Autoimmune-induced preferential depletion of myelin-associated glycoprotein (MAG) is genetically regulated in relapsing EAE (B6 x SJL) F1 mice

A Comprehensive Analysis of the Role of hnRNP A1 Function and Dysfunction in the Pathogenesis of Neurodegenerative Disease

Heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1) is a member of the hnRNP family of conserved proteins that is involved in RNA transcription, pre-mRNA splicing, mRNA transport, protein translation, microRNA processing, telomere maintenance and the regulation of transcription factor activity. HnRNP A1 is ubiquitously, yet differentially, expressed in many cell types, and due to post-translational modifications, can vary in its molecular function. While a plethora of knowledge is known about the function and dysfunction of hnRNP A1 in diseases other than neurodegenerative disease (e.g., cancer), numerous studies in amyotrophic lateral sclerosis, frontotemporal lobar degeneration, multiple sclerosis, spinal muscular atrophy, Alzheimer’s disease, and Huntington’s disease have found that the dysregulation of hnRNP A1 may contribute to disease pathogenesis. How hnRNP A1 mechanistically contributes to these diseases, and whether mutations and/or altered post-translational modifications contribute to pathogenesis, however, is currently under investigation. The aim of this comprehensive review is to first describe the background of hnRNP A1, including its structure, biological functions in RNA metabolism and the post-translational modifications known to modify its function. With this knowledge, the review then describes the influence of hnRNP A1 in neurodegenerative disease, and how its dysfunction may contribute the pathogenesis.

Comprehensive Analysis of the Immune and Stromal Compartments of the CNS in EAE Mice Reveal Pathways by Which Chloroquine Suppresses Neuroinflammation

Multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE) are neuroinflammatory diseases of the central nervous system (CNS), where leukocytes and CNS resident cells play important roles in disease development and pathogenesis. The antimalarial drug chloroquine (CQ) has been shown to suppress EAE by modulating dendritic cells (DCs) and Th17 cells. However, the mechanism of action by which CQ modulates EAE is far from being elucidated. Here, we comprehensively analyzed the CNS of CQ and PBS-treated EAE mice to identify and characterize the cells that are affected by CQ. Our results show that leukocytes are largely modulated by CQ and have a reduction in the expression of inflammatory markers. Intriguingly, CQ vastly modulated the CNS resident cells astrocytes, oligodendrocytes (OLs) and microglia (MG), with the latter producing IL-10 and IL-12p70. Overall, our results show a panoramic view of the cellular components that are affect by CQ and provide further evidence that drug repurposing of CQ will be beneficial to MS patients.

Demyelination with preferential MAG loss: A complex message from MS paraffin blocks

Multiple sclerosis (MS) is generally considered to be a demyelinating autoimmune disorder. However, neuropathological examinations of MS lesions do not support this concept. Demyelination with preferential loss of myelin-associated glycoprotein (MAG) is a common finding in MS tissues and has been reported by several groups. As MAG is located in ad-axonal myelin layers and is not accessible to infiltrating immune cells, demyelination with preferred loss of MAG may be suggestive of a primary oligodendrocytopathy in MS. Moreover, it has been shown that oligodendrocytopathy may precede the infiltration of inflammatory cells at the lesion site. In this paper, we review studies of neuropathology of MS tissues that reported this type of demyelination and then we discuss three emerging explanations that are trying to interpret this mismatched observation.

Role of IL-16 in CD4+ T cell-mediated regulation of relapsing multiple sclerosis

In an important article published in Nature Medicine, Liu and colleagues described a novel CD4⁺ FoxA1⁺ regulatory T (Treg) cell population as distinct regulators of relapsing-remitting multiple sclerosis (RRMS) and experimental autoimmune encephalomyelitis (EAE). CD4⁺ FoxA1⁺ Treg cells appear as key regulators of responsiveness to therapy with interferon beta (IFN-β) in RRMS patients. Data indicate that CD4⁺FoxA1⁺ FOXP3⁻ Treg cells develop within the central nervous system (CNS), and a potential of cerebellar granule neurons (CGN) in generation of CD4⁺FoxA1⁺PD-L1^hiFOXP3⁻ Treg cells from encephalitogenic CD4⁺ T cells.

A CD4 co-receptor specific ligand, IL-16, governs trafficking and biological properties of CD4⁺ T cells irrespective of their activation state. Functions of IL-16, relevant to Treg cells, include expansion of CD4⁺CD25⁺ T cells in long-term cultures with IL-2, de novo induction of FOXP-3 and migration of FOXP-3⁺ T cells. IL-16 is highly conserved across species including human and mouse. CGN and neurons in hippocampus contain neuronal-IL-16 (NIL-16), splice variant of immune IL-16, and express CD4 molecule. In a CD4-dependent manner, IL-16 supports cultured CGN survival.

Concomitant studies of RRMS lesions and corresponding MOG_35–55-induced relapsing EAE in (B6 × SJL)F1 (H-2^b/s) mice discovered similar roles of IL-16 in regulation of relapsing disease. In RRMS and EAE relapse, peak levels of IL-16 and active caspase-3 correlated with CD4⁺ T cell infiltration and levels of T-bet, Stat-1(Tyr⁷⁰¹), and phosphorylated neurofilaments of axonal cytoskeleton [NF (M + H) P], suggesting a role of locally produced IL-16 in regulation of CD4⁺ Th1 inflammation and axonal damage, respectively. IL-16 was abundantly present in CD4⁺ T cells, followed by CD20⁺ B, CD8⁺ T, CD83⁺ dendritic cells, and Mac-1⁺ microglia. Apart from lesions, bioactive IL-16 was located in normal-appearing white matter (NAWM) and normal-appearing grey matter (NAGM) in RRMS brain and spinal cord.

A cytokine IL-16 emerges as an important regulator of relapsing MS and EAE. Better understanding of immune cell-neuron interactions mediated by IL-16 will foster development of more specific CD4⁺ T cell subset-targeted therapies to prevent or ameliorate progression of neuroinflammation and axonal and neuronal damage. Translational studies necessitate corresponding EAE models.

Toll-like receptor 4 participates in the myelin disruptions associated with chronic alcohol abuse

Alcohol abuse and alcoholism can cause brain damage, loss of white matter, myelin fiber disruption, and even neuronal injury. The underlying mechanisms of these alterations remain elusive. We have shown that chronic ethanol intake, by activating glial toll-like receptor 4 (TLR4) receptors, triggers the production of inflammatory mediators and can cause brain damage. Because neuroinflammation may be associated with demyelination and neuronal damage, we evaluate whether the ethanol-induced TLR4-dependent proinflammatory environment in the brain could be involved in the myelin disruptions observed in alcoholics. Using brains from wild-type (WT) and TLR4 knockout (KO, TLR4(-/-) ) mice, we demonstrate that chronic ethanol treatment downregulated proteins involved in myelination [proteolipid protein (PLP), myelin basic protein (MBP), myelin-oligodendrocyte glycoprotein, 2,3-cyclic-nucleotide-3-phosphodiesterase, and myelin-associated glycoprotein], while increased chondroitin sulfate proteoglycan NG2 (NG2)-proteoglycan in several brain regions of ethanol-treated WT mice. The immunohistochemistry analysis also revealed that ethanol-treatment-altered myelin morphology reduced the number of MBP-positive fibers and caused oligodendrocyte death, as demonstrated by an increase in caspase-3-positive oligodendrocytes. The in vivo imaging system further confirmed that chronic ethanol intake markedly reduced the PLP in WT mice. Most myelin alterations were not observed in brains from ethanol-treated TLR4(-/-) mice. Electron microscopy studies revealed that although 41-47% of axons showed myelin sheath disarrangements in the cerebral cortex and corpus callosum of WT ethanol-treated mice, respectively, small focal fiber disruptions were noticed in these brain areas of ethanol-treated TLR4(-/-) mice. In summary, the present results suggest that ethanol-induced neuroinflammation might be involved in myelin disruptions and white matter loss observed in human alcoholics.