Nellie Anne Martin

A novel microglial subset plays a key role in myelinogenesis in developing brain

Microglia are resident macrophages of the central nervous system that contribute to homeostasis and neuroinflammation. Although known to play an important role in brain development, their exact function has not been fully described. Here, we show that in contrast to healthy adult and inflammation‐activated cells, neonatal microglia show a unique myelinogenic and neurogenic phenotype. A CD11c+ microglial subset that predominates in primary myelinating areas of the developing brain expresses genes for neuronal and glial survival, migration, and differentiation. These cells are the major source of insulin‐like growth factor 1, and its selective depletion from CD11c+ microglia leads to impairment of primary myelination. CD11c‐targeted toxin regimens induced a selective transcriptional response in neonates, distinct from adult microglia. CD11c+ microglia are also found in clusters of repopulating microglia after experimental ablation and in neuroinflammation in adult mice, but despite some similarities, they do not recapitulate neonatal microglial characteristics. We therefore identify a unique phenotype of neonatal microglia that deliver signals necessary for myelination and neurogenesis.

Fumarate decreases edema volume and improves functional outcome after experimental stroke

Background Oxidative stress and inflammation exacerbate tissue damage in the brain after ischemic stroke. Dimethyl‐fumarate (DMF) and its metabolite monomethyl‐fumarate (MMF) are known to stimulate anti‐oxidant pathways and modulate inflammatory responses. Considering these dual effects of fumarates, we examined the effect of MMF treatment after ischemic stroke in mice. Methods Permanent middle cerebral artery occlusion (pMCAO) was performed using adult, male C57BL/6 mice. Thirty minutes after pMCAO, 20 mg/kg MMF was administered intravenously. Outcomes were evaluated 6, 24 and 48 h after pMCAO. First, we examined whether a bolus of MMF was capable of changing expression of kelch‐like erythroid cell‐derived protein with CNC homology‐associated protein 1 (Keap1) and nuclear factor erythroid 2‐related factor (Nrf)2 in the infarcted brain. Next, we studied the effect of MMF on functional recovery. To explore mechanisms potentially influencing functional changes, we examined infarct volumes, edema formation, the expression of heat shock protein (Hsp)72, hydroxycarboxylic acid receptor 2 (Hcar2), and inducible nitric oxide synthase (iNOS) in the infarcted brain using real‐time PCR and Western blotting. Concentrations of a panel of pro‐ and anti‐inflammatory cytokines (IFN&ggr;, IL‐1&bgr;, IL‐2, IL‐4, IL‐5, IL‐6, IL‐10, IL‐12p70, TNF) were examined in both the infarcted brain tissue and plasma samples 6, 24 and 48 h after pMCAO using multiplex electrochemoluminiscence analysis. Results Administration of MMF increased the protein level of Nrf2 6 h after pMCAO, and improved functional outcome at 24 and 48 h after pMCAO. MMF treatment did not influence infarct size, however reduced edema volume at both 24 and 48 h after pMCAO. MMF treatment resulted in increased Hsp72 expression in the brain 6 h after pMCAO. Hcar2 mRNA levels increased significantly 24 h after pMCAO, but were not different between saline‐ and MMF‐treated mice. MMF treatment also increased the level of the anti‐inflammatory cytokine IL‐10 in the brain and plasma 6 h after pMCAO, and additionally reduced the level of the pro‐inflammatory cytokine IL‐12p70 in the brain at 24 and 48 h after pMCAO. Conclusions A single intravenous bolus of MMF improved sensory‐motor function after ischemic stroke, reduced edema formation, and increased the levels of the neuroprotective protein Hsp72 in the brain. The early increase in IL‐10 and reduction in IL‐12p70 in the brain combined with changes in systemic cytokine levels may also contribute to the functional recovery after pMCAO. HighlightsMonomethyl‐fumarate treatment decreased edema volume after stroke.Monomethyl‐fumarate treatment improved sensory‐motor function after stroke.Monomethyl‐fumarate treatment increased Hsp72 levels after stroke.Monomethyl‐fumarate treatment increased neuroprotective IL‐10 levels after stroke.Monomethyl‐fumarate treatment decreased IL‐12p70 levels after stroke.

BID Mediates Oxygen-Glucose Deprivation-Induced Neuronal Injury in Organotypic Hippocampal Slice Cultures and Modulates Tissue Inflammation in a Transient Focal Cerebral Ischemia Model without Changing Lesion Volume

The BH3 interacting-domain death agonist (BID) is a pro-apoptotic protein involved in death receptor-induced and mitochondria-mediated apoptosis. Recently, it has also been suggested that BID is involved in the regulation of inflammatory responses in the central nervous system. We found that BID deficiency protected organotypic hippocampal slice cultures in vitro from neuronal injury induced by oxygen-glucose deprivation. In vivo, BID-knockout (KO) mice and wild type (WT) mice were subjected to 60 min of transient middle cerebral artery occlusion (tMCAO) to induce focal cerebral ischemia, and allowed to recover for 24 h. Infarct volumes and functional outcome were assessed and the inflammatory response was evaluated using immunofluorescence, Western blotting, quantitative PCR (qPCR) and Mesoscale multiplex analysis. We observed no difference in the infarct volume or neurological outcome between BID-KO and WT mice. The inflammatory response was reduced by BID deficiency as indicated by a change in microglial/leukocyte response. In conclusion, our data suggest that BID deficiency is neuroprotective in an in vitro model and modulates the inflammatory response to focal cerebral ischemia in vivo. However, this is not translated into a robust neuroprotection in vivo.

Differentially expressed microRNA in multiple sclerosis: A window into pathogenesis?

MicroRNA are small non‐coding RNA that mediate mRNA translation repression or mRNA degradation, and thereby refine protein expression levels. More than 30–60% of all genes are regulated by microRNA. Exploring disease‐related microRNA signatures is an emerging tool in biomarker discovery, and silencing has already been used in a clinical phase 2a trial. As microRNA regulate translation of more than 100 genes, they could also provide a focused insight into important pathways, and offer a better understanding of diseases with heterogeneous pathogenesis. The number of studies investigating microRNA related to multiple sclerosis has increased significantly in recent years. Differentially expressed microRNA have been identified in the whole blood, serum, plasma, cerebrospinal fluid, peripheral blood mononuclear cells, blood‐derived cell subsets and brain lesions of patients with multiple sclerosis. Most studies applied a non‐candidate approach of screening by microarray and validation by quantitative polymerase chain reaction or next generation sequencing; others used a candidate‐driven approach. Despite a relatively high number of multiple sclerosis‐associated microRNA, just a few could be repeatedly found, even if similar biological materials were examined. Only part of the identified microRNA has been extensively studied, and the biological function has not been explored in the majority. Some of the microRNA related to multiple sclerosis are also differentially expressed in other autoimmune diseases or autoimmune models. In the present review, we discuss microRNA related to disease compartments, activity and phenotype. We also focus on several microRNA with well‐defined functions, or because of particular interest due to either validation by several independent studies or in‐depth exploration of function.

Macrophage migration inhibitory factor (MIF) modulates trophic signaling through interaction with serine protease HTRA1

Macrophage migration inhibitory factor (MIF), a small conserved protein, is abundant in the immune- and central nervous system (CNS). MIF has several receptors and binding partners that can modulate its action on a cellular level. It is upregulated in neurodegenerative diseases and cancer although its function is far from clear. Here, we report the finding of a new binding partner to MIF, the serine protease HTRA1. This enzyme cleaves several growth factors, extracellular matrix molecules and is implicated in some of the same diseases as MIF. We show that the function of the binding between MIF and HTRA1 is to inhibit the proteolytic activity of HTRA1, modulating the availability of molecules that can change cell growth and differentiation. MIF is therefore the first endogenous inhibitor ever found for HTRA1. It was found that both molecules were present in astrocytes and that the functional binding has the ability to modulate astrocytic activities important in development and disease of the CNS.

Orthologous proteins of experimental de- and remyelination are differentially regulated in the CSF proteome of multiple sclerosis subtypes

Objective Here, we applied a multi-omics approach (i) to examine molecular pathways related to de- and remyelination in multiple sclerosis (MS) lesions; and (ii) to translate these findings to the CSF proteome in order to identify molecules that are differentially expressed among MS subtypes. Methods To relate differentially expressed genes in MS lesions to de- and remyelination, we compared transcriptome of MS lesions to transcriptome of cuprizone (CPZ)-induced de- and remyelination. Protein products of the overlapping orthologous genes were measured within the CSF by quantitative proteomics, parallel reaction monitoring (PRM). Differentially regulated proteins were correlated with molecular markers of inflammation by using MesoScale multiplex immunoassay. Expression kinetics of differentially regulated orthologous genes and proteins were examined in the CPZ model. Results In the demyelinated and remyelinated corpus callosum, we detected 1239 differentially expressed genes; 91 orthologues were also differentially expressed in MS lesions. Pathway analysis of these orthologues suggested that the TYROBP (DAP12)-TREM2 pathway, TNF-receptor 1, CYBA and the proteasome subunit PSMB9 were related to de- and remyelination. We designed 129 peptides representing 51 orthologous proteins, measured them by PRM in 97 individual CSF, and compared their levels between relapsing (n = 40) and progressive MS (n = 57). Four proteins were differentially regulated among relapsing and progressive MS: tyrosine protein kinase receptor UFO (UFO), TIMP-1, apolipoprotein C-II (APOC2), and beta-2-microglobulin (B2M). The orthologous genes/proteins in the mouse brain peaked during acute remyelination. UFO, TIMP-1 and B2M levels correlated inversely with inflammation in the CSF (IL-6, MCP-1/CCL2, TARC/CCL17). APOC2 showed positive correlation with IL-2, IL-16 and eotaxin-3/CCL26. Conclusions Pathology-based multi-omics identified four CSF markers that were differentially expressed in MS subtypes. Upregulated TIMP-1, UFO and B2M orthologues in relapsing MS were associated with reduced inflammation and reflected reparatory processes, in contrast to the upregulated orthologue APOC2 in progressive MS that reflected changes in lipid metabolism associated with increased inflammation.

Experimental demyelination and axonal loss are reduced in MicroRNA-146a deficient mice

Background The cuprizone (CPZ) model of multiple sclerosis (MS) was used to identify microRNAs (miRNAs) related to in vivo de- and remyelination. We further investigated the role of miR-146a in miR-146a-deficient (KO) mice: this miRNA is differentially expressed in MS lesions and promotes differentiation of oligodendrocyte precursor cells (OPCs) during remyelination, but its role has not been examined during demyelination. Methods MicroRNAs were examined by Agilent Mouse miRNA Microarray in the corpus callosum during CPZ-induced demyelination and remyelination. Demyelination, axonal loss, changes in number of oligodendrocytes, OPCs, and macrophages/microglia was compared by histology/immunohistochemistry between KO and WT mice. Differential expression of target genes and proteins of miR-146a was analyzed in the transcriptome (4 × 44K Agilent Whole Mouse Genome Microarray) and proteome (liquid chromatography tandem mass spectrometry) of CPZ-induced de- and remyelination in WT mice. Levels of proinflammatory molecules in the corpus callosum were compared in WT versus KO mice by Meso Scale Discovery multiplex protein analysis. Results miR-146a was increasingly upregulated during CPZ-induced de- and remyelination. The absence of miR-146a in KO mice protected against demyelination, axonal loss, body weight loss, and atrophy of thymus and spleen. The number of CNP+ oligodendrocytes was increased during demyelination in the miR-146a KO mice, while there was a trend of increased number of NG2+ OPCs in the WT mice. miR-146a target genes, SNAP25 and SMAD4, were downregulated in the proteome of demyelinating corpus callosum in WT mice. Higher levels of SNAP25 were measured by ELISA in the corpus callosum of miR-146a KO mice, but there was no difference between KO and WT mice during demyelination. Multiplex protein analysis of the corpus callosum lysate revealed upregulated TNF-RI, TNF-RII, and CCL2 in the WT mice in contrast to KO mice. The number of Mac3+ and Iba1+ macrophages/microglia was reduced in the demyelinating corpus callosum of the KO mice. Conclusion During demyelination, absence of miR-146a reduced inflammatory responses, demyelination, axonal loss, the number of infiltrating macrophages, and increased the number of myelinating oligodendrocytes. The number of OPCs was slightly higher in the WT mice during remyelination, indicating a complex role of miR-146a during in vivo de- and remyelination.