Background & Aims The NACHT, LRR, and pyrin domain–containing protein 3 (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, G_i-protein–coupled receptor 81 (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-interleukin (IL)1β, NLRP3, and caspase-1 (CASP1); release of IL1β; and activation of nuclear factor-κB (NF-κB) and caspase-1. Small interfering RNAs were used to reduce levels of GPR81 and arrestin β-2 (ARRB2), and an NF-κB 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 lipopolysaccharide and D-galactosamine. Acute pancreatitis was induced by administration of lipopolysaccharide and cerulein. Some mice were given intraperitoneal injections of sodium lactate or small interfering RNA against Gpr81. Activation of NF-κB in tissue macrophages was assessed in mice that expressed a reporter transgene. Results In macrophages and monocytes, increasing concentrations of lactate reduced TLR4-mediated induction of Il1B, Nlrp3, and Casp1; activation of NF-κB; release of IL1β; and cleavage of CASP1. GPR81 and ARRB2 physically interacted and were required for these effects. The 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 NF-κB in macrophages of mice, and, when given after 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.

Much of the work on potential anti-Alzheimer's disease drugs has been focused on compounds that reduce the accumulation of neurotoxic amyloid-β peptide in the brain. This has met with little success, in part because agents that block γ-secretase also block processing of Notch, a signalling protein essential for many homeostatic functions, resulting in severe side effects. Now the discovery of a γ-secretase activating protein (GSAP) that selectively controls amyloid-β generation without influencing Notch cleavage suggests a possible new target for anti-Alzheimer's drugs. The anticancer drug imatinib (Gleevec), known to inhibit amyloid-β formation without affecting Notch cleavage, is shown to act via an effect on GSAP. This suggests that GSAP inhibitors that can cross the blood–brain barrier (unlike imatinib) may hold promise for treating Alzheimer's disease. A major hallmark of Alzheimer's disease is the accumulation in the brain of amyloid-β peptide. This is generated by γ-secretase, which is thus of interest as a target for drugs to prevent amyloid-β accumulation. A problem is that γ-secretase has other substrates, including Notch, important in development. Here, a γ-secretase activating protein is identified that increases amyloid-β production without affecting Notch. Thus this protein can serve as an amyloid-β-lowering drug target without affecting other functions of γ-secretase. Accumulation of neurotoxic amyloid-β is a major hallmark of Alzheimer’s disease1. Formation of amyloid-β is catalysed by γ-secretase, a protease with numerous substrates2,3. Little is known about the molecular mechanisms that confer substrate specificity on this potentially promiscuous enzyme. Knowledge of the mechanisms underlying its selectivity is critical for the development of clinically effective γ-secretase inhibitors that can reduce amyloid-β formation without impairing cleavage of other γ-secretase substrates, especially Notch, which is essential for normal biological functions3,4. Here we report the discovery of a novel γ-secretase activating protein (GSAP) that drastically and selectively increases amyloid-β production through a mechanism involving its interactions with both γ-secretase and its substrate, the amyloid precursor protein carboxy-terminal fragment (APP-CTF). GSAP does not interact with Notch, nor does it affect its cleavage. Recombinant GSAP stimulates amyloid-β production in vitro. Reducing GSAP concentrations in cell lines decreases amyloid-β concentrations. Knockdown of GSAP in a mouse model of Alzheimer’s disease reduces levels of amyloid-β and plaque development. GSAP represents a type of γ-secretase regulator that directs enzyme specificity by interacting with a specific substrate. We demonstrate that imatinib, an anticancer drug previously found to inhibit amyloid-β formation without affecting Notch cleavage5, achieves its amyloid-β-lowering effect by preventing GSAP interaction with the γ-secretase substrate, APP-CTF. Thus, GSAP can serve as an amyloid-β-lowering therapeutic target without affecting other key functions of γ-secretase.

Background & Aims Acute pancreatitis is characterized by early activation of intracellular proteases followed by acinar cell death and inflammation. Activation of damage-associated molecular pattern (DAMP) receptors and a cytosolic complex termed the inflammasome initiate forms of inflammation. In this study, we examined whether DAMP-receptors and the inflammasome provide the link between cell death and the initiation of inflammation in pancreatitis. Methods Acute pancreatitis was induced by caerulein stimulation in wild-type mice and mice deficient in components of the inflammasome (apoptosis-associated speck-like protein containing a caspase recruitment domain [ASC], NLRP3, caspase-1), Toll-like receptor 9 (TLR9), or the purinergic receptor P2X₇. Resident and infiltrating immune cell populations and pro–interleukin-1β expression were characterized in control and caerulein-treated adult murine pancreas. TLR9 expression was quantified in pancreatic cell populations. Additionally, wild-type mice were pretreated with a TLR9 antagonist before induction of acute pancreatitis by caerulein or retrograde bile duct infusion of taurolithocholic acid 3-sulfate. Results Caspase-1, ASC, and NLRP3 were required for inflammation in acute pancreatitis. Genetic deletion of Tlr9 reduced pancreatic edema, inflammation, and pro–IL-1β expression in pancreatitis. TLR9 was expressed in resident immune cells of the pancreas, which are predominantly macrophages. Pretreatment with the TLR9 antagonist IRS954 reduced pancreatic edema, inflammatory infiltrate, and apoptosis. Pretreatment with IRS954 reduced pancreatic necrosis and lung inflammation in taurolithocholic acid 3-sulfate–induced acute pancreatitis. Conclusions Components of the inflammasome, ASC, caspase-1, and NLRP3, are required for the development of inflammation in acute pancreatitis. TLR9 and P2X₇ are important DAMP receptors upstream of inflammasome activation, and their antagonism could provide a new therapeutic strategy for treating acute pancreatitis.