HO-1–STAT3 axis in mouse liver ischemia/reperfusion injury: Regulation of TLR4 innate responses through PI3K/PTEN signaling

Background & Aims

Signal transducer and activator of transcription 3 (STAT3), a key mediator of anti-inflammatory cytokine signaling, is essential for heme oxygenase-1 (HO-1)-induced cytoprotection. The phosphoinositide 3-kinase (PI3K)/phosphatase and tensin homolog delete on chromosome 10 (PTEN) pathways regulate diverse innate immune responses. This study was designed to investigate the role of STAT3 in the regulation of PI3K/PTEN cascade after HO-1 induction in a mouse model of innate immune-dominated liver ischemia/reperfusion injury (IRI).

Methods

Partial warm ischemia was produced in the left and middle hepatic lobes of C57BL/6 mice for 90min, followed by 6h of reperfusion.

Results

Mice subjected to Ad-HO-1 transfer were resistant to liver IRI, and this cytoprotective effect correlated with increased intrahepatic PI3K/Akt and diminished PTEN expression. In contrast, mice undergoing adjunctive Ad-HO-1 treatment and STAT3 knockdown (siRNA) remained susceptible to IR-mediated local inflammatory response and hepatocellular damage. Consistent with decreased cell apoptosis and inhibited TLR4 expression after PI3K/Akt activation, treatment with specific PI3k inhibitor increased local inflammation and recreated liver IRI despite Ad-HO-1 gene transfer. Parallel in vitro studies with bone marrow derived-macrophages have confirmed that HO-1–STAT3 axis-induced PI3K/Akt negatively regulated PTEN expression in TLR4-dependent fashion.

Conclusions

These findings underscore the role of HO-1 induced STAT3 in modulating PI3K/PTEN in liver IRI cascade. Activating PI3K/Akt provides negative feedback mechanism for TLR4-driven inflammation. Identifying molecular pathways of STAT3 modulation in the innate immune system provides the rationale for novel therapeutic approaches for the management of liver inflammation and IRI in transplant patients.

Abbreviations: Ad-HO-1, recombinant adenovirus encoding hemeoxygenase-1, Ad-β-gal, recombinant adenovirus β-galactosidase reporter gene, BMMs, bone marrow derived-macrophages, IRI, ischemia/reperfusion injury, MPO, myeloperoxidase, PI3K, phosphoinositide 3-kinase, PTEN, phosphatase and tensin homolog delete on chromosome 10, sGPT, serum glutamic pyruvic transaminase, siRNA, small interfering RNA, SEC, sinusoidal endothelial cells, TLR4, Toll-like receptor 4, TUNEL, terminal deoxyribonucleotidyl transferase (TdT)-mediated dUTP-digoxigenin Nick End Labeling

Keywords: Liver ischemia/reperfusion injury, Innate immunity, Heme oxygenase-1, STAT3, Transplantation