Endotoxin (LPS) stimulates 4E-BP1/PHAS-I phosphorylation in macrophages

Short open reading frame genes in innate immunity: from discovery to characterization

Next-generation sequencing (NGS) technologies have greatly expanded the size of the known transcriptome. Many newly discovered transcripts are classified as long noncoding RNAs (lncRNAs) which are assumed to affect phenotype through sequence and structure and not via translated protein products despite the vast majority of them harboring short open reading frames (sORFs). Recent advances have demonstrated that the noncoding designation is incorrect in many cases and that sORF-encoded peptides (SEPs) translated from these transcripts are important contributors to diverse biological processes. Interest in SEPs is at an early stage and there is evidence for the existence of thousands of SEPs that are yet unstudied. We hope to pique interest in investigating this unexplored proteome by providing a discussion of SEP characterization generally and describing specific discoveries in innate immunity.

Interactions between Autophagy and Bacterial Toxins: Targets for Therapy?

Autophagy is a physiological process involved in defense mechanisms for clearing intracellular bacteria. The autophagic pathway is finely regulated and bacterial toxins interact with this process in a complex manner. Bacterial toxins also interact significantly with many biochemical processes. Evaluations of the effects of bacterial toxins, such as endotoxins, pore-forming toxins and adenylate cyclases, on autophagy could support the development of new strategies for counteracting bacterial pathogenicity. Treatment strategies could focus on drugs that enhance autophagic processes to improve the clearance of intracellular bacteria. However, further in vivo studies are required to decipher the upregulation of autophagy and potential side effects limiting such approaches. The capacity of autophagy activation strategies to improve the outcome of antibiotic treatment should be investigated in the future.

The emerging role of mTOR signalling in antibacterial immunity

Mammalian target of rapamycin (mTOR) is a central regulator of cellular metabolic homeostasis that is highly conserved in evolution. Recent evidence has revealed the existence of a complex interplay between mTOR signalling and immunity. We review here the emerging role of mTOR signalling in the regulation of Toll-like receptor-dependent innate responses and in the activation of T cells and antigen-presenting cells. We also highlight the importance of amino-acid starvation-driven mTOR inhibition in the control of autophagy and intracellular bacterial clearance.

Expression of the interleukin 17 in cortical tubers of the tuberous sclerosis complex

The role of interleukin 17 (IL-17) to epilepsy-associated cortical tubers of tuberous sclerosis complex (TSC) is unknown. We investigated the expression patterns of the IL-17 and IL-17 receptor (IL-17R) in cortical tubers of TSC compared with normal control cortex (CTX). We found that IL-17 and IL-17R were clearly upregulated in cortical tubers at the protein levels. Immunostaining indicated that IL-17 was specifically distributed in the innate immunity cells (DNs, GCs, astrocytes, and microglia) and adaptive immunity cells (T-lymphocytes) as well as the endothelial cells of blood vessels. The overexpression and distribution patterns of IL-17 may be involved in the epileptogenicity of cortical tubers in TSC.

Toll-like receptor activation suppresses ER stress factor CHOP and translation inhibition through activation of eIF2B

Activation of toll-like receptors (TLRs) induces the endoplasmic reticulum (ER) Unfolded Protein Response (UPR) to accommodate essential protein translation^1,2. However, despite increased p-eIF2α, a TLR-TRIF-dependent pathway assures that the cells avoid CHOP induction, apoptosis, and translational suppression of critical proteins³. Because p-eIF2α decreases the functional interaction of eIF2 with eIF2B, a guanine nucleotide exchange factor (GEF), we explored the hypothesis that TLR-TRIF signaling activates eIF2B-GEF activity to counteract the effects of p-eIF2α. We now show that TLR-TRIF signaling activates eIF2B-GEF through PP2A-mediated Ser-dephosphorylation of the eIF2B ε-subunit. PP2A itself is activated by decreased Src-family-kinase-induced Tyr-phosphorylation of its catalytic subunit. Each of these processes are required for TLR-TRIF-mediated CHOP suppression in ER-stressed cells in vitro and in vivo. Thus, in the setting of prolonged, physiologic ER stress, a unique TLR-TRIF-dependent translational control pathway enables cells to carry out essential protein synthesis and avoid CHOP-induced apoptosis while still benefitting from the protective arms of the UPR.

Role of the mTOR pathway in LPS-activated monocytes: influence of hypertonic saline

BACKGROUND

As heightened protein synthesis is the hallmark of many inflammatory syndromes, we hypothesize that the mammalian target of rapamycin (mTOR) pathway, which control the cap-dependent translation initiation phase, was activated by lipopolysaccharide (LPS). In addition, we studied the effect of hypertonic saline solution (HTS) on the mTOR cascade in peripheral blood mononuclear cells (PBMCs).

MATERIALS AND METHODS

PBMCs were isolated from healthy volunteers and treated with LPS. Cells were pretreated with phosphatidylinositol 3-kinase (PI3K) and mTOR inhibitors, or with HTS. Supernatants were harvested 20 h following LPS treatment, and interleukin-10 (IL-10), interleukin-6 (IL-6) and tumor necrosis alpha (TNFα) were analyzed by ELISA. Immunoblot experiments were performed for components of the PI3K/Akt/mTOR pathway at various time points. RNA was extracted after 90 min for real-time RT-PCR quantification.

RESULTS

The mTOR pathway is activated in PBMCs within 1 h of LPS stimulation. Pretreatment with rapamycin, a specific inhibitor of mTOR, resulted in a significant decrease of IL-10 and IL-6 translation and expression but did not affect the LPS-induced TNFα production. Both the mTOR pathway and the LPS-induced IL-6 production were down-regulated by HTS pretreatment.

CONCLUSIONS

The PI3k/Akt/mTOR cascade modulates LPS-induced cytokines production differentially. IL-10 and IL-6 expression are both up-regulated by activation of the mTOR pathway in response to LPS in PBMCs, while TNFα is not controlled by the mTOR cascade. Meanwhile, pretreatment of PBMCs with a HTS solution suppresses mTOR activity as well as LPS-induced IL-6, suggesting a more central role for mTOR as a regulator of the immuno-inflammatory response.

Clinicopathological and immunohistochemical findings in an autopsy case of tuberous sclerosis complex

Tuberous sclerosis complex (TSC) is an autosomal dominant, multisystem disorder caused by mutations in either the TSC1 or TSC2 genes and characterized by developmental brain abnormalities. In the present study we discuss the neuropathological findings of a 32-year-old patient with a germ-line mutation in the TSC2 gene. Post mortem MRI combined with histology and immunocytochemical analysis was applied to demonstrate widespread anatomical abnormalities of gray and white matter structure. TSC brain lesions were analyzed for loss of heterozygosity (LOH) on chromosome 16p13. The neuropathological supratentorial abnormalities were represented by multiple subependymal nodules (SENs) and cortical tubers. In addition to cerebral cortical lesions, cerebellar lesions and hippocampal sclerosis were also observed. LOH was not found in the cortical tubers and SENs of this patient. Immunocytochemical analysis of the TSC brain lesions confirmed the cell-specific activation of the mTOR pathway in cortical tubers, SENs and cerebellum, as well as differential cellular localization of hamartin and tuberin, the TSC1 and TSC2 gene products. Examination of the pathological brain regions revealed activated microglial cells and disruption of blood-brain barrier permeability. Predominant intralesional cell-specific distribution was also detected for the multidrug transporter protein P-gp, possibly explaining the mechanisms underlying the pharmacoresistance to antiepileptic drugs. Autopsy findings confirm the complexity of the brain abnormalities encountered in TSC patients and proved useful in clarifying certain aspects of the pathogenesis, epileptogenesis and pharmacoresistance of TSC lesions.

Urocortin modulates inflammatory response and neurotoxicity induced by microglial activation

Microglia are the major inflammatory cells in the brain. Recent studies have highlighted the reciprocal roles of other brain cells in modulating the microglial inflammatory responses. Urocortin (UCN) is a member of the corticotropin-releasing hormone (CRH) family of neuropeptides that function to regulate stress responses. In the present study, we demonstrated that expression of UCN in rat substantia nigra was found to be localized principally to dopaminergic neurons. In cell culture models, the CRH receptors were expressed in microglia, and CRHR expression was up-regulated by treatment with LPS. Thus, it might be proposed that UCN regulates cellular communication between dopaminergic neurons and microglia. We show that femtomolar concentrations of UCN could inhibit LPS-induced TNF-alpha production in cultured microglia. Investigation of the underlying signaling pathway that mediated the anti-inflammatory effect of UCN the involved PI3K/Akt and glycogen synthase kinase-3beta pathway, but not cAMP pathway. Furthermore, UCN protected dopaminergic neurons against LPS-induced neurotoxicity by inhibiting microglial activation in LPS-treated mesencephalic neuron-glia cultures. These results suggest that endogenous UCN and its receptors might be involved in a complex network of paracrine interaction between dopaminergic neurons and glia.

Inflammatory processes in cortical tubers and subependymal giant cell tumors of tuberous sclerosis complex

Cortical tubers and subependymal giant cell tumors (SGCT) are two major cerebral lesions associated with tuberous sclerosis complex (TSC). In the present study, we investigated immunocytochemically the inflammatory cell components and the induction of two major pro-inflammatory pathways (the interleukin (IL)-1beta and complement pathways) in tubers and SGCT resected from TSC patients. All lesions were characterized by the prominent presence of microglial cells expressing class II-antigens (HLA-DR) and, to a lesser extent, the presence of CD68-positive macrophages. We also observed perivascular and parenchymal T lymphocytes (CD3(+)) with a predominance of CD8(+) T-cytotoxic/suppressor lymphoid cells. Activated microglia and reactive astrocytes expressed IL-1beta and its signaling receptor IL-1RI, as well as components of the complement cascade, such as C1q, C3c and C3d. Albumin extravasation, with uptake in astrocytes, was observed in both tubers and SGCT, suggesting that alterations in blood brain barrier permeability are associated with inflammation in TSC-associated lesions. Our findings demonstrate a persistent and complex activation of inflammatory pathways in cortical tubers and SGCT.

Shiga toxin 1-induced cytokine production is mediated by MAP kinase pathways and translation initiation factor eIF4E in the macrophage-like THP-1 cell line

Upon binding to the glycolipid receptor globotriaosylceramide, Shiga toxins (Stxs) undergo retrograde transport to reach ribosomes, cleave 28S rRNA, and inhibit protein synthesis. Stxs induce the ribotoxic stress response and cytokine and chemokine expression in some cell types. Signaling mechanisms necessary for cytokine expression in the face of toxin-mediated protein synthesis inhibition are not well characterized. Stxs may regulate cytokine expression via multiple mechanisms involving increased gene transcription, mRNA transcript stabilization, and/or increased translation initiation efficiency. We show that treatment of differentiated THP-1 cells with purified Stx1 resulted in prolonged activation of c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (MAPK) cascades, and lipopolysaccharides (LPS) rapidly triggered transient activation of JNK and p38 and prolonged activation of extracellular signal-regulated kinase cascades. Simultaneous treatment with Stx1 + LPS mediated prolonged p38 MAPK activation. Stx1 increased eukaryotic translation initiation factor 4E (eIF4E) activation by 4.3-fold within 4-6 h, and LPS or Stx1 + LPS treatment increased eIF4E activation by 7.8- and 11-fold, respectively, within 1 h. eIF4E activation required Stx1 enzymatic activity and was mediated by anisomycin, another ribotoxic stress inducer. A combination of MAPK inhibitors or a MAPK-interacting kinase 1 (Mnk1)-specific inhibitor blocked eIF4E activation by all stimulants. Mnk1 inhibition blocked the transient increase in total protein synthesis detected in Stx1-treated cells but failed to block long-term protein synthesis inhibition. The MAPK inhibitors or Mnk1 inhibitor blocked soluble interleukin (IL)-1beta and IL-8 production or release by 73-96%. These data suggest that Stxs may regulate cytokine expression in part through activation of MAPK cascades, activation of Mnk1, and phosphorylation of eIF4E.

Phosphatidic acid regulates systemic inflammatory responses by modulating the Akt-mammalian target of rapamycin-p70 S6 kinase 1 pathway

Macrophages are pivotal effector cells in the innate immune system. When microbial products bind to pathogen recognition receptors, macrophages are activated and release a broad array of mediators, such as cytokines, that orchestrate the inflammatory responses of the host. Phosphatidic acid (PA) has been implicated as an important metabolite of phospholipid biosynthesis and in membrane remodeling and has been further suggested to be a crucial second messenger in various cellular signaling events. Here we show that PA is an essential regulator of inflammatory response. Deleterious effects of PA are associated with the secretion of proinflammatory cytokines, such as tumor necrosis factor-alpha, interleukin-1beta, interleukin-6, and the production of nitric oxide, prostaglandin E2, which are predominantly released by macrophage Raw264.7 cells. Furthermore, the administration of PA to mice increased the serum cytokine level. Moreover, direct or lipopolysaccharide-induced PA accumulation by macrophages led to the Akt-dependent activation of the mammalian target of rapamycin-p70 S6 kinase 1, a process required for the induction of inflammatory mediators. These findings demonstrate the importance of the role of PA in systemic inflammatory responses, and provide a potential usefulness as specific targets for the development of therapies.