Preservation of peritubular capillary endothelial integrity and increasing pericytes may be critical to recovery from postischemic acute kidney injury

Abstract

Decreased renal blood flow following an ischemic insult contributes to a reduction in glomerular filtration. However, little is known about the underlying cellular or subcellular mechanisms mediating reduced renal blood flow in human ischemic acute kidney injury (AKI) or acute renal failure (ARF). To examine renal vascular injury following ischemia, intraoperative graft biopsies were performed after reperfusion in 21 cadaveric renal allografts. Confocal fluorescence microscopy was utilized to examine vascular smooth muscle and endothelial cell integrity as well as peritubular interstitial pericytes in the biopsies. The reperfused, transplanted kidneys exhibited postischemic injury to the renal vasculature, as demonstrated by disorganization/disarray of the actin cytoskeleton in vascular smooth muscle cells and disappearance of von Willebrand factor from vascular endothelial cells. Damage to peritubular capillary endothelial cells was more severe in subjects destined to have sustained ARF than in those with rapid recovery of their graft function. In addition, peritubular pericytes/myofibroblasts were more pronounced in recipients destined to recover than those with sustained ARF. Taken together, these data suggest damage to the renal vasculature occurs after ischemia-reperfusion in human kidneys. Preservation of peritubular capillary endothelial integrity and increasing pericytes may be critical to recovery from postischemic AKI.

Fig. 1.

Postoperative renal allograft function. ▪, Mean values of creatinine clearance (CrCl) of recipients of a cadaveric allograft with sustained acute kidney injury (sustained AKI); ▵, corresponding values of recipients of a cadaveric allograft with recovering function (recovery). Error bars indicate SE. POD, postoperative day. *P = 0.00325 vs. recovery on POD 0. For SI conversion for CrCl, 1 ml/min = 0.0167 ml/s.

Fig. 2.

Fluorescence microscopy of F-actin in human renal tissue showing respective degree of damage to arterial smooth muscle for scoring: 0, intact filamentous structures in most cells (most commonly observed in controls); 1, intact filamentous structure mixed with damaged ones; and 2, damaged structures in most cells. Arrows and arrowheads indicate filamentous structure and damaged disrupted or clumped structure of actin, respectively. The images were obtained by 3-dimensional reconstruction of serial images of the kidney tissue sections. Bars = 20 μm.

Fig. 3.

Fluorescence microscopy for von Willebrand factor (vWF; green) in human renal tissue showing respective degrees of damage to the arterial endothelium: 0, vWF present on >75% of the endothelial lining; 1, vWF present on 50–75% of the endothelial lining; 2, vWF present on 25–49% of the endothelial lining; 3, vWF present on <25% of the endothelial lining. The tissue samples were double-stained with phalloidin for F-actin (red). The images were obtained by 3-dimensional reconstruction of serial images of the kidney tissue sections. Arrows indicate interlobular arteries. Bars = 20 μm.

Fig. 4.

Fluorescence microscopy for vWF in human renal tissue showing respective degrees of damage to the peritubular capillary endothelium. Description of grades 0–3 are the same as for Fig. 3, except here they refer to degrees of damage to the peritubular capillary endothelium. The images were obtained by 3-dimensional reconstruction of serial images of the kidney tissue sections. Glom, glomerulus. Bars = 20 μm.

Fig. 5.

Fluorescence microscopy for α-smooth muscle actin of pericytes showing respective degrees of peritubular pericyte staining as defined by peritubular staining. Description of grades 0–3 are the same as for Fig. 3, except here they refer to degrees of peritubular pericyte staining for α-smooth muscle actin. The images were obtained by 3-dimensional reconstruction of serial images of the kidney tissue sections. AA, interlobular artery. Bars = 20 μm.

Fig. 6.

Dot plots showing the grades (0–2; mild to severe damage) of damage to vascular smooth muscle cell actin (triangles) in arteries (A) and arterioles (B) and damage to endothelium (rectangles) in arteries (C), arterioles (D), and peritubular capillaries (E) in each group. Dot plot of the grades of peritubular interstitial pericytes (circles; grades 0–2, most prominent to minimal staining) is shown in F. Closed, open, and shaded symbols denote sustained AKI, recovery, and control groups, respectively.