title: Serine protease inhibitor-6 inhibits granzyme B-mediated injury of renal tubular cells and promotes renal allograft survival.
abstract: 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.
  
  
  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-2) into nephrectomized recipients (H-2). 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).
  
  
  CONCLUSIONS
  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.
authors.affiliation: 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.
authors.forename: Arthur
authors.initials: A
authors.lastname: Lau
authors.forename: Karim
authors.initials: K
authors.lastname: Khan
authors.forename: Alex
authors.initials: A
authors.lastname: Pavlosky
authors.forename: Ziqin
authors.initials: Z
authors.lastname: Yin
authors.forename: Xuyan
authors.initials: X
authors.lastname: Huang
authors.forename: Aaron
authors.initials: A
authors.lastname: Haig
authors.forename: Weihua
authors.initials: W
authors.lastname: Liu
authors.forename: Bhagi
authors.initials: B
authors.lastname: Singh
authors.forename: Zhu-Xu
authors.initials: ZX
authors.lastname: Zhang
authors.forename: Anthony M
authors.initials: AM
authors.lastname: Jevnikar
mesh_terms: D064591:Allografts; D000818:Animals; D002478:Cells, Cultured; D004847:Epithelial Cells / Q000473:pathology; D006084:Graft Rejection; D006085:Graft Survival; D053804:Granzymes / Q000037:antagonists & inhibitors* / Q000502:physiology; D016030:Kidney Transplantation; D007684:Kidney Tubules / Q000473:pathology*; D008297:Male; D008565:Membrane Proteins / Q000502:physiology*; D051379:Mice; D008807:Mice, Inbred BALB C; D015843:Serpins / Q000502:physiology*
chemical_list: D008565:Membrane Proteins; D015843:Serpins; D053804:Granzymes; C509215:Gzmb protein, rat; C106610:Serpinb9 protein, mouse