Alpha-Defensin Research & Studies

IBD patients and murine models of colitis had lower expressions of AhR and α-defensin 1.AhR activation on IECs induces the expression of α-defensin 1 by targeting the DRE sites of its promoter.α-defensin 1, in turn, reverses gut dysbiosis seen during colitis, and attenuates colonic inflammation and colitis.Targeting AhR-α-defensin 1 signaling pathway can serve as a therapeutic modality to treat dysbiosis and colitis as well as prevent other GI disorders including cancer.

Human enteric α-defensin 5 (HD5) is an immune system peptide that acts as an important antimicrobial factor but is also known to promote pathogen infections by enhancing adhesion of the pathogens. The mechanistic basis of these conflicting functions is unknown. Here we show that HD5 induces abundant filopodial extensions in epithelial cells that capture Shigella, a major human enteroinvasive pathogen that is able to exploit these filopodia for invasion, revealing a mechanism for HD5-augmented bacterial invasion. Using multi-omics screening and in vitro, organoid, dynamic gut-on-chip and in vivo models, we identify the HD5 receptor as P2Y11, a purinergic receptor distributed apically on the luminal surface of the human colonic epithelium. Inhibitor screening identified cAMP-PKA signalling as the main pathway mediating the cytoskeleton-regulating activity of HD5. In illuminating this mechanism of Shigella invasion, our findings raise the possibility of alternative intervention strategies against HD5-augmented infections.

α-Defensin 5 is known to be secreted by Paneth cells in the small intestine and plays an important role in eliminating pathogenic microorganisms. It has been reported that a decrease in α-defensin 5 level in the human small intestine is a risk of inflammatory bowel disease (IBD). Furthermore, P-glycoprotein (P-gp), a member of the ATP-binding cassette transporter superfamily, encoded by the ABCB1/MDR1 gene, plays an important role in the front line of host defense by protecting the gastrointestinal barrier from xenobiotic accumulation and may contribute to the development and persistence of IBD. Therefore, we examined the relationship between α-defensin 5 and the expression and function of P-gp using a human gastrointestinal model cell line (Caco-2). We found that MDR1 mRNA and P-gp protein level were increased in Caco-2 cells as well as α-defensin 5 secretion corresponded with the duration of cell culture. Exposure to α-defensin 5 peptide and recombinant tumor necrosis factor-α (TNF-α) significantly increased the expression and function P-gp. The mRNA levels of interleukin (IL)-8, IL-6, TNF-α, IL-1β, and IL-2 were also increased following exposure to TNF-α, similar to α-defensin 5 treatment. These results suggest that α-defensin 5 regulates P-gp expression and function by increasing TNF-α expression in Caco-2 cells.

The mechanism underlying radiation-induced gut microbiota dysbiosis is undefined. This study examined the effect of radiation on the intestinal Paneth cell α-defensin expression and its impact on microbiota composition and mucosal tissue injury and evaluated the radio-mitigative effect of human α-defensin 5 (HD5).

Diabetes is a serious health problem that results in high mortality rates worldwide. α-defensins are antimicrobial peptides of the innate immune system that contribute to inflammation. However, data on serum levels of α-defensin in patients suffering from type 2 diabetes are limited.

The human pathogenic bacterium Clostridioides difficile produces two exotoxins TcdA and TcdB, which inactivate Rho GTPases thereby causing C. difficile-associated diseases (CDAD) including life-threatening pseudomembranous colitis. Hypervirulent strains produce additionally the binary actin ADP-ribosylating toxin CDT. These strains are hallmarked by more severe forms of CDAD and increased frequency and severity. Once in the cytosol, the toxins act as enzymes resulting in the typical clinical symptoms. Therefore, targeting and inactivation of the released toxins are of peculiar interest. Prompted by earlier findings that human α-defensin-1 neutralizes TcdB, we investigated the effects of the defensin on all three C. difficile toxins. Inhibition of TcdA, TcdB, and CDT was demonstrated by analyzing toxin-induced changes in cell morphology, substrate modification, and decrease in transepithelial electrical resistance. Application of α-defensin-1 protected cells and human intestinal organoids from the cytotoxic effects of TcdA, TcdB, CDT, and their combination which is attributed to a direct interaction between the toxins and α-defensin-1. In mice, the application of α-defensin-1 reduced the TcdA-induced damage of intestinal loops in vivo. In conclusion, human α-defensin-1 is a specific and potent inhibitor of the C. difficile toxins and a promising agent to develop novel therapeutic options against C. difficile infections.

Shigella is a Gram-negative bacterium that causes bacillary dysentery worldwide. It invades the intestinal epithelium to elicit intense inflammation and tissue damage, yet the underlying mechanisms of its host selectivity and low infectious inoculum remain perplexing. Here, we report that Shigella co-opts human α-defensin 5 (HD5), a host defense peptide important for intestinal homeostasis and innate immunity, to enhance its adhesion to and invasion of mucosal tissues. HD5 promoted Shigella infection in vitro in a structure-dependent manner. Shigella, commonly devoid of an effective host-adhesion apparatus, preferentially targeted HD5 to augment its ability to colonize the intestinal epithelium through interactions with multiple bacterial membrane proteins. HD5 exacerbated infectivity and Shigella-induced pathology in a culture of human colorectal tissues and three animal models. Our findings illuminate how Shigella exploits innate immunity by turning HD5 into a virulence factor for infection, unveiling a mechanism of action for this highly proficient human pathogen.

Alpha-defensin, a novel biomarker, has shown great potential for the accurate diagnosis of periprosthetic joint infection (PJI) in recent years: many published studies have presented encouraging results. Nevertheless, the diagnostic accuracy of alpha-defensin is inconsistent across published studies. Moreover, the optimum value of the diagnostic threshold urgently needs to be ascertained. This meta-analysis sought to estimate the precision of alpha-defensin for the diagnosis of PJI and, where possible, to confirm the threshold.

Human α-defensin 6 (HD6) is a 32-residue cysteine-rich peptide that contributes to innate immunity by protecting the host at mucosal sites. This peptide is produced in small intestinal Paneth cells, stored as an 81-residue precursor peptide named proHD6 in granules, and released into the lumen. One unusual feature of HD6 is that it lacks the broad-spectrum antimicrobial activity observed for other human α-defensins, including the Paneth cell peptide human α-defensin 5 (HD5). HD6 exhibits unprecedented self-assembly properties, which confer an unusual host-defense function. HD6 monomers self-assemble into higher-order oligomers termed "nanonets", which entrap microbes and prevent invasive gastrointestinal pathogens such as Salmonella enterica serovar Typhimurium and Listeria monocytogenes from entering host cells. One possible advantage of this host-defense mechanism is that HD6 helps to keep microbes in the lumen such that they can be excreted or attacked by other components of the immune system, such as recruited neutrophils. In this Account, we report our current understanding of HD6 and focus on work published since 2012 when Bevins and co-workers described the discovery of HD6 nanonets in the literature. First, we present studies that address the biosynthesis, storage, and maturation of HD6, which demonstrate that nature uses a propeptide strategy to spatially and temporally control the formation of HD6 nanonets in the small intestine. The propeptide is stored in Paneth cell granules, and proteolysis occurs during or following release into the lumen, which affords the 32-residue mature peptide that self-assembles. We subsequently highlight structure-function studies that provide a foundation for understanding the molecular basis for why HD6 exhibits unusual self-assembly properties compared with other characterized defensins. The disposition of hydrophobic residues in the HD6 primary structure differs from that of other human α-defensins and is an important structural determinant for oligomerization. Lastly, we consider functional studies that illuminate how HD6 contributes to mucosal immunity. We recently discovered that in addition to blocking bacterial invasion into host epithelial cells by Gram-negative and Gram-positive gastrointestinal pathogens, HD6 suppresses virulence traits displayed by the opportunistic human fungal pathogen Candida albicans. In particular, we found that C. albicans biofilm formation, which causes complications in the treatment of candidiasis, is inhibited by HD6. This observation suggests that HD6 may contribute to intestinal homeostasis by helping to keep C. albicans in its commensal state. We intend for this Account to inspire further biochemical, biophysical, and biological investigations that will advance our understanding of HD6 in mucosal immunity and the host-microbe interaction.

Periprosthetic joint infection (PJI) is a serious complication that may occur after native joint replacement leading to a severe health and economic burden. Currently, due to several confounding factors, PJI is difficult to diagnose. Today, a multidisciplinary approach is indispensable to correctly define a periprosthetic joint infection; indeed, tissue histology, microbiology cultures and clinical findings are used together to achieve this goal. Analysis of α-defensin is commonly used for PJI diagnosis, as it allows the rapid detection of α-defensin present in the synovial fluid following a microbial infection. Currently, a point-of-care testing (POCT) assay able to detect the presence of human α-defensins 1-3 in synovial fluid of patients is aimed directly at orthopedic surgeons. However, many orthopedic surgeons lack experience and training in quality laboratory practices, often failing to appreciate the significance of quality control and proper documentation when using POCT assays. To guarantee the highest quality diagnostic services, the α-defensin test should be used together with other biochemical and microbiological criteria commonly used for PJI diagnosis. Additionally, the close cooperation and communication between laboratory, pathologists and physicians is of fundamental importance in the correct diagnosis of PJI.

Human α-defensin 6 (HD6) is a host-defense peptide that contributes to intestinal innate immunity and mediates homeostasis at mucosal surfaces by forming noncovalent oligomers that capture bacteria and prevent bacterial invasion of the epithelium. This work illustrates a new role of HD6 in defending the host epithelium against pathogenic microorganisms. We report that HD6 blocks adhesion of Candida albicans to human intestinal epithelial cells and suppresses two C. albicans virulence traits, namely, invasion of human epithelial cells and biofilm formation. Moreover, a comparison of HD6 and a single-point variant F2A that does not form higher-order oligomers demonstrates that the self-assembly properties of HD6 are essential for functional activity against C. albicans. This opportunistic fungal pathogen, which resides in the intestine as a member of the gut microbiota in healthy individuals, can turn virulent and cause a variety of diseases ranging from superficial infections to life-threatening systemic infections. Our results indicate that HD6 may allow C. albicans to persist as a harmless commensal in the gastrointestinal tract. Moreover, HD6 and HD6-inspired molecules may provide a foundation for exploring new antimicrobial strategies that attenuate the virulence traits of C. albicans and other microbial pathogens.

Total joint arthroplasty (TJA) has been one of the most beneficial interventions for treating patients suffering from joint disorders. However, peri-prosthetic joint infection (PJI) is a serious complication that often accompanies TJA and the diagnosis of PJI is remains difficult. Questions remain regarding whether certain biomarkers can be valuable in the diagnosis of PJI.

Current methods to diagnose periprosthetic joint infection (PJI) before revision surgery have limited diagnostic accuracy. This meta-analysis was performed to estimate the accuracy of procalcitonin (PCT) and α-defensin for the diagnosis of PJI.

Defensins are antimicrobial peptides that contribute broadly to innate immunity, including protection of mucosal tissues. Human α-defensin (HD) 6 is highly expressed by secretory Paneth cells of the small intestine. However, in contrast to the other defensins, it lacks appreciable bactericidal activity. Nevertheless, we report here that HD6 affords protection against invasion by enteric bacterial pathogens in vitro and in vivo. After stochastic binding to bacterial surface proteins, HD6 undergoes ordered self-assembly to form fibrils and nanonets that surround and entangle bacteria. This self-assembly mechanism occurs in vivo, requires histidine-27, and is consistent with x-ray crystallography data. These findings support a key role for HD6 in protecting the small intestine against invasion by diverse enteric pathogens and may explain the conservation of HD6 throughout Hominidae evolution.

Endogenous antimicrobial peptides (AMPs) mediate innate immunity in every species in which they have been investigated. Cathelicidins and defensins are the two major AMP families in mammals, and they are abundant components of phagocytic leukocytes and are released by epithelial cells at mucosal surfaces. In the small intestine, Paneth cells at the base of the crypts of Lieberkühn secrete alpha-defensins and additional AMPs at high levels in response to cholinergic stimulation and when exposed to bacterial antigens. Paneth cell alpha-defensins evolved to function in the extracellular environment with broad-spectrum antimicrobial activities, and they constitute the majority of bactericidal peptide activity secreted by Paneth cells. The release of Paneth cell products into the crypt lumen is inferred to protect mitotically active crypt cells from colonization by potential pathogens and confers protection from enteric infection, as is evident from the immunity of mice expressing a human Paneth cell alpha-defensin transgene to oral infection by Salmonella enterica serovar Typhimurium. alpha-Defensins in Paneth cell secretions also may interact with bacteria in the intestinal lumen above the crypt-villus boundary and influence the composition of the enteric microbial flora. Mutations that cause defects in the activation, secretion, dissolution, and bactericidal effects of Paneth cell AMPs may alter crypt innate immunity and contribute to immunopathology.