Paneth cell dysfunction in radiation injury and radio-mitigation by human α-defensin 5

Introduction

The mechanism underlying radiation-induced gut microbiota dysbiosis is undefined. This study examined the effect of radiation on the intestinal Paneth cell α-defensin expression and its impact on microbiota composition and mucosal tissue injury and evaluated the radio-mitigative effect of human α-defensin 5 (HD5).

Methods

Adult mice were subjected to total body irradiation, and Paneth cell α-defensin expression was evaluated by measuring α-defensin mRNA by RT-PCR and α-defensin peptide levels by mass spectrometry. Vascular-to-luminal flux of FITC-inulin was measured to evaluate intestinal mucosal permeability and endotoxemia by measuring plasma lipopolysaccharide. HD5 was administered in a liquid diet 24 hours before or after irradiation. Gut microbiota was analyzed by 16S rRNA sequencing. Intestinal epithelial junctions were analyzed by immunofluorescence confocal microscopy and mucosal inflammatory response by cytokine expression. Systemic inflammation was evaluated by measuring plasma cytokine levels.

Results

Ionizing radiation reduced the Paneth cell α-defensin expression and depleted α-defensin peptides in the intestinal lumen. α-Defensin down-regulation was associated with the time-dependent alteration of gut microbiota composition, increased gut permeability, and endotoxemia. Administration of human α-defensin 5 (HD5) in the diet 24 hours before irradiation (prophylactic) significantly blocked radiation-induced gut microbiota dysbiosis, disruption of intestinal epithelial tight junction and adherens junction, mucosal barrier dysfunction, and mucosal inflammatory response. HD5, administered 24 hours after irradiation (treatment), reversed radiation-induced microbiota dysbiosis, tight junction and adherens junction disruption, and barrier dysfunction. Furthermore, HD5 treatment also prevents and reverses radiation-induced endotoxemia and systemic inflammation.

Conclusion

These data demonstrate that radiation induces Paneth cell dysfunction in the intestine, and HD5 feeding prevents and mitigates radiation-induced intestinal mucosal injury, endotoxemia, and systemic inflammation.

Biological sex differences in renin angiotensin system enzymes ACE and ACE2 regulate normal tissue response to radiation injury

Introduction: In experimental animal models, biological sex-differences in the manifestation and severity of normal tissue radiation injury have been well-documented. Previously we demonstrated male and female rats have differential and highly reproducible responses to high-dose partial body irradiation (PBI) with male rats having greater susceptibility to both gastrointestinal acute radiation syndrome (GI-ARS) and radiation pneumonitis than female rats. Methods: In the current study, we have investigated whether differential expression of the renin-angiotensin system (RAS) enzymes angiotensin converting enzyme (ACE) and ACE2 contribute to the observed sex-related differences in radiation response. Results: During the period of symptomatic pneumonitis, the relative ratio of ACE to ACE2 (ACE/ACE2) protein in the whole lung was significantly increased by radiation in male rats alone. Systemic treatment with small molecule ACE2 agonist diminazene aceturate (DIZE) increased lung ACE2 activity and reduced morbidity during radiation pneumonitis in both sexes. Notably DIZE treatment also abrogated morbidity in male rats during GI-ARS. We then evaluated the contribution of the irradiated bone marrow (BM) compartment on lung immune cell infiltration and ACE imbalance during pneumonitis. Transplantation of bone marrow from irradiated donors increased both ACE-expressing myeloid cell infiltration and immune ACE activity in the lung during pneumonitis compared to non-irradiated donors. Discussion: Together, these data demonstrate radiation induces a sex-dependent imbalance in the renin-angiotensin system enzymes ACE and ACE2. Additionally, these data suggest a role for ACE-expressing myeloid cells in the pathogenesis of radiation pneumonitis. Finally, the observed sex-differences underscore the need for consideration of sex as a biological variable in the development of medical countermeasures for radiation exposure.

Development of human cell-expressed tag-free rhMFG-E8 as a radiation mitigator and a therapeutic for acute kidney injury

Background

Human milk fat globule epidermal growth factor-factor VIII (MFG-E8) functions as a bridging molecule to promote the removal of dying cells by professional phagocytes. E. coli-expressed histidine-tagged recombinant human MFG-E8 (rhMFG-E8) is protective in various disease conditions. However, due to improper recombinant protein glycosylation, misfolding and possible antigenicity, E. coli-expressed histidine-tagged rhMFG-E8 is unsuitable for human therapy. Therefore, we hypothesize that human cell-expressed, tag-free rhMFG-E8 can be developed as a safe and effective novel biologic to treat inflammatory diseases such as radiation injury and acute kidney injury (AKI).

Methods

We produced a new tag-free rhMFG-E8 protein by cloning the human MFG-E8 full-length coding sequence without any fusion tag into a mammalian vector and expressed it in HEK293-derived cells. The construct includes the leader sequence of cystatin S to maximize secretion of rhMFG-E8 into the culture medium. After purification and confirmation of the protein identity, we first evaluated its biological activity in vitro. We then determined its efficacy in vivo utilizing two experimental rodent models of organ injury: partial body irradiation (PBI) and ischemia/reperfusion-induced AKI.

Results

HEK293 cell supernatant containing tag-free rhMFG-E8 protein was concentrated, purified, and rhMFG-E8 was verified by SDS-PAGE analysis and mass spectrometry. The biological activity of human cell-expressed tag-free rhMFG-E8 was superior to that of E. coli-expressed His-tagged rhMFG-E8. Toxicity, stability, and pharmacokinetic studies indicate that tag-free rhMFG-E8 is safe, highly stable after lyophilization and long-term storage, and with an adequate half-life for therapeutic applications. In the PBI model, a dose-dependent improvement of the 30-day survival rate was observed after tag-free rhMFG-E8 treatment with a 30-day survival of 89%, which was significantly higher than the 25% survival in the vehicle group. The dose modification factor (DMF) of tag-free rhMFG-E8 was 1.073. Tag-free rhMFG-E8 also attenuated gastrointestinal damage after PBI. In the model of AKI, tag-free rhMFG-E8 treatment significantly attenuated kidney injury and inflammation, and improved the 10-day survival.

Conclusion

Our new human cell-expressed tag-free rhMFG-E8 can be further developed as a safe and effective therapy to treat victims of severe acute radiation injury and patients with acute kidney injury.

Organ-Specific Endothelial Dysfunction Following Total Body Irradiation Exposure

As the single cell lining of the heart and all blood vessels, the vascular endothelium serves a critical role in maintaining homeostasis via control of vascular tone, immune cell recruitment, and macromolecular transit. For victims of acute high-dose radiation exposure, damage to the vascular endothelium may exacerbate the pathogenesis of acute and delayed multi-organ radiation toxicities. While commonalities exist between radiation-induced endothelial dysfunction in radiosensitive organs, the vascular endothelium is known to be highly heterogeneous as it is required to serve tissue and organ specific roles. In keeping with its organ and tissue specific functionality, the molecular and cellular response of the endothelium to radiation injury varies by organ. Therefore, in the development of medical countermeasures for multi-organ injury, it is necessary to consider organ and tissue-specific endothelial responses to both injury and candidate mitigators. The purpose of this review is to summarize the pathogenesis of endothelial dysfunction following total or near total body irradiation exposure at the level of individual radiosensitive organs.