We have previously reported that Ets family transcription factor PU.1 is expressed in mature adipocytes of white adipose tissue. PU.1 expression is greatly increased in mouse models of genetic or dietary induced obesity. Here, we show PU.1 expression was increased only in visceral but not subcutaneous adipose tissues of obese mice and the adipocytes are responsible for this increase of PU.1 expression. To further address PU.1's physiological function in mature adipocytes, PU.1 was knocked down in 3T3-L1 cells using retroviral mediated expression of PU.1 targeting shRNA. Consistent with previous findings that PU.1 regulates its target genes, such as NADPH oxidase subunits and pro-inflammatory cytokines in myeloid cells, the mRNA levels of pro-inflammatory cytokines (TNF-α, IL-1β and IL-6) and cytosolic components of NADPH oxidase (p47phox and p40phox) were significant down-regulated in PU.1 silenced adipocytes. NADPH oxidase is a main source for reactive oxygen species (ROS) generation. Indeed, silencing PU.1 suppressed NADPH oxidase activity and attenuated ROS in basal or hydrogen peroxide-treated adipocytes. Silencing PU.1 in adipocytes suppressed JNK1 activation and IRS-1 phosphorylation at Ser307. Consequently, PU.1 knockdown improved insulin signaling and increased glucose uptake in basal and insulin-stimulated conditions. Furthermore, knocking down PU.1 suppressed basal lipolysis but activated stimulated lipolysis. Collectively, these findings indicate that obesity induces PU.1 expression in adipocytes to up-regulate the production of ROS and pro-inflammatory cytokines, both of which lead to JNK1 activation, insulin resistance and dysregulation of lipolysis. Therefore, PU.1 might be a mediator for obesity-induced adipose inflammation and insulin resistance.
- NADPH oxidase