Gut commensals expand vitamin A metabolic capacity of the mammalian host

Exosomes-mediated retinoic acid disruption: A link between gut microbiota depletion and impaired spermatogenesis

Gut microbiota symbiosis faces enormous challenge with increasing exposure to drugs such as environmental poisons and antibiotics. The gut microbiota is an important component of the host microbiota and has been proven to be involved in regulating spermatogenesis, but the molecular mechanism is still unclear. A male mouse model with gut microbiota depletion/dysbiosis was constructed by adding combined antibiotics to free drinking water, and reproductive parameters such as epididymal sperm count, testicular weight and paraffin sections were measured. Testicular transcriptomic and serum metabolomic analyses were performed to reveal the molecular mechanism of reproductive dysfunction induced by gut microbiota dysbiosis in male mice.This study confirms that antibiotic induced depletion of gut microbiota reduces sperm count in the epididymis and reduces germ cells in the seminiferous tubules in male mice. Further study showed that exosomes isolated from microbiota-depleted mice led to abnormally high levels of retinoic acid and decrease in the number of germ cells in the seminiferous tubules and sperm in the epididymis. Finally, abnormally high levels of retinoic acid was confirmed to disrupted meiotic processes, resulting in spermatogenesis disorders. This study proposed the concept of the gut microbiota-exosome-retinoic acid-testicular axis and demonstrated that depletion of the gut microbiota caused changes in the function of exosomes, which led to abnormal retinoic acid metabolism in the testis, thereby impairing meiosis and spermatogenesis processes.

Gut microbial metabolism in ferroptosis and colorectal cancer

Ferroptosis is programmed cell death induced by iron-driven lipid peroxidation. Numerous studies have shown that ferroptosis is implicated in the progression of colorectal cancer (CRC) and has emerged as a promising strategy to combat therapy-resistant CRC. While the intrinsic antiferroptotic and proferroptotic pathways in CRC cells have been well characterized, extrinsic metabolism pathways regulating ferroptosis in CRC pathogenesis remain less understood. Emerging evidence shows that gut microbial metabolism is tightly correlated with the progression of CRC. This review provides an overview of gut microbial metabolism and discusses how these metabolites derived from intestinal microflora contribute to cancer plasticity through ferroptosis. Targeting gut microbe-mediated ferroptosis is a potential approach for CRC treatment.

Gut-Derived Exosomes Mediate the Microbiota Dysbiosis-Induced Spermatogenesis Impairment by Targeting Meioc in Mice

Diseases like obesity and intestinal inflammation diseases are accompanied by dysbiosis of the gut microbiota (DSGM), which leads to various complications, including systemic metabolic disorders. DSGM reportedly impairs the fertility of male mice; however, the regulatory mechanism is unclear. Exosomes are molecular mediators of intercellular communication, but the regulation of spermatogenesis by non-reproductive tissue-originated exosomes remains unknown. The present study shows that DSGM altered the miRNA expression profile of mouse circulating exosomes and impaired spermatogenesis. Moreover, the single-cell sequencing results indicate that circulating exosomes from mice with DSGM impaired spermatogenesis, while circulating exosomes from wild mice improved spermatogenesis by promoting meiosis. Further study demonstrates that DSGM leads to abnormal upregulation of miR-211-5p in gut-derived circulating exosomes, which inhibited the expression of meiosis-specific with coiled-coil domain (Meioc) in the testes and impaired spermatogenesis by disturbing meiosis process. In summary, this study defines the important role of gut-derived exosomes in connecting the "gut-testis" axis.

Early life microbiome influences on development of the mucosal innate immune system

The gut microbiota is well known to possess immunomodulatory capacities, influencing a multitude of cellular signalling pathways to maintain host homeostasis. Although the formation of the immune system initiates before birth in a sterile environment, an emerging body of literature indicates that the neonatal immune system is influenced by a first wave of external stimuli that includes signals from the maternal microbiota. A second wave of stimulus begins after birth and must be tightly regulated during the neonatal period when colonization of the host occurs concomitantly with the maturation of the immune system, requiring a fine adjustment between establishing tolerance towards the commensal microbiota and preserving inflammatory responses against pathogenic invaders. Besides integrating cues from commensal microbes, the neonatal immune system must also regulate responses triggered by other environmental signals, such as dietary antigens, which become more complex with the introduction of solid food during the weaning period. This "window of opportunity" in early life is thought to be crucial for the proper development of the immune system, setting the tone of subsequent immune responses in adulthood and modulating the risk of developing chronic and metabolic inflammatory diseases. Here we review the importance of host-microbiota interactions for the development and maturation of the immune system, particularly in the early-life period, highlighting the known mechanisms involved in such communication. This discussion is focused on recent data demonstrating microbiota-mediated education of innate immune cells and its role in the development of lymphoid tissues.

Epithelial regulation of microbiota-immune cell dynamics

The mammalian gastrointestinal tract hosts a diverse community of trillions of microorganisms, collectively termed the microbiota, which play a fundamental role in regulating tissue physiology and immunity. Recent studies have sought to dissect the cellular and molecular mechanisms mediating communication between the microbiota and host immune system. Epithelial cells line the intestine and form an initial barrier separating the microbiota from underlying immune cells, and disruption of epithelial function has been associated with various conditions ranging from infection to inflammatory bowel diseases and cancer. From several studies, it is now clear that epithelial cells integrate signals from commensal microbes. Importantly, these non-hematopoietic cells also direct regulatory mechanisms that instruct the recruitment and function of microbiota-sensitive immune cells. In this review, we discuss the central role that has emerged for epithelial cells in orchestrating intestinal immunity and highlight epithelial pathways through which the microbiota can calibrate tissue-intrinsic immune responses.

Nutrition during pregnancy: Influence on the gut microbiome and fetal development

Pregnancy is a finely tuned process, with the health and well-being of the developing fetus determined by the metabolic status and dietary intake of the mother. The maternal gut microbiome is remodeled during pregnancy, and this, coupled with the maternal nutrient intake during gestation shapes the production of metabolites that can cross the placenta and affect fetal development. As posited by the Developmental Origins of Health and Disease Hypothesis, such environmental influences can have major effects on the developing organ systems. When occurring at particularly sensitive gestational time points, these developmental programming events can have long lasting effects on offspring adaptation to the postnatal environment, and major health implications later in life. This review will summarize current knowledge on how pregnancy and maternal dietary intake intrinsically and extrinsically modify maternal gut microbiota composition and metabolite production. Further, we will assess how these factors shape the fetal landscape and ultimately contribute to offspring health. DOHaD, fetal development, metabolites, microbiome, nutrition, pregnancy, short-chain fatty acids.

Lactobacillus Intestinalis Primes Epithelial Cells to Suppress Colitis-Related Th17 Response by Host-Microbe Retinoic Acid Biosynthesis

Gut microbiome is integral to the pathogenesis of ulcerative colitis. A novel probiotic Lactobacillus intestinalis (L. intestinalis) exerts a protective effect against dextran sodium sulfate-induced colitis in mice. Based on flow cytometry, colitis-associated Th17 cells are the target of L. intestinalis, which is supported by the lack of protective effects of L. intestinalis in T cell-null Rag1-/- mice or upon anti-IL-17-A antibody-treated mice. Although L. intestinalis exerts no direct effect on T cell differentiation, it decreases C/EBPA-driven gut epithelial SAA1 and SAA2 production, which in turn impairs Th17 cell differentiation. Cometabolism of L. intestinalis ALDH and host ALDH1A2 contributed to elevated biosynthesis of retinoic acid (RA), which accounts for the anti-colitis effect in RAR-α -mediated way. In a cohort of ulcerative colitis patients, it is observed that fecal abundance of L. intestinalis is negatively associated with the C/EBPA-SAA1/2-Th17 axis. Finally, L. intestinalis has a synergistic effect with mesalazine in alleviating murine colitis. In conclusion, L. intestinalis and associated metabolites, RA, have potential therapeutic effects for suppressing colonic inflammation by modulating the crosstalk between intestinal epithelia and immunity.

Bifidobacterium mechanisms of immune modulation and tolerance

Bifidobacterium is a widely distributed commensal bacterial genus that displays beneficial pro-homeostatic and anti-inflammatory immunomodulatory properties. Depletion or absence of Bifidobacterium in humans and model organisms is associated with autoimmune responses and impaired immune homeostasis. At the cellular level, Bifidobacterium upregulates suppressive regulatory T cells, maintains intestinal barrier function, modulates dendritic cell and macrophage activity, and dampens intestinal Th2 and Th17 programs. While there has been a large volume of literature characterizing the probiotic properties of various Bifidobacterial species, the likely multifactorial mechanisms underlying these effects remain elusive, in particular, its immune tolerogenic effect. However, recent work has shed light on Bifidobacterium surface structural polysaccharide and protein elements, as well as its metabolic products, as commensal mediators of immune homeostasis. This review aims to discuss several mechanisms Bifidobacterium utilizes for immune modulation as well as their indirect impact on the regulation of gut microbiome structure and function, from structural molecules to produced metabolites. These mechanisms are pertinent to an increasingly networked understanding of immune tolerance and homeostasis in health and disease.

Short-Chain Fatty Acids Alleviate Vancomycin-Caused Humoral Immunity Attenuation in Rabies-Vaccinated Mice by Promoting the Generation of Plasma Cells via Akt-mTOR Pathway

Mounting evidence suggests that gut microbial composition and its metabolites, including short-chain fatty acids (SCFAs), have beneficial effects in regulating host immunogenicity to vaccines. However, it remains unknown whether and how SCFAs improve the immunogenicity of the rabies vaccine. In this study, we investigated the effect of SCFAs on the immune response to rabies vaccine in vancomycin (Vanco)-treated mice and found that oral gavage with butyrate-producing bacteria (C. butyricum) and butyrate supplementation elevated RABV-specific IgM, IgG, and virus-neutralizing antibodies (VNAs) in Vanco-treated mice. Supplementation with butyrate expanded antigen-specific CD4+ T cells and IFN-γ-secreting cells, augmented germinal center (GC) B cell recruitment, promoted plasma cells (PCs) and RABV-specific antibody-secreting cells (ASCs) generation in Vanco-treated mice. Mechanistically, butyrate enhanced mitochondrial function and activated the Akt-mTOR pathway in primary B cells isolated from Vanco-treated mice, ultimately promoting B lymphocyte-induced maturation protein-1 (Blimp-1) expression and CD138+ PCs generation. These results highlight the important role of butyrate in alleviating Vanco-caused humoral immunity attenuation in rabies-vaccinated mice and maintaining host immune homeostasis. IMPORTANCE The gut microbiome plays many crucial roles in the maintenance of immune homeostasis. Alteration of the gut microbiome and metabolites has been shown to impact vaccine efficacy. SCFAs can act as an energy source for B-cells, thereby promoting both mucosal and systemic immunity in the host by inhibiting HDACs and activation of GPR receptors. This study investigates the impact of orally administered butyrate, an SCFA, on the immunogenicity of rabies vaccines in Vanco-treated mice. The results showed that butyrate ameliorated humoral immunity by facilitating the generation of plasma cells via the Akt-mTOR in Vanco-treated mice. These findings unveil the impact of SCFAs on the immune response of the rabies vaccine and confirm the crucial role of butyrate in regulating immunogenicity to rabies vaccines in antibiotic-treated mice. This study provides a fresh insight into the relationship of microbial metabolites and rabies vaccination.

Potent Intestinal Mucosal Barrier Enhancement of Nostoc commune Vaucher Polysaccharide Supplementation Ameliorates Acute Ulcerative Colitis in Mice Mediated by Gut Microbiota

Ulcerative colitis (UC) is evolving into a global burden with a substantially increasing incidence in developing countries. It is characterized by inflammation confined to mucosa and is recognized as an intestinal barrier disease. The intestinal microbiota plays a crucial role in UC pathogenesis. N. commune has long been appreciated as a healthy food and supplement worldwide and polysaccharides account for 60%. Here, we examined the amelioration of N. commune polysaccharides against acute colitis in mice induced by DSS and assessed the mediating role of gut microbiota. An integrated analysis of microbiome, metabolomics, and transcriptomics fully elaborated it markedly enhanced intestinal mucosal barrier function, including: increasing the relative abundance of Akkermansia muciniphila, uncultured_bacterium_g__norank_f__Muribaculaceae, and unclassified_g__norank_f__norank_o__Clostridia_UCG-014; decreasing microbiota-derived phosphatidylcholines and thromboxane 2 levels mapped to arachidonic acid metabolism; improving mucin2 biosynthesis and secretion; enhancing ZO-1 and occludin expression; reducing neutrophil infiltration; regulating the level of colitis-related inflammatory cytokines; involving inflammation and immune function-associated signaling pathways. Further, the mediation effect of gut microbiota was evaluated by administering a cocktail of antibiotics. In conclusion, our results demonstrated that N. commune polysaccharides predominantly reinforced the gut microbiota-mediated intestinal mucosal barrier to confer protection against UC and exhibited dramatic prebiotic-like functions, providing an alternative or complementary treatment for UC.

Assessing the Interactions between Zinc and Vitamin A on Intestinal Functionality, Morphology, and the Microbiome In Vivo (Gallus gallus)

Dietary deficiencies in zinc (Zn) and vitamin A (VA) are among the leading micronutrient deficiencies globally and previous research has proposed a notable interaction between Zn and VA physiological status. This study aimed to assess the effects of zinc and vitamin A (isolated and combined) on intestinal functionality and morphology, and the gut microbiome (Gallus gallus). The study included nine treatment groups (n~11)-no-injection (NI); H₂O; 0.5% oil; normal zinc (40 mg/kg ZnSO₄) (ZN); low zinc (20 mg/kg) (ZL); normal retinoid (1500 IU/kg retinyl palmitate) (RN); low retinoid (100 IU/kg) (RL); normal zinc and retinoid (40 mg/kg; 1500 IU/kg) (ZNRN); low zinc and retinoid (ZLRL) (20 mg/kg; 100 IU/kg). Samples were injected into the amniotic fluid of the fertile broiler eggs. Tissue samples were collected upon hatch to target biomarkers. ZLRL reduced ZIP4 gene expression and upregulated ZnT1 gene expression (p < 0.05). Duodenal surface area increased the greatest in RL compared to RN (p < 0.01), and ZLRL compared to ZNRN (p < 0.05). All nutrient treatments yielded shorter crypt depths (p < 0.01). Compared to the oil control, ZLRL and ZNRN reduced (p < 0.05) the cecal abundance of Bifidobacterium and Clostridium genera (p < 0.05). These results suggest a potentially improved intestinal epithelium proceeding with Zn and VA intra-amniotic administration. Intestinal functionality and gut bacteria were modulated. Further research should characterize long-term responses and the microbiome profile.

Atractylodes macrocephala Koidz. volatile oil relieves acute ulcerative colitis via regulating gut microbiota and gut microbiota metabolism

Background

Atractylodes macrocephala Koidz. (AM) is a functional food with strong ant-colitis activity. AM volatile oil (AVO) is the main active ingredient of AM. However, no study has investigated the improvement effect of AVO on ulcerative colitis (UC) and the bioactivity mechanism also remains unknown. Here, we investigated whether AVO has ameliorative activity on acute colitis mice and its mechanism from the perspective of gut microbiota.

Methods

Acute UC was induced in C57BL/6 mice by dextran sulfate sodium and treated with the AVO. Body weight, colon length, colon tissue pathology, and so on were assessed. The gut microbiota composition was profiled using 16s rRNA sequencing and global metabolomic profiling of the feces was performed. The results showed that AVO can alleviate bloody diarrhea, colon damage, and colon inflammation in colitis mice. In addition, AVO decreased potentially harmful bacteria (Turicibacter, Parasutterella, and Erysipelatoclostridium) and enriched potentially beneficial bacteria (Enterorhabdus, Parvibacter, and Akkermansia). Metabolomics disclosed that AVO altered gut microbiota metabolism by regulating 56 gut microbiota metabolites involved in 102 KEGG pathways. Among these KEGG pathways, many metabolism pathways play an important role in maintaining intestine homeostasis, such as amino acid metabolism (especially tryptophan metabolism), bile acids metabolism, and retinol metabolism.

Conclusion

In conclusion, our study indicated that AVO can be expected as novel prebiotics to treat ulcerative colitis, and modulating the composition and metabolism of gut microbiota may be its pharmacological mechanism.

Vitamin A deficiency and vitamin A supplementation affect innate and T cell immune responses to rotavirus A infection in a conventional sow model

Rotavirus A (RVA) causes ~200,000 diarrheal deaths annually in children <5yrs, mostly in low- and middle-income countries. Risk factors include nutritional status, social factors, breastfeeding status, and immunodeficiency. We evaluated the effects of vitamin A (VA) deficiency/VA supplementation and RVA exposure (anamnestic) on innate and T cell immune responses in RVA seropositive pregnant and lactating sows and passive protection of their piglets post-RVA challenge. Sows were fed VA deficient (VAD) or sufficient (VAS) diets starting at gestation day (GD)30. A subset of VAD sows received VA supplementation from GD|76 (30,000IU/day, VAD+VA). Sows (6 groups) were inoculated with porcine RVA G5P[7] (OSU strain) or Minimal Essential Medium (mock) at GD~90: VAD+RVA; VAS+RVA; VAD+VA+RVA; VAD-mock; VAS-mock; and VAD+VA-mock. Blood, milk, and gut-associated tissues were collected from sows at several time points to examine innate [natural killer (NK), dendritic (DC) cells], T cell responses and changes in genes involved in the gut-mammary gland (MG)-immunological axis trafficking. Clinical signs of RVA were evaluated post inoculation of sows and post-challenge of piglets. We observed decreased frequencies of NK cells, total and MHCII+ plasmacytoid DCs, conventional DCs, CD103+ DCs and CD4+/CD8+ and T regulatory cells (Tregs) and NK cell activity in VAD+RVA sows. Polymeric Ig receptor and retinoic acid receptor alpha (RARα) genes were downregulated in mesenteric lymph nodes and ileum of VAD+RVA sows. Interestingly, RVA-specific IFN-γ producing CD4+/CD8+ T cells were increased in VAD-Mock sows, coinciding with increased IL-22 suggesting inflammation in these sows. VA supplementation to VAD+RVA sows restored frequencies of NK cells and pDCs, and NK activity, but not tissue cDCs and blood Tregs. In conclusion, similar to our recent observations of decreased B cell responses in VAD sows that led to decreased passive immune protection of their piglets, VAD impaired innate and T cell responses in sows, while VA supplementation to VAD sows restored some, but not all responses. Our data reiterate the importance of maintaining adequate VA levels and RVA immunization in pregnant and lactating mothers to achieve optimal immune responses, efficient function of the gut-MG-immune cell-axis and to improve passive protection of their piglets.

Microbiota-Derived Natural Products Targeting Cancer Stem Cells: Inside the Gut Pharma Factory

Cancer stem cells (CSCs) have drawn much attention as important tumour-initiating cells that may also be crucial for recurrence after chemotherapy. Although the activity of CSCs in various forms of cancer is complex and yet to be fully elucidated, opportunities for therapies targeting CSCs exist. CSCs are molecularly distinct from bulk tumour cells, so they can be targeted by exploiting their signature molecular pathways. Inhibiting stemness has the potential to reduce the risk posed by CSCs by limiting or eliminating their capacity for tumorigenesis, proliferation, metastasis, and recurrence. Here, we briefly described the role of CSCs in tumour biology, the mechanisms involved in CSC therapy resistance, and the role of the gut microbiota in cancer development and treatment, to then review and discuss the current advances in the discovery of microbiota-derived natural compounds targeting CSCs. Collectively, our overview suggests that dietary intervention, toward the production of those identified microbial metabolites capable of suppressing CSC properties, is a promising approach to support standard chemotherapy.

The microbiome as a major function of the gastrointestinal tract and its implication in micronutrient metabolism and chronic diseases

The composition and function of microbes harbored in the human gastrointestinal lumen have been underestimated for centuries because of the underdevelopment of nucleotide sequencing techniques and the lack of humanized gnotobiotic models. Now, we appreciate that the gut microbiome is an integral part of the human body and exerts considerable roles in host health and diseases. Dietary factors can induce changes in the microbial community composition, metabolism, and function, thereby altering the host immune response, and consequently, may influence disease risks. An imbalance of gut microbiome homeostasis (i.e., dysbiosis) has been linked to several chronic diseases, such as inflammatory bowel diseases, obesity, and diabetes. Remarkable progress has recently been made in better understanding the extent to which the influence of the diet-microbiota interaction on host health outcomes in both animal models and human participants. However, the exact causality of the gut microbiome on the development of diseases is still controversial. In this review, we will briefly describe the general structure and function of the intestine and the process of nutrient absorption in humans. This is followed by a summarization of the recent updates on interactions between gut microbiota and individual micronutrients, including carotenoids, vitamin A, vitamin D, vitamin C, folate, iron, and zinc. In the opinion of the authors, these nutrients were identified as representative of vitamins and minerals with sufficient research on their roles in the microbiome. The host responses to the gut microbiome will also be discussed. Future direction in microbiome research, for example, precision microbiome, will be proposed.

Immune Impairment Associated with Vitamin A Deficiency: Insights from Clinical Studies and Animal Model Research

Vitamin A (VA) is critical for many biological processes, including embryonic development, hormone production and function, the maintenance and modulation of immunity, and the homeostasis of epithelium and mucosa. Specifically, VA affects cell integrity, cytokine production, innate immune cell activation, antigen presentation, and lymphocyte trafficking to mucosal surfaces. VA also has been reported to influence the gut microbiota composition and diversity. Consequently, VA deficiency (VAD) results in the imbalanced production of inflammatory and immunomodulatory cytokines, intestinal inflammation, weakened mucosal barrier functions, reduced reactive oxygen species (ROS) and disruption of the gut microbiome. Although VAD is primarily known to cause xerophthalmia, its role in the impairment of anti-infectious defense mechanisms is less defined. Infectious diseases lead to temporary anorexia and lower dietary intake; furthermore, they adversely affect VA status by interfering with VA absorption, utilization and excretion. Thus, there is a tri-directional relationship between VAD, immune response and infections, as VAD affects immune response and predisposes the host to infection, and infection decreases the intestinal absorption of the VA, thereby contributing to secondary VAD development. This has been demonstrated using nutritional and clinical studies, radiotracer studies and knockout animal models. An in-depth understanding of the relationship between VAD, immune response, gut microbiota and infections is critical for optimizing vaccine efficacy and the development of effective immunization programs for countries with high prevalence of VAD. Therefore, in this review, we have comprehensively summarized the existing knowledge regarding VAD impacts on immune responses to infections and post vaccination. We have detailed pathological conditions associated with clinical and subclinical VAD, gut microbiome adaptation to VAD and VAD effects on the immune responses to infection and vaccines.

How the gut microbiota helps keep us vitaminized

Balanced intestinal retinoic acid concentrations are essential to maintain immune homeostasis in the gut. In this issue of Cell Host & Microbe, Bonakdar et al, sheds light on metabolic host-microbiota interactions and elegantly links diet, microbiota and host functions at the molecular level in the context of vitamin A metabolism.