Stroke is the third leading cause of death in the United States and the major cause of long-term disability. However, very little progress has been made in the development of treatment of acute stroke. Neuregulins are a family of growth factors implicated in a number of neuronal functions including development, plasticity, behavior and pathology. Here, we show that neuregulin-1 (NRG-1) completely blocked ischemia-induced delayed neuronal death in the brain with an extended therapeutic window. A single intra-arterial injection of NRG-1 (2.5 ng/kg) was neuroprotective if administered either before or 5.5 hours after transient middle cerebral artery occlusion (MCAO) and resulted in a significant improvement of functional neurological outcome. The neuroprotective effects of the single administration of NRG-1 were seen at least 2 weeks following treatment. NRG-1 also prevented macrophage/microglial infiltration, reactive astrogliosis, DNA fragmentation and interleukin-1â expression following stroke. We demonstrated by microarray analysis, that NRG-1 not only blocked interleukin-1 expression, but also attenuated the widespread pattern of pro-inflammatory and stress gene expression following ischemia. The microarray results showed that several hundred genes were significantly induced following MCAO compared to sham controls and treatment with NRG-1 attenuated the expression of these genes by 50% or more. Gene Ontology pathway analysis of the regulated genes indicated that there are genes induced by ischemia associated with multiple biological processes including inflammation, apoptosis, stress and cell cycle that were suppressed by NRG-1. Using CONFAC software that enables the high-throughput identification of conserved transcription factor binding sites, we determine that the regulatory regions of the ischemia and NRG-1 regulated genes were associated with novel transcription factors not previously associated with stroke and neuroprotection. These results demonstrate that NRG-1 can regulate ischemia-induced gene expression and may give new insight to the molecular mechanisms involved in the neuroprotective role of neuregulins in stroke.
