Different effects of soluble and particulate guanylyl cyclases on expression of inflammatory cytokines in rat peripheral blood mononuclear cells

Abstract

Inflammation involves the cooperation of various cells and biologically active molecules. An important intracellular messenger molecule participating in the regulation of the process is cyclic GMP (cGMP), which is synthesized by guanylyl cyclases (GCs). The GC family comprises cytosolic (soluble) and membrane-bound (particulate) enzymes. The aim of this study was to determine whether and how the synthesis of cGMP by various forms of GC affects the expression of inflammatory cytokines depending on the activity of the transcription factors NF-κB (nuclear factor-κB) and AP-1 (activator protein-1). We established that in rat peripheral blood mononuclear cells (PBMCs), synthesis of cGMP was elevated by sodium nitroprusside (SNP), the activator of soluble GC, and by atrial natriuretic peptide (ANP) and C-type natriuretic peptide (CNP), the activators of particulate GC-A and GC-B, respectively. Stimulation of various GCs differently affected the expressions of the cytokines IL-1β, IL-6, and TNF-α in control cells and in cells activated by bacterial endotoxin (LPS). In control PBMCs their expression was elevated by stimulation of soluble, but not particulate, GC. SNP caused an increase in NF-κB activity, but had no influence on the activity of AP-1. The cells treated with LPS decreased the expressions of IL-1β, IL-6, and TNF-α in response to stimulation of particulate GC-A, but not other guanylyl cyclases. This inhibitory effect was a result of suppression of the activities of NF-κB and AP-1. Both effects that of SNP and of ANP, were cGMP dependent, as shown using its membrane-permeable analog 8-Br-cGMP. The implementation of specific inhibitors showed that the stimulatory effect of SNP was mediated by soluble GC and cGMP-dependent protein kinase (PKG-I). However, PKG-I was not involved in the inhibition of NF-κB and AP-1 activities by ANP in LPS-activated cells. Taken together, these results for the first time indicate that various GCs and various cGMP-dependent signaling pathways can modulate the activity of AP-1 and/or NF-κB and thus affect the expressions of IL-1β, IL-6, and TNF-α, which play important roles in the development of inflammation.