Stem cell factor in a rat model of serum nephrotoxic nephritis

Background: Stem cell factor (SCF) has been implicated in many disease processes characterized by tissue remodelling and fibrosis. The growth factor (SCF) was evaluated in a rat model of nephrotoxic serum nephritis (NTN), characterized by early inflammation followed by later tissue fibrosis.

Methods: NTN was induced in male Wistar Kyoto rats using rabbit anti-rat glomerular basement membrane antibodies. Animals were sacrificed at days 7, 15, 30 and 45 (n = 4-10 per group). Rats' kidneys were immunostained for ED1 as marker of inflammation, CD34, SCF, c-kit, mast cell tryptase and markers of fibrosis; collagens III and IV and alpha-SMA. Changes in SCF protein and mRNA content were evaluated by Western blotting and Northern blotting, respectively.

Results: In the NTN kidney, levels of immunoreactive SCF and SCF receptor (c-kit) were significantly higher in glomerular, tubular and interstitial compartments. Mast cells were barely detectable in NTN and control rat sections. Double immunostaining showed the co-localization of SCF with alpha-SMA and of the SCF receptor with CD34 and ED1 positive cells. Immunostainable SCF protein in each of the 3 compartments, glomerular, tubular and interstitial, showed a positive linear correlation with serum creatinine, proteinuria, glomerulosclerosis score and interstitial fibrosis scores. Using multivariate analysis, immunostainable tubular SCF was a predictor of glomerular sclerosis and immunostainable glomerular SCF predicted tubular atrophy. Increased SCF immunostain was not a consequence of altered transcription as there was a fall in SCF mRNA determined by Northern blotting. Western blotting of NTN kidney homogenates revealed two bands for SCF, a 43-kDa band which decreased, and a 19-kDa band which increased throughout the study.

Conclusion: These results highlight the potential role of SCF and its receptor in the remodelling process of the NTN kidney. Upregulation of SCF may involve a translational mechanism, with the soluble SCF protein KL-S1 (19 kDa) being derived from the transmembrane SCF protein KL-1 (43 kD) by proteolytic cleavage. The immunohistochemical staining of few CD34+ cells in NTN kidneys warrants further evaluation of the nature of these cells in the context of the inflammatory as well as the fibrotic processes.