Background and purpose: Neuronal replacement has recently gained attention as a potential therapeutic target under ischemic conditions. However, the oligodendrogenic infrastructure is equally critical for restoration of brain function and is also sensitive to ischemic injury. Erythropoietin (EPO) is a neuroprotective molecule that stimulates neuronal replacement after neonatal hypoxia/ischemia (H/I) when delivered soon after the onset of reperfusion. Because EPO can improve recovery of neurological function in the absence of tissue protection, we hypothesize that EPO may improve neurological function via enhancement of white matter recovery after H/I. Thus, we sought to determine the effects of delayed administration of EPO on white matter injury and recovery of neurological function after neonatal H/I.
Methods: EPO (1000 U/kg) was injected intraperitoneally at multiple time points beginning 48 hours after H/I in postnatal day 7 rats. The effects of EPO on oligodendrogenesis, white matter injury, and neurogenesis were evaluated using bromodeoxyuridine incorporation and cell-specific immunohistochemistry. Neurological function was assessed by sensorimotor behavioral tests.
Results: Delayed administration of EPO was incapable of reducing brain volume loss but significantly increased oligodendrogenesis and maturation of oligodendrocytes and attenuated white matter injury after H/I. These effects occurred concurrently with enhanced neurogenesis. Delayed EPO treatment improved behavioral neurological outcomes 14 days after H/I injury.
Conclusions: Our study demonstrates that delayed administration of EPO promotes oligodendrogenesis and attenuates white matter injury concurrently with increased neurogenesis. These effects likely contribute to the observed improvement in neurological functional outcomes.