Fig. 4.
A, JNK activation in OLs treated with NGF or TNF-α. Adult human OLs were cultured in serum-free MEM; data are from untreated controls (lane 1) and cultures treated for 30 min with NGF at 100 ng/ml (lane 2) or with TNF-α at 10 ng/ml (lane 3). Only TNF-α significantly increased JNK activity as assessed by the level of phosphorylation of GST-jun. B, JNK activity in OLs treated with different concentrations of NGF and with C2-ceramide. Data are from OLs in serum-free MEM untreated (lane 1) or treated with NGF at 10 ng/ml for 3 hr (lane 2), with NGF at 100 ng/ml for 3 hr (lane 3), or with C2-ceramide at 25 μm (lane 4). Significant JNK activation was observed with C2-ceramide only. C, JNK activity in response to NGF treatment of OLs cultured in different conditions. Adult human OLs were cultured in DMEM/F12 with PDGF-AA/b-FGF, serum-free MEM, or DMEM/F12 without PDGF-AA/b-FGF. Cells were then treated with NGF at 100 ng/ml or C2-ceramide at 25 μm for 2 hr or left untreated (controls). JNK activity was quantified with a PhosphorImager. Values are expressed as the percent of the JNK activity of the control ± SEM. Eachbar represents the average of three different experiments. C2-ceramide induced significant JNK activation (p < 0.05) in each condition.