Background: Protease inhibitor 9 (PI-9) is an intracellular serpin that specifically inhibits granzyme B, a cytotoxic serine protease found in the cytosolic granules of cytotoxic T lymphocytes and natural killer cells. Enhanced cortical expression of PI-9 has been observed in kidney allografts with subclinical rejection, suggesting that the tubular epithelial cell (TEC) expression of this protein may have a protective role and attenuate overt allograft rejection.
Methods and Results: We demonstrate that TEC express SPI-6 protein, the murine homolog of PI-9, basally with a modest increase after cytokine exposure. Tubular epithelial cell expression of SPI-6 blocks granzyme B–mediated death because TEC from SPI-6 null kidneys have increased susceptibility to cytotoxic CD8+ cells in vitro. The role of SPI-6 was tested in a mouse kidney transplant model using SPI-6 null or wild type donor kidneys (H-2b) into nephrectomized recipients (H-2d). SPI-6 null kidney recipients demonstrated reduced renal function at day 8 after transplantation compared to controls (creatinine, 113±23 vs. 28±3 μmol/L; n=5; P<0.01), consistent with observed tubular injury and extensive mononuclear cell infiltration. Loss of donor kidney SPI-6 shortened graft survival time (20±19 vs. 66±33 days; n=8–10; P<0.001).
Conclusion: Our data show for the first time that resistance of kidney TEC to cytotoxic T-cell granzyme B–induced death in vitro and in vivo is mediated by the expression of SPI-6. We suggest that SPI-6 is an important endogenous mechanism to prevent rejection injury from perforin or granzyme B effectors and enhanced PI-9 or SPI-6 expressions by TEC may provide protection from diverse forms of inflammatory kidney injury and promote long-term allograft survival.
1 Matthew Mailing Centre for Translational Transplantation Studies, London Health Sciences Centre.
2 Department of Medicine, Western University, London, Ontario, Canada.
3 Department of Pathology, Western University, London, Ontario, Canada.
4 Department of Microbiology and Immunology, Western University, London, Ontario, Canada.
5 Address correspondence to: Zhu-Xu Zhang and Anthony M. Jevnikar, Department of Medicine, University of Western Ontario, B4-231, 339 Windermere Road, London, Ontario, Canada N6A 5A5.
This study was supported by the Canadian Institutes of Health Research (XTW-90932, MOP-111180, MOP-115048), the Kidney Foundation of Canada (A.M.J., Z.X.Z.), and the Program of Experimental Medicine (POEM) at Western University, London, Ontario, Canada.
The authors declare no conflicts of interest.
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Z.-X.Z. and A.M.J. have equal contribution.
A.L. participated in research design, writing of the article, performance of the experiments, and data analysis. K.K. participated in research design and performance of the experiments. A.P. participated in data analysis. Z.Y., X.H., and W.L. participated in the performance of the experiments. A.H. participated in data analysis. B.S. participated in research design and contribution of reagents and equipment. Z.-X.Z. participated in research design, writing of the article, and data analysis. A.M.J. participated in research design, writing of the article, data analysis, and contribution of reagents and equipment.
Received 28 January 2014. Revision requested 20 February 2014.
Accepted 8 April 2014.