Suppression of radiation-induced DNA double-strand break repair by MyD88 is accompanied by apoptosis and crypt loss in mouse colon

Radioprotective potential of probiotics against gastrointestinal and neuronal toxicity: a preclinical study

PURPOSE

Radiotherapy is a critical component of cancer treatment, along with surgery and chemotherapy. Approximately, 90% of cancer patients undergoing pelvic radiotherapy show gastrointestinal (GI) toxicity, including bloody diarrhea, and gastritis, most of which are associated with gut dysbiosis. In addition to the direct effect of radiation on the brain, pelvic irradiation can alter the gut microbiome, leading to inflammation and breakdown of the gut-blood barrier. This allows toxins and bacteria to enter the bloodstream and reach the brain. Probiotics have been proven to prevent GI toxicity by producing short-chain fatty acids and exopolysaccharides beneficial for protecting mucosal integrity and oxidative stress reduction in the intestine and also shown to be beneficial in brain health. Microbiota plays a significant role in maintaining gut and brain health, so it is important to study whether bacterial supplementation will help in maintaining the gut and brain structure after radiation exposure.

METHODS

In the present study, male C57BL/6 mice were divided into control, radiation, probiotics, and probiotics + radiation groups. On the 7th day, animals in the radiation and probiotics + radiation groups received a single dose of 4 Gy to  whole-body. Posttreatment, mice were sacrificed, and the intestine and brain tissues were excised for histological analysis to assess GI and neuronal damage.

RESULTS

Radiation-induced damage to the villi height and mucosal thickness was mitigated by the probiotic treatment significantly (p < 0.01). Further, radiation-induced pyknotic cell numbers in the DG, CA2, and CA3 areas were substantially reduced with bacterial supplementation (p < 0.001). Similarly, probiotics reduced neuronal inflammation induced by radiation in the cortex, CA2, and DG region (p < 0.01). Altogether, the probiotics treatment helps mitigate radiation-induced intestinal and neuronal damage.

CONCLUSION

In conclusion, the probiotic formulation could attenuate the number of pyknotic cells in the hippocampal brain region and decrease neuroinflammation by reducing the number of microglial cells.

Interplay Between the Intestinal Microbiota and Acute Graft-Versus-Host Disease: Experimental Evidence and Clinical Significance

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a potentially curative therapy for many hematological disorders and autoimmune diseases, but acute graft-versus-host disease (aGVHD) has remained a major obstacle that limits allo-HSCT and exhibits a daunting mortality rate. The gastrointestinal system is among the most common sites affected by aGVHD. Experimental advances in the field of intestinal microbiota research enhanced our understanding - not only of the quantity and diversity of intestinal microbiota - but also their association with homeostasis of the immune system and disease pathogenesis, including that of aGVHD. Meanwhile, ever-growing clinical evidence suggest that the intestinal microbiota is dysregulated in patients who develop aGVHD and that the imbalance may affect clinical outcomes, indicating a potential predictive role for microbiota dysregulation in aGVHD severity and prognosis. The current animal and human studies investigating the intestinal microbiota in aGVHD and the understanding of the influence and management of the microbiota in the clinic are reviewed herein. Taken together, monitoring and remodeling the intestinal microecology following allo-HSCT may provide us with promising avenues for diagnosing, preventing or treating aGVHD in the clinic.

Molecular Mechanisms of the Action of Myricetin in Cancer

Natural compounds, such as paclitaxel and camptothecin, have great effects on the treatment of tumors. Such natural chemicals often achieve anti-tumor effects through a variety of mechanisms. Therefore, it is of great significance to conduct further studies on the anticancer mechanism of natural anticancer agents to lay a solid foundation for the development of new drugs. Myricetin, originally isolated from Myrica nagi, is a natural pigment of flavonoids that can inhibit the growth of cancer cells (such as liver cancer, rectal cancer, skin cancer and lung cancer, etc.). It can regulate many intracellular activities (such as anti-inflammatory and blood lipids regulation) and can even be bacteriostatic. The purpose of this paper is to outline the molecular pathways of the anticancer effects of myricetin, including the effect on cancer cell death, proliferation, angiogenesis, metastasis and cell signaling pathway.

Hydrogen-water ameliorates radiation-induced gastrointestinal toxicity via MyD88's effects on the gut microbiota

Although radiation therapy is a cornerstone of modern management of malignancies, various side effects are inevitably linked to abdominal and pelvic cancer after radiotherapy. Radiation-mediated gastrointestinal (GI) toxicity impairs the life quality of cancer survivors and even shortens their lifespan. Hydrogen has been shown to protect against tissue injuries caused by oxidative stress and excessive inflammation, but its effect on radiation-induced intestinal injury was previously unknown. In the present study, we found that oral gavage with hydrogen-water increased the survival rate and body weight of mice exposed to total abdominal irradiation (TAI); oral gavage with hydrogen-water was also associated with an improvement in GI tract function and the epithelial integrity of the small intestine. Mechanistically, microarray analysis revealed that hydrogen-water administration upregulated miR-1968-5p levels, thus resulting in parallel downregulation of MyD88 expression in the small intestine after TAI exposure. Additionally, high-throughput sequencing showed that hydrogen-water oral gavage resulted in retention of the TAI-shifted intestinal bacterial composition in mice. Collectively, our findings suggested that hydrogen-water might be used as a potential therapeutic to alleviate intestinal injury induced by radiotherapy for abdominal and pelvic cancer in preclinical settings.

Exploring gene expression changes in the amphioxus gill after poly(I:C) challenge using digital expression profiling

Amphioxus, a cephalochordate, is a key model animal for studying the evolution of vertebrate immunity. Recently, studies have revealed that microRNA (miRNA) expression profiles change significantly in the amphioxus gill after immune stimulation, but it remains largely unknown how gene expression responds to immune stress. Elucidating gene expression changes in the amphioxus gill will provide a deeper understanding of the evolution of gill immunity in vertebrates. Here, we used high-throughput RNA sequencing technology (RNA-seq) to conduct tag-based digital gene expression profiling (DGE) analyses of the gills of control Branchiostoma belcheri and of those exposed to the viral mimic, poly(I:C) (pIC). Six libraries were created for the control and treatment groups including three biological replicates per group. A total of 1999 differently expressed genes (DEGs) were obtained, with 571 and 1428 DEGs showing up- or down-regulation, respectively, in the treatment group. Enrichment analysis of gene ontology (GO) terms and pathways revealed that the DEGs were primarily related to immune and defense response, apoptosis, human disease, cancer, protein metabolism, enzyme activity, and regulatory processes. In addition, eight DEGs were randomly selected to validate the RNA-seq data using real-time quantitative PCR (qRT-PCR), and the results confirmed the accuracy of the RNA-seq approach. Next, we screened eight key responding genes to examine the dynamic changes in expression levels at different time points in more detail. The results indicated that expressions of TRADD, MARCH, RNF31, NF-κb, CYP450, TNFRSF6B, IFI and LECT1 were induced to participate in the antiviral response against pIC. This study provides a valuable resource for understanding the role of the amphioxus gill in antiviral immunity and the evolution of gill immunity in vertebrates.

The intestinal microbiota in allogeneic hematopoietic cell transplant and graft-versus-host disease

Hematopoietic cell transplantation (HCT) is a critical treatment of patients with high-risk hematopoietic malignancies, hematological deficiencies, and other immune diseases. In allogeneic HCT (allo-HCT), donor-derived T cells recognize host tissues as foreign, causing graft-versus-host disease (GVHD) which is a main contributor to morbidity and mortality. The intestine is one of the organs most severely affected by GVHD and research has recently highlighted the importance of bacteria, particularly the gut microbiota, in HCT outcome and in GVHD development. Loss of intestinal bacterial diversity is common during the course of HCT and is associated with GVHD development and treatment with broad-spectrum antibiotics. Loss of intestinal diversity and outgrowth of opportunistic pathogens belonging to the phylum Proteobacteria and Enterococcus genus have also been linked to increased treatment-related mortality including GVHD, infections, and organ failure after allo-HCT. Experimental studies in allo-HCT animal models have shown some promising results for prebiotic and probiotic strategies as prophylaxis or treatment of GVHD. Continuous research will be important to define the relation of cause and effect for these associations between microbiota features and HCT outcomes. Importantly, studies focused on geographic and cultural differences in intestinal microbiota are necessary to define applicability of new strategies targeting the intestinal microbiota.

Sam68/KHDRBS1-dependent NF-κB activation confers radioprotection to the colon epithelium in γ-irradiated mice

Previously we reported that Src-associated-substrate-during-mitosis-of-68kDa (Sam68/KHDRBS1) is pivotal for DNA damage-stimulated NF-κB transactivation of anti-apoptotic genes (Fu et al., 2016). Here we show that Sam68 is critical for genotoxic stress-induced NF-κB activation in the γ-irradiated colon and animal and that Sam68-dependent NF-κB activation provides radioprotection to colon epithelium in vivo. Sam68 deletion diminishes γ-irradiation-triggered PAR synthesis and NF-κB activation in colon epithelial cells (CECs), thus hampering the expression of anti-apoptotic molecules in situ and facilitating CECs to undergo apoptosis in mice post whole-body γ-irradiation (WBIR). Sam68 knockout mice suffer more severe damage in the colon and succumb more rapidly from acute radiotoxicity than the control mice following WBIR. Our results underscore the critical role of Sam68 in orchestrating genotoxic stress-initiated NF-κB activation signaling in the colon tissue and whole animal and reveal the pathophysiological relevance of Sam68-dependent NF-κB activation in colonic cell survival and recovery from extrinsic DNA damage.

DOI:http://dx.doi.org/10.7554/eLife.21957.001

Radiation takes its Toll

The ability to recognize and respond to universal molecular patterns on invading microorganisms allows our immune system to stay on high alert, sensing danger to our self-integrity. Our own damaged cells and tissues in pathological situations activate similar warning systems as microbes. In this way, the body is able to mount a response that is appropriate to the danger. Toll-like receptors are at the heart of this pattern recognition system that initiates innate pro-oxidant, pro-inflammatory signaling cascades and ultimately bridges recognition of danger to adaptive immunity. The acute inflammatory lesions that are formed segue into resolution of inflammation, repair and healing or, more dysfunctionally, into chronic inflammation, autoimmunity, excessive tissue damage and carcinogenesis. Redox is at the nexus of this decision making process and is the point at which ionizing radiation initially intercepts to trigger similar responses to self-damage. In this review we discuss our current understanding of how radiation-damaged cells interact with Toll-like receptors and how the immune systems interprets these radiation-induced danger signals in the context of whole-body exposures and during local tumor irradiation.

Blockade of TLR3 protects mice from lethal radiation-induced gastrointestinal syndrome

High-dose ionizing radiation induces severe DNA damage in the epithelial stem cells in small intestinal crypts and causes gastrointestinal syndrome (GIS). Although the tumour suppressor p53 is a primary factor inducing death of crypt cells with DNA damage, its essential role in maintaining genome stability means inhibiting p53 to prevent GIS is not a viable strategy. Here we show that the innate immune receptor Toll-like receptor 3 (TLR3) is critical for the pathogenesis of GIS. Tlr3^−/− mice show substantial resistance to GIS owing to significantly reduced radiation-induced crypt cell death. Despite showing reduced crypt cell death, p53-dependent crypt cell death is not impaired in Tlr3^−/− mice. p53-dependent crypt cell death causes leakage of cellular RNA, which induces extensive cell death via TLR3. An inhibitor of TLR3–RNA binding ameliorates GIS by reducing crypt cell death. Thus, we propose blocking TLR3 activation as a novel approach to treat GIS.

Ionizing radiation damages small intestinal crypt cells, including epithelial stem cells and their progeny. Here the authors show that radiation-induced crypt cell death is amplified by the release of cellular RNA from apoptotic epithelial cells, which then triggers pro-apoptotic TLR3 signalling on neighbouring cells.

TLR4/PKC-mediated tight junction modulation: a clinical marker of chemotherapy-induced gut toxicity?

Chemotherapy-induced gut toxicity is a major clinical and economic burden to oncology practice. The mechanisms responsible for its development are ill defined, hampering the development of therapeutic interventions. In light of newly published research foci and clinical practice guidelines in supportive care in cancer, there has been renewed interest in the role tight junctions play in the pathobiology of chemotherapy-induced gut toxicity. Several preclinical studies have identified molecular defects in intestinal tight junctions following chemotherapy. Despite these findings, the mechanisms responsible for chemotherapy-induced tight junction disruption remain unclear. Recent research has highlighted roles for toll-like receptor 4 and protein kinase C signalling in the regulation of tight junctions. This critical review therefore aims to provide evidence linking toll-like receptor 4 expression, protein kinase C activation and tight junction disruption and their relationship to clinical toxicity.