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-GFP-overexpressing 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.