Retinoid X receptor ablation in adult mouse keratinocytes generates an atopic dermatitis triggered by thymic stromal lymphopoietin

Abstract

To investigate the role of retinoid X receptors (RXRs) in epidermal homeostasis, we generated RXR␣␤ ep؊/؊ somatic mutants in which both RXR␣ and RXR␤ are selectively ablated in epidermal keratinocytes of adult mice. These mice develop a chronic dermatitis mimicking that observed in atopic dermatitis (AD) patients. In addition, they exhibit immunological abnormalities including elevated serum levels of IgE and IgG, associated with blood and tissue eosinophilia, indicating that keratinocyte-selective ablation of RXRs also generates a systemic syndrome similar to that found in AD patients. Furthermore, the profile of increased expression of cytokines and chemokines in skin of keratinocyte-selective RXR␣␤-ablated mutants was typical of a T helper 2-type inflammation, known to be crucially involved in human AD pathogenesis. Finally, we demonstrate that thymic stromal lymphopoietin, whose expression is rapidly and strongly induced in RXR␣␤-ablated keratinocytes, plays a key role in initiating the skin and systemic AD-like pathologies.keratinocyte-selective gene ablation ͉ nuclear receptors ͉ conditional mutagenesis ͉ Cre-ER T2 A topic dermatitis (AD), a chronic skin inflammatory disease with a strong genetic component that affects children (10-20%) and adults (1-3%), is characterized by pruritic and eczematoid skin lesions, associated with systemic immunological abnormalities, including peripheral eosinophilia and hyper IgE immunoglobulinemia (1). Immunological mechanisms have been involved in AD pathogenesis (2), but the possible role of epidermal keratinocytes in AD initiation and maintenance is still largely unexplored (3).Nuclear receptors (NRs) belong to a superfamily of transcriptional regulators that include ligand-dependent and orphan receptors (4, 5). NRs play critical roles as signal transducers in vertebrate development and homeostasis, including immune functions (4, 6-8). Within the NR superfamily, the retinoid X receptor isotypes (RXR ␣, ␤, and ␥) play a key role as heterodimeric partners for some 15 NRs, e.g., retinoic acid receptors, 1,25-dihydroxyvitamin D 3 receptor (VDR), peroxisome proliferator-activated receptors, and liver X activated receptors (4, 5, 9). Ligand-dependent transcriptional activation by NRs requires the integrity of the core of activation function 2 (AF-2) (the ␣-helix 12 of the ligand-binding domain; see refs. 9 and 10).In epidermis, RXR␣ is predominant, RXR␤ level is lower, and RXR␥ is undetectable (11-13). Keratinocyte-selective ablation of RXR␣ in adult mouse skin results in a number of abnormalities, including a progressive alopecia, keratinocyte hyperproliferation, and abnormal differentiation, and an inflammatory reaction (11,14). In contrast, the skin of RXR␤-null mice is apparently normal (11,14,15).To investigate the origin of this inflammatory reaction and to avoid any functional redundancies between keratinocytic RXR␣ and RXR␤, we have now generated RXR␣␤ epϪ/Ϫ somatic mutants in which both RXR␣ and RXR␤ are selectively ablated in epidermal keratinocytes of adult mice. T...

Inducible expression of the proallergic cytokine thymic stromal lymphopoietin in airway epithelial cells is controlled by NFκB

“…This disease development is accompanied by increased TSLP expression in the epidermis, suggesting that RXRs are involved in repressing transcription of the TSLP gene. Consistent with this, they found two nuclear receptor binding sites in the mouse TSLP gene promoter (22). RXRs function as binding partners for a wide variety of nuclear receptors, including members of the retinoic acid receptor family (28,29) and the vitamin D receptor (30) and can act as either transcriptional activators or repressors, depending on the binding partner and the presence or absence of ligands (31)(32)(33).…”

“…Previous work has shown that epidermal ablation of the nuclear receptors Retinoid X receptor (RXR)␣ and RXR␤ resulted in development of an atopic dermatitis-like disease that included elevated expression of TSLP (22). These authors also identified two possible RXR binding sites upstream of the TSLP gene (base pairs Ϫ1049 to Ϫ1062 and base pairs Ϫ2164 to Ϫ2175).…”

Topical vitamin D3 and low-calcemic analogs induce thymic stromal lymphopoietin in mouse keratinocytes and trigger an atopic dermatitis

“…Systemic abnormalities, including elevated serum IgE and IgG levels, associated with blood and tissue eosinophilia, have been observed in RXR␣␤ epϪ/Ϫ and K14-TSLP mice, exhibiting similarities to those observed in AD patients (3). Serum IgE and IgG levels were increased in mice to which MC903 was topically applied for 16 At day 17 of MC903 treatment, an inflammation was obvious on ears of VDR CT mice, whereas VDR epϪ/Ϫ ears did not show any sign of inflammation ( Fig.…”

“…Because RXR͞NR heterodimers in which an agonistic ligand is not bound to the NR partner can act as transcriptional repressors (10), we examined whether TSLP expression could be induced by NR agonists. Four nanomoles of ligands were topically applied to whole ears of WT mice for 4 consecutive days (days [1][2][3][4], and TSLP RNA levels were determined on day 5. Application of 1␣,25-(OH) 2 D 3 (the physiologically active vitamin D3) led to a dramatic increase (Ͼ300-fold) in TSLP transcripts at day 5, whereas they were modestly but significantly increased (5-fold) upon application of a RAR␥-selective agonist (BMS961) (11) (Fig.…”

“…Because TSLP expression appears to be critically involved in the initiation of AD-like dermatitis in the mouse (3,8), we investigated whether a MC903 long-term treatment could induce an AD-like phenotype. MC903 (4 nmol) was applied daily for 16 days to ears of WT mice.…”