The receptor that tames the innate immune response

Characterization of the erythropoietin/erythropoietin receptor axis in a rat model of liver damage and cholangiocarcinoma development

It has been recently shown that the biological effects of erythropoietin (EPO) are not limited to the hematopoietic compartment but, as pleiotropic glycoprotein, this hormone can exert pro-angiogenic and tissue-protective functions also in a wide range of non-hematopoietic organs. The role of EPO and the effective functionality of its receptor in solid tumors are still a controversial point of debate. In the present work we analyzed the gene expression of EPO and its cognate receptor (EpoR) in a rat model of thioacetamide-induced damage and tumor. An analysis of the EPO/EpoR axis was also performed on human cholangiocarcinoma (CC) cell lines. A progressive increase of EPO and EpoR mRNA can already be observed during the fibrotic–cirrhotic development with a peak of expression rising at tumor formation (24.7 ± 9.9-fold increase and 15.5 ± 1.1-fold increase, respectively, for the two genes). Co-localization studies by immunofluorescence revealed hepatocytes in the regenerative cirrhotic nodules (Hep Par-1⁺) and in the dysplastic bile duct cells (CK19⁺) as the major EPO producers in this specific condition. The same cell populations, together with endothelial cells, exhibited an increased expression of EpoR, although all the non-parenchymal cell populations in the liver exhibited modest basal mRNA levels. Challenging human CC cells, Mz-Cha-2, with a combination of EPO and SCF resulted in a synergistic effect on the gene expression of EPO, CyclinD1 and PCNA. This study suggests that the autocrine and paracrine release of endogenous EPO in the microenvironment may contribute to the development and maintenance of the CC possibly in cooperation with other signaling pathways.

Bench-to-bedside review: Erythropoietin and its derivatives as therapies in critical care

Erythropoietin (EPO) is known to have numerous biological functions. Its primary function in the body is to increase red blood cell numbers by way of preventing the apoptosis of erythroid progenitor cells via the homodimeric EPO receptor. The discovery that the local production of EPO within the brain in response to hypoxia or ischemia protects neurons against injury via an anti-apoptotic effect formed the basis of the hypothesis that the local generation of EPO limits the extent of injury. Although the hypothesis proved to be true in pre-clinical models of ischemia/reperfusion injury and inflammation, the randomized, controlled clinical trials that followed demonstrated serious adverse events of EPO due to activation of the hematopoietic system. Consequently, derivatives of EPO that lacked erythropoietic activity were discovered to reduce injury in many pre-clinical models associated with ischemia and inflammation. Unfortunately, there are no published clinical trials to determine the efficacy of non-erythropoietic derivatives of EPO in humans.

Erythropoietin-induced changes in brain gene expression reveal induction of synaptic plasticity genes in experimental stroke

Erythropoietin (EPO) is a neuroprotective cytokine in models of ischemic and nervous system injury, where it reduces neuronal apoptosis and inflammatory cytokines and increases neurogenesis and angiogenesis. EPO also improves cognition in healthy volunteers and schizophrenic patients. We studied the effect of EPO administration on the gene-expression profile in the ischemic cortex of rats after cerebral ischemia at early time points (2 and 6 h). EPO treatment up-regulated genes already increased by ischemia. Hierarchical clustering and analysis of overrepresented functional categories identified genes implicated in synaptic plasticity-Arc, BDNF, Egr1, and Egr2, of which Egr2 was the most significantly regulated. Up-regulation of Arc, BDNF, Dusp5, Egr1, Egr2, Egr4, and Nr4a3 was confirmed by quantitative PCR. We investigated the up-regulation of Egr2/Krox20 further because of its role in neuronal plasticity. Its elevation by EPO was confirmed in an independent in vivo experiment of cerebral ischemia in rats. Using the rat neuroblastoma B104, we found that wild-type cells that do not express EPO receptor (EPOR) do not respond to EPO by inducing Egr2. However, EPOR-expressing B104 cells induce Egr2 early upon incubation with EPO, indicating that Egr2 induction is a direct effect of EPO and that EPOR mediates this effect. Because these changes occur in vivo before decreased inflammatory cytokines or neuronal apoptosis is evident, these findings provide a molecular mechanism for the neuroreparative effects of cytokines and suggest a mechanism of neuroprotection by which promotion of a plastic phenotype results in decreased inflammation and neuronal death.