Gout-associated monosodium urate crystal-induced necrosis is independent of NLRP3 activity but can be suppressed by combined inhibitors for multiple signaling pathways

Aug 11, 2021Acta pharmacologica Sinica

Gout crystal-triggered cell death happens without NLRP3 but can be reduced by blocking several signaling pathways

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Abstract

MSU crystals induce necrosis in murine macrophages that is not dependent on NLRP3 inflammasome activation.

Necrosis triggered by MSU crystals was not inhibited by either genetic deletion or pharmacological blockade of the NLRP3 pathway.
Inhibitors targeting ferroptosis and pyroptosis had no effect on MSU crystal-induced necrosis.
Necroptosis pathway inhibitors showed dose-dependent inhibition of necrosis caused by MSU crystals.
A combination of necroptosis inhibitors and a pan-caspase inhibitor enhanced the inhibition of necrosis.
Baicalin, an NLRP3 inhibitor, reduced both inflammasome activation and necrosis in macrophages, and improved MSU crystal-induced peritonitis in mice.

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Monosodium urate (MSU) crystals, the etiological agent of gout, are formed in joints and periarticular tissues due to long-lasting hyperuricemia. Although MSU crystal-triggered NLRP3 inflammasome activation and interleukin 1β (IL-1β) release are known to have key roles in gouty arthritis, recent studies revealed that MSU crystal-induced necrosis also plays a critical role in this process. However, it remains unknown what forms of necrosis have been induced and whether combined cell death inhibitors can block such necrosis. Here, we showed that MSU crystal-induced necrosis in murine macrophages was not dependent on NLRP3 inflammasome activation, as neither genetic deletion nor pharmacological blockade of the NLRP3 pathway inhibited the necrosis. Although many cell death pathways (such as ferroptosis and pyroptosis) inhibitors or reactive oxygen species inhibitors did not have any suppressive effects, necroptosis pathway inhibitors GSK'872 (RIPK3 inhibitor), and GW806742X (MLKL inhibitor) dose-dependently inhibited MSU crystal-induced necrosis. Moreover, a triple combination of GSK'872, GW806742X, and IDN-6556 (pan-caspase inhibitor) displayed enhanced inhibition of the necrosis, which was further fortified by the addition of MCC950 (NLRP3 inhibitor), suggesting that multiple cell death pathways might have been triggered by MSU crystals. Baicalin, a previously identified inhibitor of NLRP3, inhibited MSU crystal-induced inflammasome activation and suppressed the necrosis in macrophages. Besides, baicalin gavage significantly ameliorated MSU crystal-induced peritonitis in mice. Altogether, our data indicate that MSU crystals induce NLRP3-independent necrosis, which can be inhibited by combined inhibitors for multiple signaling pathways, highlighting a new avenue for the treatment of gouty arthritis.

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Gout-associated monosodium urate crystal-induced necrosis is independent of NLRP3 activity but can be suppressed by combined inhibitors for multiple signaling pathways

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