| Summary: | 博士 === 長庚大學 === 臨床醫學研究所 === 89 === Steroid hormones play vital roles in sustaining human life via many biological actions. Among them, aldosterone hormone exerts its function in regulating sodium/ potassium electrolyte balance and maintaining body fluid homeostasis. Our studies started from clinical unique observations in patients with aldosterone hormone hyper-secretion. We found half of our patients (49 %) presented with muscular paralysis as an initial symptom. The serum potassium levels in the paralytic patients were significantly lower than those of the nonparalytic group (1.8±0.3 vs. 2.3±0.4 mmole/L, P= 0.0001). These findings, therefore, triggered us to study aldosterone steroidogenesis.
Subsequently, we examined mechanisms of serotoninergic effect on aldosterone secretion in volunteers. We found that plasma aldosterone levels will elevated after an oral dose of cisapride, a 5-HT4 receptor agonist, and reach plateau on 2 hours. This action is independent to rennin-angiotensin axis. Furthermore, cisapride and angiotensin II exert additive effects on aldosterone secretion. We also proved that this effect is not diminished along with aging.
In order to realize the molecular mechanisms of aldosterone secretion, we studied the CYP11A1 gene expression, which controls the first and rate-limiting step of all steroid hormones biosynthesis. We constructed plasmids with 4.4-, 2.3-, 1.7- and 1.5 kb promoter sequence 5’- upstream from the transcriptional start site of this gene and fused to a LacZ reporter gene. The 5’-fragments of CYP11A1 have appreciable promoter activities in mouse Y1 cells but not in non-steroidogenic COS-1 cells, showing cell-type specificity. Transcription factor SF-1 acitivats the 2.3 kb promoter, which can be potentiated by cotransfection with c-Jun in steroidogenic JEG3 cells but not in COS-1 cells. We concluded that the 1.7 kb region of CYP11A1 contains elements enough for cell-type specific expression. Furthermore, c-Jun and SF-1 could act synergistically to activate CYP11A1 gene expression.
Finally, we generated transgenic mouse lines using 4.4- and 2.3 kb promoter fragments of CYP11A1 fused with LacZ reporter gene. The reporter gene expression presented in tissue-specific, hormonal and developmental regulated pattern. Thus, we proved that the 2.3 kb promoter of CYP11A1 contains enough elements to regulate properly in vivo. These transgenic mice, we provide, are potential useful in studying steroidogenesis with many disease aspects. For example, we can study diabetic effect, some pharmacological effects on steroidogenesis in the future.
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