Monosodium urate crystals induce lytic macrophage death partially dependent on both pyroptosis and necroptosis.

OBJECTIVES

Macrophage lytic death induced by monosodium urate (MSU) crystals is critical for gout initiation, but its mechanisms remain unclear. MSU activates the NOD-like receptor family pyrin domain-containing protein 3 (NLRP3) inflammasome and canonical pyroptosis; this study aimed to define the cell death pathways mediating MSU crystal-induced macrophage death.

METHOD: We assessed canonical inflammasome activation (apoptosis-associated speck-like protein containing a CARD (ASC) speck, caspase-1, gasdermin D (GSDMD), interleukin-1β (IL-1β)) in macrophages. Using genetically deficient macrophages (GSDMD⁻/⁻, NLRP3⁻/⁻, and caspase-1⁻/⁻) and pharmacological inhibitors, we evaluated lytic death and in vivo inflammation. We also checked caspase-3/gasdermin E (GSDME) pyroptosis, necroptosis, ferroptosis, and ROS.

RESULTS

MSU crystals strongly activated canonical inflammasome signaling, as evidenced by ASC speck formation, caspase-1 activation, GSDMD cleavage, and IL-1β secretion. However, genetic ablation of GSDMD, NLRP3, or caspase-1 did not prevent MSU crystal-induced macrophage lytic death. Similarly, deficiency of GSDMD or NLRP3 did not alleviate inflammation in mouse models of gout. MSU crystals did not trigger caspase-3/GSDME-dependent pyroptosis. While necroptosis contributed to cell death when canonical pyroptosis was blocked, inhibiting necroptosis alone was insufficient to abolish MSU crystal-induced lysis. Combined inhibition of caspases and necroptosis moderately, but significantly, reduced lytic death, whereas additional blockade of ferroptosis or reactive oxygen species (ROS) did not further enhance this protective effect.

CONCLUSIONS

MSU crystal-induced macrophage lytic death represent a complex cell death program that is not exclusively dependent on canonical pyroptosis or necroptosis. These findings uncover a previously unrecognized mechanism of MSU-mediated cytotoxicity and offer novel insights into the molecular pathogenesis of gout. Key Points • Monosodium urate (MSU) crystals trigger macrophage lytic cell death via synergistic canonical pyroptosis and necroptosis, instead of a single cell death pathway. GSDME-dependent pyroptosis, ferroptosis, and ROS are not pivotal drivers of this process. • Combined inhibition of canonical pyroptosis and necroptosis partially reduces MSU crystal-induced macrophage death.