Uric acid is a danger signal activating NALP3 inflammasome in lung injury inflammation and fibrosis.

RATIONALE: Lung injury leads to pulmonary inflammation and fibrosis through myeloid differentiation primary response gene 88 (MyD88) and the IL-1 receptor 1 (IL-1R1) signaling pathway. The molecular mechanisms by which lung injury triggers IL-1beta production, inflammation, and fibrosis remain poorly understood. OBJECTIVES: To determine if lung injury depends on the NALP3 inflammasome and if bleomycin (BLM)-induced lung injury triggers local production of uric acid, thereby activating the NALP3 inflammasome in the lung. Methods: Inflammation upon BLM administration was evaluated in vivo in inflammasome-deficient mice. Pulmonary uric acid accumulation, inflammation, and fibrosis were analyzed in mice treated with the inhibitor of uric acid synthesis or with uricase, which degrades uric acid. MEASUREMENTS AND MAIN RESULTS: Lung injury depends on the NALP3 inflammasome, which is triggered by uric acid locally produced in the lung upon BLM-induced DNA damage and degradation. Reduction of uric acid levels using the inhibitor of uric acid synthesis allopurinol or uricase leads to a decrease in BLM-induced IL-1beta production, lung inflammation, repair, and fibrosis. Local administration of exogenous uric acid crystals recapitulates lung inflammation and repair, which depend on the NALP3 inflammasome, MyD88, and IL-1R1 pathways and Toll-like receptor (TLR)2 and TLR4 for optimal inflammation but are independent of the IL-18 receptor. CONCLUSIONS: Uric acid released from injured cells constitutes a major endogenous danger signal that activates the NALP3 inflammasome, leading to IL-1beta production. Reducing uric acid tissue levels represents a novel therapeutic approach to control IL-1beta production and chronic inflammatory lung pathology.

NEUROPATHOPHYSIOLOGICAL MECHANISMS IN GLUTARIC ACIDURIA TYPE I: 3-HYDROXYGLUTARIC ACID LEADS TO AMMONIA INCREASE AND NON-APOPTOTIC CELL DEATH

A 3D in vitro model of rat organotypic brain cell cultures in aggregates was used to investigate neurotoxicity mechanisms in glutaric aciduria type I (GA-I). 1 mM glutarate (GA) or 3-hydroxyglutarate (3OHGA) were repeatedly added to the culture media at two different time points. In cultures treated with 3OHGA, we observed an increase in lactate in the medium, pointing to a possible inhibition of Krebs cycle and respiratory chain. We further observed that 3OHGA and to a lesser extend GA induced an increase in ammonia production with concomitant decrease of glutamine concentrations, which may suggest an inhibition of the astrocytic enzyme glutamine synthetase. These previously unreported findings may uncover a pathogenic mechanism in this disease which has deleterious effects on early stages of brain development. By immunohistochemistry we showed that 3OHGA increased non-apoptotic cell death. On the cellular level, 3OHGA and to a lesser extend GA led to cell swelling and loss of astrocytic fibers whereas a loss of oligodendrocytes was only observed for 3OHGA. We conclude that 3OHGAwas the most toxic metabolite in our model for GA-I. 3OHGA induced deleterious effects on glial cells, an increase of ammonia production, and resulted in accentuated cell death of non-apoptotic origin.

Serum uric acid and adiposity: deciphering causality using a bidirectional Mendelian randomization approach.

Although the relationship between serum uric acid (SUA) and adiposity is well established, the direction of the causality is still unclear in the presence of conflicting evidences. We used a bidirectional Mendelian randomization approach to explore the nature and direction of causality between SUA and adiposity in a population-based study of Caucasians aged 35 to 75 years. We used, as instrumental variables, rs6855911 within the SUA gene SLC2A9 in one direction, and combinations of SNPs within the adiposity genes FTO, MC4R and TMEM18 in the other direction. Adiposity markers included weight, body mass index, waist circumference and fat mass. We applied a two-stage least squares regression: a regression of SUA/adiposity markers on our instruments in the first stage and a regression of the response of interest on the fitted values from the first stage regression in the second stage. SUA explained by the SLC2A9 instrument was not associated to fat mass (regression coefficient [95% confidence interval]: 0.05 [-0.10, 0.19] for fat mass) contrasting with the ordinary least square estimate (0.37 [0.34, 0.40]). By contrast, fat mass explained by genetic variants of the FTO, MC4R and TMEM18 genes was positively and significantly associated to SUA (0.31 [0.01, 0.62]), similar to the ordinary least square estimate (0.27 [0.25, 0.29]). Results were similar for the other adiposity markers. Using a bidirectional Mendelian randomization approach in adult Caucasians, our findings suggest that elevated SUA is a consequence rather than a cause of adiposity.

Single amino acid charge switch defines clinically distinct proline-serine-threonine phosphatase-interacting protein 1 (PSTPIP1)-associated inflammatory diseases.

BACKGROUND: Hyperzincemia and hypercalprotectinemia (Hz/Hc) is a distinct autoinflammatory entity involving extremely high serum concentrations of the proinflammatory alarmin myeloid-related protein (MRP) 8/14 (S100A8/S100A9 and calprotectin). OBJECTIVE: We sought to characterize the genetic cause and clinical spectrum of Hz/Hc. METHODS: Proline-serine-threonine phosphatase-interacting protein 1 (PSTPIP1) gene sequencing was performed in 14 patients with Hz/Hc, and their clinical phenotype was compared with that of 11 patients with pyogenic arthritis, pyoderma gangrenosum, and acne (PAPA) syndrome. PSTPIP1-pyrin interactions were analyzed by means of immunoprecipitation and Western blotting. A structural model of the PSTPIP1 dimer was generated. Cytokine profiles were analyzed by using the multiplex immunoassay, and MRP8/14 serum concentrations were analyzed by using an ELISA. RESULTS: Thirteen patients were heterozygous for a missense mutation in the PSTPIP1 gene, resulting in a p.E250K mutation, and 1 carried a mutation resulting in p.E257K. Both mutations substantially alter the electrostatic potential of the PSTPIP1 dimer model in a region critical for protein-protein interaction. Patients with Hz/Hc have extremely high MRP8/14 concentrations (2045 ± 1300 μg/mL) compared with those with PAPA syndrome (116 ± 74 μg/mL) and have a distinct clinical phenotype. A specific cytokine profile is associated with Hz/Hc. Hz/Hc mutations altered protein binding of PSTPIP1, increasing interaction with pyrin through phosphorylation of PSTPIP1. CONCLUSION: Mutations resulting in charge reversal in the y-domain of PSTPIP1 (E→K) and increased interaction with pyrin cause a distinct autoinflammatory disorder defined by clinical and biochemical features not found in patients with PAPA syndrome, indicating a unique genotype-phenotype correlation for mutations in the PSTPIP1 gene. This is the first inborn autoinflammatory syndrome in which inflammation is driven by uncontrolled release of members of the alarmin family.