Erythropoietin prevents neuronal apoptosis after cerebral ischemia and metabolic stress

Abstract

Erythropoietin (EPO) promotes neuronal survival after hypoxia and other metabolic insults by largely unknown mechanisms. Apoptosis and necrosis have been proposed as mechanisms of cellular demise, and either could be the target of actions of EPO. This study evaluates whether antiapoptotic mechanisms can account for the neuroprotective actions of EPO. Systemic administration of EPO (5,000 units͞kg of body weight, i.p.) after middle-cerebral artery occlusion in rats dramatically reduces the volume of infarction 24 h later, in concert with an almost complete reduction in the number of terminal deoxynucleotidyltransferase-mediated dUTP nick-end labeling of neurons within the ischemic penumbra. In both pure and mixed neuronal cultures, EPO (0.1-10 units͞ml) also inhibits apoptosis induced by serum deprivation or kainic acid exposure. Protection requires pretreatment, consistent with the induction of a gene expression program, and is sustained for 3 days without the continued presence of EPO. EPO (0.3 units͞ml) also protects hippocampal neurons against hypoxia-induced neuronal death through activation of extracellular signal-regulated kinases and protein kinase Akt-1͞protein kinase B. The action of EPO is not limited to directly promoting cell survival, as EPO is trophic but not mitogenic in cultured neuronal cells. These data suggest that inhibition of neuronal apoptosis underlies short latency protective effects of EPO after cerebral ischemia and other brain injuries. The neurotrophic actions suggest there may be longer-latency effects as well. Evaluation of EPO, a compound established as clinically safe, as neuroprotective therapy in acute brain injury is further supported. E rythropoietin (EPO) was first characterized as a hematopoietic growth factor (1) and has been in clinical use by millions of patients over the last decade for the treatment of anemia. The observation that EPO and its receptor are expressed in rodent and human brain tissue (2-4), as well as by cultured neurons (5-8) and astrocytes (3,7,9), and that EPO has effects on neuronal cells (5), expanded the biological role of EPO beyond hematopoiesis. EPO gene expression in the brain is regulated by hypoxia-inducible factor-1 (1) that is activated by a variety of stressors, including hypoxia. Several independent research groups have reported that EPO protects cultured neurons against glutamate toxicity (6, 10) and reduces ischemic neuronal damage and neurological dysfunction in rodent models of stroke (6,(11)(12)(13). We recently reported that systemic administration of EPO is neuroprotective not only in animal models of cerebral ischemia, but also for mechanical trauma, excitotoxins, and neuroinflammation (11). Marked changes in EPO and EPOreceptor (EPOR) gene expression have been reported to occur in brain tissue after ischemic injury (6, 12). Specificity and biological relevance of these changes have been demonstrated by the observation that neutralization of endogenous EPO with soluble EPOR augments ischemic brain damage (13). Thus, it seems that E...

Neuroprotective effects and intracellular signaling pathways of erythropoietin in a rat model of multiple sclerosis

“…10 Increased phosphorylation of p-Akt was also shown to be involved in neuroprotection due to Epo treatment in cultured cortical neurons under hypoxic conditions. 43 Our present experiments with combined treatment of Epo together with WM, the naturally occurring inhibitor of PI3-K, 50 revealed the functional relevance of this pathway as it completely abolished the Epo-induced RGC rescue. In our previous studies, p-Akt was demonstrated to play an important role in other neuroprotective treatments as the antiapoptotic effects of insulin-like growth factor-I and tumor necrosis factor-a after surgical transection of the ON were PI3-K dependent and could be abolished by application of WM.…”

“…42 Epo acts as the main regulator of proliferation and differentiation of erythroid progenitor cells in the bone marrow. 13 Neuroprotective effects of systemically administered Epo have been shown in animal models of focal cerebral ischemia, traumatic brain injury, subarachnoid hemorrhage, and spinal cord injury, 19,[43][44][45] but the relevance of the underlying molecular mechanisms in vivo remained still unclear. Additionally, Epo treatment rescued RGCs from apoptosis in a retinal ischemia model and improved RGC function determined by ERG recordings.…”

“…In previous studies on hematopoietic progenitors as well as in a study on neuronal cell cultures, an Epo-induced activation of the MEK/MAPK pathway has been demonstrated. 43,[51][52][53] To investigate the functional significance of this part of the Epoinduced signal transduction in vivo, we treated rats with a combination of Epo and PD 98059, a selective and cellpermeable inhibitor of the single upstream kinase MEK. 54 Under this combined treatment, RGC counts were only moderately decreased when compared to Epo monotherapy, indicating that phosphorylation of MAPKs has a smaller impact on Epo-induced RGC survival than activation of PI3-K/ Akt.…”

Comparison of neuroprotective effects of erythropoietin (EPO) and carbamylerythropoietin (CEPO) against ischemia-like oxygen–glucose deprivation (OGD) and NMDA excitotoxicity in mouse hippocampal slice cultures

“…Both EPO-(F, M) and CEPO-treated OGD-exposed cultures (G, N) were able to protect against this loss in MAP2 immunohistochemistry, with CEPO having a better effect than EPO. intracellular signaling pathways have been shown to be functional also in neurons (Siren et al, 2001). By inhibiting MAPK or PI(3)K in hypoxia-cell death studies, EPO neuroprotection was abrogated, suggesting a crucial role of these pathways in EPO-induced protection (Siren et al, 2001).…”

“…intracellular signaling pathways have been shown to be functional also in neurons (Siren et al, 2001). By inhibiting MAPK or PI(3)K in hypoxia-cell death studies, EPO neuroprotection was abrogated, suggesting a crucial role of these pathways in EPO-induced protection (Siren et al, 2001). The relation between Jak2 and the transcription factor NFkB is well established (Digicaylioglu and Lipton, 2001).…”