Figure 5.

ASK1-JNK mediates troglitazone-potentiated mitochondrial oxidative stress through FOXO3a. (A) Liver homogenates were subjected to immunoblotting with pASK1^Thr845, pASK1^Ser83, ASK1, pJNK, JNK1/2, pp38, and p38 antibodies. Elevated oxidative stress from 4 weeks of troglitazone administration induced ASK1 and JNK1/2 activation. The right panel shows mean normalized density values relative to the corresponding nonphosphorylated form. (B) Immunoblot analysis of transcriptional regulators and coactivators involved in regulating nuclear-encoded mitochondrial proteins in Sod2^+/+ and Sod2^+/– mice. (C) Liver homogenates were subjected to immunoblotting with FOXO3a, pFOXO3a^Ser253, PGC-1α, PGC-1β, ERRα, NRF-1, and PPARγ antibodies. (D) Liver sections were subjected to immunohistochemistry by incubating with pFOXO3a^Ser253 antibody and counterstained. Extended administration of Sod2^+/– mice with troglitazone induced the nuclear translocation of FOXO3a in areas of hepatocytic degeneration but not the vehicle (solutol). Original magnification ×100. The inset illustrates the cytosolic localization of pFOXO3a (original magnification ×400). (E) Proposed schematic diagram showing that extended troglitazone administration coupled to increased mitochondrial oxidative stress in Sod2^+/– mice primed ASK1-JNK-FOXO3a activation, which in turn resulted in mitoproteome reconfiguration and dysregulated lipid metabolism, enhancing mitochondrial ROS regulation in a feedback loop. TRG, troglitazone.