Bone Marrow Contribution to Renal Repair Following Ischemic Injury

by Egalka, Matthew Chandler

Repair of the mammalian renal tubular epithelium following ischemia/reperfusion injury is largely effected by surviving epithelial cells and other cells resident in the kidney interstitium; however, the precise nature of the contribution of circulating extrarenal cells is unknown. The purpose of this study is to determine whether bone marrow cells have the capacity to differentiate into renal tubular epithelium. This was investigated using both an ex vivo transplantation model as well as an attempt to grow epithelial cells from bone marrow in a liquid culture system.

Recipient female C57BL/6 mice were myeloablated via irradiation and transplanted in-travenously with lineage-depleted syngeneic male bone marrow. Following this, renal ischemia was induced by surgical interruption of the renal vascular pedicle. Thin sections were assayed for donor contribution by examination by fluorescence in situ hybridization (FISH) for the Y-chromosome. Tubules incorporating donor (Y-chromosome positive) cells were only rarely found (< 2%) in the outer medulla of damaged kidneys; far more frequent were donor-derived interstitial cells, which appear not to be entirely inflammatory in phenotype.

For the tissue culture experiments, collagenase-released marrow stromal cells (CR-MSC) were obtained by collagenase treatment of bone chips following mechanical dissociation of bones harvested from C57BL/6 mice. These cells were grown in culture and examined via immu-nostaining and reverse-transcription polymerase chain reaction for epithelial markers. Unfortu-nately, the resultant cells, although appearing to form epithelial colonies, were found to not ex-press the epithelial markers cytokeratin and ZO-1 by RT-PCR and immunostaining; instead they appeared to be fibroblasts with a novel morphology. In sum, bone marrow contribution to the renal epithelium appears to be a rare phenomenon at best and as of now cannot be replicated in vitro.