Interleukin-1beta promotes repair of the CNS

Abstract

Interleukin-1beta (IL-1beta) is a proinflammatory cytokine associated with the pathophysiology of demyelinating disorders such as multiple sclerosis and viral infections of the CNS. However, we demonstrate here that IL-1beta appears to promote remyelination in the adult CNS. In IL-1beta(-/-) mice, acute demyelination progressed similarly to wild-type mice and showed parallel mature oligodendrocyte depletion, microglia-macrophage accumulation, and the appearance of oligodendrocyte precursors. In contrast, IL-1beta(-/-) mice failed to remyelinate properly, and this appeared to correlate with a lack of insulin-like growth factor-1 (IGF-1) production by microglia-macrophages and astrocytes and to a profound delay of precursors to differentiate into mature oligodendrocytes. Thus, IL-1beta may be crucial to the repair of the CNS, presumably through the induction of astrocyte and microglia-macrophage-derived IGF-1.

Fig. 1.

Expression of IL-1β during demyelination–remyelination in wild-type mice. A, Reverse transcription-PCR of RNA extracted from brains of mice at weekly intervals was examined for IL-1β and IGF-1. Mice were exposed to cuprizone for 6 weeks and allowed to recover. A representative example of three time course experiments is illustrated.B, The number of IL-1β⁺ cells in the corpus callosum at the level of the fornix. The mean and SEM bars representing the number of IL-1β⁺ cells per square millimeter are plotted for the triplicate set of samples.

Fig. 2.

Most microglia–macrophages and some astrocytes express IL-1β during demyelination–remyelination in wild-type mice. A, Few or no IL-1β⁺ cells are present in the untreated corpus callosum. B, A large accumulation of IL-1β⁺ cells begins at week 3 in the medial region of the corpus callosum posterior to the fornix.C–E, Representative sections demonstrating the colocalization (arrows) of IL-1β-expressing cells (green-stained cells in C) to nearly all of the Mac-1⁺ macrophages (red-stained cells in D and overlaid inE) in the corpus callosum at week 4.F–H, The colocalization (arrows) of a few IL-1β-expressing cells (green-stained cells in F) to GFAP⁺ astrocytes (red-stained cells in G and overlaid inH) in the corpus callosum. Scale bar, 30 μm.

Fig. 3.

Representative electron micrographs of the myelinated, demyelinated, and remyelinated axons in the corpus callosum of wild-type and IL-1β^−/− mice. Almost all axons are myelinated in the corpus callosum of untreated wild-type (A) andIL-1β^−/− (B) mice. Negligible number of myelinated axons, corresponding to peak demyelination, are present in the corpus callosum of 5 week treated wild-type (C) andIL-1β^−/− (D) mice.E, Wild-type mice show that a large portion of the axons in the corpus callosum have remyelinated, butIL-1β^−/− mice show fewer remyelinated axons at week 10 (F), 4 weeks after removal of cuprizone. Scale bar, 1.2 μm.

Fig. 4.

GST-Pi⁺ mature oligodendrocytes in the corpus callosum of wild-type andIL-1β^−/− mice during demyelination and remyelination. GST-Pi⁺ mature oligodendrocytes in the corpus callosum of untreated wild-type (A) and IL-1β^−/− (B) mice at 0 weeks. Mature oligodendrocyte recovery of wild-type (C) and IL-1β^−/−(D) mice at 5 weeks of treatment. Recovery of GST-Pi⁺ cells in the corpus callosum of wild-type (E) and IL-1β^−/−(F) mice at 10 weeks. G, The mean and SEM bars representing the number of GST-Pi⁺cells per square millimeter are plotted for the triplicate set of samples. Scale bar, 50 μm. CC, Corpus callosum. Thewhite dashed line separates the corpus callosum and fornix. *p < 0.005; **p < 0.0005.

Fig. 5.

The presence of NG2⁺ cells during demyelination and remyelination inIL-1β^−/− mice. NG2⁺oligodendrocytes accumulate in the corpus callosum of wild-type (A) and IL-1β-deficient (B) mice after 5 weeks of cuprizone treatment. A reduction in the number of NG2⁺ oligodendrocyte progenitors (450 ± 30 cells/mm²) in the corpus callosum was observed in wild-type mice (C) (only stained cells with nuclei were counted). This was in contrast to the continued presence of progenitors (703 ± 38 cells/mm²) in the corpus callosum ofIL-1β^−/− mice after 1 week of recovery after 6 weeks of cuprizone treatment (D). Scale bar, 20 μm.

Fig. 6.

The number of IGF-1⁺ cells and amount of IGF-1 protein increase within a demyelinating corpus callosum in wild-type mice but not in IL-1β^−/−mice. A, The mean and SEM bars representing the number of IGF-1⁺ cells per square millimeter in wild-type mice is plotted for the duplicate set of samples (*p < 0.001). B, The mean and SEM bars representing the amount of IGF-1 protein within the corpus callosum of wild-type and IL-1β^−/− mice is plotted for the triplicate set of samples. KO, Knock-out.

Fig. 7.

The absence of IGF-1⁺astrocytes and microglia–macrophages during demyelination and remyelination in IL-1β^−/− mice. IGF-1⁺ cells appear in the corpus callosum of wild-type mice (A) but not in IL-1β-deficient mice (B) after 5 weeks of treatment. IGF-1⁺ cells remain in the corpus callosum of wild-type mice (C) undergoing remyelination but are absent in IL-1β-deficient mice (D) after 1 week of recovery after 6 weeks of cuprizone treatment.E–J, Representative sections from wild-type mice demonstrating the colocalization of IGF-1 to GFAP⁺cells and Mac-1⁺ cells within the demyelinating corpus callosum at 4 weeks. E–G, The colocalization (arrows) of IGF-1⁺ cells (green-stained cells in E) to nearly all of the GFAP⁺ astrocytes (red-stained cells in F and overlaid inG) within the lesion. H–J, The colocalization (arrows) of a few IGF-1⁺ cells (green-stainedcells in H) to Mac-1⁺microglia–macrophages (red-stained cells inI and overlaid in J) within the lesion. Scale bars: A–D, 20 μm; E–H, 10 μm.