Objective: 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.
Methods: 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.
Results: 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.
Discussion: 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.