Chronic Salmonella infected mouse model

Overexpression of Vitamin D Receptor in Intestinal Epithelia Protects Against Colitis via Upregulating Tight Junction Protein Claudin 15

BACKGROUND AND AIMS

Dysfunction of the vitamin D receptor [VDR] contributes to the aetiology of IBD by regulating autophagy, immune response, and mucosal permeability. VDR directly controls the paracellular tight junction protein Claudin-2. Claudin-2 and Claudin-15 are unique in maintaining paracellular permeability. Interestingly, claudin-15 mRNA was downregulated in patients with ulcerative colitis. However, the exact mechanism of Claudin-15 regulation in colitis is still unknown. Here, we investigated the protective role of VDR against intestinal inflammation via upregulating Claudin-15.

METHODS

We analysed the correlation of Claudin-15 with the reduction of VDR in human colitis. We generated intestinal epithelial overexpression of VDR [O-VDR] mice to study the gain of function of VDR in colitis. Intestinal epithelial VDR knockout [VDR∆IEC] mice were used for the loss of function study. Colonoids and SKCO15 cells were used as in vitro models.

RESULTS

Reduced Claudin-15 was significantly correlated with decreased VDR along the colonic epithelium of human IBD. O-VDR mice showed decreased susceptibility to chemically and bacterially induced colitis and marked increased Claudin-15 expression [both mRNA and protein] in the colon. Correspondingly, colonic Claudin-15 was reduced in VDR∆IEC mice, which were susceptible to colitis. Overexpression of intestinal epithelial VDR and vitamin D treatment resulted in a significantly increased Claudin-15. ChIP assays identified the direct binding of VDR to the claudin-15 promoter, suggesting that claudin-15 is a target gene of VDR.

CONCLUSION

We demonstrated the mechanism of VDR upregulation of Claudin-15 to protect against colitis. This might enlighten the mechanism of barrier dysfunction in IBD and potential therapeutic strategies to inhibit inflammation.

A simple and sensitive method to detect vitamin D receptor expression in various disease models using stool samples

Vitamin D receptor (VDR) executes the main biological functions of its ligand vitamin D. VDR/vitamin D plays critical roles in regulating host immunity, maintaining barrier functions, and shaping gut microbiome. Reduction of intestinal VDR has been reported in various diseases, including inflammatory diseases and colon cancer. However, it is always challenging to get biopsies to test the pathologic changes of VDR in intestine. In the current study, we reported a simple and sensitive quantitative PCR (qPCR) method to detect reduction of intestinal VDR using fecal samples. We validated this method in several experimental models, such as colitis, bacterial infection, and aging. We further correlated the qPCR data of VDR with the protein level of VDR in colon or serum 25 (OH)D₃ in mice with different VDR status (VDR^+/+, VDR^+/-, and VDR^−/−). Our data indicate that the qPCR method to test VDR using fecal samples could detect the expression level of intestinal VDR in various diseases. Our study highlights the feasibility, sensitivity, and simplicity of a molecular method to study the status of VDR as a biomarker.

Lack of Vitamin D Receptor Leads to Hyperfunction of Claudin-2 in Intestinal Inflammatory Responses

BACKGROUND

Vitamin D3 and vitamin D receptor (VDR) are involved in the pathogenesis of inflammatory bowel disease (IBD) and bacterial infection. Claudin-2 is a junction protein that mediates paracellular water transport in epithelia. Elevation of Claudin-2 is associated with active IBD. However, VDR involved in epithelial junctions under inflammation and infection remains largely unknown. We investigated the mechanisms on how VDR and Claudin-2 are related in inflamed states.

METHODS

Using cultured VDR-/- enteroids, human intestinal epithelial cells, VDR-/- mice with Salmonella- or DSS-colitis, and human IBD samples, we investigated the mechanisms how VDR and Claudin-2 are related in inflamed states.

RESULTS

After Salmonella infection had taken place, we observed significantly enhanced Claudin-2 and an increased bacterial invasion and translocation. A lack of VDR regulation led to a robust increase of Claudin-2 at the mRNA and protein levels post-infection. In DSS-treated VDR-/- mice, Claudin-2 was significantly increased. Location and quantification of Claudin-2 protein in the mouse colons treated with DSS also confirmed these results. Inflammatory cytokines were significantly higher in the serum and mRNA levels in intestine, which are known to increase Claudin-2. Furthermore, in inflamed intestine of ulcerative colitis patients, VDR expression was low and Claudin-2 was enhanced. Mechanistically, we identified the enhanced Claudin-2 promoter activity through the binding sites of NF-κB and STAT in inflamed VDR-/- cells.

CONCLUSIONS

Our studies have identified a new role for intestinal epithelial VDR in regulating barrier functions in the context of infection and inflammation.

Animal models to study acute and chronic intestinal inflammation in mammals

Acute and chronic inflammatory diseases of the intestine impart a significant and negative impact on the health and well-being of human and non-human mammalian animals. Understanding the underlying mechanisms of inflammatory disease is mandatory to develop effective treatment and prevention strategies. As inflammatory disease etiologies are multifactorial, the use of appropriate animal models and associated metrics of disease are essential. In this regard, animal models used alone or in combination to study acute and chronic inflammatory disease of the mammalian intestine paired with commonly used inflammation-inducing agents are reviewed. This includes both chemical and biological incitants of inflammation, and both non-mammalian (i.e. nematodes, insects, and fish) and mammalian (i.e. rodents, rabbits, pigs, ruminants, dogs, and non-human primates) models of intestinal inflammation including germ-free, gnotobiotic, as well as surgical, and genetically modified animals. Importantly, chemical and biological incitants induce inflammation via a multitude of mechanisms, and intestinal inflammation and injury can vary greatly according to the incitant and animal model used, allowing studies to ascertain both long-term and short-term effects of inflammation. Thus, researchers and clinicians should be aware of the relative strengths and limitations of the various animal models used to study acute and chronic inflammatory diseases of the mammalian intestine, and the scope and relevance of outcomes achievable based on this knowledge. The ability to induce inflammation to mimic common human diseases is an important factor of a successful animal model, however other mechanisms of disease such as the amount of infective agent to induce disease, invasion mechanisms, and the effect various physiologic changes can have on inducing damage are also important features. In many cases, the use of multiple animal models in combination with both chemical and biological incitants is necessary to answer the specific question being addressed regarding intestinal disease. Some incitants can induce acute responses in certain animal models while others can be used to induce chronic responses; this review aims to illustrate the strengths and weaknesses in each animal model and to guide the choice of an appropriate acute or chronic incitant to facilitate intestinal disease.

Utilization of plant-derived recombinant human β-defensins (hBD-1 and hBD-2) for averting salmonellosis

We describe the use of plant-made β-defensins as effective antimicrobial substances for controlling salmonellosis, a deadly infection caused by Salmonella typhimurium (referred to further as S. typhi). Human β-defensin-1 (hBD-1) and -2 (hBD-2) were expressed under the control of strong constitutive promoters in tobacco plants, and bio-active β-defensins were successfully extracted. In the in vitro studies, enriched recombinant plant-derived human β-defensin-1 (phBD-1) and -2 (phBD-2) obtained from both T1 and T2 transgenic plants showed significant antimicrobial activity against Escherichia coli and S. typhi when used individually and in various combinations. The 2:1 peptide combination of phBD-1:phBD-2 with peptides isolated from T1-and T2-generation plants reduced the growth of S. typhi by 96 and 85 %, respectively. In vivo studies employing the mouse model (Balb/c) of Salmonella infection clearly demonstrated that the administration of plant-derived defensins individually and in different combinations enhanced the mean survival time of Salmonella-infected animals. When treatment consisted of the 2:1 phBD-1:phBD-2 combination, approximately 50 % of the infected mice were still alive at 206 h post-inoculation; the lowest number of viable S. typhi was observed in the liver and spleen of infected animals. We conclude that plant-made recombinant β-defensins (phBD-1 and phBD-2) are promising antimicrobial substances and have the potential to become additional tools against salmonellosis, particularly when used in combination.

Salmonella-infected crypt-derived intestinal organoid culture system for host-bacterial interactions

The in vitro analysis of bacterial-epithelial interactions in the intestine has been hampered by a lack of suitable intestinal epithelium culture systems. Here, we report a new experimental model using an organoid culture system to study pathophysiology of bacterial-epithelial interactions post Salmonella infection. Using crypt-derived mouse intestinal organoids, we were able to visualize the invasiveness of Salmonella and the morphologic changes of the organoids. Importantly, we reported bacteria-induced disruption of epithelial tight junctions in the infected organoids. In addition, we showed the inflammatory responses through activation of the NF-κB pathway in the organoids. Moreover, our western blot, PCR, and immunofluorescence data demonstrated that stem cell markers (Lgr5 and Bmi1) were significantly decreased by Salmonella infection (determined using GFP-labeled Lgr5 organoids). For the first time, we created a model system that recapitulated a number of observations from in vivo studies of the Salmonella-infected intestine, including bacterial invasion, altered tight junctions, inflammatory responses, and decreased stem cells. We have demonstrated that the Salmonella-infected organoid culture system is a new experimental model suitable for studying host-bacterial interactions.

Effective control of Salmonella infections by employing combinations of recombinant antimicrobial human β-defensins hBD-1 and hBD-2

We successfully produced two human β-defensins (hBD-1 and hBD-2) in bacteria as functional peptides and tested their antibacterial activities against Salmonella enterica serovar Typhi, Escherichia coli, and Staphylococcus aureus employing both spectroscopic and viable CFU count methods. Purified peptides showed approximately 50% inhibition of the bacterial population when used individually and up to 90% when used in combination. The 50% lethal doses (LD50) of hBD-1 against S. Typhi, E. coli, and S. aureus were 0.36, 0.40, and 0.69 μg/μl, respectively, while those for hBD-2 against the same bacteria were 0.38, 0.36, and 0.66 μg/μl, respectively. Moreover, we observed that bacterium-derived antimicrobial peptides were also effective in increasing survival time and decreasing bacterial loads in the peritoneal fluid, liver, and spleen of a mouse intraperitoneally infected with S. Typhi. The 1:1 hBD-1/hBD-2 combination showed maximum effectiveness in challenging the Salmonella infection in vitro and in vivo. We also observed less tissue damage and sepsis formation in the livers of infected mice after treatment with hBD-1 and hBD-2 peptides individually or in combination. Based on these findings, we conclude that bacterium-derived recombinant β-defensins (hBD-1 and hBD-2) are promising antimicrobial peptide (AMP)-based substances for the development of new therapeutics against typhoid fever.