Involvement of the JAK-STAT pathway and SOCS3 in the regulation of adiponectin-generated reactive oxygen species in murine macrophage RAW 264 cells

Adiponectin is a protein hormone produced by differentiating adipocytes and has been proposed to have anti‐diabetic and immunosuppressive properties. We previously reported that the globular form of adiponectin (gAd) induces the generation of reactive oxygen species (ROS) and nitric oxide (NO), followed by caspase‐dependent apoptotic cell death in RAW 264 cells. Here, we demonstrate that gAd‐induced ROS generation and apoptosis were diminished by suppressor of cytokine signaling 3 (SOCS3). The phosphorylation level of signal transducer and activator of transcription (STAT) 3 detected by Western blotting was highest at 20 min in gAd‐treated RAW 264 cells. This phosphorylation was inhibited by AG490, a specific inhibitor of janus‐activator kinase (JAK). The gAd‐induced ROS and NO were reduced by administration of AG490 and Jak‐2‐specific siRNA in RAW 264 cells. The gAd stimulation transiently induced SOCS3 mRNA expression and protein production. We examined SOCS3‐overexpressing RAW 264 cells to investigate the role of the JAK‐STAT pathway in gAd‐induced ROS and NO generation. SOCS3 overexpression significantly reduced both ROS and NO generation. Additionally, gAd‐induced caspase activation and apoptotic cell death were reduced in SOCS3 transfectants compared with vector control transfectants. These results suggest that the JAK‐STAT pathway, which can be suppressed by SOCS3 expression, is involved in gAd‐induced ROS and NO generation followed by apoptotic cell death. J. Cell. Biochem. 111: 597–606, 2010. © 2010 Wiley‐Liss, Inc.