TWEAK/Fn14 system and crescent formation in IgA nephropathy

Abstract

Background: The TNF-like weak inducer of apoptosis (TWEAK) contributes to kidney inflammation producing secretion by renal cells. The present study examined whether the level of TWEAK is associated with histologic findings in patients with IgA nephropathy (IgAN).

Methods: The levels of urinary TWEAK (uTWEAK) from 116 IgAN patients, 50 non-IgA kidney disease patients, and 50 healthy individuals were measured by ELISA. Histological findings of renal biopsy specimens of patients with IgAN were evaluated according to the Oxford classification and histological classification for IgAN in Japan. We investigated the expression of TWEAK/Fn14 in renal tissues of those patients and assessed the effect of TWEAK in glomerular mesangial cells and podocytes.

Results: The levels of uTWEAK in the patients with IgAN and other renal diseases were significantly higher than in the healthy controls (P < 0.001). In the IgAN patients, the levels of uTWEAK correlated significantly with urinary protein excretion and extracapillary proliferation (r = 0.54, P < 0.001 and r = 0.32, P < 0.001, respectively). In a comparison of the levels of uTWEAK at diagnosis with that of follow-up, the levels of uTWEAK in patients with clinical and partial remission decreased significantly. We showed not only increased expression of both TWEAK and Fn14 in IgAN patients with glomerular crescents but also TWEAK-induced cell motility in podocytes.

Conclusions: The relationship between the levels of uTWEAK and clinicopathological findings observed in this study suggests that TWEAK/Fn14 system affects crescent formation and proteinuria in patients with IgAN.

Figure 1

Relationship between the levels of uTWEAK and clinical and histopathologic characteristics in patients with IgAN. The levels uTWEAK at the time of renal biopsy in 116 IgAN patients showed significantly correlations with: (A) urinary protein excretion, r = 0.54, P < 0.001; and (B) extracapillary proliferation, r = 0.32, P < 0.001. (C) There was no significant association between the levels of serum TWEAK (sTWEAK) and uTWEAK (r = 0.05, P = 0.65). (D) Box plots of the levels of uTWEAK with different histological grades in patients with IgAN. The level of uTWEAK in Grade III + IV (n = 12, median: 145.7, IQR 97.5-195.6 pg/mgCr) was significantly higher than those in Grade I (n = 63, median: 78.6, IQR 52.3-115.7 pg/mgCr; **P < 0.001) or Grade II (n = 41, median: 103.7, IQR 70.9–162.5 pg/mgCr; *P < 0.05). The lines in the box plots and the error bars are median and 10–90 percentiles.

Figure 2

The changes in the levels of uTWEAK in patients with IgAN during follow-up. (A) Patients with clinical remission (n = 12): the levels of uTWEAK at the time of biopsy (median: 149.2, IQR 113.8–181.8 pg/mgCr) decreased significantly compared with those of therapy-induced clinical remission (median: 53.8, IQR 33.6–88.5 pg/mgCr; P = 0.003). (B) Patients with partial remission (n = 25): the levels of uTWEAK at the time of biopsy (median: 87.3, IQR 67.1–134.3 pg/mgCr) also decreased compared with those of therapy-induced partial remission (median: 58.4, IQR 42.6-81.3 pg/mgCr; P = 0.009). Wilcoxon signed-rank test.

Figure 3

Expression of TWEAK and Fn14 in renal biopsies from IgAN patients was examine. Immunohistochemistry for both TWEAK (A, B) and Fn14 (D, E) were detected in glomerular crescents (the areas delineated by the squares). In the controls [renal biopsies from patients with minimal change disease (C, F)], there was very slight staining for TWEAK and Fn14 in glomeruli, while intense staining was observed in renal tubular cells. Scale bar = 50 μm.

Figure 4

TWEAK actions on renal cells in vitro . (A) TWEAK modulates mesangial cells proliferation. The proliferation of MMC is significantly increased following stimulation with TWEAK (10–1000 ng/ml) for a 24-hour incubation. Data are expressed as mean ± SD of five independent experiments. **P < 0.001 vs. control; *P < 0.05 vs. control. (B) MCP-1 secretion in response to TWEAK stimulation is dose and time dependent. MCP-1 protein levels in TWEAK stimulated MMC supernatants are shown. Data are expressed as mean ± SD of three independent experiments. *P < 0.05, TWEAK at 10, 100 ng/ml vs. control. (C) TWEAK stimulates podocyte motility as evaluated by wound healing assay. After the scraping of the podocyte cell layer, cells have started to migrate into the wound track. The wound closures were significantly enhanced in the presence of TWEAK (100, 1000 ng/ml) at 24 hours. Compared with the control, TWEAK enhanced directed cell migration in differentiated podocytes. Data are expressed as mean ± SD of five independent experiments. *P < 0.05, TWEAK at 100, 1000 ng/ml vs. control 24 hours. Scale bar = 200 μm.