Figure 1

Overview of crosstalk between SMF and IL-6. Connections between SMF and IL-6 are shown in black, TLR4 in blue, gangliosides in green, feed-forward regulation of IL-6 on itself in purple, and whole cell responses (e.g., differentiation) in orange. Connections supported by data collected in this work are shown by solid lines (and the location of this data in subsequent figures is provided); dotted lines show connections based on the literature, as referenced. (A) SMF exposure modulates calcium flux (Fig. 3C and Fig. 11A). (B) Early increases in IL-6 mRNA levels (within 2 h, Fig. 3A) occur followed by increased levels of secreted IL-6 (within 7 h, Fig. 3B). (C) Likewise, SMF activates TLR4 (Fig. 3D), resulting in (D) feed-forward self-stimulation [41]. (E) In turn, TLR4 leads to IL-6 activation either through (F) a reported Ca²⁺-dependent route [39] or (G) through changes to p38 phosphorylation (Fig. 4A) that (H) transiently hinder proliferation in hEBD LVEC cells (Fig. 4B) without leading to apoptosis (Fig. 4C& D). SMF also has early-acting effects on NEU3 (I) and ST3GAL5 (J) mRNA levels (Fig. 8F) with (K) a concomitant decrease in ganglioside levels (Fig. 8B&C). (L) In the absence of SMF, exogenously-added ganglioside GM3 suppresses IL-6 production (Fig. 6A) and (M) TLR4 [38]. (N) IL-6 reduces ganglioside levels (Fig. 6B) through changes to (O) NEU3 and (P) ST3GAL5 mRNA levels (Fig. 7D) that (R) involve ERK1/2 phosphorylation (Fig. 7B&C). 'Downstream' responses to the combined administration of (S) IL-6 and (T) SMF include reproducible changes in cell morphology (Fig. 9E) and biochemical markers consistent with pre-oligodendrocyte differentiation (Fig. 10).