Date Published: April 15, 2019
Publisher: Public Library of Science
Author(s): Asunción García-Sánchez, Elena Marcos-Vadillo, Catalina Sanz, Miguel Estravís, María Isidoro-García, Ignacio Dávila, Yeonseok Chung.
Functional studies suggest that promoter polymorphisms of the Prostaglandin D Receptor (PTGDR) gene can be involved in asthma. All-trans Retinoic acid (ATRA) has also been linked to allergic diseases. We have previously described the PTGDR promoter activation mediated by ATRA through response elements (RARE) at position -549T> C. In this study we aimed to analyze the effect of retinoic acid (RA) on the expression of PTGDR, the production of cytokines as well as to evaluate the binding of RA receptors to RA-Response Elements (RARE) sequences. A549 cells were transfected with vectors carrying different PTGDR haplotypes and treated with all-Trans Retinoic Acid (ATRA). PTGDR expression was measured by qPCR. Chromatin Immunoprecipitation assays (ChIP) were performed in ATRA stimulated KU812 cells and in PBMCs of patients carrying CTCT, CCCC or CCCT haplotypes. In addition, a broad panel of cytokines was analyzed by cytometric bead assay in A549 cells. The expression of PTGDR increased in A549 cells transfected with PTGDR-variants. The CCCC haplotype showed a significantly higher expression compared with CTCT. However, we found that RA up-regulated PTGDR expression through RARα mainly in the CTCT variant. Experiments on PBMCs from allergic patients carrying the -549T and -549C variant of the PTGDR promoter after ATRA and RAR antagonist administration confirmed the modulation of PTGDR by ATRA. The cytokine analysis showed that IL4 and IL6 levels were significantly increased in A549 cells transfected with PTGDR. In addition, ATRA treatment decreased the levels of IL4, IL6 and TNFα in A549 cells, whereas it increased IL4 and TNFα levels in PTGDR-transfected cells. We observed genetic differences in the regulation of PTGDR by ATRA that could contribute to the phenotypic differences observed in allergic patients. Our findings showed that RAR modulation by PTGDR might have an impact on Th2 responses, suggesting that RAR could be a potential therapeutic target in allergic inflammation.
Asthma is a chronic inflammatory disease affecting more than 358 million people . The inflammatory response in asthma involves the participation of the respiratory epithelium, the innate immune system and the adaptive immunity [2,3]. Prostaglandin D2 (PGD2) is the major cyclooxygenase (COX) metabolite of arachidonic acid produced in response to allergens and has been proposed as a mast cell activation marker . There are two types of transmembrane receptors of PGD2, the D prostanoid receptor, known as PTGDR, DP or DP1, and the chemoattractant receptor-homologous expressed on Th2 (CRTH2) or DP2 [4,5]. Several PTGDR polymorphisms have been previously reported [4,6–8]. Promoter variants have shown a different binding of transcription factors that controls the expression of PTGDR, and this could be related to the development of asthma susceptibility [4,6].
Epidemiological studies have related vitamin A with allergy by affecting the Th1-Th2 balance [9,14]. However, the role of RA in asthma and allergy is still controversial, [11,12,14]. We have previously reported that RA activated the PTGDR promoter, identifying RAREs in the promoter region and showing that transcription motifs were affected by genetic variants . In the present study, we report for the first time the molecular mechanism of regulation of PTGDR expression by RA.