Nuclear and cytosolic fractions were isolated from the liver and kidney from normal wild type (WT) mice and at 4 and 24 hours after AKI in WT and IL-6−/− mice and total and phosphorylated STAT3 (pSTAT3) was determined by ELISA. (A, B) In the liver. pSTAT3 increased and completely translocated to the nuclei at 24 hours in WT, but not IL-6−/− mice, with AKI. (C, D) In the kidney, pSTAT3 increased and translocated to the nucleus in both WT and IL-6−/− mice at 4 and 24 hours. IL-6 and an inhibitor of STAT3 phosphorylation (STATTIC) was added to murine (AML12) and human (HepG2) hepatocyte cell lines in vitro. IL-6 was added 1 hour after addition of Stattic; media NGAL was determined 4 hours after adding IL-6. (E-H) NGAL was increased with addition of IL-6 and reduced with IL-6+STATTIC in AML12 and HepG2. IL-6 was unchanged by STATTIC in AML12 and HepG2. Data represent the expression values for 3 to 5 mice per group from 1 experiment. Results are expressed as mean ±SEM. Data were analyzed by t test, *P < 0.05, **P < 0.01 and ***P < 0.001 vs. WT normal (uninjured) mice or vs. vehicle in cell culture experiments.