Isolation and characterization of nontubular Sca-1⁺Lin ^- multipotent stem/progenitor cells from adult mouse kidney

Tissue engineering and cell therapy approaches aim to take advantage of the repopulating ability and plasticity of multipotent stem cells to regenerate lost or diseased tissue. Recently, stage-specific embryonic kidney progenitor tissue was used to regenerate nephrons. Through fluorescence-activated cell sorting, microarray analysis, in vitro differentiation assays, mixed lymphocyte reaction, and a model of ischemic kidney injury, this study sought to identify and characterize multipotent organ stem/progenitor cells in the adult kidney. Herein is reported the existence of nontubular cells that express stem cell antigen-1 (Sca-1). This population of small cells includes a CD45-negative fraction that lacks hematopoietic stem cell and lineage markers and resides in the renal interstitial space. In addition, these cells are enriched for β1-integrin, are cytokeratin negative, and show minimal expression of surface markers that typically are found on bone marrow-derived mesenchymal stem cells. Global gene profiling reveals enrichment for many genes downstream of developmental signaling molecules and self-renewal pathways, such as TGF-β/bone morphogenic protein, Wnt, or fibroblast growth factor, as well as for those that are involved in specification of mesodermal lineages (myocyte enhancer factor 2A, YY1-associated factor 2, and filamin-β). In vitro, they are plastic adherent and slowly proliferating and result in inhibition of alloreactive CD8⁺ T cells, indicative of an immuneprivileged behavior. Furthermore, clonal-derived lines can be differentiated into myogenic, osteogenic, adipogenic, and neural lineages. Finally, when injected directly into the renal parenchyma, shortly after ischemic/reperfusion injury, renal Sca-1⁺Lin^- cells, derived from ROSA26 reporter mice, adopt a tubular phenotype and potentially could contribute to kidney repair. These data define a unique phenotype for adult kidney-derived cells, which have potential as stem cells and may contribute to the regeneration of injured kidneys.