A NOVEL SITE OF ERYTHROPOIETIN PRODUCTION - OXYGEN-DEPENDENT PRODUCTION IN CULTURED RAT ASTROCYTES

It has been shown that neurons express erythropoietin (Epo) receptor, but the production of Epo protein in neural tissues has not been demon strated. Cerebral cells of rat fetuses were cultured, and Epo in the s pent medium was measured with an enzyme-linked immunoassay. Production of the immunoreactive Epo was dependent on O-2 tension for cell cultu re; hypoxia enhanced the production. The immunoreactive Epo purified f rom the spent medium stimulated the growth of Epo-dependent myeloid ce lls and formation of fetal liver erythroid colonies. These biological activities were completely inhibited by the anti-Epo antiserum and the extracellular domain of the Epo receptor capable of binding with Epo. When brain Epo was compared with serum Epo, brain Epo was smaller in size and more active in vitro at low ligand concentrations. These diff erences appear to be caused by the different extent of sialylation. An alyses with the reverse transcription-polymerase chain reaction method indicated that the regulation of Epo production by oxygen operates at the level of its mRNA. Immunochemical staining of the immortalized cl onal cells revealed that astrocytes produced brain Epo. These results provide a novel site of Epo production and suggest that Epo acts on ne urons in a paracrine fashion.