Mobilisation of the splenic monocyte reservoir and peripheral CX₃CR1 deficiency adversely affects recovery from spinal cord injury

RNA-Seq Analysis of Microglia Reveals Time-Dependent Activation of Specific Genetic Programs following Spinal Cord Injury

Neurons have inherent competence to regrow following injury, although not spontaneously. Spinal cord injury (SCI) induces a pronounced neuroinflammation driven by resident microglia and infiltrating peripheral macrophages. Microglia are the first reactive glial population after SCI and participate in recruitment of monocyte-derived macrophages to the lesion site. Both positive and negative influence of microglia and macrophages on axonal regeneration had been reported after SCI, raising the issue whether their response depends on time post-lesion or different lesion severity. We analyzed molecular alterations in microglia at several time-points after different SCI severities using RNA-sequencing. We demonstrate that activation of microglia is time-dependent post-injury but is independent of lesion severity. Early transcriptomic response of microglia after SCI involves proliferation and neuroprotection, which is then switched to neuroinflammation at later stages. Moreover, SCI induces an autologous microglial expression of astrocytic markers with over 6% of microglia expressing glial fibrillary acidic protein and vimentin from as early as 72 h post-lesion and up to 6 weeks after injury. We also identified the potential involvement of DNA damage and in particular tumor suppressor gene breast cancer susceptibility gene 1 (Brca1) in microglia after SCI. Finally, we established that BRCA1 protein is specifically expressed in non-human primate spinal microglia and is upregulated after SCI. Our data provide the first transcriptomic analysis of microglia at multiple stages after different SCI severities. Injury-induced microglia expression of astrocytic markers at RNA and protein levels demonstrates novel insights into microglia plasticity. Finally, increased microglia expression of BRCA1 in rodents and non-human primate model of SCI, suggests the involvement of oncogenic proteins after CNS lesion.

Multipotent Adult Progenitor Cells Enhance Recovery After Stroke by Modulating the Immune Response from the Spleen

Stem cell therapy modulates not only the local microenvironment of the brain but also the systemic immune responses. We explored the impact of human multipotent adult progenitor cells (MAPC) modulating splenic activation and peripheral immune responses after ischemic stroke. Hundred twenty-six Long-Evans adult male rats underwent middle cerebral artery occlusion. Twenty-four hours later, they received IV MAPC or saline treatment. At 3 days after infusion, RNA was isolated from the injured cortex and spleen for microarray analysis. Spleen mass, splenocyte phenotype, and releasing cytokines were measured. Serum cytokines, MAPC biodistribution, brain lesion sizes and neurofunctional deficits were compared in rats treated with MAPC or saline with and without spleens. Stroked animals treated with MAPC exhibited genes that more closely resembled animals with sham surgery. Gene categories downregulated by MAPC included leukocyte activation, antigen presentation, and immune effector processing, associated with the signaling pathways regulated by TNF-α, IL-1β, IL-6, and IFN-γ within the brain. MAPC treatment restored spleen mass reduction caused by stroke, elevated Treg cells within the spleen, increased IL-10 and decreased IL-1β released by splenocytes. MAPC reduced IL-6 and IL-1β and upregulated IL-10 serum levels. Compared with saline, MAPC enhance stroke recovery in rats with intact spleens but had no effects in rats without spleens. MAPC restores expression of multiple genes and pathways involved in immune and inflammatory responses after stroke. Immunomodulation of the splenic response by the intravenous administration of MAPC may create a more favorable environment for brain repair after stroke. Stem Cells 2017;35:1290-1302.

Neuroinflammation as Fuel for Axonal Regeneration in the Injured Vertebrate Central Nervous System

Damage to the central nervous system (CNS) is one of the leading causes of morbidity and mortality in elderly, as repair after lesions or neurodegenerative disease usually fails because of the limited capacity of CNS regeneration. The causes underlying this limited regenerative potential are multifactorial, but one critical aspect is neuroinflammation. Although classically considered as harmful, it is now becoming increasingly clear that inflammation can also promote regeneration, if the appropriate context is provided. Here, we review the current knowledge on how acute inflammation is intertwined with axonal regeneration, an important component of CNS repair. After optic nerve or spinal cord injury, inflammatory stimulation and/or modification greatly improve the regenerative outcome in rodents. Moreover, the hypothesis of a beneficial role of inflammation is further supported by evidence from adult zebrafish, which possess the remarkable capability to repair CNS lesions and even restore functionality. Lastly, we shed light on the impact of aging processes on the regenerative capacity in the CNS of mammals and zebrafish. As aging not only affects the CNS, but also the immune system, the regeneration potential is expected to further decline in aged individuals, an element that should definitely be considered in the search for novel therapeutic strategies.

Role of splenic reservoir monocytes in pulmonary vascular monocyte accumulation in experimental hepatopulmonary syndrome

BACKGROUND AND AIM

Pulmonary monocyte infiltration plays a significant role in the development of angiogenesis in experimental hepatopulmonary syndrome (HPS) after common bile duct ligation (CBDL). Hepatic monocytes are also increased after CBDL, but the origins remain unclear. Splenic reservoir monocytes have been identified as a major source of monocytes that accumulate in injured tissues. Whether splenic monocytes contribute to monocyte alterations after CBDL is unknown. This study evaluates monocyte distributions and assesses effects of splenectomy on monocyte levels and pulmonary vascular and hepatic abnormalities in experimental HPS.

METHODS

Splenectomy was performed in CBDL animals. Monocyte levels in different tissues and circulation were assessed with CD68. Pulmonary alterations of HPS were evaluated with vascular endothelial growth factor-A (VEGF-A) levels, angiogenesis, and alveolar-arterial oxygen gradient (AaPO₂ ). Liver abnormalities were evaluated with fibrosis (Sirius red), bile duct proliferation (CK-19), and enzymatic changes.

RESULTS

Monocyte levels increased in the lung and liver after CBDL and were accompanied by elevated circulating monocyte numbers. Splenectomy significantly decreased monocyte accumulation, VEGF-A levels, and angiogenesis in CBDL animal lung and improved AaPO₂ levels. In contrast, hepatic monocyte levels, fibrosis, and functional abnormalities were further exacerbated by spleen removal.

CONCLUSIONS

Splenic reservoir monocytes are a major source for lung monocyte accumulation after CBDL, and spleen removal attenuates the development of experimental HPS. Liver monocytes may have different origins, and accumulation is exacerbated after depletion of splenic reservoir monocytes. Tissue specific monocyte alterations, influenced by the spleen reservoir, have a significant impact on pulmonary complications of liver disease.

Spinal Cord Injury Suppresses Cutaneous Inflammation: Implications for Peripheral Wound Healing

People who suffer a traumatic spinal cord injury (SCI) are at increased risk for developing dermatological complications. These conditions increase cost of care, incidence of rehospitalization, and the risk for developing other infections. The consequences of dermatological complications after SCI are likely exacerbated further by post-injury deficits in neural-immune signaling. Indeed, a functional immune system is essential for optimal host defense and tissue repair. Here, we tested the hypothesis that SCI at high spinal levels, which causes systemic immune suppression, would suppress cutaneous inflammation below the level of injury. C57BL/6 mice received an SCI (T3 spinal level) or sham injury; then one day later complete Freund's adjuvant (CFA) was injected subcutaneously below the injury level. Inflammation was quantified by injecting mice with V-Sense, a perfluorocarbon (PFC) tracer that selectively labels macrophages, followed by in vivo imaging. The total radiant efficiency, which is proportional to the number of macrophages, was measured over a 4-day period at the site of CFA injection. Fluorescent in vivo imaging revealed that throughout the analysis period, the macrophage reaction in SCI mice was reduced ∼50% compared with sham-injured mice. Radiant efficiency data were confirmed using magnetic resonance imaging (MRI), and together the data indicate that SCI significantly impairs subcutaneous inflammation. Future studies should determine whether enhancing local inflammation or boosting systemic immune function can improve the rate or efficiency of cutaneous wound healing in individuals with SCI. Doing so also could limit wound infections or secondary complications of impaired healing after SCI.

Neural Stem Cell-Conditioned Medium Suppresses Inflammation and Promotes Spinal Cord Injury Recovery

Spinal cord injury (SCI) causes functional impairment as a result of the initial injury followed by secondary injury mechanism. SCI provokes an inflammatory response that causes secondary tissue damage and neurodegeneration. While the use of neural stem cell (NSC) engraftment to mitigate secondary injury has been of interest to many researchers, it still faces several limitations. As such, we investigated if NSC-conditioned medium (NSC-M) possesses therapeutic potential for the treatment of SCI. It has been proposed that many of the beneficial effects attributed to stem cell therapies are due to secreted factors. Utilizing primary cell culture and murine models of SCI, we determined that systemic treatment with NSC-M was able to significantly improve motor function and lesion healing. In addition, NSC-M demonstrated significant anti-inflammatory potential in vitro and in vivo, reducing inflammatory cytokine expression in both activated macrophages and injured spinal cord tissues. NSC-M was also able to reduce the expression of inducible nitric oxide synthase (iNOS) within the spleen of injured animals, indicating an ability to reduce systemic inflammation. Thus, we believe that NSC-M offers a possible alternative to direct stem cell engraftment for the treatment of SCI.

Analysis of the Role of CX3CL1 (Fractalkine) and Its Receptor CX3CR1 in Traumatic Brain and Spinal Cord Injury: Insight into Recent Advances in Actions of Neurochemokine Agents

CX3CL1 (fractalkine) is the only member of the CX3C (delta) subfamily of chemokines which is unique and combines the properties of both chemoattractant and adhesion molecules. The two-form ligand can exist either in a soluble form, like all other chemokines, and as a membrane-anchored molecule. CX3CL1 discloses its biological properties through interaction with one dedicated CX3CR1 receptor which belongs to a family of G protein-coupled receptors (GPCR). The CX3CL1/CX3CR1 axis acts in many physiological phenomena including those occurring in the central nervous system (CNS), by regulating the interactions between neurons, microglia, and immune cells. Apart from the role under physiological conditions, the CX3CL1/CX3CR1 axis was implied to have a role in different neuropathologies such as traumatic brain injury (TBI) and spinal cord injury (SCI). CNS injuries represent a serious public health problem, despite improvements in therapeutic management. To date, no effective treatment has been determined, so they constitute a leading cause of death and severe disability. The course of TBI and SCI has two consecutive poorly demarcated phases: the initial, primary injury and secondary injury. Recent evidence has implicated the role of the CX3CL1/CX3CR1 axis in neuroinflammatory processes occurring after CNS injuries. The importance of the CX3CL1/CX3CR1 axis in the pathophysiology of TBI and SCI in the context of systemic and direct local immune response is still under investigation. This paper, based on a review of the literature, updates and summarizes the current knowledge about CX3CL1/CX3CR1 axis involvement in TBI and SCI pathogenesis, indicating possible molecular and cellular mechanisms with a potential target for therapeutic intervention.

Intravenous multipotent adult progenitor cell treatment decreases inflammation leading to functional recovery following spinal cord injury

Following spinal cord injury (SCI), immune-mediated secondary processes exacerbate the extent of permanent neurological deficits. We investigated the capacity of adult bone marrow-derived stem cells, which exhibit immunomodulatory properties, to alter inflammation and promote recovery following SCI. In vitro, we show that human multipotent adult progenitor cells (MAPCs) have the ability to modulate macrophage activation, and prior exposure to MAPC secreted factors can reduce macrophage-mediated axonal dieback of dystrophic axons. Using a contusion model of SCI, we found that intravenous delivery of MAPCs one day, but not immediately, after SCI significantly improves urinary and locomotor recovery, which was associated with marked spinal cord tissue sparing. Intravenous MAPCs altered the immune response in the spinal cord and periphery, however biodistribution studies revealed that no MAPCs were found in the cord and instead preferentially homed to the spleen. Our results demonstrate that MAPCs exert their primary effects in the periphery and provide strong support for the use of these cells in acute human contusive SCI.

Fractalkine Receptor Deficiency Is Associated with Early Protection but Late Worsening of Outcome following Brain Trauma in Mice

An impaired ability to regulate microglia activation by fractalkine (CX3CL1) leads to microglia chronic sub-activation. How this condition affects outcome after acute brain injury is still debated, with studies showing contrasting results depending on the timing and the brain pathology. Here, we investigated the early and delayed consequences of fractalkine receptor (CX3CR1) deletion on neurological outcome and on the phenotypical features of the myeloid cells present in the lesions of mice with traumatic brain injury (TBI). Wild type (WT) and CX3CR1(-/-) C57Bl/6 mice were subjected to sham or controlled cortical impact brain injury. Outcome was assessed at 4 days and 5 weeks after TBI by neuroscore, neuronal count, and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining. Compared with WT mice, CX3CR1(-/-) TBI mice showed a significant reduction of sensorimotor deficits and lower cellular damage in the injured cortex 4 days post-TBI. Conversely, at 5 weeks, they showed a worsening of sensorimotor deficits and pericontusional cell death. Microglia (M) and macrophage (μ) activation and polarization were assessed by quantitative immunohistochemistry for CD11b, CD68, Ym1, and inducible nitric oxide synthase (iNOS)-markers of M/μ activation, phagocytosis, M2, and M1 phenotypes, respectively. Morphological analysis revealed a decreased area and perimeter of CD11b(+) cells in CX3CR1(-/-) mice at 4 days post-TBI, whereas, at 5 weeks, both parameters were significantly higher, compared with WT mice. At 4 days, CX3CR1(-/-) mice showed significantly decreased CD68 and iNOS immunoreactivity, while at 5 weeks post-injury, they showed a selective increase of iNOS. Gene expression on CD11b(+) sorted cells revealed an increase of interleukin 10 and insulin-like growth factor 1 (IGF1) at 1 day and a decrease of IGF1 4 days and 5 weeks post-TBI in CX3CR1(-/-), compared with WT mice. These data show an early protection followed by a chronic exacerbation of TBI outcome in the absence of CX3CR1. Thus, longitudinal effects of myeloid cell manipulation at different stages of pathology should be investigated to understand how and when their modulation may offer therapeutic chances.

Traumatic spinal cord injury in mice with human immune systems

Mouse models have provided key insight into the cellular and molecular control of human immune system function. However, recent data indicate that extrapolating the functional capabilities of the murine immune system into humans can be misleading. Since immune cells significantly affect neuron survival and axon growth and also are required to defend the body against infection, it is important to determine the pathophysiological significance of spinal cord injury (SCI)-induced changes in human immune system function. Research projects using monkeys or humans would be ideal; however, logistical and ethical barriers preclude detailed mechanistic studies in either species. Humanized mice, i.e., immunocompromised mice reconstituted with human immune cells, can help overcome these barriers and can be applied in various experimental conditions that are of interest to the SCI community. Specifically, newborn NOD-SCID-IL2rg(null) (NSG) mice engrafted with human CD34(+) hematopoietic stem cells develop normally without neurological impairment. In this report, new data show that when mice with human immune systems receive a clinically-relevant spinal contusion injury, spontaneous functional recovery is indistinguishable from that achieved after SCI using conventional inbred mouse strains. Moreover, using routine immunohistochemical and flow cytometry techniques, one can easily phenotype circulating human immune cells and document the composition and distribution of these cells in the injured spinal cord. Lesion pathology in humanized mice is typical of mouse contusion injuries, producing a centralized lesion epicenter that becomes occupied by phagocytic macrophages and lymphocytes and enclosed by a dense astrocytic scar. Specific human immune cell types, including three distinct subsets of human monocytes, were readily detected in the blood, spleen and liver. Future studies that aim to understand the functional consequences of manipulating the neuro-immune axis after SCI should consider using the humanized mouse model. Humanized mice represent a powerful tool for improving the translational value of pre-clinical SCI data.

Delayed Imatinib Treatment for Acute Spinal Cord Injury: Functional Recovery and Serum Biomarkers

With no currently available drug treatment for spinal cord injury, there is a need for additional therapeutic candidates. We took the approach of repositioning existing pharmacological agents to serve as acute treatments for spinal cord injury and previously found imatinib to have positive effects on locomotor and bladder function in experimental spinal cord injury when administered immediately after the injury. However, for imatinib to have translational value, it needs to have sustained beneficial effects with delayed initiation of treatment, as well. Here, we show that imatinib improves hind limb locomotion and bladder recovery when initiation of treatment was delayed until 4 h after injury and that bladder function was improved with a delay of up to 24 h. The treatment did not induce hypersensitivity. Instead, imatinib-treated animals were generally less hypersensitive to either thermal or mechanical stimuli, compared with controls. In an effort to provide potential biomarkers, we found serum levels of three cytokines/chemokines--monocyte chemoattractant protein-1, macrophage inflammatory protein (MIP)-3α, and keratinocyte chemoattractant/growth-regulated oncogene (interleukin 8)--to increase over time with imatinib treatment and to be significantly higher in injured imatinib-treated animals than in controls during the early treatment period. This correlated to macrophage activation and autofluorescence in lymphoid organs. At the site of injury in the spinal cord, macrophage activation was instead reduced by imatinib treatment. Our data strengthen the case for clinical trials of imatinib by showing that initiation of treatment can be delayed and by identifying serum cytokines that may serve as candidate markers of effective imatinib doses.

The Complement Receptor C5aR Controls Acute Inflammation and Astrogliosis following Spinal Cord Injury

This study investigated the role of the complement activation fragment C5a in secondary pathology following contusive spinal cord injury (SCI). C5ar(-/-) mice, which lack the signaling receptor for C5a, displayed signs of improved locomotor recovery and reduced inflammation during the first week of SCI compared with wild-type mice. Intriguingly, the early signs of improved recovery in C5ar(-/-) mice deteriorated from day 14 onward, with absence of C5aR ultimately leading to poorer functional outcomes, larger lesion volumes, reduced myelin content, and more widespread inflammation at 35 d SCI. Pharmacological blockade of C5aR with a selective antagonist (C5aR-A) during the first 7 d after SCI improved recovery compared with vehicle-treated mice, and this phenotype was sustained up to 35 d after injury. Consistent with observations made in C5ar(-/-) mice, these improvements were, however, lost if C5aR-A administration was continued into the more chronic phase of SCI. Signaling through the C5a-C5aR axis thus appears injurious in the acute period but serves a protective and/or reparative role in the post-acute phase of SCI. Further experiments in bone marrow chimeric mice suggested that the dual and opposing roles of C5aR on SCI outcomes primarily relate to its expression on CNS-resident cells and not infiltrating leukocytes. Additional in vivo and in vitro studies provided direct evidence that C5aR signaling is required during the postacute phase for astrocyte hyperplasia, hypertrophy, and glial scar formation. Collectively, these findings highlight the complexity of the inflammatory response to SCI and emphasize the importance of optimizing the timing of therapeutic interventions.

The ischemic environment drives microglia and macrophage function

Cells of myeloid origin, such as microglia and macrophages, act at the crossroads of several inflammatory mechanisms during pathophysiology. Besides pro-inflammatory activity (M1 polarization), myeloid cells acquire protective functions (M2) and participate in the neuroprotective innate mechanisms after brain injury. Experimental research is making considerable efforts to understand the rules that regulate the balance between toxic and protective brain innate immunity. Environmental changes affect microglia/macrophage functions. Hypoxia can affect myeloid cell distribution, activity, and phenotype. With their intrinsic differences, microglia and macrophages respond differently to hypoxia, the former depending on ATP to activate and the latter switching to anaerobic metabolism and adapting to hypoxia. Myeloid cell functions include homeostasis control, damage-sensing activity, chemotaxis, and phagocytosis, all distinctive features of these cells. Specific markers and morphologies enable to recognize each functional state. To ensure homeostasis and activate when needed, microglia/macrophage physiology is finely tuned. Microglia are controlled by several neuron-derived components, including contact-dependent inhibitory signals and soluble molecules. Changes in this control can cause chronic activation or priming with specific functional consequences. Strategies, such as stem cell treatment, may enhance microglia protective polarization. This review presents data from the literature that has greatly advanced our understanding of myeloid cell action in brain injury. We discuss the selective responses of microglia and macrophages to hypoxia after stroke and review relevant markers with the aim of defining the different subpopulations of myeloid cells that are recruited to the injured site. We also cover the functional consequences of chronically active microglia and review pivotal works on microglia regulation that offer new therapeutic possibilities for acute brain injury.

Interleukin-33 treatment reduces secondary injury and improves functional recovery after contusion spinal cord injury

Interleukin-33 (IL-33) is a member of the interleukin-1 cytokine family and highly expressed in the naïve mouse brain and spinal cord. Despite the fact that IL-33 is known to be inducible by various inflammatory stimuli, its cellular localization in the central nervous system and role in pathological conditions is controversial. Administration of recombinant IL-33 has been shown to attenuate experimental autoimmune encephalomyelitis progression in one study, yet contradictory reports also exist. Here we investigated for the first time the pattern of IL-33 expression in the contused mouse spinal cord and demonstrated that after spinal cord injury (SCI) IL-33 was up-regulated and exhibited a nuclear localization predominantly in astrocytes. Importantly, we found that treatment with recombinant IL-33 alleviated secondary damage by significantly decreasing tissue loss, demyelination and astrogliosis in the contused mouse spinal cord, resulting in dramatically improved functional recovery. We identified both central and peripheral mechanisms of IL-33 action. In spinal cord, IL-33 treatment reduced the expression of pro-inflammatory tumor necrosis factor-alpha and promoted the activation of anti-inflammatory arginase-1 positive M2 microglia/macrophages, which chronically persisted in the injured spinal cord for up to at least 42 days after the treatment. In addition, IL-33 treatment showed a tendency towards reduced T-cell infiltration into the spinal cord. In the periphery, IL-33 treatment induced a shift towards the Th2 type cytokine profile and reduced the percentage and absolute number of cytotoxic, tumor necrosis factor-alpha expressing CD4+ cells in the spleen. Additionally, IL-33 treatment increased expression of T-regulatory cell marker FoxP3 and reduced expression of M1 marker iNOS in the spleen. Taken together, these results provide the first evidence that IL-33 administration is beneficial after CNS trauma. Treatment with IL33 may offer a novel therapeutic strategy for patients with acute contusion SCI.

Central nervous system regenerative failure: role of oligodendrocytes, astrocytes, and microglia

Animal studies are now showing the exciting potential to achieve significant functional recovery following central nervous system (CNS) injury by manipulating both the inefficient intracellular growth machinery in neurons, as well as the extracellular barriers, which further limit their regenerative potential. In this review, we have focused on the three major glial cell types: oligodendrocytes, astrocytes, and microglia/macrophages, in addition to some of their precursors, which form major extrinsic barriers to regrowth in the injured CNS. Although axotomized neurons in the CNS have, at best, a limited capacity to regenerate or sprout, there is accumulating evidence that even in the adult and, especially after boosting their growth motor, neurons possess the capacity for considerable circuit reorganization and even lengthy regeneration when these glial obstacles to neuronal regrowth are modified, eliminated, or overcome.

CX3CR1 signaling on monocytes is dispensable after intracerebral hemorrhage

Intracerebral hemorrhage is a subset of stroke for which there is no specific treatment. The Ly6Chi CCR2+ monocytes have been shown to contribute to acute injury after intracerebral hemorrhage. The other murine monocyte subset expresses CX3CR1 and lower Ly6C levels, and contributes to repair in other disease models. We hypothesized that the Ly6Clo CX3CR1+ monocytes would contribute to recovery after intracerebral hemorrhage. Intracerebral hemorrhage was modeled by blood injection in WT and CX3CR1-null bone marrow chimeras. Neurological outcomes and leukocyte recruitment were quantified at various time points. Functional outcomes were equal at 1, 3, 7, and 14 days after intracerebral hemorrhage in both genotypes. No differences were observed in leukocyte recruitment between genotypes on either 3 or 7 days after intracerebral hemorrhage. A few hundred Ly6Clo monocytes were found in the ipsilateral hemisphere in each genotype and they did not change over time. Peripherally derived CX3CR1+ monocytes were observed in the perihematomal brain 7 and 14 days after intracerebral hemorrhage. Our data suggests CX3CR1 signaling on monocytes does not play an influential role in acute injury or functional recovery after intracerebral hemorrhage and therefore CX3CR1 is not a therapeutic target to improve outcome after intracerebral hemorrhage.

Hematogenous macrophage depletion reduces the fibrotic scar and increases axonal growth after spinal cord injury

Spinal cord injury (SCI) leads to formation of a fibrotic scar that is inhibitory to axon regeneration. Recent evidence indicates that the fibrotic scar is formed by perivascular fibroblasts, but the mechanism by which they are recruited to the injury site is unknown. Using bone marrow transplantation in mouse model of spinal cord injury, we show that fibroblasts in the fibrotic scar are associated with hematogenous macrophages rather than microglia, which are limited to the surrounding astroglial scar. Depletion of hematogenous macrophages results in reduced fibroblast density and basal lamina formation that is associated with increased axonal growth in the fibrotic scar. Cytokine gene expression analysis after macrophage depletion indicates that decreased Tnfsf8, Tnfsf13 (tumor necrosis factor superfamily members) and increased BMP1-7 (bone morphogenetic proteins) expression may serve as anti-fibrotic mechanisms. Our study demonstrates that hematogenous macrophages are necessary for fibrotic scar formation and macrophage depletion results in changes in multiple cytokines that make the injury site less fibrotic and more conducive to axonal growth.

PI3Kδ inhibition reduces TNF secretion and neuroinflammation in a mouse cerebral stroke model

Stroke is a major cause of death worldwide and the leading cause of permanent disability. Although reperfusion is currently used as treatment, the restoration of blood flow following ischaemia elicits a profound inflammatory response mediated by proinflammatory cytokines such as tumour necrosis factor (TNF), exacerbating tissue damage and worsening the outcomes for stroke patients. Phosphoinositide 3-kinase delta (PI3Kδ) controls intracellular TNF trafficking in macrophages and therefore represents a prospective target to limit neuroinflammation. Here we show that PI3Kδ inhibition confers protection in ischaemia/reperfusion models of stroke. In vitro, restoration of glucose supply following an episode of glucose deprivation potentiates TNF secretion from primary microglia-an effect that is sensitive to PI3Kδ inhibition. In vivo, transient middle cerebral artery occlusion and reperfusion in kinase-dead PI3Kδ (p110δ(D910A/D910A)) or wild-type mice pre- or post-treated with the PI3Kδ inhibitor CAL-101, leads to reduced TNF levels, decreased leukocyte infiltration, reduced infarct size and improved functional outcome. These data identify PI3Kδ as a potential therapeutic target in ischaemic stroke.