The potential role of macrophage migration inhibitory factor on the migration of vascular smooth muscle cells

Roles of macrophage migration inhibitory factor in Guillain-Barré syndrome and experimental autoimmune neuritis: beneficial or harmful?

INTRODUCTION

Macrophage migration inhibitory factor (MIF) plays an important role in the pathogenesis of Guillain-Barré syndrome (GBS) and its animal model experimental autoimmune neuritis (EAN), which may offer an opportunity for the development of the novel therapeutic strategies for GBS. Areas covered: 'macrophage migration inhibitory factor' and 'Guillain-Barré syndrome' were used as keywords to search for related publications on Pub-Med, National Center for Biotechnology Information (NCBI), USA. MIF is involved in the etiology of various inflammatory and autoimmune disorders. However, the roles of MIF in GBS and EAN have not been summarized in the publications we identified. Therefore, in this review, we described and analyzed the major roles of MIF in GBS/EAN. Primarily, this molecule aggravates the inflammatory responses in this disorder. However, multiple studies indicated a protective role of MIF in GBS. The potential of MIF as a therapeutic target in GBS has been recently demonstrated in experimental and clinical studies, although clinical trials have been unavailable to date. Expert opinion: MIF plays a critical role in the initiation and progression of GBS and EAN, and it may represent a potential therapeutic target for GBS.

Hypoxia-induced endothelial secretion of macrophage migration inhibitory factor and role in endothelial progenitor cell recruitment

Macrophage migration inhibitory factor (MIF) is a pleiotropic inflammatory cytokine that was recently identified as a non-cognate ligand of the CXC-family chemokine receptors 2 and 4 (CXCR2 and CXCR4). MIF is expressed and secreted from endothelial cells (ECs) following atherogenic stimulation, exhibits chemokine-like properties and promotes the recruitment of leucocytes to atherogenic endothelium. CXCR4 expressed on endothelial progenitor cells (EPCs) and EC-derived CXCL12, the cognate ligand of CXCR4, have been demonstrated to be critical when EPCs are recruited to ischemic tissues. Here we studied whether hypoxic stimulation triggers MIF secretion from ECs and whether the MIF/CXCR4 axis contributes to EPC recruitment. Exposure of human umbilical vein endothelial cells (HUVECs) and human aortic endothelial cells (HAoECs) to 1% hypoxia led to the specific release of substantial amounts of MIF. Hypoxia-induced MIF release followed a biphasic behaviour. MIF secretion in the first phase peaked at 60 min. and was inhibited by glyburide, indicating that this MIF pool was secreted by a non-classical mechanism and originated from pre-formed MIF stores. Early hypoxia-triggered MIF secretion was not inhibited by cycloheximide and echinomycin, inhibitors of general and hypoxia-inducible factor (HIF)-1α-induced protein synthesis, respectively. A second phase of MIF secretion peaked around 8 hrs and was likely due to HIF-1α-induced de novo synthesis of MIF. To functionally investigate the role of hypoxia-inducible secreted MIF on the recruitment of EPCs, we subjected human AcLDL⁺ KDR⁺ CD31⁺ EPCs to a chemotactic MIF gradient. MIF potently promoted EPC chemotaxis in a dose-dependent bell-shaped manner (peak: 10 ng/ml MIF). Importantly, EPC migration was induced by supernatants of hypoxia-conditioned HUVECs, an effect that was completely abrogated by anti-MIF- or anti-CXCR4-antibodies. Thus, hypoxia-induced MIF secretion from ECs might play an important role in the recruitment and migration of EPCs to hypoxic tissues such as after ischemia-induced myocardial damage.

Macrophage migration inhibitory factor: a multifunctional cytokine in rheumatic diseases

Macrophage migration inhibitory factor (MIF) was originally identified in the culture medium of activated T lymphocytes as a soluble factor that inhibited the random migration of macrophages. MIF is now recognized to be a multipotent cytokine involved in the regulation of immune and inflammatory responses. Moreover, the pivotal nature of its involvement highlights the importance of MIF to the pathogenesis of various inflammatory disorders and suggests that blocking MIF may be a useful therapeutic strategy for treating these diseases. This paper discusses the function and expressional regulation of MIF in several rheumatic diseases and related conditions.

Hypoxia stimulates the expression of macrophage migration inhibitory factor in human vascular smooth muscle cells via HIF-1alpha dependent pathway

Background

Hypoxia plays an important role in vascular remodeling and directly affects vascular smooth muscle cells (VSMC) functions. Macrophage migration inhibitory factor (MIF) is a well known proinflammatory factor, and recent evidence suggests an important role of MIF in the progression of atherosclerosis and restenosis. However, the potential link between hypoxia and MIF in VSMC has not been investigated. The current study was designed to test whether hypoxia could regulate MIF expression in human VSMC. The effect of modulating MIF expression on hypoxia-induced VSMC proliferation and migration was also investigated at the same time.

Results

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 to be dependent on hypoxia-inducible transcription factor-1α(HIF-1α) since knockdown of HIF-1α 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 demonstrated that in VSMCs, hypoxia increased MIF gene expression and protein production. The hypoxia-induced HIF-1α activation, reactive oxygen species (ROS) generation and ERK activation might be involved in this response. Both MIF and HIF-1α mediated the hypoxia response of vascular smooth muscle cells, including cell migration and proliferation.

Induction of MIF expression by oxidized LDL via activation of NF-kappaB in vascular smooth muscle cells

Macrophage migration inhibitory factor (MIF) is a pleiotropic cytokine playing important roles in atherosclerosis. MIF gene deficiency and neutralizing antibodies against MIF have been reported to exert anti-atherosclerotic effects in various animal models. However, the mechanism by which MIF is induced in atherosclerotic lesions remains unclear. In the present studies, we cloned a 540bp full-length rabbit MIF cDNA by screening a rabbit uterine library. The cDNA contains a 348bp open-reading frame which encodes a deduced 115-amino acid polypeptide with approximately 90% similarity to human and mouse homologs. Constitutive MIF mRNA expression was detected in most rabbit tissues including aortas. The expression of MIF obviously abounded in vascular smooth muscle cells (VSMCs) of the atherosclerotic plaques. In cultured VSMCs, MIF expression was significantly induced by a pro-atherogenic factor, oxidized low-density lipoprotein (oxLDL). Promoter analysis showed there were two NF-kappaB binding sites in the MIF proximal promoter region. Deletion or mutation of the two sites abolished oxLDL-enhanced MIF promoter activity. Moreover, the induction of MIF by oxLDL can be blocked by IkappaB-alpha overexpression. Taken together, our results revealed that MIF expression can be induced by oxLDL in VSMCs via a NF-kappaB dependent manner, which may contribute to the pathogenesis of atherosclerosis.

Macrophage migration inhibitory factor: a key cytokine in RA, SLE and atherosclerosis

Originally discovered and named as an in vitro inhibitor of macrophage migration, the cytokine macrophage migration inhibitory factor (MIF) has now been shown to be a key regulator of acute and chronic immuno-inflammatory conditions including rheumatoid arthritis (RA), atherosclerosis, and more recently systemic lupus erythematosus (SLE). Common inflammatory events in these diseases include activation of cells and infiltration by immune cells at the site of injury. MIF actively participates in multiple stages of the inflammatory response, acting on cells directly and/or potentiating the effects entrained by other stimuli. The overlap of inflammatory processes operating in these diseases, the known activities of MIF, and the observation of atherosclerosis as a major comorbidity of RA and SLE, make MIF a strong candidate for therapeutic targeting in these diseases. Moreover, the unique relationship between MIF and glucocorticoids, commonly used in the treatment of RA and SLE but associated with significant side effects, highlights the potential of MIF as a 'steroid sparing' therapeutic target encompassing all three conditions.