Urine protein from patients with lupus nephritis stimulates transdifferentiation and high expression of collagen in renal tubular cells

Abstract

To investigate the effects of urine protein on the renal tubular-interstitial fibrosis in the patients with lupus nephritis (LN). Protein was isolated and purified from the urine of six patients with primary LN, 1 male and 5 females, aged 27.4, and incubated with renal tubular cells of the line HK-2 for 0, 1, 2, 12, 24, or 48 h respectively. The mRNA expressions of transforming growth factor beta1(TGF-beta1), collagen I (COL I), and alpha-smooth muscle actin (alpha-SMA) in the HK-2 cells were detected by RT-PCR, and the. protein expressions of TGF-beta1, COL I, and alpha-SMA were detected with Western blotting and indirect immunofluorescence. The urine protein from the LN patients dose-and time-dependently increased the mRNA and protein expressions of TGF-beta1, COL I, and alpha-SMA in the HK-2 cells. The TGF-beta1 mRNA level 48 h after incubation was 0.39 +/- 0.03, significantly higher than that at the beginning of incubation (0.27 +/- 0.02, P < 0.01), and the TGF-beta1 protein level 48 h after incubation was 0.37 +/- 0.03, 1.7 times that at the beginning of incubation (0.27 +/- 0.04, P < 0.01). The COL I mRNA level 48 h after incubation was 0.38 +/- 0.02, significantly higher than the baseline level (0.22 +/- 0.03, P < 0.01); and the COL I protein level 48 h after incubation was 0.44 +/- 0.03, significantly higher than the baseline level (0.19 +/- 0.02, P < 0.01). The alpha-SMA mRNA level 48 h after incubation was 0.66 +/- 0.04, significantly higher than the baseline level (0.44 +/- 0.03, P < 0.01), and the alpha-SMA protein level 48 h after incubation was 0.43 +/- 0.02, significantly higher than the baseline level (0.24 +/- 0.03, P < 0.01). Urine protein may play an important role in the renal tubular-interstitial fibrosis by inducing the production of extracellular matrix and phenotype change in HK-2 cells.