Erythropoietin does not attenuate cytokine production and inflammation in microglia — Implications for the neuroprotective effect of erythropoietin in neurological diseases

Abstract

Erythropoietin is a hematopoietic cytokine which is also produced in the brain under hypoxia. Since this pathology is associated with glial cell activation and release of cytotoxic molecules, we investigated the expression of EPO receptors (EPO-R) and effects of erythropoietin on microglial cell functions in vitro using RT-PCR, Western immunoblotting, nitric oxide measurement, tumor necrosis factor-alpha-(TNF-alpha)-ELISA and gel shift assay analyses. Furthermore, we examined if erythropoietin could modulate proliferation of microglia. As shown by reverse transcription-polymerase chain reaction and immunocytochemistry, rat microglial cells and the murine microglia cell line BV-2 express the EPO-R. However, EPO showed no effect on the release of the proinflammatory mediators' nitric oxide and TNF-alpha. Moreover, EPO was not able to reduce the LPS (lipopolysaccharide) stimulated translocation of the proinflammatory transcription factor NF-kappaB into the nucleus of murine microglia, but induced (3)H-thymidine incorporation into DNA of microglial cells. These results show that microglia are target cells for erythropoietin which possesses mitogenic, but not anti-inflammatory effects on microglia. Therefore, the well-documented neuroprotective effects of erythropoietin could not be ascribed to an anti-inflammatory effect on microglia.