Circulating TNF receptors are significant prognostic biomarkers for idiopathic membranous nephropathy

Abstract

Idiopathic membranous nephropathy (iMN) is a common cause of nephrotic syndrome in adults. A biomarker to accurately indicate the severity of iMN and predict long-term prognosis is insufficient. Here, we evaluated the clinical significance of circulating tumor necrosis factor receptors (cTNFRs) as prognostic biomarkers of iMN with nephrotic syndrome. A total of 113 patients with biopsy-proven iMN and 43 healthy volunteers were enrolled in this study. Ninety patients with iMN had nephrotic range proteinuria. Levels of cTNFRs were measured by using serum samples collected at the time of initial diagnosis. Levels of cTNFRs were higher in the patients with nephrotic syndrome than in those with subnephrotic range proteinuria or in the healthy volunteers (P for trend <0.001). Estimated glomerular filtration rate and proteinuria tended to worsen as the cTNFRs levels increased. Having a cTNFR1 level within the highest tertile was a significant risk factor for renal progression after adjustment, in comparison with the other tertiles (hazard ratio [HR], 3.39; 95% confidence interval [95% CI], 1.48-7.78; P = 0.004). The cTNFR2 level within the highest tertile also significantly increased the risk of renal progression (HR, 3.29; 95% CI, 1.43-7.54; P = 0.005). Renal tubular TNFRs expression was associated with cTNFRs level. However, the cTNFRs levels were not associated with autoantibody against phospholipase A2 receptor reactivity/levels or treatment response. This study demonstrated that cTNFRs levels at the time of initial diagnosis could predict renal progression in patients with iMN.

Figure 1. Circulating TNFRs levels in the patients with iMN compared with those in the healthy volunteers.

**P<0.001, *P<0.05.

Figure 2. Proportion of the patients based on severity of pathological findings according to circulating TNFRs levels.

(A) Correlation between the pathological findings and the circulating TNFR1 tertiles. (B) Correlation between the pathological findings and circulating TNFR2 tertiles.

Figure 3. Kaplan-Meier survival curves of renal progression.

(A) The patients with cTNFR1 level within the highest tertile had a significantly faster renal progression compared with those with cTNFR1 level within the other tertiles (P<0.001, log-rank test). (B) The patients with cTNFR2 level within the highest tertile also had a significantly faster renal progression compared with those with cTNFR2 level within the other tertiles (P<0.001, log-rank test). (C) ROC curves for circulating TNFR1 (cTNFR1), circulating TNFR2 (cTNFR2), UPCR, and serum creatinine (sCr) determining renal progression. The AUCs for cTNFR1, cTNFR2, sCr, and UPCR were 0.719 (95% confidence interval [95% CI]: 0.597–0.841), 0.724 (95% CI: 0.599–0.849), and 0.520 (95% CI: 0.375–0.666), 0.607 (95% CI: 0.479–0.735), respectively.

Figure 4. Correlation between the circulating TNFRs levels and autoantibody against phospholipase A₂ receptor (anti-PLA₂R).

(A) The statistically insignificant relationship between Ln cTNFR1 level and anti-PLA₂R. (B) The statistically insignificant relationship between Ln cTNFR2 level and anti-PLA₂R.

Figure 5. Renal expression of TNFRs according to circulating TNFRs.

(A) Immunohistochemical staining of TNFRs expression in paraffin-embedded kidney biopsy sections. TNFR1 is expressed in the glomeruli and tubules in the patients with subnephrotic proteinuria, low cTNFRs levels, and high cTNFRs levels, respectively. TNFR2 is expressed in the tubules but rarely in the glomeruli in the patients with subnephrotic proteinuria, low cTNFRs levels, and high cTNFRs levels, respectively. The intensity of the TNFR2 expression was relatively weaker than that of TNFR1 expression. Original magnification, ×20. (B) Quantitative immunohistochemical analysis of renal TNFRs expression. The quantitative immunohistochemical staining value (QISV, %) was calculated as the integrated optical density divided by the total area occupied by the stained sections in each slide by using computer-assisted quantitative analysis (Qwin3, Leica, Rijswijk, Netherlands). (C) Renal expression of TNFRs in the glomeruli or tubules by performing real-time quantitative reverse transcription-polymerase chain reaction. The Kruskal-Wallis test with Dunn’s method was used. *P<0.05.