6-Hydroxydopamine induces nuclear translocation of apoptosis inducing factor in nigral dopaminergic neurons in rat

Abstract

Parkinson’s disease (PD) is a progressive neurodegenerative disorder, characterized by relatively selective death of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNpc). 6-Hydroxydopamine (6-OHDA), a neurotoxin that causes the death of DA neurons, is commonly used to produce experimental PD model in rodents. Accumulating evidences suggest that caspase-independent apoptotic programmed cell death (PCD) could also be involved in the progression of various neurodegenerative diseases in addition to caspase-dependent neuronal PCD. Apoptosis-inducing factor (AIF), a mitochondrial intermembrane oxidoreductase, has been identified as a key protein implicated in caspase-independent apoptosis. However, little is known about the role of AIF in death of nigral DA neurons in PD. Therefore, we undertook this study in an effort to clarify the involvement of AIF in DA neuronal death by 6-OHDA administration. Ten and twenty micrograms of 6-OHDA was infused into the medial forebrain bundle (MFB) unilaterally, and the experimental rats were sacrificed at various time point. The DA neuronal loss was identified in the ipsilateral SN in the dose-dependent manner by using NeuN and tyrosine hydroxylase immunohistochemical staining and western blot assay. Numerous degenerating neurons, showing apoptotic features which are characterized by the shrunken nuclei with eosinophilic perikarya were observed in the ipsilateral SNpc. Activating transcription factor 3 (ATF3), the specific marker for neuronal damage, was expressed in the ipsilateral DA neurons only. Immunohistochemistry and immunofluorescence staining demonstrated that nuclear localization of AIF in the ipsilateral degenerating DA neurons. These results suggest that AIF could induce DA neuronal death by caspase-independent apoptosis in 6-OHDA treated model, although other cell death cascades should not be rule out.