The role of macrophage migration inhibitory factor in obesity-associated type 2 diabetes in mice

Defective immunosuppressive function of Treg cells in visceral adipose tissue in MIF deficient mice

Obesity, a global health problem nowadays, is a state of low-grade chronic inflammation of adipose tissue (AT) associated with increased adipocyte growth and proliferation and immune cell polarization towards an inflammatory phenotype within the stromal vascular fraction (SVF). Pro-inflammatory cells in the AT produce mediators of inflammation (IL-1β, TNF, macrophage migration inhibitory factor - MIF), thereby surpassing the anti-inflammatory response mediated by IL-10 and TGF-β, cytokines produced by regulatory T (Treg) cells. In this study we demonstrate that the absence of the pro-inflammatory cytokine MIF led to obesity and inflammation in the visceral AT (VAT) in 6 months old MIF^-/- mice. Besides the increment of pro-inflammatory AT macrophages and the enhanced production of TNF and IL-1β, VAT of MIF^-/- mice contained increased numbers of Treg cells. In situ proliferation of Treg cells did not differ between MIF^-/- and wild type mice, but Treg cells isolated from the VAT of MIF-deficient mice, and not from the cervical lymph nodes, exhibited lower expression and production of IL-10 and TGF-β. Additionally, SVF cells had significantly lower levels of STAT3 and IL-33, altogether indicating that VAT Treg cells in MIF^-/- mice, albeit abundantly present, are not fully functional. These results indicate that MIF is a new regulator of VAT Treg cell function, necessary for their immunosuppressive activities.

MIF and insulin: Lifetime companions from common genesis to common pathogenesis

Pro-inflammatory nature of macrophage migration inhibitory factor (MIF) has been generally related to the propagation of inflammatory and autoimmune diseases. But this molecule possesses many other peculiar functions, unrelated to the immune system, among which is its supportive role in the post-translational modifications of insulin. In this way MIF enables proper insulin conformation within the pancreatic beta cell and its full activity. The inherent or acquired changes in MIF expression might therefore lead to different insulin processing and initiation of autoimmunity. The relation between MIF and insulin does not stop at this point; these two molecules continue to interact during pathological states characterized by inflammation and insulin resistance. In this context, MIF indirectly and negatively influences insulin action by boosting inflammatory environment and disabling target cells to respond to insulin. On the other side, insulin might interfere with MIF action as well, acting as an anti-inflammatory mediator. Therefore, the proper interaction between MIF and insulin is crucial for maintaining homeostasis, while anti-inflammatory therapies based on the systemic MIF blockage may disturb this balance. This review covers MIF-insulin relationship in the physiological and pathological conditions and discusses the approaches for MIF inhibition and their net effect specifically considering possible impact on insulin misfolding and the possible misinterpretation of previous results due to the discovery of MIF functional homolog D-dopachrome tautomerase.

Mif deficiency promotes adiposity in fructose-fed mice

The macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine involved in inflammation, regulation of energy metabolism and glucocorticoid action. Chronic low-grade inflammation may be caused by fructose intake, contributing to visceral adipose tissue (VAT) dysfunction. Since MIF is a known antagonist of glucocorticoid signaling, and deregulated glucocorticoid signaling can contribute to lipid metabolism disturbances, we hypothesized that altered MIF signaling might underlie fructose-induced adiposity through glucocorticoid action. We analyzed physiological and biochemical parameters, adipose tissue histology, insulin sensitivity and lipid metabolism in WT and MIF-/- C57Bl/6J mice consuming 20% fructose solution for 9 weeks. Glucocorticoid prereceptor metabolism and glucocorticoid receptor (GR) protein level were examined in VAT, together with the expression of glucocorticoid-target genes involved in lipid metabolism. The expression of adipogenic and lipogenic transcriptional regulators peroxisome proliferator-activated receptor gamma (PPARG) and sterol regulatory element-binding protein 1c (SREBP1c) was also assessed. Results showed disturbed insulin sensitivity in all MIF-/- mice, regardless of the diet. Mice on fructose diet had increased energy intake, but increased visceral adiposity and enlarged adipocytes were observed only in fructose-fed MIF-/- mice. Increased VAT corticosterone level and 11 beta-hydroxysteroid dehydrogenase type 1, hexose-6-phosphate dehydrogenase and GR protein levels were observed in the same animals, together with induced expression of examined lipogenic genes and accumulation of PPARG and SREBP1c. In conclusion, the results showed that dietary fructose was associated with increased visceral adiposity through activation of GR-regulated lipogenic genes, but only in the absence of MIF, which set the state of hyperinsulinemia and insulin resistance.

The Role of Macrophage Migration Inhibitory Factor in the Function of Intestinal Barrier

Macrophage migration inhibitory factor (MIF) is a multifunctional protein that is involved in the development of gut-related inflammation. To investigate the role of MIF in the function of the intestinal barrier, we have explored intestinal permeability and gut-associated immune response in MIF-deficient (MIF-KO) mice. The absence of MIF provoked impairment of tight and adherens epithelial junctions in the colon through the disturbance of E-cadherin, zonula occludens-1, occludin and claudin-2 expression, which lead to the increase of intestinal barrier permeability. In these circumstances the diversity and content of gut microbiota in MIF-KO mice was considerably different compared to wild type mice. This change in microbiota was accompanied by an increased intestinal IgA concentration and a higher production of pro-inflammatory cytokines TNF and IFN-γ in mesenteric lymph nodes of MIF-KO mice. The forced changes of microbiota executed by antibiotics prevented the "leakage" of the barrier in MIF-KO mice, probably through up-regulation of occludin expression and normalization of cellular pore diameters. In addition, cytokine secretion was normalized after the treatment with antibiotics. These results suggest that MIF participates in the maintenance of physiological microbiota diversity and immunosurveillance, which in turn enables the proper intestinal barrier function.

Macrophage Migration Inhibitory Factor and Malondialdehyde as Potential Predictors of Vascular Risk Complications in Type 2 Diabetes Mellitus: Cross-Sectional Case Control Study in Saudi Arabia

Background. Malondialdehyde (MDA) has been implicated in the development of many acute inflammatory, autoimmune diseases as well as chronic inflammatory metabolic disorders. Involvement of inflammatory response and oxidative stress is currently suggested as a mechanism underlying development of diabetes and its complications. Objective. To evaluate the clinical utility of MDA, macrophage migration inhibitory factor (MIF), LDL-C/HDL-C, and TG/HDL-C ratio as noninvasive laboratory markers for prediction of T2DM vascular complications. Method. 63 Saudi T2DM patients and 16 age and sex matched controls were included. Serum MDA and MIF were assayed by thiobarbituric acid reactive substances and ELISA, respectively. TG/HDL-C and LDL-C/HDL-C ratios were calculated. Results. Uncontrolled DM patients had significantly higher levels of MDA, MIF, TG/HDL-C, and LDL-C/HDL-C ratios when compared with controlled DM patients and control group (p < 0.001). MDA had 100% sensitivity and 88% specificity. MIF showed 97% sensitivity and 100% specificity and LDL-C/HDL-C had 97% sensitivity and 95% specificity. Meanwhile, TG/HDL-C had the lowest sensitivity and specificity in identifying diabetic patients who would suffer from vascular complications. Conclusion. MDA, MIF, and LDL-C/HDL-C could be new predictors of metabolic disturbance which promote vascular complications in T2DM.

The critical role of macrophage migration inhibitory factor in insulin activity

Macrophage migration inhibitory factor (MIF) is a molecule with plethora of functions such as regulation of immune response, hormone-like, enzymatic and chaperone-like activity. Further, MIF is a major participant in glucose homeostasis since it is an autocrine stimulator of insulin secretion. MIF absence in male knockout mice (MIF-KO) results in development of glucose intolerance, while sensitivity to insulin is fully preserved. Since our results confirm that beta cells from MIF-KO mice express, produce and secrete insulin similarly to beta cells of their wild type (WT) counterparts C57BL/6 mice, we hypothesize that MIF-KO-derived insulin is less active. Indeed, insulin from MIF-KO islets is unable to significantly induce glucose uptake into hepatocytes and to efficiently promote insulin-triggered Akt phosphorylation determined by immunoblot. However, MIF's tautomerase function is not crucial for insulin biosynthesis since MIF inhibitors had no impact on WT insulin activity. Importantly, MIF recognition by anti-MIF antibody (ELISA) after in vitro co-incubation with purified insulin was significantly lower suggesting that insulin covers MIF immunodominant epitope. In addition, MIF binds insulin within beta cell as confirmed by co-immunoprecipitation. WT and MIF-KO-derived insulin exhibited different cleavage patterns suggesting different protein conformations. Finally, pre-incubation of recombinant MIF with insulin promotes formation of insulin hexamers. These results imply that MIF probably enables proper insulin folding what results in insulin full activity. This newly discovered feature of the cytokine MIF could be potentially important for commercially produced insulin, for increasing its stability and/or bioavailability.