Heme proteins such as myoglobin or hemoglobin, when released into the extracellular space, can instigate tissue toxicity. Myoglobin is directly implicated in the pathogenesis of renal failure in rhabdomyolysis. In the glycerol model of this syndrome, we demonstrate that the kidney responds to such inordinate amounts of heme proteins by inducing the heme-degradative enzyme, heme oxygenase, as well as increasing the synthesis of ferritin, the major cellular repository for iron. Prior recruitment of this response with a single preinfusion of hemoglobin prevents kidney failure and drastically reduces mortality (from 100% to 14%). Conversely, ablating this response with a competitive inhibitor of heme oxygenase exacerbates kidney dysfunction. We provide the first in vivo evidence that induction of heme oxygenase coupled to ferritin synthesis is a rapid, protective antioxidant response. Our findings suggest a therapeutic strategy for populations at a high risk for rhabdomyolysis. (J. Clin. Invest. 1992. 90:267-270.)

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Acute kidney injury is followed by regeneration of damaged renal tubular epithelial cells. The purpose of this study was to test the hypothesis that renal stem cells exist in the adult kidney and participate in the repair process. A unique population of cells that behave in a manner that is consistent with a renal stem cell were isolated from rat kidneys and were termed multipotent renal progenitor cells (MRPC). Features of these cells include spindle-shaped morphology; self-renewal for >200 population doublings without evidence for senescence; normal karyotype and DNA analysis; and expression of vimentin, CD90 (thy1.1), Pax-2, and Oct4 but not cytokeratin, MHC class I or II, or other markers of more differentiated cells. MRPC exhibit plasticity that is demonstrated by the ability of the cells to be induced to express endothelial, hepatocyte, and neural markers by reverse transcriptase-PCR and immunohistochemistry. The cells can differentiate into renal tubules when injected under the capsule of an uninjured kidney or intra-arterially after renal ischemia-reperfusion injury. Oct4 expression was seen in some tubular cells in the adult kidney, suggesting these cells may be candidate renal stem cells. It is proposed that MRPC participate in the regenerative response of the kidney to acute injury.

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