| Summary: | 碩士 === 國立陽明大學 === 神經科學研究所 === 90 === We have previously identified and characterized a novel gene encoding a protein designated as LUZP with an estimated molecular weight of 140 kDa. One of the unique features of LUZP is the presence at its NH2 terminus of three sets of leucine zipper motifs, which is the hallmark of many transcription factors. Subsequent Western blot analyses in various tissues clearly indicate its predominant expression in the adult brain. Immunocytochemical staining further revealed the nuclear localization of LUZP in neurons of cerebral cortex, hippocampus, striatum and cerebellum.
The hippocampus is a target of stress hormones and it is a particularly plastic and vulnerable region of the brain. As LUZP is expressed in adult hippocampus, a paradigm capable of perturbing its expression should provide clues as to its expression regulation and putative functions. Supplement of corticosterone (CT) at high level after adrenalectomy (ADX) was used as a chronic stress paradigm in the present study to monitor the expression change of LUZP by immunohistochemistry.
The serum level of CT was determined by RIA and the results indicated by day3 post-ADX, the CT level has already decreased to 2.5 mg/dl in contrast to that of control (14.0mg/dl) and the level stays low for 20 days (the longest time point examined). If supplemented by implantation of a cholesterol pellet containing 40 mg of CT in ADX-mice from 3 days and on to 17 days; the serum CT level was determined to be 10-fold (167.5 mg/dl), 5-fold (67.9 mg/dl, 56.1 mg/dl) and 2-fold (26.6 mg/dl) of the control level at day 2, 6,10 and 17post CT-supplement, respectively.
Corresponding LUZP expression pattern in the hippocampus of control, ADX and ADX-CT- supplemented mice were assessed by immunohistochemistry and analyzed by NIH image analyses. Results indicated that constitutive expression of LUZP are present in hippocampus of control mice, while no change of LUZP expression was found in the CA3 regions in ADX-mice at 5, 9, 20 days, significantly reduced expression was however, noted in ADX-mice at 13 days post-ADX. The observation thereby suggests that prolonged effect of low serum CT level will down regulate the expression of LUZP, and this phenomenon is reversible. In mice supplemented with CT for 2 days and 6 days, the LUZP expression was not changed when compared to control, despite the serum level of CT for 2 days is already very high (167.5 mg/dl). In contrast, 10 days after CT supplement, the CT level has tapered off to 5 fold (56.1 mg/dl) of the control, significant decline in LUZP expression is observed in the CA3 region. It appears that sustained level of high CT will also be able to down regulate LUZP expression in CA3 of hippocampus, and not only stops decrease but restores the protein expression.
Expression level of a stress receptor; i.e., glucocorticoid receptor (GR) were monitored simultaneously in all groups. It was intriguing to find that the level of GR expression parallel to that of LUZP. In addition, the expression change of LUZP and GR were also examined in dentate gyrus and the results indicated that the down regulation of LUZP and GR observed in CA3 pyramidal neurons were not observed in dentate granule neurons; thereby suggest that the expression of LUZP is differentially regulated in CA3 and dentate gyrus. Whether down regulation of LUZP in response to ADX (low CT) and high CT level are mediated via the same mechanism should await further investigation.
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