Localization of the transcription factor, sterol regulatory element binding protein-2 (SREBP-2) in the normal rat brain and changes after kainate-induced excitotoxic injury

Abstract

The transcription factor sterol regulatory element binding protein-2 (SREBP-2) has a key role in regulating cholesterol biosynthesis. In view of ongoing cholesterol biosynthesis in the brain, the present study was carried out to examine the distribution of the SREBP-2 in the normal rat brain, and possible changes after kainate-induced excitotoxicity. Western immunoblot analysis of SREBP-2 showed a dense band at 70 kDa corresponding to the transcriptionally active form of SREBP-2 in homogenates from the rat hippocampus, cortex and striatum. SREBP-2 immunolabeled sections showed dense labeling of pyramidal neurons in field CA1 and CA3 of the hippocampus, moderately dense labeling of pyramidal and non-pyramidal neurons of the cerebral neocortex, and moderate labeling of putative medium spiny neurons in the caudate nucleus and putamen. Label was observed in the somatic cytoplasm, nucleus and apical dendrites of pyramidal neurons, and dendritic shafts and spines in the neuropil in the hippocampus. The expression of SREBP-2 was also elucidated after excitotoxic neuronal injury induced by intracerebroventricular injections of kainate. Real time RT-PCR analyses showed that mRNA level of SREBP-2 was significantly reduced at both 1 day and 2 weeks post-kainate injection. Immunohistochemical analyses showed significantly reduced SREBP-2 immunoreactivity in the kainate-induced lesions, in support of the real time RT-PCR results. Taken together, the above results show that there is high level of SREBP-2 expression in the normal hippocampus, and that neuronal injury results in a significant reduction of SREBP-2 expression in the damaged areas.