Introduction
Delayed neuronal cell death is a major hallmark of ischemic stroke and a primary target for neuroprotective strategies. Apoptosis-inducing factor (AIF) promotes caspase-independent apoptosis upon translocation to the nucleus.
Methods & Results
Here we show that AIF translocates to the nucleus and is associated with apoptotic DNA damage in primary neurons and immortalized HT22 hippocampal neurons after oxygen-glucose-deprivation or exposure to glutamate. In order to provide evidence for the essential role of AIF in glutamate-induced neuronal cell death we employed AIF targeted small interfering RNA (siRNA) to downregulate the protein. Both, mRNA levels and protein levels were reduced to less than 20% in primary neurons or HT22 cells after AIF-siRNA treatment for 48 h. Moreover, RNA interference (RNAi)-mediated downregulation of AIF provided profound protection against excitotoxic cell death in primary neurons and HT22 cells. In a mouse model of reversible middle cerebral artery occlusion, rapid AIF translocation to the nucleus was associated with apoptotic nuclear morphology and DNA damage, and occurred prior to cytochrom c release in ischemic neurons. Furthermore, mutant mice expressing AIF at low levels exhibited significant decreases in infarct volume and delayed neuronal cell death after transient cerebral ischemia.
Conclusion
These results provide compelling evidence for the primary involvement of AIF in neuronal cell death in models of neuronal apoptosis related to cerebral ischemia and suggest that therapies targeting caspase-independent cell death signaling may provide protection in cerebrovascular disease or other pathological conditions where programmed cell death is prominent.