Transplantation of Endothelial Cells to Mitigate Acute and Chronic Radiation Injury to Vital Organs

Microenvironmental determinants of endothelial cell heterogeneity

During development, endothelial cells (ECs) undergo an extraordinary specialization by which generic capillary microcirculatory networks spanning from arteries to veins transform into patterned organotypic zonated blood vessels. These capillary ECs become specialized to support the cellular and metabolic demands of each specific organ, including supplying tissue-specific angiocrine factors that orchestrate organ development, maintenance of organ-specific functions and regeneration of injured adult organs. Here, we illustrate the mechanisms by which microenvironmental signals emanating from non-vascular niche cells induce generic ECs to acquire specific inter-organ and intra-organ functional attributes. We describe how perivascular, parenchymal and immune cells dictate vascular heterogeneity and capillary zonation, and how this system is maintained through tissue-specific signalling activated by vasculogenic and angiogenic factors and deposition of matrix components. We also discuss how perturbation of organotypic vascular niche cues lead to erasure of EC signatures, contributing to the pathogenesis of disease processes. We also describe approaches that use reconstitution of tissue-specific signatures of ECs to promote regeneration of damaged organs.

Radiation-Induced Tissue Regeneration: Pathways, Mechanisms, and Therapeutic Potential

This article explores the paradoxic nature of radiation as both a destructive and regenerative force. The article examines the interplay of signaling pathways, immune modulation, and stem cells in tissue regeneration post radiation, emphasizing the roles of key pathways like Wnt, Hedgehog, Notch, and p53. It highlights advancements in low-dose radiation therapy, extracellular vesicles, and stem cell-based interventions. Furthermore, the immune system's dual role in repair and damage is dissected, along with technologies such as artificial intelligence and bioengineered scaffolds that enhance therapeutic outcomes. The article offers a roadmap for integrating therapeutic innovation with regenerative medicine to improve patient outcomes.

Cord Blood-Derived Endothelial Progenitor Cells Promote In Vivo Regeneration of Human Hematopoietic Bone Marrow

PURPOSE

Victims of acute radiation exposure are susceptible to hematopoietic toxicity due to bone marrow damage and loss of mature blood elements. Here, we evaluated cord blood-derived endothelial progenitor cells (CB-EPCs) as a potential cellular therapy for mitigation of hematologic acute radiation syndrome. CB-EPCs express endothelial cell markers and maintain their growth characteristics beyond 10+ passages without diminishing their doubling capacity. Further, CB-EPCs can be cryopreserved in vapor-phase liquid nitrogen and easily recovered for propagation, making them an attractive nonimmunogenic cellular therapy for off-the-shelf use. Importantly, we show CB-EPCs have the capacity to potently expand adult human bone marrow hematopoietic progenitor cells both in vitro and in vivo.

METHODS AND MATERIALS

To demonstrate the role of CB-EPCs in promoting in vivo human immune reconstitution after irradiation, we employed a novel humanized mouse model established by transplant of CD34+ bone marrow cells from 9 unique adult organ donors into immunocompromised NSG-SGM3 mice. The response of the humanized immune system to ionizing irradiation was then tested by exposure to 1 Gy followed by subcutaneous treatment of CB-EPCs, Food and Drug Administration-approved growth factor pegfilgrastim (0.3 mg/kg), or saline.

RESULTS

At day 7, total human bone marrow was decreased by 80% in irradiated controls. However, treatment with either growth factor pegfilgrastim or CB-EPCs increased recovery of total human bone marrow by 2.5-fold compared with saline. Notably, CB-EPCs also increased recovery of both human CD34+ progenitors by 5-fold and colony-forming capacity by 3-fold versus saline. Additionally, CB-EPCs promoted recovery of endogenous bone marrow endothelial cells as observed by both increased vessel area and length compared with saline.

CONCLUSIONS

These findings indicate the feasibility of using humanized mice engrafted with adult bone marrow for radiation research and the development of CB-EPCs as an off-the-shelf cellular therapy for mitigation of hematologic acute radiation syndrome.

Comparison the therapeutic effects of bone marrow CD144+ endothelial cells and CD146+ mesenchymal stem cells in POF rats

Introduction

Premature ovarian insufficiency (POI) is a challenging issue in terms of reproduction biology. In this study, therapeutic properties of bone marrow CD146+ mesenchymal stem cells (MSCs) and CD144+ endothelial cells (ECs) were separately investigated in rats with POI.

Methods

POI rats were classified into control POI, POI + CD146+ MSCs, and POI + CD144+ ECs groups. Enriched CD146+ MSCs and CD144+ ECs were directly injected into ovarian tissue (15 × 104 cells/10 μL) in relevant groups. After 4 weeks, follicle-stimulating hormone (FSH), luteinizing hormone (LH), and estradiol (E2) levels were measured in blood samples. Ovarian tissues were collected and subjected to Hematoxylin-Eosin and Masson's trichrome staining. The expression of angp-2, vegfr-2, smad-2, -4, -6, and tgf-β1 was studied using qRT-PCR analysis. Histopathological examination indicated an increased pattern of atretic follicles in the POI group related to the control rats (P<0.0001).

Results

Data indicated that injection of POI + CD146+ MSCs and CD144+ ECs in POI rats reduced atretic follicles and increased the number of normal follicles (P<0.01). Along with these changes, the content of blue-colored collagen fibers was diminished after cell transplantation. Besides, cell transplantation in POI rats had the potential to reduce increased FSH, and LH levels (P<0.05). In contrast, E2 content was increased in POI + CD146+ MSCs and POI + CD144+ ECs groups compared to control POI rats, indicating restoration of follicular function. CD144+ (smad-2, and -4) and CD146+ (smad-6) cells altered the activity of genes belonging TGF-β signaling pathway. Unlike POI + CD146+ MSCs, aberrant angiogenesis properties were significantly down-regulated in POI + CD144+ ECs related to the control POI group (P<0.05).

Conclusion

The transplantation of bone marrow CD146+ and CD144+ cells can lead to the restoration of ovarian tissue function in POI rats via modulating different mechanisms associated with angiogenesis and fibrosis.

Circulating cell-free methylated DNA reveals tissue-specific, cellular damage from radiation treatment

Radiation therapy is an effective cancer treatment, although damage to healthy tissues is common. Here we analyzed cell-free, methylated DNA released from dying cells into the circulation to evaluate radiation-induced cellular damage in different tissues. To map the circulating DNA fragments to human and mouse tissues, we established sequencing-based, cell-type-specific reference DNA methylation atlases. We found that cell-type-specific DNA blocks were mostly hypomethylated and located within signature genes of cellular identity. Cell-free DNA fragments were captured from serum samples by hybridization to CpG-rich DNA panels and mapped to the DNA methylation atlases. In a mouse model, thoracic radiation-induced tissue damage was reflected by dose-dependent increases in lung endothelial and cardiomyocyte methylated DNA in serum. The analysis of serum samples from patients with breast cancer undergoing radiation treatment revealed distinct dose-dependent and tissue-specific epithelial and endothelial responses to radiation across multiple organs. Strikingly, patients treated for right-sided breast cancers also showed increased hepatocyte and liver endothelial DNA in the circulation, indicating the impact on liver tissues. Thus, changes in cell-free methylated DNA can uncover cell-type-specific effects of radiation and provide a readout of the biologically effective radiation dose received by healthy tissues.

Angiopoietin 2 Is Associated with Vascular Necroptosis Induction in Coronavirus Disease 2019 Acute Respiratory Distress Syndrome

Vascular injury is a well-established, disease-modifying factor in acute respiratory distress syndrome (ARDS) pathogenesis. Recently, coronavirus disease 2019 (COVID-19)-induced injury to the vascular compartment has been linked to complement activation, microvascular thrombosis, and dysregulated immune responses. This study sought to assess whether aberrant vascular activation in this prothrombotic context was associated with the induction of necroptotic vascular cell death. To achieve this, proteomic analysis was performed on blood samples from COVID-19 subjects at distinct time points during ARDS pathogenesis (hospitalized at risk, N = 59; ARDS, N = 31; and recovery, N = 12). Assessment of circulating vascular markers in the at-risk cohort revealed a signature of low vascular protein abundance that tracked with low platelet levels and increased mortality. This signature was replicated in the ARDS cohort and correlated with increased plasma angiopoietin 2 levels. COVID-19 ARDS lung autopsy immunostaining confirmed a link between vascular injury (angiopoietin 2) and platelet-rich microthrombi (CD61) and induction of necrotic cell death [phosphorylated mixed lineage kinase domain-like (pMLKL)]. Among recovery subjects, the vascular signature identified patients with poor functional outcomes. Taken together, this vascular injury signature was associated with low platelet levels and increased mortality and can be used to identify ARDS patients most likely to benefit from vascular targeted therapies.

Developmental angiocrine diversification of endothelial cells for organotypic regeneration

Adult organs are vascularized by specialized blood vessels. In addition to inter-organ vascular heterogeneity, each organ is arborized by structurally and functionally diversified populations of endothelial cells (ECs). The molecular pathways that are induced to orchestrate inter- and intra- organ vascular heterogeneity and zonation are shaped during development and fully specified postnatally. Notably, intra-organ specialization of ECs is associated with induction of angiocrine factors that guide cross-talk between ECs and parenchymal cells, establishing co-zonated vascular regions within each organ. In this review, we describe how microenvironmental tissue-specific biophysical, biochemical, immune, and inflammatory cues dictate the specialization of ECs with zonated functions. We delineate how physiological and biophysical stressors in the developing liver, lung, and kidney vasculature induce specialization of capillary beds. Deciphering mechanisms by which vascular microvasculature diversity is attained could set the stage for treating regenerative disorders and promote healing of organs without provoking fibrosis.

Identifying Candidate Biomarkers of Ionizing Radiation in Human Pulmonary Microvascular Lumens Using Microfluidics-A Pilot Study

The microvasculature system is critical for the delivery and removal of key nutrients and waste products and is significantly damaged by ionizing radiation. Single-cell capillaries and microvasculature structures are the primary cause of circulatory dysfunction, one that results in morbidities leading to progressive tissue and organ failure and premature death. Identifying tissue-specific biomarkers that are predictive of the extent of tissue and organ damage will aid in developing medical countermeasures for treating individuals exposed to ionizing radiation. In this pilot study, we developed and tested a 17 µL human-derived microvascular microfluidic lumen for identifying candidate biomarkers of ionizing radiation exposure. Through mass-spectrometry-based proteomics, we detected 35 proteins that may be candidate early biomarkers of ionizing radiation exposure. This pilot study demonstrates the feasibility of using humanized microfluidic and organ-on-a-chip systems for biomarker discovery studies. A more elaborate study of sufficient statistical power is needed to identify candidate biomarkers and test medical countermeasures of ionizing radiation.

PEG-G-CSF and L-Citrulline Combination Therapy for Mitigating Skin Wound Combined Radiation Injury in a Mouse Model

Radiation combined injury (RCI, radiation exposure coupled with other forms of injury, such as burn, wound, hemorrhage, blast, trauma and/or sepsis) comprises approximately 65% of injuries from a nuclear explosion, and greatly increases the risk of morbidity and mortality when compared to that of radiation injury alone. To date, no U.S. Food and Drug Administration (FDA)-approved countermeasures are available for RCI. Currently, three leukocyte growth factors (Neupogen®, Neulasta® and Leukine®) have been approved by the FDA for mitigating the hematopoietic acute radiation syndrome. However these granulocyte-colony-stimulating factor (G-CSF) and granulocyte-macrophage colony-stimulating factor (GM-CSF) products have failed to increase 30-day survival of mice after RCI, suggesting a more complicated biological mechanism is in play for RCI than for radiation injury. In the current study, the mitigative efficacy of combination therapy using pegylated (PEG)-G-CSF (Neulasta) and -citrulline was evaluated in an RCI mouse model. L-citrulline is a neutral alpha-amino acid shown to improve vascular endothelial function in cardiovascular diseases. Three doses of PEG-G-CSF at 1 mg/kg, subcutaneously administered on days 1, 8 and 15 postirradiation, were supplemented with oral -citrulline (1 g/kg), once daily from day 1 to day 21 postirradiation. The combination treatment significantly improved the 30-day survival of mice after RCI from 15% (vehicle-treated) to 42%, and extended the median survival time by 4 days, as compared to vehicle controls. In addition, the combination therapy significantly increased body weight and bone marrow stem and progenitor cell clonogenicity in RCI mice, and accelerated recovery from RCI-induced intestinal injury, compared to animals treated with vehicle. Treatment with -citrulline alone also accelerated skin wound healing after RCI. In conclusion, these data indicate that the PEG-G-CSF and -citrulline combination therapy is a potentially effective countermeasure for mitigating RCI, likely by enhancing survival of the hematopoietic stem/progenitor cells and accelerating recovery from the RCI-induced intestinal injury and skin wounds.

Bioengineering the Bone Marrow Vascular Niche

The bone marrow (BM) tissue is the main physiological site for adult hematopoiesis. In recent years, the cellular and matrix components composing the BM have been defined with unprecedent resolution, both at the molecular and structural levels. With the expansion of this knowledge, the possibility of reproducing a BM-like structure, to ectopically support and study hematopoiesis, becomes a reality. A number of experimental systems have been implemented and have displayed the feasibility of bioengineering BM tissues, supported by cells of mesenchymal origin. Despite being known as an abundant component of the BM, the vasculature has been largely disregarded for its role in regulating tissue formation, organization and determination. Recent reports have highlighted the crucial role for vascular endothelial cells in shaping tissue development and supporting steady state, emergency and malignant hematopoiesis, both pre- and postnatally. Herein, we review the field of BM-tissue bioengineering with a particular focus on vascular system implementation and integration, starting from describing a variety of applicable in vitro models, ending up with in vivo preclinical models. Additionally, we highlight the challenges of the field and discuss the clinical perspectives in terms of adoptive transfer of vascularized BM-niche grafts in patients to support recovering hematopoiesis.

Molecular determinants of nephron vascular specialization in the kidney

Although kidney parenchymal tissue can be generated in vitro, reconstructing the complex vasculature of the kidney remains a daunting task. The molecular pathways that specify and sustain functional, phenotypic and structural heterogeneity of the kidney vasculature are unknown. Here, we employ high-throughput bulk and single-cell RNA sequencing of the non-lymphatic endothelial cells (ECs) of the kidney to identify the molecular pathways that dictate vascular zonation from embryos to adulthood. We show that the kidney manifests vascular-specific signatures expressing defined transcription factors, ion channels, solute transporters, and angiocrine factors choreographing kidney functions. Notably, the ontology of the glomerulus coincides with induction of unique transcription factors, including Tbx3, Gata5, Prdm1, and Pbx1. Deletion of Tbx3 in ECs results in glomerular hypoplasia, microaneurysms and regressed fenestrations leading to fibrosis in subsets of glomeruli. Deciphering the molecular determinants of kidney vascular signatures lays the foundation for rebuilding nephrons and uncovering the pathogenesis of kidney disorders.

The kidney is vascularized with highly specialized and zonated endothelial cells that are essential for its filtration function. Here, Barry et al. provide a single-cell RNA sequencing analysis of the kidney vasculature that highlights its transcriptional heterogeneity and uncovers pathways important for its development and function.

Dislocation Engineered PtPdMo Alloy With Enhanced Antioxidant Activity for Intestinal Injury

Radiotherapy is the mainstay for abdomen and pelvis cancers treatment. However, high energy ray would inflict gastrointestinal (GI) system and adversely disrupt the treatment. The anti-oxidative agents provide a potential route for protecting body from radiation-induced injuries. Herein, highly catalytic nanocubes with dislocation structure are developed for treatment of intestinal injury. Structural and catalytic properties show that Mo incorporation can enhance antioxidant activity by dislocation structure in the alloy. In vitro studies showed that PtPdMo improved cell survival by scavenging radiation-induced ROS accumulation. Furthermore, after animals were exposed to lethal dose of radiation, the survival was increased by 50% with the PtPdMo i.p. treatment. Radioprotection mechanism revealed that PtPdMo alleviated the oxidative stress in multi-organs especially the small intestine by inhibiting intestinal epithelium apoptosis, reducing DNA strands breaks and enhancing repairing ability. In addition, PtPdMo protected hematopoietic system by improving the number of bone marrow and peripheral blood cells.

Vascular Niche in Lung Alveolar Development, Homeostasis, and Regeneration

Endothelial cells (ECs) constitute small capillary blood vessels and contribute to delivery of nutrients, oxygen and cellular components to the local tissues, as well as to removal of carbon dioxide and waste products from the tissues. Besides these fundamental functions, accumulating evidence indicates that capillary ECs form the vascular niche. In the vascular niche, ECs reciprocally crosstalk with resident cells such as epithelial cells, mesenchymal cells, and immune cells to regulate development, homeostasis, and regeneration in various organs. Capillary ECs supply paracrine factors, called angiocrine factors, to the adjacent cells in the niche and orchestrate these processes. Although the vascular niche is anatomically and functionally well-characterized in several organs such as bone marrow and neurons, the effects of endothelial signals on other resident cells and anatomy of the vascular niche in the lung have not been well-explored. This review discusses the role of alveolar capillary ECs in the vascular niche during development, homeostasis and regeneration.

Use of Growth Factors and Other Cytokines for Treatment of Injuries During a Radiation Public Health Emergency

Due to the threat of a radiological or nuclear incident that could impact citizens, the U.S. Department of Health and Human Services tasked the National Institute of Allergy and Infectious Diseases (NIAID) with identifying and funding early- to mid-stage medical countermeasure (MCM) development to treat radiation-induced injuries. Given that the body's natural response to radiation exposure includes production of growth factors and cytokines, and that the only drugs approved by the U.S. Food and Drug Administration to treat acute radiation syndrome are growth factors targeting either the granulocyte (Neupogen^® or Neulasta^®) or granulocyte and macrophage (Leukine^®) hematopoietic cell lineages, there is interest in understanding the role that these factors play in responding to and/or ameliorating radiation damage. Furthermore, in an environment where resources are scarce, such as what might be expected during a radiation public health emergency, availability of growth factor or other treatments may be limited. For these reasons, the NIAID partnered with the Radiation Injury Treatment Network (RITN), whose membership includes medical centers with expertise in the management of bone marrow failure, to explore the use of growth factors and other cytokines as MCMs to mitigate/treat radiation injuries. A workshop was convened that included government, industry and academic subject matter experts, with presentations covering the anticipated concept of operations during a mass casualty incident including triage and treatment, growth factors under development for a radiation indication, and how the practice of medicine can inform other potential approaches, as well as considerations for administration of these products to diverse civilian populations. This report reviews the information presented, and provides an overview of the discussions from a guided breakout session.

Endothelial Cell-Derived Extracellular Vesicles Mitigate Radiation-Induced Hematopoietic Injury

PURPOSE

Extracellular vesicles (EVs) are shed vesicles that bear a combination of nucleic acids and proteins. EVs are becoming recognized as a mode of cell-to-cell communication. Because hematopoietic stem cells reside in proximity to endothelial cells (ECs), we investigated whether EC-derived EVs could regulate hematopoietic stem cell regeneration after ionizing radiation.

METHODS AND MATERIALS

We generated EVs derived from primary murine marrow ECs. We sought to determine the response of irradiated hematopoietic stem and progenitor cells to syngeneic or allogeneic EVs in culture assays. Starting 24 hours after either sublethal or lethal irradiation, mice were treated with EVs or saline or cultured primary marrow endothelial cells to determine the hematopoietic response in vivo.

RESULTS

We demonstrate that EVs bear nuclear material and express EC-specific markers. Treatment with EVs promoted cell expansion and increased the number of colony-forming units compared to irradiated, hematopoietic cell cultures treated with cytokines alone. After total body irradiation, EV-treated mice displayed preserved marrow cellularity, marrow vessel integrity, and prolonged overall survival compared with controls treated with saline. Treatment of irradiated hematopoietic stem/progenitor cells (HSPCs) with EVs from different genetic strains showed results similar to treatment of HSPCs from syngeneic EVs. Mechanistically, treatment of irradiated HSPCs with EVs resulted in decreased levels of annexin V+ apoptotic cell death, which is mediated in part by tissue inhibitor of metalloproteinase-1.

CONCLUSIONS

Our findings show that syngeneic or allogeneic EVs could serve as cell-derived therapy to deliver physiologic doses of nucleic acids and growth factors to hematopoietic cells to accelerate hematopoietic regeneration.

Cellular Therapies for Treatment of Radiation Injury: Report from a NIH/NIAID and IRSN Workshop

In recent years, there has been increasing concern over the possibility of a radiological or nuclear incident occurring somewhere in the world. Intelligence agencies frequently report that terrorist groups and rogue nations are seeking to obtain radiological or nuclear weapons of mass destruction. In addition, there exists the real possibility that safety of nuclear power reactors could be compromised by natural (such as the tsunami and subsequent Fukushima accident in Japan in March, 2011) or accidental (Three Mile Island, 1979 and Chernobyl, 1986) events. Although progress has been made by governments around the world to prepare for these events, including the stockpiling of radiation countermeasures, there are still challenges concerning care of patients injured during a radiation incident. Because the deleterious and pathological effects of radiation are so broad, it is desirable to identify medical countermeasures that can have a beneficial impact on several tissues and organ systems. Cellular therapies have the potential to impact recovery and tissue/organ regeneration for both early and late complications of radiation exposure. These therapies, which could include stem or blood progenitor cells, mesenchymal stromal cells (MSCs) or cells derived from other tissues (e.g., endothelium or placenta), have shown great promise in treating other nonradiation injuries to and diseases of the bone marrow, skin, gastrointestinal tract, brain, lung and heart. To explore the potential use of these therapies in the treatment of victims after acute radiation exposure, the National Institute of Allergy and Infectious Diseases co-sponsored an international workshop in July, 2015 in Paris, France with the Institut de Radioprotection et de Sûreté Nucléaire. The workshop included discussions of data available from testing in preclinical models of radiation injury to different organs, logistics associated with the practical use of cellular therapies for a mass casualty incident, as well as international regulatory requirements for authorizing such drug products to be legally and readily used in such incidents. This report reviews the data presented, as well as key discussion points from the meeting.