Lipopolysaccharide-induced myocardial protection against ischaemia/reperfusion injury is mediated through a PI3K/Akt-dependent mechanism.

AIMS: The ability of lipopolysaccharide (LPS) pre-treatment to induce cardioprotection following ischaemia/reperfusion (I/R) has been well documented; however, the mechanisms have not been fully elucidated. LPS is a Toll-like receptor 4 (TLR4) ligand. Recent evidence indicates that there is cross-talk between the TLR and phosphoinositide 3-kinase/Akt (PI3K/Akt) signalling pathways. We hypothesized that activation of PI3K/Akt signalling plays a critical role in LPS-induced cardioprotection.

METHODS AND RESULTS: To evaluate this hypothesis, we pre-treated mice with LPS 24 h before the hearts were subjected to ischaemia (45 min) and reperfusion (4 h). We examined activation of the PI3K/Akt/GSK-3beta signalling pathway. The effect of PI3K/Akt inhibition on LPS-induced cardioprotection was also evaluated. LPS pre-treatment significantly reduced infarct size (71.25%) compared with the untreated group (9.3+/-1.58 vs. 32.3+/-2.92%, P<0.01). Cardiac myocyte apoptosis and caspase-3 activity in LPS-pre-treated mice were significantly reduced following I/R. LPS pre-treatment significantly increased the levels of phospho-Akt, phospho-GSK-3beta, and heat shock protein 27 in the myocardium. Pharmacological inhibition of PI3K by LY294002 or genetic modulation employing kinase-defective Akt transgenic mice abolished the cardioprotection induced by LPS.

CONCLUSION: These results indicate that LPS-induced cardioprotection in I/R injury is mediated through a PI3K/Akt-dependent mechanism.