To test this idea, several putative signaling pathways that are frequently linked to OL
proliferation, survival, and myelination were assessed in OPCs upon exposure to the conditioned medium. The phosphorylated Akt (both ser308 and ser473), Erk1/2, CREB, and STAT-3, as well as the total form of these kinases, were detected by Western blot following treatment with the conditioned medium (Fig. (Fig.5A).5A). Surprisingly, ACDM strongly activated all these pathways Inhibitors,research,lifescience,medical in OPCs, in a time-dependent manner. pAkt, pErk, and pCREB were rapidly activated in OPCs but then quickly returned to baseline level within 2 h, while pSTAT3 levels remained high at 24 h. In contrast to the simultaneous activation of multiple signaling pathways by ACDM, MCDM only weakly activated CREB pathways in OPCs. Using specific inhibitors, we further showed that PD98059 (Erk1/2 inhibitor), but not SH5 (Akt inhibitor), significantly reduced ACDM-enhanced OL survival (Fig. (Fig.55B). Figure 5 Activation of multiple signaling Inhibitors,research,lifescience,medical pathways in OPCs upon exposure to the conditioned medium. (A) OPCs were exposed to the control or conditioned medium for indicated times and the phosphorylated as well as the Inhibitors,research,lifescience,medical total form of
several signaling pathways were … MCDM, but not ACDM, strongly promotes myelination in vitro Finally, the effect of MCDM and ACDM on myelination was tested in a myelinating neuron-OL coculture. After being exposed to ACDM or MCDM for 4 weeks, the number of myelinated
internodes (MBP/pNF double-labeled axons) was determined. Consistent with its ability to enhance OL differentiation, MCDM exposure significantly Inhibitors,research,lifescience,medical increased the extent of myelination (Fig. (Fig.6A6A and B). In contrast, Inhibitors,research,lifescience,medical ACDM had no discernable effect on myelination. It appears that neither conditioned medium affected axonal density (Fig. (Fig.6A,6A, pNF panels). Figure 6 MCDM enhances myelination in vitro. Myelinating OL-neuron cocultures were exposed to ACDM, MCDM, or the control medium from DIV7 to DIV35. Myelinated internodes were revealed by coimmunolabeling with MBP and pNF (merged Bafilomycin A1 cell line panels in A), and myelination index … Discussion Rebamipide The major finding of the current study is that ACDM and MCDM preferentially affect OL development and myelination, which are underlined by distinct cytokine patterns in the conditioned medium and by selectively activated intracellular signaling pathways in OLs. The finding that ACDM promotes OPC proliferation is consistent with early studies. For example, OPCs grown on top of astrocyte monolayer had higher proliferation rate than without astrocytes, whereas PDGF was identified as the primary mitogen (Hardy and Reynolds 1991). Based on in vivo studies, PDGF has been suggested as one of the key growth factors to regulate OPC numbers during early OL development.