Endothelial Progenitor Cell
A Lay Summary
The endothelial progenitor cell (EPC) has one essential function in both the developing embryo and adult: forming new blood vessels.  The process of forming new blood vessels is known as neovascularization and the sprouting of new vessels from old vasculature is known as angiogenesis.  Blood vessels bring essential nutrients and proteins to tissues and cells all over the body.  In the embryo, this process is critical for overall embryogenesis or development of the embryo into a new born.   In the adult, it is important for overall maintenance of the body and brain.

EPCs reside in the adult bone marrow, peripheral circulating blood and umbilical cord blood.  EPCs can home to ischemic tissue (tissue damaged by decreased blood flow) such as the heart and injured blood vessels.  They do so to mediate repair at such sites by maturing into endothelial cells which make up the lining of vessels or even into smooth muscle cells (contractile cells) and cardiomyocytes (heart muscle cells) as well.  This process of cell maturation is known as differentiation.

Further understanding of the events that mediate repair is necessary to further develop potential EPC derived therapies.  Several animal model studies have shown the potential for therapeutic treatment with the use of endothelial progenitor cells.  These studies have shown enhanced mobilization of EPCs to the blood.  Additionally, direct injection of EPCs via catheterization (inserting a hollow tubular device into a blood vessel) expedites repair. 
Recent research suggests that EPC levels in the circulation have prognostic value for individuals with hypertension. Additionally, it is hypothesized that the level of EPCs is increased in patients with significant coronary artery disease.  Thus, the true prognostic value of EPC level in the peripheral blood is unclear, but should offer additional insight into the importance that EPCs play in vascular health.

EPCs could become instrumental in every day wound healing. If harnessed into a successful and cost effective therapeutic agent EPCs could speed up surgical recovery time allowing for a decrease length of rehabilitation, less hospital stay, and decreased length of infection exposure as a just a few benefits.

Additionally, understanding angiogenesis and neovasculogenesis may prove important in the battle against cancer.  Cancer can manipulate the mechanisms of angiogenesis and neovasculogenesis to help tumors grow and become malignant.  Therefore, understanding how to block these mechanisms or even targeting cancer cells with modified EPCs may be an important step in cancer therapy.

There is still uncertainty regarding the identification markers and reproduction capability of endothelial progenitor cells.  An ideal EPC would be defined as one that can be easily be identified via discernable cell markers, expand readily in vitro, and be efficient in tissue repair when administered in vivo.  A cell marker is any biochemical characteristic, usually a protein such as a receptor that has some distinguishable and discriminatory function to that cell.  Although several identifying cell markers suggest the presence of an EPC, it has yet to be determined which ones are absolutely definitive.  Also, expanding EPCs (increasing the quantity of EPCs without causing them to mature) in vitro has been a slow and relatively unsuccessful road.  Once the ideal endothelial progenitor cell can be identified and expanded with ease, then there will be great opportunity for clinical success.

The future is certainly bright with EPCs as the scientific community is making great strides in moving from the laboratory to clinical medicine.  This progress can mean a lot to patients with a variety of conditions and disorders including diabetes, tumors, rheumatoid arthritis, psoriasis, and atherosclerosis.

Acknowledgements
This review was prepared by the following graduate students in the Stem Cell Biology Class, Graduate School of Biomedical Sciences, UMDNJ:  Tamunotonye Briggs, Krista D. Buono, Michael Mitchel, Chimaobi Odumuko, Elisa Wolenuk, (in alphabetical order, 2005).

Teaching Assistant:  Raghav Murthy

Updated Fall 2006 by Jason Aptaker, Fenwick Garvey and John Le (in alphabetical order).

Teaching Assistant (Fall 2006):  Krista Buono