| Advancement in therapeutic strategies targeting kidney injury and repair has been hampered by the lack of an appropriate model and remained elusive over the past 50 years. Despite the ability to repair moderate tubular and microvascular damage, human kidneys are unable to fully regenerate after severe injury. The inability of the kidney to regenerate is in contrast to the repair response of the liver. It was recently discovered that the terminal digit phalanx in adult mice re-grows after its removal, similar to what occurs in children in humans. The ability for such regeneration is a subject of debates whether it is a result of resident stem cells, or the dedifferentiation of resident mature cells to form pluripotent cells that can use pathways distinct from those used during development to form limb structures. Understanding the process of renal tubular and vascular repair may allow us to maximize these processes for kidney regeneration after injury. We attempted to examine and characterize endogenous kidney repair after induction of a novel cryo-injury, in which application of a liquid nitrogen cooled cryo probe induces a localized kidney injury characterized by vascular and tubular cell death. After induction of a cryo injury approximately 1.0x106 mum3 in size to an adult mouse kidney, the injury area was reduced by 75% within four weeks. After injury, the directly cryo-injured area and the peripheral (penumbral) area of damage sustained a 62% and 30% reduction in blood flow, respectively (Laser-Doppler flowmetry). At four weeks post injury, blood flow in the penumbral area was restored to normal levels while in the directly cryo-injured area was still reduced by 50%. The penumbral and the directly cryo-injured areas demonstrated a peak in tubular and perivascular cell proliferation (K-i67 staining) at 4 days post injury, and a peak in apoptosis (TUNEL staining) at 7 days. Glomeruli showed an earlier peak in cell proliferation within the first 2 days after injury in both the penumbral and the directly cryo- injured areas. Apoptosis of glomerular cells also peaked within the first 2 days after injury in the penumbral region, but remained minimal throughout all time points in the directly cryo-injured area. Infiltration of macrophages was first observed in the penumbral region at 4 days, then in the directly cryo-injured area, and peaked in both areas at 7 days post injury. Wnt9b (a factor involved in differentiation of progenitor cells to tubular cells) expression increased at 4 days post injury, peaked at 7 days, and remained elevated for the next 4 weeks. Vascular CD31 staining was lowest 7 days after injury, while fibrosis peaked at this same time point. In conclusion, kidney cryo injury facilitates the study of endogenous kidney repair dynamics. Furthermore, the exogenous application of LIF (Leukemia Inhibitory Factor), an inducer of epithelial repair, did not show a significant acceleration in repair after injury, but it enhanced tubular and perivascular cell proliferation as well as vessels repair. |
