Publications by authors named "Egle Cekanaviciute"

22 Publications

  • Page 1 of 1

Knowledge Network Embedding of Transcriptomic Data from Spaceflown Mice Uncovers Signs and Symptoms Associated with Terrestrial Diseases.

Life (Basel) 2021 Jan 12;11(1). Epub 2021 Jan 12.

Space Biosciences Division, NASA Ames Research Center, Moffett Field, CA 94035, USA.

There has long been an interest in understanding how the hazards from spaceflight may trigger or exacerbate human diseases. With the goal of advancing our knowledge on physiological changes during space travel, NASA GeneLab provides an open-source repository of multi-omics data from real and simulated spaceflight studies. Alone, this data enables identification of biological changes during spaceflight, but cannot infer how that may impact an astronaut at the phenotypic level. To bridge this gap, Scalable Precision Medicine Oriented Knowledge Engine (SPOKE), a heterogeneous knowledge graph connecting biological and clinical data from over 30 databases, was used in combination with GeneLab transcriptomic data from six studies. This integration identified critical symptoms and physiological changes incurred during spaceflight.
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http://dx.doi.org/10.3390/life11010042DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7828077PMC
January 2021

Fundamental Biological Features of Spaceflight: Advancing the Field to Enable Deep-Space Exploration.

Cell 2020 Nov;183(5):1162-1184

KBR, Space Biosciences Division, NASA Ames Research Center, Moffett Field, CA 94035, USA; Stanley Center for Psychiatric Research, Broad Institute of MIT and Harvard, Cambridge, MA 02142, USA. Electronic address:

Research on astronaut health and model organisms have revealed six features of spaceflight biology that guide our current understanding of fundamental molecular changes that occur during space travel. The features include oxidative stress, DNA damage, mitochondrial dysregulation, epigenetic changes (including gene regulation), telomere length alterations, and microbiome shifts. Here we review the known hazards of human spaceflight, how spaceflight affects living systems through these six fundamental features, and the associated health risks of space exploration. We also discuss the essential issues related to the health and safety of astronauts involved in future missions, especially planned long-duration and Martian missions.
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http://dx.doi.org/10.1016/j.cell.2020.10.050DOI Listing
November 2020

Circulating miRNA Spaceflight Signature Reveals Targets for Countermeasure Development.

Cell Rep 2020 Dec 25;33(10):108448. Epub 2020 Nov 25.

KBR, Space Biosciences Division, NASA Ames Research Center, Moffett Field, CA 94035, USA; Stanley Center for Psychiatric Research, Broad Institute of MIT and Harvard, Cambridge, MA 02142, USA. Electronic address:

We have identified and validated a spaceflight-associated microRNA (miRNA) signature that is shared by rodents and humans in response to simulated, short-duration and long-duration spaceflight. Previous studies have identified miRNAs that regulate rodent responses to spaceflight in low-Earth orbit, and we have confirmed the expression of these proposed spaceflight-associated miRNAs in rodents reacting to simulated spaceflight conditions. Moreover, astronaut samples from the NASA Twins Study confirmed these expression signatures in miRNA sequencing, single-cell RNA sequencing (scRNA-seq), and single-cell assay for transposase accessible chromatin (scATAC-seq) data. Additionally, a subset of these miRNAs (miR-125, miR-16, and let-7a) was found to regulate vascular damage caused by simulated deep space radiation. To demonstrate the physiological relevance of key spaceflight-associated miRNAs, we utilized antagomirs to inhibit their expression and successfully rescue simulated deep-space-radiation-mediated damage in human 3D vascular constructs.
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http://dx.doi.org/10.1016/j.celrep.2020.108448DOI Listing
December 2020

DNA Damage Baseline Predicts Resilience to Space Radiation and Radiotherapy.

Cell Rep 2020 Dec 25;33(10):108434. Epub 2020 Nov 25.

NASA Ames Research Center, Space Biosciences, Moffett Field, CA 94035, USA. Electronic address:

Deep space exploration will require real-time, minimally invasive monitoring of astronaut health to mitigate the potential health impairments caused by space radiation and microgravity. Genotoxic stress in humans can be monitored by quantifying the amount of DNA double-strand breaks (DSBs) in immune cells from a simple finger prick. In a cohort of 674 healthy donors, we show that the endogenous level of DSBs increases with age and with latent cytomegalovirus infection. To map the range of human responses to space radiation, we then study DSB induction and repair in immune cells from 319 healthy donors after the cells are exposed to galactic cosmic ray components and lymphocytes from 30 cancer patients after radiotherapy. Individuals with low baseline DSB have fewer clinical complications, enhanced DNA damage repair responses, and a functional dose-dependent cytokine response in healthy donor cells. This supports the use of DSB monitoring for health resilience in space.
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http://dx.doi.org/10.1016/j.celrep.2020.108434DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7784531PMC
December 2020

Neutrophil-to-Lymphocyte Ratio: A Biomarker to Monitor the Immune Status of Astronauts.

Front Immunol 2020 2;11:564950. Epub 2020 Nov 2.

Space Biosciences Division, NASA Ames Research Center, Moffett Field, CA, United States.

A comprehensive understanding of spaceflight factors involved in immune dysfunction and the evaluation of biomarkers to assess in-flight astronaut health are essential goals for NASA. An elevated neutrophil-to-lymphocyte ratio (NLR) is a potential biomarker candidate, as leukocyte differentials are altered during spaceflight. In the reduced gravity environment of space, rodents and astronauts displayed elevated NLR and granulocyte-to-lymphocyte ratios (GLR), respectively. To simulate microgravity using two well-established ground-based models, we cultured human whole blood-leukocytes in high-aspect rotating wall vessels (HARV-RWV) and used hindlimb unloaded (HU) mice. Both HARV-RWV simulation of leukocytes and HU-exposed mice showed elevated NLR profiles comparable to spaceflight exposed samples. To assess mechanisms involved, we found the simulated microgravity HARV-RWV model resulted in an imbalance of redox processes and activation of myeloperoxidase-producing inflammatory neutrophils, while antioxidant treatment reversed these effects. In the simulated microgravity HU model, mitochondrial catalase-transgenic mice that have reduced oxidative stress responses showed reduced neutrophil counts, NLR, and a dampened release of selective inflammatory cytokines compared to wildtype HU mice, suggesting simulated microgravity induced oxidative stress responses that triggered inflammation. In brief, both spaceflight and simulated microgravity models caused elevated NLR, indicating this as a potential biomarker for future in-flight immune health monitoring.
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http://dx.doi.org/10.3389/fimmu.2020.564950DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7667275PMC
November 2020

53BP1 Repair Kinetics for Prediction of In Vivo Radiation Susceptibility in 15 Mouse Strains.

Radiat Res 2020 11;194(5):485-499

Space Biosciences Division, NASA Ames Research Center, Mountain View, California 94035.

We present a novel mathematical formalism to predict the kinetics of DNA damage repair after exposure to both low- and high-LET radiation (X rays; 350 MeV/n 40Ar; 600 MeV/n 56Fe). Our method is based on monitoring DNA damage repair protein 53BP1 that forms radiation-induced foci (RIF) at locations of DNA double-strand breaks (DSB) in the nucleus and comparing its expression in primary skin fibroblasts isolated from 15 mice strains. We previously reported strong evidence for clustering of nearby DSB into single repair units as opposed to the classic "contact-first" model where DSB are considered immobile. Here we apply this clustering model to evaluate the number of remaining RIF over time. We also show that the newly introduced kinetic metrics can be used as surrogate biomarkers for in vivo radiation toxicity, with potential applications in radiotherapy and human space exploration. In particular, we observed an association between the characteristic time constant of RIF repair measured in vitro and survival levels of immune cells collected from irradiated mice. Moreover, the speed of DNA damage repair correlated not only with radiation-induced cellular survival in vivo, but also with spontaneous cancer incidence data collected from the Mouse Tumor Biology database, suggesting a relationship between the efficiency of DSB repair after irradiation and cancer risk.
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http://dx.doi.org/10.1667/RADE-20-00122.1DOI Listing
November 2020

Ionizing radiation-induced risks to the central nervous system and countermeasures in cellular and rodent models.

Int J Radiat Biol 2020 Oct 20:1-19. Epub 2020 Oct 20.

Space Biosciences Division, NASA Ames Research Center, Moffett Field, CA, USA.

Purpose: Harmful effects of ionizing radiation on the Central Nervous System (CNS) are a concerning outcome in the field of cancer radiotherapy and form a major risk for deep space exploration. Both acute and chronic CNS irradiation induce a complex network of molecular and cellular alterations including DNA damage, oxidative stress, cell death and systemic inflammation, leading to changes in neuronal structure and synaptic plasticity with behavioral and cognitive consequences in animal models. Due to this complexity, countermeasure or therapeutic approaches to reduce the harmful effects of ionizing radiation include a wide range of protective and mitigative strategies, which merit a thorough comparative analysis.

Materials And Methods: We reviewed current approaches for developing countermeasures to both targeted and non-targeted effects of ionizing radiation on the CNS from the molecular and cellular to the behavioral level.

Results: We focus on countermeasures that aim to mitigate the four main detrimental actions of radiation on CNS: DNA damage, free radical formation and oxidative stress, cell death, and harmful systemic responses including tissue death and neuroinflammation. We propose a comprehensive review of CNS radiation countermeasures reported for the full range of irradiation types (photons and particles, low and high linear energy transfer) and doses (from a fraction of gray to several tens of gray, fractionated and unfractionated), with a particular interest for exposure conditions relevant to deep-space environment and radiotherapy. Our review reveals the importance of combined strategies that increase DNA protection and repair, reduce free radical formation and increase their elimination, limit inflammation and improve cell viability, limit tissue damage and increase repair and plasticity.

Conclusions: The majority of therapeutic approaches to protect the CNS from ionizing radiation have been limited to acute high dose and high dose rate gamma irradiation, and few are translatable from animal models to potential human application due to harmful side effects and lack of blood-brain barrier permeability that precludes peripheral administration. Therefore, a promising research direction would be to focus on practical applicability and effectiveness in a wider range of irradiation paradigms, from fractionated therapeutic to deep space radiation. In addition to discovering novel therapeutics, it would be worth maximizing the benefits and reducing side effects of those that already exist. Finally, we suggest that novel cellular and tissue models for developing and testing countermeasures in the context of other impairments might also be applied to the field of CNS responses to ionizing radiation.
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http://dx.doi.org/10.1080/09553002.2020.1820598DOI Listing
October 2020

Dose, LET and Strain Dependence of Radiation-Induced 53BP1 Foci in 15 Mouse Strains Introducing Novel DNA Damage Metrics.

Radiat Res 2019 07 13;192(1):1-12. Epub 2019 May 13.

a Biological Systems and Engineering Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720.

We present a comprehensive comparative analysis on the repair of radiation-induced DNA damage in 15 strains of mice, including 5 inbred reference strains and 10 collaborative-cross strains, of both sexes, totaling 5 million skin fibroblast cells imaged by three-dimensional highthroughput conventional microscopy. Non-immortalized primary skin fibroblasts derived from 76 mice were subjected to increasing doses of both low- and high-LET radiation (X rays; 350 MeV/n 40Ar; 600 MeV/n 56Fe), which are relevant to carcinogenesis and human space exploration. Automated image quantification of 53BP1 radiation-induced foci (RIF) formation and repair during the first 4-48 h postirradiation was performed as a function of dose and LET. Since multiple DNA double-strand breaks (DSBs) are induced in a dose- and LET-dependent manner, our data suggest that when DSBs are formed within the same discrete nuclear region, referred to as the "repair domain", novel mathematical formalisms used to report RIF allowed us to conclude that multiple DSBs can be present in single RIF. Specifically, we observed that the number of RIF per Gy was lower for higher X-ray doses or higher LET particles (i.e., 600 MeV/n Fe), suggesting there are more DSBs per RIF when the local absorbed dose increases in the nucleus. The data also clearly show that with more DSBs per RIF, it becomes more difficult for cells to fully resolve RIF. All 15 strains showed the same dose and LET dependence, but strain differences were preserved under various experimental conditions, indicating that the number and sizes of repair domains are modulated by the genetic background of each strain.
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http://dx.doi.org/10.1667/RR15338.1DOI Listing
July 2019

Disease-modifying therapies alter gut microbial composition in MS.

Neurol Neuroimmunol Neuroinflamm 2019 01 26;6(1):e517. Epub 2018 Oct 26.

Department of Neurology (I.K.S., A.N., R.B., Y.B.), Department of Neuroscience (Y.Z., P.C.), and Department of Genetics & Genomic Sciences, Icahn Institute for Genomics & Multiscale Biology (J.C.C.), Icahn School of Medicine at Mount Sinai; Department of Neurology (E.C., E.C.-H., S.S., B.A.C.C., S.E.B.), Weill Institute for Neurosciences, University of California, San Francisco; E.C. is now with Universities Space Research Association, Space Biosciences Division, NASA Ames Research Center, Moffett Field, CA; Department of Pediatrics (J.D., R.K.), Department of Computer Science & Engineering (R.K.), and Center for Microbiome Innovation (R.K.), University of California, San Diego; and Neuroscience Initiative (P.C.), Advanced Research Science Center at the Graduate Center of the City University of New York.

Objective: To determine the effects of the disease-modifying therapies, glatiramer acetate (GA) and dimethyl fumarate (DMF), on the gut microbiota in patients with MS.

Methods: Participants with relapsing MS who were either treatment-naive or treated with GA or DMF were recruited. Peripheral blood mononuclear cells were immunophenotyped. Bacterial DNA was extracted from stool, and amplicons targeting the V4 region of the bacterial/archaeal 16S rRNA gene were sequenced (Illumina MiSeq). Raw reads were clustered into Operational Taxonomic Units using the GreenGenes database. Differential abundance analysis was performed using linear discriminant analysis effect size. Phylogenetic investigation of communities by reconstruction of unobserved states was used to investigate changes to functional pathways resulting from differential taxon abundance.

Results: One hundred sixty-eight participants were included (treatment-naive n = 75, DMF n = 33, and GA n = 60). Disease-modifying therapies were associated with changes in the fecal microbiota composition. Both therapies were associated with decreased relative abundance of the and families. In addition, DMF was associated with decreased relative abundance of the phyla Firmicutes and Fusobacteria and the order Clostridiales and an increase in the phylum Bacteroidetes. Despite the different changes in bacterial taxa, there was an overlap between functional pathways affected by both therapies.

Interpretation: Administration of GA or DMF is associated with differences in gut microbial composition in patients with MS. Because those changes affect critical metabolic pathways, we hypothesize that our findings may highlight mechanisms of pathophysiology and potential therapeutic intervention requiring further investigation.
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http://dx.doi.org/10.1212/NXI.0000000000000517DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6278850PMC
January 2019

Central Nervous System Responses to Simulated Galactic Cosmic Rays.

Int J Mol Sci 2018 Nov 20;19(11). Epub 2018 Nov 20.

Space Biosciences Division, NASA Ames Research Center, Moffett Field, CA 94035, USA.

In preparation for lunar and Mars missions it is essential to consider the challenges to human health that are posed by long-duration deep space habitation via multiple stressors, including ionizing radiation, gravitational changes during flight and in orbit, other aspects of the space environment such as high level of carbon dioxide, and psychological stress from confined environment and social isolation. It remains unclear how these stressors individually or in combination impact the central nervous system (CNS), presenting potential obstacles for astronauts engaged in deep space travel. Although human spaceflight research only within the last decade has started to include the effects of radiation transmitted by galactic cosmic rays to the CNS, radiation is currently considered to be one of the main stressors for prolonged spaceflight and deep space exploration. Here we will review the current knowledge of CNS damage caused by simulated space radiation with an emphasis on neuronal and glial responses along with cognitive functions. Furthermore, we will present novel experimental approaches to integrate the knowledge into more comprehensive studies, including multiple stressors at once and potential translation to human functions. Finally, we will discuss the need for developing biomarkers as predictors for cognitive decline and therapeutic countermeasures to prevent CNS damage and the loss of cognitive abilities.
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http://dx.doi.org/10.3390/ijms19113669DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6275046PMC
November 2018

Multiple Sclerosis-Associated Changes in the Composition and Immune Functions of Spore-Forming Bacteria.

mSystems 2018 Nov-Dec;3(6). Epub 2018 Nov 6.

UCSF Weill Institute for Neurosciences, Department of Neurology, University of California, San Francisco, California, USA.

Multiple sclerosis (MS) is an autoimmune disease of the central nervous system characterized by adaptive and innate immune system dysregulation. Recent work has revealed moderate alteration of gut microbial communities in subjects with MS and in experimental, induced models. However, a mechanistic understanding linking the observed changes in the microbiota and the presence of the disease is still missing. Chloroform-resistant, spore-forming bacteria, which primarily belong to the classes and in the phylum , have been shown to exhibit immunomodulatory properties and , but they have not yet been characterized in the context of human disease. This study addresses the community composition and immune function of this bacterial fraction in MS. We identify MS-associated spore-forming taxa (primarily in the class ) and show that their presence correlates with impaired differentiation of IL-10-secreting, regulatory T lymphocytes . Colonization of antibiotic-treated mice with spore-forming bacteria allowed us to identify some bacterial taxa favoring IL-10 lymphocyte differentiation and others inducing differentiation of proinflammatory, IFN-γ T lymphocytes. However, when fed into antibiotic-treated mice, both MS and control-derived spore-forming bacteria were able to induce similar IL-10-expressing Treg immunoregulatory responses, thus ameliorating symptoms of experimental allergic encephalomyelitis (EAE). Our analysis also identified Akkermansia muciniphila as a key organism that may interact either directly or indirectly with spore-forming bacteria to exacerbate the inflammatory effects of MS-associated gut microbiota. Thus, changes in the spore-forming fraction may influence T lymphocyte-mediated inflammation in MS. This experimental approach of isolating a subset of microbiota based on its functional characteristics may be useful to investigate other microbial fractions at greater depth. To address the impact of microbiome on disease development, it is essential to go beyond a descriptive study and evaluate the physiological importance of microbiome changes. Our study integrates computational analysis with and exploration of inflammatory properties of spore-forming microbial communities, revealing novel functional correlations. We specifically show that while small differences exist between the microbiomes of MS patients and healthy subjects, these differences are exacerbated in the chloroform-resistant fraction. We further demonstrate that, when purified from MS patients, this fraction is correlated with impaired immunomodulatory responses .
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http://dx.doi.org/10.1128/mSystems.00083-18DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6222044PMC
November 2018

Comparing Photon and Charged Particle Therapy Using DNA Damage Biomarkers.

Int J Part Ther 2018 21;5(1):15-24. Epub 2018 Sep 21.

NASA Ames Research Center, Moffett Field, CA, USA.

Treatment modalities for cancer radiation therapy have become increasingly diversified given the growing number of facilities providing proton and carbon-ion therapy in addition to the more historically accepted photon therapy. An understanding of high-LET radiobiology is critical for optimization of charged particle radiation therapy and potential DNA damage response. In this review, we present a comprehensive summary and comparison of these types of therapy monitored primarily by using DNA damage biomarkers. We focus on their relative profiles of dose distribution and mechanisms of action from the level of nucleic acid to tumor cell death.
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http://dx.doi.org/10.14338/IJPT-18-00018.1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6871597PMC
September 2018

Global transcriptomic analysis suggests carbon dioxide as an environmental stressor in spaceflight: A systems biology GeneLab case study.

Sci Rep 2018 03 8;8(1):4191. Epub 2018 Mar 8.

NASA, Space Biosciences Division, NASA Ames Research Center, Mountain View, CA, USA.

Spaceflight introduces a combination of environmental stressors, including microgravity, ionizing radiation, changes in diet and altered atmospheric gas composition. In order to understand the impact of each environmental component on astronauts it is important to investigate potential influences in isolation. Rodent spaceflight experiments involve both standard vivarium cages and animal enclosure modules (AEMs), which are cages used to house rodents in spaceflight. Ground control AEMs are engineered to match the spaceflight environment. There are limited studies examining the biological response invariably due to the configuration of AEM and vivarium housing. To investigate the innate global transcriptomic patterns of rodents housed in spaceflight-matched AEM compared to standard vivarium cages we utilized publicly available data from the NASA GeneLab repository. Using a systems biology approach, we observed that AEM housing was associated with significant transcriptomic differences, including reduced metabolism, altered immune responses, and activation of possible tumorigenic pathways. Although we did not perform any functional studies, our findings revealed a mild hypoxic phenotype in AEM, possibly due to atmospheric carbon dioxide that was increased to match conditions in spaceflight. Our investigation illustrates the process of generating new hypotheses and informing future experimental research by repurposing multiple space-flown datasets.
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http://dx.doi.org/10.1038/s41598-018-22613-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5843582PMC
March 2018

Gut microbiota from multiple sclerosis patients enables spontaneous autoimmune encephalomyelitis in mice.

Proc Natl Acad Sci U S A 2017 10 11;114(40):10719-10724. Epub 2017 Sep 11.

Hertie Senior Professor Group, Max Planck Institute of Neurobiology, 82152 Martinsried, Germany;

There is emerging evidence that the commensal microbiota has a role in the pathogenesis of multiple sclerosis (MS), a putative autoimmune disease of the CNS. Here, we compared the gut microbial composition of 34 monozygotic twin pairs discordant for MS. While there were no major differences in the overall microbial profiles, we found a significant increase in some taxa such as in untreated MS twins. Furthermore, most notably, when transplanted to a transgenic mouse model of spontaneous brain autoimmunity, MS twin-derived microbiota induced a significantly higher incidence of autoimmunity than the healthy twin-derived microbiota. The microbial profiles of the colonized mice showed a high intraindividual and remarkable temporal stability with several differences, including , an organism shown to induce a protective immunoregulatory profile in vitro. Immune cells from mouse recipients of MS-twin samples produced less IL-10 than immune cells from mice colonized with healthy-twin samples. IL-10 may have a regulatory role in spontaneous CNS autoimmunity, as neutralization of the cytokine in mice colonized with healthy-twin fecal samples increased disease incidence. These findings provide evidence that MS-derived microbiota contain factors that precipitate an MS-like autoimmune disease in a transgenic mouse model. They hence encourage the detailed search for protective and pathogenic microbial components in human MS.
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http://dx.doi.org/10.1073/pnas.1711233114DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5635914PMC
October 2017

Gut bacteria from multiple sclerosis patients modulate human T cells and exacerbate symptoms in mouse models.

Proc Natl Acad Sci U S A 2017 10 11;114(40):10713-10718. Epub 2017 Sep 11.

Department of Neurology, University of California, San Francisco, CA 94158;

The gut microbiota regulates T cell functions throughout the body. We hypothesized that intestinal bacteria impact the pathogenesis of multiple sclerosis (MS), an autoimmune disorder of the CNS and thus analyzed the microbiomes of 71 MS patients not undergoing treatment and 71 healthy controls. Although no major shifts in microbial community structure were found, we identified specific bacterial taxa that were significantly associated with MS. and , both increased in MS patients, induced proinflammatory responses in human peripheral blood mononuclear cells and in monocolonized mice. In contrast, , which was reduced in MS patients, stimulated antiinflammatory IL-10-expressing human CD4CD25 T cells and IL-10FoxP3 Tregs in mice. Finally, microbiota transplants from MS patients into germ-free mice resulted in more severe symptoms of experimental autoimmune encephalomyelitis and reduced proportions of IL-10 Tregs compared with mice "humanized" with microbiota from healthy controls. This study identifies specific human gut bacteria that regulate adaptive autoimmune responses, suggesting therapeutic targeting of the microbiota as a treatment for MS.
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http://dx.doi.org/10.1073/pnas.1711235114DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5635915PMC
October 2017

Astrocytes: Integrative Regulators of Neuroinflammation in Stroke and Other Neurological Diseases.

Neurotherapeutics 2016 10;13(4):685-701

Department of Neurology and Neurological Sciences, Stanford Medical School, Stanford, CA, 94305, USA.

Astrocytes regulate neuroinflammatory responses after stroke and in other neurological diseases. Although not all astrocytic responses reduce inflammation, their predominant function is to protect the brain by driving the system back to homeostasis after injury. They receive multidimensional signals within the central nervous system and between the brain and the systemic circulation. Processing this information allows astrocytes to regulate synapse formation and maintenance, cerebral blood flow, and blood-brain barrier integrity. Similarly, in response to stroke and other central nervous system disorders, astrocytes detect and integrate signals of neuronal damage and inflammation to regulate the neuroinflammatory response. Two direct regulatory mechanisms in the astrocyte arsenal are the ability to form both physical and molecular barriers that seal the injury site and localize the neuroinflammatory response. Astrocytes also indirectly regulate the inflammatory response by affecting neuronal health during the acute injury and axonal regrowth. This ability to regulate the location and degree of neuroinflammation after injury, combined with the long time course of neuroinflammation, makes astrocytic signaling pathways promising targets for therapies.
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http://dx.doi.org/10.1007/s13311-016-0477-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5081110PMC
October 2016

Immune cell-specific transcriptional profiling highlights distinct molecular pathways controlled by Tob1 upon experimental autoimmune encephalomyelitis.

Sci Rep 2016 08 22;6:31603. Epub 2016 Aug 22.

Department of Neurology, University of California San Francisco, San Francisco, California 94158, USA.

Multiple sclerosis (MS) is an autoimmune disease of the central nervous system characterized by focal lymphocytic infiltration, demyelination and neurodegeneration. Despite the recent advances in understanding MS molecular basis, no reliable biomarkers have been identified yet to monitor disease progression. Our group has previously reported that low levels of TOB1 in CD4(+) T cells are strongly associated with a higher risk of MS conversion in individuals experiencing an initial demyelinating event. Consistently, Tob1 ablation in mice exacerbates the clinical phenotype of the MS model experimental autoimmune encephalomyelitis (EAE). To shed light on Tob1 molecular functions in the immune system, we have conducted the first cell-based transcriptomic analysis in Tob1(-/-) and wildtype mice upon EAE. Next-generation sequencing was employed to characterize the changes in gene expression in T and B cells at pre- and post-symptomatic EAE stages. Remarkably, we found only modest overlap among the different genetic signatures, suggesting that Tob1 may control distinct genetic programs in the different cytotypes. This hypothesis was corroborated by gene ontology and global interactome analyses, which highlighted specific cellular pathways in each cellular subset before and after EAE induction. In summary, our work pinpoints a multifaceted activity of Tob1 in both homeostasis and disease progression.
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http://dx.doi.org/10.1038/srep31603DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4992865PMC
August 2016

Astrocytic TGF-β signaling limits inflammation and reduces neuronal damage during central nervous system Toxoplasma infection.

J Immunol 2014 Jul 23;193(1):139-49. Epub 2014 May 23.

Department of Neurology and Neurological Sciences, Stanford University, Stanford, CA 94305; Department of Neurosurgery, Stanford University, Stanford, CA 94305

The balance between controlling infection and limiting inflammation is particularly precarious in the brain because of its unique vulnerability to the toxic effects of inflammation. Astrocytes have been implicated as key regulators of neuroinflammation in CNS infections, including infection with Toxoplasma gondii, a protozoan parasite that naturally establishes a chronic CNS infection in mice and humans. In CNS toxoplasmosis, astrocytes are critical to controlling parasite growth. They secrete proinflammatory cytokines and physically encircle parasites. However, the molecular mechanisms used by astrocytes to limit neuroinflammation during toxoplasmic encephalitis have not yet been identified. TGF-β signaling in astrocytes is of particular interest because TGF-β is universally upregulated during CNS infection and serves master regulatory and primarily anti-inflammatory functions. We report in this study that TGF-β signaling is activated in astrocytes during toxoplasmic encephalitis and that inhibition of astrocytic TGF-β signaling increases immune cell infiltration, uncouples proinflammatory cytokine and chemokine production from CNS parasite burden, and increases neuronal injury. Remarkably, we show that the effects of inhibiting astrocytic TGF-β signaling are independent of parasite burden and the ability of GFAP(+) astrocytes to physically encircle parasites.
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http://dx.doi.org/10.4049/jimmunol.1303284DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4075480PMC
July 2014

Astrocytic transforming growth factor-beta signaling reduces subacute neuroinflammation after stroke in mice.

Glia 2014 Aug 15;62(8):1227-40. Epub 2014 Apr 15.

Department of Neurology and Neurological Sciences, Stanford University School of Medicine, Stanford, California; Neurosciences Graduate Program, Stanford University, Stanford, California.

Astrocytes limit inflammation after CNS injury, at least partially by physically containing it within an astrocytic scar at the injury border. We report here that astrocytic transforming growth factor-beta (TGFβ) signaling is a second, distinct mechanism that astrocytes utilize to limit neuroinflammation. TGFβs are anti-inflammatory and neuroprotective cytokines that are upregulated subacutely after stroke, during a clinically accessible time window. We have previously demonstrated that TGFβs signal to astrocytes, neurons and microglia in the stroke border days after stroke. To investigate whether TGFβ affects astrocyte immunoregulatory functions, we engineered "Ast-Tbr2DN" mice where TGFβ signaling is inhibited specifically in astrocytes. Despite having a similar infarct size to wildtype controls, Ast-Tbr2DN mice exhibited significantly more neuroinflammation during the subacute period after distal middle cerebral occlusion (dMCAO) stroke. The peri-infarct cortex of Ast-Tbr2DN mice contained over 60% more activated CD11b(+) monocytic cells and twice as much immunostaining for the activated microglia and macrophage marker CD68 than controls. Astrocytic scarring was not altered in Ast-Tbr2DN mice. However, Ast-Tbr2DN mice were unable to upregulate TGF-β1 and its activator thrombospondin-1 2 days after dMCAO. As a result, the normal upregulation of peri-infarct TGFβ signaling was blunted in Ast-Tbr2DN mice. In this setting of lower TGFβ signaling and excessive neuroinflammation, we observed worse motor outcomes and late infarct expansion after photothrombotic motor cortex stroke. Taken together, these data demonstrate that TGFβ signaling is a molecular mechanism by which astrocytes limit neuroinflammation, activate TGFβ in the peri-infarct cortex and preserve brain function during the subacute period after stroke.
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http://dx.doi.org/10.1002/glia.22675DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4061255PMC
August 2014

Suppression of inflammation with conditional deletion of the prostaglandin E2 EP2 receptor in macrophages and brain microglia.

J Neurosci 2013 Oct;33(40):16016-32

Departments of Neurology and Neurological Sciences, Molecular and Cellular Physiology, Microbiology and Immunology, and Neurosurgery, Stanford University School of Medicine, Stanford, California 94305, Neurosciences Graduate Program, Stanford University, Stanford, California 94305, and Center for Health Sciences, SRI International, Menlo Park, California 94025.

Prostaglandin E2 (PGE2), a potent lipid signaling molecule, modulates inflammatory responses through activation of downstream G-protein coupled EP(1-4) receptors. Here, we investigated the cell-specific in vivo function of PGE2 signaling through its E-prostanoid 2 (EP2) receptor in murine innate immune responses systemically and in the CNS. In vivo, systemic administration of lipopolysaccharide (LPS) resulted in a broad induction of cytokines and chemokines in plasma that was significantly attenuated in EP2-deficient mice. Ex vivo stimulation of peritoneal macrophages with LPS elicited proinflammatory responses that were dependent on EP2 signaling and that overlapped with in vivo plasma findings, suggesting that myeloid-lineage EP2 signaling is a major effector of innate immune responses. Conditional deletion of the EP2 receptor in myeloid lineage cells in Cd11bCre;EP2(lox/lox) mice attenuated plasma inflammatory responses and transmission of systemic inflammation to the brain was inhibited, with decreased hippocampal inflammatory gene expression and cerebral cortical levels of IL-6. Conditional deletion of EP2 significantly blunted microglial and astrocytic inflammatory responses to the neurotoxin MPTP and reduced striatal dopamine turnover. Suppression of microglial EP2 signaling also increased numbers of dopaminergic (DA) neurons in the substantia nigra independent of MPTP treatment, suggesting that microglial EP2 may influence development or survival of DA neurons. Unbiased microarray analysis of microglia isolated from adult Cd11bCre;EP2(lox/lox) and control mice demonstrated a broad downregulation of inflammatory pathways with ablation of microglial EP2 receptor. Together, these data identify a cell-specific proinflammatory role for macrophage/microglial EP2 signaling in innate immune responses systemically and in brain.
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http://dx.doi.org/10.1523/JNEUROSCI.2203-13.2013DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3787507PMC
October 2013

Delayed administration of a small molecule tropomyosin-related kinase B ligand promotes recovery after hypoxic-ischemic stroke.

Stroke 2012 Jul 24;43(7):1918-24. Epub 2012 Apr 24.

Department of Neurology and Neurological Sciences, Stanford University School of Medicine, 1201 Welch Road, MSLS Building, P209, Stanford, CA 94305-5489, USA.

Background And Purpose: Stroke is the leading cause of long-term disability in the United States, yet no drugs are available that are proven to improve recovery. Brain-derived neurotrophic factor stimulates neurogenesis and plasticity, processes that are implicated in stroke recovery. It binds to both the tropomyosin-related kinase B and p75 neurotrophin receptors. However, brain-derived neurotrophic factor is not a feasible therapeutic agent, and no small molecule exists that can reproduce its binding to both receptors. We tested the hypothesis that a small molecule (LM22A-4) that selectively targets tropomyosin-related kinase B would promote neurogenesis and functional recovery after stroke.

Methods: Four-month-old mice were trained on motor tasks before stroke. After stroke, functional test results were used to randomize mice into 2 equally, and severely, impaired groups. Beginning 3 days after stroke, mice received LM22A-4 or saline vehicle daily for 10 weeks.

Results: LM22A-4 treatment significantly improved limb swing speed and accelerated the return to normal gait accuracy after stroke. LM22A-4 treatment also doubled both the number of new mature neurons and immature neurons adjacent to the stroke. Drug-induced differences were not observed in angiogenesis, dendritic arborization, axonal sprouting, glial scar formation, or neuroinflammation.

Conclusions: A small molecule agonist of tropomyosin-related kinase B improves functional recovery from stroke and increases neurogenesis when administered beginning 3 days after stroke. These findings provide proof-of-concept that targeting of tropomyosin-related kinase B alone is capable of promoting one or more mechanisms relevant to stroke recovery. LM22A-4 or its derivatives might therefore serve as "pro-recovery" therapeutic agents for stroke.
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http://dx.doi.org/10.1161/STROKEAHA.111.641878DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3383889PMC
July 2012

TGFβ signaling in the brain increases with aging and signals to astrocytes and innate immune cells in the weeks after stroke.

J Neuroinflammation 2010 Oct 11;7:62. Epub 2010 Oct 11.

Department of Neurology and Neurological Sciences, Stanford University Medical School, Stanford, CA 94305-5489, USA.

Background: TGFβ is both neuroprotective and a key immune system modulator and is likely to be an important target for future stroke therapy. The precise function of increased TGF-β1 after stroke is unknown and its pleiotropic nature means that it may convey a neuroprotective signal, orchestrate glial scarring or function as an important immune system regulator. We therefore investigated the time course and cell-specificity of TGFβ signaling after stroke, and whether its signaling pattern is altered by gender and aging.

Methods: We performed distal middle cerebral artery occlusion strokes on 5 and 18 month old TGFβ reporter mice to get a readout of TGFβ responses after stroke in real time. To determine which cell type is the source of increased TGFβ production after stroke, brain sections were stained with an anti-TGFβ antibody, colocalized with markers for reactive astrocytes, neurons, and activated microglia. To determine which cells are responding to TGFβ after stroke, brain sections were double-labelled with anti-pSmad2, a marker of TGFβ signaling, and markers of neurons, oligodendrocytes, endothelial cells, astrocytes and microglia.

Results: TGFβ signaling increased 2 fold after stroke, beginning on day 1 and peaking on day 7. This pattern of increase was preserved in old animals and absolute TGFβ signaling in the brain increased with age. Activated microglia and macrophages were the predominant source of increased TGFβ after stroke and astrocytes and activated microglia and macrophages demonstrated dramatic upregulation of TGFβ signaling after stroke. TGFβ signaling in neurons and oligodendrocytes did not undergo marked changes.

Conclusions: We found that TGFβ signaling increases with age and that astrocytes and activated microglia and macrophages are the main cell types that undergo increased TGFβ signaling in response to post-stroke increases in TGFβ. Therefore increased TGFβ after stroke likely regulates glial scar formation and the immune response to stroke.
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http://dx.doi.org/10.1186/1742-2094-7-62DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2958905PMC
October 2010