The erythropoietin receptor: molecular structure and hematopoietic signaling pathways

Deciphering the intracellular signaling of erythropoietin in neuronal cells

The search for potential drugs to treat neurodegenerative diseases has been intense in the last two decades. Among many candidates, erythropoietin (EPO) was identified as a potent protectant of neurons suffering from various adverse conditions. A wide array of literature indicates that endogenous or exogenous recombinant human erythropoietin and its variants activate cell signaling that initiates survival-promoting events in neurons and neuronal cells. This chapter gives an overview of the pro-survival signaling induced by endogenous and exogenous erythropoietin in vitro and in vivo and provides methods to further investigate the intracellular signaling. It is important to know that EPO is neuroprotective, but it will greatly enhance our chances to establish EPO as a new drug candidate if we know how EPO protects neurons.The descriptions below summarize our current knowledge in non-neuronal and neuronal signaling pathways induced by EPO. The signaling pathways involved in EPO are multiple; some are well known whereas others are still under intense investigation and few are observed in very specific cell types. It is important to note that neuronal signaling events triggered by EPO are still incomplete and require further research. Therefore, excellent review articles that explore specific EPO-signaling events are referenced.

Effects of simian betaretrovirus serotype 1 (SRV1) infection on the differentiation of hematopoietic progenitor cells (CD34+) derived from bone marrow of rhesus macaques (Macaca mulatta)

Peripheral blood cytopenias, particularly persistent anemia and neutropenia, are commonly associated with simian betaretrovirus infection of Asian monkeys of the genus Macaca. The pathogenetic mechanisms underlying these hematologic abnormalities are not well understood. The current study investigated the in vitro tropism of simian betaretrovirus (SRV) for both hematopoietic progenitor (CD34(+)) and stromal cells obtained from rhesus macaque bone marrow and assessed the effects of infection on hematopoietic progenitor cell differentiation in vitro. After in vitro exposure, SRV proviral DNA could be demonstrated by real-time PCR in cells and the reverse transcriptase assay in supernatants from SRV-exposed progenitor-associated stroma, but not in differentiated colonies derived from SRV-exposed progenitors. Furthermore, in vitro exposure involving cell-cell contact of uninfected CD34(+) progenitor cells with SRV-infected stromal cells resulted in a statistically significant reduction in granulocyte-macrophage colony formation in absence of detectable SRV-infection of progenitor cells. Reduction in colony formation occurred in a 'dose-dependent' fashion with increasing contact time. No effects on erythroid lineages and RBC differentiation were noted. Our results suggest that hematologic abnormalities observed during SRV disease (natural or experimental) of rhesus macaques may not result from direct effects of viral infection of progenitor cell populations, but rather be (at least in part) a consequence of SRV infection of supportive bone marrow stroma with secondary effects on differentiation of associated progenitor cells.