Adrenergic stimulation alters the expression of inflammasome components and interleukins in primary human monocytes

Abstract

Prior to their release, interleukin (IL)-1β and IL-18 are cleaved to their bioactive forms by a multiprotein complex known as an inflammasome, which is comprised of a number of elements that are subject to nuclear factor-κB-dependent transcription. Catecholamines have been indicated to exert an enhancing effect on the IL-1β release. The aim of the present study was to determine whether alterations in inflammasome gene expression may be responsible for the modified IL-1β and IL-18 secretion following lipopolysaccharide (LPS) and catecholamine co-stimulation. Monocytes were isolated from the peripheral blood of 21 healthy volunteers using CD14⁺ microbeads. Following stimulation with LPS (2 µg/ml) and/or phenylephrine (PE; 10 µM) for 24 h, the supernatants were subjected to ELISA to evaluate the ex vivo protein expression levels of IL-1β and IL-18. In addition, the gene expression levels of inflammasome components associated with the cleavage of IL-1β and IL-18, including NLRP1, NLRP3, caspase-1 and PYCARD were determined using polymerase chain reaction. The results indicated that LPS significantly increased IL-1β expression compared with the unstimulated control samples. Co-stimulation with LPS + PE significantly enhanced IL-1β expression compared with LPS alone. Furthermore, IL-18 expression was significantly reduced by LPS and LPS + PE co-stimulation. The gene expression levels of IL-18, NLRP1, caspase-1 and PYCARD were comparable in the LPS- and LPS + PE-stimulated cells. LPS significantly induced the expression levels of IL-1β and NLRP3, and to a lesser degree, the expression of NLRP1, compared with the control. By contrast, PE markedly induced the expression levels of IL-18 and NLRP1, while LPS reduced the gene expression of IL-18. In conclusion, adrenergic stimulation suppressed NLRP3 expression and enhanced NLRP1 expression, indicating that NLRP3 may regulate IL-1β secretion and NLRP1 may regulate the release of IL-18.

Keywords: LRR and PYD domains-containing protein; NACHT; adrenergic effects; catecholamines; inflammasome; interleukin-1β; monocytes.

Figure 1.

LPS and/or PE stimulation induced distinct IL-1β and IL-18 expression in CD14⁺ monocytes isolated from peripheral mononuclear blood cells, by positive selection using CD14-magnetic beads. Cells from healthy volunteers (n=21) were stimulated with LPS and/or PE. Supernatants were collected after 24 h and the protein expression of (A) IL-1β and (B) IL-18 was measured by enzyme-linked immunosorbent assay. Data are presented as the mean ± standard error of the mean. *P<0.05. IL-1β, interleukin-1β; ctrl, control; LPS, lipopolysaccharide; PE, phenyephrine; IL-18, interleukin-18.

Figure 2.

LPS and/or PE stimulation results in distinct gene expression pattern of inflammasome components in CD14⁺ monocytes, which were isolated from peripheral mononuclear blood cells from healthy volunteers (n=21) by positive selection using CD14-magnetic beads. Cells were stimulated with LPS and/or PE and the gene expression levels (A) IL-β, (B) IL-18, (C) NLRP3, (D) NLRP1, (E) caspase-1 and (F) PYCARD were measured. Data are shown as the mean ± standard error of the mean. *P<0.05. IL, interleukin; LPS, lipopolysaccharide; PE, phenylephrine; NLRP, NACHT, LRR and PYD domains-containing protein; casp1, caspase-1; PYCARD, apoptosis-associated speck-like protein containing a caspase recruitment domain.