Radiation-induced Gastrointestinal Syndrome Research Articles

Oral administration of probiotic spore ghosts for efficient attenuation of radiation-induced intestinal injury

Radiation-induced intestinal injury is the most common side effect during radiotherapy of abdominal or pelvic solid tumors, significantly impacting patients’ quality of life and even resulting in poor prognosis. Until now, oral application of conventional formulations for intestinal radioprotection remains challenging with no preferred method available to mitigate radiation toxicity in small intestine. Our previous study revealed that nanomaterials derived from spore coat of probiotics exhibit superior anti-inflammatory effect and even prevent the progression of cancer. The aim of this work is to determine the radioprotective effect of spore coat (denoted as spore ghosts, SGs) from three clinically approved probiotics (B.coagulans, B.subtilis and B.licheniformis). All the three SGs exhibit outstanding reactive oxygen species (ROS) scavenging ability and excellent anti-inflammatory effect. Moreover, these SGs can reverse the balance of intestinal flora by inhibiting harmful bacteria and increasing the abundance of Lactobacillus. Consequently, administration of SGs significantly reduce radiation-induced intestinal injury by alleviating diarrhea, preventing X-ray induced apoptosis of small intestinal epithelial cells and promoting restoration of barrier integrity in a prophylactic study. Notably, SGs markedly improve weight gain and survival of mice received total abdominal X-ray radiation. This work may provide promising radioprotectants for efficiently attenuating radiation-induced gastrointestinal syndrome and promote the development of new intestinal predilection.

P53 promotes revival stem cells in the regenerating intestine after severe radiation injury

Ionizing radiation induces cell death in the gastrointestinal (GI) epithelium by activating p53. However, p53 also prevents animal lethality caused by radiation-induced acute GI syndrome. Through single-cell RNA-sequencing of the irradiated mouse small intestine, we find that p53 target genes are specifically enriched in regenerating epithelial cells that undergo fetal-like reversion, including revival stem cells (revSCs) that promote animal survival after severe damage of the GI tract. Accordingly, in mice with p53 deleted specifically in the GI epithelium, ionizing radiation fails to induce fetal-like revSCs. Using intestinal organoids, we show that transient p53 expression is required for the induction of revival stem cells and is controlled by an Mdm2-mediated negative feedback loop. Together, our findings reveal that p53 suppresses severe radiation-induced GI injury by promoting fetal-like reprogramming of irradiated intestinal epithelial cells.

P53 suppresses MHC class II presentation by intestinal epithelium to protect against radiation-induced gastrointestinal syndrome

Radiation-induced gastrointestinal syndrome is a major complication and limiting factor for radiotherapy. Tumor suppressor p53 has a protective role in radiation-induced gastrointestinal toxicity. However, its underlying mechanism remains unclear. Here we report that regulating the IL12-p40/MHC class II signaling pathway is a critical mechanism by which p53 protects against radiation-induced gastrointestinal syndrome. p53 inhibits the expression of inflammatory cytokine IL12-p40, which in turn suppresses the expression of MHC class II on intestinal epithelial cells to suppress T cell activation and inflammation post-irradiation that causes intestinal stem cell damage. Anti-IL12-p40 neutralizing antibody inhibits inflammation and rescues the defects in intestinal epithelial regeneration post-irradiation in p53-deficient mice and prolongs mouse survival. These results uncover that the IL12-p40/MHC class II signaling mediates the essential role of p53 in ensuring intestinal stem cell function and proper immune reaction in response to radiation to protect mucosal epithelium, and suggest a potential therapeutic strategy to protect against radiation-induced gastrointestinal syndrome.

Systemically delivered adipose stromal vascular fraction mitigates radiation-induced gastrointestinal syndrome by immunomodulating the inflammatory response through a CD11b+ cell-dependent mechanism

BackgroundStromal vascular fraction (SVF) treatment promoted the regeneration of the intestinal epithelium, limiting lethality in a mouse model of radiation-induced gastrointestinal syndrome (GIS). The SVF has a heterogeneous cell composition; the effects between SVF and the host intestinal immunity are still unknown. The specific role of the different cells contained in the SVF needs to be clarified. Monocytes–macrophages have a crucial role in repair and monocyte recruitment and activation are orchestrated by the chemokine receptors CX3CR1 and CCR2.MethodsMice exposed to abdominal radiation (18 Gy) received a single intravenous injection of SVF (2.5 × 106 cells), obtained by enzymatic digestion of inguinal fat tissue, on the day of irradiation. Intestinal immunity and regeneration were evaluated by flow cytometry, RT-PCR and histological analyses.ResultsUsing flow cytometry, we showed that SVF treatment modulated intestinal monocyte differentiation at 7 days post-irradiation by very early increasing the CD11b+Ly6C+CCR2+ population in the intestine ileal mucosa and accelerating the phenotype modification to acquire CX3CR1 in order to finally restore the F4/80+CX3CR1+ macrophage population. In CX3CR1-depleted mice, SVF treatment fails to mature the Ly6C−MCHII+CX3CR1+ population, leading to a macrophage population deficit associated with proinflammatory environment maintenance and defective intestinal repair; this impaired SVF efficiency on survival. Consistent with a CD11b+ being involved in SVF-induced intestinal repair, we showed that SVF-depleted CD11b+ treatment impaired F4/80+CX3CR1+macrophage pool restoration and caused loss of anti-inflammatory properties, abrogating stem cell compartment repair and survival.ConclusionsThese data showed that SVF treatment mitigates the GIS-involving immunomodulatory effect. Cooperation between the monocyte in SVF and the host monocyte defining the therapeutic properties of the SVF is necessary to guarantee the effective action of the SVF on the GIS.

Radiation-induced gastrointestinal (GI) syndrome as a function of age

Previous studies show increased sensitivity of older mice (28–29 months) compared with young adult mice (3 months, possessing a mature immune system) to radiation-induced GI lethality. Age-dependent lethality was associated with higher levels of apoptotic stem cells in small intestinal crypts that correlated with sphingomyelinase activity, a source of pro-apoptotic ceramide. The objective of this study is to determine whether the cycling crypt base columnar cells (CBCs) in aging animals are specifically more sensitive to radiation effects than the CBCs in young adult mice, and to identify factors that contribute to increased radiosensitivity. Mortality induced by subtotal body radiation was assessed at different doses (13 Gy, 14 Gy, and 15 Gy) in young adult mice versus older mice. Each dose was evaluated for the occurrence of lethal GI syndrome. A higher death rate due to radiation-induced GI syndrome was observed in older mice as compared with young adult mice: 30 vs. 0% at 13 Gy, 90 vs. 40% at 14 Gy, and 100 vs. 60% at 15 Gy. Radiation-induced damage to crypts was determined by measuring crypt regeneration (H&E staining, Ki67 expression), CBC biomarkers (lgr5 and ascl2), premature senescence (SA-β-gal activity), and apoptosis of CBCs. At all three doses, crypt microcolony survival assays showed that the older mice had fewer regenerating crypts at 3.5 days post-radiation treatment. Furthermore, in the older animals, baseline CBCs numbers per circumference were significantly decreased, correlating with an elevated apoptotic index. Analysis of tissue damage showed an increased number of senescent CBCs per crypt circumference in older mice relative to younger mice, where the latter was not significantly affected by radiation treatment. It is concluded that enhanced sensitivity to radiation-induced GI syndrome and higher mortality in older mice can be attributed to a decreased capacity to regenerate crypts, presumably due to increased apoptosis and senescence of CBCs.

Histological assessment of intestinal injury by ionizing radiation.

Given the potential risk of radiological terrorism and disasters, it is essential to develop plans to prepare for such events. In these hazardous scenarios, radiation-induced gastrointestinal (GI) syndrome is one of the many manifestations that may happen after the organism is exposed to a lethal dose of ionizing radiation. Therefore, it is critical to better understand how the intestinal tissues initiate and orchestrate regeneration following severe radiation injury. In this chapter, we aimed to provide several key considerations for researchers who utilize histological assessment to study radiation-induced intestinal injury. Rigor and reproducibility are critical in experimental design and can be achieved by maintaining proper radiation administration, maintaining consistency in sample collection, and selecting and using appropriate controls. We also provided technical details of histological preparation of the intestines with tips on dissecting, cleaning, fixing, and preserving. Step-by-step descriptions of both bundling and Swiss rolling are provided with discussion on how to choose between the two approaches. In the following section, we detailed several histological assessment methods and then provided suggestions on how to use histological assessment to study cellular dynamics in the small intestines. Finally, we touched on some non-histological assessments. We hope that the information provided in this chapter will contribute to the research society of radiation-induced intestinal injury with an ultimate goal of promoting the development of radiation countermeasures against the GI acute radiation syndrome.

Taurine Deficiency in Tissues Aggravates Radiation-Induced Gastrointestinal Syndrome.

Ionizing radiation administered for cancer treatment or from nuclear plant accidents are two common causes of radiation exposure. Ionizing radiation exposure generates reactive oxygen species and free radicals, which cause oxidative stress. We previously reported that taurine contributes to the recovery from radiation-induced injuries, suggesting its potential as a radioprotector and radiation mitigator. However, the effect of taurine on radiation-induced gastrointestinal syndrome remains poorly understood. The aim of this study was to examine the effect of taurine tissue depletion on radiation-induced gastrointestinal syndrome. Mouse models of radiation-induced gastrointestinal syndrome were established in TauT+/+ and TauT-/- mice by whole-body X-irradiation. We examined the 30-day survival rate, as well as the crypt-villus structure and proliferation of proliferating cell nuclear antigen (PCNA)+cells in the small intestine. The survival rate of TauT-/- mice was significantly lower than that of TauT+/+ mice. The villi in the small intestine of TauT-/- mice were significantly shorter than those in TauT+/+ mice. Additionally, there were significantly fewer PCNA+ cells in TauT-/- mice than in TauT+/+ mice. These data demonstrate that taurine is a key regulator of crypt stem cells and plays an important regulatory role in intestinal cell survival, proliferation, and fate. Therefore, taurine may reduce radiation-induced gastrointestinal syndrome.

Methods for induction and assessment of intestinal permeability in rodent models of radiation injury.

Ionizing radiation (IR) is a significant contributor to the contemporary market of energy production and an important diagnostic and treatment modality. Besides having numerous useful applications, it is also a ubiquitous environmental stressor and a potent genotoxic and epigenotoxic agent, capable of causing substantial damage to organs and tissues of living organisms. The gastrointestinal (GI) tract is highly sensitive to IR. This problem is further compounded by the fact that there is no FDA-approved medication to mitigate acute radiation-induced GI syndrome. Therefore, establishing the animal model for studying IR-induced GI-injury is crucially important to understand the harmful consequences of intestinal radiation damage. Here, we discuss two different animal models of IR-induced acute gastrointestinal syndrome and two separate methods for measuring the magnitude of intestinal radiation damage.

An Active Fraction of Trillium tschonoskii Promotes the Regeneration of Intestinal Epithelial Cells After Irradiation.

Despite significant scientific advances toward the development of safe and effective radiation countermeasures, no drug has been approved for use in the clinic for prevention or treatment of radiation-induced acute gastrointestinal syndrome (AGS). Thus, there is an urgent need to develop potential drugs to accelerate the repair of injured intestinal tissue. In this study, we investigated that whether some fractions of Traditional Chinese Medicine (TCM) have the ability to regulate intestinal crypt cell proliferation and promotes crypt regeneration after radiation. By screening the different supplements from a TCM library, we found that an active fraction of the rhizomes of Trillium tschonoskii Maxim (TT), TT-2, strongly increased the colony-forming ability of irradiated rat intestinal epithelial cell line 6 (IEC-6) cells. TT-2 significantly promoted the proliferation and inhibited the apoptosis of irradiated IEC-6 cells. Furthermore, in a small intestinal organoid radiation model, TT-2 promoted irradiated intestinal organoid growth and increased Lgr5+ intestinal stem cell (ICS) numbers. More importantly, the oral administration of TT-2 remarkably enhanced intestinal crypt cell proliferation and promoted the repair of the intestinal epithelium of mice after abdominal irradiation (ABI). Mechanistically, TT-2 remarkably activated the expression of ICS-associated and proliferation-promoting genes and inhibited apoptosis-related gene expression. Our data indicate that active fraction of TT can be developed into a potential oral drug for improving the regeneration and repair of intestinal epithelia that have intestinal radiation damage.

The stromal vascular fraction mitigates radiation-induced gastrointestinal syndrome in mice

BackgroundThe intestine is particularly sensitive to moderate-high radiation dose and the development of gastrointestinal syndrome (GIS) leads to the rapid loss of intestinal mucosal integrity, resulting in bacterial infiltration, sepsis that comprise patient survival. There is an urgent need for effective and rapid therapeutic countermeasures. The stromal vascular fraction (SVF) derived from adipose tissue is an easily accessible source of cells with angiogenic, anti-inflammatory and regenerative properties. We studied the therapeutic impact of SVF and its action on the intestinal stem cell compartment.MethodsMice exposed to the abdominal radiation (18 Gy) received a single intravenous injection of stromal vascular fraction (SVF) (2.5 × 106 cells), obtained by enzymatic digestion of inguinal fat tissue, on the day of irradiation. Mortality was evaluated as well as intestinal regeneration by histological analyses and absorption function.ResultsThe SVF treatment limited the weight loss of the mice and inhibited the intestinal permeability and mortality after abdominal irradiation. Histological analyses showed that SVF treatment stimulated the regeneration of the epithelium by promoting numerous enlarged hyperproliferative zones. SVF restored CD24+/lysozyme− and Paneth cell populations in the ISC compartment with the presence of Paneth Ki67+ cells. SVF has an anti-inflammatory effect by repressing pro-inflammatory cytokines, increasing M2 macrophages in the ileum and anti-inflammatory monocyte subtypes CD11b+Ly6clowCX3CR1high in the spleen.ConclusionsThrough the pleiotropic effects that contribute to limiting radiation-induced lethality, SVF opens up attractive prospects for the treatment of emergency GIS.

CeRNA regulatory network of FIH inhibitor as a radioprotector for gastrointestinal toxicity by activating the HIF-1 pathway

Given the relentless renewal ability of intestinal crypt-base stem cells, small intestine in the gastrointestinal (GI) tract is more vulnerable to radiation-induced disruption. Through promoting epithelial integrity and reducing intracellular reactive oxygen species (ROS) levels, hypoxia-inducible factors (HIFs) have been proved to exhibit radioprotective effects in the GI tract. Therefore, enhancing stability or transcriptional activity of HIFs might be a therapeutic strategy for developing radioprotectors. Factor inhibiting HIF (FIH or HIF-1AN) can hamper transcriptional capacity of HIF-1α via interacting with Asn803 in its C-terminal domain. Previously, we discovered promoting HIF-1α transcriptional activity in vitro by FIH inhibitor-N-oxalyl-D-phenylalanine (NOFD) exerts radioprotection on cells. However, the radioprotective effect of FIH inhibitor on the GI tract and its competing endogenous RNA (ceRNA) regulatory network from the FIH/HIF axis has never been addressed. Here we verified radioprotection of NOFD for the GI tract by an animal model and performed whole-transcriptome analysis to fully elucidate the radioprotective mechanism from the FIH/HIF axis against GI syndrome. We identified two novel circular RNAs (circRNAs) (circRNA_2909 and circRNA_0323) and two long non-coding RNAs (lncRNAs) (NONMMUT140549.1 and NONMMUT148249.1) that promote expression of HIF1A and NOS2 in the HIF-1 pathway by sponging microRNAs (miRNAs), especially mmu-miR-92a-1-5p. The de-repression of HIF-1α transcriptional capacity by inhibiting FIH proteomic activity suggests a new therapeutic strategy in alleviating radiation-induced GI syndrome.

CBP/P300 Inhibitors Mitigate Radiation-Induced GI Syndrome by Promoting Intestinal Stem Cell-Mediated Crypt Regeneration.

Radiation-induced gastrointestinal syndrome (RIGS) is currently the main cause of death for people exposed to a high dose of irradiation during nuclear incidents, and there is currently no approved effective therapy. Here, we found that CBP/P300 inhibitors, with high efficacy and low toxicity, might be promising radiation mitigators that can cure RIGS. Exvivo 3D organoid cultures derived from mouse jejunum and human ileum and colon were used to examine the radio-mitigative effects of CBP/P300 inhibitors. The radio-mitigative effect was evaluated by quantifying the survival rate and size of organoids after radiation. SGC-CBP30 (50 mg/kg body weight), an inhibitor of CBP/P300, was intraperitoneally injected into C57B/6J mice 24 hours after subtotal-body irradiation or whole-body irradiation. The regenerated crypts and animal survival were determined by microcolony assay and the Kaplan-Meier method, respectively. Lgr5-lacZ mice were used to evaluate the survival of intestinal stem cells after treatments. We found that CBP/P300 inhibitors were effective mitigators that could be used to treat RIGS. CBP/P300 inhibition promoted the regeneration of intestinal organoids invitro and of crypts invivo. Remarkably, the administration of CBP/P300 inhibitors to mice 24 hours after lethal irradiation promoted Lgr5+ intestinal stem cell and crypt recovery, resulting in improved mouse survival. Moreover, our data show that CBP/P300 inhibitors rescued irradiated mice from RIGS by delaying intestinal epithelial cell cycle progression after radiation. These data demonstrate that CBP/P300 inhibitors are effective medical countermeasures to mitigate gastrointestinal toxicity from radiation.

Radiation-induced gastrointestinal syndrome is alleviated in NDRG2-deficient mice.

Radiation-induced gastrointestinal syndrome (GIS) often occurs after therapeutic or accidental exposure to high doses of radiation. Unfortunately, there are still no effective medical treatments for GIS. N-Myc downstream regulated gene 2 (NDRG2), is a tumor suppressor gene and promotes cell apoptosis and differentiation. The aim of our study was to identify the role of NDRG2 in the progression of GIS and explore the potential mechanism. We generated Ndrg2ΔG mice, lacking NDRG2 specifically in the intestinal epithelium. Survival analysis was performed to validate the effect of NDRG2 on GIS, and other common indicators (body weight loss and diarrhea) were used for the assessment of GIS. Enzyme-linked immunosorbent assay (ELISA) and reverse transcription-polymerase chain reaction (RT-PCR) were conducted to obtain the expression of pro-inflammatory interleukin (IL)-1β, IL-6, and tumor necrosis factor alpha (TNF-α). TUNNEL and western blotting were further adopted to determine the relationship between NDRG2 and apoptosis. Finally, we performed histology and immunohistochemistry assays to explore the morphological alternations and changes of proliferation-related molecules, including Ki-67 and proliferating cell nuclear antigen (PCNA). We found that after 8 gray of total body ɤ-irradiation (TBI), the deletion of NDRG2 in the intestine revealed longer survival time, considerably milder symptoms of GIS, and milder damage to jejunal tissue, compared with the WT mice. Moreover, the Ndrg2ΔG mice significantly inhibited the expression of pro-inflammatory IL-1β, IL-6, and TNF-α, which were typically increased by irradiation. Apoptosis of the epithelial cells in the Ndrg2ΔG mice was significantly milder while the ratio of proliferation cells was larger in the epithelium of mice 8 days after TBI when compared with the WT mice. These findings all indicated that NDRG2 deficiency in the intestine protects mice against radiation-induced GIS mainly through promoting proliferation and suppressing apoptosis of epithelial cells.

SIRT1 inhibitors mitigate radiation-induced GI syndrome by enhancing intestinal-stem-cell survival.

High-dose radiation exposure induces gastrointestinal (GI) stem cell death, resulting in denudation of the intestinal mucosa and lethality from GI syndrome, for which there is currently no effective therapy. Studying an intestinal organoid-based functional model, we found that Sirtuin1(SIRT1) inhibition through genetic knockout or pharmacologic inhibition significantly improved mouse and human intestinal organoid survival after irradiation. Remarkably, mice administered with two doseages of SIRT1 inhibitors at 24 and 96h after lethal irradiation promoted Lgr5+ intestinal stem cell and crypt recovery, with improved mouse survival (88.89% of mice in the treated group vs. 0% of mice in the control group). Moreover, our data revealed that SIRT1 inhibition increased p53 acetylation, resulting in the stabilization of p53 and likely contributing to the survival of intestinal epithelial cells post-radiation. These results demonstrate that SIRT1 inhibitors are effective clinical countermeasures to mitigate GI toxicity from potentially lethal radiation exposure.

Ghrelin reverts intestinal stem cell loss associated with radiation-induced enteropathy by activating Notch signaling

BackgroudExposure to high-dose radiation, such as after a nuclear accident or radiotherapy, elicits severe intestinal damage and is associated with a high mortality rate. In treating patients exhibiting radiation-induced intestinal dysfunction, countermeasures to radiation are required. In principle, the cellular event underlying radiation-induced gastrointestinal syndrome is intestinal stem cell (ISC) apoptosis in the crypts. High-dose irradiation induces the loss of ISCs and impairs intestinal barrier function, including epithelial regeneration and integrity. Notch signaling plays a critical role in the maintenance of the intestinal epithelium and regulates ISC self-renewal. Ghrelin, a hormone produced mainly by enteroendocrine cells in the gastrointestinal tract, has diverse physiological and biological functions. PurposeWe investigate whether ghrelin mitigates radiation-induced enteropathy, focusing on its role in maintaining epithelial function. MethodsTo investigate the effect of ghrelin in radiation-induced epithelial damage, we analyzed proliferation and Notch signaling in human intestinal epithelial cell. And we performed histological analysis, inflammatory response, barrier functional assays, and expression of notch related gene and epithelial stem cell using a mouse model of radiation-induced enteritis. ResultsIn this study, we found that ghrelin treatment accelerated the reversal of radiation-induced epithelial damage including barrier dysfunction and defective self-renewing property of ISCs by activating Notch signaling. Exogenous injection of ghrelin also attenuated the severity of radiation-induced intestinal injury in a mouse model. ConclusionThese data suggest that ghrelin may be used as a potential therapeutic agent for radiation-induced enteropathy.

Specific Taxa of the Intestinal Microbiome Mitigate the Radiation-Induced Gastrointestinal Syndrome

Specific Taxa of the Intestinal Microbiome Mitigate the Radiation-Induced Gastrointestinal Syndrome

Extracellular vesicles derived from mesenchymal stromal cells mitigate intestinal toxicity in a mouse model of acute radiation syndrome

BackgroundHuman exposure to high doses of radiation resulting in acute radiation syndrome and death can rapidly escalate to a mass casualty catastrophe in the event of nuclear accidents or terrorism. The primary reason is that there is presently no effective treatment option, especially for radiation-induced gastrointestinal syndrome. This syndrome results from disruption of mucosal barrier integrity leading to severe dehydration, blood loss, and sepsis. In this study, we tested whether extracellular vesicles derived from mesenchymal stromal cells (MSC) could reduce radiation-related mucosal barrier damage and reduce radiation-induced animal mortality.MethodsHuman MSC-derived extracellular vesicles were intravenously administered to NUDE mice, 3, 24, and 48 h after lethal whole-body irradiation (10 Gy). Integrity of the small intestine epithelial barrier was assessed by morphologic analysis, immunostaining for tight junction protein (claudin-3), and in vivo permeability to 4 kDa FITC-labeled dextran. Renewal of the small intestinal epithelium was determined by quantifying epithelial cell apoptosis (TUNEL staining) and proliferation (Ki67 immunostaining). Statistical analyses were performed using one-way ANOVA followed by a Tukey test. Statistical analyses of mouse survival were performed using Kaplan-Meier and Cox methods.ResultsWe demonstrated that MSC-derived extracellular vesicle treatment reduced by 85% the instantaneous mortality risk in mice subjected to 10 Gy whole-body irradiation and so increased their survival time. This effect could be attributed to the efficacy of MSC-derived extracellular vesicles in reducing mucosal barrier disruption. We showed that the MSC-derived extracellular vesicles improved the renewal of the small intestinal epithelium by stimulating proliferation and inhibiting apoptosis of the epithelial crypt cells. The MSC-derived extracellular vesicles also reduced radiation-induced mucosal permeability as evidenced by the preservation of claudin-3 immunostaining at the tight junctions of the epithelium.ConclusionsMSC-derived extracellular vesicles promote epithelial repair and regeneration and preserve structural integrity of the intestinal epithelium in mice exposed to radiation-induced gastrointestinal toxicity. Our results suggest that the administration of MSC-derived extracellular vesicles could be an effective therapy for limiting acute radiation syndrome.

Radiation-induced gastrointestinal syndrome is exacerbated in vitamin C-insufficient SMP30/GNL knockout mice.

Accidental exposure to high-dose radiation causes life-threatening acute radiation syndrome, features that include gastrointestinal syndrome (GIS) and hematopoietic syndrome (HS). Administration of vitamin C (VC), a free radical scavenger, has been reported to increase survival of mice in GIS and HS models. The effect of nutritional VC status on radiation injury remains unknown because, unlike humans, mice can synthesize VC. The aim of this study was to investigate the effect of VC insufficiency on acute radiation syndrome using senescence marker protein 30 (SMP30)/gluconolactonase knockout (SMP30-KO) mice. SMP30-KO mice, which cannot synthesize VC, were given water with or without sufficient VC supplementation, and were analyzed in GIS and HS models. In the GIS model, in which bone marrow failure is rescued by bone marrow transplantation, VC-insufficient mice had a lower survival rate than VC-sufficient mice. The intestine of VC-insufficient GIS mice showed epithelial cell atrophy, inflammatory cell infiltration, and decreased crypt cell proliferation. We observed rapid VC oxidation after total body irradiation in the intestine of mice supplemented with VC-sufficient water. In the HS model, which was not combined with bone marrow transplantation, there was no difference in survival between VC-insufficient and -sufficient mice. The results of this study demonstrated that nutritionally sufficient VC exerts a radioprotective effect against radiation-induced GIS.

LIF is essential for ISC function and protects against radiation-induced gastrointestinal syndrome

Leukemia inhibitory factor (LIF) is a cytokine essential for maintaining pluripotency of mouse embryonic stem cells. However, its role in adult intestinal stem cells (ISCs) is unclear. The adult intestinal epithelium has a high self-renewal rate driven by ISCs in crypts. Here, we find that LIF is present in the ISC niche in crypts and critical for the function of ISCs in maintaining the intestinal epithelial homeostasis and regeneration. Mechanistically, LIF maintains β-catenin activity through the AKT/GSK3β signaling to regulate ISC functions. LIF deficiency in mice impairs the renewal of the intestinal epithelium under the physiological condition. Further, LIF deficiency in mice impairs the regeneration of intestinal epithelium in response to radiation and shortens the lifespan of mice after high doses of radiation due to gastrointestinal (GI) syndrome, which can be rescued by administering recombinant LIF (rLIF). Importantly, LIF exhibits a radioprotective role in wild-type (WT) mice by protecting mice from lethal radiation-induced GI syndrome; administering rLIF promotes intestinal epithelial regeneration and prolongs survival in WT mice after radiation. These results reveal a previously unidentified and a crucial role of LIF in ensuring ISC function, promoting regeneration of the intestinal epithelium in response to radiation and protecting against radiation-induced GI syndrome.

TIGAR/AP-1 axis accelerates the division of Lgr5\u2212 reserve intestinal stem cells to reestablish intestinal architecture after lethal radiation

During radiologic or nuclear accidents, high-dose ionizing radiation (IR) can cause gastrointestinal syndrome (GIS), a deadly disorder that urgently needs effective therapy. Unfortunately, current treatments based on natural products and antioxidants have shown very limited effects in alleviating deadly GIS. Reserve intestinal stem cells (ISCs) and secretory progenitor cells are both reported to replenish damaged cells and contribute to crypt regeneration. However, the suppressed β-catenin/c-MYC axis within these slow-cycling cells leads to limited regenerative response to restore intestinal integrity during fatal accidental injury. Current study demonstrates that post-IR overexpression of TIGAR, a critical downstream target of c-MYC in mouse intestine, mounts a hyperplastic response in Bmi1-creERT+ reserve ISCs, and thus rescues mice from lethal IR exposure. Critically, by eliminating damaging reactive oxygen species (ROS) yet retaining the proliferative ROS signals, TIGAR-overexpression enhances the activity of activator protein 1, which is indispensable for initiating reserve-ISC division after lethal radiation. In addition, it is identified that TIGAR-induction exclusively gears the Lgr5− subpopulation of reserve ISCs to regenerate crypts, and intestinal TIGAR-overexpression displays equivalent intestinal reconstruction to reserve-ISC-restricted TIGAR-induction. Our findings imply that precise administrations toward Lgr5− reserve ISCs are promising strategies for unpredictable lethal injury, and TIGAR can be employed as a therapeutic target for unexpected radiation-induced GIS.