Multiple sclerosis (MS) is a chronic, inflammatory, demyelinating disease of the CNS, most frequently starting with a series of bouts, each followed by complete remission and then a secondary, progressive phase during which the neurological deficit increases steadily. The underlying molecular mechanisms responsible for disease progression are still unclear. Herein, we demonstrate that high mobility group box chromosomal protein 1 (HMGB1), a DNA-binding protein with proinflammatory properties, is evident in active lesions of MS and experimental autoimmune encephalomyelitis (EAE) and that HMGB1 levels correlate with active inflammation. Furthermore, the expression of the innate HMGB1 receptors—receptor for advanced glycation end products, TLR2, and TLR4—was also highly increased in MS and rodent EAE. Additionally, in vitro activation of rodent CNS-derived microglia and bone marrow-derived macrophages demonstrated that microglia were equally as capable as macrophages of translocating HMGB1 following LPS/IFN-γ stimulation. Significant expression of HMGB1 and its receptors on accumulating activated macrophages and resident microglia may thus provide a positive feedback loop that amplifies the inflammatory response during MS and EAE pathogenesis.

Adult neural stem cells (NSCs) are believed to facilitate CNS repair and tissue regeneration. However, it is not yet clear how these cells are influenced when the cellular environment is modified during neurotrauma or neuroinflammatory conditions. In this study, we determine how different proinflammatory cytokines modulate the expression of TLR2 and TLR4 in NSCs and how these cells respond to TLR2 and TLR4 agonists. Primary cultures of neural stem/progenitor cells isolated from the subventricular zone of brains from adult Dark Agouti rats were exposed to 1) supernatants from activated macrophages; 2) proinflammatory cytokines IFN-γ, TNF-α, or both; and 3) agonists for TLR2 and TLR4. Both TLR2 and TLR4 were expressed during basal conditions and their mRNA levels were further increased following cytokine exposure. TLR4 was up-regulated by IFN-γ and this effect was reversed by TNF-α. TLR2 expression was increased by supernatants from activated macrophages and by TNF-α, which synergized with IFN-γ. TLR agonists induced the expression of TNF-α mRNA. Importantly, TNF-α could be translated into protein and released into the supernatants where it was quantified by cytokine ELISA. In conclusion, we demonstrate that NSCs constitutively express TLR2 and TLR4 and that their expression is increased as a consequence of exposure to proinflammatory mediators. Additionally, activation of these receptors can induce production of proinflammatory cytokines. These findings suggest that NSCs may be primed to participate in cytokine production during neuroinflammatory or traumatic conditions.

Hydrogen peroxide (H ₂ O ₂ ) is a reactive oxygen species that is involved in immunity and neuroinflammation. Here, we investigated whether and how pathophysiological levels of H ₂ O ₂ influenced the differentiation of neural progenitor cells (NPCs). H ₂ O ₂ levels within the range measured at neuroinflammatory events were applied to rat primary NPC cultures during 24 h, and effects were assessed directly after exposure or in NPCs that were differentiated for 7 days after H ₂ O ₂ removal. Exposed differentiated NPCs showed significantly increased numbers of neurons and oligodendrocytes compared with unexposed controls. To identify the possible origin of this differentiation result, we characterized the undifferentiated culture and found a significant increase in both OLIG2 ⁺ cells and proliferative ASCL1 ⁺ C cells that could contribute to both more neurons and oligodendrocytes. In addition, H ₂ O ₂ -induced neurogenesis was supported by western blot and paralleled by gene expression analyses, which revealed an increased expression of the proneural gene Ngn2 and the neuronally expressed gene β-III tubulin. To investigate potential mechanisms for the observed effects on NPC differentiation, we performed gene expression profile analyses for oxidative stress and antioxidant-related and chromatin modification genes where the expression of several important genes was affected by the exposure. Increased oligodendrocyte numbers correlated with increased expression of the chromatin modification enzyme Sirt2, suggesting the involvement of Sirt2 in oligodendrocyte differentiation. Our results suggest a modulatory effect on the differentiation potential of NPCs by H ₂ O ₂ . Our findings indicate that H ₂ O ₂ exposure has significant effects on NPC proliferation, differentiation, and vulnerability. These results have implications for regeneration after any neuroinflammatory event.

Regeneration of cells in the central nervous system is a process that might be affected during neurological disease and trauma. Because nitric oxide (NO) and its derivatives are powerful mediators in the inflammatory cascade, we have investigated the effects of pathophysiological concentrations of NO on neurogenesis, gliogenesis, and the expression of proneural genes in primary adult neural stem cell cultures. After exposure to NO, neurogenesis was downregulated, and this corresponded to decreased expression of the proneural gene neurogenin-2 and beta-III-tubulin. The decreased ability to generate neurons was also found to be transmitted to the progeny of the cells. NO exposure was instead beneficial for astroglial differentiation, which was confirmed by increased activation of the Janus tyrosine kinase/signal transducer and activator of transcription transduction pathway. Our findings reveal a new role for NO during neuroinflammatory conditions, whereby its proastroglial fate-determining effect on neural stem cells might directly influence the neuroregenerative process.