To this end, we exposed CXCR3−/− hepatocytes to CXCL10 or vehicle. Interestingly, CXCL10 also induced this website apoptosis in these cells, as evidenced by increased levels of active caspase-3

and caspase-8 (Fig. 6A,B) as well as by prolonged Akt phosphorylation (Fig. 6C and Supporting Fig. 3B). To exclude a contamination of the recombinant CXCL10 by lipopolysaccharide, we preincubated CXCR3−/− hepatocytes with polymyxin B. In fact, this preparation did not change caspase-3 and Akt activation (Supporting Fig. 3C,D), demonstrating a CXCL10-specific effect on hepatocyte apoptosis. Importantly, in contrast to CXCL10, the related chemokine (CXCL9) did not affect hepatocyte apoptosis, as evidenced by measurement of caspase-3 activity (data not shown). Because CXCR3 is not involved in hepatocyte apoptosis, we became interested whether

see more an alternative receptor could trigger CXCL10-induced apoptosis in hepatocytes. Recently, Schulthess et al.24 identified TLR4 as a receptor for CXCL10 in pancreatic β-cells. First, we confirmed the expression of TLR4 on hepatocytes by PCR analysis (Supporting Fig. 4A). Next, we stimulated TLR4−/− hepatocytes with CXCL10 or vehicle. Indeed, we found no caspase-3 and caspase-8 activation (Fig. 6D,E). These results were confirmed by lack of Akt phosphorylation (Fig. 6F and Supporting Fig. 4B) subsequent to CXCL10 stimulation of these cells. Thus, activation of TLR4 signaling appears essential to trigger CXCL10-induced hepatocyte apoptosis. In light of these in vitro data, we hypothesized that systemic administration of CXCL10 might also induce liver cell apoptosis

in vivo. Indeed, a single injection of CXCL10 led to a low, but increased, number of TUNEL-positive liver cells, compared to vehicle treatment (Fig. 7A). The apoptotic response in CXCL10-treated animals was also reflected by increased caspase-3 and caspase-8 activity within livers of these animals (Fig. 7B and Supporting Fig. 4C). Moreover, treatment with CXCL10 increased AST serum levels (Fig. 7C) and reduced intrahepatic mRNA expression of the antiapoptotic factor, BCL-2 PAK5 (Fig. 7D). Importantly, in this experimental setting, TLR4−/− mice were almost completely protected from the proapoptotic effects of CXCL10. In contrast to WT mice, treatment of TLR4−/− mice with CXCL10 neither resulted in augmented cell death (Fig. 7A) nor in caspase-3 or caspase-8 activation (Fig. 7B and Supporting Fig. 4C). In line with these results, lack of TLR4 also triggered no changes in AST and BCL-2 levels after CXCL10 challenge, compared to their vehicle-treated counterparts (Fig. 7C,D), identifying the CXCL10/TLR4 axis as an important chemokine-based apoptotic pathway within the murine liver in vivo. Here, we provide in vitro and in vivo evidence that CXCL10 exerts proapoptotic effects in hepatocytes through its noncognate receptor (TLR4).