However, the role of hypoxia and HIF-1 in atherosclerosis remains largely unknown. Recently, macrophage migration inhibitory factor (MIF) has emerged as a key factor in vascular remodeling and in the development and progression of atherosclerosis [10-13]. Expression of MIF mRNA and protein was up-regulated as early as 2 hours in cultured human VSMCs after exposed to moderate hypoxia condition (3% O2). The up-regulation of MIF expression appears Mouse monoclonal to CEA to be dependent on hypoxia-inducible transcription factor-1(HIF-1) since knockdown of HIF-1 inhibits the hypoxia induction of MIF gene and protein expression. The hypoxia induced expression of MIF was attenuated by antioxidant treatment as well as by inhibition of extracellular signal-regulated kinase (ERK). Under moderate hypoxia conditions (3% O2), both cell proliferation and cell migration were increased in VSMC cells. Blocking the MIF by specific small interference RNA to MIF (MIF-shRNA) resulted in the suppression of proliferation and migration of VSMCs. == Conclusion == Our results exhibited that in VSMCs, hypoxia increased MIF gene expression and protein production. The hypoxia-induced HIF-1 activation, reactive oxygen species (ROS) generation and ERK activation might be involved in this response. Both MIF and HIF-1 mediated the hypoxia response of vascular easy muscle cells, including cell migration and proliferation. == Background == Tissue hypoxia is an essential feature of chronic inflammatory diseases. In the cardiovascular system, for example, when arterial wall thickens and blood-diffusion capacity is usually low in atherosclerotic lesions, hypoxia plays a key role in the development of atherosclerosis [1,2]. The cellular effects of hypoxia are primarily mediated by the hypoxia-inducible transcription factor-1 (HIF-1). It is a heterodimeric transcription factor composed of and subunits. HIF-1 is usually constitutively expressed in many cell types. HIF-1, the active subunit of HIF-1, is usually undetectable under normoxia because of quick proteasomal degradation. But it is usually stabilized under hypoxia conditions [3]. HIF-1 specifically binds hypoxic response element (HRE)-driven promoters on a number of genes such as vascular endothelial growth factor (VEGF), heme oxygenase and erythropoietin. In human atherosclerosis, HIF-1 protein co-localizes with macrophages [2]. HIF-1 may play a role in foam cell formation [4]. Evidences suggest that the HIF-1 pathway is usually associated with the progression and angiogenesis of human atherosclerosis [2,5,6]. Recent studies have shown that in normal oxygen conditions, G-protein-coupled receptor agonists including angiotensin II [7,8] and thrombin [9], potently stimulate and activate HIF-1 in vascular easy muscle cells. These results suggest a more general role of this transcription factor in the vascular response to injury. However, the role of hypoxia and HIF-1 in atherosclerosis remains largely unknown. Recently, macrophage migration inhibitory factor (MIF) has emerged as a key factor in vascular remodeling and in the development and progression of atherosclerosis [10-13]. MIF is an essential, upstream component of the inflammatory cascade and has a crucial role in several inflammatory conditions [10]. It can be expressed by vascular endothelial cells, VSMCs and macrophages. Increased expression of vascular Droxidopa MIF is usually associated with foam cell transformation during atherogenesis. MIF is usually expressed in atherosclerotic lesions, and has Droxidopa been suggested to be involved in atherosclerotic plaque development [12]. Several pro-atherosclerotic mediators such as oxidized LDL [14], CD40-L and angiotensin II are able to stimulate MIF expression [12]. However, the regulation of MIF expression in vascular cells, and its mechanisms of action have received little attention in atherosclerosis research. MIF has recently been shown to be up-regulated by hypoxia in several tumor cell Droxidopa types in vitro including breast carcinoma cells [15,16]. However, there are few data about the direct effects of hypoxia around the expression of MIF in VSMCs. VSMCs are one of the major constituents of blood vessels. VSMCs are also essential to atherosclerotic lesions. In the view of the increased expression of MIF in the atherosclerosis, we hypothesized that MIF might be up-regulated by hypoxia in VSMCs, and the up-regulation of MIF could be mediated via HIF-1 dependent pathway. In order to test our hypothesis, we examined.