Josef Pfeilschifter

Cyclooxygenase-independent actions of cyclooxygenase inhibitors

Several studies have demonstrated unequivocally that certain nonsteroidal anti‐inflammatory drugs (NSAIDs) such as sodium salicylate, sulindac, ibuprofen, and flurbiprofen cause anti‐inflammatory and antiproliferative effects independent of cyclooxy‐genase activity and prostaglandin synthesis inhibition. These effects are mediated through inhibition of certain transcription factors such as NF‐κB and AP‐1. The respective NSAIDs might interfere directly with the transcription factors, but their effects are probably mediated predominantly through alterations of the activity of cellular kinases such as IKKß, Erk, p38 MAPK, or Cdks. These effects apparently are not shared by all NSAIDs, since indomethacin failed to inhibit NF‐κB and AP‐1 activation as well as Erk and Cdk activity. In contrast, indomethacin was able to activate PPARγ, which was not affected by sodium salicylate or aspirin. The differences in cyclooxygenase‐independent mechanisms may have consequences for the specific use of these drugs in individual patients because additional effects may either enhance the efficacy or reduce the toxicity of the respective compounds.—Tegeder, I., Pfeilschifter, J., Geisslinger, G. Cyclooxygenase‐independent actions of cyclooxygenase inhibitors FASEB J. 15, 2057–2072 (2001)

Biglycan, a Danger Signal That Activates the NLRP3 Inflammasome via Toll-like and P2X Receptors

The role of endogenous inducers of inflammation is poorly understood. To produce the proinflammatory master cytokine interleukin (IL)-1β, macrophages need double stimulation with ligands to both Toll-like receptors (TLRs) for IL-1β gene transcription and nucleotide-binding oligomerization domain-like receptors for activation of the inflammasome. It is particularly intriguing to define how this complex regulation is mediated in the absence of an infectious trigger. Biglycan, a ubiquitous leucine-rich repeat proteoglycan of the extracellular matrix, interacts with TLR2/4 on macrophages. The objective of this study was to define the role of biglycan in the synthesis and activation of IL-1β. Here we show that in macrophages, soluble biglycan induces the NLRP3/ASC inflammasome, activating caspase-1 and releasing mature IL-1β without the need for additional costimulatory factors. This is brought about by the interaction of biglycan with TLR2/4 and purinergic P2X4/P2X7 receptors, which induces receptor cooperativity. Furthermore, reactive oxygen species formation is involved in biglycan-mediated activation of the inflammasome. By signaling through TLR2/4, biglycan stimulates the expression of NLRP3 and pro-IL-1β mRNA. Both in a model of non-infectious inflammatory renal injury (unilateral ureteral obstruction) and in lipopolysaccharide-induced sepsis, biglycan-deficient mice displayed lower levels of active caspase-1 and mature IL-1β in the kidney, lung, and circulation. Our results provide evidence for direct activation of the NLRP3 inflammasome by biglycan and describe a fundamental paradigm of how tissue stress or injury is monitored by innate immune receptors detecting the release of the extracellular matrix components and turning such a signal into a robust inflammatory response.

Leptin enhances wound re-epithelialization and constitutes a direct function of leptin in skin repair

Wound-healing disorders are a therapeutic problem of extensive clinical importance. Leptin-deficient ob/ob mice are characterized by a severely delayed wound healing that has been explained by the mild diabetic phenotype of these animals. Here we demonstrate that systemically and topically supplemented leptin improved re-epithelialization of wounds in ob/ob mice. Leptin completely reversed the atrophied morphology of the migrating epithelial tongue observed at the wound margins of leptin-deficient animals into a well-organized hyperproliferative epithelium. Moreover, topically supplemented leptin accelerated normal wound-healing conditions in wild-type mice. As assessed by immunohistochemistry, proliferating keratinocytes located at the wound margins specifically expressed the leptin-receptor subtype ObRb during repair. Additionally, leptin mediated a mitogenic stimulus to the human keratinocyte cell line HaCaT and human primary keratinocytes in vitro. Therefore, leptin might represent an effective novel therapeutic factor to improve impaired wound-healing conditions.

Nitric oxide triggers enhanced induction of vascular endothelial growth factor expression in cultured keratinocytes (HaCaT) and during cutaneous wound repair

Recently, we demonstrated a large induction of inducible nitric oxide synthase (iNOS) during cutaneous wound repair. In this study, we investigated the role of nitric oxide (NO) for the expression of vascular endothelial growth factor (VEGF), which represents the most important angiogenic factor during the proliferative phase of skin repair. Since keratinocytes are the major source of VEGF production during this process, we used cultured keratinocytes (HaCaT cell line) as an in vitro model to investigate NO action on growth factor‐ and cytokine‐stimulated VEGF expression. Exogenously added NO enhanced transforming growth factor‐β1‐, keratinocyte growth factor‐, interleukin‐1β‐, tumor necrosis factor‐α‐, and interferon‐γ‐induced VEGF mRNA and protein synthesis in keratinocytes. We could demonstrate that high‐level expression of cytokine‐induced VEGF mRNA in keratinocytes is dependent on endogenously produced NO, as inhibition of the coinduced iNOS by NG‐monomethyl‐L‐arginine (L‐NMMA) markedly decreased cytokine‐triggered VEGF mRNA levels in the cells. We also established an in vivo model in mice to investigate the role of NO during wound healing. During excisional wound repair, mice were treated with L‐N6‐(1‐iminoethyl)lysine (L‐NIL), a selective inhibitor of iNOS enzymatic activity. Compared to control mice, L‐NIL‐treated animals were characterized by markedly reduced VEGF mRNA levels during the inflammatory phase of repair. Immunohistochemistry demonstrated reduced VEGF protein expression and a completely disorganized pattern of VEGF‐expressing keratinocytes within the hyperproliferative epithelium at the wound edge in L‐NIL‐treated mice. We demonstrate that triggering of VEGF expression is a crucial molecular mechanism underlying NO function during wound healing.— Frank, S., Stallmeyer, B., Kämpfer, H., Kolb, N., Pfeilschifter, J. Nitric oxide triggers enhanced induction of vascular endothelial growth factor expression in cultured keratinocytes (HaCaT) and during cutaneous wound repair. FASEB J. 13, 2002–2014 (1999)

A transgenic mouse model of inducible macrophage depletion: effects of diphtheria toxin-driven lysozyme M-specific cell lineage ablation on wound inflammatory, angiogenic, and contractive processes.

Whether the wound macrophage is a key regulatory inflammatory cell type in skin repair has been a matter of debate. A transgenic mouse model mediating inducible macrophage depletion during skin repair has not been used to date to address this question. Here, we specifically rendered the monocyte/macrophage leukocyte lineage sensitive to diphtheria toxin by expressing the lysozyme M promoter-driven, Cre-mediated excision of a transcriptional STOP cassette from the simian DT receptor gene in mice (lysM-Cre/DTR). Application of diphtheria toxin to lysM-Cre/DTR mice led to a rapid reduction in both skin tissue and wound macrophage numbers at sites of injury. Macrophage-depleted mice revealed a severely impaired wound morphology and delayed healing. In the absence of macrophages, wounds were re-populated by large numbers of neutrophils. Accordingly, macrophage-reduced wound tissues exhibited the increased and prolonged persistence of macrophage inflammatory protein-2, macrophage chemoattractant protein-1, interleukin-1beta, and cyclooxygenase-2, paralleled by unaltered levels of bioactive transforming growth factor-beta1. Altered expression patterns of vascular endothelial growth factor on macrophage reduction were associated with a disturbed neo-vascularization at the wound site. Impaired wounds revealed a loss of myofibroblast differentiation and wound contraction. Our data in the use of lysM-Cre/DTR mice emphasize the pivotal function of wound macrophages in the integration of inflammation and cellular movements at the wound site to enable efficient skin repair.

Amplification of IL-1β-Induced Matrix Metalloproteinase-9 Expression by Superoxide in Rat Glomerular Mesangial Cells Is Mediated by Increased Activities of NF-κB and Activating Protein-1 and Involves Activation of the Mitogen-Activated Protein Kinase Pathways

The modulation of cell signaling by free radicals is important for the pathogenesis of inflammatory diseases. Recently, we have shown that NO reduces IL-1β-induced matrix metalloproteinase (MMP-9) expression in glomerular mesangial cells (MC). Here we report that exogenously administrated superoxide, generated by the hypoxanthine/xanthine oxidase system (HXXO) or by the redox cycler 2,3-dimethoxy-1,4-naphtoquinone, caused a marked amplification of IL-1β-primed, steady state, MMP-9 mRNA level and an increase in gelatinolytic activity in the conditioned medium. Superoxide generators alone were ineffective. Cytokine-induced steady state mRNA levels of TIMP-1, an endogenous inhibitor of MMP-9, were affected similarly by HXXO. Transient transfection of rat mesangial cells with 0.6 kb of the 5′-flanking region of the rat MMP-9 gene proved a transcriptional regulation of MMP-9 expression by superoxide. HXXO augmented the IL-1β-triggered nuclear translocation of p65 and c-Jun and, in parallel, increased DNA binding activities of NF-κB and AP-1. Mutation of either response element completely prevented MMP-9 promoter activation by IL-1β. Moreover, specific inhibitors of the classical extracellular signal-regulated kinase (ERK) pathway and p38 mitogen-activated protein kinase (MAPK) cascade, partially reversed the HXXO-mediated effects on MMP-9 mRNA levels, thus demonstrating involvement of ERKs and p38 MAPKs in MMP-9 expression. Furthermore, IL-1β-triggered phosphorylation of all three MAPKs, including p38-MAPK, c-Jun N-terminal kinase, and ERK, was substantially enhanced by superoxide. Our data identify superoxide as a costimulatory factor amplifying cytokine-induced MMP-9 expression by interfering with the signaling cascades leading to the activation of AP-1 and NF-κB.

IL-1 family nomenclature

To the Editor: Newly cloned interleukin 1 (IL-1) family members1–3 were originally given an IL-1 family (IL-1F) designation4, but as functions have now been elucidated for several of these5,6, we propose that each now be assigned an individual interleukin designation. IL-1F6, IL-1F8 and IL-1F9 are encoded by distinct genes but use the same receptor complex (IL-1Rrp2 and AcP), are proinflammatory and deliver nearly identical signals7–12. We propose these be designated IL-36α, IL-36β and IL-36γ, respectively. IL-1F5 also binds to IL-1Rrp2 but antagonizes those cytokines in a manner analogous to that used by IL-1Ra to antagonize IL-1α and IL-1β7–9. We propose that IL-1F5 be renamed IL-36Ra (for ‘receptor antagonist’). In the IL-1 nomenclature, IL-1Ra is used for the natural product, whereas IL-1ra is used for the recombinant product; therefore, IL-36Ra is appropriate for natural IL-1F5. IL-1F7 produces anti-inflammatory effects by suppressing innate immune responses; it does this by decreasing the production of inflammatory cytokines induced by Toll-like receptor agonists as well as that of IL-1 and tumor necrosis factor13,14. We propose this IL-1 family member be renamed IL-37. IL-1F7 has various splice forms1,2,15,16, of which IL-1F7b is the most studied. We propose that IL-1F7a, IL-1F7b and so on be renamed IL-37a, IL-37b and so on. The one remaining IL-1 family member, for which no function has yet been demonstrated, is IL-1F10; however, as evidence of its properties remains limited, we suggest that it retain its IL-1F designation until a function is clearly identified, although it might be prudent to reserve the designation IL-38 for this eventuality.

Translational Control of Inducible Nitric Oxide Synthase by IL-13 and Arginine Availability in Inflammatory Macrophages

Inducible NO synthase (iNOS) and its generation of NO from l-arginine are subject to transcriptional as well as posttranscriptional control by cytokines. In this study, we describe a novel, translational mechanism of iNOS regulation by arginine availability. Using mouse inflammatory peritoneal macrophages stimulated with IFN-γ plus LPS, we demonstrate that the suppression of iNOS protein, which is observed after a 16-h (but not after a 6-h) pretreatment with IL-13, despite an unaltered iNOS mRNA level, results from arginine depletion by arginase. The addition of arginase inhibitors (in the pretreatment phase) or of arginine (in the stimulation phase) completely blocked the down-regulation of iNOS protein by IL-13. The rescuing effect of arginine supplementation was not due to a positive feedback regulation of iNOS expression via enhanced production of NO. A striking suppression of iNOS protein (but not of iNOS mRNA) was also seen, when IL-13 was replaced by purified arginase or when macrophages were stimulated with IFN-γ/LPS in arginine-free medium. Arginine deficiency specifically impaired the de novo synthesis and the stability of iNOS protein, but did not affect the production of TNF and the overall protein synthesis of the macrophages. From these results, we conclude that arginine not only functions as a substrate for iNOS, but is also critical for maintaining normal levels of iNOS protein in cytokine-stimulated macrophages.

Anti-inflammatory properties of pro-inflammatory interferon-γ

Production of interferon-gamma (IFNgamma) in response to infection is a hallmark of innate and adaptive immunity. In addition to the pivotal role of IFNgamma in host defense, its excessive release has been associated with the pathogenesis of chronic inflammatory and autoimmune diseases. In fact, knockout models reveal that IFNgamma plays a key role in mediating a number of pathological processes related to chronic immune activation. On the other hand, evidence has been accumulated in recent years that supports the concept of a dual role of IFNgamma in inflammation. Here, we review anti-inflammatory aspects of IFNgamma in the regulatory network of cytokine biology. These include induction of anti-inflammatory molecules such as interleukin (IL)-1 receptor antagonist (IL-1Ra) and IL-18 binding protein (IL-18BP), modulation of pro-inflammatory cytokine production, activation of apoptosis, and interference with the signal transduction machinery by induction of suppressors of cytokine signaling (SOCS).

Signalling pathways regulating nucleo-cytoplasmic shuttling of the mRNA-binding protein HuR.

During the last decade evidence from numerous studies has been accumulated demonstrating that posttranscriptional gene regulation including mRNA turnover and translation is an important paradigm of eukaryotic gene expression contributing to the vast majority of cellular processes including cell growth and differentiation, metabolism, migration, and cellular senescence. Accordingly, a large number of reports have documented that the Human antigen R (HuR), a ubiquitously expressed member of the ELAV protein family, is one of the major actors in this scenario. Consequently, HuR is implicated in a large variety of pathologies in which deregulated stabilisation of many short-lived key mRNAs is causally linked with the onset and course of disease. Since HuR is most abundantly localised within the cell nucleus, export of HuR to the cytoplasm seems a major prerequisite for its stabilising effects on its cognate target adenylate- and uridylate-rich elements (AREs) containing cargo mRNAs. Although, the list of reports demonstrating a critical involvement of different signalling cascades in HuR-triggered mRNA functions is steadily growing, the mechanisms underlying HuR trafficking are not well understood. For this reason, the review will cover the most recent advances of knowledge of signalling cascades involved in the stimulus-dependent nucleo-cytoplasmic HuR shuttling and a special emphasis will be put on the possible regulatory role of posttranslational HuR modification.