(a,b) The percentage of EdU-positive tubular cells was smaller in the kidneys of old mice at 72 h after 28 min of IRI compared with young mice after 35 min of IRI. The photomicrographs of the inner cortex and outer medulla are shown with a magnification of 200× (a). (b) The percentage of EdU-positive tubular cells/high power field in the inner cortex and outer medulla. Approximately 20 HPFs (magnification, 200 ×) per individual mouse (5 HPFs per slide, four slides per animal) were evaluated. Values are means ± SD, n = 6–8 in each group, **P < 0.01 vs. young mice with 35 min of IRI. (c) Expression of the proximal tubular cell injury marker Kim1 and the dedifferentiation markers Pax2 and vimentin at 72 h in sham kidneys, young kidneys that underwent 35 min of IRI and old kidneys that underwent 28 min of IRI (original magnification, 600×). (d) Western blot for Kim1, Pax2, and vimentin expression in whole-kidney lysates from young mice that underwent 35 min of IRI and old mice that underwent 28 min of IRI (each lane represents a separate mouse). (e) Relative quantification of the Kim1, Pax2, and vimentin expression in (d), normalized to actin. Values are means ± SD, n = 4 in each group, **P < 0.01 vs. young mice with 35 min of IRI.