Synthesis and structure-activity relationship of beta-defensins, multi-functional peptides of the immune system

A Novel Beta-Defensin Isoform from Malabar Trevally, Carangoides malabaricus (Bloch & Schneider, 1801), an Arsenal Against Fish Bacterial Pathogens: Molecular Characterization, Recombinant Production, and Mechanism of Action

Antimicrobial peptides (AMPs), including beta-defensin from fish, are a crucial class of peptide medicines. The focus of the current study is the molecular and functional attributes of CmDef, a 63-amino acid beta-defensin AMP from Malabar trevally, Carangoides malabaricus. This peptide demonstrated typical characteristics of AMPs, including hydrophobicity, amphipathic nature, and +2.8 net charge. The CmDef was recombinantly expressed and the recombinant peptide, rCmDef displayed a strong antimicrobial activity against bacterial fish pathogens with an MIC of 8 µM for V. proteolyticus and 32 µM for A. hydrophila. The E. tarda and V. harveyi showed an inhibition of 94% and 54%, respectively, at 32 µM concentration. No activity was observed against V. fluvialis and V. alginolyticus. The rCmDef has a multimode of action that exerts an antibacterial effect by membrane depolarization followed by membrane permeabilization and ROS production. rCmDef also exhibited anti-cancer activities in silico without causing hemolysis. The peptide demonstrated stability under various conditions, including different pH levels, temperatures, salts, and metal ions (KCl and CaCl2), and remained stable in the presence of proteases such as trypsin and proteinase K at concentrations up to 0.2 µg/100 µl. The strong antibacterial efficacy and non-cytotoxic nature suggest that rCmDef is a single-edged sword that can contribute significantly to aquaculture disease management.

Antimicrobial activity of yak beta-defensin 116 against Staphylococcus aureus and its role in gut homeostasis

Staphylococcus aureus (S. aureus) is one of the most common food-borne poisoning microbial agent. However, the antimicrobial activity of β-defensin 116 in yak and its application in S. aureus-induced diarrheal disease have not been reported. In this study, 303 bp cDNA sequence of yak DEFB116 gene was obtained. In addition, the prokaryotic expression vector of DEFB116 protein with a molecular weight of 16 kDa was successfully constructed and expressed. The yak DEFB116 gene can encode 19 amino acids, the percentage of hydrophobic amino acids is 36 % and the total positive charge is 6, which has potential antibacterial potential. Sufficient DEFB116 protein concentration and time can destroy the integrity of the bacterial cell membrane, resulting in leakage of intracellular solutes and thus killing S. aureus. The intestinal histopathological features and the number of inflammatory cells were improved in the diarrhea mouse model under the action of DEFB116 protein. The decrease of goblet cells was reversed, the expression of mucoprotein was increased. DEFB116 protein increased the abundance of Lactobacillus johnsonii, Lactobacillus reuteri and Desulfovibrio, and inhibited the reproduction of pathogenic bacteria. These findings provide new insights into the potential future applications of yak β-defencins in the food industry and medical fields.

Yak DEFB124 alleviates intestinal injury caused by Staphylococcus aureus infection

To investigate the characteristics and functions of yak β-defensin 124 (DEFB124), prokaryotic expression, analysis of gut microbiological and other methods were used in this study. The results showed that the sequence of yak DEFB124 gene was 306 bp in length and 207 bp in open reading frame, which encoded 68 amino acids. Yak DEFB124 protein was highly conserved and had the closest relationship with cattle. Yak DEFB124 protein was a secreted cationic β-defensin. The recombinant expression plasmid pET32a-DEFB124 was constructed, and an about 24 kDa protein was successfully expressed. Yak DEFB124 protein had inhibitory activity against Staphylococcus aureus (S. aureus), and its MIC value was 64 μg/mL. After treating with yak DEFB124 protein, the activities of alkaline phosphatase (AKP) and total superoxide dismutase (T-SOD) were higher (P < 0.01) in the jejunum tissue, but the activity of lysozyme (LZM) was lower (P < 0.01). The number of goblet cells in the duodenum, jejunum, and ileum of the mice in the DEFB124 group was increased (P < 0.01). Besides, the expressions of MUC2 mRNA and protein were increased (P < 0.05) after the treatment with yak DEFB124 protein. Furthermore, the relative abundance of Lactobacillus in jejunum of mice in DEFB124 group was also increased. In summary, yak DEFB124 protein could increase the number of goblet cells in mice intestine and the abundance of intestinal probiotics Lactobacillus, thereby protecting the intestinal tract and alleviating intestinal damage.

Exploring the impact of the recombinant Escherichia coli strain on defensins antimicrobial activity: BL21 versus Origami strain

The growing emergence of microorganisms resistant to antibiotics has prompted the development of alternative antimicrobial therapies. Among them, the antimicrobial peptides produced by innate immunity, which are also known as host defense peptides (HDPs), hold great potential. They have been shown to exert activity against both Gram-positive and Gram-negative bacteria, including those resistant to antibiotics. These HDPs are classified into three categories: defensins, cathelicidins, and histatins. Traditionally, HDPs have been chemically synthesized, but this strategy often limits their application due to the high associated production costs. Alternatively, some HDPs have been recombinantly produced, but little is known about the impact of the bacterial strain in the recombinant product. This work aimed to assess the influence of the Escherichia coli strain used as cell factory to determine the activity and stability of recombinant defensins, which have 3 disulfide bonds. For that, an α-defensin [human α-defensin 5 (HD5)] and a β-defensin [bovine lingual antimicrobial peptide (LAP)] were produced in two recombinant backgrounds. The first one was an E. coli BL21 strain, which has a reducing cytoplasm, whereas the second was an E. coli Origami B, that is a strain with a more oxidizing cytoplasm. The results showed that both HD5 and LAP, fused to Green Fluorescent Protein (GFP), were successfully produced in both BL21 and Origami B strains. However, differences were observed in the HDP production yield and bactericidal activity, especially for the HD5-based protein. The HD5 protein fused to GFP was not only produced at higher yields in the E. coli BL21 strain, but it also showed a higher quality and stability than that produced in the Origami B strain. Hence, this data showed that the strain had a clear impact on both HDPs quantity and quality.

The cecropin-prophenoloxidase regulatory mechanism is a cross-species physiological function in mosquitoes

This study's aim was to investigate whether the cecropin-prophenoloxidase regulatory mechanism is a cross-species physiological function among mosquitoes. BLAST and phylogenetic analysis revealed that three mosquito cecropin Bs, namely Aedes albopictus cecropin B (Aalcec B), Armigeres subalbatus cecropin B2 (Ascec B2), and Culex quinquefasciatus cecropin B1 (Cqcec B1), play crucial roles in cuticle formation during pupal development via the regulation of prophenoloxidase 3 (PPO 3). The effects of cecropin B knockdown were rescued in a cross-species manner by injecting synthetic cecropin B peptide into pupae. Further investigations showed that these three cecropin B peptides bind to TTGG(A/C)A motifs within each of the PPO 3 DNA fragments obtained from these three mosquitoes. These results suggest that Aalcec B, Ascec B2, and Cqcec B1 each play an important role as a transcription factor in cuticle formation and that similar cecropin-prophenoloxidase regulatory mechanisms exist in multiple mosquito species.

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Cecropin B is able to regulate PPO 3 expression in the pupae

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Cecropin B binds to TTGG(A/C)A motifs within the PPO 3 DNA

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The knockdown of cecropin B was rescued by sequence-similar cecropin B peptides

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The cecropin B-prophenoloxidase 3 regulatory mechanism is conserved in mosquitoes

Differentially expressed genes in the femur cartilage transcriptome clarify the understanding of femoral head separation in chickens

Locomotor problems are among one of the main concerns in the current poultry industry, causing major economic losses and affecting animal welfare. The most common bone anomalies in the femur are dyschondroplasia, femoral head separation (FHS), and bacterial chondronecrosis with osteomyelitis (BCO), also known as femoral head necrosis (FHN). The present study aimed to identify differentially expressed (DE) genes in the articular cartilage (AC) of normal and FHS-affected broilers by RNA-Seq analysis. In the transcriptome analysis, 12,169 genes were expressed in the femur AC. Of those, 107 genes were DE (FDR < 0.05) between normal and affected chickens, of which 9 were downregulated and 98 were upregulated in the affected broilers. In the gene-set enrichment analysis using the DE genes, 79 biological processes (BP) were identified and were grouped into 12 superclusters. The main BP found were involved in the response to biotic stimulus, gas transport, cellular activation, carbohydrate-derived catabolism, multi-organism regulation, immune system, muscle contraction, multi-organism process, cytolysis, leukocytes and cell adhesion. In this study, the first transcriptome analysis of the broilers femur articular cartilage was performed, and a set of candidate genes (AvBD1, AvBD2, ANK1, EPX, ADA, RHAG) that could trigger changes in the broiler´s femoral growth plate was identified. Moreover, these results could be helpful to better understand FHN in chickens and possibly in humans.

Identification of a crocodylian β-defensin variant from Alligator mississippiensis with antimicrobial and antibiofilm activity

β-defensin host defense peptides are important components of the innate immune system of vertebrates. Although evidence of their broad antimicrobial, antibiofilm and immunomodulatory activities in mammals have been presented, β-defensins from other vertebrate species, like crocodylians, remain largely unexplored. In this study, five new crocodylian β-defensin variants from Alligator mississippiensis and Crocodylus porosus were selected for synthesis and characterization based on their charge and hydrophobicity values. Linear peptides were synthesized, folded, purified and then evaluated for their antimicrobial and antibiofilm activities against the bacterial pathogens, Salmonella enterica serovar Typhimurium, Staphylococcus aureus, Enterobacter cloacae and Acinetobacter baumannii. The Am23SK variant (SCRFSGGYCIWNWERCRSGHFLVALCPFRKRCCK) from A. mississippiensis displayed promising activity against both planktonic cells and bacterial biofilms, outperforming the human β-defensin 3 under the experimental conditions. Moreover, Am23SK exhibited no cytotoxicity towards mammalian cells and exerted immunomodulatory effects in vitro, moderately suppressing the production of proinflammatory mediators from stimulated human bronchial epithelial cells. Overall, our results have expanded the activity landscape of crocodylian and reptilian β-defensin in general.

Influence of disulfide bonds in human beta defensin-3 on its strain specific activity against Gram-negative bacteria

Antimicrobial peptides (AMPs) play an important role in the host defense against various microbes. One of the most efficient human AMPs is the human beta defensin-3 (hBD-3) which is produced by, e.g. keratinocytes and lung epithelial cells. However, the structure-function relationship for AMPs and in particular for defensins with their typical three disulfide bonds is still poorly understood. In this study the importance of the three disulfide bonds for the activity of the AMPs is investigated with biological assays and with biophysical experiments utilizing different membrane reconstitution systems. The activities of natural hBD-3, hBD-3-c (cyclic variant with one disulfide bond), and hBD-3-l (linear variant without disulfide bonds) and fragments thereof were tested against specific Gram-negative bacteria. Furthermore, hemolytic and cytotoxic activities were analyzed as well as the potency to neutralize immune cell stimulation of lipopolysaccharide (LPS). Experiments using reconstituted lipid matrices composed of phospholipids or LPS purified from the respective Gram-negative bacteria, showed that the membrane activity of all three hBD-3 peptides is decisive for their capability to kill bacteria and to neutralize LPS. In most of the test systems the linear hBD-3-l showed the highest activity. It was also the only peptide significantly active against polymyxin B-resistant Proteus mirabilis R45. However, the stability of hBD-3 against protease activity decreases with decreasing number of disulfide bonds. This study demonstrates that the refining of AMP structures can generate more active compounds against certain strains.

Unlocking NuriPep 1653 From Common Pea Protein: A Potent Antimicrobial Peptide to Tackle a Pan-Drug Resistant Acinetobacter baumannii

While the antibiotic era has come and gone, antimicrobial peptides (AMPs) hold promise as novel therapies to treat multidrug resistant (MDR) pathogens in an age where the threat of multidrug resistance escalates worldwide. Here, we report the bactericidal properties of NuriPep 1653, a novel 22 mer and non-modified peptide. NuriPep 1653 was identified within the sequence of the non-antimicrobial P54 protein, which is involved in nutrient reservoir activity in Pisum sativum. Total bacterial clearance of Acinetobacter baumannii cells (1 × 108 cells/mL) was observed using only 4 × MIC (48 μg/mL) of NuriPep 1653 after just 20 min of treatment. We uncovered a synergistic interaction between NuriPep 1653 and another antimicrobial peptide, colistin. The MIC of NuriPep 1653 and colistin dropped from 12 and 8 μg/mL to 2 and 1 μg/mL, respectively, when they were combined. NuriPep 1653 exhibits no cytotoxicity in different human cell lines and has a low propensity to induce bacterial resistance in a colistin resistant clinical isolate of A. baumannii. The existence of these peptides embedded in proteins unearths potentially new classes of antimicrobials with activity against clinically relevant pathogens. Our findings push the boundaries of traditional peptide discovery and represent a leading edge for natural bioactive compounds which may have a common existence in nature but remain unexposed.

Characterization of the β-defensin genes in giant panda

β-Defensins are small antimicrobial proteins expressed in various organisms and have great potential for improving animal health and selective breeding programs. Giant pandas have a distinctive lineage in Carnivora, and it is unclear whether β-defensin genes have experienced different selective pressures during giant panda evolution. We therefore characterized the giant panda (Ailuropoda melanoleuca) β-defensin gene family through gap filling, TBLASTN, and HMM searches. Among 36 β-defensins identified, gastrointestinal disease may induce the expression of the DEFB1 and DEFB139 genes in the digestive system. Moreover, for DEFB139, a significant positive selection different from that of its homologs was revealed through branch model comparisons. A Pro-to-Arg mutation in the giant panda DEFB139 mature peptide may have enhanced the peptide’s antimicrobial potency by increasing its stability, isoelectric point, surface charge and surface hydrophobicity, and by stabilizing its second β-sheet. Broth microdilution tests showed that the increase in net charge caused by the Pro-to-Arg mutation has enhanced the peptide’s potency against Staphylococcus aureus, although the increase was minor. We expect that additional gene function and expression studies of the giant panda DEFB139 gene could improve the existing conservation strategies for the giant panda.

Comparative expression of host defense peptides in turkey poults

Host defense peptides (HDPs) are a large group of small, positively charged peptides that play an important role in innate immunity, particularly at early ages when other components of the immune system have not fully developed. There are 3 classes of avian HDPs: avian beta defensins (AvBDs), cathelicidins (Cath), and liver-expressed antimicrobial peptide 2 (LEAP-2). The objective was to compare expression of HDP mRNAs in male turkey poults at day of hatch (d 0), d 7, d 14, d 21 and d 28 from the thymus, spleen, bursa, duodenum, jejunum, and ileum. The expression of AvBD1, AvBD2, AvBD8, AvBD9, AvBD10, AvBD13, Cath2, Cath3, and LEAP-2 mRNA was measured using qPCR (n = 6 birds/tissue/age). Data were analyzed by one-way ANOVA and Tukey's test, and significance considered at P < 0.05. AvBDs and Caths exhibited greater expression in immune organs (thymus, spleen, and bursa) than intestinal tissues. In the thymus, expression of all AvBDs examined, except AvBD8, showed an increase from d 0 to d 21. In the spleen, AvBD1 and AvBD2 exhibited reduced expression from d 0 to d 7 and low expression thereafter. In the intestine, AVBD1, AVBD8, and AvBD13 increased expression from d 0 to d 28 in the duodenum, while AvBD10 showed the greatest expression at d 0 that declined to d 7 and stayed low thereafter in the duodenum, jejunum, and ileum. Cath2 and Cath3 demonstrated the highest expression in the spleen, which was greatest at d 0 then declined to d 7 through d 28. Conversely, LEAP-2 showed greater expression in the intestinal tissues than in the immune organs. LEAP-2 expression was upregulated from d 0 to d 7 and then remained elevated from d 7 through d 14 in the duodenum. In the jejunum, LEAP-2 increased from d 0 to d 21 and d 28. Understanding the differential expression of HDPs could reveal the innate immune status of turkey poults, and may subsequently allow improvement of their health through appropriate mitigation strategies.

A crucial role of paralogous β-defensin genes in the Chinese alligator innate immune system revealed by the first determination of a Crocodilia defensin cluster

The β-defensin, one of the antimicrobial peptides (AMPs), is a significant component of the innate immune with a broad range of antimicrobial activities. Differing from the widely-studied mammals and birds, limited information about β-defensins has been reported in reptiles, especially in crocodilians. As a same ancient species as dinosaurs and the most endangered species of 23 crocodilians, the survival of Chinese alligator (Alligator sinensis) means a powerful immune system and possible involvement of AMPs in its immune resistance. In this study, we identified 20 novel Alligator sinensisβ-defensin genes (AsBDs) from a 390 kb region using bioinformatic and experimental approaches, and successfully distinguished six orthologous AsBDs to birds and nine paralogous AsBDs undergoing gene duplication events. The amino acid alignment shows that the AsBD paralogs, like α-defensins, encode a significantly longer pro-piece comparing with the orthologs. The calculation of non-synonymous (d_N) and synonymous (d_S) substitutions in the mature peptide reveals that the AsBD paralogs experience a significantly higher selective pressure (d_N/d_S) than the orthologs, but a similar evolutionary force to α-defensins. The gene expression result indicates that the AsBD paralogs have a significantly higher expression level than the orthologos in gastrointestinal tract where the host is vulnerable to enteric pathogenic bacteria, as observed in α-defensins. These three pieces of evidence demonstrate that the AsBD paralogs do play an important role in maintaining long-term survival of this endangered reptile. Thus, this survey of AsBDs on the genomic structure, evolutionary characteristics, and expression pattern provides a genetic and immunological foundation for further investigating their antimicrobial function and alternative antibiotics potentiality.

Structural determinants of Neosartorya fischeri antifungal protein (NFAP) for folding, stability and antifungal activity

The recent global challenges to prevent and treat fungal infections strongly demand for the development of new antifungal strategies. The structurally very similar cysteine-rich antifungal proteins from ascomycetes provide a feasible basis for designing new antifungal molecules. The main structural elements responsible for folding, stability and antifungal activity are not fully understood, although this is an essential prerequisite for rational protein design. In this study, we used the Neosartorya fischeri antifungal protein (NFAP) to investigate the role of the disulphide bridges, the hydrophobic core, and the N-terminal amino acids in the formation of a highly stable, folded, and antifungal active protein. NFAP and its mutants carrying cysteine deletion (NFAPΔC), hydrophobic core deletion (NFAPΔh), and N-terminal amino acids exchanges (NFAPΔN) were produced in Pichia pastoris. The recombinant NFAP showed the same features in structure, folding, stability and activity as the native protein. The data acquired with mass spectrometry, structural analyses and antifungal activity assays of NFAP and its mutants proved the importance of the disulphide bonding, the hydrophobic core and the correct N-terminus for folding, stability and full antifungal function. Our findings provide further support to the comprehensive understanding of the structure-function relationship in members of this protein group.

Characterization of the antimicrobial peptide family defensins in the Tasmanian devil (Sarcophilus harrisii), koala (Phascolarctos cinereus), and tammar wallaby (Macropus eugenii)

Defensins comprise a family of cysteine-rich antimicrobial peptides with important roles in innate and adaptive immune defense in vertebrates. We characterized alpha and beta defensin genes in three Australian marsupials: the Tasmanian devil (Sarcophilus harrisii), koala (Phascolarctos cinereus), and tammar wallaby (Macropus eugenii) and identified 48, 34, and 39 defensins, respectively. One hundred and twelve have the classical antimicrobial peptides characteristics required for pathogen membrane targeting, including cationic charge (between 1+ and 15+) and a high proportion of hydrophobic residues (>30%). Phylogenetic analysis shows that gene duplication has driven unique and species-specific expansions of devil, koala, and tammar wallaby beta defensins and devil alpha defensins. Defensin genes are arranged in three genomic clusters in marsupials, whereas further duplications and translocations have occurred in eutherians resulting in four and five gene clusters in mice and humans, respectively. Marsupial defensins are generally under purifying selection, particularly residues essential for defensin structural stability. Certain hydrophobic or positively charged sites, predominantly found in the defensin loop, are positively selected, which may have functional significance in defensin-target interaction and membrane insertion.

β-defensins and the epididymis: contrasting influences of prenatal, postnatal, and adult scenarios

β-defensins are components of host defense, with antimicrobial and pleiotropic immuno-modulatory properties. Research over the last 15 years has demonstrated abundant expression of a variety of β-defensins in the postnatal epididymis of different species. A gradient of region- and cell-specific expression of these proteins is observed in the epithelium of the postnatal epididymis. Their secretion into the luminal fluid and binding to spermatozoa as they travel along the epididymis has suggested their involvement in reproduction-specific tasks. Therefore, continuous attention has been given to various β-defensins for their role in sperm function and fertility. Although β-defensins are largely dependent on androgens, the underlying mechanisms regulating their expression and function in the epididymis are not well understood. Recent investigation has pointed out to a new and interesting scenario where β-defensins emerge with a different expression pattern in the Wolffian duct, the embryonic precursor of the epididymis, as opposed to the adult epididymis, thereby redefining the concept concerning the multifunctional roles of β-defensins in the developing epididymis. In this review, we summarize some current views of β-defensins in the epididymis highlighting our most recent data and speculations on their role in the developing epididymis during the prenatal-to-postnatal transition, bringing attention to the many unanswered questions in this research area that may contribute to a better understanding of epididymal biology and male fertility.

Structure-function analysis of Avian β-defensin-6 and β-defensin-12: role of charge and disulfide bridges

Background

Avian beta-defensins (AvBD) are small, cationic, antimicrobial peptides. The potential application of AvBDs as alternatives to antibiotics has been the subject of interest. However, the mechanisms of action remain to be fully understood. The present study characterized the structure-function relationship of AvBD-6 and AvBD-12, two peptides with different net positive charges, similar hydrophobicity and distinct tissue expression profiles.

Results

AvBD-6 was more potent than AvBD-12 against E. coli, S. Typhimurium, and S. aureus as well as clinical isolates of extended spectrum beta lactamase (ESBL)-positive E. coli and K. pneumoniae. AvBD-6 was more effective than AvBD-12 in neutralizing LPS and interacting with bacterial genomic DNA. Increasing bacterial concentration from 10⁵ CFU/ml to 10⁹ CFU/ml abolished AvBDs’ antimicrobial activity. Increasing NaCl concentration significantly inhibited AvBDs’ antimicrobial activity, but not the LPS-neutralizing function. Both AvBDs were mildly chemotactic for chicken macrophages and strongly chemotactic for CHO-K1 cells expressing chicken chemokine receptor 2 (CCR2). AvBD-12 at higher concentrations also induced chemotactic migration of murine immature dendritic cells (DCs). Disruption of disulfide bridges abolished AvBDs’ chemotactic activity. Neither AvBDs was toxic to CHO-K1, macrophages, or DCs.

Conclusions

AvBDs are potent antimicrobial peptides under low-salt conditions, effective LPS-neutralizing agents, and broad-spectrum chemoattractant peptides. Their antimicrobial activity is positively correlated with the peptides’ net positive charges, inversely correlated with NaCl concentration and bacterial concentration, and minimally dependent on intramolecular disulfide bridges. In contrast, their chemotactic property requires the presence of intramolecular disulfide bridges. Data from the present study provide a theoretical basis for the design of AvBD-based therapeutic and immunomodulatory agents.

Cloning and Expression of β-Defensin from Soiny Mullet (Liza haematocheila), with Insights of its Antibacterial Mechanism

Beta-defensins are important part of innate immunity of fish, which are the first defense line against invading pathogens. In this study, the β-defensin (Lhβ-defensin) gene was cloned from spleen tissue of soiny mullet (Liza haematocheila). Lhβ-defensin cDNA was 747 bp in length, encoding 63 amino acids. Sequence alignment revealed that Lhβ-defensin contained six conserved cysteine residues and shared 97.5% sequence identities with grouper (Epinephelus coioides) β-defensin. Realtime PCR revealed that Lhβ-defensin was highest expressed in the immune related organs, such as spleen, kidney and gut of healthy fish. Following Streptococcus dysgalactiae infection, Lhβ-defensin was up-regulated in immune related organs, e.g. 17.6-fold in spleen and 10.87-fold in gut at 24 h post infection (hpi). Lhβ-defensin possessed a monomeric structure of a three-stranded anti-parallel β-sheet and an α-helix stabilized by three disulfide bonds formed by Cys30-Cys58, Cys36-Cys52, and Cys40-Cys59. In addition to the experimental work, computer simulation was also carried out to determine the possible conformation of β-defensin and its interaction with palmitoyloleoylphosphatidylglycerol (POPG), a model of bacteria membrane. The Lhβ-defensin was found to form dimeric structure stabilized by the van der Waals contacts of Leu35 and Cys37 in two anti-parallel β1-strands and the cation-π interaction between Tyr32 and Arg54 respectively in the two β1-strands. The most important interactions between β-defensin and membrane are the electrostatic interactions between Arg residues in β-defensin and head group of POPG bilayer as well as hydrogen bond interactions between them. Our results were useful for further understanding the potential mechanism of antimicrobial property of fish β-defensins.

Targeted inactivation of the mouse epididymal beta-defensin 41 alters sperm flagellar beat pattern and zona pellucida binding

During epididymal maturation, sperm acquire the ability to swim progressively by interacting with proteins secreted by the epididymal epithelium. Beta-defensin proteins, expressed in the epididymis, continue to regulate sperm motility during capacitation and hyperactivation in the female reproductive tract. We characterized the mouse beta-defensin 41 (DEFB41), by generating a mouse model with iCre recombinase inserted into the first exon of the gene. The homozygous Defb41(iCre/iCre) knock-in mice lacked Defb41 expression and displayed iCre recombinase activity in the principal cells of the proximal epididymis. Heterozygous Defb41(iCre/+) mice can be used to generate epididymis specific conditional knock-out mouse models. Homozygous Defb41(iCre/iCre) sperm displayed a defect in sperm motility with the flagella primarily bending in the pro-hook conformation while capacitated wild-type sperm more often displayed the anti-hook conformation. This led to a reduced straight line motility of Defb41(iCre/iCre) sperm and weaker binding to the oocyte. Thus, DEFB41 is required for proper sperm maturation.

Characterization of β-defensin 42 expressed in principal cells at the initial segment of the rat epididymis

β-defensins, preferentially expressed in male reproductive tracts, particularly in the testes and epididymis with region-specific patterns, play an important role in both innate immunity and sperm fertility. Expressed in the caput region of epididymis, β-defensins have been known to contribute to innate immunity, sperm motility initiation, and maintenance. However, β-defensins of the initial region remain to be uncharacterized. In this study, rat β-defensin 42 (Defb42) was revealed to be exclusively located in the principal cells at the initial segment of the rat epididymis and its sperm's acrosome. Furthermore, the expression of Defb42 was dependent on luminal testicular factors and developmental phases. The recombinant Defb42 was predominantly antimicrobial not against Candida albicans, but against Escherichia coli and Staphylococcus aureus. Based on these findings, Defb42 was suggested to play a dual role in sperm fertility and host defense in rat epididymis.

Design and activity of a cyclic mini-β-defensin analog: a novel antimicrobial tool

We have designed a cyclic 17-amino acid β-defensin analog featuring a single disulfide bond. This analog, designated "AMC" (ie, antimicrobial cyclic peptide), combines the internal hydrophobic domain of hBD1 and the C-terminal charged region of hBD3. The novel peptide was synthesized and characterized by nuclear magnetic resonance spectroscopy. The antimicrobial activities against gram-positive and gram-negative bacteria as well as against herpes simplex virus type 1 were analyzed. The cytotoxicity and serum stability were assessed. Nuclear magnetic resonance of AMC in aqueous solution suggests that the structure of the hBD1 region, although not identical, is preserved. Like the parent defensins, AMC is not cytotoxic for CaCo-2 cells. Interestingly, AMC retains the antibacterial activity of the parent hBD1 and hBD3 against Pseudomonas aeruginosa, Enterococcus faecalis, and Escherichia coli, and exerts dose-dependent activity against herpes simplex virus type 1. Moreover, while the antibacterial and antiviral activities of the oxidized and reduced forms of the parent defensins are similar, those of AMC are significantly different, and oxidized AMC is also considerably more stable in human serum. Taken together, our data also suggest that this novel peptide may be added to the arsenal of tools available to combat antibiotic-resistant infectious diseases, particularly because of its potential for encapsulation in a nanomedicine vector.

Heat-killed probiotic bacteria differentially regulate colonic epithelial cell production of human β-defensin-2: dependence on inflammatory cytokines

The inducible antimicrobial peptide human β-defensin-2 (hBD-2) stimulated by pro-inflammatory cytokines and bacterial products is essential to antipathogen responses of gut epithelial cells. Commensal and probiotic bacteria can augment such mucosal defences. Probiotic use in the treatment of inflammatory bowel disease, however, may have adverse effects, boosting inflammatory responses. The aim of this investigation was to determine the effect of selected probiotic strains on hBD-2 production by epithelial cells induced by pathologically relevant pro-inflammatory cytokines and the role of cytokine modulators in controlling hBD-2. Caco-2 colonic intestinal epithelial cells were pre-incubated with heat-killed probiotics, i.e. Lactobacillus casei strain Shirota (LcS) or Lactobacillus fermentum strain MS15 (LF), followed by stimulation of hBD-2 by interleukin (IL)-1β and tumour necrosis factor alpha (TNF-α) in the absence or presence of exogenous IL-10 or anti-IL-10 neutralising antibody. Cytokines and hBD-2 mRNA and protein were analysed by real-time quantitative polymerase chain reaction and enzyme-linked immunosorbent assay. LcS augmented IL-1β-induced hBD-2, whereas LF enhanced TNF-α- and suppressed IL-1β-induced hBD-2. LF enhanced TNF-α-induced TNF-α and suppressed IL-10, whereas augmented IL-1β-induced IL-10. LcS upregulated IL-1β-induced TNF-α mRNA and suppressed IL-10. Endogenous IL-10 differentially regulated hBD-2; neutralisation of IL-10 augmented TNF-α- and suppressed IL-1β-induced hBD-2. Exogenous IL-10, however, suppressed both TNF-α- and IL-1β-induced hBD-2; LcS partially rescued suppression in TNF-α- and IL-1β-stimulation, whereas LF further suppressed IL-1β-induced hBD-2. It can be concluded that probiotic strains differentially regulate hBD-2 mRNA expression and protein secretion, modulation being dictated by inflammatory stimulus and resulting cytokine environment.

Β-defensin in Nile tilapia (Oreochromis niloticus): Sequence, tissue expression, and anti-bacterial activity of synthetic peptides

Beta-defensins (β-defensins) are small cationic amphiphilic peptides that are widely distributed in plants, insects, and vertebrates, and are important for their antimicrobial properties. In this study, the β-defensin (Onβ-defensin) gene of the Nile tilapia (Oreochromis niloticus) was cloned from spleen tissue. Onβ-defensin has a genomic DNA sequence of 674 bp and produces a cDNA of 454 bp. Sequence alignments showed that Onβ-defensin contains three exons and two introns. Sequence analysis of the cDNA identified an open reading frame of 201 bp, encoding 66 amino acids. Bioinformatic analysis showed that Onβ-defensin encodes a cytoplasmic protein molecule containing a signal peptide. The deduced amino acid sequence of this peptide contains six conserved cysteine residues and two conserved glycine residues, and shows 81.82% and 78.33% sequence similarities with β-defensin-1 of fugu (Takifugu rubripes) and rainbow trout (Oncorhynchus mykiss), respectively. Real-time quantitative PCR showed that the level of Onβ-defensin expression was highest in the skin (307.1-fold), followed by the spleen (77.3-fold), kidney (17.8-fold), and muscle (16.5-fold) compared to controls. By contrast, low levels of expression were found in the liver, heart, intestine, stomach, and gill (<3.0-fold). Artificial infection of tilapia with Streptococcus agalactiae (group B streptococcus [GBS] strain) resulted in a significantly upregulated expression of Onβ-defensin in the skin, muscle, kidney, and gill. In vitro antimicrobial experiments showed that a synthetic Onβ-defensin polypeptide had a certain degree of inhibitory effect on the growth of Escherichia coli DH5α and S. agalactiae. The results indicate that Onβ-defensin plays a role in immune responses that suppress or kill pathogens.

N-Terminal fatty acylation of peptides spanning the cationic C-terminal segment of bovine β-defensin-2 results in salt-resistant antibacterial activity

Peptides spanning the C-terminal segment of bovine-β-defensin-2 (BNBD-2) rich in cationic amino acids, show antimicrobial activity. However, they exhibit considerably reduced activity at physiological concentration of NaCl. In the present study, we have investigated whether N-terminal acylation (acetylation and palmitoylation) of these peptides would result in improved antimicrobial activity. N-terminal palmitoylation though increased hydrophobicity of the peptides, did not enhance antimicrobial potency. However, antibacterial activity of these peptides was not attenuated by NaCl. Biophysical studies on the palmitoylated peptides have indicated that antibacterial activity in the presence of NaCl arises due to the ability of the peptides to interact with membranes more effectively. These peptides showed hemolytic activity which was attenuated considerably in the presence of serum and lipid vesicles. In defensin related peptides, fatty acylation would be a convenient way to generate analogs that are active in the presence of salt.

The blood-epididymis barrier and inflammation

The blood-epididymis barrier (BEB) is a critical structure for male fertility. It enables the development of a specific luminal environment that allows spermatozoa to acquire both the ability to swim and fertilize an ovum. The presence of tight junctions and specific cellular transporters can regulate the composition of the epididymal lumen to favor proper sperm maturation. The BEB is also at the interface between the immune system and sperm. Not only does the BEB protect maturing spermatozoa from the immune system, it is also influenced by cytokines released during inflammation, which can result in the loss of barrier function. Such a loss is associated with an immune response, decreased sperm functions, and appears to be a contributing factor to post-testicular male infertility. Alterations in the BEB may be responsible for the formation of inflammatory conditions such as sperm granulomas. The present review summarizes current knowledge on the morphological, physiological and pathological components associated with the BEB, the role of immune function on the regulation of the BEB, and how disturbance of these factors can result in inflammatory lesions of the epididymis.

Qualitative and quantitative peptidomic and proteomic approaches to phenotyping chicken semen

Understanding of the avian male gamete biology is essential to improve the conservation of genetic resources and performance in farming. In this study, the chicken semen peptidome/proteome and the molecular phenotype related to sperm quality were investigated. Spermatozoa (SPZ) and corresponding seminal plasma (SP) from 11 males with different fertilizing capacity were analyzed using three quantitative strategies (fluid and intact cells MALDI-MS, SDS-PAGE combined to LC-MS/MS with spectral counting and XIC methods). Individual MALDI profiling in combination with top-down MS allowed to characterize specific profiles per male and to identify 16 biomolecules (e.g.VMO1, AvBD10 and AvBD9 including polymorphism). Qualitative analysis identified 1165 proteins mainly involved in oxidoreduction mechanisms, energy processes, proteolysis and protein localization. Comparative analyses between the most and the least fertile males were performed. The enzymes involved in energy metabolism, respiratory chain or oxido-reduction activity were over-represented in SPZ of the most fertile males. The SP of the most and the least fertile males differed also on many proteins (e.g. ACE, AvBD10 and AvBD9, NEL precursor, acrosin). Thus proteomic is a "phenomic molecular tool" that may help to discriminate avian males on their reproductive capacity. The data have been deposited with ProteomeXchange (identifiers PXD000287 and PXD001254).

BIOLOGICAL SIGNIFICANCE

This peptidomic and proteomic study i) characterized for the first time the semen protein composition of the main domestic avian species (Gallus gallus) by analysis of ejaculated spermatozoa and corresponding seminal plasma; ii) established a characteristic molecular phenotype distinguishing semen and males at an individual level; and iii) proposedthe first evidence of biomarkers related to fertility.

Effect of selectively introducing arginine and D-amino acids on the antimicrobial activity and salt sensitivity in analogs of human beta-defensins

We have examined the antimicrobial activity of C-terminal analogs of human β-defensins HBD-1and-3 wherein lysines have been selectively replaced by L- and D-arginines and L-isoleucine substituted with its D-enantiomer. The analogs exhibited antibacterial and antifungal activities. Physiological concentration of NaCl did not attenuate the activity of the peptides against Gram-negative bacteria considerably, while some attenuation of activity was observed against S. aureus. Variable attenuation of activity was observed in the presence of Ca²⁺ and Mg²⁺. Introduction of D-amino acids abrogated the need for a disulfide bridge for exhibiting activity. Confocal images of carboxyfluorescein (CF) labeled peptides indicated initial localization on the membrane and subsequent translocation into the cell. Analogs corresponding to cationic rich segments of human defensins substituted with L- and D-arginine, could be attractive candidates for development as future therapeutic drugs.

The novel human β-defensin 114 regulates lipopolysaccharide (LPS)-mediated inflammation and protects sperm from motility loss

Lipopolysaccharide (LPS) is an important pathological factor involved in serious inflammatory diseases and male reproductive impairments. Emerging evidence demonstrates that antimicrobial peptides possess protective activity in response to LPS-induced inflammation. However, the LPS-binding and/or immunosuppressive activity of β-defensins (DEFBs) has been underestimated. In the present work, we characterized a novel human defensin, DEFB114, which was expressed predominantly in the epididymis and gingival cells at the RNA level. Homogenous recombinant DEFB114 peptides were prepared and characterized using mass spectrometry. DEFB114 protein exhibited a broad spectrum of antimicrobial activity with salt sensitivity against typical pathogenic microbes (i.e. Escherichia coli, Staphylococcus aureus, and Candida albicans). Interestingly, DEFB114 demonstrated novel LPS-binding activity in vitro and inhibited TNF-α release in RAW264.7 cultures through the inhibition of MAPK p42/44 when challenged with LPS. Moreover, DEFB114 could also rescue the LPS-induced reduction of human sperm motility in vitro and protect d-galactosamine-sensitized C57BL/6 mice from LPS-induced lethality in vivo. The protective activity of DEFB114 on RAW264.7, human sperm, and the d-galactosamine-sensitized mice was disulfide bond-dependent because alkylated DEFB114 lost its activity. The low cytotoxicity of the DEFB114 peptide toward human erythrocytes is indicative of its potential therapeutic use in the treatment of LPS-induced inflammation, LPS contamination, and potentially septic shock.

Chimeric beta-defensin analogs, including the novel 3NI analog, display salt-resistant antimicrobial activity and lack toxicity in human epithelial cell lines

Human beta-defensins (hBDs) are crucial peptides for the innate immune response and are thus prime candidates as therapeutic agents directed against infective diseases. Based on the properties of wild-type hBD1 and hBD3 and of previously synthesized analogs (1C, 3I, and 3N), we have designed a new analog, 3NI, and investigated its potential as an antimicrobial drug. Specifically, we evaluated the antimicrobial activities of 3NI versus those of hBD1, hBD3, 1C, 3I, and 3N. Our results show that 3NI exerted greater antibacterial activity against Pseudomonas aeruginosa, Escherichia coli, and Enterococcus faecalis than did hBD1 and hBD3, even with elevated salt concentrations. Moreover, its antiviral activity against herpes simplex virus 1 was greater than that of hBD1 and similar to that of hBD3. Subsequently, we investigated the cytotoxic effects of all peptides in three human epithelial carcinoma cell lines: A549 from lung, CaCo-2 from colon, and Capan-1 from pancreas. None of the analogs significantly reduced cell viability versus wild-type hBD1 and hBD3. They did not induce genotoxicity or cause an increase in the number of apoptotic cells. Using confocal microscopy, we also investigated the localization of the peptides during their incubation with epithelial cells and found that they were distributed on the cell surface, from which they were internalized. Finally, we show that hBD1 and hBD3 are characterized by high resistance to serum degradation. In conclusion, the new analog 3NI seems to be a promising anti-infective agent, particularly given its high salt resistance--a feature that is relevant in diseases such as cystic fibrosis.

Antimicrobial activity of human β-defensin 4 analogs: insights into the role of disulfide linkages in modulating activity

Human β-defensins (HBDs) are cationic antimicrobial peptides that are components of the innate immune system. They are characterized by three disulfide bridges. However, the number of cationic residues as well as the presence of lysine and arginine residues vary. In HBD4, the cationic residues occur predominantly in the N-terminal segment, unlike in HBD1-3. We have examined the antimicrobial activity of peptides spanning the N- and C-terminal segments of HBD4. We have introduced one, two and three disulfide bridges in the peptides corresponding to the N-terminal segments. Peptides corresponding to the N-terminal segment had identical sequences and variation was only in the number and spacing of cysteines and disulfide bridges. Antimicrobial activity to varying extents was observed for all the peptides. When two disulfide bridges were present, decrease in antimicrobial potency as well as sensitivity of activity to salt was observed. Enhanced antimicrobial activity was observed when three disulfide bridges were present. The antimicrobial potency was similar to HBD4 except against Escherichia coli and was attenuated in the presence of salt. While the presence of three disulfide bridges did not constrain the peptide to a rigid β-sheet, the activity was considerably more as compared to the peptides with one or two disulfide bridges. The peptides enter bacterial and fungal cells rapidly without membrane permeabilization and appear to exert their activity inside the cells rather than at the membrane.

Defensin like peptide from Panulirus argus relates structurally with beta defensin from vertebrates

Naturally occurring antimicrobial peptides take place in the first line of host defense against pathogen as part of the humoral innate immune response. β-defensins are among the most abundant antimicrobial peptides in mammals, and thought to be solely found in vertebrates until a recent report describing the cloning and sequencing of defensin like peptides in the spiny lobster Panulirus japonicus. In the current study, we cloned and sequenced two genes from the hemocytes of the spiny lobster Panulirus argus encoding for two isoforms of defensin-like peptides, thus confirming the presence of this protein in the Panulirus genus. The 44 amino acids mature peptides showed the conservation of cysteine pattern characterizing the β-defensins, as well as known amino acids residues critical to exert their antimicrobial activity. They are also amphipathics, hydrophobics, and display an overall positive charge (+1) located at the C-terminus. The tertiary structure obtained by homology modeling indicated that likely conformations of lobster peptides are highly similar to β-defensins from vertebrates. The phylogenetic study carried out by probabilistic methods confirmed the relation with ancestral β-defensin from vertebrates. The finding of a putative defensin-like peptide in the expressed sequence tag (EST) of the lobster Homarus americanus with high homology with those of P. argus described in this study, would indicate the presence of this peptides in Palinuridae family. Taking into account all similarities between these peptides with β-defensins from vertebrates, it is conceivable to further support the finding of a new family of β-defensins in invertebrate.

Identification of structural traits that increase the antimicrobial activity of a chimeric peptide of human β-defensins 2 and 3

Antimicrobial peptides participate in the first line of defence of many organisms against pathogens. In humans, the family of β-defensins plays a pivotal role in innate immunity. Two human β-defensins, β-defensin-2 and -3 (HBD2 and HBD3), show substantial sequence identity and structural similarity. However, HBD3 kills Staphylococcus (S.) aureus with a 4- to 8-fold higher efficiency compared to HBD2, whereas their activities against Escherichia (E.) coli are very similar. The generation of six HBD2/HBD3-chimeric molecules led to the identification of distinct molecular regions which mediate their divergent killing properties. One of the chimeras (chimera C3) killed both E. coli and S. aureus with an even higher efficacy compared to the wild-type molecules. Due to the broad spectrum of its antimicrobial activity against many human multidrug-resistant pathogens, this HBD2/HBD3-chimeric peptide represents a promising candidate for a new class of antibiotics. In order to investigate the structural basis of its exceptional antimicrobial activity, the peptide's tertiary structure was determined by NMR spectroscopy, which allowed its direct comparison to the published structures of HBD2 and HBD3 and the identification of the activity-increasing molecular features.

Wounding in lizards results in the release of beta-defensins at the wound site and formation of an antimicrobial barrier

After tail loss in lizards no infections occur indicating the presence of an effective anti-microbial barrier in the exposed tissues of the tail stump. Previous molecular studies on the lizard Anolis carolinensis have identified some beta-defensin-like genes and the deduced peptides that may be involved in anti-infective protection. The present study has analyzed the tissues of wounded and normal tails in lizards in order to immune-localize one of the beta-defensins previously found (AcBD15) and to detect variation in its gene expression during wounding. No immunoreactivity for this beta-defensin is present in normal tissues or in the epidermis of lizards, except for some sparse granulocytes. The latter are seen during the first 1-6 days after tail amputation and AcBD15 immunoreactivity is present in their granules. Degenerating granulocytes are incorporated, together with dead erythrocytes, platelets and keratinocytes into the scab. Real time RT-PCR and western blotting analysis indicates up-regulation of AcBD15 expression during wounding with respect to normal tissues, indicating that production, storage and release of this beta-defensin from granulocytes are active following wounding. The production of beta-defensins from granulocytes would allow protection of exposed tissues from microbial invasion avoiding a persistent inflammation, a process that leads to tissue regeneration.

Antibacterial and neutralizing effect of human β-defensins on Enterococcus faecalis and Enterococcus faecalis lipoteichoic acid

INTRODUCTION

Enterococcus faecalis is frequently found in the root canal of teeth, is a major microorganism of endodontic therapy failure, and is associated with chronic apical periodontitis. Human β-defensins (HBDs) are known to play critical roles in defending the host against infectious microbes and producing dental pulp in healthy and patients. The purpose of the present study was to investigate the bactericidal and neutralizing effects of HBDs on E. faecalis and E. faecalis lipoteichoic acid (Ef LTA) as a major virulence factor of E. faecalis.

METHODS

HBD-1, -2, -3, and -4 were synthesized and investigated the susceptibility against E. faecalis. Also, the neutralizing effects of HBDs on cytokine and intercellular adhesion molecule 1 (ICAM-1) expression by activity of E. faecalis and Ef LTA were analyzed using enzyme-linked immunosorbent assay and flow cytometry.

RESULTS

HBD-1 and -2 were weakly susceptible, and HBD-3 and HBD-4 were strongly susceptible to E. faecalis. All of the HBDs exhibited neutralizing effects on the activity of Ef LTA, and HBD-3 strongly neutralized the activity of E. faecalis in tumor necrosis factor-α, interleukin-8, and ICAM-1 expression. The neutralizing effects of HBDs were to inhibit E. faecalis or Ef LTA binding to the host cells.

CONCLUSIONS

These results suggest that the induction of HBDs might have great potential as endodontic therapeutic agents.

Bioinformatic and molecular characterization of beta-defensins-like peptides isolated from the green lizard Anolis carolinensis

The high resistance of lizards to infections indicates that anti-microbial peptides may be involved. Through the analysis of the green lizard (Anolis carolinensis) genome and the expressed sequence tag (EST) libraries 32 beta-defensin-like-peptides have been identified. The level of expression of some of these genes in different tissues has been determined by semi-quantitative RT-PCR. Gene expression and structure analysis suggest the presence of alternative splicing mechanisms, with a number of exons ranging from two to four, similar to that for beta-defensins genes in mammals. Lizard beta-defensin-like peptides present the characteristic cysteine-motif identified in mammalian and avian beta-defensins. Phylogenetic analysis indicates that some lizard beta-defensins-like peptides are related to crotamine and crotamin-like peptides of snakes and lizards suggesting that beta-defensins and venomous peptides have a common ancestor gene.

Native thrombocidin-1 and unfolded thrombocidin-1 exert antimicrobial activity via distinct structural elements

Chemokines (chemotactic cytokines) can have direct antimicrobial activity, which is apparently related to the presence of a distinct positively charged patch on the surface. However, chemokines can retain antimicrobial activity upon linearization despite the loss of their positive patch, thus questioning the importance of this patch for activity. Thrombocidin-1 (TC-1) is a microbicidal protein isolated from human blood platelets. TC-1 only differs from the chemokine NAP-2/CXCL7 by a two-amino acid C-terminal deletion, but this truncation is crucial for antimicrobial activity. We assessed the structure-activity relationship for antimicrobial activity of TC-1. Reduction of the charge of the TC-1-positive patch by replacing lysine 17 with alanine reduced the activity against bacteria and almost abolished activity against the yeast Candida albicans. Conversely, augmentation of the positive patch by increasing charge density or size resulted in a 2-3-fold increased activity against Staphylococcus aureus, Escherichia coli, and Bacillus subtilis but did not substantially affect activity against C. albicans. Reduction of TC-1 resulted in loss of the folded conformation, but this disruption of the positive patch did not affect antimicrobial activity. Using overlapping 15-mer synthetic peptides, we demonstrate peptides corresponding to the N-terminal part of TC-1 to have similar antimicrobial activity as intact TC-1. Although we demonstrate that the positive patch is essential for activity of folded TC-1, unfolded TC-1 retained antimicrobial activity despite the absence of a positive patch. This activity is probably exerted by a linear peptide stretch in the N-terminal part of the molecule. We conclude that intact TC-1 and unfolded TC-1 exert antimicrobial activity via distinct structural elements.

The synthetic peptides bovine enteric β-defensin (EBD), bovine neutrophil β-defensin (BNBD) 9 and BNBD 3 are chemotactic for immature bovine dendritic cells

Human and murine immature DCs (iDCs) are highly efficient in antigen capture and processing, while as mature cells they present antigen and are potent initiators of cell-mediated immune responses. Consequently, iDCs are logical targets for vaccine antigens. Originally discovered for their antimicrobial activity, and thought of as strictly part of the innate immune system, studies with defensins such as human β (beta)-defensin 2 (hBD2) and murine β-defensin 2 (mBD2) have shown that they can function as chemo-attractant for iDCs and, in vaccination strategies, can enhance antigen-specific adaptive immune responses. Most studies to date have been conducted in mice. In contrast, little is known about defensins in cattle. To expand our understanding of the role of defensins in modulating immune responses in cattle, DCs were generated from bovine monocytes and the immature state of these bovine DCs was characterized phenotypically and through functional assays. By day 3 (DC3), bovine monocyte-derived DCs stained positively for DC-specific receptors CD1, CD80/86, CD205, DC-Lamp and MMR. When compared to conventional 6-day DC cultures or DCs cultured for 10 days with and without maturation factors, these DC3 were functionally at their most immature stage. Fourteen of the 16 known bovine β-defensins were synthesized and the synthetic peptides were screened for their ability to attract bovine iDCs. Bovine DC3 were consistently attracted to BNBD3, an analog of BNBD3 (aBNBD3), BNBD9 and bovine EBD in vitro and to aBNBD3 in vivo. These results are the first to describe chemotactic ability of synthetic bovine β-defensins for immature bovine monocyte-derived DCs.

Effect of human beta-defensin-3 on the proliferation of fibroblasts on periodontally involved root surfaces

Human beta-defensin-3 (HBD-3) has versatile antibacterial activity against oral bacteria and can promote the proliferation of fibroblasts. The goal of the present study was to investigate the effect of HBD-3 on attachment and proliferation of periodontal ligament cells (PDL) onto the periodontitis affected root surfaces. PDL cells were seeded onto healthy and diseased root specimens with scaling and root planing (SRP), SRP & HBD-3 (100 ng/ml), or SRP & HBD-3 (200 ng/ml) treatment for 1, 3, and 7 days incubation. The results showed that HBD-3, especially in the 200 ng/ml group, significantly promoted fibroblast attachment and proliferation onto the diseased root surfaces. The cell number in the HBD-3 group was much greater than in the group treated with SRP alone. On day 7, the cells in the HBD-3 were well-spread and formed a network similar to those on the surfaces of the healthy root specimens. These results suggest that HBD-3 could play an important role in antibacterial activity and fibroblast proliferation, thus promoting periodontal regeneration. Meanwhile, HBD-3 might act as a potent regeneration-promoter in infectious diseases.

The epididymis-specific antimicrobial peptide β-defensin 15 is required for sperm motility and male fertility in the rat (Rattus norvegicus)

Spermatozoa acquire forward motility and fertilizing capacity during their transit through the epididymis. The maturation process involves modifications of the sperm surface by different proteins that are secreted by a series of specialized regions in the epididymal epithelium. Here we show that the rat epididymis-specific β-defensin 15 (Defb15) exhibits an androgen-dependent expression pattern, and it can bind to the acrosomal region of caput sperm. Coculture of caput spermatozoa with Defb15 antibody in vitro resulted in a significant decline in sperm motility. Moreover, the total and progressive motility of the spermatozoa dramatically decreased in rats when Defb15 was downregulated by lentivirus-mediated RNAi in vivo. Remarkably, knock down of Defb15 led to a reduction in fertility and embryonic development failure. In addition, the recombinant Defb15 showed antimicrobial activity in a dose-dependent fashion. These results suggest that Defb15 plays a dual role in both sperm maturation and pathogen defense in rat epididymis.