Map kinase activation by mu-opioid receptor in cord blood CD34+/CD38- cells

We compared 2 sources of stem cells used for allogeneic transplantation: cord blood (CB) CD34+ cells and peripheral blood (PB) G-CSF mobilized CD34+ cells. It has long been known that the CB stem cells are more primitive, they produce long term repopulating stem cells in-vivo, they grow larger colonies and have longer telomers. These properties give them a proliferative advantage that should compensate for the relatively low number of stem cells contained in a single unit of CB. The aim of the study was to compare the mRNA expression patterns of CB and PB CD34+ cells. This, of-course, can be accomplished by using standard techniques such as RT-PCR or Northern blot analysis. These methods focus only on a few candidate genes at a time and they rely on genes whose sequence is known. Alternatively, we used a more relevant approach that analyses multiple genes simultaneously. This we achieved by hybridizing an entire cDNA population to nucleic acid arrays. A single hybridization experiment generates an expression profile for hundreds or thousands of genes at once. The most prominent difference in gene expression, in favor of CB CD34+ cells, was observed in the mu-receptor gene. This receptor was mainly expressed on the CB CD34+/CD38- subpopulation. In addition to the preferential expression of the mu-receptor in CB cells we showed the activation of a signal transduction cascade by this receptor. This was achieved by demonstrating the phosphorylation/ activation of MAP kinase and by a functional assay showing phosphorylation of a known MAP kinase substrate (Elk-1) by MAP kinase . As the mu-receptor signal transduction cascade has a proliferative potential and as MAP kinase has been shown to have antiapoptotic effects, the existence of this receptor on early CB progenitors may have a bearing on CD34+ cell expansion. The existence of a traditionally regarded neuronal receptor on CB CD34+ cells will be discussed with regard to its future role in the treatment of neurologic diseases.