TLR2 ligands attenuate cardiac dysfunction in polymicrobial sepsis via a phosphoinositide 3-kinase-dependent mechanism

Abstract

Myocardial dysfunction is a major consequence of septic shock and contributes to the high mortality of sepsis. In the present study, we examined the effect of Toll-like receptor 2 (TLR2) ligands, peptidoglycan (PGN), and Pam3CSK4 (Pam3) on cardiac function in cecal ligation and puncture (CLP)-induced sepsis in mice. We also investigated whether the phosphoinositide 3-kinase (PI3K)/Akt signaling pathway is involved in the effect of TLR2 ligands on cardiac function in CLP mice. PGN was administered to C57B6/L mice 1 h before the induction of CLP. Sham surgically operated mice served as a control. Cardiac function indexes (rate of change in left ventricular pressure, stroke work, cardiac output, and ejection fraction) were examined by a microconductance pressure catheter. Cardiac function was significantly decreased 6 h after CLP-induced sepsis compared with sham-operated control. In contrast, PGN administration attenuated CLP-induced cardiac dysfunction. Importantly, the therapeutic treatment with Pam3 1 h after CLP also significantly attenuated cardiac dysfunction in CLP mice. However, the beneficial effect of TLR2 ligands on cardiac dysfunction in CLP-mice was abolished in TLR2-deficient mice. PGN administration significantly increased the levels of phospho-Akt and phospho-GSK-3beta in the myocardium compared with the levels in untreated CLP mice. PI3K inhibition abolished the PGN-induced attenuation of cardiac dysfunction in CLP mice. In conclusion, these data demonstrate that the administration of TLR2 ligands, PGN, or Pam3 attenuates cardiac dysfunction in septic mice via a TLR2/PI3K-dependent mechanism. More significantly, Pam3 therapeutic treatment will have a potential clinical relevance.

Fig. 1.

Toll-like receptor 2 (TLR2) ligands, peptidoglycan (PGN), and Pam3CSK4 (Pam3) attenuated cardiac dysfunction in cecal ligation and puncture (CLP)-induced sepsis. A: PGN was administrated to mice by intraperitoneal injection 1 h before the mice were subjected to CLP. Surgically operated mice served as sham-operated control. Fluid resuscitation was immediately performed following surgical operation. Six hours after CLP, left ventricle hemodynamic parameters were measured using a microconductance pressure catheter (Millar Instruments). B: Pam3CSK4 was administered 1 h after CLP. Cardiac function was evaluated by echocardiography before and 6 h after CLP. There were 4–8 mice in each group. *P < 0.05 compared with indicated groups. Sham, sham-operated control. dP/dt_max, maximum rate of change in left ventricular pressure; LVESV, left ventricular end-systolic volume; LVEDV, left ventricular end-diastolic volume; SW, stroke work; CO, cardiac output; EF, ejection fraction; P_ES, end-systolic pressure; P_ED, end-diastolic pressure; V_ES, end-systolic volume; V_ED, end-diastolic volume.

Fig. 2.

TLR2 deficiency abolished PGN and Pam3CSK4-induced attenuation of cardiac dysfunction in CLP-septic mice. A: CLP was induced in TLR2 knockout (TLR2^−/−) and age-matched wild-type (WT) mice. Surgically operated mice served as sham-operated controls. Six hours after CLP, cardiac function was examined with a microconductance pressure catheter. B: Pam3CSK4 was administered to TLR2^−/− and age-matched WT mice 1 h after CLP. Cardiac function was examined by echocardiography before and 6 h after CLP. There were 6 mice in each group. *P < 0.05 compared with indicated groups.

Fig. 3.

PGN administration increased the levels of phospho-Akt (p-Akt) and phospho-GSK-3β (p-GSK-3β) in the myocardium of CLP mice. PGN was administered to mice by intraperitoneal injection 1 h before the mice were subjected to CLP. Surgically operated mice served as sham-operated controls (S). Six hours after CLP, hearts were harvested and the cellular proteins were isolated for measurement of phosphorylated Akt/total Akt (A) and phosphorylated GSK-3β (Ser-9)/total GSK-3β (B) by Western blot analysis with specific antibodies. LY-294002 (LY) was administered 15 min before PGN administration. There were 4–6 mice in each group. *P < 0.05 compared with indicated groups.