Uric Acid Induces High Mobility Group Box1 Protein Release in Monocytes/Macrophages through P38 MAPK, ERK1/2, JNK and AP-1 Activation.

Uric acid, a final metabolite of purine metabolism has gained attention for its pathogenic role in the development of hypertension, vascular disease, renal disease, and cardiovascular events. Recent studies have shown that soluble uric acid induces proliferation as well as synthesis of proinflammatory chemokine, monocyte chemoattractant protein 1 in rat vascular smooth muscle cells. It also stimulates human monolayer cells to produce IL-1B. IL-6 and TNF alpha. However, high mobility group box 1(HMGB1), a non histone DNA binding protein which is recently identified as a proinflammatory cytokine and can be released from cells of the macrophage/monocyte lineage by proinflammatory stimuli or by cells undergoing necrotic cell death pathway. In the present study, we hypothesized that soluble uric acid may stimulates monocytes/macrophages to release HMGB1. Here we demonstrate that crystal and endotoxin free uric acid triggers the release of HMGB1 in a time and dose dependant fashion in mouse macrophage cells, Raw 264.7, human leukemic promonocytes(THP-1 cells) as well as in macrophages but not in fibroblast obtained from synovial fluid of rheumatoid arthritis patients. Moreover, translocation of HMGB1 to the cytoplasm before secreted in the extracellular milieu was significantly detected within 6h of Uric acid exposure. No loss of cell viability was observed in our experimental condition as judged by trypan blue exclusion, MTT reduction and LDH release assays, indicating that HMGB1 release was not due to cell death. Uric acid treatment resulted in the activation of p38 mitogen activated protein kinase(MAPK), c-Jun N terminal kinase(JNK) and extracellular regulatroy kinase (ERK1/2). Inhibition of each of p38 MAPK, ERK1/2 and JNK by using potent and selective inhibitors, SB203580, U0126 and SP60012 respectively, almost completely blocked uric acid-induced HMGB1 release. Furthermore, Curcumin, a potent inhibitor of the transcription factor, activator protein 1(AP-1) strongly suppressed HMGB1 release, indicating that these signaling patways are essential for the induction of HMGB1 release in response to uric acid. In conclusion, our data suggest that uric acid may regulate critical proinflammatory pathways at least in part through its action as a monocyte/macrophage derived potent proinflammatory cytokine, HMGB1 release. This may play pathologic role for hyperuricemia-induced morbidities including arthritis, atherosclerosis, renal disease and so on.