Shear stress induces hepatocyte PAI-1 gene expression through cooperative Sp1/Ets-1 activation of transcription

Department of Digestive and General Surgery, Graduate School of Medicine, Niigata University, Niigata, Japan.
AJP Gastrointestinal and Liver Physiology (Impact Factor: 3.74). 08/2006; 291(1):G26-34. DOI: 10.1152/ajpgi.00467.2005
Source: PubMed

ABSTRACT Partial hepatectomy causes hemodynamic changes that increase portal blood flow in the remaining lobe, where the expression of immediate-early genes, including plasminogen activator inhibitor-1 (PAI-1), is induced. We hypothesized that a hyperdynamic circulatory state occurring in the remaining lobe induces immediate-early gene expression. In this study, we investigated whether the mechanical force generated by flowing blood, shear stress, induces PAI-1 expression in hepatocytes. When cultured rat hepatocytes were exposed to flow, PAI-1 mRNA levels began to increase within 3 h, peaked at levels significantly higher than the static control levels, and then gradually decreased. The flow-induced PAI-1 expression was shear stress dependent rather than shear rate dependent and accompanied by increased hepatocyte production of PAI-1 protein. Shear stress increased PAI-1 transcription but did not affect PAI-1 mRNA stability. Functional analysis of the 2.1-kb PAI-1 5'-promoter indicated that a 278-bp segment containing transcription factor Sp1 and Ets-1 consensus sequences was critical to the shear stress-dependent increase of PAI-1 transcription. Mutations of both the Sp1 and Ets-1 consensus sequences, but not of either one alone, markedly prevented basal PAI-1 transcription and abolished the response of the PAI-1 promoter to shear stress. EMSA and chromatin immunoprecipitation assays showed binding of Sp1 and Ets-1 to each consensus sequence under static conditions, which increased in response to shear stress. In conclusion, hepatocyte PAI-1 expression is flow sensitive and transcriptionally regulated by shear stress via cooperative interactions between Sp1 and Ets-1.

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    • "Too intense cell culture medium flow compromises metabolic functions of hepatocytes and induces significant morphological changes. Moreover, the viability of hepatocytes cultured under high shear conditions is usually lower than that of static controls (Park et al. 2007; Nakatsuka et al. 2006; Powers et al. 2002b; Tanaka et al. 2006). Therefore, it is important to adapt the culture medium flow rates in such a manner that an optimal balance between oxygen/nutrient supply and shear stress level is achieved. "
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    • "Several reports describe the effects of flow and shear stress on hepatocyte cultures (Mufti and Shuler, 1995; Nakatsuka et al., 2006; Powers et al., 2002b; Tanaka et al., 2006). Moreover, many investigators have shown that the viability of hepatocyte cultures under high shear is usually lower than that of static controls, indicating that the cells are under conditions of stress (Park et al., 2007). "
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    • "Our findings indicate a divergent role for Ets-1 in response to shear stress stimulation, as illustrated by the upregulation of protease inhibitors. While there is precedence for the shear stress dependent transcriptional regulation and increased DNA binding activity of Ets-1, which were observed in rheumatic synovial cells (Sun and Yokota, 2001) and cultured hepatocytes (Nakatsuka et al., 2006), the effect of fluid shear stress on Ets-1 expression in endothelial cells has not been reported previously. Previous studies indicate that shear stress downregulates expression of MMPs and uPA in endothelial cells (Yun et al., 2002; Sokabe et al., 2004; Milkiewicz et al., 2006). "
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