Characterization of the cathelicidin cluster in the Japanese quail (Coturnix japonica )

Assessment of the antimicrobial and immunomodulatory activity of QS-CATH, a promising therapeutic agent isolated from the Chinese spiny frogs (Quasipaa spinosa)

Cathelicidins are important antimicrobial peptides in various vertebrate species where they are crucial parts of the innate immune system. The current understanding of amphibian cathelicidins is limited, particularly with regard to their immunomodulatory effects. To address this knowledge gap, we produced the cDNA sequence of the cathelicidin gene from a skin transcriptome of the Chinese spiny frog Quasipaa spinosa. The amino acid sequence of the Quasipaa spinosa cathelicidin (QS-CATH) was predicted to consist of a signal peptide, a cathelin domain, and a mature peptide. Comparative analysis of the QS-CATH amino acid sequence with that of other amphibian cathelicidins revealed high variability in the functional mature peptide among amphibians, whereas the cathelin domain was conserved. The QS-CATH gene was expressed in several tissues, with the highest level of expression in the spleen. Upregulation of QS-CATH after Aeromonas hydrophila infection occurred in the kidney, gut, spleen, skin, and liver. Chemically synthesized QS-CATH exhibited pronounced antibacterial activity against Shigella flexneri, Staphylococcus warneri, Escherichia coli, Salmonella enterica, and Listeria monocytogenes. Furthermore, QS-CATH disrupted the cell membrane integrity of S. flexneri, as evidenced by a lactate dehydrogenase release assay, and it hydrolyzed the genomic DNA of S. flexneri. Additionally, QS-CATH elicited chemotaxis and modulated the expression of inflammatory cytokine genes in RAW264.7 mouse leukemic monocyte/macrophage cells. These findings confirm the antimicrobial effects of amphibian cathelicidin and its ability to influence immune cell function. This will expedite the potential utilization of amphibian antimicrobial peptides as therapeutic agents.

Discovery of Ll-CATH: a novel cathelicidin from the Chong'an Moustache Toad (Leptobrachium liui) with antibacterial and immunomodulatory activity

BACKGROUND

Cathelicidins are vital antimicrobial peptides expressed in diverse vertebrates, crucial for immunity. Despite being a new field, amphibian cathelicidin research holds promise.

RESULTS

We isolated the cDNA sequence of the cathelicidin (Ll-CATH) gene from the liver transcriptome of the Chong'an Moustache Toad (Leptobrachium liui). We confirmed the authenticity of the cDNA sequence by rapid amplification of cDNA ends and reverse transcription PCR, and obtained the Ll-CATH amino acid sequence using the Open Reading Frame Finder, an online bioinformatics tool. Its translated protein contained a cathelin domain, signal peptide, and mature peptide, confirmed by amino acid sequence. The comparative analysis showed that the mature peptides were variable between the amphibian species, while the cathelin domain was conserved. The concentration of Ll-CATH protein and the expression of its gene varied in the tissues, with the spleen showing the highest levels. The expression levels of Ll-CATH in different tissues of toads was significantly increased post infection with Aeromonas hydrophila. Chemically synthesized Ll-CATH effectively combated Proteus mirabilis, Staphylococcus epidermidis, Vibrio harveyi, V. parahaemolyticus, and V. vulnificus; disrupted the membrane of V. harveyi, hydrolyzed its DNA. Ll-CATH induced chemotaxis and modulated the expression of pro-inflammatory cytokine genes in RAW264.7 macrophages.

CONCLUSIONS

This study unveiled the antibacterial and immunomodulatory potential of amphibian cathelicidin, implying its efficacy against infections. Ll-CATH characterization expands our knowledge, emphasizing its in a bacterial infection therapy.

Molecular Cloning, Expression Analyses, and Physiological Roles of Cathelicidins in the Bursa of Fabricius of the Japanese Quail, Coturnix japonica

Antimicrobial peptides (AMPs) act directly on pathogens and maintain the anti-inflammatory effects and activation of immunocompetent cells. Therefore, the activation of the immune system in poultry via the elevation of endogenous AMPs has been attempted. In this study, we focused on the host defense mechanisms in the bursa of Fabricius (BF) of Japanese quail, cloned the cDNA of cathelicidin (CATH)-1 to -3, and analyzed their expression sites. In situ hybridization experiments revealed the mRNA expression of the CATHs in the interfollicular epithelium surrounding the lumen of the quail BF, which suggests that each CATH may exert its antimicrobial action directly in the BF. The intravenous injection of bacterial lipoteichoic acid and lipopolysaccharide endotoxins into the quail promoted the mRNA expression of CATH-1 and CATH-3 in the BF. The addition of CATH-1 or CATH-2 at the time of the antigen injection into mice resulted in antiserum with high antibody titers. Ad libitum administration of butyrate, a short-chain fatty acid, in the drinking water induced an increase in CATH-2 mRNA expression in the BF under certain conditions. These results may improve the defense mechanisms of quail by stimulating CATH expression in the BF through their diet.

Antimicrobial Peptides: An Update on Classifications and Databases

Antimicrobial peptides (AMPs) are distributed across all kingdoms of life and are an indispensable component of host defenses. They consist of predominantly short cationic peptides with a wide variety of structures and targets. Given the ever-emerging resistance of various pathogens to existing antimicrobial therapies, AMPs have recently attracted extensive interest as potential therapeutic agents. As the discovery of new AMPs has increased, many databases specializing in AMPs have been developed to collect both fundamental and pharmacological information. In this review, we summarize the sources, structures, modes of action, and classifications of AMPs. Additionally, we examine current AMP databases, compare valuable computational tools used to predict antimicrobial activity and mechanisms of action, and highlight new machine learning approaches that can be employed to improve AMP activity to combat global antimicrobial resistance.

Analysis of the Diversity of the AvBD Gene Region in Japanese Quail

The avian β-defensin (AvBD) gene region is an important component of the innate immune system, encoding a variety of antimicrobial peptides. The AvBD region forms a multigene cluster in a specific chromosomal region. Comparison of the AvBD region among various birds suggests the presence of defects, duplications, and pseudogenization at many loci. The AvBD region in certain galliform birds, namely chicken, turkey, and bobwhite quail, includes AvBD3, -6, and -7, with the latter exhibiting copy number variants (CNVs) in chickens. DNA for genomic analysis was extracted from the peripheral blood of 99 randomly selected quail (Coturnix japonica) from 6 inbred lines. Nine CjAvBD1 and 8 CjAvBD12 alleles were detected. Ten haplotypes, including three that were strain specific, were found in alleles from the quail AvBD1 (CjAvBD1) and -12 (CjAvBD12) loci. Next-generation sequencing was used to determine the nucleotide sequences of the CjAvBD gene region (56-70 kb) for 7 homozygous diplotypes of these 10 haplotypes. These 7 haplotypes contained between 12 and 16 CjAvBD genes and were composed of 11 common loci: CjAvBD1, -2, -4, -5, -8, -9, -10, -11, -12, -13, and -14, but lacked CjAvBD3 and -7. Furthermore, up to 5 CjAvBD101 (AvBD6 ortholog) CNVs were observed among the 7 haplotypes. In addition, we detected amino acid substitutions causing net charge mutations that could affect antimicrobial activity in CjAvBD4, -13, -14, and -101. These results suggest that the CjAvBD region is unique among the Galliformes and that its diversity results in potential functional variation in innate immunity.

Genetic diversity of Japanese quail cathelicidins

Japanese quail is a low-fat, meat-bird species exhibiting high disease resistance. Cathelicidins (CATHs) are host defense peptides conserved across numerous vertebrate species that play an important role in innate immunity. The activity of host defense peptides can be affected by amino acid substitutions. However, no polymorphisms in avian CATH genes have been reported to date. The aim of this study was to clarify the polymorphisms in CATHs in Japanese quail. DNA for genomic analyses was extracted from the peripheral blood of 99 randomly selected quail from 6 inbred lines. A total of 6, 4, 6, and 4 CjCATH1, -2, -3, and -B1 alleles were identified, respectively. Nine haplotypes, including 4 strain-specific haplotypes, were identified by combining alleles at the CjCATH1, -2, -3, and -B1 loci. In addition, 2 and 1 amino acid substitutions (I145F, Q148H, and P245H) predicted by PROVEAN and PolyPhen-2 to have deleterious effects were detected in CjCATH2 and -B1, respectively. Synthetic CjCATH2 and -B1 peptides exhibited greater antibacterial activity against Escherichia coli than chicken CATH2 and -B1, respectively. Furthermore, the CjCATHB1∗04 peptide exhibited less potent antimicrobial activity than other CjCATHB1 peptides examined. This is the first report of amino acid substitutions accompanied by changes in antibacterial activity in avian CATHs. These findings could be employed as indicators of improvements in innate immune response in poultry.

Avian host defense cathelicidins: structure, expression, biological functions, and potential therapeutic applications

Host defense peptides (HDP) are multifunctional effectors of the innate immune system, which has antimicrobial and pleiotropic immunomodulatory functions. Although there is a very sophisticated superposition of adaptive immune systems in vertebrates, this system is still essential. As an important family of HDP, cathelicidins are also known for their broad-spectrum antibacterial activity against bacteria, fungi, and enveloped viruses. It has been found in humans and other species, including cattle, pigs, sheep, goats, chickens, rabbits, and some kind of fish. Among them, cathelicidins in birds were described for the first time in 2005. This review focuses on the structure, biological activities, expression, and regulation of avian cathelicidin, especially main effects of host defense cathelicidin on potential therapeutic applications. According to the results obtained both in vitro and in vivo, good perspectives have been opened for cathelicidin. Nevertheless, further studies are needed to better characterize the mechanisms of action underlying the beneficial effects of cathelicidin as novel therapeutic alternatives to antibiotics.

Genomic Identification and Expression Analysis of the Cathelicidin Gene Family of the Forest Musk Deer

Simple Summary

Cathelicidins are a group of host defense peptides in vertebrates with both antimicrobial and immunomodulatory activities. In the present study, we identified the entire repertoire of the cathelicidin gene family from the forest musk deer genome. Sequence comparison, phylogenetic topology, and gene and genomic organizations collectively suggest that all cathelicidin genes have already been fixed in the genome of forest musk deer before the split of moschidae and bovidae, while independent pseudogenization events have occurred after species divergence. In addition, real-time PCR analysis suggested that all functional cathelicidins play important roles in the immune system. The results of this study will be helpful for further evolutionary and functional studies.

Abstract

The forest musk deer (Moschus berezovskii) is a small-sized artiodactyl species famous for the musk secreted by adult males. In the captive population, this species is under the threat of infection diseases, which greatly limits the increase of individual numbers. In the present study, we computationally analyzed the repertoire of the cathelicidin (CATHL) family from the genome of forest musk deer and investigated their expression pattern by real-time PCR. Our results showed that the entire genome of forest musk deer encodes eight cathelicidins, including six functional genes and two pseudogenes. Phylogenetic analyses further revealed that all forest musk deer cathelicidin members have emerged before the split of the forest musk deer and cattle and that forest musk deer CATHL3L2 and CATHL9 are orthologous with two cattle pseudogenes. In addition, the gene expression results showed that the six functional genes are not only abundantly expressed in the spleen and lung, but are also differently expressed in response to abscesses, which suggests that forest musk deer cathelicidins may be involved in infections. Taken together, identification and characterization of the forest musk deer cathelicidins provide fundamental data for further investigating their evolutionary process and biological functions.