The Second Hospital affiliated to Zhejiang University, College of Medicine Hangzhou, Zhejiang, China
Disclosure(s): No financial relationships with ineligible companies to disclose
Background/Purpose: While aggregated neutrophil extracellular traps (aggNETs) constitute the primary structural component of tophi, the susceptible population for tophaceous gout remains poorly characterized. We investigated a familial case of early-onset tophaceous gout to elucidate novel mechanisms underlying tophus formation.While aggregated neutrophil extracellular traps (aggNETs) constitute the primary structural component of tophi, the susceptible population for tophaceous gout remains poorly characterized. We investigated a familial case of early-onset tophaceous gout to elucidate novel mechanisms underlying tophus formation. Methods: Whole-exome sequencing was performed on a multigenerational family with early-onset tophaceous gout affecting the proband, his father, and brother. Molecular cloning generated wild-type and mutant macrophage migration inhibitory factor (MIF) expression vectors, with subsequent structural and functional characterization using three-dimensional modeling and circular dichroism spectroscopy. Tophaceous mice administered by MIF or mutant MIF vectors, Mif knockout mice and in vitro models assessed tophus degradation dynamics. Transwell assays with fluorescence labeling evaluated macrophage-mediated phagocytosis and intracellular processing of aggNETs. Results: We identified a pathogenic MIF variant (p.Ile65Met, hereafter referred to as I65M) segregating with disease in the affected family. Structural analysis revealed this mutation induces conformational changes in the PD-D/E(X)K domain. Functional studies demonstrated: (1) significantly reduced nuclease activity of MIF(I65M) compared to wild-type; (2) impaired tophus degradation capacity of MIF(I65M) in both murine models and in vitro systems; (3) preserved macrophage phagocytosis but defective cytoplasmic degradation of aggNETs through a lysosome-independent pathway. Conclusion: This study establishes a novel pathogenesis framework for familial tophaceous gout, demonstrating how MIF mutations lead to aggNETs accumulation through impaired clearance mechanisms. Our findings identify defective aggNETs degradation as a central pathophysiological process, offering new therapeutic targets for tophaceous gout management.
