Macrophage polarization plays a key role in inflammatory response. Various ion channels expressed in macrophages has been documented, but very little is known about their roles in macrophage polarization. We find that knockdown or blockade of Kir2.1 channel significantly inhibits M1 polarization, but promotes M2 polarization. LPS induced M1 polarization is also remarkably suppressed in high extracellular K+ solutions (70 mM K+), and this inhibition is partially abolished by adding Ca2+ in the culture medium. Calcium imaging shows that Ca2+ influx is dependent on the hyperpolarized membrane potential generated by Kir2.1 channel. The upregulation of p-CaMK II, p-ERK1/2, and p-NF-κB proteins in RAW264.7 macrophages stimulated with LPS are significantly reversed by blocking Kir2.1 channel or culturing the cells with 70 mM K+ medium. Furthermore, in vivo study shows that mice treated with Kir2.1 channel blocker are protected from LPS-induced peritonitis. In summary, our data reveal the essential role of Kir2.1 channel in regulating macrophage polarization via Ca2+ / CaMK II / ERK1/2 / NF-κB pathway.

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A water-soluble acacetin prodrug has been synthesized and reported by our group previously. Acetaminophen (APAP) overdose is a leading cause of acute liver injury. We found that subcutaneous injection of acacetin prodrug (5, 10, 20 mg/kg) decreased serum ALT, AST, and ALP, corrected the abnormal MDA and GSH in liver, and improved intrahepatic hemorrhage and destruction of liver structures in APAP (300 mg/kg)-treated mice. Molecular mechanism analysis revealed that the expressions of endoplasmic reticulum (ER) stress markers ATF6, CHOP, and p-PERK, apoptosis-related protein BAX, and cleaved caspase 3 were decreased by acacetin in a dose-dependent manner in vivo and in vitro. Moreover, via the acacetin-upregulated peroxisome-proliferator-activated receptor gamma (PPARγ) of HepG2 cells and liver, the suppressive effect of acacetin on ER stress and apoptosis was abolished by PPARγ inhibitor (GW9662) or PPARγ-siRNA. Molecular docking revealed that acacetin can bind to three active pockets of PPARγ, mainly by hydrogen bond. Our results provide novel evidence that acacetin prodrug exhibits significant protective effect against APAP-induced liver injury by targeting PPARγ, thereby suppressing ER stress and hepatocyte apoptosis. Acacetin prodrug is likely a promising new drug candidate for treating patients with acute liver injury induced by APAP.