood vessels, in endothelium and in pericytes. Hepcidin was also present in glial cells and in the olfactory bulb, sub-ventricular zone and dentate gyrus, areas where neurogenesis and synaptic plasticity are maintained throughout adult life. The hepcidin species identified by Western blotting in sub-ventricular zone, cortex and hippocampus migrated as a ~2.8 kDa band, identical in size to hepcidin present in normal rat serum suggesting that hepcidin in brain was the full-length biologically active 25 amino acid peptide. Hepcidin co-localised with ferroportin in ependymal cells of the sub-ventricular zone and in the corpus callosum consistent with a regulatory role in iron metabolism at these sites.

Conclusions

Hepcidin protein was widely expressed in brain parenchyma while levels of hepcidin gene transcription appeared to be below the limits of detection of the in situ hybridisation probes. This disparity suggests that not all hepcidin in the brain is transcribed in situ and may originate in part outside the brain. The properties of hepcidin as a cationic peptide hormone are reflected in the finding of hepcidin in the walls of blood vessels and in pericytes and glia, cells that may be involved in transporting the peptide into brain interstitium.

Characterization, evolution and functional analysis of the liver-expressed antimicrobial peptide 2 (LEAP-2) gene in miiuy croaker

As an evolutionarily older defense strategy, the innate immune is the dominant immune system and provides a first line of antimicrobial host defense in teleost. Liver-expressed antimicrobial peptide-2 (LEAP-2) is a critical molecule of the innate immune system and plays a very important role in resistance against bacterial infections. We reported comprehensive analysis and characterization of LEAP-2 gene from miiuy croaker (Miichthys miiuy) in here. The complete cDNA of miiuy croaker LEAP-2 consists 2360 bp, including a 5' terminal untranslated region (UTR) of 170 bp, an open reading frame (ORF) of 312 bp, and a 3'-UTR of 1878 bp. Interestingly, two polyadenylation signals (AATTAAA) which may involve the stability, translation efficiency, or localization of an mRNA in a tissue were found in 3'-UTR. Genomic DNA of miiuy croaker LEAP-2 includes three exons and two introns, which is similar to LEAP-2 genes in other mammals and fish. The deduced 103 amino acids consist of signal peptide, prodomain and mature peptide. Four highly conserved cysteine residues involved two disulfide bridges in mature peptide. Real-time PCR results showed that LEAP-2 was ubiquitously expressed in all tissues and the expression level was highest in liver. Significantly, the expression levels were increased after infection with Vibrio anguillarum in liver and spleen. The antimicrobial activity analysis result of LEAP-2 in vitro indicated that LEAP-2 of miiuy croaker was effective in controlling Aeromonas hydrophila. In addition, we performed evolutionary analysis in order to estimate the selective constraints on the LEAP-2 gene. The result indicated that no positive selection exists in LEAP-2 gene sequences, which may be on account of irreplaceable function constrains. Meanwhile, we compared the structure of LEAP-2 with that of another Liver-expressed antimicrobial peptide (LEAP-1, also named HAMP), and found the LEAP-2 from miiuy croaker comprises of α-helix, β-sheet, and β-turn while the LEAP-1 of miiuy croaker only contains β-sheet.

Molecular characterization of hepcidin gene in common carp (Cyprinus carpio L.) and its expression pattern responding to bacterial challenge

Hepcidin is a cysteine-rich cationic antimicrobial peptide (AMP), which plays an important role in host innate immune system and iron regulation. A great many of hepcidin genes have been identified from vertebrates, including various fish species. Here we report the cloning and identification of a hepcidin cDNA from the liver of common carp (Cyprinus carpio L.). The full-length cDNA of the common carp hepcidin was 647 bp, which contained an ORF of 276 bp encoding a prepropeptide of 91 amino acid residues. The predicted preprohepcidin consisted of three domains: a signal peptide of 24 amino acids, a prodomain of 42 amino acids and a mature peptide of 25 amino acids, which containd eight cysteine residues at the identical conserved position. The genomic organization of common carp hepcidin was identified, which contained three exons and two introns, similarly to corresponding genes in mammals and other fish species. Sequence alignment and phylogenetic analysis showed that hepcidins were conserved in different species, and common carp hepcidin was type 1 hepcidin according to the phylogenetic tree, which had the highest identity with mud loach and zebrafish. Real-time PCR assay showed that the hepcidin gene was mostly expressed in liver, and expressed in all the other tested tissues of common carp in different levels. When challenged with pathogenic bacterium, Vibrio anguillarum, the expression level of common carp hepcidin was quickly up-regulated in liver, spleen, head kidney and hindgut, implying that hepcidin may be an important component of the innate immune system of common carp and involved in mucosal immune response against invading pathogens.

Molecular cloning, recombinant expression, and antimicrobial activity of EC-hepcidin3, a new four-cysteine hepcidin isoform from Epinephelus coioides

Hepcidin, a cysteine-rich antimicrobial peptide, is widespread in fish and shows multiple activities, including antimicrobial, antivirus, and antitumor. Here, a new four-cysteine hepcidin isoform gene, EC-hepcidin3, was cloned from the marine-cultured orange-spotted grouper (Epinephelus coioides). The complete cDNA sequence consisted of 603 bases with an open reading frame (ORF) of 270 bases. The genomic DNA sequence was composed of two introns and three exons, and its 312-bp upstream region had multiple putative transcription factor binding sites. Soluble recombinant protein EC-proHep3 containing a His-tag at the C-terminus was obtained from expression plasmid pET-28a/EC-proHep3 in Escherichia coli Rosetta. It was purified by immobilized metal affinity chromatography (IMAC), and it showed antibacterial activity in vitro. Kinetic studies indicated that recombinant EC-proHep3 has strong, rapid activity against Staphylococcus aureus and Pseudomonas stutzeri. The results indicate that EC-hepcidin3 might be an effective component in the innate immune system of groupers.

Avian iron storage disease: variations on a common theme?

Many frugivorous avian species kept in captivity develop iron storage disease (ISD) as indicated by high concentrations of hepatic iron and hemosiderin deposits in hepatocytes or phagocytes. In several susceptible species fed diets containing moderate levels of iron, ISD develops because of an inability to match rates of iron absorption to tissue needs. Evidence suggests that the pathophysiologic basis of excess iron absorption is due to high levels of expression of divalent metal transporter-1 that transports iron into enterocytes in the proximal intestine, and ferroportin that exports iron to the circulation. The regulatory basis for this inability to sufficiently down-regulate iron absorption is unknown, but disruptions in the hepcidin-ferroportin axis are likely candidates based on recent research in humans and laboratory rodents. It is likely that ISD-susceptible avian species evolved on foods that were very low in bioavailable iron, so there was strong selection pressure for the efficient capture of the small amount of dietary iron but low selection pressure for preventing iron toxicities. Thus, the transporters and regulatory networks for iron absorption seem to be heavily skewed toward iron storage even when food items that are high in iron are consumed. Infections, trauma and neoplasias that trigger an acute phase response may exacerbate ISD in susceptible species and may be the primary cause in species that are normally resistant to ISD (i.e., those that are normally able to shut down intestinal iron absorption when iron stores are replete). The evolutionary basis that resulted in some avian species to be susceptible to ISD (e.g., dietary cause) seems to differ from many inherited ISD disorders in humans that are thought to have evolved to bolster protection against infectious diseases. However the evolutionary basis of ISD in other mammalian species might be more similar to that in ISD-susceptible avian species.

Miiuy croaker hepcidin gene and comparative analyses reveal evidence for positive selection

Hepcidin antimicrobial peptide (HAMP) is a small cysteine-rich peptide and a key molecule of the innate immune system against bacterial infections. Molecular cloning and genomic characterization of HAMP gene in the miiuy croaker (Miichthys miiuy) were reported in this study. The miiuy croaker HAMP was predicted to encode a prepropeptide of 99 amino acids, a tentative RX(K/R)R cleavage motif and eight characteristic cysteine residues were also identified. The gene organization is also similar to corresponding genes in mammals and fish consisting of three exons and two introns. Sequence polymorphism analysis showed that only two different sequences were identified and encoded two proteins in six individuals. As reported for most other species, the expression level was highest in liver and an up-regulation of transcription was seen in spleen, intestine and kidney examined at 24 h after injection of pathogenic bacteria, Vibrio anguillarum, the expression pattern implied that miiuy croaker HAMP is an important component of the first line defense against invading pathogens. In addition, we report on the underlying mechanism that maintains sequences diversity among fish and mammalian species, respectively. A series of site-model tests implemented in the CODEML program revealed that moderate positive Darwinian selection is likely to cause the molecular evolution in the fish HAMP2 genes and it also showed that the fish HAMP1 genes and HAMP2 genes under different selection pressures.

Role of hepcidin in iron metabolism and potential clinical applications

The relatively recent discovery of hepcidin has stimulated renewed research interest in iron metabolism and iron-related disorders, emphasizing the importance of this hormone in many normal and pathologic processes. Important questions still remain to be answered; however, research to date offers promising diagnostic and therapeutic implications for both humans and veterinary species.

Genomic organization and tissue-specific expression of hepcidin in the pacific mutton hamlet, Alphestes immaculatus (Breder, 1936)

Hepcidin is a cysteine-rich peptide involved in iron metabolism, inflammatory response and as antimicrobial peptide. Despite the fact that hepcidins have been identified in several fish species, only few have been completely characterized. This study, described the identification and complete molecular characterization of the hepcidin antimicrobial peptide 1 (HAMP1) gene of Alphestes immaculatus. Moreover, its specific expression level at both basal and lipopolysaccharide (LPS)-induced conditions in different tissues was also determined by real-time PCR. Results showed that the HAMP1gene consists of three exons and two introns encoding a preprohepcidin composed of 90 aa (24 aa for signal peptide, 40 aa for prodomain and 26 aa for mature peptide). The promoter region analysis revealed a TATA box sequence and several putative transcription factor binding sites. A comparative analysis showed CEBPα, CEBPβ, NF-kB, HNF3, GATA-1 and c-Rel as the most common found in fishes. The mature peptide possesses a pI of 8.34, which is the average among fish hepcidin. In addition, the structural modeling showed a hairpin structure with four putative disulfide bonds. A phylogenetic analysis revealed that this hepcidin gene is a HAMP1 class, and is clustered into the same group with the Serranid fish Epinephelus moara and the Antarctic fish Lycodichthys dearborni. Finally, the relative expression levels showed high basal values in liver and muscle, whereas in LPS-induced fish the relative expression tendency changed, with the highest values in spleen and head kidney tissues. This study describes the completely characterized HAMP1 gene of A. immaculatus and their patterns of expression level at different conditions and in different tissues, showing by first time muscle hepcidin expression could be relevant in the immune response in fish.

Lipopolysaccharide infusion up-regulates hepcidin mRNA expression in equine liver

Hepcidin has been found to be the key regulator of iron metabolism that leads to hypoferremia during inflammation. Recent work has shown that equine hepcidin is predominantly expressed in the liver of horses. In this study, hepcidin gene expression was determined in the liver and bone marrow of six healthy horses after iv infusion of Escherichia coli O55:B5 LPS. The IL-6 gene expression was also determined in liver and bone marrow samples. Clinical and laboratory evaluations were measured at multiple time points between 0 and 240 h post-LPS infusion (PI). Liver and bone marrow biopsies were taken immediately before (baseline) and at 6 and 18 h PI. In response to endotoxin infusion, all horses showed characteristic clinical signs of endotoxemia. Plasma iron concentration was decreased significantly from the pre-infusion level at 8 h PI. Hypoferremia peak was observed at 12 h and returned to normal levels at 30 h PI. Relative real-time RT-PCR analysis showed that liver hepcidin and IL-6 mRNA expression was up-regulated at 6 h PI. Bone marrow hepcidin relative expression was not influenced by LPS infusion. In another experiment, equine monocyte cultures were stimulated with LPS (1 µg/ml). Monocyte hepcidin and IL-6 gene expression was significantly induced after 2 h of LPS stimulus and returned to baseline levels thereafter. The present study describes that, in horses, LPS infusion up-regulates hepatic hepcidin mRNA expression resulting in early observed hypoferremia and suggests that hepcidin may act as an acute-phase protein in horses.

Influence of experimental inflammatory response on hepatic hepcidin gene expression and plasma iron concentration in sheep

Hepcidin is a highly conserved disulfide-bonded peptide that plays a central role in iron homeostasis. During systemic inflammation, hepcidin up-regulation is responsible for hypoferremia. This study aimed to analyze the influence of the inflammatory process induced by complete Freund's adjuvant (CFA) or lipopolysaccharide (LPS) on the liver expression of hepcidin mRNA transcripts and plasma iron concentration of sheep. The expression levels of hepcidin transcripts were up-regulated after CFA or LPS. Hypoferremic response was observed at 12 h (15.46 ± 6.05 μmol/L) or 6h (14.59 ± 4.38μmol/L) and iron reached its lowest level at 96 h (3.08 ± 1.18 μmol/L) or 16h (4.06 ± 1.58 μmol/L) after CFA administration or LPS infusion, respectively. This study demonstrated that the iron regulatory hormone hepcidin was up-regulated in sheep liver in response to systemic inflammation. These findings extend our knowledge on the relationship between the systemic inflammatory response, hepcidin and iron, and provide a starting point for additional studies on iron metabolism and the inflammatory process in sheep.

Molecular characterization of hepcidin AS-hepc2 and AS-hepc6 in black porgy (Acanthopagrus schlegelii): expression pattern responded to bacterial challenge and in vitro antimicrobial activity

There are more diversified isoforms of the hepcidin gene that exist in fishes than in mammals, and elucidating the differences between these isoforms should provide insight into the functioning of hepcidin in fishes. In our study, AS-hepc2 and AS-hepc6 hepcidin isoforms from black porgy were characterized for their in vivo expression patterns following bacterial challenge, and their in vitro antimicrobial activities against Gram-positive and Gram-negative bacteria as well as fungi. As a result, two isoforms were observed to be widely distributed in all the tissues tested. AS-hepc2 was a liver-expressed hepcidin peptide which was always highly more expressed in the liver than in the other tissues tested no matter whether this was before or after bacterial challenge. AS-hepc6 was detected mainly in the head kidney and trunk kidney of normal fish, but, in the challenged fish, its expression involved more tissues than just the kidneys. The mature peptides of AS-hepc2 and AS-hepc6 were modeled for 3D structure and then synthesized for antimicrobial assay. AS-hepc6 had a wider antimicrobial spectrum than AS-hepc2 and, in particular, had more potent antifungal activity. Our study indicated that the two hepcidin isoforms had different characteristics in terms of their expression patterns and antimicrobial activity, and they were assumed to play an overlapping role in the innate immune system of black porgy against invading pathogens.

Hepcidin, an antimicrobial peptide is downregulated in ceruloplasmin-deficient mice

Hepcidin, a principle regulator of iron metabolism, is synthesized by the liver. Contradictory results have been reported on the regulation of hepcidin expression in response to serum transferrin saturation and liver iron content. In the present study, we explore the expression of murine hepcidin mRNA and further analyze the relationship between liver hepcidin mRNA expression, liver iron stores, and serum iron level utilizing ceruloplasmin gene knockout mice. We find that hepcidin expression correlates significantly with serum transferrin saturation, whereas there is a negative correlation of hepcidin expression with liver tissue iron level.

Expression, purification and structural characterization of recombinant hepcidin, an antimicrobial peptide identified in Japanese flounder, Paralichthys olivaceus

The cysteine-rich peptide hepcidin is an antimicrobial peptide and iron transport regulator that has been found in vertebrates including birds, fish and mammals. To elucidate the structure and biological function of fish hepcidin, which is difficult to produce synthetically, we have cloned several plasmid constructs encoding hepcidin from Japanese flounder, Paralichthys olivaceus, and tested expression of recombinant peptides, each with an N-terminal hexahistidine (6xHis) tag, in inclusion bodies or the periplasmic space of Escherichia coli. Hepcidin expressed in inclusion bodies was reduced, and subsequently refolded using a dilution technique with a cysteine redox system. The oxidized His-hepcidin monomer was separated from protein multimers and mass spectrometry analysis showed that the peptide was of the predicted size and contained four disulfide bonds. Removal of the 6xHis tag was attempted using enzymatic cleavage by Factor Xa and tobacco etch virus (TEV) protease or chemical cleavage by hydroxylamine. The Factor Xa cleavage was unsuccessful and hydroxylamine cleavage resulted in aggregation of cleaved peptide. TEV protease cleavage was successful but immediately resulted in hexamer formation despite varying reaction conditions (redox, non-redox, pH, temperature, target protein concentration, type of buffer). However, the recombinant His-hepcidin fusion peptide monomer showed considerable antimicrobial activity. NMR-based studies showed that hepcidin contained a rare vicinal disulfide linkage at the top of a loop structure and a short beta-sheet structure encompassing residues 7-13 and 19-25 that is stabilized by three disulfide bonds.

Evolution of the hepcidin gene in primates

Background

Hepcidin/LEAP-1 is an iron regulatory hormone originally identified as an antimicrobial peptide. As part of a systematic analysis of the evolution of host defense peptides in primates, we have sequenced the orthologous gene from 14 species of non-human primates.

Results

The sequence of the mature peptide is highly conserved amongst all the analyzed species, being identical to the human one in great apes and gibbons, with a single residue conservative variation in Old-World monkeys and with few substitutions in New-World monkeys.

Conclusion

Our analysis indicates that hepcidin's role as a regulatory hormone, which involves interaction with a conserved receptor (ferroportin), may result in conservation over most of its sequence, with the exception of the stretch between residues 15 and 18, which in New-World monkeys (as well as in other mammals) shows a significant variation, possibly indicating that this structural region is involved in other functions.