Monosodium urate crystals trigger Nrf2- and heme oxygenase-1-dependent inflammation in THP-1 cells

Abstract

Gouty arthritis is an inflammatory disease that is caused by an accumulation of monosodium urate (MSU) crystals in the joints. MSU is capable of activating the nucleotide-binding oligomerization domain-like receptor pyrin domain containing 3 (NLRP3) inflammasome, leading to interleukin-1b (IL-1b) secretion. Reactive oxygen species (ROS) are major mediators of the NLRP3/IL-1b interaction. Although nuclear factor E2-related factor 2 (Nrf2) is recognized as a transcription factor that is involved in the response to oxidative stress, the effect of MSU on Nrf2 and on Nrf2-mediated antioxidant enzymes remains unclear. The treatment of THP-1 monocytes using phorbol 12-myristate 13-acetate (PMA) was shown to initiate inflammatory responses. Here, we showed that THP-1 cells, following treatment with MSU crystals, significantly increased IL-1b release, NLRP3 inflammasome activation and ROS production. MSU also promoted the nuclear translocation of Nrf2 and activated lysosomal destabilization. Moreover, the levels of heme oxygenase-1 (HO-1) in gene and protein expressions were upregulated by MSU. MSU-induced IL-1b secretion and NLRP3 inflammasome activation were inhibited by the knockdown of Nrf2 and via the HO-1 inhibitor zinc (II) protoporphyrin IX (ZnPP). In addition, HO-1 inhibition increased the level of superoxide anion production and the consumption of glutathione. These findings suggest that Nrf2 and HO-1 mediate redox homeostasis and interact with pro-inflammatory factors in MSU-challenged THP-1 cells, thereby providing new insight into how MSU-induced gouty inflammation is mediated by specific mechanisms that are involved in the Nrf2/Ho-1 antioxidant signaling pathway.

Critical role of IL‐1α in IL‐1β‐induced inflammatory responses: cooperation with NF‐κBp65 in transcriptional regulation

“…In the RA pathogenesis, resident macrophages are the main source of IL-1a and IL-1b to RASFs, which then respond to these proinflammatory cytokines by producing IL-6 and IL-8. Extending our findings to test whether knockdown of IL-1a in macrophages influences their ability to produce IL-1a and IL-1b, we stimulated THP-1 macrophages with monosodium urate (MSU), an agent known to trigger the inflammasome pathway to produce IL-1b (19). Western blot analysis results showed that IL-1a siRNA markedly reduced the constitutive as well as the MSU-induced pro-IL-1b expression in THP-1 macrophages (Fig.…”

Nuclear Factor E2-Related Factor-2 Negatively Regulates NLRP3 Inflammasome Activity by Inhibiting Reactive Oxygen Species-Induced NLRP3 Priming

“…It was found that excessive ROS could inhibit NLRP3-mediated caspase-1 activation and that NLRP3 inflammasome activation and IL-1b secretion were suppressed by HO-1 inhibitor zinc (II) protoporphyrin IX (ZnPP) and the knockdown of Nrf2 and with the consumption of GSH-induced superoxide anion production (15). Studies also showed that in SOD1-deficient mice, persistent high ROS levels in macrophages were able to inhibit the activity of caspase-1 and the maturation of IL-1b (31).…”

ABCG2 polymorphisms in gout: insights into disease susceptibility and treatment approaches

“…When autophagy is not effective, p62 accumulates, causing nuclear factor E2-related factor 2 (Nrf2), a transcription factor involved in oxidative stress responses, to be released from its repressor, kelch-like ECH-associated protein 1 (keap-1), and translocate to the nucleus. Previously, Nrf2 has been shown to induce transcription of heme oxygenase-1 and superoxide dismutase, which can in turn also activate the NLRP3 inflammasome 112. Finally, ABCG2 expression has been shown to be upregulated by Nrf2, which promotes cancer stem cell survival 46.…”