Expression of prostaglandin D synthase and the prostaglandin D2 receptors DP and CRTH2 in human nasal mucosa

https://doi.org/10.1016/j.prostaglandins.2003.12.002Get rights and content

Abstract

Background: Prostaglandin D2 (PGD2) is released from mast cells during the allergic response. Objective: Since PGD2 has been shown to induce nasal congestion in humans, we investigated the distribution of hematopoietic prostaglandin D synthase (PGDS) and the two PGD2 receptors, DP and CRTH2 in human nasal mucosa from healthy subjects and subjects suffering from polyposis, a severe form of chronic rhinosinusitis. Methods: DP mRNA expression was detected by in situ hybridization while PGDS, CRTH2 and various leukocyte markers expression were revealed by immunohistochemistry. Results: In the normal mucosa, PGDS was only detected in few resident mast cells while CRTH2 was undetectable. In contrast, DP receptor mRNA was detected in epithelial goblet cells, serous glands and in the vasculature. In the nasal mucosa of subjects suffering from polyposis: (1) PGDS was detected in mast cells and other large infiltrating inflammatory cells, (2) both DP mRNA and CRTH2 were detected in eosinophils and (3) CRTH2 was detected on a subset of infiltrating T cells. Although DP mRNA could not be detected in the T cells invading the nasal mucosa, it was found to be expressed in the T cells present in the lymph node and the thymus from normal individuals. Conclusion: This study indicates that cells capable of producing PGD2 are present in the nasal mucosa and that both PGD2 receptors, DP and CRTH2, might play a role in inflammatory disease of the upper airways.

Introduction

Prostaglandin D2 (PGD2) is the major arachidonic acid metabolite released from mast cells along with histamine during an allergic response [1], [2]. In these cells, PGD2 is converted from a common precursor, PGH2, by an enzyme called H-PGDS, an hematopoietic form of prostaglandin D synthase. Another prostaglandin D synthase, L-PGDS (lipocalin form) also catalyzes this reaction and is found mainly in the brain. Nasal allergen challenge in patients with allergic rhinitis has been shown to cause a significant elevation of PGD2 levels in nasal lavage fluid [3], [4]. PGD2 may play a critical role in the allergic response since it has been reported to mediate a number of pro-inflammatory effects including an increase in vascular permeability [5], [6], an increase in nasal congestion [7] and eosinophil infiltration [8].

The two receptors with the highest affinity for PGD2 are the G-protein coupled receptors DP (prostanoid receptor for PGD2) and CRTH2 (chemoattractant receptor-like molecule expressed on TH2 cells; also named DP2) with respective Ki values of 1.7 and 2.4 nM [9]. Although DP and CRTH2 share the same ligand, they have little sequence homology. DP shares the highest amino acid sequence identity with the other prostanoid receptors, TP, FP, EP1–4 and IP while CRTH2 is more closely related to members of the leukocyte chemoattractant receptor subfamily which includes the N-formyl peptide receptors and the complement 5a receptor [10].

The precise mechanism through which PGD2 manifests its pro-inflammatory effects in human airways is still unclear. Both DP and CRTH2 have been shown by in situ hybridization to be expressed on peripheral blood eosinophils [9], [11]. Activation of DP causes an increase in eosinophil survival while the activation of CRTH2 is associated with an increase in chemokinesis, degranulation and expression of the adhesion molecule CD11b [11], [12]. In addition, CRTH2 was demonstrated by immunological methods to be selectively expressed on human peripheral blood Th2 and Tc2 T-lymphocytes [13]. Interestingly, circulating CRTH2-positive Th2 cell number is significantly increased in atopic dermatitis patients [14]. Activation of CRTH2 on T cells was shown to be associated with an increase in chemotaxis, Th2 cytokine secretion and expression of the adhesion molecule CD11a [10], [15]. The DP receptor has been shown by in situ hybridization to be localized to the mucus-secreting goblet cells and the columnar epithelium within rat and human gastrointestinal tract [16], [17]. It was also shown that DP activation stimulates mucus secretion from a human colonic adenocarcinoma cell line [17]. However, it is still unknown whether DP is expressed on human airway epithelial cells and if it is involved in the regulation of mucus production in pathophysiological conditions. Nonetheless, evidence does suggest that the DP receptor is involved in allergic responses since DP-receptor knockout mice show a decreased airway inflammatory response to allergen challenge [18].

Little is known about the cellular distribution of PGDS, DP and CRTH2 in human airways as well as in lymphoid organs. In order to better understand the biological effects of PGD2 in the upper airways and its potential role in inflammatory diseases, we used in situ hybridization and immunohistochemical methods to evaluate the expression of PGDS, DP and CRTH2 in human nasal mucosa from healthy patients as well as patients with polyposis, a chronic inflammatory disease (rhinosinusitis) of the upper airways characterized by the infiltration of inflammatory cells [19]. In addition, since the expression of DP and CRTH2 have only been evaluated on peripheral leukocytes, we also investigated the distribution of DP and CRTH2 in hematopoietic tissues such as thymus, spleen and lymph node.

Section snippets

Sample preparation

Human nasal mucosa tissues were obtained following surgical procedure or by biopsy from three normal individuals and six subjects with polyposis. Sex, age and diagnostic for each subject are described in Table 1. Tissues were fixed in formalin and embedded in paraffin blocks. The tissues were then cut with a microtome at 6 uM thickness and mounted on SuperFrost slides (Fisher). Paraffin-embedded human lymph node, spleen and thymus (from subjects 10–12, respectively) were purchased from BioChain

Prostaglandin D2 synthase (PGDS) is expressed in cells infiltrating the nasal mucosa of patients with polyposis

PGDS protein expression was determined in human nasal mucosa samples obtained from healthy individuals and subjects with polyposis. In the normal nasal mucosa from subjects 1 and 2, an average of four PGDS-positive cells per field (200× magnification) was detected. All the PGDS-positive cells found in the normal nasal mucosa were positively co-labeled with a mast cell tryptase antibody, a selective marker for mast cells (data not shown). In the nasal mucosa of subjects with polyposis (subjects

Discussion

In this study, we investigated the tissue expression of the major peripheral PGD2 synthesizing enzyme and two receptors for PGD2 in the upper airways and tissues of the immune system in human (summarized in Table 3). We found that DP mRNA is expressed in epithelial goblet cells and serous glands in the nasal mucosa. In a previous paper, we showed that DP mRNA is present in mucus-secreting goblet cells of the human colon and that DP stimulation on a human colonic cell line triggers mucus

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  • Cited by (0)

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    Present address: IPS Pharma, Institute of Pharmacology of Sherbrooke, Sherbrooke, Que., Canada J1H 5N4.

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