Because the Alb-TLR4−/− mice were significantly protected, we further investigated the mechanisms by which this was taking place. Among the most proximal inflammatory signaling events after I/R is the activation of mitogen-activated protein (MAP) kinases.23, 24 To determine whether HC TLR4 was involved in the activation of MAP kinase signaling, we performed western blotting analysis on liver lysates from WT, Alb-TLR4−/−, selleck compound and global TLR4−/− mice after I/R. Phosphorylation of the MAP kinases, JNK and ERK, were substantially reduced at 3 hours of reperfusion in both Alb-TLR4−/− and global TLR4−/− mice, when
compared to WT mice (Fig. 5). We found no role for HC TLR4 in p38 phosphorylation at this time point; however, p38 phosphorylation occurs very early after reperfusion.23 buy Alectinib This may account for the lack of difference noted at 3 hours of reperfusion. Notably, we did not observe major differences in MAP
kinase activation at either the 1-hour or 6-hour time points. To confirm that these findings were related to the local effects of I/R and not systemic inflammatory mediators, we demonstrated no increased phosphorylation of these proteins in the nonischemic lobes (Fig. 5). Therefore, HC TLR4 seems to be an important mediator of MAP kinase activation after I/R. Our above-described experiments found that HC TLR4 was involved in the activation of JNK signaling in the liver after I/R. JNK is activated click here by exposure of cells to cytokines and environmental stress and has previously been demonstrated to be activated in HCs by both hypoxia and liver I/R.25, 26 Therefore, we exposed WT HCs to hypoxia and rapidly observed increased phosphorylation of JNK and p38, compared to normoxia (Fig. 6A). When TLR4−/− HCs were exposed to hypoxia, the phosphorylation of JNK, c-Jun (the downstream target of JNK),
and p38 was substantially reduced, compared to WT HCs (Fig. 6B). We observed no increase in NF-κB (p65) or ERK phosphorylation with hypoxia exposure (Fig. 6B). To confirm that this response was, in fact, the result of the lack of functional TLR4 and not some other mechanism, HCs from TLR4−/− mice were then transfected with either a control adenoviral vector (AdLacZ) or recombinant adenovirus encoding TLR4 (AdTLR4). TLR4 expression using AdTLR4 was confirmed by western blotting (Fig. 6C). Transfection of TLR4−/− HCs with AdTLR4 restored JNK and p38 phosphorylation in response to hypoxia (Fig. 6D), indicating that this is, in fact, a TLR4-dependent response. Thus, these results demonstrate that HCs respond to hypoxic stress with a rapid activation of JNK and p38 in a TLR4-dependent manner. We next sought to determine whether the release of HMGB1 was mediated by JNK phosphorylation. Therefore, we added the JNK inhibitor (SP600125) to the media of HCs exposed to hypoxia. Phosphorylation of the target of JNK, c-Jun, was inhibited with the addition of the JNK inhibitor (Fig. 7A).