Amplification of Inflammation by Lubricin Deficiency Implicated in Incident, Erosive Gout Independent of Hyperuricemia.

OBJECTIVE: In gout, hyperuricemia promotes urate crystal deposition, which stimulates the NLRP3 inflammasome and interleukin-1ß (IL-1ß)-mediated arthritis. Incident gout without background hyperuricemia is rarely reported. To identify hyperuricemia-independent mechanisms driving gout incidence and progression, we characterized erosive urate crystalline inflammatory arthritis in a young female patient with normouricemia diagnosed as having sufficient and weighted classification criteria for gout according to the American College of Rheumatology (ACR)/EULAR gout classification criteria (the proband). METHODS: We conducted whole-genome sequencing, quantitative proteomics, whole-blood RNA-sequencing analysis using serum samples from the proband. We used a mouse model of IL-1ß-induced knee synovitis to characterize proband candidate genes, biomarkers, and pathogenic mechanisms of gout. RESULTS: Lubricin level was attenuated in human proband serum and associated with elevated acute-phase reactants and inflammatory whole-blood transcripts and transcriptional pathways. The proband had predicted damaging gene variants of NLRP3 and of inter-α trypsin inhibitor heavy chain 3, an inhibitor of lubricin-degrading cathepsin G. Changes in the proband's serum protein interactome network supported enhanced lubricin degradation, with cathepsin G activity increased relative to its inhibitors, SERPINB6 and thrombospondin 1. Activation of Toll-like receptor 2 (TLR-2) suppressed levels of lubricin mRNA and lubricin release in cultured human synovial fibroblasts (P < 0.01). Lubricin blunted urate crystal precipitation and IL-1ß induction of xanthine oxidase and urate in cultured macrophages (P < 0.001). In lubricin-deficient mice, injection of IL-1ß in knees increased xanthine oxidase-positive synovial resident M1 macrophages (P < 0.05). CONCLUSION: Our findings linked normouricemic erosive gout to attenuated lubricin, with impaired control of cathepsin G activity, compounded by deleterious NLRP3 variants. Lubricin suppressed monosodium urate crystallization and blunted IL-1ß-induced increases in xanthine oxidase and urate in macrophages. The collective activities of articular lubricin that could limit incident and erosive gouty arthritis independently of hyperuricemia are subject to disruption by inflammation, activated cathepsin G, and synovial fibroblast TLR-2 signaling.

Intracardiac administration of neutrophil protease cathepsin G activates noncanonical inflammasome pathway and promotes inflammation and pathological remodeling in non-injured heart.

BACKGROUND: Inflammatory serine proteases (ISPs) play an important role in cardiac repair after injury through hydrolysis of dead cells and extracellular matrix (ECM) debris. Evidence also suggests an important role of ISPs in the coordination of the inflammatory response. However, the effect of ISPs on inflammation is obfuscated by the confounding factors associated with cell death and inflammatory cell infiltration induced after cardiac injury. This study investigated whether neutrophil-derived cathepsin G (Cat.G) influences inflammation and remodeling in the absence of prior cardiac injury and cell death. METHODS AND RESULTS: Intracardiac catheter delivery of Cat.G (1 mg/kg) in rats induced significant left ventricular (LV) dilatation and cardiac contractile dysfunction at day 5, but not at day 2, post-delivery compared to vehicle-treated animals. Cat.G delivery also significantly increased matrix metalloprotease activity and collagen and fibronectin degradation at day 5 compared to vehicle-treated rats and these changes were associated with increased death signaling pathways and myocyte apoptosis. Mechanistic analysis shows that Cat.G-treatment induced potent chemotactic activity in hearts at day 2 and 5 post-delivery, characterized by processing and activation of interleukin (IL)-1ß and IL-18, stimulation of inflammatory signaling pathways and accumulation of myeloid cells when compared to vehicle-treated rats. Cat.G-induced processing of IL-1ß and IL-18 was independent of the canonical NLRP-3 inflammasome pathway and treatment of isolated cardiomyocytes with inhibitors of NLRP-3 or caspase-1 failed to reduce Cat.G-induced cardiomyocyte death. Notably, rats treated with IL-1 receptor antagonist (IL-1Ra) show reduced inflammation and improved cardiac remodeling and function following Cat.G delivery. CONCLUSIONS: Cat.G exerts potent chemoattractant and pro-inflammatory effects in non-stressed or injured heart in part through processing and activation of IL-1 family cytokines, subsequently leading to adverse cardiac remodeling and function. Thus, targeting ISPs could be a novel therapeutic strategy to reduce cardiac inflammation and improve cardiac remodeling and function after injury or stress.