Bone marrow-derived endothelial progenitor cells and endothelial cells may contribute to endothelial repair in the kidney immediately after ischemia-reperfusion

Abstract

In ischemic acute kidney injury, renal blood flow is decreased. We have previously shown that reperfused, transplanted kidneys exhibited ischemic injury to vascular endothelium and that preservation of peritubular capillary endothelial integrity may be critical to recovery from ischemic injury. We hypothesized that bone marrow-derived (BMD) endothelial progenitor cells (EPCs) might play an important role in renal functional recovery after ischemia. We tested this hypothesis in recipients of cadaveric renal allografts before and for 2 weeks after transplantation. We found that the numbers of circulating CD34-positive EPCs and CD146-positive endothelial cells (ECs) decreased immediately after ischemia-reperfusion. In renal allograft tissues obtained 1 hr after reperfusion, CD34-positive cells were more frequently observed along the endothelial lining of peritubular capillaries compared with non-ischemic controls. Moreover, 0-17.5% of peritubular capillary ECs were of recipient origin. In contrast, only 0.1-0.7% of tubule cells were of recipient origin. Repeat graft biopsy samples obtained 35 and 73 days after transplant did not contain capillary ECs of recipient origin, whereas 1.4% and 12.1% of tubule cells, respectively, were of recipient origin. These findings suggest that BMD EPCs and ECs may contribute to endothelial repair immediately after ischemia-reperfusion.

Figure 1

Box plots of circulating CD34-positive endothelial progenitor cells (A,B) and CD146-positive endothelial cells (ECs) (C,D) (per 5 ml of processed peripheral blood) in cadaveric renal allograft recipients showing prompt recovery of graft function (A,C), in those who sustained acute kidney injury (B,D) immediately before (preop) and 2 hr, 3 days, and 14 days after transplant (postop), and in healthy controls. N indicates the number of samples analyzed in each group. @ indicates an outlier; *p<0.05 vs control and preop; **p<0.05 vs control; ^#p<0.05 vs recovery on 14 days postop.

Figure 2

Fluorescence microscopy of human renal tissues showing ECs staining for von Willebrand Factor (vWF) in a non-ischemic control (A) and in a cadaveric renal allograft after ischemia–reperfusion (B), and CD34-positive ECs in a non-ischemic control (C) and in a cadaveric renal allograft after ischemia–reperfusion (D). Staining for vWF-positive and CD34-positive ECs is shown in green and blue, respectively, and staining for actin is shown in red. After ischemia–reperfusion, compared with respective controls (A,C), vWF-positive ECs decreased (B), whereas CD34-positive ECs increased (D). Images were obtained by three-dimensional reconstruction of serial images of kidney tissue sections. Immunohistochemistry was followed by fluorescence in situ hybridization to detect X and Y chromosomes in intraoperative renal graft biopsy tissues from two male subjects who had received kidney grafts from female donors: Subjects 11 (E) and 1 (F), and in a repeat graft biopsy sample from Subject 1 on postoperative day 73 (G). Arrows indicate Y chromosomes in green in an endothelial cell (F) and tubule cells (G), demonstrating cells of recipient bone marrow origin. Peritubular capillary ECs are identified by PECAM-1 in orange (E) or red (F). Red dots in nuclei indicate the X chromosome; glom denotes glomerulus. Bar = 20 μm.