Inflamació i macròfags

Els macròfags tenen un paper clau en la inflamació. Durant l'inici del procés inflamatori aquestes cèl·lules s'activen i mostren una potent funció fagocítica i microbicida que pot tenir efectes destructius en els teixits on actua. L'activació dels macròfags implica la inducció de més de quatre-cents gens, i dóna com a resultat més capacitat per eliminar els bacteris i per regular moltes altres cèl·lules a través de l'alliberament de citocines i quimiocines. L'activació excessiva d'aquestes cèl·lules té efectes perjudicials, com ara el xoc sèptic, que pot conduir a la síndrome de disfunció orgànica múltiple i a la mort. En altres situacions la persistència dels resultats de l'activitat proinflamatòria pot contribuir al desenvolupament de processos d'inflamació crònica, com l'artritis reumatoide, la psoriasi i la malaltia inflamatòria de l'intestí. Per evitar aquests efectes indesitjables els macròfags han desenvolupat diversos mecanismes per regular l'excés d'activació, de manera que es condueix a la desactivació dels macròfags i a la resolució de la inflamació.Macrophages play key roles in inflammation. During the onset of the inflammatory process, these phagocytic cells become activated and have destructive effects. Macrophage activation, which involves the induction of more than 400 genes, results in an increased capacity to eliminate bacteria and to regulate many other cells through the release of cytokines and chemokines. However, excessive activation has damaging effects, such as septic shock, which can lead to multiple organ dysfunction syndrome and death. In other situations, persistence of pro-inflammatory activity results in the development of chronic inflammation, such as rheumatoid arthritis, psoriasis and inflammatory bowel disease. To prevent undesirable effects, several mechanisms have evolved to control excess activation, thereby leading to macrophage deactivation and the resolution of inflammation. In this review we will discuss the molecular mechanisms of proliferation, activation and survival of macrophages

Inflamació i macròfags

Els macròfags tenen un paper clau en la inflamació. Durant l'inici del procés inflamatori aquestes cèl·lules s'activen i mostren una potent funció fagocítica i microbicida que pot tenir efectes destructius en els teixits on actua. L'activació dels macròfags implica la inducció de més de quatre-cents gens, i dóna com a resultat més capacitat per eliminar els bacteris i per regular moltes altres cèl·lules a través de l'alliberament de citocines i quimiocines. L'activació excessiva d'aquestes cèl·lules té efectes perjudicials, com ara el xoc sèptic, que pot conduir a la síndrome de disfunció orgànica múltiple i a la mort. En altres situacions la persistència dels resultats de l'activitat proinflamatòria pot contribuir al desenvolupament de processos d'inflamació crònica, com l'artritis reumatoide, la psoriasi i la malaltia inflamatòria de l'intestí. Per evitar aquests efectes indesitjables els macròfags han desenvolupat diversos mecanismes per regular l'excés d'activació, de manera que es condueix a la desactivació dels macròfags i a la resolució de la inflamació

Deacetylase activity is required for STAT5-Dependent GM-CSF functional activity in macrophages and differentiation to dendritic cells.

After interaction with its receptor, GM-CSF induces phosphorylation of the -chain in two distinct domains in macrophages. One induces activation of mitogen-activated protein kinases and the PI3K/Akt pathway, and the other induces JAK2-STAT5. In this study we describe how trichostatin A (TSA), which inhibits deacetylase activity, blocks JAK2-STAT5-dependent gene expression but not the expression of genes that depend on the signal transduction induced by the other domain of the receptor. TSA treatment inhibited the GM-CSF-dependent proliferation of macrophages by interfering with c-myc and cyclin D1 expression. However, M-CSF-dependent proliferation, which requires ERK1/2, was unaffected. Protection from apoptosis, which involves Akt phosphorylation and p21waf-1 expression, was not modified by TSA. GM-CSF-dependent expression of MHC class II molecules was inhibited because CIITA was not induced. The generation of dendritic cells was also impaired by TSA treatment because of the inhibition of IRF4, IRF2, and RelB expression. TSA mediates its effects by preventing the recruitment of RNA polymerase II to the promoter of STAT5 target genes and by inhibiting their expression. However, this drug did not affect STAT5A or STAT5B phosphorylation or DNA binding. These results in GM-CSF-treated macrophages reveal a relationship between histone deacetylase complexes and STAT5 in the regulation of gene expression

Mitogen-activated protein kinases and mitogen kinase phosphatase 1: a critical interplay in macrophage biology

Macrophages are necessary in multiple processes during the immune response or inflammation. This review emphasizes the critical role of the mitogen-activated protein kinases (MAPKs) and mitogen kinase phosphatase-1 (MKP-1) in the functional activities of macrophages. While the phosphorylation of MAPKs is required for macrophage activation or proliferation, MKP-1 dephosphorylates these kinases, thus playing a balancing role in the control of macrophage behavior. MKP-1 is a nuclear-localized dual-specificity phosphatase whose expression is regulated at multiple levels, including at the transcriptional and post-transcriptional level. The regulatory role of MKP-1 in the interplay between MAPK phosphorylation/dephosphorylation makes this molecule a critical regulator of macrophage biology and inflammation

Distinct Responses to IL4 in Macrophages Mediated by JNK

IL(Interleukin)-4 is the main macrophage M2-type activator and induces an anti-inflammatory phenotype called alternative activation. The IL-4 signaling pathway involves the activation of STAT (Signal Transducer and Activator of Transcription)-6 and members of the MAPK (Mitogen-activated protein kinase) family. In primary-bone-marrow-derived macrophages, we observed a strong activation of JNK (Jun N-terminal kinase)-1 at early time points of IL-4 stimulation. Using selective inhibitors and a knockout model, we explored the contribution of JNK-1 activation to macrophages' response to IL-4. Our findings indicate that JNK-1 regulates the IL-4-mediated expression of genes typically involved in alternative activation, such as Arginase 1 or Mannose receptor, but not others, such as SOCS (suppressor of cytokine signaling) 1 or p21Waf−1 (cyclin dependent kinase inhibitor 1A). Interestingly, we have observed that after macrophages are stimulated with IL-4, JNK-1 has the capacity to phosphorylate STAT-6 on serine but not on tyrosine. Chromatin immunoprecipitation assays revealed that functional JNK-1 is required for the recruitment of co-activators such as CBP (CREB-binding protein)/p300 on the promoter of Arginase 1 but not on p21Waf−1. Taken together, these data demonstrate the critical role of STAT-6 serine phosphorylation by JNK-1 in distinct macrophage responses to IL-4

Arginine transport is impaired in C57Bl/6 mouse macrophages as a result of a deletion in the promoter of slc7a2 (CAT2) and Leishmania infection is reduced

Host genetic factors play a crucial role in immune response. To determine whether the differences betweenC57Bl/6 and BALB-C mice are due only to the production of cytokines by T-helper 1 cells or T-helper 2 cells,we obtained bone marrow–derived macrophages from both strains and incubated them with these cytokines.Although the induction of Nos2 and Arg1 was similar in the 2 strains, infectivity to Leishmania major differed,as did macrophage uptake of arginine, which was higher in BALB-C macrophages. The levels of interferon γ–and interleukin 4–dependent induction of the cationic amino acid transporter SLC7A2 (also known as “cationicamino acid transporter 2,” or “CAT2”) were decreased in macrophages from C57Bl/6 mice. This reductionwas a result of a deletion in the promoter of one of the 4 AGGG repeats. These results demonstrate that theavailability of arginine controls critical aspects of macrophage activation and reveal a factor for susceptibility to Leishmania infection

Induction of CIITA by IFN-γ in macrophages involves STAT1 activation byJAK and JNK

The induction of major histocompatibility complex (MHC) class II proteins by interferon gamma (IFN-γ) in macrophages play an important role during immune responses. Here we explore the signaling pathways involved in the induction by IFN-γ of the MHC II transactivator (CIIta) required for MHC II transcriptional activation. Cyclophilin A (CypA) is required for IFN-γ-dependent induction of MHC II in macrophages, but not when it is mediated by GM-CSF. The effect of CypA appears to be specific because it does not affect the expression of other molecules or genes triggered by IFN-γ, such as FcγR, NOS2, Lmp2, and Tap1. We found that CypA inhibition blocked the IFN-γ-induced expression of CIIta at the transcriptional level in two phases. In an early phase, during the first 2 h of IFN-γ treatment, STAT1 is phosphorylated at Tyrosine 701 and Serine 727, residues required for the induction of the transcription factor IRF1. In a later phase, STAT1 phosphorylation and JNK activation are required to trigger CIIta expression. CypA is needed for STAT1 phosphorylation in this last phase and to bind the CIIta promoter. Our findings demonstrate that STAT1 is required in a two-step induction of CIIta, once again highlighting the significance of cross talk between signaling pathways in macrophages

The transcription factor PU.1 is involved in macrophage proliferation

PU.1 is a tissue-specific transcription factor that is expressed in cells of the hematopoietic lineage including macrophages, granulocytes, and B lymphocytes. Bone marrow-derived macrophages transfected with an antisense PU.1 expression construct or treated with antisense oligonucleotides showed a decrease in proliferation compared with controls. In contrast, bone marrow macrophages transfected with a sense PU.1 expression construct displayed enhanced macrophage colony- stimulating factor (M-CSF)-dependent proliferation. Interestingly, there was no effect of sense or antisense constructs of PU.1 on the proliferation of the M-CSF-independent cell line, suggesting that the response was M-CSF dependent. This was further supported by the finding that macrophages transfected with a sense or an antisense PU.1 construct showed, respectively, an increased or a reduced level of surface expression of receptors for M-CSF. The enhancement of proliferation seems to be selective for PU.1, since transfections with several other members of the ets family, including ets-2 and fli-1, had no effect. Various mutants of PU.1 were also tested for their ability to affect macrophage proliferation. A reduction in macrophage proliferation was found when cells were transfected with a construct in which the DNA-binding domain of PU.1 was expressed. The PEST (proline-, glutamic acid-, serine-, and threonine-rich region) sequence of the PU.1 protein, which is an important domain for protein-protein interactions in B cells, was found to have no influence on PU.1- enhanced macrophage proliferation when an expression construct containing PU.1 minus the PEST domain was transfected into bone marrow- derived macrophages. In vivo, PU.1 is phosphorylated on several serine residues. The transfection of plasmids containing PU.1 with mutations at each of five serines showed that only positions 41 and 45 are critical for enhanced macrophage proliferation. We conclude that PU.1 is necessary for the M-CSF-dependent proliferation of macrophages. One of the proliferation-relevant targets of this transcription factor could be the M-CSF receptor

IRF1 is required for MDA5 (IFIH1) induction by IFN-α, LPS and poly(I:C) in murine macrophages

Melanoma differentiation-associated protein 5 (MDA5) induces type I interferons (IFNs) after the recognition of viral RNA. In addition, gain-of-function mutations in the interferon induced with helicase C domain 1 (IFIH1) gene, which encodes MDA5, lead to type I interferonopathies. Here, we show that Mda5 is highly expressed in murine macrophages and is regulated by pro-inflammatory stimuli such as the cytokines IFN-α and IFN-γ, the TLR ligand LPS, and a mimic of dsRNA, poly(I:C). Mda5 induction is mediated through the production of reactive oxygen species. The induction by IFN-α or LPS occurs at the transcriptional level since the Mda5 mRNA half-life before and after induction is very stable. Interestingly, STAT1 is required for Mda5 induction by IFN-α, LPS, or poly(I:C). The time course of induction of at least 3 h and the need for protein synthesis indicate that Mda5 requires an intermediate protein for transcription. In transient transfection experiments, we found that a 105-bp fragment of this gene, between −1153 and −1258 bp relative to the transcription start site, is required for transcription. In this specific region, we observed a sequence containing an IRF-binding motif, which, when mutated, abolishes the induction of Mda5. This sequence is strongly conserved in the IFIH1 promoters of eutherian mammals and in other distant species. Kinetic experiments, chromatin immunoprecipitation assays, and gene-silencing experiments revealed that IRF1 is required for induction of Mda5 expression

Identification and characterization of a membrane protein (y+L amino acid transporter-1) that associates with 4F2hc to encode the amino acid transport activity y+L. A candidate gene for lysinuric protein intolerance

We have identified a new human cDNA (y+L amino acid transporter-1 (y+LAT-1)) that induces system y+L transport activity with 4F2hc (the surface antigen 4F2 heavy chain) in oocytes. Human y+LAT-1 is a new member of a family of polytopic transmembrane proteins that are homologous to the yeast high affinity methionine permease MUP1. Other members of this family, the Xenopus laevis IU12 and the human KIAA0245 cDNAs, also co-express amino acid transport activity with 4F2hc in oocytes, with characteristics that are compatible with those of systems L and y+L, respectively. y+LAT-1 protein forms a approximately 135-kDa, disulfide bond-dependent heterodimer with 4F2hc in oocytes, which upon reduction results in two protein bands of approximately 85 kDa (i.e. 4F2hc) and approximately 40 kDa (y+LAT-1). Mutation of the human 4F2hc residue cysteine 109 (Cys-109) to serine abolishes the formation of this heterodimer and drastically reduces the co-expressed transport activity. These data suggest that y+LAT-1 and other members of this family are different 4F2 light chain subunits, which associated with 4F2hc, constitute different amino acid transporters. Human y+LAT-1 mRNA is expressed in kidney >> peripheral blood leukocytes >> lung > placenta = spleen > small intestine. The human y+LAT-1 gene localizes at chromosome 14q11.2 (17cR approximately 374 kb from D14S1350), within the lysinuric protein intolerance (LPI) locus (Lauteala, T., Sistonen, P. , Savontaus, M. L., Mykkanen, J., Simell, J., Lukkarinen, M., Simmell, O., and Aula, P. (1997) Am. J. Hum. Genet. 60, 1479-1486). LPI is an inherited autosomal disease characterized by a defective dibasic amino acid transport in kidney, intestine, and other tissues. The pattern of expression of human y+LAT-1, its co-expressed transport activity with 4F2hc, and its chromosomal location within the LPI locus, suggest y+LAT-1 as a candidate gene for LPI