Induction of Golli-MBP expression in CNS macrophages during acute LPS-induced CNS inflammation and experimental autoimmune encephalomyelitis (EAE)

Classic and Golli Myelin Basic Protein have distinct developmental trajectories in human visual cortex

Traditionally, myelin is viewed as insulation around axons, however, more recent studies have shown it also plays an important role in plasticity, axonal metabolism, and neuroimmune signaling. Myelin is a complex multi-protein structure composed of hundreds of proteins, with Myelin Basic Protein (MBP) being the most studied. MBP has two families: Classic-MBP that is necessary for activity driven compaction of myelin around axons, and Golli-MBP that is found in neurons, oligodendrocytes, and T-cells. Furthermore, Golli-MBP has been called a “molecular link” between the nervous and immune systems. In visual cortex specifically, myelin proteins interact with immune processes to affect experience-dependent plasticity. We studied myelin in human visual cortex using Western blotting to quantify Classic- and Golli-MBP expression in post-mortem tissue samples ranging in age from 20 days to 80 years. We found that Classic- and Golli-MBP have different patterns of change across the lifespan. Classic-MBP gradually increases to 42 years and then declines into aging. Golli-MBP has early developmental changes that are coincident with milestones in visual system sensitive period, and gradually increases into aging. There are three stages in the balance between Classic- and Golli-MBP expression, with Golli-MBP dominating early, then shifting to Classic-MBP, and back to Golli-MBP in aging. Also Golli-MBP has a wave of high inter-individual variability during childhood. These results about cortical MBP expression are timely because they compliment recent advances in MRI techniques that produce high resolution maps of cortical myelin in normal and diseased brain. In addition, the unique pattern of Golli-MBP expression across the lifespan suggests that it supports high levels of neuroimmune interaction in cortical development and in aging.

Myelin-derived lipids modulate macrophage activity by liver X receptor activation

Multiple sclerosis is a chronic, inflammatory, demyelinating disease of the central nervous system in which macrophages and microglia play a central role. Foamy macrophages and microglia, containing degenerated myelin, are abundantly found in active multiple sclerosis lesions. Recent studies have described an altered macrophage phenotype after myelin internalization. However, it is unclear by which mechanisms myelin affects the phenotype of macrophages and how this phenotype can influence lesion progression. Here we demonstrate, by using genome wide gene expression analysis, that myelin-phagocytosing macrophages have an enhanced expression of genes involved in migration, phagocytosis and inflammation. Interestingly, myelin internalization also induced the expression of genes involved in liver-X-receptor signaling and cholesterol efflux. In vitro validation shows that myelin-phagocytosing macrophages indeed have an increased capacity to dispose intracellular cholesterol. In addition, myelin suppresses the secretion of the pro-inflammatory mediator IL-6 by macrophages, which was mediated by activation of liver-X-receptor β. Our data show that myelin modulates the phenotype of macrophages by nuclear receptor activation, which may subsequently affect lesion progression in demyelinating diseases such as multiple sclerosis.

Inflammatory responses in aggregating rat brain cell cultures subjected to different demyelinating conditions

To study inflammatory reactions occurring in relation to demyelination, aggregating rat brain cell cultures were subjected to three different demyelinating insults, i.e., (i) lysophosphatidylcholine (LPC), (ii) interferon-gamma combined with lipopolysaccharide (IFN-gamma+LPS), and (iii) anti-MOG antibodies plus complement (alpha-MOG+C). Demyelination was assessed by measuring the expression of myelin basic protein (MBP) and myelin oligodendrocyte glycoprotein (MOG), and the activity of 2',3'-cyclic nucleotide 3'-phosphohydrolase (CNP). The accompanying inflammatory reactions were examined by the quantification of microglia-specific staining, by immunostaining for glial fibrillary acidic protein (GFAP), and by measuring the mRNA expression of a panel of inflammation-related genes. It was found that all three demyelinating insults decreased the expression of MBP and MOG, and induced microglial reactivity. LPC and alpha-MOG+C, but not IFN-gamma+LPS, decreased CNP activity; they also caused the appearance of macrophagic microglia, and increased GFAP staining indicating astrogliosis. LPC affected also the integrity of neurons and astrocytes. LPC and IFN-gamma+LPS upregulated the expression of the inflammation-related genes IL-6, TNF-alpha, Ccl5, Cxcl1, and iNOS, although to different degrees. Other inflammatory markers were upregulated by only one of the three insults, e.g., Cxcl2 by LPC; IL-1beta and IL-15 by IFN-gamma+LPS; and IFN-gamma by alpha-MOG+C. These findings indicate that each of the three demyelinating insults caused distinct patterns of demyelination and inflammatory reactivity, and that of the demyelinating agents tested only LPC exhibited general toxicity.

Immunoproteasome LMP2 60HH variant alters MBP epitope generation and reduces the risk to develop multiple sclerosis in Italian female population

Background

Albeit several studies pointed out the pivotal role that CD4+T cells have in Multiple Sclerosis, the CD8+ T cells involvement in the pathology is still in its early phases of investigation. Proteasome degradation is the key step in the production of MHC class I-restricted epitopes and therefore its activity could be an important element in the activation and regulation of autoreactive CD8+ T cells in Multiple Sclerosis.

Methodology/Principal Findings

Immunoproteasomes and PA28-αβ regulator are present in MS affected brain area and accumulated in plaques. They are expressed in cell types supposed to be involved in MS development such as neurons, endothelial cells, oligodendrocytes, macrophages/macroglia and lymphocytes. Furthermore, in a genetic study on 1262 Italian MS cases and 845 controls we observed that HLA-A*02+ female subjects carrying the immunoproteasome LMP2 codon 60HH variant have a reduced risk to develop MS. Accordingly, immunoproteasomes carrying the LMP2 60H allele produce in vitro a lower amount of the HLA-A*0201 restricted immunodominant epitope MBP_111–119.

Conclusion/Significance

The immunoproteasome LMP2 60HH variant reduces the risk to develop MS amongst Italian HLA-A*02+ females. We propose that such an effect is mediated by the altered proteasome-dependent production of a specific MBP epitope presented on the MHC class I. Our observations thereby support the hypothesis of an involvement of immunoproteasome in the MS pathogenesis.

Myelin basic protein binds to and inhibits the fibrillar assembly of Abeta42 in vitro

The deposition of amyloid beta-protein (Abeta) fibrils into plaques within the brain parenchyma and along cerebral blood vessels is a hallmark of Alzheimer's disease. Abeta peptides are produced through the successive cleavage of the Abeta precursor protein by beta- and gamma-secretase, producing peptides between 39 and 43 amino acids in length. The most common of these are Abeta40 (the most abundant) and Abeta42. Abeta42 is more fibrillogenic than Abeta40 and has been implicated in early Abeta plaque deposition. Our previous studies determined that myelin basic protein (MBP) was capable of inhibiting fibril formation of a highly fibrillogenic Abeta peptide containing both E22Q (Dutch) and D23N (Iowa) mutations associated with familial forms of cerebral amyloid angiopathy [Hoos, M. D., et al. (2007) J. Biol. Chem. 282, 9952-9961]. In this study, we show through a combination of biochemical and ultrastructural techniques that MBP is also capable of inhibiting the beta-sheet fibrillar assembly of the normal Abeta42 peptide. These findings suggest that MBP may play a role in regulating the deposition of Abeta42 and thereby also may regulate the early formation of amyloid plaques in Alzheimer's disease.

Differential gene expression in LPS/IFNgamma activated microglia and macrophages: in vitro versus in vivo

Two different macrophage populations contribute to CNS neuroinflammation: CNS-resident microglia and CNS-infiltrating peripheral macrophages. Markers distinguishing these two populations in tissue sections have not been identified. Therefore, we compared gene expression between LPS (lipopolysaccharide)/interferon (IFN)γ-treated microglia from neonatal mixed glial cultures and similarly treated peritoneal macrophages. Fifteen molecules were identified by quantative PCR (qPCR) as being enriched from 2-fold to 250-fold in cultured neonatal microglia when compared with peritoneal macrophages. Only three of these molecules (C1qA, Trem2, and CXCL14) were found by qPCR to be also enriched in adult microglia isolated from LPS/IFNγ-injected CNS when compared with infiltrating peripheral macrophages from the same CNS. The discrepancy between the in vitro and in vivo qPCR data sets was primarily because of induced expression of the ‘microglial’ molecules (such as the tolerance associated transcript, Tmem176b) in CNS-infiltrating macrophages. Bioinformatic analysis of the ∼19000 mRNAs detected by TOGA gene profiling confirmed that LPS/IFNγ-activated microglia isolated from adult CNS displayed greater similarity in total gene expression to CNS-infiltrating macrophages than to microglia isolated from unmanipulated healthy adult CNS. In situ hybridization analysis revealed that nearly all microglia expressed high levels of C1qA, while subsets of microglia expressed Trem2 and CXCL14. Expression of C1qA and Trem2 was limited to microglia, while large numbers of GABA+ neurons expressed CXCL14. These data suggest that (i) CNS-resident microglia are heterogeneous and thus a universal microglia-specific marker may not exist; (ii) the CNS micro-environment plays significant roles in determining the phenotypes of both CNS-resident microglia and CNS-infiltrating macrophages; (iii) the CNS microenvironment may contribute to immune privilege by inducing macrophage expression of anti-inflammatory molecules.