using a model of total hepatic I/R with bowel congestion,20, 33 a model with direct TLR4 activation through LPS release. In TLR4−/− mice, KC depletion leads to increased hepatocellular injury and decreased IL-10 response.33 We have shown previously that TLR4 signaling is necessary for hepatic I/R response, and that this response is, in part, mediated by HMGB1.5,

19 Here, we demonstrate the role HCs play in this response, with release of HMGB1 significantly reduced with lack of functional HC TLR4 signaling, approximately equal to mice with global TLR4 deficiency. Furthermore, there was an intermediate decrease in serum HMGB1 with lack of TLR4 in myeloid cells, even though the hepatocellular injury was not significantly different in these mice. These findings suggest that HCs are the primary cell type responsible BAY 80-6946 manufacturer for TLR4-dependent HMGB1 release after I/R, which is a novel finding and contrary to the current thought that HMGB1 release is primarily dependent on immune cells.34 However, it certainly seems plausible that

HCs may be the primary producer of HMGB1 early in I/R, because, in our previous work, we have shown that HCs can actively release HMGB1 in response to oxidative stress in a regulated process.15, 19, 35 There are a number of cellular pathways involved with hypoxia-induced HMGB1 release by HCs, all of which are actively regulated.15, 19, 35, 36 The hyperacetylation of HMGB1, Selleckchem LY2157299 which is largely regulated by histone deacetylases, leads Sulfite dehydrogenase to the shuttling of nuclear HMGB1 into the cytoplasm.35, 36 Additionally, HMGB1 translocation and subsequent extracellular release is also dependent on calcium/calmodulin-dependent kinases and also on functional interferon regulatory factor 1 (IRF-1).15, 19 JNK has recently been shown to be able to induce expression of IRF-1,37 substantiating our hypothesis

that JNK is upstream of other known pathways leading to HMGB1 release. Although JNK inhibition has been shown to be protective in I/R, these effects are noted at time points >6 hours, despite JNK activation occurring much earlier. Therefore, we hypothesized that JNK activation may be responsible for the release of a proinflammatory mediator, rather than directly contributing to injury. Here, we provide evidence that the role of JNK includes the facilitation of HMGB1 release from hepatocytes both in vitro and in vivo, thus providing one possible solution. In summary, we use cellular-specific TLR4−/− Tg mice to establish that TLR4 may either worsen or alleviate hepatocellular injury after I/R, depending on cell type. The role of TLR4 on both myeloid and HCs is primarily proinflammatory, compared to DCs, in which TLR4 plays a primarily anti-inflammatory role (Fig. 8). We are intrigued that parenchymal cells, such as HCs, are not mere passive recipients of injury during I/R, but active participants in the sterile inflammatory process.