The identification of intracellular signalling pathway through HMGB-1/TLR2 axis on myocardial ischemia/reperfusion injury-induced apoptosis

Myocardial ischemia/reperfusion injury (MIR), termed as the heart attack, is a worldwide health problem. Although the mechanism of MIR has been intensely investigated, it still has some unresolved issues. High Mobility Group Box-1 (HMGB1) is one of the nonhistone proteins. The protein secreted passively from stressed or dying cells is an alarming molecule. When HMGB1 is secreted to the intercellular space, it can bind to the TLR or RAGE receptors. TLR2 and TLR4 are excessively expressed in the heart tissue. TLR2 levels are more increased compare to the TLR4 in dilated heart failure. Although the role of the HMGB-1/TLR4 axis in MIR has been widely investigated, there is a limited study available on the role of the HMGB-1/TLR2/gp96-PP5 axis in MIR-induced apoptosis. The hypothesis was tested in the study as follows: Disulfide form of HMGB1 (DHMGB1) produced via oxidative modification which is induced by MIR can trigger apoptotic cell death through its interaction with TLR2. To test the hypothesis, total four groups was conducted as: a sham-operated group, sham-operated with DHMGB1 treated group, MIR group, MIR with DHMGB1 treated group. After 24-hours reperfusion period, left ventricular and blood pressures and ECG were recorded, then heart tissue was taken. Some protein analyzing and biochemical measurements were measured by using heart tissue. MIR caused heart damage, which mediated the development of arrhythmias and loss of heart function. Administration of DHMGB1 before ischemia resulted in healing in muscle damage and this in turn improved heart function, but failed to attenuation of arrhythmias. While MIR decreased the cytosolic amounts of HMGB1, TLR2 and TLR4, it increased the amount of HMGB1 in plasma. DMIR made an improvement in these values. While MIR decreased the protein expression of TLR2 and TLR4, DMIR also decreased TLR2 while the protein expression of TLR4 was eleveted vs MIR. While MIR decreased the protein expression of gp96, JNK and ERK1/2, DMIR further decreased the protein expression of JNK and increased the value of ERK1/2. The protein expression of PP5 was higher in DMIR vs MIR. In conclusion, the protective effect of DHMGB1 on MIR injury is important for the TLR2/gp96-PP5 pathway.