Ex-FABP: a fatty acid binding lipocalin developmentally regulated in chicken endochondral bone formation and myogenesis

Antimicrobial Proteins and Peptides in Avian Eggshell: Structural Diversity and Potential Roles in Biomineralization

The calcitic avian eggshell provides physical protection for the embryo during its development, but also regulates water and gaseous exchange, and is a calcium source for bone mineralization. The calcified eggshell has been extensively investigated in the chicken. It is characterized by an inventory of more than 900 matrix proteins. In addition to proteins involved in shell mineralization and regulation of its microstructure, the shell also contains numerous antimicrobial proteins and peptides (AMPPs) including lectin-like proteins, Bacterial Permeability Increasing/Lipopolysaccharide Binding Protein/PLUNC family proteins, defensins, antiproteases, and chelators, which contribute to the innate immune protection of the egg. In parallel, some of these proteins are thought to be crucial determinants of the eggshell texture and its resulting mechanical properties. During the progressive solubilization of the inner mineralized eggshell during embryonic development (to provide calcium to the embryo), some antimicrobials may be released simultaneously to reinforce egg defense and protect the egg from contamination by external pathogens, through a weakened eggshell. This review provides a comprehensive overview of the diversity of avian eggshell AMPPs, their three-dimensional structures and their mechanism of antimicrobial activity. The published chicken eggshell proteome databases are integrated for a comprehensive inventory of its AMPPs. Their biochemical features, potential dual function as antimicrobials and as regulators of eggshell biomineralization, and their phylogenetic evolution will be described and discussed with regard to their three-dimensional structural characteristics. Finally, the repertoire of chicken eggshell AMPPs are compared to orthologs identified in other avian and non-avian eggshells. This approach sheds light on the similarities and differences exhibited by AMPPs, depending on bird species, and leads to a better understanding of their sequential or dual role in biomineralization and innate immunity.

Transcriptome-based biomarker gene screening and evaluation of the extracellular fatty acid-binding protein (Ex-FABP) on immune and angiogenesis-related genes in chicken erythrocytes of tibial dyschondroplasia

BACKGROUND

Tibial dyschondroplasia (TD) is a bone disorder in which dead chondrocytes accumulate as a result of apoptosis and non-vascularization in the tibial bone of broiler chickens. The pathogenicity of TD is under extensive research but is yet not fully understood. Several studies have linked it to apoptosis and non-vascularization in the tibial growth plate (GP). We conceived the idea to find the differentially expressed genes (DEGs) in chicken erythrocytes which vary in expression over time using a likelihood-ratio test (LRT). Thiram was used to induce TD in chickens, and then injected Ex-FABP protein at 0, 20, and 50 μg^.kg^-1 to evaluate its therapeutic effect on 30 screened immunity and angiogenesis-related genes using quantitative PCR (qPCR). The histopathology was also performed in TD chickens to explore the shape, circularity, arrangements of chondrocytes and blood vessels.

RESULTS

Clinical lameness was observed in TD chickens, which decreased with the injection of Ex-FABP. Histopathological findings support Ex-FABP as a therapeutic agent for the morphology and vascularization of affected chondrocytes in TD chickens. qPCR results of 10 immunity (TLR2, TLR3, TLR4, TLR5, TLR7, TLR15, IL-7, MyD88, MHCII, and TRAF6) and 20 angiogenesis-related genes (ITGAV, ITGA2, ITGB2, ITGB3, ITGA5, IL1R1, TBXA2R, RPL17, F13A1, CLU, RAC2, RAP1B, GIT1, FYN, IQGAP2, PTCH1, NCOR2, VAV-like, PTPN11, MAML3) regulated when Ex-FABP is injected to TD chickens.

CONCLUSION

Immunity and angiogenesis-related genes can be responsible for apoptosis of chondrocytes and vascularization in tibial GP. Injection of Ex-FABP protein to thiram induced TD chickens decrease the chondrocytes damage and improves vascularization.

Comparative proteomic analysis of hen egg yolk plasma proteins during embryonic development

Avian egg yolk provides essential nutrients and physiological support for the developing embryo. To reveal the dynamics of yolk proteins during the entire period of incubation, we analyzed the alterations of egg yolk plasma proteins at different times during incubation (day 0, 7, 14, and 18). Day 14 (D14) of incubation was considered as the key point on the alteration of egg yolk proteins according to the SDS-PAGE analysis. The two-dimensional electrophoresis-based comparative proteomic analysis was conducted, and 26 spots representing 13 proteins were detected with significant changes in abundance. An accelerating transfer of ovalbumin from egg white into egg yolk was observed at D14 in fertilized eggs but not detected in unfertilized eggs, indicating an unrevealed absorbing pathway for the egg proteins/peptides particularly in fertilized eggs. Meanwhile, the abundance of yolk riboflavin-binding protein constantly decreased after D14, which might meet the need for essential riboflavin during embryo development. PRACTICAL APPLICATIONS: These findings provide fundamental insight into the effects of incubation on egg yolk plasma protein alterations during the entire embryonic development for a better understanding of plasma protein biological functions, especially in nutrient transportations and the formation of embryonic organs.

Siderocalins: Siderophore binding proteins evolved for primary pathogen host defense

Bacterial pathogens use siderophores to obtain iron from the host in order to survive and grow. The host defends against siderophore-mediated iron acquisition by producing siderocalins. Siderocalins are a siderophore binding subset of the lipocalin family of proteins. The design of the siderophore binding pocket gives siderocalins the ability to bind a wide variety of siderophores and protect the host against several pathogens. Siderocalins have been identified in humans, chickens, and quail, among other animals. The differences in the respective siderocalins suggest that each was developed in response to the most serious pathogens encountered by that animal. Additionally, siderocalins have been observed in many roles unrelated to pathogen defense including differentiation, embryogenesis, inflammation, and cancer.

A lipocalin-derived Peptide modulating fibroblasts and extracellular matrix proteins

Lipocalin family members have been implicated in development, regeneration, and pathological processes, but their roles are unclear. Interestingly, these proteins are found abundant in the venom of the Lonomia obliqua caterpillar. Lipocalins are β-barrel proteins, which have three conserved motifs in their amino acid sequence. One of these motifs was shown to be a sequence signature involved in cell modulation. The aim of this study is to investigate the effects of a synthetic peptide comprising the lipocalin sequence motif in fibroblasts. This peptide suppressed caspase 3 activity and upregulated Bcl-2 and Ki-67, but did not interfere with GPCR calcium mobilization. Fibroblast responses also involved increased expression of proinflammatory mediators. Increase of extracellular matrix proteins, such as collagen, fibronectin, and tenascin, was observed. Increase in collagen content was also observed in vivo. Results indicate that modulation effects displayed by lipocalins through this sequence motif involve cell survival, extracellular matrix remodeling, and cytokine signaling. Such effects can be related to the lipocalin roles in disease, development, and tissue repair.

Polymorphisms in chicken extracellular fatty acid binding protein gene

In this study, we report the investigation of extracellular fatty acid binding protein gene (Ex-FABP) genetic polymorphism in a sample of 360 chicken individuals. The screening of the coding regions with their intron-exon boundaries and the proximal flanking regions was performed through a PCR-SSCP strategy. Following sequence analysis revealed 35 novel single nucleotide polymorphisms (SNPs) of chicken Ex-FABP gene. Among the 35 SNPs, twenty-five were found in the introns. And the remaining seven and three SNPs were in the coding region and the 5'UTR, respectively. Two SNPs in the coding region caused two missense mutants and the other five did not result in any amino acid changes. The nature and the distribution of Ex-FABP mutations in three chicken breeds were analyzed. Variations detected here might have an impact on Ex-FABP activity and function and underpin the development of gene markers for chicken fatty deposition and metabolism. The polymorphism, generated by C4715T mutation in exon5, was significantly associated with thickness of subcutaneous fat plus skin in cocks. Subcutaneous fat plus skin of cocks was more thick in TT genotype than in CC genotype (P < 0.05). The Ex-FABP gene could be a candidate locus or linked to a QTL that significantly affects fatty deposition and metabolism in chicken.

Synthesis of carbapyochelins via diastereoselective azidation of 5-(ethoxycarbonyl)methylproline derivatives

Two configurationally stable carbon-based analogues of pyochelin have been prepared from Boc-pyroglutamic acid-tert-butyl ester in 11 and 13 steps. Introduction of the amino group was achieved by a highly diastereoselective electrophilic azidation reaction to afford novel bis-alpha-amino acid proline derivatives.

Acute endotoxemia is associated with upregulation of lipocalin 24p3/Lcn2 in lung and liver

Acute endotoxemia is associated with production of acute phase proteins which regulate inflammatory responses to tissue injury. Consistent with DNA microarray experiments, we found that acute endotoxemia, induced by administration of lipopolysaccharide (LPS) to mice (1 mg/kg) or rats (5 mg/kg), resulted in increased expression of the hepatic acute phase protein, lipocalin 24p3, which was evident within 4 h and persisted for 24-48 h. Increases in 24p3 expression were also observed in the lung after LPS administration, as well as in isolated liver and lung macrophages, and Type II alveolar epithelial cells. The actions of LPS are dependent, in part, on Toll-like receptor (TLR) proteins. Macrophages from C3H/HeJ mice, which possess a nonfunctional TLR-4, expressed low levels of 24p3 mRNA when compared to cells from control C3H/OuJ mice. Whereas LPS administration increased 24p3 expression in lung and liver macrophages from control C3H/OuJ mice, minimal effects were observed in TLR-4 mutant mice demonstrating that TLR-4 is important in regulating 24p3 expression during acute endotoxemia. Promoters for genes encoding lipocalin proteins including 24p3 contain consensus sequences for transcription factors including NF-kappaB, and C/EBP. Acute endotoxemia resulted in NF-kappaB nuclear binding activity in both alveolar macrophages and Type II cells. In contrast, C/EBP activation was evident only in Type II cells, suggesting differential effects of LPS on these cell types. These data suggest that the acute phase response to acute endotoxemia involves induction of 24p3 in both the lung and liver. This protein may be important in restoring tissue homeostasis following LPS-induced injury.

Proteomic analysis of the acid-soluble organic matrix of the chicken calcified eggshell layer

The major difference between inorganic minerals and biominerals is the presence of an organic matrix consisting of proteins, glycoproteins, proteoglycans, and polysaccharides, which is synthesized by specialized cells under genetic control before or during mineralization. The organic matrix is thought to play a major role in the assembly of the biomineral and determination of its mechanical properties. The recent elucidation of the chicken genome provided an opportunity to explore the matrix proteome of a biomineral using up-to-date MS-based technology. We identified 520 proteins in this matrix including the ten matrix proteins already known before. The identified proteins were divided into three abundance groups using the exponentially modified protein abundance index described recently which was roughly calibrated with the few known data on protein yield derived from Edman sequence analysis. A small group of 32 highly abundant proteins contained the presently known eggshell-specific proteins and all of the other known eggshell matrix constituents identified before with much less sensitive conventional methods. The present study, which is the first comprehensive proteomic study of a vertebrate biomineral, is intended as a starting point for the detailed molecular characterization of eggshell matrix proteins, their interactions in the matrix network and functional studies.

Proteomic analysis of hen egg white

Hen egg white is an original biological fluid in which major proteins have been widely studied, unlike the minor components. In this study, two-dimensional electrophoresis associated with mass spectrometry enabled the separation of 69 protein spots and their matching with major proteins, which were already known, and with minor proteins. Sixteen proteins were identified, and among them, two had never been previously detected in hen egg white, i.e., Tenp, a protein with strong homology with a bacterial permeability-increasing protein family (BPI), and VMO-1, an outer layer vitelline membrane protein. Thirteen proteins present a very wide polymorphism (ovotransferrin, ovomucoid, clusterin, etc.), some of them up to nine isoforms (ovoinhibitor). Eleven functional protein families were identified (serpin, transferrin, protease inhibitors Kazal, glycosyl hydrolases, lipocalin, bactericidal permeability-increasing protein, clusterin, UPAR/CD59/Ly6/ snake neurotoxin, cysteine protease inhibitor, VMO-1, and folate receptor families). These various biological functions could be interesting for further valorizations. In addition, three spots remain unidentified, probably because these proteins are not yet indexed in the international protein databanks.

Acute phase lipocalin Ex-FABP is involved in heart development and cell survival

Ex-FABP is an extracellular fatty acid binding protein, expressed during chicken embryo development in cartilage, muscle fibers, and blood granulocytes. Transfection of chondrocytes and myoblasts with anti-sense Ex-FABP cDNA results in inhibition of cell proliferation and apoptosis induction. Ex-FABP expression is dramatically enhanced by inflammatory stimuli and in pathological conditions. In this paper, by in situ whole mount and immunohistochemistry analysis we show that, at early developmental stage, Ex-FABP is diffuse in all tissues of chick embryos. Particularly high level of transcript and protein are expressed in the heart. During acute phase response (APR) induced by endotoxin LPS injection, a marked increase of Ex-FABP mRNA was observed in embryos, highest Ex-FABP expression being in heart and liver. To investigate in vivo the biological role of Ex-FABP, we have directly microinjected chicken embryos with antibody against Ex-FABP. Almost 70% of chicken embryos died and the target tissue was the heart. We detected in heart of the treated embryos a significant increase of apoptotic cells and high level of fatty acids. We propose that the accumulation of fatty acid, specific ligand of Ex-FABP, in the cell microenvironment is responsible of heart cell death, and we suggest that Ex-FABP may act as a survival protein by playing a role as scavenger for fatty acids.

Siderocalin (Lcn 2) Also Binds Carboxymycobactins, Potentially Defending against Mycobacterial Infections through Iron Sequestration

Siderocalin, a member of the lipocalin family of binding proteins, is found in neutrophil granules, uterine secretions, and at markedly elevated levels in serum and synovium during bacterial infection; it is also secreted from epithelial cells in response to inflammation or tumorigenesis. Identification of high-affinity ligands, bacterial catecholate-type siderophores (such as enterochelin), suggested a possible function for siderocalin: an antibacterial agent, complementing the general antimicrobial innate immune system iron-depletion strategy, sequestering iron as ferric siderophore complexes. Supporting this hypothesis, siderocalin is a potent bacteriostatic agent in vitro under iron-limiting conditions and, when knocked out, renders mice remarkably susceptible to bacterial infection. Here we show that siderocalin also binds soluble siderophores of mycobacteria, including M. tuberculosis: carboxymycobactins. Siderocalin employs a degenerate recognition mechanism to cross react with these dissimilar types of siderophores, broadening the potential utility of this innate immune defense.

Cell Transformation by the v-myc Oncogene Abrogates c-Myc/Max-mediated Suppression of a C/EBPβ-dependent Lipocalin Gene

Using differential hybridization techniques, a cDNA clone (Q83) was isolated that corresponds to a highly abundant mRNA in quail embryo fibroblasts transformed by the v-myc oncogene. The deduced 178 amino acid protein product of Q83 contains an N-terminal signal sequence and a lipocalin sequence motif, the hallmark of a family of secretory proteins binding and transporting small hydrophobic molecules of diverse biological function, including retinoids and steroids. The quail Q83 protein displays 87% sequence identity with a developmentally regulated chicken protein, termed p20K or Ch21. Cell transformation specifically by v-myc, but not by other oncogenic agents, induces high-level expression of Q83 mRNA and of the Q83 protein. Nucleotide sequence analysis and transcriptional mapping revealed that the Q83 gene encompasses seven exons with the coding region confined to exons 1 through 6. The promoter region contains consensus binding sites for the transcriptional regulators Myc and C/EBP beta. Transcriptional activation of Q83 is principally dependent on C/EBP beta, but is blocked in normal cells by the endogenous c-Myc/Max/Mad transcription factor network. In v-myc-transformed cells, high-level expression of the v-Myc protein and formation of highly stable v-Myc/Max heterodimers leads to abrogation of Q83 gene suppression and activation by C/EBP beta. A 157 amino acid residue recombinant protein representing the secreted form of Q83 was used for structure determination by nuclear magnetic resonance spectroscopy. Q83 folds into a single globular domain of the lipocalin-type. The central part consists of an eight-stranded up-and-down beta-barrel core flanked by an N-terminal 3(10)-like helix and a C-terminal alpha-helix. The orientation of the C-terminal alpha-helix is partially determined by a disulfide bridge between Cys59 and Cys152. The three-dimensional structure determination of the Q83 protein will facilitate the identification of its authentic ligand and the assessment of its biological function, including the putative role in myc-induced cell transformation.

Tissue involution and the acute phase response

After their roles in reproduction are completed, the mass of the uterus and the mammary gland decrease rapidly by the process of involution that involves an ordered series of events including apoptosis, neutrophil entry, the release of degradative enzymes, and phagocytosis of cellular debris. The acute phase proteins are produced by the liver and other tissues in response to inflammation or a toxic challenge. Uterocalin (SIP24/24p3) is one of these proteins. During involution, the mammary gland and uterus express high levels of uterocalin that reach an average of 0.2-0.5% of the total extractable protein at its peak. Uterocalin and its orthologues have been demonstrated in vitro to (1). bind certain fatty acids and (2). specifically induce apoptosis in neutrophils and other leukocytes. The period of uterocalin expression during involution is consistent with the hypothesis that one of its physiological roles is to induce apoptosis of invading neutrophils and delay the entry of neutrophils into the tissue until the second phase of involution. Interestingly, it has been shown that uterocalin expression remains higher in primiparous gland than in virgin glands after the pregnant glands have completely involuted. This observation and the known protective effect of early pregnancy on later development of breast cancer suggest that the ability of uterocalin to induce apoptosis in neutrophils might also decrease oxidative and carcinogenic activity in the gland and result in a lower mutation rate and thus a lower probability of cancer in the primiparous gland.

Differentiation-dependent activation of the extracellular fatty acid binding protein (Ex-FABP) gene during chondrogenesis

Chicken hypertrophic chondrocytes secrete the extracellular fatty acid binding protein (Ex-FABP), a lipocalin not expressed by their undifferentiated precursors. Genomic clones coding for the full protein are here structurally and functionally analyzed. We first determined that the promoter sequence markedly differs from that reported for the homologous p20K, and we confirmed by genomic DNA Southern analysis the exactness of our sequence. This is of relevance since we have identified another lipocalin gene within the region of discrepancy, indicating thereby the existence of a lipocalin cluster within the same chromosomal locus. By transient transfections with 5'-deletions and the chloramphenicol acetyl transferase (CAT) reporter gene, the region between nt -926 and nt -629 was shown to be strongly active, specifically in hypertrophic chondrocytes and not in dedifferentiated cells. Responsive elements for several potential transcription factors lay within this sequence. Among those, activating protein-1 (AP-1) was shown to be involved in the regulation of the Ex-FABP gene during chondrocyte differentiation, as indicated by electrophoretic mobility shift assay, AP-1 site mutagenesis and functional interference assays.

Neutrophil gelatinase-associated lipocalin is a marker for dysregulated keratinocyte differentiation in human skin

Neutrophil gelatinase-associated lipocalin (NGAL) is a 25-kDa protein initially isolated from the specific granules of human neutrophils. It is a member of the highly heterogeneous lipocalin protein family, which shares a common tertiary structure. Its synthesis is induced in gastrointestinal epithelium in association with inflammation and malignancy. To gain insight into its potential role in other epithelia we have investigated the expression of NGAL in human skin embryonic development, in normal adult skin, and in skin associated with inflammation and neoplastic transformation. In the present study we report that the embryonic expression of NGAL appears to be regulated in a spatio-temporal pattern. It was induced in the interfollicular epidermis at 20-24 weeks of gestational age but thereafter progressively receded towards the hair follicles. In normal adult skin, NGAL was detected solely in association with hair follicles. However, strong induction of NGAL in the epidermis was seen in a variety of skin disorders characterized by dysregulated epithelial differentiation such as psoriasis, pityriasis rubra and squamous cell carcinoma. In these tissues production of NGAL was confined to spatially distinct subpopulations of keratinocytes underlying areas of parakeratosis, whereas skin samples lacking parakeratotic epithelium such as lichen ruber planus, acute contact eczema and basal cell carcinoma were negative for NGAL. Consistent with being a marker for disturbed terminal differentiation, NGAL immunoreactivity showed an inverse pattern when compared with that of the differentiation marker filaggrin. The biologic functions of NGAL in epithelia are not fully known, although an immunomodulatory role in host defense has been proposed. In addition, the transient interfollicular NGAL expression during skin embryogenesis along with the induction of NGAL in adult parakeratotic epidermis suggests it play a role in epithelial differentiation pathways.

CALbeta, a novel lipocalin associated with chondrogenesis and inflammation

We have previously demonstrated the association of the chicken lipocalin Ex-FABP with cartilage formation and inflammatory responses as a marker of these processes (Descalzi Cancedda et al., Biochim. Biophys. Acta 1482, 127-135, 2000). Here we report the isolation and characterisation of a new lipocalin gene laying upstream the Ex-FABP, thus representing the second member of a possible genomic cluster. This gene contains an open reading frame coding for a polypeptide of about 19 kDa. The amino-acid sequence revealed a conserved lipocalin secondary structure. Tissue distribution of the protein in developing embryos showed a preferential expression in the heart although mRNA transcripts could be detected also in muscle, lung and liver. The lowest expression was observed in the stomach, brain and skin. During endochondral formation of long bones, the protein is differentially distributed, as the transcripts, evidenced in the tibia by in situ hybridisation, are present in the hypertrophic cone of the cartilage and mostly absent in the area of the proliferating chondrocytes. Such developmental regulation was observed also in vitro in cultured chondrocytes where the transcripts were barely detectable in dedifferentiated cells but highly expressed in hypertrophic chondrocytes. The protein was also significantly induced by lipopolysaccharide stimulation of chondrocytes, indicating a possible involvement in acute phase response. Raising specific antibodies in a rabbit allowed validating, at the protein level, all the transcriptional data. Moreover, we gained evidence that the protein is actively secreted in the extracellular matrix surrounding the chondrocytes. Because of its peculiar expression in cartilage, this new protein was named chondrogenesis-associated lipocalin beta (thereafter referred to as CAL beta). The close similarity between Ex-FABP and CAL beta expression patterns supports the hypothesis of a genomic organisation in a cluster where both genes could be co-ordinately regulated.