Antonio Celada

Homogeneous Conjugation of Peptides onto Gold Nanoparticles Enhances Macrophage Response

Murine bone marrow macrophages were able to recognize gold nanoparticle peptide conjugates, while peptides or nanoparticles alone were not recognized. Consequently, in the presence of conjugates, macrophage proliferation was stopped and pro-inflammatory cytokines such as TNF-alpha, IL-1beta, and IL-6, as well as nitric oxide synthase (NOS2) were induced. Furthermore, macrophage activation by gold nanoparticles conjugated to different peptides appeared to be rather independent of peptide length and polarity, but dependent on peptide pattern at the nanoparticle surface. Correspondingly, the biochemical type of response also depended on the type of conjugated peptide and could be correlated with the degree of ordering in the peptide coating. These findings help to illustrate the basic requirements involved in medical nanoparticle conjugate design to either activate the immune system or hide from it in order to reach their targets before being removed by phagocytes.

Arginase and polyamine synthesis are key factors in the regulation of experimental leishmaniasis in vivo.

Arginase 1, an enzyme induced by Th2 cytokines, is a hallmark of alternatively activated macrophages and is responsible for the hydrolysis of l‐arginine into ornithine, the building block for the production of polyamines. Upregulation of arginase 1 has been observed in a variety of diseases, but the mechanisms by which arginase contributes to pathology are not well understood. We reveal here a unique role for arginase 1 in the pathogenesis of nonhealing leishmaniasis, a prototype Th2 disease, and demonstrate that the activity of this enzyme promotes pathology and uncontrolled growth of Leishmania parasites in vivo. Inhibition of arginase activity during the course of infection has a clear therapeutic effect, as evidenced by markedly reduced pathology and efficient control of parasite replication. Despite the clear amelioration of the disease, this treatment does not alter the Th2 response. To address the underlying mechanisms, the arginase‐induced l‐arginine catabolism was investigated and the results demonstrate that arginase regulates parasite growth directly by affecting the polyamine synthesis in macrophages.

Transcription factors that regulate monocyte/macrophage differentiation.

Although all the cells in an organism contain the same genetic information, differences in the cell phenotype arise from the expression of lineage‐specific genes. During myelopoiesis, external differentiating signals regulate the expression of a set of transcription factors. The combined action of these transcription factors subsequently determines the expression of myeloid‐specific genes and the generation of monocytes and macrophages. In particular, the transcription factor PU.1 has a critical role in this process. We review the contribution of several transcription factors to the control of macrophage development. J. Leukoc. Biol. 63: 405–417; 1998.

The kinase p38|[alpha]| serves cell type|[ndash]|specific inflammatory functions in skin injury and coordinates pro- and anti-inflammatory gene expression

The mitogen-activated protein kinase p38 mediates cellular responses to injurious stress and immune signaling. Among the many p38 isoforms, p38α is the most widely expressed in adult tissues and can be targeted by various pharmacological inhibitors. Here we investigated how p38α activation is linked to cell type–specific outputs in mouse models of cutaneous inflammation. We found that both myeloid and epithelial p38α elicit inflammatory responses, yet p38α signaling in each cell type served distinct inflammatory functions and varied depending on the mode of skin irritation. In addition, myeloid p38α limited acute inflammation via activation of anti-inflammatory gene expression dependent on mitogen- and stress-activated kinases. Our results suggest a dual function for p38α in the regulation of inflammation and show mixed potential for its inhibition as a therapeutic strategy.

Interferon γ Induces the Expression of p21waf-1 and Arrests Macrophage Cell Cycle, Preventing Induction of Apoptosis

Incubation of bone marrow macrophages with lipopolysaccharide (LPS) or interferon gamma (IFN gamma) blocks macrophage proliferation. LPS treatment or M-CSF withdrawal arrests the cell cycle at early G1 and induces apoptosis. Treatment of macrophages with IFN gamma stops the cell cycle later, at the G1/S boundary, induces p21Waf1, and does not induce apoptosis. Moreover, pretreatment of macrophages with IFN gamma protects from apoptosis induced by several stimuli. Inhibition of p21Waf1 with antisense oligonucleotides or using KO mice shows that the induction of p21Waf1 by IFN gamma mediates this protection. Thus, IFN gamma makes macrophages unresponsive to apoptotic stimuli by inducing p21Waf1 and arresting the cell cycle at the G1/S boundary. Therefore, the cells of the innate immune system could only survive while they were functionally active.

Macrophage activation revisited

Macrophages are extremely adaptable cells, able to modify their behavior in response to diverse signals from other cells and the extracellular matrix. A recent workshop provided insights into current research on these remarkable cells.

The key role of PU.1/SPI-1 in B cells, myeloid cells and macrophages

Abstract PU.1 is a member of the transcription factor family Ets that is expressed selectively on B cells, myeloid cells and macrophages. PU.1 regulates the expression of several genes, including those encoding immunoglobulins, receptors and enzymes. The expression of these genes is crucial for macrophage and B-cell differentiation and for the functional activity of neutrophils.

The Differential Time-course of Extracellular-regulated Kinase Activity Correlates with the Macrophage Response toward Proliferation or Activation*

Bone marrow-derived macrophages proliferate in response to specific growth factors, including macrophage colony-stimulating factor (M-CSF). When stimulated with activating factors, such as lipopolysaccharide (LPS), macrophages stop proliferating and produce proinflammatory cytokines. Although triggering opposed responses, both M-CSF and LPS induce the activation of extracellular-regulated kinases (ERKs) 1 and 2. However, the time-course of ERK activation is different; maximal activation by M-CSF and LPS occurred after 5 and 15 min of stimulation, respectively. Granulocyte/macrophage colony-stimulating factor, interleukin 3, and TPA, all of which induced macrophage proliferation, also induced ERK activity, which was maximal at 5 min poststimulation. The use of PD98059, which specifically blocks ERK 1 and 2 activation, demonstrated that ERK activity was necessary for macrophage proliferation in response to these factors. The treatment with phosphatidylcholine-specific phospholipase C (PC-PLC) inhibited macrophage proliferation, induced the expression of cytokines, and triggered a pattern of ERK activation equivalent to that induced by LPS. Moreover, PD98059 inhibited the expression of cytokines induced by LPS or PC-PLC, thus suggesting that ERK activity is also required for macrophage activation by these two agents. Activation of the JNK pathway did not discriminate between proliferative and activating stimuli. In conclusion, our results allow to correlate the differences in the time-course of ERK activity with the macrophagic response toward proliferation or activation.

Protein kinase C epsilon is required for the induction of mitogen-activated protein kinase phosphatase-1 in lipopolysaccharide-stimulated macrophages.

LPS induces in bone marrow macrophages the transient expression of mitogen-activated protein kinase (MAPK) phosphatase-1 (MKP-1). Because MKP-1 plays a crucial role in the attenuation of different MAPK cascades, we were interested in the characterization of the signaling mechanisms involved in the control of MKP-1 expression in LPS-stimulated macrophages. The induction of MKP-1 was blocked by genistein, a tyrosine kinase inhibitor, and by two different protein kinase C (PKC) inhibitors (GF109203X and calphostin C). We had previously shown that bone marrow macrophages express the isoforms PKCβI, ε, and ζ. Of all these, only PKCβI and ε are inhibited by GF109203X. The following arguments suggest that PKCε is required selectively for the induction of MKP-1 by LPS. First, in macrophages exposed to prolonged treatment with PMA, MKP-1 induction by LPS correlates with the levels of expression of PKCε but not with that of PKCβI. Second, Gö6976, an inhibitor selective for conventional PKCs, including PKCβI, does not alter MKP-1 induction by LPS. Last, antisense oligonucleotides that block the expression of PKCε, but not those selective for PKCβI or PKCζ, inhibit MKP-1 induction and lead to an increase of extracellular-signal regulated kinase activity during the macrophage response to LPS. Finally, in macrophages stimulated with LPS we observed significant activation of PKCε. In conclusion, our results demonstrate an important role for PKCε in the induction of MKP-1 and the subsequent negative control of MAPK activity in macrophages.

Molecular Mechanisms Involved in Macrophage Survival, Proliferation, Activation or Apoptosis

Macrophages play a critical role during the immune response. Like other cells of the immune system, macrophages are produced in large amounts and most of them die through apoptosis. Macrophages survive in the presence of soluble factors, such as IFN-gamma, or extracellular matrix proteins like decorin. The mechanism toward survival requires the blocking of proliferation at the G1/S boundary of the cell cycle that is mediated by the cyclin-dependent kinase (cdk) inhibitor, p27kip and the induction of a cdk inhibitor, p21waf1. At the inflammatory loci, macrophages need to proliferate or become activated in order to perform their specialized activities. Although the stimuli inducing proliferation and activation follow different intracellular pathways, both require the activation of extracellular signal-regulated kinases (ERKs) 1 and 2. However, the kinetics of ERK-1/2 activation is different and is determined by the induction of the MAP-kinase phosphatase-1 (MKP-1) that dephosphorilates ERK-1/2. This phosphatase plays a critical role in the process of proliferation versus activation of the macrophages.