Transfection of primary brain capillary endothelial cells for protein synthesis and secretion of recombinant erythropoietin: a strategy to enable protein delivery to the brain
Erythropoietin, the principal regulator of erythroids progenitor cells, also promotes neuronal survival. Using primary cultures of rat hippocampal neurons, we investigated whether erythropoietin could mediate neuroprotection favouring the transcription of brain-derived neurotrophic factor (BDNF). Erythropoietin 2.7 nm reduced by approximately 50% the neuronal death triggered by the prototypic neurotoxicant trimethyltin (TMT) and time-dependently induced BDNF mRNA. This effect resulted in an increased production of biologically active BDNF, which led to a sustained activation of the specific BDNF receptor tyrosine kinase B (TrkB). Reduction of TMT-induced neuronal death by erythropoietin was specifically prevented by a neutralizing anti-BDNF antibody (15 microg/mL), indicating the involvement of this neurotrophin in erythropoietin neuroprotective effect. Intracerebroventricular administration of erythropoietin in mice significantly increases BDNF mRNA expression in brain, supporting the idea of the involvement of this neurotrophin in erythropoietin action within the CNS. BDNF expression in neuronal cells is induced by activation of voltage Ca(2+)-channels and recruitment of Ca(2+)-sensitive transcription factors. Consistently, 2.7 nm erythropoietin increased intracellular Ca(2+) in 5 min and cAMP response element binding protein (CREB) phosphorylation at Ser 133 in 30 min. Both effects were abolished by 1 microm nitrendipine, a selective blocker of L-type voltage Ca(2+)-channels. These data demonstrate that erythropoietin activates the CREB transcription pathway and increases BDNF expression and production, which contributes to erythropoietin mediated neuroprotection.