Gut commensal bacteria, Paneth cells and their relations to radiation enteropathy

Sex Differences of Radiation Damage in High-Fat-Diet-Fed Mice and the Regulatory Effect of Melatonin

The consumption of a high-fat diet (HFD) and exposure to ionizing radiation (IR) are closely associated with many diseases. To evaluate the interaction between HFDs and IR-induced injury, we gave mice whole abdominal irradiation (WAI) to examine the extent of intestinal injury under different dietary conditions. Melatonin (MLT) is a free radical scavenger that effectively prevents hematopoietic, immune, and gastrointestinal damage induced by IR. However, its effects on WAI-induced intestinal injury in HFD-fed mice remain unclear. We demonstrated that MLT can promote intestinal structural repair following WAI and enhance the regeneration capacity of Lgr5⁺ intestinal stem cells. In addition, we investigated the effects of radiation damage on sexual dimorphism in HFD-fed mice. The results showed that the degree of IR-induced intestinal injury was more severe in the HFD-fed female mice. MLT preserved the intestinal microbiota composition of HFD-fed mice and increased the abundance of Bacteroides and Proteobacteria in male and female mice, respectively. In conclusion, MLT may reduce the negative effects of HFD and IR, thereby providing assistance in preserving the structure and function of the intestine.

FABP4 in Paneth cells regulates antimicrobial protein expression to reprogram gut microbiota

Antimicrobial proteins possess a broad spectrum of bactericidal activity and play an important role in shaping the composition of gut microbiota, which is related to multiple diseases such as metabolic syndrome. However, it is incompletely known for the regulation of defensin expression in the gut Paneth cells. Here, we found that FABP4 in the Paneth cells of gut epithelial cells and organoids can downregulate the expression of defensins. FABP4^fl/flpvillin^CreT mice were highly resistance to Salmonella Typhimurium (S.T) infection and had increased bactericidal ability to pathogens. The FABP4-mediated downregulation of defensins is through degrading PPARγ after K48 ubiquitination. We also demonstrate that high-fat diet (HFD)-mediated downregulation of defensins is through inducing a robust FABP4 in Paneth cells. Firmicutes/Bacteroidetes (F/B) ratio in FABP4^fl/flpvillin^CreT mice is lower than control mice, which is opposite to that in mice fed HFD, indicating that FABP4 in the Paneth cells could reprogram gut microbiota. Interestingly, FABP4-mediated downregulation of defensins in Paneth cells not only happens in mice but also in human. A better understanding of the regulation of defensins, especially HFD-mediated downregulation of defensin in Paneth cells will provide insights into factor(s) underlying modern diseases.Abbreviations: FABP4: Fatty acid binding protein 4; S. T: Salmonella Typhimurium; HFD: High-fat diet; Defa: α-defensin; 930 HD5: Human α-defensin 5; HD6: Human α-defensin 6; F/B: Firmicutes/Bacteroidetes; SFB: Segmental filamentous bacteria; AMPs: Antimicrobial peptides; PPARγ: Peroxisome proliferator-activated receptor γ; P-PPAR: Phosphorylated PPAR; Dhx15: DEAD-box helicase 15; 935 EGF: Epidermal growth factor; ENR: Noggin and R-spondin 1; CFU: Colony forming unit; Lyz1: Lysozyme 1; Saa1: Serum amyoid A 1; Pla2g2a: Phospholipase A2, group IIA; MMP-7: Matrix metalloproteinase; AU-PAGE: Acid-urea polyacrylamide gel electrophoresis; PA: Palmitic 940 acid; GPR40: G-protein-coupled receptor; GF: Germ-free; EGF: Epidermal growth factor; LP: Lamina propria; KO: Knock out; WT: Wild-type.

The Protective Effects of Sour Orange (Citrus aurantium L.) Polymethoxyflavones on Mice Irradiation-Induced Intestinal Injury

Sour orange (Citrus aurantium L.) is one of the biological sources of polymethoxyflavones (PMFs), which are often used to deal with gastrointestinal diseases. The intestine is highly sensitive to irradiation damage. However, limited certain cures have been released for irradiation-induced gastrointestinal injury, and the potentials of sour orange PMFs as radio-resistance agents have not been fully discussed yet. The present study aims to (1) investigate the PMF components in 12 sour orange cultivars, (2) determine the protective effects of PMFs on irradiation-induced intestinal injury by treating mice that received 12 Gy abdominal irradiation with different doses of PMFs and observing the changes in organ indexes and pathological sections and (3) test cytotoxicity of PMFs by CCK-8 method. The results showed that sour orange PMFs appeared to have high intraspecies similarity. Besides, PMFs protected mice from irradiation-induced injury by alleviating body weight loss, reliving organ index changing and maintaining the intestinal structure. Finally, IC₅₀ concentrations to cell line CCD 841 CoN of PMFs and nobiletin were calculated as 42.23 μg/mL and 51.58 μg/mL, respectively. Our study uncovered PMF contents in 12 sour orange materials and determined the protective effects on irradiation-induced intestinal injuries, providing guidance for the utilization of sour orange resources.

Bacterial dysbiosis incites Th17 cell revolt in irradiated gut

Th17 cells are critical members in mediating immune responses of adaptive immunity. In humans and mice, gut is a main site where Th17 cells are resided, and Th17 cell polarization also occurs in the gut. This process can be mediated by many factors, such as commensal bacteria, dendritic cells and cytokines, such as TGF-β and IL-6. Physiologically, polarized Th17 cells function in anti-infection and maintaining the integrity of intestinal epithelium. However, Th17 cells are plastic. For example, they will become pro-inflammatory cells if being exposed to IL-23. The pathogenic roles of Th17 cells have been well documented in inflammatory bowel disease. Besides, Th17 cells can accumulate in irradiated gut as well. Critically, radiation enteritis and inflammatory bowel disease present several similarities in disease pathology and pathophysiology. Herein, bacterial dysbiosis highly correlates with the pathogenicity of Th17 cells in inflammatory bowel disease. To our knowledge, radiation serves as a factor in inducing bacterial dysbiosis. Using this action, can Th17 cells be incited to promote inflammation in irradiated gut? In this review, we will sequentially introduce polarization of Th17 cells at steady state, radiation-induced Th17 accumulation in the gut, and advances in the management of radiation enteritis by using pharmacological therapy for bacterial dysbiosis.