Acidic Microenvironment Aggravates the Severity of Hepatic Ischemia/Reperfusion Injury by Modulating M1-Polarization Through Regulating PPAR-γ Signal

Hepatic injury induced by ischemia and reperfusion (HIRI) is a major clinical problem after liver resection or transplantation. The polarization of macrophages plays an important role in regulating the severity of hepatic ischemia/reperfusion injury. Recent evidence had indicated that the ischemia induces an acidic microenvironment by causing increased anaerobic glycolysis and accumulation of lactic acid. We hypothesize that the acidic microenvironment might cause the imbalance of intrahepatic immunity which aggravated HIRI. The hepatic ischemia/reperfusion injury model was established to investigate the effect of the acidic microenvironment to liver injury. Liposomes were used to deplete macrophages in vivo. Macrophages were cultured under low pH conditions to analyze the polarization of macrophages in vitro. Activation of the PPAR-gamma signal was determined by Western blot. PPAR-gamma agonist GW1929 was administrated to functionally test the role of PPAR-gamma in regulating macrophage-mediated effects in the acidic microenvironment during HIRI. We demonstrate that acidic microenvironment aggravated HIRI while NaHCO3 reduced liver injury through neutralizing the acid, besides, liposome abolished the protective ability of NaHCO3 through depleting the macrophages. In vivo and vitro experiment showed that acidic microenvironment markedly promoted M1 polarization but inhibited M2 polarization of macrophage. Furthermore, the mechanistic study proved that the PPAR-gamma signal was suppressed during the polarization of macrophages under pH = 6.5 culture media. The addition of PPAR-gamma agonist GW1929 inhibited M1 polarization under acidic environment and reduced HIRI. Our results indicate that acidic microenvironment is a key regulator in HIRI which promoted M1 polarization of macrophages through regulating PPAR-gamma. Conversely, PPAR-gamma activation reduced liver injury, which provides a novel therapeutic concept to prevent HIRI.

Automated summary

Exacerbated by an acidic microenvironment, HIRI was alleviated by NaHCO3 through neutralizing acid, however, its protection was compromised by liposome-mediated macrophage depletion. The acidic microenvironment promoted M1 polarization while suppressing M2 polarization of macrophages, and PPAR-gamma activation could reduce HIRI by inhibiting M1 polarization under acidic conditions.