Systemic Lipopolysaccharide Challenge Research Articles

Inflammatory Response to Intravenously Administered Lipopolysaccharide (LPS) in the Bone Marrow of Healthy Volunteers As a Model for Early Phase Drug Development

Introduction Inflammatory responses in the peripheral and central hematological compartments are important for identification of new biomarkers and drug targets in early phase drug development. There is an increasing interest to investigate the modulation of the inflammatory response upon experimental drug exposure using cellular and molecular analyses, specifically in the central compartment. The lipopolysaccharide (LPS) challenge model allows to study TLR4-mediated local and systemic inflammation and therefore the effects of anti-inflammatory compounds. In addition, there is an interest in the effects of TLR4 agonists on early immune cell populations. The aim of the current study is to investigate the effects of intravenous (i.v.) LPS on the peripheral blood and central bone marrow compartment and to perform a proof-of-methodology study for bone marrow analysis in early phase drug research in healthy volunteers. Methods This was an open-label study in 13 healthy young male subjects, aged 18 - 35 years (inclusive). The study was conducted at the Centre for Human Drug Research, Leiden, The Netherlands. The study protocol was approved by the Medical Ethics Committee. All subjects provided written informed consent prior to any study activity. Subjects were divided into control group (n=3), 1 ng/kg i.v. LPS group (n=5) and 2 ng/kg i.v. LPS group (n=5). Blood and bone marrow samples were collected at baseline and at 4h post-dose timepoints. Primary objective was to evaluate the safety and tolerability of bone marrow sampling in healthy volunteers, by continuous safety monitoring, visual analogue scale (VAS) for pain and subject experience questionnaires. To investigate the pharmacodynamic (PD) effects of i.v. LPS challenge on the bone marrow and whole-blood immune compartments, flow cytometry, cytokine analysis and RNA sequencing was performed. Results All 13 subjects completed the study. Adverse events were mild and reversible, and included puncture site pain related to bone marrow puncture, and flu-like symptoms related to LPS administration. Twelve subjects (92%) indicated they would undergo the procedure again in the future. There was an observable difference in VAS pain score between the baseline bone marrow puncture and LPS treatment groups, but no difference between 1 ng/kg and 2 ng/kg groups. Phenotypic changes of inflammatory signatures in peripheral blood and bone marrow cell populations upon LPS administration were detected by multi-parameter flow cytometry. An LPS-induced inflammatory cytokine profile was present. RNA sequencing revealed differential gene expression in inflammatory gene signatures between peripheral blood mononuclear cells and bone marrow cells. Conclusion We demonstrated that bone marrow analysis is feasible and well-tolerable in early phase studies with healthy volunteers and can be used to assess inflammatory responses in the central hematological compartment upon systemic LPS challenge. Access to bone marrow can provide important novel insights into drug effects on the hematopoiesis and differentiation of immune cells and provides added value to early drug development.

Mapping acute neuroinflammation in vivo with diffusion-MRI in rats given a systemic lipopolysaccharide challenge

It is becoming increasingly apparent that neuroinflammation plays a critical role in an array of neurological and psychiatric disorders. Recent studies have demonstrated the potential of diffusion MRI (dMRI) to characterize changes in microglial density and morphology associated with neuroinflammation, but these were conducted mostly ex vivo and/or in extreme, non-physiological animal models. Here, we build upon these studies by investigating the utility of well-established dMRI methods to detect neuroinflammation in vivo in a more clinically relevant animal model of sickness behavior. We show that diffusion tensor imaging (DTI) and neurite orientation dispersion and density imaging (NODDI) indicate widespread increases in diffusivity in the brains of rats given a systemic lipopolysaccharide challenge (n = 20) vs. vehicle-treated controls (n = 12). These diffusivity changes correlated with histologically measured changes in microglial morphology, confirming the sensitivity of dMRI to neuroinflammatory processes. This study marks a further step towards establishing a noninvasive indicator of neuroinflammation, which would greatly facilitate early diagnosis and treatment monitoring in various neurological and psychiatric diseases.

Delayed microglial activation associated with the resolution of neuroinflammation in a mouse model of sublethal endotoxemia-induced systemic inflammation

Systemic inflammation affects brain functions. In our previous study in which lipopolysaccharide (LPS) was injected intraperitoneally into mice at sublethal doses, choroid plexus macrophages produced interleukin-1β and stimulated neighboring stromal cells. Activated stromal cells stimulate choroid plexus epithelial cells, and then choroid plexus epithelium-derived cytokines enter the brain parenchyma and stimulate astrocytes. Stimulated astrocytes then produce cytokines such as CCL11, CXCL10 and G-CSF and change the brain parenchymal microenvironment. However, the effects of an altered brain microenvironment on other brain cells remain to be determined. In the present study, we hypothesized that microglia are activated in response to astrocyte-induced changes in the brain microenvironment. Using the brains of mice treated with intraperitoneal LPS injection, Luminex multiplex cytokine immunoassays revealed increased hippocampal concentrations of CCL11, CXCL10 and G-CSF at 48 h after systemic LPS challenge. The concentrations of all cytokines examined returned to control levels at 72 h after LPS injection, which indicated a resolution of the neuroinflammation. Immunohistochemistry revealed that microglia were hypertrophied in mice at 48 h after systemic LPS challenge. Following isolation of microglial cells from the brain using magnetic-activated cell sorting, gene expression assays were performed with real-time reverse transcriptase-polymerase chain reaction. Isolated microglial cells exhibited much higher gene expression of the receptors for CCL11, CXCL10 and G-CSF than other brain cells. Microglial cells isolated from the brains of mice at 48 h after systemic LPS challenge exhibited the M2-like phenotype. In conclusion, microglial hypertrophy occurs following astrocytic reactions in a mouse model of sublethal endotoxemia-induced systemic inflammation, and hypertrophic microglia are polarized toward the M2-like phenotype and involved in the resolution of neuroinflammation.

Systemic administration of \u03b2-glucan induces immune training in microglia

BackgroundAn innate immune memory response can manifest in two ways: immune training and immune tolerance, which refers to an enhanced or suppressed immune response to a second challenge, respectively. Exposing monocytes to moderate-to-high amounts of bacterial lipopolysaccharide (LPS) induces immune tolerance, whereas fungal β-glucan (BG) induces immune training. In microglia, it has been shown that different LPS inocula in vivo can induce either immune training or tolerance. Few studies focused on impact of BG on microglia and were only performed in vitro. The aim of the current study was to determine whether BG activates and induces immune memory in microglia upon peripheral administration in vivo.MethodsTwo experimental designs were used. In the acute design, mice received an intraperitoneal (i.p.) injection with PBS, 1 mg/kg LPS or 20 mg/kg BG and were terminated after 3 h, 1 or 2 days. In the preconditioning design, animals were first challenged i.p. with PBS, 1 mg/kg LPS or 20 mg/kg BG. After 2, 7 or 14 days, mice received a second injection with PBS or 1 mg/kg LPS and were sacrificed 3 h later. Microglia were isolated by fluorescence-activated cell sorting, and cytokine gene expression levels were determined. In addition, a self-developed program was used to analyze microglia morphological changes. Cytokine concentrations in serum were determined by a cytokine array.ResultsMicroglia exhibited a classical inflammatory response to LPS, showing significant upregulation of Tnf, Il6, Il1β, Ccl2, Ccl3 and Csf1 expression, three h after injection, and obvious morphological changes 1 and 2 days after injection. With an interval of 2 days between two challenges, both BG and LPS induced immune training in microglia. The training effect of LPS changed into immune tolerance after a 7-day interval between 2 LPS challenges. Preconditioning with BG and LPS resulted in increased morphological changes in microglia in response to a systemic LPS challenge compared to naïve microglia.ConclusionsOur results demonstrate that preconditioning with BG and LPS both induced immune training of microglia at two days after the first challenge. However, with an interval of 7 days between the first and second challenge, LPS-preconditioning resulted in immune tolerance in microglia.

Decoding the temporal nature of brain GR activity in the NF\u03baB signal transition leading to depressive-like behavior

The fine-tuning of neuroinflammation is crucial for brain homeostasis as well as its immune response. The transcription factor, nuclear factor-κ-B (NFκB) is a key inflammatory player that is antagonized via anti-inflammatory actions exerted by the glucocorticoid receptor (GR). However, technical limitations have restricted our understanding of how GR is involved in the dynamics of NFκB in vivo. In this study, we used an improved lentiviral-based reporter to elucidate the time course of NFκB and GR activities during behavioral changes from sickness to depression induced by a systemic lipopolysaccharide challenge. The trajectory of NFκB activity established a behavioral basis for the NFκB signal transition involved in three phases, sickness-early-phase, normal-middle-phase, and depressive-like-late-phase. The temporal shift in brain GR activity was differentially involved in the transition of NFκB signals during the normal and depressive-like phases. The middle-phase GR effectively inhibited NFκB in a glucocorticoid-dependent manner, but the late-phase GR had no inhibitory action. Furthermore, we revealed the cryptic role of basal GR activity in the early NFκB signal transition, as evidenced by the fact that blocking GR activity with RU486 led to early depressive-like episodes through the emergence of the brain NFκB activity. These results highlight the inhibitory action of GR on NFκB by the basal and activated hypothalamic-pituitary-adrenal (HPA)-axis during body-to-brain inflammatory spread, providing clues about molecular mechanisms underlying systemic inflammation caused by such as COVID-19 infection, leading to depression.

Acute neuroinflammation, sickness behavior and working memory responses to acute systemic LPS challenge following noradrenergic lesion in mice

Locus coeruleus (LC)-derived noradrenaline is important in cognition and decreases with age, but the impact of prior noradrenaline deficiency on vulnerability to inflammation-induced acute cognitive dysfunction is unclear. Here we assessed whether noradrenergic depletion, in female mice, impacted upon inflammation, locomotor activity and working memory directly after acute systemic immune challenge with bacterial lipopolysaccharide (LPS), a paradigm we have previously used to capture delirium-like acute cognitive deficits. Mice received 2 doses of the LC-selective noradrenergic toxin N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4; 50 mg/kg i.p.) and were challenged, 2 weeks later, with LPS (100 μg/kg i.p.). DSP-4 dramatically reduced noradrenaline concentrations and tyrosine hydroxylase-positive afferents in the frontal cortex and hippocampus. This did not significantly alter numbers of Pu.1-positive microglia, Iba1-positive microglial morphology or mRNA expression of microglia-associated gene transcripts (Tyrobp, Sall1, Cd68, Sra2, Clec7a) in the hippocampus or frontal cortex and produced modest reductions in Cx3cr1 and P2ry12. LPS induced blood and brain cytokine levels, cFOS activation and locomotor responses that were highly similar in DSP-4- and vehicle-treated mice, although LPS-induced plasma TNF-α was significantly reduced in those treated with DSP-4. Importantly, prior noradrenergic depletion did not predispose to LPS-induced T-maze working memory deficits. The data demonstrate that significant depletion of noradrenaline in the hippocampus and frontal cortex does not prompt acutely exaggerated neuroinflammation or leave the brain vulnerable to acute, transient working memory deficits upon low dose LPS challenge. These findings have implications for our understanding of the impact of systemic inflammation on the aging and vulnerable brain during septic encephalopathy and delirium.

Intrinsic DNA damage repair deficiency results in progressive microglia loss and replacement.

The DNA excision repair protein Ercc1 is important for nucleotide excision, double strand DNA break, and interstrand DNA crosslink repair. In constitutive Ercc1‐knockout mice, microglia display increased phagocytosis, proliferation and an enhanced responsiveness to lipopolysaccharide (LPS)‐induced peripheral inflammation. However, the intrinsic effects of Ercc1‐deficiency on microglia are unclear. In this study, Ercc1 was specifically deleted from Cx3cr1‐expressing cells and changes in microglia morphology and immune responses at different times after deletion were determined. Microglia numbers were reduced with approximately 50% at 2–12 months after Ercc1 deletion. Larger and more ramified microglia were observed following Ercc1 deletion both in vivo and in organotypic hippocampal slice cultures. Ercc1‐deficient microglia were progressively lost, and during this period, microglia proliferation was transiently increased. Ercc1‐deficient microglia were gradually replaced by nondeficient microglia carrying a functional Ercc1 allele. In contrast to constitutive Ercc1‐deficient mice, microglia‐specific deletion of Ercc1 did not induce microglia activation or increase their responsiveness to a systemic LPS challenge. Gene expression analysis suggested that Ercc1 deletion in microglia induced a transient aging signature, which was different from a priming or disease‐associated microglia gene expression profile.

Involvement of innate immunity in the course of choroidal neovascularization in mice

AbstractPurposeTo investigate the effect of retinal microglia depletion, and the effect of systemic lipopolysaccharide (LPS) exposure, in the course of laser‐induced choroidal neovascularization (CNV) in mice.MethodsFor microglia depletion, C57BL6/J mice were kept under a diet containing the colony‐stimulating factor 1 receptor (CSF‐1R) inhibitor PLX5622, for 1 week prior to CNV induction and until the end of the experiments. To evaluate the effect of systemic LPS challenge on the CNV course, LPS (1 mg/kg) was given intravenously in control‐fed mice for 1 or 4 consecutive days, immediately after CNV. Mice were imaged with optical coherence tomography (OCT) and fluorescein angiography (FA) at baseline, and at day 3, 7 and 14 after CNV. CNV lesions were measured in the FA images and flow cytometry was used to investigate the effects of PLX5622 on the innate immune cell populations in the retina and the choroid‐RPE of CNV‐subjected mice.ResultsPLX5622 led to microglia depletion in the retina, reduced numbers of dendritic cells, macrophages and leukocytes in the choroid‐RPE and a faster involution of CNV. Retinal swelling, vasodilation and accumulation of microglia/macrophages around retinal vessels were observed at day 4 after the first LPS challenge but not 1 day after a single LPS injection. Moreover, a single LPS injection led to exacerbation of the CNV lesion, while 4 consecutive LPS injections did not affect the CNV size compared to non‐injected mice.ConclusionsThe data suggest that suppression of the ocular innate immune response leads to a faster involution of CNV, while activation of innate immune cells with an acute systemic inflammatory stimulus results in increased CNV areas and slower involution. Moreover, chronic systemic LPS exposure do not affect the course of CNV. These findings highlight the importance of innate immunity in the course of experimental CNV and the different effects of acute and chronic systemic inflammation in the diseased retina.

Naringenin ameliorates learning and memory impairment following systemic lipopolysaccharide challenge in the rat

Systemic inflammation following infection is usually associated with long-term complications including cognitive deficit and dementia. Neuroinflammation and cognitive decline are also main hallmarks of several neurological conditions. Naringenin is a citrus flavanone with anti-inflammatory, neuroprotective, and antioxidant potential. In this study, the protective effect of naringenin against lipopolysaccharide (LPS)-induced cognitive decline was evaluated in the rat. LPS was daily injected at a dose of 167 μg/kg for 1 week and naringenin was administered p.o. at doses of 25, 50, or 100 mg/kg/day. Treatment of LPS-injected rats with naringenin dose-dependently improved spatial recognition memory in Y maze, discrimination ratio in novel object discrimination task, and retention and recall capability in passive avoidance test. Furthermore, naringenin lowered hippocampal malondialdehyde (MDA) as an index of lipid peroxidation and improved antioxidant defensive system comprising superoxide dismutase (SOD), catalase, and glutathione (GSH) in addition to decreasing acetylcholinesterase (AChE) activity. Additionally, naringenin was able to lower hippocampal nuclear factor-kappaB (NF-κB), toll-like receptor 4 (TLR4), tumor necrosis factor α (TNFα), cyclooxygenase-2 (COX2), inducible nitric oxide synthase (iNOS), glial fibrillary acidic protein (GFAP) level and its immunoreactivity, and to elevate nuclear factor (erythroid-derived 2)-like 2 (Nrf2). Taken together, naringenin could alleviate LPS-induced cognitive deficits and neuroinflammation, as was evident from attenuation of oxidative stress and AChE and modulation of Nrf2/NF-κB/TNFα/COX2/iNOS/TLR4/GFAP.

Goats without Prion Protein Display Enhanced Proinflammatory Pulmonary Signaling and Extracellular Matrix Remodeling upon Systemic Lipopolysaccharide Challenge.

A naturally occurring mutation in the PRNP gene of Norwegian dairy goats terminates synthesis of the cellular prion protein (PrPC), rendering homozygous goats (PRNPTer/Ter) devoid of the protein. Although PrPC has been extensively studied, particularly in the central nervous system, the biological role of PrPC remains incompletely understood. Here, we examined whether loss of PrPC affects the initial stage of lipopolysaccharide (LPS)-induced acute lung injury (ALI). Acute pulmonary inflammation was induced by intravenous injection of LPS (Escherichia coli O26:B6) in 16 goats (8 PRNPTer/Ter and 8 PRNP+/+). A control group of 10 goats (5 PRNPTer/Ter and 5 PRNP+/+) received sterile saline. Systemic LPS challenge induced sepsis-like clinical signs including tachypnea and respiratory distress. Microscopic examination of lungs revealed multifocal areas with alveolar hemorrhages, edema, neutrophil infiltration, and higher numbers of alveolar macrophages, with no significant differences between PRNP genotypes. A total of 432 (PRNP+/+) and 596 (PRNPTer/Ter) genes were differentially expressed compared with the saline control of the matching genotype. When assigned to gene ontology categories, biological processes involved in remodeling of the extracellular matrix (ECM), were exclusively enriched in PrPC-deficient goats. These genes included a range of collagen-encoding genes, and proteases such as matrix metalloproteinases (MMP1, MMP2, MMP14, ADAM15) and cathepsins. Several proinflammatory upstream regulators (TNF-α, interleukin-1β, IFN-γ) showed increased activation scores in goats devoid of PrPC. In conclusion, LPS challenge induced marked alterations in the lung tissue transcriptome that corresponded with histopathological and clinical findings in both genotypes. The increased activation of upstream inflammatory regulators and enrichment of ECM components could reflect increased inflammation in the absence of PrPC. Further studies are required to elucidate whether these alterations may affect the later reparative phase of ALI.

Effects of Orally Ingested Arsenic on Respiratory Epithelial Permeability to Bacteria and Small Molecules in Mice.

Background:Arsenic exposure via drinking water impacts millions of people worldwide. Although arsenic has been associated epidemiologically with increased lung infections, the identity of the lung cell types targeted by peroral arsenic and the associated immune mechanisms remain poorly defined.Objectives:We aimed to determine the impact of peroral arsenic on pulmonary antibacterial host defense.Methods:Female C57BL/6 mice were administered drinking water with 0, , or sodium arsenite for 5 wk and then challenged intratracheally with Klebsiella pneumoniae, Streptococcus pneumoniae, or lipopolysaccharide. Bacterial clearance and immune responses were profiled.Results:Arsenic had no effect on bacterial clearance in the lung or on the intrapulmonary innate immune response to bacteria or lipopolysaccharide, as assessed by neutrophil recruitment to, and cytokine induction in, the airspace. Alveolar macrophage production was unaltered. By contrast, arsenic-exposed mice had significantly reduced plasma in response to systemic lipopolysaccharide challenge, together suggesting that the local airway innate immune response may be relatively preserved from arsenic intoxication. Despite intact intrapulmonary bacterial clearance during pneumonia, arsenic-exposed mice suffered dramatically increased bacterial dissemination to the bloodstream. Mechanistically, this was linked to increased respiratory epithelial permeability, as revealed by intratracheal FITC-dextran tracking, serum Club Cell protein 16 measurement, and other approaches. Consistent with barrier disruption at the alveolar level, arsenic-exposed mice had evidence for alveolar epithelial type 1 cell injury.Conclusions:Peroral arsenic has little effect on local airway immune responses to bacteria but compromises respiratory epithelial barrier integrity, increasing systemic translocation of inhaled pathogens and small molecules. https://doi.org/10.1289/EHP1878

Activation of retinal microglia and accumulation of sub‐retinal fluid after systemic challenge with Lipopolysaccharide in mice

PurposeRetinal pathology such as diabetic retinopathy can be exacerbated by systemic viral illness. However, little is known whether systemic inflammation causes activation of retinal microglia. The aim of the present study was to investigate the effect of a systemic inflammatory stimulus with lipopolysaccharide (LPS) on retinal microglia activation.MethodsLPS (1 mg/kg) was administered intravenously for 4 days in Cx3cr1gfp/+ mice, specifically expressing gfp in microglia/macrophages. Retinas were examined with optical coherence tomography, fluorescein angiography and autofluorescence imaging before and after the LPS challenge. A group of mice was fed with the colony stimulating factor‐1 receptor (CSF‐1R) inhibitor PLX5622, which has been shown to deplete retinal microglia after 48 hours, for 7 days and until the end of the experiments. PLX‐fed mice were challenged with LPS as above, imaged and euthanized at day 4 of the LPS challenge.ResultsAccumulation of sub‐retinal fluid and leakage of fluorescein was observed in the retinas of LPS mice, suggesting disruption of the blood retinal barrier (BRB). In vivo imaging and histology showed increased numbers of gfp+ cells in retinas and brains and accumulation around retinal vessels in the LPS group. Increase of gfp+ cell numbers was partially attributed to proliferation, based on Ki67 staining. PLX attenuated the numbers of gfp+ cells and reversed the effects of LPS on sub‐retinal fluid accumulation.ConclusionsOur data suggest that systemic LPS challenge initiates inflammatory responses in the retina and can lead to disruption of the BRB, whose integrity seems to be highly dependent on retinal microglia and/or invading macrophages. Pathology is completely abrogated in microglia depleted mice, suggesting that novel CSF‐1R inhibitors may be a promising target for inflammation mediated retinal diseases.

Disruption of the ATP/adenosine balance in CD39-/- mice is associated with handling-induced seizures.

Seizures are due to excessive, synchronous neuronal firing in the brain and are characteristic of epilepsy, the fourth most prevalent neurological disease. We report handling-induced and spontaneous seizures in mice deficient for CD39, a cell-surface ATPase highly expressed on microglial cells. CD39-/- mice with handling-induced seizures had normal input-output curves and paired-pulse ratio measured from hippocampal slices and lacked microgliosis, astrogliosis or overt cell loss in the hippocampus and cortex. As expected, however, the cerebrospinal fluid of CD39-/- mice contained increased levels of ATP and decreased levels of adenosine. To determine if immune activation was involved in seizure progression, we challenged mice with lipopolysaccharide (LPS) and measured the effect on microglia activation and seizure severity. Systemic LPS challenge resulted in increased cortical staining of Iba1/CD68 and gene array data from purified microglia predicted increased expression of interleukin-8, triggering receptor expressed on myeloid cells 1, p38, pattern recognition receptors, death receptor, nuclear factor-κB , complement, acute phase, and interleukin-6 signalling pathways in CD39-/- versus CD39+/+ mice. However, LPS treatment did not affect handling-induced seizures. In addition, microglia-specific CD39 deletion in adult mice was not sufficient to cause seizures, suggesting instead that altered expression of CD39 during development or on non-microglial cells such as vascular endothelial cells may promote the seizure phenotype. In summary, we show a correlation between altered extracellular ATP/adenosine ratio and a previously unreported seizure phenotype in CD39-/- mice. This work provides groundwork for further elucidation of the underlying mechanisms of epilepsy.

Testicular expression of SP-A, SP-D and MBL-A is positively regulated by testosterone and modulated by lipopolysaccharide

Pattern recognition proteins viz., Surfactant Protein-A (SP-A), Surfactant Protein-D (SP-D) and Mannan Binding Lectin-A (MBL-A) regulate inflammatory immune responses. In view of their plausible contribution to immune privilege in testis, the present study explored their expression and regulation in murine testis. The testicular expression of SP-A, SP-D and MBL-A significantly increased at puberty and was significantly down-regulated in testosterone suppression model. Of the isolated germ cells, Sertoli cells, myoid cells and Leydig cells, germ cells expressed SP-A, SP-D and MBL-A while myoid cells were found to express MBL-A. SP-A and SP-D were localised on head and tail of murine caudal sperm, whereas MBL-A was observed on the connecting piece and tail. Systemic lipopolysaccharide challenge significantly up-regulated SP-A and SP-D levels in murine testis after 24h. Positive regulation of collectins by testosterone and their modulation in response to inflammation implicates their involvement in testicular immune-privilege.

Molecular and cellular neuroinflammatory status of mouse brain after systemic lipopolysaccharide challenge: importance of CCR2/CCL2 signaling.

BackgroundGenetic and environmental factors are critical elements influencing the etiology of major depression. It is now accepted that neuroinflammatory processes play a major role in neuropsychological disorders. Neuroinflammation results from the dysregulation of the synthesis and/or release of pro- and anti-inflammatory cytokines with central or peripheral origin after various insults. Systemic bacterial lipopolysaccharide (LPS) challenge is commonly used to study inflammation-induced depressive-like behaviors in rodents. In the present study, we investigated immune-to-brain communication in mice by examining the effects of peripheral LPS injection on neuroinflammation encompassing cytokine and chemokine production, microglia and central nervous system (CNS)-associated phagocyte activation, immune cell infiltration and serotonergic neuronal function.MethodsLPS was administered to C57BL/6 J mice by intraperitoneal injection; brains were collected and pro-inflammatory cytokine mRNA and proteins were measured. To examine the relative contribution of the different populations of brain immune cells to the occurrence of neuroinflammation after acute systemic inflammation, we precisely characterized them by flow cytometry, studied changes in their proportions and level of activation, and measured the amount of cytokines they released by Cytometric Bead Array™ after cell sorting and ex vivo culture. Because of the central role that the chemokine CCL2 seems to play in our paradigm, we studied the effect of CCL2 on the activity of serotonergic neurons of the raphe nucleus using electrophysiological recordings.ResultsWe report that systemic LPS administration in mice caused a marked increase in pro-inflammatory IL-1β, IL-6, TNFα and CCL2 (monocyte chemoattractant protein-1) mRNA and protein levels in the brain. Moreover, we found that LPS caused microglia and CNS-associated phagocyte activation characterized by upregulation of CCR2, TLR4/CD14, CD80 and IL-4Rα, associated with overproduction of pro-inflammatory cytokines and chemokines, especially CCL2. LPS also induced a marked and selective increase of CCR2+ inflammatory monocytes within the brain. Finally, we showed that CCL2 hyperpolarized serotonergic raphe neurons in mouse midbrain slices, thus probably reducing the serotonin tone in projection areas.ConclusionTogether, we provide a detailed characterization of the molecular and cellular players involved in the establishment of neuroinflammation after systemic injection of LPS. This highlights the importance of the CCL2/CCR2 signaling and suggests a possible link with depressive disorders.

Immune priming and experimental glaucoma: the effect of prior systemic lipopolysaccharide challenge on tissue outcomes after optic nerve injury

Microglial activation is a prominent feature throughout the optic pathway in experimental glaucoma. Pro-inflammatory microglial activation may contribute to neurodegeneration through the release of pro-inflammatory cytokines and other inflammatory mediators. Systemic administration of lipopolysaccharide stimulates microglia to produce pro-inflammatory cytokines and chemoattractants. A preliminary investigation demonstrated pro-inflammatory microglial activation throughout the optic pathway following systemic lipopolysaccharide challenge. The aim of the current work was to investigate whether microglial priming with lipopolysaccharide would exacerbate optic nerve injury in rats following experimental glaucoma. Adult female Sprague-Dawley rats were divided into lipopolysaccharide treatment (n = 15) and saline treatment groups (n = 15). Microglial priming was induced with a 2.5-mg/kg intraperitoneal injection of lipopolysaccharide; control animals received saline. Experimental glaucoma was induced 48 h later in the right eyes of animals by laser photocoagulation of the trabecular meshwork. Animals were sacrificed 9 days after laser treatment. The estimated number of axons per optic nerve was 51 327 ± 3868 (mean ± standard error of the mean) in the lipopolysaccharide group and 54 569 ± 6687 (mean ± standard error of the mean) in the saline group. Optic nerve axon counts were not significantly different between lipopolysaccharide and saline groups (P = 0.67). Systemic lipopolysaccharide challenge had no discernible effect on optic nerve injury in laser-induced experimental glaucoma. These findings do not support the hypothesis that this model of experimental glaucoma involves inflammation and instead suggest that microglial activation may occur secondary to chronic neurodegeneration.

Intravital Imaging Reveals Differential Roles Of Neutrophilic and Stromal Toll-Like Receptor 4 In Hyper-Acute Bone Marrow Response To Systemic Lipopolysaccharide Challenge

IntroductionNeutrophils are the first defenders of host innate immune response against a variety of pathogens. Produced in large quantities from myeloid progenitor cells in the bone marrow, neutrophils are rapidly mobilized and released from the marrow cavity into the general circulation in response to inflammation and invading pathogens. While how neutrophils are released from the bone marrow as a result of interplay among CXCL12 (osteoblastic) and CXCL1/CXCL2 (perivascular) gradients have been studied at a time scale of hours to days post systemic lipopolysaccharide (LPS) challenge, little is known about how the neutrophil and marrow stroma react on a single-cell level in vivo during the hyper-acute (minutes to hours) phase following LPS challenge. MethodsWe performed intravital two-photon microscopy (TPM) on intact cranium of live, anesthetized mice, in which the green fluorescent protein (GFP) is expressed under the Lysozyme M (LysM) promoter expressed predominantly in neutrophils and monocytes, before and immediately after systemic LPS challenge. The behavior of neutrophils and surrounding stroma was analyzed and correlated with systemic neutrophilic responses. Bone marrow chimeras were generated in order to differentiate TLR4-mediated responses in hematopoietic and radio-resistant stromal elements. Neutralizing antibodies to relevant chemokines responsible for neutrophil mobilizations were used to observe changes in intra-marrow neutrophil response following LPS challenge. ResultsWe observed a 2.5-fold increase in the average instantaneous speed, as well as the formation of dynamic GFP+ cellular clusters in 50% of the marrow-resident neutrophils between 30 minutes to 60 minutes following i.v. administration of 100ng of LPS, with the GFP+ neutrophils achieving a peak average speed of 8.4um/min. This was accompanied by release of neutrophils into the systemic circulation as evidenced by a 40% reduction in the overall GFP fluorescence intensity 90 minutes following LPS challenge. Bone marrow chimera experiments revealed that while intra-marrow migration and cellular clustering are dependent on TLR4 signaling in neutrophils, the release of neutrophils into systemic circulation is facilitated by TLR4 signaling on stromal elements. Blocking CXCR2 signaling on neutrophils resulted in the same phenotype as chimeras expressing TLR4-defective stroma, further revealing that marrow stromal elements modulate TLR4-mediated neutrophil mobilization and release via CXCL1/CXCL2 chemokine signaling during this hyper-acute phase of marrow response to LPS. ConclusionsIntravital imaging provides real-time insights to the mechanisms of dynamic regulation of marrow responses to hyper-acute systemic LPS challenge in vivo at a single-cell level within live hosts, and reveals differential contribution of TLR4 signaling on neutrophils and stroma in the bone marrow's response to systemic LPS challenge. Disclosures:No relevant conflicts of interest to declare.

Dynamic real-time imaging of marrow-resident neutrophils interacting with human mesenchymal stem cells during systemic lipopolysaccharide challenge.

e22158 Background: Human mesenchymal stem cells (hMSCs) have gained intense interest due to their immune-modulatory, tissue differentiating and homing properties to sites of inflammation and tumor microenvironment, as evidenced by more than 200 ongoing clinical trials using hMSCs in a variety of clinical settings. Despite evidence demonstrating the bio-distribution of infused hMSCs in target organs using static fluorescence imaging or whole-body imaging techniques, there is controversy regarding how hMSCs exert their biological effects, and very little is known about how they behave dynamically within host tissues on a single-cell level in vivo. Methods: We infused fluorescently labeled clinical-grade hMSCs into immune-competent mice in which neutrophils and monocytes express a second fluorescent marker under the Lysozyme M (LysM) promoter. The recipient mice were then subjected to serial 4-D (xyzt) imaging of the bone marrow cavity with intravital two-photon microscopy (TPM) during acute systemic Lipopolysaccharide (LPS) challenges to observe changes in MSC and neutrophil migration behavior. Results: We were able, for the first time, to capture dynamic interactions between and migration pattern of hMSCs and LysM+granulocytes in the bone marrow of live mice during systemic LPS challenge. Contrary to some published reports, many of the infused hMSCs remained intact despite repeated cellular contacts with host neutrophils. However, we also observed the destruction and subsequent phagocytosis of some hMSCs by surrounding granulocytes. Conclusions: Our imaging platform provides opportunities to gain insight into the biology and therapeutic mechanisms of hMSCs in vivo at a single-cell level within live hosts.

Abstract 199: Anticoagulant Heparan Sulfate Conveys Anti-Inflammatory Activity of Antithrombin

Antithrombin (AT) therapy reduces morbidity/mortality in systemic inflammatory response syndromes, such as septic shock. These effects stem from the ability of AT to directly initiate cell signaling, which requires AT engagement with heparan sulfate proteoglycans. It is presently unclear if this process involves anticoagulant heparan sulfate (HS AT+ ), a specific motif with high affinity for AT that is produced by endothelial cells. If HS AT+ regulates anti-inflammatory signaling, then Hs3st1 -/- mice, which lack endothelial HS AT+ , should exhibit a proinflammatory state and should not benefit from AT treatment. We tested these hypotheses using a mouse model of lipopolysaccharide (LPS)-induced septic shock. Hemodynamics were monitored with a left ventricle pressure-volume catheter. Both Hs3st1 +/+ and Hs3st1 -/- mice die of cardiogenic shock. However, Hs3st1 -/- , compared to Hs3st1 +/+ , mice exhibited a much more rapid onset of death. Left ventricular gene expression profiles of mice with systemic LPS challenge showed enhanced expression of leukocyte recruitment genes (P-selectin, Cxcl10) in Hs3st1 -/- mice. Consistent with these data, LPS-treated Hs3st1 -/- mice, compared to Hs3st1 +/+ , exhibited enhanced leukocyte rolling flux within cremaster muscle venules. Thus, mice lacking HS AT+ exhibit a proinflammatory phenotype. AT treatment of Hs3st1 +/+ mice reduced both LPS-induced lethality and leukocyte-endothelial interactions. Conversely AT treatment of Hs3st1 -/- mice enhanced both LPS-induced lethality and leukocyte-endothelial interactions. Thus, AT failed to elicit anti-inflammatory effects in mice lacking HS AT+ . Our results indicate that endothelial HS AT+ is one component that mediates AT’s anti-inflammatory activity. These findings provide an initial step towards elucidating the role of HS AT+ and AT in a novel natural anti-inflammatory pathway of the blood vessel wall. This pathway is an ideal target for developing therapeutics to combat the devastating outcomes of septic shock.

Dynamic Imaging of Marrow-Resident Granulocytes Interacting with Human Mesenchymal Stem Cells upon Systemic Lipopolysaccharide Challenge

Human mesenchymal stem cells (hMSCs) have gained intense research interest due to their immune-modulatory, tissue differentiating, and homing properties to sites of inflammation. Despite evidence demonstrating the biodistribution of infused hMSCs in target organs using static fluorescence imaging or whole-body imaging techniques, surprisingly little is known about how hMSCs behave dynamically within host tissues on a single-cell level in vivo. Here, we infused fluorescently labeled clinical-grade hMSCs into immune-competent mice in which neutrophils and monocytes express a second fluorescent marker under the lysozyme M (LysM) promoter. Using intravital two-photon microscopy (TPM), we were able for the first time to capture dynamic interactions between hMSCs and LysM+ granulocytes in the calvarium bone marrow of recipient mice during systemic LPS challenge in real time. Interestingly, many of the infused hMSCs remained intact despite repeated cellular contacts with host neutrophils. However, we were able to observe the destruction and subsequent phagocytosis of some hMSCs by surrounding granulocytes. Thus, our imaging platform provides opportunities to gain insight into the biology and therapeutic mechanisms of hMSCs in vivo at a single-cell level within live hosts.