Erythropoietin and erythropoietin receptor expression after experimental spinal cord injury encourages therapy by exogenous erythropoietin.

OBJECTIVE: Erythropoietin (EPO) is a pleiotropic cytokine originally identified for its role in erythropoiesis. Recent studies have demonstrated that EPO and its receptor (EPO-R) are expressed in the central nervous system, where EPO exerts neuroprotective functions. Because the expression of the EPO and EPO-R network is poorly investigated in the central nervous system, the aim of the present study was to investigate whether the resident EPO and EPO-R network is activated in the injured nervous system. METHODS: A well-standardized model of compressive spinal cord injury in rats was used. EPO and EPO-R expression was determined by immunohistochemical analysis at 8 hours and at 2, 8, and 14 days in the spinal cord of injured and noninjured rats. RESULTS: In noninjured spinal cord, weak immunohistochemical expression of EPO and EPO-R was observed in neuronal and glial cells as well as in endothelial and ependymal cells. In injured rats, a marked increase of expression of EPO and EPO-R was observed in neurons, vascular endothelium, and glial cells at 8 hours after injury, peaking at 8 days, after which it gradually decreased. Two weeks after injury, EPO immunoreactivity was scarcely detected in neurons, whereas glial cells and vascular endothelium expressed strong EPO-R immunoreactivity. CONCLUSION: These observations suggest that the local EPO and EPO-R system is markedly engaged in the early stages after nervous tissue injury. The reduction in EPO immunoexpression and the increase in EPO-R staining strongly support the possible usefulness of a therapeutic approach based on exogenous EPO administration.

Increased expression of erythropoietin receptor on blood vessels in the human epileptogenic hippocampus with sclerosis.

Microvascular (capillary) proliferation is a readily observed, but largely ignored phenomenon of the mesial temporal lobe epilepsy (MTLE) hippocampus. Here, we report that the proliferated capillaries in surgically resected MTLE hippocampi were strongly immunoreactive for erythropoietin receptor (EPO-r). Further, we found that these capillaries were most prominent in areas of the MTLE hippocampus with extensive neuronal loss and gliosis, i.e. the CA3, CA1, and dentate hilus. High-resolution immunogold electron microscopy revealed that the capillary EPO-r was localized to the luminal and abluminal plasma membrane of endothelial cells, to endosome-like structures of these cells, and to pericapillary astrocytic end-feet. Previous studies have shown that systemically administered EPO appears in the cerebrospinal fluid in experimental animals, and the present results are consistent with the idea that EPO enters the brain via receptor-mediated endocytosis. The enrichment of EPO-r shown here suggests a highly efficient uptake of plasma EPO into the MTLE hippocampus and a possible role for this cytokine in epileptogenesis. Moreover, the presence of EPO-r in the MTLE hippocampus may provide a new vehicle for highly efficient delivery of hitherto impermeable drugs into the epileptic brain.

Erythropoietin exerts an anti-inflammatory effect on the CNS in a model of experimental autoimmune encephalomyelitis.

In recent work we reported that systemically administered erythropoietin (EPO) crosses the blood-brain barrier and has protective effects in animal models of cerebral ischemia, brain trauma and in a rat model of experimental autoimmune encephalomyelitis (EAE). Here we characterize the effect of systemic EPO on the inflammatory component of actively induced, acute EAE in Lewis rats. Administration of EPO at doses of 500-5000 U/kg bw i.p., daily from day 3 after immunization with myelin basic protein (MBP), delayed the onset of EAE and decreased its clinical score at peak time (days 12-13). Immunohistochemical analysis of the spinal cord using anti-glial fibrillary acidic protein (GFAP) and anti-CD11b antibodies showed that EPO markedly diminished inflammation and glial activation/proliferation. EAE induced significant levels of TNF and IL-6 in the spinal cord, where IL-6 was maximum at the onset of the disease (day 10) and TNF at its peak (day 12). EPO delayed the increase of TNF levels, without altering their peak levels, and markedly reduced those of IL-6 suggesting that the decreased inflammation and clinical score may be in part upon attenuation of IL-6. On the other hand, EPO was without effect in a model of adjuvant-induced arthritis in Lewis rats, suggesting a specificity towards autoimmune demyelinating diseases. These data suggest that EPO might act as a protective cytokine in inflammatory pathologies of the CNS.

Endogenous parathyroid hormone-related protein functions as a neuroprotective agent.

Parathyroid hormone-related protein (PTHrP) was discovered a dozen years ago as a product of malignant tumors. It is now known that PTHrP is a paracrine factor with multiple biological functions. One such function is to relax smooth muscle by inhibiting calcium influx into the cell. In the central nervous system, PTHrP and its receptor are widely expressed in neurons in the cerebral cortex, hippocampus and cerebellum. The function of PTHrP in the CNS is not known. Previous work has shown that expression of the PTHrP gene is depolarization-dependent in cultured cerebellar granule cells and depends specifically on L-type voltage sensitive calcium channel (L-VSCC) Ca(2+) influx. PTHrP has also been found to be capable of protecting these cells against kainic acid-induced excitotoxicity. Here, we tested the idea that mice with a PTHrP-null CNS might display hypersensitivity to kainic acid excitotoxicity. We found that these mice were six-fold more sensitive than control littermate mice to kainic-acid-induced seizures as well as hippocampal c-Fos expression. PTHrP-null embryonic mixed cerebral cortical cultures were more sensitive to kainic acid than control cultures, and PTHrP addition was found to be protective against kainate toxicity in both PTHrP-null and control cultures. By whole-cell techniques, PTHrP was found to reduce L-VSCC Ca(2+) influx in cultured mouse neuroblastoma cells. We conclude that PTHrP functions as a component of a neuroprotective feedback loop that is structured around the L-type calcium channel. This loop appears to be operative in vivo as well as in vitro.