ABSTRACT
BACKGROUND: The peroxisome proliferator-activated receptors (PPARs) alpha, beta/delta, and gamma are ligand-activated transcription factors belonging to the nuclear receptor superfamily. In addition to their regulatory role on lipid and glucose metabolism, they exert anti-inflammatory properties. In skin both PPAR-alpha and PPAR-beta/delta regulate keratinocyte proliferation/differentiation and contribute to wound healing. The 3 PPAR isoforms are expressed by several cell types recruited into the dermis during inflammation. OBJECTIVE: We have investigated the role of PPAR-alpha in the regulation of atopic dermatitis (AD), a common skin inflammatory disease. METHODS: We chose a mouse model of inflammatory dermatosis with immunologic features of AD and used epicutaneous sensitization with ovalbumin in the absence of adjuvant, which mimics the human pathology. RESULTS: On antigen sensitization, PPAR-alpha-deficient mice display increased epidermal thickening, dermal recruitment of inflammatory cells, lung inflammation, airway hyperresponsiveness, and IgE and IgG2a production compared with their wild-type counterparts. Increased inflammation was correlated to an enhancement of TH2 and, to a greater extent, TH1 responses and to increased skin expression of nuclear factor kappaB. Interestingly, PPAR-alpha expression was decreased in eczematous skin from patients with AD compared with skin from nonatopic donors, suggesting that defective PPAR-alpha expression might contribute to the pathology. Topical application of WY14643, a specific PPAR-alpha agonist, significantly decreased antigen-induced skin inflammation in the AD model. CONCLUSION: PPAR-alpha acts as a negative regulator of skin inflammation in AD.
Subject(s)
Dermatitis, Atopic/immunology , Dermatitis, Atopic/pathology , Immunoglobulin E/biosynthesis , Immunoglobulin G/biosynthesis , Inflammation Mediators/physiology , PPAR alpha/physiology , Administration, Cutaneous , Administration, Topical , Adult , Animals , Bronchial Hyperreactivity/immunology , Bronchial Hyperreactivity/metabolism , Bronchial Hyperreactivity/pathology , Dermatitis, Atopic/metabolism , Disease Models, Animal , Female , Humans , Inflammation Mediators/metabolism , Male , Mice , Mice, Inbred BALB C , Mice, Knockout , Ovalbumin/administration & dosage , Ovalbumin/immunology , PPAR alpha/deficiency , PPAR alpha/genetics , Pyrimidines/administration & dosage , Pyrimidines/pharmacologyABSTRACT
Allergic pathologies are often associated with IgE production, mast cell activation, and eosinophilia. PGD2 is the major eicosanoid, among several inflammatory mediators, released by mast cells. PGD2 binds to two membrane receptors, D prostanoid receptor (DP)1 and DP2, endowed with antagonistic properties. In humans, DP2 is preferentially expressed on type 2 lymphocytes, eosinophils, and basophils and mediates chemotaxis in vitro. Although not yet supported by in vivo studies, DP2 is thought to be important in the promotion of Th2-related inflammation. Herein, we demonstrate that mouse eosinophils express both DP1 and DP2 and that PGD2 exerts in vitro chemotactic effects on eosinophils through DP2 activation. Furthermore, 13,14-dihydro-15-keto-PGD2, a specific DP2 agonist not only increases eosinophil recruitment at inflammatory sites but also the pathology in two in vivo models of allergic inflammation: atopic dermatitis and allergic asthma. By contrast, DP1 activation tends to ameliorate the pathology in asthma. Taken together, these results support the hypothesis that DP2 might play a critical role in allergic diseases and underline the interest of DP2 antagonists in human therapy.
