Abstract
The central nervous system has the ability for modulating immune responses, but the molecular mechanisms of such interactions are only partly understood. Interleukin-27 (IL-27) is a heterodimeric protein and structurally related to the IL-12 family of cytokines. IL-27 is composed of the subunits EBI3 and p28. The biological functions of IL-27 have been described as either anti-inflammatory or pro-inflammatory depending on the experimental models studied. In the current study, we investigated how production of Interleukin-27 (IL-27) is regulated by neuroendocrine hormones. We focused our work on the subunit p28, since EBI3 is also present in IL-35 and therefore is not a specific component of IL-27.
First, we used F4/80+CD11b+ macrophages from C57BL/6J mice derived either from the bone marrow (BMDM) or elicited by intra-peritoneal injection of thioglycollate (PEM). IL-27 was abundantly expressed and secreted in cultures of macrophages (PEM and BMDM) when these cells were activated by lipopolysaccharide (LPS). The addition of neuroendocrine hormones of the sympathetic nervous system (adrenaline and noradrenaline) greatly reduced the capacity of LPS-activated macrophages to generate IL-27p28 at all time points studied (0-24 h; Fig. 1A, 1B). The effects of these catecholamines were dose-dependent over a range of 1 µM – 0.01 µM. To study the intracellular signaling events related to suppression of IL-27p28 by neuroendocrine hormones, we used bead-based multiplexing assays with antibodies specific for phosphorylated signaling proteins (Akt, c-Jun, CREB, ERK1/2, JNK, MEK1, NFκB, p38 MAPK, STAT3). Activation of macrophages with LPS within 20-60 min induced a 3-5-fold increase in phosphorylation of multiple signaling pathways including c-Jun N-terminal kinases (JNK) at threonine-183/tyrosine-185. Treatment of macrophages with adrenaline or noradrenaline greatly reduced phosphorylation of JNK following LPS. Inhibition of JNK-signaling using the small molecule inhibitor, SP600125, reduced the release of IL-27p28 from macrophages. This suggested that neuroendocrine hormones (adrenaline, noradrenaline) modulate IL-27p28-dependent immune responses via a JNK-dependent mechanism.
To investigate the relevance of our findings regarding neuroendocrine regulation of IL-27p28 during acute inflammation, we used a model of endotoxic shock induced by intra-peritoneal injection of LPS (10 mg/kg body weight). Mice with genetic deficiency of the IL-27 receptor (IL-27RA-/-, WSX-1-/-) were significantly protected following endotoxic shock as compared to wild type control mice. These data suggest that IL-27 signaling promotes lethal outcomes of endotoxic shock. To further characterize the role of catecholamines, C57BL/6J mice underwent surgical removal of the adrenal glands for interrupting the secretion of adrenaline, noradrenaline and glucocorticoids. When adrenalectomized mice were subjected to endotoxic shock, these animals displayed 2-3-fold higher concentrations of IL-27p28 in plasma after 8 h. This observation may not only be explained by reduced concentrations of catecholamines in adrenalectomized mice, but also by a disruption of the pituitary-adrenal axis, since glucocorticoids in vitro also suppressed IL-27p28.
In summary, these data describe novel interactions of endocrine transmitters of the nervous system and macrophage-derived IL-27. The hyperproduction of IL-27 observed in adrenalectomized mice provides a new explanation for the known susceptibility of such animals in experimental models of sepsis and other acute inflammatory diseases.
Disclosures:
No relevant conflicts of interest to declare.
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