Identification and characterization of novel bi-functional cathelicidins from the black-spotted frog (Pelophylax nigromaculata) with both anti-infective and antioxidant activities

A non-bactericidal cathelicidin with antioxidant properties ameliorates UVB-induced mouse skin photoaging via intracellular ROS scavenging and Keap1/Nrf2 pathway activation

Cathelicidins, a category of critical host defense molecules in vertebrates, have been extensively studied for their bactericidal functions, but little is known about their non-bactericidal properties. Herein, a novel cathelicidin peptide (Atonp2) was identified from the plateau frog Nanorana ventripunctata. It did not exhibit bactericidal activity but showed significant therapeutic effects in chronic UVB radiation-induced mouse skin photoaging through inhibiting thickening, pyroptosis and inflammation in the epidermis, while inhibiting cellular senescence, collagen fibre breakage and type Ⅰ collagen reduction in the dermis. Further studies indicated that Atonp2 effectively scavenged UVB-induced intracellular ROS via tyrosines at positions 9 and 10, while activating the Keap1/Nrf2 pathway to protect epidermal keratinocytes against UVB radiation, which in turn indirectly reversed the senescence and collagen degradation of dermal fibroblasts, thereby ameliorating UVB-induced skin photoaging. As such, this study identified a non-bactericidal cathelicidin peptide with potent antioxidant functions, highlighting its potential to treat and prevent skin photoaging.

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.

Synergistic collaboration between AMPs and non-direct antimicrobial cationic peptides

Non-direct antimicrobial cationic peptides (NDACPs) are components of the animal innate immune system. But their functions and association with antimicrobial peptides (AMPs) are incompletely understood. Here, we reveal a synergistic interaction between the AMP AW1 and the NDACP AW2, which are co-expressed in the frog Amolops wuyiensis. AW2 enhances the antibacterial activity of AW1 both in vitro and in vivo, while mitigating the development of bacterial resistance and eradicating biofilms. AW1 and AW2 synergistically damage bacterial membranes, facilitating cellular uptake and interaction of AW2 with the intracellular target bacterial genomic DNA. Simultaneously, they trigger the generation of ROS in bacteria, contributing to cell death upon reaching a threshold level. Moreover, we demonstrate that this synergistic antibacterial effect between AMPs and NDACPs is prevalent across diverse animal species. These findings unveil a robust and previously unknown correlation between AMPs and NDACPs as a widespread antibacterial immune defense strategy in animals.

Cathelicidin-HG Alleviates Sepsis-Induced Platelet Dysfunction by Inhibiting GPVI-Mediated Platelet Activation

Platelet activation contributes to sepsis development, leading to microthrombosis and increased inflammation, which results in disseminated intravascular coagulation and multiple organ dysfunction. Although Cathelicidin can alleviate sepsis, its role in sepsis regulation remains largely unexplored. In this study, we identified Cath-HG, a novel Cathelicidin from Hylarana guentheri skin, and analyzed its structure using nuclear magnetic resonance spectroscopy. The modulatory effect of Cath-HG on the symptoms of mice with sepsis induced by cecal ligation and puncture was evaluated in vivo, and the platelet count, degree of organ damage, and microthrombosis were measured. The antiplatelet aggregation activity of Cath-HG was studied in vitro, and its target was verified. Finally, we further investigated whether Cath-HG could regulate thrombosis in vivo in a FeCl3 injury-induced carotid artery model. The results showed that Cath-HG exhibited an α-helical structure in sodium dodecyl sulfate solution and effectively reduced organ inflammation and damage, improving survival in septic mice. It alleviated sepsis-induced thrombocytopenia and microthrombosis. In vitro, Cath-HG specifically inhibited collagen-induced platelet aggregation and modulated glycoprotein VI (GPVI) signaling pathways. Dot blotting, enzyme-linked immunosorbent assay, and pull-down experiments confirmed GPVI as the target of Cath-HG. Molecular docking and amino acid residue truncations/mutations identified crucial sites of Cath-HG. These findings suggest that GPVI represents a promising therapeutic target for sepsis, and Cath-HG may serve as a potential treatment for sepsis-related thrombocytopenia and thrombotic events. Additionally, identifying Cath-HG as a GPVI inhibitor provides insights for developing novel antithrombotic therapies targeting platelet activation mediated by GPVI.

Cath-DM-NT, a peptide derived from the skin of Duttaphrynus melanostictus, shows dual lectin-like and antioxidant activity

Chansu, a mixture extracted from Duttaphrynus melanostictus or Bufo gargarizans Cantor, is a traditional Chinese medicine with a broad range of medical applications. However, the peptides/proteins in it have not received adequate attention. Herein, a Cathelicidin-DM-derived peptide named Cath-DM-NT was identified from the skin of D. melanostictus. Previous studies have shown that Cathelicidin-DM has significant antibacterial activity, while Cath-DM-NT has no antibacterial activity. In this study, Cath-DM-NT is found to have lectin-like activity which can agglutinate erythrocytes and bacteria, and bind to lipopolysaccharide (LPS). In addition, Cath-DM-NT has antioxidant activity, which can scavenge 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS), 1,1-diphenyl-2-picrylhydrazyl (DPPH), and nitric oxide (NO) radicals and reduce Fe3+. Consistently, Cath-DM-NT can protect PC12 cells from H2O2-induced oxidative damage and carrageenan-induced paw edema, reduce malondialdehyde (MDA) and reactive oxygen species (ROS) accumulation, and restore superoxide dismutase (SOD) and glutathione (GSH) levels. Our study suggests that Cath-DM-NT can serve as a lead compound for the development of drugs with dual lectin and antioxidant effects.

Functional Analyses of Three Targeted DNA Antimicrobial Peptides Derived from Goats

With the increase in drug-resistant bacteria, new antibacterial drugs have emerged as a prominent area of research and development. Antimicrobial peptides (AMPs), as innate immune agents, have garnered significant attention due to their potent, rapid, and broad-spectrum antibacterial activity. This study focused on investigating the functionality of three AMPs (CATH 1, CATH 2, and MAP34-B) derived from goat submandibular glands. Among these AMPs, CATH 2 and MAP34-B exhibited direct antibacterial activity against both Gram-negative and Gram-positive bacteria, primarily targeting the bacterial membrane. Additionally, these two AMPs were found to have the potential to induce reactive oxygen species (ROS) production in bacterial cells and interact with bacterial genome DNA, which may play a crucial role in their mechanisms of action. Furthermore, both CATH 1 and CATH 2 demonstrated significant antioxidant activity, and all three AMPs exhibited potential anti-inflammatory activity. Importantly, the cytotoxic activity of these AMPs against mammalian cells was found to be weak, and their hemolytic activity was extremely low. Overall, the characteristics of these three AMPs found in goat submandibular glands offer new insights for the study of host protection from an immunological perspective. They hold promise as potential candidates for the development of novel antibacterial agents, particularly in the context of combating drug-resistant bacteria.

The Contribution of Antimicrobial Peptides to Immune Cell Function: A Review of Recent Advances

The development of novel antimicrobial agents to replace antibiotics has become urgent due to the emergence of multidrug-resistant microorganisms. Antimicrobial peptides (AMPs), widely distributed in all kingdoms of life, present strong antimicrobial activity against a variety of bacteria, fungi, parasites, and viruses. The potential of AMPs as new alternatives to antibiotics has gradually attracted considerable interest. In addition, AMPs exhibit strong anticancer potential as well as anti-inflammatory and immunomodulatory activity. Many studies have provided evidence that AMPs can recruit and activate immune cells, controlling inflammation. This review highlights the scientific literature focusing on evidence for the anti-inflammatory mechanisms of different AMPs in immune cells, including macrophages, monocytes, lymphocytes, mast cells, dendritic cells, neutrophils, and eosinophils. A variety of immunomodulatory characteristics, including the abilities to activate and differentiate immune cells, change the content and expression of inflammatory mediators, and regulate specific cellular functions and inflammation-related signaling pathways, are summarized and discussed in detail. This comprehensive review contributes to a better understanding of the role of AMPs in the regulation of the immune system and provides a reference for the use of AMPs as novel anti-inflammatory drugs for the treatment of various inflammatory diseases.

A Frog-Derived Cathelicidin Peptide with Dual Antimicrobial and Immunomodulatory Activities Effectively Ameliorates Staphylococcus aureus-Induced Peritonitis in Mice

As antimicrobial resistance poses an increasing threat to public health, it is urgent to develop new antimicrobial agents. In this paper, we identify a novel 30-residue peptide (Nv-CATH, NCNFLCKVKQRLRSVSSTSHIGMAIPRPRG) from the skin of the frog Nanorana ventripunctata, which belongs to the cathelicidin family. Nv-CATH exhibited broad-spectrum antimicrobial activity against Gram-positive and Gram-negative bacteria. Nv-CATH significantly protected mice from lethal infections caused by Staphylococcus aureus. Furthermore, the peptide suppressed excessive and harmful inflammatory responses by repressing the production of NO, IL-6, TNF-α, and IL-1β. The NF-κB-NLRP3 and MAPK inflammatory signaling pathways were involved in the protection in vitro and in vivo. Nv-CATH also modulated macrophage/monocyte and neutrophil trafficking to the infection site by stimulating CXCL1, CXCL2, and CCL2 production in macrophages. Nv-CATH augmented immunocyte-mediated bacterial killing by modestly promoting neutrophils' phagocytosis and PMA-induced NET formation. Thus, Nv-CATH protects mice against bacterial infection by antimicrobial-immunomodulatory duality. The combination of these two characteristics makes Nv-CATH a promising molecule template for the development of novel antimicrobial and antibiotic-resistant agents.

Multiple roles of ribosomal antimicrobial peptides in tackling global antimicrobial resistance

In the last century, conventional antibiotics have played a significant role in global healthcare. Antibiotics support the body in controlling bacterial infection and simultaneously increase the tendency of drug resistance. Consequently, there is a severe concern regarding the regression of the antibiotic era. Despite the use of antibiotics, host defence systems are vital in fighting infectious diseases. In fact, the expression of ribosomal antimicrobial peptides (AMPs) has been crucial in the evolution of innate host defences and has been irreplaceable to date. Therefore, this valuable source is considered to have great potential in tackling the antimicrobial resistance (AMR) crisis. Furthermore, the possibility of bacterial resistance to AMPs has been intensively investigated. Here, we summarize all aspects related to the multiple applications of ribosomal AMPs and their derivatives in combating AMR.

Defensing role of novel piscidins from largemouth bass (Micropterus salmoides) with evidence of bactericidal activities and inducible expressional delineation

Micropterus salmoides is an economical important species of freshwater-cultured fish, the in-depth knowledge of its immune system is in urgent development to cope with serious infectious diseases. Piscidin is an important antimicrobial peptide (AMP) family existing in almost all teleosts. However, no piscidin has been reported in largemouth bass. In this study, three novel piscidins (MSPiscidin-1, -2, and -3) were firstly identified and characterized from the largemouth bass. The predicted mature peptides of MSPiscidin-1, -2, and -3 (consists of 24, 27, 25 amino acid residues, respectively) all adopted an amphipathic α-helical conformation representative of cationic AMPs that are important for membrane permeabilization and antibacterial activity. MSPiscidin-2 and -3 indeed displayed strong, broad-spectrum, and highly efficient antimicrobial activities in vitro against aquatic pathogens, but MSPiscidin-1 didn't show direct antimicrobial activity. MSPiscidin-2 and -3 killed bacteria mainly by inducing membrane permeabilization, in addition, they also can interact with bacterial genomic DNA, which might influence the DNA replication and transcription. Besides, MSPiscidin-2 and -3 could effectively inhibit the formation of the bacterial biofilm and eliminate the preformed biofilms. In vivo, MSPiscidin-1-3 genes showed an inducible expression pattern in the tested tissues upon Vibrio harveyi infection, which further indicated the key roles of piscidins in innate immunity in largemouth bass. Overall, this study will supplement the understanding of M. salmoides innate immune system and provide candidates for the design of novel peptide antibacterial agents used in aquaculture.

The Prepropalustrin-2CE2 and Preprobrevinin-2CE3 Gene from Rana Chensinensis: Gene Expression, Genomic Organization, and Functional Analysis of the Promoter Activity

BACKGROUND

Palustrin-2CE2 and brevinin-2CE3 are antimicrobial peptides from Rana chensinensis. In R. chensinensis tadpoles, the expression of prepropalustrin-2CE2 and preprobrevinin-2CE3 increased with the developmental stage. In addition, the expression of the two genes was dramatically upregulated with stimulation by Escherichia coli, Staphylococcus aureus, and the chemical lipopolysaccharide (LPS). The genomic organization of the two antimicrobial peptide genes was confirmed. Both prepropalustrin-2CE2 and preprobrevinin-2CE3 contain three exons separated by two large introns. Additionally, several presumed transcription factor binding sites were identified in the promoter sequence. Functional analysis of the promoter was performed using a luciferase reporter system, and further confirmed by yeast one-hybrid experiment and EMSA assay. The results indicated that the transcription factors NF-κB and RelA are involved in regulating the expression of prepropalustrin-2CE2 and preprobrevinin-2CE3. As amphibian populations decline globally, this study provides new data demonstrating how frogs defend against pathogens from the environment by regulating AMP expression. For amphibians, antimicrobial peptides are innate immune molecules that resist adverse external environmental stimuli. However, the regulation mechanism of antimicrobial peptide gene expression in frogs is still unclear.

OBJECTIVE

The two antimicrobial peptides, palustrin-2CE2 and brevinin-2CE3, are produced under external stimulation in Rana chensinensis. Using this model, we analyzed the gene structure and regulatory elements of the two antimicrobial peptide genes and explored the regulatory effects of related transcription factors on the two genes.

METHOD

Different stimuli such as E. coli, S. aureus, and chemical substance lipopolysaccharide (LPS) were applied to Rana chensinensis tadpoles at different developmental stages, and antimicrobial peptide expression levels were detected by RT-PCR. Bioinformatics analysis and 5'-RACE and genome walking technologies were employed to analyze the genome structure and promoter region of the antimicrobial peptide genes. With dual-luciferase reporter gene assays, yeast one-hybrid experiment and EMSA assays, we assessed the regulatory effect of the endogenous regulators of the cell on the antimicrobial peptide promoter.

RESULTS

The transcription levels of prepropalustrin-2CE2 and preprobrevinin-2CE3 were significantly upregulated after different stimulations. Genomic structure analysis showed that both genes contained three exons and two introns. Promoter analysis indicated that there are binding sites for regulatory factors of the NF-κB family in the promoter region, and experiments showed that endogenous NF-κB family regulatory factors in frog cells activate the promoters of the antimicrobial peptide genes. Yeast one-hybrid experiment and EMSA assay demonstrated that RelA and NF-κB1 might interact with specific motifs in the prepropalustrin-2CE2 promoter.

CONCLUSION

In this paper, we found that the gene expression levels of the antimicrobial peptides, palustrin-2CE2 and brevinin-2CE3, in R. chensinensis will increase under environmental stimuli, and we verified that the changes in gene expression levels are affected by the transcription factors RelA and NF-κB1. The yeast one-hybrid experiment and EMSA assay confirmed that RelA and NF-κB1 could directly interact with the frog antimicrobial peptide gene promoter, providing new data for the regulatory mechanism of antimicrobial peptides in response to environmental stimuli.

Discovery of Antioxidant Peptides from Amphibians: A Review

In recent years, bioactive peptide drugs have attracted growing attention due to the increasing difficulty in developing new drugs with novel chemical structures. In addition, many diseases are linked to excessive oxidation in the human body. Therefore, the role of peptides with antioxidant activity in counteracting diseases related to oxidative stress is worth exploring. Amphibians are a major repository for bioactive peptides that protect the skin from biotic and abiotic stresses, such as microbial infection and radiation injury. We characterized the first amphibian- derived gene-encoded antioxidant peptides in 2008. Since then, a variety of antioxidant peptides have been detected in different amphibian species. In this work, the physicochemical properties of antioxidant peptides identified from amphibians are reviewed for the first time, particularly acquisition methods, amino acid characteristics, antioxidant mechanisms, and application prospects. This review should provide a reference for advancing the identification, structural analysis, and potential therapeutic value of natural antioxidant peptides.

Molecular characterization of cathelicidin in tiger frog (Hoplobatrachus rugulosus): Antimicrobial activity and immunomodulatory activity

Cathelicidins are an important antimicrobial peptide family and are expressed in many different vertebrates. They play an important role in the innate immune system of the host. However, amphibian cathelicidins are poorly understood. In this study, the cDNA of the cathelicidin gene was obtained from the skin transcriptome of tiger frog (Hoplobatrachus rugulosus). The predicted amino acid sequence of tiger frog cathelicidin (HR-CATH) comprises a signal peptide, a cathelin domain, and a mature peptide. The HR-CATH amino acid sequence alignment with other frog cathelicidins showed that the functional mature peptide is highly variable in amphibians, whereas the cathelin domain is conserved. A phylogenetic tree analysis showed that HR-CATH is most closely related to cathelicidin-NV from Nanorana ventripunctata. HR-CATH was chemically synthesized and its in vitro activity was determined. It had high antibacterial activity against Vibrio parahaemolyticus, Staphylococcus aureus, and the pathogenic bacterium Aeromonas hydrophila. HR-CATH damaged the cell membrane integrity of A. hydrophila according to a lactate dehydrogenase release assay and was able to hydrolyze the genomic DNA from A. hydrophila in a dose-dependent manner. Furthermore, in RAW264.7 cells (mouse leukemic monocyte/macrophage cell line), HR-CATH induced chemotaxis and enhanced respiratory burst. Our study shows that amphibian cathelicidin has antimicrobial activity and an immunomodulatory effect on immune cells.