Mechanisms of HSC activation and exhaustion. (A) Phosphorylated p38 MAPK activity; (B) LTC-IC activity with 100 μM NAC, 10 μM p38 inhibitor, 10 μM JNK inhibitor, 10 μM MEK inhibitor, and 1 μM rapamycin; ROS level (C); and phosphorylated p38 and mTOR levels (D) of viable Lin⁻CD45⁺ marrow cells after in vivo antioxidant treatment. Values represent the means plus or minus SEM. *P < .05; **P < .01.