VNN1 promoted the secretion of transforming growth factor beta of renal tubular cell and aggravated renal fibrosis in obstructive renal injury

Objective To elucidate the role and related mechanisms of VNN1 in the process of renal interstitial fibrosis after obstructive renal injury. Methods Balb/c wild-type and VNN1 gene knockout male mice were selected for sham operation and operation groups respectively. Urine and kidney tissue specimens from obstructed renal pelvis were collected at Day 0 and 14 post-operation and the urinary level of transforming growth factor beta(TGF-β) was detected. The expression level of VNN1 in renal tissue was measured by immunohistochemistry. Renal tissue is improved by periodic acid-Schiff(PAS) stain to determine the severity of renalinjury. Masson stain and immunohistochemistry were utilized for detecting the expression of α-smooth muscle actin(α-SMA) in renal tissue to determine the severity of renal tissue fibrosis. Primary renal tubular epithelial cells were harvested from wild-type and VNN1 knockout mice, propagated to the second generation and stimulated with angiotensin forsimulate anobstructive kidney injury model in vivo. Both cells and supernatant were collected for detecting the level of VNN1 protein and supernatant TGF-β level. Results At Day 14 after obstructive renal injury, PAS stain in operation group hinted at overt renal tissue damageand immunohistochemistry indicated a significant up-regulation of VNN1 in renal tissue. Masson stain of renaltissue was further improved and the level of α-SMA was detected by immunohistochemistry. The level of interstitial fibrosis worsened morein wild-type mice than that of VNN1 knockout counterparts while the level of α-SMA spiked greatly. Further testing the urinary level of TGF-β on the obstructive side indicated that the urinary level of TGF-β on the obstructive side of VNN1 gene knockout mice declined obviously. It was further confirmed through cell experiments that after a stimulation of angiotensin, there was a marked up-regulation of VNN1 protein in wild-type murine renal tubular cells and the supernatant level of TGF-β was significantly higher in wild-type murine renal tubular cells than that of VNN1 gene knockout counterparts. Conclusion VNN1 can promote the secretion of TGF-β and aggravate fibrosis in renal tubular epithelial cells after obstructive injury.