Molecular targets for disrupting leukocyte trafficking during multiple sclerosis

High-salt diet suppresses autoimmune demyelination by regulating the blood-brain barrier permeability

Dietary salt intake has been considered an important risk factor for autoimmune diseases like multiple sclerosis (MS). Here we studied the effects of a high-salt diet (HSD) using a spontaneous autoimmune disease mouse model resembling MS. We found that high-salt consumption protects mice from developing the neurological disease by promoting the tightening of the blood–brain barrier and preventing the migration of autoreactive T cells into the CNS. Our results emphasize the multifarious effects of high-salt consumption in autoimmune disease susceptibility.

Sodium chloride, “salt,” is an essential component of daily food and vitally contributes to the body’s homeostasis. However, excessive salt intake has often been held responsible for numerous health risks associated with the cardiovascular system and kidney. Recent reports linked a high-salt diet (HSD) to the exacerbation of artificially induced central nervous system (CNS) autoimmune pathology through changes in microbiota and enhanced T_H17 cell differentiation [M. Kleinewietfeld et al., Nature 496, 518–522 (2013); C. Wu et al., Nature 496, 513–517 (2013); N. Wilck et al., Nature 551, 585–589 (2017)]. However, there is no evidence that dietary salt promotes or worsens a spontaneous autoimmune disease. Here we show that HSD suppresses autoimmune disease development in a mouse model of spontaneous CNS autoimmunity. We found that HSD consumption increased the circulating serum levels of the glucocorticoid hormone corticosterone. Corticosterone enhanced the expression of tight junction molecules on the brain endothelial cells and promoted the tightening of the blood–brain barrier (BBB) thereby controlling the entry of inflammatory T cells into the CNS. Our results demonstrate the multifaceted and potentially beneficial effects of moderately increased salt consumption in CNS autoimmunity.

Straightforward method for singularized and region-specific CNS microvessels isolation

BACKGROUND

Current methods for murine brain microvasculature isolation requires the pooling of brain cortices while disregarding the rest of the CNS, making the analysis of single individuals non feasible.

NEW METHOD

Efficient isolation of brain microvessels requires the elimination of meninges, vessels of high caliber vessels and choroid plexus, commonly done by rolling the over filter paper, but can't be done on other CNS regions. We overcome this hurdle by using a double-pronged pick, as well as elution and filtration through cell strainers after centrifugation.

RESULTS

We were able to develop a region-specific murine CNS microvessels isolation, that allows for the comparison of the neurovascular unit from these regions both within the same individual and between multiple individuals and/or treatment groups without pooling. Additionally, we were able to adapt this method to macaque CNS tissue.

COMPARISON WITH EXISTING METHOD(S)

Although similar to a previously published method that requires no enzymatic dissociation and no ultracentrifugation, it does differ in its ability to isolate from a single experimental animal and from non-cortical tissues. However, it relies heavily on the researcher dissecting skills and careful elution and filtration of re-suspended samples.

CONCLUSIONS

CNS region-specific microvessels comparison can inform of molecular and/or cellular differences that would otherwise be obscured by excluding non-cortical tissue. Additionally, it allows for the unmasking of variations between individuals that remained hidden when pooling of multiple samples is the norm. Lastly, isolation of region-specific microvessels for non-human primate CNS allows for more translationally relevant studies of the BBB.

Pathology of multiple sclerosis and related inflammatory demyelinating diseases

This article provides a comprehensive overview of the pathology of multiple sclerosis (MS), including recent insights into its molecular neuropathology and immunology. It shows that all clinical manifestations of relapsing and progressive MS display the same basic features of pathology, such as chronic inflammation, demyelination in the white and gray matter, and diffuse neurodegeneration within the entire central nervous system. However, the individual components of the pathological spectrum vary quantitatively between early relapsing and late progressive MS. Widespread confluent and plaque-like demyelination with oligodendrocyte destruction is the unique pathological hallmark of the disease, but axonal injury and neurodegeneration are additionally present and in part extensive. Remyelination of existing lesions may occur in MS brains; it is extensive in a subset of patients, while it fails in others. Active tissue injury in MS is always associated with inflammation, consistent with T-cell and macrophage infiltration and microglia activation. Recent data suggest that oxidative injury and subsequent mitochondrial damage play a major pathogenetic role in neurodegeneration. Finally we discuss similarities and differences of the pathology between classical MS and other inflammatory demyelinating diseases, such as neuromyelitis optica, concentric sclerosis, or acute disseminated encephalomyelitis.

Lipocalin 2 is a novel immune mediator of experimental autoimmune encephalomyelitis pathogenesis and is modulated in multiple sclerosis

Experimental autoimmune encephalomyelitis (EAE) is a widely used animal model of multiple sclerosis (MS), an inflammatory, demyelinating disease of the central nervous system (CNS). EAE pathogenesis involves various cell types, cytokines, chemokines, and adhesion molecules. Given the complexity of the inflammatory response in EAE, it is likely that many immune mediators still remain to be discovered. To identify novel immune mediators of EAE pathogenesis, we performed an Affymetrix gene array screen on the spinal cords of mice at the onset stage of disease. This screening identified the gene encoding lipocalin 2 (Lcn2) as being significantly upregulated. Lcn2 is a multi-functional protein that plays a role in glial activation, matrix metalloproteinase (MMP) stabilization, and cellular iron flux. As many of these processes have been implicated in EAE, we characterized the expression and role of Lcn2 in this disease in C57BL/6 mice. We show that Lcn2 is significantly upregulated in the spinal cord throughout EAE and is expressed predominantly by monocytes and reactive astrocytes. The Lcn2 receptor, 24p3R, is also expressed on monocytes, macrophages/microglia, and astrocytes in EAE. In addition, we show that EAE severity is increased in Lcn2(-/-) mice as compared with wild-type controls. Finally, we demonstrate that elevated levels of Lcn2 are detected in the plasma and cerebrospinal fluid (CSF) in MS and in immune cells in CNS lesions in MS tissue sections. These data indicate that Lcn2 is a modulator of EAE pathogenesis and suggest that it may also play a role in MS.

The importance of NAD in multiple sclerosis

The etiology of multiple sclerosis (MS) is unknown but it manifests as a chronic inflammatory demyelinating disease in the central nervous system (CNS). During chronic CNS inflammation, nicotinamide adenine dinucleotide (NAD) concentrations are altered by (T helper) Th1-derived cytokines through the coordinated induction of both indoleamine 2,3-dioxygenase (IDO) and the ADP cyclase CD38 in pathogenic microglia and lymphocytes. While IDO activation may keep auto-reactive T cells in check, hyper-activation of IDO can leave neuronal CNS cells starving for extracellular sources of NAD. Existing data indicate that glia may serve critical functions as an essential supplier of NAD to neurons during times of stress. Administration of pharmacological doses of non-tryptophan NAD precursors ameliorates pathogenesis in animal models of MS. Animal models of MS involve artificially stimulated autoimmune attack of myelin by experimental autoimmune encephalomyelitis (EAE) or by viral-mediated demyelination using Thieler's murine encephalomyelitis virus (TMEV). The Wld(S) mouse dramatically resists razor axotomy mediated axonal degeneration. This resistance is due to increased efficiency of NAD biosynthesis that delays stress-induced depletion of axonal NAD and ATP. Although the Wld(S) genotype protects against EAE pathogenesis, TMEV-mediated pathogenesis is exacerbated. In this review, we contrast the role of NAD in EAE versus TMEV demyelinating pathogenesis to increase our understanding of the pharmacotherapeutic potential of NAD signal transduction pathways. We speculate on the importance of increased SIRT1 activity in both PARP-1 inhibition and the potentially integral role of neuronal CD200 interactions through glial CD200R with induction of IDO in MS pathogenesis. A comprehensive review of immunomodulatory control of NAD biosynthesis and degradation in MS pathogenesis is presented. Distinctive pharmacological approaches designed for NAD-complementation or targeting NAD-centric proteins (SIRT1, SIRT2, PARP-1, GPR109a, and CD38) are outlined towards determining which approach may work best in the context of clinical application.