Uric acid priming in human monocytes is driven by the AKT–PRAS40 autophagy pathway

Abstract

Metabolic triggers are important inducers of the inflammatory processes in gout. Whereas the high serum urate levels observed in patients with gout predispose them to the formation of monosodium urate (MSU) crystals, soluble urate also primes for inflammatory signals in cells responding to gout-related stimuli, but also in other common metabolic diseases. In this study, we investigated the mechanisms through which uric acid selectively lowers human blood monocyte production of the natural inhibitor IL-1 receptor antagonist (IL-1Ra) and shifts production toward the highly inflammatory IL-1β. Monocytes from healthy volunteers were first primed with uric acid for 24 h and then subjected to stimulation with lipopolysaccharide (LPS) in the presence or absence of MSU. Transcriptomic analysis revealed broad inflammatory pathways associated with uric acid priming, with NF-κB and mammalian target of rapamycin (mTOR) signaling strongly increased. Functional validation did not identify NF-κB or AMP-activated protein kinase phosphorylation, but uric acid priming induced phosphorylation of AKT and proline-rich AKT substrate 40 kDa (PRAS 40), which in turn activated mTOR. Subsequently, Western blot for the autophagic structure LC3-I and LC3-II (microtubule-associated protein 1A/1B-light chain 3) fractions, as well as fluorescence microscopy of LC3-GFPoverexpressing HeLa cells, revealed lower autophagic activity in cells exposed to uric acid compared with control conditions. Interestingly, reactive oxygen species production was diminished by uric acid priming. Thus, the Akt-PRAS40 pathway is activated by uric acid, which inhibits autophagy and recapitulates the uric acid-induced proinflammatory cytokine phenotype.uric acid | interleukin-1 | interleukin-1 receptor antagonist | AKT | autophagy

Triggers of acute attacks of gout, does age of gout onset matter? A primary care based cross-sectional study

“…This is consistent with the observation that gout attacks most frequently occur in both summer [22] and winter months [23]. These observations raise the possibility that temporary increases in serum uric acid may trigger gout attacks via a pro-inflammatory effect [24], as does abrupt reductions in the SUA via crystal dissolution. Additionally, activation of the NALP-3 inflammasome or toll like receptor by exposure to food items such as saturated fatty acids or alcohol may also trigger gout attacks [25–28].…”

Urate‐induced immune programming: Consequences for gouty arthritis and hyperuricemia

“…When the same setting was applied to PBMCs from gout patients, it revealed that urate priming enhanced IL‐1β production to a lesser degree in cells from gout patients compared to healthy controls and that these patients had higher basal IL‐1β transcript levels . Monocytes exposed to soluble urate showed enhanced phosphorylation of proline‐rich AKT substrate 40 kD (Pras40) and a decrease in C3 II‐positive autophagosome formation (Figure ) . Pras40 is a substrate of Akt and a component of mammalian target of rapamycin complex 1 (mTORC1).…”

“…However, the redox‐dependent inflammasome activation by urate might be owing to experimental settings and cell origin, without a clear mechanism being established yet. In a setting of urate priming of PBMCs from patients with chronic granulomatous disease (CGD), a genetic disorder characterized by a deficiency in phagocyte NADPH oxidase 2 activity, and inability to efficiently produce reactive oxygen compounds, the pro‐inflammatory shift in cytokine pattern induced by soluble urate could still be reproduced . This argues against the dependence of urate priming on NADPH oxidase–derived ROS; nevertheless, it does not exclude a redox regulation of the NLRP3 via alternative sources of reactive oxygen species (ROS).…”

“…It has also been shown that inhibition of mTOR with rapamycin in macrophages induces autophagy and targets pro‐IL‐1β for degradation, resulting in a decrease of NLRP3 inflammasome activation . As presented in previous section, in urate priming of human monocytes, the phosphorylation of PRAS40 inducing mTOR activation with subsequent decrease in autophagosome formation was described, while the pharmacological inhibition of PI3K recapitulated the effects of soluble urate exposure . Collectively, these data enforce that similar pathways to the ones described in trained macrophages are involved in soluble urate– and crystalline urate–induced inflammatory responses.…”

Fructose metabolism as a common evolutionary pathway of survival associated with climate change, food shortage and droughts

“…One of the mechanisms by which fructose may activate the immune system is via the production of advanced glycation endproducts , but there is also increasing evidence that uric acid, a metabolite generated during fructose metabolism, may also have a critical role. While crystalline uric acid is a well‐known activator of the immune system, leading to stimulation of inflammasome‐dependent IL‐1β secretion , soluble and/or microcrystalline uric acid can also can activate dendritic cells and T cells and monocytes , as well as stimulate inflammasome generation and NF‐κB activation in nonimmune cells .…”