Exacerbation of lung radiation injury by viral infection: the role of Clara cells and Clara cell secretory protein

Cytological changes in radiation-induced lung injury

Radiation-induced lung injury (RILI) is a prevalent complication associated with radiotherapy for thoracic tumors. Based on the pathological progression, it can be categorized into two stages: early radiation pneumonitis and late radiation pulmonary fibrosis. The occurrence of RILI not only constrains the therapeutic dose that can be administered to the tumor target area but also significantly impairs patients' health and quality of life, thereby limiting the efficacy and applicability of radiotherapy. To effectively prevent and mitigate the development of RILI, it is crucial to disclose its underlying mechanisms. This review aims to elucidate the specific mechanisms involved in RILI and to examine the roles of various cell types, including lung parenchymal cells and different immune cells. The functions and interactions of lung epithelial cells, pulmonary vascular endothelial cells, a variety of immune cells, and fibroblasts during different stages of inflammation, tissue repair, and fibrosis following radiation-induced lung injury are analyzed. A comprehensive understanding of the dynamic changes in these cellular components is anticipated to offer new strategies for the prevention of RILI.

Thoracic Proton Minibeam Radiation Therapy: Tissue Preservation and Survival Advantage Over Conventional Proton Therapy

PURPOSE

Proton minibeam radiation therapy (pMBRT) is an innovative radiation therapy approach that highly modulates the spatial dimension of the dose delivery using narrow, parallel, and submillimetric proton beamlets. pMBRT has proven its remarkable healthy tissue preservation in the brain and skin. This study assesses the potential advantages of pMBRT for thoracic irradiations compared with conventional radiation therapy in terms of normal tissue toxicity. The challenge here was the influence of respiratory motion on the typical peak and valley dose patterns of pMBRT and its potential biologic effect.

METHODS AND MATERIALS

The whole thorax of naïve C57BL/6 mice received one fraction of high dose (18 Gy) pMBRT or conventional proton therapy (CPT) without any respiratory control. The development of radiation-induced pulmonary fibrosis was longitudinally monitored using cone beam computed tomography. Anatomopathologic analysis was carried out at 9 months postirradiation and focused on the reaction of the lungs' parenchyma and the response of cell types involved in the development of radiation-induced fibrosis and lung regeneration as alveolar type II epithelial cells, club cells, and macrophages.

RESULTS

pMBRT has milder effects on survival, skin reactions, and lung fibrosis compared with CPT. The pMBRT-induced lung changes were more regional and less severe, with evidence of potential reactive proliferation of alveolar type II epithelial cells and less extensive depletion of club cells and macrophage invasion than the more damaging effects observed in CPT.

CONCLUSIONS

pMBRT appears suitable to treat moving targets, holding a significant ability to preserve healthy lung tissue, even without respiratory control or precise targeting.

Mitigating Viral Impact on the Radiation Response of the Lung

Inflammation is a key factor in both influenza and radiation-induced lung pathophysiology. This implies a commonality of response to pulmonary damage from these insults and suggests exacerbated pathology may occur after combined exposure. We therefore tested the hypothesis that past inflammation from viral infection alters the lung microenvironment and lowers tolerance for radiation injury. Mice were inoculated with influenza A virus (IAV) and three weeks later, after virus clearance, mice received total-body irradiation (TBI). Survival as well as systemic and local lung inflammation were assessed, and strategies to mitigate pulmonary injury were investigated. After IAV infection alone, body condition recovered within 3 weeks, however inflammatory pathways remained active for 15 weeks. IAV infection exacerbated subsequent TBI responses, evident by increased lethality, enhanced histologically evident lung injury and an altered lung macrophage phenotype. To mitigate this enhanced sensitivity, captopril [an angiotensin converting enzyme inhibitor (ACEi)] was administered to limit tissue inflammation, or inflammatory monocyte-derived macrophage recruitment was blocked with a C-C chemokine receptor type 2 (CCR2) inhibitor. Both treatments abrogated the changes in circulating immune cells observed 4 weeks after TBI, and attenuated pro-inflammatory phenotypes in lung alveolar macrophages, appearing to shift immune cell dynamics towards recovery. Histologically apparent lung injury was not improved by either treatment. We show that latent lung injury from viral infection exacerbates radiation morbidity and mortality. Although strategies that attenuate proinflammatory immune cell phenotypes can normalize macrophage dynamics, this does not fully mitigate lung injury. Recognizing that past viral infections can enhance lung radiosensitivity is of critical importance for patients receiving TBI, as it could increase the incidence of adverse outcomes.

Associations of Serum Clara Cell Protein 16 with Severity and Prognosis in Adults with Community-Acquired Pneumonia

Background

Clara cell protein 16 (CC16) has multiple functions, including antioxidant, anti-inflammatory, and immune regulation properties. Nevertheless, the concrete function of CC16 in adult patients with community-acquired pneumonia (CAP) remained blurred.

Methods

A total of 541 adult patients with CAP were recruited on admission. Peripheral blood specimens, clinical parameters, and demographic characteristics were collected. The concentration of serum CC16 was evaluated through ELISA. The relationships between serum CC16 and clinical parameters were appraised by Spearman or Pearson correlative analyses. The correlations of serum CC16 with severity and prognosis were assessed using linear or logistic regression models.

Results

The level of CC16 was gradually decreased across with the elevated severity scores system of CAP. After treatment, the level of serum CC16 was upregulated. Correlative analyses found that serum CC16 was negatively related to inflammatory cytokines. Additionally, multivariate linear and logistic regression models revealed that serum CC16 was inversely associated with severity scores system. In addition, reduced serum CC16 on admission elevated the risks of vasoactive agent usage, ICU admission, and death during hospitalization. We observed an almost discriminatory ability for severity and death between serum CC16 and severity scores system, and were all obviously elevated compared to routine inflammatory and infectious markers.

Conclusion

There are substantially inverse correlations between serum CC16 level on admission with severity scores and poorly prognostic outcomes, indicating that CC16 is involved in the pathophysiological process of CAP. This study is helpful for establishing the potential application of serum CC16 in risk evaluation and targeted treatment.

A cluster onset of acute and accelerated silicosis cases in workers of ramming mass industries in Jharkhand, Eastern India

INTRODUCTION AND METHODOLOGY

A cross-sectional study was conducted among workers of ramming mass industries in the East Singhbhum district of Jharkhand, eastern India. Workers had occupational exposure to respirable crystalline silica dust of varied duration between 1 and 6 years. A total of 122 subjects participated in it. Relevant epidemiological information was collected from them. All were x-rayed using 300 mA radiation for the detection of the presence of silicotic opacities if any as described by the International Labour Organisation (ILO) for the detection of silicosis.

RESULTS

The study revealed that 61.4% (n = 75) of subjects had silicosis. Of them, 19 had acute silicosis (having a duration of silica dust exposure of 2 years or lesser) and 56 had accelerated silicosis (a duration of occupational exposure of > 2 to 6 years). The offending agent was clouds of respirable crystalline silica dust from the ramming mass industries.

EPIDEMIOLOGICAL INTERPRETATION

To the best of our knowledge, this is the first report of an outbreak of acute and accelerated silicosis cases because of occupational inhalational exposure to ramming mass in India with a sizable portion of female workers with silicosis. Regional as well as national authorities need to take appropriate interventional measures in a programmatic mode as soon as possible.

CONCLUSION

An in-depth investigation on the existence and magnitude of the problem of silico-tuberculosis is needed to be performed in them as silicosis increases the vulnerability of pulmonary tuberculosis among the affected workers.

Influence of the irradiated pulmonary microenvironment on macrophage and T cell dynamics

BACKGROUND

The lung is sensitive to radiation, increasing normal tissue toxicity risks following radiation therapy. Adverse outcomes include pneumonitis and pulmonary fibrosis, which result from dysregulated intercellular communication within the pulmonary microenvironment. Although macrophages are implicated in these pathogenic outcomes, the impact of their microenvironment is not well understood.

MATERIALS AND METHODS

C57BL/6J mice received 6Gyx5 irradiation to the right lung. Macrophage and T cell dynamics were investigated in ipsilateral right lungs, contralateral left lungs and non-irradiated control lungs 4-26wk post exposure. Lungs were evaluated by flow cytometry, histology and proteomics.

RESULTS

Following uni-lung irradiation, focal regions of macrophage accumulation were noted in both lungs by 8wk, however by 26wk fibrotic lesions were observed only in ipsilateral lungs. Infiltrating and alveolar macrophages populations expanded in both lungs, however transitional CD11b + alveolar macrophages persisted only in ipsilateral lungs and expressed lower CD206. Concurrently, arginase-1 + macrophages accumulated in ipsilateral but not contralateral lungs at 8 and 26wk post exposure, while CD206 + macrophages were absent from these accumulations. While radiation expanded CD8 + T cells in both lungs, T regulatory cells only increased in ipsilateral lungs. Unbiased proteomics analysis of immune cells revealed a substantial number of differentially expressed proteins in ipsilateral lungs when compared to contralateral lungs and both differed from non-irradiated controls.

CONCLUSIONS

Pulmonary macrophage and T cell dynamics are impacted by the microenvironmental conditions that develop following radiation exposure, both locally and systemically. While macrophages and T cells infiltrate and expand in both lungs, they diverge phenotypically depending on their environment.

Epithelial Responses in Radiation-Induced Lung Injury (RILI) Allow Chronic Inflammation and Fibrogenesis

Radiation models, such as whole thorax lung irradiation (WTLI) or partial-body irradiation (PBI) with bone-marrow sparing, have shown that affected lung tissue displays a continual progression of injury, often for months after the initial insult. Undoubtably, a variety of resident and infiltrating cell types either contribute to or fail to resolve this type of progressive injury, which in lung tissue, often develops into lethal and irreversible radiation-induced pulmonary fibrosis (RIPF), indicating a failure of the lung to return to a homeostatic state. Resident pulmonary epithelium, which are present at the time of irradiation and persist long after the initial insult, play a key role in the maintenance of homeostatic conditions in the lung and have often been described as contributing to the progression of radiation-induced lung injury (RILI). In this study, we took an unbiased approach through RNA sequencing to determine the in vivo response of the lung epithelium in the progression of RIPF. In our methodology, we isolated CD326+ epithelium from the lungs of 12.5 Gy WTLI C57BL/6J female mice (aged 8-10 weeks and sacrificed at regular intervals) and compared irradiated and non-irradiated CD326+ cells and whole lung tissue. We subsequently verified our findings by qPCR and immunohistochemistry. Transcripts associated with epithelial regulation of immune responses and fibroblast activation were significantly reduced in irradiated animals at 4 weeks postirradiation. Additionally, alveolar type-2 epithelial cells (AEC2) appeared to be significantly reduced in number at 4 weeks and thereafter based on the diminished expression of pro-surfactant protein C (pro-SPC). This change is associated with a reduction of Cd200 and cyclooxygenase 2 (COX2), which are expressed within the CD326 populations of cells and function to suppress macrophage and fibroblast activation under steady-state conditions, respectively. These data indicate that either preventing epithelial cell loss that occurs after irradiation or replacing important mediators of immune and fibroblast activity produced by the epithelium are potentially important strategies for preventing or treating this unique injury.

Considerations of Medical Preparedness to Assess and Treat Various Populations During a Radiation Public Health Emergency

During a radiological or nuclear public health emergency, given the heterogeneity of civilian populations, it is incumbent on medical response planners to understand and prepare for a potentially high degree of interindividual variability in the biological effects of radiation exposure. A part of advanced planning should include a comprehensive approach, in which the range of possible human responses in relation to the type of radiation expected from an incident has been thoughtfully considered. Although there are several reports addressing the radiation response for special populations (as compared to the standard 18-45-year-old male), the current review surveys published literature to assess the level of consideration given to differences in acute radiation responses in certain sub-groups. The authors attempt to bring clarity to the complex nature of human biology in the context of radiation to facilitate a path forward for radiation medical countermeasure (MCM) development that may be appropriate and effective in special populations. Consequently, the focus is on the medical (as opposed to logistical) aspects of preparedness and response. Populations identified for consideration include obstetric, pediatric, geriatric, males, females, individuals of different race/ethnicity, and people with comorbidities. Relevant animal models, biomarkers of radiation injury, and MCMs are highlighted, in addition to underscoring gaps in knowledge and the need for consistent and early inclusion of these populations in research. The inclusion of special populations in preclinical and clinical studies is essential to address shortcomings and is an important consideration for radiation public health emergency response planning. Pursuing this goal will benefit the population at large by considering those at greatest risk of health consequences after a radiological or nuclear mass casualty incident.

Pulmonary endogenous progenitor stem cell subpopulation: Physiology, pathogenesis, and progress

Lungs are structurally and functionally complex organs consisting of diverse cell types from the proximal to distal axis. They have direct contact with the external environment and are constantly at risk of various injuries. Capable to proliferate and differentiate, pulmonary endogenous progenitor stem cells contribute to the maintenance of lung structure and function both under homeostasis and following injuries. Discovering candidate pulmonary endogenous progenitor stem cell types and underlying regenerative mechanisms provide insights into therapeutic strategy development for lung diseases. In this review, we reveal their compositions, roles in lung disease pathogenesis and injury repair, and the underlying mechanisms. We further underline the advanced progress in research approach and potential therapy for lung regeneration. We also demonstrate the feasibility and prospects of pulmonary endogenous stem cell transplantation for lung disease treatment.

Biomonitoring Exposure and Early Diagnosis in Silicosis: A Comprehensive Review of the Current Literature

Silicosis is a particular form of lung fibrosis attributable to occupational exposure to crystalline silica. The occupational exposure to crystalline silica also increases the risk of chronic obstructive pulmonary disease (COPD), cancer and lung infections, especially pulmonary tuberculosis. Silicosis is currently diagnosed in previously exposed workers by standard chest X-ray, when lesions are visible and irreversible. Therefore, it would be necessary to find specific and non-invasive markers that could detect silicosis in earlier stages, before the occurrence of X-ray opacities. In this narrative review, we present several diagnostic, monitoring and predictive biomarkers with high potential in the management of silicosis, such as: pro- and anti-inflammatory cytokines (TNF (Tumour necrosis factor-α), IL-1 (Interleukin-1), IL-6, IL-10), CC16 (Clara cell 16, an indirect marker of epithelial cell destruction), KL-6 (Krebs von den Lungen 6, an indirect marker of alveolar epithelial damage), neopterin (indicator of cellular immunity) and MUC5B gene (Mucin 5B, a gel-forming mucin in mucus). Studies have shown that all the aforementioned markers have a high potential for early diagnosis or evaluation of progression in silicosis and represent promising alternatives to radiology. We consider that a multicentric study is needed to evaluate these biomarkers in correlation with occupational history, histopathological examination, imaging signs and pulmonary functions tests on large groups of subjects to better evaluate the accuracy of the presented biomarkers.

Preclinical Model of Stereotactic Ablative Lung Irradiation Using Arc Delivery in the Mouse: Is Fractionation Worthwhile?

Lung stereotactic body radiation therapy is characterized by a reduction in target volumes and the use of severely hypofractionated schedules. Preclinical modeling became possible thanks to rodent-dedicated irradiation devices allowing accurate beam collimation and focal lung exposure. Given that a great majority of publications use single dose exposures, the question we asked in this study was as follows: in incremented preclinical models, is it worth using fractionated protocols or should we continue focusing solely on volume limitation? The left lungs of C57BL/6JRj mice were exposed to ionizing radiation using arc therapy and 3 × 3 mm beam collimation. Three-fraction schedules delivered over a period of 1 week were used with 20, 28, 40, and 50 Gy doses per fraction. Lung tissue opacification, global histological damage and the numbers of type II pneumocytes and club cells were assessed 6 months post-exposure, together with the gene expression of several lung cells and inflammation markers. Only the administration of 3 × 40 Gy or 3 × 50 Gy generated focal lung fibrosis after 6 months, with tissue opacification visible by cone beam computed tomography, tissue scarring and consolidation, decreased club cell numbers and a reactive increase in the number of type II pneumocytes. A fractionation schedule using an arc-therapy-delivered three fractions/1 week regimen with 3 × 3 mm beam requires 40 Gy per fraction for lung fibrosis to develop within 6 months, a reasonable time lapse given the mouse lifespan. A comparison with previously published laboratory data suggests that, in this focal lung irradiation configuration, administering a Biological Effective Dose ≥ 1000 Gy should be recommended to obtain lung fibrosis within 6 months. The need for such a high dose per fraction challenges the appropriateness of using preclinical highly focused fractionation schedules in mice.

All for one, though not one for all: team players in normal tissue radiobiology

PURPOSE

As part of the special issue on 'Women in Science', this review offers a perspective on past and ongoing work in the field of normal (non-cancer) tissue radiation biology, highlighting the work of many of the leading contributors to this field of research. We discuss some of the hypotheses that have guided investigations, with a focus on some of the critical organs considered dose-limiting with respect to radiation therapy, and speculate on where the field needs to go in the future.

CONCLUSIONS

The scope of work that makes up normal tissue radiation biology has and continues to play a pivotal role in the radiation sciences, ensuring the most effective application of radiation in imaging and therapy, as well as contributing to radiation protection efforts. However, despite the proven historical value of preclinical findings, recent decades have seen clinical practice move ahead with altered fractionation scheduling based on empirical observations, with little to no (or even negative) supporting scientific data. Given our current appreciation of the complexity of normal tissue radiation responses and their temporal variability, with tissue- and/or organ-specific mechanisms that include intra-, inter- and extracellular messaging, as well as contributions from systemic compartments, such as the immune system, the need to maintain a positive therapeutic ratio has never been more urgent. Importantly, mitigation and treatment strategies, whether for the clinic, emergency use following accidental or deliberate releases, or reducing occupational risk, will likely require multi-targeted approaches that involve both local and systemic intervention. From our personal perspective as five 'Women in Science', we would like to acknowledge and applaud the role that many female scientists have played in this field. We stand on the shoulders of those who have gone before, some of whom are fellow contributors to this special issue.

Wound Trauma Exacerbates Acute, but not Delayed, Effects of Radiation in Rats: Mitigation by Lisinopril

The goal of this study is to understand and mitigate the effects of wounds on acute radiation syndrome (ARS) and delayed effects of acute radiation exposure (DEARE), for preparedness against a radiological attack or accident. Combined injuries from concomitant trauma and radiation are likely in these scenarios. Either exacerbation or mitigation of radiation damage by wound trauma has been previously reported in preclinical studies. Female WAG/RijCmcr rats received 13 Gy X-rays, with partial-body shielding of one leg. Within 2 h, irradiated rats and non-irradiated controls were given full-thickness skin wounds with or without lisinopril, started orally 7 days after irradiation. Morbidity, skin wound area, breathing interval and blood urea nitrogen were measured up to 160 days post-irradiation to independently evaluate wound trauma and DEARE. Wounding exacerbated morbidity in irradiated rats between 5 and 14 days post-irradiation (during the ARS phase), and irradiation delayed wound healing. Wounding did not alter delayed morbidities from radiation pneumonitis or nephropathy after 30 days post-irradiation. Lisinopril did not mitigate wound healing, but markedly decreased morbidity during DEARE from 31 through 160 days. The results derived from this unique model of combined injuries suggest different molecular mechanisms of injury and healing of ARS and DEARE after radiation exposure.

Preclinical Model of Stereotactic Ablative Lung Irradiation Using Arc Delivery in the Mouse: Effect of Beam Size Changes and Dose Effect at Constant Collimation

PURPOSE

Stereotactic body radiation therapy is a therapeutic option offered to high surgical risk patients with lung cancer. Focal lung irradiation in mice is a new preclinical model to help understand the development of lung damage in this context. Here we developed a mouse model of lung stereotactic therapy using arc delivery and monitored the development of lung damage while varying the beam size and dose delivered.

METHODS AND MATERIALS

C57BL/6JRj mice were exposed to 90 Gy focal irradiation on the left lung using 1-mm diameter, 3 × 3 mm², 7 × 7 mm², or 10 × 10 mm² beam collimation for beam size effect and using 3 × 3 mm² beam collimation delivering 20 to 120 Gy for dose effect. Long-term lung damage was monitored with micro-computed tomography imaging with anatomopathologic and gene expression measurements in the injured patch and the ipsilateral and contralateral lungs.

RESULTS

Both 1-mm diameter and 3 × 3 mm² beam collimation allow long-term studies, but only 3-mm beam collimation generates lung fibrosis when delivering 90 Gy. Dose-effect studies with constant 3-mm beam collimation revealed a dose of 60 Gy as the minimum to obtain lung fibrosis 6 months postexposure. Lung fibrosis development was associated with club cell depletion and increased type II pneumocyte numbers. Lung injury developed with ipsilateral and contralateral consequences such as parenchymal thickening and gene expression modifications.

CONCLUSIONS

Arc therapy allows long-term studies and dose escalation without lethality. In our dose-delivery conditions, dose-effect studies revealed that 3 × 3 mm² beam collimation to a minimum single dose of 60 Gy enables preclinical models for the assessment of lung injury within a 6-month period. This model of lung tissue fibrosis in a time length compatible with mouse life span may offer good prospects for future mechanistic studies.

Modeling radiation-induced lung injury: lessons learned from whole thorax irradiation

Models of thoracic irradiation have been developed as clinicians and scientists have attempted to decipher the events that led up to the pulmonary toxicity seen in human subjects following radiation treatment. The most common model is that of whole thorax irradiation (WTI), applied in a single dose. Mice, particularly the C57BL/6J strain, has been frequently used in these investigations, and has greatly informed our current understanding of the initiation and progression of radiation-induced lung injury (RILI). In this review, we highlight the sequential progression and dynamic nature of RILI, focusing primarily on the vast array of information that has been gleaned from the murine model. Ample evidence indicates a wide array of biological responses that can be seen following irradiation, including DNA damage, oxidative stress, cellular senescence and inflammation, all triggered by the initial exposure to ionizing radiation (IR) and heterogeneously maintained throughout the temporal progression of injury, which manifests as acute pneumonitis and later fibrosis. It appears that the early responses of specific cell types may promote further injury, disrupting the microenvironment and preventing a return to homeostasis, although the exact mechanisms driving these responses remains somewhat unclear. Attempts to either prevent or treat RILI in preclinical models have shown some success by targeting these disparate radiobiological processes. As our understanding of the dynamic cellular responses to radiation improves through the use of such models, so does the likelihood of preventing or treating RILI.

Apoptosis Resistance in Fibroblasts Precedes Progressive Scarring in Pulmonary Fibrosis and Is Partially Mediated by Toll-Like Receptor 4 Activation

Inhalation of environmental toxicants such as cigarette smoke, metal or wood dust, silica, or asbestos is associated with increased risk for idiopathic pulmonary fibrosis (IPF). IPF involves progressive scarring of lung tissue, which interferes with normal respiration and is ultimately fatal; however, the complex cellular mechanisms of IPF pathogenesis remain unclear. Fibroblast apoptosis is essential in normal wound healing but is dysregulated in IPF. Recent studies suggest that Toll-like receptor 4 (TLR4) is key in the onset of IPF. Here, radiation-induced PF was used as a model for IPF because it very closely mimics the progressive and intractable nature of IPF. Female C57BL/6J (C57) and C57BL/6J TLR4-/- mice were exposed to a single dose of 13 Gy whole-thorax ionizing radiation. Although both strains showed similar levels of immediate radiation-induced damage, C57 mice exhibited more extensive fibrosis at 22-week postirradiation (PI) than TLR4-/- mice. Isolated C57 primary 1° MLFs showed decreased apoptosis susceptibility as early as 8-week postirradiation, a phenotype that persisted for the remainder of the radiation response. TLR4-/- 1° mouse lung fibroblasts did not exhibit significant apoptosis resistance at any point. Systemic release of high mobility group box 1, a TLR4 agonist, during the pneumonitis phase of the radiation response may act through TLR4 to contribute to fibroblast apoptosis resistance and thus interfere with wound resolution. These findings demonstrate that apoptosis resistance occurs earlier in pulmonary fibrosis pathogenesis than previously assumed, and that TLR4 signaling is a key mediator in this process.

A Potential Biomarker for Predicting the Risk of Radiation-Induced Fibrosis in the Lung

Biomarkers could play an essential role during triage in the aftermath of a radiological event, where exposure to radiation will be heterogeneous and complicated by concurrent trauma. Used alongside biodosimetry, biomarkers can identify victims in need of treatment for acute radiation effects, and might also provide valuable information on later developing consequences that need to be addressed as part of a treatment strategy. Indeed, because the lung is particularly sensitive to radiation and resultant late effects not only affect quality of life, but can also lead to morbidity, the risk of developing downstream pulmonary complications in exposed individuals requires assessment. In this study, analyses of changes in pulmonary and circulating content of club cell secretory protein (CCSP) and surfactant protein D (SP-D), expressed by epithelial club cells and type II pneumocytes in the lung, respectively, were used to evaluate pulmonary epithelial damage in several lung injury models. Using a combined radiation exposure model, fibrosis-susceptible C57BL/6J (C57) and alveolitis-prone C3H/HeJ (C3H) mice received 5 Gy total-body irradiation plus 2.5-10 Gy whole-lung irradiation, and lung and plasma samples were collected throughout the course of the radiation response, at time points ranging from 24 h to 26 weeks postirradiation. Radiation significantly reduced bronchiole CCSP coverage in C57 mice at 26 weeks, a response that varied in extent among animals, but correlated with the severity of fibrosis in each animal. Interestingly, plasma CCSP content was elevated in C57 mice at multiple time points preceding and during the fibrotic period; this response that was not observed in C3H mice. Circulating CCSP/SP-D ratios, calculated as an index of lung integrity, were similarly increased throughout the time course in C57, but not C3H, mice. Furthermore, when the thoracic doses were reduced to subthreshold levels for fibrosis induction (2.5 or 7.5 Gy), although the CCSP/SP-D ratio in lung homogenates demonstrated dose-responsive changes, this was not reflected in the plasma ratios at acute and late time points. Importantly, plasma CCSP/SP-D ratios also were not significantly altered in C57 mice exposed to LPS, and only transiently decreased in influenza-exposed mice, demonstrating a level of specificity for radiation-induced lung injury. These results indicate that the CCSP/SP-D ratio, measured in plasma, is sensitive to individual variation in radiation sensitivity, correlates with fibrosis development, can be detected early after exposure and is specific to radiation-induced injury. This suggests that the CCSP/SP-D ratio may be useful as a biomarker of radiation-induced pulmonary fibrosis.

A Single Exposure to Low- or High-LET Radiation Induces Persistent Genomic Damage in Mouse Epithelial Cells In Vitro and in Lung Tissue

Exposures to low- and high-linear energy transfer (LET) radiation induce clustered damage in DNA that is difficult to repair. These lesions are manifested as DNA-associated foci positive for DNA repair proteins and have been shown to persist in vitro and in vivo for days in several cell types and tissues in response to low-LET radiation. Although in some experimental conditions these residual foci have been linked with genomic instability and chromosomal aberrations, it remains poorly understood what type of damage they represent. Because high-LET radiation induces complex DNA lesions more efficiently than low-LET radiation, we compared the efficacy of several heavy ions (oxygen, silicon and iron) in a range (17 , 70 and 175 keV/μm, respectively) of LET and X rays at a 1 Gy dose. Persistent genomic damage was measured by γ-H2AX-53BP1-positive residual foci and micronucleus levels during the first three days and up to a week after in vitro and in vivo irradiation in lung cells and tissue. We demonstrate that in an in vitro irradiated mouse bronchial epithelial cell line, the expression of residual foci is readily detectable at 24 h with levels declining in the following 72 h postirradiation, but still persisting elevated over background at day 7. At this time, foci numbers are low but significant and proportional to the dose and quality of the radiation. The expression of residual foci in vitro was mirrored by increased micronuclei generation measured in cytokinesis-blocked cells, indicating long-term, persistent effects of genomic damage in this cell type. We also tested the expression of residual foci in lung tissue of C57BL/6 mice that received whole-body X-ray or heavy-ion irradiation. We found that at day 7 postirradiation, Clara/Club cells, but not pro-SPC-positive pneumocytes, contained a subpopulation of cells expressing γ-H2AX-53BP1-positive foci in a radiation quality-dependent manner. These findings suggest that in vivo persistent DNA repair foci reflect the initial genotoxic damage induced by radiation and a differential vulnerability among cells in the lung.

Effects of IL-4 on pulmonary fibrosis and the accumulation and phenotype of macrophage subpopulations following thoracic irradiation

PURPOSE

Thoracic irradiation injures lung parenchyma, triggering inflammation and immune cell activation, leading to pneumonitis and fibrosis. Macrophage polarization contributes to these processes. Since IL-4 promotes pro-fibrotic macrophage activation, its role in radiation-induced lung injury was investigated.

MATERIALS AND METHODS

Lung macrophage subpopulations were characterized from 3-26 weeks following exposure of WT and IL-4-/- mice to 0 or 12.5 Gray single dose thoracic irradiation.

RESULTS

Loss of IL-4 did not prevent fibrosis, but blunted macrophage accumulation within the parenchyma. At 3 weeks following exposure, cell numbers and expression of F4/80 and CD206, an alternative activation marker, decreased in alveolar macrophages but increased in infiltrating macrophages in WT mice. Loss of IL-4 impaired recovery of these markers in alveolar macrophages and blunted expansion of these populations in infiltrating macrophages. CD206+ cells were evident in fibrotic regions of WT mice only, however Arg-1+ cells increased in fibrotic regions in IL-4-/- mice only. Radiation-induced proinflammatory Ly6C expression was more apparent in alveolar and interstitial macrophages from IL-4-/- mice.

CONCLUSIONS

IL-4 loss did not prevent alternative macrophage activation and fibrosis in irradiated mice. Instead, a role is indicated for IL-4 in maintenance of macrophage populations in the lung following high single dose thoracic irradiation.

A survey of changing trends in modelling radiation lung injury in mice: bringing out the good, the bad, and the uncertain

Within this millennium there has been resurgence in funding and research dealing with animal models of radiation-induced lung injury to identify and establish predictive biomarkers and effective mitigating agents that are applicable to humans. Most have been performed on mice but there needs to be assurance that the emphasis on such models is not misplaced. We therefore considered it timely to perform a comprehensive appraisal of the literature dealing with radiation lung injury of mice and to critically evaluate the validity and clinical relevance of the research. A total of 357 research papers covering the period of 1970-2015 were extensively reviewed. Whole thorax irradiation (WTI) has become the most common treatment for studying lung injury in mice and distinct trends were seen with regard to the murine strain, radiation dose, intended pathology investigated, length of study, and assays. Recently, the C57BL/6 strain has been increasingly used in the majority of these studies with the notion that they are susceptible to pulmonary fibrosis. Nonetheless, many of these investigations depend on animal survival as the primary end point and neglect the importance of radiation pneumonitis and the anomaly of lethal pleural effusions. A relatively large variation in survival times of C5BL/6 mice is also seen among different institutions pointing to the need for standardization of radiation treatments and environmental conditions. An analysis of mitigating drug treatments is complicated by the fact that the majority of studies are limited to the C57BL/6 strain with a premature termination of the experiments and do not establish whether the treatment actually prevents or simply delays the progression of radiation injury. This survey of the literature has pointed to several improvements that need to be considered in establishing a reliable preclinical murine model of radiation lung injury. The lethality end point should also be used cautiously and with greater emphasis on other assays such as non-invasive lung functional and imaging monitoring in order to quantify specific pulmonary injury that can be better extrapolated to radiation toxicity encountered in our own species.

Normal Human Lung Epithelial Cells Inhibit Transforming Growth Factor-β Induced Myofibroblast Differentiation via Prostaglandin E2

Introduction

Idiopathic pulmonary fibrosis (IPF) is a chronic progressive disease with very few effective treatments. The key effector cells in fibrosis are believed to be fibroblasts, which differentiate to a contractile myofibroblast phenotype with enhanced capacity to proliferate and produce extracellular matrix. The role of the lung epithelium in fibrosis is unclear. While there is evidence that the epithelium is disrupted in IPF, it is not known whether this is a cause or a result of the fibroblast pathology. We hypothesized that healthy epithelial cells are required to maintain normal lung homeostasis and can inhibit the activation and differentiation of lung fibroblasts to the myofibroblast phenotype. To investigate this hypothesis, we employed a novel co-culture model with primary human lung epithelial cells and fibroblasts to investigate whether epithelial cells inhibit myofibroblast differentiation.

Measurements and Main Results

In the presence of transforming growth factor (TGF)-β, fibroblasts co-cultured with epithelial cells expressed significantly less α-smooth muscle actin and collagen and showed marked reduction in cell migration, collagen gel contraction, and cell proliferation compared to fibroblasts grown without epithelial cells. Epithelial cells from non-matching tissue origins were capable of inhibiting TGF-β induced myofibroblast differentiation in lung, keloid and Graves’ orbital fibroblasts. TGF-β promoted production of prostaglandin (PG) E₂ in lung epithelial cells, and a PGE₂ neutralizing antibody blocked the protective effect of epithelial cell co-culture.

Conclusions

We provide the first direct experimental evidence that lung epithelial cells inhibit TGF-β induced myofibroblast differentiation and pro-fibrotic phenotypes in fibroblasts. This effect is not restricted by tissue origin, and is mediated, at least in part, by PGE₂. Our data support the hypothesis that the epithelium plays a crucial role in maintaining lung homeostasis, and that damaged and/ or dysfunctional epithelium contributes to the development of fibrosis.

Examining the Effects of External or Internal Radiation Exposure of Juvenile Mice on Late Morbidity after Infection with Influenza A

A number of investigators have suggested that exposure to low-dose radiation may pose a potentially serious health risk. However, the majority of these studies have focused on the short-term rather than long-term effects of exposure to fixed source radiation, and few have examined the effects of internal contamination. Additionally, very few studies have focused on exposure in juveniles, when organs are still developing and could be more sensitive to the toxic effects of radiation. To specifically address whether early-life radiation injury may affect long-term immune competence, we studied 14-day-old juvenile pups that were either 5 Gy total-body irradiated or injected internally with 50 μCi soluble (137)Cs, then infected with influenza A virus at 26 weeks after exposure. After influenza infection, all groups demonstrated immediate weight loss. We found that externally irradiated, infected animals failed to recover weight relative to age-matched infected controls, but internally (137)Cs contaminated and infected animals had a weight recovery with a similar rate and degree as controls. Externally and internally irradiated mice demonstrated reduced levels of club cell secretory protein (CCSP) message in their lungs after influenza infection. The externally irradiated group did not recover CCSP expression even at the two-week time point after infection. Although the antibody response and viral titers did not appear to be affected by either radiation modality, there was a slight increase in monocyte chemoattractant protein (MCP)-1 expression in the lungs of externally irradiated animals 14 days after influenza infection, with increased cellular infiltration present. Notably, an increase in the number of regulatory T cells was seen in the mediastinal lymph nodes of irradiated mice relative to uninfected mice. These data confirm the hypothesis that early-life irradiation may have long-term consequences on the immune system, leading to an altered antiviral response.

plethy: management of whole body plethysmography data in R

BACKGROUND

Characterization of respiratory phenotypes can enhance complex trait and genomic studies involving allergic/autoimmune and infectious diseases. Many aspects of respiration can be measured using devices known as plethysmographs that can measure thoracic movement. One such approach (the Buxco platform) performs unrestrained whole body plethysmography on mice which infers thoracic movements from pressure differences from the act of inhalation and exhalation. While proprietary software is available to perform basic statistical analysis as part of machine's bundled software, it is desirable to be able to incorporate these analyses into high-throughput pipelines and integrate them with other data types, as well as leverage the wealth of analytic and visualization approaches provided by the R statistical computing environment.

RESULTS

This manuscript describes the plethy package which is an R/Bioconductor framework for pre-processing and analysis of plethysmography data with emphasis on larger scale longitudinal experiments. The plethy package was designed to facilitate quality control and exploratory data analysis. We provide a demonstration of the features of plethy using a dataset assessing the respiratory effects over time of SARS and Influenza infection in mice.

CONCLUSION

The plethy package provides functionality for users to import, perform quality assessment and exploratory data analysis in a manner that allows interoperability with existing modelling tools. Our package is implemented in R and is freely available as part of the Bioconductor project http://www.bioconductor.org/packages/release/bioc/html/plethy.html .