Activation of mitochondrial apoptotic pathways in human renal allografts after ischemiareperfusion injury

Abstract

Background: Ischemia-reperfusion injury in cadaveric (CAD) kidney allografts is associated with tubular cell injury, delayed graft function, and an increased incidence of acute and chronic rejection. We tested the hypothesis that activation of specific apoptotic pathways represents a mechanism for tubular cell death after CAD kidney transplantation.

Methods: Serial tissue sections from paraffin-embedded needle biopsy specimens obtained at approximately 1 hr of reperfusion after transplantation of 13 CAD and 12 living-related donor (LRD) renal allografts were examined by using the terminal deoxynucleotide transferase-mediated dUTP nick-end labeling assay to detect apoptosis and by immunohistochemistry for expression of key pro-apoptotic molecules (Bax, Bak, tumor necrosis factor receptor [TNFR]-1, Fas, and cytochrome c).

Results: Apoptosis was detected primarily in tubular cells, with a mean+/-standard deviation of 6.8+/-2.2 apoptotic cells per 100 cells examined in CAD renal allografts compared with 1.8+/-2.7 cells per 100 in LRD (P<0.001) renal allografts. There was a significant correlation between apoptosis rate and cold ischemia time in CAD (r=0.86, P<0.001) renal allografts. Bax was expressed in 100% of CAD versus 17% of LRD renal allografts (P<0.001), Bak in 92% of CAD versus 17% of LRD renal allografts (P<0.001), and TNFR-1 in 100% of CAD versus 58% of LRD renal allografts (P<0.05). Fas was expressed in only a small number of samples (23% of CAD and 17% of LRD renal allografts, P=not significant). Bax and Bak were expressed predominantly in apoptotic cells. Cytochrome c was detected as a mitochondrial pattern in LRD renal allografts, but in a diffuse cytosolic distribution in CAD renal allografts.

Conclusions: Ischemia-reperfusion injury in CAD kidney transplants is associated with a duration-dependent increase in tubular cell apoptosis, mediated at least in part by activation of mitochondrial pathways.