Prajapati Kanaiyalal D, Sharma Shyam S, Roy Nilanjan
Department of Pharmacology and Toxicology, National Institute of Pharmaceutical Education and Research, Sector-67, S.A.S. Nagar, Punjab, India.
Neurol Res. 2012 Jan;34(1):25-31. doi: 10.1179/1743132811Y.0000000052.
Exogenous human albumin has been shown to be neuroprotective in experimental ischemic stroke and it is currently investigated in clinical trials. However, the role of endogenous expression of albumin and its transcriptional regulation in the ischemic brain is not known. We have previously reported the upregulation of de novo synthesis of albumin in the ischemic rat brain (at 0 and 22 hours of reperfusion after 2 hours of ischemia). In this study, we analyzed the role of transcription factors in albumin expression in ischemic rat brain.
The putative transcription factor binding sites for the albumin promoter was analyzed using transcription factor search computational tool and validated in rat middle cerebral artery occlusion model of transient cerebral ischemia.
Computational analysis predicted approximately 20 transcription factor binding sites including hepatocyte nuclear factor-1alpha (HNF-1alpha). We found for the first time mRNA and protein expression of HNF-1alpha in the control and ischemic rat brain. There was no significant difference in mRNA and protein expression of HNF-1alpha between control and ischemic (0, 2 and 22 hours of reperfusion) group but there was increased interaction of HNF-1alpha with p300 (known interacting partner for HNF-1alpha, a histone acetyl-transferase) in 0- and 22-hour reperfusion groups. Also albumin promoter binding activity of HNF-1alpha in ischemic animals of 0- and 22-hour reperfusion groups significantly increased compared to respective control group animals.
Although, HNF-1alpha is mainly expressed in the rat liver and involved in hepatic expression of albumin, our study conclusively shows for the first time de novo synthesis of HNF-1alpha in rat brain. Moreover, an increased interaction of HNF-1alpha with p300 and albumin promoter seems to be responsible for overexpression of albumin in ischemic conditions.
外源性人白蛋白已被证明在实验性缺血性卒中中具有神经保护作用，目前正在进行临床试验研究。然而，白蛋白内源性表达及其在缺血性脑内的转录调控作用尚不清楚。我们之前报道过缺血大鼠脑内白蛋白从头合成上调（缺血2小时后再灌注0小时和22小时）。在本研究中，我们分析了转录因子在缺血大鼠脑内白蛋白表达中的作用。
使用转录因子搜索计算工具分析白蛋白启动子的假定转录因子结合位点，并在大鼠短暂性脑缺血大脑中动脉闭塞模型中进行验证。
计算分析预测了约20个转录因子结合位点，包括肝细胞核因子-1α（HNF-1α）。我们首次在对照和缺血大鼠脑内发现了HNF-1α的mRNA和蛋白表达。对照和缺血（再灌注0小时、2小时和22小时）组之间HNF-1α的mRNA和蛋白表达无显著差异，但在再灌注0小时和22小时组中，HNF-1α与p300（已知的HNF-1α相互作用伴侣，一种组蛋白乙酰转移酶）的相互作用增加。此外，与各自对照组动物相比，再灌注0小时和22小时组缺血动物中HNF-1α的白蛋白启动子结合活性显著增加。
尽管HNF-1α主要在大鼠肝脏中表达并参与白蛋白的肝脏表达，但我们的研究首次确凿地表明大鼠脑内有HNF-1α的从头合成。此外，HNF-1α与p300和白蛋白启动子相互作用的增加似乎是缺血条件下白蛋白过表达的原因。
