TGF-β is elevated in hyperuricemic individuals and mediates urate-induced hyperinflammatory phenotype in human mononuclear cells

Abstract

Background Soluble urate leads to a pro-inflammatory phenotype in human monocytes characterized by increased production of IL-1β and downregulation of IL-1 receptor antagonist, the mechanism of which remains to be fully elucidated. Previous transcriptomic data identified differential expression of genes in the transforming growth factor (TGF)-β pathway in monocytes exposed to urate in vitro. In this study, we explore the role of TGF-β in urate-induced hyperinflammation in peripheral blood mononuclear cells (PBMCs). Methods TGF-β mRNA in unstimulated PBMCs and protein levels in plasma were measured in individuals with normouricemia, hyperuricemia and gout. For in vitro validation, PBMCs of healthy volunteers were isolated and treated with a dose ranging concentration of urate for assessment of mRNA and pSMAD2. Urate and TGF-β priming experiments were performed with three inhibitors of TGF-β signalling: SB-505124, 5Z-7-oxozeaenol and a blocking antibody against TGF-β receptor II. Results TGF-β mRNA levels were elevated in gout patients compared to healthy controls. TGF-β-LAP levels in serum were significantly higher in individuals with hyperuricemia compared to controls. In both cases, TGF-β correlated positively to serum urate levels. In vitro, urate exposure of PBMCs did not directly induce TGF-β but did enhance SMAD2 phosphorylation. The urate-induced pro-inflammatory phenotype of monocytes was partly reversed by blocking TGF-β. Conclusions TGF-β is elevated in individuals with hyperuricemia and correlated to serum urate concentrations. In addition, the urate-induced pro-inflammatory phenotype in human monocytes is mediated by TGF-β signalling. Future studies are warranted to explore the intracellular pathways involved and to assess the clinical significance of urate-TGF-β relation.

Hyperuricemia Remodels the Serum Proteome Toward a Higher Inflammatory State

“…80 In a previous report investigating TGF-b in urate-induced inflammatory priming, we were not able to observe major differences in TGF-b or VEGFA levels during gout flares compared to inter-critical patients with gout. 79 Possibly due to the different number of samples, in the present study, we were able to observe significant differences for VEGFA and nominally significant increase in TGF-b-LAP. This is in line with other studies showing TGF-b increase over the course of gout flares and potential involvement in the resolution of inflammation.…”

“…The interstitial collagenase MMP-1 has also been shown to be produced by synovial fibroblasts in response to MSU crystals. 78 Previously, TGF-b has been shown to have context-dependent pro-inflammatory and anti-inflammatory roles, mediating urate-induced inflammation, 79 as well as limiting acute gouty inflammation when added exogenously in a synovium-like air pouch mouse model. 80 In a previous report investigating TGF-b in urate-induced inflammatory priming, we were not able to observe major differences in TGF-b or VEGFA levels during gout flares compared to inter-critical patients with gout.…”

Hyperuricemia remodels the serum proteome toward a higher inflammatory state

“… 80 In a previous report investigating TGF-β in urate-induced inflammatory priming, we were not able to observe major differences in TGF-β or VEGFA levels during gout flares compared to inter-critical patients with gout. 79 Possibly due to the different number of samples, in the present study, we were able to observe significant differences for VEGFA and nominally significant increase in TGF-β-LAP. This is in line with other studies showing TGF-β increase over the course of gout flares and potential involvement in the resolution of inflammation.…”

“…The interstitial collagenase MMP-1 has also been shown to be produced by synovial fibroblasts in response to MSU crystals. 78 Previously, TGF-β has been shown to have context-dependent pro-inflammatory and anti-inflammatory roles, mediating urate-induced inflammation, 79 as well as limiting acute gouty inflammation when added exogenously in a synovium-like air pouch mouse model. 80 In a previous report investigating TGF-β in urate-induced inflammatory priming, we were not able to observe major differences in TGF-β or VEGFA levels during gout flares compared to inter-critical patients with gout.…”