Histochemical and molecular-biological study on apoptosis in the model of renal failure

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Although ischemia-reperfusion of mouse kidney is known to cause severe renal failure due to tubular cell death, the exact cellular mechanism responsible for this phenomenon is not clear. In order to investigate the spatial and temporal development of renal cell death and the role of Fas/APO-1/CD95 (Fas) in this process, we occluded the left renal vessels in a group of mice for 30,60 or 120 min followed by reperfusion for 24h (N=4 for each group). Analysis of the isolated DNA in agarosegel electrophoresis revealed a typical ladder pattern of bands consisting of multiples of 180-200 base pairs, considered as the hallmark of apoptosis. The intensity of the bands increased proportionately with the duration of ischemia. Histochemical analysis using TUNEL showed the presence of nuclei with DNA double-strand breaks specifically in distal renal tubules of the outer medulla. We also confirmed the presence of apoptosis by electron microscopy. Analysis of total RNA by Northern blotting revealed one appropriate-sized band for Fas mRNA in the normal kidney which intensified in the ischemia-reperfused kidney. Moreover, nonradioactive in situ hybridization revealed that distal renal tubular epithelial cells were positive for Fas mRNA in the outer medulla. Fas antigen was also localized to the renal tubular epithelial cells of the outer medulla by immunohistochemistry. The number of apoptotic cells in the ischemia-reperfusion kidney of the lpr/lpr mouse was low. Our findings strongly indicate that ischemia-reperfusion of the kidney induces apoptosis of a specific area of tubular epithelial cells in the outer medulla through the Fas system.