DIFFERENTIAL EFFECTS OF NERVE GROWTH FACTOR ON TOLL-LIKE RECEPTOR-MEDIATED CYTOKINE PRODUCTION IN HUMAN MONOCYTES

Autor: Bracci-Laudiero L 1, 3, Prencipe G 1, Strippoli R 1, De Pasquale L 1, Petrini S 2, De Benedetti F 1
Jazyk: angličtina
Rok vydání: 2009
Předmět:
Zdroj: EULAR 2009, pp. 362, Copenhagen, Denmark, 10-13 June 2009
info:cnr-pdr/source/autori:Bracci-Laudiero L 1,3, Prencipe G 1, Strippoli R 1, De Pasquale L 1, Petrini S 2, De Benedetti F 1/congresso_nome:EULAR 2009/congresso_luogo:Copenhagen, Denmark/congresso_data:10-13 June 2009/anno:2009/pagina_da:362/pagina_a:/intervallo_pagine:362
Popis: Background: The neurotrophin Nerve Growth Factor (NGF) is ubiquitously present in the organism and its levels are markedly up-regulated in inflamed tissues, including synovial fluids of patients with chronic arthritis. Although immune cells are known to express specific NGF receptors, TrkA and p75-NTR, it is not clear how basal and enhanced NGF levels affect immune cell activity during the inflammatory response. Since neutralization of NGF has recently emerged as a potential treatment of pain in inflammatory and non-inflammatory conditions, a better knowledge of the mechanisms and the effects of NGF action on inflammatory response can help to identify indications and define schedules of treatment. Objectives: The aim of our study was to investigate the effects of NGF on cytokine production induced by pathogen-associated molecular patterns (PAMPs) in human monocytes. Methods: Using peripheral blood monocytes, purified by Percoll discontinuous gradient centrifugation, we investigated the NGF effects on human monocytes after Toll-like receptor (TLR) activation in two experimental conditions: a) basal condition: to mimic the physiological condition in which the cells are constantly exposed to NGF, we pre-incubated monocytes with NGF before adding TLR ligands. b) inflammatory condition: to mimic the inflammatory condition in which there is a tissue increase in NGF concentration, monocytes were stimulated with TLR ligands and NGF was added either contemporary or at later times. Cells and supernatants were collected at different time points and the expression of NGF receptors and TLRs, the activation of signalling pathways and the synthesis of IL-6 and IL-1b were evaluated using real-time PCR, western blot, flow cytometry and ELISA. Results: In the basal condition, when cells were previously pre-incubated with NGF, we observed a two-fold NGF dose-dependent increase of IL-6 synthesis in monocytes exposed to TLR ligands (LPS, LTA, PAM). NGF alone did not have any effect. The NGF pre-treated cells showed an up-regulation in TLR-2 and TLR-4 expression after ligand addition. On the contrary, in the inflammatory condition, the addition of NGF at different times after TLR stimulation induced a two-fold reduction in IL-6 and IL-1b synthesis and a down-regulation of TLR expression. These dual, apparently opposite, effects of NGF on monocytes appears to be related to a modified ratio of TrkA/p75-NTR expression observed in these two experimental conditions. We observed that the activation of their specific pathway of signalling can either enhance or inhibit the TLR response. NGF can interfere with the downstream pathway of TLR activation by influencing activation of NF-kB and MAPK pathways. Conclusion: In basal conditions NGF amplifies monocyte activation via TLRs, maintaining monocyte reactivity and favouring an efficient response. During inflammation, elevated levels of NGF cause hypo-responsiveness to TLR ligands and may contribute to the down-regulation of the inflammatory response. These results are consistent with a dual role of NGF in maintaining the homeostasis of responses to PAMPS and suggest that NGF is part of a physiological mechanism regulating inflammatory response.
Databáze: OpenAIRE
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