Erythropoietin Promotes Neuronal Replacement Through Revascularization and Neurogenesis After Neonatal Hypoxia/Ischemia in Rats

Abstract

Background and Purpose-Erythropoietin (EPO) has been well characterized and shown to improve functional outcomes after ischemic injury, but EPO may also have unexplored effects on neurovascular remodeling and neuronal replacement in the neonatal ischemic brain. The current study investigates the effects of exogenous administration of EPO on revascularization and neurogenesis, 2 major events thought to contribute to neuronal replacement, in the neonatal brain after hypoxia/ischemia (H/I). Methods-Seven-day-old rat pups were treated with recombinant human EPO or vehicle 20 minutes after H/I and again on postischemic days 2, 4, and 6. Rats were euthanized 7 or 28 days after H/I for evaluation of infarct volume, revascularization, neurogenesis, and neuronal replacement using bromodeoxyuridine incorporation, immunohistochemistry, and lectin labeling. Neurological function was assessed progressively for 28 days after H/I by gait testing, righting reflex and foot fault testing. Results-We demonstrate that exogenous EPO-enhanced revascularization in the ischemic hemisphere correlated with decreased infarct volume and improved neurological outcomes after H/I. In addition to vascular effects, EPO increased both neurogenesis in the subventricular zone and migration of neuronal progenitors into the ischemic cortex and striatum. A significant number of newly synthesized cells in the ischemic boundary expressed neuronal nuclei after EPO treatment, indicating that exogenous EPO led to neuronal replacement. Conclusions-Our data suggest that treatment with EPO contributes to neurovascular remodeling after H/I by promoting tissue protection, revascularization, and neurogenesis in neonatal H/I-injured brain, leading to improved neurobehavioral outcomes.

High-Dose Erythropoietin and Hypothermia for Hypoxic-Ischemic Encephalopathy: A Phase II Trial

“…41 Epo exhibits antiapoptotic and antiinflammatory effects acutely after neonatal brain injury [42][43][44][45][46] and promotes neurogenesis, plasticity, and tissue remodeling after hypoxia-ischemia. 15,[47][48][49][50] In animal models of neonatal stroke, Epo increases proliferation, migration, and differentiation of neuronal precursors, resulting in increased neurogenesis in the injured basal ganglia and cortex. 47,51,52 Although therapeutic hypothermia has improved the outlook of infants with HIE, 53,54 there remains a pressing need for neuroprotective therapies that will further reduce the high rate of neurologic disabilities.…”

“…15,[47][48][49][50] In animal models of neonatal stroke, Epo increases proliferation, migration, and differentiation of neuronal precursors, resulting in increased neurogenesis in the injured basal ganglia and cortex. 47,51,52 Although therapeutic hypothermia has improved the outlook of infants with HIE, 53,54 there remains a pressing need for neuroprotective therapies that will further reduce the high rate of neurologic disabilities. [55][56][57] We reported the safety and pharmacokinetics of high-dose Epo when given together with hypothermia.…”

Future Perspectives for the Treatment of Neonatal Hypoxic-Ischemic Encephalopathy

“…Erythropoietin treatment reduces apoptotic cell death (Sun et al, 2004) and brain edema (Brissaud et al, 2010) and has an anti-inflammatory effect in the HI brain (Juul et al, 2009). It affects regenerative processes, promoting an increase in functional revascularization, in NSPC proliferation in the SVZ and in the number of new neurons that migrate to the striatum and to the cerebral cortex (Iwai et al, 2007). However, one study showed that erythropoietin reduced brain damage and prevented neurological deficits only in females (Fan et al, 2011), suggesting that more attention should be given to the gender-dependent effects of this treatment.…”

The Protective Role of Erythropoietin in the Developing Brain

“…Epo may contribute to the brain repair process after insult as it has a promoting capacity on neurogenesis both in vitro and in vivo (Shingo et al, 2001). Repeated doses of Epo treatment immediately after HI contribute to neurovascular remodeling by promoting tissue protection, revascularization, and neurogenesis in the neonatal injured brain and improve neurobehavioral outcomes (Iwai et al, 2007). If hippocampal progenitor cultures were stimulated into differentiation, Epo directed cells to a neuronal cell fate (Osredkar et al, 2010).…”