Lactate Reduces Liver and Pancreatic Injury in Toll-Like Receptor– and Inflammasome-Mediated Inflammation via GPR81-Mediated Suppression of Innate Immunity

Abstract

BACKGROUND & AIMS The NLRP3 inflammasome induces inflammation in response to organ injury, but little is known about its regulation. Toll-like receptors (TLRs) provide the first signal required for activation of the inflammasome and stimulate aerobic glycolysis to generate lactate. We examined whether lactate and the lactate receptor, GPR81, regulate TLR induction of signal 1 and limit inflammasome activation and organ injury. METHODS Primary mouse macrophages and human monocytes were incubated with TLR4 agonists and lactate and assayed for levels of pro-IL1β, NLRP3, and CASP1; release of IL1β; and activation of NFκB and caspase 1. Small interfering (si)RNAs were used to reduce levels of GPR81andARRB2, and an NFκB luciferase reporter transgene was transfected in RAW 264.7 cells. Cell lysates were analyzed by immunoprecipitation with an antibody against GPR81. Acute hepatitis was induced in C56BL/6N mice by administration of lipopolysaccharaide (LPS) and D-galactosamine. Acute pancreatitis was induced by administration of LPS and caerulein. Some mice were given intraperitoneal injections of sodium lactate or siRNA against Gpr81. Activation of NFκB in tissue macrophages was assessed in mice that express a reporter transgene. RESULTS In macrophages and monocytes, increasing concentrations of lactate reduced TLR4-mediated induction of Il1B, Nlrp3, and Casp1; activation of NFκB; release of IL1β; and cleavage of CASP1. GPR81 and ARRB2 physically interacted and were required for these effects. Administration of lactate reduced inflammation and organ injury in mice with immune hepatitis; this reduction required Gpr81 dependence in vivo. Lactate also prevented activation of NFκB in macrophages of mice, and when given following injury, reduced the severity of acute pancreatitis and acute liver injury. CONCLUSIONS Lactate negatively regulates TLR induction of the NLRP3 inflammasome and production of IL1β, via ARRB2 and GPR81. Lactate could be a promising immunomodulatory therapy for patients with acute organ injury.

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