Objectives This study was aimed to assess the relationship between serum uric acid (SUA) level and the clinical, pathological phenotype of IgA nephropathy (IgAN), and to determine the role of SUA level in the progression and prognosis of IgAN. Methods A total of 208 patients with IgAN were included in this study, and were classified into the normo-uricemia group and hyperuricemia group according to the SUA level. The clinical data at baseline, IgAN Oxford classification scores (MEST-C scoring system), and other pathological features were collected and further analyzed. All patients were followed up and the prognosis was assessed using Kaplan-Meier survival curves. GraphPad Prism 7.0 and SPSS 23.0 were used for statistical analyses. Results In clinical indicators, patients with hyperuricemia had the significantly higher proportion of males to females, mean arterial pressure, the levels of total cholesterol, triglyceride, Scr, BUN, 24 hour-urine protein, C3, and C4, the lower levels of high-density lipoprotein cholesterol and eGFR than those without (p < 0.05). In terms of pathological characteristics, the tubular atrophy/interstitial fibrosis scores, vascular injury scores, and glomerular sclerosis percentage were significantly higher in patients with hyperuricemia compared with those without (p < 0.01). There was no significant difference in the scores of mesangial hypercellularity, endocapillary hypercellularity, focal segmental glomerulosclerosis, as well as crescents between the two groups (p > 0.05). As for the depositions of immune complexes deposition in IgAN, the hyperuricemia group had less deposition of immunoglobulin G and FRA than the normo-uricemia group (p < 0.05), while the deposition of immunoglobulin A, immunoglobulin M, and complement C3 in the two groups showed no statistical difference. The survival curve suggested that patients in the hyperuricemia group have significantly poorer renal outcome than those in the normo-uricemia group (p = 0.0147). Results also revealed that the SUA level is a valuable predictor of renal outcome in patients with IgAN. The optimal cutoff value was 361.1 µmol/L (AUC = 0.76 ± 0.08167) and 614 µmol/L (AUC = 0.5728 ± 0.2029) for female and male, respectively. Conclusions The level of SUA is associated with renal function level and pathological severity of IgAN, and maybe a prognostic indicator of IgAN.
Protein tyrosine (Tyr) nitration, the covalent addition of a nitro group (•NO2) to Tyr residues, is emerging as a candidate mechanism of endothelial dysfunction. Previous studies have shown that Tyr nitration is primarily induced by nitrosative stress, a process characterized by the production of reactive nitrogen species, especially peroxynitrite anion (ONOO−), which is considered a secondary product of NO in the presence of superoxide radicals (O2•−). However, the impact of nitrosative stress–induced Tyr nitration on endothelial dysfunction has not been thoroughly elucidated to date. We developed an endothelial dysfunction model, a process called “endothelial‐to‐mesenchymal transition (EndMT),” and evaluated the production of NO, O2•−, and protein nitration during EndMT. The results showed that TGF‐β1 stimulation induced EndMT and elevated endothelial NO and O2•− production as well as nitration of the catalytic subunit of protein phosphatase (PP)2A. Mass spectrometry analysis showed that Tyr265 was the nitration site in the catalytic subunit of protein phosphatase (PP)2A, and this Tyr nitration increased PP2A activity and disrupted endothelial integrity. To devise an endothelial‐targeted anti‐PP2Ac nitration strategy, a mimic peptide, tyrosine 265 wild type (Y265WT), conjugated with the cell‐penetrating peptide HIV‐1 TAT protein (TAT) was synthesized. PP2Ac nitration and PP2A activity were significantly inhibited by pretreatment with TAT‐265WT, and the integrity of endothelial cells was maintained. Furthermore, injection of TAT‐265WT attenuated renal nitration formation and caused anticapillary rarefaction in a unilateral urethral obstructive nephropathy model. Taken together, these results offer preclinical proof of concept for TAT‐265WT as a tractable agent to protect against nitrosative stress‐induced endothelial dysfunction in renal microvessels.—Deng, Y., Cai, Y., Liu, L., Lin, X., Lu, P., Guo, Y., Han, M., Xu, G. Blocking Tyr265 nitration of protein phosphatase 2A attenuates nitrosative stress–induced endothelial dysfunction in renal microvessels. FASEB J. 33, 3718–3730 (2019). http://www.fasebj.org
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