The Association between Clonal Hematopoiesis and Gout

Background: Gout is a highly prevalent arthritis associated with debilitating joint pain and functional impairment. It is caused by elevated serum uric acid levels (hyperuricemia) and triggered by precipitation of urate crystals in and around joints. Urate crystals are ingested by macrophages and provoke an innate immune response with subsequent secretion of inflammatory cytokines including interleukin 1 beta (IL-1B). Clonal hematopoiesis of indeterminate potential (CHIP) is a precursor to hematologic malignancies defined by somatic mutations in hematopoietic cells that drive clonal expansion and inflammation. Specifically, CHIP is associated with an increased risk of cardiovascular events and can accelerate atherosclerosis. Mutations in TET2, one of the most commonly mutated genes in CHIP, lead to increased expression of IL-1B through inflammasome activation. Here we investigate the role of CHIP in the development of gout using a combination of human genetic studies and mouse models of CHIP.

Methods: To determine the clinical association between CHIP and gout, we analyzed exome sequencing and clinical data from >50,000 individuals included in the UK Biobank (UKB) and Mass General Brigham Biobank (MGBB). To test whether mutant blood cells can promote gout, Tet2- and Dnmt3a-deficient mouse models were used.

Results: CHIP was more prevalent in individuals with gout than without gout (MGBB: 12.3% vs. 7.9%, P=0.017; UKB: 8.2% vs. 5.8%, P=0.011) and individuals with CHIP were at increased risk of developing gout (UKB: hazard ratio [HR], 1.59; 95% confidence interval [CI], 1.27-2.00; P<0.001). In multivariable analyses, CHIP with variant allele fraction (VAF) ≥10% was associated with higher risk of incident gout compared to no CHIP after adjusting for common gout risk factors (UKB: HR, 1.46; 95% CI, 1.07-2.01; P=0.019). To determine if somatically mutated blood cells directly contribute to the aberrant immune response in gout, we utilized a mouse model of MSU-mediated peritonitis. Compared to control animals, mice with hematopoietic-specific Tet2 deficiency demonstrated markedly increased IL-1B serum levels after injection with MSU (P<0.05). To study gene-specific contributions to joint tissue injury, we established an in vivo model that closely represents the clinical phenotype of gout. Following MSU treatment in situ, Tet2-deficient animals developed exacerbated paw edema compared to wild-type controls (P<0.05). We next generated bone-marrow derived macrophages (BMDM) from Tet2- and Dnmt3a-deficient mice to specifically investigate the MSU-induced cytokine profile in mutant macrophages. Consistent with our in vivo data, IL-1B was the most differentially secreted cytokine after MSU treatment in both Tet2-deficient and Dnmt3a-deficient BMDM compared to wild-type cells (P<0.05). RNA-sequencing confirmed a strong pro-inflammatory gene expression signature of MSU-treated Tet2- and Dnmt3a-deficient macrophages. Finally, we found that pharmacologic inhibition or genetic loss of inflammasome abrogated IL-1B secretion in Tet2- and Dnmt3a-deficient macrophages treated with MSU.

Conclusion: CHIP is associated with an increased risk of having and developing gout in human cohorts and distinct mouse models confirm a direct influence of mutant hematopoietic cells on gout-induced inflammation and arthropathy. CHIP may provide a mechanistic explanation for the heterogeneity in clinical symptoms and inflammation due to gout. Our findings substantiate the biologic rationale for interventional strategies directed at CHIP-associated inflammatory conditions beyond cardiovascular disease and thereby define a path for clinical evaluation of targeted therapies for patients with CHIP-positive gout.