Evi Lemmens

The role of mast cells in neuroinflammation

Mast cells (MCs) are densely granulated perivascular resident cells of hematopoietic origin and well known for their pathogenetic role in allergic and anaphylactic reactions. In addition, they are also involved in processes of innate and adaptive immunity. MCs can be activated in response to a wide range of stimuli, resulting in the release of not only pro-inflammatory, but also anti-inflammatory mediators. The patterns of secreted mediators depend upon the given stimuli and microenvironmental conditions, accordingly MCs have the ability to promote or attenuate inflammatory processes. Their presence in the central nervous system (CNS) has been recognized for more than a century. Since then a participation of MCs in various pathological processes in the CNS has been well documented. They can aggravate CNS damage in models of brain ischemia and hemorrhage, namely through increased blood–brain barrier damage, brain edema and hemorrhage formation and promotion of inflammatory responses to such events. In contrast, recent evidence suggests that MCs may have a protective role following traumatic brain injury by degrading pro-inflammatory cytokines via specific proteases. In neuroinflammatory diseases such as multiple sclerosis, the role of MCs seems to be ambiguous. MCs have been shown to be damaging, neuroprotective, or even dispensable, depending on the experimental protocols used. The role of MCs in the formation and progression of CNS tumors such as gliomas is complex and both positive and negative relationships between MC activity and tumor progression have been reported. In summary, MCs and their secreted mediators modulate inflammatory processes in multiple CNS pathologies and can thereby either contribute to neurological damage or confer neuroprotection. This review intends to give a concise overview of the regulatory roles of MCs in brain disease.

Mast cells protect from post-traumatic brain inflammation by the mast cell-specific chymase mouse mast cell protease-4

Mast cells (MCs) are found abundantly in the brain and the meninges and play a complex role in neuroinflammatory diseases, such as stroke and multiple sclerosis. Here, we show that MC‐deficient KitW/KitWv mice display increased neurodegeneration in the lesion area after brain trauma. Furthermore, MC‐deficient mice display significantly more brain inflammation, namely an increased presence of macrophages/microglia, as well as dramatically increased T‐cell infiltration at days 4 and 14 after injury, combined with increased astrogliosis at day 14 following injury. The number of proliferating Ki67+ macrophages/microglia and astrocytes around the lesion area is more than doubled in these MC‐deficient mice. In parallel, MC‐deficient KitW‐sh/W‐sh mice display increased presence of macrophages/microglia at day 4, and persistent astrogliosis at day 4 and 14 after brain trauma. Further analysis of mice deficient in one of the most relevant MC proteases, i.e., mouse mast cell protease 4 (mMCP‐4), revealed that astrogliosis and T‐cell infiltration are significantly increased in mMCP‐4‐knockout mice. Finally, treatment with an inhibitor of mMCP‐4 significantly increased macrophage/microglia numbers and astrogliosis. These data suggest that MCs exert protective functions after trauma, at least in part via mMCP‐4, by suppressing exacerbated inflammation via their proteases.—Hendrix, S., Kramer, P., Pehl, D., Warnke, K., Boato, F., Nelissen, S., Lemmens, E., Pejler, G., Metz, M., Siebenhaar, F., Maurer, M. Mast cells protect from post‐traumatic brain inflammation by the mast cell‐specific chymase mouse mast cell protease‐4. FASEB J. 27, 920–929 (2013). www.fasebj.org

Mast cells protect from post-traumatic spinal cord damage in mice by degrading inflammation-associated cytokines via mouse mast cell protease 4.

Mast cells (MCs) are found abundantly in the central nervous system and play a complex role in neuroinflammatory diseases such as multiple sclerosis and stroke. In the present study, we show that MC-deficient Kit(W-sh/W-sh) mice display significantly increased astrogliosis and T cell infiltration as well as significantly reduced functional recovery after spinal cord injury compared to wildtype mice. In addition, MC-deficient mice show significantly increased levels of MCP-1, TNF-α, IL-10 and IL-13 protein levels in the spinal cord. Mice deficient in mouse mast cell protease 4 (mMCP4), an MC-specific chymase, also showed increased MCP-1, IL-6 and IL-13 protein levels in spinal cord samples and a decreased functional outcome after spinal cord injury. A degradation assay using supernatant from MCs derived from either mMCP4(-/-) mice or controls revealed that mMCP4 cleaves MCP-1, IL-6, and IL-13 suggesting a protective role for MC proteases in neuroinflammation. These data show for the first time that MCs may be protective after spinal cord injury and that they may reduce CNS damage by degrading inflammation-associated cytokines via the MC-specific chymase mMCP4.

Late blocking of peripheral TNF-α is ineffective after spinal cord injury in mice

Spinal cord injury (SCI) is characterized by different phases of inflammatory responses. Increasing evidence indicates that the early chronic phase (two to three weeks after SCI) is characterized by a dramatic invasion of immune cells and a peak of pro-inflammatory cytokine levels, such as tumor necrosis factor-α (TNF-α) derived from the injured spinal cord as well as from injured skin, muscles and bones. However, there is substantial controversy whether these inflammatory processes in later phases lead to pro-regenerative or detrimental effects. In the present study, we investigated whether the inhibition of peripheral TNF-α in the early chronic phase after injury promotes functional recovery in a dorsal hemisection model of SCI. Three different approaches were used to continuously block peripheral TNF-α in vivo, starting 14 days after injury. We administered the TNF-α blocker etanercept intraperitoneally (every second day or daily) as well as continuously via osmotic minipumps. None of these administration routes for the TNF-α inhibitor influenced locomotor restoration as assessed by the Basso mouse scale (BMS), nor did they affect coordination and strength as evaluated by the Rotarod test. These data suggest that peripheral TNF-α inhibition may not be an effective therapeutic strategy in the early chronic phase after SCI.

Oncostatin M Reduces Lesion Size and Promotes Functional Recovery and Neurite Outgrowth After Spinal Cord Injury

The family of interleukin (IL)-6 like cytokines plays an important role in the neuroinflammatory response to injury by regulating both neural as well as immune responses. Here, we show that expression of the IL-6 family member oncostatin M (OSM) and its receptor is upregulated after spinal cord injury (SCI). To reveal the relevance of increased OSM signaling in the pathophysiology of SCI, OSM was applied locally after spinal cord hemisection in mice. OSM treatment significantly improved locomotor recovery after mild and severe SCI. Improved recovery in OSM-treated mice was associated with a reduced lesion size. OSM significantly diminished astrogliosis and immune cell infiltration. Thus, OSM limits secondary damage after CNS trauma. In vitro viability assays demonstrated that OSM protects primary neurons in culture from cell death, suggesting that the underlying mechanism involves direct neuroprotective effects of OSM. Furthermore, OSM dose-dependently promoted neurite outgrowth in cultured neurons, indicating that the cytokine plays an additional role in CNS repair. Indeed, our in vivo experiments demonstrate that OSM treatment increases plasticity of serotonergic fibers after SCI. Together, our data show that OSM is produced at the lesion site, where it protects the CNS from further damage and promotes recovery.

In vitro and in vivo neuronal electrotaxis: a potential mechanism for restoration?

Electrical brain stimulation used to treat a variety of neurological and psychiatric diseases is entering a new period. The technique is well established and the potential complications are well known and generally manageable. Recent studies demonstrated that electrical fields (EFs) can enhance neuroplasticity-related processes. EFs applied in the physiological range induce migration of different neural cell types from different species in vitro. There are some evidences that also the speed and directedness of cell migration are enhanced by EFs. However, it is still unclear how electrical signals from the extracellular space are translated into intracellular actions resulting in the so-called electrotaxis phenomenon. Here, we aim to provide a comprehensive review of the data on responses of cells to electrical stimulation and the relation to functional recovery.

Cell-Based Delivery of Interleukin-13 Directs Alternative Activation of Macrophages Resulting in Improved Functional Outcome after Spinal Cord Injury

Summary The therapeutic effects of mesenchymal stem cell (MSC) transplantation following spinal cord injury (SCI) to date have been limited. Therefore, we aimed to enhance the immunomodulatory properties of MSCs via continuous secretion of the anti-inflammatory cytokine interleukin-13 (IL-13). By using MSCs as carriers of IL-13 (MSC/IL-13), we investigated their therapeutic potential, compared with non-engineered MSCs, in a mouse model of SCI. We show that transplanted MSC/IL-13 significantly improve functional recovery following SCI, and also decrease lesion size and demyelinated area by more than 40%. Further histological analyses in CX3CR1EGFP/+ CCR2RFP/+ transgenic mice indicated that MSC/IL-13 significantly decrease the number of resident microglia and increase the number of alternatively activated macrophages. In addition, the number of macrophage-axon contacts in MSC/IL-13-treated mice was decreased by 50%, suggesting a reduction in axonal dieback. Our data provide evidence that transplantation of MSC/IL-13 leads to improved functional and histopathological recovery in a mouse model of SCI.

In Vivo Interleukin-13-Primed Macrophages Contribute to Reduced Alloantigen-Specific T Cell Activation and Prolong Immunological Survival of Allogeneic Mesenchymal Stem Cell Implants

Transplantation of mesenchymal stem cells (MSCs) into injured or diseased tissue—for the in situ delivery of a wide variety of MSC‐secreted therapeutic proteins—is an emerging approach for the modulation of the clinical course of several diseases and traumata. From an emergency point‐of‐view, allogeneic MSCs have numerous advantages over patient‐specific autologous MSCs since “off‐the‐shelf” cell preparations could be readily available for instant therapeutic intervention following acute injury. Although we confirmed the in vitro immunomodulatory capacity of allogeneic MSCs on antigen‐presenting cells with standard coculture experiments, allogeneic MSC grafts were irrevocably rejected by the hosts immune system upon either intramuscular or intracerebral transplantation. In an attempt to modulate MSC allograft rejection in vivo, we transduced MSCs with an interleukin‐13 (IL13)‐expressing lentiviral vector. Our data clearly indicate that prolonged survival of IL13‐expressing allogeneic MSC grafts in muscle tissue coincided with the induction of an alternatively activated macrophage phenotype in vivo and a reduced number of alloantigen‐reactive IFNγ‐ and/or IL2‐producing CD8+ T cells compared to nonmodified allografts. Similarly, intracerebral IL13‐expressing MSC allografts also exhibited prolonged survival and induction of an alternatively activated macrophage phenotype, although a peripheral T cell component was absent. In summary, this study demonstrates that both innate and adaptive immune responses are effectively modulated in vivo by locally secreted IL13, ultimately resulting in prolonged MSC allograft survival in both muscle and brain tissue. Stem Cells 2016;34:1971–1984

Intracerebral transplantation of interleukin 13-producing mesenchymal stem cells limits microgliosis, oligodendrocyte loss and demyelination in the cuprizone mouse model

BackgroundPromoting the neuroprotective and repair-inducing effector functions of microglia and macrophages, by means of M2 polarisation or alternative activation, is expected to become a new therapeutic approach for central nervous system (CNS) disorders in which detrimental pro-inflammatory microglia and/or macrophages display a major contribution to the neuropathology. In this study, we present a novel in vivo approach using intracerebral grafting of mesenchymal stem cells (MSC) genetically engineered to secrete interleukin 13 (IL13-MSC).MethodsIn the first experimental setup, control MSC and IL13-MSC were grafted in the CNS of eGFP+ bone marrow chimaeric C57BL/6 mice to histologically evaluate IL13-mediated expression of several markers associated with alternative activation, including arginase1 and Ym1, on MSC graft-recognising microglia and MSC graft-infiltrating macrophages. In the second experimental setup, IL13-MSC were grafted on the right side (or on both the right and left sides) of the splenium of the corpus callosum in wild-type C57BL/6 mice and in C57BL/6 CX3CR1eGFP/+CCR2RFP/+ transgenic mice. Next, CNS inflammation and demyelination was induced by means of a cuprizone-supplemented diet. The influence of IL13-MSC grafting on neuropathological alterations was monitored by non-invasive T2-weighted magnetic resonance imaging (MRI) and quantitative histological analyses, as compared to cuprizone-treated mice with control MSC grafts and/or cuprizone-treated mice without MSC injection.ResultsIn the first part of this study, we demonstrate that MSC graft-associated microglia and MSC graft-infiltrating macrophages are forced into alternative activation upon grafting of IL13-MSC, but not upon grafting of control MSC. In the second part of this study, we demonstrate that grafting of IL13-MSC, in addition to the recruitment of M2 polarised macrophages, limits cuprizone-induced microgliosis, oligodendrocyte death and demyelination. Furthermore, we here demonstrate that injection of IL13-MSC at both sides of the splenium leads to a superior protective effect as compared to a single injection at one side of the splenium.ConclusionsControlled and localised production of IL13 by means of intracerebral MSC grafting has the potential to modulate cell graft- and pathology-associated microglial/macrophage responses, and to interfere with oligodendrocyte death and demyelinating events in the cuprizone mouse model.

Interleukin-25 is detrimental for recovery after spinal cord injury in mice

BackgroundThe cytokine, interleukin (IL)-25, is thought to be critically involved in inducing a type 2 immune response which may contribute to regeneration after central nervous system (CNS) trauma. We investigated whether applying recombinant IL-25, locally or systemically, in a mouse model of spinal cord injury (SCI) improves functional and histological recovery.FindingsRepeated systemic administration of IL-25 did not influence functional recovery following SCI. In contrast, a single local administration of IL-25 significantly worsened locomotor outcome, which was evident from a decreased Basso mouse scale (BMS) score compared with phosphate-buffered saline (PBS)-treated controls. This was accompanied by a significant increase in lesion size, demyelination, and T helper cell infiltration.ConclusionsThese data show for the first time that IL-25 is either ineffective when applied systemically or detrimental to spinal cord recovery when applied locally. Our findings question the potential neuroprotective role of IL-25 following CNS trauma.