Regulation of platelet-activating factor receptor gene expression in vivo by endotoxin, platelet-activating factor and endogenous tumour necrosis factor

Abstract

A competitive PCR assay was developed to quantify platelet-activating factor (PAF) receptor (PAF-R) transcripts in rat tissues using a synthetic RNA as a competitor. We found PAF-R mRNA constitutively expressed in the eight organs tested, with the ileum containing the highest concentration [(3.49±0.15)×107 molecules/μg of RNA]. Significant but lower levels were also detected in the jejunum, spleen, lungs, kidneys, heart, stomach and liver. Furthermore we defined the regulatory role of inflammatory mediators in ileal PAF-R gene expression using a rat model of intestinal injury induced by PAF or lipopolysaccharide (LPS). Injection of LPS or low-dose PAF resulted in a marked increase in ileal PAF-R mRNA within 30 min. The up-regulation on PAF-R elicited by PAF was biphasic, peaking first at 90 min, then again at 6 h. In contrast, LPS elicited a weak monophasic response. The second phase of PAF-R mRNA increase after PAF administration was completely abolished by WEB 2170, a PAF antagonist, and partially inhibited by anti-tumour necrosis factor (TNF) antibody. These observations indicate the involvement of endogenous PAF and TNF in this event. In conclusion, we found: (a) preferential PAF-R expression in the ileum, suggesting a role for PAF in intestinal inflammation; (b) induction of PAF-R expression in vivo by its own agonist; (c) a complex regulation of PAR-R gene expression in vivoinvolving a network of various pro-inflammatory mediators.

Adrenomedullin increases the expression of calcitonin-like receptor and receptor activity modifying protein 2 mRNA in human microvascular endothelial cells

“…This could suggest that the initial increase in mRNA levels are a direct response to the AM stimulation, whereas the later CL and RAMP2 induction might be mediated by distinct second messenger system components. In rat ileum, platelet-activating factor (PAF) increases the mRNA levels of PAF receptor (PAF-R) in a bi-phasic manner after 30 min and 6 h post-stimulation (Wang et al 1997). PAF has been known to stimulate tumor necrosis factor (TNF) secretion in rat ileum cells, which in turn increases endogenous PAF levels.…”

Study progress on mechanism of severe acute pancreatitis complicated with hepatic injury

“…Main actions of PAF (Kingsnorth, 1996;Wang et al, 1997;Roudebush et al, 2000;Reinhardt et al, 1999) include activation of platelet, promotion of platelet adhesion and aggregation, formation of thrombus; elevation of adhesion factor β 2 -integrin, change of endothelial cell skelemin, increase of capillary permeability, massive effusion of plasma, blood viscosity increase, slow down of blood flow, participation of ischemia-reperfusion injury; stimulation of vasoactive substances, generation of cytokine and inflammatory mediators, and so on.…”

Intestinal Epithelial Cell Apoptosis, Immunoregulatory Molecules, and Necrotizing Enterocolitisb

“…PAFR signaling specifically, is known to regulate gene expression as activation of the PAFR leads to expression of immediate, early oncogenes in rat fibroblasts [64], HEC-1A endometrial carcinoma cells [53], and in A-431 human epithelial carcinoma cells [65]. More importantly from the point of view of enteral health, PAFR activation leads to intestinal TNFα, PLA2-II, PAFR gene expression in an in vivo, PAF-perfusioninduced bowel necrosis model [66][67][68]. As discussed above, signaling via the PAFR results in the activation of transcription factors such as STAT [55] and NFĸB [58,59].…”