Renal capsule as a stem cell niche.

Renal resident stem cells were previously reported within the renal tubules and papillary area. The aim of the present study was to determine whether renal capsules harbor stem cells and whether this pool can be recruited to the renal parenchyma after ischemic injury. We demonstrated the presence of label-retaining cells throughout the renal capsule, at a density of ∼10 cells/mm(2), and their close apposition to the blood vessels. By flow cytometry, in vitro cultured cells derived from the renal capsule were positive for mesenchymal stem cell (MSC) markers (CD29+, vimentin+, Sca-1+, nestin+) but did not express hematopoietic and endothelial stem cell markers. Moreover, renal capsule-derived cells also exhibited self-renewal, clonogenicity, and multipotency in differentiation conditions, all favoring stem cell characteristics and identifying them with MSC. In situ labeling of renal capsules with CM-DiI CellTracker demonstrated in vivo a directed migration of CM-DiI-labeled cells to the ischemic renal parenchyma, with the rate of migration averaging 30 μm/h. Decapsulation of the kidneys during ischemia resulted in a modest, but statistically significant, deceleration of recovery of plasma creatinine compared with ischemic kidneys with intact renal capsule. Comparison of these conditions allows the conclusion that renal capsular cells may contribute ∼25-30% of the recovery from ischemia. In conclusion, the data suggest that the renal capsule may function as a novel stem cell niche harboring MSC capable of participating in the repair of renal injury.