Glia-Selective Deletion of Complement C1q Prevents Radiation-Induced Cognitive Deficits and Neuroinflammation

Pharmacologic Manipulation of Complement Receptor 3 Prevents Dendritic Spine Loss and Cognitive Impairment After Acute Cranial Radiation

PURPOSE

Cranial irradiation induces healthy tissue damage that can lead to neurocognitive complications, negatively affecting patient quality of life. One damage indicator associated with cognitive impairment is loss of neuronal spine density. We previously demonstrated that irradiation-mediated spine loss is microglial complement receptor 3 (CR3) and sex dependent. We hypothesized that these changes are associated with late-delayed cognitive deficits and amenable to pharmacologic intervention.

METHODS AND MATERIALS

Our model of cranial irradiation (acute, 10 Gy gamma) used male and female CR3-wild type and CR3-deficient Thy-1 YFP mice of C57BL/6 background. Forty-five days after irradiation and behavioral testing, we quantified spine density and markers of microglial reactivity in the hippocampal dentate gyrus. In a separate experiment, male Thy-1 YFP C57BL/6 mice were treated with leukadherin-1, a modulator of CR3 function.

RESULTS

We found that male mice demonstrate irradiation-mediated spine loss and cognitive deficits but that female and CR3 knockout mice do not. These changes were associated with greater reactivity of microglia in male mice. Pharmacologic manipulation of CR3 with LA1 prevented spine loss and cognitive deficits in irradiated male mice.

CONCLUSIONS

This work improves our understanding of irradiation-mediated mechanisms and sex dependent responses and may help identify novel therapeutics to reduce irradiation-induced cognitive decline and improve patient quality of life.

HIV-1 infection promotes neuroinflammation and neuron pathogenesis in novel microglia-containing cerebral organoids

Cerebral organoids (COs) are a valuable tool to study the intricate interplay between glial cells and neurons in brain development and disease, including HIV-associated neuroinflammation. We developed a novel approach to generate microglia containing COs (CO-iMs) by co-culturing hematopoietic progenitors and induced pluripotent stem cells. This approach allowed for the differentiation of microglia within the organoids concomitantly to the neuronal progenitors. CO- iMs exhibited higher efficiency in generation of CD45 + /CD11b + /Iba-1 + microglia cells compared to conventional COs with physiologically relevant proportion of microglia (∼7%). CO-iMs exhibited substantially higher expression of microglial homeostatic and sensome markers as well as markers for the complement cascade. CO-iMs showed susceptibility to HIV infection resulting in a significant increase in several pro-inflammatory cytokines/chemokines and compromised neuronal function, which were abrogated by addition of antiretrovirals. Thus, CO-iM is a robust model to decipher neuropathogenesis, neurological disorders, and viral infections of brain cells in a 3D culture system.

Ultra-High Dose Rate Helium Ion Beams: First In Vivo Evidence for Neuroprotective FLASH Effect

Purpose

To investigate ultra-high-dose rate helium ion irradiation and its potential FLASH sparing effect with the endpoint acute brain injury in preclinical in vivo settings.

Material and methods

Raster-scanned helium ion beams were administered to explore and compare the impact of dose rate variations between standard dose rate (SDR at 0.2 Gy/s) and FLASH (at 141 Gy/s) radiotherapy (RT). Irradiation-induced brain injury was investigated in healthy C57BL/6 mice via DNA damage response kinetic studies using nuclear γH2AX as a surrogate for double-strand breaks (DSB). The integrity of the neurovascular and immune compartments was assessed via CD31+ microvascular density and microglia/macrophages activation. Iba1+ ramified and CD68+ phagocytic microglia/macrophages were quantified, together with the expression of inducible nitric oxide synthetase (iNOS).

Results

Helium FLASH RT significantly prevented acute brain tissue injury compared with SDR. This was demonstrated by reduced levels of DSB and structural preservation of the neurovascular endothelium after FLASH RT. Moreover, FLASH RT exhibited reduced activation of neuroinflammatory signals compared with SDR, as detected by quantification of CD68+ iNOS+ microglia/macrophages.

Conclusion

To our knowledge, this is the first report on the FLASH-sparing neuroprotective effect of raster scanning helium ion radiotherapy in vivo.

Dynamin-1 is a potential mediator in Cancer-Related Cognitive Impairment

Dynamin-1 (DNM1) consolidates memory through synaptic transmission and modulation and has been explored as a therapeutic target in Alzheimer's disease. Through a two-prong approach, this study examined its role in cancer-related cognitive impairment (CRCI) pathogenesis using human and animal models. The human study recruited newly diagnosed, chemotherapy-naïve adolescent and young adult cancer and non-cancer controls to complete a cognitive instrument (FACT-Cog) and blood draws for up to three time points. Concurrently, a syngeneic young-adult WT (C57BL/6 female) mouse model of breast cancer was developed to study DNM1 expression in the brain. Samples from eighty-six participants with 30 adolescent and young adult (AYA) cancer and 56 non-cancer participants were analyzed. DNM1 levels were significantly lower among cancer participants compared to non-cancer prior to treatment. While receiving cancer treatment, cognitively impaired patients were found with a significant downregulation of DNM1, but not among those without impairment. In murine breast cancer-bearing mice receiving chemotherapy, we consistently found a significant decline in DNM1 immunoreactivity in the hippocampal CA1 and CA3 subregions. Observed in both human and animal studies, the downregulation of DNM1 is linked with the onset of CRCI. Future research should explore the potential of DNM1 in CRCI pathogenesis and therapeutics development.

Longitudinal Neuropathological Consequences of Extracranial Radiation Therapy in Mice

Cancer-related cognitive impairment (CRCI) is a consequence of chemotherapy and extracranial radiation therapy (ECRT). Our prior work demonstrated gliosis in the brain following ECRT in SKH1 mice. The signals that induce gliosis were unclear. Right hindlimb skin from SKH1 mice was treated with 20 Gy or 30 Gy to induce subclinical or clinical dermatitis, respectively. Mice were euthanized at 6 h, 24 h, 5 days, 12 days, and 25 days post irradiation, and the brain, thoracic spinal cord, and skin were collected. The brains were harvested for spatial proteomics, immunohistochemistry, Nanostring nCounter® glial profiling, and neuroinflammation gene panels. The thoracic spinal cords were evaluated by immunohistochemistry. Radiation injury to the skin was evaluated by histology. The genes associated with neurotransmission, glial cell activation, innate immune signaling, cell signal transduction, and cancer were differentially expressed in the brains from mice treated with ECRT compared to the controls. Dose-dependent increases in neuroinflammatory-associated and neurodegenerative-disease-associated proteins were measured in the brains from ECRT-treated mice. Histologic changes in the ECRT-treated mice included acute dermatitis within the irradiated skin of the hindlimb and astrocyte activation within the thoracic spinal cord. Collectively, these findings highlight indirect neuronal transmission and glial cell activation in the pathogenesis of ECRT-related CRCI, providing possible signaling pathways for mitigation strategies.

Cranial irradiation disrupts homeostatic microglial dynamic behavior

Cranial irradiation causes cognitive deficits that are in part mediated by microglia, the resident immune cells of the brain. Microglia are highly reactive, exhibiting changes in shape and morphology depending on the function they are performing. Additionally, microglia processes make dynamic, physical contacts with different components of their environment to monitor the functional state of the brain and promote plasticity. Though evidence suggests radiation perturbs homeostatic microglia functions, it is unknown how cranial irradiation impacts the dynamic behavior of microglia over time. Here, we paired in vivo two-photon microscopy with a transgenic mouse model that labels cortical microglia to follow these cells and determine how they change over time in cranial irradiated mice and their control littermates. We show that a single dose of 10 Gy cranial irradiation disrupts homeostatic cortical microglia dynamics during a 1-month time course. We found a lasting loss of microglial cells following cranial irradiation, coupled with a modest dysregulation of microglial soma displacement at earlier timepoints. The homogeneous distribution of microglia was maintained, suggesting microglia rearrange themselves to account for cell loss and maintain territorial organization following cranial irradiation. Furthermore, we found cranial irradiation reduced microglia coverage of the parenchyma and their surveillance capacity, without overtly changing morphology. Our results demonstrate that a single dose of radiation can induce changes in microglial behavior and function that could influence neurological health. These results set the foundation for future work examining how cranial irradiation impacts complex cellular dynamics in the brain which could contribute to the manifestation of cognitive deficits.

Radiotherapy for non-cancer diseases: benefits and long-term risks

PURPOSE

The discovery of X-rays was followed by a variety of attempts to treat infectious diseases and various other non-cancer diseases with ionizing radiation, in addition to cancer. There has been a recent resurgence of interest in the use of such radiotherapy for non-cancer diseases. Non-cancer diseases for which use of radiotherapy has currently been proposed include refractory ventricular tachycardia, neurodegenerative diseases (e.g. Alzheimer's disease and dementia), and Coronavirus Disease 2019 (COVID-19) pneumonia, all with ongoing clinical studies that deliver radiation doses of 0.5-25 Gy in a single fraction or in multiple daily fractions. In addition to such non-cancer effects, historical indications predominantly used in some countries (e.g. Germany) include osteoarthritis and degenerative diseases of the bones and joints. This narrative review gives an overview of the biological rationale and ongoing preclinical and clinical studies for radiotherapy proposed for various non-cancer diseases, discusses the plausibility of the proposed biological rationale, and considers the long-term radiation risks of cancer and non-cancer diseases.

CONCLUSIONS

A growing body of evidence has suggested that radiation represents a double-edged sword, not only for cancer, but also for non-cancer diseases. At present, clinical evidence has shown some beneficial effects of radiotherapy for ventricular tachycardia, but there is little or no such evidence of radiotherapy for other newly proposed non-cancer diseases (e.g. Alzheimer's disease, COVID-19 pneumonia). Patients with ventricular tachycardia and COVID-19 pneumonia have thus far been treated with radiotherapy when they are an urgent life threat with no efficient alternative treatment, but some survivors may encounter a paradoxical situation where patients were rescued by radiotherapy but then get harmed by radiotherapy. Further studies are needed to justify the clinical use of radiotherapy for non-cancer diseases, and optimize dose to diseased tissue while minimizing dose to healthy tissue.

The Distant Molecular Effects on the Brain by Cancer Treatment

Cancer survivors experience cancer-related cognitive impairment (CRCI) secondary to treatment. Chemotherapy and radiation therapy independently contribute to cognitive dysfunction; however, the underlying mechanisms leading to dysfunction remain unclear. We characterized brain gene expression changes in a mouse model of CRCI to identify the mechanistic underpinnings. Eleven-to-twelve-week-old SKH1 mice were treated with doxorubicin (DOX), hindlimb radiation (RT), concurrent hindlimb radiation and doxorubicin (DOX-RT), or no treatment (control). Sixteen days following treatment, gene expression was measured from murine brains using the NanoString nCounter® glial profiling panel. Gene expression was normalized and compared between groups. No two groups shared the same expression pattern, and only Gnb1 and Srpr were upregulated in multiple treatment groups. Brains from DOX-treated mice had upregulated Atf2, Atp5b, Gnb1, Rad23b, and Srpr and downregulated Sirt5 expression compared to control brains. Brains from RT-treated mice demonstrated increased Abcg2 and Fgf2 and decreased C1qa and C1qb expression compared to control brains. Brains from DOX-RT-treated mice had upregulated Adar, E2f3, Erlec1, Gnb1, Srpr, Vim, and Pdgfra expression and downregulated Rock2 and Inpp5f expression compared to control brains. The gene expression changes demonstrated here highlight roles for neuronal transmission and oxidative stress in the pathogenesis of doxorubicin-related CRCI and inflammation in RT-related CRCI.

Analysis of complement system and its related factors in Alzheimer's disease

Alzheimer's disease (AD) is a primary cause of dementia. The complement system is closely related to AD pathology and may be a potential target for the prevention and treatment of AD. In our study, we conducted a bioinformatics analysis to analyze the role of the complement system and its related factors in AD using Gene Expression Omnibus (GEO) data. We also conducted a functional analysis. Our study verified that 23 genes were closely related to differentially expressed complement system genes in diseases after intersecting the disease-related complement system module genes and differentially expressed genes. The STRING database was used to predict the interactions between the modular gene proteins of the differential complement system. A total of 21 gene proteins and 44 interaction pairs showed close interactions. We screened key genes and created a diagnostic model. The predictive effect of the model was constructed using GSE5281 and our study indicated that the predictive effect of the model was good. Our study also showed enriched negative regulation of Notch signaling, cytokine secretion involved in the immune response pathway, and cytokine secretion involved in immune response hormone-mediated apoptotic signaling pathway. We hope that our study provides a promising target to prevent and delay the onset, diagnosis, and treatment of AD.

Advances in the study of the molecular biological mechanisms of radiation-induced brain injury

Radiation therapy is one of the most commonly used treatments for head and neck cancers, but it often leads to radiation-induced brain injury. Patients with radiation-induced brain injury have a poorer quality of life, and no effective treatments are available. The pathogenesis of this condition is unknown. This review summarizes the molecular biological mechanism of radiation-induced brain injury and provides research directions for future studies. The molecular mechanisms of radiation-induced brain injury are diverse and complex. Radiation-induced chronic neuroinflammation, destruction of the blood-brain barrier, oxidative stress, neuronal damage, and physiopathological responses caused by specific exosome secretion lead to radiation-induced brain injury.

Skin Wound following Irradiation Aggravates Radiation-Induced Brain Injury in a Mouse Model

Radiation injury- and radiation combined with skin injury-induced inflammatory responses in the mouse brain were evaluated in this study. Female B6D2F1/J mice were subjected to a sham, a skin wound (SW), 9.5 Gy ⁶⁰Co total-body gamma irradiation (RI), or 9.5 Gy RI combined with a skin puncture wound (RCI). Survival, body weight, and wound healing were tracked for 30 days, and mouse brain samples were collected on day 30 after SW, RI, RCI, and the sham control. Our results showed that RCI caused more severe animal death and body weight loss compared with RI, and skin wound healing was significantly delayed by RCI compared to SW. RCI and RI increased the chemokines Eotaxin, IP-10, MIG, 6Ckine/Exodus2, MCP-5, and TIMP-1 in the brain compared to SW and the sham control mice, and the Western blot results showed that IP-10 and p21 were significantly upregulated in brain cells post-RI or -RCI. RI and RCI activated both astrocytes and endothelial cells in the mouse brain, subsequently inducing blood-brain barrier (BBB) leakage, as shown by the increased ICAM1 and GFAP proteins in the brain and GFAP in the serum. The Doublecortin (DCX) protein, the "gold standard" for measuring neurogenesis, was significantly downregulated by RI and RCI compared with the sham group. Furthermore, RI and RCI decreased the expression of the neural stem cell marker E-cadherin, the intermediate progenitor marker MASH1, the immature neuron cell marker NeuroD1, and the mature neuron cell marker NeuN, indicating neural cell damage in all development stages after RI and RCI. Immunohistochemistry (IHC) staining further confirmed the significant loss of neural cells in RCI. Our data demonstrated that RI and RCI induced brain injury through inflammatory pathways, and RCI exacerbated neural cell damage more than RI.

Monocyte production of C1q potentiates CD8 + T cell effector function following respiratory viral infection

Respiratory viral infections remain a leading cause of morbidity and mortality. Using a murine model of human metapneumovirus (HMPV), we identified recruitment of a C1q-producing inflammatory monocyte population concomitant with viral clearance by adaptive immune cells. Genetic ablation of C1q led to reduced CD8 + T cell function. Production of C1q by a myeloid lineage was sufficient to enhance CD8 + T cell function. Activated and dividing CD8 + T cells expressed a putative C1q receptor, gC1qR. Perturbation of gC1qR signaling led to altered CD8 + T cell IFN-γ production and metabolic capacity. Autopsy specimens from fatal respiratory viral infections in children demonstrated diffuse production of C1q by an interstitial population. Humans with severe COVID-19 infection also demonstrated upregulation of gC1qR on activated and rapidly dividing CD8 + T cells. Collectively, these studies implicate C1q production from monocytes as a critical regulator of CD8 + T cell function following respiratory viral infection.

BDNF Augmentation Using Riluzole Reverses Doxorubicin-Induced Decline in Cognitive Function and Neurogenesis

Cancer-related cognitive impairment (CRCI) considerably affects the quality of life of millions of cancer survivors. Brain-derived neurotrophic factor (BDNF) has been shown to promote survival, differentiation, and maintenance of in vivo dentate neurogenesis, and chemotherapy induces a plethora of physiological and cellular alterations, including a decline in neurogenesis and increased neuroinflammation linked with cognitive impairments. In our clinical studies, breast cancer patients treated with doxorubicin (Adriamycin®, ADR) experienced a significant reduction in the blood levels of BDNF that was associated with a higher risk of CRCI. Our past rodent studies in CRCI have also shown a significant reduction in dentate neurogenesis accompanied by cognitive impairment. In this study, using a female mouse model of ADR-induced cognitive decline, we tested the impact of riluzole (RZ), an orally active BDNF-enhancing medication that is FDA-approved for amyotrophic lateral sclerosis. ADR-treated mice receiving RZ in the drinking water for 1 month showed significant improvements in hippocampal-dependent learning and memory function (spatial recognition), fear extinction memory consolidation, and reduced anxiety-like behavior. RZ prevented chemotherapy-induced reductions of BDNF levels in the hippocampus. Importantly, RZ mitigated chemotherapy-induced loss of newly born, immature neurons, dentate neurogenesis, and neuroinflammation. In conclusion, this data provides pre-clinical evidence for a translationally feasible approach to enhance the neuroprotective effects of RZ treatment to prevent CRCI.

Uncovering the Protective Neurologic Mechanisms of Hypofractionated FLASH Radiotherapy

Implementation of ultra-high dose-rate FLASH radiotherapy (FLASH-RT) is rapidly gaining traction as a unique cancer treatment modality able to dramatically minimize normal tissue toxicity while maintaining antitumor efficacy compared with standard-of-care radiotherapy at conventional dose rate (CONV-RT). The resultant improvements in the therapeutic index have sparked intense investigations in pursuit of the underlying mechanisms. As a preamble to clinical translation, we exposed non-tumor-bearing male and female mice to hypofractionated (3 × 10 Gy) whole brain FLASH- and CONV-RT to evaluate differential neurologic responses using a comprehensive panel of functional and molecular outcomes over a 6-month follow-up. In each instance, extensive and rigorous behavioral testing showed FLASH-RT to preserve cognitive indices of learning and memory that corresponded to a similar protection of synaptic plasticity as measured by long-term potentiation (LTP). These beneficial functional outcomes were not found after CONV-RT and were linked to a preservation of synaptic integrity at the molecular (synaptophysin) level and to reductions in neuroinflammation (CD68+ microglia) throughout specific brain regions known to be engaged by our selected cognitive tasks (hippocampus, medial prefrontal cortex). Ultrastructural changes in presynaptic/postsynaptic bouton (Bassoon/Homer-1 puncta) within these same regions of the brain were not found to differ in response to dose rate. With this clinically relevant dosing regimen, we provide a mechanistic blueprint from synapse to cognition detailing how FLASH-RT reduces normal tissue complications in the irradiated brain.

Significance

Functional preservation of cognition and LTP after hypofractionated FLASH-RT are linked to a protection of synaptic integrity and a reduction in neuroinflammation over protracted after irradiation times.

Complement C3 mediates podocyte injury through TLR4/NFΚB-P65 signaling during ischemia-reperfusion acute kidney injury and post-injury fibrosis

BACKGROUND

The aim of this study was to explore the mechanism of complement C3a mediating podocyte injury during ischemia-reperfusion acute kidney injury (IR-AKI) and post-injury fibrosis.

METHODS

Renal artery clamping was used to establish IR-AKI and post-injury fibrosis model. HE and Masson staining were performed to observe renal fibrosis. The protein abundance levels were measured along with inflammatory markers, renal complement C3. Podocytes were treated with C3a with or without Toll-like receptor 4(TLR4) inhibitor. The effects of TLR4 up-regulation by TLR4 plasmids were examined.

RESULTS

C3^-/- resulted in amelioration of renal dysfunction by reducing podocyte damage and renal fibrosis. Immunoblot with renal tissue homogenates from IR-AKI mice revealed that C3^-/- decreased TLR4/Nuclear Factor-κB (NFκB)-P65.

CONCLUSION

Our results indicate that modulating C3/TLR4/NFκB-P65 signaling pathway is a novel therapeutic target for the IR-AKI and post-injury fibrosis.

Interactions of glial cells with neuronal synapses, from astrocytes to microglia and oligodendrocyte lineage cells

The mammalian brain is a complex organ comprising neurons, glia, and more than 1 × 10¹⁴ synapses. Neurons are a heterogeneous group of electrically active cells, which form the framework of the complex circuitry of the brain. However, glial cells, which are primarily divided into astrocytes, microglia, oligodendrocytes (OLs), and oligodendrocyte precursor cells (OPCs), constitute approximately half of all neural cells in the mammalian central nervous system (CNS) and mainly provide nutrition and tropic support to neurons in the brain. In the last two decades, the concept of "tripartite synapses" has drawn great attention, which emphasizes that astrocytes are an integral part of the synapse and regulate neuronal activity in a feedback manner after receiving neuronal signals. Since then, synaptic modulation by glial cells has been extensively studied and substantially revised. In this review, we summarize the latest significant findings on how glial cells, in particular, microglia and OL lineage cells, impact and remodel the structure and function of synapses in the brain. Our review highlights the cellular and molecular aspects of neuron-glia crosstalk and provides additional information on how aberrant synaptic communication between neurons and glia may contribute to neural pathologies.

Spatial Gene Expression Changes in the Mouse Heart After Base-Targeted Irradiation

PURPOSE

Radiation cardiotoxicity (RC) is a clinically significant adverse effect of treatment for patients with thoracic malignancies. Clinical studies in lung cancer have indicated that heart substructures are not uniformly radiosensitive, and that dose to the heart base drives RC. In this study, we aimed to characterize late changes in gene expression using spatial transcriptomics in a mouse model of base regional radiosensitivity.

METHODS AND MATERIALS

An aged female C57BL/6 mouse was irradiated with 16 Gy delivered to the cranial third of the heart using a 6 × 9 mm parallel opposed beam geometry on a small animal radiation research platform, and a second mouse was sham-irradiated. After echocardiography, whole hearts were collected at 30 weeks for spatial transcriptomic analysis to map gene expression changes occurring in different regions of the partially irradiated heart. Cardiac regions were manually annotated on the capture slides and the gene expression profiles compared across different regions.

RESULTS

Ejection fraction was reduced at 30 weeks after a 16 Gy irradiation to the heart base, compared with the sham-irradiated controls. There were markedly more significant gene expression changes within the irradiated regions compared with nonirradiated regions. Variation was observed in the transcriptomic effects of radiation on different cardiac base structures (eg, between the right atrium [n = 86 dysregulated genes], left atrium [n = 96 dysregulated genes], and the vasculature [n = 129 dysregulated genes]). Disrupted biological processes spanned extracellular matrix as well as circulatory, neuronal, and contractility activities.

CONCLUSIONS

This is the first study to report spatially resolved gene expression changes in irradiated tissues. Examination of the regional radiation response in the heart can help to further our understanding of the cardiac base's radiosensitivity and support the development of actionable targets for pharmacologic intervention and biologically relevant dose constraints.

Hippocampal Inflammation and Gene Expression Changes in Peripheral Lipopolysaccharide Challenged Mice Showing Sickness and Anxiety-Like Behaviors

Neuroinflammation is often associated with the development of depressive and anxiety disorders. The hippocampus is one of the brain regions affected by inflammation that is associated with these symptoms. However, the mechanism of hippocampal inflammation-induced emotional behavior remains unknown. The aim of this study was to clarify temporal changes in the neuroinflammatory responses in the hippocampus and the response of dentate gyrus (DG) neurons using peripheral lipopolysaccharide (LPS)-challenged mice. LPS administration induced anxiety-like activity in the elevated plus maze test and social interaction test after 24 h, at which time the mice had recovered from sickness behavior. We examined the hippocampal inflammation-related gene expression changes over time. The expression of interleukin-1β (Il1b) and tumor necrosis factor α (Tnfa) was rapidly enhanced and sustained until 24 h after LPS administration, whereas the expression of Il6 was transiently induced at approx. 6 h. IL-6-dependent downstream signaling of transducer and activator of transcription 3 (STAT3) was also activated approx. 3-6 h after LPS treatment. The expression of innate immune genes including interferon-induced transmembrane proteins such as interferon-induced transmembrane protein 1 (Ifitm1) and Ifitm3 and complement factors such as C1qa and C1qb started to increase approx. 6 h and showed sustained or further increase at 24 h. We also examined changes in the expression of several maturation markers in the DG and found that LPS enhanced the expression of calbindin 1 (Calb1), tryptophan-2,3-dioxigenase 2 (Tdo2), Il1rl, and neurotrophin-3 (Ntf3) at 24 h after LPS treatment. Collectively, these results demonstrate temporal changes of inflammation and gene expression in the hippocampus in LPS-induced sickness and anxiety-like behaviors.

Radiation and CNS effects: summary of evidence from a recent symposium of the Radiation Research Society

This article summarizes a Symposium on 'Radiation risks of the central nervous system' held virtually at the 67th Annual Meeting of the Radiation Research Society, 3-6 October 2021. Repeated low-dose radiation exposure over a certain period could lead to reduced neuronal proliferation, altered neurogenesis, neuroinflammation and various neurological complications, including psychological consequences, necessitating further research in these areas. Four speakers from radiation biology, genetics and epidemiology presented the latest data from their studies seeking insights into this important topic. This symposium highlighted new and important directions for further research on mental health disorders, neurodegenerative conditions and cognitive impairment. Future studies will examine risks of mental and behavioral disorders and neurodegenerative diseases following protracted radiation exposures to better understand risks of occupational exposures as well as provide insights into risks from exposures to galactic cosmic rays.

Microglia: Rheostats of space radiation effects in the CNS microenvironment

Microglia are innate immune cells within the brain that arise from a distinct myeloid lineage. Like other tissue resident macrophages, microglia respond to injury or immune challenges and participate in reparative processes such as phagocytosis to preserve normal function. Importantly, they also participate in normal homeostatic processes including maintenance of neurogenic niches and synaptic plasticity associated with development. This review highlights aspects of microglial biology and how repeated insults that occur with age, neurodegenerative disease and possibly radiation exposure may heighten microglial responses and contribute to their dysfunction, creating a situation where their normal reparative mechanisms are no longer sufficient to maintain brain health. These ideas are discussed in the context of an evolving literature focused on microglial responses as possible targets for mitigation of late CNS radiation effects that represent potential risks for future exploration of deep space environments.

Neuron-Glial Interactions in Health and Brain Cancer

Brain tumors are devastating diseases of the central nervous system. Brain tumor pathogenesis depends on both tumor-intrinsic oncogenic programs and extrinsic microenvironmental factors, including neurons and glial cells. Glial cells (oligodendrocytes, astrocytes, and microglia) make up half of the cells in the brain, and interact with neurons to modulate neurodevelopment and plasticity. Many brain tumor cells exhibit transcriptomic profiles similar to macroglial cells (oligodendrocytes and astrocytes) and their progenitors, making them likely to subvert existing neuron-glial interactions to support tumor pathogenesis. For example, oligodendrocyte precursor cells, a putative glioma cell of origin, can form bona fide synapses with neurons. Such synapses are recently identified in gliomas and drive glioma pathophysiology, underscoring how brain tumor cells can take advantage of neuron-glial interactions to support cancer progression. In this review, it is briefly summarized how neurons and their activity normally interact with glial cells and glial progenitors, and it is discussed how brain tumor cells utilize neuron-glial interactions to support tumor initiation and progression. Unresolved questions on these topics and potential avenues to therapeutically target neuron-glia-cancer interactions in the brain are also pointed out.

The role of the complement system in Multiple Sclerosis: A review

The complement system has been involved in the pathogenesis of multiple neuroinflammatory and neurodegenerative conditions. In this review, we evaluated the possible role of complement activation in multiple sclerosis (MS) with a focus in progressive MS, where the disease pathogenesis remains to be fully elucidated and treatment options are limited. The evidence for the involvement of the complement system in the white matter plaques and gray matter lesions of MS stems from immunohistochemical analysis of post-mortem MS brains, in vivo serum and cerebrospinal fluid biomarker studies, and animal models of Experimental Autoimmune Encephalomyelitis (EAE). Complement knock-out studies in these animal models have revealed that this system may have a “double-edge sword” effect in MS. On the one hand, complement proteins may aid in promoting the clearance of myelin degradation products and other debris through myeloid cell-mediated phagocytosis. On the other, its aberrant activation may lead to demyelination at the rim of progressive MS white matter lesions as well as synapse loss in the gray matter. The complement system may also interact with known risk factors of MS, including as Epstein Barr Virus (EBV) infection, and perpetuate the activation of CNS self-reactive B cell populations. With the mounting evidence for the involvement of complement in MS, the development of complement modulating therapies for this condition is appealing. Herein, we also reviewed the pharmacological complement inhibitors that have been tested in MS animal models as well as in clinical trials for other neurologic diseases. The potential use of these agents, such as the C5-binding antibody eculizumab in MS will require a detailed understanding of the role of the different complement effectors in this disease and the development of better CNS delivery strategies for these compounds.

C1q as a target molecule to treat human disease: What do mouse studies teach us?

The complement system is a field of growing interest for pharmacological intervention. Complement protein C1q, the pattern recognition molecule at the start of the classical pathway of the complement cascade, is a versatile molecule with additional non-canonical actions affecting numerous cellular processes. Based on observations made in patients with hereditary C1q deficiency, C1q is protective against systemic autoimmunity and bacterial infections. Accordingly, C1q deficient mice reproduce this phenotype with susceptibility to autoimmunity and infections. At the same time, beneficial effects of C1q deficiency on disease entities such as neurodegenerative diseases have also been described in murine disease models. This systematic review provides an overview of all currently available literature on the C1q knockout mouse in disease models to identify potential target diseases for treatment strategies focusing on C1q, and discusses potential side-effects when depleting and/or inhibiting C1q.

Microglia as Therapeutic Target for Radiation-Induced Brain Injury

Radiation-induced brain injury (RIBI) after radiotherapy has become an increasingly important factor affecting the prognosis of patients with head and neck tumor. With the delivery of high doses of radiation to brain tissue, microglia rapidly transit to a pro-inflammatory phenotype, upregulate phagocytic machinery, and reduce the release of neurotrophic factors. Persistently activated microglia mediate the progression of chronic neuroinflammation, which may inhibit brain neurogenesis leading to the occurrence of neurocognitive disorders at the advanced stage of RIBI. Fully understanding the microglial pathophysiology and cellular and molecular mechanisms after irradiation may facilitate the development of novel therapy by targeting microglia to prevent RIBI and subsequent neurological and neuropsychiatric disorders.

Impact of IL-21-associated peripheral and brain crosstalk on the Alzheimer's disease neuropathology

Alzheimer’s disease (AD) is associated with dysregulated immune and inflammatory responses. Emerging evidence indicates that peripheral immune activation is linked to neuroinflammation and AD pathogenesis. The present study focuses on determining the role of IL-21 in the pathogenesis of AD using human samples and the 5xFAD mice model. We find that the levels of IL-21 are increased in the periphery of both humans and mice in AD. In addition, the proportions of IL-21 target cells, Tfh and B plasma cells as well as activation of monocytes is increased in PBMCs from AD and mild cognitively impaired (MCI) subjects as compared to age-matched controls, indicating immune activation. In contrast, the percentage of B1 cells that control inflammation is decreased. These changes are due to IL-21 as the expression of IL-21 receptor (IL-21R) is higher on all these cells in AD. Furthermore, treatment with recombinant IL-21 in AD mice also leads to similar alterations in Tfh, B, B1, and macrophages. The effect of IL-21 is not confined to the periphery since increased expression of IL-21R is also observed in both humans and mice hippocampus derived from the AD brains. In addition, mice injected with IL-21 display increased deposition of amyloid beta (Aβ) plaques in the brain which is reduced following anti-IL-21R antibody that blocks the IL-21 signaling. Moreover, activation of microglia was enhanced in IL-21-injected mice. In keeping with enhanced microglial activation, we also observed increased production of pro-inflammatory cytokines, IL-18 and IL-6 in IL-21-injected mice. The microglial activation and cytokines were both inhibited following IL-21R blockage. Altogether, IL-21 escalates AD pathology by enhancing peripheral and brain immune and inflammatory responses leading to increased Aβ plaque deposition.

Stratification of radiosensitive brain metastases based on an actionable S100A9/RAGE resistance mechanism

Whole-brain radiotherapy (WBRT) is the treatment backbone for many patients with brain metastasis; however, its efficacy in preventing disease progression and the associated toxicity have questioned the clinical impact of this approach and emphasized the need for alternative treatments. Given the limited therapeutic options available for these patients and the poor understanding of the molecular mechanisms underlying the resistance of metastatic lesions to WBRT, we sought to uncover actionable targets and biomarkers that could help to refine patient selection. Through an unbiased analysis of experimental in vivo models of brain metastasis resistant to WBRT, we identified activation of the S100A9–RAGE–NF-κB–JunB pathway in brain metastases as a potential mediator of resistance in this organ. Targeting this pathway genetically or pharmacologically was sufficient to revert the WBRT resistance and increase therapeutic benefits in vivo at lower doses of radiation. In patients with primary melanoma, lung or breast adenocarcinoma developing brain metastasis, endogenous S100A9 levels in brain lesions correlated with clinical response to WBRT and underscored the potential of S100A9 levels in the blood as a noninvasive biomarker. Collectively, we provide a molecular framework to personalize WBRT and improve its efficacy through combination with a radiosensitizer that balances therapeutic benefit and toxicity.

Astrocytic 4R tau expression drives astrocyte reactivity and dysfunction

The protein tau and its isoforms are associated with several neurodegenerative diseases, many of which are characterized by greater deposition of the 4-repeat (4R) tau isoform; however, the role of 4R tau in disease pathogenesis remains unclear. We created antisense oligonucleotides (ASOs) that alter the ratio of 3R to 4R tau to investigate the role of specific tau isoforms in disease. Preferential expression of 4R tau in human tau-expressing (hTau-expressing) mice was previously shown to increase seizure severity and phosphorylated tau deposition without neuronal or synaptic loss. In this study, we observed strong colocalization of 4R tau within reactive astrocytes and increased expression of pan-reactive and neurotoxic genes following 3R to 4R tau splicing ASO treatment in hTau mice. Increasing 4R tau levels in primary astrocytes provoked a similar response, including a neurotoxic genetic profile and diminished homeostatic function, which was replicated in human induced pluripotent stem cell-derived (iPSC-derived) astrocytes harboring a mutation that exhibits greater 4R tau. Healthy neurons cultured with 4R tau-expressing human iPSC-derived astrocytes exhibited a higher firing frequency and hypersynchrony, which could be prevented by lowering tau expression. These findings support a potentially novel pathway by which astrocytic 4R tau mediates reactivity and dysfunction and suggest that astrocyte-targeted therapeutics against 4R tau may mitigate neurodegenerative disease progression.

Treatment of Radiation-Induced Brain Necrosis

Radiation-induced brain necrosis (RBN) is a serious complication of intracranial as well as skull base tumors after radiotherapy. In the past, due to the lack of effective treatment, radiation brain necrosis was considered to be progressive and irreversible. With better understanding in histopathology and neuroimaging, the occurrence and development of RBN have been gradually clarified, and new treatment methods are constantly emerging. In recent years, some scholars have tried to treat RBN with bevacizumab, nerve growth factor, and gangliosides and have achieved similar results. Some cases of brain necrosis can be repairable and reversible. We aimed to summarize the incidence, pathogenesis, and treatment of RBN.

HDAC6 inhibition reverses long-term doxorubicin-induced cognitive dysfunction by restoring microglia homeostasis and synaptic integrity

Breast cancer is the most common female malignancy in both the developed and developing world. Doxorubicin is one of the most commonly used chemotherapies for breast cancer. Unfortunately, up to 60% of survivors report long-term chemotherapy-induced cognitive dysfunction (CICD) characterized by deficits in working memory, processing speed and executive function. Currently, no therapeutic standard for treating CICD exists. Here, we hypothesized that treatment with a blood-brain barrier permeable histone deacetylase 6 (HDAC6) inhibitor can successfully reverse long-term doxorubicin-induced cognitive dysfunction. Methods: The puzzle box test and novel object/place recognition test were used to assess cognitive function following a therapeutic doxorubicin dosing schedule in female mice. Mitochondrial function and morphology in neuronal synaptosomes were evaluated using the Seahorse XF24 extracellular flux analyzer and transmission electron microscopy, respectively. Hippocampal postsynaptic integrity was evaluated using immunofluorescence. Hippocampal microglia phenotype was determined using advanced imaging techniques and single-nucleus RNA sequencing. Results: A 14-day treatment with a blood-brain barrier permeable HDAC6 inhibitor successfully reversed long-term CICD in the domains of executive function, working and spatial memory. No significant changes in mitochondrial function or morphology in neuronal synaptosomes were detected. Long-term CICD was associated with a decreased expression of postsynaptic PSD95 in the hippocampus. These changes were associated with decreased microglial ramification and alterations in the microglia transcriptome that suggest a stage 1 disease-associated microglia (DAM) phenotype. HDAC6 inhibition completely reversed these doxorubicin-induced alterations, indicating a restoration of microglial homeostasis. Conclusion: Our results show that decreased postsynaptic integrity and a neurodegenerative microglia phenotype closely resembling stage 1 DAM microglia contribute to long-term CICD. Moreover, HDAC6 inhibition shows promise as an efficacious pharmaceutical intervention to alleviate CICD and improve quality of life of breast cancer survivors.

Preservation of neurocognitive function in the treatment of brain metastases

Neurocognitive function (NCF) deficits are common in patients with brain metastases, occurring in up to 90% of cases. NCF deficits may be caused by tumor-related factors and/or treatment for the metastasis, including surgery, radiation therapy, chemotherapy, and immunotherapy. In recent years, strategies to prevent negative impact of treatments and ameliorate cognitive deficits for patients with brain tumors have gained momentum. In this review, we report on research that has established the efficacy of preventative and rehabilitative therapies for NCF deficits in patients with brain metastases. Surgical strategies include the use of laser interstitial thermal therapy and intraoperative mapping. Radiotherapy approaches include focal treatments such as stereotactic radiosurgery and tailored approaches such as hippocampal avoidant whole-brain radiotherapy (WBRT). Pharmacologic options include use of the neuroprotectant memantine to reduce cognitive decline induced by WBRT and incorporation of medications traditionally used for attention and memory problems. Integration of neuropsychology into the care of patients with brain metastases helps characterize cognitive patterns, educate patients and families regarding their management, and guide rehabilitative therapies. These and other strategies will become even more important for long-term survivors of brain metastases as treatment options improve.

Animal models of brain metastasis

Modeling of metastatic disease in animal models is a critical resource to study the complexity of this multi-step process in a relevant system. Available models of metastatic disease to the brain are still far from ideal but they allow to address specific aspects of the biology or mimic clinically relevant scenarios. We not only review experimental models and their potential improvements but also discuss specific answers that could be obtained from them on unsolved aspects of clinical management.

The Role of Complement in Synaptic Pruning and Neurodegeneration

The complement system, an essential part of the innate immune system, is composed of a group of secreted and membrane proteins that collectively participate in maintaining the function of the healthy and diseased brain. However, an inappropriate activation of the complement system has been related to an inflammatory response in multiple diseases, such as stroke, traumatic brain injury, multiple sclerosis, and Alzheimer's disease, as well as Zika infection and radiotherapy. In addition, C1q and C3 (initial activation components of the complement cascade) have been shown to play a key beneficial role in the refinement of synaptic circuits during developmental stages and adult plasticity. Nevertheless, excessive synaptic pruning in the adult brain can be detrimental and has been associated with synaptic loss in several pathological conditions. In this brief review, we will discuss the role of the complement system in synaptic pruning as well as its contribution to neurodegeneration and cognitive deficits. We also mention potential therapeutic approaches to target the complement system to treat several neuroinflammatory diseases and unintended consequences of radiotherapy.

A Complementary Strategy to Mitigate Radiation-Induced Cognitive Decline

Cranial radiation activates an upstream complement cascade component, C1q, leading to brain injury. Microglia-specific deletion of C1q prevents astrocyte and microglial activation, synaptic loss, neuroinflammation, and cognitive impairment. Therapeutically inhibiting complement activation may help mitigate radiation-induced cognitive decline.See related article by Markarian et al., p. 1732.