Macrophage migration inhibitory (MIF) factor is an immunoregulatory cytokine whose effect on arresting random immune cell movement was recognized several decades ago. Despite its historic name, MIF also has a direct chemokine-like function and promotes cell recruitment. Multiple clinical studies have pointed to the utility of MIF as a biomarker for different diseases that have an inflammatory component; these include systemic infections and sepsis, autoimmune diseases, cancer, and metabolic disorders such as type 2 diabetes and obesity. The identification of functional promoter polymorphisms in the MIF gene (MIF) and their association with the susceptibility or severity of different diseases has served not only to validate MIF’s role in disease development but opened the possibility of using MIF genotype information to better predict risk and outcome. In this article, we review the clinical data of MIF and discuss its potential as a biomarker for different disease applications.

Wnt signaling plays a central regulatory role across a remarkably diverse range of functions during embryonic development, including those involved in the formation of bone and cartilage. Wnt signaling continues to play a critical role in adult osteogenic differentiation of mesenchymal stem cells. Disruptions in this highly-conserved and complex system leads to various pathological conditions, including impaired bone healing, autoimmune diseases and malignant degeneration. For reconstructive surgeons, critically sized skeletal defects represent a major challenge. These are frequently associated with significant morbidity in both the recipient and donor sites. The Wnt pathway is an attractive therapeutic target with the potential to directly modulate stem cells responsible for skeletal tissue regeneration and promote bone growth, suggesting that Wnt factors could be used to promote bone healing after trauma. This review summarizes our current understanding of the essential role of the Wnt pathway in bone regeneration and repair.

The role of the cytokine macrophage migration inhibitory factor (MIF) and its receptor, CD74, was assessed in autoimmune hepatitis (AIH) and primary biliary cirrhosis (PBC). Two MIF promoter polymorphisms, a functional -794 CATT5–8 microsatellite repeat (rs5844572) and a -173 G/C single nucleotide polymorphism (rs755622), were analyzed in DNA samples from over 500 patients with AIH, PBC, and controls. We found a higher frequency of the pro-inflammatory and high expression -794 CATT7 allele in AIH compared to PBC, while lower frequency was found in PBC compared to both AIH and healthy controls. MIF and soluble MIF receptor (CD74) were measured by ELISA in 165 serum samples of AIH, PBC, and controls. Circulating serum and hepatic MIF expression was elevated in patients with AIH and PBC vs. healthy controls. We also identified a truncated circulating form of the MIF receptor CD74 that is released from hepatic stellate cells and that binds MIF, neutralizing its signal transduction activity. Significantly higher levels of CD74 were found in patients with PBC vs. AIH and controls. Conclusions These data suggest a distinct genetic and immunopathogenic basis for AIH and PBC at the MIF locus. Circulating MIF and MIF receptor profiles distinguish PBC from the more inflammatory phenotype of AIH and may play a role in the pathogenesis and as biomarkers of these diseases.

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.

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Hair is a defining feature of mammals and has critical functions, including protection, production of sebum, apocrine sweat and pheromones, social and sexual interactions, thermoregulation, and provision of stem cells for skin homeostasis, regeneration, and repair. The hair follicle (HF) is considered a “mini-organ,” consisting of intricate and well-organized structures which originate from HF stem and progenitor cells. Dermal papilla cells are the main components of the mesenchymal compartments in the hair bulb and are instrumental in generating signals to regulate the behavior of neighboring epithelial cells during the hair cycle. Mesenchymal-epithelial interactions within the dermal papilla niche drive HF embryonic development as well as the postnatal hair growth and regeneration cycle. This review summarizes the current understanding of HF development, repair, and regeneration, with special focus on cell signaling pathways governing these processes. In particular, we discuss emerging paradigms of molecular signaling governing the dermal papilla-epithelial cellular interactions during hair growth and maintenance and the recent progress made towards tissue engineering of human hair follicles.

Since the survival of ingrowing cells in biomaterials for regenerative processes largely depends on the supply of nutrients and oxygen, angiogenesis plays an important role in the development of new materials for tissue engineering. In this study we investigated the possibility of enhancing the angiogenic properties of collagen matrices by covalent incorporation of the vascular endothelial growth factor (VEGF). In a previous paper we already reported the use of homo- and heterobifunctional cross-linking agents for modifying collagen matrices [1]. In the present work the angiogenic growth factor was linked to the collagen with the homobifunctional cross-linker disuccinimidyldisuccinatepolyethyleneglycol (SS-PEG-SS) in a two step procedure. The efficiency of the first reaction step-the reaction of SS-PEG-SS with VEGF--was evaluated by western blot analysis. After 10 minutes virtually all of the dimeric molecules VEGF were on average modified by conjugation with 1 cross-linking molecule. The biological activity of the conjugate was investigated by exposing endothelial cells to non-modified VEGF and to VEGF conjugated to the cross-linker. The conjugation only had a limited effect on the mitogenic activity of VEGF. We therefore applied the cross-linking reaction to the VEGF-collagen system. In a first approach the changes were evaluated by the in vitro exposure of HUVECs to non-modified matrices, to matrices in which the VEGF was simply admixed and to matrices in which the VEGF was covalently incorporated. The angiogenic properties were evaluated in vivo with the chorioallantois membrane model. In this assay the chorioallantois membrane of the chicken embryo was exposed to the same set of matrices. The covalent incorporation of VEGF has a small but significant effect both on the formation of microvessels in the chorioallantois membrane and the tissue ingrowth into the implant. The covalent incorporation of angiogenic growth factors may thus be considered as a promising approach for enhancing the angiogenic capabilities of collagen matrices. Also the cross-linking with the homobifunctional cross-linking agent has a positive effect on the angiogenic potential of the collagen matrices.

Macrophage migration inhibitory factor (MIF) is a pleiotropic cytokine and has been implicated in inflammatory diseases. However, little is known about the regulation of MIF in adipose tissue and its impact on wound healing. The aim of this study was to investigate MIF expression in inflamed adipose and determine its role in inflammatory cell recruitment and wound healing. Adipose tissue was harvested from subcutaneous adipose tissue layers of 24 healthy subjects and from adipose tissue adjacent to acutely inflamed wounds of 21 patients undergoing wound debridement. MIF protein and mRNA expression were measured by ELISA and RT-PCR. Cell-specific MIF expression was visualized by immunohistochemistry. The functional role of MIF in cell recruitment was investigated by a chemotaxis assay and by flow cytometry of labeled macrophages that were injected into Mif –/–and wildtype mice. Wound healing was evaluated by an in vitro scratch assay on human fibroblast monolayers. MIF protein levels of native adipose tissue and supernatants from acutely inflamed wounds were significantly elevated when compared to healthy controls. MIF mRNA expression was increased in acutely inflamed adipose tissue indicating the activation of MIF gene transcription in response to adipose tissue inflammation. MIF is expressed in mature adipocytes and in infiltrated macrophages. Peripheral blood mononuclear cell migration was significantly increased towards supernatants derived from inflamed adipose tissue. This effect was partially abrogated by MIF-neutralizing antibodies. Moreover, when compared to wildtype mice, Mif –/–mice showed reduced infiltration of labeled macrophages into LPS-stimulated epididymal fat pads in vivo. Finally, MIF antibodies partially neutralized the detrimental effect of MIF on fibroblast wound healing. Our results indicate that increased MIF expression and rapid activation of the MIF gene in fat tissue adjacent to acute wound healing disorders may play a role in cell recruitment to the site of inflammation and wound healing.