Figure 8. Activin-A is an M2-derived factor that drives oligodendrocyte differentiation during remyelination.

(a) Percentage of activin-A immunopositive cells per field in M1, M2a, and M2c microglia ± s.e.m. (b) Control corpus callosum lesions at 3 and 10 dpl (top and middle panels) and MCL-injected lesion at 10 dpl (bottom panel) immunostained for activin-A (red) and iNOS or MR (green). Scale bar, 25 μm. (c) Representative images of NG2+ OPCs (green) in remyelinating lesions expressing activin receptors Acvr2A, Acvr2B, and Acvr1B (red; arrows). Scale bar, 10 μm. (d) Percentage of MBP+ cells ± s.e.m. in OPC cultures treated with activin-A. One way ANOVA and Newman-Keuls post-hoc test, *p<0.05 (n=4 separate experiments, df=15). (e) Percentage of MBP+ cells ± s.e.m. in OPC cultures treated with combinations of M2a conditioned media, goat isotype control IgG, or goat anti-activin-A antibody. One way ANOVA and Newman-Keuls post-hoc test, **p<0.01 (n=4 separate experiments, df=11), ns=p>0.05. (f) 300 μm sagittal sections of cerebellum and attached hindbrain were taken from newborn mouse brain to obtain organotypic cultures, demyelinated with lysolecithin (LPC) and treated with M2 conditioned media and either anti-activin-A IgG or control goat IgG. (g) Representative images of slices treated with M2 conditioned media and goat IgG (left) or anti-activin-A antibody (right) immunostained for CC1 (white) and MBP (red). Scale bar, 25 μm. (h) Percentage of CC1+ oligodendrocytes normalized to values obtained from slices treated with IgG alone. 2-tailed one-sample or Student’s t-test (respectively), M2 conditioned media + IgG vs. IgG, P=0.0213; M2 conditioned media + IgG vs. M2 conditioned media + anti-activin-A IgG, P=0.0071 (n=8 slices, df=14). Box plots indicate median (centre line), 25^th-75^th percentile (box limits), minimum and maximum (whiskers).