Kidney Stem Cells and Renal Progenitors
Lay Summary

Kidney stem cells (KSCs) are yet to be identified and located.  However, the researchers have revealed the existence of Renal Progenitor Cells (RPCs) located in the human adult kidney.  These RPCs may also be referred to as multipotent renal progenitor cells (MRPCs).  MRPCs are being researched extensively for there potential ability to repair kidney damage.  Additionally, adult kidney stem cells may present therapeutic value for the treatment of acute renal failure and renal autoimmune diseases. 

The difficulty in identifying the growth factors, repair mechanisms, and adult kidney progenitor's location is primarily due to the limited regenerative capability of adult kidney cells.  It is believed the renal papilla serves as a niche for kidney stem cells but research on the identification of kidney stem cell markers has yielded few definitive results (Figure 1).  Thus finding these markers are currently an ongoing process that will contribute to absolute localization of KSCs.

It is theorized that the kidney stem cells are responsible for the majority of renal cell regeneration during ischemic acute renal injury and ischemic chronic renal injury.  RPCs have been found during ischemic episodes to release cytokine in the area of injury that mobilize progenitor cells to the site of injury.  While kidney stem cells and MPRCs hold a potential for therapeutic usage, so far they have been found to be less than effective.  Research has been conducted to define the molecular pathways and events associated with the renal repair process, and strategies are being instrumented to test in animal and human models.

When the kidney reaches an end-stage failure, the two most viable treatment options are dialysis and transplantation.  Dialysis treatment is painful for patients, and kidney transplant offers the solution to end that pain.  Thus, if it is possible to someday bioengineer a functional kidney from either fetal or adult kidney stem cells, then it will be possible to eliminate the need to match organs for transplantation, in addition to eliminating transplantation waiting lists, pain from dialysis, viral infections and sepsis, and the financial cost placed upon the healthcare system and patients.

Scientists hope to someday reprogram embryonic stem cells (ESCs) to develop kidney cells or an entire organ due to their ability to differentiate into various cells and undergo transdifferentiation [to change between tissue lineages to form new differentiated cells].  In the United States, the current political issues involved with stem cell research and the lack of new embryonic stem cell lines have made the development of potential ESC based therapies difficult.

The study of renal progenitor cells is still in its infancy, but promises to provide future benefit with further research.  It is important that investigations continue to attempt to identify the existence of kidney stem cells as they hold great potential for the treatment of renal disorders.

Figure 1: Anatomy of kidney and suspected location of kidney stem cells

Acknowledgements
This review was prepared by the following graduate students in the Stem Cell Biology Class, Fall 2006, at the Graduate School of Biomedical Sciences, University of Medicine and Dentistry of New Jersey: Jason Aptaker, Fenwik Garvey, John Le  
Teaching Assistant:  Krista Buono