Stem cells are defined as a subpopulation of cells which retain the ability of self-renewal and differentiation into a specialized cell type. Stem cells specific to many tissue types have been identified (e.g., hematopoietic stem cells, brain stem cells, etc) and the question arises: are there kidney stem cells?
Obviously, the renal tubular epithelium is capable of regeneration: the majority of patients who experience ATN will regain renal function as a result of a robust regenerative response which repopulates the denuded basement membrane with new tubular epithelial cells over time. There are three possible sources of new tubular cells:
1. Adjacent, less damaged tubular cells could repopulate the epithelium under the right conditions.
2. Circulating, bone marrow-derived stem cells may exist.
3. “Resident kidney stem cells” refers to the possibility of a subpopulation niche of renal cells that lives in the kidney which could be responsible for tubular regeneration when required.
Thus far, the evidence seems to point to (1)–that all renal epithelial tubule cells, if they can survive the injury, have the capacity to repopulate the tubular epithelium. Perhaps understanding this pathway more completely would allow us to generate new pharmacologic therapies to stimulate or hasten the repair response.
It is important also to point out that this field is still young, and perhaps there really are “kidney stem cells” that we don’t have the technology to detect yet. Resident kidney stem cells do appear to exist in other organisms, such as some fish.