Reactive oxygen species differently regulate renal tubular epithelial and interstitial cell proliferation after ischemia and reperfusion injury.

Reactive oxygen species (ROS) function as an inducer of cell death and survival or proliferative factor, in a cell-type-specific and concentration-dependent manner. All of these roles are critical to ischemia-induced renal functional impairment and progressive fibrotic changes in the kidney. In an effort to define the role of ROS in the proliferation of tubular epithelial cells and of interstitial cells in kidneys recovering after ischemia and reperfusion (I/R) injury, experimental mice were subjected to 30 min of bilateral kidney ischemia and administered with manganese(III) tetrakis(1-methyl-4-pyridyl) porphyrin (MnTMPyP), a superoxide dismutase mimetic, from 2 to 15 days after I/R for 14 days daily (earlier and longer) and from 8 to 15 days after I/R for 8 days daily (later and shorter). Cell proliferation was assessed via 5'-bromo-2'-deoxyuridine (BrdU) incorporation assays for 20 h before the harvest of kidneys. After I/R, the numbers of BrdU-incorporating cells increased both in the tubules and interstitium. MnTMPyP administration was shown to accelerate the proliferation of tubular epithelial cells, presenting tubule-specific marker proteins along tubular segments, whereas it attenuated the proliferation of interstitial cells, evidencing α-smooth muscle actin, fibroblast-specific protein-1, F4/80, and NADPH oxidase-2 proteins; these results indicated that ROS attenuates tubular cell regeneration, but accelerates interstitial cell proliferation. Earlier and longer MnTMPyP treatment more effectively inhibited tissue superoxide formation, the increment of interstitial cells, and the decrement of epithelial cells compared with later and shorter treatment. After I/R, apoptotic cells appeared principally in the tubular epithelial cells, but not in the interstitial cells, thereby indicating that ROS is harmful in tubule cells, but is not in interstitial cells. In conclusion, ROS generated after I/R injury in cell proliferation and death performs a cell-type-specific and concentration-dependent role, even within the same tissues, and timely intervention of ROS is crucial for effective therapies.