A novel site of erythropoietin production. Oxygen-dependent production in cultured rat astrocytes.

Abstract

It has been shown that neurons express erythropoietin (Epo) receptor, but the production of Epo protein in neural tissues has not been demonstrated.Cerebral cells of rat fetuses were cultured, and Epo in the spent medium was measured with an enzyme-linked immunoassay.Production of the immunoreactive Epo was dependent on 0, tension for cell culture; hypoxia enhanced the production.The immunoreactive Epo purified from the spent medium stimulated the growth of Epo-dependent myeloid cells 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 differences appear to be caused by the different extent of sialylation.Analyses 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 clonal cells revealed that astrocytes produced brain Epo.These results provide a novel site of Epo production and suggest that Epo acts on neurons in a paracrine fashion.Epo' is the glycoprotein that plays a major role in the regulation of erythropoiesis by stimulating the proliferation and differentiation of erythroid precursor cells (1,2).The kidney is the major organ of Epo production in adult (3) whereas the liver is the primary site in fetus (4).Peritubular interstitial cells in the kidney (5, 6) and more recently peritubular interstitial fibroblasts (7) have been shown to express Epo mRNA.In the liver, hepatocytes and also non-parenchymal cells express Epo (8-10). Oxygen controls the Epo production; hypoxic conditions activate expression of the Epo gene in animals (11-15) and Epo-producing hepatic cells (10, 16-18).Epo has been thought to exclusively act on erythroid precursor cells in vivo, but there is growing evidence that neurons respond to Epo.Neuronal cells express Epo-R, and binding of Epo increases intracellular concentrations of Ca" and monoamines (19).Epo augments choline acetyltransferase in cultured embryonal neurons and supports the in vivo survival of *This work was supported by grants-in-aid from the Ministry of Education, Science and Culture of Japan.The costs of publication of this article were defrayed in part by the payment of page charges.This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C.Section 1734 solely to indicate this fact.