Vitamin D differentially regulates Salmonella-induced intestine epithelial autophagy and interleukin-1β expression

Long-chain unsaturated fatty acids sensor controlling the type III/VI secretion system is essential for Edwardsiella piscicida infection

Edwardsiella piscicida is an acute marine pathogen that causes severe damage to the aquaculture industry worldwide. The pathogenesis of E. piscicida is dependent mainly on the type III secretion system (T3SS) and type VI secretion system (T6SS), both of which are critically regulated by EsrB and EsrC. In this study, we revealed that fatty acids influence T3SS expression. Unsaturated fatty acids (UFAs), but not saturated fatty acids (SFAs), directly interact with EsrC, which abolishes the function of EsrC and results in the turn-off of T3/T6SS. Moreover, during the in vivo colonization of E. piscicida, host fatty acids were observed to be transported into E. piscicida through FadL and to modulate the expression of T3/T6SS. Furthermore, the esrCR38G mutant blocked the interaction between EsrC and UFAs, leading to dramatic growth defects in DMEM and impaired colonization in HeLa cells and zebrafish. In conclusion, this study revealed that the interaction between UFAs and EsrC to turn off T3/T6SS expression is essential for E. piscicida infection.

Unveiling the Novel Benefits of Co-Administering Butyrate and Active Vitamin D3 in Mice Subjected to Chemotherapy-Induced Gut-Derived Pseudomonas aeruginosa Sepsis

Cancer patients face increased susceptibility to invasive infections, primarily due to ulcerative lesions on mucosal surfaces and immune suppression resulting from chemotherapy. Pseudomonas aeruginosa (P. aeruginosa) bacteremia is notorious for its rapid progression into fatal sepsis, posing a significant threat to cancer patients, particularly those experiencing chemotherapy-induced neutropenia. This bacterial infection contributes significantly to morbidity and mortality rates among such individuals. Our latest report showed the mutually beneficial effects of postbiotic butyrate on 1,25-dihydroxyvitamin D3 (1,25D3)-controlled innate immunity during Salmonella colitis. Hence, we investigated the impact of butyrate and 1,25D3 on chemotherapy-induced gut-derived P. aeruginosa sepsis in mice. The chemotherapy-induced gut-derived P. aeruginosa sepsis model was established through oral administration of 1 × 107 CFU of the P. aeruginosa wild-type strain PAO1 in C57BL/6 mice undergoing chemotherapy. Throughout the infection process, mice were orally administered butyrate and/or 1,25D3. Our observations revealed that the combined action of butyrate and 1,25D3 led to a reduction in the severity of colitis and the invasion of P. aeruginosa into the liver and spleen of the mice. This reduction was attributed to an enhancement in the expression of defensive cytokines and antimicrobial peptides within the cecum, coupled with decreased levels of zonulin and claudin-2 proteins in the mucosal lining. These effects were notably more pronounced when compared to treatments administered individually. This study unveils a promising alternative therapy that involves combining postbiotics and 1,25D3 for treating chemotherapy-induced gut-derived P. aeruginosa sepsis.

Gut microbiota in pre-clinical rheumatoid arthritis: From pathogenesis to preventing progression

Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by progressive polyarthritis that leads to cartilage and bone damage. Pre-clinical RA is a prolonged state before clinical arthritis and RA develop, in which autoantibodies (antibodies against citrullinated proteins, rheumatoid factors) can be present due to the breakdown of immunologic self-tolerance. As early treatment initiation before the onset of polyarthritis may achieve sustained remission, optimize clinical outcomes, and even prevent RA progression, the pre-clinical RA stage is showing the prospect to be the window of opportunity for RA treatment. Growing evidence has shown the role of the gut microbiota in inducing systemic inflammation and polyarthritis via multiple mechanisms, which may involve molecular mimicry, impaired intestinal barrier function, gut microbiota-derived metabolites mediated immune regulation, modulation of the gut microbiota's effect on immune cells, intestinal epithelial cells autophagy, and the interaction between the microbiome and human leukocyte antigen alleles as well as microRNAs. Since gut microbiota alterations in pre-clinical RA have been reported, potential therapies for modifying the gut microbiota in pre-clinical RA, including natural products, antibiotic therapy, fecal microbiota transplantation, probiotics, microRNAs therapy, vitamin D supplementation, autophagy inducer-based treatment, prebiotics, and diet, holds great promise for the successful treatment and even prevention of RA via altering ongoing inflammation. In this review, we summarized current studies that include pathogenesis of gut microbiota in RA progression and promising therapeutic strategies to provide novel ideas for the management of pre-clinical RA and possibly preventing arthritis progression.

Microbiota-derived short-chain fatty acids and modulation of host-derived peptides formation: Focused on host defense peptides

The byproducts of bacterial fermentation known as short-chain fatty acids (SCFAs) are chemically comprised of a carboxylic acid component and a short hydrocarbon chain. Recent investigations have demonstrated that SCFAs can affect intestinal immunity by inducing endogenous host defense peptides (HDPs) and their beneficial effects on barrier integrity, gut health, energy supply, and inflammation. HDPs, which include defensins, cathelicidins, and C-type lectins, perform a significant function in innate immunity in gastrointestinal mucosal membranes. SCFAs have been demonstrated to stimulate HDP synthesis by intestinal epithelial cells via interactions with G protein-coupled receptor 43 (GPR43), activation of the Jun N-terminal kinase (JNK) and Mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) pathways, and the cell growth pathways. Furthermore, SCFA butyrate has been demonstrated to enhance the number of HDPs released from macrophages. SCFAs promote monocyte-to-macrophage development and stimulate HDP synthesis in macrophages by inhibiting histone deacetylase (HDAC). Understanding the etiology of many common disorders might be facilitated by studies into the function of microbial metabolites, such as SCFAs, in the molecular regulatory processes of immune responses (e.g., HDP production). This review will focus on the current knowledge of the role and mechanism of microbiota-derived SCFAs in influencing the synthesis of host-derived peptides, particularly HDPs.

The Critical Role of Acyl Hydrocarbon Receptor on the Combined Benefits of Postbiotic Propionate on Active Vitamin D3-Orchestrated Innate Immunity in Salmonella Colitis

Our recent study observed the combined beneficial effects of postbiotic butyrate on active vitamin D3-orchestrated innate immunity to Salmonella Colitis. There is increasing interest in the role of acyl hydrocarbon receptor (AhR) on colitis and innate immunity. Therefore, we investigated the involvement of AhR in the effects. Salmonella colitis model is conducted with 6-8 w/o male C57BL/6 mice: Streptomycin (20 mg/mouse p.o.)-pretreated C57BL/6 mice were mock infected with sterile PBS or infected orally with 1 × 10⁸ CFU of an S. typhimurium wild-type strain SL1344 for 48 h. Before and after the colitis induction, mice were oral gavage with active vitamin D3 0.2 μg/25 g mice (VD3) and/or postbiotics propionate (PP), in the absence of the presence of intraperitoneal injection of AhR inhibitor for 4 and 7 days, respectively. We observed AhR inhibitor counteracted the synergistic effects of PP and VD3 on reducing the severity of Salmonella colitis and body weight loss in C57BL/6 mice, reducing the cecal inflammatory but enhancing antimicrobial peptide mRNAs expression, and reducing the bacterial translocation in liver/spleen, compared to single treatment. It suggests the involvement of AhR on the synergistic effects of postbiotics PP and VD3 on the antibacterial and anti-inflammatory responses in Salmonella colitis and the potential biological treatment of Salmonella colitis.

Vitamin–Microbiota Crosstalk in Intestinal Inflammation and Carcinogenesis

Inflammatory bowel disease (IBD) and colitis-associated colorectal cancer (CAC) are common diseases of the digestive system. Vitamin deficiencies and gut microbiota dysbiosis have a close relationship with the risk, development, and progression of IBD and CAC. There is a strong link between vitamins and the gut microbiome. Vitamins are extremely crucial for maintaining a healthy gut microbiota, promoting growth and development, metabolism, and innate immunity. Gut microbiota can not only influence the transport process of vitamins, but also produce vitamins to compensate for insufficient food intake. Emerging evidence suggests that oral vitamin supplementation can reduce inflammation levels and improve disease prognosis. In addition, improving the diet structure and consuming foods rich in vitamins not only help to improve the vitamin deficiency, but also help to reduce the risk of IBD. Fecal microbiota transplantation (FMT) and the application of vitamin-producing probiotics can better assist in the treatment of intestinal diseases. In this review, we discuss the interaction and therapeutic roles of vitamins and gut microbiota in IBD and CAC. We also summarize the methods of treating IBD and CAC by modulating vitamins. This may highlight strategies to target gut-microbiota-dependent alterations in vitamin metabolism in the context of IBD and CAC therapy.

Vitamin D/vitamin D receptor, autophagy, and infection

Vitamin D plays an important role in mineral and bone homeostasis, immune responses, cardiovascular function and keratinocyte proliferation and differentiation. Vitamin D performs most of its functions by binding to vitamin D receptors (VDR), which interact with other intracellular signaling pathways to regulate bone metabolism, inflammation, immunity, cell cycle progression and apoptosis. Autophagy is a basic stress response in yeast, plants and mammals, and plays a critical role in maintaining optimal functional states at the level of cells and organs. Vitamin D/VDR plays an anti-infection role via inducing and regulating autophagy.

The Interleukins Orchestrate Mucosal Immune Responses to Salmonella Infection in the Intestine

Salmonella infection remains one of the major public health problems in the world, with increasing resistance to antibiotics. The resolution is to explore the pathogenesis of the infection and search for alternative therapy other than antibiotics. Immune responses to Salmonella infection include innate and adaptive immunity. Flagellin or muramyl dipeptide from Salmonella, recognized by extracellular Toll-like receptors and intracellular nucleotide-binding oligomerization domain2, respectively, induce innate immunity involving intestinal epithelial cells, neutrophils, macrophages, dendric cells and lymphocytes, including natural killer (NK) and natural killer T (NKT) cells. The cytokines, mostly interleukins, produced by the cells involved in innate immunity, stimulate adaptive immunity involving T and B cells. The mucosal epithelium responds to intestinal pathogens through its secretion of inflammatory cytokines, chemokines, and antimicrobial peptides. Chemokines, such as IL-8 and IL-17, recruit neutrophils into the cecal mucosa to defend against the invasion of Salmonella, but induce excessive inflammation contributing to colitis. Some of the interleukins have anti-inflammatory effects, such as IL-10, while others have pro-inflammatory effects, such as IL-1β, IL-12/IL-23, IL-15, IL-18, and IL-22. Furthermore, some interleukins, such as IL-6 and IL-27, exhibit both pro- and anti-inflammatory functions and anti-microbial defenses. The majority of interleukins secreted by macrophages and lymphocytes contributes antimicrobial defense or protective effects, but IL-8 and IL-10 may promote systemic Salmonella infection. In this article, we review the interleukins involved in Salmonella infection in the literature.

Role of Intestinal Alkaline Phosphatase in Innate Immunity

Intestinal alkaline phosphatase (IAP) is a multi-functional protein that has been demonstrated to primarily protect the gut. The role of IAP in maintaining intestinal homeostasis is underscored by the observation that IAP expression is defective in many gastrointestinal-related disorders such as inflammatory bowel disease IBD, necrotizing enterocolitis, and metabolic syndrome and that exogenous IAP supplementation improves the outcomes associated with these disorders. Additionally, studies using transgenic IAP-knock out (IAP-KO) mouse models further support the importance of the defensive role of IAP in the intestine. Supplementation of exogenous IAP and cellular overexpression of IAP have also been used in vitro to dissect out the downstream mechanisms of this protein in mammalian cell lines. Some of the innate immune functions of IAP include lipopolysaccharide (LPS) detoxification, protection of gut barrier integrity, regulation of gut microbial communities and its anti-inflammatory roles. A novel function of IAP recently identified is the induction of autophagy. Due to its critical role in the gut physiology and its excellent safety profile, IAP has been used in phase 2a clinical trials for treating conditions such as sepsis-associated acute kidney injury. Many excellent reviews discuss the role of IAP in physiology and pathophysiology and here we extend these to include recent updates on this important host defense protein and discuss its role in innate immunity via its effects on bacteria as well as on host cells. We will also discuss the relationship between IAP and autophagy and how these two pathways may act in concert to protect the gut.

The Combined Beneficial Effects of Postbiotic Butyrate on Active Vitamin D3-Orchestrated Innate Immunity to Salmonella Colitis

Salmonella spp. Remains a major public health problem globally. Biomedicine is the cornerstone of modern health care and could be a solution for antibiotic-resistant Salmonellosis. Although postbiotics seem to be an effective treatment in various clinical conditions, their clinical effects on Salmonella colitis have not been reported. Our previous report revealed that active vitamin D attenuates the severity of Salmonella colitis and invasiveness by reducing inflammation and enhancing the production of antimicrobial peptides. Therefore, we investigated the synergistic effects of butyrate, the most studied postbiotic, and active vitamin D on the severity of Salmonella colitis, invasiveness of Salmonella, and host immune responses, as well as its novel mechanisms, using in vitro and in vivo studies. We demonstrated that a combination of butyrate and active vitamin D (1 alpha, 25-dihydroxyvitamin D3) synergically reduced the severity of Salmonella colitis in C57BL/6 mice and reduced cecal inflammatory mIL-6, mIL-8, mTNF-α, and mIL-1β mRNA expression, but enhanced the antimicrobial peptide mhBD-3 mRNA, compared to a single treatment. Additionally, upregulated vitamin D receptor (VDR) plays a critical role in the synergistic effects. This suggests combined benefits of butyrate and active vitamin D on Salmonella colitis through VDR-mediated antibacterial and anti-inflammatory responses. The combined use of both supplements could be a potential biomedicine for infectious and autoimmune colitis.

The Cooperation of Bifidobacterium longum and Active Vitamin D3 on Innate Immunity in Salmonella Colitis Mice via Vitamin D Receptor

Salmonella spp. remains a major public health problem for the whole world. Intestinal epithelial cells serve as an essential component of the mucosal innate immune system to defend against Salmonella infection. Our in vitro studies showed probiotics and active vitamin D have similar effects on innate immunity in Salmonella-infected intestinal epithelial cells, including antimicrobial peptide and inflammatory responses, to protect the host against infection while downregulating detrimental overwhelming inflammation. Hence, we investigated the synergistic effects of probiotics and active vitamin D on Salmonella colitis and translocation to liver and spleen by in vitro and in vivo studies. The Salmonella colitis model is conducted with 6–8 w/o male C57BL/6 mice: Streptomycin (20 mg/mouse p.o.)-pretreated C57BL/6 mice are mock infected with sterile PBS or infected orally with 1 × 10⁸ CFU of a S. Typhimurium wild-type strain SL1344 for 48 h. The mice in the treated groups received 1, 25D daily (0.2 ug/25 g/d) and/or 1 × 10⁸ CFU of probiotics, Lactobacillus rhamnosus GG (LGG) and Bifidobacterium longum (BL) by intragastric administration for 14 days. The in vivo study demonstrated the combination of probiotic Bifidobacterium longum and active vitamin D3 had the synergistic effects on reducing the severity of Salmonella colitis and body weight loss in C57BL/6 mice by reducing cecal inflammatory mIL-6, mIL-8, mTNF-α and mIL-1β mRNA responses, blocking the translocation of bacteria while enhancing the antimicrobial peptide mhBD-3 mRNA in comparison to the infection only group. However, LGG did not have the same synergistic effects. It suggests the synergistic effects of Bifidobacterium longum and active vitamin D on the antibacterial and anti-inflammatory responses in Salmonella colitis. Therefore, our in vivo studies demonstrated that the combination of probiotic Bifidobacterium longum and active vitamin D3 has the synergistic effects on reducing the severity of Salmonella colitis via the suppression of inflammatory responses, and blocking the translocation of bacteria through the enhancement of antimicrobial peptides.

Vitamin D in autophagy signaling for health and diseases: Insights on potential mechanisms and future perspectives

Vitamin D regulates the pleiotropic effect to maintain cellular homeostasis and epidemiological evidence establishes an association between vitamin D deficiency and various human diseases. Here, the role of autophagy, the cellular self-degradation process, in vitamin D-dependent function is documented in different cellular settings and discussed the molecular aspects for treating chronic inflammatory, infectious diseases, and cancer. Vitamin D activates autophagy through a genomic and non-genomic signaling pathway to influence a wide variety of physiological functions of different body organs along with bone health and calcium metabolism. Moreover, it induces autophagy as a protective mechanism to inhibit oxidative stress and apoptosis to regulate cell proliferation, differentiation, and immune modulation. Furthermore, vitamin D and its receptor regulate autophagy signaling to control inflammation and host immunity by activating antimicrobial defense mechanisms. Vitamin D has been revealed as a potent anticancer agent and induces autophagy to increase the response to radiation and chemotherapeutic drugs for potential cancer therapy. Increasing vitamin D levels in the human body through timely exposure to sunlight or vitamin D supplements could activate autophagy as part of the homeostasis mechanism to prevent multiple human diseases and aging-associated dysfunctions.

Active vitamin D3 attenuates the severity of Salmonella colitis in mice by orchestrating innate immunity

INTRODUCTION

Salmonella spp. pose major public health problems worldwide. A better understanding of the pathogenesis of these foodborne pathogens is a prerequisite for the design of improved intervention strategies that could reduce the use of antimicrobial agents and drug-resistant Salmonellosis. Accumulating evidence indicates that vitamin D is involved in regulating innate immunity, and may, therefore, play a key role in human responses to infection. Studies have suggested 1,25-dihydroxyvitamin D3 (1,25D3), the active form of vitamin D, effectively ameliorates colitis. These findings have broad implications for the use of vitamin D compounds in colitis. This study investigated the effect of active vitamin D3 on the severity of Salmonella colitis.

METHODS

A Salmonella colitis model was established with 6-8-week-old male C57BL/6 mice: Streptomycin-pretreated C57BL/6 mice were infected orally with Salmonella enterica serova Typhimurium wild-type strain SL1344 for 48 h. The mice were randomly assigned to control, model, and 1,25(OH)2 D3 -treated groups. After the experiment, the mice were sacrificed, and intestinal, spleen, and liver tissue samples were removed to analyze bacterial colonization, western blot for protein levels, and real-time-polymer chain reaction for messenger RNA (mRNA) expression.

RESULTS

We observed that 1,25D3 reduced the severity of Salmonella colitis in C57BL/6 mice by reducing cecal mIL-1beta, mIL-6, mTNF-alpha, and mIL-8 mRNA expressions, bacterial colonization (CFU/mg tissue) in the liver and spleen, but increased the human β-defensin-2 mRNA and autophagy protein expression, compared to those of the SL1344 infection only.

CONCLUSIONS

Our results document that active vitamin D3 reduced Salmonella colitis by decreasing inflammation, and bacterial translocation via induction of killing and autophagic clearance of pathogenic organisms.

Artesunate interacts with the vitamin D receptor to reverse sepsis-induced immunosuppression in a mouse model via enhancing autophagy

BACKGROUND AND PURPOSE

Immunosuppression is the predominant cause of mortality for sepsis because of failure to eradicate pathogens. No effective and specific drugs capable of reversing immunosuppression are clinically available. Evidences implicate the involvement of the vitamin D receptor (NR1I1) in sepsis-induced immunosuppression. The anti-malarial artesunate was investigated to determine action on sepsis-induced immunosuppression.

EXPERIMENTAL APPROACH

The effect of artesunate on sepsis-induced immunosuppression was investigated in mice and human and mice cell lines. Bioinformatics predicted vitamin D receptor as a candidate target for artesunate, which was then identified using PCR and immunoblotting. Vdr, Atg16l1 and NF-κB p65 were modified to investigate artesunate 's effect on pro-inflammatory cytokines release, bacterial clearance and autophagy activities in sepsis-induced immunosuppression.

KEY RESULTS

Artesunate significantly reduced the mortality of caecal ligation and puncture (CLP)-induced sepsis immunosuppression mice challenged with Pseudomonas aeruginosa and enhanced pro-inflammatory cytokine release and bacterial clearance to reverse sepsis-induced immunosuppression in vivo and in vitro. Mechanistically, artesunate interacted with vitamin D receptor, inhibiting its nuclear translocation, which influenced ATG16L1 transcription and subsequent autophagy activity. Artesunate inhibited the physical interaction between vitamin D receptor and NF-κB p65 in LPS-tolerant macrophages and then promoted the nuclear translocation of NF-κB p65, which activated the transcription of NF-κB p65 target genes such as pro-inflammatory cytokines.

CONCLUSION AND IMPLICATIONS

Our findings provide evidence that artesunate interacted with vitamin D receptor to reverse sepsis-induced immunosuppression in an autophagy and NF-κB-dependent manner, highlighting a novel approach for sepsis treatment and drug repurposing of artesunate has a bidirectional immunomodulator.

Vitamin D reduces autophagy by regulating NF-κB resistance to Aspergillus fumigatus infection

Vitamin D is one of the indispensable nutrients of human body. When vitamin D is deficient, it can cause a series of related diseases, such as respiratory tract infection. The regulatory role of vitamin D in inflammatory immune response and defense has attracted more and more attention. However, few studies have shown that vitamin D regulates inflammation and autophagy in Aspergillus fumigatus infected lungs. In this study, we will explain the mechanism of vitamin D regulating inflammation and autophagy in Aspergillus fumigatus infected lungs.

METHODS

Different concentrations of Aspergillus fumigatus spores were injected into mice with deficien diets (VitD-) or sufficient vitamin D (VitD + ) , and the survival rates were recorded. Then, the weight changes of rats were measured every other time. At the same time, a gauze was used to filter the lapped lung tissue to get the pulmonary spores and measured the amount of the spores. The mice with the same concentration of Aspergillus fumigatus infected were cut off and the lung tissue for pathological examination in the deficien diets (VitD-) group or sufficient vitamin D (VitD + ) group. Moreover, the expression of inflammation related factors TNF-α, IL-1β, IL-6 in lung was measured by immunohistochemical method. The expression of TNF-α, IL-1β, IL-6 in the serum of vitamin D deficiency and sufficient mice were measured by ELISA. In vitro, we obtained macrophages from healthy mice and mixed cultures of Aspergillus fumigatus spores and lung macrophages in medium with or without vitamin D. After the cells were infected with Aspergillus fumigatus spores, the expressions of NF-κB and IL-8 were detected by RT-PCR and Western blot. The RAW264.7 cells transfected with GFP-LC3BII were mixed with Aspergillus fumigatus spores, and the expression of cell fluorescence was observed by the fluorescence microscope with or without chloroquine and rapamycin , and the autophagy flow of the cells was measured by Western blot. In the RAW264.7 cells, Lentivirus transfection and SiRNA technologies were used to enhance or reduce the expression of the NF-κB gene (siNF-κB) for investgating the influence of high or low expression of NF-κB in the autophagic flow of vitamin D + or vitamin D-treated RAW264.7 cells.

RESULTS

The survival rate of vitamin D deficient mice infected Aspergillus fumigatus was significantly lower than that of vitamin D sufficient mice, while the number of spores, spore activity, pathological changes of lungs and inflammation in the lungs of vitamin D deficient mice were more severe than that of vitamin D sufficient mice. In vitro cell experiments, when cell was stimulated with vitamin D, the expressions of NF-κB and IL-8 in cells were lower. The autophagic flux and TNF-α, IL-1β, IL-6 and LC3BII in vitamin D group were significantly lower than those in vitamin D deficiency group.

CONCLUSIONS

Vitamin D deficiency can aggravate the inflammatory damage in the lungs of Aspergillus fumigatus. When the body is sufficient in vitamin D, if the lungs infect Aspergillus fumigatus spores, the body may resist the infection of Aspergillus fumigatus by reducing the expression of NF-κB, inflammatory factors and autophagy.

Salmonella Interacts With Autophagy to Offense or Defense

Autophagy is an important component of the innate immune system in mammals. Low levels of basic autophagy are sustained in normal cells, to help with the clearance of aging organelles and misfolded proteins, thus maintaining their structural and functional stability. However, when cells are faced with challenges, such as starvation or pathogenic infection, their level of autophagy increases significantly. Salmonella is a facultative intracellular pathogen, which imposes an economic burden on the poultry farming industry and human public health. Previous studies have shown that Salmonella can induce the autophagy of cells following invasion, which to a certain extent helps to protect the cells from bacterial colonization. This review summarizes the latest research in the field of Salmonella-induced autophagy, including: (i) the autophagy induction and escape mechanisms employed by Salmonella during the infection of host cells; (ii) the effect of autophagy on intracellular Salmonella; (iii) the important autophagy adaptors that recognize intracellular Salmonella in host cells; and (iv) the effect of autophagy-modulating drugs on Salmonella infection.

Vitamin D-Cathelicidin Axis: at the Crossroads between Protective Immunity and Pathological Inflammation during Infection

Vitamin D signaling plays an essential role in innate defense against intracellular microorganisms via the generation of the antimicrobial protein cathelicidin. In addition to directly binding to and killing a range of pathogens, cathelicidin acts as a secondary messenger driving vitamin D-mediated inflammation during infection. Recent studies have elucidated the biological and clinical functions of cathelicidin in the context of vitamin D signaling. The vitamin D-cathelicidin axis is involved in the activation of autophagy, which enhances antimicrobial effects against diverse pathogens. Vitamin D studies have also revealed positive and negative regulatory effects of cathelicidin on inflammatory responses to pathogenic stimuli. Diverse innate and adaptive immune signals crosstalk with functional vitamin D receptor signals to enhance the role of cathelicidin action in cell-autonomous effector systems. In this review, we discuss recent findings that demonstrate how the vitamin D-cathelicidin pathway regulates autophagy machinery, protective immune defenses, and inflammation, and contributes to immune cooperation between innate and adaptive immunity. Understanding how the vitamin D-cathelicidin axis operates in the host response to infection will create opportunities for the development of new therapeutic approaches against a variety of infectious diseases.

Vitamin D in Acute Campylobacteriosis-Results From an Intervention Study Applying a Clinical Campylobacter jejuni Induced Enterocolitis Model

Human Campylobacter infections are progressively rising and of high socioeconomic impact. In the present preclinical intervention study we investigated anti-pathogenic, immuno-modulatory, and intestinal epithelial barrier preserving properties of vitamin D applying an acute campylobacteriosis model. Therefore, secondary abiotic IL-10^−/− mice were perorally treated with synthetic 25-OH-cholecalciferol starting 4 days before peroral Campylobacter jejuni infection. Whereas, 25-OH-cholecalciferol application did not affect gastrointestinal pathogen loads, 25-OH-cholecalciferol treated mice suffered less frequently from diarrhea in the midst of infection as compared to placebo control mice. Moreover, 25-OH-cholecalciferol application dampened C. jejuni induced apoptotic cell responses in colonic epithelia and promoted cell-regenerative measures. At day 6 post-infection, 25-OH-cholecalciferol treated mice displayed lower numbers of colonic innate and adaptive immune cell populations as compared to placebo controls that were accompanied by lower intestinal concentrations of pro-inflammatory mediators including IL-6, MCP1, and IFN-γ. Remarkably, as compared to placebo application synthetic 25-OH-cholecalciferol treatment of C. jejuni infected mice resulted in lower cumulative translocation rates of viable pathogens from the inflamed intestines to extra-intestinal including systemic compartments such as the kidneys and spleen, respectively, which was accompanied by less compromised colonic epithelial barrier function in the 25-OH-cholecalciferol as compared to the placebo cohort. In conclusion, our preclinical intervention study provides evidence that peroral synthetic 25-OH-cholecalciferol application exerts inflammation-dampening effects during acute campylobacteriosis.