The Protective Role of Nitric Oxide in a Neurotoxicant- Induced Demyelinating Model

Abstract

Demyelination is often associated with acute inflammatory events involving the recruitment-activation of microglia/macrophage, astrocytes, and leukocytes. The ultimate role of inflammatory products in demyelinating disease and in the survival of oligodendrocytes, the myelin forming cells, is unresolved. The current study examines the role of inducible NO synthase (iNOS)-derived NO in a neurotoxicant-induced model of demyelination. NO levels were greatly elevated in the midline corpus callosum during demyelination in genetically intact C57BL/6 mice, and this NO was due solely to the induction of iNOS, as the correlates of NO were not found in mice lacking iNOS. C57BL/6 mice lacking iNOS exhibited more demyelination, but did not display an increased overall cellularity in the corpus callosum, attributable to an unimpeded microglia/macrophage presence. An enhanced course of pathology was noted in mice lacking iNOS. This was associated with a greater depletion of mature oligodendrocytes, most likely due to apoptosis of oligodendrocytes. Microglia and astrocytes did not undergo apoptosis during treatment. Our results suggest a moderately protective role for NO during acute inflammation-association demyelination.

Identification of a microglia phenotype supportive of remyelination

“…E: Galectin 3 mRNA was gradually upregulated in microglia in the course of demyelination and remyelination, became detectable at the protein level at 5WD (data not shown), and remained upregulated up to 2WR (5WD, 5 weeks of demyelination; 1WR, 1 week of remyelination; 2WR, 2 weeks of remyelination; Tgfb, transforming growth factor beta; Spp1, osteopontin; Iba1, ionized calcium-binding adaptor molecule 1; IB4, isolectin B4; Slpi, antileukoproteinase; Cd11c, integrin alpha-X, a dendritic cell marker; Gal3, galectin-3; calibration bars in our study, both of which have been shown to be indispensable for remyelination to occur (Arnett et al, 2001;Mason et al, 2001). Interestingly, inducible nitric oxide synthase (iNOS) was found to be induced in the cuprizone model in microglia (Arnett et al, 2002;Liñares et al, 2006) and was moderately protective against demyelination (Arnett et al, 2002). Nonetheless, iNOS was not among the genes expressed in our study.…”

The Inflammasome Sensor, NLRP3, Regulates CNS Inflammation and Demyelination via Caspase-1 and Interleukin-18

“…Together, these data indicate that NLRP3 delays demyelination but does not obviate this process, suggesting the existence of other compensatory mechanisms. This is consistent with studies of other inflammatory genes in the cuprizone model (Arnett et al, 2001(Arnett et al, , 2002Mason et al, 2001;Plant et al, 2007). A TUNEL assay was used to assess differences in cell death after 3 weeks of cuprizone-induced demyelination.…”

“…To examine demyelination, paraffin sections were rehydrated through a graded series of alcohol washes and stained with Luxol fast blue-periodic acid/Schiff base (LFB-PAS) (Sigma-Aldrich) as described previously (Arnett et al, 2002). Sections were read by three blinded readers and graded on a scale from 0 (complete myelination) to 3 (complete demyelination).…”

“…Immunohistochemistry was performed on 5 m paraffin embedded sections that were deparaffinized and rehydrated through alcohols as described previously (Arnett et al, 2002). For the detection of mature oligodendrocytes, the sections were processed by boiling in antigen unmasking solution (1:100; Vector) for 13 min in a microwave.…”

Gas6 Deficiency Increases Oligodendrocyte Loss and Microglial Activation in Response to Cuprizone-Induced Demyelination

“…In vitro studies have demonstrated that microglia can either be directly toxic to oligodendrocytes (Nicholas et al, 2003;Li et al, 2005) or can support oligodendrocyte survival (Pang et al, 2000;Nicholas et al, 2001Nicholas et al, , 2002, with the predominant effect being context dependant. Dichotomous effects of microglia also appear to occur in vivo with reports of either deleterious Mana et al, 2006;Pasquini et al, 2007) or protective effects in response to cuprizone-induced demyelination, the latter particularly predominant during the remyelination phase (Arnett et al, 2001(Arnett et al, , 2002(Arnett et al, , 2003.…”