A meta-analysis of genome-wide association studies of growth differentiation Factor-15 concentration in blood

Blood levels of growth differentiation factor-15 (GDF-15), also known as macrophage inhibitory cytokine-1 (MIC-1), have been associated with various pathological processes and diseases, including cardiovascular disease and cancer. Prior studies suggest genetic factors play a role in regulating blood MIC-1/GDF-15 concentration. In the current study, we conducted the largest genome-wide association study (GWAS) to date using a sample of ∼5,400 community-based Caucasian participants, to determine the genetic variants associated with MIC-1/GDF-15 blood concentration. Conditional and joint (COJO), gene-based association, and gene-set enrichment analyses were also carried out to identify novel loci, genes, and pathways. Consistent with prior results, a locus on chromosome 19, which includes nine single nucleotide polymorphisms (SNPs) (top SNP, rs888663, p = 1.690 × 10-35), was significantly associated with blood MIC-1/GDF-15 concentration, and explained 21.47% of its variance. COJO analysis showed evidence for two independent signals within this locus. Gene-based analysis confirmed the chromosome 19 locus association and in addition, a putative locus on chromosome 1. Gene-set enrichment analyses showed that the“COPI-mediated anterograde transport” gene-set was associated with MIC-1/GDF15 blood concentration with marginal significance after FDR correction (p = 0.067). In conclusion, a locus on chromosome 19 was associated with MIC-1/GDF-15 blood concentration with genome-wide significance, with evidence for a new locus (chromosome 1). Future studies using independent cohorts are needed to confirm the observed associations especially for the chromosomes 1 locus, and to further investigate and identify the causal SNPs that contribute to MIC-1/GDF-15 levels

Associations of serum short-chain fatty acids with circulating immune cells and serum biomarkers in patients with multiple sclerosis

Altered composition of gut bacteria and changes to the production of their bioactive metabolites, the short-chain fatty acids (SCFAs), have been implicated in the development of multiple sclerosis (MS). However, the immunomodulatory actions of SCFAs and intermediaries in their ability to influence MS pathogenesis are uncertain. In this study, levels of serum SCFAs were correlated with immune cell abundance and phenotype as well as with other relevant serum factors in blood samples taken at first presentation of Clinically Isolated Syndrome (CIS; an early form of MS) or MS and compared to healthy controls. There was a small but significant reduction in propionate levels in the serum of patients with CIS or MS compared with healthy controls. The frequencies of circulating T follicular regulatory cells and T follicular helper cells were significantly positively correlated with serum levels of propionate. Levels of butyrate associated positively with frequencies of IL-10-producing B-cells and negatively with frequencies of class-switched memory B-cells. TNF production by polyclonally-activated B-cells correlated negatively with acetate levels. Levels of serum SCFAs associated with changes in circulating immune cells and biomarkers implicated in the development of MS

Blockade of chloride intracellular ion channel 1 stimulates Abeta phagocytosis

In amyloid-\u3b2 (A\u3b2)-stimulated microglial cells, blockade of chloride intracellular ion channel 1 (CLIC1) reverts the increase in tumor necrosis factor-\u3b1 and nitric oxide (NO) production and results in neuroprotection of cocultured neurons. This effect could be of therapeutic efficacy in Alzheimer's disease (AD), where microglial activation may contribute to neurodegeneration, but it could reduce A\u3b2 phagocytosis, which could facilitate amyloid plaque removal. Here, we analyzed the CLIC1 blockade effect on A\u3b2-stimulated mononuclear phagocytosis. In the microglial cell line BV-2, A\u3b225-35 treatment enhanced fluorescent bead phagocytosis, which persisted also in the presence of IAA-94, a CLIC1 channel blocker. The same result was obtained in rat primary microglia and in BV2 cells, where CLIC1 expression had been knocked down with a plasmid producing small interfering RNAs. To address specifically the issue of A\u3b2 phagocytosis, we treated BV-2 cells with biotinylated A\u3b21-42 and measured intracellular amyloid by morphometric analysis. IAA-94-treated cells showed an increased A\u3b2 phagocytosis after 24 hr and efficient degradation of ingested material after 72 hr. In addition, we tested A\u3b21-42 phagocytosis in adult rat peritoneal macrophages. Also, these cells actively phagocytosed A\u3b21-42 in the presence of IAA-94. However, the increased expression of inducible NO synthase (iNOS), stimulated by A\u3b2, was reverted by IAA-94. In parallel, a decrease in NO release was detected. These results suggest that blockade of CLIC1 stimulates A\u3b2 phagocytosis in mononuclear phagocytes while inhibiting the induction of iNOS and further point to CLIC1 as a possible therapeutic target in AD

Macrophage inhibitory cytokine 1 in fetal membranes and amniotic fluid from pregnancies with and without preterm labour and premature rupture of membranes

The placenta and fetal membranes are the site of expression of macrophage inhibitory cytokine (MIC-1), a member of the transforming growth factor (TGF)-β superfamily. We hypothesized that MIC-1 may act as an immune regulator in pregnancy complications associated with intrauterine inflammation. Decidual cells, chorionic trophoblasts and amnion epithelial cells were identified by immunohistochemistry as the predominant MIC-1-containing cell type in term membranes. Amnion and choriodecidual explants all produced MIC-1 in culture, the latter having the greatest production rate (206 ± 74.5 pg/mg tissue/24 h, n = 6; mean ± SEM). Production was not responsive to stimulation by pro-inflammatory cytokines. MIC-1 was detectable in 217 transabdominal amniotic fluid (AF) samples taken from 15 to 41 weeks gestation, concentrations ranging from 0.9-51.1 ng/ml. AF MIC-1 concentrations in pregnancies with premature rupture of membranes (PROM) or preterm labour, either with or without microbial invasion of the amniotic cavity, were not significantly different from those delivered at term either with or without labour. Treatment with MIC-1 (0.25-25 ng/ml) did not alter production of interleukin-6 or -8 by amnion or choriodecidual cells in vitro. We conclude that AF MIC-1 is derived from the fetal membranes and decidua, but that MIC-1 is unlikely to be involved in the pathophysiology of preterm birth or PROM

CLIC1 function is required for beta-amyloid-induced generation of reactive oxygen species by microglia

The Alzheimer's disease (AD) brain is characterized by plaques containing beta-amyloid (Abeta) protein surrounded by astrocytes and reactive microglia. Activation of microglia by Abeta initiates production of reactive oxygen species (ROS) by the plasmalemmal NADPH oxidase; the resultant oxidative stress is thought to contribute to neurodegeneration in AD. We have previously shown that Abeta upregulates a chloride current mediated by the chloride intracellular channel 1 (CLIC1) protein in microglia. We now demonstrate that Abeta promotes the acute translocation of CLIC1 from the cytosol to the plasma membrane of microglia, where it mediates a chloride conductance. Both the Abeta induced Cl(-) conductance and ROS generation were prevented by pharmacological inhibition of CLIC1, by replacement of chloride with impermeant anions, by an anti-CLIC1 antibody and by suppression of CLIC1 expression using siRNA. Thus, the CLIC1-mediated Cl(-) conductance is required for Abeta-induced generation of neurotoxic ROS by microglia. Remarkably, CLIC1 activation is itself dependent on oxidation by ROS derived from the activated NADPH oxidase. We therefore propose that CLIC1 translocation from the cytosol to the plasma membrane, in response to redox modulation by NADPH oxidase-derived ROS, provides a feedforward mechanism that facilitates sustained microglial ROS generation by the NAPDH oxidase

Crystal structure of the soluble form of the redox-regulated chloride ion channel protein CLIC4

The structure of CLIC4, a member of the CLIC family of putative intracellular chloride ion channel proteins, has been determined at 1.8 angstrom resolution by X-ray crystallography. The protein is monomeric and it is structurally similar to CLIC1, belonging to the GST fold class. Differences between the structures of CLIC1 and CLIC4 are localized to helix 2 in the glutaredoxin-like N-terminal domain, which has previously been shown to undergo a dramatic structural change in CLIC1 upon oxidation. The structural differences in this region correlate with the sequence differences, where the CLIC1 sequence appears to be atypical of the family. Purified, recombinant, wild-type CLIC4 is shown to bind to artificial lipid bilayers, induce a chloride efflux current when associated with artificial liposomes and produce an ion channel in artificial bilayers with a conductance of 30 pS. Membrane binding is enhanced by oxidation of CLIC4 while no channels were observed via tip-dip electrophysiology in the presence of a reducing agent. Thus, recombinant CLIC4 appears to be able to form a redox-regulated ion channel in the absence of any partner proteins

Involvement of the intracellular ion channel CLIC1 in microglia-mediated beta-amyloid-induced neurotoxicity

It is widely believed that the inflammatory events mediated by microglial activation contribute to several neurodegenerative processes. Alzheimer's disease, for example, is characterized by an accumulation of \u3b2-amyloid protein (A\u3b2) in neuritic plaques that are infiltrated by reactive microglia and astrocytes. Although A\u3b2 and its fragment 25-35 exert a direct toxic effect on neurons, they also activate microglia. Microglial activation is accompanied by morphological changes, cell proliferation, and release of various cytokines and growth factors. A number of scientific reports suggest that the increased proliferation of microglial cells is dependent on ionic membrane currents and in particular on chloride conductances. An unusual chloride ion channel known to be associated with macrophage activation is the chloride intracellular channel-1 (CLIC1). Here we show that A\u3b2 stimulation of neonatal rat microglia specifically leads to the increase in CLIC1 protein and to the functional expression of CLIC1 chloride conductance, both barely detectable on the plasma membrane of quiescent cells. CLIC1 protein expression in microglia increases after 24 hr of incubation with A\u3b2, simultaneously with the production of reactive nitrogen intermediates and of tumor necrosis factor-\u3b1 (TNF-\u3b1). We demonstrate that reducing CLIC1 chloride conductance by a specific blocker [IAA-94 (R(+)-[(6,7-dichloro-2-cyclopentyl-2,3-dihydro-2-methyl-1-oxo-1H-inden-5yl)-oxy] acetic acid)] prevents neuronal apoptosis in neurons cocultured with A\u3b2-treated microglia. Furthermore, we show that small interfering RNAs used to knock down CLIC1 expression prevent TNF-\u3b1 release induced by A\u3b2 stimulation. These results provide a direct link between A\u3b2-induced microglial activation and CLIC1 functional expression

Elevated levels of MIC-1/GDF15 in the cerebrospinal fluid of patients are associated with glioblastoma and worse outcome.

For patients with brain tumors identification of diagnostic and prognostic markers in easy accessible biological material, such as plasma or cerebrospinal fluid (CSF), would greatly facilitate patient management. MIC-1/GDF15 (growth differentiation factor 15) is a secreted protein of the TGF-beta superfamily and emerged as a candidate marker exhibiting increasing mRNA expression during malignant progression of glioma. Determination of MIC-1/GDF15 protein levels by ELISA in the CSF of a cohort of 94 patients with intracranial tumors including gliomas, meningioma and metastasis revealed significantly increased concentrations in glioblastoma patients (median, 229 pg/ml) when compared with control cohort of patients treated for non-neoplastic diseases (median below limit of detection of 156 pg/ml, p < 0.0001, Mann-Whitney test). However, plasma MIC-1/GDF15 levels were not elevated in the matching plasma samples from these patients. Most interestingly, patients with glioblastoma and increased CSF MIC-1/GDF15 had a shorter survival (p = 0.007, log-rank test). In conclusion, MIC-1/GDF15 protein measured in the CSF may have diagnostic and prognostic value in patients with intracranial tumors

Anoxia induces macrophage inhibitory cytokine-1 (MIC-1) in glioblastoma cells independently of p53 and HIF-1.

Human astrocytic brain tumors select for mutations in the p53 tumor suppressor gene early in malignant progression. p53 is activated upon various kinds of cellular stress leading to apoptosis or cell cycle arrest, but is also implicated in complex biological processes such as inhibition of angiogenesis and metastasis. In an effort to shed light on consequences mediated by p53 inactivation in gliomas, we established the Tet-On system for p53 in the LN-Z308 glioblastoma cell line. The macrophage inhibitory cytokine-1 (MIC-1) gene was identified as a most prominent p53 target gene upon gene expression profiling. Oxygen deprivation, an important cellular stress, revealed MIC-1 as an anoxia responsive gene in glioblastoma cell lines. MIC-1 up-regulation by anoxia is mediated through an alternative, p53 and hypoxia inducible factor 1 (HIF-1) independent pathway. Furthermore, ectopic expression of MIC-1 in LN-Z308 cell line completely abolished its inherent tumorigenicity in nude mice, while proliferation in vitro was not affected. In the present experimental model MIC-1 may exert its anti-tumorigenic properties via a paracrine mechanism mediated by host cells in vivo. Taken together, these data suggest that MIC-1 is an important downstream mediator of p53 function, while acting itself as an intercessor of cellular stress signaling and exerting anti-tumorigenic activities