Janus kinase/signal transducers and activators of transcription (JAK/STAT) signaling is one of the major pathways for
cytokine signal transduction. However, the role of the JAK/STAT pathway in liver
ischemia/reperfusion is not clear. This study focuses on Janus kinase-2 (JAK2), which functions upstream of
signal transducer and activator of transcription 1 (STAT1) in JAK/STAT, and its role in the mechanism of liver
ischemia/reperfusion injury (IRI). Partial
warm ischemia was produced in the hepatic lobes of C57BL/6 mice for 90 minutes, and this was followed by 6 hours of reperfusion. Mice were treated with a JAK2 inhibitor (
tyrphostin AG490; 40 mg/kg intraperitoneally) or vehicle 60 minutes prior to ischemic insult. JAK2 blockade resulted in a significant reduction of hepatocyte apoptosis and liver injury. Macrophage and neutrophil infiltration, as assessed by immunohistochemistry, was markedly decreased in AG490-treated livers in comparison with controls. The expression of pro-inflammatory
cytokines [
tumor necrosis factor alpha,
interleukin 6 (IL-6), and IL-1beta] and
chemokines [
chemokine (C-X-C motif) ligand 10 (CXCL-10) and CXCL-2] was also significantly reduced in the AG490-treated group in comparison with controls. AG490-treated livers showed fewer cells positive for
terminal deoxynucleotidyl transferase-mediated
deoxyuridine triphosphate nick-end labeling and reduced cleaved
caspase-3 protein expression in parallel with increased
B-cell lymphoma extra large expression. We employed
AG490 (75 mM) in primary bone marrow-derived macrophage (BMM) and
hepatoma cell (CRL1830) cultures, which were both stimulated with
lipopolysaccharide (LPS; 10 ng/mL). In BMM cultures,
AG490 depressed otherwise LPS-induced pro-inflammatory gene expression programs (IL-6, IL-12p40, IL-1beta, CXCL-10, and
inducible nitric oxide synthase). In
hepatoma cells,
AG490 reduced cleaved
caspase-3 expression. Moreover, JAK2 blockade inhibited STAT1 and STAT3 phosphorylation. This is the first report documenting that JAK2 signaling is essential in the pathophysiology of liver IRI, as its selective blockage ameliorated the disease process and protected livers from
inflammation and apoptosis.